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The use of raifix to enhance fines and filler retention in mechanical groundwood pulps Trigylidas, Dennis 1999

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The Use of Raifix to Enhance Fines and Filler Retention in Mechanical Groundwood Pulps by Dennis Trigylidas FJ.Eng., McGill University, 1997 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Chemical and Bio-Resource Engineering) We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA August 1999 © Dennis Trigylidas, 1999  In  presenting  degree  this  at the  thesis  in  University of  freely available for reference copying  of  department publication  this or of  thesis for by  this  his  or  partial  fulfilment  of  British  Columbia,  I agree  and study.  requirements that the  I further agree  scholarly purposes her  the  representatives.  may be It  thesis for financial gain shall not  is  that  an  advanced  Library shall make it  permission for extensive  granted  by the  understood be  for  that  allowed without  head  of  my  copying  or  my written  permission.  Department of  C^-g^^yC^c^  The University of British Columbia Vancouver, Canada  Date  DE-6  (2/88)  H~  (^cp- -  (^-^ju^c-c£_  ^ . ^ . ^ v ^ f i ^ w v ^  ABSTRACT  This work investigates the use of Raifix as a retention enhancing ATC in clay and PCC filled mechanical groundwood pulp suspensions. Raifix is a starch based Anionic Trash Collector (ATC) which is patented and produced by Raisio Chemicals of Finland. Raifix coagulates the anionic Dissolved and Colloidal Substances (DCS) present in a pulp furnish and attaches them to the fibre. These are subsequently flocculated by a high molecular weight retention aid polymer. In this work, Raifix was used in conjunction with a Poly(ethylene oxide)-Phenol Formaldehyde Resin (PEO-PFR) retention aid system. In first pass retention experiments conducted with a Dynamic Drainage Jar (DDJ), when Raifix was added prior to PFR and PEO, the retention of fines and clay increased by as much as 18% and 31% respectively. In contrast, Raifix had a detrimental effect on retention in the PCC filled pulp suspension. In both cases, the cationic demand and turbidity of the DDJ filtrate (analogous to a mill's white water) decreased as Raifix dosage was increased. Laser diffraction particle size analyses were also performed to observe the aggregation behaviour of clay and PCC filler. When Raifix was added prior to PFR and PEO, the rate of aggregation and aggregate size of clay increased by as much as 1000% and 150% respectively. Once again, Raifix had a detrimental effect on PCC aggregation. Finally, experiments were performed using Fourier Transform Infrared Analysis to observe the molecular interactions between PEO, PFR and Raifix. The results of these experiments show evidence of hydrogen bonding interactions between PEO and PFR as well as Raifix and PFR. This was indicated by a shift of the hydrogen bonded O-H peak to a lower frequency.  ii  TABLE OF CONTENTS  ABSTRACT  ii  LIST OF TABLES  vii  LIST OF FIGURES  viii  ACKNOWLEDGMENTS  xvi  CHAPTER  1  Introduction  1. Poly(ethylene oxide)  1  1.1 Poly(ethylene oxide) as a Retention Aid in Papermaking  3  1.2 The Poly(ethylene oxide)-Cofactor Dual Retention Aid System  5  1.3 Retention Enhancement with and without Cofactors  8  2. Raifix Polymers  9  2.1 Raifix Polymers as Anionic Trash Collectors (ATC) 3. Research Obj ectives  CHAPTER  2  11 14  Experimental Methods  1. Materials  15  1.1 Anionic Trash Collector (ATC)  15  1.2 Clay Filler  15  1.3 Ethylenediaminetetraacetic Acid (EDTA)  15  1.4 Formaldehyde  15  1.5 Phenol Formaldehyde Resin (PFR) Cofactor  16  1.6 Phosphoric Acid  16  1.7 Poly(diallyl dimethyl ammonium chloride) (PDADMAC)  16  iii  1.8 Poly(ethene sodium sulfonate) (Pes-Na)  16  1.9 Polyethylene oxide) (PEO)  16  1.10  Potassium Chloride (KCL)  17  1.11  Precipitated Calcium Carbonate (PCC) Filler  17  1.12  Pulp  17  1.13  Sodium Hydroxide  18  1.14  Water  18  2. Instrumentation and Analysis  18  2.1 Characterization of Materials  18  2.1.1 Apparatus  18  2.1.1.1 Brookfield DV-II+ Programmable Viscometer with UL Adapter  18  2.1.1.2 Dynamic Drainage Jar  19  2.1.1.3 Kajaani FS-200 Fibre Analyzer  19  2.1.1.4 pH and Conductivity Meters  19  2.1.2 Procedure  20  2.1.2.1 Fibre Length Analysis  20  2.1.2.2 Fines Fractionation  21  2.1.2.3 PEO Viscosity Measurements  21  2.1.2.4 pH and Conductivity Analysis  22  2.2 Aggregation of Filler 2.2.1  22  Apparatus  22  2.2.1.1 Malvern Mastersizer 2000 with Hydro MU Cell 2.2.1.2 Zeta-Meter System 3.0  22 22  2.2.2 Procedure  23  2.2.2.1 Aggregation of Filler  23 iv  2.2.2.2 Zeta Potential Analysis  24  2.3 Solubility of Precipitated Calcium Carbonate (PCC) in Pulp Suspension 2.3.1 Apparatus  25 25  2.3.1.1 pH and Conductivity Meters  25  2.3.1.2 Glas-Col Variable Speed Stirrer  25  2.3.1.3 Mettler DL25 Titrator with DP550 Phototrode  25  2.3.1.4 Millipore Pressure Filter  25  2.3.2 Procedure  26  2.4 First Pass Retention  26  2.4.1  Apparatus  26  2.4.1.1 Dynamic Drainage Jar  26  2.4.1.2 Mettler DL25 Titrator with DP550 Phototrode  26  2.4.1.3 Millipore Pressure Filter  26  2.4.1.4 Muetek PCD 03 Particle Charge Detector  26  2.4.1.5 Hach 21 OOP Portable Turbidimeter 2.4.2 Procedure  28  2.4.2.1 Cationic Demand Analysis  28  2.4.2.2 First Pass Retention  28  2.5 Fourier Transform Infrared Spectroscopy 2.5.1  Apparatus  29 29  2.5.1.1 Perkin Elmer 1600 FT-IR Spectrophotometer 2.5.2 Procedure  CHAPTER 3  27  29 29  Theory  1. Fourier Transform Infrared Spectroscopy  32 v  2. Muetek PCD 03 Particle Charge Detector  33  3. Low Angle Laser Light Scattering  34  CHAPTER 4  Results and Discussion  1. Characterization of Materials  35  1.1 Pulp Characterization  35  1.2 Poly(ethylene oxide) Characterization  36  2. Aggregation of Filler  37  2.1 Clay Filler  37  2.2 Precipitated Calcium Carbonate (PCC) Filler  46  3. Solubility of Precipitated Calcium Carbonate (PCC) in Pulp Suspension  52  4. First Pass Retention  54  4.1 Clay Filler  54  4.2 Precipitated Calcium Carbonate (PCC) Filler  67  5. Fourier Transform Infrared Spectroscopy  CHAPTER 5  69  Conclusions  1. Conclusions  73  2. References  76  APPENDIX I  First Pass Retention  1. Calculation of First Pass Retention in a Clay Filled Pulp Suspension  84  2. Calculation of First Pass Retention in a PCC Filled Pulp Suspension  85  APPENDIX II  Aggregation of Filler  1. Clay Aggregation with Raifix, PFR and PEO vi  86  LIST OF T A B L E S  CHAPTER  1  Introduction  Table 1 The effect of various ions on the C P T of the PEO-water system Table 2 The results o f various mill trials using P E O as a retention aid Table 3  1 A comparison of conventional cationic starches and Raifix polymers  Table 4  1 A comparison of Raifix with other A T C polymers  CHAPTER  2  Experimental Methods  Table 1  1  Filler properties  CHAPTER 4  Results and Discussion  Table 1  :  Pulp properties  vii  3  LIST OF FIGURES  CHAPTER  1  Introduction  Figure 1  3  Flocculation Figure 2  5  Polymeric hydrogen bonding in the PEO-PFR complex Figure 3  6  Schematics of Association-Induced Polymer Bridging Figure 4  7  PEO-PFR retention mechanisms Figure 5  9  The base monomer in Raifix polymers Figure 6  9  Reaction of modified starch with cationizing agent Figure 7  10  Raifix's highly branched structure with a close-up of the glucose monomer Figure 8  12  Raifix and Poly(DADMAC) in open and closed-cycle mills Figure 9  12  Patch Flocculation Figure 10  13  Turbidity and charge demand of TMP treated with Raifix  viii  Experimental Methods  CHAPTER 2  Figure 1  20  Dynamic Drainage Jar Figure 2  23  The Malvern Mastersizer 2000 with Hydro M U C e l l Figure 3  27  Muetek P C D 03 and the Hach 21 OOP Turbidimeter Figure 4  30  Calculation o f First Pass Retention  Theory  CHAPTER 3  Figure 1  33  The electromagnetic spectrum Figure 2  33  Approximate stretching vibration frequencies o f various common bonds  Results and Discussion  CHAPTER 4  Figure 1  36  Kajaani fibre length analysis (295 K ) Figure 2  .'  37  Viscosity of P E O solutions over time (295 K , 60 rpm) Figure 3  38  The aggregation o f clay with P E O ( P E O = 5000 g/T, 295 K , 1250 rpm, Conductivity = 1.62 S/ c m , p H = 6.33)  ix  Figure 4  39  The effect of PEO and PFR dosage on the rate of aggregation of clay (PFR/PEO - 0.5, 295 K, 1250 rpm, Conductivity = 1.62 S/ c m, pH = 6.33) Figure 5  39  The effect of PEO and PFR dosage on the aggregate size of clay (PFR/PEO = 0.5, 295 K, 1250 rpm, Conductivity = 1.62 S/ cm, pH = 6.33) Figure 6  40  The effect of the PFR/PEO ratio on the rate of aggregation of clay (PEO = 5000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/ cm, pH = 6.33) Figure 7  40  The effect of the PFR/PEO ratio on the aggregate size of clay (PEO = 5000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/ c m, pH = 6.33) Figure 8  42  The effect of Raifix dosage on the rate of aggregation of clay (295 K, 1250 rpm, Conductivity = 1.62 S /cm, pH = 6.33) Figure 9  42  The effect of Raifix dosage on the aggregate size of clay (295 K, 1250 rpm, Conductivity = 1.62 S / cm, pH = 6.33) Figure 10  43  The effect of Raifix on the zeta potential of clay aggregates (295 K, 1250 rpm, Conductivity = 1.62 S /cm, pH = 6.33) Figure 11 The effect of order of addition on the rate of aggregation of clay (Raifix (1) = 10000 g/T, PFR (2) = 500 g/T, PEO (3) = 1000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/cm, pH = 6.33)  43  Figure 12  44  The effect of order of addition on the aggregate size of clay (Raifix (1) = 10000 g/T, PFR (2) = 500 g/T, PEO (3) = 1000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/cm, pH = 6.33) Figure 13  45  The effect of Raifix dosage on the rate of aggregation of clay (PEO = 1000 g/T, PFR = 500 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/ cm, pH = 6.33) Figure 14  45  The effect of Raifix dosage on the aggregate size of clay (PEO = 1000 g/T, PFR = 500 g/T, 295 K, 1250 rpm, Conductivity = 1.62 S/ c m, pH = 6.33) Figure 15  47  The effect of PEO dosage on the rate of aggregation of PCC (295 K, 1250 rpm, Conductivity = 43.4 S / cm, pH = 9.58) Figure 16  48  The effect of PEO dosage on the aggregate size of PCC (295 K, 1250 rpm, Conductivity = 43.4 S / cm, pH = 9.58) Figure 17  48  The effect of the PFR/PEO ratio on the rate of aggregation of PCC (PEO = lOOg/T, 295 K, 1250 rpm, Conductivity = 43.4 S/ cm, pH = 9.58) Figure 18  49  The effect of the PFR/PEO ratio on the aggregate size of PCC (PEO = lOOg/T, 295 K, 1250 rpm, Conductivity = 43.4 S/ c m, pH = 9.58) Figure 19  49  The effect of Raifix dosage on the rate of aggregation of PCC (295 K, 1250 rpm, Conductivity = 43.4 S /cm, pH = 9.58) xi  Figure 20  50  The effect of Raifix dosage on the aggregate size of PCC (295 K, 1250 rpm, Conductivity = 43.4 S /cm, pH = 9.58) Figure 21  50  The effect of Raifix on the zeta potential of PCC aggregates (295 K, 1250 rpm, Conductivity = 43.4 S / cm, pH = 9.58) Figure 22  51  The effect of Raifix dosage on the rate of aggregation of PCC (PEO = 100 g/T, PFR = 50 g/T, 295 K, 1250 rpm, Conductivity = 43.4 S/ cm, pH = 9.58) Figure 23  52  The effect of Raifix dosage on the aggregate size of PCC (PEO = 100 g/T, PFR = 50 g/T, 295 K, 1250 rpm, Conductivity = 43.4 S/ cm, pH = 9.58) Figure 24  53  The conductivity of the PCC filled pulp suspension over time (295 K, 1000 rpm) Figure 25  53  [Ca ] of the PCC filled pulp suspension over time (295 K, 1000 rpm) ++  Figure 26  54  pH of the PCC filled pulp suspension over time (295 K, 1000 rpm) Figure 27  55  The effect of PEO and PFR dosage on first pass retention (1000 rpm, 295 K, PFR/PEO=0.5, 200 mesh screen, Conductivity = 262-263 S/ c m, pH = 6.33 -7) Figure 28  55  The effect of PEO and PFR dosage on first pass retention (1000 rpm, 295 K, xii  PFR/PEO = 2, 200 mesh screen, Conductivity = 262-266 S/ c m, pH = 6.33-7)  Figure 29  57  The effect of the PFR/PEO ratio on first pass retention (PEO = 50 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 269 S / cm, pH = 6.33 - 7) Figure 30  57  The effect of the PFR/PEO ratio on first pass retention (PEO = 100 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 269 S / cm, pH = 6.76 - 7) Figure 31  58  The effect of the PFR/PEO ratio on first pass retention (PEO =150 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 266 S / cm, pH = 6.4 - 6.93) Figure 32  58  The effect of the PFR/PEO ratio on first pass retention (PEO = 100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 244 S / cm, pH = 7.02) Figure 33  59  The effect of the PFR/PEO ratio on first pass retention (PEO =150 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 244 S / cm, pH = 7.02) Figure 34  61  The effect of mixing time on fines retention (PEO =100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02) Figure 35  61  The effect of mixing time on clay retention (PEO = 100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02) Figure 36  62  xiii  The effect of mixing time on total retention (PEO =100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02)  Figure 37  63  The effect of the order of addition on first pass retention (Raifix (1) = 1000 g/T, PFR (2) = 50 g/T, PEO (3) = 100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S / cm, pH = 7.18) Figure 38  65  The effect of Raifix dosage on cationic demand (70 mesh screen, 295 K, 1000 rpm, Conductivity = 244 - 246 S / cm, pH = 7.02 - 7.18) Figure 39  65  The effect of Raifix dosage on first pass retention (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S/ c m, pH = 7.18) Figure 40  66  The effect of Raifix dosage on cationic demand (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S / cm, pH = 7.18) Figure 41  66  The effect of Raifix dosage on turbidity (PEO =100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S / cm, pH = 7.18) Figure 42  68  The effect of Raifix dosage on first pass retention (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S/ cm, pH = 6.9 - 7.18) Figure 43  68  The effect of Raifix dosage on cationic demand (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S/ cm, pH = 6.9 - 7.18) xiv  Figure 44  69  The effect of Raifix dosage on turbidity (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S / cm, pH = 6.9 - 7.18) Figure 45  70  The FTIR Spectra of PEO, PFR and the PEO-PFR Complex Figure 46  72  The FTIR Spectra of PFR, Raifix, and the Raifix-PFR Complex  XV  ACKNOWLEDGEMENTS  I would like to thank the following for their support during the course of my studies at UBC. First, I would like to thank PAPRICAN for awarding me with the Otto Maas Scholarship, which has provided financial support over the past year. I would like to thank the Network of Centres of Excellence for Mechanical Pulps for also providing financial support. I would like to thank Forest Renewal B.C. for financial assistance in purchasing equipment. I would like to thank my two supervisors, Dr. Peter Englezos of UBC, and Dr. Ian Thorburn of Raisio Chemicals, for their guidance and moral support. I would like to thank Raisio Chemicals for supplying me with the necessary chemicals. I would like to thank Dr. Denys Leclerc of PAPRICAN's Vancouver lab for allowing me to use their FTIR equipment. I would like to thank the Department of Mining and Metallurgy at the University of British Columbia for allowing me to use their Zeta-Meter. Finally, special thanks to my family and friends who have given me nothing but love and support and who have helped me to maintain sanity throughout the course of my academic life.  xvi  CHAPTER 1  Introduction  1. Poly(ethylene oxide) Poly(ethylene oxide) (PEO) resins are high molecular weight homopolymers consisting of repeating ethylene oxide units (-CH2-CH2-O-) [4,8]. They are produced by the heterogeneous catalytic polymerization of ethylene oxide [8]. PEO polymers are available in a broad range of molecular weights, from 0.1 to 8 million. Lower molecular weight ethylene oxide polymers (<100 000) are referred to as Poly(ethylene glycol) (or PEG) [16]. PEG polymers have properties very different from those of PEO due to the increased effect of reactive hydroxyl end groups on the shorter PEG chains [21]. The ether oxygen on PEO allows it to participate in hydrogen bonding. This accounts for the polymer's high solubility in water [25]. PEO is water soluble over a wide range of molecular weights, from oligomers to molecular weights in the millions, and at moderate temperatures [21]. However, near the boiling point of water (approximately 95°C), the PEO-water system separates into a PEO-rich and PEO-lean phase [4,8,14,22,23,25]. The temperature at which phase separation occurs is referred to as the Cloud Point Temperature (CPT). The presence of inorganic salts in aqueous PEO solutions can reduce the CPT [1,4,7,8,14,22,23]. The CPT has been shown to decrease in proportion to the salt concentration. In addition, smaller hydrated ions have a greater effect on reducing the CPT [1]. The effect of various anions and cations on the CPT of the PEO-water system is shown in Table 1. The viscosity of an aqueous PEO solution depends on the polymer concentration and molecular weight, the concentration of inorganic salts, temperature, and shear rate [4,8]. The viscosity of a PEO solution increases with concentration and molecular weight and becomes more dependent on concentration as the molecular weight is increased. The viscosity decreases as temperature, shear, and salt concentration are increased [4,8]. Aqueous solutions of high 1  Table 1: The effect of various ions on the CPT of the PEO-water system [1] Anions  Cations  PCV  K , Rb , Na , C s +  3  HP0 "  +  Effect +  +  High  2  4  S2CV  Sr  2  H2PO4"  F  + 2  1  Ba , Ca + 2  1  + 2  HCO2"  1  CH3CO2"  1  NH  + 1 4  Br"  1  r  1  Li  +  Low  molecular weight PEO are viscoelastic. This is demonstrated by their tendency to climb a rotating shaft. Their viscoelasticity is due to the flexibility of the ether linkages combined with the length of the high molecular weight chain [21]. In addition, concentrated aqueous PEO solutions are pseudoplastic [8]. This means that the viscosity decreases with an increase in the shear rate used for measurement. This property becomes more pronounced as the molecular weight is increased. PEO polymers are susceptible to oxidative and mechanical degradation [4,8]. Oxidative degradation occurs when the C-O-C linkage is split by exposure to oxygen. This reaction can be catalyzed by UV light, metal ions, and heat [21]. Mechanical degradation occurs when excessive shear is applied to the PEO solution. Oxidative and mechanical degradation have the effect of reducing the chain size and thus, the molecular weight of the PEO polymer. Since the viscosity of a PEO solution is a function of its molecular weight, degradation can be detected by a decrease in the viscosity of the solution [16,21]. PEO solutions find many uses in industry due to their high water solubility, low toxicity, unique solution rheology, complexation with organic acids, low ash content, and thermoplasticity  2  [8]. PEO solutions are used in adhesives, acid cleaners, contact-lens fluids, lubricants, detergents, lotions, paints, coatings, and many other applications [8]. High molecular weight PEO solutions are used as flocculants in the retention of fines and filler in papermaking. This application will be discussed in the next section.  1.1 Poly(ethylene oxide) as a Retention Aid in Papermaking PEO is used in the pulp and paper industry as a retention aid due to its ability to flocculate fibre fines and filler [38,39]. To be effective as a retention aid, PEO must have a molecular weight in excess of 4 million [21,38]. PEO is most effective on mechanical groundwood and unbleached kraft pulps. It is least effective on bleached chemical pulps. Generally speaking, it is most effective on furnishes which are "dirty", anionic, extractives laden, and have a high fines content [21]. PEO has an advantage over cationic retention aids when used with these furnishes because it is non-ionic and is unaffected by the high concentration of anionic Dissolved and Colloidal Substances (DCS) commonly associated with them. In addition, these furnishes contain a high concentration of lignin derivatives which provide naturally occurring bonding sites for PEO [21]. It is believed that PEO interacts with the phenolic hydroxyl groups present in the lignin derivatives by hydrogen bonding via its ether oxygen. These interactions allow PEO to adsorb onto fibre surfaces. Additionally, if PEO has a high enough molecular weight, it can adsorb onto two separate fibre surfaces and flocculate them (refer to Figure 1).  Figure 1: Flocculation [21] 3  PEO is less effective at retaining filler particles than it is at retaining fibre fines. Previous work has shown that well-dissolved PEO can adsorb onto clay, but it cannot aggregate clay in an aqueous suspension [57]. However, flocculation of clay in an aqueous fibre suspension has been explained via heteroflocculation by Assymetric Polymer Bridging [60]. According to this theory, PEO adsorbs onto the clay particle first. This modifies its configuration and reduces the entropic barrier for adsorption onto the fibre surface, thus bridging the two. PEO has also been shown to be ineffective.at retaining ground.calcium carbonate (GCC) and precipitated calcium carbonate (PCC) fillers [2]. The retention of positively charged or neutral scalenohedral PCC in papermaking can be attributed to electrostatic and van der Waals attractions with the negatively charged fibres [2,20,21]. PEO has been used commercially as a retention aid since the mid-eighties. It has been most successful with standard newsprint grades such as TMP, TMP/groundwood, or TMP/RMP. Table 2 shows the effect that PEO has had on fines retention at various newsprint mills. PEO is available commercially as a fine granular solid. It is commonly prepared at low concentrations (0.1-0.2%) and is usually fed at a dosage of 45 to 225 grams per tonne of dry fibre and filler.  Table 2: The results of various mill trials using PEO as a retention aid [21] Mill Description  PEO Concentration (lb/ton) ^  Increase in Retention  U.S. Mill #2  0.5  15%  Swedish Mill  0.3  15%  U.S. Mill #3  0.4  15%  U  S  M j | j #  1  * Increase in first pass retention  4  1.2 The Poly(ethylene oxide)-Cofactor Dual Retention Aid System The retention performance of PEO is greatly enhanced when used in conjunction with a co factor. Cofactors are low molecular weight polymers which contain phenolic hydroxyl groups. Common examples of cofactors are Sulphonated Kraft Lignin (SKL), Tannic Acid (TA), and Phenol Formaldehyde Resins (PFR). In laboratory and mill studies, PFR cofactors have been shown to be the most effective at improving retention of fines and filler [5,40]. These cofactors form a complex with PEO, presumably through hydrogen bonding interactions (refer to Figure 2) [21]. Pelton at al. have recently suggested that hydrophobic interactions also play a role in the formation of the PEO-cofactor complex. An example of how the PEO-cofactor complex bridges two negatively charged surfaces is shown in Figure 3. In diagram a), PEO is a long, flexible polymer, which is unable to bridge the two surfaces. In diagram b), the configuration of PEO is modified by complexation with the cofactor. The cofactor stiffens the structure of PEO, thus lowering the entropic barrier for adsorption. This allows PEO to overcome the electrical double layer between the two surfaces and bridge them. An alternate mechanism is shown in diagram c). In this case, the cofactor adsorbs onto the colloid surface and acts as an anchor point for the PEO to flocculate. These mechanisms are known as Association-Induced Polymer Bridging and have been developed by  -O-CH2-CH2-O-CH2-CH2-O-  Figure 2: Polymeric hydrogen bonding in the PEO-PFR complex 5  van de Ven et al.. A similar theory has been developed by Pelton et al. (refer to Figure 4). They determined that the most likely flocculation mechanism is that of Complex Bridging Flocculation [65], which is shown in Figure 4 as the sequence: 1,3,4,5,7,9. Another significant flocculation mechanism has the cofactor acting as an anchor point, which is shown as the sequence: 2,5,7,9. Also shown is the mechanism for network flocculation (1,3,6,8). This was originally believed to be the primary flocculation mechanism. Although network formation between PEO and PFR is possible, both groups have shown that it does not contribute significantly to flocculation. In papermaking applications, cofactors are fed to the stock early in the system, while the PEO is added after the selectifier screen [21]. Cofactor is usually added at a ratio of 0.5:1 to 8:1 dry cofactor to dry PEO. The ratio of cofactor to PEO will vary according to the application. Pulp furnishes containing a high concentration of lignin derivatives (ex. mechanical groundwood, unbleached kraft) tend to require less cofactor due to the abundance of naturally occurring bonding sites for PEO.  / / / / / / / / / /  / / / / / / / / / /  / / /_./ / / / _ / / /  / / / / / / / / / /  a)  b)  c)  Figure 3: Schematics of Association-Induced Polymer Bridging [59]  6  Free  Figure 4: PEO-PFR retention mechanisms [65]  7  1.3 Retention Enhancement with and without Cofactors The retention performance of PEO can be further enhanced by two methods. The first method involves the addition of a cationic polymer prior to the addition of cofactor and PEO [49]. These are usually low molecular weight, highly charged solution polymers which coagulate the anionic dissolved and colloidal substances present in a papermaking furnish. Coagulation is an aggregation phenomenon whereby, negatively charged colloidal particles are neutralized by a highly cationic polymer and aggregated [13]. The aggregates are subsequently flocculated by the PEO-cofactor complex. This improves the retention of fines and filler in the paper sheet. The polymers operate mainly on charge attraction, but some are also capable of hydrogen bonding. These polymers are commercially known as Anionic Trash Collectors (ATC). A comparison of various ATC's is given in Table 4. The second method for enhancing the retention performance of PEO involves the phase separation of the PEO-water system and does not require the addition of any cofactor. This method was first established by Englezos et al. [22,23]. In this method, the Cloud Point Temperature (CPT) of the PEO-water system is lowered to papermaking conditions by adding an inorganic salt. Previous work by Englezos et al. has shown that fines and clay retention can be increased by 27.2% and 40.2 % respectively when operating above the CPT. In their work, the CPT was lowered to 59°C by adding 2 moles/L of KC1 to a pulp suspension. First pass retention experiments were then performed at a temperature below (30°C) and above (70°C) the CPT with a 5 million MW PEO. Subsequent experiments using the Photometric Dispersion Analyzer have also shown that PEO is more readily adsorbed onto fibre, clay and chalk at temperatures above the CPT [22]. The enhanced adsorption and flocculation is attributed to a modification in the state of PEO at temperatures above the CPT. The modification of PEO leads to a reduction in the entropic barrier for adsorption and flocculation to occur. This is similar to the way a cofactor  8  operates. In both cases, when the PEO structure is modified it becomes thermodynamically advantageous for it to leave the water phase and adsorb onto a surface.  2. Raifix Polymers Raifix polymers are low molecular weight, highly cationic starch molecules [62,63]. The base monomer in Raifix polymers is a-Anhydroglucose (refer to Figure 5). Rather than being synthesized from the base monomer, the starting material in the production of Raifix polymers is potato starch. Starch is a high molecular weight natural polymer consisting of linear (amylose) and branched (amylopectin) polymers of glucose units [64]. Amylopectin has a branch point roughly every nine glucose units. The molecular weight of amylose varies between 0.16 and 0.7 million while that of amylopectin varies between 50 000 and 1 million [64].  CH OH 2  Cl  OH  OCH CHCH N (CH3) +  2  2  3  OH  Figure 5: The base monomer in Raifix polymers [41]  OH +  CH -CH-CH -N(CH ) CI" 2,3-epoxypropylene trimethylammonium chloride +  2  2  3  3  Figure 6: Reaction of modified starch with cationizing agent [41] 9  RAIFIX POLYMERS  During the manufacture of Raifix polymers, the molecular weight of starch is reduced. The modified starch is then reacted with cationizing agent to produce Raifix polymers (refer to Figure 6). The resuting polymer has a molecular weight of 0.5 to 1.5 million and is highly branched due to the presence of amylopectin (refer to Figure 7). Raifix polymers are highly cationic, having a charge density which can be varied between 10% and 80 % [41]. The source of the cationic l  charge is a quaternary amine, which can retain its charge over a wide pH range [62,63]. Raifix polymers also have the ability to hydrogen bond due to the abundance of OFf-groups on the glucose monomers. Raifix polymers are highly water soluble and can be supplied as solutions. In contrast, high molecular weight cationic starches are typically supplied in granular form and have to be cooked. A comparison of conventional high molecular weight cationic starches and Raifix polymers is given in Table 3.  Figure 7: Raifix's highly branched structure with a close-up of the glucose monomer [41]  ' Charge density is defined as the percentage of repeating units which have a charge associated with them. 10  Table 3: A comparison of conventional cationic starches and Raifix polymers [41] Conventional Cationic Starch  Raifix polymer  Base Monomer  a-Anhydroglucose  a-Anhydroglucose  Chemical Composition  Amylose & Amylopectin  Amylose & Amylopectin  Molecular Weight  1 - 500 million  0.5 - 1.5 million  Physical Form  Granules  Solution  Charge Density  2 % - 5 %  10 % - 80 %  Use in Papermaking  Strength Development  Anionic Trash Collector  2.1 Raifix Polymers as Anionic Trash Collectors (ATC) Raifix polymers are used in papermaking as Anionic Trash Collectors (ATC) due to their ability to patch flocculate the anionic DCS present in a papermaking furnish [63]. Patch flocculation occurs when cationic islets are formed on the negatively charged colloid surface. These cationic islets attract negatively charged adjacent particles (refer to Figure 9). In addition, Raifix attaches these anionic DCS to the fibres which exit the system with the paper sheet. This has the effect of improving retention of fines and filler in the paper sheet. The benefits of this are improved runnability of the paper machine, fewer process variations, lower demand on other process additives (such as size, retention aid, etc.), and improved overall paper quality [13,41,62,63]. Raifix polymers have several unique properties which distinguish them from other solution polymers which are currently being used as ATC's (refer to Table 4). To begin, Raifix polymers are semi-synthetic (based on starch) whereas other solution polymers are synthesized from monomers. Secondly, the charge density in Raifix polymers can be adjusted for specific applications, whereas other solution polymers have a fixed 100 % charge density. Thirdly, Raifix polymers are capable of hydrogen bonding whereas other solution polymers have limited or no hydrogen bonding ability. This allows Raifix polymers to interact with the anionic DCS by combined hydrogen bonding and electrostatic interactions. Fourthly, Raifix polymers can retain 11  their positive charge over a wide range of pH since the cationic group is a quaternary amine. In contrast, polymers such as Poly(ethylene imine) (PEI) lose their positive charge at high pH. This is due to the presence of 1°, 2°, and 3° amines which become de-protonated at high pH. Finally, because of its rigid structure and hydrophilic nature, Raifix is more immune to high concentrations of dissolved ions. The benefits of this are seen in closed-cycle mills where high concentrations of dissolved ions will cause less hydrophilic and less rigid structures such as Poly(DADMAC) to coil up, thus reducing their efficiency (refer to Figure 8).  Table 4: A comparison of Raifix with other ATC polymers [41] Raifix  Poly(amine)  Poly(DADMAC)  Poly(ethylene imine)  Chemistry  Semi-synthetic  Synthetic  Synthetic  Synthetic  Molecular Weight  0.5 - 1.5 M  20 - 100 K  100 - 500 K  400 - 800 K  Degree of Branching  High  Low  None  High  Charge Density  10 - 80 %  100 %  100 %  100 %  Cationic Source  4° Amine  4° Amine  4° Amine  1°, 2°, 3°, 4° Amines  Hydrophilicity  High  Medium  Low  Medium  Hydrogen Bonding  Strong  Slight  None  None  Figure 8: Raifix and Poly(DADMAC) in open  Figure 9: Patch Flocculation [13]  (above) and closed-cycle mills (below) [41]  12  Raifix polymers are a new development and have only recently found use in the paper industry. One case in which Raifix has been used is in a Finnish mill producing a coated woodcontaining sheet [41]. The mill was experiencing runnability problems due to deposit from T M P pitch and white pitch from the coated broke. Figure 10 shows the effect that Raifix had on the turbidity and charge demand of the T M P . Several benefits were observed when using Raifix. These included a tenfold decrease of pitch particles in the white water, better retention, and improved runnability.  250 , 200 Turbidity, 150 NTU  H  100 50 0 -  ,«*T***T  2  6  4  8  10  12  ^«T —i T  l  14  16  14  16  Day # - * - Untreated  Treated with Raifix  0 , -0.5 -1 Charge Demand, -1.5 mmol/L  -2  H  -2.5 -3 -  -i  1  2  1  1  4  1  1  1  6  i  1  8  1  10  i  r  12  Day# Untreated  Treated with Raifix  Figure 10: Turbidity and charge demand of T M P treated with Raifix [41] 13  3. Research Objectives There were two main objectives to this thesis work. The first objective was to observe the effect on fines and filler retention when using Raifix as an ATC. Raifix was used in conjunction with a PEO-PFR retention aid system. First pass retention experiments were performed on a mechanical groundwood pulp furnish containing either clay or PCC filler. Laser diffraction and zeta potential experiments were also performed to observe the aggregation behaviour of clay and PCC filler in the presence of Raifix, PEO,. and PFR. These experiments were performed to give further insight into the colloidal interactions which are responsible for the retention offillerin papermaking. The second objective of this thesis was to use Fourier Transform Infrared Spectroscopy in order to observe the molecular interactions between PEO, PFR, and Raifix which are fundamental to the mechanisms behind retention.  14  CHAPTER 2  Experimental Methods  1. Materials 1.1 Anionic Trash Collector (ATC) A cationic starch ATC was supplied by Raisio Chemicals of Vancouver, British Columbia. The commercial name of the ATC is Raifix 120. Raifix 120 has a charge density of 2.8 meq/g and a molecular weight of 0.5 to 1.5 million. It was received in solution and stored in a sealed container at 5°C. It was prepared at low concentrations daily (0.1-1% as received). Various properties of Raifix polymers are discussed in Chapter 1, Section 2.  1.2 Clay Filler A calcined kaolin clay filler was supplied by Englehard Corporation of Iselin, New Jersey. The commercial name of the clay is Ansilex 93. The clay was received in a dry powder form. A slurry of 25% consistency was prepared and mixed continuously to avoid settling. Various properties of Ansilex 93 are given in Table 1.  1.3 Ethylenediaminetetraacetic Acid (EDTA) Analytical grade EDTA was supplied by VWR Scientific Products of West Chester, Pennsylvania. It was received as a 0.01 M solution and stored in a sealed container at room temperature.  1.4 Formaldehyde An analytical grade formaldehyde solution was supplied by BDH Chemicals of Toronto, Ontario. It was received as a solution and stored in a sealed container at room temperature.  15  1.5 Phenol Formaldehyde Resin (PFR) Cofactor A phenol formaldehyde resin cofactor was supplied by Raisio Chemicals of Vancouver, British Columbia. The commercial name of the cofactor is Netbond FRB. The cofactor was received at a consistency of 36%. It was prepared at low concentrations daily (<0.36% wt). The cofactor solution was stored in a sealed container at 5°C.  1.6 Phosphoric Acid .. Analytical grade phosphoric acid was supplied by Aldrich Chemical Company Inc. of Milwaukee, Wisconsin. It was received in crystalline form and prepared as a IM solution. The crystalline form of phosphoric acid was stored in a sealed container in the freezer at all times while the solution was stored in a sealed container at room temperature.  1.7 Poly(diallyl dimethyl ammonium chloride) (PDADMAC) Analytical grade PDADMAC was supplied by Muetek Analytic GmbH of Hamilton, Ontario. It was received as a 0.001 N solution and stored in a sealed container at room temperature.  1.8 Poly(ethene sodium sulfonate) (Pes-Na) Analytical grade Pes-Na was supplied by Muetek Analytic GmbH of Hamilton, Ontario. It was received as a 0.001 N solution and stored in a sealed container at room temperature.  1.9 Polyethylene oxide) (PEO) PEO with an average molecular weight of 7 million was supplied by Raisio Chemicals of Vancouver, British Columbia. The commercial name of the PEO is Netbond FRA. PEO with an average molecular weight of 4 million was supplied by Aldrich Chemical Company Inc. of Milwaukee, Wisconsin. Both products were received in fine powder form. PEO stock solutions 16  were prepared at 0.05% wt and gently mixed for 16 hours at room temperature with minimal exposure to sunlight. The solutions were stored in sealed containers at 5°C with no direct exposure to sunlight. Various properties of PEO are discussed in Chapter 1, Section 1.  1.10  Potassium Chloride (KC1)  Analytical grade KC1 was supplied by Fischer Scientific of Nepean, Ontario. The KC1 was received in dry granular, form and stored in a sealed container at room temperature.  1.11  Precipitated Calcium Carbonate (PCC) Filler  A PCC filler was supplied by Specialty Minerals of Bethlehem, Pennsylvania. The commercial name of the PCC filler is Albafil. The PCC was received in slurry form at 15% consistency. The slurry was mixed continuously to avoid settling. Various Properties of Albafil are given in Table 1. Table 1: Filler properties Ansilex 93  Albafil  Brightness  92.7  96.2  Refractive Index  1.61  1.57  PH*  6.33  9.58  Conductivity* (uS/cm)  1.62  43.4  Zeta Potential* (mV)  -40.4  -13.2  Volume Median Diameter* (um)  2.42  5.26  *Suspended in de-ionized water (0.01%wt)  1.12  Pulp  A mechanical groundwood pulp was supplied by an integrated newsprint mill in British Columbia. The pulp was collected from a sample point just before the blend chest. It was  17  received at a consistency of approximately 4%. The pH of the pulp varied between 5.9 and 6.47, while the conductivity varied between 1.362 S / cm and 2.09 S/ cm. The pulp was stored in a sealed container at 5 °C. A small quantity of formaldehyde was also added as a preservative. Various properties of the pulp are given in Chapter 4, Section 1.  1.13  Sodium Hydroxide  Sodium Hydroxide was supplied by Fischer Scientific of Nepean, Ontario. It was received as a 0.1 M solution and stored at room temperature.  1.14  Water  All water used in experiments was distilled and de-ionized using an Elgastat UHQ (Ultra High Quality) unit. The Elgastat UHQ was supplied by Fischer Scientific of Nepean, Ontario.  2. Instrumentation and Analysis 2.1 Characterization of Materials 2.1.1 Apparatus 2.1.1.1 Brookfield DV-II+ Programmable Viscometer with UL Adapter The Brookfield DV-II+ Programmable Viscometer was used to measure the viscosity of PEO solutions in centipoise (cP). The viscometer was used with the UL Adapter which consists of a precision cylindrical spindle rotating inside an accurately machined tube. The UL Adapter provides extremely accurate viscosity measurements and shear rate determinations. The UL Adapter can accommodate a 17 mL sample volume. The instrument was supplied by CAN-AM Instruments Ltd. of Oakville, Ontario.  18  2.1.1.2 Dynamic Drainage Jar The Dynamic Drainage Jar (DDJ) is a standard instrument which is used to perform first pass retention and fines fractionation experiments (refer to Figure 1). The DDJ is a single screen classifier which is used to simulate the wet end of a paper machine. The DDJ consists of a plastic cylinder with a detachable base. The base contains an air chamber, on top of which a wire mesh is placed. The DDJ is drained from a flow-controlled plastic tube connected to the base. A GlasCol variable speed stirrer simulates the shear in a paper machine. The shaft of the stirrer is 150mm long and carries a three-blade propeller. The blades are circular, with a diameter of 17.5 mm and have a pitch of 30°. The distance between the propeller and the screen is approximately 3 mm. The stirrer is connected to an integrally-wound motor-generator with servo feedback amplifier type motor drive. The stirrer motor maintains 99% of set speed within the range of 50 rpm to 3000 rpm. The direction of stirring is counterclockwise, so that the material is pushed towards the screen. The Dynamic Drainage Jar was supplied by Paper Research Materials Inc. of Gig Harbour, Washington.  2.1.1.3 Kajaani FS-200 Fibre Analyzer The Kajaani FS-200 Fibre Analyzer measures the fibre length distribution, coarseness value and wood species correlation of a pulp suspension. The Kajaani FS-200 was used in this work to determine the fibre length distribution of mechanical groundwood pulps. The instrument was supplied by Valmet Automation Ltd. of Kirkland, Quebec.  2.1.1.4 pH and Conductivity Meters Conductivity measurements were performed using the Orion Model 160 Conductivity Meter. pH measurements were performed using the Metrohm 691 pH Meter. The instruments were supplied by Fischer Scientific Ltd. of Edmonton, Alberta. 19  Figure 1: Dynamic Drainage Jar  2.1.2  Procedure  2.1.2.1 Fibre Length Analysis Fibre length analyses were performed periodically on the pulp samples which were being used for first pass retention experiments. The pulp samples were diluted with de-ionized water to approximately 0.03% consistency. The dilution ratio was adjusted to bring the fibre measurement frequency within the range of 40 to 60 fibres per second. Approximately 500 mL of the diluted pulp suspension was used for each analysis.  20  2.1.2.2 Fines Fractionation Fines fractionation experiments were performed at room temperature using the DDJ. A 500 g mechanical groundwood pulp suspension of 0.5% consistency was prepared. The DDJ stirrer was set at 750 rpm. The suspension was poured into the DDJ and allowed to mix for 30 seconds. The suspension was then drained to a level of 5mm in the DDJ. Once drainage was complete, 500 mL of distilled, de-ionized water were poured into the DDJ and allowed to mix with the retained fibres for 30 seconds. The DDJ was drained again and subsequently refilled with distilled, deionized water. This procedure was repeated until the DDJ filtrate became visually clear (approximately 8 cycles). On the last cycle, the DDJ was completely drained. The retained fibres were removed from the DDJ and weighed into a glass dish. The sample was dried in an oven at 110°C for 8 hours. Once dry, the sample was removed from the oven and placed in a dessicator for 5 minutes before weighing. Once the weight of the retained fibres was known, the percentage of fines in the pulp was calculated. The fines fractionation experiments were performed four times and the average values were reported.  2.1.2.3 PEO Viscosity Measurements The viscosity of PEO solutions was measured using the Brookfield DV-II+ Programmable Viscometer with U L Adapter. The degradation of a PEO solution can be detected by a drop in viscosity [16,21]. Since the viscosity of a PEO solution is directly related to its molecular weight, the high molecular weight PEO solutions were compared with a 4 million molecular weight solution over time to ensure that no degradation had occurred. Since viscosity is also temperature dependent, all measurements were performed at room temperature. Special attention was given to ensure that no bubbles were present in the sample.  21  2.1.2.4 pH and Conductivity Analysis Conductivity and pH measurements were performed on pulp samples at room temperature. The pH probe and the conductivity probe, along with its temperature probe were inserted into the well-mixed pulp suspension and allowed to equilibrate for several seconds before measurements were taken.  2.2 Aggregation of Filler 2.2.1 Apparatus 2.2.1.1 Malvern Mastersizer 2000 with Hydro MU Cell The Malvern Mastersizer 2000 is a laser diffraction particle size analyzer. It was used to determine the size distribution and rate of aggregation of filler particles. The Mastersizer 2000 came equipped with the Hydro MU cell. The Hydro MU cell is used to analyze particles in liquid suspension. The cell is connected to a re-circulation unit. The unit can accommodate a beaker of 600 mL to 1000 mL capacity. The unit also contains a variable speed stirrer (0 rpm to 4000 rpm) and an ultrasonic mixer. The Malvern Mastersizer 2000 and Hydro MU Cell were supplied by Malvern Instruments Inc. of Southborough, Massachusetts. The instrument is shown in Figure 2.  2.2.1.2 Zeta-Meter System 3.0 The Zeta-Meter System 3.0 was used to measure the zeta potential of filler aggregates. The instrument consists of a microscope, a cell, and a power source which applies a potential difference across the cell. The cell handles liquid suspensions. Colloidal particles are tracked manually using a tracking device connected to a computer. The computer translates the speed and direction of the particles into zeta potential. The instrument was supplied by Zeta-Meter Inc. of Staunton, Virginia. The experiments were performed at the Department of Mining and Metallurgy at the University of British Columbia in Vancouver, British Columbia. 22  Figure 2: The Malvern Mastersizer 2000 with Hydro MU Cell (centre)  2.2.2 Procedure 2.2.2.1 Aggregation of Filler Filler aggregation experiments were performed using the Malvern Mastersizer 2000 with Hydro MU cell. A background measurement was performed on 500 mL of de-ionized water. Clay or PCC filler were then added to the water at a consistency of 0.01%. The suspension was mixed at 1250 rpm and re-circulated through the Hydro MU cell at a flow rate of approximately 8.5 mL/s. The measurement time was set at 3 seconds. An irregular particle shape and a multimodal size distribution were assumed. The refractive index of the clay filler was set at 1.61,  23  while that of PCC filler was set at 1.57 (information provided by suppliers). The initial particle size distribution of the filler was measured prior to performing the aggregation experiments. After this, the suspension was removed from the apparatus and the chemicals were added while hand-stirring. The suspension was stirred for 10 seconds between each chemical addition. The suspension was then placed back into the apparatus and measurements were commenced. The volume median diameter was measured every 15 seconds until a maximum was achieved. This is reported as the maximum aggregate size. The rate of aggregation was also determined by dividing the maximum aggregate size by the time required to reach it. Each experiment was repeated three times and the average values were reported.  2.2.2.2 Zeta Potential Analysis Zeta potential measurements were performed using the Zeta-Meter System 3.0. Filler was suspended in de-ionized water at a consistency of 0.01% wt. Raifix was added to the suspension at varying dosages. The sample was poured into a cell which was placed under a microscope and connected to a power source. The speed and direction of the filler aggregates was observed under the microscope while a potential difference was applied. The particles were tracked manually with a tracking device connected to a computer. The computer translated the speed and direction of the filler aggregates into zeta potential. These calculations were based on the electrophoretic mobility of the aggregates. Samples were measured four times and the average values were reported.  24  2.3 Solubility of Precipitated Calcium Carbonate (PCC) in Pulp Suspension 2.3.1 Apparatus 2.3.1.1 pH and Conductivity Meters Refer to section 2.1.1.4  2.3.1.2 Glas-Col Variable Speed Stirrer A Glas-Col variable speed stirrer was used to provide controlled mixing in the PCC solubility experiments. The stirrer is identical to the one used with the DDJ. Refer to section 2.1.1.2 for more information.  2.3.1.3 Mettler DL25 Titrator with DP550 Phototrode The Mettler DL25 Titrator with DP550 Phototrode performs automatic photometric titrations for calcium ions in solution. The instrument was used to determine the calcium ion concentration in PCC filled pulp suspensions. The Mettler DL25 Titrator with DP550 Phototrode was supplied by Fischer Scientific Ltd. of Edmonton, Alberta.  2.3.1.4 Millipore Pressure Filter The Millipore pressure filter was used to filter colloidal material from pulp suspensions. It consists of a stainless steel cylinder with a removable head at each end. The bottom head contains a wire mesh upon which a disposable membrane is placed. The top head contains a pressure valve. When air pressure is applied, the suspension is filtered through the membrane and the filtrate is collected from an outlet valve in the bottom head. The pressure filter and membranes were supplied by Millipore Corporation of Nepean, Ontario.  25  2.3.2 Procedure A suspension consisting of 0.45% wt mechanical groundwood and 0.05% wt PCC filler was prepared. The suspension was stirred at 1000 rpm using the variable speed stirrer. The pH, conductivity, and calcium ion concentration were monitored over a 30 hour period. Experiments were performed at room temperature. Once every hour, 60 mL of suspension were collected and pressure filtered through a 0.22 m membrane. Approximately 30 mL of the filtrate was collected and diluted with de-ionized water to 60 mL. Approximately 0.25 g of hydroxy naphthol blue (calcium ion indicator) was added to the solution. The pH was adjusted to 12.1-12.2 with 0.1 M NaOH. The change of pH was indicated by a colour change from blue to pink. The solution was then automatically titrated back to blue with 0.01 M EDTA using the Mettler DL25 Titrator with DP550 Phototrode. The calcium ion concentration was calculated automatically.  2.4 First Pass Retention 2.4.1 Apparatus 2.4.1.1 Dynamic Drainage Jar Refer to section 2.1.1.2 2.4.1.2 Mettler DL25 Titrator with DP550 Phototrode Refer to section 2.3.1.3 2.4.1.3 Millipore Pressure Filter Refer to section 2.3.1.4  2.4.1.4 Muetek PCD 03 Particle Charge Detector The Muetek PCD 03 is a standard instrument used to measure cationic demand in a mill's process water (refer to Figure 3). It was used in this work to measure the cationic demand of the DDJ filtrate. The Muetek PCD 03 cell consists of a plastic vessel with a piston. The piston 26  connects to an oscillating motor, which makes it move up and down in the cell orifice. The cell can hold up to 10 mL of sample. The Muetek PCD 03 comes equipped with an automatic titrator. The instrument was supplied by Muetek Analytic GmbH of Hamilton, Ontario.  1.4.1.5 Hach 21 OOP Portable Turbidimeter The Hach 21 OOP portable turbidimeter was used to measure the turbidity of the DDJ filtrate supernatant (refer to Figure 3). The Hach 21 OOP measures turbidity in nephelometric turbidity units (NTU). The instrument was supplied by Prairiechem Inc. of Richmond, British Columbia.  Figure 3: Muetek PCD 03 (on the right) and the Hach 21 OOP Turbidimeter (on the left) 27  2.4.2 Procedure 2.4.2.1 Cationic Demand Analysis Cationic demand analyses were performed on the DDJ filtrate. A sample volume of 10 mL was weighed into the Muetek PCD cell. The piston was inserted into the cell and connected to the oscillating motor. The motor switch was turned on and the piston was allowed to oscillate for 30 seconds. The sample was then automatically titrated to the isoelectric point with 0.001 N Poly-DADMAC. For positively charged furnishes, a 0.001 N Pes-Na titrant was used.  2.4.2.2 First Pass Retention A suspension consisting of 0.45% wt mechanical groundwood pulp and 0.05% wt clay or PCC filler was prepared. Approximately 500g of the suspension was weighed into a 600 mL beaker. In experiments where PCC filler was used, the pH of the suspension was adjusted to ~7 with phosphoric acid. This was done in order to conduct experiments at neutral papermaking conditions while inhibiting the dissolution of PCC. The DDJ stirrer was set to 1000 rpm. The suspension was poured into the DDJ and allowed to mix for 10 seconds. The chemicals were added directly into the DDJ while mixing continued. In experiments where Raifix was the first chemical to be added, 20 seconds of mixing was allowed prior to the addition of the other chemicals. This was done to allow enough time for Raifix to thoroughly coagulate the anionic DCS in the suspension. In all other cases, 10 seconds of mixing was allowed between the addition of each chemical. Once the last chemical was added, the suspension was mixed for an additional 5 seconds and drained. The first 40 mL of DDJ filtrate was discarded. The next 100 mL of DDJ filtrate was collected for analysis. In experiments where cationic demand was measured, an extra 10 mL of filtrate was collected and taken for analysis (refer to 2.4.2.1). The filtrate was allowed to settle for 5 minutes after which a turbidity measurement was performed on the supernatant (the entire DDJ filtrate was too turbid to be measured directly). The filtrate 28  was then weighed and pressure filtered at 40 psi through a 0.22 m pore size membrane of known weight. The filter cake and membrane were removed and dried in the oven for 2 hours at 110°C.In cases where calcium ion concentration had to be determined, the filtrate was taken for analysis (refer to section 2.3.2). Once dry, the filter cake and membrane were placed in the dessicator for 5 minutes before weighing. The filter cake was separated from the membrane and placed in a furnace-dried crucible of known weight. The crucible was then placed in the furnace for ashing at 525°C for 2 hours. Once ashing was complete, the crucible was placed in a dessicator for 30 minutes before weighing. First pass retention for fines and filler were calculated using the equation shown in Figure 4. Experiments were repeated four times and the average values were reported.  2.5 Fourier Transform Infrared Spectroscopy 2.5.1 Apparatus 2.5.1.1 Perkin Elmer 1600 FT-IR Spectrophotometer Fourier Transform Infrared (FTIR) analysis was performed using the Perkin Elmer 1600 FTIR Spectrophotometer, equipped with a diffuse-reflectance attachment. The analyses were performed at PAPRICAN in Vancouver, British Columbia.  2.5.2 Procedure FTIR analyses were performed on the following samples: PEO, PFR, PEO-PFR complex, Raifix, and Raifix-PFR complex. Solutions of PEO (0.05% wt), PFR (0.036% wt), and Raifix (1% as received) were prepared. The PFR-PEO complex was prepared at a dry ratio of 0.5:1 respectively. The Raifix-PFR complex was prepared at a dry ratio of 1:1. Samples were prepared by placing 2 g of analytical grade KC1 in a crucible and wetting it with the solution. The sample was vacuum dried for 2 hours at 110°C. Once dry, the sample was re-wetted with solution and 29  First Pass Retention =  ai-bi  *100  For Clay Filler: Fines fi = 1) ai = Total Fines ( g ) ai = wtsuspension ( g ) * Pulp Concentration (wt/wt) * Fines Fraction (wt/wt) bi = Unretained Fines ( g ) = wtfmes m filter cake ( g ) * wt pension ( g ) / w t j nitrate ( g ) SUS  DD  Clay (i = 2) a  2  = Total Clay (g) = wt pension (g) * Clay Concentration (wt/wt) SUS  b = Unretained Clay (g) = wtd 2  ay i n  |  fi ter  ca  ke (g) * wt pension (g)/ wt SUS  DD  j filtrate (g)  Total fi = 3) a  3  = Total SolidSsuspension (wt/wt)  a3 = Pulp Concentration (wt/wt) + Clay Concentration (wt/wt) b  = Total SolidSfiitrate (Wt/wt) = Wtflitercake (g)/ WtoDJ filtrate (g)  3  For PCC Filler: PCC fi = 2^ a  2  = Total PCC (g) = wt spension (g) * (PCC Concentration (wt/wt) SU  - ([Ca ] ++  ension - [ C a ] + +  susp  i ) (mole/L) * 10"  (L/g) * M W c (g/mole))  3  p U  P  PC  b = Unretained PCC (g) = wt c in filter cake (g) * Wtsuspension (g)/ Wt DJ filtrate (g) 2  PC  D  Total fi = 3) a  3  = Total SolidSsuspension (wt/wt) = Pulp Cone, (wt/wt) + PCC Cone, (wt/wt) - ([Ca ] uspension - [ C a ] i ) (mole/L) * l O ' (L/g) * MW c (g/mole)' ++  + +  S  b  3  3  p u  p  PC  = Total SolidSfiitrate (Wt/wt) = Wtflitercake (g)/ W t  Figure 4: Calculation of First Pass Retention  30  D D  J filtrate (g)  placed back in the vacuum oven. This was repeated four times. After the final drying cycle, the sample was removed from the crucible and ground into a fine powder. A background measurement was performed on KC1. Once this was completed, the sample was analyzed. Sixtyfour scans were collected and averaged. An internal computer compared the absorption spectrum of the sample with that of the background KC1 to produce a transmission spectrum which was visually deciphered.  31  CHAPTER 3  Theory  1. Fourier Transform Infrared Spectroscopy Infrared spectroscopy is a technique which is used to determine the molecular structure of inorganic and organic molecules [26,37]. The technique operates by radiating target samples with infrared radiation (4000 - 200 cm"). These wavenumbers correspond to the vibrational 1  region of the infrared spectrum (refer to Figure 1). When target samples absorb this energy, they become excited to a higher energy state. Energy changes occur in the range of 2 to 10 kcal/mole. This energy range corresponds to that of stretching and bending vibrational frequencies of most covalent bonds. The absorption of infrared energy is a quantized process. Only selected frequencies will be absorbed by any given sample. Therefore, only the frequencies which match the natural vibrational frequencies of the molecules present in the sample will be absorbed. Thus, a transmission spectrum which is unique for every sample will be produced. It is important to note that only those bonds which have a dipole moment are capable of absorbing infrared radiation. Symmetric bonds such as H2 or CI2 will not absorb any energy. A general guide to identifying FTIR transmission spectra is shown in Figure 2. The OH stretching frequencies of para- and meta-substituted phenols in the vapour phase appear as a sharp band in the region of 3660-3642 cm". In dilute C C I 4 solution, the v(OH) band 1  of phenol occurs at 3611 cm". For meta- and para-substituted phenols in dilute 1  CCI4,  the  characteristic absorption falls in the region of 3613-3592 cm". When the OH group on the 1  phenol is hydrogen bonded, the stretching frequency is shifted downwards. Generally, the stronger the hydrogen bond, the lower the OH stretching frequency is shifted. When phenolic resins undergo hydrogen bonding in polymeric fashion (refer to Chapter 1, Figure 2), they produce a broad peak which lies between 3400 and 3200 cm' . 1  32  high  -Frequency  low  —  low  Energy  1  $  I I  INFRARED:  VvVAV.E  RADIO  f'Hf Ol.JENUY  No d e a r  : Msg neitc;.. Resonance :  ;  " BLUE  "  " ' REOV  Figure 1: The electromagnetic spectrum [37] F R E Q U E N C Y (cm  4000 0-H  C-H  1SOO  2000  2500  C=C  1  VERY  } 1650  650  1550  « 1  C=N  C=>0  c-o  FEW  C-H  SANDS  c-c  ;' C=C  j  X=C=Y •  5  5.5  6.  6.5:  15.4  WAVELENGTH  Figure 2: Approximate stretching vibration frequencies of various common bonds [37]  2. Muetek PCD 03 Particle Charge Detector The Muetek PCD 03 is a standard instrument which is used to measure the cationic demand (or anionicity) of a mill's process water. Cationic demand is an indication of the amount of anionic dissolved and colloidal substances present in the sample. These have a direct effect on the quality of the paper and the efficiency of the papermaking process. The Muetek PCD 03 operates on the principle that dissolved and colloidal substances will adsorb onto the plastic surfaces of its piston and cell walls under the action of van der Waals forces. Since these 33  substances are negatively charged, they attract oppositely charged counter-ions to their surfaces. When shear is applied to a sample, the counter-ions are removed from the negatively charged surfaces, producing a streaming current which can be measured in mV. The sample is then titrated with an oppositely charged polyelectrolyte of known charge density.  3. Low Angle Laser Light Scattering Low Angle Laser Light Scattering is a standard method which is used to characterize the size distribution of particles within the range of 0.02 to 2000 m [43]. This method is also known as Laser Diffraction. A typical Laser Diffraction instrument contains a He-Ne gas laser (=0. 6 3 m) of high intensity and fixed wavelength. The instrument also contains several light detectors. These usually contain photosensitive silicon. In order for a measurement to be taken, the sample must pass through the path of the laser beam. Dry samples are usually blown through the path of the beam by pressure and collected by vacuum. Wet samples are usually re-circulated through a transparent cell which is placed in the path of the laser beam. When the laser beam passes through the sample, it produces a diffraction pattern. The angle of diffraction is inversely proportional to the particle size. The diffraction pattern is deciphered using the Fraunhofer and Mie theories to obtain a particle size distribution of the sample. The Fraunhofer theory assumes that the particle is much larger than the wavelength of light used to measure it (typically 5). It also assumes that all particle sizes have the same scattering efficiencies and that the particles are opaque discs. These assumptions are inaccurate for most materials. The Mie theory gives a more accurate prediction of the interactions between light and matter. The Mie theory assumes that the particles are spherical and that they transmit as well as reflect light. The Mie theory requires that the refractive indices of the material and medium are known and the absorption part of the refractive index be known or guessed. Both theories can be used in conjunction when analyzing samples. 34  Results and Discussion  CHAPTER 4  1.  Characterization of Materials  1.1 Pulp Characterization Kajaani fibre length analyses were performed periodically on the pulp samples used in experiments. As shown in Figure 1, the fibre length distribution of Sample 1 stayed, relatively constant over a 6 month period. In addition, a second sample, which was obtained from the same mill 6 months after the first, had the same fibre length distribution. This indicates that the pulp used in experiments had a consistent fibre length distribution. Other properties such as pH, conductivity, consistency, and fines fraction were also measured periodically. The data for these measurements are given in Table 1. The pH of the pulp slightly increased over time due to biological activity. Meanwhile, the conductivity, consistency, and fines fraction stayed relatively constant. Sample 2 had a lower conductivity, consistency, and had a higher initial pH and fines fraction than pulp Sample 1. Table 1: Pulp properties Pulp Sample  Date  PH  Conductivity  Consistency  Fines Fraction  (uS/cm)  (% wt)  (% wt)  la)  8/19/98  5.92  2.09  4.68  32.16*  lb)  8/28/98  5.90  2.00  4.24  31.79*  lc)  10/18/98  5.97  2.04  4.54  31.76*  Id)  11/12/98  6.00  2.09  4.69  35.93*  le)  12/1/98  6.02  2.06  4.59  33.90*  If)  1/7/99  6.19  2.04  4.61  48.31**  ig)  2/1/99  6.47  2.07  4.60  49.48**  2 a)  3/3/99  6.19  1.37  3.86  55.85**  2 b)  4/7/99  6.25  1.37  3.77  54.16**  2 c)  5/24/99  6.14  1.36  3.85  55.00**  * 200 mesh screen  ** 70 mesh screen  35  25  I = I Sample 1 (8/17/98) v:mm Sample 1 (2/25/99) ESMSS Sample 2 (2/25/99)  20 cu cn c ru  15  al c  10  0  A  n  o  fe  0  a  o*o  fc*  O A *  f c/s.'/'" ' " ^ f \ ' 3 " oc ,i .>^' \ r ^ ? > -  Fibre Length (mm) Figure 1: Kajaani fibre length analysis (295 K)  1.2 Poly(ethylene oxide) Characterization The viscosity of PEO solutions was measured periodically to ensure that no degradation had occurred. Since viscosity is directly related to molecular weight, the viscosity of the high molecular weight PEO solutions was compared with that of a lower molecular weight PEO solution [16,21]. As shown in Figure 2, the viscosity of the high molecular weight PEO solution was greater than that of the lower molecular weight PEO solution. In addition, the viscosity of the high molecular weight PEO solution fluctuated over time, whereas the viscosity of the lower molecular weight PEO solution stayed relatively constant. This could be due to an increased sensitivity to temperature, shear, and other environmental factors at high molecular weights [8,21]. Despite fluctuations, the high molecular weight PEO solutions maintained a viscosity which was roughly 15% greater than that of the lower molecular weight PEO solutions. This indicated that the PEO used in experiments was well preserved and maintained its flocculation ability. 36  3.2  - * — 1 (7 million) —o- 2 (7 million) —r - 3 (4 million) —v— 4 (7 million) 5 (7 million)  3.0 g  2.8  2.6 o .2 2.4 > t  2.2 2.0 1\  V  Date Figure 2: Viscosity of PEO solutions over time (295 K, 60 rpm)  2. Aggregation of Filler 2.1 Clay Filler Experiments were performed to observe the effect of various paper chemicals on the aggregation of clay filler in aqueous suspension. Figure 3 demonstrates the effect of PEO dosage on clay aggregation. PEO was found to be ineffective at aggregating the clay. Only at a PEO dosage of 5000 g/T (grams of dry PEO per tonne of dry clay) was a marginal amount of aggregation observed. At this dosage, the rate of aggregation and maximum aggregate size were 0.0018  m/s and 3.5  m respectively. Higher PEO dosages did not produce increased  aggregation. Therefore, it seems that PEO adsorbs onto clay and some aggregation occurs. However, the extent of aggregation is minimal. This is probably due to the inability of the PEO chain to overcome the electrostatic double layer between the clay particles. This confirms previous work done in this area [57]. Figures 4 and 5 demonstrate the effect of PEO and PFR dosage on clay aggregation. The PEO dosage was varied between 0 g/T and 5000 g/T, while the PFR/PEO ratio was set at 0.5. 37  . •  4.0 E  3.5  • J  <u M  In  a, 3.0 (D CT OJ CT  <CT  2.5  1  ^  0  o oooOOooooo 8  0 0 0  "  r °  >  2.0 0  200  400  600  800  1000  a b c 1200  Time (s) Figure 3: The aggregation of clay with PEO (PEO = 5000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33) The rate of aggregation and aggregate size increased linearly between 500 g/T and 5000 g/T of PEO (250 g/T and 2500 g/T of PFR). At 500 g/T of PEO (250 g/T of PFR), almost no aggregation had occurred. Aggregation was only observed at and above lOOOg/T of PEO (500 g/T of PFR). Figures 6 and 7 demonstrate the effect of the PFR/PEO ratio on clay aggregation. A PEO dosage of 5000 g/T was chosen in order to obtain a clear comparison between the various PFR/PEO ratios. As previously shown, PEO was not effective at aggregating clay when used alone. However, when 2500 g/T of PFR was added prior to PEO (PFR/PEO = 0.5), the rate of aggregation increased from 0.0018 pm/s to 0.32 pm/s and the aggregate size increased from 3.5 pm to 140 um. The maximum was achieved at a PFR/PEO ratio of 1.5. At this point, the rate of aggregation and aggregate size were 1.5 pm/s and 279 pm respectively. Beyond this point, the rate of aggregation and aggregate size decreased. The reasons for this are not known. However, it appears that certain PEO-PFR complexes are more effective at aggregating clay than others. This phenomenon will be further examined in Section 4. 38  CO  0.35  I 0.30 0.25 QJ CO  Ql  C  0.20 0.15  o  0.10  cn cn <  0.05 0.00 0  1000 2000 3000 4000 5000 PEO Dosage (g/T)  Figure 4: The effect of PEO and PFR dosage on the rate of aggregation of clay (PFR/PEO = 0.5, 295 K, 1250 rpm, Conductivity = 1.62 uS/cm, pH = 6.33)  CO  160  E 140 cu N  120  CO  & Si 100  9  80  at  60  E  40  E  20  "8  0 1000  2000 3000 4000 5000  PEO Dosage (g/T)  Figure 5: The effect of PEO and PFR dosage on the aggregate size of clay (PFR/PEO = 0.5, 295 K, 1250 rpm, Conductivity = 1.62 uS/cm, pH = 6.33) 39  to  2.0  1.5  iB  c 1.0 o ro  §? 0.5 0.0 0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 6: The effect of the PFR/PEO ratio on the rate of aggregation of clay (PEO = 5000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33)  300  E  «= .L ' 250 CU N  to  B  200  ro  ? 150 a 100 1  E §E x  50 t  0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 7: The effect of the PFR/PEO ratio on the aggregate size of clay (PEO = 5000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33) 40  Figures 8 and 9 demonstrate the effect of Raifix dosage on clay aggregation. As shown, Raifix was capable of aggregating clay on its own. At 10000 g/T of Raifix, the rate of aggregation and aggregate size were 0.14 m/s and 18 m respectively. Presumably, the positively-charged Raifix aggregated the negatively-charged clay via electrostatic interactions. There is also evidence that hydrogen bonding interactions contribute to aggregation. As shown in Figure 10, the iso-electric point occurred at a Raifix dosage of approximately 20000 g/T. At 35000 g/T of Raifix, the clay aggregates had a zeta potential of +19 mV. Since Raifix has no electrostatic affinity for the clay beyond the iso-electric point, it must adsorb onto the clay by other means. The most likely explanation is that hydrogen bonding interactions exist between the hydroxyl groups on Raifix and the SiOH groups on the clay surface. Therefore, Raifix has the ability to adsorb onto the clay surface via hydrogen bonding and reverse the particle charge to positive. It is also interesting to note that the maximum aggregate size achieved with Raifix was much smaller than that achieved with PEO. This is because Raifix is a low molecular weight patch flocculant, whereas PEO is a high molecular weight macroflocculant [13]. As a result, the aggregates formed by Raifix are smaller because they are weaker and more susceptible to shear. The effect of shear on filler aggregation with Raifix will be further examined in Section 2.2. Subsequent experiments were performed using Raifix in conjunction with PEO and PFR. The first objective was to determine an optimal order of addition. The PEO, PFR, and Raifix dosages were set at 1000 g/T, 500 g/T, and 10000 g/T respectively. As shown in Figures 11 and 12, the optimal order of addition was: Raifix, PFR, PEO. This gave a rate of aggregation and aggregate size of 0.2 m/s and 61 m respectively. In this sequence, the Raifix was adsorbed onto the clay surface, thus lowering the electrostatic double layer. Next, the PFR was added to the suspension, some of which was adsorbed onto the clay, thus acting as an anchor point. Finally, the PEO was added to flocculate the clay. The second best order of addition was: PFR, PEO, Raifix. This gave a rate of aggregation and aggregate size of 0.17 mJ s and 58 m. This was followed by: 41  0.16  in  0.14 0.12  CU 4—>  S c g  *4->  0.10 0.08 0.06  ro cn 0.04  cn cn <  0.02 0.00 2000 4000 6000 8000 10000 Raifix Dosage (g/T)  Figure 8: The effect of Raifix dosage on the rate of aggregation of clay (295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33)  20 ~E 18 CU 16 N lo 14 Bro 12 10 ? cn 8 cn < 6 E 4 E x ro 2 0 2000 4000 6000 8000 10000 Raifix Dosage (g/T)  Figure 9: The effect of Raifix dosage on the aggregate size of clay (295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33) 42  30 *s  > E  Is  20 10 0  c -10 cu 4—> o -20  Q_  S3 -30 f cu  M  -40 -50  0  10000  20000  30000  Raifix Dosage (g/T)  Figure 10: The effect of Raifix on the zeta potential of clay aggregates (Clay = 0.01% wt, 295 K, 1250 rpm, Conductivity = 1.62 uS/cm, pH = 6.33)  to |  0.25 0.20  cu  ro 0.15 cL c o 0.10 4-> ro cn cu £ 0.05 cn cn < 4-1  0.00 1,2,3  2,3,1  1,3,2  3,2,1  Order of Addition Figure 11: The effect of order of addition on the rate of aggregation of clay (Raifix (1) = 10000 g/T, PFR (2) = 500 g/T, PEO (3) = 1000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 uS/cm, pH = 6.33) 43  65 cu 60 N  lo  & 55 ro  ? 50 cn E E 45 x (O  40  1,2,3  2,3,1  1,3,2  3,2,1  Order of Addition Figure 12: The effect of order of addition on the aggregate size of clay (Raifix (1) = 10000 g/T, PFR (2) = 500 g/T, PEO (3) = 1000 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33)  Raifix, PEO, PFR (0.21 pm/s and 52 pm) and PEO, PFR, Raifix (0.14 pm/s and 46 pm). Once an optimal order of addition was established, the effect of Raifix dosage on clay aggregation could be observed. A PEO dosage of 1000 g/T and a PFR dosage of 500 g/T were chosen based on previous experiments. The Raifix dosage was varied between 0 g/T and 40000 g/T. As shown in Figures 13 and 14, the rate of aggregation and aggregate size were dramatically increased by adding Raifix prior to the PFR and PEO. When no Raifix was added, the rate of aggregation and aggregate size were 0.026 pm/s and 26 pm respectively. When Raifix was added prior to the PFR and PEO, the rate of aggregation and aggregate size increased by as much as 0.29 pm/s and 64 pm respectively. This was achieved at a Raifix dosage of 20000 g/T, which coincides with the iso-electric point. When Raifix dosage was further increased, the aggregate size decreased. This was due to the charge reversal of the clay aggregates (refer to Figure 10), which has an adverse effect on aggregation. 44  CO  0.35  I 0.30 0.25  B  8.0.20 C O  0.15  ro cn  0.10  cn cn <  0.05  4->  0.00 10000  20000  30000  40000  Raifix Dosage (g/T)  Figure 13: The effect of Raifix dosage on the rate of aggregation of clay (PEO = 1000 g/T, PFR = 500 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33)  70 cu N CO  60  & 50 ro  g  40  E E x ro  30 20 10000  20000  30000  40000  Raifix Dosage (g/T)  Figure 14: The effect of Raifix dosage on the aggregate size of clay (PEO = 1000 g/T, PFR = 500 g/T, 295 K, 1250 rpm, Conductivity = 1.62 pS/cm, pH = 6.33) 45  2.2 Precipitated Calcium Carbonate (PCC) Filler Experiments were performed to observe the effect of various paper chemicals on the aggregation of PCC filler in aqueous suspension. Figures 15 and 16 demonstrate the effect of PEO dosage on PCC aggregation. As shown, PEO was capable of aggregating the PCC filler on its own. At 500 g/T of PEO, the rate of aggregation and aggregate size were 0.16 m/s and 46 m respectively. However, when the PEO dosage was increased to 1000 g/T, the rate of aggregation and aggregate size dropped to 0.06 m/ s and 23 m respectively. This is possibly due to a steric hindrance effect, whereby the particle surfaces become excessively covered with PEO and are unable to aggregate. Figures 17 and 18 demonstrate the effect of varying the PFR/PEO ratio on PCC aggregation. The PEO dosage was set at 100 g/T, while the PFR/PEO ratio was varied between 0 and 2. When no PFR was added, the rate of aggregation and aggregate size were 0.08 m/s  and 36 m  respectively. However, when 50 g/T of PFR was added prior to the PEO (PFR/PEO = 0.5), the rate of aggregation and aggregate size jumped to 0.17 ml s and 56 m respectively. These continued to increase as the PFR/PEO ratio was increased. At a PFR/PEO ratio of 1, the rate of aggregation and aggregate size were 0.18 m/s and 59 m respectively. These remained relatively unchanged up to a ratio of 2. Once again, a difference in aggregation was observed for each PFR/PEO ratio. Figures 19 and 20 demonstrate the effect of Raifix dosage on PCC aggregation. Raifix was capable of aggregating PCC on its own. The maximum rate of aggregation and aggregate size achieved were 0.14 m/s and 20 m respectively. These were achieved at a Raifix dosage of 10000 g/T. Unlike clay, PCC aggregation occurred via electrostatic interactions only. This is demonstrated in Figure 21, which plots the zeta potential of the PCC aggregates as a function of Raifix dosage. As shown, the zeta potential increased as Raifix dosage was increased. The isoelectric point occurred at a Raifix dosage of approximately 10000 g/T. At higher Raifix dosages, 46  the zeta potential remained neutral. In contrast, Raifix was capable of adsorbing onto the clay (presumably by hydrogen bonding interactions) even after the iso-electric point had been reached, thus reversing its charge to positive. The effect of shear on PCC aggregation was also examined. As shown in Figures 19 and 20, there are two points plotted at a Raifix dosage of 10000 g/T. The bottom point was measured at a stir rate of 1250 rpm and the upper point at a stir rate of 800 rpm. At 1250 rpm, the rate of aggregation and aggregate size were 0.14 prn/s and 20 um respectively. When the stir rate was decreased to 800 rpm, the rate of aggregation and aggregate size increased to 0.15 um/s and 34 um respectively. Therefore, aggregate growth with Raifix was limited by shear. In addition, the aggregates could be broken by increasing the stir rate, and subsequently reformed by decreasing the stir rate. This is a common characteristic of patchflocculationand coagulation (refer to Chapter 1, Section 2).  co E  & ro  0.20 0.15 0.10  CO  j? 0.05 cn cn <  0.00 0  500  1000  1500  PEO Dosage (g/T)  Figure 15: The effect of PEO dosage on the rate of aggregation of PCC (295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  47  50 45 cu 40 N In 35 cu 30 25 20 E u 15 E '13 10 5 0  500  1000  1500  PEO Dosage (g/T)  Figure 16: The effect of PEO dosage on the aggregate size of PCC (295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  CO  0.20  E  ZL CL)  -t—>  0.15  C  o  4-1  ro cn CJ i_ cn cn <  0.10  0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 17: The effect of the PFR/PEO ratio on the rate of aggregation of PCC (PEO = lOOg/T, 295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58) 48  65 cu N  lo ro  60 55 50  ? 45 cn 40 E 35 Z3  E x ro  30  2  0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 18: The effect of the PFR/PEO ratio on the aggregate size of PCC (PEO = lOOg/T, 295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  s/wri) <D  0.15  0.10  Aggi*egat  c o  0.05  0.00 0  2500  5000  7500  10000  Raifix Dosage (g/T) Figure 19: The effect of Raifix dosage on the rate of aggregation of PCC (295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58) 49  E n. cu  * to N  40  800 rpm •  30  B  ro  ff Ol Ol  20  < E 10 E x  •  i  i • •  ro  0 0  2500, 5000  7500  10000  Raifix Dosage (g/T)  Figure 20: The effect of Raifix dosage on the aggregate size of PCC (295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  10 5  > E  0  75 4-»  -5  c cu  to Q_  •10  M  _  JS cu  1  5  •20 5000  10000  15000  20000  Raifix Dosage (g/T) Figure 21: The effect of Raifix on the zeta potential of PCC aggregates (PCC = 0.01% wt, 295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58) 50  Subsequent experiments were performed to observe the effect of adding Raifix prior to PFR and PEO (refer to Figures 22 and 23). A PEO dosage of 100 g/T and a PFR dosage of 50 g/T were chosen based on previous experiments. The Raifix dosage was varied between 0 g/T and 5000 g/T. In contrast to the results obtained in the clay experiments, Raifix had a detrimental effect on the aggregation of PCC. When no Raifix was added, the maximum aggregate size achieved was 56 pm. This stayed relatively unchanged up to a dosage of 100 g/T. Beyond this point, the aggregate size decreased as Raifix dosage was increased. At a Raifix dosage of 5000 g/T, the aggregate size was 34 pm. Meanwhile, the rate of aggregation stayed relatively constant. These results were surprising since both Raifix and the PEO-PFR complex were individually capable of aggregating PCC. However, when they are used together, aggregation is adversely affected. This will be further examined in Section 4.  _ 0.25  1 0.20 QJ  S. °-  I  15  0.10  cn  go.05 cn cn <  0.00  M M  0  "T"  100  1  I  I I I I IT"  1000  -1  1—I  I I  1I  10000  Raifix Dosage (g/T) Figure 22: The effect of Raifix dosage on the rate of aggregation of PCC (PEO = 100 g/T, PFR = 50 g/T, 295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  51  70 65 cu N  lo  60  & 55 to  ff 50 Ol Ol 45  < E 40 Z3  E 35 x ro  30  -7 /  0  "T"  ' T ' T  I I I I I'l  I  I  I  1000  100  I  I I I I  10000  Raifix Dosage (g/T) Figure 23: The effect of Raifix dosage on the aggregate size of PCC (PEO = 100 g/T, PFR = 50 g/T, 295 K, 1250 rpm, Conductivity = 43.4 pS/cm, pH = 9.58)  3. Solubility of Precipitated Calcium Carbonate (PCC) in Pulp Suspension Experiments were performed to observe the dynamic behaviour of PCC in a pulp suspension. The results of these experiments are shown in Figures 24 to 26. Figure 24 shows the conductivity of the PCCfilledpulp suspension as a function of time. The initial conductivity of the suspension was 240 pS/cm. The conductivity rose gradually over time until an equilibrium of approximately 320 pS/cm was reached. An increase in conductivity indicates an increase in calcium ion concentration. This is confirmed in Figure 25, which shows the calcium ion concentration increasing over time. The initial calcium ion concentration was approximately 2.8E-4 M. This rose gradually until it reached an equilibrium concentration of approximately 6.8E-4 M. Figure 26 shows the change in pH over time. The initial pH was approximately 8.3. After an initial rise, the pH dropped to approximately 7.5. Since PCC dissolution is inversely related to pFL this confirms the trends seen in conductivity and calcium ion concentration. An  52  equilibrium in conductivity, calcium ion concentration and pH was reached after approximately 15 hours.  340  f C/D  320 300  -crt>-  ••|* 280 "§ 260 t  Q 240 t  Experiment 1 Experiment 2  o  220 0  5  10  15  20  25  30  35  Time (hours) Figure 24: The conductivity of the PCC fdled pulp suspension over time (295 K, 1000 rpm)  8e-4 7e-4  8 6e-4 o  J L 5e-4  + 4e-4 m  U  "  3e-4  o i  2e-4  Experiment 1 Experiment 2  0  i  i  5  10  15  i  20  25  30  35  Time (hours) Figure 25: [Ca ] of the PCCfilledpulp suspension over time (295 K, 1000 rpm) ++  53  9 6  o  Experiment 1 Experiment 2  .p„.  o  o  oo  o  7 0  5  10  15 20  25  30 35  Time (hours) Figure 26: pH of the PCC filled pulp suspension over time (295 K, 1000 rpm)  4. First Pass Retention 4.1 Clay Filler First pass retention experiments were performed to observe the retention performance of various papermaking chemicals. Experiments were performed on a clay filled mechanical groundwood pulp suspension using a Dynamic Drainage Jar (DDJ) with a 200 mesh screen. Figure 27 demonstrates the effect of PEO dosage on first pass retention. The PEO dosage was varied between 0 g/T and 200 g/T (grams of dry PEO per tonne of dry fibre andfiller),while keeping the PFR/PEO ratio constant at 0.5. When no chemicals were added, the retention of fines and clay were 43% and 9% respectively. At 50 g/T of PEO (25 g/T of PFR), the retention of fines and clay increased to 59% and 53% respectively. The retention continued to increase up to a dosage of 150 g/T of PEO (75 g/T of PFR), where the fines and clay retention were 85% and 90% respectively. These experiments were repeated using a PFR/PEO ratio of 2 (refer to Figure 28). Despite the four-fold increase in the PFR/PEO ratio, the results were very similar to those obtained with a ratio of 0.5. The maximum total retention was achieved at a PEO dosage of 54  C  o 4—»  QJ  4—>  QJ  CO CO  fU CL 4—>  to  100 90 80 70 60 50 40 30 20 10 0  • ...A...  • Q  Q  Fines Clay Total 0  50  100  150  200  PEO Dosage (g/T)  Figure 27: The effect of PEO and PFR dosage on first pass retention (1000 rpm, 295 K, PFR/PEO=0.5, 200 mesh screen, Conductivity = 262-263 S/ cm, pH = 6.33 -7)  100 ^5 90 80 C o 70 c 60 QJ QJ 50 40 to to ro 30 Q_ 20 CO 10 0  • • - -  - -  4-J  9  4-J  •  ,  • •  o  \  (—i  • ° *  4-»  0  50  100  150  Fines Clay Total 200  PEO Dosage (g/T)  Figure 28: The effect of PEO and PFR dosage on first pass retention (1000 rpm, 295 K, PFR/PEO = 2, 200 mesh screen, Conductivity = 262-266 S/ c m, pH = 6.33-7) 55  200 g/T and a PFR dosage of 400 g/T. At this point, the fines and clay retention were 89% and 87% respectively. In both sets of experiments, a limit in retention was reached at approximately 200 g/T of PEO. In this case, the retention was limited by the mesh size and the DDJ stir rate. Figure 29 demonstrates the effect of varying the PFR/PEO ratio on first pass retention. The PFR/PEO dosage was varied between 0 and 2 while keeping the PEO dosage constant at 50 g/T. When no PFR was added, the fines and clay retention were 49% and 42% respectively. At a PFR/PEO ratio of 0.5, the fines and clay retention increased to 59% and 53% respectively. At higher PFR/PEO ratios, the fines and clay retention stayed relatively constant. It was difficult to distinguish a difference in retention between the various PFR/PEO ratios due to the low polymer dosage. Therefore, these experiments were repeated using an increased PEO dosage of 100 g/T. As shown in Figure 30, when no PFR was added, the fines and clay retention were 59% and 57% respectively. When 50 g/T of PFR was added prior to the PEO (PFR/PEO = 0.5), the fines and clay retention increased to 73% and 80% respectively. The maximum total retention was achieved at a PFR/PEO ratio of 1. At this point, the fines and clay retention were both 82%. Beyond this point, the retention decreased. These experiments were repeated again, this time using a PEO dosage of 150 g/T. As shown in Figure 31, when no PFR was added, the fines and clay retention were 72% and 75% respectively. At a PFR/PEO ratio of 0.5, the fines and clay retention increased to 84% and 90% respectively. Beyond this point, the retention decreased as the PFR/PEO ratio was increased. Subsequent experiments were performed using a 70 mesh.screen. The wider mesh size was used to perform more stringent tests for retention. As shown in Figure 32, the PFR/PEO ratio was varied between 0 and 2 while keeping the PEO dosage constant at 100 g/T. When no PFR was added, the fines and clay retention were both 62%. When 50 g/T of PFR was added prior to the PEO (PFR/PEO = 0.5), the fines and clay retention increased to 69% and 75% respectively. The maximum total retention was achieved at a PFR/PEO ratio of 1, beyond which the retention 56  100 90 80 c o 70 4—1 c 60 <D 50 CD al 40 to to 30 ro CL 20 4—1 to 10 I— u_ 0  •  •  V  • 5  "  m  •  •  •  •  ... n  §  Fines Clay  O  •  0.0  0.5  1.0  Total  1.5  2.0  PFR/PEO  Figure 29: The effect of the PFR/PEO ratio onfirstpass retention (PEO = 50 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 269 S/ cm, pH = 6.33 - 7)  100 6  s  C o 4—1  c CD  4-J  QJ  Cd to to ro  90  v  7L.  80  m  ~  —  ^  ,.„  J  i  70  CO  _  {  60  • ° -  50 40 0.0  0.5  '  ^  »  i T  CL 4-1  "  1.0  1.5  Fines Clay Total 2.0  PFR/PEO  Figure 30: The effect of the PFR/PEO ratio onfirstpass retention (PEO = 100 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 269 S/ cm, pH = 6.76 - 7) 57  6  s  c o c CU  4-1  4-1  CL)  to to ru o_ 4-»  to  0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 31: The effect of the PFR/PEO ratio on first pass retention (PEO =150 g/T, 200 mesh screen, 295 K, 1000 rpm, Conductivity = 262 - 266 S/ c m, pH = 6.4 - 6.93)  100 ^  c  o  I  90 *  cu  70  to  18 Q_ to u_  •  80  6  0  _  }  _i . . J5_  - -I  -  40 0.5  •  • ° -  50 0.0  *  1.0  Fines Clay Total  1.5  2.0  PFR/PEO  Figure 32: The effect of the PFR/PEO ratio on first pass retention (PEO = 100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity =244 S/c m, pH = 7. 58  100 ^5  c o  4-1  c CD CD CO  to ro  CL  4—»  CO  0.0  0.5  1.0  1.5  2.0  PFR/PEO  Figure 33: The effect of the PFR/PEO ratio on first pass retention (PEO = 150 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 244 S/c m, pH = 7.02)  decreased. These experiments were repeated using an increased PEO dosage of 150 g/T. As shown in Figure 33, when no PFR was added, the fines and clay retention were 69% and 71% respectively. When 50 g/T of PFR was added prior to PEO (PFR/PEO = 0.5), the fines and clay retention were 80% and 78% respectively. Once again, the maximum total retention was achieved at a PFR/PEO ratio of 1, beyond which retention decreased. Figures 30 to 33 demonstrate the effect of varying the PFR/PEO ratio on fines and clay retention. As shown in these figures, the retention of fines and clay varied according to the PFR/PEO ratio which was used. Retention increased with increasing PFR/PEO ratio until a maximum was achieved. In most cases, the maximum total retention was achieved at a PFR/PEO ratio of 1. In all cases, the retention decreased beyond the maximum. The same trend was observed in the clay aggregation experiments (refer to Chapter 4, Section 2.1). Since aggregate size is directly related to retention [46], the results of the two experiments can be compared. In 59  the clay aggregation experiments the maximum aggregate size was achieved at a PFR/PEO ratio of 1.5. This was 50% higher than in thefirstpass retention experiments. The difference can be attributed to the presence of natural cofactors in the pulp suspension. These are usually lignin derivatives which interact with PEO. Since the clay suspension did not contain natural cofactors, more synthetic cofactor had to be added to achieve a maximum aggregate size. This also explains why PEO is capable of improving retention when used alone. What is less clear is why certain PFR/PEO ratios produce larger aggregates (or higher retention) than others. It is possible that certain PFR/PEO ratios produce stronger floes than others. This possibility was investigated, and the results are shown in Figures 34 to 36. As shown, the mixing time was varied between 5 and 2  30 seconds. Three different PFR/PEO ratios were tested (0, 1, and 2). At a mixing time of 5 seconds, the 1:1 (PFR:PEO) complex gave a fines and clay retention of 73% and 71% respectively. Meanwhile, the 2:1 complex gave afinesand clay retention of 68% and 65% respectively. The 0:1 complex produced the lowest result withfinesand clay retention both at 62%. At a mixing time of 10 seconds, the 1:1 and 2:1 complexes retained almost the same amount offinesand clay, while the 0:1 complex retained far less. Since a difference in retention between the 1:1 and 2:1 complexes was not observed at mixing times above 5 seconds, the experiments were inconclusive. Therefore, if there is a strength difference between the 1:1 and 2:1 complex, it is only visible at mixing times less than 10 seconds. Meanwhile, these experiments demonstrated the adverse effect of shear on retention. When the mixing time was increased to 10 seconds, the 1:1 and 2:1 complexes gave a lower total retention than the 0:1 complex at 5 seconds mixing time. When the mixing time was increased further, thefinesand clay retention continued to decrease.  2  Defined as the amount of mixing time between the last chemical addition and drainage. 60  80 c> C  i  65  4->  to  u_  f  i  c£ 60  to to ro Q_  *  i  1'  £Z CU 4-1 cu  PFR/PEO = 0 PFR/PEO = 1 PFR/PEO = 2  0  o 70  '1 _l  •  75  55  i Q  50  •  0  45 0  10  15  20 25  30  35  Mixing Time (s)  Figure 34: The effect of mixing time on fines retention (PEO =100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02)  80 c> C  •  70  o r  o 60 4-> C  cu  •  t  i  50  4->  cu to to ro Q_ 4-J  to  PFR/PEO = 0 PFR/PEO = 1 PFR/PEO = 2  i •  40 j  30  „  „ „  m  •  20 0  10  15  20  f t  25  30 35  Mixing Time (s)  Figure 35: The effect of mixing time on clay retention (PEO =100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02) 61  ltion (  c  90  -I  • ° *  85 80  PFR/PEO = 0 PFR/PEO = 1 PFR/PEO = 2  QJ  _1  1 *1  First Pass  QJ  75  ¥  70  _o.  _  65 60 0  5  0  15  20  25  30  35  Mixing Time (s)  Figure 36: The effect of mixing time on total retention (PEO =100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 204 - 244 S / cm, pH = 6.97 - 7.02)  Subsequent experiments were performed to observe the effect of using Raifix in conjunction with PEO and PFR. The first objective was to determine an optimal order of addition. PEO, PFR, and Raifix were added at 100 g/T, 50 g/T, and 1000 g/T respectively. In papermaking applications, the ATC (i.e. Raifix) is usually added prior to the PEO and cofactor. This is done in order to fix the anionic trash onto the fibres and thus improve the retention performance of the PEO-cofactor complex. In addition, the cofactor is usually added prior to the PEO so it can adsorb onto fibre and filler surfaces and act as an anchor point [59, 65]. The results shown in Figure 37 confirm these practices. It was found that the optimal order of addition was: Raifix, PFR, PEO. This gave a fines and clay retention of 63% and 70% respectively. The second best order of addition was: PFR, PEO, Raifix. This gave a fines and clay retention 58% and 54% respectively. This was followed by: Raifix, PEO, PFR and PEO, PFR, Raifix. The worst results were obtained when PEO was added early to the system. As shown previously, retention is 62  adversely affected by shear. In this case, when the flocculant (PEO) was added early to the system, the floes were subjected to additional shear. This led to a lower fines and clay retention. These results confirm those obtained in the clay aggregation experiments. However, the results of the clay aggregation experiments suggest that there may also be a kinetic advantage to the sequence: Raifix, PFR, PEO. This is because the aggregates were exposed to the same amount of shear in each sequence.  1-2-3 2-3-1 1-3-2 3-2-1 '  i Fines Clay sssssssssa Total  Figure 37: The effect of the order of addition on first pass retention (Raifix (1) = 1000 g/T, PFR (2) = 50 g/T, PEO (3) = 100 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S /cm, pH = 7.18)  63  Experiments were performed to observe the effect of Raifix on the cationic demand of the DDJ filtrate. The Raifix dosage was varied between 0 g/T and 50000g/T. As shown in Figure 38, the cationic demand of the DDJ filtrate decreased as the Raifix dosage was increased. The isoelectric point occurred at approximately 36000 g/T of Raifix. At higher Raifix dosages, the DDJ filtrate became positively charged. Once again, this demonstrated Raifix's ability to adsorb onto colloid surfaces via hydrogen bonding and reverse the charge to positive. Finally, experiments were performed to observe the effect of Raifix dosage on first pass retention. The Raifix dosage was varied between 0 g/T and 3000 g/T, while PEO and PFR were kept constant at 100 g/T and 50 g/T respectively. As shown in Figure 39, when no Raifix was added, the fines and clay retention were 56% and 48% respectively. However, when only 50 g/T of Raifix was added prior to the PFR and PEO, the fines and clay retention jumped to 63% and 62% respectively. The maximum retention was achieved at 100 g/T of Raifix. At this point, the fines and clay retention were 66% and 63% respectively. These remained relatively unchanged at higher Raifix dosages due to the retention limitations of the DDJ. The cationic demand and turbidity of the DDJ filtrate were also measured (refer to Figures 40 and 41). The cationic demand decreased from -97 e q/L to -69 e q/L as the Raifix dosage was increased from 0 g/T to 3000 g/T. The turbidity also decreased from 172 NTU to 103 NTU within this range of dosages. These results indicate that Raifix coagulated the anionic DCS present in the pulp suspension and attached them onto the fibres. These were subsequently flocculated by the PEOPFR complex, resulting in a higher total retention, with a lower cationic demand and turbidity in the DDJ filtrate.  64  60 40  cr 1>  20  ZL  0  TJ C  -20  ru  -40  E cu Q y  -60 -80 •100  g  •120  4->  ro U  DDJ Filtrate  •140 10000  20000  30000  40000  50000  Raifix Dosage (g/T)  Figure 38: The effect of Raifix dosage on cationic demand (70 mesh screen, 295 K, 1000 rpm, Conductivity = 244 - 246 pS/cm, pH = 7.02 - 7.18)  90  y/  i  1  c>  C  *  +  »  w  *  o £  i  80  70  v) 6 0  • ° -  CO  ro CL ^ 50 to  Fines Clay Total  40  0  50 100  1000  10000  Raifix Dosage (g/T)  Figure 39: The effect of Raifix dosage onfirstpass retention (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 pS/cm, pH =7.18) 65  cr QJ ^—^  C  E  QJ Q u 'c O 4-1  ro U  -65 i -70 -75 -80 -85 -90 -95 -100 -105  V/-  -  DDJ Filtrate  0  50 100  1000  10000  Raifix Dosage (g/T)  Figure 40: The effect of Raifix dosage on cationic demand (PEO =100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S/ cm, pH = 7.18)  180  0 500 1000 1500 2000 2500 3000 3500 Raifix Dosage (g/T)  Figure 41: The effect of Raifix dosage on turbidity (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 246 S / cm, pH = 7.18) 66  4.2 Precipitated Calcium Carbonate (PCC) Filler First pass retention experiments were performed on a PCCfilledmechanical groundwood pulp suspension. A DDJ with a 70 mesh screen was used in these experiments. A PEO dosage of 100 g/T and a PFR dosage of 50 g/T were chosen based onfilleraggregation experiments (refer to Section 2). The Raifix dosage was varied between 0 g/T and 5000 g/T. The chemicals were added in the sequence: Raifix, PFR, PEO. In contrast to the results obtained with the clay filler, the retention of PCC was adversely affected by Raifix. As shown in Figure 42, when no chemicals were added, thefinesand PCC retention were 45% and 6% respectively. At 100 g/T of PEO and 50 g/T of PFR, thefinesand PCC retention were 67% and 60% respectively. As Raifix dosage was increased, retention gradually decreased. At a Raifix dosage of 5000 g/T, the retention offinesand PCC dropped to 59% and 45% respectively. The cationic demand and turbidity of the DDJfiltratewere also measured. As shown in Figure 43, the cationic demand decreased from -114 eq/L to -68 e q/L as the Raifix dosage was increased from 0 to 5000 g/T. In addition, the turbidity decreased from 180 NTU to 80 NTU within this range of dosages (refer to Figure 44). This was unexpected, since the turbidity of the DDJfiltrateis supposed to increase as retention decreases. However, it is important to note that the turbidity of the supernatant was measured and not the entire DDJfiltrate.This is because the DDJfiltratewas too turbid to measure directly. These results indicate that Raifix successfully coagulated the anionic DCS present in the pulp furnish, but that these were not retained in the DDJ. These results are even more intriguing if one considers that Raifix also had a detrimental effect in the PCC aggregation experiments. It is possible that Raifix over-charged the aggregates and interfered with the PEOPFR flocculation mechanism. However, this cannot be confirmed.  67  100 90 0 c 80 g 70 4—> c 60 CU 4-1 50 CU cd. 40 CO 30 tn CD 20 Q_ 4—» 10 tn 0  y/—  s  * I  •  f  3  •  • Fines ° PCC • Total * 0  500  1000  10000  Raifix Dosage (g/T)  Figure 42: The effect of Raifix dosage on first pass retention (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S / cm, pH = 6.9 - 7.18) (* No chemicals added)  -50 cr cu  -60  j  -70 TJ C  ro E  -80  v -90  y •100 •110 ro  U  DDJ Filtrate  •120  i  * 0  i  500  i  i  i  i  1000  10000  Raifix Dosage (g/T) Figure 43: The effect of Raifix dosage on cationic demand (PEO = 100 g/T, PFR = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S / cm, pH = 6.9 - 7.18) (* No chemicals added) 68  900  •  850  DDJ Filtrate v  800 250 A  A  200  lo  150  ZJ  100 50 0  T  *  0  1—i—i—r—r-  500  1000  10000  Raifix Dosage (g/T) Figure 44: The effect of Raifix dosage on turbidity ( P E O = 100 g/T, P F R = 50 g/T, 70 mesh screen, 295 K, 1000 rpm, Conductivity = 337 - 365 S / c m , p H = 6.9 - 7.18) (* N o chemicals added)  5.  Fourier Transform Infrared Spectroscopy Experiments were performed using Fourier Transform Infrared Spectroscopy to observe the  molecular interactions between P E O , Phenol Formaldehyde Resin (PFR), and Raifix. The results of these experiments are shown in Figures 45 and 46. In Figure 45, the F T I R spectra of P E O , P F R , and the P E O - P F R complex are shown. The top spectra is that of P E O . In this spectrum, one can observe the  peaks representing  C - H , C - C , and C - 0  bonds. These  are  located  at  approximately 2900 cm" , 1450 cm" , and 1100 cm" respectively. The middle spectrum is that of 1  1  1  the P F R . In this spectrum, the major peaks which are present are those representing C - H , C=C, C - C , and free O - H bonds. The C = C peak is located at 1600 cm" . The free O - H stretching 1  frequency occurs at approximately 3650 cm" . It is a one sided peak, which drops from the left 1  and plateaus. This type of peak represents a free O - H group (i.e. an O - H group which isn't hydrogen bonded). There are also a small amount of hydrogen bonded O - H groups which 69  4000  3000  2000  1000  Wavenumber (cm"!) Figure 45: The FTIR Spectra of PEO (top), PFR (middle) and the PEO-PFR Complex (bottom)  70  produce a small peak with a minimum at 3292 cm". The bottom spectrum is that of the PEO1  PFR complex. The major peaks which are present are those of hydrogen bonded O-H, C-H, C=C, C-C, and C-0 groups. The hydrogen bonded O-H stretching frequency has a minimum at 3146 cm". This is 146cm" lower than the stretching frequency for hydrogen bonded O-H in the PFR 1  1  spectrum. As mentioned previously (Chapter 3, Section 1), when an O-H group is hydrogen bonded, the stretching frequency is shifted downwards. Therefore, there is evidence that a complex between PEO and PFR is formed through polymeric hydrogen bonding. Similar experiments were performed to determine whether hydrogen bonding could occur between PFR and Raifix. The results of these experiments are shown in Figure 46. The top spectrum is that of PFR. The bottom spectrum is that of Raifix. The major peaks which are present for Raifix are those of hydrogen bonded O-H, C-H, C-C, and C-0 groups. The O-H peak has a minimum at 3240 cm". The middle spectrum is that of the Raifix-PFR complex. The major 1  peaks which are present in this spectrum are those of hydrogen bonded O-H, C-H, C-C, and C-0 groups. The O-H peak has a minimum of 3174 cm". This is 66 cm" lower than the minimum in 1  1  the Raifix spectrum. Therefore, there is evidence that polymeric hydrogen bond stretching also occurs between Raifix and PFR.  71  4000  3000  2000  1000  Wavenumber ( c r r f l ) Figure 46: The FTIR Spectra of PFR (top), Raifix (bottom), and the Raifix-PFR Complex (middle)  72  CHAPTER 5  Conclusions  1. Conclusions This work investigated the use of Raifix as a retention enhancing ATC in mechanical groundwood pulps. Raifix was used in conjunction with a PEO-PFR retention aid system. Laser diffraction particle size analyses were performed to observe the aggregation behaviour of clay and PCC filler with various paper chemicals. PEO was found to adsorb onto clay, but was not capable of aggregating it. In contrast, PEO was capable of aggregating PCC particles within a certain range of dosages. When PFR was added prior to PEO, the aggregation of clay and PCC filler was greatly enhanced. The optimum PFR/PEO ratio for both fillers was approximately 1.5. Raifix was also shown to be capable of aggregating clay and PCC filler. The maximum aggregate size achieved with Raifix was approximately 20 m. Aggregation with Raifix was shown to be limited by shear. In addition, the aggregates could be broken and re-formed to their original size. These were identified as characteristics of patch flocculation. In the case of the PCC filler, aggregation was attributed to electrostatic interactions. In the case of the clay filler, aggregation was attributed to combined electrostatic and hydrogen bonding interactions. It was presumed that hydrogen bonding occurred between the hydroxyl groups on Raifix and the SiOH groups on the clay surface. This was demonstrated by Raifix's ability to adsorb onto the clay particles and reverse their charge to positive. When Raifix was used in conjunction with PFR and PEO, it enhanced clay aggregation. The optimal order of addition was found to be: Raifix, PFR, PEO. When Raifix was added at varying dosages, it was found to have a maximum effect at 20000 g/T (PEO = 1000 g/T, PFR = 500 g/T). At this point, the rate of aggregation and aggregate size were 0.29 ml s and 64 m r e spectively. Meanwhile, when no Raifix was added, the rate of aggregation and aggregate size were 0.026 m/s and 26 m respectively. At 40000 g/T of Raifix, the rate of aggregation and aggregate size 73  decreased from the maximum. This was attributed to the charge reversal of the clay particles, which has an adverse effect on aggregation. In the case of PCC filler, Raifix was shown to have a detrimental effect on aggregation when used in conjunction with PFR and PEO. Experiments were performed to observe the dynamic behaviour of PCC in a mechanical groundwood pulp suspension. Conductivity and calcium ion concentration were shown to increase over time until an equilibrium was reached after 15 hrs. The equilibrium conductivity and calcium ion concentration were 320 m/s and 6.8E-4 M respectively. The pH decreased as the PCC dissolved into the suspension. The equilibrium pH was approximately 7.5. First pass retention experiments were performed to observe the retention performance of various paper chemicals. PEO was found to be capable of improving the retention of fines and clay on its own. This was attributed to the presence of natural cofactors in the pulp suspension. When PFR was added prior to PEO, the retention of fines and clay were greatly enhanced. The optimum PFR/PEO ratio was found to be 1. This was lower than the optimum ratio obtained in the clay aggregation experiments. The difference was attributed to the presence of natural cofactors in the pulp suspension. As in the clay aggregation experiments, retention varied according to the PFR/PEO ratio which was used. This phenomenon was further examined by measuring the retention performance of several PFR:PEO complexes while varying the mixing time. It was believed that certain complexes produce stronger floes than others. However, these experiments proved to be inconclusive at mixing times higher than 5 seconds. These experiments also demonstrated the adverse effect of shear on retention. First pass retention experiments were performed to observe the effect of using Raifix in conjunction with PEO and PFR. The first objective was to determine an optimal order of addition. This was found to be: Raifix, PFR, PEO. This supported the results obtained in the clay aggregation experiments and is in agreement with common industrial practice. Subsequent experiments observed the effect of varying Raifix dosage on retention. Raifix was found to 74  enhance retention in the clay filled pulp suspension. When Raifix was added at 100 g/T (PEO = 100 g/T, PFR = 50 g/T), the fines and clay retention were 66% and 63% respectively. Meanwhile, when no Raifix was added, the fines and clay retention were 56% and 48% respectively. Raifix was also shown to reduce the cationic demand and turbidity of the DDJ filtrate. In contrast, Raifix had an adverse effect on retention in the PCC filled pulp suspension. This was despite a drop in cationic demand and turbidity in the DDJ filtrate. It was concluded that Raifix was successful in coagulating the anionic DCS in the pulp suspension, but that these were not retained in the DDJ. Finally, experiments were performed using Fourier Transform Infrared Analysis to observe the molecular interactions between PEO, PFR and Raifix. The results of these experiments show evidence of hydrogen bonding interactions between PEO and PFR as well as Raifix and PFR. This was indicated by a shift of the hydrogen bonded O-H peak to a lower frequency.  75  2. References  [1] Ataman, M., "PROPERTIES OF AQEUOUS SALT SOLUTIONS OF POLY(ETHYLENE OXIDE) CLOUD POINTS,  TEMPERATURES", Colloid and Polymer Science, 265(1),  19-25 (1987) [2] Alince, B., Porubska, J., and van de Ven, T. G. M., "GROUND AND PRECIPITATED CaC0 DEPOSITION ON FIBRES IN THE PRESENCE OF PEO AND KRAFT LIGNIN", 3  Paper Technology, 38(2), 51-54 (1997) [3] Alince, B., and van de Ven, T. G. 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First Pass Retention  Calculation of First Pass Retention in a Clay Filled Pulp Suspension  Experiment Date Pulp Sample Temperature (K) PH Conductivity ( S/cm) DDJ Stirring Speed (rpm)  A 70 a) 8/2/99 1fl) 295 7.18 246 1000  B 70 b) 8/2/99 1fl) 295 7.18 246 1000  100 50  c  295 7.18 246 1000  ig)  D 70 d) 8/2/99 1Q) 295 7.18 246 1000  100 50  100 50  100 50  0.45 0.05 49.475 500.09 96.58  0.45 0.05 49.475 501.31 104.38  0.45 0.05 49.475 501.17 104.05  0.45 0.05 49.475 501.94 112.26  0.1302 0.0276 0.1026  0.1279 0.0263 0.1016  0.13 0.0267 0.1033  0.1307 0.0268 0.1039  70 c) 8/2/99  Chemical Dosage (g/T) PEO PFR  Pulp Suspension Pulp Consistency (%) Clay Consistency (%) Fines Fraction (%) Weight of Pulp Suspension  (g)  Weight of DDJ Filtrate (g) Filter Cake Weight of Filter Cake (g) Weight of Clay (g) Weight of Fines (g)  First Pass Retention =  'a,-b,^ V  a  i J  *100  First Pass Retention of Fines (i = 1): ai =A15*A12*A14/10000 = 1.1134 bi =A20*A15/A16 = 0.5313 First Pass Retention of Fines = 52.28 % First Pass Retention of Clay (i = 2): a = A15*A13/100 = 0.25 2  b = A19*A15/A16 = 0.1429 2  First Pass Retention of Clay = 42.84 % Total First Pass Retention (i = 3): a  3  = (A12 + A13)/100 = 0.005 b = A18/A16 = 0.001348 3  Total First Pass Retention = 73.04% 84  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  2. Calculation of First Pass Retention in a PCC Filled Pulp Suspension 1 Experiment Date Pulp Sample Temperature (K) PH Conductivity ( S/cm) Initial Calcium Ion Concentration (M) DDJ Stirring Speed (rpm) Chemical Dosage (g/T) PEO PFR Pulp Suspension Pulp Consistency (%) PCC Consistency (%) Fines Fraction (%) Weight of Pulp Suspension (g) DDJ Filtrate Weight of DDJ Filtrate (g) Calcium Ion Concentration (M) Filter Cake Weight of Filter Cake (g) Weight of PCC (g) Weight of Fines (g)  D A | B C 99 a) 99 b) 99 c) 99 d) 10/06/99 10/06/99 10/06/99 10/06/99 2 c) 2 c) 2 c) 2 c) 295 295 295 295 7.07 7.1 7.12 7.01 347 349 350 351 3.3323E-05 3.3323E-05 3.3323E-05 3.3323E-05 1000 1000 1000 1000 100 50  100 50  100 50  100 50  0.45 0.05 55 498.51  0.45 0.05 55 501.03  0.45 0.05 55 500.43  0.45 0.05 55 500.86  87.96 8.88E-04  99.53 8.87E-04  99.83 9.06E-04  104.71 8.98E-04  0.0877 0.0107 0.077  0.1117 0.021 0.0907  0.0932 0.0159 0.0773  0.1013 0.0179 0.0834  First Pass Retention =  v  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23  *100 a  i J  First Pass Retention of Fines (i = 1): a! =A16*A13*A15/10000 = 1.2338 b! =A23*A16/A18 = 0.5313 First Pass Retention of Fines = 64.63 % First Pass Retention of P C C (i = 2): a  2  = A16*[A14/100 - (A19 - A7)*100.088/1000] = 0.2066 b  = A22*A16/A18 = 0.06064  2  First Pass Retention of P C C = 70.65 % Total First Pass Retention (i = 3): a  3  = (A13 + A14)/100 - (A19 - A7)*100.088/1000 = 4.9145E-3 b  3  = A21/A18 = 9.9704E-4  Total First Pass Retention = 79.71 % 85  APPENDIX II  Aggregation of Filler  1. Clay Aggregation with Raifix, PFR and PEO Experiment 23 a) 23 b) 23 c) 23 d) 23 e) 5/10/99 5/10/99 5/10/99 5/28/99 5/28/99 Date 295 295 295 295 295 Temperature (K) 6.33 6.33 6.33 6.33 6.33 PH 1,62 1,62 1,62 1,62 1,62 Conductivity ( S/cm) 1250 1250 1250 1250 1250 Stir Rate (rpm) 0.01 0.01 0.01 0.01 0.01 Clay Concentration (%) Chemical Dosage (g/T) 10000 10000 10000 10000 10000 Raifix 1000 1000 1000 1000' 1000 PEO 500 500 500 500 500 PFR Maximum Aggregate Size ( m) 61.22 60.16 61.54 61.31 61.39 61.12 Average 0.24 Standard Error of the Mean Aggregation Rate ( m/s) 0.1862 | 0.1920 | 0.1788 | 0.2185 | 0.2183 0.1987 Average 0.0082 Standard Error of the Mean Maximum Aggregation Rate ( m/s) 0.604 | 0.5706 | 0.626 | 0.6386 | 0.592 0.6062 Average 0.012 Standard Error of the Mean Time (s) Volume Median Diameter ( m) 0 2.55 2.55 2.54 2.44 2.31 15 7.42 6.35 4.76 5.72 6.13 30 14.95 11.5 11.07 11.83 12.04 23.97 45 20.21 19.55 20.55 20.92 28.77 60 33.03 28.94 30.13 29.76 75 39.81 36.61 36.53 38.27 37.26 90 45.11 42.52 42.25 44.04 43.57 X  J.  86  J,  ±  ±  ±  

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