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Mechanism of purification of cellulose in acidified aqueous acetone Awad El-Karim, Salah El-Din El-Siddique 1995

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MECHANISM OF PURIFICATION OF CELLULOSE IN  ACIDIFIED  AQUEOUS ACETONE  by SALAH EL-DIN EL—SIDDIQUE AWAD EL-KARIM M.Sc., Leningrad Technical Forestry Academy, 1976 M.Sc., University of Manchester, Institute of Scienc e and Technology (UMIST), 1981  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  THE FACULTY OF GRADUATE STUDIES THE FACULTY OF FORESTRY Department of Wood Science We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June,  1995  © Salah El-Din El-Siddique Awad El-Karim,  1995  in presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  (Signature)  Department of  W,L  c L-C  The University of British Columbia Vancouver, Canada  Date J.Lj 121 f95  DE-6 (2188)  II  ABSTRACT  This  project  deals  with  solvent  purification,  a  new  approach for the preparation of high-yield dissolving pulp with  characteristics  standards.  At  technique  aims  unmodified,  the  similar same  at  to  time,  removing  those the  and  recommended  solvent  the  purification  recovering  low molecular weight sugars that  by  chemically  could  further  be processed as by—products. In addition, the process offers a  reduction  dissolving  in  pulp  waste  water  purification  and  amounts  associated  economical  reuse  with  of  the  solvent.  Thus,  account.  The current technology is unable to achieve these  environmental  abatement  is  also  taken  into  goals. The major objective of this work is the elucidation and characterization purification this  of  process,  thesis  a  the i.e.,  detailed  purification of cellulose been carried out.  mechanism the study  of  acetonation on  the  the  solvent  mechanism.  In  mechanism  of  in acidified aqueous  aceton has  The mechanism has been proved to be of a  physico—chemical character. The physical phenomenon has been found  to  be  based  on the H-bond  disruption/destruction  crystalline cellulose by acetone as a solvent. hand,  in  On the other  the chemical hypothesis of the mechanism is verified  to be the formation of isopropylidene groups on carbohydrate chains that protection  leads to disproportionation of the polymer of  the  sugar  ring.  The  validity  of  and  these  111  hypotheses has been investigated as follows; cotton has been used throughout this study as a model compound and different techniques such as DRIFT,  Ge,  HPLC,  C-13 CP/MAS solid state  NMR, X—ray diffraction, GPC, and viscosity measurements have been employed. Factors as acidity, acetone  affecting  residence time,  concentration  investigation that has rather  solvent purification  of  helped than  temperature,  have  those  also  factors  elucidation  optimization  was  of  of  been  treatment  type of  the  acid,  investigated.  conducted  the  such  in  acetonation solvent  a  and The  manner  mechanism  purification  technique. Their impact on hydrogen bonding (ist hypothesis) fld hypothesis) has been observed to 2 and isopropylidenation ( vary considerably. Results derivatives, and  obtained  on  crystallinity,  viscosity  of  cotton  hydrogen molecular  residues  are  bonding,  weight in  sugar  distribution,  accord  with  the  above assumptions. Based  on  the  experimental  findings  of  this  work,  a  mechanism of purification of cellulose in acidified aqueous acetone is described.  iv TABLE OF CONTENTS  Page ABSTRACT  .  .  .  ii  .  .  .  .  .  .  .  .  TABLE OF CONTENTS  .  .  .  .  .  .  .  .  LIST OF TABLES  .  .  .  .  .  .  .  .  •  .  xiii  .  .  .  .  .  .  .  .  •  .  xvi  LIST OF ABBREVIATIONS  .  .  .  .  .  .  xxv  ACKNOWLEDGEMENTS  .  .  .  .  .  .  .  .  xxvii  DEDICATION  .  .  .  .  .  .  .  .  xxix  .  .  LIST OF FIGURES  .  .  1  INTRODUCTION  .  .  .  .  .  .  .  2  LITERATURE REVIEW.  .  .  .  .  .  .  2.1  Bleaching Operations)  iv  .  •  •  .1  •  .  •  10  (Pulping and .  .  2.1.1  Acid Suiphite Pulping  2.1.2 2.1.3  .  .  .  10 •  .  12  Prehydrolysis Kraft Pulping  •  .  .  15  Bleaching  •  .  .  17  .  21  .  21  .  .  .  .  .  Development  -  Hydrogen Bonding Acceptor Solvents  2.2.2  .  •  The Hydrogen Bond 2.2.1  -  .  —  .  H-bond Donor! .  .  •  .  .  Hydrogen Bonding in Cellulosic Material  2.3  .  .  Trends of Current Dissolving Pulp Purification Processes  2.2  •  .  .  .  .  28  .  Solvent Effect on Stereochemistry and Mechanism  .  •  •  .  .  .  .  .  .  .  .  .  36  V  2.4  Isopropylidene Chemistry of  2.5  Ketals  .  .  .  .  .  .  .  .  .  .  .  .  41  .  .  .  .  .  .  47  .  .  .  .  .  49  .  .  .  58  Derivatives of Pentoses  2.4.2  Derivatives of Aldohexoses  2.4.3  A Study of Sucrose  -  Disaccharide  Elucidation and Characterization of a .  .  .  .  .  .  .  .  .  .  .  .  .  64  .  .  .  .  .  .  .  .  64  2.5.1  IR Investigation  2.5.2  Sugar Hydrolysis with the Involvement of Acetone  2.5.3  .  .  .  .  .  .  .  .  .  .  68  .  .  .  .  71  .  .  73  The CP/MAS NMR Spectrometric Investigation  .  .  .  .  .  2.5.4  X—ray Diffraction Characterization  2.5.5  Molecular Weight Distribution Characterization  MPTERIAL AND METHODS 3.1  .  2.4.1  Mechanism  3  Formation  -  .  .  .  .  .  .  .  .  .  .  .  .  75  .  .  .  .  .  .  .  .  79  .  .  .  .  .  .  .  79  .  .  .  .  .  .  .  79  .  .  .  79  .  .  .  80  .  .  .  81  Sample Preparation Procedures 3.1.1  Raw Material  3.1.2  Raw Material Preparation for the Analysis  .  .  .  .  .  .  .  .  3.1.3  Solvent Extraction of Sugars  3.1.4  Isolation of Sugars from the Spent  .  .  Liquor and their Preparation for HPLC Analysis  .  .  .  .  .  .  .  vi  3.1.5  Secondary Hydrolysis of Nonreducing Sugars and Oligosaccharides  3.1.6  .  Sugar Hydrolysis Preparation  3.1.9  81  .  .  .  .  .  .  .  .  82  Acetonation of Cotton Hydrolysate Reducing Sugars  3.1.8  .  Preparation of Hydrolysate for Gas Chromatographic Analysis  3.1.7  .  .  -  .  -  .  .  -  .  .  .  .  .  82  .  .  .  .  .  .  83  .  .  .  .  83  .  .  .  84  .  .  .  84  .  85  .  85  Mixture of  Standards Preparation 3.1.10 Sugar Hydrolysis  .  Standards  .  Sugar Hydrolysis  .  .  .  .  Isopropylidene  Derivatives of Sugars Standards Preparation  .  .  .  .  .  .  .  3.1.11 Solvent Extraction of Cotton using C—13 Labeled Acetone  .  .  .  .  3.1.12 Preparation of Cotton Residues for X—ray Diffraction Analysis  3.2  .  .  .  .  3.1.13 Cotton Residue Carbanilation  .  .  .  .  3.1.14 Viscosity Determination  .  .  .  .  .  .  86  .  .  .  .  .  .  88  .  .  88  Analytical Methods 3.2.1  IR Analysis  .  —  .  .  .  Diffuse Reflectance  Infrared Fourier Transformer 3.2.2  —  (DRIFT)  Detection of Isopropylidene Derivatives by Gas Chromatography  .  .  .  .  .  89  vii  3.2.3  Sugar Analysis  High Performance  —  Liquid Chromatography (HPLC) 3.2.4  Cotton Solid State Study  .  .  .  .  89  C—13  —  CP/MAS NNR Spectrometry  .  .  .  .  .  .  91  3.2.5  X—ray Diffraction  .  .  .  .  .  .  92  3.2.6  Gel Permeation Chromatography  .  .  .  .  95  3.2.7  Viscosity Measurement  .  .  .  96  .  .  97  .  .  .  97  .  .  .  97  .  .  .  97  .  .  .  99  4 RESULTS AND DISCUSSION 4.1  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  Mechanism of Purification of Cellulose in Acidified Aqueous Acetone: Elucidation and Characterization 4.1.1  .  .  .  .  .  .  .  Characteristics of the Raw Material used for the Elucidation of the Mechanism.  4.2.1  IR  (DRIFT)  Changes  .  .  Study  (i.e.,  .  -  .  .  .  .  Hydrogen Bonding  hydrogen bond  disruption/destruction) Purification Treatment 4.1.2.1  .  during Solvent .  .  .  .  Acetone Effect on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  .  .  .  .  .  .  vii’  4.1.2.2  Other Factors Affecting Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  4.1.2.3  .  .  .  107  Effect of Type of Acid Catalyst and Acid Concentration on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  4.1.2.4  .  .  .  107  .  .  115  Effect of Temperature on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  4.1.2.5  .  Effect of Residence Time on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  4.1.3  .  .  .  119  .  .  .  126  Cotton Hydrolysis during Solvent Purification Treatment 4.1.3.1  .  .  Gas Chromatographic Investigation  .  (GC)  Isopropylidene  -  Derivatives of Sugars, Identification during Solvent  4.1.3.2  Purification Treatment  .  .  .  126  HPLC Analysis  .  .  .  134  .  .  .  ix  4.1.3.2.1  Deacetonation  —  Epimerization 4.1.3.2.2  Quantitation  .  —  .  .  134  .  150  153  the  Predominance of Acetonation Sugar Product Formation during theSolvent Purification Treatment 4.1.3.2.3  .  .  .  Changes in Weight Loss during Solvent Purification Treatment  4.1.4  .  .  .  .  .  .  .  .  .  C—13 CP/MAS solid state NNR Investigation  Isopropylidene  —  Intermediates in Residual Cotton during Solvent Purification Treatment 4.1.5  .  .  .  .  .  .  X-ray Diffraction Analysis  .  -  .  —  168  Changes  in Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  .  .  181  x  4.1.5.1  Acetone Effect on Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  4.1.5.2  .  .  .  181  Effect of Type of Acid Catalyst and Acid Concentration on Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  4.1.5.3  .  .  .  .  .  .  190  .  Effect of Temperature on Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  4.1.5.4  .  .  .  .  .  .  .  .  195  .  199  .  203  Effect of Residence Time on Crystallinity and Crystallite Breadth of Cotton Residue during Solvent Purification Treatment  4.1.6  .  .  .  .  .  .  .  Molecular Weight Distribution (MWD) Analysis  —  Changes in Molecular Weight  Distribution of Solvent Purified Cotton Residues  .  .  .  .  .  .  x  4.1.6.1  Effect of Acid Concentration and Type of Acid Catalyst on Molecular Weight Distribution of Solvent Purified Cotton Residues  4.1.6.2  .  .  .  .  .  .  .  .  204  .  212  .  220  Effect of Temperature on Molecular Weight Distribution of Solvent Purified Cotton Residues  4.1.6.3  .  .  .  .  .  .  Effect of Residence Time on Molecular Weight Distribution of Solvent Purified Cotton Residues  4.1.7  .  Viscosity Analysis  -  .  .  .  .  .  .  Changes in Viscosity  of Cotton Residues during Solvent Purification Treatment 4.1.7.1  .  .  .  .  .  .  224  Effect of Acetone Concentration on Viscosity of Cotton Residues during Solvent Purification Treatment  4.1.7.2  .  .  .  .  .  .  .  .  224  Effect of Acid Concentration on Viscosity of Cotton Residues during Solvent Purification Treatment  .  .  .  .  .  .  .  .  228  xli  4.1.7.3  Effect of Temperature on Viscosity of Cotton Residues during Solvent Purification Treatment  4.1.7.4  .  .  .  .  .  .  .  232  .  .  235  .  Effect of Residence Time on Viscosity of Cotton Residues during Solvent Purification Treatment  5  .  .  .  .  .  .  OVERALL MECHANISM OF PURIFICATION OF CELLULOSE IN ACIDIFIED AQUEOUS ACETONE  .  .  .  .  240  6  SUMRY  .  .  .  .  245  7  CONCLUSIONS AND RECOMt4ENDATIONS  .  .  .  .  .  .  .  250  7.1  Conclusions  .  .  .  .  .  .  .  250  7.2  Recommendations  .  .  259  .  .  260  8  .  .  .  LITERATURE CITED  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  xlii  LIST OF TABLES  Table # 1.1  Desirable characteristics of dissolving Pulps  2.1  Page  .  .  .  .  .  .  .  .  .  .  .  Bleaching Sequences for dissolving pulps  .  .  .  .  4  .  .  .  .  19  .  .  152  .  188  4.1.3.2.1 Reducing sugar (primary + secondary hydrolyses) yield in cotton hydrolysate following the treatment with: acetone: water: 90:10; 2 hr; 0.16 N HC1; 150 °C 4.1.5.1  Acetone effect on the crystallinity index and crystallite breadth of cotton residues treated with different concentrations of acetone, while other variables were kept constant (liquor/solid ratio: 10/1; 2 hr; 150 °C; no acid catalyst added) .  4.1.5.2  .  .  .  .  .  .  193  .  Effect of type of acid catalyst on the crystallinity and crystallite breadth of cotton residues treated with different acid concentrations, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1;2 hr; 150 °C; HC1)  4.1.5.4  .  Effect of type of acid catalyst on the crystallinity and crystallite breadth of cotton residues treated with different acid concentrations, while other variables were kept constant (acetone:water: 90:10; 2 hr; 150 °C; TFA) .  4.1.5.3  .  .  .  .  .  .  .  .  .  .  .  .  .  .  Effect of temperature on the crystallinity index and crystallite breadth of cotton residues treated at different temperatures, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA) .  .  .  .  .  .  .  .  193  .  198  xiv 4.1.5.5  Effect of residence time on the crystallinity index and crystallite breadth of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 1.5 N TFA)  .  202  Effect of residence time on the crystallinity and crystallite breadth of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 0.16 NHC1)  .  4.1.5.6  .  202  Effect of acid concentration on molecular weight distribution and polydispersity of cotton residues when TFA was used as catalyst (acetone:water: 90: 10; liquor/solid ratio: 10/1; 2 hr; 150 °C, TFA)  .  .  .  .  208  Effect of acid concentration on molecular weight distribution and polydispersity of cotton residues when HC1 was used as catalyst (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; HC1)  .  .  .  208  Effect of temperature on molecular weight distribution and polydispersity of cotton residues when TFA was used as catalyst (acetone:water: 90:10; liquor/ solid ratio: 10/1; 2 hr; 1.5 N TFA)  .  .  216  Effect of temperature on molecular weight distribution and polydispersity of cotton residues when HC1 was used as catalyst (acetone:water: 90:10; liquor/ solid ratio: 10/1; 1 hr; 0.16 N HC1)  .  .  216  Effect of temperature on molecular weight distribution and polydispersity of cotton residues when HC1 was used as catalyst (acetone:water: 90:10; liquor/ solid ratio: 10/1; 2 hr; 0.16 N HC1)  .  .  218  .  .  4.1.6.4  .  4.1.6.5  .  .  .  .  4.1.6.3  .  .  .  .  4.1.6.2  .  .  .  4.1.6.1  .  .  xv 4.1.6.6  Effect of residence time on molecular weight distribution and polydispersity of cotton residues when TFA was used as catalyst (acetone:water: 90:10; liquor! solid ratio: 10/1; 130 °C; 1.5 N TFA) .  .  .  223  xvi LIST OF FIGURES Fig. # 2.2.1.1  Page  Homo-intermolecular hydrogen bond in alcohols, carboxylic acids and amides (the hydrogen bonds are denoted by dotted lines) .  2.2.1.2  .  .  .  .  .  .  .  .  .  24  2—nitrophenol breaks its intramolecular H-bond to form an intermolecular one  .  .  24  Unit cell of native cellulose according to Meyer and Misch  .  .  29  Schematic cross—sections of cellulose chains according to Meyer (1942) ovals are glucose rings, and small circles are soda molecules  .  .  30  2.2.2.3  Intra—chain hydrogen bonds in cellulose  .  .  31  2.2.2.4  View of chain segments in cellulose I .  .  .  32  End view of cellulose chains in a unit cell  .  .  .  33  The two-part mechanisms of conversion of cellulose I into Na—cellulose I  .  .  .  35  Effect of increasing concentration of dimethylsulphoxide (DMSO) on the specific rotations at 25 °C of solutions (about 1%) of methyl 3-deoxy-3-Lerythro—pentopyranoside and of 1,2-0— isopropylidene 4-0-methyl—13-Dsorbopyranoside in ethylene chloride .  .  .  38  2.4.1  Preparation of 2-methyldioxolane  .  .  .  .  43  2.4.2  c&D-glucose  (pyranoid form)  .  .  .  44  2.4.3  cx—D-glucose  (furanoid form)  .  .  44  2.4.4  j3-D—mannose  (pyranoid form)  .  .  45  2.4.5  —D—mannose  (furanoid form)  .  .  45  .  2.2.2.1  .  2.2.2.2  .  .  .  .  .  .  —  .  crystal  2.2.2.5  .  2.2.2.6  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  2.3.1  .  .  .  .  .  .  .  xvii 2.4.6  The formation of a six-membered 4,6-dioxane ring .  .  .  .  .  • 47  •  2.4.1.1  2, 3-O—isopropylidene-D—ribofuranose  • 48  2.4.1.2  1,2:3, 4—di—O—isopropylidene-D—arabinose  • 48  2.4.1.3  1,2:3, 5-di-O-isopropylidene-D-xylose  • 48  2.4 .2.1  The formation of 1,2:3,4-di-Oisopropyl idene-a-D-galactopyranos ide  • 50  The formation of 1,2:5,6—di—O— isopropylidene-a-D—glucofuranose.  • 51  Partial hydrolysis of 1,2:5,6—0i sopropyl idene-D-gluco furanos e  • 52  2.4.2.2  2.4.2.3  2.4.2.4  Formation of an isomeric di-0isopropylidene-D-glucose in position the 1,2:3,5 .  • 53  Formation of 6-chloro-6-deoxy1,2:3, 5-di—0—isopropylidene—D— glucofuranose  .  54  6—acetyl—1, 2—O-isopropylidene—D— glucofuranose  .  • 55  Formation of 2,3:5,6—di-0— isopropyl idene-D-mannofuranose  .  • 56  1,2:3, 4-di-0-isopropylidene-Dgalactopyranose  .  • 57  .  2.4.2.5  .  .  2.4.2.6  .  2.4.2.7 2.4.2.8  .  .  .  .  2.4.2.9  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  1, 2-0-isopropylidene-D-galactopyranose  .  58  2.4.3.1 to 9 Synthesis reaction of sucrose  .  62  2.4.3.10  Acetylation of sucrose  .  • 62  2.4.3.11  Scheme for hydration of anhydrosugars during the hydrolysis of glycosidic structures  63  Proposed 0-isopropylidene intermediates for cellulose during high temperature in acidified aqueous acetone  70  .  2.5.1.1  .  .  .  .  .  .  .  .  .  .  .  .  .  xviii 4.1.2.1  Effect of acetone on hydrogen bonding of cotton residues treated with different acetone concentrations (liquor/solid ratio: 10/1; 150 °C; 2 hr; no acid catalyst added)  4.1.2.2  .  .  .  .  .  .  .  .  .  .  .  Effect of acid concentration on hydrogen bonding of solvent purified cotton when TFA was used as catalyst (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C) .  4.1.2.3  .  .  99  109  .  Effect of HC1 acid catalyst concentration on hydrogen bonding of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C)  .  .  .  111  Effect of temperature on hydrogen bonding of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA)  .  .  .  117  Effect of temperature on hydrogen bonding of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1)  .  .  .  118  Effect of residence time on hydrogen bonding of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA)  .  .  .  121  Effect of residence time on hydrogen bonding of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1)  .  .  123  4.1.3.1  1,2—O—isopropylidene—a—D—glucofuranose  .  .  127  4.1.3.2  1,2:5, 6—di—O—isopropylidene—a—D— glucofuranose  .  4.1.2.4  .  4.1.2.5  .  4.1.2.6  .  4.1.2.7  .  .  .  4.1.3.3  .  .  .  .  .  .  .  .  .  .  2,3:5, 6—di—O—isopropylidene—D— mannofuranose .  .  .  .  .  .  .  .  .  .  .  .  .  .  127  .  .  .  .  128  xix 4.1.3.4 4.1.3.5  1,2:3,4—di—O—isopropylidene—a—D— galactopyranose  .  128  .  132  GC chromatogram of acetonated reducing sugars of cotton hydrolysate of solvent purification treatment (acetone :water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; 0.16 N HC1)  .  .  133  HPLC sugar chromatogram of cotton hydrolysate obtained at 150 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; no acid catalyst) .  .  137  HPLC sugar chromatogram of cotton hydrolysate obtained at 130 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA) .  .  138  HPLC sugar chromatogram of cotton hydrolysate obtained at 130 °C (acetone: water: 90:10; liquor/solid ratio; 10/1; 2 hr; 0.16 N HC1) .  .  139  HPLC sugar chromatogram of cotton hydrolysate obtained at 150 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA) .  .  140  HPLC sugar chromatogram of cotton hydrolysate obtained at 150 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 0.16 N HC1) .  .  141  HPLC sugar chromatogram of cotton hydrolysate obtained at 180 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 1 hr; 1.5 N TFA) .  .  142  HPLC sugar chromatogram of cotton hydrolysate obtained at 180 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 1 hr; 0.16 N HC1)  .  143  GC chromatogram of nonreducing sugars of the cotton hydrolysate of solvent purification treatment (acetone :water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; 0.16 N HC1) .  4.1.3.6  .  4.1.3.2.1  .  .  .  4.1.3.2.2  .  4.1.3.2.3  .  4.1.3.2.4  .  4.1.3.2.5  .  4.1.3.2.6  .  4.1.3.2.7  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  xx 4.1.3.2.8  HPLC sugar chromatogram of 1,6anhydroglucose  .  144  HPLC sugar chromatogram of cotton hydrolysate obtained at 180 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 3hr;1.5NTFA) .  .  146  HPLC sugar chromatogram of cotton hydrolysate obtained at 180 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 3 hr; 0.16 N HC1) .  .  147  HPLC sugar chromatogram of cotton hydrolysate obtained at 150 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 0.8 N HC1) .  .  148  HPLC sugar chromatogram of cotton hydrolysate obtained at 150 °C (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 3 N TFA)  .  149  .  156  .  159  .  4.1.3.2.9  .  .  4.1.3.2.10  .  4.1.3.2.11  .  4.1.3.2.12  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  4.1.3.2.3.1 Effect of acetone concentration on the weight loss of solvent purified cotton (150 °C; 2 hr; no acid catalyst) 4.1.3.2.3.2 Effect of temperature on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA) .  .  .  .  .  .  .  .  4.1.3.2.3.3 Effect of temperature on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1)  .  160  4.1.3.2.3.4 Effect of residence time on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA)  .  162  4.1.3.2.3.5 Effect of residence time on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1)  .  163  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  —  xd 4.1.3.2.3.6 Effect of acid concentration on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; TFA)  .  166  4.1.3.2.3.7 Effect of acid concentration on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; HC1)  .  167  C—13 CP/MIS NMR spectrum of the residual cotton treated with normal acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; 0.16 N HC1) .  .  170  C-13 CP/MAS NMR spectrum of untreated cotton (control)  .  .  171  C-13 CP/MS NNR spectrum of the residual cotton treated with C-13 labeled acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; 0.16 N HC1) .  .  172  Non quaternary carbons NNR Spectrum of the residual cotton treated with C—13 labeled acetone (acetone:water: 90:10; liquor/solid ratio: 10/1, 2 hr; 150 °C; 0.16 N HC1) .  .  .  173  Proposed formation of isopropylidene groups along the cellulose chain  .  .  .  177  .  178  .  .  179  Comparison of diffraction patterns of treated (acetone:water: 50:50; liquor! solid ratio: 10/1, 2 hr; 150 °C) with untreated cotton (control)  .  .  185  Comparison of diffraction patterns of treated (acetone:water: 70:30, 80:20, and 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C) with untreated cotton (control)  .  .  186  .  .  4.1.4.1  .  .  .  .  .  .  .  4.1.4.2  .  4.1.4.3a  .  .  .  .  .  .  4.1.4.3b  .  4.1.4.4  .  .  .  .  .  .  .  .  .  .  .  .  4.1.5.2  .  .  Solvent purified cellulose chain of residual cotton .  4.1.5.1  .  .  Proposed formation of isopropylidene groups along the cellulose chain at higher temperatures .  4.1.4.6  .  .  .  4.1.4.5  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  xxii 4.1.5.3  Comparison of diffraction patterns of treated (acetone:water: 90:10; liquor! solid ratio: 10/1; 2 hr; 150 °C) with untreated cotton (control)  .  .  187  Comparison of diffraction patterns of treated cotton at different acid concentrations (acetone:water: 90: 10; liquor/solid ratio: 10/1; 2 hr; 150 °C; TFA)  .  .  191  Comparison of diffraction patterns of treated cotton at different acid concentrations (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; HC1)  .  .  192  .  197  .  200  .  201  .  206  .  207  .  4.1.5.4  .  4.1.5.5  .  .  .  .  .  4.1.5.6  4.1.6.2  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  Comparison of diffraction patterns of of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 0.16 N HC1)  4.1.6.1  .  Comparison of diffraction patterns of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C, 1.5 N TFA)  4.1.5.8  .  Comparison of diffraction patterns of cotton residues treated at different temperatures, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA) .  4.1.5.7  .  .  .  .  .  .  .  .  .  .  .  .  .  Effect of acid concentration on the molecular weight distribution of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C) Effect of acid concentration on the molecular weight distribution of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C)  Xxii  4.1.6.3  Effect of temperature on the molecular weight distribution of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor! solid ratio: 10/1; 2 hr; 1.5 N TFA)  .  214  Effect of temperature on the molecular weight distribution of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor! solid ratio: 10/1; 1 hr; 0.16 N HC1)  .  215  Effect of temperature on the molecular weight distribution of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor! solid ratio: 10/1; 2 hr; 0.16 N HC1)  .  217  .  4.1.6.4  .  .  4.1.6.5  .  4.1.6.6  Effect of residence time on the molecular weight distribution of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 130 °C; 1.5 N TFA)  4.1.7.1  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  °C)  .  .  .  .  .  .  .  .  .  .  .  °C)  .  .  .  .  .  .  .  .  .  .  .  .  227  .  230  .  231  Effect of temperature on viscosity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr)  233  Effect of temperature on viscosity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr)  234  .  4.1.7.5  222  .  Effect of acid concentration on viscosity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150  4.1.7.4  .  Effect of acid concentration on viscosity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150  4.1.7.3  .  Effect of acetone concentration on viscosity of cotton residues when no acid catalyst added (liquor/solid ratio: 10/1; 2 hr; 150 °C .  4.1.7.2  .  .  .  .  xxiv 4.1.7.6  Effect of residence time on viscosity of cotton residues when TEA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA)  237  Effect of residence time on viscosity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1) Mechanism ofpurification of cellulose in acidified aqueous acetone at higher temperatures  .  4.1.7.7 •  .  5.1  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  238  .  .  244  xxv LIST OF ABBREVIATIONS  DP  -  CP  —  CP/MAS  -  NNR  -  GPC  —  IR DRIFT  -  -  GC  -  HPLC  -  -  M CTH TFA AOX HBD HBA  A  -  -  -  -  -  -  -  -  Hz Cr1  -  -  A  -  DMF  -  r.t.  —  HNF  -  CuEn  -  Degree of Polymerization Centipoise Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance Gel Permeation Chromatography Infrared Diffuse Reflectance Infrared Fourier Transform Gas Chromatography High Performance Liquid Chromatography Weight-average Molecular Weight Number-average Molecular Weight Control Temperature and Humidity Trifluoroacetic Acid Adsorbable Organic Halides Hydrogen Bond Donor Hydrogen Bond Acceptor Angstrom Micron Hertz Crystallinity Index Wavelength Dimethylformamide Retention Time Hydroxymethylfurfural Cupriethylenediamine  —  xx’ FWHN  -  S.D.  -  MWD MW/ME  —  -  L  -  mL  —  —  g  -  hr  —  1 cm.  —  DMSO  -  —  mg  -  ppm  —  Ac  -  M  -  psi  Molecular Weight Distribution  Methyl Litre Millilitre Microlitre gram hour wavenumber  —  C  I  Standard Deviation  Polydispersity  —  Me  Full Width at Half Maximum Height  —  N  -  o.d.  -  XRD  -  G  —  TAPPI  -  Celsius Dimethylsuiphoxide Intensity Milligram Parts Per Million Acetyl Molarity Pound Per Square Inch Normality oven dry X-ray Diffraction Glucose Tecnhnical Association of the Pulp and Paper Industry  THF  -  GC-MS  -  —  Tetrahydrofuran Gas Chromatography-Mass Spectrometry  xxvii ACKNOWLEDGEMENTS  I  would  Professor,  like  to  thank my  supervisor  Faculty of  Forestry,  for his help,  Dr.  L.  Paszner,  interest  and  guidance throughout the duration of this work. Thanks are due to Dr. J.B. Farmer, Chemistry Department, The University of British Columbia, Dr. S.C. Ellis, Forestry,  The University of British Columbia,  Faculty of  Dr. D.M. Ouchi,  Simons International, Vancouver and the late Dr. P.R. Steiner, Faculty of Forestry,  The University of British Columbia,  their useful suggestions,  criticisms,  for  and encouragement  Acknowledgement and appreciation are extended to Dr. H. Grondey,  Chemistry  Columbia,  for her assistance in obtaining invaluable C—13 NNR  spectra,  Department,  are extended to Dr.  Research Institute of Canada the  University  of  British  interest and constructive criticism in this area.  Thanks  use  The  diffuse  spectrometer  Leclerc,  (PAPRICAN),  reflectance  (DRIFT)  D.  Pulp and Paper  for permitting me to  infrared  Fourier  transform  and helping obtain invaluable information  in hydrogen bonding. Many thanks to Dr. M.M. Nazhad for his assistance in X ray diffraction and GPC analyses. Acknowledgement is due to Dr.  C.  Jeong for his help in  HPLC and GC analyses. The help given to me by Mr. S.K. Yatich in statistical  xxviii  analysis, Faculty of Forestry (Remote Sensing), The University of British Columbia,  is duly acknowledged.  Grateful acknowledgement is made to Dr. H.A. Yassin, M.  Hassan,  Columbia,  Geography Department, and Mr.  E.  Faculty of Forestry;  Lee,  Dr.  The University of British  Department  of  Forest  Sciences,  for the various software programs that  helped me to produce many figures and their help in printing the thesis versions at different stages. Sincere graduate  acknowledgement  studies,  (Emeritus)  Faculty  goes of  to  former  Forestry;  Dr.  directors J.W.  of  Wilson  and Dr. D.L. Golding for their support and care.  Acknowledgement  is  made  to  the  Sudanese  Community  in  Vancouver for their support. Many  thanks  are  extended  to  my  brothers,  sisters,  relatives and friends for their encouragement and support. Finally, Awatif,  son,  deep gratitude is expressed to my wife, Teto,  and daughter, Azza for their patience,  endurance, unceasing support and encouragement.  —  xxix  DED ICAT ION  to my wife, Awatif  and  to the memory of my parents  1 INTRODUCTION  1.  North years,  American  have  been  environmental and  suiphite  Competition  dissolving hurt  pressures mills  from  by at  that  growing  pulp  high  many  are  producers, production  older  not  in  costs  prehydrolysis  economical  acceptance  recent  of  and kraft  clean  to  low—cost  synthetic  fibers and films is another major concern. Rayon staple, example,  is  polyster,  while plastic  displacing  under  enormous  cellophane  competitive  films  (oriented  (Mikulenka,  pressure  U.S.  for from  polypropylene)  1989).  up.  are  dissolving  pulp production declined from a level of 1.4 million metric tons  in the mid  1982  recession.  seventies to The  a  low of  Canadian  991000  dissolving  tons  in the  pulp  markets  followed a similar trend; declining from a peak of about 0.5 million metric tons  in 1969 to around 0.2  in 1990  (Durbak,  1993). Today, the U.S. dissolving pulp capacity is about 1.5 million tons,  tons,  largely  and  the  under  Canadian  utilized.  around  0.3  Dissolving  million  pulp  metric  manufacture  has remained more expensive than synthetic fibers becau.e of the  stringent  purity  cellulose yields Although different  (Durbak,  dissolving  pulping  requirements  and  low  processed  1993). grade  processes  and  pulps  are  under  varying  prepared  by  bleaching  conditions, at the end, the product cellulose should possess the following characteristics: 1- high alpha—cellulose content 2— low hemicellulose content  2  3- relatively high degree of polymerization (DP) 4— low ash content 5— good molecular uniformity. In  this  respect,  the  feasibility  competitiveness of dissolving pulp the yield of purified pulp. content  represents  However  the  total  amount  of  parameter  of  pulp  alpha-cellulose  purity.  originally  higher than the 28—32% retained in purified pulps 50%).  In  purification a  remarkable  this  respect,  the  losses  (pulping and bleaching) shrinkage  considerable  yield  hemicellulose  and  in  loss  lignin  but  15—18%  (i.e,  during  revenue  only  also  in  43  pulp  operations account for  industrial not  on  alpha-cellulose  wood remaining in the pulp is in the range of about  to  and  largely dependent  In other words,  important  an  is  manufacture  of  due  from  cellulose  to  the  removal  of  itself.  These  losses are reflected in the dissolving pulp price. At the present time, the lack of appropriate technology applicable to the manufacture of high-yield dissolving pulp appears to be the main reason for the appreciable losses in alpha-cellulose yield and quality acid  suiphite  used  in  pulping process,  manufacture  delignification under  harsh  and  of  for  dissolving  hemicellulose  acidic  of  cooking  a  pulp  in  long  pulp. removal  general.  time,  In  this  are  conditions.  has  The been  process,  accomplished Within  such  conditions also a considerable amount of degraded cellulose is the  removed final  in the pulp  spent  yield  of  cooking high  liquor.  As  a  alpha-cellulose  consequence, content  is  3  around 28-32% of that of the original wood During the  last decades the acid suiphite pulping  has witnessed a decline the world. sharp  (Golden,  This  is  switch  to  dissolving  pulp  proved  be  to  in the number of mills  due to the the  fact  that  prehydrolysis  manufacturing suitable  for  all  around  there has  been a  the  types  industry  all  kraft  because  1955).  of  pulping kraft raw  in  process  materials  (including resinous species)  that the acid suiphite process  was unable to pulp (Rydholm,  1965).  Prehydrolysis in kraft pulping is a pretreatment of the raw material to achieve the following:  1— to lower the substrate, and  hemicellulose  content  in  the  2- to give a better pore opening in the cell wall for easier liquor penetration during subsequent treatments (bleaching and alkali extraction). Hemicelluloses, particularly the xylans respond well to removal by prehydrolysis (Rydholm, 1965). Methods  for  attainment  of high  alpha-cellulose  purity  in wood puips are complex and a number of schemes for alkali extraction  of  high  brightness  bleached  pulps  have  proposed for removal of alkali-soluble impurities 1971;  Kleinert,  solubility acetate  been  found  Golden,  alone  puips.  acetylation,  1956). do  Other  However,  not  ensure  factors  filterability, to  1955).  qualify  the  brightness high  such  as  and  quality  (Schempp,  low  accessibility  products  alkali  viscose  and determination of pulp  been  during  haze  (Rydholm,  and  have 1965.  As for alpha—cellulose content in dissolving  pulp manufacture,  it is accepted to be in the range of  89—  4  97%.  Desirable  parameters  of  illustrated in Table 1 (Golden,  Table 1. Desirable (Golden, 1955). Pulp type  Bleached pulp yield  dissolving  puips  are  1955).  Characteristics ci-cellulose  of  Dissolving  Pentosans/ Mannan  Puips  Viscosity  %  CP  Acetate  28—32  95—97  <2.1  30—70  Viscose  32—36  89—94  <4.5  5—20  To reduce such losses  (i.e 2/3  of wood)  the current technological operations, a  novel  technique,  appears  to  resulting from  solvent purification,  offer  numerous  advantages.  These can be summarized as follows;  1.  high  alpha-cellulose  yield  by  provision  of  selective simultaneous carbohydrate hydrolysis  (no  cellulose unit degradation) and delignificatin of conventional unbleached puips, 2. the  maximum exploitation of the chemical value released  facilitated modification  by -  products  —  dissolution  sugar  and  lignin,  (hydrolysis)  without  (due to the formation of protecting  groups), 3.  of  cutting down bleaching costs,  5  4.  elimination of chlorine and chlorine compounds  as reagents in bleaching operations, 5.  reduction of process  effluents by recovery of  the solvent, and 6.  more uniform molecular weight  distribution of  the purified cellulose.  Obviously, sustainable less”,  such gains will be consistent with the new  development  whereby,  a  principle  significant  and  increase  “making in  the  more  from  industrial  revenue could be achieved. The mechanism of solvent purification has been proposed to  be  of  a  physico—chemical  character.  The  physical  phenomenon is based on the hydrogen bond disruption in the crystalline cellulose by acetone as a solvent. hand,  On the other  the chemical hypothesis of the mechanism is suggested  to be the formation of isopropylidene groups on carbohydrate chains that  lead to disproportionation of  the polymer  protection of the monomer sugar thus generated. Hence, hypotheses;  the  study  pursues  the  following  and  —  major  each one being supported by a number of sub—set  of hypotheses;  6  1-  H-bond  disruption/destruction  by  the  interaction  of  acetone with the cellulose hydroxyls  a—  acetone,  as  (acetone/water) molecules  and  a  major  volume  has  the  ability  brings  about  fraction to  in  the  deactivate  irreversible  solvent  the  weakness  water in  the  leads  to  hydrogen bonding system of the cellulosic material.  b—  interaction  stereochemical  of  acetone  changes  (i.e,  with  cellulose  rotational).  This  phenomenon  brings about rearrangement in hydrogen bonding that leads to considerable  disruption  of  the  H-bonding  system  of  the  cellulosic material.  c- acetone,  aided with high temperature and acid catalyst,  is able to interact with cellulose and give rise to further stereochemical  alterations  (i.e,  configurational  and  conformational) that subsequently disrupt/destroy the H-bond of the cellulose system.  d-  accessibility  reaction time,  of  cellulose  —  is  affected  acetone concentration,  by  temperature,  type of acid catalyst  and acid concentration and provides conditions for selective purification of dissolving puips.  7  2—  Formation  cellulosics  of  by  isoproDylidene  the  reaction  intermediates acetone  of  on  with  the  cellulose  molecules  a— acetone, of  in the presence of an acid catalyst,  interacting  uniformly  with  cellulose  is capable  and  forming  isopropylidene groups along the chains.  b— material removed by solvent purification consists largely of reducing and non—reducing sugars.  c—  formation  produces  a  of  isopropylidene  cellulosic  groups  material  on  with  cellulose high  chains  molecular  uniformity.  d— a major volume fraction of acetone, acid catalyst,  in the presence of an  leads to significant degradation  (i.e.,  drop  in CuEn viscosity) of the cellulose.  e— isopropylidene intermediates contribute simultaneously to decrystallization  of  the  original  cellulosic  material  and  enhancement of the residues crystallinity.  f— temperature, of  acid  acetone concentration,  catalyst  and  acid  reaction time,  concentration  differently to the removal of cellulose.  type  contribute  8  To investigate the validity of these hypotheses cotton has  been  used  throughout  Cotton  consists  amount  of  al., 1-  other  of  this  glucose  study  units  substances  are  as  a  mainly;  found  model  compound.  however,  in cotton  trace  (Hudson  et  1948). The following methods have been employed:  Infrared  i.e.,  (DRIFT)  hydrogen  study  bond  changes  -  in  hydrogen  disruption/destruction  bonding,  during  the  solvent purification treatment. 2- Cotton hydrolysis during solvent purification treatment. 2.1-  Gas  chromatographic  isopropylidene derivatives  (GC)  sugars  of  investigation  identification  -  during  solvent purification treatment. 2.2analysis  High i.  -  performance  liguid  deacetonation,  chromatography quantitation  ii.  predominance of acetonation sugar products, and iii.  (HPLC) -  the  changes  in weight loss during the solvent purification treatment. 3— C—13 cross polarization/magic angle spinning (CP/MAS) structural  investigation  —  formation  of  NMR  isopropylidene  intermediates in the solid state during solvent purification treatment. 4- x-ray diffraction analysis  -  changes in crystallinity and  crystallite breadth during solvent purification treatment. 5— Gel permeation chromatographic in  molecular  weight  distribution  (GPC)  analysis  (molecular  -  changes  uniformity)  during solvent purification treatment. 6— Viscosity analysis  —  changes  in viscosity,  i.e.,  degree  of polymerization during solvent purification treatment.  9  Factors  affecting  concentration,  residence  treatment time,  such  as  temperature,  type  acetone of  acid  catalyst and acid concentration have also been investigated. Since,  the main objective of this  study is the elucidation  and characterization of the mechanism, the  factors  will  be  carried  out  in  the investigation of  a way  that would  help  elucidate the mechanism of the solvent treatment rather than optimization of the process.  10  2  LITERATURE REVIEW  2.1 Trends of Current Dissolving Pulp Purification Processes (Pulping and Bleaching Operations)  and  The current pulp purification processes  (i.e.,  bleaching  be  operations)  are  chemical by-product generators. original  wood  (Golden,  1955).  economics  of  potential  is  lost  to  consequently,  during processing  These  losses  dissolving  reduction  known  in  have  pulp  In  this  purpose  effects  production  revenue.  tremendous  65-70% of the  for  adverse  pulping  and  this  on  the  represent  respect,  a  new  purification process of high specificity in delignification and hemicellulose removal is vitally needed. Conceptually, achieved  by  the  higher  application  conventional puips. the  of  of  content  hemicellulose  and  offers the potential  products  without  solvent  in  chemical  puips  can  be  purification  to  is expected to puips  lignin  further cellulose fragmentation. process  dissolving  This treatment  alpha-cellulose  removal  yield  by  the  without  increase selective  leading  On the other hand,  for recovery of  modification,  such a  chemical  ensures  to  by  solvent  recovery, and enhances the properties of the dissolving pulp (e.g., accessibility, Dissolving cellulose (Golden,  with 1955).  puips  molecular- uniformity etc.). are  highly  alpha-cellulose They  are  used  purified content  to  produce  grades  of  about  man—made  of  wood  89—97% fibres  11  (rayon and acetate), acetates),  and  (cellophane), plastics  films  chemicals  carboxymethylcellulose).  (methyl  produce dissolving puips,  cellulose  pulping processes  Two  mainly,  (cellulose and  are used to  from soft— and hardwoods.  These are the acid sulphite and prehydrolysis kraft pulping processes  (Rydhoim,  1965).  different pulp grades  of  By  means  of  these  varying quality  can  be  processes prepared,  each one suitable for a specific end—use. The  quality  required  of  a  dissolving  pulp  for  specific purpose depends on its purity and reactivity. example,  acid  “reactive”  sulphite  pulps,  dissolving  suitable  for  are  pulps  production  rayon  cellophane prepared under lenient rayon (viscose) conditions.  Prehydrolysis  kraft  pulps,  in  For  considered of  a  as and  processing  general,  are  assigned to produce stronger rayon fibres for uses such as high-wet-modulus textile rayon and high tenacity rayons for tire cords to  (Mikulen]ca,  produce  (Mikulenka,  1989).  cellulose  Cotton linters are also used  acetates  and  cellulose  plastics  1989).  —  Dissolving pulp products can be divided into two major groups based on the conversion products,  i.e.,  esters,  and  ethers.  Rayon and acetate cellulosic fibres are believed to  consume  77%  of  dissolving  pulp  production  (Durbak,  1993).  The products constitute viscose rayon staple, filament yarn, acetate  staple,  primarily  for  and  acetate  textiles,  fibres  tire  products and cigarette filters  (tow)  cords, (Durbak,  which  various 1993).  are  used  industrial  12  Cellulose cosmetics,  ethers  are  detergents,  additives  for  oil  widely  used  food products,  well  drilling  in  pharmaceutical,  superabsorbants,  muds.  Finally,  and  cellulose  nitrates are used in printing inks, laquers and rocket fuels (Mikulenka, The  1989). objectives  of  dissolving  pulp  purification  processes are as follows;  1— maximum removal of the lignin contained in the pulp before excessive cellulose degradation takes place, 2— depolymerization of hemicelluloses in order to facilitate their removal either during cooking (prehydrolysis) or in subsequent bleaching and steeping operations (sulphite), 3— control of cellulose depolymerization in order to achieve the required viscosity levels, and 4- attainment of various end—uses.  2.1.1  required  quality  levels  for  Acid Suiphite Pulping  The suiphite dissolving pulp processing conditions are considerably different from those for paper pulp production. The  retention  advantage, effect  of  while  hemicelluloses  in  in dissolving pulps  on the quality,  paper  pulps  they have  i.e the presence of  an  is  an  adverse  hemicelluloses  and lignin impair the molecular uniformity of the dissolving puips. The  sulphite  cooking  conditions  for  dissolving  pulps  are generally, characterized by fast temperature rise times,  13  high  maximum  temperatures,  sulphur dioxide  high  acidity  and  low  combined  The energies of activation of the sulphite  .  dissolving pulp cooks have been found to be as follows;  1- for delignification about 22 Kcal/mol 1942; Morud,  (Yorston,  1958)  2— for hemicellulose hydrolysis around 28 Kcal/mol (Konkin et al., 3—  1959)  for cellulose hydrolysis  (Wise et al.,  about  28—44  Kcal/mol  1952).  The action of acid sulphite liquors on hemicellulose removal during  dissolving  reactions  of  pulping  corresponds  carbohydrates.  These  to  include  hydrolysis the  acidic  hydrolysis of glycosidic bonds to form low molecular weight fragments  (reduction  solubility  in  oligomeric  and  the  galactose Usually,  of were  cooking  usually  Investigations of course  DP)  monomeric  hemicelluloses  the  of  a  spent  liquor sugars.  precedes sulphite  softwood  the  leading  cook,  first  sugars  to and  their  ultimate  degradation  to  hydrolysis  of  The that  of  cellulose.  liquor composition during showed  that  dissolved  arabinose (Wenzl,  and  1970).  this takes place at a temperature of about 100 C 0.  Xylose appears next followed by mannose and small quantities of glucose at a higher cooking temperature of 130 C 0.  This  has been substantiated by analysis of the sugars in the side relief  condensate  constitute more than  (Wenzl, 60%  of  1970).  Arabinose  the total  sugars  and found  xylose in the  14  pulping  effluent  originates  stream.  from  the  arabinofuranose)  In  acid  side  originates  in the spent the  total  nature  liquor,  sugars  and  cleaved  pyranosides. arabinose factors  This  in  the  prevail  much  accounts suiphite  over  1970).  (Wenzl,  (Hamilton,  more  Similarly,  for  the  cook.  chemical  In  The  the  15-25%  of  polymeric  Furanosidic  than  rapid  contrast,  carbohydrates  1962).  easily  4—0—  only  1970).  involving  (L  a  arabinose constitutes  detected  arabinose  on  from galactoglucomannan.  reaction mechanism  are  the  arabinofuran  (Wenzl,  has been studied by Hamilton bonds  labile unit  methylgiucuronoarabinoxylan galactose  softwoods,  those  of  dissolution  However,  of  morphological  considerations,  in  that  the  rate of hydrolysis of glucomannan and xylan is about 15-3 0 times  greater  than  that  of  cellulose,  about  or  4—5  times  that predictable with model compounds. In addition to glycosidic hydrolysis reactions,  acetyl  groups on the hemicelluloses are also hydrolyzed (split off) yielding acetic acid. Other  carbohydrate  reactions  taking  place  in  the  sulphite cooking liquor include conversion of aldoses  into  alpha- hydroxysuiphonic acids, as well as aldonic acids. The alpha- hydroxysuiphonic of the  loosely combined  acids represent a sulphur dioxide  large proportion in  spent  liquors.  Under suiphite pulping conditions xylose can be dehydrated to furfural, while glucose, is  decomposed  to  at relatively high temperature,  levulinic  and  formic  acids  from  15  hydroxymethylfurfural product.  as  the  Dehydration reactions  high temperature such as pulp-type  cooking.  intermediate are  favoured by  are normally  Details  the  found  low pH  and  in dissolving  decomposition  reactions  occurring in the spent liquor are shown elsewhere  (Ingruber  et al.,  2.1.2  1970).  Prehydrolysis Kraft Pulping  Earlier,  before  1950,  produced exclusively (Rydholm, method  by  dissolving  the  acid  grade  sulphite  puips  were  pulping process  1965). Although the suiphite process is still the  of  choice  dissolving  for  puips  production  the  (Schempp,  recent remarkable decline and  of  dehydration  worldwide  change  in  1971),  certain  of  partly  because  in the number of the  raw  types  material  of  of the  sulphite mills base,  sulphite  pulping for dissolving grade puips has now been considerably replaced al.,  by  the  prehydrolysis  kraft  process  (Simmonds  et  1953; Richter, 1956). This process is vital for pulping  resinous non—woody suitable  species  such  materials raw  as  pines,  (e.g.,  materials  for  jute  Douglas—fir, and  pulping  kenaf) by  the  larches  which acid  are  and not  suiphite  process. In addition, the conventional kraft process is known to stabilize  residual  reaction,  whereas  hemicelluloses it  is  against  not possible to  further obtain  alkaline  acceptable  quality dissolving pulp through subsequent treatment in the  16  bleach plant.  In order to prepare a dissolving grade pulp by  the kraft process, acidic  it is of importance to give the chips an  pretreatment  (Rydhoim,  before  the  alkaline  pulping  stage  considerable  amount  1965).  During  prehydrolysis  of material,  treatment,  in the order of  a  10% of the original wood,  removed in the acidic solution. Under these conditions 130 C 0,  2 hr),  (Bernardin,  of  1958).  the  (100-  the cellulose is fairly resistant to attack However,  the  hemicelluloses  greatly degraded to a much shorter chain length 30%  is  original  (Bernardin,  DP)  have  been  (i.e about  1958)  and  can,  therefore, be easily removed in the subsequent kraft cook by means  of  Primary cook.  peeling  and  other  delignification However,  because  alkaline  also  takes  of  in  unbleached  place  possible  reactions during the prehydrolysis lignin  hydrolysis  prehydrolysis  reactions.  during  the  kraft  lignin  condensation  treatment,  the residual  puips  is  difficult  to  solublize during bleaching as compared to conventional kraft puips  (Rydhoim,  1965).  —  Prehydrolysis in kraft pulping is assigned primarily as a  pretreatment  of  chips  to  reduce  only  not  the  residual  hemicellulose content in the final pulp, but also to provide a better pore opening in the fibre wall matrix in wood chips for  easier  1965).  penetration  It  is  treatment  is  also  of  the  alkaline  worth mentioning  designed to  afford  hemicellulose content species.  that  xylose  This  liquor the  prehydrolysis  recovery  could be  (Rydholm,  of  from high economical  17  value. While recovery of hemicellulose values from suiphite waste  liquor  by  fermentation  to  ethanol  protein is a well known process similar  processes  based  proposed by Suizer as  yet.  alkali  In  on  conclusion,  extracted)  the  high  single  (Sjolander et al.,  kraft  (Switzerland)  and  prehydrolysates  cell  1938),  although  have not been implemented  final  purified  alpha-cellulose  (bleached  pulp  yield  and by  prehydrolysis kraft pulping process is in the range of 3236% from the original wood (Simmonds et al.,  2.1.3  1953).  Bleaching  The object of bleaching in dissolving pulp manufacture is the removal of residual  lignin,  residual hemicelluloses  and resins. For this reason, bleaching is considered to be a continuation of the cooking process. The bleaching operation used is completely dependent upon the characteristics of the cooked  pulp  and  the  end—use  (e.g.,  cellophane,  nitrate,  acetate, etc.). Bleaching  results  colouring materials conventional bleaching  conversion.  removal  from puips.  purification  operations),  hemicelluloses, impurities,  in  ash,  which Puips  bleached  degraded  intended  it for  residual  However,  processes  the  make  of  lignin  with the  (i.e.,  cellulose unsuitable conversion  current  pulping  product and for to  and  and  contains other chemical  viscose  or  cellulose derivatives must also meet exacting specifications  18  with respect to alpha—cellulose content and viscosity. A low content of ash and resin is also desirable. In current kraft pulping technology partial removal of hemicelluloses  is  achieved  by  prehydrolysis  treatment.  Purification of dissolving puips by alkali treatment, and by additional steps in some cases,  is carried out in connection  with the bleaching operations. In these processes the attack on the Jayme  cellulose and (1938)  consequent yield  losses,  are  severe.  stated that an increase of the alpha—cellulose  content of pulp from 88  to 96% by the hot alkali refining  process will result in a weight loss of 25-30% of the pulp. Richter  (1940)  pointed out that the upper  limit of alpha-  cellulose obtainable by hot refining was 95%, alpha—cellulose  could  processing conditions. to  considerable  also  reached  be  Those treatments,  degradation  of  the  although 97%  under  however,  cellulose  harsher also  led  chains  and  were associated with a decrease in viscosity. Currently,  chlorine compounds are in wide use  in pulp  bleaching. This is because they are most effective oxidizing agents  (i.e  stable  brightness  selective  alpha-cellulose delignification cellulose  yield  delignification),  and  leaving  content. proved since  a  On  to  pulp the  occur  relatively other  at  significant  the  compounds  serious  environmental  are  highly problems  toxic  a  highly rich  hand,  expense  hydrolytic  also took place on the cellulose fibres. chlorine  offering  pulp of  (e.g.,  the  degradation  In addition, and  in  these  contribute dioxins,  to and  19  adsorbable organic halides  (AOX)).  As  a result millions  of  dollars have been spent on pollution control projects by the pulp  and  paper  industry  to  eliminate  toxic  organochiorine  compounds from bleach plant effluents. Typical  bleaching  sequences  illustrated in Table 2.1  for  dissolving  (Ingruber et al.,  pulps  1983).  Table 2.1 Bleaching Sequences for Dissolving Puips et al., 1983). End Use  Cook Type  Plastic Filler Suiphite  are  (Ingruber  Bleach Sequence CEDED,  CEDPD,  Prehydrolyzed Kraft  CEHDED  Nitration  Suiphite Prehydro lyz ed Kraft  CE C 0 H,  Textile Rayon  Suiphite Prehydrolysis Kraft  CE°CHD, CEHDED CHEDED  Regular Acetate  Suiphite Prehydrolyzed Kraft  CE°CHD, CE°HD ECEHD XDEDH, CEHXDED XCEHDED  Tire Cord  Prehydrolyzed Kraft  CEHXD, CEHDX, XDEDH, CHEDX XCEHDED  Plastics  Suiphite  ECE°HXD  CE°CH  CE°HD,  CE°CH  Where: C 0 E E D P X H  = =  = = = = =  Chioronation Pressure hot caustic extraction (HCE) Mild (less than atmospheric HCE) Chlorine Dioxide Peroxide Cold caustic extraction Hypochlorite  20  It must be noted that nearly all bleaching sequences in the  above  series  start  with  chioronation  (C),  a  step  now  definitely linked with dibenzofurane and dioxin formation in bleach  plants  realized (such  (Rotluff,  that  as  a  1989).  compromise  a  C/D)  is  less  on  At  the  this  same  first  acceptable  time  it  bleaching  stage  dissolving  for  is  pulp  purification because of the decisive effect of bleaching on the  final  quality  of  dissolving  pulps.  Thus  the  lack  of  suitable alternative bleaching sequences which can guarantee the same high purity as the CED,  CEDED,  CEH sequences will  certainly put new pressures on dissolving pulp manufacturers to take a look at new pulp processing systems pulping  and  purification),  line  with  known  to  be  (e.g.,  solvent  environmentally  benign. In  conventional  these  chemical  efforts,  pulps  solvent  could  be  desirable new approach in this respect. treatment  removing  in  polysaccharides  offers  cellulose content. can  easily  oxidizing dioxide. of  be  readily such  pulp  The  practical  and  specificity of  molecular  yield with  weight  high  alpha  bleached as  with  hydrogen  mild,  peroxide  less and  toxic  chlorine  solvent pulping is known to produce pulps  low extractives  1985).  higher  low  and  a  of  Residual colour in solvent purified pulp  reagents Further,  lignin  purification  (Quinde,  1990)  and ash content  (Behera,  21  2.2  The Hydrogen Bond  In  this  work,  Development  -  acetone  is  used  as  the  solvent  of  purification due to the fact that acetone has the ability to penetrate  into  considerable  cellulosic  stereochemical  acetone  is  solvent,  i.e.,  Isaacs,  the  classified HBA,  1974)).  as  material  changes. a  Thus,  the  At  dipolar  (Frey—Wyssling,  and  hypothesis  1953;  the  same  time,  aprotic  hydrophilic  Bax et al.,  irreversible  prompted  -  about  the  changes  hydrogen bonding of the cellulose by acetone disruption  bring  -  1972;  caused  in  hydrogen bond  following  review  on  hydrogen bond theory and practices.  2.2.1  Hydrogen Bonding  H-bond Donor/Acceptor Solvents  -  Hydrogen bonding is of stabilization living  and  shape  organisms  carbohydrates general  such  bound  another atom,  of  solvent)  a  biological  forms  et  bond a  is  for the  molecules  nucleic  Jeffrey  hydrogen atom  importance  acids,  al.,  in and  1991J.  that  secondary  when bond  A a to  the second bond is referred to as a hydrogen  system  lead to changes the  1988;  the  1974).  interaction of in  large  proteins,  hydrogen  bond (Joesten et al., The  as  (Reichardt,  definition  covalently  of  significant  at  different molecules certain  reaction  in rate of the reaction  substrate,  Consequently,  (e.g.,  solute—  conditions  might  and structure  these  of  structural  22  (stereochemical)  changes have a  modification of  the hydrogen  considerable  bonding of  the pulp industry, mercerization (e.g.,  impact on the  the  substrate.  18-30% NaOH)  for the provision of accessible cellulose.  In  is used  In other words,  the accessibility of cellulose can explicitly be understood as a new spatial rearrangement of the hydroxyls of the sugar residues, the  i.e.,  cellulosic  new positioning of hydrogen bonding within system.  Thus,  hydrogen  bond  disruption  by  acetone represents a major hypothesis in this study. The 1919  concept  by Huggins  bonding  —  of  hydrogen  (1971).  applied to the  The  bonding has first  been  outlined  publication  on  in  hydrogen  association of water molecules  —  was in 1920 by Latimer and Rodebush (1920). However, earlier than this publication hydrogen bonding was pointed out to be the cause of association in ammonium salts whereby a proton links the ammonia molecule to the ion (Werner, A hydrogen bond R  -  X  -  H and :Y  R  -  X  is  formed by  1903).  interaction  between  -  R according to the following equation  -  H + :Y  -  R  R  =  -  X  -  H...Y  the  R  -  where: R  —  X  —  electron  H is the proton donor and :Y pair  for  the  bridging  —  R makes available an  bond.  In  this  context  hydrogen bonding can be regarded as a preliminary step in a Bronsted  acid—base  reaction product R  reaction —  X...H  -  which Y  -  R.  leads  to  X and Y  a  are  dipolar atoms  of  23  higher electronegativity than hydrogen such as C, N, P, 0,  F,  etc.  is  Both  inter-  and  intramolecular  hydrogen  bonding  possible, the latter when X and Y belong to the same molecule. The  most  important  electron  pair  donors  (EPD)  i.e  hydrogen bond acceptors (HBA) are the oxygen atoms in ethers, carbonyl compounds, as well as nitrogen atoms in amines and N— heterocycles. mides, hydroxy—, amino— and carboxyl groups are the most important proton donor groups (HBD). bonds are formed by the pairs 0 H...0, weaker ones by N and  C 2 C1  H...N  —  —  -  H.. .0,  0  Strong hydrogen -  H.  .  .N,  H.. .N, and weakest by C1 C 2  (Reichardt,  1988).  However,  and N  -  H.. .0,  —  very  strong  hydrogen bonds are considered to be developed by carboxylic acids  (13  Kcal/mol)  (Biermann,  1993).  Thus,  the  bond  dissociation enthalpy for normal hydrogen bonds is between 1 to 10 Kcal/mol When  two  intermolecular 2.2.1.1. molecules  (Biermann,  On  or  equal  hydrogen  the  for  more  other  1993)  bond hand,  instance R  —  intermolecular hydrogen bond.  molecules is the  0  —  formed  associate, as  shown  association H.  .  .N  is  of  called  homo—  in  Fig.  different a  hetero—  24  R  R  0”H-O RC,,CR  0 H°H H ..  Figure 2.2.1.1. Homo—intermolecular alcohols, carboxylic acids and amides are denoted by dotted lines).  Hydrogen  bonds  can  be  either  O”H-N  hydrogen bond in (the hydrogen bonds  intermolecular  or  intramolecular. Both types of hydrogen bonds can be broken. For example 2—nitrophenol breaks its intramolecular hydrogen bond to form an intermolecular one with electron pair donor (EPD)  solvents  triamide  —  (e.g,  HMPT etc.),  anisole, see Fig.  hexaniethylphosphoric  acid  2.2.1.2.  00  -H••EPD  Figure 2.2.1.2. 2-nitrophenol breaks its intramolecular H bond to form an intermolecular one.  25  Hydrogen structural  and  bonds,  generally,  spectroscopic  have  the  characteristics  following (Schuster,  1976) ; 1- The distance between the neighbouring atoms involved in the hydrogen bond (X and Y) are smaller than the sum of their van—der—Waals radii. 2- The X H bond length is increased and hydrogen bond formation causes its IR stretching mode to be shifted towards lower frequencies. 3- The dipolarity of the X H bond increases on hydrogen bond formation, in turn, this gives rise to a larger dipole moment of the complex than expected from vectorial addition of its dipolar components R X H and Y R. 4— Due to reduced electron density at protons involved in hydrogen bonds, they are deshielded, resulting in remarkable downfield shifts of their -H-NNR signals. 1 5- In heteromolecular hydrogen bond, a shift of the Bronsted acid/base equilibrium R X H. . . Y R = R X...H Y R to the right hand side with increasing solvent polarity is found. -  -  -  -  -  -  -  Similar  -  conclusions  -  -  -  on  the  hydrogen  bond  energy  were  already drawn by Coulson at the symposium held in Ljubljana in  (1957).  He found that the theoretical net hydrogen bond  energy for ice develops as the result of the following four terms,  each  being  of  the  order  of  magnitude  of  the  bond  energy itself. The contributions are as follows: a— electrostatic  +6  Kcal/mole/bond  b— delocalization  +8  Kcal/mole/ bond  c— repulsive overlap of electron clouds  -8.4Kcal/mole/bond  d— dispersion  +3  Total  Kcal/mole/bond  +8. 6Kcal/mole/bond  26  Coulson noted that the experimental value for Kcal/mole/bond.  He  attributed  the  ice was +6.1  difference  between  the  experimental and the theoretical values to the variation in length of the hydrogen bond. Regarding the nature of the forces in the hydrogen bond (Vinogradov can  be  et  al.  ,  1971;  considered  interaction.  as  Kortum,  1972),  dipole—dipole  the  hydrogen  as  or  a  Since hydrogen bonding prevails  bond  resonance  only when the  hydrogen bond is bound to an electronegative atom, the first speculation that R  —  it X  —  concerning the  consists H.  .  .Y  of  R  -  a  nature  of  the hydrogen  bond  is  interaction  such  as  dipole-dipole  (Vinogradov et al.,  1971.  Kortum,  1972).  This assumption is supported by the fact that the strongest hydrogen bond  is  formed  in pairs  in which the hydrogen  bound to the most electronegative element H=155  KJ/mol).  The  greater  strength  of  compared with nonspecific dipole-dipole  (e.g., the  atom.  more easily. for  the  linear  This  allows  it to  linear  geometry  arrangement  Furthemore,  interaction  .  F,  bond  is due  relative to  approach another dipole  of  the  the  maximizes  hydrogen  the  (Reichardt,  shortness  to  repulsive  bond,  attractive  forces.  forces  bonds  radii  Also  because  a  and  1988).  of hydrogen  considerable overlap of van—der—Waals rise  H..  In conclusion this dipole assumption accounts  minimizes the repulsive ones  give  —  hydrogen  to the much smaller size of the hydrogen atom, any other  F  is  the  indicates  and this would existence  of  symmetrical hydrogen bonds of the type F...H...F can not be  27  explained in terms of electrostatic modelling. When the X  -  Y  distance is extremely short, an overlap of the orbitals of the X  H  -  bond  and  the  electron  pair  covalent interaction (Simmering,  of  1964)  :Y  could  lead  to  a  as shown below:  R-X-H...Y-R=R-X...H-Y-R  According to the above equation, described by two  this situation can be  contributing protomeric  structures,  which  differ only in the position of the proton. Solvents containing proton—donor groups are called protic solvents  or  acceptor  groups  1976).  HBD  (Parker, are  1962).  designated  Solvents  HBA  having  solvents  (Taft  protonet  al.,  The abbreviations HBD and HBA refer to hydrogen bond  donor and acceptor,  respectively and not to electron pairs  involved in hydrogen bonding. Aprotic solvents are those which are without proton-donor groups. Typical alcohols, hand  solvents  (HBD)  are  water,  carboxylic acids and primary amides.  dipolar  ketones,  protic  and  aprotic  (HBA)  sulphoxides  solvents (i.e.,  are  CH C 3 N,  ammcmia,  On the other  ethers, 2 N 3 CH , O  amines, (CH C 2 ) 3 0,  (CH S 2 ) 3 O). In the case of protic solvents (HBD), the solute acts as HBA  -  base and the solvent as HBD  -  acid while for dipolar  solvents the reaction is reversed (Taft et al.,  1976).  28  Hydrogen Bonding in Cellulosic Material  2.2.2  The hydroxyl groups of the cellulose units involved in hydrogen  bonding with neighbouring  ones  and with  those  of  adjacent óhains, have been the centre of investigations for many years.  Cellulosic  treatments  differ  crystallinity,  as  investigative cellulose  from  considerably evidenced  methods.  (i.e.,  consequences  materials  and  in  their  degree  of  a  large  number  of  super—structure  of  the  bonding  for the pulping,  sources  by  Since  hydrogen  various  system)  has  important  purification and papermaking  processes as well as for the cellulose reactivity in the end use,  this  part  of  the  review  will  focus  on  it  at  some  length. In 1937, Meyer and Misch (1937)  in their elucidation of  the supermolecular structural nature of cellulose proposed a model of a unit cell. It is illustrated in Fig.  2.2.2.1. The  arrangement of the crystalline region was deduced from X—ray data.  The dimensions  of  their monoclinic unit  follows:  a b c f3  = = = =  8.3 A 10.3 A 7.9 A 84°  cell  are as  29  Tr L___  4.  Lr  ‘t—-  kcZJJZ7  _TS/ 0  V  i  IC  a—8.35A  Figure 2.2.2.1. Unit cell of native cellulose according to Meyer and Misch (Meyer et al., 1937). —  Meyer  (1942)  about natural  has  also been able to give,  and synthetic polymers,  for Celluloses I, II,  in his  different  III and IV as shown in Fig.  book  structures 2.2.2.2.  30  Native cellulose (cellulose I)  Cellulose ti  Cellulose IV V  Soda cellulose Ui  Soda cellulose IV  (WOf..r  CeLLcc1ose)  Figure 2.2.2.2. Schematic cross—sections of cellulose chains according to Meyer (1942) ovals are glucose rings, and small circles are soda molecules. —  It  is  of  importance  forties Hermans of  Cellulose  possibilities  (1949),  Fibers”, for  to  point  in his book,  out  that  the  late  “Physics and Chemistry  published diagrams  intra-chain  in  hydrogen  illustrating many  bonds  in  the  state. This was the first attempt in this area. Fig.  solid  2.2.2.3  31  shows  the  possibility  intra-chain hydrogen  of  bond  in  the  cellulose.  (a.)  Figure 2.2.2.3. (Hermans, 1949).  Later workers 1958) a  in  Intra—chain  1959,  hydrogen  particularly  (Petitpas et al,  bonds  after  in  Hermans  1956; Caristrom,  cellulose  and  other  1957; Honjo et al,  postulation of intra-molecular hydrogen bonds imposing  twist  in  the  Liang et al., because  it  infra—red  is  molecules  (Liang  and  Marchessault,  1959;  1959) questioned the Meyer and Misch unit cell unable  spectral  to  show  analysis,  this they  twist.  Based  proposed  the  on  their  crystal  32  lattice  model  for  Cellulose  which  I,  intra— and intermolecular hydrogen bonds  demonstrates (see Figs.  both  2.2.2.4  and 2.2.2.5).  IOTpLan o-’-4%. .1-f bo n cJ s IO( p4ont  ,/J-\orcHBon4si  4 -e k- a. C Ji, A  ott  H bods in  ‘4 ore. wrochoin H bondt  /  ‘1  b  Figure 2.2.2.4. View of chain crystal (Liang et al., 1959).  segments  in  cellulose  I  33  •  p1o  I  ‘IS •t%  I  I’ I\  I\  ocy2.  H m I  /  I  /  / / / F  I I I’  JL7Q O4L FL Hoii1  I• I I  r  002.  i  ‘1 I’  F  S  I  ‘  ‘  ‘°<Figure 2.2.2.5. End view of cellulose chains in a unit cell (Liang et al., 1959). The  intramolecular hydrogen  bonds  are responsible  for  the stiffness and rigidity of the cellulose molecule and for the  stabilization  of  the  two-fold  helical  structure.  In  addition, this intramolecular hydrogen bonding also sustains the 1.03 accord  ma crytallographic repeating distance which is  with  the  conformational  energy  relation to bond rotations for the C-i 0—4 glucosidic bonds The  relative  (Sarko,  considerations 0-1 and the C-4  in in —  1978).  positioning  of  the  cellulose  molecules  with respect to one another in the unit cell determines the possibility bonds.  for  the  formation  of  intermolecular  The development of van—der—Waals  hydrogen  forces between the  fOTp(&.  34  neighbouring molecules inside the same crystal lattice plane is  also  hydrogen  influenced bonds  are  by a  positioning.  this  significant  factor  Intermolecular  for  the  internal  packing of the cellulose chains in the crystal lattice.  The  density  and  of  the  interchain  between the planes  hydrogen  affects  to  bonding  inside  a great extent the  swelling  action and the accessibility of the crystalline domains. Later,  Nishimura  Sarko  and  (1987)  studied  the  conversion  of  structure.  The analysis of crystallite sizes of cellulose I  Na—cellulose  and alkali cellulose I  cellulose  from the  I  crystal  I  during the transformation  indicated  that the change took place in two steps; the first is a fast step and resulted in conversion of 65% of cellulose I Na-cellulose  I.  The  alkali  cellulose  second  step  crystallite  I were  it was  62  and  observed  sizes 35  A,  for  cellulose  respectively. et al.,  (Nishimura  into I  and  At the  1987)  that  the conversion process was slow and the crystallite size of cellulose  I  decreased  gradually until  disappearance,  while  that of Na-cellulose I increased steadily to reach 50 was  also  noted  (Nishimura  et  al.,  1987)  that  A.  It  during  mercerization  a simultaneous change in unit cell parameters  of  I  cellulose  took  place.  In  this  mechanism for mercerization (see Fig. conversion zone 1987)  of  process  the  was  cellulose,  assumed was  to  communication,  2.2.2.6),  start  proposed  in  a  in which the  the  (Nishimura  amorphous et  al.,  35  NaOH  l l liI N1 •  •  •  NaOH  CELL. I  • •  •  •  •  NaOH  CELL. I Na-CELL.!  Na-CELL.!  Figure 2.2.2.6. The two—part mechanisms of conversion cellulose I into Na—cellulose I (Nishimura et al., 1987).  Currently, suitable  for  obtaining  accessibility,  dimensional  a  purified  molecular  uniformity  stability mercerization  on bleached puips.  are weakened.  improved out  both the inter- and  The transformatin of  native cellulose to mercerized cellulose to II)  and  with  is usually carried  During this process,  intramolecular H—bonds  cellulose  (from cellulose  is an irreversible exothermic phenomenon because  the modification of the crystalline network (Petitpas, Petitpas et al.,  1950; Lal,  of  I of  1948;  1974).  General procedures for mercerization vary depending on the aim to be achieved. Mercerization is usually carried out at  NaOH  concentrations  of  18-25%,  for  different  time  36  intervals and at different temperatures. In this process the treated pulp is subjected to degradation and results  in an  appreciable loss of fibrous material. To  attain  enhancement  of  accessibility, crystallinity  molecular  and  to  uniformity,  reduce  solvent purification could be the practical  such  answer  losses in this  respect.  2.3.  Solvent Effect on Stereochemistry and Mechanism  In this work the influence of acetone as a solvent on the  structural  alterations)  may  physicochemical about on both acetone  be  quite  changes  as  a  could  stereochemical The  expected  are  substantial  to  insoluble portions  major  well  (i.e •,  profound.  which  soluble and  (i.e.,  composition)  transformations  volume  be  fraction  demonstrated  of  of  in  be  brought  cotton by  the  the  solvent  following  chapter (Results and Discussion). It has been verified 1968;  Stoddart,  solvents  have  1971;  (Tchoubar,  Amis,  considerable  1966;  1966; effect  Lemieux et_al.,  Reichard, on  stereochemistry of the reaction course.  the  1988)  that  mechanism  and  In other words,  the  solvent can influence both the rate and the mechanism of a reaction.  Lemieux  et  al  (1968)  studied  the  changes  in  conformational equilibria of the methyl 2-deoxy-13-L-- and 3deoxy-3-L-erythro-pentopyranosides different  solvents  such  as  by  dissolving  acetone,  them  in  chloroform,  37  dimethylsuiphoxide, water etc. 1968)  that  marked  changes  It was noted  in  optical  rotation  place. These changes were attributed to solvation  of  specific  the  substrate  solute—solvent  by  (Lemieux et al, taken  the specificity of  different  solvation  had  has  solvents.  brought  change in electron density of the system,  This  about  i.e.,  some  the change  in the electronic state of the oxygen atoms involved in the hydrogen bonds with a solvent appears to have a considerable influence on the  conformational  equilibrium.  Using nuclear  magnetic resonance and polarimetry techniques Lemieux et al. (1969)  studied  the  effect  of  dimethylsuiphoxide  (DMSO)  concentration on the specific rotation at 25 0 C of solutions of  methyl  3-deoxy-J3-L-erythro-pentopyranoside  isopropylidene dichioride,  and  4 -O-methyl-f3-D-sorbopyranos ide  see Fig.  2.3.1.  It was  noted  in  1,2-0ethylene  (Lemieux  et  al.,  1969)  that with increase of DMSO the numerical rotation of  sugar  derivatives  was  increased  conformation had taken place. al.,  1969)  groups  and  It was  concluded  in a hydrogen bond with a base  oxygen atom. hydrogen  change  in  (Lemieux et  (i.e.,  DMSO)  results  in the direction of  the  This makes the oxygen atom a relatively better  acceptor  (Lemieux  et  in hydrogen al.,  between two  opposing  solvent,  much  is  gradual  that the engagement of the hydrogen of hydoxyl  in a polarization of the H-0 bond  added  a  1969)  axial  greater  bond  formation.  that  the  hydoxyl than  when  It  dipole  groups, both  also  interaction  both of  was  the  bonded  to  hydroxyl  groups are acylated by electron withdrawing acyl groups.  38  ‘$0  [aID  ::E  :  \ -k ‘>  -40  .20  40  20  60  SQ  2 DNSO . C C1ICL A ...CH . Figure. 2.3.1 Effect of increasing concentration of dimethylsulphoxide (DMSO) on the specific rotations at 25 0 C of solutions (about 1%) of methyl 3-deoxy-f3-L-erythropentopyranoside and of 1,2-0-isopropylidene 4-O-methy1-Dsorbopyranoside in ethylene dichioride (Lemieux et al., 1969). Note:  the  publication  structure  of  sorbopyranoside, to  C—i  only.  error  in  Fig.  2.3.1  1,2—0-isopropylidene  regarding  the  4-O-methyl-f3-D-  where the 0-isopropylidene group is linked  However,  the  appropriate  formation  of  the  dioxolane ring is on both carbons in the position 1,2 of the sugar ring.  39  The been  importance  of  the  nature  emphasized by Stoddart  “Stereochemistry of large in solvents  of  and  constant  water)  his  in  Carbohydrates”.  tetrachioride) (e.g.,  (1971)  solvent  the  of  has  also  informative  book  anomeric  The  low dielectric constant  small  in  solvents  (Stoddart,  of  1971).  effect  (e.g.,  is  carbon  high  dielectric  However,  the effect  of the dielectric constant on the anomeric effect and hence on  conformational  equilibria,  often  is  found  not  to  be  remarkable,  such as the solvation effects involving hydrogen  bonding.  For  example,  methyl  3-deoxy-f3-L-erythro-  pentopyranoside exists predominantly as the C—i conformation in  solvents  such  as  chloroform  which  hydrogen  bonds with hydrogen atoms  In  case,  this  the  C-i  conformation  intramolecular  hydrogen  hydroxyl groups.  On the other hand,  engaged  (DMSO)  acceptors  (1966)  as  ionising  have  reaction. tertiary  impact  For  or  the  which  on  instance,  influence  both  rate  These  were  on and  bimolecular  attack by the hydroxide ions,  an  syn—axiai  are  1971).  —  electophilicity, hydrogen mechanism  of  strong  of the solvents  in the hydrolysis of  a  by  dimethylsuiphoxide  (Stoddart,  nucleophilicity,  power,  groups.  stabilized  is  solvents  alkyl halides two mechanisms  identified.  hydroxyl  strong  when hydroxyl groups are  pyridine  as  the  noted that the properties  soivation,  cohesion, etc.,  such  form  not  involving  1-C conformation is favoured  Amis such  bond  in hydrogen bonding with  hydrogen  of  do  bonding, of  the  secondary and  substitution were  mechanism  involving  and a unimolecular mechanism  40  kinetically dependent on the  (1’inis,  1966).  If  R  ionization of  represents  represents the halide,  the  the alkyihalide  alkyl  radical  these mechanisms can be  and  X  illustrated  as follows: RX + OH-  =  ROH + X- bimolecular  RX=R+X  followed by R+ + OH-  =  ROH  (instantaneously),  unimolecular The  changeover  was  attributed  to  the  reaction  medium,  concentration, and the alkyl group involvement (Amis, Tchoubar the  (1966)  ascertained that the difference between  electronegativities  mobility  II  of  1966).  of  electrons  oxygen  results  and in  carbonyl group is strongly polarized.  the  carbon  and  the  fact  that  the  In line with the high  polarisability of the pi bond, this polarity is the cause of many  heterolytic  group.  In  contrast  hydrocarbons, is the  reactions to  carbonyl  place  atom,  i.e.,  nature in  of the  the  at  groups  the polarisation direction  independent of the carbon  taking  case  the  in  carbonyl  unsaturated  of the C=O group  substituents  taken by  of  of  addition  polar  molecules to the carbon—oxygen double bond, the negative end of  the  molecule  attaches  itself  to  positive one to the oxygen (Tchoubar,  the  carbon,  while  the  1966).  Regarding the literature reviewed on the importance of hydrogen bonding and the solvent effect on this area,  it is  41  likely that acetone has  the  cellulosic material under  ability  to penetrate  suitable conditions.  into the  At the  same  time acetone is classified as a dipolar aprotic protophylic solvent  (HBA).  This means,  solvent composition consequences; cellulose, and  the high ratio of acetone in the  (> 80%)  might bring about the following  predominance of acetone  and  stereochemical  intramolecular  in the reaction with  changes.  hydrogen  bonds  Hence,  are  both  expected  inter— to  be  affected due to these reactions. On the other hand, prepared  by  presence  of  it is been known  condensation an  acid  of  sugars  catalyst  that ]cetals can be  with  acetone  (Stanek  et  al.,  in  the  1963).  Depending on the stereochemistry of these sugar derivatives, pentoses or hexoses form either five— or six—membered acetal ring which can easily be distinguished by NNR, GC, (Buck  et  al.,  acetone  with  1965;  Kiso  cellulose  et is  al.,  1976).  anticipated  Thus to  and GC-MS  reaction  offer  of  similar  isopropylidene derivatives as with sugars.  2.4  Isopropylidene Chemistry  It  has  been  known  for  -  Formation of Ketals  some  time  that  isopropylidene  acetals can be formed by condensation of sugars with acetone in the presence of an acid catalyst Throughout  the  many workers, NNR  have  course  of  numerous  (Stanek et al., studies  using different techniques  repeatedly  proven  that  the  in  this  1963). field,  such as GC—MS  hydroxyl  groups  and of  42  sugars  have  1963).  The formation of  ring  of  (solid  been  the  replaced by  soluble  state)  of  isopropylidene  ones  isopropylidene groups  portion  the  (solution)  cellulose  is  on the sugar insoluble  and one  (Stanek,  of  the  one  major  hypotheses in this work. ketal  A  is  an  acetal  derived  from  ketone.  a  Isopropylidene ketals are prepared by condensation of sugars with acetone in the presence of a Lewis acid catalyst. Five— membered fused ring systems are preferred and adjacent cis hydroxyls  are  necessary  (Stanek  et  al.,  1963).  Mild  hydrolysis will cleave ketals fairly easily. There is enough difference primary  in  stability  alcohol  between  function  (C-6)  the and  ketals that  involving  at  C-i  so  the that  selective acid hydrolysis is possible. It with  is  sugar  known  that  alcohol  in  yield acetals or ketals  the  reaction  of  carbonyl  the  presence  of  acid  (Stanek et al.,  to  form  a  five—membered  catalyst  may  1963). This reaction  is not restricted to monohydric alcohols, polyol  compounds  but proceeds with  dioxolane  or  six—memkered  1,3—dioxane ring. The Wurtz  first (in  reaction  Stanek  et  of  this  al.,  type 1963),  was  carried  who  out  prepared  by 2-  methyldioxolane by heating ethylene glycol with acetaidehyde in the presence of hydrogen chloride,  (see Fig.  2.4.1).  43  Ha CHOI-(  I.  CH — 2 O +  )  OHC—CH  C)-f O 2 H  Figure 2.4.1.  These  0 1 H  Preparation of 2-methyldioxolane.  condensations  dehydrating  agents  chloride  etc.  ,  ÷  1 CH—CH  CH — 1 O’  such  This  chemistry by Fischer  are  as  acetalized  sulphuric  reaction (1895)  was  acid,  by  acidic  anhydrous  introduced  zinc  into  sugar  who was guided by the presence  of vicinal hydroxyl groups in the molecule of sugar alcohols to the idea of condensing these groups with acetone.  Thus,  the condensing effect of hydrogen chloride was utilized to prepare  isopropylidene  together  with  derivatives  other  alkylidene  of  saccharides,  derivatives  which  assume  a  remarkable position mainly from the view point of synthesis. Besides long  line  the of  isopropylidene  other  compounds were  condensation  studied.  In  this  have been prepared by means benzylidene benzaldehyde, etc.  derivatives respectively.  derivatives  are  derivatives  of  by  products  sugars,  of  a  carbonyl  way methylene derivatives aldehyde and ethylidene or  means  of  acetaldehyde  Cyclohexylidene,  likewise  of  known  as  or  furfurylidene,  products  of  the  44  reaction between a sugar and cyclohexene, oxo—compounds (Stanek et al., The  most  investigated  1963).  significant,  products  compounds with sugars,  furfural or other  and  formed  by  are the  also  most  condensation  thoroughly of  carbonyl  isopropylidene derivatives,  designated in the older literature as acetone sugars. are  prepared  derivatives,  in namely  a  similar by  the  way  reaction  as of  other  alkylidene  acetone  sugar in the presence of condensation agents,  They  with  the  (i.e., an acid  catalyst). At the most two isopropylidene groups can be introduced into the molecule of pentose or hexose sugars. for the entrance of these groups  into the sugar molecule,  apart from a  few exceptions such as xylose or  the  of  presence  vicinal  A condition  cis-hydroxyl  groups.  sorbose, It  is  is  clear  from the given examples of D—glucose and D—mannose that the furanoid form of both sugars permits the introduction of two acetone molecules. Only pyranoid structures can in this case form monoisopropylidene derivatives.  CHOH  ‘HQ—CH  HO HO  Fig.  OH i.  2.4.2. cL—D-glucose (pyranoid form)  Fig. 2.4.3. cL—D—glucose (furanoid form)  45  ‘HO—CH, 0  Fig. 2.4.4 —D—mannose (pyranoid form) Note:  Fig. 2.4.5 f3—D—mannose (furanoid form)  the arrows indicate those hydroxyl groups at which a  dioxolane (C 3 HO 2  On  the  ) ring can be formed.  basis  of  the  established  isopropylidene derivatives of various sugars,  structures  of  the empirical  rule has been postulated that the sugar reacts with acetone always in such a structure as to permit the formation of a di-isopropylidene derivative. This rule is in agreement with the  fact  that  galactose  or  the  pyranoid  fructose  introduction  of  consequently  the  two  structures  present  no  isopropylidene  di—isopropylidene  of  obstacle groups  derivative  arabinose, to  the  and of  that these  sugars exists in the form of pyranose. The  existence  compounds established.  of  of  sugars From  this  various and it  types  their follows  of  isopropylidene  stability for  instance  are that  well the  dioxolane ring on furanose structures is relatively stable, whereas the ring attached to the side-chain is more labile and  preferentially  exemplified  by  hydrolyzed the  and  conversion  hydrogenolised of  (as  l,2:5,6—di—O-  46  isopropylidene-D--glucofuranose  into  1, 2-O-isopropylidene-D-  glucofuranose). Another result of conformation analysis is that in the bicyclic  system composed  of  two  five membered rings  contains the least number of endo—substituents, the  isomer  is  always  stable.  isopropylidene—D—ribose  For  this  formation of  reason,  favoured  is  which  2,3—0—  over  1,2—0—  isopropylidene—D—ribose. Some inconsistencies, however, have as  yet  not  been  isopropylidene structure unprepared  explained.  derivative  which but  is  For  of  obviously  example,  D-galactose more  theoretically  that has  stable  the a  than  likewisely  di-0-  pyranoid the  thus  advantageous  1,2:5, 6—di—0—isopropylidene—D—galactofuranose. The furanoid or pyranoid arrangement of isopropylidene derivatives of sugars is unambiguous in those cases in which it  is  predetermined.  glucopyranoside structure  during  (see Fig.  For 2.4.6)  condensation.  instance,  methyl-cL—D  can not assume a In  this  case,  furanoid  however,  the  formation of a six—membered 4,6—dioxane ring is encountered which otherwise is rare among isopropylidene derivatives.  47  CH 0 1 H  H  Figure  2.4.6.  01-4  H  01-I  The  formation  of  six—membered  a  4,6—dioxane  ring.  Considering  these  stereochemical  effects  it  must  be  emphasized that the question of which form of the furanoid or  pyranoid  arrangement  of  alkylidene sugar compound, the sugar existed prior to  an  isopropylidene,  or  other  is favoured depends on the form its reaction with the carbonyl  compound.  2.4.1  Derivatives of Pentoses  Isopropylidene derivatives of known  (Stanek et.  ribofuranose,  al,  1963)  namely  all common pentoses are l,3-O-isopropylidene-D-  1,2:3, 4-di-O-isopropylidene-D-arabinose,  1,2:3, 4—di—O—isopropylidene—L—arabinose, isopropylidene-D-xylose, lyxofuranose.  1,2:3, 5—di—O—  1,2:3, 5-di-O-isopropylidene-cc-D-  48  CHOH  I/0\ OH  00 C  /\  Figure 2.4.1.1.  2, 3-O-isopropylidene-D-ribofuranose.  Figure 2.4.1.2.  1,2:3, 4-di—O—isopropylidene—D—arabinose.  Cit C—C  H 3 H Figure 2.4.1.3.  1,2:3,5-di—O-isopropylidene-D—xylose.  49  By partial hydrolysis,  the di-isopropylidenes of D and  L—xyloses can be easily converted into corresponding 1,2—0— isopropylidene-D-L-xylofuranoses  respectively.  derivatives  have  Careful  of  these  compounds  isopropylidenation  of  3, 4-O—isopropylidene-D arabinopyranose. derivative was  Moreover,  also  arabinose  The  been  may  5-deoxy  prepared.  also  lead  to  or  3, 4-O-isopropylidene-L-  the  5—deoxy—1, 2—0—isopropylidene  indirectly prepared  from a  5-substituted L  arabinose. Di—isopropylidene derivatives of pentoses containing a free  aldehyde  group  were  also  isopropylidene-D—arabinose  formed.  was  obtained  1,2:3, 4—di--O-isopropylidene-D-mannitol (Wiggins,  1946)  or  obtained  from  by  2,3:4,5-di—0— oxidation  with  tetra-acetate  1952). The same substance can  2,3:4, 5-di-0-isopropylidene-D-arabinose  diethyl dithioacetal by action of mercuric chloride et al., can  1938).  be  (Gatzi  Further 2,3 :4,5-di—O-isopropylidene—D-xylose  formed  by  isopropylidene-L-iditol al.,  of  3,4:5, 6-di—O—isopropylidene--D—mannitol  with periodate (Bourre et al., be  Thus,  the  oxidation  with  sodium  of  1,2:3,4-di—0-  periodate  (Bourre  or ketals  comes  et  1952).  2.4.2  Derivatives of Aldohexoses  The result  formation of  aldehydes  the and  of  cyclic  condensation ketones  if  the  acetals of  1,2  diol  is  and  1,3—diols  itself  cyclic,  as  a  with the  50  acetal or ketal forms only when two OH groups are cis,  for  geometric reasons. Since aldohexoses are polyhydroxy compounds, undergo  similar  reactions.  The  reaction  is  they also  in  general  complicated by the fact that the ring size in the product is not the same as in the free sugar. This actually takes place when the more stable pyranose form does not have cis vicinal hydroxyl groups,  but the furanose form does.  Thus galactose  reacts with acetone to give the diketal shown below because, in the  A  form,  the reaction,  which is present under acidic conditions of there are two pairs of vicinal OH groups  to  yield the diacetal.  CHOH  :2? Figure 2.4.2.1. The formation isopropyl idene-cc-D-galactopyranos ide.  of  l,2:3,4—di—O—  51  On furanose  the  other  form,  hand,  since  ct—glucose  this  the  is  reacts only  by  way  glucose  of  the  structure  possible with a pair of cis-hydroxyl groups, as follows:  1011 CHO’  •  cLcHCo  o  •  c . 3 • 1 j(,/  Figure 2.4.2.2. The formation isopropylidene—ct—D—glucofuranose. Partial glucofuranose  hydrolysis (see  of Fig.  of  1,2:5,6—di—O—  1,2:5, 6—di-O-isopropylidene—D— 2.4.2.3)  isopropylidene—D—glucofuranose, as:  yields  1,2—0—  52  o—CH  H  H  •HNH/0 0\3 H 01  Figure 2.4.2.3. Partial hydrolysis isopropylidene—D—glucofuranose.  This removal of one of two  of  l,2:5,6—di—O-  isopropylidene groups  from  the molecule of 1,2:5,6—di-O—isopropylidene is made possible by  the  fact  accessible  that  to  the  5,6-0-isopropylidene  hydrolysis  more  readily  than  group  is  the  0-  isopropylidene group in the position 1,2. On the other hand, the  reverse  into  its  can  be  conversion  of  l,2—O—isopropylidene—D—glucose  di-isopropylidene derivative proceeds  effected by  acetone (Ohie,  1922).  means  of  anhydrous  copper  readily sulphate  and in  53  An  isomeric  di-O-isopropylidene-D-glucose  isopropylidene residue in the position 1,2:3,5,  with  the  however,  is  also known (Fig.  2.4.2.4). Derivatives of this substance are  formed  reaction  by  the  of  acetone  with  6-substituted  derivatives of D—glucose, as:  CI-OTj  HI  CIjOTs  0\  OIH  OH  HO  Figure 2.4.2.4. Formation of an isomeric isopropylidene-D-glucose in the position 1,2:3,5.  di—O—  The same type of compound is obtained by the action of phosphorous  pentachioride upon  D—glucofuranose,  which  1,2:5, 6-di-O-isopropylidene-  instead of  the  expected  3—chloro—3—  deoxy derivative gives the 6-chloro-6-deoxy derivative with simultaneous rearrangement of the isopropylidene groups Fig.  2.4.2.5):  (see  54  1/ H  O\f  H  \H  o\I  3  3 CIt  3  Figure 2.4.2.5. Formation of 6—chloro-6-deoxy—l, 2:3, 5—di--O— isopropylidene—D—glucofuranose.  An interesting product is formed in the reaction of D— glucose with acetone the ester.  in the presence of boric acid.  1, 2—O—isopropylidene-D-glucofuranose This  compound  is  split  of  3,5-boric  the borate residue,  It  is  acid thus  permitting a convenient preparation of 6-substituted 1,2—0isopropylidene 2.4.2.6).  derivative  of  D-glucofuranose  (see  Fig.  55  CHOAc  TH  L’°i” Figure 2.4.2.6. glucofuranose.  H  O\j/CH \C3  6-acetyl-1, 2-O-isopropylidene--D-  Isopropylidene derivatives of L—glucose have also been prepared (Stanek et al., The Fig.  1963).  di—O—isopropylidene  2.4.2.7)  iuutarotation  is  remarkable  and  may  derivative in that  be  its  oxidized  of  D—mannose  solution to  (see  exhibits  2,3:5,6-di-O-  isopropylidene-D-mannonic acid. This supports the assumption that  the  hemiacetal  unsubstituted,  hydroxyl  group  of  this  compound  is  and that here 2,3:5, 6—di-O-isopropylidene—D-  mannofuranose is concerned.  The proof of the structure was  carried out by converting di—O-isopropylidene--D—mannose into its  di-O-isopropylidene-D-mannonic  lactone,  which  is  identical  with  acid,  the  or  product  into prepared  direct isopropylidenation of —D—mannose with acetone,  as:  its by  56  C 1 H  COOK  (°) I H  H  -  2°  °\ ,“ HtC-CH5  C 3 H  1 H  Figure 2.4.2.7. mannofuranose.  Formation of  D—galactose whose  CH O 2 H  is  the  only  di-O-isopropylidene  structure.  Partial  2,3:5, 6-di-O-isopropylidene-D-  easily  derivative  hydrolysis  isopropylidene—D—galactopyranose. almost  groups, analogous  equal  this  ease  of  reaction  is  procedure  in  has of  isopropylidene-D-galactopyranose  the  accessible a  aldohexose pyranoid  l2:3,4-di-O-  yields However,  splitting  1,2-0-  with  both  regards  to  isopropylidene  less  advantageous  the  glucose  than  series.  the The  57  monoisopropylidene intermediate  in  derivative  the  also  has  preparation  of  the  been  obtained  di-isopropylidene  derivatives, as:  CH I  01-1 LS0o II + 3 CCH CH H HO OH H  as  0  Hco o  C  3 CH  Figure 2.4.2.8. l,2:3,4—di—O-isopropylidene-D— galactopyranose.  58  CHOH  Fig.  2.4.2 • 9 1, 2—O—isopropylidene—D-galactopyranose.  2.4.3  A Study of Sucrose  Using  a  combination  dimethylformamide, Mufti  (1975)  and  —  Disaccharide  of  2,2-dimethyoxypropane,  toluene-p-sulphonic  acid  studied the synthesis of sucrose.  N,N  Khan  and  Treatment of  sucrose with acetalation reagents afforded a mixture which, after treatment with acetic anhydride and pyridine followed by  chromatography  1,2:4,5—diacetal  on  Fig.  spectrum  of  Fig.  appeared  at  relatively  respectively).  silica 2.4.3.1  2.4.3.1,  the  higher  gel, in  gave 15%  signals field  the  crystalline  yield.  In  the  NNR  due  H-i  and  H-4  (t  =  to  6.15  and  6.25,  The signals for these protons usually appear  in the region t 4.5—5.4 for acetylated derivative of sucros e  59  (Khan et  al.,  suggested  1975).  that  C-4  acetal linkages. p.m.r. 8.56,  and  Further  shift to higher  C-2  were  It was stated  spectrum of Fig. 8.64,  Fig.  The  field  involved  the  presumed  1975)  that the  in  (Khan et al.,  therefore,  2.2.3.1 showed four methyl peaks at  8.77, and 8.85 due to two isopropylidene groups.  proof  2.4.3.1  acetate Fig.  of  the  was  presence  supplied  of  cyclic  the  by  acetal  groups  information  of  in  tetra  2.4.3.2 on treatment with 60% acetic acid at 90  °C for 10 minutes.  Although the signals due to H-2  were not allocated in the p.m.r.  and H-4  spectrum of Fig.  2.4.3.2,  they were shown by spin-decoupling experiments to be in the region  of  5.55,  6.5  in deuteriochloroform and  5.2,  5.5  in  deuteriobenzene. The shift of these signals to higher field would  be  instead  expected of  C-2  acetoxyl  Reacetalation 2.4.3.2)  if  of  groups  3,3’  afforded  the  and  ,  4’  ,  C-4  carried  (Khan  et  free  hydroxyl  al.,  1975).  6 ‘—tetra-O-acetylsucrose  diacetal  Fig.  2.4.3.1  in  80%  (Fig. yield,  which confirmed that no acetyl migration occurred during the deacetalation of  1’ ,2:4, 6-di-O-isopropylidenesucrose tetra  acetate  2.4.3.1)  (Fig.  acetylsucrose (Fig. The position Fig.  to  give  3,3’,4’,6’-tetra—O—  2.4.3.2). of  the  remaining two hydroxyl  groups  in  2.4.3.2 were established by the following sequence of  reactions  (Khan  et  al.,  1975).  Treatment  with trityl chloride and pyridine at 88 the ditrityl ether compound (Fig. the monotrityl ether Fig.  2.4.3.3)  of  Fig.  C for 4 0  2.4.3.2 hr,  gave  as the minor,  and  2.4.3.4 as the major product.  The  60  trityl  group  at  converting 3,3’ 2.4.3.4)  noted  ,4’,6  into  (Otake,  the  in  Fig.  yield.  ,  was  established  et  by  ‘-tetra-O-acetyl-6-O-tritylsucrose (Fig. known,  6-0-tritylsucrose  al.,  1975)  that  conducted at 90 0 C for 24 hr, O—acetyl—1’  2.4.3.4  hepta-acetate  using acetic anhydride and pyridine.  1970), (Khan  C-6  when  It was  tritylation  was  it afforded 3,3’,4’,6’-tetra-  6—di—O—tritylsucrose  (Fig.  2.4.3.3)  in  The slow tritylation treatment given to Fig.  85%  2.4.3.3  indicated that the second primary hydroxyl group was at C1’.  This  was  verified  by  treatment  acetylsucrose  (Fig 2.4.3.2)  and  to  pyridine  which,  with  give  3,3’,4’,6’—tetra-O—  with methane-suiphonyl chloride  the  ref luxing  a  of  tetra-sulphonate solution  of  Fig.  sodium  iodide  butanone, gave the 6-deoxy-6-iodo derivative Fig. high yield.  The structure of Fig.  2.4.3.5 in  2.4.3.6 in  2.4.3.6 was identified by  its p.m.r. spectrum. The involvement of C-4 in Fig.  2.4.3.1 in cyclic acetal  formation was also studied (Khan et al., 3,3’  ,  1975). Treatment of  4’, 6’ -tetra—O—acetyl—l’ ,6-di-O-tritylsucrose  2.4.3.3)  with  afforded  methane-suiphonyl  2,4-disuiphonate  Detritylation  of  3,3’  ,  4’  1’, 6-di-O-tritylsucrose bromide acetic 2.4.3.8.  in  acetic  acid The  established  at  0  acid, C, 0  structure by  its  ,  chloride  compound  in  Fig.  -(-Fig. pyridine 2.4.3.7.  6’ -tetra-O—acetyl—2 , 4-di—O—mesyl— 2.4.3.7),  (Fig. in gave of  a  mixture  using of  chloroform  l’,6-dihydroxy the  p.m.r.  latter  Fig.  spectrum.  hydrogen  compound  and Fig.  2.4.3.8  was  Addition  of  61 trichioroacetyl isocyanate to a solution of 3,3’,4’,6’—tetra— O—acetyl—2, 4—di—O—mesylsucrose  (Fig.  2.4.3.8)  in  deuteriochloroform generated two singlets at .72 and 1.02 in the p.m.r. spectrum, due to the imino protons of the resulting carbamate.  group,  thereby  hydroxyl groups in Fig.  confirming  2.4.3.8.  the  presence  of  two  The mass spectrum of Fig.  2.4.3.8  showed ions due to hexopyranosyl and ketofuranosyl  cations  at  m/e  361  and  289,  respectively.  Acetylation  of  3,3’,4’ , 6 ‘—tetra-O-acetyl—2 ,4—di—O-mesylsucrose (Fig. 2.4.3.8) gave the corresponding hexa-acetate compound (Fig.  2.4.3.9).  The  that  p.m.r.  result  of  sucroseocta—acetate  signals for 11-2 and 11-4 in Fig. higher field,  showed  the  2.4.3.9 appeared at slightly  i.e at t 5.35 and 5.2,  respectively.  This was  considered a further evidence that the two sulphonates in Fig. 2.4.3.9 were located at C—2 and C—4. The mass spectrum of Fig 2.4.3.9 and  (Khan etal.,  1975)  showed the expected ions at nile 403  331 due to the hexopyranosyl and ketofuranosyl cations,  respectively. Similar treatment to 2,4-di-O-mesylsucrose hexa— acetate  (Fig.  2.4.3.9),  using  sodium  benzoate  in  hexomethyiphosphoric triamide, gave a product with inversion of configuration at C—4. confirmed  the  The mass spectrum and p.m.r.  oc—D_galacto  conformation for Fig.  2.4.3.10.  configuration  and  the  data 1 C 4  62  2 O—CH  1 0 2 CI4 R  CH2OR2  CH O 2 Ac 0  2 CMe  CH O 2 Ac  OAc  OR  OAc  I  Fig.  2.4.3.1 Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.  2.4.3.2 2.4.3.3 2.4.3.4 2.4.3.5 2.4.3.6 2.4.3.7 2.4.3.8 2.4.3.9  Figure 2.4.3.1 to 2.4.3.9.  CI-i O 2 Ac BzO  R=R1=R2=R3=H R = R3 = H, Ri = R2 = Tr R = R2 = R3 = H, Ri = Tr R = Ri = R2 = R3 = Ms R = R2 = R3 = 14s, OR1 = I R = R3 = Ms, Ri = R2 = Tr R = R3 = Ms, Ri = R2 = H R = R3 = Ms, Ri = R2 = Ac  Synthesis reaction of sucrose.  CH O 2 Ac  OMS  Figure 2.4.3.10. Acetylation of sucrose.  63  In  conclusion,  it  is  worth  mentioning  that  all  isopropylidene chemistry research (i.e formation, synthesis, kinetics  etc.)  has  been  accomplished  at  temperatures and under anhydrous conditions.  room  or  low  No hydrolysis  of sucrose to glucose and fructose has been reported under these conditions, temperature. amount  of  i.e.,  However, water  acidified aqueous acetone and high  in  in  this  the  work  reaction  the  presence  medium  is  of  small  vital  for  hydration of anhydrosugars that are cleaved during cellulose hydrolysis.  This  Shallenberger et al.  is  fairly  clearly  demonstrated  by  (1975), see Fig. 2.4.3.11. below:  cqHOH  Figure 2.4.3.11. Scheme for hydration of anhydrosugars during the hydrolysis of glycosidic structures (Shallenberger et al., 1975).  64  2.5  Elucidation and Characterization of a Mechanism  A  study  purification practical  of of  the  reaction  cellulose  aspects.  physico—chemical  In  is  this  mechanism  extremely  context,  transformations  of  crucial  type  for  hydrolysis suitable  of  acid,  better  process.  that  take  to  temperature  provide  methods  answers  place  such as  etc. of  which  for  in  understanding  optimization  The  solvent  important  cellulose and the effect of other factors composition,  the  are  the  of  the  on  the  solvent  appear  the  many  to  be  organosolv particularly  elucidation  and  characterization of the mechanism are reviewed below.  2.5.1  Infrared Investigation  Measurement absorption  and  spectra  identification of  interpretation represent  means  specific compounds  as well as quantitative estimation of  their  regarded  relative as  structure.  an  aid  Earlier  spectroscopy to  in  in  applications  infrared of  (IR)  qualitative  (Marchessault,  1962),  (O’Connor et al., 1958) mixtures,  elucidation  cellulose were  cellulose molecule, crystalline  proportions  of  of  and  of  the  infrared  confined to  are  also  molecular absorption  studies  of  the  investigations of physical, optical, and  properties,  i.e.,  crystallinity  modifications of more or less pure celluloses.  and  crystal  65  One of the difficulties to be taken into consideration in a study of limited  cellulose by IR spectroscopy  number  interpreted  of  in  absorption  terms  of  study  by  can  molecular  problem that could account the  bands  is that  be  vibrations.  polymers,  Another  encountered in containing  crystalline and amorphous regions, such as cellulose, absorption overlapping of these two regions al.,  a  satisfactorily  for difficulties  IR spectroscopy of  only  both  is the  (Sutherland et  1950). The  hydrogen  cellulose)  bonding  system  carbohydrates  of  (e.g.,  in the solid state produces complex 0-H  stretch  in the frequency range of 3600 to 3000 cm 1 region.  Due to  this complexity of -OH absorptions it is quite difficult to evaluate the significance of individual hydrogen bonds. In  this  Hurtubise  et  spectroscopy  aspect,  many workers  al.,1960; for  Nelson  (O’Connor  et  quantification  al,  1964)  and  et  al.,  have  1958;  used  IR  characterization  of  modified celluloses with respect to hydrogen bonding. was  carried  out  by  measurement  different treatments. of  the  changes  band  O’Connor et al.  absorptivities  at  1429  and  (1958)  893  1 cm  absorbances  that  (ethylamine)  treatments. both  It was  mechanical  treatments  decrystallization  concluded  to  follow the  of  the  had treated  spectroscopy Hurtubise et al.  (O’connor  (grinding)  (1960)  an  at  used the ratio  in hydrogen bonding of different cellulose  at various 1958)  of  This  and  impact  celluloses.  samples et  al.,  chemical on Using  the IR  studied the changes in  66  the fine structure  (lateral order)  of cotton and unbleached  suiphite birch and spruce puips at different mercerization treatments. showed  Their  that  IR  calculation  throughout  cotton had maintained  (Hurtubise  various  et  al.,  mercerization  1960)  treatments  a relatively higher degree of lateral  order than the other puips and this was  attributed to  its  high crystallinity. Recently, using deconvolution processing of IR spectra, numerous studies on  (Fengel,  quantification  of  1992;  Fengel,  changes  brought  1993)  have focussed  about  by  treatments on the structure of cellulose.  different  Emphasis was also  made to characterize the degree of crystallinity by relative heights of different bands etc.), and  (985 cm-,  1165 cm , 1  1430 cm’  and to find a correlation between hydrogen bonding  the  system  processing  of  IR  cellulose-water. spectra  better  resolved bands  in  still  remains  the  about  Although  produced the  deconvolution  well—separated  —OH region,  position  of  much  and  much  controversy  bands.  This  band  shifting problem has been noted in both of Fengel’s ppers (Fengel,  1992;  3350 cm , 1  3418 cm , 1  1470 cm , 1 was  Fengel,  3378 1 cm ,  also  observed  transformation  of  1993);  bands  1280  , 1 cm  1460  cm’,  3466 cm 1 well shifted to 1270 cm-, 3440 cm’,  3506 cm-, respectively.  (Fengel, cellulose  1992) I  to  that  during  cellulose  II,  It the the  disappearance and appearance of some bands in the —OH region such  as  3285  observable.  1 cm  and  3560  cm-,  respectively,  well  67  These spectral changes in band positioning and heights are  essentially  character.  due  Such  to  alterations  variations  the  of  occurring  stereochemical  upon  different  treatments were found to be affected by a number of factors such as the temperature and nature of the solvent (Brewster, 1959; Durette et al.,  1969).  In conclusion, these changes in  band positioning and the reconsideration different bands in the  (Fengel,  1993)  of  cellulose-water system could justify  the limitation of deconvolution processing of IR spectra in quantitative analysis. Thus, acceptor  the involvement of acetone, with its great H—bond potential,  attraction  of  both  with inter—  cellulose and  molecules  intramolecular  through H-bond  the  would  lead to stereochemical changes in amorphous and crystalline zones.  This  type  irreversible intramolecular  of  alteration  H-bond hydrogen  is  expected to bring about  disruption bonding  at level  both and  inter-  cause  and  permanent  weakness in the hydrogen bonding system of the cellulose.  In  order to investigate the validity of this hypothesis diffuse reflectance infrared fourier transformer (DRIFT) in this work.  This technique  is employed  is designed to provide enough  information about the OH stretching.  In other words,  it is  fairly sensitive to follow up any changes that may occur in hydrogen bonding system of a material.  68  2.5.2 Sugar Hydrolysis with the involvement of Acetone  The  use  of  acetone  as  solvent  a  dates back to 1933 when Dreyfus  in  (1933)  wood  hydrolysis  admixed concentrated  sulphuric acid with acetone and ether in the ratio of 7 to 3,  respectively.  the  solution  He  in  also  order  impregnated to  compressed  deposit  and  the  solvent  Thereafter,  the  system wood  was  achieved  residue  was  with  distribute  quantities of the acid within the wood matrix. of  wood  by  small  The removal  distillation.  boiled  in  water  for  dissolution of carbohydrates. The Dreyfus process was unable to produce directly soluble sugars but could effect strong acid hydrolysis at lower temperatures. Later,  Chang  et  al.(l976)  developed  a  process  which  could dissolve the total wood biomass at high temperatures (180—210 °C)  in acid catalyzed aqueous acetone.  Kinetics of  acid catalyzed organosolv saccharification was published in 1977  (Chang  process stage  has  et  al,  been  1977).  released  the  process  for  acidified  acetone  of  the reducing theoretical  (  up to 95%)  a  concentration in the  Further  process  Acid  et  al,  patent  on  1981).  At_that  saccharification 50  range  to of  improvement  of  70%. 60 in  wood  this  used  Recovery  to  72%  sugar  of  of the  recovery  was attained by merely increasing the acetone  concentration to greater than 80% The  Canadian  (Paszner  total  sugars was yield.  Also  Catalyzed  chemistry  that  (Paszner et al.,  Organosolv lead  to  1986).  Saccharification a  significant  (ACOS)  high-rate  69  hydrolysis  and  thermal  stability  of  dissolved  the  sugars  (Paszner et al,  1988)  Grethlein (1988)  suggested that the dissolved glucose was in  the  has not yet been verified.  1,6-anhydroglucose  form  which  can  Ward and  readily  be  post-  hydrolyzed to glucose. However,  Paszner  isopropylidene  et  chemistry  concepts  from the pressure vessel disagreed with Ward  al.  (1988), and  relying loss  the  of  (for reasons other than  and  Grethlein’s  (1988)  on  acetone  leakage),  assumption.  In  addition, the formation of 1,6—anhydrohexopyranoses is known to occur in aqueous acidic solutions where high energies are applied (Stoddart,  1971).  In early investigations of Chang et al. acetonation of  cellulosic materials much  devoted to the kinetics and optimization was  noted  (Chang  hydrolytic (160—170  et  al.,  dissolution  °C)  found  to  dissolution.  be  acetone  neither changes  of  first  was  both  used.  It  these works  was  Paszner  hypothetically,  order  al.,  at  low  i.e.,  all  Paszner  et  focus  1977)  in was It  that  temperature,  bulk hydrolysis  (200 °C)hydroysis  the  way  al. (1986,  to  total  1988)  and  observed total saccharification of biomass  resulting  Nonetheless,  ,  et  At high temperature  However,  Ward et al. (1988) when  of wood mass  the  of  1977)  of the process.  Chang  occurred in two stages,  and main hydrolysis. was  1976;  (1976,  is  able  from et  noteworthy  the al  to  to  mention  demonstrate  acetonation  (1988),  managed  that  structural treatment. to  throw,  some light on the mechanism of acetonation.  70  It was concluded (Paszner et al., 1988) that the possibility of  isopropylidene derivatives of  and shown  transient in  Fig.  (hemi)  2.4.1.1  depolymerization  glucose.  Thus  the  as  final  products  ketal formation on the cellulose, might  significantly  glycosidic linkages in cellulose. rapid  sugars  of  high  weaken  as the  This eventually leads to  cellulose sugar  to  isopropylidenated  yield  obtained  during  acetonation of wood biomass was attributed  (Paszner et al.,  1988)  residues,  to  derivatization  of  cellulose  isopropylidene group formation on the sugar ring, avoiding dehydration to otherwise  possible  furfural  under  the  i.e.,  thereby,  and hydroxymethylfurfural  prevailing  saccharification  conditions.  l4C\  _.c  I  C  C HG’  Fig. 2.5.1.1 Proposed 0—isopropylidene cellulose during high temperature in acetone.  CH  intermediates for acidified aqueous  71  2.5.3  The C-13 CP/MAS NMR Spectrometric Investigation  Isopropylidene have  found  protective Belder, has  wide  use  role  of  1977).  been much  (Mills,  groups,  in  the  form  carbohydrate  in diol  functions  in  their  1955; Woifrom et al.,  cyclic  chemistry (De  In addition to their interest  of  for  Belder,  chemical  acetals their  1965;  value,  conformational  De  there  structures  1974; Barker et al,  1952).  C-13 MMR has frequently been used in structural studies of  isopropylidene chemistry.  C—13  NNR,  studied  several  Buchanan  et al.  carbohydrate  (1980),  using  isopropylidenes  unknown structure. It was noted (Buchanan et al.,  1980)  of  that  the C-13 chemical shifts of the methyl groups were separated from each other by about 10 p.p.m. This large difference was attributed  to  the  difference  in  environment  of  the  equatorial and axial methyl groups in the chair conformation and that the higher field signal was due to the axial group which was more bulky. While the methyl groups of  5-membered  acetals were slightly separated from each other.  This could  be  (Buchanan  mobility  of  et the  al.,  1980)  system  and  due to  to  the  the  fact  conformational  that  the  methyl  groups were pseudoequatorial and pseudoaxial. Buchanan structural draw  more  dioxolane, (Buchanan  et  studies  al. of  (1982),  et  al.,  a  continuation  isopropylidene acetals,  conclusions 1,3—dioxane  in  on and  1982)  the  acetal  1,3—dioxepane.  that  the  ring It  chemical  of  their  were able size; was shift  to  1,3—  observed of  the  72  acetal carbon of 1,3—dioxolane rings was in the range 108.1— 115.7 p.p.m,  while those of  1,3-dioxane rings were between  97.9 and 101.1 p.p.m. This was attributed to the flexibility of the former ring. carbon 1982)  chemical to  be  In the case of 1,3—dioxepanes the acetal  shift  value  intermediate,  was  found  nearer  (Buchanan  to  that  in  et  al.,  the  1,3-  of  2,2-  dioxanes. Christophe  (1984),  dimethoxypropane,  acetone  isopropylidenate glucitol.  The  using and  large  excess  sulphuric  acid,  was  able  2-acetamido-4, 6-O-benzylidene-2-deoxy-D-  investigation of the  latter compound by C-13  NMR spectroscopy showed that the benzylidene acetal resonated at 101.2 gave  a  signal  to  at  p.p.m, 99.9  while that of  p.p.m.  These  carbon  isopropylidene one  values  indicated  that  both acetal rings were 1,3—dioxanes. Also, C—l3 NMR spectrum of  this  methyl  compound groups  illustrated  were  separated  that  the  chemical  shifts  by  10.9  p.p.m.,  which  within the expected range for dioxanes The  synthesis  of  codensation with  was  of  -D-glucopyranosyl)  achieved  (Couto  1,2:4, 5-di-O-isopropylidene-  during  5  showed  two  hr.  1984).  et  f3  -  al.,  The  signals  the  presence  of  mercuric  C-13  NMR  spectrum  of  the  dioxolane carbon atoms  112.0  and  (Couto et al.,  108.9 1984).  by  bromide  -D-fructopyranose  in  at  -D  1984)  tetra—O—acetyl -c-D—glucopyranosyl  nitromethane—benzene  was  1,2:4, 5-di-O-isopropylidene3-O-  (2,3,4, 6—tetra--O-acetyl-f3 fructopyranose  (Christophe,  of  in  1:1  cyanide  disaccharide  p.p.m.  for  the  73  x-ray Diffraction Characterization  2.5.4  X-ray diffraction  the  is  only  technique  used  for  the  characterization of polysaccharides of ordered structures at an atomic resolution level.  The structural information that  can be deduced from x—ray diffraction analysis is dependent on the organization and packing arrangement of the specimen of interest (i.e.,  fiber). Fibrous materials contain ordered  three—dimensional units  crystallites or micelles)  (i.e.,  atoms within their elementary and inicrofibrils.  of  Fibrils are  the main structural components of the cell walls. Therefore, x—ray diffraction data can be used to assess the structural changes which have been brought about by a certain treatment of the cellulosic material. The  existence  celluloses  has  dif fraction  diagrams  al.,  1960),  1958), al.,  for  1960).  in  been  Valonia  cotton  exhibited  of  (Segal The  sharp  terms  of  a  three—dimensional  verified of  such  al.,  diagrams reflections three  x—ray  substrates  ventricosa et  by  of  and  as  cellulose  1959), these  which  in  electron—  ramie  (Mann  (Honjo  et  and Fortisan cellulosic  could  dimensional  arrangement  only  et  al.,  (Mann  et  materials accounted  be  co—ordinates.  All  the  reflections from the typical cellulose II structure could be interpreted  in  approximate 3  =62.7°  cellulose  terms  dimensions:  of  a  a=7.92  (Wellard,  1954).  I)  determined  were  The  monoclinic  A,  unit  b=10.34  dimensions (Wellard,  A, for  1954)  cell  of  c=9.08  A,  ramie to  be  (i.e as  74  follows; stated  A,  b=lo.34  A,  1962)  that  even  a=8.17 (Mann,  illustrate  the  orientation, contribute  existence  they to  do  the  sharp  though  3=83.6°.  these  confirm  that  reflections  all of  It  was  observations  three—dimensional  of  not  A,  c=7.85  crystalline  regions  the  diagrams show the same degree of crystallinity.  which  diffraction This might  be attained only if good agreement could be obtained between calculated  intensities  for  crystalline  a  model  and  the  observed intensities. However, today, by the appropriate use of  computer  model  dimensional  models  details  the  of  building for  ordered  to  select  comparison  with  structures  numerous cellulosic materials (Rees, The lateral packing order,  reasonable x-ray  have  been  three—  data, drawn  many for  1977).  which is formed by hydrogen  bonds with hydroxyls of adjacent cellulose chains,  provides  more structural information by bringing about various Bragg diffractions.  With these diffractions  unit  cell  dimensions  and the space group can be determined. Rozmarin  (1977)  studied the effect of  on the supermolecular structure of cellulose in  crystallinity  index).  He  also  acid hydrolysis (i.e variation  investigated  different  parameters contributing to the hydrolysis reaction. pointed out  (Rozmarin,  1977)  It was  that with the increase of acid  concentration, the crystallinity index decreased rapidly and temperature cellulose.  exerted  the  largest  effect  on  hydrolysis  of  75  Recently, structure  of  irreversible  in  an  interesting  cellulose, change  review  Hayashi  from  (1985)  cellulose  either to the difference of  on  skeletal  stated  to  I  supermolecular  II  could  antiparallel).  It was added  be  the due  chain conformation or  the difference in the chain packing polarity vs.  that  (Hayashi,  (i.e parallel  1985)  that it is  not possible to establish the crystal structure of cellulose with  the  limited  amount  of  x-ray  data  now  available.  To  accomplish an accurate description of the crystal structure of  cellulose,  strengthened  the by  x—ray  other  information  chemical  and  obtained physical  should  be  methods  of  structural analysis.  2.5.5  Molecular Weight Distribution Characterization  Information concerning molecular weight distribution is essential properties cellulose  in relation to our understanding of the physical of  many  industrially  derivatives.  Many  important  different  celluloses  methods  and  have_been  known so far for determining molecular weight distribution. Solutional  and  precipitational  were very popular many  in the past  investigations  have  fractionations,  especially,  for that purpose.  been  carried  Recently,  out  on  determination of molecular weight distribution of by  gel  permeation  traditional methods  (exclusion) (e.g.,  chromatography  solvent precipitation)  the  polymers  (GPC).  The  are time-  76  consuming and accurate molecular weight distribution is not obtained. Gel  permeation  technique  chromatography  applicable  to  rapid  is  a  relatively  determination  weight distribution of polymers.  of  simple  molecular  Usually in this technique  polymer molecules are separated according to their molecular size  in  solution.  The  polymer  solution  flows  through  a  column packed with porous packing on which larger molecules are excluded  (eluted first) while the smaller molecules are  retained  the  in  suitable  packing  calibration  distribution molecular  can  intersticial technique,  then  weight  be  spaces.  the  obtained  distribution.  In  By  using  molecular  and this  a  size  converted  into  procedure,  two  important steps must be taken into considerations; 1-  to  ensure  solution)  that  of  the  complete sample  solubility  in  the  (true  solvent  is  attained, and 2— to use suitable calibration standards. In  this  regard,  the  major  factor  in  determining  the  molecular weight distribution of cellulosic materials is in conversion  of  for analysis. nitration 1973).  the  1965)  drawbacks  and of  instability of the nitrates, and the  to  derivatives  suitable  Two methods are available for derivatizing  (Timell,  The  polysaccharides  impossibility  the other hand,  of  carbanilation  the  former  (Hall  method  et are  :  al, the  insolubility of nitrated xylan  achieving  complete  nitration,  On  carbanilation has repeatedly been verified  77  to provide complete substitution of polysaccharides without degradation (El Ashmawy et al., 1974). Carbanilated celluloses are readily soluble in tetrahydrofuran (THF), the solvent of choice for GPC. gel  Analysis of carbanilated polysaccharides by  permeation  chromatography  satisfactory results  has  (Danhelka et al.,  usually  provided  1976).  The polydispersity of celluloses represents the extent of variation in molecular size, values  for  molecular  i.e.,  weight  experimentally determined  distribution  are  obtained  averages, which are dependent on the method used.  as  Commonly,  molecular weight determination provides both weight-average N and  number—average  ratio  M  molecular  weight  distributions.  of weight—average molecular weight to  molecular  weight  defines  (M/M)  the  The  number—average  polydispersity,  i.e,  generally, the greater the relative difference between M and M  the  wider  is  the  spread  in  molecular  weights  (polydispersity) of the sample of interest. Values with narrow polydispersity are considered excellent for dissolving pulp manufacturing  (Rydholm,  1965).  —  The degradation of cellulose may result from different mechanisms hydrolysis,  such  as  thermal,  base-catalyzed  oxidative,  oxidation  enzymatic,  and mechanical.  acid— Their  common impact on the cellulosic material is the diminishing molecular weight. Several parameters affect the course of the mechanism (i.e., the extent of degradation). temperature,  reaction time,  Factors such as  catalysts, reaction media,  gases  78  molecular weight distribution (MWD) were studied (Suleman et al.,  1987).  It was  distribution was chloride they  has  produced  been  concluded  acted,  found that the  used  that  through  in  as the  different  a  lowest molecular weight  acidic  when  medium  catalyst.  the  On  catalyst,  palladium  other  hand,  dicobaltoctacarbonyl  reactions,  as  a  cellulose  stabilizer from further degradation. Chang et al. distribution of treatment.  (1973)  investigated the molecular weight  different celluloses  They  observed  that  after  the  acid hydrolysis  total  number  of  crystallites was decreased during hydrolysis while the chain length distribution remained constant.  They also noted that  the crystallites were broken down into molecular fragments. In (GPC)  the is  employed  distribution (cotton).  present  (MWD)  study  gel  permeation  to  investigate  of  treated  the  and  chromatography  molecular  untreated  weight  substrates  Uniformity of molecular weight distribution is an  important acetonation  parameter treatment  for  predicting  the  on  cellulosic  material  indicator for dissolving grade quality.  performance and  as  of an  79  3 MATERIAL AND METHODS  3.1 Sample Preparation Procedures  3.1.1 Raw Material  100% used  pure cotton for pharmaceutical purposes has been  throughout  compound, University  the  obtained of  duration from  British  the  of  this  study  University  Columbia  as  Pharmacy  (UBC)  model  a  at  premises.  The Its  characteristics were determined as follows; the percentage of moisture  free  cotton  standard T 258 os—76.  was  determined  to  TAPPI  Extractives were determined according  to TAPPI standard 204 os-76.  Alpha—cellulose was determined  according to TAPPI standard 203  os-74.  investigation  in  are  according  illustrated  the  The results of this following  chapter  (Results and Discussion).  3.1.2 Raw Material Preparation for the Analysis  Cotton was extracted with alcohol—benzene (2:1) according to TAPPI standard T 204 os-76. To  remove any extractives that may  interfere with the  results, cotton was extracted with alcohol—benzene for 72 hr. Then it was extracted with only alcohol in order to remove the residual benzene. After alcohol extraction the cotton was left  80  overnight in the fumehood for evaporation of the solvent. The purified  cotton was  humidity  room  dried  (CTH),  in  a  controlled temperature  which  conditions; temperature 23  maintained  ±2 °C,  the  and  following  and relative humidity 50  ±2%, for a week and by the end of this step it was ready for the analysis.  3.1.3 Solvent Extraction of Sugars  The hydrolysis runs of cotton were performed in stainless steel  bombs  equipped  described earlier Paszner  et  al.,  with  glass  (Chang et al., 1983;  Paszner  served as a heating source. cook  with  5  liners  gram  of  1976;  et  al.,  similar  to  those  Chang et al.,  1977;  1988).  An  oil  bath  The bombs were charged for each  extracted  organosolv liquor (acetone  cotton  to  which  acidified  water) was added. The bombs were  then immersed in the oil bath at an assigned temperature for a specified length of time. At the end of the sugar extraction run the bombs were chilled  water  in  and  the  contents  filtered  on  a  Buchner  funnel. The residue was washed with several portions of fresh liquor.  The  filtrate was  stored  in the  fridge  for  further  treatment and analysis. The pulp residue was neutralized with ammonia solution, thoroughly washed with distilled water and dried  at  treatments.  60  °C  for  weight  loss  determination  and  other  81  3.1.4 Isolation of Sugars from the Spent Liquor and their Preparation for HPLC Analysis  In sugars  the in  case  the  of  spent  trifluoroacetic liquor  (acetone,  acid  as  water  a  and  catalyst, TFA)  were  isolated by evaporation of the acetone and partial removal of water. The contents of the flask (i.e viscous solution) were diluted with distilled water and filtered. The filtrate, once again, was rotary evaporated and filtered in order to remove the impurities that may negatively affect the sugar analysis results by HPLC analysis. When hydrochloric neutralization  with  acid  (HC1)  ammonia  was  solution  used  as  was  a  catalyst,  done  first.  Filtration, evaporation and dissolution followed.  3.1.5 Secondary Oligosacoharides  Hydrolysis  of  Nonreducing  Sugars  and  After the adjustment of the acid concentration of the primary hydrolysate  (acetone, acidified water and sugars)  to  3%, the contents were placed in a glass liner of a stainless steel bomb. The pressure vessel with the contents was heated in an oil bath at 120 °C for different specified times. post—hydrolysate was  neutralized with ammonia  The  solution and  left to stand at room temperature for 2 hr in order to allow the ammonium salt to precipitate.  Then the hydrolysate was  filtered and evaporated on a rotary evaporator.  The viscous  82 solution was once again dissolved with distilled water and filtered to ensure high degree of purity for HPLC analysis.  3.1.6 Preparation Analysis  of  Hydrolysate  for  Gas  Chromatographic  The spent liquor (acetone, acidified water and sugars) of cotton solvent treatment was neutralized with animonia solution and left to stand for 2 hr in order to allow ammonium salt to precipitate.  The  contents  were  filtered,  column of ion exchange resin (XAD-16) impurities  that  isopropylidene filtrate  was  might  negatively  derivatives rotary  a  in order to remove the  affect  results  evaporated.  eluted through  by  The  the  analysis  analysis.  GC  viscous  solution  of The was  extracted with chloroform. The chloroform extract was filtered through a microfilter prior to GC analysis.  3.1.7 Acetonation of Cotton Hydrolysate Reducing Sugars  The  cotton  hydrolysate  was  rotary  evaporated  and  concentrated to a syrup. An amount of 100 mL of fresh acetone and 2 mL of concentrated hydrochloric acid were mixed and the mixture was added to the syrupy residue in the flask with the magnetic rod. magnetic  The flask with the contents was placed over a  stirrer  temperature  for  and 20  stirring  hr.  -was  conducted  Neutralization,  at  filtration  room and  purification steps were similar to those described in section 3.1.6.  83  3.1.8 Sugar Hydrolysis  Standards Preparation  -  The monomeric composition of cotton hydrolysate extracted with  acid  variables  catalyzed (i.e.,  aqueous  acetone  temperature,  at  various  reaction  time,  kinetic acid  concentration etc.) was investigated using different standards of sugars arabinose  .  25 mg of each sugar and  xylose)  volumetric flask  was  (glucose, weighed,  (25 mL cap.)  and adjusted to the mark.  galactose, mannose, transferred  into  a  and deionized water was added  The contents were well shaken to  ensure a uniform concentration throughout the solution. These standard  sugar  solutions  were  used  for  identification  of  different sugar retention times.  3.1.9 Sugar Hydrolysis  -  Mixture of Standards Preparation  20 mg of each sugar standard were weighed and all were mixed together to make up 100 mg. preparation procedure was section 3.1.8.  The mixture of standards  identical  to  that  described in  84  3.1.10 Sugar Hydrolysis Preparation Derivatives of Sugar Standards  of  -  Isopropylidene  1,2:5, 6-di-O-isopropylidene-ct-D-glucofuranose,  1,2—0-  isopropylidene—c-D—g1ucofuranose, 2,3:5, 6—di-O-isopropylidene— 13—D-mannofuranose  and  1,2:3, 4—di-O-isopropylidene-cx-D-  galactopyranose were obtained from Sigma Chemical Laboratories and  used  as  standards  investigation.  Procedures  for for  gas their  chromatographic preparation  (GC)  are  quite  similar to those of the simple sugars as described earlier in section 3.1.8 with the exception that chloroform was used as a volatile solvent for the solublization of the isopropylidene derivatives.  3.1.11 Solvent Extraction of Cotton using C-13 labeled Acetone  An extracted sample of cotton  (140 mg  (o.d)) was placed  in a tube positioned in a glass liner with glass beads and dried for a week over phosphorous pentoxide in a desiccator. To the  1  g of C—13  water (0.16 N HC1)  labeled acetone an amount of acidified  (105 pL) was added. The fresh liquor  labeled acetone and acidified water)  (C-13  was transferred to the  tube containing the cotton and the glass liner containing the sample was placed in the stainless steel bomb. pressurized  to  Neutralization,  450  psi  and  filtration  heated  and  to  residue  The bomb was  150 °C washing  for steps  2  hr. were  carried out similar to those described in section 3.1.3. The  85  filtrate was collected in a vial and stored in the fridge for further analysis. The residue was dried in the CTH room for 48 hr. The residue was studied by C-13 CP/MAS solid state NMR.  3.1.12 Preparation of Cotton Residues for X-ray Diffraction Analysis  Sample preparation was conducted according to Nelson et al. (1964). Samples, which were treated with acid catalyzed aqueous acetone, were prepared for X-ray diffraction (XRD) the fibrous material in a 1 in and  the  content  was  (2.54 cm)  transferred  onto  by placing  square metal frame a  hydraulic  press.  Pressing of the fibrous material was carried out at 15000 psi (1050 kg/cm ) 2  for 5 mm.  Samples such as untreated cotton and those which were treated with acetone and water without the acid catalyst ground  in a Wiley microgrinder to pass  a  30-mesh  (0.6  were mm)  screen prior to pressing. Pressing was conducted in a similar manner as described above.  3.1.13 Cotton Residue Carbanilation  Carbanilation of cotton fibrous material  (i.e.,  solvent  treated and untreated cotton) was done according to Schroeder et al.  (1979)  with some modifications.  The cotton sample equivalent to 0.1 g (o.d.) was dried in  86  a quick fit flask (250 mL cap.) at 60 °C.  Anhydrous pyridine  at least overnight in an oven  (100 mL)  and phenyl isocyanate  (7.2 mL) were added to the flask. Then the reaction flask was capped,  sealed with  parafilm and placed  thermostated oil bath at 80 °C for 2 days. allowed to cool  slightly and methanol  in a  circulating  The mixture was  (4 mL)  was added to  react with the excess phenyl isocyanate. The mixture was mixed with an  equal  volume of  dioxane,  filtered through  a  glass  filter paper in a Buchner funnel, and transferred to a beaker (1 L). A mixture of methanol  (800 mL)  and acetic acid (5 mL)  was added to the contents of the beaker and the formation of white particles in the solution were immediately observed. The suspension was  left  over—night  in the  fumehood to  settle,  after which the clear solution was carefully decanted and the wet precipitated polymer left in the fumehood for 2 days to dry.  Using  a  spatula,  the  sticky precipitated polymer was  removed into a vial and kept over phosphorus pentoxide in a desiccator for further use.  3.1.14 Viscosity Determination  Viscosity of cotton residues was determined according to TAPPI standard T 230 os-76. An amount of air-dry residue equivalent to 0.250 g o.d. was  weighed  and  transferred  into  containing several 6 mm glass beads.  a  dissolving  bottle  After adding 25 mL of  87  distilled water,  the bottle was capped and shaken for a few  minutes.  Then the bottle was  minutes  while  purging  allowed to stand for  with  nitrogen  (N ) 2 .  about  25  mL  2 of  cupriethylenediamine (CuEn) was added and purging with N 2 was continued  for  1  more  minute.  The  bottle  was  then  capped  and shaken until the fibers were completely dissolved (i.e., no fibers stuck on the walls of the bottle). The viscometer was filled by immersing its small diameter leg  into  the  solution  and  drawing  the  liquid  into  the  instrument by applying suction to the other end. After drawing the liquid level to the second etch mark, the tube was removed from the solution, cleaned and returned to its normal vertical position. The viscometer was placed in a constant temperature water bath at 25 °C for at least 5 mm reach the  temperature.  measuring  leg  of  the  The  for the solution to  solution was  viscometer with  drawn up  a  suction  into the bulb,  and  allowed to drain so that the inner surfaces of the viscometer were wetted. the  liquid  The efflux time was then determined by drawing above  the  upper  mark  and  measuring  the  time  required for the meniscus to pass between the two marks. The measurement  of  efflux time was  repeated three  times.  This  procedure was carried out on all residues which were treated with acetone, water and acid catalyst. In the case of untreated cotton and those treated with just  acetone  (CuEn)  and water,  1  M  cupriethylenediamine  solution  25 mL was added first to the residue with a two-  88  minute nitrogen purging, after which the bottle was capped and shaken frequently for 10 mm.  Then 25 niL of distilled water  was added to the bottle and shaking was continued for 20 mm. The rest of the procedure was similar to that described above.  3.2 Analytical Methods  3.2.1 IR Analysis Transformer (DRIFT)  —  Diffuse  Reflectance  Infrared  Fourier  The average absorbance peak height around 3400 cm’ (gross hydroxyl range) obtained.  of differently treated cotton specimens was  This was conducted in a way that the intensity of  the hydroxyl band could be read without being influenced by the intervening factors. Such factors that could be taken into consideration  are  the  variations  in  peak  location  stereochemical changes and noise perturbation. was  maintained  infrared  on  a  spectrometer  reflectance  Perkin—Elmer  equipped with a  attachment,  potassium chloride.  1610  with  the  to  The analysis  Fourier  transform  Perkin-Elmer  sample  due  placed  on  diffuse ground  The spectrum of pure potassium chloride  was ratioed against that of each sample. The spectra resulted from measurements involving 64 scans at a spectral resolution of 8 cm’. The  hydrogen  measurements.  bonding  test  is  the  mean  for  three  89  3.2.2 Detection of Chromatography (GC)  Gas  Isopropylidene  chromatographic  Derivatives  investigation  of  by  Gas  isopropylidene  derivatives of sugars was carried out on a Hewlett Packard 5890A  gas  chromatograph,  equipped with  a  flame  ionization  detector and an HP 3396A integrator. The reports generated on the HP 3396A printer,  after each chromatographic run,  were  transferred to a computer for data storage. The  column  used  for  the  derivatives was Supelcowax 10,  separation  of  isopropylidene  30 m x 0.25 mm 1.0. The inlet  pressure for the column was 10 psi. The carrier gas was helium and the flow rate was  1 mL/min.  The injection and detector  temperatures were 200 °C and 300 °C, respectively.  3.2.3 Sugar Analysis (HPLC)  -  High Performance Liquid Chromatography  The samples prepared as described in sections 3.1.5 and 3.1.6 were directly injected into the high performance liquid chromatograph (HPLC) DIONEX  HPLC  autosampler, was used.  column without any further treatment. A  (Dionex  Corp.,  Sunnyvale,  CA)  equipped  with  gradient pump and pulsed amperometric detector  The eluent was degassed by vacuum for 20 mm  and  degassed again by DIONEX eluent degas module using helium, before the sample run.  90  The  columns  CarboPac PAl  used  (4x250  were  mm),  exchange  anion  and  a  guard  resin  column  columns,  (4x50  mm)  to  protect the main analytical column from contamination. An MGi guard column was also placed before the CarboPac PAl column to remove any impurities such as phenolic materials that might form  in  the  hydrolysate.  The  CarboPac  column  contained  polymeric nonporous Microbead resins which exhibit rapid mass transport, fast diffusion  ,  high pH stability (pH 0-14), and  excellent mechanical stability (>4,000 psi). The Pulsed kmperometric Detector (PAD) had a flow-through cell with a gold working electrode, electode,  stainless steel counter  and a silver/silver chloride reference electrode.  The potential  of  the working  electrode was  cycled through  three values to let the electrode surface be cleaned and the current be stabilized before sampling the oxidative current from the flow—through solution. Working electrode potentials were set as follows; El=0.005 V (300 ms),  E2=0.60 V (120 ms),  E3=—O.80 V (300 ms) with a sampling time of 200 ms from 100 ms to 300 ms.  The E2 and E3 pulses remove remaining sugars and  then reactivate the gold surface, respectively. The response time was 1.0 sec and the output range was 100 nA. The main analytical eluent used was degassed, distilled and  deionized  water  prepared  by  a  Millipore  Mill-Q  Water  System. The column was regenerated after every injection with 250  mM  NaOH  which  was  prepared  as  follows;  the  distilled  deionized water used was degassed first by helium gas for 15  91  mm  before mixing with the NaOH solution to avoid carbonate  formation. The  flow  introduced  rate  into  the  was  1.0  mixing  mL/min cell  and  from  a  500  mM  NaOH  post—column  was pump  (Varian 5000 HPLC) at the flow rate of 1.0 mL/min All samples before loading onto the column were filtered through a 0.4 urn syringe filter (NALGENE ). All tubings used were made of metal tm free PEEK. Regarding accuracy of sugar analysis, were  made  for  each  sample  and  the  three injections  standard  solution  was  injected after different interval times to monitor possible variations in the column or detector conditions. Calibration curves were prepared by using standard solutions of arabinose xylose,  galactose,  glucose and mannose at three different  concentration levels. The data were processed by DIONEX AI-450 software  using  computer used  a  DIONEX  advanced  computer  interface.  The  is Hewlett Packard 486 Vectra with Microsoft  Window 3.1.  3.2.4 Solid State Cotton Study  -  C-13 CP/MAS  NMR spectrometry  CP/M1S C-13 NMR spectra of cotton residues were obtained from a Bruker MSL-400 spectrometer operating at 100.6 MHz. The spectral conditions used were as follows: a— spin contact time:  2ms,  90° proton pulse:  the relaxing delay was 4 sec.  6.5 j.sec.,  and  92  b— MAS spinning rate  —  3500-4500 Hz.  The spectra were recorded by using a spectral width of 41.666 KH2.  3.2.5 x-ray Diffraction  X-ray diffraction technique was employed in this work to investigate the crystalline structural changes brought about by the solvent purification treatment on cotton cellulose. The X—ray diffraction data of the samples were recorded using a Siemens Diffractometer equipped with a D—5000 rotating anode X—ray generator. The wavelength of the Cu/Kax radiation source was 0.154 nm and the spectra were obtained at 30 mA with an accelerating voltage of 40 kV.  Samples were scanned on the  automated diffractometer from 9° to 40° of 2  (Bragg angle),  with data acquisition taken at intervals of 0.04° for 1 sec. A peak resolution program was used to calculate both the crystallinity index of cellulose and the dimensions of the crystallites (Hindeleh et al., resolution  of  contributions  the of  X-ray each  1978). This program allowed the  diffraction  of  the  pattern  diffraction  into  the  planes.  The  background was attributed to the amorphous part of cellulose. Generally,  the Voigt function  (Chung,  1989)  resulted in the  best fit of the X-ray diffraction patterns and was routinely used for the determination of both the crystallinity index of cellulose and the dimensions of the crystallites through peak  93  broadening  (full  width  crystallinity index,  at  which  half  maximum  height).  The  is defined as the ratio of the  resolved peak area to the total area under the unresolved peak profile, was calculated using the the following equation;  f1 d 7 0  -  kflAdU  firdo  where Cr1 is the crystallinity index of the cellulose,  ‘T  is  the total intensity of diffraction in the diffractogram,  ‘A  is  the  total  intensity  of  diffraction  due  to  the  portion of the sample, 0 is the diffraction angle,  amorphous and k is  the ratio of the crystalline and amorphous intensities at a particular 20 value outside of the crystalline peak region (Wims,  et al.,  1986).  In this work,  the value of k was not  determined for each sample used and was taken to be equal to one in all cases for convenience of calculations. The  crystallinity  index  of  the  cellulose  was Thiso  calculated by the empirical method described by Segal et al. (1959), using the equation described below,  4O2 -  100 ‘AM  94  where  is  1002  the  maximum  intensity  of  the  002  lattice  diffraction (reflection attributed to the crystalline region of the sample) and Iintensity of diffraction at Bragg angle 20  18° (reflection attributed to the amorphous region of the  =  sample). Nevertheless, the latter approach does not include any correction for the background (unresolved peak profile). Results obtained using both methods were in good agreement. The apparent dimensions of the cellulose crystallites were determined by applying the Scherrer’s equation to the data  obtained by the peak resolution program.  The  average  thickness of the crystallite (i.e., relative values)  at each  plane  of  diffraction  was  calculated  using  the  following  equation;  t(hki)  B.csO  where, t is the thickness of the crystal at the (hkl) plane of diffraction,  A is the wavelength of X-ray source,  Scherrer’s constant (for pretreated cellulose, K  =  K i the 0.9), and  B is the peak full width at the half maximum height (Cullity, 1956). The  crystalline  crystallite breadth)  test  (the  crystallinity  index  is the mean for three measurements.  and  95  3.2.6 Gel Permeation chromatography  The study  of  gel  permeation  molecular  chromatograph  weight  (GPC)  distribution  used,  (MWD)  for  of  the  solvent  treated cotton materials, was a Spectra-Physics SP8810 liquid chromatograph. Samples of cellulose tricarbanilate dissolved in  tetrahydrofuran  (THF)  were  membrane with a pore size of  filtered  through  a  teflon  0.45 ,um and analyzed using a  series of four TSK—GEL type 118 columns. Tetrahydrofuran was used as the eluting solvent at a flow rate of 1 mL/min. The samples in the eluent were detected by a IJV spetrophotometer detector  (Spectrof low 757)  at the wavelength of 235 mu.  The  signal from the detector was fed to the integrator SP4229 for peak integration and illustration of integral and differential distributions of molecular weights. Due to the lack of commercially available standards of cellulose tricarbanilate, the GPC calibration curve (i.e., the correlation  of  elution  volume  with  molecular  weight)  was  established from the elution profile of polystyrene stanards with narrow MW distributions (Danhelka et al., al.,  1970; Valtasaari et al.,  1975).  1976; Coil et  The following equation  was used:  (I+o,)LM.  Mp+L i 4 . Ckp/Kc)  96  where Mc. and M are the MW of cellulose tricarbanilate and polystyrene, respectively. The Mark—Houwink coefficients used in the present analysis for polystyrene in THF, K and =  a,  =  0.74,  =  1.18 X10 4  and for cellulose tricarbanilate in THF,  K  2.01 X i0 4 and ac= 0.92, were those reported by Valtasaari  et al.  (1975).  3.2.7 Viscosity Measurement  This was measured according to TAPPI standard 230 os— 76. The viscosity test in the following chapter (Results and Discussion)  is the mean for 3 measurements.  97  4 RESULTS AND DISCUSSION  4.1 Mechanism of Purification of Cellulose in Acidified Aqueous Acetone: Elucidation and Characterization  4.1.1. Characteristics of the Raw Material used for the Elucidation of the Mechanism  100%  pure  cotton  for pharmaceutical  used throughout the duration of this compound.  Its  follows:  1—  extractives  characteristics the  moisture  content  content was 98.2%. absorbance index  and  height,  was  determined  content and  as  was 3—  has  been  a  model  to  4.85%,  be 2—  as the  alpha—cellulose  the  Other characteristics determined such as  (hydrogen crystallite  FWHN),  study  were  0.02%,  purposes  etc.  bonding), breadth  viscosity,  (full  width  crystallinity  at  maximum  half  are discussed where appropriate  in the  text.  4.1.2. IR (DRIFT) Study - Hydrogen Bonding Changes (i.e., hydogen bond disruption/destruction) during Solvent Purification Treatment  The  aim  acetonation,  of  studying  with  the use  spectrometer reflectance effect  of  equipped attachment,  the  treatment  residual of  a  Fourier  with is  a  to  on  cotton  transform  Perkin-Elmer  verify,  the  samples  after  infrared diffuse  quantitatively,  hydrogen  bonding  of  the the  98  cellulosic  material  hypothesis). the  macromolecular  the locus of  functions provides  1936;  hydrogen  disruption  bond  physico—chemical  1987)  of  processes  cellulose  and  (Sarko,  the  1978;  and because of their importance as  interaction between molecules and between the  interactions. al.,  of  structure  Nishimura et al.,  bond  the  Hydrogen bonds have occupied a key position in  interpretation  nearby  (i.e.,  in the special  same molecule. promise  for  Thus, the  the  study  It has been known for a long time  Ellis et al.,  1940)  hydrogen of  such  (Hubert et  that the observed stretching  frequency of a covalently bound hydrogen atom is perturbed in a specific way when that atom gets involved in hydrogen bonding  to  given us for  a  an  al.,  bonding,  (Liang et al.,  this context, et  group.  broad knowledge  hydrogen  levels  acceptor  1968)  both 1959;  of at  These the  infrared  structural  inter-  and  a  change  in  solvent  has  have  requirements  intramolecular  Marchessault et al.,  it has also been verified (ALnis, that  shifts  1960).  In  1966; Lemieux a  substantial  impact on the mechanism and stereochemistry of the reaction course system.  and hence Acetone  on the hydrogen bonding as  a  solvent appeared  of  the  to  follow  trend as has been confirmed in the present work.  specified such  a  99  4.1.2.1. Acetone Effect on Hydrogen Bonding Residues during Solvent purification Treatment  of  Cotton  Absorbance 2  1.8  1  E :z: : : :z: : : .: :.:.:. : .: :  a) -  ci) 0  0.4 02 0 40  p  I  50  60 70 80 Acetone Concentration (%)  90  Figure 4.1.2.1. Effect of acetone on hydrogen bonding of cotton residues treated with different acetone concentrations (liquor/solid ratio: 10/1; 150 0 C; 2 hr; no acid catalyst added). -  *  Means with different. **  the  same  letter  are  Significance at 95% confidence level.  not  significantly  100  100  The  spectral  fundamental  changes  stretching  effect on cellulose,  in  range,  the that  vicinity  of  accompany  the  are shown in Fig.  4.1.2.1.  the  0-H  solvent  The results  indicate that the average height of the 0-H band  (3400 cm ) 1  has increased with the increase of acetone concentration in the solvent composition.  Fig.  4.1.2.1 also shows that there  is a sharp increase in band height especially in the 80 to 90% range in acetone concentration. The statistical analysis shows that the treatments of concentrations  are  (Duncan’s  multiple  intensity  of  increase the  of  significantly range  the  0-H  acetone  reaction  of  cotton with different acetone different,  test).  range  band  concentration  acetone  The  with  Fig.  increase  (3400  cm-)  is due to  the  4.1.2.1  the  cellulose  in  the  with  the  fact  hydroxyls  expected to weaken the hydrogen bonding in the system. attenuation spacings accord  of  in the  with  the  the  hydrogen  bonds  leads  to  These  earlier  recorded  results  water pulping of wood species (Zarubin et al., was found  on  1989)  spacing cellulose  in  acetone—  that the physical/mechanical properties of paper  physical  al.,  are  of  1989) when it  were lowered due to acetone treatment. However, in  is  This  provision  cellulosic material. observations  that  strength solely  (i.e., is  of  to  paper  hydrolysis  accessibility)  dependent  was  on  discussed later in the text.  a  attributed  reactions.  in  number  hydrogen of  the decrease (Zarubin  The  extent  bonding  factors  as  of  will  et of a be  101  Fig.  4.1.2.1 illustrates that the solvent purification  treatment  has  irreversible  brought H—bond  about,  within  rearrangement  residual  the that  seems  cotton,  to  cause  permanent weakness in the H—bonded system. The most probable explanation for the hydrogen bond attenuation is due to the interaction of acetone  (HBA)  of the cellulose molecules to  what  extent  water  with the polar hydroxyl groups  (HBD). can  It is not well understood  penetrate  the  crystalline  cellulose, but in any case it is known that such penetration does  not  bring  about  crystallites (Libby, On  the  absorbance increase system  of  hand,  acetone  is  systematic  appears  dipolar  a  means  is  hydrophylic  that  similar  solvent  dimethylformamide  to  the  to  increase  with the the  in hold  of  state  to  (DMF),  these  aprotic  the  such  hexamethyiphosphoric properties  in  of  successive  acetone—water  for  an  important  The probable explanation for this phenomenon is  this  suffice  the  concentration  4.1.2.1)  acetone  cellulose  spacings  of  1962).  other  (Fig.  Hence,  change  (attenuation of the H—bond)  phenomenon. that  any  behaviour any  as  of  other  acetone  owing  with  aprotic  dimethylsulphoxide  (DMSO),  dimethylacetamide  solvents  solvent.  dipolar  triamide  that  protophylic  (HNPT). are  to  (DMA),  The  solvation  characteristic.  their  molecular  and  It  will  structure  they are much better able to solvate cations than anions. other  words,  cellulose.  they  Hence  act  their  as role  hydrogen can  also  bond be  acceptors confined  to  In  with the  102  swelling of cellulose.  It follows  from these results  shown  in Fig. 4.1.2.1 that acetone can be considered as a swelling agent  for  cellulose.  fact that,  This  earlier,  interpretation  Bax et al.  proton—solvating  property  (1972)  of  based  is  on  the  emphasized that the  acetone—water  systematically increases with the rise  mixtures  in concentration of  acetone reaching a maximum in pure acetone.  They attributed  the  charge  protophylicity  of  acetone  the  to  density  distribution in the acetone molecule,  in conjuction with its  spatial  favours  structure,  positive  ions  explanation noted  by  other  hand,  which  over  about  affinities  surfaced  et  the  al.,  increasing  (1953)  previous  of  and  works  acetone—water differences  1969)  acetone  negative  of  protophylicity  Frey-Wyssling  properties  (Fong  that  the  some  strongly  that  the  content  of  ones. acetone  concerning  the  of  and  opinion.  It  enhancement  1969)  by  solvation  the of  of  acidity was  better proton.  anion Beyond  interpreted  solvation this  limit,  noted with  mixtures  Even though, (Fong  rather any  et  al.,  than  the  increase  acetone content in a water—acetone system will reduction of the dielectric constant,  proton  was  acetone—water  the  the  solvation  acidity  of  also  On  their  could be attained with up to 42 wt % acetone. this  was  (1974).  systems  of  Similar  Isaacs  enhancement  in  solvation  of  lead to the  and hence  it retards  the dissociation constant of an acid. Later, Waggoner et al. (1982) proton  claimed, activity  in  his  using  investigation  of  acetone—water  mixtures,  medium  effect that  on the  103  reason range  for of  the  20  enhanced  to  40  wt  protophylicity  %  acetone  was  of  due  acetone to  the  in  the  specific  proton—solvating properties of acetone—water complexes that could  be  Waggoner  formed et  at  these  al.  compositions.  (1982)  contended  In  other  words,  the  mutual  that  interactions of the solvent constituents would possibly play a significant role  in determining the proton affinities  in  the acetone—water systems. The  weakness  of  hydrogen  bonds  ,  resulting  the  in  residual cotton during the acetonation,  might be due to the  length and nonlinearity of these bonds.  In this concept,  a  comprehensive  investigated  comparative  the  geometry  study and  Schemer  energies  between carbonyl and hydroxyl oxygens.  of  al.  (1985)  hydrogen  bonds  They stated that the  CO...OH 2 (H y  instability developed into  et  in  by increase of  the angle from 107° to 180° has in turn been attributed to the weakening  of the  the O—I-I...O atoms.  H-bond caused by the nonlinearity  of  In the case of hydrogen bonds between two  hydroxylic molecules  (i.e.,  OH...0H 2 H ) ’ the H-bond wa not  weakened because the central proton remained along the O...O axis. Their results indicated that the rigidity of the angle  (COH)  in 2 H C OH prevented the central proton from following  the water molecule as it rotated down to the angle of 1800. The experimental results showed (Schemer et al.,  1985)  an  bring  energy  of  hydrogen bond,  16.3  kcal/xnol  was  required  to  formed between a carbonyl group and  that the  hydroxyl  compounds, to linearity. However, the hydrogen bonds,  formed  104  between  hydroxyl compounds,  maintain (1991) less  linear  noted  position.  that  sensitive  to  1991)  hydrogen  that  bonds  bond donors other  In  the  carbonyl  the  changes  single C-O bond length. al.,  consumed only  the  addition, (C=O) in  Jeffrey  bond  bond  character  their  acids  offer  hydroxyl  fairly  weak  hydrogen  bonds  carbonyl  group.  Apparently,  this  much  than  very as  the  strong  hydrogen  they form with through  carbonyl groups (C=O) as hydrogen bond acceptors was attributed (Jeffrey et al., 1991)  is  al.  (Jeffrey et  groups  (HBD). However, on the contrary,  molecules  et  length  It was also emphasized  carboxylic  through  4.6 kcal/mol to  their  (HBA). This  to the rigidity of the  nonlinearity  of  hydrogen  bonding in conjuction with the provision of longer hydrogen bonds, as  in the case of carbonyl groups,  the  mechanism  of  hydrogen  could be thought of  bond  disruption  in  the  cellulosic material by acetone. In addition, the systematic, irreversible increase  attenuation  of  acetone  of  hydrogen  concentration,  bonding, suggests  with a  the new  orientation of the hydroxyls on the cellulose. However,_such a  phenomenon  can  be  only  attained  through  intramicellar  swelling of the cellulose (Frey-Wissling,  1953; Sarko,  Jeffrey et al.,  this  1991).  In  other words,  1978;  intramicellar  swelling is anticipated to be accompanied with a new type of crystal packing order, unit cell dimensions.  i.e., provision of a different set of  105  Regarding the literature reviewed on the importance of hydrogen  bonding,  (Huggins,  1971;  H—bond  Saenger,  donor/acceptor 1979;  solvents  Simmering,  1964;  etc.  Parker,  1962), and the results obtained in the present work, confirm that  acetone  has  the  ability  to  penetrate  cellulosic material under suitable conditions.  into  the  At the same  time acetone is classified as a dipolar aprotic hydrophylic rather than hydrophobic solvent 1953; Bax et al.,  1972;  ratio  (around  acetone  of  (i.e.,  usually acetone  Isaacs,  +  90%)  (i.e.  HBA)  (Frey-Wyssling,  1974). This means, in  protic  the  solvent  solvent)  the high  composition  brings  about the  following consequences;  1—  predominance  cellulose,  of  acetone  in  the  reaction  zone  with  i.e., better solvation and  2— stereochemical changes produced by structural alterations such as solid  the presence of isopropylidene intermediates in the  state of the cellulose confirmed by C-13  CP/MAS NMR  analysis. Consequently, the formation of those intermediates brings about considerable weakness  in the hydrogen bonding  (inter—  system  and  hydrophobic material. the  intramolecular isopropylidene  bonds) groups  on  by  formation  the  of  cellulosic  This phenomenon can be explained by the fact that  electron  isopropylidene  density group  on  hydrogen  formation  on  is the  reduced sugar  because  ring  and  of the  removal of some hydrogen in condensed water molecules as a  106  result  of  and  acetone  sugar  movements  the  fibre  hypothesis  of  of  out  structure. In  conclusion,  for  the  disruption/destruction of H-bond of cellulose (carbohydrate) by acetone in the solvent purification of pulp,  one relies  on the following considerations: a—  deactivation  cellulose  when  of  water  acetone  molecules  comprises  to  interact  the  major  into  with  volume  the  of  the  solvent composition, b—  penetration  of  acetone  molecules  of  acetone  with  the  cellulose  fibres, c—  interaction  molecules brings  through  about  their  hydroxyl  stereochemical  cellulose groups.  changes  (carbohydrate) This  (i.e.,  presumably  rotational)  at  the beginning that disrupt and permanently weaken the H-bond of crystalline cellulose, d- at high temperatures and in the presence of acid catalyst (hydrolysis), now,  solvent interaction with cellulose molecules,  is evident to cause further significant stereochejical  alterations  (i.e.,  rotational,  configurational,  and  conformational). The validity of these assumptions has been proven by the results obtained by GC, HPLC, solid  state  NNR  analyses.  These  and C-13 CP/MAS  structural  changes  disrupt/destroy both inter- and intramolecular H-bond of the material (amorphous and crystalline regions), e—  at  high  temperature  acetone remarkably  concentrations increases  the  (around rate  90%), of  high  cellulose  107  (carbohydrate)  dissolution  (effect  acetone at high temperature)  overpressure  of  of  by hydrolysis to low molecular  weight fragments.  4.1.2.2. Other Factors Affecting Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  Further  investigation  into  the  solvent  purification  treatment has revealed that other variables such as type of acid, have  acid  concentration,  variable  material. catalyst)  effects  However,  on  the  temperature hydrogen  and  bonding  solvent’s  (i.e.  residence of  the  type  time  treated of  acid  effect on hydrogen bonding appears to be the one  most crucial among these parameters when other variables are kept  constant  as  it  is  demonstrated  in  the  following  results.  4.1.2.3. Effect of Type of Acid Catalyst and Acid Concentration on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment —  The  bonding  effect  has  of  the  been  concentrations.Figs.  type  of  examined  acid  catalyst  with  4.1.2.2 and 4.1.2.3  on  hydrogen  different  acid  show the effect of  acid concentration on hydrogen bonding with different acid catalysts.Both Figs.  4.1.2.2 and 4.1.2.3 show that there is  a sharp fall of absorbance (i.e., for TFA and 1.06 for HC1)  from 1.61 to 1.05 and 0.86  at low concentration of acid  of  108  the  solvent  phenomenon  purification  is  the  treatment.  decrease  in the  The  second  peak height  in  common the  0-H  stretching range with the use of different acid catalysts. Fig. 1.61 TFA. is  4.1.2.2 illustrates that the peak height goes down from (no acid catalyst added) However,  a  difference  test,  the  concentrations 4.1.2.2.  0.86  the statistical analysis in  the  behaviour  regards to bydrogen bonding. range  to  (TFA)  While  concentrations  treatments are  those  (HC1)  of  absorbance  N  the  two  acids  with  According to Duncan’s multiple of  cotton  treated  significantly different (Fig.  1.5  indicates that there  with  different  significantly different,  (except  at  0.0  with N  HC1)  4.1.2.3).  see  different appear  to  acid Fig. acid  be  not  109  2 C) I  0  U)  1  C  E z  I  1.8 A  1.6  1.4 1.2 1 0.8  N  0.6 0.4 0.2 0  0  1  2  3  4  id Concentration (N)  Figure 4.1.2.2. Effect of acid concentration on hydrogen bonding of solvent purified cotton when TFA was used as catalyst (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C). * Means with different. **  the  same  letter  are  Significance at 95% confidence level.  not  significantly  5  110  However, band  at higher acid concentrations  intensity of 0—H range has  (3 and 4 N TFA)  successively  reach 1.42 absorbance. On the other hand, Fig.  increased  the to  4.1.2.3 shows  that the peak height of the 3400 cm 1 has sharply decreased from 1.61 to 1.05 absorbance at 0.16 N HCl.  Further increase  in acid concentration (0.4 and 0.8 N HCL) resulted only in a very slight further decrease in absorbance.  111  2 0 C .0 0 .0 I  .0  E C  1.8 1.6 1.4 1.2 I  E  0.8  ()  0.6  0 0 0  .4-  0  4-  0) 4)  z  0.4 0.2  4)  a-  0  0  0.2  0.4  0.6  0.8  Acid Concentrabon (N)  Figure 4.1.2.3. Effect of HC1 acid catalyst concentration on hydrogen bonding of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C). * Means with different. **  the  same  letter  are  Significance at 95% confidence level.  not  significantly  I  112  Figs.  4.1.2.2  aspects.  The  strength  of  first  and  3  trend  hydrogen  concentration  of  show  acid  is  bond of  the  much  similarity  the  sharp  of  the  increase material  treatment.  This  in  two  in  the  at  is  low  probably  associated with the ease of removal of considerable amounts of amorphous cellulose at the beginning of the treatment. On the other hand, acid  in  the second observation  solvent  generally,  to  a  purification stronger  is that the use  treatment  hydrogen  bond  gives  in  the  of  rise,  residual  material, no matter what type of acid catalyst is used. This can  be  attributed  facilitates  the  to  the  process  fact  of  that  structural  the  acid  catalyst  transformations  to  take place by the protonation of already solvated molecules (i.e.,  isopropylidenated sugars). Hence, the strength of the  hydrogen changes  bond  of  and  the  the  cellulose  removal  of  relies  sugar  on  the  structural  derivatives  into  the  that  the  solution. The  result  variation of  shown  in  Fig.  4.1.2.2  acid concentration  of TFA  indicates  in the presence  acetone has given cotton residues with different hydrogen  bond  concentrations hydrogen dominates  strength. (i.e.,  bonding and  hydrogen bonds  at  0.75 and 1.5 N TFA)  between  renders  Apparently,  TFA  even  and  the  residual  (0.86 absorbance)  of  levels of  lower  acid  the formation of  cellulose cotton  with  molecules stronger  than that of the untreated  113  cotton  (1.08  absorbance)  concentrations likely  to  (Geddes,  (3  and  develop 1956;  reactions  with  N  4  for  case  the  TFA),  1965;  ratio  of  favourable  TFA—acetone  Harris, high  In  .  in  are  reactions  1985).  acetone  acid  conditions  suggested  March,  of  higher  In  the  turn, solvent  composition provide better chances for acetone to attenuate the hydogen bonds in the cellulosic material. In conclusion,  the variation in hydrogen bond strength  is probably due to the different reactions associated with the use of TFA as a catalyst of  hydrogen  bonding  with  (i.e.,  both  protonation,  hydroxyl  formation  groups  of  the  cellulose and water molecules, and TFA—acetone reaction). On the other hand, the  it was  carbohydrates  bonding  stated  resemble  behaviour.  They  (Jeffrey et al.,  water  can,  molecules  with  their  have both donor and acceptor properties, depending  on  the  reaction  medium.  In  cellulose acts as hydrogen bond donor of  acetone,  presence  of  while  in  acetone  lower it  as  in  i.e.,  other  (HBD)  that  hydrogen  hydroxyl  groups,  amphiprotic  words,  cotton  in the abundance  concentrations  behaves  1991)  hydrogen  of  TFA  bond  in  the  acceptor  (HBA). Fig.  4.1.2.3 shows the changes in hydrogen bonding that  have taken place at different concentrations in the residual cotton samples when HC1 was used as  an acid  catalyst.  The  figure illustrates that the hydrogen bonding was stronger in the  initial  cellulosic material.  A significant drop  occurs  on acidifying the system. Higher acid concentrations applied  114  have slight effect on hydrogen bond system. the hydrogen bond,  in the  case of  HC1,  The strength of  could probably  be  attributed to the fact that HC1 is known to be an efficient acid in hydrolysis and it seems that HC1 is less involved in similar  side  reactions  than  TFA.  Thus,  the  solvation  of  solvent—solute, more or less, proceeds much easier and hence leads  to  pronounced  cellulosic material.  In turn,  easily be protonated, and  dissolved  in  structural  transformations  in  the  these acetonated sugars could  in the case of HC1 acid as catalyst,  the  solution.  Thus,  efficient hydrolysis with HCl will  the  result  process  of  in provision of  cellulose with relatively stronger hydrogen bonds than that offered by the acetonation treatment in the absence  of an  acid catalyst. The slight increase in the strength of hydrogen bonding associated with higher concentrations of HC1 acid could only be attributed to further removal of amorphous cellulose in the solution. HC1 is considered to form a weak hydrogen bond with other compounds. Hence one of the requirements for the formation  of  strong  hydrogen  bonds  is  that  the  element  covalently bonded to the hydrogen must have a small atomic size (Mortimer, 1971). However, this is not the case in HCl. The  chlorine  diffuse weakness  atom  electron of  is  fairly  cloud.  hydrogen  bond  A  large  and,  similar formed  by  therefore,  explanation HC1  compounds was given by Vinogradov et al.  acid (1971).  has  for  with  a  the other  He stated  115  that the HC1 molecule,  even though it  is a polar one,  has  weak dispersion forces.  4.1.2.4. Effect of Temperature on Hydrogen Bonding of Cotton Residues during Solvent Purification Treatment  Figs.  4.1.2.4  temperature  on  and  hydrogen  4.1.2.5 bonding  show  of  the  cotton  effect  residues  of  during  the solvent purification treatment. The statistical analysis indicates  that  temperatures  the  (130,  significantly  treatments  150,  and 180 °C)  different,  in  the  a  catalyst,  treatments  at  different.  Fig.  130  0, C  when  cellulosic  the 130  of  TFA  However,  statisical and  cotton  150  This  various  analysis  C 0  are  as  catalyst  a  when HC1 was used shows  not  that  significantly  TFA  was  structure  used  as  with  a  catalyst,  weakened  a  has  afforded  hydrogen  bond.  (1.17,  be  explained  boiling point  solvent  by  the  (i.e.,  fact 56  °C)  that with  acetone a  small  a  The  l.4 and  are all higher than that of the untreated one can  the  4.1.2.4 shows that the solvent treatment at  absorbancies of the treated cotton samples 1.52)  at  for hydrogen bonding are  use  (Duncan’s multiple range test). as  of  (1.08).  as  a  low  molecule  has the ability to penetrate and interact with the cellulose molecules (amorphous and crystalline) spacing acceptor  in  the  (HBA).  hydrogen  bond  Nonetheless,  and bring about larger  network  as  hydrogen  bond  the molecular size of water is  normally smaller than that of the acetone  (the diameter of  116  the water molecule is 2.78 A; Frey-Wyssling, the  acetone  pronounced  effect than  properties  of  (i.e.,  that a  intramicellar  of  water.  solvent  swelling)  Hence,  affecting  1953). However,  other  is  more  important  penetrability  and  swellabillty should be taken into account such as molecular structure and reactivity Isaacs, et  1974).  al.,  (Tchoubar,  In addition,  1993)  that  with  1966;  Bax et al.,1972;  it was also emphasized  the  increase  of  (Bradley  temperature  the  molecules are more free and faster to reorient and interact. At 150 0 C the treatment offers cellulose with much stronger hydrogen  bonding  Apparently, bond,  due  groups  at to  of  (0.66,  this  temperature  interaction the  Nonetheless,  the  of  solvent  structures  general.  This  with  and the  TFA  cellulose  yielded  temperatures,  0.86  1.14  absorbance).  formation  (HBD)  with  molecules,  treated stronger  cotton  of  hydrogen  the  hydroxyl  predominates. at  hydrogen  can be explained by the  180  C 0  has  bonding  fact that  in  at higher  favourable conditions are expected to develop  for better diffusion of both acetone and acid catalyst into the  cellulosic material.  Hence,  stereochemical  alterations  could proceed more effectively under more extensive solvent— solute  solvation  and  bring  about  changes  in  the  crystallinity index and the crystallite size. Fig. (F,  G)  4.1.2.4  for  different  2  also shows that three points  different  treatments)  treatments  are  and  one  thermodynamically  (H) at  (two points for  the  3  equilibria.  117  Apparently,  this means that the structures are similar for  the treated samples at these points.  2 4) (U  1.6 4) .0  E C  I  1.4 1.2 1 0.8 0.6 0.4 0.2 0 120  130  140  150  160  170  180  Temperature (Degrees Celsius)  Figure 4.1.2.4. Effect of temperature on hydrogen bonding on cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA).  190  118  However,  Fig.  4.1.2.5  shows  that  the  solvent  purification treatment using HC1 at all temperatur es applied (except 180 °C) slight  changes  has generally rendered residual cotton with in hydrogen bonding.  this phenomenon is twofold. increase  of  temperature  First,  may  lead  The  interpretation for  it is possible that the to  an  increase  in  the  removal of both amorphous and crystalline cellulose.  2 Cs  -0- I HR  1.6  -zi-  2 HR  Lj-3HR  1.4 1.2  b__  :  -j  0.4 O.2 o0 120  130  140  150  160  170  180  Temperature (Degrees Celsius)  Figure 4.1.2.5. Effect of temperature on hydrogen bondin g of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1).  190  119  In turn,  this treatment is expected to offer cellulose with  stronger  hydrogen  hydrogen bonding and  diverse.  interactions (CH C 2 ) 3 0,  bonding,  This of  H 0 2 ,  shown  as  is  in  Fig.  likely  various HC1,  however,  be  the  outcome  4.1.2.5 due  solvents  to  and  C0.H 2 ) 3 (CH 0 ,  of  the  is  unremarkable  the  multilateral  complexes  (CH C 2 ) 3 0.HC1,  (i.e., I1 0 2 .HC1,  C 2 ) 3 (CH 0 .HC1 0.H ) available in the system in conjuction with the also  presence noted  somewhat  of  weak hydrogen  (Mortimer,  different  1971)  properties  bond  acid  that  these  than  catalyst.  those  It  was  complexes  have  of  pure  their  compounds.  4.1.2.5.Effect of Residence Time on Hydrogen Bonding Cotton Residues during Solvent Purification Treatment  The  object  of  this  part  of  the  study  on  the  of  solvent  purification treatment has been to investigate the influence of reaction time on hydrogen bonding of the treated cotton materials.  The reason for this interest is because hydrogen  bonds are usually involved processes.  in solvation and acid catalysis  In this respect, the time factor has an effect on  them. Fig.  4.1.2.6  shows  different  behaviour  of  hydrogen  bonding within the cellulosic materials treated at different temperatures with TFA as the catalyst. Fig.  4.1.2.6  indicate that  the  The results shown in  hydrogen  bond  strength  cotton treated at 130 °C appears to change with time  for  (i.e.,  120  1.41  1  —  hr,  1.52  —  2  hr,  and  1.17  hydrogen bonding of the treated cotton at steadily in absorbance with time 1.14  3 hr)  —  (0.66  —  hr).  3  —  While  150 0 C increased  1 hr,  0.86  2 hr,  —  indicating that the hydrogen bond was getting  weaker. At 180 °C the hydrogen bond strength is found in the opposite direction, in  the  hydrogen  bonding  temperature treatments  to go  i.e., getting stronger. This flip  behaviour  of  the  (150 and 180 °C)  two  different  within a comparable  reaction times (1 to 3hr) may be due to the fact that 150 0 C provides suitable conditions for TFA to be involved with the reactants  in  side  reactions.  In  turn,  this  situation  may  offer better chances for acetone as a major volume fraction in the solvent composition to develop weaker H—bonds within the cellulose. In other words, TFA  to  bring  crystalline the two and  3  about  cellulose.  150 0 C is not high enough for  significant The  results  temperature treatments  hr)  lend  4.42%, and 7.11%,  support 12.02%,  to  this  18.07%,  (150  changes of  the  0, C  within  weight  180  assumption; repectively.  0, C  the  loss for  2.84%,  1,  for 2,  3.38%,  121  2 0 C a  0  —0— 130 Deg. Celsius -er- 150 Deg. Celsius 180 Deg. Celsius  1.8 1.6  L?  1.4 1.2 I 0.8 0.6 0.4 0.2 0  0  I  2  3  Residence Time (Hrs)  Figure 4.1.2.6 Effect of residence time on hydrogen bonding of cotton residues during solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA).  4  122  These  results  carbohydrate  at  explicitly 180  C 0  indicate  treatment  removal  the  with  different  of  reaction  times. These results, also, demonstrate that the temperature is a more critical factor than the reaction time when other parameters  were  treatment.  In addition,  kept  constant  in  the  solvent  purification  the statistical analysis shows that  the treatments of cotton for hydrogen bonding at different reaction  times  significantly  (Figs.  different  both acid catalysts 4.1.2.7  Fig.  4.1.2.6 (except  3  and  4.1.2.7)  are  not  hr  treatment,  HC1)  for  (Duncan’s multiple range test). shows  the  effect  residence  of  time  on  hydrogen bonding of residual cotton when HC1 was used as a catalyst  in  solvent  purification  treatment.  The  results  shown in this figure demonstrate that the hydrogen bond gets slightly stronger with  increase  may  the  be  explained  solvation the  by  conditions  environment  of  in the reaction time.  fact  that  chances  increase with time already  solvated  due  to  for  This  better  changes  molecules  in  (i.e.,  isopropylidenated sugars). Another most possible exp1antion may be that the residue which remains after such hydrolysis treatment  is  microcrystalline  cellulose  of  higher  crystallinity. This is consistent with the findings of Chang et al.  (1977).  123  2 4) C) C (5 .0 0 .0 4) .0  E C  1.8  —0- 130 Deg. Celsius x 150 Deg. Celsius 180 Deg. Celsius  1.6  [-  1.4 1.2  I 0.8 0.6 0.4  I  0.2 0  0  1  2  3  Residence lime (I-Irs)  Figure 4.1.2.7. Effect of residence time on hydrogen bondin g of cotton residues during solvent purification (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1).  4  124  The results, and 4.1.2.6, the  Figs.  4.1.2.2,  4.1.2.4  indicate that the use of TFA as a catalyst in  presence  hydrogen  which are shown in Figs.  of  acetone  bonding  4.1.2.3,  bond changes,  has  behaviour.  4.1.2.5  and  led  much  to  However, 4.1.2.7  the  complexity  results  show that  shown  the  in in  hydrogen  in the case of hydrochloric acid, appear to be  relatively simple and progressive. It was emphasized in the literature that the nature of the  solvent,  position of  more  or  has  less,  Lemieux  rotation  Thus,  al.,  1959)  by  (Brewster,  Also,  1968).  about  the  the  and hence the  1959;  changes  solvent  on  in  effect  Stoddart, molecular  were  noted  to be sensitive to changes in temperature.  involvement  bonding, use  et  brought  (Brewster,  effect  equilibria between conformations  molecular rotation of a compound 1971;  some  the  of  TFA  in  the  formation  of  hydrogen  with more complexity than that resulting  from the  of  HC1  as  a  catalyst,  justifications.  Trifluoroacetic acid  a  (HBD)  polar protic  Reichardt,  (Amis,  1988).  Jeffrey et al.,  Further,  it  the  following  is classified as  ionizing  power  and  the TFA molecule has a  Tchoubar,  1966;  Besides,  1991)  (TFA)  solvent with high  fairly low nucleophilicity. resonance effect  have  can  was  1966;  noted  March,  (Nissan,  1985; 1977;  that the strength of hydrogen bond is  fairly dependent on the molecular structure of the hydrogen bond donor  solvent,  i.e.,  the  strong hydrogen  bond  of  TFA  arises due to the presence of the highly electronegative F atom in the TFA molecule.  Apparently,  such properties make  125  TFA  a  strong  carboxylic  acid  with  a  very  strong  hydrogen  bond. Based on these facts TFA can develop a strong hydrogen bond with cellulose and form addition products with water, ketones,  ethers and amines (Geddes,  it seems to be that TFA, hydrogen turn,  bonding  with  these reactions,  1956; March,  most probably, cellulose,  1985). Now,  is involved through  acetone,  and  water.  In  in conjuction with other parameters,  have different implications on the hydrogen bond strength of cotton that would take place during the solvent purification treatment.  However,  irreversible derivatives  the  major  structural of  the acetonation.  sugars)  reaction  changes  within  the  that  (i. e.,  GC, HPLC, and C-13 CP/MAS solid state NMR.  about  isopropylidene  cellulosic  This has been confirmed,  brings  material,  is  in this work,  by  126  4.1.3 Cotton Treatment  Hydrolysis  during  Purification  Solvent  4.1.3.1. Gas Charomatographic (GC) Investigation Isopropylidene Derivatives of Sugars, Identification during Solvent Purification Treatment —  Hydrolysis acetone  is  acetone,  novel  on  1976;  polyols  Excoffier et al., 1975;  Ueno  saccharide reported  et  1984;  et  al.,  residues  in  the  groups  of  Hasegawa  al.,  (Paszner  et  al.,  high  1988).  On  acidified  et  1983;  Hydrolysis  these  et  1973;  Khan et al., substituted  has hand,  other  cis—  (Kiso  al.,  of  conditions the  aqueous  involving  Hasegawa  Glushka et al.,  under  at  anhydrous  disaccharides  and  1981).  catalyzed  formed  1973;  literature.  sugars,  In  are  mono-  catalyzed aqueous acetone, monomeric  acid  in  technique.  isopropylidene  hydroxyls al.,  a  cellulose  of  not  been  in  acid  rapid hydrolysis of cellulose to temperature, Their  work  has  been  indicated  observed that  the  hydrolysis of cellulose in the presence of acetone was up to 700  times  faster  than  conventional  in  aqueous  acid  hydrolysis. In  order  derivatives sugars) authentic 4.1.3.1),  in  to  separate  the  hydrolysate  obtained solutions  on of  solvent  identify  and  reducing  purification  of  cotton,  glucofuranose  glucofuranose  mannofuranose  isopropylidene  (nonreducing  1,2—mono—acetal  1,2:5,6—diacetal  2,3:5, 6—diacetal  and  (Fig.  (Fig.  4.1.3.3)  and  (Fig.  4.1.3.2), 1,2:3,4—  127  diacetal  galactopyranose  (Fig.  4.1.3.4)  were prepared with  commercially available model compounds.  HO—CH  r.t.  Figure 4.1.3.1.  21.649 mm  1, 2-O-isopropylidene-cL-D--glucofuranose.  H  °\cC3 r.t.  Figure 4.1.3.2 glucofuranose.  =  22.006 mm  1,2:5, 6—di-O-isopropylidene—x—D-  128  o HCR  r.t.  Figure 4.1.2.3.  =  32.647 mm  2,3:5, 6—di—O—isopropylidene—D—inannofuranose.  HOH  ::. r.t.  =  Figure 4.1.2.4. galactopyranose.  19.850 mm  1,2: 3,4-di-O-isopropylidene-x—D-  129  The  structures  4.1.3.5 manner  of  the  cotton  4.1.3.6)  and  have  been  suggested by Tomori  retention  times  with  hydrolysate  et  established  al.  those  compounds  (1984)  of  in  by  (Fig.  similar  comparison of  authentic.  nonreducing sugars in the hydrolysate  a  (Figs.  ones.  4.1.3.5)  The appear  to have two major isomers; one of them at the retention time 20.57 mm  is unknown,  21.91 mm  is 1,2:5,6—diacetal glucofuranose. Reducing sugars  while the other at the retention time  isolated from the hydrolysate on acetonation  (Fig.  4.1.3.6)  were found to have more than five major isomers; two of them have been identified 1,2:3,4—diacetal galactopyranose  (r.t.  19.69  mm.)  22.02  mm).  It is noteworthy to mention that due to the fact that  there  and  are  1,2:5,6—diacetal glucofuranose  limited  isopropylidene  derivatives  commercial sources, major  isomers  logical under  to  number  these  model  compounds  sugars  of  available  of from  it was not possible to identify all the  developed  assume  of  (r.t.  in  that  all  conditions  temperature treatment.  the  hydrolysate.  derivatized  and  sugars  would  Nonetheless,  Neither  survive  are  is  it  stable  the _high  isomers such as acetals  of allose, altrose, gulose,  idose, etc. could be anticipated  to  mixture  exist  in  the  reaction  of  the  acetonation  of  cellulose. Both of  Fig.  cotton  versatility.  4.1.3.5 and 4.1.3.6 suggest that acetonation  provides In  other  for  a  words,  remarkable much  is  stereochemical  characterized  by  isomerisation and interconversion reactions of glucose units  130  of  cotton  cellulose.  isomerization  has  The led  equilibrium.  It  carbohydrate  residues  must  ketones  in  acetals  (Stoddart,  the  conditions,  be  figures  to  the  conceded  react  presence  an  two  of  cyclic  readily  is  with  after  that  of  and  an  acyclic  aldehydes  catalyst  Thus,  equilibrium  indicate  establishment that  acid  1971).  also  to  form  suitable  eventually  and  cyclic  reaction  established  in  which the composition of the reaction mixture is determined by the relative free enegies of the cyclic acetals. However, from the stereochemical point of view, complex. cyclic  In other words, acetals  isomerization with  has  to  configurational  (Stoddart,  1971).  acetonation occur  of  taken  and/or  ring into  forms  addition,  all  sizes, account  the  two that  together,  acetal in  conformational  illustrate explicitly  three  in  In  when an equilibrium exists between  different be  equilibrium is often  ring  conjuction  isomerizations  figures  on  cotton  isomerization does  i.e.,  constitutional,  conformational and configurational. Fig. 4.1.3.6.  4.1.3.5 Further  shows the  amount  appears to be different. difference unknown  in  fewer  stability  isomer at 20.57  isomers  and  number  than of  that  of  major  Fig.  isomers  This could be attributable to the of  the various  mm.  isomers,  retention time  is more stable than the other major isopropylidene—cx—D—glucofuranose.  isomer  (Fig. —  i.e.,  the  4.1.3.5)  1,2:5,6—di—O—  In this respect,  a number  of factors are involved in the stability and flexibility of isopropylidene  derivatives.  These  are:  the  dioxolane  and  131  dioxane ring system, sugar ring (pyranoid vs. electronic  interactions  between  the  the molecular size of the derivatives Tomori et al., Thus,  when  isomerization,  1984;  Tomori et al.,  equilibrium  is  furanoid),  the  groups  and  functional  (DeJong et al., Stoddart,  1984;  reached  in  is  1971).  solution  by  the proportions of the different isomers are  determined by their relative free energies (Stoddart, It  1964;  significant  and  unexpected,  however,  1971). that  isopropylidene derivatives of glucose have survived the high temperature hydrolysis conditions of presence of water.  cellulose  even  in the  132  LI’ LI’ Lf (‘4  1•  HOL<  r.t.  =  21.913 mm  rc’ 0•. -i  (‘4  (It’,.. I..’t.  Cs. U:  -1  • ct’ -(  ck. Ct  e cc,  z, C:ft: cr: I—.  Figure 4.1.3.5. GC chroniatogram of nonreducing sugars of the cotton hydrolysate of solvent purification treatment (acetone:water: 90:10; liquor/solid ratio; 10/1; 2 hr; 150 °C; 0.16 N HC1).  133  I’41  HC  KOHH)I  ‘I  H\Lfr’o H  r.t.  =  22.02 mm  (I  CHOH  :<  ci  “-I  H  O\  ci LI.  c. (I  r.t.  =  19.69  mm  ‘-I TI  —I  I—.  2: a: Cr: I--  *  (SI  Figure 4.1.3.6. GC chromatogram of acetonated reducing sugars of cotton hydrolysate of solvent purification treatment (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 0 C; 0.16 N Hel).  134  4.1.3.2 HPLC Analysis  The purpose out  which  of  sugars  know whether  qualitative  are  extracted  isomerization  sugar from  analysis the  is  cotton,  (epimerization)  to  find  i.e.,  to  taken place  has  in the removal of acetone from isopropylidene derivatives of sugars.  On the other hand,  the quantitative sugar analysis  is to assist in the determination of the predominance of the isopropylidenation  reaction  (derivatives formation) and  preventing  the  as  the  major  mechanism  responsible for the rapid hydrolysis  monomeric  sugars  from  undergoing  acid  catalyzed dehydration. Factors affecting the solvent purification treatment of cotton  such  residence  as  acetone  time,  concentration,  temperature,  and  acid  type  acid,  of  concentration  vs  weight loss have also been studied (section 4.1.3.2.3).  4.1.3.2.1— Deacetonation  Not altogether 5,  6,  7,  (epimers)  show in  Epimerization  unexpectedly Figs.  the  the  -  presence  different  of  hydrolysate.  4.1.3.2.1,  These  resulted  2,  3,  4,  sugar  isomers  from  various  ketals as the result of the removal of isopropylidene groups by  hydrolysis  conditions, reaction  and  i.e.,  time.  deacetonation type  The  remained the major  of  acid  results reducing  under  different  catalyst,  also sugar  temperature,  indicate among  treatment  the  and  that  glucose  other  epimers  135  resulting  from  the  removal  of  acetone.  addition,  In  the  results also demonstrate the presence of minor by—products in  small  quantities  4.1.3.2.8),  such  furfural,  as  and  1,6-anhydroglucose  (Fig.  hydroxymethylfurfural.  The  appearance of small peak of furfural in all chromatograms of cotton hydrolysate small  amounts  Although,  of  cotton  could be pectic  is  attributed  substances  considered  as  a  to  in  the  literature  (Hudson et al.,  1948)  presence  cotton  pure  consists of glucose units only), however,  the  of  cellulose.  cellulose  (i.e.,  it was reported in  that the constituents  of mature cotton are as follows:  Constituent Cellulose Protein (N x 6.25) Pectic substances Ash Wax Total sugars Pigment Other  % of dry weight 94.0 1.3 1.2 1.2 0.6 0.3 Trace 1.4  These pectic substances are defined (Pigman et al., a  group  of  polysaccharides  consists  that  of  galactans and largely polygalacturonide chains. it was noted (Frey—Wyssling, acids acid  are water—solube group)  is  1953)  by  H,  as  arabixians, Furthermore,  that the polygalacturonic  and when their  replaced  1948)  we  sixth  obtain  C  atom  the  (i.e.,  xylans  or  polyarabinans. On the other hand,  the unlabeled peaks of the reducing  sugars indicated in the HPLC chromatograms are other isomers of glucose  (i.e.,  not galactose and mannose).  Isomers  such  136  as allose, exist  gulose,  altrose,  under  those  idose etc.  conditions  in  could be expected to reaction  the  mixture.  Unfortunately, due to the fact that there are limited number of  model  compounds  commercial sources, isomers produced to  mention  of  reducing  sugars  from  it was not possible to identify all the  in the hydrolysate.  that  available  the  reducing  is also noteworthy  It  sugars  (e.g.,  glucose,  galactose) have experienced a shift of the retention time in different chromatograms.  This may be  explained by the fact  that the column used for the separation of reducing sugars was  an anion exchange resin one and these type  are  known  to  be  investigation.  sensitive  to  the  of  pH  the  of  columns  sample  under  In other words, the lower the pH of the sugar  sample the shorter the retention time is. The  presence  hydrolysate  has  of  been  1,6—anhydroglucose investigated  by  in  the  running  an  cotton aqueous  model compound of this sugar on HPLC. This is illustrated in Fig.  4.1.2.2.8. The  epimers  difference in  the  accessibility  of  in  the  hydrolysate  proportions is  isopropylidene  due  to  groups  found to be different (Stanek et al.,  of  the to  the fact  various that  the  hydrolysis  was  1963). For example,  in  the hydrolysis of 1,2:5, 6-di-O-isoproplidene-D-glucofuranose the  5,6-0-isopropylidene  hydrolysis position.  than In  the  other  group  is  0-isopropylidene words,  steric  more  sensitive  group  factors  in  and  the  to 1,2  electronic  rt  0  CD  0  4000  6000  0  I  I  10  HMP  I  I  I  15  GLUCOSO  I  I  I  20  I  I  25  I  of cotton chromatogram sugar HPLC Figure 4.1.3.2.1. 90:10; (acetone:water: 0 at 150 C hydrolysate obtained liquor/solid rtio: 10/1; 2 hr; no acid catalyst added).  5  IULJ\  PURPURA1  I  I  I  30  I-I.  12000  CD  0  CD  ci  —I  0) I-I ci  0) c-I  CD  o  ci-  00 I-’  g  C)  CD  $1  o  0  00 H  0  14000  ci  0’ C)  o H  CD  rt  H  CD  1<  toQ  12O  14  16Oc,  MItci  OALCTOSE  OL.UCQSE  chromatogram of sugar 4.1.3.2.2. HPLC Figure (acetone:water: °C obtained 130 at hydrolysate liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA).  1,6-ANHYDROOLUCOSR  cotton 90:10;  Go  0  2000  tDOO  Mute  Figure 4.1.3.2.3. HPLC sugar chromatogram of hydrolysate obtained at 130 0 C (acetone:water: liquor/so)4d ratio: 10/1; 2 hr; 0.16 N HC1).  1,6.ANHYDROGLUCOSfl  GLUCOSE  cotton 90:10;  0  2000  60D  10000  U  Figure 4.1.3.2.4. HPLC sugar chromatogram of hydrolysate obtained at 150 0 C (acetone:water: liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA).  16-ANIIYDROOLUCOSE  cotton 90:10;  C  0  4000  10000  14000  liMP  10  GLUCOSB  IS MIautc  20  Figure 4.1.3.2.5. chromatOgrafll UPLC sugar of hydrolysate obtained (acetoneWat€r at 150 °C liquor/solid rat i?: 10/1; 2 hr; 0.16 N HC1).  1,6-ANHYDROGt.UCOSU  cotton 90:10;  25  30  FURPUR  S  1,6.ANHYDROGLUCOSE  10 Mhtcs  OALACFOSE  20  GLUCOSE  Figure 4.1.3.2.6. HPLC sugar chromatogram of hydrolysate obtained at 180 0 C (acetone:water: liquor/solid ra tio: 10/1; 1 hr; 1.5 N TFA). 1  0  2OO  iox  cotton 90:10;  25  HMF  15 Wnátc.  20  GWCOSE  Figure 4.1.3.2.7. HPLC sugar chromatogram of hydrolysate obtained at (acetone:water: 180 C 0 liquor/solid rtio: 10/1; 1 hr; 0.16 N HCl).  2000  40  sA 5000  6000  9000  cotton 90:10;  :1  30  I I  $  I.6ANHYDROOLUCOSB  4.1.3.2.8. Figure anhydroglucose.  0  2000  4000  $000  10000  1o  t4  HPLC  10  sugar  chromatogram  MIntcs  of  1,6-  I  ‘I  145  With  HC1  temperature  the  as  (180  catalyst  and  °C)  for  treatment  the  longer reaction  at  times  high (3  hr)  has given rise to a considerable increase in the amount of hydroxymethylfurfural  (HMF)  as dehydration product,  at  the  expense of other epimers. This is well illustrated in Figs. 4.1.3.2.9 acid  10.  and  concentration  The of  moderate  temperature  increase  of  However, (TFA)  also  suggest  hydrochloric (150  °C)  acid  has  hydroxymethylfurfural  led (see  that  the  high  (HC1)  even  to  remarkable  a  Fig.  at  a  4.1.3.2.11).  higher acid concentrations of trifluoroacetic acid  in  effect  results  the  on  presence  the  of  formation  acetone of  appear  to  have  hydroxymethylfurfural  little (Fig.  4.1.3.2.12) Although enough  the results  protection  solvent  by  purification  confirm that  isopropylidene treatment,  the  sugar  groups  however,  ring  formed  high  has  during  temperature  exposure for prolonged reaction times is likely to increase the this  chances would  structures reactions.  of  profound  bring more  stereochemical  about,  accessible  to to  a  changes.  greater  degradation  In  extent, and  turn, sugar  dehydration  iA  4O  6O  •I2O  Z4  16  MInutc  Figure 4.1.3.2.9. HPLC sugar chromatogram of hydrolysate obtained at 180 °C (acetone:water: liquor/scplicI ratio: 10/1; 3 hr; 1.5 N TFA).  ,1,6-ANHYDROOLUCOSE  cotton 90:10;  4.  2O  400  EGQ  0 RAS0  Ixco  14OO  IMP  Mu..ta  of chromatogram sugar HPLC 4.1.3.2.10. Figure (acetone:water: 180 °C obtained at hydrolysate liquor/sdlid ratio: 10/1; 3 hr; 0.16 N HC1).  1,6-ANHYDRflGLUCOSE  cotton 90:10;  Minutes  4.1i.3.2.11. HPLC chromatogram of Fig. sugar (acetone:water: hydrolysate obtained at 150 C 0 liquor/solid ratio: 10/1; 2 hr; 0.8 N HC1).  1000  2000  3000  4000  ‘5000  8000  7000  8000  9000  10000  cotton 90:10;  0  2000  6000  8000 V  10 Mgti  20  Figure 4.1.3.2.12. HPLC chronlatogra!tl sugar of hydrolysate obtained at (acetone:Water 150 °C liquor/spud ratio: 10/1; 2 hr; 3 N TFA).  1,6-ANHYDROOLUCOSE  25  cotton 90:10;  30  150  From these experiments it is apparent that TFA would be an effective but milder acid catalyst in the purification of cellulose  that  could  altogether  dissolved sugars (Fig. 4.1.3.2.9,  4.1.3.2.2. Quantitation Sugar Product Formation Treatment  Using a  -  avoid  dehydration  of  the  4.1.3.2.12).  the Predominance of Acetonation during the Solvent Purification  sugar analyzer  (HPLC),  the different  sugars (identifiable and unidentifiable)  reducing  resulting from both  primary and secondary hydrolyses have been considered as of glucose origin. determined  by  acetonation  Their concentration the  sugar  programmed products  in the hydrolysate was  HPLC  was  system.  calculated  The  yield  based  on  weight loss. Table 4.1.3.2.2.1 shows the sugar yields, set of  the for a  solvent purification treatments conducted under the  following conditions: 150  of  0. C  The  total  acetone:water 90:10; 2 hr; 0.16 N HC1;  sugar  recovered  was  86.33%.  From  this  result about 40% of the potential sugar yield is found to be in  reducing  form,  i.e.,  the  primary  hydrolysate.  However,  the remaining amounts of the acetonation sugar yield 46%)  were  reducing  nonreducing  form  illustrated result  shows  is  in  attained  Table  that  sugars  the  and  through  their  conversion  secondary  4.1.3.2.2.1.  Thus,  acetonation  sugar  (around  the  into  hydrolysis sugar  products  yield  are  predominant part of the soluble hydrolyzed cellulose.  as  the  It is  151  worth noting that the quantitative total sugar yield agreement with that al.,  1983;  that  the  stated by previous workers  Ward et al., sugar  1988).  yield  Also,  resulting  is  in  (Paszner et  the results indicate after  the  secondary  hydrolysis increased with the extent of the reaction time. It  is  analysis,  important  to  deacetonation,  treatment  of  mention  that  the  and quantitation)  cotton  with  results  (GC  obtained by  acidified  aqueous  the  acetone  (acetone:water:  90:10)  the literature.  It has been confirmed for many decades that  cyclic with  and  acyclic  acetone  in  cyclic acetals other  hand  in accord with that reported in  carbohydrate  the presence  (Stanek et al.,  the  4.1.3.2.2)  are  results  are  not  of  derivatives acid  an  4.1.3.1,  agreement  readily  catalyst  1963; Stoddart,  (subsection in  react  to  1971).  on the  4.1.3.2.1  with  the  Ward  Grethlein’s interpretation. It was noted (Ward et al., that  the  formation  of  1,6-anhydroglucose  form  is  the  and and  1988)  dominant  mechanism responsible for the enhancement of the sugar yield in  acidified  aqueous  acetone  hydrolysis.  However,  that  is  not the case, because the formation of 1,6—anhydroglucose is expected to dominate in aqueous acidic solutions where high energies  are  applied  (Stoddart,  1971).  addition,  In  the  formation of 1,6—anhydroglucose on cellulose units does not explain  the  acetonation  high  hydrolysis  process.  isopropylidene  groups  In  rates  conclusion, on  the  of the  cellulose possibility  cellulose  significantly weaken the glycosidic  linkages  units in  in of  might  cellulose.  152  In  this  turn,  could  lead  to  rapid  a  depolymerization  of  cellulose to isopropylidenated sugars. Now  it  is  evident  that  the  yield  of  reducing  sugars  obtained during solvent purification treatment of cotton is fairly high. explained  This high degree of sugar survival can only be  by  the  formation  of  protecting  groups  (i.e.,  isopropylidenes) on the sugar rings. The (around  undetermined 13%),  most  isopropylidenated stable  losses  probably,  oligomers,  isopropylidene  luonoacetals  of  quantitative  contain  endo  small  dioxolane  of ring  analysis  quantities  1,6-anhydroglucose  derivatives  isopropylidene—mannofuranose) ring form (e.g.  in  and  sugars (e.g.  of  fairly  such  as  2,3—0—  or/and monoacetals of pyranoid  1, 2-O-isopropylidene-cc-D-glucopyranose).  Table 4.1.3.2.2.1. Reducing sugar + (primary secondary hydrolysis) yield in hydrolysate cotton following the treatment with: acetone:water: 90:10; 2 hr; 0.16 N HC1; 150 oc. Type of Hydrolysis  Amount  Yield  Total Sugars Prim. + Sec. Hyd. Amount Yield mg  Primary Hydrolysis  108  40.45  ---  Second. Hydrolysis 1/2 hr treatment  90  33.71  198  74.16  Second. Hydrolysis 1 hr treatment  122.5  45.88  230.5  86.33  153  4.1.3.2.3 Changes in Weight Loss during Solvent Purification Treatment  The  obvious  measure  of  extent  the  of  cellulose  hydrolysis is the weight loss arising from the production of soluble sugars. Hence, a  measure  solvent  to  in this work, weight loss is taken as  examine  the  purification  effect  treatment.  each  of  factor  such  Factors  as  on  the  acetone  concentration (with and without acid catalyst), temperature, residence time, acid concentration and type of acid catalyst have been investigated. The  result  given  in  4.1.3.2.3.1  Fig.  shows  that  the  successive increase in acetone concentration has been found to give rise to a systematic increase in weight loss. result  is  consistent  with  obtained  those  in  This the  investigation of reaction rates in stationary hydrolysis of cotton  linters  as  (Paszner et al.,  a  function  1988).  of  acetone  concentration  This result is also consistent with  that obtained for the effect of acetone on hydrogen bonding of the  cellulose  accessible  the  (Fig.  cellulose,  reactions take place. shows  that  the  concentrations different  4.1.2.1).  (except  the 2  much  In addition,  treatments for  the  In  of  treatments),  (Duncan’s multiple range test).  easier  the  the more hydrolysis  the statistical analysis  cotton  weight  other words,  with  loss see  -  various  are Fig.  acetone  significantly 4.1.3.2.3.1  154  In regards to the hydrolysis of cotton which occurred during  solvent  purification  just  acetone and water  this  can  be  treatment  (i.e.,  attributed  no  the  to  in  presence  the  acid catalyst was protonation  of  added)  glucosidic  of  linkages with acetone/water mixture and the acids of pectic substances although  precent cotton  polymer  (i.e.,  in  is  the  cotton  considered  consists  recorded (Hudson et al.,  of  6.25)  total  1.3%,  sugars  pectic 0.3%,  pectic  substances  group  of  galactose  units  Furthermore, galacturonic  defined  it was stated  and  it  was  that  protein  1.2%,  other et  wax  as  a  arabinose,  of  1953)  In  Those  1948)  polygalacturonic  (Frey-Wyssling,  (N  0.6%,  1.4%.  al.,  consists  water-soluble.  are  only),  ash  (Pigman  largely  and  acids  1.2%,  traces,  polysaccharides  cellulosic  cellulose 94.0%,  substances  were  units  However,  in the literature that cotton  1948)  pigment  homogeneous  glucose  has the following constituents; x  a  cellulose.  acids.  that these  addition,  the  formation of acetic acid and methyl alcohol was ascertained by Ehrlich et al. presence  of  (1929).  small  On  quantities  of  the  other  water  in  hand,  the  the  solvent  composition at relatively high temperatures appears to give rise  to  acetone  the with  been reached, the  solvent  150 °C)  formation the  water  of  a  complex  molecules.  in the present work, treatment  buffer  from 7.46 to 5.77.  from  This  the  reaction  interpretation  of has  due to the drop in pH of  (acetone:water:  90:10;  2  hr;  This assumption is given due to  the fact that the pH of cotton hydrolysate dropped from 7.46  155  to 459 within identical treatment conditions. hand,  the  noted  by  acidity Fong  However,  the  et  of al.  the  acetone/water  (1969)  explanation,  and  given  complex  Waggoner  earlier  On the other  et  by  was  al.  also  (1982).  Zarubin  et  al.  (1989)  when they used acetone  study,  was due to the hydrolysis of polysaccharides by the  acid  (acetic  addition, 1.0%) (50  the  acid)  formed  increase  and water  during  in weight  90%)  to  is  likely  to  occur  pulping  the loss  maintained with the increasing  their  for  pulping  process.  (from around  In  0.5  to  acetone concentration  from  the  better  solvent—  solute solvation that could take place in both amorphous and crystalline zones. This process of solvation will apparently lead to the opening up of hydrogen bonding and provision of strained Thus,  glycosidic  the  adjacent  formation  linkages of  sugar residues  reasonable  explanation  on  isopropylidenated  isopropylidene (Khan for  et the  al.,  groups 1975)  ease  of  glycosidic linkages in the cellulose chains.  sugars.  between  could  the  offer  breakage  a of  156  0.5  :: : 0.2 0.1 I  &  40  I  70 60 80 Acetone Concentration (%)  100  Figure 4.1.3.2.3.1. Effect of acetone concentration on the weight loss of solvent purified cotton (liquor/solid ratio: 10/1; 150 0 C; 2 hr; no acid catalyst was added). * -Means different. **  with  the  same  letter  are  Significance at 95% confidence level.  not  significantly  157  Figs.  4.1.3.2.3.2  increase in the weight  and  3  illustrate  effect  the  on  C to 0  weight  remarkable  loss of solvent purified cotton due  to the increase in temperature to temperature from 130  the  loss  (180 C 0 ).  150 0 C of  The increase of  is shown to have  treated  cotton.  It  important to mention that the temperatue increase  slight  is  also  from 150  °C to 180 0 C caused a nonlinear increase in the dissolution of  cellulose,  temperature.  increasing However,  disproportionately  the  statistical  at  the  analysis  higher  indicates  that the treatments of cotton at different temperatures for the weight loss,  in the case of the two acid catalysts,  significantly different  are  (Duncan’s multiple range test).  These results are consistent with those of Chang et al. (1976,  1977)  and Paszner et al.  (1988)  on wood. It was noted  that low temperarure hydrolytic dissolution of wood in acid catalyzed aqueous acetone occurred in two stages, and  main  hydrolysis,  hydrolysis  became  while  first  at  order  all  high the  i.e., bulk  temperature way  to  complete  dissolution.  —  Higher temperature system.  In turn,  increases the reaction rate  this would lead to further  changes that can bring about, bond  disruption  more active be  available  the  in  the  stereochemical  to a greater extent,  cellulosic  of the  material.  more H—  Consequently,  sites  (i.e.,  H-bond-free hydroxyl  groups)  to  undergo  isopropylidenation.  Besides,  will the  reactivity of both acetone and acid catalyst increases with increased  temperature  as  does  the  system  pressure.  This  158  would also  speed up the  isopropylidenation process  by the  involvement of more acetone molecules and hydrogen ions with the glucose units to yield isopropylidene groups along the cellulose  chains.  On the  other hand,  dissociation of  water and acid catalyst molecules into ions the increase in temperature and this will, to  a  considerable participation of  both  increases with  eventually,  hydronium  and  lead  hydrogen  ions in the cleavage of glycosidic linkages. This impact  process,  on  most probably,  stereochemical  isopropylidene intramolecular  (i.e., between  configurational isomerism explanation chemical equation.  for  the  reactions  -  effect is  have  alterations  groups H-bond  will  of  given  the C6  from  and  f3  and  to cL).  the  formation  destruction glycosidic However,  temperature in  significant  a  on  the  classical  of of  0  +  the best rate  of  Arrhenius  159  20  16 0  ‘—12  /*  U) U)  0 —I  8  4  0 120  130  140 150 160 170 Temperature (Degrees Celsius)  180  Figure 4.1.3.2.3.2. Effect of temperatu re on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA ).  190  160  45 40 35 30 0’  U)  Cl) 0  1 .10  I  25 20  /7  .  15 .  10 5 0. 120  130  140 150 160 170 Temperature (Degrees Celsius)  180  Figure 4.1.3.2.3.3. Effect of temperature on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1).  I 90  161  Figs.  4.1.3.2.3.4  and  5  show  increased  the  that  reaction time from 1 to 3 hr at lower temperatures and  150  loss at  °C)  resulted  only  in  a  slight  (from 1.76 to 3.15% at 130 °C,  150  weight  °C,  in  the  loss  is  between  7.96%  at  hand,  longer  150  temperatures weight loss  °C)  case  of  of  TFA  as  1.88  and  4.58%  (180 °C)  time  (3  in  C 0  weight  and from 2.84 to 4.42% catalyst,  solvent treated  residence  increase  (130  at  130  cotton.  HC1  0, C  3.56  On  coupled  hr)  for  the  the to  other  with  higher  appear to have a marked effect on the  (18.07% and 41.9% for TFA and HC1,  respectively)  of solvent purified cotton. However, the statisical analysis demonstrates  that  reaction times acid  the  for  catalysts  treatments  the weight  (TFA  of  loss,  HC1),  and  cotton for  are  at  different  different type not  of  significantly  different (Duncan’s multiple range test). The  time  factor  is  found  carbohydrate  (weight)  purification  treatment  when  reduced  removal  constant.  The  loss  to  have  after other of  a  lesser  the  effect  initial  parameters  carbohydrates  on  solvent are  in  kept  such  a  case can be explained by the fact that the stereochemistry of isopropylidinated units may bring about more or less the some  effect  implications accessible  on  on  the  more  adjacent  H-bond  cellulose  molecules  disruption  units  .  allowing  to  isopropylidenation and hydrolysis reactions.  undergo  This  has  the  more rapid  162  20  i______________  0 130 Deg. Celsius -*- 150 Deg. Celsius O— 180 Deg. Celslufj  16 -p  o-.  rr  Cl) Cl)  0  4  0  0  1  2 Residence Time (Hrs)  3  Figure 4.1.3.2.3.4. Effect of residence time on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA).  4  163  45 40  -0- 130 Deg. Celsiusf___________ 150 Deg. Celsius —0-- 180 Deg. CeIsj!j ——  35  ._J  30  /7  25 20 15 10 5 0  0  1  2  -  3  Residence Time (Hrs)  Figure 4.1.3.2.3.5. Effect of residence time on the weight loss of solvent purified cotton (acetone:water 90:10; liquor/solid ratio: 10/1; 0.16 N HC1).  4  164  The effect of acid concentration for both hydrochloric acid has  (HC1) also  trifluoroacetic  and  been  investigated.  show  that  acid  concentration  However, (4.9%  weight  33.5%)  cellulose  Both  Figs.  different  the  (TFA)  increased  also  in  (cotton)  has  of  results  the  vs  loss  acid  indicate  weight  4.1.3.2.3.6  with  type  weight  on  and  increase  the  of  loss  acid  7 of  catalysts.  that  greater  increase  of  solvent  purified  loss  has been attained by the use of HC1 than  with TFA. The results also are in agreement with those found for mineral acids in the previous work with wood by Paszner et al., that  (1988).  the  Nonetheless,  treatments  of  concentrations  for  the  catalysts  and  HC1),  (TFA  Figs. 4.1.3.2.3.6 and 7  the statistical analysis shows cotton  weight are  with  loss,  different  for  significantly  the  acid  two  acid  different,  see  (Duncan’s multiple range test).  The increase of weight loss with the increase in acid concentration attributed  regardless  to  higher  of  the  catalyst  acid  concentration  can  hydrogen  of  ions  be for  protonation of glycosidic linkages. The  inefficiency of trifluoroacetic acid  presence of weight loss)  acetone  in the  hydrolysis  of  (TFA)  in the  cellulose  (lower  is due to the fact that the two solvents have  fairly different properties that probably lead them to react with  each  Harris  other  (1965),  as  it was  Isaacs  noted  (1974),  between catalyst and acetone hydrolysis  of  cellulose  before  by  March  (1985).  is most  likely  (i.e.,  competing  Geddes This to  (1956), reaction  retard  the  reactions).  In  165  addition, take  the  part  blocked  in  by  not  be  developing (Isaacs,  hydrogen  1991).  with  out  strong  to  cellulose.  hydrogen 1977;  this  in  due  molecules also  have  the  interaction  unique  this  with  other  March,  1985;  Jeffrey  break  up  the  been of  factor  properties  bonds  respect  which  may  However,  since TFA has  Nissan,  Thus,  cellulose  reaction  bonding  acid  ruled  1974;  of  hydrolysis  the  trifluoroacetic can  centres  active  for  compounds  of  et  al.,  hydrogen  bonding between TFA and cellulose requires more energy to be applied occur.  in  order  Nonetheless,  polar  protic  with  a  high  acetone  1974)  and with  a  However,  both  (Tchoubar,  (i.e.  ionizing (Isaacs, is  faster  hydrolysis  a  hydroxylic) power  1974;  dipolar  and  March,  aprotic  (Frey-Wyssling,  (Reichardt,  of  1966;  to  reactive them  carbonyl  have  Reichardt,  a  1985). (i.e.,  1953:  group  molecular  1988).  1988),  particularly  with a high nucleophilicity  very  reactions  trifluoroacetic acid is classified as a  hydrophylic solvent Isaacs,  attain  solvent  nucleophilicity hand,  to  On  the  low other  nonhydroxylic)  Bax et al.,  1972;  (Reichardt,  1988)  (Tchoubar,  1966).  resonance  effect  Suggestions  of  similar  reactions between acetone and TFA were also noted elsewhere (Geddes,  1956; Harris,  1965; March,  1985).  166  6 5  U) U)  03 -J  c /0  o7  I 0  0  0.5  1  1.5 2 2.5 Acid Concentration (N)  3  3.5  Figure 4.1.3.2.3.6. Effect of acid concentration on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 0 C; TFA). *  Means different. **  with  the  same  letter  are  Significance at 95% confidence level.  not  significantly  4  167  40 35  >)  30  25 2O  .215 10  0.2  0.4 0.6 Acid Concentration (N)  0.8  Figure 4.1.3.2.3.7. Effect of acid concentration on the weight loss of solvent purified cotton (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 0 C; HC1) *  Means  with  the  same  letter  are  different. **  Significance at 95% confidence level.  not  significantly  1  168  4.1.4 CP/MAS C—13 solid state Investigation NMR — Isopropylidene Intermediates Residual in Cotton during Solvent Purification Treatment  High—resolution C-13 interest  in  last  the  spectroscopy has  NMR  decades  as  a  powerful  gained much  tool  for  the  structural elucidation of natural polysaccharides.  However,  native  assessed  and  modified  extensively  by  properties  this  technique  insolubility  as  solution—viscosities Nonetheless,  celluloses  in  in  of  solvents  Attalla,  CP/MAS  whether cellulose  such  and  intrinsic  fairly  their  of  1985;  (Saito,  et al.,  Hoshino et al.,  useful information about celluloses. C—13  been  high  dissolution.  with magic—angle spinning and cross  polarization has been found 1981;  because  case  the  not  it has been clear for some time that C—13 solid  state NNR spectroscopy,  al.,  have  has  NMR  acetone in  been  employed  molecules  the  react  solid  state  1981;  1989) In  Saito et  to provide this  work,  clarification  for  covalently (i.e.,  with  formation  of the of  isopropylidene intermediates on the cellulose molecules_as a first step in the hydrolytic breakdown) purification  treatment.  isopropylidenation  on  In  during the solvent  addition,  decrystallization  the of  effect  residual  of  cotton  has also been investigated. Fig. residual  4.1.4.1 shows the C-13 CP/MAS NMR spectrum of the cotton  treated  with  natural abundance is 1.11%), of  untreated  one  (Fig.  normal  acetone  (i.e.,  C—13  and the spectrum resembles that 4.1.4.2).  However,  no  signals  169  appeared in the methyl group region.  Fig.  4.l.4.3a shows the  C-13 CP/MAS NMR spectrum of the residual cotton treated with C—13  labeled  acetone.  The  results  illustrated  in  Fig.  4.l.4.3a show that the acetonated cotton residue has given two peaks can  be  26.5  assigned  disappear Fig.  at  in  the  4.1.4.3b).  and to non  31.8  be  ppm,  methyl  quaternary  respectively. groups  since  suppresion  Those peaks they  do  spectrum  not (see  i0  -  -  I  i4Q  ,  -  .  I 20  -  100.  pP$  0  60  40  Figure 4.1.4.1L C-13 CP/MAS NNR spectrum of the residual cotton treated with normal acetone (acetone:water: 90:10; C; 0.16 N HC1). liquor/solid ratio: 10/1; 2 hr; 150 0  i80  .__L_  20  C  i40  i20  .  Figure 4.1.4.2. (control).  -  80  PPM  60  40  CP/MAS C—13 NMR spectrum of untreated cotton  iOO  20  1  i50  .  I  i40  90:10;  cotton  Figure  —  I  £20  £00  ratio:  I  A  6O  •  _L 40  •  .  the  0  t  —20  residual  .  (acetone:water:  of  20  150 oC; 0.16 N HC1).  acetone  spectrum  •  4.1.4.3a. C-13 CP/MAS NMR treated with C—13 labeled liquor/solid 10/1; 2 hr;  •  2  H?  and/or  HOC  OH  ____________________________  —  I —  220  •  S  200  •  180  —  0’  i0  S  140  -  •  S  120 PPM  100  •  I  80  •  S  60  -  S  40  g  b  •  t9•  20  S  qLa  ‘  I  0  Figure 4.1.4.3b. Non quaternary carbon NMR spectrum of the residual cotton treated with C-13 labeled acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C; 0.16 N HCl).  240  1’  •  174  Furthermore,  these  methyl  physically adsorbed acetone was used. 30 ppm, Even  Therefore,  signals  cannot  because triply  be  due  labeled  to  acetone  additional to methyl signals at around  a carboxyl signal at around 210 ppm should be found. there might  though  residue,  (see Fig.  be  a  4.l.4.3b,  small  amount present  in  the  very weak signal at 212 ppm)  the methyl signals are too large to originate from adsorbed acetone.  Therefore,  the  evidence  is  have reacted with the cellulose to  that  the  form an  acetone  must  isopropylidene.  The possible form of such an intermediate has been shown in Fig.  4.1.4.3a. In general the integral in C-13 CP/MAS spectroscopy is  a  much  spins  more than  reliable that  allows us to  in  measure  solution  for  the  C-13  NMR.  relative In  other  numbers  of  words,  it  estimate how many of the cellulose units  involved in this reaction.  There are  are  6 carbons per glucose  unit. The natural abundance of C-13 is 1.11%. Per  acetone  molecule,  there  are  2  methyl  groups  with  isotope abundance of 99%, and 1  carbonyl  carbon  with  —  abundance  99%  covered  within  cellulose carbon peaks (between 80 and 90 ppm), hence Ii  =  [(6 x 1.11)  12  =  (2 X fl X 99 )Io  11/12  =  +  (6 x 1.11)  (n x 99) =  +  0.7  ) 10  =  10.4  (from the spectrum)  (6 x 1.11)  +  (99 x n)  (6 x 1.11)  =  [10.4/(0.7 x 2 x 99 x n))  6.66  =  (n x 99)  (from the spectrum)  (n x 99)/(2 x n x 99) =  =  10.4/0.7  10.4/(0.7(2 x 99 x n)  [2(10.4/0.7)  an  —  1]  —  99 x n  the  175  n  =  -  where  1/430 I,  glucose  and  12, unit,  I  two  are the methyl  intensities groups,  of  and  carbon  13  carbon  1  for  atom,  respectively. This means there is only one isopropylidene group per every 400-500 glucose units of solvent purified cotton treated at C (acetone:water; 90:10, 150 0 N HC1).  In other words,  liquor/solid; 10/1, 2 hr,  around  400-500  0.16  glucose units have  remained unaffected by isopropylidenation at this designated treatment condition. viscosity value treatment limiting  This calculation is in accord with the  (about  condition DP  of  3.5  and  300  is  in  these  conditions  deacetonation 4.1.3.2.1).  see  just  (Rydhoim,  been determined, treatment  CP,  Hence,  this  Also,  equal yield  is  86.33%  fraction  into the solution  (hydrolysate).  of  cellulose  already  been  In addition,  under  and  the  (Table  the  has  the  than  loss  5.34%  that  at this  has  it  to  suggests  isopropylidenated  higher  that the weight  is  product  4.1.7.4.)  slightly  1965).  this work,  sugar  Fig.  major removed  by usingacid  catalyzed aqueous acetone in solvent purification of cotton the  viscosity  4.1.7.3  has  (viscosity  attributed  to  the  dramatically analysis  dropped  section).  formation of  as  shown  This  could  isopropylidene  in  Fig.  also  groups  at  be a  uniform interval pattern between the glucose residues along the cellulose chains as it is proposed in Fig. is  also  noteworthy  isopropylidene groups  to  mention  between the  that  the  adjacent  4.1.4.4.  formation  It of  sugar units has  176  already  been  established  by Khan  et  in  al.  1975  in  their  study on sucrose (a comprehensive review is given in chapter 2).  On the other hand,  the possibility of the  reaction of  acetone molecules with C6 and the hemiacetal oxygen can not be ruled out, present one,  although neither the previous works,  nor the  were able to substantiate this possibility as  the number of isopropylidene substituents would be expected to be much larger than found in this work. However, the drop in CuEn viscosity is substantially increased in the presence of  acid  catalyst  illustrated 2.7  CP).  with  in Figs.  This  the  4.1.7.4  increase and  temperature  of  4.1.7.5  (from  28.5  CP  as to  indicates very rapid penetration of the acid  throughout the  entire cellulose matrix but not necessarily  involving also the crystalline regions,  the destruction of  which is possible only with concentrated acids, but not with dilute trend  solutions. (from  0.93  The to  interpreted as follows:  weight  loss  42.3%).  All  has these  also  shown  results  similar  would  be  177  Cellulose Chain +  I + bl  /  Unaffected parts of cellulose ctiain  T(>1 OOb) 01 C.J  (4  V 4 \AI isopropylidene groups between glucose residues  2 HOH  v= A  Figure 4.1.4.4. Proposed formation of iSOpropyljdene groups along the cellulose chain.  178  a— higher temperature increases the reaction rate of the system. In turn, this would lead to further stereochemical changes that can bring about,  to a  greater extent, more H—bond disruption/destruction in  the  cellulosic  material.  Consequently,  more  active sites (H-bond free hydroxyl groups) will be available to undergo isopropylidenation.  Besides,  the reactivity of acetone molecules increases with increased temperature as does the system pressure. This  would  process molecules  by  also the with  speed  up  the  isopropylidenation  involvement glucose  isopropylidene groups  of units  along the  more to  cellulose  acetone yield chain.  This can be illustrated in Fig. 4.1.4.5.  Unaffected pail otcellutose chain  CeHulose chain  Isoprop4idene groups between glucose residues  Figure 4.1.4.5. Proposed formation of isopropylidene groups along the cellulose chain at higher temperatures.  179  b—  dissociation of  molecules  into  both water  ions  and acid  increases  with  catalyst  increase  in  temperature  (Bernal et al.,  eventually,  lead to considerable participation of  hydrogen  ions  linkages.  This process,  have  remarkable  a  alterations  in  and  the  1933)  and this will,  cleavage  of  glycosidic  most probably,  will  also  impact  on  stereochemical  formation  of  isopropylidene  groups, i.e., the destruction of intramolecular H— bond  between  C6  and  configurational isomerism In  consequence,  the  glycosidic —  from  removal  J3  oxygen  +  to cx.  of  isopropylidene  derivatives of sugars in the solution during the hydrolysis reactions would lead to disproportionation of the cellulose chain.  Apparently,  cellulose  with  the  short  disproportionation chains  offers  isopropylidenated  reducing and/or non-reducing sugar terminals,  residual at  however,  the the  most likely one can be shown in Fig. 4.1.4.6.  /  1  Figure 4.1.4.6. Solvent purified cellulose chain of residua l cotton.  180  Concerning  the  intermediates  during  appearance  the  of  spectrum given that  acetone  in  Fig.  as  a  It  also  illustrate  the  in  a  solid  react  in  (5.3  ppm)  on  the  ring  explicitly (solid)  shift  for  the  suggests  probability of a skewed form of  small of of  the the the  1985)  1980; Buchanan  that the acetal carbon  rings resonates in the range of 100.6—101.1  Nonetheless, (i.e.,  atoms  of  1,3-dioxane ring would not  Grindley et al.,  rings  Fig.  However,  et al.,  ppm.  The  formation  unit.  the  formation  carbon  It was stated (Buchanan et al.,  of such cyclic  with  signals shown  the  be ruled out. 1982;  solvent  traces  cotton.  the  cellulose  the  HPLC  NNR  indication  covalently by  the  state  strong  fraction  shown  residual  chemical  groups  dioxolane  as  the  is  ,  volume to  in  treatment,  is evident that the two methyl  in  difference,  purification  4. l.43a  capable  isopropylidene  of  signals  major  is  4.l.4.3a  monoketal  methyl  methyl  molecules  4.1.3.2.1.  solvent  in Fig.  (acetone/water) cellulose  formation  it  is  possible  1,3—dioxolane  and  a mixture  1,3-dioxane)  of is  both  acetal  presenj  in  the solvent treated cotton residues. In  conclusion,  structure  of  glucopyranose glucopyranose  one  interest —  reducing  could  indicated in Fig.  also  4.1.4.6.  may  suggest is  sugar,  that  the  monoacetal  1,2-O-isopropylidene-c1-Dhowever  be possible  (but  a  4,6—monoacetal less  likely)  as  181 4.1.5 X-ray Diffraction Analysis - Changes in Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  The main purpose of this work is to study the effect of solvent purification treatment on the crystalline structure of cotton residues.  Also,  it  is of  interest to  follow the  progressive crystalline changes that have taken place in the cellulose  when  factors  such  as  acetone  concentration,  temperature, and acid concentration are tested.  4.1.5.1 Acetone Effect on Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  The  acetone  cellulose,  in  effect  this  on  work,  the  was  crytalline  tested  by  structure  using  of  different  acetone concentrations in the treatment without adding acid catalyst.  Figs.  4.1.5.1,  4.1.5.2  and 4.1.5.3  show that the  successive increase in acetone concentration has resulted in hightening the intensities of 101,  101,  and 002 planes.  The  increase in peak heights of 101 and 101 can be attributed to reorientation of hydrogen bonding (spacing) effect of acetone  on the cellulosic material.  in peak height observed at the enhancement  of  as result of the  crystallinity.  002  plane  A similar  The increase  demonstrates  trend  of  a  the  slight  increase in crystallinity index of treated cotton in 50% of acetone is illustrated in Table 4.1.5.1. Also, results given in Table  4.1.5.1  show that  the  crystallite  breadth,  i.e.,  182  full width at half maximum height, increased.  In  crystallite  size  other is  words, slightly  FWHM  this  (10!)  is  indicates  decreased  since  slightly that  the  crystallite  breadth is inversely proportional to crystallite size (Ahtee et al.,  1983).  The results illustrated in Figs.  4.1.5.1,  2,  and shown  in Table 4.1.5.1 correlate well with those of the hydrogen bonding  (Fig.  4.1.2.1).  This can be explained by the  fact  that the successive decrease in the strength of the hydrogen bond of the cellulosic material with the increase of acetone content has led to a progressive decrease in the crystallite size. In other words, presumably, the new orientation of the hydroxyl groups  (i.e., weak H—bonds)  of cellulose molecules  does not provide suitable conditions for the crystallites to pack  tighter  order.  They  obtained  also  at  4.1.3.2.3.1). successive was  together  as  coalesce  correlate  different  well  acetone  in  stronger  with  the  lateral  weight  concentrations  loss (Fig.  This can be interpreted by the fact that the  increase  associated  index  and  the  with  in weight  loss  systematic  acetone  of the  increase  concentration  treated cottons in  was  crystallinity consecutively  increased in the solvent composition. On the other hand, the systematic increase in crystallinity index of the residual cotton  (Table  4.1.5.1)  as  the  acetone  content  was  successively increased in the treatment correlates well with the progressive loss of the hydrogen bond strength cellulose  (Fig.  4.1.2.1).  of the  This explicitly means that within  183  the prevalence of selective removal of amorphous higher  degree  crystallinity  of  can  be  cellulose  attained  in  an  accessible cellulose .The results given in Table 4.1.5.1 for crystallite breadth agree well with those for hydrogen bonds obtained at different acetone concentrations (Fig. 4.1.2.1). The  higher  hydrogen reduced  the  bond,  acetone  concentration,  the  bigger  the  crystallite  size).  Thus,  our belief that acetone solvent, the  cellulose  swells them, words,  fibres  crystallite these  weaker  breadth  results  the  changes  and  crystalline  intramicellar  crystallinity  (i.e.,  has  taken  zones), In other  index  crystallite size)  swelling  (i.e.,  in this process, penetrates  (amorphous  in  the  strengthen  and brings about structural changes.  crystallite breadth an  the  and  the  indicate that  place  during  acetonation of cellulose. It was noted (Frey—Wyssling,  the 1953)  that in intramicellar swelling there is a stronger affinity between  the  swelling  binding forces  agent  and  chain  in the chain lattice.  molecules  Usually,  than  the  in this type  of swelling the solvent penetrates into the crystal lattice and widens changes  it.  that  This widening can  be  diffraction technique  is  followed  accompanied by by  (Frey-Wyssling,  means  of  1953).  structural the  It  X—ray  seems most  likely that the enhancement of crystallinity was attained in the solvent purification treatment by the selective removal of  amorphous  accessibility and  cellulose  in  conjuction  with  the  greater  (i.e., weaker hydrogen bonding at both inter  intramolecular  levels)  of  cellulose.  However,  the  184  selective removal of the amorphous cellulose by the solvent treatment  could  be  enhancement  of  correlation  held  considered  as  crystallinity. among  the  main  reason  regards  With  accessibility,  weight  for to  the the  loss,  and  enhancement of crystallinity, this is strongly indicative of the superiority of the solvent purification treatment over the  current  purification  processes.  Hence,  the  ability  of  the solvent technique to ensure advantages such as increased accessibility specificity  (reactivity)  in  the  of cellulose,  removal  enhancement of crystallinity)  of  and high degree of  amorphous  cellulose  (i.e.,  is a practical answer to the  problems encountered with the current processes.  185  350G 002 r Cotton treated wIth 50% acetone conc. ./ (no acid catalyst) Untreated cotton  C’,  E  •2000  1500 C,  101 1000  101  500  0  5  20  25  Bragg’s angie (2 theta)  30  35  Figure 4.1.5.1. Comparison of diffraction patterns of treated (acetone:water 50:50; liquor/solid ratio: 10/1; 2 hr; 150 °C) with untreated cotton (control).  40  186  4000  3500  002 1Cotton treated wfth 70-80% acetone cone. (no acid catalyst)  3000-  Cotton treated wfth 90% acetone cone . (no acid catalyst) Untreated cotton  2500U-.  0 I  C)  •2000z  a)  1500-  101 1000-  5:  5  10  15  20  25  Bragg’s angIe (2 theta)  30  35  Figure 4.1.5.2. Comparison diffraction of patterns of treated (acetofle:Water: 70:30, 80:20, and 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C) with untreated cotton (control).  40  187  3500  002 Cotton eated wIth 90% acetone conc.  (no add catalyst)  3000  h Untreated cotton  U,  E  2000r  150&  i00o,___bJ1O  c$.  Bragg’s angie (2 theta)  Figure 4.1.5.3. Comparison diffraction of patterns of treated (acetone:Water, 90:10: liquor/solid ratio: 10/1; 2 hr; 150 °C) with untreated cotton (control).  188 Table 4.1.5.1. Acetone effect on crystallinity index and crystallite breadth of cotton residues treated with different concentrations of acetone, while other variables were kept constant (liquor/solid ratio: 10/1; 2 hr; 150 °C; no acid catalyst added). Acetone Concentration  CI  S.D.  002 FWHM  (Degree) Untreat. cotton  74.37  0.21  2.01  50  74.38  0.24  2.14  60  74.34  0.32  2.16  70  74.62  0.10  2.15  80  74.74  0.22  2.17  90  75.44  0.34  2.16  Usually  aqueous  acid  hydrolysis  brings  about  considerable broadening of the reflection peaks of 101, and  002  have  planes.  been  Besides,  noticed  (Kulshreshtha  et  to  the peak heights experience  al.,  1973).  of  these  appreciable  Those  ioT,  planes  decrease  changes  in  acid  hydrolysis indicate that decrystallization is the result of a  decrease  in crystallite  size and  an  increase  in  lattice  disorder. It was stereotype size  also  material. is  stated by Nishimura et al. decrystallization  takes  place  For instance,  achieved  by  in  and  the  (1987)  reduction  mercerization  that similar of  crytallite  of •cellulosic  the formation of alkali Cellulose I  lowering the  crystallinity  of  the  original  189  cellulose. In this respect, Cellulose II is less crystalline than Cellulose I (Nishiiuura et al., 1987). However,  the  interesting  features  of  enhancement  of  crystallinity, with the slight decrease in crystallite size, and  increase  acetone,  of  can  peak be  heights  of  101  and  considered  as  one  of  ioT the  planes many  advantages of the solvent purification treatment. results presented here,  important conclusions  by  major  From the  can be drawn  as follows: It  appears  that  there  is  decrystallization  and  hand”  purification  in  solvent  decrystallization acetone,  crystallization,  can  be  provision  of  nonlinear)  (Schemer et al.,  into  types  their of  go  hand  Apparently,  the  in the  interaction  in  protophylicity  the  1985).  (1st  of  in  cellulosic  of  is  4.1.2.1  atoms  (i.e.,  and  weak  or  This also gives us some hydrogen  material,  hypothesis).  acetone  Figs.  hydrogen  H-bonds  how acetone disrupts  disruption  work,  through  certain  accessibility)  this  by  between  as swelling agent, with the hydroxyl groups of the molecules  bond  “they  treatment.  achieved  cellulose  insight  reconciliation  a  In  explicitly and  bonding i.e.,  (i.e.,  hydrogen  addition,  the  demonstrated,  4.1.3.2.3.1,  i.e.,  in the  higher acetone content, the greater extent of accessibility, the  higher  degree  of  removal  of  amorphous  cellulose.  Furthermore,  it  Isaacs,  earlier that acetone could be classified as a  1974)  was  also  emphasized  dipolar aprotic protophylic solvent.  (Bax  et  al.,  1972;  On the other hand,  the  190  enhancement removal  of  of  crystallinity can  attained  be  the derivatized sugars.  by  selective  They appear to be more  susceptible to hydrolysis reactions than the free sugars. On the other hand, Table  4.1.5.1  bonds has  it is interesting that the results given in indicate  that  the  strength  of  the  hydrogen  no effect on the crystallinity index.  The major  impact on crystallinity index is likely to result from the packing order of the crystal lattice and selective removal of the amorphous cellulose. However, 4.1.5.1, clear  from  4.1.5.2,  that  the  the  results  4.1.5.3  and  shown  Table  rearrangement  of  in  Fig.  4.1.5.1  hydrogen  it  4.1.2.1, is  fairly  bonding  considerable impact on the crystallite size.  has  This has been  reflected by the changes that have taken place on 101, planes  and  the  slight  systematic  increase  a  in  loT  crystallite  breadth.  4.1.5.2. Effect of Type of Acid Catalyst and Acid Concentration on Cristallinity and Crytallite Breadth of Cotton Residues during Solvent Purification Treatment  In  the  present  work,  results  solvent purification process  is,  have  more or  shown less,  that  the  affected by  the type of acid catalyst. This is well demonstrated by the selective conditions cellulose were  removal which (i.e.,  carried  out  of  sugars  provide  (  i.e.,  maintenance  hydrogen bonding). to  weight  examine  the  of  Similar  effect  of  loss)  an  under  accessible  investigations type  of  acid  191  catalyst on the crystallinity and crystallite size of cotton during  acetonation.  This  was  accomplished  by  employing  different acid concentrations for each type of acid catalyst (i.e., TFA and HC1, respectively).  ‘uv  Cottontreatedwfthl.5NTFAat  -  00  1500,2hr.  2000  Cotton treated wIth 0.75 N TFA at 150 C, 2 hr.  COLLOII treated with acetone .*.water  Cotton treated wIth 3 N1FA at  1500  150 C, 2 hr.  at  (no acid catalyst)  1500,2hr.  Untreated cotton  E z ‘  I.  1000  101  ‘I  10i  .  500  0 5  0  -  Bragg’s angIe (2 theta)  Figure 4.1.5.4. Comparison diffraction of patterns of treated cotton at different acid concentrations (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C, TFA).  40  192  002  2000-  Cotton treated with 0.16 N HCI at  I  1SOC,2hr.  Cotton treated with acetone + water at  Cotton treated with 0.8 N HOt at  1500-  150 C 2 hr.  150C2hr.  I  0) .0  100& 101  Untreated óotton  ii  —  101  —  (no add catalyst)  500  .1 U  5  I  20 25 Braggss angle (2 theta)  I  30  I  35  Figure 4.1.5.5. Comparison of diffraction patterns of treated cotton at different acid concentrations (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C, HC1).  40  193 Table 4.1.5.2. Effect type of of catalyst acid on crystallinity and crystallite breadth of cotton residues treated at different acid concentrations, other while variables were constant kept (acetone:water: 90:10; liquor/solid ratio: 10/1; 2hr; 150 0 C; TFA). Acid Concentration N  Untreat.  CI  S.D.  002 FWHM  %  cotton  (Degree)  74.37  0.21  2.01  0.75  74.87  0.19  2.04  1.5  75.15  0.27  2.23  3.0  71.50  0.15  2.31  Table 4.1.5.3. Effect of type of acid catalyst on crystallinity and crystallite breadth of cotton residues treated at different acid concentrations, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 0 C; HC1). Acid Concentration N  Untreat.  CI  S.D.  002 FWHM (Degree)  cotton  74.37  0.21  2.01  75.44  0.24  2.16  0.16  74.48  0.15  2.23  0.8  71.82  0.27  2.35  Treted with acetone + water (no catalyst used)  Figs. 4.1.5.3  4.1.5.4  show  that  crystallinity (i.e.,  and there  4.1.5.5 is  a  and  Tables  slight  74.37% for untreated,  4.1.5.2  decrease  in  and both  71.50% and 71.82%  194  for  treated  with  ones  crystallite size  (2.01  TFA  and  HC1,  for untreated cotton,  for the treated ones with TFA and HC1, since  crystallite  respectively)  breadth  is  2.31 and 2.35  respectively),  inversely  and  i.e.,  proportional  to  crytallite size. Usually, the influence of acid and alkaline solutions defined  in  conventional the  by  removal  hydrolysis of  In turn,  this offers a  index  reduced  crystallite  decrease Tables  in  crystallinity  4.1.5.2  criterion,  and  size.  and  4.1.5.3  fairly  does  and  for  However,  not  amorphous  low crystallinity  crystallite  the  size  correspond  small  shown to  in  this  the weight loss obtained with 3 N TFA is 4.9%,  while that with 0.8 N HC1 is 33.7%,  2.35  and  is  in the case of the solvent purification process.  For example,  indices  mercerization  hemicelluloses  cellulose. and  and  crystallite  TFA  and HC1,  sizes  but their crystallinity  (71.50*,  respectively)  71.82%,  are  similar.  and  2.31,  From the  results, one may draw the following conclusions: 1—  acetonation  ensures  a  high  removing amorphous cellulose, is  a  simultaneous  decrystallization take  place  alterations  due  during would  i.e.,  action to  degree  the  selectivity  of  crystallization  stereochemical  at  in  it is likely that there  acetonation.  prevail  of  These  both  changes  and that  stereochemical  hydrogen  bonding  and  derivatization levels, and 2—  the  solvent  structural  purification  transformations  treatment (i.e.,  bonds and isopropylidene groups)  weak  offers  irreversible  nonlinear  hydrogen  and they appear to have the  195  considerable  effects  crystallite size.  the  on  crystallinity  In other words,  (new type of lattice)  these  index  and  structural  brought about on cellulose  the  changes  (cotton)  by  acetonation, are the primary factors responsible for shaping the crystal packing order. The Tables  results  shown  4.1.5.2  in  and  Figs.  4.1.5.4  4.1.5.3  and  illustrate  4.1.5.5 that  and acid  concentration has only a slight effect on crystallinity and crystallite size although the hydrolysis rates may be quite different.  This  effect  is  determined  by  the  extent  of  catalyst contribution to hydrogen bonding of the cellulosic material, are  because  influenced  (Marchesault,  both  crystallinity  by  hydrogen  1962; WConnor et al.,  crystallite  and  bonding  size  rearrangements  1958; Hurtubise et al.,  1960; Sarko et al.,  1973). These observations are consistent  with  in  those  made  investigation)  the  preceding  section  (i.e.,  IR  of this work.  4.1.5.3. Effect of Temperature on Crystallinity and Crystallite Breadth Cotton of Residues during Solvent Purification Treatment  In most physico—chemical important parameter.  This  processes,  temperature  fact explicitly appears  in  is  an  those  reactions which take place when assisted with better solvent penetration.  Thus,  the  crystalline  structure  of  the  196  cellulose,  under the solvent purification treatment,  should  be affected by temperature. Fig.  4.1.5.6  shows  the  effect  of  temperature  on  cryctallinity index and crystallite size of cotton residues when different temperatures were applied during acetonation of  cellulose.  In  general,  the  diffractograms  exposure to three levels temperature  (130,  150,  following  and 180 °C)  show a slight increase in the peak heights of 101,  101,  and  002 reflections, however the three peaks which appear in the Fig.  4.1.5.6  overlap  each  other.  The  increase  in  peak  heights of 101 and ioi planes is strongly indicative of the changes that have taken place at  inter— and  hydrogen  the  bonding  treatment.  levels  Nonetheless,  during explicit  intramolecular  solvent  information  purification about  the  crystalline changes that have taken place during acetonation is given in Table 4.1.5.4. 4.1.5.4  show  crystallinity  a  The results illustrated in Table  moderately  index,  while  increasing the  tendency  crystallite  in  the  size  has  decreased slightly as the temperature was increased from 130 to 180 DC.  197  Cottontreatedwlthl.5NTFAat 130 C, 2 hr.  200&  002  Cotton treated with 1.5 N WA at 150 C, 2 hr. Cotton treated with acetone + water at 150C,2hr.(noacldcatalysO  Cotton treated wIth 1.5 N WA at IBOC,2hr. :3  8 1 50G .4-  I  0  i.  E  Untreated cotton  :3  I,  Ii  ‘1000 101 101 500  .4  it K  If  ,.  15  20 25 Bragg’s angle (2 theta)  0 5  30  35  Figure 4.1.5.6. Comparison of diffraction patterns of cotton residues treated at different temperatures, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA).  40  198 Table 4.1.5.4. Effect of temperature on the crystallinity index and crystallite breadth of cotton residues treated at different temperatures, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA). Temperature  CI  S.D.  FWHM 002 (Degree)  Untreated cotton  74.37  0.21  2.01  130  74.48  0.17  2.18  150  75.00  0.26  2.20  180  75.05  0.23  2.11  Higher temperature system.  In turn,  increases the reaction  this would  H—bond  disruption/destruction  free hydroxyl  isopropylidenation. molecules system  pressure.  (Vinogradov molecules reaction  et  system.  (Bradley  al.,  density. hydrogen  Besides,  the  in  the  cellulosic  et  the  by In  that  to  of  bonding  with the  the  much  to  the  (i.e., undergo  of  acetone  as does the  also  solvent  speed up the (i.e.,  to  emphasized  energy  temperature  the  due  was  kinetic  reorient  reaction medium also  it  the  addition,  molecules  This would  available  reactivity  respect,  raising  1993)  be  increased temperature  1971)  increases  the  in  will  this  In  al.,  temperature  faster  groups)  increases with  the  and to a greater extent,  material is observed. Consequently, more active sites H-bond  of  lead to further stereochemical  changes that can be brought about, more  rate  or the of  increase are  more  of  believed  freely  lowering  formation  the  of  accessibility)  of  and the  weaker and  199  isopropylidenation  processes  by  the  involvement  of  more  acetone molecules with glucose units to yield isopropylidene groups along the cellulose chain. view,  such  could  considerably  thermal  changes affect  Thus,  brought the  from this point of  about  by  crystalline  temperature  structure  and  reactivity of the cellulose.  4.1.5.4 Effect of Residence Time on Crystallinity and Crystallite Breadth of Cotton Residues during Solvent Purification Treatment  Fig. time  4.1.5.7 and 4.1.5.8  show the effect of residence  crystalline  structure  solvent  purification  treatment.  figures  indicate  on  index  of  treated  increase  of  that  a  cotton  of  slight  The  residues  results  increase  samples  reaction time.  cotton  has  Also,  attained  4.1.5.7  show that the peak heights of the 101,  these  two  crystallinity  in  been  Fig.  in  during  and  the  by  4.1.5.8  and 101 planes have  increased.  The increase in intensities of both the 101 and  iot planes  strongly suggests that the  solvent purification  treatment has brought about structural transformations  (new  type  both  of  inter—  lattice), and  addition,  intramolecular similar  crystallinity maximum  height  crystallite  and hence  index  (FWHM),  width  of  illustrating  increase  which  (i.e.,  changes  H—bonding  results and  these  is  in  the the  full  inversely  crystallite  influenced  size)  cellulose.  In  increase  of  width  at  half  proportional are  shown  to in  200  Tables  4.1.5.5  and  4.1.5.6.  These  results  correlate  well  with those showing the effect of residence time on hydrogen bonding.  250G Cottontreatedwlthl.SNTFAat 150 C, 2 hr.  2ooo-  002 Cotton treated with 1.5 N TFA at 1SOC,lhr.  Cotton treted with 1.5 N WA at 150C,3hr.  Cotton treated with acetone +watec at 150C,2hr. (noacldcatalyst)  8 15oo E0)  Untreated cotton  .0  E  iooo 101  Ii —  Bragg’s angIe (2 theta)  Figure 4.1.5.7. Comparison of diffraction patterns of cotton residues treated at different residence times, while other variables were kept constant (acetone:wate: 90:10; liquor/solid ratio: 10/1; 150 0 C; 1.5 N TFA).  201  002  Cottontieatedwltho.16NHGIat 1SOC,3hr.  2000  1500  Cotton treated with 0.16 N 1401 at 150 C,2hr. Cotton treated with acetone+ water at 150C2hr (noacldcatatyst)  Cottontreatedwltho.l6NHClat 1500, lhr.  2  Untreated cotton  E  z  I.  11000  101 ioT 500  tt. Ij  5  I  15  I  I  20 25 Bragg’s angIe (2 theta)  35  Figure 4.1.5.8. Comparison of diffraction patterns of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 0.16 N HC1).  40  202  Table 4.1.5.5. Effect of residence time on the crystallinity index and crystallite breadth of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 1.5 N TFA). Residence Time hr  %  Untreated cotton  74.37  0.21  2.01  1  75.15  0.12  2.04  2  76.16  0.10  2.30  3  76.24  0.22  2.30  CI  S.D.  002 FWHM  (Degree)  Table 4.1.5.6. Effect of residence time on the crystallinity index and crystallite breadth of cotton residues treated at different residence times, while other variables were kept constant (acetone:water: 90:10; liquor/solid ratio: 10/1; 150 °C; 0.16 N HC1). Residence Time hr  %  Untreated cotton  74.37  0.21  2.01  1  74.48  0.11  2.23  2  74.72  0.21  2.33  3  75.65  0.18  2.33  CI  The time crystallinity treatment when  S.D.  (Degree)  factor was  shown to have a  index after the other  002 FWHN  initial  parameters  were  lesser  effect  on  solvent purification kept  constant  (i.e.,  203  temperature, acidity,  solvent composition,  see Fig.  4.1.5.6).  The  liquor to solid ratio and  4.1.5.7 and 4.1.5.8 and Table 4.1.5.5 and  slight  increase  in  crystallinity  index  and  reduced crystallite size can be explained by the fact that the  interaction  of  stereochemistry of about,  more  or  molecules.  acetone  more  isopropylidenated  less,  This  with  the  has  some  OH  groups  and  sugar units may bring  effect  implications  on  the  on  adjacent  more  H—bond  disruption/destruction indicating further structural change s within the cellulosic material.  4.1.6 Molecular Weight Distribution (MWD) Analysis Changes in Molecular Weight Distribution (i.e., molecular uniformity) of Solvent Purified Cotton Residues -  Depolymerization of cellulose may result from different degradative  reactions  such  hydrolysis,  enzymatic  hydrolsis,  mechanical can  be  reactions,  assessed  distribution cellulose. weight  the  the  (MWD)  the  the  aqueous  Successful of  useful  degradation  process.  For  weight  alkaline  thermal  molecular of  determination  provides  or  and  depolymerization  polydispersity  depolymerization  molecular  acid  oxidative,  shape  in which  purification  into  acetonation,  the  respect,  the way  solvent  insight  and  this  distribution  understanding  well.  from  curves In  as  as  the of  treated  molecular  information takes  getting of  weight  place a  of  in  better  cellulose  distribution  for  in  solvent  204  purified cellulose was investigated under different reaction conditions.  this  In  work,  variables  molecular weight distribution,  believed  such as  acid  to  influence  concentration,  temperature and residence time, were investigated.  4.1.6.1 Effect of Acid Concentration on Molecular Distribution of Solvent Purified Cotton Residues  Figs.  4.1.6.1  and  4.1.6.2  and  Tables  Weight  4.1.6.1  and  4.1.6.2 show that the treatment of cotton with just acetone and  water  (90:lO),i.e.,  depolymerizion  of  depolymerization buffer  the  has  present  linkages of the cellulose consistent with 1989)  to  the  Apparently,  the  action  acids  cellulose  caused  on  of  of  pectic  glycosidic  (cotton) molecules. This result is  previous  observation  (Zarubin  et  al.,  when acetone and water were used as a pulping liguor.  However, al.,  the  due  and  cotton  has  material.  place  mixture)  in  catalyst  cotton  taken  (acetone/water  substances  no  the  1989)  hydrolysis  action  was  attributed  (Zarubin  et  to acetic acid that resulted from the reaction of  water molecules with the acetyl groups of the hemicelluloses present  in  the  results obtained, pH,  i.e.,  cellulose  pulp).  in the present work,  Nonetheless,  in  part,  be  acid  indicate that the hydrolysis achieved  the  on the change of the  before and after the treatment when no  raw material were used, possibly,  (wood  through  the  and  could  action  of  205  acetone/water complex.  This  is because the pH was found to  drop within differnt treatments. This has been observed when the control solution  (acetone—water)  temperature (150 °C) and  the  dropped  pH  of  from  for 2 hr the pH fell from 7.46 to 5.77,  cotton  7.46  tests  indicate  the  which  appears  to  was heated at reaction  to  hydrolysate 4.59.  identical  Apparently,  formation be  at  weakly  of  an  these  conditions  experimental  acetone—water  acidic.  In  turn,  complex,  since  the  acetone—water complex possesses a weak acidic property (pH 5.77),  it can be expected to contribute to the hydrolysis of  glycosidic linkages. acetone—water (Fong et al., involvement  On the other hand,  complex  was  also  observed  1969; Waggoner et al., of  acids  resulting  reactions may not be ruled out. cotton  =  during  solvent  the acidity of the by  other  workers  1982). In addition,  from  cotton  in  the  hydrolysis  The formation of acids from  purification  treatment  been discussed in subsection 4.1.3.2.3.  has  earlier  206  1.6-  ftt_.  I  1.4-  f  Untreated cotton  1-  1’  j i I I lt• I :  —i—  ;  ‘  0.6c  j:  .0  !  .  U.Q  0  •.  II : :  0.4  I ,  A  1.2Cotton treated with acotone+waterat 150 C,2hr. (no acid catalyst)  Cotton treated wIth 3 N WA at 150C,2hr.  ‘:  Ii  ‘‘ Cotton treated with OJS N WA at 1500,21w.  i  1.: i  ‘v  %‘  III  I  I  Cotton treated wIth 1.5 N WA at C,2hr.  I  ‘  i,:4. Ii!’  ‘.  ‘  I  i;  02  Elutlon volume (mL)  -  Figure 4.1.6.1. Effect of acid concen tration on molecular weight distribution of cotton residue s when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C).  32  207  4 I’ I’ tj  1.4  —i  Untreated cotton  12  1:  i  t  I  a  —  1  II  CoedwIth acetone + water 15002hr. (no acid catalyst)  :  ‘. *  I:  I  0.8  Cotten treated wIth 0.8 N HOt at ,.f150C,2hr.  .  ‘:  ,  I  ‘  Cottontreatedwttho.l6NHCIat  r150C,2hr.  .5 a  06  II  0.4  02__  &  14  I  16  18  I  20  I  I  22 24 Elutlon volume (mL)  I  26  28  30  Figure 4.1.6.2. Effect of acid concentration on molecular weight distribution of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; solid/liquor ratio: 10/1; 2 hr; 150 °C).  32  208 Table 4.1.6.1. Effect of acid con centration on molecular weight distribution and polydispersit y of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 C; TFA). 0 Sample Acidity N  Polydispersity  3 (x1 ) 0  Untreated cotton (control)  3 (x1 ) 0  902  296  3.05  0 N  450  67  6.72  0.75 N  188  103  1.82  1.50 N  158  83  1.89  3.00 N  145  54  2.70  Table 4.1.6.2. Effect of acid con centration on molecular weight distribution and polydispe rsity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C). Sample Acidity N  Polydispersity 3 (x1 ) 0  3 (xl ) O  902  296  3.05  Untreated cotton (control) 0 N  450  67  6.72  0.08 N  175  93  1.88  0.16 N  1248  122  10.21  0.80 N  1452  82  17.64  Results as  expected,  shown that  in  Figs an  4.1.6.1  increase  and  4.1.6.2  in  acid  —  illustrate,  concentration  209  acetonation  offers  more  low  molecular  weight  fractions  (i.e., the MWD curve shifts towards the low molecular region —  greater elution volumes). The tables, also show that lower  acid  concentrations  provide narrow  more  for  uniform  both  molecular  polydispersity)  explained  by  the  acid  fact  catalysts  weight  than  the  that  lower  (TFA  and  distribution  higher acid  ones.  This  HC1)  (i.e., may  concentrations  be are  more suitable for the protonation of the strained glycosidic linkages,  i.e., under isopropylidenation reactions. However,  differences observed. Table  between  the  two  acid  The results given in Fig.  4.1.6.1  and  4.1.6.2  uniform  molecular  polydispersity), produced broader  by and  HC1  while at  explicitly  was  noted  nonuniformity with range  the of  Rantanen  appearance the  to  et  molecular weight  MWD  of  a  curve  those  molecule  clusters  and  solution  during the  GPC  al.  due  presence of molecule aggregates, due to the nonequivalence  narrow  distributions  of  are  the  become  original  impossibility. that_ the  distribution  accompanied  in  to  aggregates analysis.  at  (1986)  shoulder is  be  symmetrical  concentrations  compared  TFA  (i.e.,  weight  This may appear a physical by  of  as  distributions  acid  also  that  offered more  molecular  higher  bimodal  untreated sample. It  weight  can  4.1.6.1 and 4.1.6.2 and  show  different acid concentrations has and  catalysts  the  the  high  presence  remaining  The  molecular  in  explanation  in this case,  of  long  sample for  the  is probably  in steric effects and electronic  interactions among the cellulosic units,  resulting from the  210  acetonation reactions with cellulose in conjuction with the abundance of an effective acid cata lyst (HC1). This is because it would be inappropriate if the large-sized ion (C1) is taken into account as the main reason for impaired penetrability of a solvent. In spite of a large number of publications on the swelling, the avail able literature on the penetration process is scanty. However , penetration and swelling can be considered in some degree as two phenomena that resemble and complement each other. The influence of ions on the swelling phenomena was earlier explained on the basis of the diameter and hydration layer s. It was noted (Frey-Wyssling, 1953) that the lesser degr ee of swelling can be attained the stronger hydration layer of the ion, i.e., small ions have thicker hydration layer s. This can be explained by the fact that the water dipo les are attracted more strongly as the distance between the centre of gravity and the surface of the ion decreases. Thus , the ion size for hydrochloric acid in penetration and swel ling aspects does not  seem to  addition,  be  the  a  problem,  performance  (depolymerization) broader NWD, molecular  other  i.e., of  thin hydration  HC1  than  in  hydrolysis  these  two  fractions  with  narrow  -  (Fengel et al.,  et  in  al.,  1984)  cellulose.  to  be  However,  selective  hydrolysis  that is not the case,  its loose hydrogen atom  (Tchoubar,  with  offering low  polydispersity.  the other hand, TFA was claimed  In  reactions  incidents  appears to resemble that of TFA  weight  layer.  1979;  On  Fanta  reactions  of  because TFA with  1966; Amis,  1966; March,  211  1985) might form different complexes with various compounds. Reactions addition 1985),  such  as  involvement  reactions  TFA  molecules  with  in  (Geddes,  water  of  TFA  1956;  (Geddes,  strong hydrogen  with  Harris,  1956)  and  bonding  acetone 1965;  with  (section  in  March,  cellulose  4.1.2,  Fig.  4.1.2.2 and 4.1.2.4)  may undermine the activity of TFA,  well.  in  In  addition,  support  of  our  belief  that  as the  efficiency of TFA is likely retarded due to these reactions, it  was  usually  used  for  longer  periods  in  hydrolysis  reactions in order to obtain a reasonable amount of soluble sugars.  The treatment  (Fanta  et  al.,  1984)  of  wheat  with 1 N TFA for 7 hr at 100 0 C yielded around 23% based  upon  initial  straw  weight.  On  the  other  straw xylose  hand,  the  stability of sugars in response to hydrolysis reactions was found to be different  (Harris,  1975),  and the hemicellulose  sugars were most accessible to hydrolysis. Furthermore, into  the  penetration  cellulosic  of  materials  these is  acids  usually  and  solvents  accompanied  by  different reactions. These reactions can be such as hydrogen bonding  reorientation,  protonation,  derivatization  (acetonation), and in some cases redistribution of substrate components complexity  (Wong et. of  factors  such  Isaacs,  1974),  March,  1985),  the as  al.,  1988).  whole  molecular  Thus,  process  of  structure  with regards to the penetration, (Bax  reactivity of the molecules chemical environment  et  al.,  (Tchoubar,  other 1972; 1966;  (Lindstrom et al.,  1980),  and apparently electronic properties of the molecules  (i.e.,  22  dipole moment, into  dielectric constant)  account.  significance molecular  However, of  these  size of  would have to be taken  further  investigations  factors  reagents to  in  conjuction  in  the  with  the  the penetration process  are  needed.  4.1.6.2 Effect of Temperature on Molecular Distribution of Solvent Purified Cotton Residues  Figs. cotton  4.1.6.3 and 4.1.6.4  residues  shift  suggests  that more  place  at  along  the  cleavage  different  sites  cellulose  explicitly  show that the MWD curves of  towards  distribution region with the  of  suggests that the  a  lower  increase of  chain.  Weight  molecular  in temperature.  glycosidic  bonds  has  isopropylidenated In  weight  other  increase  words, of  This taken  molecules  the  effect  temperature  leads  to production of shorter cellulose chains on acetonation of cellulose.  This has not been observed in the literature for  acetonation of  oligomeric  1983;  1983)  Aamlid,  in  sugar the  residues  past.  The  (Glushka two  et._al.,  figures  also  illustrate that the shift of the cellulose MWD curve for the  residues, towards  treated with the HC1 catalyst,  the  low molecular weight  distribution region  that for the samples treated with TFA. Fig.  4.1.6.4  illustrate  that  is more extensive than  The results shown in  the  molecular  weight  distribution curves for the treatments at 150 0 C and 180 0 C temperature  apparently  coincide  with  each  other,  however,  213  the  results  shown  weight—average distributions and  graphical  indicate  polydispersity  due  recently the  to  the  were  excellent  method (Schwantes et al., Furthermore,  must  in  weight  fact different  differ. shown  the  that  molecular  for the two treatments are  deviations  significant  4.1.6.4  number—average  and  their  hence  Table  in  GPC  Minor  to  be  reproducibility  highly the  of  1994).  2  hr  results  illustrated  Fig.  in  4.1.6.5 and Table 4.1.6.5 provide further evidence that an increase  in  treatment)  temperature of  (with  solvent  the  exception  the  treatment  cellulose with  lower molecular weights  number—average  molecular  Table  4.1.6.5  show  weights).  that  an  offers  C 0  150  residual  (weight-average  The  results  increase  acossiated with longer reaction time  of  of  (2 hr)  and  given  in  temperature  has resulted in  production of shorter cellulose chains than that with lesser residence time  (1 hr),  in Table 4.1.6.5,  see Table 4.1.6.4.  also,  The results shown  indicate that the polydispersity of  the treated cellulose (except 150 °C treatment) with  the  Tables  increase  4.1.6.3,  of  temperature.  4.1.6.4  and  those shown in section 4.1.3, other words,  the higher the  the greater the weight loss, chain of the treated sample.  i.e.,  results  The  4.1.6.5  has narowed  are  given  consistent  with  weight loss results.  temperature  of  the  in  In  treatment,  and the shorter the cellulose  214  1.6 I  11  1.4-  /  i  i  Untreated cotton  j  l.i,  I  4 i1  Cotton treated wIth 1.5 N IFA at 150C,2hr.  i’  %  1.2-  1  ii  Cotton treatedwlth  I  acetone.i-waterat  I:  : :  1SOC,2hr. (no acid catalyst)  I  ;  : :  : .  €  ‘i  Ii  0.6-  :  Cotton treated with 1.5 N TFA at 130C,2hr.  Cottontreatedwithl.5NTFAat 180C,2hr.  i  f..J /  s; ‘:  I! t  i:t  0.4  0.2-  14  -  I  16  I  18  —  I  20  I  I  22 24 Elutlon volume (mL)  I  26  28  30  Figure 4.1.6.3. Effect of temperature on molecular weight distribution of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA).  32  215  1.6  1’  Untreated cotton  I  j  1.4  Cottontreatedwlth0.I6NHCtat  I  1.2  130C,Ihr.  :i with acetone + water at 1SOC,2hr. (no acid catalyst)  I  :  _  —!—I I:  >  ,A/  li 1 ‘? I ‘ ‘L’ II”.!  I;  I  Cotton treated with 0.16 N HOl at  g  €  Ij  1j  j:  If  t  1500,lh  :‘  0.6  iii  \  IiI 04-  Ii  /  02-  ‘i\ ‘,  I  ,  1!  I  I  16  Cotton treated wIth 0.16 N HOt at 18OC1h  I  I  I  I  & 14  /  ‘  -%  I  18  20  22 24 Elutlon volume (mL)  26  28  30  Figure 4.1.6.4. Effect of temperature on molecular weight distribution of cotton residues when HCl was used as catalyst aqueous in acetone (acetone:water 90:10; liquor/solid ratio: 10/1; 1 hr; 0.16 N HC1).  32  216  Table 4.1.6.3. Effect of temperature on molecular weight distribution and polydispersity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10, liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA). Temperature Treatment °C  Polydispersity ) 3 (x10  ) 3 (xl0  902  296  3.05  130  165  86  1.93  150  158  83  1.89  180  137  78  1.77  Untreated cotton (control)  Table 4.1.6.4. Effect of temperature on molecular weight distribution and polydispersity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 1 hr; 0.16 N HCl). Temperature Treatment  Polydispersity ) 3 (x10  Untreated cotton (control)  ) 3 (x10  902  296  3.05  130  164  51  3.22  150  171  82  2.09  180  108  54  2.00  217  1.64 ‘1  ‘I  1.4Untreated cotton  —j  1.2-  I I  .  i  Cotton treated wIth 0.16 N HCI at 180 C, 2 hr.  I : Cotton treated with acetone+waterat ISOC,2hr. (no acid catalyst)  Cottontreatedwlth0.16NHCIatI300,2hr.  t  f  U.O  r-COttOfl treated wIth 0.16 N HOt at I 150C,2hr.  U -  o  Ii O.4  1!  1  02  0 Elutlon volume (mL)  832  Figure 4.1.6.5 Effect of temperature on molecular weight distribution of cotton residues when HC1 was- used as catalyst aqueous in acetone (acetone: water: 90:10; liquor/solid ratio: 10/1; 2 hr; 0.16 N HC1).  218 Table 4.1.6.5 Effect of temperature on molecular weight distribution and polydispersity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 0.16 N I-Id). Temperature Treatment °C  Polydispersity ) 3 (x10  ) 3 (x10  902  296  3.05  130  150  74  2.02  150  1248  122  10.21  180  103  54  1.92  Untreated cotton (control)  The results given in Table 4.1.6.3, show  that  the  considerable increase of results with  solvent  degradation  increase  purification  it  the  celluose  is  a  temperature. clear  treatment  distribution is  in  in  causes the  a  residual  with  the  However,  the  narrowness  that  more  about  index decreases  The  evidence  brings  chains  temperature during the treatment.  polydispersity  Now,  of  treatment  illustrate that the polydispersity  the  weight  purification  4.1.6.4 and 4.1.6.5  the  of  solvent  uniform  molecular  cellulosic  material.  postulated that this uniform disproportionation  of the treated celluloses could be due to the formation of isopropylidene groups at regular intervals on the cellulose chains. cotton  The presence of residues  has  isopropylidene groups  been  results obtained from Gd,  confirmed, HPLC,  in  this  on the solid work,  by  the  and C-13 CP/MAS solid state  NMR analyses. However, these analyses allow no statements as  219  to the distribution and location of isopropylidene groups on the cellulose chains themselves. Probably, the uniformity of disproportionation  of  cellulose  the  arises  chain  from  repeated equivalent steric and electronic effects along the cellulose chain due to acetone reactions with cellulose. Regarding cellulose  the  chain  electronic  last  statement  attributed  effects),  there  to  (i.e.,  uniformity  equivalence  is  no  evidence  of  steric  that  the  of and  chain  length distribution of cellulose within a finite element of cellulose  as  the  crystallite  is uniform.  To  the  contrary,  while the molecular weight itself may be increasing with the crystallite size,  the MWD pattern may not provided that a  certain  crystallinity  (high)  is  maintained.  crystallinity index drops to a certain limit  If  the  ( 75%) the  MWD  will broaden due to the contribution from chains running in the amorphous cellulose.  In the present work,  an enhancement of crystallinity is attained, has  not  results,  (see crystallinity section)  the crystallinity index of the treated samples  exceeded  narrowness  even though,  has  however,  76%. also it  In  addition,  been did  not  a  similar  indicated  by  approach  unity  trend  of  polydispersity that  one  may  justify a cellulose sample of chains of similar lengths.  On  the  be  other  hand,  single-phased  cotton  types  of  and  ramie  cellulose,  are  considered  however,  structure was found to be highly imperfect al.,  their  to  lattice  (Kulshreshtha et  1973). This observation lends support to the concept of  the limited molecular uniformity of cotton residues achieved  220  solvent  through  purification  results obtained,  treatment.  in this work,  weight distribution,  addition,  In  on crystallinity,  and polydispersity  are  the  molecular  not  applicable  to the two—phase hypothesis of cellulose (Viswanathan, Viswanathan,  1967).  In  other words,  the  state  of  1966;  order  in  the fibrous structure of cellulose is much more complex than the  oversimplified  theory.  The  material  as  structural  two—phase a  picture  concept  drawn  visualizes  two—state—ordered  matter;  by  cellulosic  materials  correlation coefficient the  crystallinity  (Viswanathan,  cellulosic  one  completely  enough  evidence  structure al.,  in  the  sample,  Viswanathan,  against  cellulose  different  to  for every analysis,  of  1966;  but  the  in  the  present  extents,  in the  no matter what  should  1967).  latter  the  crystalline and the other completely amorphous, all  the  be  However,  unity  there  hypothesis  of  literature  (Kulshreshtha  a  is  two—phase et  1973).  4.1.6.3 Effect Residence of Time on Molecular Distribution of Solvent Purified Cotton Residues  Fig.  4.1.6.5  illustrates  the  changes  in  Weight  molecular  weight distribution resulting from the influence of reaction time  on  acetonation  of  cotton.  As  curves show slight shifts towards the  anticipated,  the  MWD  low molecular weight  221  distribution region with the increase in residence time. The results  given  successive average time.  Table  in  reduction  molecular  The  in  results  4.1.6.5  differences  also  distribution with  and in  explicitly,  weight—average  with  the  show that  increase  the  show  and in  the  number— residence  polydispersity  index  increase in residence time.  Also,  Table  changes  and  increasing  both  weights  becomes smaller with the Fig.  4.1.6.6,  4.1.6.6 between  polydispersity reaction  time.  illustrate both  has  that  molecular  narrowed  Particularly,  the  weight  remarkably this  effect  appears to be clear between the 2 and 3 hr treatments. little  difference  in change  extended reaction time  can be  of MWD  and polydispersity  attributed to  hydrolysis reactions become predominant, times,  This  the  fact  at  that  at longer reaction  in the crystalline regions and hence the frequency of  disproportionation is  increased.  The results  given  in Fig.  4.1.6.5 and Table 4.1.6.6 are consistent with those obtained for weight 4.1.3.2.3.5,  loss,  hydrogen  bonding  and  4.1.2.7 and Table 4.1.5.6).  crystallinity  (Fig. —  222  1.8 —  Cotton treated wIth 1.5 N WA atl3OC,2hr.  1 .6  4.  Cotton treated with 1.5 N WA  Untreated cuon  ail3OC,3hr.  1.4 12  z (0  .  I  cotton treated with acetone + water at 130C,2hr. (no acid catalyst)  f I  [—v-f 4:  •1•  :  I  i  I  I  :11  1; ‘. I’  •:  I  I;  0.6  1’I ‘1 I,  ‘  ‘  41  I  a:  I  is I I, Ii  0.2  I  I  ‘I:  It  I  1  I  £ I  -  0.4  Cotton treated wIth 1.5 N WA 8t 130 C, 1 hr.  :  It  14  ‘  .  o .5  ‘  I  I  ii 14  16  I  18  Figure 4.1.6.6. Effect of distribution of cotton catalyst in aqueous liquor/solid ratio: 10/1;  20  I  I  .22 24 Elution volume (mL)  I  26  I  28  I  30  residence time on molecular weight residues when TFA was used as acetone (acetone:water: 90:10; 130 °C; 1.5 N TFA).  32  223  Table 4.1.6.6. Effect of residence time on molecular weight distribution and polydispersity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 130 °C; 1.5 TFA). Residence Time (hr) Untreated cotton (control)  Polydispersity  n 1 (x10 ) 3  ) 3 (x10  902  296  3.05  1  213  111  1.91  2  155  86  1.81  3  152  84  1.81  From 4.1.6.6. effect  the  results  is  evident  it on  solvent  that  in  the  disproportionation  purification  constant.  shown  when  Fig. time  of  4.1.6.6 factor  cellulose  other  and  Table  a  lesser  chains  during  has  parameters  are  kept  The lesser degradation of cellulose chains can be  explained  by  the  fact  that  the  stereochemistry  of  isopropylidenated sugar units may bring about, more or less, the  some  effect  on  implications  on  allowing  more  rapid  the  more  workers  is  accessible  based  (Brewster,  1969; Stoddart,  adjacent  steric  isopropylidenation  assumption  al.,  the  on  1959; 1971)  and  and  molecules electronic  cellulose hydrolysis  experimental Lemieux et  .  units  to  undergo  reactions.  1968;  has  interactions  findings  al.,  This  of  This other  Lemieux  in the area of stereochemistry.  et  224  4.1.7 Viscosity Analysis - Changes in Viscosity of Cotton Residues during Solvent Purification Treatment  Viscosity measurements, perform,  have  been  used  which are relatively simple to  widely  because  they  provide  can  valuable information both on the physico—chemical behaviour of  a  cellulose  and  addition,  viscosity  dissolving  pulp  control work.  on  the  is  one  analysis  for  Thus,  size  of  its  important both  molecules. parameter  research  and  In for  quality  the viscosity test makes it possible to  check the degree of degradation brought about by hydrolysis reactions,  which  greatly  influence  the  quality  of  the  dissolving puips. The the  purpose  resistance  of  this  investigation  cellulose  of  to  is  to  characterize  degradation  by  solvent  purification with the acidified acetone-water system.  4.1.7.1 Effect of Acetone Concentration on Viscosity Cotton Residues during Solvent Purification Treatment  Fig.  4.1.7.1  residues, the  composition,  content.  illustrates acetone  that  the  viscosity  treated with different acetone  solvent  acetone  shows  that  In  addition,  the  the  treatments  of  concentrations  different,  decreases  see Fig.  for  4.1.7.1,  with  of  increase  statistical cotton  the viscosity  cotton  concentrations the  with  are  of  in in  analysis different  significantly  (Duncan’s multiple range test).  225  This  result  hydrgen words, met  is  agreement  in  bonding,  weight  loss,  those  and  obtained  for  crystallinity.  In  the  other  the progressive increase in acetone concentration is  with  a  systematic  (accessibility),  decrease  cellulose.  in  hydrogen  bond  strength  increase in carbohydrate removal,  increase  in crystallinity index the  with  (selectivity),  general,  In  and decrease in DP of  apparently,  the  decrease  in  viscosity of cotton residues treated with just acetone and water  (no acid catalyst)  is due to the action  water  system  released  and  acids  from  acetone—  of  pectic  substances  present in cotton cellulose on strained glucosidic linkages. This stress on the glycosidic linkages  is  from  cellulose  the  engagement  isopropylidenation. on the  of The  two  adjacent  formation  of  likely to result  isopropylidene  cellulose molecules during acetonation  in this work by GC,  HPLC,  and C-13  units  is  in  groups  confirmed  CP/MAS solid state NMR  analyses. With residues  regards that  to  took  the  hydrolysis  place  during  reactions  the  on  solvent  cotton  treatment  (acetone/water) when no catalyst was added, are probably, one hand, (pH  =  on  due to the acidic nature of acetone/water mixture  5.77)  at higher temperature.  This conclusion has been  drawn when the initial acetone—water mixture (pH  =  7.46)  was  dropped to 5.77 when heated for two hr at 150 0 C, and the pH of  cotton  7.46  to  acidity  hydrolysate 4.59  of  .  Thus,  (identical the  acetone/water  pH  conditions)  result  system  dropped  indicates  developed  during  that  from the  solvent  226  treatment  may  (protonation)  lead  along  to  the  depolyinerization  cellulose  chains.  reactions acidity  Such  of  the acetone—water system was also indicated by Fong et al. (1969),  and Waggoner et al.  contribution  of  acids  (1982).  released  On the other hand,  from  cotton  during  solvent  treatment to hydrolysis reactions might also be taken consideration. acids  from  The possible explanation for  the  cotton  during  cited in subsection 4.1.3.2.3.  treatment  However, that  took  pulping  their place  of  different  interpretation was  soley  into  the release of  has  already  been  Similar hydrolysis reactions  were observed earlier by Zarubin et al., acetone—water  the  of  the  reasoned  (1989)  wood  on studying  raw  hydrolysis by  the  acetic acid formed during the pulping process.  materials. reactions  action  of  the  227  30  27-  18  15 40  p  p  70 80 Acetone Concentration (%)  100  Figure 4.1.7.1. Effect of acetone concentration on vicosity cotton of residues when no acid catalyst was added (liquor/solid ratio: 10/1; 2 hr; 150 °C). * Means different. **  with  the  same  letter  are  Significance at 95% confidence level.  not  significantly  228  The results given  in Fig.  4.1.7.1  indicate the  sensitivity  of glycosidic linkages under isopropylidenation reactions to acids.  In  other  acid hydrolysis  words,  usually,  conditions  under  (i.e.,  conventional  high energy  are  required  to  the  case  of  acetonation,  these  probably,  be  placed  considerable  formation  of  cellulose  units.  protonate  glycosidic  under  isopropylidene The  gradual  oxygens.  glycosidic  groups  and  acidity)  However,  linkages  strain  between  decrease  forced  due  the  of  in  may,  to  the  adjacent  viscosity  is  attributable to the better solvation of cellulose molecules by  solvent  (i.e.,  isopropylidenation)  at  both  levels  hydrogen  -  bonding  and  at higher acetone concentrations.  4.1.7.2 Effect of Acid Concentration on Viscosity of Cotton Residues during Solvent Purification Treatment  Fig.  4.1.7.2  and  4.1.7.3  show  the  dramatic  drop  of  viscosity (from 18.3 CP for the acetone:water treated cotton to  3.68  and  3.49  respectively)  when  CP  (0.75  catalysts respectively purification  for  treatment  TFA N  and  TFA  HC1  and  catalyzed  0.16  N  runs,  HC1)  acid  were used in the initial in solvent of  cotton.  This  is  strongly  indicative of the destabilization of glycosidic linkages due to  the presence  of  isopropylidene  groups  on  the molecules  along the cellulose chain. The results given in Fig. and  4.1.7.3  illustrate  that  further  increase  4.1.7.2 in  acid  229  concentration viscosity other  little  had  after  factors  liquor/solid,  the  initial as  such  contribution acid  solvent  the  to  drop  concentration  composition,  of  when  the  temperature,  and reaction time are kept constant.  However,  the statistical analysis shows that the treatments of cotton with  different  acid  concentrations  significantly different (Fig.  for  viscosity  the  4.1.7.2 and 4.1.7.3),  are  Duncan’s  multiple range test. The lower rate of viscosity loss at the higher acid concentration can be explained by the fact that: a-  the  limiting  stereochemistry  DP  has  been  reached,  b-  and  already  isopropylidenated  about,  more  or  less,  adjacent molecules.  This  has  would  bring  of  bond disruption/destruction  the  some  sugar  effect  implications  some  that  on  the  units on  the  more  H—  destabilization of sugar  (i.e.,  conformations)  allowing the more accessible cellulose units  to  rapid  undergo  reactions.  Fig.  isopropylidenation  4.1.7.2  and  viscosities obtained for HC1 for TFA. HC1  is  This a  can,  stronger  in part, acid  4.1.7.3  are  and  hydrolysis  show  that  lower than those obtained  be explained by the  than  the  TFA  and,  in  fact_that  part,  by  the  competing reactions that may take place in the presence of solvents with different properties such as acetone addition reactions  (March,  Consequently,  such  1985)  hydrogen  reactions  could  bond  formation  etc.  retard  remakably  the  reactivity of TFA towards hydrolysis reactions.  230  20  16  012 0  \\  Cl)  0  o8 U) >  4  0  0  0.5  1  1.5  2  2.5  3  3.5  Acid Concentration (N)  Figure 4.1.7.2. Effect of acid concentration on Viscosity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/so1i ratio: 10/1; 2 hr; 150 °C). * Means with the same letter are not significantly different. **  Significance at 95% confidence level.  4  231  20 A  16 0 C-)  12  U)  0 0  U)  8  >  4  0  0  0.2  0.6 0.4 Acid Concentration (N)  0.8  Figure 4.1.7.3. Effect of acid concentration on viscosity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 150 °C). *  Means different. **  with  the  same  letter  are  Significance at 95% confidence level  not  significantly  1  232  4.1.7.3 Effect Temperature of on Viscosity Residues during Solvent Purification Treatment  Fig.  4.1.7.4 and 4.1.7.5 show the effect of temperature  on the residual viscosity of cotton residues solvent purification treatment. indicate  considerable  a  reaction temperature. viscosities  drop  even  limiting  though  DI’  is  in  viscosity with also,  to  proceed  the  limiting  about  following the  The results in both figures  results,  The  continued  temperature (the  Cotton  of  250-3 00  show  with DP or  increasing  the  drop  increase  has  been  2.5—3.0  in in  reached  CI’).  Fig.  4.1.7.4 and 4.1.7.5 show that the viscosities obtained with TFA at different temperatures are higher than those obtained with  HC1  as  catalyst.  explained  by  the  difference  partly,  by the  acids  and,  reactions  as  This  described  limiting in  acid  effect strengths  involvement previously.  of TFA  can of in  be the  best two  competing  Nonetheless,  the  statistical analysis indicates that the treatments of cotton at different temperatures are significantly different jFig. 4.1.7.4 and 4.1.7.5),  Duncan’s multiple range test.  233  5.7  .  I  I0-1HR1  I--2HRI__ ±°3J  5.2  t  4.7 a-  .0  4.2 C,)  0 C.)  0  3.7 3.2 2.7 120  ,..  130  140  150  160  170  —  180  Temperature (Degrees Celsius)  Figure 4.1.7.4. Effect of temperature on viscosity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 1.5 N TFA).  19c  234  5  I  4.5  -0- 1 HR —&• 2 HR HR  L-_3  N%%% 0  0  4  Cl)  0  C.) U)  3.5  > 3  2.5 120 ..  ...  130  140  150  160  170  Temperature (Degrees Celsius)  180 —  Figure 4.1.7.5. Effect of temperature on viscosity of cotton residues when HC1 was used as ctalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 2 hr; 0.16 N HC1).  190  235  The  results  temperature  be  can  increases  interpreted  the  reaction  as  follows;  rate  higher  the  of  system.  Consequently, this would give rise to further stereochemical alterations reorient, greater  (i.e.,  molecules  Bradley et al.,  extent,  more  cellulosic material. bond  free  system  1993)  H—bond  hydroxyl  groups)  pressure.  will  active  be  the  sites  available  to a  in  the  (i.e.,  H—  undergo  to  reactivity  to  of  acetone  increased temperature as does the  This  isopropylidenation  faster  and  that can bring about,  more  Besides,  increases with  freer  disruption/destruction  In turn,  isopropylidenation. molecules  are  should  process  by  also  the  speed  involvement  up  the  of  more  acetone molecules with glucose units to yield isopropylidene groups along the cellulose chain.  4.1.7.4 Effect of Residence Time on Viscosity Residues during Solvent Purification Treatment  Fig. time  on  4.1.7.6 and 4.1.7.7 viscosities  purification show  a  4.1.7.6  treatment.  slight  increase  of and  residence  drop  in  residence 4.1.7.7,  time  temperature  of  is  on  the  cotton The  residues  viscosity  also  The  of  in  cotton  results  drop  higher  during  given  illustrate  viscosity  relatively  Cotton  show the effect of residence  results  time.  of  than  solvent  both  figures  cellulose  shown  that at  the  the  130  °C  that  in  on  Fig.  effect  of  treatment at  higher  236  temperatures  (150 and 180 °C).  Probably,  this could be due  to the fact that the hydrolysis reactions proceeed primarily in  the  amorphous  zones.  shows  that  times  for the viscosity,  the  However,  treatments  of for  the  cotton  statistical  analysis  different  reaction  at  both acid catalysts,  are  significantly different (Duncan’s multiple range test).  not  237  5.7 —0— 130 Deg. Celsius —& 150 Deg. Celsius —0— 180 Deg. Celsius  5.2 —‘.4.7 0  4.2 .Q) 0  3.7 3.2 2.7  ..  0  1  2 Residence Time (Hrs)  3  Figure 4.1.7.6. Effect of residence time on viscosity of cotton residues when TFA was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 1.5 N TFA).  4  238  5 —0— 130 Deg. Celsius 150 Deg. Celsius 180 —0— Deg. Celsius  ——  4.5 a  0  c%%  4  Cl)  0  0 Cl)  3.5  > 3  2.5  0  1  2 Residence Time (HR)  3  Figure 4.1.7.7. Effect of residence time on viscosity of cotton residues when HC1 was used as catalyst in aqueous acetone (acetone:water: 90:10; liquor/solid ratio: 10/1; 0.16 N HC1).  4  239  The  time  factor  is  shown to have  lesser  a  effect  on  drop in viscosity (DP) especially at the higher (150 and 180 °C)  temperatures following the initial solvent purification  treatment (solvent acidity).  when  all  other  composition, The  parameters  temperature,  reduced  rate  of  were  kept  liquor/solid viscosity  ratio,  loss  explained by the fact a- the limiting DP has and b- that the stereochemistry of  constant  can  and be  been reached  isopropylidenated sugar  units may bring about, more or less, the some effect on the adjacent  molecules.  This  disruption/destruction cellulose  units  to  hydrolysis reactions.  has  implications  allowing  undergo  rapid  the  on  more  more  H—bond  accessible  isopropylidenation  and  240  5 OVERALL MECHANISM OP PURIFICATION OP CELLULOSE IN ACIDIFIED AQUEOUS ACETONE  The  mechanism  catalyzed  aqueous  cellulose  of  acetone  has  purification  been  proposed  in  to  acid of  be  a  physico—chemical character. The physical phenomenon is based on the hydrogen  bond disruption/destruction  cellulose by acetone as the solvent.  crystalline  in  On the other hand,  the  chemical hypothesis of the mechanism is suggested to be the formation that  isopropylidene  of  lead  to  groups  on  disproportionation  carbohydrate  of  the  protection of the dissolved sugar ring. validity  of  these  assumptions  To  of  glucose  substances  units  only.  Nonetheless,  were reported to be  has  of  been  i.e.,  trace  a part  polymer  and  investigate the  cotton  throughout this work as a model compound,  chains  it consists  amount its  used  other  of  constituents  (see section 4.1.3, HPLC Analysis). The different using  mechanistic  study  techniques,  on  acetone  in  the  carried  solvent presence  out  by  purification of  acid  employing of  cotton  catalyst  has  established the following findings: 1—  interaction of  acetone with cellulose molecules through  their hydroxyl groups brings about irreversible attenuation in  hydrogen  4.1.2.1).  bonding  of  the  cellulosic  material  (Fig.  This suggests that the hydroxyls of the cellulose  have adopted new orientations (i.e.,  stereochemical changes)  241  as the result of acetonation.  These structural changes have  disrupted both the inter- and intramolecular H—bonds of the material, 4.1.5.1,  i.e.,  amorphous  4.1.5.2,  crystallinity (decrease)  and  and 4.1.5.3).  index  crystalline  regions  In addition,  the changes in  (increase)  (see Table 4.1.4.1)  and  (Figs.  crystallite  size  confirm that the acetonation  of cellulose is achieved by intramicellar swelling. 2—  the  with  systematic  the  increase  correlated index high  with  degree  the  of  in  and  increase size.  the  cellulose  is  linearly  crystallinity  in This  attained  is  during  of  concentration  crystallite  indicates removal  in  solvent  a of  purification  4.1.2.1 and Table 4.1.5.1).  acid  catalyzed  aqueous  purification of cellulose both reducing  accessibility  acetone  specificity  (see Fig.  using  in  subsequent  cellulose  treatment by  of  decrease  and  amorphous  3—  increase  nonreducing  acetone  large amounts  sugars  were  in  of  solvent  acetonated  found  the  in  hydrolysate. Two of the isopropylidene derivatives of sugars (different  isomers)  glucofuranose  and  were  identified  1,2:3,4-diacetal  as  1,2:5,6—diacetal  galactopyranose  (Figs.  4.1.3.5 and 4.1.3.6). 4—  In  cotton  a  similar  manner  hydrolysate  simple sugars  has  (epimers)  the  deacetonated  offered  a  solvent  considerable  purified  quantity  such as glucose and galactose  of  (Fig.  4.1.3.2.5). 5- the quantitative analysis of the reducing sugars cotton  hydrolysate  has  shown  that  the  in the  predominance  of  242  deacetonated sugar products  is to be as high as  86.33%  of  the weight loss (Table 4.1.3.2.1). 6- the treatment at high temperatures about significant removal of sugars up  to  42.3%  of  the  original  (180 °C)  (i.e.,  cotton).  has brought  weight loss went  This  is  explicitly  illustrated in Fig. 4.1.3.2.3.3. 7-  the  using  structural C—13  CP/MAS  investigation solid  of  state  the  NMR,  residual  has  cotton,  confirmed  the  formation of isopropylidene groups on the sugar rings in the cellulose  chain  or  chain  ends.  However,  the  quantitative  analysis conducted in this regard has shown that only small amounts  of  isopropylidene  groups  remain  in  the  residual  cellulose (i.e., at the reducing and nonreducing terminals), (see  section  other words, cellulose  4.1.4 one  units  Figs.  4.1.4.3a  isopropylidene group at  liquor/solid ratio: 8- C-13  and  the  treatment;  and  is  4.1.4.3b).  fond  In  per  400-500  acetone:water:  90:10;  10/1; 2 hr; 0.16 N HC1;  150 °C).  CP/MAS solid state NMR spectrum has confirmed that  the adsorbed amount of acetone by cellulose is too small for the unreactive solvent in comparison to that consumed on the formation of methyl groups. 9— by using acid as catalyst for aqueous acetone in solvent purification  of  cellulose,  material drops dramatically  the  viscosity  of  as shown in Fig.  the  treated  4.1.7.3.  This  can be explained by the disproportionation of the fibres due to the  formation of  cellulose  units  at  isopropylidene groups regular  intervals  between adjacent  along  the  cellulose  243  chains.  CuEn  temperature  viscosity in  the  is  decreased  presence  illustrated in Figs.  4.1.7.4  CP).  are  Similar  weight  trends  distributions  residues.  of  of  with  the  acid  and 4.1.7.5  also  observed  the  increase  catalysts,  of as  (from 28.5 to 2.7 for  solvent  The treatment has offered  the  the  molecular  purified  uniform  cotton  (symmetrical)  molecular weight distrbutions (see Figs. 4.1.6.3 and 4.1.6.4 and Tables 4.1.6.3 and 4.1.6.4) which would be preferred for the  dissolving  pulp  manufacture  if  the  weight  losses  and  decrease in viscosity could be suppressed. The results of the present work, mechanism  of  5.1. below:  cellulose  acetonation  as  support the following illustrated  in  Fig.  __ _____  _____  ____  244  Cellulose Chain +  (‘4  Unaffected pads of celMose chain  \  I .1  U  (‘4  /  ropyrene groups  Me  Z  \/ L[’ ‘\\j  1  2 j Me Furfural 1-IMF 1,6.anhydroglucose Isopopytidenatedoligomeq. minor  Key;  2 HoOf  Isopropylidene derivatives of sugar such as 1.2 6 1 -dlacotat 5 glucofuranose and 1 12 4 -diacetaI 3 gatactopyranose  (Acetonation Products)  major  4 4JC’ +  °“  V=A=4EF°1<>L O f’-’.c 2i /C  G=glucose Me  —  Methyl  z Furfural I-IMF I .6-anhydrogTucose oligomer 1  Reducing sugars sucli a 1 g lUcoS&td galactose  minor (Deacetonation Products)  Figure 5.1. Mechanism of purification of cellu lose in acidified aqueous acetone at higher temperatu res.  major  245  6  A detailed  study  SUMMARY  on the mechanism  purification  of  cellulose in acidified aqueous acetone was carried out.  of The  mechanism  has  character.  The physical phenomenon has been verified to be  based  on  been  the  interaction  found  hydrogen  of  This  are  (chapter hypothesis  action  formation that  section  of of  lead  the  cellulose  has  resulted  protection quantitative  monomer  analysis  (amorphous  and  and  been  groups  on  sugar  conducted  These changes Discussion  The  proved  chemical to  carbohydrate  of  the  ring on  crystallinity  and  4.1.5.  has  irreversible  in  Results  in  mechanism  the  the  (decreased).  disproportionation  of  by  (weaker H-bonds),  4.1.2  isopropylidene to  physico—chemical  the  illustrated  4),  a  with  and crystallite size  explicitly  of  disruption/destruction  changes in hydrogen bonding (enhanced),  be  bond  acetone  crystalline).  to  the  chains  polymer  and  formed.  The  hydrolysate  has  thus  the  be  indicated that the isopropylidene derivatives of sugar were the  predominent  experimental Discussion 4.1.7.  product  findings (chapter  For  the  of are  4),  the  dissolved  demonstrated  section  investigation  4.1.3,  of  the  material. in  These  Results  and  4.1.6,  and  4.1.4, validity  of  these  assumptions cotton was used throughout this work as a model compound, CP/MAS  and  solid  different state  techniques  NMR,  Viscosity) were employed.  X-ray  (DRIFT,  GC,  HPLC,  C-13  Diffraction,  GPC,  and  246  Factors  affecting  concentration,  solvent  residence  treatment  time,  temperature,  catalyst and acid concentration were also is  noteworthy  to  mention  such  that  the  as  acetone  type  acid  of  investigated.  investigation  factors was conducted in a manner that helped  of  It the  elucidation  of the acetonation mechanism rather than optimization of the process.  Elucidation  and  characterization  of  the  purification mechanism was the main objective of this work. Parametric contributions to the mechanism of the process are as follows:  Acetone Concentration  The increase of acetone concentration was associated  with  significant  a  systematic  absorbance height of OH stretching, H—bonds  (Fig.  4.1.2.1).  i.e.,  found to be increase  in  provision of weak  In other words, the accessibility of  cellulose was progressively  increased with the  increase of  acetone concentration. The  weight  loss  was  increased  consecutively  increase of acetone concentration (Fig. In  crystallinity,  concentration  was  the  found  successive to  give  with  the  4.1.3.2.3.1). increase  rise  to  a  of  acetone  systematic  increase in crystallinity index, and decrease in crystallite size  (Table  4.1.5.1).  A  confirmatory  trend  of  acetone  concentration was also shown by the viscosity results 4.1.7.1)  (Fig.  247  Tve of Acid Catalyst  acid  Two  catalysts  were  used  this  in  study;  TFA  (organic), and HC1 (mineral). The effect of the type of acid catalyst,  on  hydrogen  bonding,  hydrolysis  (i.e.,  deacetonated sugar products and weight loss), crystallinity, molecular weight distribution,  and viscosity,  was examined.  This was observed to be dependent on the molecular structure and properties  of  nucleophilicity various  the  acid  etc.).  This  and  tables  figures  (i.e., is  protic,  ionizing power,  explicitly  of  chapter  illustrated 4  (Results  in and  Discussion). HC1 was found to be more effective than TFA in many different ways  illustrated  in  chapter  4  (Results  and  Discussion).  Acid Concentration  The effect of acid concentration on hydrogen boning, hydrolysis, crystallinity, molecular weight distribution and viscosity  was  catalyst,  i.e.,  found  to  depend  upon  the  type  of  acid  it is dependent on molecular structure and  the properties of the catalyst. This is indicated throughout the  whole  However,  text it  illustrated concentrations  of  is in  chapter  important this  of  TFA  work are  4 to  (Results note have  effective  and that  shown but  Discussion). the that  milder  results higher in  the  248  hydrolysis  reactions  (i.e •,  minimum  dehydration  products),  while those of HC1 are detrimental and “aggressive” quality  and quantity  (DP)  (yield)  of the product,  to the  see Figs.  4.1.3.2.10 and 4.1.3.2.11.  Temperature  Different temperatures were applied in this work 150,  and 180 °C).  hydrolysis, and  significant (yield)  From the experiments on hydrogen bonding,  crystallinity,  viscosity  was  it  the  These  tables  chapter  in  4.1.2.4,  and  5,  were  (Results  4.1.3.2.3.2,  weight  that  and and  (DP)  material  shown  distribution,  temperature  quality  cellulosic  results 4  the  on  treated  treatment.  molecular  apparent  influence  of  (130,  in  and  many  a  quantity  during  solvent  figures  Discussion), 3,  has  see  and  Figs.  and  Tables  4.1.5.4,  time,  on  different  4.1.6.3 and 4.  Residence Time  The  effect  characteristics treatment, The  effect  hydrolysis, and  was  of of  the  the  cellulosic  investigated  of  residence  crystallinity,  viscosity  was  reaction  noticed  at  material  different  time  on  molecular to  solvent—solute solvation conditions.  periods  hydrogen weight  provide  during  of  time.  bonding,  distribution,  chances  However,  solvent  for  better  the extent of  249  strength of the hydrogen bond with increase in reaction time  was  found  be  to  properties  dependent  on  the  solvent  and  solute  (Figs. 4.1.2.6 and 4.1.2.7).  Furthermore, the time factor was shown to have a lesser effect on the carbohydrate removal viscosity  (DP)  treatment  when  after other  the  solvent  4.1.3.2.3.4,  4.1.3.2.3.5,  4.1.5.5, In  initial  parameters  temperature,  (weight loss) solvent  were  composition  kept  and  4.1.7.6,  and drop in purification  constant  acidity),  and  (i.e.,  see  4.1.7.7  Figs.  and  Tables  4.1.5.6, and 4.1.6.5. summary,  solvent  purification  of  cellulose  the  in  presence of an acid catalyst is a complex phenomena largely depending catalyst  on  the  solvent  concentration  concentration  (Hj  temperature and residence  and  type  (reaction)  (acetone), as  time.  well  the  as  At high  the  solvent  {acetone} concentration hydrogen bond disruption even in the crystalline  domains  accompanied followed reduced  by  by  cellulose can  formation  of  Solvent whereby  or  treatment the  be  ketals  disproportionation  DP).  purification  of  in  the  chain does  crystallite  uniform especially as the limiting  observed which solid  breaking  lead size  to  phase (i.e.,  physical  becomes  (leveling off)  is  more  DP of the  cellulose is approached.  Substantially the same effects can  be  weaker  observed  trifluoroacetic levels.  with acid,  a  however  organic at  much  acid, less  such  as  destructive  250  CONCLUSIONS AND RECOMMENDATIONS  7  7.1.  1.  Conclusions  The  solvent purification treatment has  within the residual cotton,  significant,  brought  irreversible  bond rearrangement that seems to cause permanent (disruption)  in  the  hydrogen  bonding  confirms  stereochemical changes)  the  H-  weakness  system.  irreversible hydrogen bonding rearrangement, as acetonation,  about,  This  result  reorientation  of hydroxyls of the  of  (i.e.,  cellulose  molecules.  2.  The  systematic  increase  in  absorbance  height  of  OH  stretching with the increase of acetone concentration is due to the increased interaction of acetone (HBA) with cellulose (HBD),  3.  i.e., provision of weak (nonlinear)  The accessibility of cellulose is  solvent  purification  acetone  with  treatment  cellulose  due  molecules  hydrogen bonds.  increased during the  to  the  through  interaction their  of  hydroxyl  groups by provision of weaker hydrogen bonds.  4.  The  hydrogen (i.e.,  effect bonding  of  the  are  acid  catalyst  dependent  on  concentration  the molecular  type of atoms in the molecule)  acid (i.e., protic,  and  on  structure  and properties of the  ionizing power, and nucleophilicity).  251  5.  Temperature has a significant influence on the hydrogen  bonding  of  treatment.  the This  penetration,  cellulose is  and  during  explained  freer  and  solvent  by  better  the  faster  purification solvent  reorientation  of  the  molecules (i.e., increase of the reaction rate).  6.  The effect of residence time on hydrogen bonding of the  cellulose is explained by a provision of chances for better solvent—solute solvation conditions.  However,  the extent of  strength or weakness of the hydrogen bond with increase in reaction  time  is  dependent  on  the  solvent  and  solute  properties.  7.  Acetonation  stereocheiuical  of  cotton  versatility.  provides In  other  for  a  remarkable  words,  much  is  characterized by isomerization and interconversion reactions of  glucose  obtained  on  isopropylidenation  of  cotton  of  sugars,  cellulose.  8.  The  products  of  isopropylidene derivatives  such as 1,2:5,6—diacetal glucofuranose and 1,2:3,4—diacetal galactopyranose,  resulting  from  acetonation  of  cotton,  confirm that isomerization has led to the establishment of a dynamic equilibrium.  9.  The  identified  diacetals  isopropylidene-x-D-glucofuranose  (i.e.,  1,2:5,6—di—O—  and  1,2:3, 4-di-O-  252  isopropylidene-cL-D-galactopyranose) that  isomerization  sugars,  i.e.,  has  occurred  illustrate in  constitutional,  three  explicitly  forms  of  conformational  all and  configurational.  10.  The isomers of nonreducing sugars are fewer in number  than those of the reducing sugar type. This is attributable to the difference in stability of the various isomers.  11.  It  is  derivatives  of of  significance, glucose have  however, survived  that the  isopropylidene  high  temperature  hydrolysis conditions of cellulose even in the presence of water.  12.  The removal of isopropylidene groups by hydrolysis and  deacetonation type  of  acid  under  different  catalyst,  treatment  temperature,  conditions  and  (i.e  reaction  •,  time)  resulted in a provision of different sugar isomers (epimers) in the hydrolysate.  13.  It  reducing  is sugar  evident  —  that  glucose  in the hydrolysate  has  remained  among the  the  other  major  epimers  resulting from the removal of acetone.  14.  1,6-anhydroglucose,  furfural, and hydroxymethylfurfural  are minor by—products of the solvent purification treatment.  253  15.  Although  the  sugar  ring  has  some  protection  by  isopropylidene formed during solvent purification treatment, high temperature exposure for prolonged time chances  of  dehydration  increases the  products  (i.e.,  hydroxymethylfurfural).  16.  From  hydrolyses predominant  both  primary  the  acetonation  part  (about  (86.33%)  40%)  and  sugar of  secondary  products  the  soluble  (46%)  are  the  hydrolyzed  cellulose.  17. the  The successive increase of acetone solvent  composition  (acetone—water)  concentration in  has  been  found  to  give rise to a systematic increase in weight loss.  18.  The increase of temperature,  while other factors are  kept constant (i.e., acid concentration, residence time, and acetone content),  has led to a significant increase in the  weight loss of the cellulose.  19.  The time factor is found to have a lesser effect on  carbohydrate  (weight)  purification  treatment  constant.  loss when  after  the  other  parameters  initial  solvent are  kept  254  The  20.  increased  weight  loss  significantly  of  the  with  cellulosic the  material  increase  of  has acid  concentration of the different types of acid catalysts.  21.  The  greater  increase  (4.9%  vs  33.5%)  in the weight  loss of solvent purified cellulose has been attained by the use of HC1 rather than TFA as the acid catalyst.  The spectrum of C—13 CP/MAS NNR of the residual cotton  22.  solids  after  treatment with  normal  acetone,  does  not  give  chemical shifts in the methyl group region.  The  23.  C-13  CP/MAS  solid  state  residual cotton treated with C-13  NMR  spectrum  of  the  labeled acetone has given  two methyl groups at 26.5 and 31.8 ppm, respectively.  24.  There is only one isopropylidene group per every 400-  500  cellulose units  150  C 0  of  (acetone:water:  solvent purified 90:10;  cotton  liqour/solid  treated  ratio:  iD/iL;  at 2  hr; 0.16 N HC1).  25.  Most  of  isopropylidene derivatives  of  sugars  formed  during acetonation of cotton are rapidly solublized  in the  hydrolysate.  255  26.  DisproportiOflatiOn  of  the  cellulose  chains  is  the  result of removal of isopropylidene derivatives of sugars in the solution during the hydrolysis reactions.  27.  The  derivatives cellulose  process  of  of  sugars  with  short  the  in  removal  the  chains  of  solution  isopropylidene offers  residual  isopropylidenated  at  the  reducing and non—reducing terminals.  28.  The isopropylidene derivatives of sugars formed in the  residual cotton are monoacetals of pyranoid sugar struc ture, i.e.,  1, 2—O—isopropylidene--cL-D-glucofuranose  and  4,6-0—  isopropylidene-D-glucopyranose.  29.  The  water)  of  solvent celluose  purification has  treatment  increased  the  (i.e.,  intensities  acetone— of  101,  icTr, and 002 planes.  30.  The successive  increase in acetone concentration has  resulted in a systematic increase of the crystallin ity index of the cotton residues.  31.  The  purification  increase liquor  of  of  acetone  cotton  content  cellulose  has  in led  solvent to  systematic decrease in crystallite size of the residue s.  a  256  32.  With  solvent  the  increase  composition,  of  the  acetone  concentration  accessibility  of  the  in  cellulose  is  progressively increased, i.e., weaker hydrogen bonds.  33.  The systematic increase in accessibility of cellulose  with  the  increase  of  acetone  concentration  is  linearly  correlated to successive increase in crystallinity index and decrease in crystallite size in acetonation treatment.  34.  Catalyst and acidity in solvent purification treatment  have no direct effect on crystalline changes. However, their involvement in the shaping of  crystallinity and crystallite  size can be used in determining how much they contribute to the accessibility of the cellulose,  and the selectivity of  the removal of the amorphous cellulose.  35.  Temperature has  rate of would  the  lead  a  remarkable  effect  solvent purification treatment. to  considerable  stereochemical  the  on  reaction  In turn,  this  changes,  which  affect both crystallinity and crystallite size.  36.  Residence  crystallite  size  stereochemical  37.  time by  contributes provision  ,  of  to  crystallinity  chances  for  and  further  i e., structral alterations.  Depolymerization of the cellulose  (cotton),  which has  taken place in the unacidified acetone—water mixture  (i.e.,  257  no catalyst added), the  acetone/water  is largely due to the mutual action of complex,  water molecules with the and  the  acids  from  resulted  from  the  reaction  acetone at a higher  the  pectic  of  temperature,  substances  in  cotton  cellulose.  38.  The  increase  in  acid  concentration,  in  general,  has  offered higher proportions of low molecular weight fractions of cotton residues in the solvent purification treatment.  39.  Increase  of  temperature  has  led  to  production  of  shorter cellulose chains on acetonation of cellulose.  40.  The  molecular  weight  shown shifts towards the  distribution  (MWD)  curves  have  low molecular weight distribution  region with the increase in residence time.  41.  The  resulting  disproportionation from  concentration,  the  increase  temperature,  the  of  of and  a  cellulose  parameter  residence  such  time  is  chain, as _acid usually  accompanied with formation of narrower polydispersities acetonation,  i.e.,  more  uniform  molecular  in  weight  distribution.  42. the  The progressive solvent  increase  purification  in  acetone  treatment  concentration  affords  a  in  significant  systematic decrease of the degree of polymerization  (DP)  of  258  the  cellulose.  The  drop  in  DP  may  be  severe  too  for  the  purpose of dissolving pulp manufacturing.  43.  Cellulose  (significantly) catalyst  has  viscosity  when been  acetone used  dropped  in  in  the  high  dramatically  presence temperature  of  acid  solvent  purification treatment of cotton.  44.  Temperature has  viscosity  a  cotton  of  significant residues  effect  on the residual  following  the  solvent  purification treatment.  45. to  The time factor has little (insignificant) the  drop  of  viscosity  (DP)  after  purification treatment when temperature, and acidity are kept constant.  the  contribution  initial  solvent  liquor/solid ratio,  259  7•2  Recommendations  1.  Further studies on the mechanism of acetonation on other  pulp  components,  such  as  xylans  and  lignin  would  be  of  importance.  2.  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