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Photo-resistance of alkylammonium compound treated wood Zhang, Xueyuan 2003-12-31

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Photo-resistanceof Alkylammonium Treated Wood  Compound  by  XUEYUAN ZHANG  A THESIS S U B M I T T E D IN P A R T I A L F U L F I L M E N T OF T H E R E Q U I R E M E N T F O R T H E D E G R E E OF  M A S T E R OF S C I E N C E  IN  T H E F A C U L T Y OF G R A D U A T E STUDffiS (Department o f W o o d Science, Faculty o f Forestry) W e accept this thesis as conforming to the required standard  T H E U N I V E R S I T Y OF BRITISH C O L U M B I A February 2003 © X U E Y U A N Z H A N G , 2003  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department  or by his or  her  representatives.  It  is  understood  that  copying  or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department The University of British Columbia Vancouver, Canada  DE-6 (2/88)  ABSTRACT The potential o f alkylammonium compounds ( A A C s ) as wood preservatives, was recognized during the 1970s. The problems associated with AAC-treated  wood,  particularly treated with didecyldimethylammonium chloride ( D D A C ) , are severe surface degradation and discoloration compared to untreated wood. The aims o f this study were to assess the performance o f A A C based chemically treated wood to ultraviolet ( U V ) irradiation and also determine photo-resistance o f wood treated with a combination o f selected additives plus D D A C , during U V irradiation. Southern pine sapwood thin sections were treated with the new biocides and then exposed to artificial U V light. The compositional changes i n the treated and untreated wood sections were examined using Fourier transformed infrared spectroscopy (FTIR), which provides a rapid and nondestructive analysis o f the wood during U V irradiation. The relative lignin degradation and the formation o f carbonyl groups were quantitatively analyzed based on the peaks at 1510 and 1730 cm" in the F T I R spectra. The studies 1  showed that only the new biocides containing the cobiocide copper, slowed wood photodegradation by inhibiting the formation o f carbonyl groups and delignification compared to the untreated wood and wood treated with only  organic  biocide  formulations. DDAC  treatment  accelerates  delignification  and demethoxylation  v i a the  formation o f free radicals. In order to increase the photo-resistance o f D D A C treated wood, additives including butylated hydroxytoluene ( B H T ) , lignosulfonic acid ( L S A ) , tannic acid and wood extractives, isolated from Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja plicata) and Scots pine (Pinus sylvestris) heartwood, were used with D D A C . F T I R was used to examine the effectiveness o f the additives in slowing the photodegradation o f D D A C treated wood during U V irradiation. The F T I R spectra showed that tannic acid and Douglas-fir extractives greatly improved the photo-resistance of D D A C treated wood based on the changes to the peak at 1510 cm" which presents 1  aromatic skeletal vibrations in lignin. A quantitative analysis o f the F T I R spectra was used to assess the lignin degradation and the formation o f carbonyl groups. The results showed that the addition o f Douglas-fir extractives, and tannic acid to D D A C reduced lignin degradation. Douglas-fir and cedar extractives also reduced the formation o f  ii  carbonyl groups of the wood to some degree. Douglas-fir extractives and tannic acid contain polyphenolic  components, which have antioxidant  potential. The  results  suggested that the antioxidant properties o f the additives slowed the oxidation process of lignin in the wood during U V exposure by terminating the formation o f free radicals from lignin, generated by U V light. A washing study showed that the action o f washing might wash off the additives and D D A C in the wood sections, because their F T I R spectra showed no clear difference on the peak intensity after 6 days of U V exposure. The color changes in photoexposed samples were examined by a M i n o l t a C M 2600d spectrophotometer for the wood sections treated with additives plus D D A C during U V irradiation. It was found that the color change was greatly retarded in the wood treated with Douglas-fir  or cedar extractives. Douglas-fir  and cedar  extractives  effectively resisted color change and also provided an excellent brightness stability when combined with up to 5% D D A C treated wood. The discoloration study o f wood sections treated with additives plus D D A C by U V irradiation and washing showed that the action o f washing may wash out some of the additives in the wood, but Douglas-fir and cedar extractives still resisted color change to some degree and provided brightness stability for D D A C treated wood.  iii  T A B L E OF CONTENTS  ABSTRACT  ii  T A B L E OF CONTENTS  iv  LIST OF TABLES  viii  LIST OF FIGURES  ix  LIST OF ABBREVIATIONS ACKNOWLEDGMENTS  CHAPTER 1  xviii xix  BACKGROUND  1  1.1.  Trends in use of treated wood  1  1.2.  Pressure on preservative acceptability  2  1.3.  QAC wood preservatives  3  1.4.  Objectives  4  1.5.  Study outline  4  C H A P T E R 2 LITERATURE REVIEW  7  2.1.  7  Photodegradation of wood by light  2.1.1. 2.1.2. 2.1.3. 2.1.4. 2.1.5  Phenomena o f wood exposed to light Physical changes Chemical changes Discoloration o f wood by light Chemistry of wood photodegradation  10 10 11 12 13  2.2.  Photodegradation of QAC treated wood  15  2.3.  FTIR spectral analysis of photo-exposed wood  16  2.4.  Wood protection against photodegradation  17  2.4.1. 2.4.2.  Painting Inorganic treatment  18 18  iv  2.4.3.  Organic chemical protections  CHAPTER 3  METHODOLOGY  19 22  3.1.  Wood sample preparation  22  3.2.  Chemicals  22  3.2.1. 3.2.2. 3.2.3.  Biocides Additives Extraction o f wood extractives  22 25 28  3.3.  Wood sample treatment  29  3.4.  Leaching  30  3.5.  U V irradiation and FTIR measurements  30  3.6.  Quantitative analysis of FTIR spectra  31  3.7.  Color measurement  32  4.1.3. 4.1.3.  Theory Methodology  CHAPTER 4  32 33  PHOTO-RESISTANCE OF ALKYLAMMONIUM  C O M P O U N D T R E A T E D W O O D T O UV IRRADIATION  35  4.1. The photodegradation of sapwood treated with amine oxide or Q A C compounds 4.1.1. Effect o f the treatment 4.1.2. Overview o f the F T I R during photoexposure 4.1.3. Effect o f the washing  35 35 38 39  4.2. Treatment of QAC related chemicals containing copper 4.2.1. Effect o f copper chemicals as observed by F T I R 4.2.2. Effect o f Q A C related chemicals containing copper on wood photodegradation by U V irradiation 4.2.3. Effect o f copper concentration on the F T I R spectra 4.2.4. Effect o f sample washing after photoexposure, on the F T I R spectra  51 52 52  4.3.  The relative delignification rate and the formation of carbonyl groups  59  4.4.  Conclusions  64  CHAPTER 5  50 50  P H O T O D E G R A D A T I O N O F W O O D T R E A T E D WITH  D D A C P L U S ADDITIVES  66  5.1.  FTIR studies  5.1.1. Effect 5.1.2. Effect treated wood 5.1.3. Effect 5.1.4. Effect  o f B H T on photodegradation o f D D A C treated wood o f l,4-diazabicyclo(2,2,2)octane on photodegradation o f D D A C  66 66  66 o f wood extractives on photodegradation o f D D A C treated wood — 69 o f lignosulfonic acid on photodegradation o f D D A C treated wood— 80  5.2. Effect of washing UV irradiated samples on the FTIR spectra of wood treated with DDAC and additives  83  5.3.  Effect of treatment on FTIR spectra —  92  5.4.  Quantitative analysis of FTIR spectra  5.4.1. 5.4.2. 5.4.3.  5.5.  The relative delignification rate Explanation for the differences observed Formation o f carbonyl groups  Conclusions  95 95 103 104  105  C H A P T E R 6 C O L O R C H A N G E S O F D D A C P L U S ADDITIVES T R E A T E D W O O D DURING UV IRRADIATION  112  6.0.  Introduction  112  6.1.  Results and Disscusion  113  6.1.1. Effect o f additives on the color of treated wood during U V irradiation — 114 6.1.1.1. Douglas-fir extractives + D D A C 114 6.1.1.2. Cedar extractives + D D A C 115 6.1.1.3. Scots pine extractives + D D A C 116 6.1.1.4. Lignosulfonic acid ( L S A ) + D D A C 117 6.1.2. Effect o f additives on brightness o f D D A C treated wood during U V irradiation 122 6.1.2.1. Douglas-fir extractives + D D A C 122 6.1.2.2. Western red cedar extractives + D D A C 123 6.1.2.3. Scots pine extractives + D D A C 123 6.1.2.4. Lignosulfonic + D D A C 124 6.1.2.5. General observation 124 6.1.3. Effect o f additives on the color and brightness o f treated wood subject to U V irradiation and leaching 129 6.1.3.1. Effect on color stability 129 6.1.3.1.1. Douglas-fir extractives + D D A C 129 6.1.3.1.2. Western red cedar extractives + D D A C 129 6.1.3.1.3. Scots pine extractives + D D A C 130 6.1.3.1.4. Lignosulfonic acid ( L S A ) + D D A C — 130 6.1.3.2. Effect on brightness 135 6.1.3.2.1. Douglas-fir extractives + D D A C 135 6.1.3.2.2. Western red cedar extractives + D D A C 135  vi  6.1.3.2.3. Scots pine extractives + D D A C 6.1.3.2.4. Lignosulfonic acid + D D A C 6.1.4. A comparison of the effect o f additives on their ability to retard color changes and brightness o f D D A C treated wood 6.1.4.1. The effect o f additives and D D A C on color changes 6.1.4.2. The effect o f additives and D D A C on the brightness changes  6.2.  Conclusions  6.2.1. 6.2.2.  Discoloration o f the treated wood by U V irradiation Discoloration o f the treated wood by U V irradiation and washing  C H A P T E R 7 SUMMARY AND RECOMMENDATIONS  136 136 141 141 143  145 145 145  146  7.1.  Summary  146  7.2.  Recommendations  147  REFERENCES  148  LIST OF TABLES  Table 3.1: Chemicals supplied by Lonza.  23  Table 3.2: The concentration of the chemicals used to treat wood samples.  24  Table 3.3: The solutions of the additives into DDAC prepared for the research. — 28 Table 4.1: The assignments of absorption peaks in IR spectra of southern pine. —37 Table 5.1: Relative delignification rate after 6 days of UV irradiation.  97  LIST OF FIGURES  Figure 2.1. Ultraviolet spectra of (a) wood, (b) lignin, and (c) cellulose (after Hon, 1991a). Figure 2.2. Approximate bond energy of chemical bonds in woods (after Hon, 1991a). Figure 2.3. Formation of o- and p-quinonoid structures during ultraviolet light irradiation of lignin (Hon, 1991b). 14 Figure 3.1: Structure of butylated hydroxytoluene (BHT). 26 Figure 3.2: Structure of 1,4-diazabicyclo (2,2,2) octane. 27 Figure 3.3: Structure of lignosulfonic acid. 27 Figure 3.4: Structure of tannic acid (Bravo, 1998). 27 Figure 3.5: Soxhlet extraction apparatus. 29 Figure 3.7: Spectrophotometer CM-2600d from Minolta. 34 Figure 3.7: Representation of CIELAB color system. 33 Figure 4.1.1a: FTIR spectra of untreated wood sections: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. 40 Figure 4.1.1b: FTIR spectra of untreated washed wood sections: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. '• 40 Figure 4.1.2a: FTIR spectra of wood sections treated with 2% wp-40: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 41 Figure 4.1.2b: FTIR spectra of wood sections treated with 2% wp-40: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 41 Figure 4.1.3a: FTIR spectra of wood sections treated with 2% wp-41: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 42 Figure 4.1.3b: FTIR spectra of wood sections treated with 2% wp-41: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 42 Figure 4.1.4a: FTIR spectra of wood sections treated with 2% wp-46: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. ~ 43 Figure 4.1.4b: FTIR spectra of wood sections treated with 2% wp-46: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 43 Figure 4.1.5a: FTIR spectra of wood sections treated with 2% wp-47: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 44 Figure 4.1.5b: FTIR spectra of wood sections treated with 2% wp-47: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 44 Figure 4.1.6a: FTIR spectra of wood sections treated with 5% wp-48: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 45  ix  Figure 4.1.6b: FTIR spectra of wood sections treated with 5% wp-48: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 45 Figure 4.1.7a: FTIR spectra of wood sections treated with 5% wp-62: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 46 Figure 4.1.7b: FTIR spectra of wood sections treated with 5% wp-62: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 46 Figure 4.1.8a: FTIR spectra of wood sections treated with 5% wp-63: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. ~ 47 Figure 4.1.8b: FTIR spectra of wood sections treated with 5% wp-63: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 47 Figure 4.1.9a: FTIR spectra of wood sections treated with 5% wp-64: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 48 Figure 4.1.9b: FTIR spectra of wood sections treated with 5% wp-64: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 48 Figure 4.1.10: FTIR spectra of wood sections treated with 2% DDAC: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days' UV irradiation. - 49 Figure 4.1.11: FTIR spectra of wood sections treated with 2% benzyldimethyldodecylammonium chloride: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation. 49 Figure 4.2.1a: FTIR spectra of wood sections treated with 2% wp-42: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 54 Figure 4.2.1b: FTIR spectra of wood sections treated with 2% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation and washed. 54 Figure 4.2.2a: FTIR spectra of wood sections treated with 1% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation. 55  Figure 4.2.2b: FTIR spectra of wood sections treated with 1% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation and washed. 55 Figure 4.2.3a: FTIR spectra of wood sections treated with 0.5% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation. 56 Figure 4.2.3b: FTIR spectra of wood sections treated with 0.5% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation and washed. 56 Figure 4.2.4a: FTIR spectra of wood sections treated with 0.25% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation. 57 Figure 4.2.4b: FTIR spectra of wood sections treated with 0.25% wp-42: a) before UV irradiation, and after b) 7 hours, c) 28 hours, and d) 6 days of UV irradiation and washed. 57  x  Figure 4.2.5a: FTIR spectra of wood sections treated with 2% wp-43: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days. — 58 Figure 4.2.5b: FTIR spectra of wood sections treated with 2% wp-43: a) before UV irradiation, and after irradiation for b) 7 hours, c) 28 hours, and d) 6 days and washed. 58 Figure 4.2.6: FTIR spectra of wood sections treated with different concentrations of wp-42 after 6 days of UV irradiation. 59 Figure 4.3.1: The relative ratios of delignification of different chemical treated wood. 61 Figure 4.3.2: The relative ratios of delignification of different chemical treated wood. 61 Figure 4.3.3: The relative ratios of delignification of different chemical treated wood. 62 Figure 4.3.4: The relative ratio of the formation of carbonyl groups of UV irradiated wood: the effect of various treatments. 62 Figure 4.3.5: The relative ratio of the formation of carbonyl groups of UV irradiated wood: the effect of various treatments. 63 Figure 4.3.6: The relative ratio of the formation of carbonyl groups of UV irradiated wood: the effect of solution concentrations. 63 Figure 5.1.1: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% BHT treated, UV irradiated; d) 2% BHT + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, irradiated. 67 Figure 5.1.2: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% 1,4-diazabicyclo (2,2,2) octane treated, UV irradiated; d) 2% 1,4-diazabicyclo (2,2,2) octane + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, irradiated. 68 Figure 5.1.3: Structure of taxifolin. 69 Figure 5.1.4: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% DF extractives treated, UV irradiated; d) 2% DF extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, irradiated. 72 Figure 5.1.5: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% DF extractives treated, UV irradiated; d) 2% DF extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, irradiated. 73 Figure 5.1.6: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% cedar extractives treated, UV irradiated; d) 2% cedar extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 74 Figure 5.1.7: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b)  xi  untreated, UV irradiated; c) 2% cedar extractives treated, UV irradiated; d) 2% cedar extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. 75 Figure 5.1.8: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% tannic acid treated, UV irradiated; d) 2% tannic acid + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, irradiated. 76 Figure 5.1.9: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% tannic acid treated, UV irradiated; d) 2% tannic acid + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, irradiated. 77 Figure 5.1.10: FTIR of untreated and chemically treated wood sections before UV irradiation and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% pine extractives treated, UV irradiated; d) 2% pine extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 78 Figure 5.1.11: FTIR of untreated and chemically treated wood sections before UV irradiation and after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% pine extractives treated, UV irradiated; d) 2% pine extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. » 79 Figure 5.1.12: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiated; b) untreated, UV irradiated; c) 2% lignosulfonic acid treated, UV irradiated; d) 2% lignosulfonic acid + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, irradiated. 81 Figure 5.1.13: FTIR of untreated and chemically treated wood sections before and after 6 days of UV irradiation: a) untreated, before UV irradiated; b) untreated, UV irradiated; c) 2% lignsosulfonic acid treated, UV irradiated; d) 2% lignsosulfonic acid + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, irradiated. 82 Figure 5.2.1: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiated; b) untreated, UV irradiated; c) 2% Douglas-fir extractives treated, UV irradiation; d) 2% Douglas-fir extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 84 Figure 5.2.2: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% Douglas-fir extractives treated, UV irradiated; d) 2% Douglas-fir extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. 85 Figure 5.2.3: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% cedar extractives treated, UV  xii  irradiated; d) 2% cedar extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 86 Figure 5.2.4: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% cedar extractives treated, UV irradiated; d) 2% cedar extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. 87 Figure 5.2.5: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% lignosulfonic acid treated, UV irradiated; d) 2% lignosulfonic acid + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 88 Figure 5.2.6: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% lignosulfonic acid treated, UV irradiated; d) 2% lignosulfonic acid + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. 89 Figure 5.2.7: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% pine extractives treated, UV irradiated; d) 2% pine extractives + 2% DDAC treated, UV irradiated; and e) 2% DDAC treated, UV irradiated. 90 Figure 5.2.8: FTIR of untreated and chemically treated wood sections before UV irradiation and washed after 6 days of UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% pine extractives treated, UV irradiated; d) 2% pine extractives + 5% DDAC treated, UV irradiated; and e) 5% DDAC treated, UV irradiated. 91 Figure 5.3.1: FTIR spectra of untreated wood sections and wood sections treated with wood extractives. 93 Figure 5.3.2: FTIR spectra of untreated wood sections and wood sections treated with 5% lignosulfonic acid and 5% tannic acid. 94 Figure 5.4.1: The relative ratios of delignification of (a) untreated; (b) Douglas-fir extractives treated; (c) Douglas-fir extractives + DDAC treated; and (d) DDAC treated wood. 98 Figure 5.4.2: The relative ratios of delignification of (a) untreated; (b) Douglas-fir extractives treated; (c) Douglas-fir extractives + DDAC treated; and (d) DDAC treated wood. 98 Figure 5.4.3: The relative ratios of delignification of (a) untreated; (b) Cedar extractives treated; (c) Cedar extractives + DDAC treated; and (d) DDAC treated wood. 99 Figure 5.4.4: The relative ratios of delignification of (a) untreated; (b) Cedar extractives treated; (c) Cedar extractives + DDAC treated; and (d) DDAC treated wood. 99 Figure 5.4.5: The relative ratios of delignification of (a) untreated; (b) Pine extractives treated; (c) Pine extractives + DDAC treated; and (d) DDAC treated wood. 100  xiii  Figure 5.4.6: The relative ratios of delignification of (a) untreated; (b) Pine extractives treated; (c) Pine extractives + DDAC treated; and (d) DDAC treated wood. 100 Figure 5.4.7: The relative ratios of delignification of (a) untreated; (b) Tannic acid treated; (c) Tannic acid + DDAC treated; and (d) DDAC treated wood. 101 Figure 5.4.8: The relative ratios of delignification of (a) untreated; (b) Tannic acid treated; (c) Tannic acid + DDAC treated; and (d) DDAC treated wood. 101 Figure 5.4.9: The relative ratios of delignification of (a) untreated; (b) Lignosulfonic acid treated; (c) Lignosulfonic acid + DDAC treated; and (d) DDAC treated wood. 102 Figure 5.4.10: The relative ratios of delignification of (a) untreated; (b) Lignosulfonic acid treated; (c) Lignosulfonic acid + DDAC treated; and (d) DDAC treated wood. 102 Figure 5.4.11: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% Douglas-fir extractives; (b) 2% DF extractives + 2% DDAC; (c) 2% DDAC. 107 Figure 5.4.12: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% Douglas-fir extractives; (b) 2% DF extractives + 5% DDAC; (c) 5% DDAC. 107 Figure 5.4.13: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% cedar extractives; (b) 2% cedar extractives + 2% DDAC; (c) 2% DDAC. 108 Figure 5.4.14: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% cedar extractives; (b) 2% cedar extractives + 5% DDAC; (c) 5% DDAC. 108 Figure 5.4.15: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% pine extractives; (b) 2% pine extractives + 2% DDAC; (c) 2% DDAC. 109 Figure 5.4.16: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% pine extractives; (b) 2% pine extractives + 5% DDAC; (c) 5% DDAC. 109 Figure 5.4.17: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% tannic acid; (b) 2% tannic acid + 2% DDAC; (c) 2% DDAC. 110 Figure 5.4.18: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% tannic acid; (b) 2% tannic acid + 5% DDAC; (c) 5% DDAC. 110 Figure 5.4.19: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% lignosulfonic acid; (b) 2% lignosulfonic acid + 2% DDAC; (c) 2% DDAC. 111 Figure 5.4.20: The relative formation of carbonyl groups of untreated wood sections and wood sections treated with (a) 2% lignosulfonic acid; (b) 2% lignosulfonic acid + 5% DDAC; (c) 5% DDAC. 111 Figure 6.1.1.1a: Changes in color of treated and untreated wood sections before and after UV irradiation. 118  xiv  Figure 6.1.1.1b: Changes in color of treated and untreated wood sections before and after UV irradiation. 118 Figure 6.1.1.2a: Changes in color of treated and untreated wood sections before and after UV irradiation. 119 Figure 6.1.1.2b: Changes in color of treated and untreated wood sections before and after UV irradiation. 119 Figure 6.1.1.3a: Changes in color of treated and untreated wood sections before and after UV irradiation. 120 Figure 6.1.1.3b: Changes in color of treated and untreated wood sections before and after UV irradiation. 120 Figure 6.1.1.4a: Changes in color of treated and untreated wood sections before and after UV irradiation. 121 Figure 6.1.1.4b: Changes in color of treated and untreated wood sections before and after UV irradiation. 121 Figure 6.1.2.1a: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 125 Figure 6.1.2.1b: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 125 Figure 6.1.2.2a: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 126 Figure 6.1.2.2b: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 126 Figure 6.1.2.3a: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 127 Figure 6.1.2.3b: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 127 Figure 6.1.2.4a: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 128 Figure 6.1.2.4b: Changes in brightness of treated and untreated wood sections before and after UV irradiation. 128 Figure 6.1.3.1.1a: Changes in color of treated and untreated wood sections before UV irradiation and with washing after UV irradiation. 131 Figure 6.1.3.1.1b: Changes in color of treated and untreated wood sections before UV irradiation and with washing after UV irradiation. 131 Figure 6.1.3.1.2a: Changes in color of treated and untreated wood sections before UV irradiation and with washing after treatment and UV irradiation. 132 Figure 6.1.3.1.2b: Changes in color of treated and untreated wood sections before UV irradiation and with washing after treatment and UV irradiation. 132 Figure 6.1.3.1.3a: Changes in color of treated and untreated wood sections before UV irradiation and with washing after treatment and UV irradiation. 133 Figure 6.1.3.1.3b: Changes in color of treated and untreated wood sections before UV irradiation and with washing after treatment and UV irradiation. 133 Figure 6.1.3.1.4a: Changes in color of treated and untreated wood sections before UV irradiation and with washing after UV irradiation. 134 Figure 6.1.3.1.4b: Changes in color of treated and untreated wood sections before UV irradiation and with washing after UV irradiation. 134  xv  Figure 6.1.3.2.1a: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after UV irradiation. 137 Figure 6.1.3.2.1b: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after UV irradiation. 137 Figure 6.1.3.2.2a: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after treatment and UV irradiation. 138 Figure 6.1.3.2.2b: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after treatment and UV irradiation. 138 Figure 6.1.3.2.3a: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after treatment and UV irradiation. 139 Figure 6.1.3.2.3b: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after treatment and UV irradiation. 139 Figure 6.1.3.2.4a: Changes in brightness of treated and untreated wood sections before UV irradiation and washed after UV irradiation. 140 Figure 6.1.3.2.4b: Changes in Brightness of treated and untreated wood sections before UV irradiation and washed after UV irradiation. 140 Figure 6.1.4.1.1: The effect of combinations of additives and DDAC on the color change of treated and untreated wood after 6 days of UV irradiation. 141 Figure 6.1.4.1.2: The effect of combinations of additives and DDAC on the color change of treated and untreated wood after 6 days of UV irradiation and washed after UV irradiation. 142 Figure 6.1.4.2.1: The effect of combinations of additives and DDAC on the loss of brightness of treated and untreated wood after 6 days of UV irradiation. —143 Figure 6.1.4.2.2: The effect of combinations of additives and DDAC on the loss of brightness of treated and untreated wood after 6 days of UV irradiation and washed after UV irradiation. 144  xvi  LIST OF ABBREVIATIONS  AACs  Alkylammonium compounds  ACQ  Ammoniacal copper quaternary ammonium compound  BHT  Butylatedhydroxytoluene  CCA  Chromated copper arsenate  Cu-EA  Copper ethanolamine  Cu-MEAH  Copper monoethanolamine  DDAC  Didecyldimethyl ammonium chloride  DF  Douglas-fir  FTIR  Fourier transform infrared spectroscopy  IR  Infrared spectroscopy  LSA  Lignosulfonic acid  QAC  Quaternary ammonium compounds  UV  Ultraviolet  WGs  Weight gains  xvii  ACKNOWLEDGMENT  First o f all, I would like to sincerely thank Dr. John N.R. Ruddick, my supervisor, for his patient guidance, encouragement and support throughout my research work. I would also like to express my appreciation to the members o f my thesis committee, Dr. Phil Evans and Dr. Simon Ellis, for their invaluable advice and help on my research work and also in preparation o f this thesis. I would like to thank Dr. Robert Kozak for his assistance on the color measurement experiment. M y thanks also go to the members of Professor Ruddick's research group, past and present, for their help, discussions, and friendship. This project was sponsored by Lonza Inc. Finally, I thank my wife, Ningping Chen, and my son, Guangxin Zhang, for their constant support and understanding over the past years.  xviii  Chapter 1 Background 1.1.  Trends in use of treated wood W o o d possesses numerous attractive properties, such as an aesthetic appeal, l o w  density, low thermal expansion, and desirable mechanical strength and hence it is the most versatile and widely used structural material (Hon and Chang, 1984). Despite their favorable combination o f properties, most wood species are susceptible to deterioration by biological organisms and need to be treated with chemicals to enhance their durability. In 1992 the value o f treated lumber produced in Canada was $547 million, and the value o f the total volume o f treated wood installed i n Canada was i n excess o f $10 billion (Stephens et al., 1994). The wood preservation industry is therefore an important contributor to the Canadian economy. In a recent review o f the evolution o f the wood preservation industry, it was noted that profound changes have occurred (Preston, 2000). During the first half o f the 2 0  th  century treated wood was mainly used for ground-contact applications (e.g., cross-ties, piles, and poles) whereas today a greater proportion o f treated wood is used for above ground applications (e.g., decks). While the volume o f industrial products, such as ties and poles, produced has remained static over the last 30 years, the "consumer" construction materials segment has grown from around 40% to around 70% o f all treated wood products (Preston, 2000). In this market, i n contrast to the merits needed for industrial wood products, the appearance o f the treated wood and its resistance to weathering are important considerations.  1  1.2.  Pressure on preservative acceptability The most widely used preservative in North America is chromated copper  arsenate ( C C A ) (Micklewright, 1998). In 2000, the production o f treated lumber in North America was estimated to be about 15 million m /yr (Canada Industry Statistics Development Team, 2000), and over 70% the products were treated with C C A (http://www.ccaresearch.org). C C A has achieved this dominant position because o f the following characteristics: 1) it is a very effective preservative; 2) it fixes well to the wood despite its solubility in water; 3) it exhibits a lack o f bleeding after the treatment; and 4) it is relatively inexpensive. However, pressure is increasing to abandon the use o f C C A because o f its negative influence on the environment, and the increasing cost o f disposal o f treated wood when its service life is over. These pressures have led to the development and use o f alternative wood preservatives, in Europe and Japan for example, o f alkaline ammoniacal copper quat ( A C Q ) , or copper azole which are more environmentally friendly wood preservatives than C C A . In A p r i l 2002, both the U S A and Canadian producers decided to move towards the use o f such alternative wood preservatives for the consumer purchased treated wood market. It is anticipated that no pressure-treated wood that contains arsenic w i l l be available for sale to the residential material by December 31, 2003  (http://www.epa.gov/pesticides/citizens/lfile.htm).  This  transition  affects  all  residential uses o f wood treated with C C A , including wood used for decks, playstructures,  picnic  tables,  landscaping  timbers,  residential  fencing,  patios and  walkways/boardwalks. The environmental concerns that led to the industry abandoning the marketing o f C C A have been the major driving forces behind the development o f new wood preservatives i n recent years.  2  1.3.  QAC wood preservatives Quaternary ammonium compounds ( Q A C s ) have received considerable attention  in recent years because o f their potential as biocidal agents in wood preservatives. Didecyldimethylammonium chloride ( D D A C ) , which is a component o f A C Q - type B and D, is stable, colorless, water or solvent soluble, and is relatively inexpensive. Also, it exhibits l o w mammalian toxicity and creates few environmental problems.  DDAC  belongs to the group o f chemicals that are commonly used i n household disinfectants, swimming pool algicides, fabric softeners and asphalt emulsifiers, etc. (Lewis and Wee, 1983; Boethling, 1984). When used to treat wood, D D A C does not create problems for people handling the treated wood. The disposal o f the treated wood at the end o f its service life is relatively straightforward compared to the problems associated with disposal o f C C A treated wood. D D A C is a very effective preservative against decay organisms under laboratory conditions (Butcher et al, 1977a; Butcher, 1979; Hedley et al., 1982; Preston and Nicholas, 1982; Preston, 1983). In both laboratory and field tests, D D A C has effectively protected wood from termite attack (Howick et al., 1982; Tsunoda and Nishimoto, 1983). However, its performance against fungi in laboratory and field tests has varied widely.  For example, in fungal cellar and field tests, it failed to  adequately protect wood against decay (Ruddick, 1981 and 1983). Failure relates to the degradation by early colonizes. However, when combined with other co-biocides, D D A C can provide good protection to wood. A s mentioned above, the resistance o f treated wood to weathering is an important consideration when wood is used above ground. In this regard a study by L i u and Ruddick (1993) indicated that DDAC-treatment accelerated the weathering o f wood. They confirmed that wood treated with 2% D D A C showed significantly increased lignin  3  degradation compared to untreated wood. The consequence delignification  was undesirably  rapid  changes  o f this  in the wood's  accelerated  appearance, i.e.,  discoloration, loss o f gloss and lightness, roughening, considerable latewood defibration and severe early wood erosion, and checking o f surfaces (Jin et al., 1991).  1.4.  Objectives Clearly there is a need to find ways o f preventing or slowing the deleterious  effects o f D D A C on the weathering o f wood. The experiments in this thesis examined the photodegradation o f treated wood and untreated controls under laboratory conditions. The first phase focused on measuring the relative photo-resistance o f wood treated with selected novel biocidal. formulations based on Q A C or related co-amine components together with triazoles. The second phase o f the thesis concentrated on determining the effectiveness o f selected additives in improving the photodegradation resistance o f wood treated with Q A C s (in particular D D A C ) . The specific aims o f the research reported i n this thesis were:  •  T o measure the relative weatherability o f wood treated with selected novel biocidal formulations based on Q A C or related co-amines together with triazoles.  •  T o determine  the effectiveness  o f selected  additives  i n improving the  photodegradation resistance o f Q A C (or D D A C ) treated wood exposed under laboratory and field conditions.  1.5.  Study outline This thesis is sub-divided into seven chapters. Chapter 1 o f the thesis introduces  4  the importance of this study and the specific objectives of the work. Chapter  2 reviews  the relevant  literature  on photodegradation  of  wood.  Information on how wood is degraded by light and the physical and chemical changes that take place during photo-exposure are described. Chapter 2 also reviews the photodegradation of Q A C or D D A C treated wood. Information on the mechanism by which Q A C or D D A C treated wood enhances lignin degradation during U V irradiation is also covered. Some methods that have been used to protect wood from photodegradation are also described. Chapter 3 outlines the materials and methods used in the thesis. Relevant information on a) recently developed biocides that may be used as new preservatives for above ground applications, and b) additives that may have antioxidant properties, are described. The chapter also describes the methodology (notably, F T I R spectroscopy and colorimetry) used to analyze the photo-resistance o f treated and untreated wood during U V irradiation. Chapter 4 examines the photo-resistance o f wood treated with alkylammonium compounds that have been developed by Lonza Inc. Such components may be used as components o f new wood preservatives for above ground application (e.g., decks). It is important therefore, to obtain information on how they affect the photo-resistance o f wood. The resistance of the treated wood was compared with that o f untreated wood using F T I R spectroscopy. The rate of lignin degradation and the formation o f carbonyl groups, as determined by F T I R spectroscopy, were used quantitatively to compare the effect o f alkylammonium compounds on photo-resistance. Quantitative analysis o f the F T I R spectra were made based on the lignin peak at 1510 cm" and the carbonyl groups 1  5  peak at 1730 cm" . 1  Chapter 5 examines the ability o f certain additives to improve the photoresistance o f D D A C treated wood. Wood extractives (Douglas-fir, cedar and pine extractives), tannic acid and butylated hydroxytoluene ( B H T ) (an antioxidant commonly used in the food industry) were selected as photostabilizing additives. F T I R spectroscopy was again used to analyze the lignin degradation occurring in wood during U V irradiation. It is important to consumers that treated wood used outdoors retains its color and brightness. Hence Chapter 6 examines the changes in color (based on  CIELAB  parameters) o f D D A C and additives treated wood during U V irradiation. The color stability and brightness o f extractives plus D D A C treated wood were determined using a spectrophotometer. Finally, Chapter 7 gives an overview of the findings o f the study. Conclusions and recommendations for future research on improving the photo-resistance o f Q A C or D D A C treated wood are also made.  6  Chapter 2 Literature Review 2.1. Photodegradation of wood by light W o o d is a complex biopolymer composed o f principally cellulose and the aromatic polymer, lignin. Because o f the chromophoric groups present in wood, for example phenolic hydroxyl groups, aromatic skeletons, double bonds and carbonyl groups, lignin strongly absorbs ultraviolet ( U V ) light that leads to its radical-induced photodegradation. Research has shown (Figure 2.1) that lignin absorbs magnetic radiation strongly below 200 nm and a strong absorption occurs at 280 nm, with absorption reduce through the visible region. The combined U V absorption curves o f cellulose and lignin make up the absorption curve o f wood. According to Norrstrom (1969), lignin contributes 80-95% o f the absorption coefficient, while the carbohydrates contribute 5-20%, and the extractives about 2%. Because o f lignin's predominant light-absorption properties, it absorbs more light, resulting in more degradation, than cellulose. Moreover, because o f lignin's phenolic based structure, the photon energy absorbed by cellulose is likely to delocalize and transfer to lignin, so the presence o f lignin w i l l to some extent protect cellulosic components from photodegradation (Hon, 1975b). Therefore, the absorbed energy may well be specific enough to trigger undesired photophysical and photochemical processes. The quantum energies associated with light at the short ultraviolet end o f the sunlight spectrum are more than sufficient to break many  o f the chemical  bonds  present  in wood  constituents,  namely,  cellulose,  hemicellulose, and particularly lignin (Figure 2.2). The functional groups o f lignin responsible for the photodegradation process have been identified. The carbonyl chromophore was shown to be one o f the most effective reaction centers ( L i n and  7  Kringstad, 1970b; and Forsskahl, 1984a). Free phenolic hydroxyl groups are the major source o f protons to be donated for the hydrogen abstraction reaction, and they are further oxidized in the presence of molecular oxygen ( L i n and Kringstad, 1970 and 1971; Gellerstedt and Peterson, 1977; and Forsskahl, 1984a). Visible light o f 400-700 nm is insufficient to cleave chemical bonds in any o f the wood constituents because the energy is less than 70 kcal/mol (Hon and Shiraishi, 2001). Evans et al. (1992a) have reported that the acid insoluble lignin content o f Radiata pine veneers (85 um in thickness) initially decreased rapidly over the first five days o f natural exposure from 26.2% to 20.3%), and continued to decrease at a lower rate with further exposure. The lignin degradation during photo-exposure can be observed using FTIR. IR studies revealed that, during U V irradiation o f wood, absorption due to carbonyl groups at 1720 cm" and 1735 cm" increased, whereas the absorption for lignin 1  1  at 1265 cm" and 1510 cm" gradually decreased. The enhanced carbonyl groups were the 1  1  result of oxidation of cellulose and lignin. The reduction in the amount o f lignin was due to its degradation by light (Feist and Hon, 1984).  8  ooo  '  1  1  200  1  1  250  1  300  '  1  1  350  1  1  400  450  Wavelength, nm  Figure 2.1. Ultraviolet spectra o f (a) wood, (b) lignin, and (c) cellulose (after H o n , 1991a).  105  - i  65-I  1 250  1  1 300  1  1 350  1  1 400  1  1 450  Wavelength, nm  Figure 2.2. Approximate bond energy o f chemical bonds in woods (after Hon, 1991a).  9  2.1.1. Phenomena of wood exposed to light The interaction o f wood and U V light is essentially a surface reaction, i n which the U V light does not penetrate wood deeper than 75 u m (Hon and Ifju, 1978). When wood is exposed to daylight or U V irradiation, the first sign o f change at the wood surface is yellowing. According to H o n (1981b), the changes i n wood color follow a pattern o f yellowing to bleaching, and eventually to a brown color, depending on the exposure span. Leary (1967) reported that wood turned yellow, followed by bleaching after exposure to U V irradiation. The major cause o f the color changes is due to the chemical conversion and degradation o f lignin and extractives that readily interact with sunlight or artifical U V light (Hon, 1981b; Feist and Hon, 1984). The direct consequence of the discoloration of woods is their loss o f aesthetic appearance, which is an important criterion to customers, followed by the loosening o f wood fibers. R a i n washes the degraded woody  materials  from the surfaces, causes dimensional  changes, and  accelerates the surface erosion.  2.1.2. Physical changes The  effects  o f photo-induced  degradation on the structure  and chemical  composition o f wood are superficial i n nature. They do not affect mechanical properties of the wood significantly. Photodegradation o f wood and stresses generated by cyclical wetting and drying result i n the formation o f microscopic checks where adjacent cells or tissues differ in cell wall thickness or strength. It was shown that checks often develop at growth ring boundaries and at the interfaces between rays and tracheids.  The lignin-rich middle  lamella that bonds adjacent tracheids or fibers together are rapidly eroded during  10  weathering, and adjacent primary and secondary cell wall layers show progressive thinning with increasing exposure. The most obvious changes to the microscopic structure o f longitudinal surfaces are the formation o f microchecks originating in bordered and half-bordered pits and the degradation o f ray tissues (Evans, 2001).  2.1.3. Chemical changes Photodegradation and photooxidation o f wood result in changes in chemical and physical properties. Discoloration, loss o f lightness, roughening o f surfaces, damage to the microstructure, and loss o f weight, as a result o f U V irradiation, indicate that severe chemical modification o f the structure o f wood components, especially lignin, is taking place. When lignin-containing materials (especially wood and high yield pulp) were exposed to daylight, yellowing or discoloration became observable after a short period o f exposure (Leary, 1967 and 1968; Kringstad, 1969). During photo-irradiation, in the initial stages up to 1 h, only C O , CO2, H2, and H2O were detected as gaseous products. A t longer exposure times, however, methane, ethane and ethylene hydrocarbon gases were found. The solubility o f photo-irradiated wood  in  water,  benzene,  alcohol,  and alkaline  aqueous  solutions,  increased.  Carbohydrates and phenolic compounds were detectable from the solutions (Hon et al., 1982). H o n and Chang (1984) also used U V visible spectroscopy to analysis watersoluble fragments collected from U V irradiated wood. They found that the l o w molecular weight, water-soluble products were derived mostly from lignin. The degradation products contained carbonyl-conjugated phenolic hydroxyl groups and had a weightaverage  molecular  weight  of  about  900, as  determined  by  gel  permeation  chromatography.  11  Hon and Chang (1984) studied southern pine that was U V irradiated for up to 40 days. The IR spectra showed that the absorption bands at 1510 and 1265 cm" became 1  low in intensity, but did not disappear, until after 40 days o f U V irradiation. This observation indicated that the structure o f lignin molecules had been subjected to significant photochemical degradation. The lignin content o f wood surfaces after 40 days irradiation decreased from 28% to 14.5%, determined from the 1510 cm"  1  absorption  bands. The absorption at 1735 and 1720 cm" increased after U V irradiation, thus 1  indicating an increase in the concentration o f carboxylic and /or carbonyl groups that were derived from the lignin.  2.1.4. Discoloration of wood by light W o o d is an excellent material for light absorption and light reflection. The color characteristics depend on the chemical components o f wood that interact with light. Hence, the reaction o f wood components to light, heat, and chemicals w i l l change the color o f wood. Extensive studies and observations have shown that most, i f not all, wood species o f commercial importance, and in particular those used for furniture, paneling, and decks, are prone to discoloration with age. Discoloration occurs both indoors and outdoors, particularly in those used outdoors i n above ground applications. Ultraviolet light plays an important role in the discoloration o f wood. The color o f unprotected wood surface changed rapidly, because o f the degradation o f lignin and the formation o f carbonyl groups (Hon, 1991b).  12  2.1.5. Chemistry of wood photodegradation The precise mechanisms and pathways involved in the photodegradation o f lignin and cellulose in wood have yet to be elucidated. However, it is clear that the key step is absorption o f U V light by lignin and photolysis and fragmentation o f lignin resulting i n the formation o f aromatic and other radicals (Feist and Hon, 1984). Research has shown that the aromatic lignin component o f wood strongly absorbs ultraviolet light with a distinct maximum at 280 nm and a tail extending beyond 400 nm into the visible portion of the spectrum (Figure 2.1). Energy from absorbed radiation can be dissipated i n the polymer through the cleavage o f molecular bonds (photolysis) resulting in the formation o f a free radical. Because o f the complexity o f the lignin structure, identifying the free radical sites formed is extremely difficult. However, several aspects o f the photochemical reactions have been determined and can be summarized as follows: •  Lignin is degraded relatively easily by light o f wavelength shorter than 350 nm, while photobleaching or whitening o f lignin can be observed when it is exposed to light o f wavelength longer than 400 nm.  •  Reduction o f the methoxyl content o f lignin occurs.  •  Phenoxy radicals are produced readily from phenolic hydroxy groups.  •  Carbon-carbon bonds adjacent to a-carbonyl groups are photodissociated v i a the Norrish Type I reaction.  •  The Norrish Type I reaction does not occur efficiently in those components with ether bonds adjacent to the a-carbonyl groups. Photodissociation takes place at the ether bond.  13  •  Compounds  bearing  benzoyl  alcohol  groups  are  not  susceptible  to  photodissociation except when photosensitizers are present. •  a-carbonyl groups function as photosensitizers in the photodegradation o f lignin (Feist, 1984). Because o f the high proportion phenolic hydroxy groups and ether bonds in  lignin, the phenoxy radicals are the major intermediate formed in photoirradiated lignin. Although phenoxy radicals are rather stable intermediates, they are capable of being excited by light, or reacting with oxygen to induce demethylation o f the guaiacyl unit o f lignin to produce o-quinonoid structures (Figure 2.4). Leary (1968) suggested that oquinone is the end product of the reaction. Consequently, quinonoid moieties formed in wood are apparently the major chromophoric groups contributing to the discoloration o f lignin and wood materials.  i  1  Figure 2.3: Formation of o- and p-quinonoid structures during ultraviolet light irradiation of lignin (Hon, 1991b).  14  2.2. Photodegradation of QAC treated wood The  role  of  quaternary  ammonium  compounds  (QAC),  such  as  didecyldimethylammonium chloride ( D D A C ) in accelerating the weathering o f wood was reported in the early 1990's by Jin et al. (1991). L i u and Ruddick (1993) reported the F T I R spectroscopic study of D D A C treated wood during U V exposure. The IR spectra o f D D A C treated earlywood sections showed that the bands at 1267, 1510 and 1600 cm" , which represent benzene ring skeletal 1  vibrations, were decreased faster than untreated controls. However, a band at 1735 cm" , 1  indicative o f a carbonyl stretching vibration in either ketones or carboxylic  acid  compounds, increased markedly. Cellulose was less affected. The changes at bonds 1267, 1510, and 1600 cm" are related to delignification and demethoxylation which contribute 1  to the discoloration o f wood surface by generating new chromophoric groups, such as carbonyl-containing compounds (IR spectra peak at 1730 cm" ). 1  The role that Q A C or D D A C treatment plays in accelerating delignification and demethoxylation during photo-exposure were studied by L i u (1997). It was found that both fixed and absorbed D D A C accelerate photodegradation of wood. Electron spin resonance studies (Liu, 1997) of D D A C treated wood suggested that D D A C functioned as a photosensitizer during the photodegradation o f wood, as demonstrated by the spectra o f FeCb-treated wood. The sensitization takes place via the D D A C - l i g n i n complex, which can promote free radical formation by energy transfer. It was also concluded that both the physically absorbed D D A C  and chemically  fixed  DDAC  impact on the  formation and decay o f the phenoxy free radicals, based on the influence o f D D A C leaching and retention on the free radical formation and decay.  15  2.3. FTIR spectral analysis of photo-exposed wood F T I R spectroscopy is a useful method for a rapid and convenient characterization o f a thin wood sample and its major components. The F T I R technique has four important characteristics that contribute to its usefulness in detecting compositional changes o f wood. They are: a) no two molecules have the same infrared spectrum; b) several characteristic peaks exist in wood (i.e., peaks that always occur in the same wavelength region); c) the infrared spectra o f mixtures are additive and the absorption o f the key peaks is proportional to the concentration o f the chemical studied; and d) the IR spectra can be obtained non-destructively. The F T I R spectrum is obtained by passing a beam o f infrared radiation o f constantly varying frequency through a sample o f the compound. A detector generates a plot o f percent transmission o f radiation vs. the wavenumber. The bonds in the irradiated molecules are constantly vibrating. A stretching vibration is a vibration occurring along the axis o f the bond, while a bending vibration occurs out o f the axis o f the bond. Each stretching and bending vibration o f a bond is associated with a certain frequency. When a chemical is irradiated with an energy that exactly matches the energy required for the vibration frequency o f one o f its bonds, the vibrating bond w i l l absorb energy and generate an absorption peak in the F T I R spectrum. The wavenumber range o f interest lies between 4000 cm" to 400 cm" . The fingerprint region (1800 cm" to 1000 cm" ) contains 1  1  1  1  many complex signals generally resulting from bond bending that are unique for each compound. The IR spectrum o f wood is due to the combined absorption o f individual components, namely, cellulose, hemicellulose, and lignin and extractives. The absorption bands in the 1740-1720 cm" region are due primarily to the carbonyl stretching 1  16  vibrations o f carboxylic and acetyl groups. Several characteristics bands at 1600, 1510, and 1265 cm" are due to the C=C stretching vibrations o f the benzene ring presented in 1  lignin. The changes noted in the IR spectra o f wood after irradiation with U V light are indicative o f changes in chemical compositions at exposed surfaces. One indication o f chemical changes in wood surfaces is an increase in cellulose content and a decrease o f lignin content o f the weathered wood surfaces (Evans et al., 1992; Wang and L i n 1991; Hon 1994). The photodegradation process is initiated by the formation o f free radicals, presumably with oxidation o f phenolic hydroxyl groups (Hon 1981). Free radicals generated in wood are known to react readily with oxygen to produce hydroperoxides (Hon and Chang 1984; H o n and Feist 1992). The wood photodegradation results i n a decrease in methoxyl and lignin content and an increase i n carboxyl i n wood (Evans et al., 1992). IR absorbance o f carbonyl groups at 1720 and 1735 cm" was also observed to 1  be reduced because o f the washing o f the carbonyl rich components by rain (Feist and H o n 1984).  2.4. Wood protection against photodegradation Because photo-induced discoloration and deterioration o f wood are undesirable, much work  has been done to protect wood and woody material surface  from  photodegradation in outdoor applications. One or a combination o f the following methods may be adopted to prevent photo-induced degradation (Hon, 1991b). •  Cutting off the U V light,  •  Modifying the light absorbing structures present in wood,  •  Destroying the structures participating in discoloration,  17  •  Eliminating oxygen or capturing O2,  •  Scavenging the free radicals formed during photo-exposure.  2.4.1. Painting Painting is a common method to protect wood surfaces from weathering. Paints contain pigments that screen wood from solar radiation and because they form a f i l m over the wood surface they also prevent surface wetting and erosion. A correctly applied and maintained paint system, including a primer and at least two topcoats, can greatly reduce the deleterious effects o f weathering on wood. However, paints are less effective i n controlling decay and dimensional movement and therefore, they often perform better on wood that has been pretreated with a water-repellent preservative (Evans, 2001). For end users, it is often important that the wood retains its natural color or texture. A clear coating is often used. However, although clear coatings often contain U V stabilizers and a biocide, are limited i n their ability to protect wood from weathering because they transmit light, which can degrade the underlying wood surface. Hence they perform badly on wood used outdoors and invariably fail by peeling and cracking within 2-3 years o f application (Evans, 1991). In order to enhance the performance o f clear finishing o n wood, a pretreatment with photostabilizers or U V absorbers is often required.  2.4.2. Inorganic treatment The protection o f wood and wood-based materials from weathering has been widely studied. Certain inorganic preservative or chemical treatments have been reported that have the potential to protect wood surfaces from ultraviolet degradation (Feist, 1978; 1979; Chang and Hon, 1982; Zhang and Kamkem, 2000). Research found that the  18  formation of complexes between wood components and inorganic ions was efficient in controlling wood weathering (Chang et al,  1982). Jin et al. (1991) reported that  ammoniacal copper quat ( A C Q ) and chromated copper arsenate ( C C A ) treatment of southern pine made it far less prone to surface weathering than untreated controls. Zhang and Kamdem (2000) reported that wood treated with copper monoethanolamine (CuM E A H ) showed much less lignin degradation than untreated and ethanolamine treated wood, based on the changes to the peak intensity at 1510 cm" . Treatment with water1  soluble salts o f chromium, iron and copper were also used and effectively increased the weathering resistance of wood (Feist, 1979; Feist, 1983; Feist and Williams, 1991; Jin et al., 1991; Evans et al., 1994). A greater preservative content in treated wood generally resulted in greater resistance to weathering and improved surface durability. It was hypothesized  that  wood-ion  complexes  formed  at  the  wood  surfaces  provided  photoprotection by blocking the free phenolic groups, which are the reactive site o f photochemical reactions (Hon and Chang, 1985; Ross and Feist, 1991).  2.4.3. O r g a n i c chemical protections A large number o f organic chemicals have been used to modify wood ( L i n and Kringstad, 1970b; Gierer and L i n , 1972; Evans et al., 2000; Evans et al., 2002). Since the a-carbonyl, conjugated C = C double bond and phenolic hydroxyl groups are the principle chromophoric groups in wood, they must be modified to reduce photodegradation. Acetylation, methylation, hydrogenation and benzoylation efficiently decrease photoinduced oxidation. If spruce milled wood lignin is first reduced with sodium borohydride, followed by catalytic hydrogenation o f the conjugated double bonds, it is completely stable towards U V light (Lin and Kringstad, 1970b). The effect o f acetylation on the  19  weathering performance o f Scots pine wood veneers was studied by Evans et al. (2000). Scots pine wood veneers were acetylated to different weight gains ( W G s ) up to 20% and then exposed to nature weathering. It was found that acetylation o f wood veneers to low W G s o f 5 and 10% increased the susceptibility o f lignin to degradation and also the depolymerisation o f cellulose during weathering. A t acetylation to higher W G s (20%), holocellulose was protected, but lignin was not protected. They suggested that the substitution o f lignin phenolic hydroxyl groups, which occurs preferentially at low W G s , reduces the photostability of wood. Acetylation at low W G s may open up the wood matrix and increase the accessibility o f cellulose to photodegradation, but further substitution blocks off the susceptible areas from degradation (Evans et al., 2000). Recently, Evans et al. (2002) used benzoyl chloride to modify wood surfaces. They found that benzoylation o f wood to high weight gains (~70%) was effective at protecting wood from photodegradation and stabilizing lignin. Benzoylation reduced the quantity o f free radicals formed in wood, when it was exposed to U V light. The findings suggested that the benzoyl groups in wood may absorb U V light or scavenge free radicals. Grafting o f UV  absorbers to wood can also retard the photo-induced discoloration o f wood  (Williams, 1983; Grelier et al., 1997). However, this system has a number o f limitations in that it requires the synthesis o f a functionalised U V absorber and the use o f high temperatures or microwave irradiation to bond the U V absorber to wood (Evans et al., 2002). The weathering process is related to the ability o f free radicals to be produced under the exposure o f the wood to U V light. The generation o f peroxy or phenoxy free radicals has been hypothised as a principal pathway by which wood is weathered.  20  Therefore strategies for slowing weathering have generally been based on interfering with the formation o f these free radicals. The strategies include the use o f free radical scavengers, free radical inhibitors and anti-oxidants.  21  Chapter 3 Methodology 3.1.  Wood sample preparation Southern pine (Pinus sp.) sapwood blocks measuring 10 m m (tangential) x 10 m m  (radial) x 40 m m (longitudinal) (3-4 annual rings) were vacuum pressure impregnated with distilled water to soften them. Earlywood sections approximately 60 u m (in thickness) were cut from the longitudinal x tangential surface using a microtome (Spencer-lens). Sections were air-dried for 2 days, and then kept flat in the dark prior to chemical treatment.  3.2.  Chemicals  3.2.1. Biocides Lonza has developed a number o f new alkylammonium compound ( A A C ) based biocides formulated for wood protection in above ground applications. A s mentioned preciously, it is important for treated wood to resist photodegradation when used i n outdoors. Therefore, this study examined the ability o f these new A A C compounds to prevent the photodegradation o f wood. The chemicals provided by L o n z a Inc are listed in Table 3.1. The concentrations o f chemical used i n the treatment o f wood samples are listed in Table 3.2.  22  Table 3.1: Chemicals supplied by Lonza. Code Names WP-40 Alkyl(Ci Ci Ci6)dimethylamine oxide Propiconazole Inerts 2  4  (w/w), % 5.2 0.5 94.3  WP-41  Didecyldimethylammonium chloride Propiconazole Inerts  4.78 0.45 94.7  WP-42  A l k y l ( C C i C i ) d i m e t h y l a m i n e oxide copper carbonate, basic Inerts  5.8 8.4 85.8  WP-43  *Alkylbenzylhydroxyethylimidazolinium chloride copper (II) carbonate, basic Inerts  5.7 8.4 85.9  WP-46  A l k y l ( C i C i C | ) d i m e t h y l a m i n e oxide Cyproconazole Inerts  5.2 0.1 94.7  WP-47  Didecylmethylpoly(oxyethyl)ammonium Propionate Cyproconazole Inerts  4.7 0.1 95.2  WP-48  A l k y l ( C i C i C i ) d i m e t h y l a m i n e oxide Cyproconazole Inerts  9.0 0.5 90.5  WP-62  Didecyldimethylammonium carbonate Inerts  16 84  WP-63  Didecyldimethylammonium chloride Inerts  16 84  WP-64  Didecyldimethylammonium chloride Propiconazole Inerts  16 1.5 82.5  12  4  2  2  6  4  6  4  6  * 1 -hydroxyethyl-1 -benzyl-2-alkylimidazolinium Chloride  23  Table 3.2: The concentration of the chemicals used to treat wood samples. Chemicals or codes  Original concentrations, %  Benzyldimethyldodecyl ammonium chloride DDAC  77  Concentrations o f active components in formulated products (copper as copper oxide) 1%, 2%  80  2%  Wp-40  5.2  2%  Wp-41  4.78  2%  Wp-42  8.4  0.25%, 0.5%, 1%, 2%  Wp-43  8.4  2%  Wp-46  5.2  2%  Wp-47  4.7  2%  Wp-48  9.0  5%  Wp-62  16  5%  Wp-63  16  5%  Wp-64  16  5%  Containing copper Containing copper  24  3.2.2. Additives Butylated hydroxytoluene ( B H T ) (Figure 3.1) is a phenolic compound that is used as an antioxidant by the food industry. Antioxidants are compounds capable  of  interrupting the autoxidation chain reaction, thus preventing the free-radical autoxidation processes that occur during thermal and photoxidative degradation o f materials. To accomplish  this,  antioxidant  compounds  contain  extractable  hydrogen  atoms.  Antioxidants, represented as A H below, react with free radicals, hydrogenating them and becoming themselves radicals. However, instead o f propagating the reaction, they react with other radicals to sequester them and form stable covalently bonded compounds. Thus they terminate the free radical and become consumed during the process. The kinetics of the antioxidant reaction may be described as (Seewald, 1998): ROO* + A H -> R O O H + A*  (1)  A* + ROO* -> R O O A  (2)  2A* -> A - A  (3)  A* + R H -> R* + A H  (4)  where ROO* is the free radical generated, A* is free radical from antioxidants. For a hindered phenolic antioxidant, such as B H T , reactions (2) and (3) are the dominant ones. For non-hindered antioxidants, all reactions are equally competitive. There has been increasing interest in using phenolics derived from food and plants as antioxidants and scavengers of free radicals (Bors and Saran, 1987; Bors et al., 1990; Yuting et al., 1990). The use o f such chemicals for the photoprotection o f wood is also attractive. The antioxidant activity o f phenolics is mainly due to their redox properties,  25  which allow them to act as reducing agents, hydrogen donators, and singlet oxygen quenchers (Rice-Evans et al., 1995). Although antioxidant activity traditionally has been attributed only to soluble phenolic compounds (extractable polyphenols), a recent report (Hagerman et al., 1998) suggests that nonextractable polyphenols  (polymeric proanthocyanidins  and high-  molecular-weight hydrolysable tannins) are 15 to 30 times more effective at quenching peroxyl radicals than simple phenols. In the current study, the additives incorporated into solutions o f D D A C included: butylated  hydroxy  toluene  (BHT),  1,4-diazabicyclo  (2,2,2)  octane  (Figure 3.2),  lignosulfonic acid (Figure 3.3), tannic acid (Figure 3.4), polar extractives from Douglasfir (Pseudotsuga menziesii) bark, western red cedar {Thuja plicata) heartwood, and Scots pine {Pinus sylvestris) heartwood. The chemicals B H T (10, 823-5), 1,4-diazabicyclo (2,2,2) octane (D2, 780-2), tannic acid (21, 671-2) and lignosulfonic acid (37, 097-5) were purchased from Aldrich. They were prepared as solutions i n methanol or distilled water containing 2% (w/w) additives with either 2% or 5% D D A C (Table 3.3).  CH  3  Figure 3.1: Structure o f butylated hydroxytoluene ( B H T ) .  26  Figure 3.2: Structure o f 1,4-diazabicyclo (2,2,2) octane.  Figure 3.3: Structure of lignosulfonic acid.  Table 3.3: The solutions o f the additives into D D A C prepared for the research. Additives, 2%* Treating solution  DDAC  BHT  1,4diazabicyclo (2,2,2) octane  Douglasfir bark extractives  2%  V  5%  A/  western red cedar extractives  y  1  Methanol Methanol Distilled water *based on air-dried weight, for wood extractives  Solvents  Methanol  Tannic acid  Scots pine extractives  LSA  A/  A/  V  Distilled water  Distilled water  A/  Methanol  3.2.3. Extraction of wood extractives Douglas-fir bark, western red cedar heartwood and Scots pine heartwood sawdust were prepared by grinding up thin chips, using a W i l e y mill, until the sawdust passed through a 20 mesh screen. About 8.0 g o f air-dried sawdust from each species was weighed into cellulose extraction thimbles. A cone-shaped piece o f filter paper with a cotton ball was placed i n the thimbles to prevent the loss o f sawdust during Soxhlet extraction. The thimble containing the sawdust was placed in the Soxhlet apparatus (Figure 3.5), and extracted overnight for 24 hours with 200 m L o f 50:50 methanol-water solvents, at a minimum rate o f 4 siphonings per hour. After the extraction phase was completed, the solution containing the extractives was transferred to a round bottom flask, and the majority o f the solvent removed using a Rotavapor. The concentrated extract solution was then transferred to large diameter Petri plates and any remaining solvent allowed to evaporate. The residual extractive solids were then kept i n a desiccator for use during the preparation additives solutions.  28  Figure 3.5: Soxhlet extraction apparatus.  3.3. Wood sample treatment When mixed lignosulfonic acid or tannic acid with D D A C , insoluble materials.were formed. Therefore, the treatment was done by first soaking a wood sample in 50 m L o f D D A C solution for 2 hours. After being air-dried for 24 hours at ambient temperature (18-20°C), it was then soaked i n lignosulfonic acid or tannic acid solution for 2 hours. F o r the other treatments, wood samples were soaked in the formulated chemical solution (Tables 3.2 and 3.3) for 2 hours. After treatment, the samples were removed from the solution, and excess liquid on the sample was removed with a Kimwipe® tissue. The samples were then air-dried overnight at 18-20°C. After the final air-drying the treated 29  samples and untreated control were placed in the U V chamber for U V irradiation (see section 3.5 below). Three replicates were used for F T I R measurements. Untreated sections treated with distilled water (as above) were used as controls.  3.4. Leaching T o examine whether the photoprotectants were soluble, a leaching study was done. After U V irradiation, treated samples and untreated controls were soaked i n distilled water for 15 minutes. They were then air-dried before examination by F T I R and color analysis.  3.5. UV irradiation and FTIR measurements To photoirradiate the thin sections, they were placed in pyrex Petri dishes about 10 cm from a U V lamp, located in the cooling well o f a photoreactor chamber from A C E GLASS  incorporated (12160-10/12162-07) operating at room temperature (25°C).  Samples were irradiated with a medium pressure quartz mercury lamp (450 watts). A l l wood sections were examined at four stages: a) before irradiation; b) after 7 hours irradiation; c) after 28 hours irradiation; and d) after 6 days irradiation. Following each period o f U V irradiation, the samples were collected and placed in a cardboard holder for F T I R measurements. The F T I R spectra were obtained at a resolution o f 8 cm" , 64 scans 1  per sample over the range 400-4000 cm" using a Perkin-Elmer F T I R 1600 series 1  instrument. In the plots o f combined spectra, the transmission scale o f the offset spectra is omitted for the sake o f clarity.  30  3.6. Quantitative analysis of FTIR spectra F T I R spectra were examined quantitatively to more precisely determine the effects of treatment and exposure on the photodegradation o f wood during exposure to U V light. Since  a large  number  o f the F T I R  absorption peak  in wood  change  during  photodegradation, it is important to select an internal reference peak that is unaffected by U V irradiation. In this study, the relatively stable glucopyranose ring vibration at 1162 cm"  was used as an internal reference (Segal et al., 1960). The typical  1  lignin  characteristic peak at 1510 cm" (C=C ring stretching i n aromatic lignin units) was chosen 1  to monitor lignin degradation in the wood, and the peak at 1730 cm" was used to 1  evaluate the formation o f carbonyl groups (Hon and Feist, 1986). Peak areas o f interest were calculated by drawing a baseline from the point o f transmittance at the beginning o f the peak to its end using the spectrometer software for peak area determination (IR Spectra v2.0 ™ ) . Changes in areas o f the peaks at 1510 and 1730 cm" relative to the 1  internal reference peak at 1162 cm" were used to quantify delignification and the 1  formation o f carbonyl groups during U V irradiation, respectively. The delignification rate o f treated and untreated wood after U V irradiation was also expressed by subtracting relative absorption areas o f treated wood from the initial relative absorption areas. Because o f changes in the spectra when copper was present i n the formulation, the relative changes i n the areas o f the peaks due to the lignin (1510 cm" ) or carbonyl (1730 1  cm" ) compared to the internal standard were used. For the second phase o f research 1  where additives were combined with D D A C , the percentage changes i n the areas o f the lignin peak compared to that before irradiation were calculated. 31  3.7. Color and brightness measurement 3.7.1. Theory The surface color o f wood was determined according to the ISO 2470 standard and the C I E parameter. The C I E L A B system expresses three parameters a* b*, and L* (Figure 3.6). The L* axis represents the lightness, whereas a* and b* are the chromaticity coordinates. The +a* and -a* parameters represent red and green, respectively. The +b* parameter represents yellow, whereas -b* represents blue. L* can vary from 100 (white) to zero (black). L* together with a* and b* color parameters were measured on each sample, before and after exposure to U V light. Measurements o f color used a D65 light source, as recommended by C I E 1976 (Billmeyer and Saltzman, 1981). Color parameters were used to calculate the color change A E * as a function o f the UV-irradiation period according to Eqs. (5), (6), (7), and (8).  A L * = L * - L|*  (5)  Aa* = af* - a;*  (6)  Ab* = b * - bi*  (7)  f  f  AE*  =VAI* +Aa* +Ab* 2  2  2  (8)  Where, A L * , Aa*, and Ab* are the changes between the initial (i) and final (f) values. L*, a* and b* contribute to the color change A E * . A l o w A E * corresponds to a low color change or a stable color.  32  Figure 3.6: Representation o f C L E L A B color system.  3.7.2.  Methodology The surface color and brightness o f the wood sections were measured by a  Minolta CM-2600d spectrophotometer (Figure 3.7). A l l samples were measured before U V irradiation and after 7 hours, 28 hours, and 6 days o f continuous U V irradiation. Several measurements have made in the center o f the wood sections, o f the color and brightness o f the wood surfaces. Each measurement represented the average o f the area illuminated (3 mm diameter). Also, three replicates were used. The average changes in color (AE*) and brightness (L*) data for both untreated and treated samples, were plotted against the irradiation time. According to H o n (2000), it w i l l not be possible to detect changes in color with the naked eye, when they are calculated to be less than 3, using the C I E L A B color system. 33  CM-2600d Figure 3.7: Spectrophotometer CM-2600d from Minolta.  34  Chapter 4 Photo-resistance of Alkylammonium Compound Treated Wood to UV Irradiation 4.1.  The photodegradation of sapwood treated with amine oxide or QAC compounds  4.1.1. Effect of the treatment The infrared absorption at approximately 1510 cm" is often used to monitor 1  lignin in wood, arising from the C=C stretching vibrations of the aromatic ring present in lignin (Table 4.1). This peak usually appears i n the region o f 1515-1500 cm" depending 1  on the ring substituents. It was noticed that the peak intensity at 1510 cm" was reduced 1  for the wood sections treated with 5% wp-62, wp-63 and wp-64 (Figures 4.1.7a, 4.1.8a, and 4.1.9a) compared with the untreated control (Figure 4.1.1a). The decrease i n intensity of this peak after the treatment implied that the substituents o f the aromatic rings have been changed by the chemical bonding o f the biocides. L i u (1997) reported the decrease in the peak intensity o f the phenolic hydroxyl group following D D A C or A C Q treatment and suggested that an interaction o f the hydroxyl group with D D A C and A C Q had taken place. The F T I R results confirmed that a cation exchange reaction took place between D D A C and the protons i n the carboxylic acid and phenol i n wood (Jin and Preston, 1992 and Doyle, 1995). Compared with untreated controls an increase i n the peak intensity at 1730 cm" , 1  which represents carbonyl groups, was observed after wood sections treated with 2% wp40, 2% wp-41, 2% wp-46, 2% wp-47, 5% wp-62, 5% wp-63, and 5% wp-64 (Figures, 4.1.1a, 4.1.2a, 4.1.3a, 4.1.4a, 4.1.5a, 4.1.7a, 4.1.8a, and 4.1.9a). This may be caused by the chemical treatment resulting in oxidation o f - O H groups in secondary alcohol in lignin and forming carbonyl groups. 35  Examination o f the F T I R spectra o f treated samples showed a new peak at 1460 cm" , which represents the C - N stretching vibration, occurred in the F T I R spectra after 1  treatment (Figures 4.1.4a, 4.1.6a, 4.1.7a, 4.1.8a, and 4.1.9a). This was particularly noticeable in the sections treated with the higher (5%) solution concentrations (Figures 4.1.8a and 4.1.9a) confirming that its presence was due to the addition o f the bound or absorbed chemicals.  36  Table 4.1: The assignments of absorption peaks in IR spectra o f southern pineFrequency, cm'  Group or class  Assignments & remarks  O H in wood H-bonded  O H stretching vibration  - C H attached to O & N  C H stretch  C = 0 in unconjugated ketones aldehydes & carboxyl compounds C = 0 in para-OH substituted aryl ketone, quinone C=C in alkenes, etc.  C = 0 stretching  C=C in aromatic ring in lignin  Aromatic skeletal vibration  COO"  C O O " antisymmetrical stretching  1510-1515  C=C in aromatic ring of lignin  Aromatic skeletal vibration  1425  C=C in aromatic ring  Aromatic skeletal vibration  CH2 in carbohydrates  CH2 bending  1420-1300  C0 "  Symmetrical stretching vibration  1370  C - H in all components in wood  C - H deformation (bending)  1315  CH2 in cellulose  CH  1267  C O in lignin and hemicellulose  1162  C-O-C in cellulose  1035  Aromatic C - H  Guaiacyl ring breathing with C O stretching Antisymmetrical bridge oxygen stretching C - H in plane deformation  2860  1  3  1720-40  1645-60  1600-1610  2  Same C=C stretching  2  wagging  37  4.1.2. Overview of the FTIR during photoexposure In evaluating the weathered wood, attention was focused on the changes o f absorption peaks at 1720-40, 1600, 1510, 1267, and 1162 cm" . The peaks at 1720-1740 1  cm" are associated with the carbonyl group (C=0) stretching vibrations o f esters and 1  carboxylic acids. The peaks at 1600 and 1510 cm" are due to the C = C stretching 1  vibration from the benzene ring (from lignin) (Sarkanen et al., 1967). The peak at 1162 cm" (C-O-C) is the antisymmetrical bridging oxygen stretching vibration i n cellulose. It 1  w i l l allow changes in cellulose to be monitored. The intensity o f these peaks is considered important, since they can be correlated to changes i n functional groups and chemical structure o f wood components. The infrared spectra o f treated and untreated earlywood sections before and after weathering, but without any washing, are shown in Figures 4.1.1a to 4.1.9a, and Figures 4.1.10, to 4.1.11. For the untreated controls changes in the F T I R spectra were noticed after 6 days o f U V irradiation. Firstly, the intensities o f the peaks at 1600, 1510, and 1267 cm" were decreased. Secondly, the peak at 1720-1740 1  cm" increased in area and broadened. For the wood sections treated with 2% wp-40, 2% 1  wp-41, 2% wp-46, 2% wp-47, 5% wp-48, 5% wp-62, 5% wp-63, 5% wp-64, didecyldimethylammonium chloride ( D D A C ) , and benzyldimethyldodecylammonium chloride and untreated sections (Figures 4.1.2a to 4.1.9a, 4.1.10 to 4.1.11), similar changes were found in the intensity o f the peaks at 1600, 1510, 1267, and 1730 cm" to 1  those observed in the untreated wood (Figure 4.1.1a). This suggested that none o f these chemicals are able to prevent degradation o f lignin. However, while the lignin i n the wood sections treated with 5% wp-48 was clearly degraded based on the reduction in the intensity o f the peaks at 1510 and 1600 cm" , there was no corresponding increase in the 1  peak at 1730 cm" which arises from the resulting quinone, suggesting that the treatment 1  38  o f wood with wp-48 (Figure 4.1.6a) prevented the formation o f carbonyl rich compounds. When wood was treated with 2% benzyldimethyldodecylammonium chloride, it slowed down the delignification based on the changes in the peak at 1510 cm" , when compared 1  with those in the untreated control. These changes at peaks 1510, 1600 and 1267 cm" are 1  related to delignification and demethoxylation which contribute to the discoloration of wood surface by generating new chromophoric groups, such as carbonyl-containing compounds and quinones ( L i u et al, 1994).  4.1.3. Effect o f the washing While the photodegradation action was monitored on samples after periods o f exposure, such changes cannot examine whether the resulting products are water-soluble. To study these chemically treated wood, samples were leached in distilled water for 15 minutes following U V irradiation for 7 hours, 28 hours and 6 days. After leaching, the sections were air-dried, before being examined using FTIR. The main differences in the spectra (Figures 4.1.1a, 4.1.1b to 4.1.9a, 4.1.9b) o f the leached and unleached wood samples were i n the changes to the transmission peaks at 1730 and 1460 cm" . The peak at 1730 cm" , which is related to the C = 0 group stretching 1  1  vibrations in aldehydes, unconjugated ketones, esters and carboxylic acids, became weaker (Figures 4.1.1b to 4.1.9b). This is due to the removal of the soluble quinone type materials, which are clearly water-soluble. The peak at 1460 cm" , which represents the 1  C - N stretching vibration in the A A C , became visible after treatment (Figures 4.1.4a, 4.1.6a, 4.1.7a, 4.1.8a, and 4.1.9a) and sharply decreased after washing (Figures 4.1.4b, 4.1.6b, 4.1.7b, 4.1.8b, and 4.1.9b). This is interpreted as implying that unfixed chemicals in wood were leached during washing.  39  (S  x>  41  42  |<8 * c •g .2 CO  a  TJ  . a <o  •2 «« 8  s s  8 O  _•» co • is -Q  u > cs a. L-> srf  g H soireuiujsirejx  —  H f £  S  SoNO  N XI  cS  a  T3  o  I TJ  E  c • —H  o ts a>  TJ  o o  i~ 4> CC  T3 C CO  C O  -a  2 o '5 -3 ^ RJ T J  ee)  i IS * C  30irettimsuB.il  .. * cs o  T  03  c  43  •a .2  ~ t C  -  o « O  «S  CO  ^  _  C  O  -  0  G  co  >>  £ .3  -g  «— J  9!  I o 1 .5*"2  «g  : »  00  .. «° M  aouBHiujsueji  .2  T3 4-*  CO  -a  at  .a «  +3 O  <C S  05  «3  CO  -o o o  CO  T3 C M  O  ca 03 -O  E  fa  T3  CX !  3 O  | 90UBUILUSU6JJ,  c2 -C 00  CO  00  H  »  v> J>  -o  .2  co cO ^ 2 cO  * J  ° fc cn • —  C o  •_  1>  '& <c  U CO  <U —• oo "O  CO  o o  CO  g o  a  '-S --^  ea  co T3  • g § i H <& to « oo aOUBHILUSUBJl  ..  ts  CO O r - v  vq|  *  o  OO  co  e  f* 0  tU  N  /  «/^ .£>  45  o  90UBUIUJSUBJ1  CO  r-  fa  1 <s •o .2 w  i  co  CO  E 0)  ea  eS O - co O R >.  TJ  CO  CO T J  §.5-2  « > S « b co  8 3 P HS<S -e  » oo  eoueniwsueJi  CO ^  ^  (N  £2  a. 3 5  JS  +5  —  c  CO  o 1  .Q  -o 03  t X) 03  1) co  T3 O O  g r.  £ .2 .a  o  03  o to  i>  T3  03  I  ^  CO  03  ^3 —  T3  s  co p 3  H [I*  90UBJJ!UJSUBJ1  JO 00  O  oo CM  S 5b N O tm x>  47  48  eoueuitusuBJi  ce  4.2.  Treatment of QAC related chemicals containing copper  4.2.1. Effect of copper chemicals as observed by FTIR Several changes in the F T I R were noted when the wood sections were treated with the copper containing formulations wp-42 and wp-43. Firstly the absorption at 1730 cm' became weaker (Figures 4.2.1a and 4.2.5a). Secondly, a peak around 1630 cm" 1  1  sharply increased, and also a new band around 1320 cm" , assigned to the C O O " 1  symmetrical stretching vibration, was observed (Figures 4.2.1a, 4.4.2a, and 4.2.5a). This was particularly noticeable when a high solution concentration was used (Figures 4.2.1a and 4.2.5a). In the spectra o f the wood samples treated with wp-42 and wp-43 (Figures 4.2.1a to  4.2.5a),  very  weak  peak  intensities  at 1720-1740  cm" were 1  noted  before  photoexposure. They did not show significant change even after 6 days o f U V irradiation. The reduction o f the peak at 1730 cm" during treatment indicated that copper reacted 1  with the carbonyl containing groups in wood. The carbonyl peak at 1730 cm" was shifted 1  to around 1630 cm" , which sharply increased after treatment. It has been suggested by 1  several authors that basic copper preservatives can react with carboxylic and groups i n the uronic acid in hemicellulose, causing either their cleavage or their involvement in complex formation (Zhang and Kamdem, 2000; Jiang, 2001). These authors examined the interactions between copper ethanolamine and phenolic hydroxyl, carboxylic, and ester groups in wood components, by FTIR. It was concluded that hemicellulose and lignin play a significant role in bonding copper, while the role o f cellulose in retaining copper was negligible. They concluded that the carboxylic groups in hemicellulose and the phenolic hydroxyl and ester groups in lignin are major bonding sites for copper.  50  4.2.2. Effect  of  Q A C related  chemicals  containing  copper  on  wood  photodegradation by UV irradiation The I R spectra o f wood sections treated with Q A C biocides containing copper, before and after U V irradiation, are shown in Figures 4.2.1a to 4.2.5a. The extent o f the delignification o f U V exposed wood is indicated by the changes in the characteristic stretching vibration o f lignin at 1600 and 1510 cm" and the peak associated with lignin at 1  1267 cm" . In the spectra the peaks at 1510 and 1267 cm" observed in the untreated 1  1  control (Figure 4.1.1a) remained relatively intense following treatment with 2% wp-42 and wp-43 or even 0.25% wp-42 (Figures 4.2. l a to 4.2.5a) after 6 days o f U V irradiation. Also, the absorption peak at 1730 cm" that represents carboxylic and carbonyl groups, 1  remained almost unchanged in wood treated with wp-42 and wp-43 (Figures 4.2.1a to 4.2.5a). Clearly, treatment with biocides that contained copper, prevented  lignin  degradation and also the formation o f byproducts containing carbonyl groups. Previous research suggested that copper(U) in A C Q treatments is able to significantly reduce wood photodeterioration (Liu, 1994; Jin et al, 1991). This resistance to photodegradation has been explained by the chelating o f the copper(II) with the guaiacyl groups in lignin. These chelates can photostabilize wood. A similar mechanism had been proposed by Feist (1979) and confirmed by Evans et al. (1992a) who proposed that photostable lignin complexes were responsible for the enhanced weathering resistance o f chromium trioxide treated wood. They hypothesized that wood ion complexes formed at the wood surfaces provide  photoprotection  by blocking  the free phenolic  groups,  which  are the  photochemical reactive sites (Hon and Chang, 1985, Ross and Feist, 1991). From the current study, the chemicals containing copper(II) (wp-42, wp-43) clearly provided better  51  protection against delignification and also prevented the formation o f carbonyl groups (Figures 4.1.1a, 4.2. l a to 4.2.5a).  4.2.3. Effect of copper concentration on the FTIR spectra When the copper content increased, the absorption peak at 1730 cm" i n the 1  treated sections became weaker (Figures, 4.2.1a to 4.2.4a, 4.2.6), while the absorption around 1630 cm" became more intense (Figures 4.2.1a to 4.2.4a, 4.2.6). During photo 1  exposure the peak at 1510 cm" decreased less than i n untreated wood (Figures 4.2.1a to 1  4.2.4a). This confirms a beneficial effect o f copper on slowing lignin degradation. A peak around 1320 cm" , due to the C O O " symmetrical stretching vibration, formed during 1  treatment with 2% or 1% wp-42 or wp-43 (Figures, 4.2.1a, 4.2.2a, and 4.2.5a), and remained relatively stable during photoexposure (Figures, 4.2.1a, 4.2.2a, and 4.2.5a).  4.2.4. Effect of sample washing after photoexposure, on the FTIR spectra When the wood sections were washed after U V exposure, several absorption bands, which were formed during treatment, decreased or disappeared. Firstly, the absorption peak at 1630 cm" , which is observed when conjugated alpha-carbonyl groups 1  and quinines are present, rapidly decreased (Figures, 4.2.1a, 4.2.2a, 4.2.3a, and 4.2.5a). The reduction o f the peak at 1630 cm" could be due to hydrolysis o f a carboxylate salt 1  formed i n the wood and which resulted i n the increase o f the peak at 1600 cm" . 1  Secondly, the peak at 1460 cm' , arising from the C - N stretching vibration i n the A A C , 1  sharply decreased (Figures, 4.2.1a, 4.2.2a, and 4.2.5a). This can be explained by the washing out o f unfixed A A C . Thirdly, the peak at 1320 cm" almost disappeared (Figure, 1  52  4.2.1a, 4.2.2a, and 4.2.5a) suggesting that the action o f washing leached out water soluble carboxylate salt formed during the treatment.  53  54  —  % cn <U o cn *~ C >-< O «  t> cd 8-2  •9  d  S.2  c .2 o "S * -2 O  .1 .1  cu S c3  s; 9  a. i  cn  cn i OJ  CCS  H 90UBHJUJSUBJJ.  03 CM  CM CM  3  ^ '  s00 3  1  o=  NO  00 CM  f£ * a  T>  .2  fi -s  ^ CO Ca '  — at  ~ t -o g  co  ~ - -5  O <U 2 O  (!)  r  „ co  O  0 d  • - *°  1 i » 00 . . - ° <N  eoueniujsueji  £ ^1? <N rn of  i  * t  M D  a  S3 O  -o ' I td  1  TJ  CO  C O  tS to  <0  m ed  -o -o e O o Cd _r  <*>  C >> O ed  O  I *° ed ed  v£)  T3 o fc T3 o  8-! i g H  ti-  90UBUIOISUBJ1  ed  3 O J3 00  'ed CO  5 ?  u. 3 O JS  58  Figure 4.2.6: F T I R spectra o f wood sections treated with different concentrations o f wp42 after 6 days o f U V irradiation.  4.3.  The relative delignification rate and the formation of carbonyl groups Figures 4.3.1 to 4.3.3 show the relative changes o f the lignin peak area at 1510  cm" in chemically treated wood, and untreated wood, during photo-exposure. Based on 1  the relative peak area changes in the spectra o f the treated and untreated samples, the lignin was degraded rapidly during the first 28 hours o f U V irradiation, and thereafter more gradually (Figures, 4.3.1, 4.3.2, and 4.3.3). This suggested that at least 6 days o f  59  photo-exposure was needed to determine the relative delignification rate. W o o d sections treated with wp-47 showed rapid delignification over the whole 6 days (Figure, 4.3.2). It was clear that the chemical treatment enhanced the delignification. In Figure 4.3.2 treatment accelerated delignification with the worst being observed for 5% wp-64 treatment. However, sections treated with wp-41, showed exaggerated delignification similar to D D A C (Figure 4.3.1). While treatment with wp-46 and wp-40 was accelerated the delignification to less extent, it was still worse than in untreated controls. Only benzyldimethyldodecylammonium  chloride  treatment  (B)  slowed  delignification,  possibly due to the benzyl group acting as a sacrificial molecule in place o f lignin. Figures 4.3.4 to 4.3.6 allow the formation o f carbonyl groups o f the chemically treated and untreated wood to be observed. It was clear that wood treated with 2% wp-40, 2% D D A C , 2% wp-47, and 5% wp-62, 5% wp-64, and 5% wp-64 showed more carbonyl groups formed than untreated wood and wood treated with other chemicals (Figures, 4.3.4 to 4.3.6). The wood treated with wp-48, wp-42 (containing Cu) and wp-43 (containing Cu) showed less formation o f carbonyl groups comparing with the untreated controls (Figures, 4.3.5 and 4.3.6).  60  0.5 0.4 0  50  100  150  U V irradiation, hours -•— untreated wp-40, 2%  -m-B,2% -*-wp-41,2%  D D A C , 2% •wp-46, 2%  Figure 4.3.1: The relative ratios o f delignification o f different chemical treated wood.  Figure 4.3.2: The relative ratios o f delignification o f different chemical treated wood.  0.6 0  50  100  150  U V irradiation, hours | |  -•—untreated wp-42, 1%  -"-wp-42,2%  wp-43,2%  - * - wp-42, 0.5%  wp-42, 0.25%  I  Figure 4.3.3: The relative ratios o f delignification o f different chemical treated wood.  3.5  2  I  0  I  1  50  100  :  .—J  150  U V irradiation, hours -•-untreated  - " - B , 2%  - * - wp-40, 2%  - * - wp-41, 2%  D D A C , 2% - • - wp-46, 2%  Figure 4.3.4: The relative ratio o f the formation o f carbonyl groups o f U V irradiated wood: the effect o f various treatments.  62  Figure 4.3.5: The relative ratio o f the formation o f carbonyl groups o f U V irradiated wood: the effect o f various treatments.  0.5  13  0  1  1  50  100  1  150  U V irradiation, hours untreated - x - w p - 4 2 , 1%  -m- wp-42, 2%  wp-43,2%  - * - wp-42, 0.5%  wp-42, 0.25%  Figure 4.3.6: The relative ratio o f the formation o f carbonyl groups o f U V irradiated wood: the effect o f solution concentrations.  63  4.4.  Conclusions From the quantitative analysis o f the F T I R spectra (Figures 4.3.1 to 4.3.6), the  degree o f degradation o f lignin in the treated and untreated sections increased after 6 days of  UV  irradiation  in  the  order.  2%  wp-42,  wp-43-treated  wood  < 2%  benzyldimethyldodecylammonium chloride treated wood < control-wood < 2% wp40 = 2% wp-46 = 5% wp-48 treated wood < 2% wp-41 = 2% wp-47 = 5% wp-62 = 5% wp-64 = 2% D D A C < 5% wp-63 treated wood (Figures 4.3.1 to 4.3.3). Formation o f carbonyl groups after 6 days o f U V irradiation increased in the order: 2% wp-42, wp-43 treated wood < 5% wp-48 treated wood < control-wood = 2% wp-41 treated wood < 2% benzyldimethyldodecylammonium chloride treated wood s 2% wp-46 treated wood < 2% D D A C treated wood < 5% wp-63 treated wood < 2% wp-40 treated wood < 5% wp-64 treated wood < 2% wp-47 treated wood (Figures 4.3.4 to 4.3.6). None o f the provided formulations showed significant resistance to photodegradation. A s observed by previous researchers the inclusion o f copper in the wood treatment  formulations  enhanced  the  resistance  to  photodegradation.  Higher  concentrations o f copper reduced both delignification and the formation o f carbonyl groups (Figures 4.3.3 to 4.3.6). None o f the alternative organic formulated preservatives provided improved resistance to photodegradation. Hence, it is more probable that additives w i l l be needed to improve the photoresistance o f D D A C treated wood, to at least achieve that that observed  64  for untreated wood. O f the all organic formulations, benzyldimethyldodecylammonium chloride provided the best resistance to delignification.  65  Chapter 5 Photodegradation of Wood Treated With DDAC Plus additives  5.1.  FTIR studies  5.1.1. Effect of BHT on photodegradation of DDAC treated wood The spectra of the untreated control, 2% BHT, 2% BHT with 2% DDAC, and 2% DDAC treated wood sections before and after 6 days of UV irradiation are shown in Figure 5.1.1. From the changes in absorption at 1510, 1600 and 1267 cm' that can be 1  related to delignification and demethoxylation, it was found that 2% BHT treatment was not able to reduce delignification. Nor did it prevent the formation of molecules with carbonyl groups during photodegradation, when compared with untreated controls. It may be concluded that 2% BHT is not able to reduce photodegradation in 2% DDAC treated wood.  5.1.2. Effect of l,4-diazabicyclo(2,2,2)octane on photodegradation of DDAC treated wood From the spectra in Figure 5.1.2, 2% l,4-diazabicyclo(2,2,2)octane treatment either when used alone, or in combination with 2% DDAC, had no affect in reducing delignification compared to reference material without the additive.  66  Figure 5.1.1: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% B H T treated, U V irradiated; d) 2% B H T + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, irradiated.  67  Figure 5.1.2: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% 1,4-diazabicyclo (2,2,2) octane treated, U V irradiated; d) 2% 1,4-diazabicyclo (2,2,2) octane + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, irradiated.  68  5.1.3. Effect of wood extractives on photodegradation of DDAC treated wood  Douglas-fir extractives  Figures 5.1.4 and 5.1.5 show the F T I R spectra o f  sections treated with 2% Douglas-fir extractives either alone or in combination with 2% D D A C or 5% D D A C . It was clear that 2% Douglas-fir extractives reduced delignification and prevented the formation o f carbonyl groups when added to both 2% and 5% D D A C treated wood, based on changes to F T I R peaks at 1510 and 1730 cm" . The effectiveness 1  o f Douglas-fir extractives in retarding the photodegradation process is most probably due to the presence o f polyhydroxyphenols, such as taxifolin (Figure 5.1.3) in the extractives. Taxifolin is a major component o f Douglas-fir extractives, comprising up to 12% in Douglas-fir bark (Rydholm, 1965).  OH  O  Figure 5.1.3: Structure o f taxifolin.  Western red cedar extractives  F T I R spectra o f sections treated with 2%  cedar extractives in combination with 2% and 5% D D A C treated wood are shown in Figures 5.1.6 and 5.1.7, respectively. Based on the absorptions at 1510 and 1730 cm" , 1  69  cedar extractives reduced lignin degradation and the formation o f carbonyl groups in wood sections treated with cedar extractives alone and in combination with 2% or 5% DDAC. The effectiveness o f western red cedar extractives in reducing the delignification process may be due to the high concentration o f tropolones present that can exert a protective effect on lignin.  Tannic acid  When tannic acid was added to wood it helped to reduce  delignification (Figures 5.1.8 and 5.1.9). W o o d sections treated with 2% tannic acid showed less lignin degradation than untreated controls and prevented the formation o f carbonyl groups. Antioxidant activity traditionally has been attributed primarily to soluble phenolic compounds (extractable polyphenols). Although a recent report has suggested that nonextractable polyphenols (polymeric proanthocyanidins and high-molecular-weight hydrolysable tannins) are 15 to 30 times more effective at quenching peroxyl radicals than are simple phenols (Hagerman et al., 1998).  Scots pine extractives Pine extractives did not reduce lignin degradation, based on changes to the F T I R peak at 1510 cm* (Figures 5.1.10 and 5.1.11). This may be due to 1  the low polyphenol content in Scots pine extractives, since fats and waxes are the  70  common components in pinewood. Alternatively the stilbene functionality may prevent the pinosylvin and related compounds from acting as free radical inhibitors.  71  Figure 5.1.4: F T I R o f untreated and chemically treated wood sections before and after 6 days o f UV irradiation: a) untreated, before UV irradiation; b) untreated, UV irradiated; c) 2% D F extractives treated, UV irradiated; d) 2% D F extractives + 2% D D A C treated, UV irradiated; and e) 2% D D A C treated, irradiated.  72  1800  1600  1400  1200  Wavenumbers, cm-  1000  800  1  Figure 5.1.5: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% D F extractives treated, U V irradiated; d) 2% D F extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, irradiated.  73  1800  1600  1400  1200  1000  Wavenumbers, crrr  800  1  Figure 5.1.6: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% cedar extractives treated, U V irradiated; d) 2% cedar extractives + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated.  74  1800  1600  1400  1200  Wavenumbers, crrr  1000  800  1  Figure 5.1.7: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% cedar extractives treated, U V irradiated; d) 2% cedar extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated. 75  Figure 5.1.8: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% tannic acid treated, U V irradiated; d) 2% tannic acid + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, irradiated. 76  Figure 5.1.9: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% tannic acid treated, U V irradiated; d) 2% tannic acid + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, irradiated.  77  1800  1600  1400  1200  1000  Wavenumbers, c m  800  1  Figure 5.1.10: F T I R o f untreated and chemically treated wood sections before U V irradiation and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% pine extractives treated, U V irradiated; d) 2% pine extractives + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated.  78  1800  1600  1400  1200  1000  Wavenumbers, crrr  800  1  Figure 5.1.11: F T I R o f untreated and chemically treated wood sections before U V irradiation and after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% pine extractives treated, U V irradiated; d) 2% pine extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated.  79  5.1.4. Effect of lignosulfonic acid on photodegradation of DDAC treated wood Figures 5.1.12 and 5.1.13 show that, lignosulfonic acid was able to reduce delignification comparing to D D A C treatment only based on reduction to F T I R peaks at 1510, 1267 and 1600 cm" . When wood sections were treated with 2% lignosulfonic acid 1  solution in combination with 5% D D A C lignin degradation was noticeably reduced, compared to 5% D D A C treated sections (Fig. 5.1.13).  80  Figure 5.1.12: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiated; b) untreated, U V irradiated; c) 2% lignosulfonic acid treated, U V irradiated; d) 2% lignosulfonic acid + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, irradiated.  81  1800  1600  1400  1200  Wavenumbers, crrr  1000  800  1  Figure 5.1.13: F T I R o f untreated and chemically treated wood sections before and after 6 days o f U V irradiation: a) untreated, before U V irradiated; b) untreated, U V irradiated; c) 2% lignsosulfonic acid treated, U V irradiated; d) 2% lignsosulfonic acid + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, irradiated.  82  5.2. Effect of washing UV irradiated samples on the FTIR spectra of wood treated with DDAC and additives The impact o f the removal o f the soluble by-products o f photodegradation by washing, is shown i n the FTER spectra in Figures 5.2.1 to 5.2.8, for Douglas-fir extractives (Figures 5.2.1 and 5.2.2), cedar extractives (Figures 5.2.3 and 5.2.4), lignosulfonic acid (Figures 5.2.5 and 5.2.6), and Scots pine extractives (Figures 5.2.7 and 5.2.8). Based on the F T I R spectra, it was found that washing o f the photoexposed wood sections, whether untreated, or treated with combinations o f D D A C and different wood extractives, produced similar peak intensities at 1510, 1267, and 1600 cm" (which are 1  related lignin peak concentrations), and also at 1730 cm" (which reflects the carbonyl 1  groups), after 6 days o f U V irradiation. The results confirmed the known solubility o f the by-products o f photodegradation.  83  \  1162 I  I  1800  i  I  1600  i  I  1400  i  I  i  v  1200  Wavenumbers, crrr  I  1000  i  i  800  1  Figure 5.2.1: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiated; b) untreated, U V irradiated; c) 2% Douglas-fir extractives treated, U V irradiation; d) 2% Douglas-fir extractives + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated. 84  1800  1600  1400  1200  Wavenumbers, cm-  1000  800  1  Figure 5.2.2: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% Douglas-fir extractives treated, U V irradiated; d) 2% Douglas-fir extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated. 85  Figure 5.2.3: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% cedar extractives treated, U V irradiated; d) 2% cedar extractives + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated. 86  Figure 5.2.4: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% cedar extractives treated, U V irradiated; d) 2% cedar extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated.  87  Figure 5.2.5: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% lignosulfonic acid treated, U V irradiated; d) 2% lignosulfonic acid + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated.  88  1800  1600  1400  1200  Wavenumbers, crrr  1000  800  1  Figure 5.2.6: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% lignosulfonic acid treated, U V irradiated; d) 2% lignosulfonic acid + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated. 89  1800  1600  1400  1200  1000  Wavenumbers, crrr  800  1  Figure 5.2.7: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% pine extractives treated, U V irradiated; d) 2% pine extractives + 2% D D A C treated, U V irradiated; and e) 2% D D A C treated, U V irradiated.  90  cCD -4—'  1800  1600  1400  1200  Wavenumbers, crrr  1000  800  1  Figure 5.2.8: F T I R o f untreated and chemically treated wood sections before  UV  irradiation and washed after 6 days o f U V irradiation: a) untreated, before U V irradiation; b) untreated, U V irradiated; c) 2% pine extractives treated, U V irradiated; d) 2% pine extractives + 5% D D A C treated, U V irradiated; and e) 5% D D A C treated, U V irradiated.  91  5.3. Effect of treatment on FTIR spectra Figure 5.3.1 shows the F T I R spectra o f untreated wood sections and wood sections treated with Douglas-fir, western red cedar and Scots pine extractives, before U V irradiation. Examination o f the spectra confirms that no significant changes have occurred as a result o f the treatment. Since the extractives used are largely phenolic compounds finding is not unexpected. Figure 5.3.2 shows the F T I R spectra o f untreated wood sections, as w e l l as sections treated with 5% lignosulfonic acid and 5% tannic acid. F o r 5% lignosulfonic acid treated wood there was no discernible difference in the F T I R spectra o f the treated and untreated wood. In the spectrum o f 5% tannic acid treated wood sections, peaks were observed due to the presence o f the carboxylic functional groups at 1600 and 1320 cm" and the 1  hydroxyl groups present in the tannic acid.  92  94  5.4. Quantitative analysis of FTIR spectra 5.4.1. The relative delignification rate The relative delignification rate was calculated from the differences in the 1510 cm" absorption peak areas o f weathered (Af) and unweathered (A;) samples relative to 1  the unweathered peak areas ( A ) - The delignification o f untreated and treated wood samples, during 7 hours to 6 days U V irradiation, is shown in Figures 5.4.1 to 5.4.10 and summarized i n Table 5.1. They show that the relative delignification as indicated by the reduction in the absorption at 1510 cm" increased rapidly during the first 7 hours o f U V 1  exposure, and then more slowly during the next 21 hours o f U V exposure. The  wood  sections  treated  with  Douglas-fir  extractives  and Douglas-fir  extractives plus D D A C showed almost the same extent o f delignification, about 50% after 6 days o f U V irradiation (Figures 5.4.1 and 5.4.2). Both were less than untreated wood (59.7%), 2% D D A C treated wood (71.3%), and 5% D D A C treated wood (83.4%). This suggested that Douglas-fir extractives could greatly reduce the lignin degradation o f 5% D D A C treated wood. Cedar extractives were slightly effective in reducing delignification o f D D A C treated wood. The relative delignification rates o f untreated wood, wood treated with cedar extractives (2%), and cedar extractives (2%) plus D D A C (both 2% and 5%) were similar, approximately 55% to 60% (Figures 5.4.3 and 5.4.4). Thus cedar extractives were able to reduce the photodegradation in D D A C treated wood and so that o f untreated wood. The relative delignification rates o f untreated wood sections and wood sections treated with pine extractives (2%), and pine extractives (2%) plus D D A C (both 2% and  95  5%) were almost the same, about 55%. A l l were less than that observed in 2% D D A C treated wood (70%) and 5% D D A C treated wood (80%) (Figures 5.4.5 and 5.4.6). The relative delignification o f untreated wood sections and wood sections treated with tannic acid (2%), and tannic acid (2%) plus D D A C (both 2% and 5%) are shown in Figures 5.4.7 and 5.4.8. The delignification increased in the order: tannic acid treated wood < tannic acid + D D A C treated wood < untreated control < D D A C treated wood. The relative delignification o f tannic acid treated wood was 31.8% after 6 days o f U V irradiation. F o r untreated control, it was about 60%. For 2% tannic acid + 5% D D A C treated wood, it was 47.4%. For 5% D D A C treated wood, it was 83.4%. This suggested that tannic acid is able to greatly retard lignin degradation when used alone or with either 2% or 5% D D A C treated wood. Lignosulfonic acid showed limited effectiveness, being slightly more effective than pine extractives but having lower activity than cedar extractives. It showed some ability to reduce dehgnification when D D A C was present (Figures 5.4.9 and 5.4.10).  96  Table 5.1: Relative delignification rate after 6 days of U V irradiation. (Ai - Af) / Ai x 100% at 1510 cm" , % Samples 2% additives 2% additives Additives + 2% DDAC + 5% DDAC 1  ( antral DFext', 2%  ^  47 0  i , DF'ext;2% + DDAC 2%  Douglas-fir  48 6  7 DFext, 2% +DDAC i  v  50 1  DDAC, 2%  71 3  ^ , ' D D A C ; V/o  83 4  4  r  Control  60.8  Cedar ext., 2%  53.4  Cedar ext., 2% + DDAC, 2%  Cedar  54.9  Cedar ext., 2% + DDAC, 5%  5  59.0  DDAC, 2%  70.2  DDAC, 5%  84.1  Control  56 9  ^.^Pinie!ext». 2%  53 4  Pine c\t »2°/o + DDAC 2%  Scots pine  55 0 SA 7  Pine c\t. 2% + DDAC S% DDAC; 2% :  DDAC? 5 % f V  s  08 o -" ' «W*79*2-  r  Control  56.9  Tannic acid, 2%  31.8  Tannic acid, 2% + DDAC, 2%  Tannic acid  '  45.3 47.4  Tannic acid, 2% + DDAC, 5% DDAC, 2%  68.6  DDAC, 5%  79.2  Control  59 7  LSA, 2%  55 8  LSA, 2% +DDAC, 2%  LSA  52 1 55 1  LSA*2% + DDAC,5% DPAC 2% DDAC, 5% /  *'  71 3 >'\  83 4  97  80  0  20  40  60  80  100  120  140  UV irradiation, hours  • - Control  DF ext., 2%  DF ext., 2% +DDAC, 2%  - * - DDAC, 2%  Figure 5.4.1: The relative ratios o f delignification o f (a) untreated; (b) Douglas-fir extractives treated; (c) Douglas-fir extractives + D D A C treated; and (d) D D A C treated wood.  90  UV irradiation, hours  - • - Control - ^ D F ext., 2% +DDAC, 5%  DF ext., 2% - * - DDAC, 5%  Figure 5.4.2: The relative ratios o f delignification o f (a) untreated; (b) Douglas-fir extractives treated; (c) Douglas-fir extractives + D D A C treated; and (d) D D A C treated wood.  98  80  20  40  60  80  100  120  140  UV irradiation, hours  Control  Cedar ext., 2%  Cedar ext., 2% + DDAC, 2%  DDAC, 2%  Figure 5.4.3: The relative ratios o f delignification o f (a) untreated; (b) Cedar extractives treated; (c) Cedar extractives + D D A C treated; and (d) D D A C treated wood.  0  20  40  60  80  100  120  140  UV irradiation, hours  - • - Control  Cedar ext., 2%  - * - Cedar ext, 2% + DDAC, 5% - a - DDAC, 5% Figure 5.4.4: The relative ratios o f delignification o f (a) untreated; (b) Cedar extractives treated; (c) Cedar extractives + D D A C treated; and (d) D D A C treated wood.  99  0  — i — •  0  20  40  60  80  100  120  1—  140  UV irradiation, hours  - • - Control  - • - Pine ext., 2%  Pine ext., 2% + DDAC, 2%  DDAC, 2%  Figure 5.4.5: The relative ratios o f delignification o f (a) untreated; (b) Pine extractives treated; (c) Pine extractives + D D A C treated; and (d) D D A C treated wood.  90  0  20  40  60  80  100  120  140  UV irradiation, hours  Control  - « - Pine ext., 2%  Pine ext., 2% + DDAC, 5% - * - DDAC, 5% Figure 5.4.6: The relative ratios o f delignification o f (a) untreated; (b) Pine extractives treated; (c) Pine extractives + D D A C treated; and (d) D D A C treated wood.  100  0 0  -i  1  1  1  1  1  20  40  60  80  100  120  1  —  140  UV irradiation, hours  -*— Tannic acid, 2% ; -•— Control ! Tan. acid, 2% + DDAC, 2% - * - DDAC, 2% Figure 5.4.7: The relative ratios o f delignification o f (a) untreated; (b) Tannic acid treated; (c) Tannic acid + D D A C treated; and (d) D D A C treated wood.  UV irradiation, hours  ! - • - Control  - * - Tannic acid, 2%  \ - * Tan. acid, 2% + DDAC, 5% - * - DDAC, 5% Figure 5.4.8: The relative ratios o f delignification o f (a) untreated; (b) Tannic acid treated; (c) Tannic acid + D D A C treated; and (d) D D A C treated wood. 101  80  0  20  40  60  80  100  120  140  UV irradiation, hours  Control  - • - LSA, 2%  LSA, 2% + D DAC , 2 %  -*—D DAC,  2%  Figure 5.4.9: The relative ratios o f delignification o f (a) untreated; (b) Lignosulfonic acid treated; (c) Lignosulfonic acid + D D A C treated; and (d) D D A C treated wood.  90  T  0  20  40  60  80  100  120  140  UV irradiation, hours  Control  - « - LSA, 2%  LSA, 2% + DDAC, 5% - * - DDAC, 5% Figure 5.4.10: The relative ratios o f delignification o f (a) untreated; (b) Lignosulfonic acid treated; (c) Lignosulfonic acid + D D A C treated; and (d) D D A C treated wood.  102  5.4.2. Explanation for the differences observed Although the precise mechanisms and reaction pathways which occur during the photodegradation o f each wood component have yet to be elucidated, it is clear that the key step involved in the photodegradation o f wood is photolysis and fragmentation o f lignin resulting in the formation o f phenoxy free radicals (Feist and Hon, 1984; Gierer and L i n , 1972; Hon, 1975a, b, and c; H o n and Feist, 1981.). These free radicals may then cause further degradation o f lignin and photo-oxidation o f cellulose and hemicellulose (Evans et al., 2002). The ability o f additives to reduce lignin degradation is likely due to the aromatic molecules present in the additives. They function as sacrificial molecules as has proposed for benzyldimethyldodecylammonium chloride (See data in Chapter 4). It was also noted that tannic acid and Douglas-fir extractives have a better performance in reducing lignin degradation than other additives. The differences i n the performance could also due to the polyphenolic structure o f tannic acid or polyphenols present in Douglas-fir extractives, e.g. taxifolin. In addition to acting as sacrificial molecules i n place o f lignin, polyphenols may also function as antioxidants.  The efficiency o f  polyphenols as antioxidants has been recognized previously (Bravo, 1998). Phenolic antioxidants function as terminators o f free radical reactions by rapid donation o f a hydrogen atom to radicals, as illustrated in the following reaction sequences: R O O + P P H ->• R O O H + PP» R O « + P P H -> R O H + PP* Moreover, the phenoxy radical intermediates are relatively stable; therefore, a new chain reaction is not easily initiated. The phenoxy radical intermediates also act as terminators o f the propagation route by reacting with other free radicals (Shahidi, 1992): R O O » + PP« -> R O O P P 103  R O + PP« -> R O P P The effectiveness o f polyphenols as antioxidants is strongly influenced by their chemical structure. Phenol itself is inactive as an antioxidant, but /, 2- and 1, 3diphenols have antioxidant characteristics, which increase with the substitution o f hydrogen atoms by ethyl or n-butyl groups (Shahidi, 1992). This may explain w h y Douglas-fir and cedar extractives retard more lignin degradation than pine extractives. Tannic acid which is a gallotannin consisting o f a pentagalloylglucose molecule shows its potential antioxidant capacity among the additives used in this study. This may be due to the structure, which readily donates hydrogen atoms, thereby terminating the free radical reaction and protecting lignin from free radical attack.  5.4.3. Formation of carbonyl groups The relative rate o f carbonyl group formation was determined by comparing the areas o f the F T I R carbonyl absorption at 1730 cm" with that o f the relatively stable 1  cellulose absorption peak at 1162 cm" after various periods o f U V irradiation. Based on a 1  quantitative analysis after 6 days o f U V irradiation, more carbonyl containing chemicals were formed i n wood impregnated with D D A C than i n either untreated wood, or wood treated with any o f the additives alone (Figures 5.4.11 to 5.4.16, 5.4.19 and 5.4.20). This observation reinforces earlier suggestions that D D A C acts to accelerate photodegradation in wood but does not induce a new mechanism o f delignification (Liu, 1997). It is then clear that the results o f carbonyl formation should mirror those for delignification and this is largely the case. The explanation for this is likely that the antioxidants i n these additives terminate the free radical reaction initiated by U V irradiation, and which occurs during lignin degradation. This termination o f the free radical chain reaction prevents 104  photodegraded lignin fragments from forming colored, unsaturated, carbonyl compounds, as indicated when wood yellows when exposed to light (Evans et a l , 2002). The efficiency i n reducing the formation o f carbonyl compounds differs for different types o f phenolic compounds and also their concentration in the extractives used to modify the behavior o f the D D A C . This may probably explain why fewer carbonyl groups were identified when wood was treated with Douglas-fir extractives, than by cedar or pine extractives and lignosulfonic acid. A s expected, tannic acid reduced lignin degradation but not the formation o f carbonyl groups (Figures 5.4.7 and 5.4.8, 5.4.17 and 5.4.18). Tannic acid contains carboxyl groups and when used to treat wood w i l l increase the F T I R peak at 1730 cm" . 1  It should be noted that more carbonyl groups were formed i n 2% tannic acid + 5% D D A C treated wood than in simple 5% D D A C treated wood (Figure 5.4.18).  5.5. Conclusions Butylated hydroxy tolune ( B H T ) , 1,4-diazabicyclo (2,2,2) octane were found not to reduce delignification i n D D A C treated wood, during photo-exposure. They also had no impair on delignification o f wood when used alone. W o o d treated with Douglas-fir extractives and exposed to a U V source, showed reduced delignification and also there was less change in the formation o f carbonyl groups. This was particularly noticed when the Douglas-fir extractives were combined with D D A C during wood treatment. Lignosulfonic acid and cedar extractives showed some ability to reduce both delignification and the formation o f carbonyl groups, both i n the additive treated wood and also when combined with D D A C during w o o d treatment. 105  The addition o f pine extractives to the treating solution appeared to reduce the delignification o f wood treated with D D A C . Tannic acid treatment was very effective in preventing lignin degradation both when applied to wood alone or when used as an additive to D D A C treating solutions.  106  0  50  100  150  U V irradiation, hours Control  -*— D F extractives, 2%  D F ext., 2% + D D A C , 2%  - * - D D A C , 2%  Figure 5.4.11: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% Douglas-fir extractives; (b) 2% D F extractives + 2% D D A C ; (c) 2% D D A C .  0.2 4  1  1  0  50  100  1 150  U V irradiation, hours —•— Control D F ext., 2% + D D A C , 5%  —•— D F extractives, 2% - * - D D A C , 5%  Figure 5.4.12: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% Douglas-fir extractives; (b) 2% D F extractives + 5% D D A C ; (c) 5% D D A C .  107  0.2 4  1  1  0  50  100  1  150  UV i r r a d i a t i o n , hours Control  —•— Cedar extractives, 2%  Cedar ext., 2% + D D A C , 2% - * - D D A C , 2%  Figure 5.4.13: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% cedar extractives; (b) 2% cedar extractives + 2% D D A C ; (c) 2% D D A C .  1.8 <N  o en  1. 6 1. 4 1. 2  1 0.8 0.6 0.4 0. 2  1 0  50  100  150  U V irradiation, hours Control  — C e d a r extractives, 2%  Cedar ext., 2% + D D A C , 5% - * - D D A C , 5% Figure 5.4.14: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% cedar extractives; (b) 2% cedar extractives + 5% D D A C ; (c) 5% D D A C .  108  1.  2  0  50  100  150  U V irradiation, hours Control  - * - Pine extractives, 2%  Pine ext., 2% + D D A C , 2%  i  D D A C , 2%  Figure 5.4.15: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% pine extractives; (b) 2% pine extractives + 2% D D A C ; (c) 2% D D A C .  1.4  0  50  100  150  U V irradiation, hours i —•— Control Pine ext., 2% + D D A C , 5%  -*— Pine extractives, 2% D D A C , 5%  Figure 5.4.16: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% pine extractives; (b) 2% pine extractives + 5% D D A C ; (c) 5% D D A C .  109  1.4  UV i r r a d i a t i o n , hours I —•— Control  Tannic acid, 2%  ! - A - Tannic acid, 2% + D D A C , 2% - * - D D A C , 2%  Figure 5.4.17: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% tannic acid; (b) 2% tannic acid + 2% D D A C ; (c) 2% DDAC.  0  50  100  150  U V irradiation, hours —•— Control  —•— Tannic acid, 2%  Tannic acid, 2% + D D A C , 5% - * - D D A C , 5%  Figure 5.4.18: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% tannic acid; (b) 2% tannic acid + 5% D D A C ; (c) 5% DDAC.  110  0.2  J  1  1  0  50  100  1 150  U V irradiation, hours -•-Control  -»-LSA,2%  L S A , 2% + D D A C , 2%  - * - D D A C , 2%  Figure 5.4.19: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% lignosulfonic acid; (b) 2% lignosulfonic acid + 2% D D A C ; (c) 2% D D A C .  UV i r r a d i a t i o n , hours Control  -*-LSA,2%  L S A , 2% + D D A C , 5%  - * - D D A C , 5%  Figure 5.4.20: The relative formation o f carbonyl groups o f untreated wood sections and wood sections treated with (a) 2% lignosulfonic acid; (b) 2% lignosulfonic acid + 5% D D A C ; (c) 5% D D A C .  Ill  CHAPTER 6 Color Changes of DDAC Plus Additives Treated Wood During UV Irradiation 6.0.  Introduction In Chapter 5, it was found that Douglas-fir and western red cedar extractives  greatly reduced lignin degradation and also the formation o f carbonyl groups o f D D A C treated wood. Photodegradation is essentially a surface phenomenon, which results in the discoloration o f the wood as well as the degradation o f lignin. The color o f wood should be stable for many applications and therefore it is important to determine whether the Douglas^fir and western red cedar extractives are able to enhance the color stability o f D D A C treated wood. The color changes in wood induced by U V light can be readily observed by the human eye after 7 hours o f U V irradiation: irradiated wood surfaces become darker and more  yellow  to varying  degrees.  Such  changes  can be quantified  using  a  spectrophotometer operating in the visible range, and presenting results using the C I E L*, a*, b* color coordinate system. Zhang and Kamdem (2000) studied the weathering o f copper-famine treated wood using a Q U V Weathering Tester. Southern pine treated with copper ethanolamine ( C u E A ) was exposed to 2 hours U V irradiation followed by 18 minutes o f water spray for a total time o f 1200 hours. F T I R studies showed that C u - E A treated wood retarded lignin degradation and formation o f carbonyl groups based on the peaks at 1510 and 1730 c m ' . 1  The color changes (AE*) o f untreated and treated wood showed that 1.5% C u - E A treatment o f wood effectively reduced the color change compared with untreated controls, which was about 5 for C u - E A treated wood and 18.6 for the controls after 1200  112  hours o f Q U V exposure. The treatment also showed lightness stability. However, the surface color o f copper-amine-treated wood changes to blue-green, which gives an unattractive appearance to users (Grelier et al., 2000). D D A C treatment is colorless. Therefore, color changes in D D A C treated wood are more important than those i n A C Q treated wood because the later is colored. In this Chapter the color changes o f wood treated with the D D A C solutions containing Douglas-fir and western red cedar extractives, following exposure to U V light are examined. Color changes are compared with those o f untreated controls and wood treated with D D A C only. The aim was to determine whether the extractives were able to retard the color changes o f D D A C  treated wood during U V irradiation and the  relationship ( i f any) with chemical degradation o f the treated wood (examined i n Chapter 5) and color changes.  6.1.  Results and Disscusion The color changes (AE*) o f untreated and treated samples versus the irradiation  time are shown i n Figures 6.1.1.1 to 6.1.1.4. The Figures clearly show that rapid color changes occurred at the wood surface after U V irradiation. This is in accord with the previous F T I R results i n Chapter 5, which showed that a high proportion o f lignin was degraded resulting i n the formation o f carbonyl groups. The A E * for the untreated exposed controls was about 14 after 6 days o f U V exposure, which is a clear indication o f rapid color change. The color changes are larger for untreated wood and wood treated with D D A C than the additive treated wood or D D A C plus additive treated wood surfaces. It was also observed that the color changes o f untreated wood and D D A C treated wood  113  surfaces were very similar, despite the observation i n Chapter 5 that lignin degradation and formation o f carbonyl groups were greater in D D A C treated wood sections during irradiation than i n untreated wood sections. The differences, however, are not large, and clearly color was affected by the dramatic loss o f lignin i n the case o f treated and untreated wood surfaces. Results presented and discussed here are divided into four sections. 1) Effect o f additives on the color o f treated wood during U V irradiation; 2) Effect o f additives on the brightness o f treated wood during U V irradiation; 3) Effect o f additives on the color o f treated wood subjected to U V irradiation and leaching with water; and 4) A comparison o f the effects o f additives on their ability to retard color changes and brightness o f D D A C treated wood.  6.1.1. Effect of additives on the color of treated wood during U V irradiation 6.1.1.1.  Douglas-fir extractives + DDAC  2% Douglas-fir extractives + 2% DDAC  The untreated controls and wood  sections treated with 2% D D A C showed similar color changes during exposure to U V irradiation. The magnitude o f the color change o f D D A C treated wood samples after 6 days exposure was 14 and that o f the untreated was 13 (Figure 6.1.1.1a). The color changes o f 2% Douglas-fir treated and 2% D D A C plus 2% Douglas-fir extractives treated wood sections were much lower than those o f the D D A C and untreated sections clearly suggesting that Douglas-fir extractives are able to improve the color stability o f wood i n the presence o f 2% D D A C .  114  2% Douglas-fir extractives + 5% DDAC  Figure  6.1.1.1b  shows  the color  changes o f untreated sections and wood treated with 2% Douglas-fir extractives, 2% Douglas-fir extractives + 5% D D A C , and 5% D D A C wood sections. The color change o f 5% D D A C treated wood sections was slightly larger than untreated control i n contrast to wood treated with 2% D D A C which showed slightly lower color change than the untreated control (Figure 6.1.1.1b). This suggests that in the absence o f extractives color changes o f D D A C treated wood are influenced by the concentration o f D D A C . Overall, the Douglas-fir extractives reduced the color change o f the D D A C treated wood surfaces. The color change (AE*) for both 2% Douglas-fir extractives + 2% D D A C and 2% Douglas-fir extractives + 5% D D A C treated wood was less than 8 compared with D D A C or untreated wood which was around 14 after 6 days' U V irradiation. This result was unaffected by the concentration o f the D D A C in the treatment solution, since the extractives appeared to be effective when added to solutions containing 2 and 5% D D A C .  6.1.1.2.  Cedar extractives + DDAC  2% cedar extractives + 2% DDAC  The color stability during U V irradiation o f  untreated control and wood sections treated with 2% cedar extractives, 2% cedar extractives + 2% D D A C , and 2% D D A C are shown in Figure 6.1.1.2a. W o o d sections treated with 2% cedar extractives + 2% D D A C showed the smallest color changes during irradiation. The color change o f wood sections treated with 2% cedar extractives + 2% D D A C was 4.8, while those o f the untreated control and wood sections treated with 2% cedar extractives and 2% D D A C were around 14, 7 and 13, respectively (Figure 6.1.1.2a). This suggested that the cedar extractives were able to reduce the color change o f wood treated with 2% D D A C . 115  2% cedar extractives + 5% DDAC  Figures 6.1.1.2a and 6.1.1.2b, indicate that  the color o f wood sections was more stable when they were treated with D D A C containing cedar extractives. Color changes were lower for wood sections treated with 2% cedar extractives + 2% D D A C than those o f wood treated with 2% cedar extractives +5% D D A C (Figures 6.1.1.2a and 6.1.1.2b). The color change o f wood sections treated with 2% cedar extractives + 2% D D A C after 6 days irradiation was 4.8, whereas that o f wood treated with 2% cedar extractives + 5% D D A C was 5.5 (Figures 6.1.1.2a and 6.1.1.2b). This suggests that the ability o f cedar extractives to restrict color changes o f D D A C treated wood is affected by concentration o f D D A C . The combination o f both 2% cedar extractives + 2% D D A C and 2% cedar extractives + 5% D D A C treated wood showed the lowest and almost the same color change. This suggested that effect was not only due to the additive itself and also the D D A C had some effect in this case.  6.1.1.3.  Scots pine extractives + DDAC  2% pine extractives + 2% DDAC  The color  stabilities  o f untreated  wood  sections and wood sections treated with 2% pine extractives and 2% D D A C were very similar. A treatment containing 2% pine extractives + 2% D D A C was only slightly effective i n reducing loss o f color (Figure 6.1.1.3a) suggesting that Scots pine extractives are not effective additives for protecting the discoloration o f wood during exposure to U V light.  2%pine extractives + 5% DDAC  The effect o f 2% pine extractives + 5%  D D A C on color change was similar to that o f the treatment o f 2% pine extractives + 2% D D A C (Figure 6.1.1.3b) The difference i n color o f wood treated with D D A C and 2% 116  pine extractives and that o f the untreated control was 3 units, which is considered unacceptable for industrial applications ( H o n and Feist, 1986). This is in accord with F T I R results, which showed pine extractives not preventing lignin degradation and the formation o f carbonyl groups when wood is exposed to U V light.  6.1.1.4.  Lignosulfonic acid (LSA) + DDAC  2% LSA + 2% DZX4CFigure 6.1.1.4a indicates that lignosulfonic acid was not effective at restricting color changes o f wood treated 2% D D A C . The difference o f color (AE*) o f wood treated with L S A and D D A C and the controls were 3 which is not distinguishable to the naked eye (Hon, 2000).  2% LSA + 5% DDAC The color stability o f wood sections treated with 2% L S A + 5% D D A C was better than that o f wood treated with 2% L S A + 2% D D A C (Figures 6.1.1 4a and 6.1.1 4b). The value o f A E * for 2% L S A + 5% D D A C treated wood was 8.5, while that for 5% D D A C treated wood was 15. It is possible that unfixed D D A C or some fixed D D A C reacted with lignosulfonic acid and formed a complex that prevented the color change.  117  U V irradiation, hours - • — Control  -*— D F extractives, 2%  D D A C , 2% + D F ext., 2%  - * - D D A C , 2%  Figure 6.1.1.1a: Changes in color o f treated and untreated wood sections before and after U V irradiation.  0  50  100  150  U V irradiation, hours |  —•— Control  —•— D F extractives, 2%  - ± - D D A C , 5% + D F ext., 2%  - * - D D A C , 5%  Figure 6.1.1.1b: Changes in color o f treated and untreated wood sections before and after U V irradiation. 118  U V irradiation, hours Control  - • — Cedar ext., 2%  D D A C , 2% + cedar ext., 2%  - * - D D A C , 2%  Figure 6.1.1.2a: Changes in color o f treated and untreated wood sections before and after U V irradiation.  16  0  50  100  150  U V irradiation, hours Control D D A C , 5% + cedar ext., 2%  Cedar ext, 2% - * - D D A C , 5%  Figure 6.1.1.2b: Changes in color o f treated and untreated wood sections before and after U V irradiation.  119  50  100  150  U V irradiation, hours —•— Control  - * - Pine extractives, 2%  D D A C , 2% + pine ext., 2%  - * - D D A C , 2%  Figure 6.1.1.3a: Changes in color o f treated and untreated wood sections before and after U V irradiation.  0  50  100  U V irradiation, hours —•— Control D D A C , 5% + pine ext., 2%  - • — Pine extractives, 2% - * - D D A C , 5%  Figure 6.1.1.3b: Changes in color o f treated and untreated wood sections before and after U V irradiation.  120  U V irradiation, hours —•— Control  — L i g n o s u l f o n i c acki,2%  D D A C , 2% + L S A , 2%  D D A C , 2%  Figure 6.1.1.4a: Changes in color o f treated and untreated wood sections before and after U V irradiation.  U V irradiation, hours —•— Control D D A C , 5% + L S A , 2%  - « — Lignosulfonic acid,2% - * - D D A C , 5%  Figure 6.1.1.4b: Changes in color o f treated and untreated wood sections before and after U V irradiation.  121  6.1.2. Effect of additives on brightness of DDAC treated wood during U V irradiation  Figures 6.1.2.1 to 6.1.2.4 show the changes i n brightness o f treated and untreated wood surfaces during U V irradiation.  6.1.2.1.  Douglas-fir extractives + DDAC  2% Douglas-fir extractives + 2% DDAC  The brightness  o f untreated and  wood sections treated with 2% D F extractives, 2% D F extractives + 2% D D A C , and 2% D D A C versus U V irradiation time are shown i n Figure 6.1.2.1a. The brightness o f the wood is clearly reduced as a result o f exposure to U V light, possibly because o f the accumulation o f unsaturated lignin photodegradation products on the surface o f the wood (Hon, 1981). The brightness o f wood surfaces was reduced when the wood was treated with solutions containing Douglas-fir extractives, as expected (Figures 6.1.2.1a, and 6.1.2.1b). The change i n brightness (AL*) for wood sections treated with 2% Douglas-fir extractives + 2% D D A C after 6 days o f U V exposure, was less than 2 units, which clearly indicates that Douglas-fir extractives significantly improve brightness stability o f wood treated with 2% D D A C .  2% Douglas-fir extractives + 5% DDAC  From Figures 6.1.2.1a and 6.1.2.1b,  it is apparent that wood treated with 2% Douglas-fir extractives + 2% D D A C and exposed to U V irradiation was darker than wood treated with 2% Douglas-fir extractives + 5% D D A C and exposed to U V irradiation. The A L * for 2% Douglas-fir extractives + 5% D D A C treated wood was around 3, which is lower than those o f wood, treated with  122  5% D D A C and 5% Douglas-fir extractives and the untreated wood. This indicates that Douglas-fir extractives are able to improve the brightness stability o f wood treated with 5% D D A C  6.1.2.2.  Western red cedar extractives + DDAC  2% cedar extractives + 2% DDAC  Figure 6.1.2.2a indicates that the brightness  change (AL*) o f wood surfaces treated with 2% cedar extractives + 2% D D A C and exposed to 6 days U V irradiation was less than 1. This suggests that the cedar extractives are able to improve the brightness stability o f D D A C treated wood.  2% cedar extractives + 5% DDAC  The A L * for 2% cedar extractives + 5%  D D A C treated wood was also less than 1 unit after 6 days o f U V exposure confirming the ability o f cedar extractives to improve the brightness stability o f D D A C treated wood (Figure 6.1.2.2b). The combination o f cedar extractives + D D A C significantly reduced the brightness change o f wood.  6.1.2.3.  Scots pine extractives + DDAC  The brightness changes o f wood treated with D D A C , pine extractives, pine extractives + D D A C and that o f untreated wood were similar. The inability o f 2% pine extractives + 2% D D A C and 2% pine extractives + 5% D D A C treatments to restrict brightness changes (Figures 6.1.2.3a and 6.1.2.3b) accords with the F T I R studies, which showed that Scots pine extractives did not prevent the formation o f carbonyl groups.  123  6.1.2.4.  Lignosulfonic + DDAC  The A L * for untreated and treated wood were almost the same after 6 days o f U V irradiation (Figures 6.1.2.4a and 6.1.2.4b) suggesting that lignosulfonic acid had little effect on the brightness stability o f D D A C treated wood.  6.1.2.5.  General observation  From the data plotted i n Figures 6.1.2.1 to 6.1.2.4, several conclusions can be drawn: 1) the additives render the surface darker, 2) the changes in brightness for both untreated and D D A C treated wood surfaces were similar. This suggests that D D A C treatment does not significantly alter change in the brightness o f the wood surfaces even though lignin degradation and the formation o f carbonyl groups was higher i n D D A C treated wood during U V irradiation than in the untreated control. Combinations o f Douglas-fir or cedar extractives with D D A C , performed better than either chemical alone, and produced wood surfaces that exhibited very little loss o f brightness.  124  0  50  100  150  U V irradiation, hours Control  — D F extractives, 2%  D D A C , 2% + D F ext., 2%  - * - D D A C , 2%  Figure 6.1.2.1a: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  Js 72  00 £ 70 CO 68 66 64  0  50  100  150  U V irradiation, hours -•-Control D D A C , 5% + D F ext., 2%  -a- D F extractives, 2% -x—DDAC, 5%  Figure 6.1.2.1b: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  125  50  100  150  U V irradiation, hours —•— Control  -  D D A C , 2% + cedar ext., 2%  Cedar ext., 2%  - * - D D A C , 2%  Figure 6.1.2.2a: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  0  50  100  150  U V irradiation, hours 4— Control D D A C , 5% + cedar ext., 2%  Cedar ext, 2% - * - D D A C , 5%  Figure 6.1.2.2b: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  126  70  1  1  1  0  50  100  1  150  U V irradiation, hours —•— Control  - * - Pine extractives, 2%  D D A C , 2% + pine ext., 2%  - x - D D A C , 2%  Figure 6.1.2.3a: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  80 i  I ?  78 1 76 74  m  .  72 70  i  i  ()  50  100  150  U V irradiation, hours —•—Control  - " — P i n e extractives, 2%  - A - D D A C , 5% + pine ext., 2%  - * - D D A C , 5%  Figure 6.1.2.3b: Changes in brightness o f treated and untreated wood sections before and after U V irradiation.  127  0  50  100  150  UV irradiation, hours Control  -m— Lignosulfonic acid, 2%  DDAC, 2%+LSA, 2%  - * - DDAC, 2%  Figure 6.1.2.4a: Changes in brightness of treated and untreated wood sections before and after UV irradiation.  0  50  100  150  UV irradiation, hours Control  LigiosvJfonic acid, 2%  DDAC, 5% +LSA, 2%  DDAC, 5%  Figure 6.1.2.4b: Changes in brightness of treated and untreated wood sections before and after U V irradiation.  128  6.1.3. Effect of additives on the color and brightness of treated wood subject to UV irradiation and leaching 6.1.3.1.  Effect on color stability  6.1.3.1.1. Douglas-fir extractives + D D A C The color changes o f treated wood and untreated controls were rapid during the first 7 hours o f U V irradiation. Thereafter for the wood sections treated with Douglas-fir extractives (2%), 2% Douglas-fir extractives + 2% D D A C ,  and 2% Douglas-fir  extractives + 5% D D A C , the color remained relatively stable. In contrast sections treated with D D A C and the untreated controls continued to change i n color with increasing exposure to U V irradiation, and at the end o f the trial they were significantly more discolored than wood treated with D D A C plus extractives (Figures 6.1.3.1.1a and 6.1.3.1.1b). The value o f A E * for wood treated with 2% Douglas-fir extractives + 2% D D A C and 2% Douglas-fir extractives + 5% D D A C treated wood and exposed to U V light for 6 days was 4 units compared to 14 for similarly exposed untreated and D D A C treated wood sections. This clearly indicates that Douglas-fir extractives greatly improve the color stability o f D D A C treated wood exposed to U V light and subject to leaching.  6.1.3.1.2. Western red cedar extractives + D D A C In the case o f wood treated with D D A C solutions containing western red cedar extractives, the color change after 6 days o f U V irradiation increased i n this order: Cedar extractives + D D A C treated < cedar extractives treated < untreated, and D D A C treated (Figures 6.1.3.1.2a and 6.1.3.1.2b). F T I R spectroscopy suggested that leaching removed chemicals from treated wood sections, and also the carbonyl groups formed during U V irradiation. However, sufficient extractives may still have been retained within the wood to slow down color changes. 129  6.1.3.1.3.  Scots pine extractives + D D A C  Figures 6.1.3.1.3a and 6.1.3.1.3b show the color changes o f the wood sections treated with 2% pine extractives, 2% pine extractives + 2% D D A C , 2% pine extractives + 5% D D A C , 2% D D A C , 5% D D A C , and untreated control after 6 days o f U V exposure and leaching. The results were similar for treated wood sections that were exposed to U V light without leaching, and showed no beneficial effect due to Scots pine extractives.  6.1.3.1.4. Lignosulfonic acid ( L S A ) + D D A C 2% LSA + 2% DDACThe  color changes for the untreated and D D A C treated  wood sections were similar. The color changes o f wood sections treated with 2% L S A and 2% L S A + 2% D D A C were lower than those o f D D A C treated and untreated controls, particularly in the case o f D D A C plus L S A treated sections (Figure 6.1.3.1.4a). The difference in color changes o f D D A C + L S A and L S A treated sections after 6 days irradiation was less than 2, which is not distinguishable to the naked eye. 2% LSA + 5% DDAC The A E * for 2% L S A + 5% D D A C treated wood was 7.5 compared to 15 for 5% D D A C treated wood (Figure 6.1.3.1.4b). This suggests that the L S A at 2% concentration is more effective at restricting color changes when higher concentrations o f D D A C are used to treat wood. A s suggested earlier this might be due to the reaction o f L S A and D D A C forming an insoluble complex, which prevented color changes and resisting leaching.  130  0  50  100  150  U V irradiation, hours D F extractives, 2%  —•— Control —*— D D A C , 2% + D F ext, 2%  -^DDAC,2%  Figure 6.1.3.1.1a: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after U V irradiation.  U V irradiation, hours j - • — Control D D A C , 5% + D F ext, 2%  - • — D F extractives, 2% D D A C , 5%  Figure 6.1.3.1.1b: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after U V irradiation.  131  50  100  150  U V irradiation, hours Control  Cedar ext., 2%  D D A C , 2 % + cedar ext.,2%  D D A C , 2%  Figure 6.1.3.1.2a: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after treatment and U V irradiation.  18  50  100  150  U V irradiation, hours i - • - Control |  - • — Cedar ext., 2%  D D A C , 5 % + cedar ext,2% - * - D D A C , 5%  Figure 6.1.3.1.2b: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after treatment and U V irradiation.  132  0  50  100  150  U V irradiation, hours Pine extractives, 2%  Control D D A C , 2% + pine ext., 2%  - * - D D A C , 2%  Figure 6.1.3.1.3a: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after treatment and U V irradiation.  0  50  100  150  U V irradiation, hours —•— Control  -*— Pine extractives, 2%  —A— D D A C , 5% + pine ext., 2%  - * - D D A C , 5%  Figure 6.1.3.1.3b: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after treatment and U V irradiation.  133  D D A C , 2% + L S A , 2%  - * - D D A C , 2%  Figure 6.1.3.1.4a: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after U V irradiation.  U V irradiation, hours —•— Control  — L i g n o s u l f o n i c acid, 2%  —A— D D A C , 5% + L S A , 2%  - K - D D A C , 5%  Figure 6.1.3.1.4b: Changes in color o f treated and untreated wood sections before U V irradiation and with washing after U V irradiation.  134  6.1.3.2.  Effect on brightness  6.1.3.2.1. Douglas-fir extractives + D D A C 2% DF extractives + 2% DDAC  The brightness o f wood sections treated writh  Douglas-fir extractives, and Douglas-fir extractives + D D A C was lower than untreated and D D A C treated wood (Figures 6.1.3.2.1a and 6.1.3.2.1b), because the extractives made the wood surface darker. The brightness o f the wood surface treated with 2% Douglas-fir extractives and 2% Douglas-fir extractives + 2% D D A C was however relatively stable during U V irradiation and leaching (Figure 6.1.3.2.1a). 2% DF extractives + 5% DDAC  The brightness o f wood sections treated wdth  2% Douglas-fir extractives + 5% D D A C was stable during U V irradiation and hence at the end o f exposure period their brightness approached that o f the untreated control and D D A C treated wood, which darkened during exposure. Sections treated with Douglas-fir extractives darkened for the first 24 hours o f exposure, but their brightness remained unchanged thereafter (Figure 6.1.3.2.1b).  6.1.3.2.2.  Western red cedar extractives + D D A C  The brightness o f the wood treated with cedar extractives and cedar extractives + D D A C and exposed to U V irradiation followed by leaching was relatively stable. In contrast the brightness o f the untreated and D D A C treated sections decreased as a result o f U V irradiation and leaching (Figures 6.1.3.2.2a and 6.1.3.2.2b). The brightness after exposure and leaching increased as follows: 2% cedar extractives treated « 2% cedar extractives + 2% D D A C treated < 2% cedar extractives + 5% D D A C < untreated and D D A C treated. The lower brightness o f wood treated with cedar extractives is due to the dark color o f the cedar extractives. After leaching some o f the cedar extractives washed  135  out, so increases in brightness were observed, particular during the early stages o f the exposure trial.  6.1.3.2.3.  Scots pine extractives + D D A C  The brightness changes o f treated and untreated sections during U V irradiation were quite similar (Figures 6.1.3.2.3a and 6.1.3.2.3b) suggesting that the Scots pine extractives were largely ineffectively at restricting changes in brightness o f wood following U V irradiation and leaching. These findings are in accord with earlier results for similarly treated sections exposed to U V light in the absence o f leaching.  6.1.3.2.4. Lignosulfonic acid + D D A C The brightness changes o f treated and untreated sections during U V irradiation were quite similar. The wood sections treated with 2% L S A , 2% L S A + 2% D D A C , and 2% L S A + 5% D D A C were a little darker than untreated, 2% D D A C treated, and 5% D D A C treated (Figures 6.1.3.2.4a and 6.1.3.2.4b).  136  68 4—; 0  ,  ,  50  100  = l  h  150  U V irradiation, hours »— Control  -»  D D A C , 2% + D F ext, 2%  D F extractives, 2%  - * - D D A C , 2%  Figure 6.1.3.2.1a: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after U V irradiation.  0  50  100  150  U V irradiation, hours —Control -nkr- D D A C , 5% + D F ext., 2%  » - D F extractives, 2% - * - D D A C , 5%  Figure 6.1.3.2.1b: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after U V irradiation.  137  80 , 78 ' at  | 76 •g> 74 f - » 03 72 1  70  »—  _i  0  i  50  100  '  150  U V irradiation, hours —Control  Cedar ext., 2%  D D A C , 2% + cedar ext., 2%  - * - D D A C , 2%  Figure 6.1.3.2.2a: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation.  0  50  100  150  U V irradiation, hours | -•-Control D D A C , 5% + cedar ext., 2%  - » - Cedar ext., 2% - * - D D A C , 5%  Figure 6.1.3.2.2b: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation.  138  U V irradiation, hours —•— Control  —•— Pine extractives, 2%  D D A C , 2% + pine ext., 2%  - x - D D A C , 2%  Figure 6.1.3.2.3a: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation.  U V irradiation, hours —•— Control D D A C , 5% + pine ext., 2%  — P i n e extractives, 2% - x - D D A C , 5%  Figure 6.1.3.2.3b: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation.  139  100  50  150  U V irradiation, hours Control D D A C , 2% + L S A , 2%  Lignosulfonic acid, 2% D D A C , 2%  Figure 6.1.3.2.4a: Changes in brightness o f treated and untreated wood sections before U V irradiation and washed after U V irradiation.  0  50  100  U V irradiation, hours Control  -»— Lignosulfonic acid, 2%  D D A C , 5 % + L S A , 2%  • * - D D A C , 5%  Figure 6.1.3.2.4b: Changes in Brightness o f treated and untreated wood sections before U V irradiation and washed after U V irradiation. 140  6.1.4. A comparison of the effect of additives on their ability to retard color changes and brightness of DDAC treated wood 6.1.4.1.  The effect of additives and DDAC on color changes  Figure 6.1.4.1.1 shows color changes o f treated wood sections and untreated control after 6 days o f U V irradiation, i n the absence o f leaching. The following conclusions can be drawn: 1) untreated controls, 2% pine extractives, and D D A C treated wood showed similar large color changes; 2) the combination o f additives and D D A C was more effective at restricting color changes than additives or D D A C alone; 3) the combinations o f cedar extractives and D D A C were the most effective at restricting color changes; 4) the combination o f pine extractives and D D A C did not restrict color changes o f the wood.  16  Figure 6.1.4.1.1: The effect o f combinations o f additives and D D A C on the color change o f treated and untreated wood after 6 days o f U V irradiation.  141  Figure 6.1.4.1.2 shows the color change o f treated and untreated wood after 6 days o f U V irradiation and leaching. The results are quite similar to those presented in Figure 6.1.4.1.1 for sections subjected to U V irradiation in the absence o f leaching, with one notable exception. The combinations o f Douglas-fir extractives and D D A C remained highly effective in restricting color changes even when irradiated sections were subjected to leaching.  16  Figure 6.1.4.1.2: The effect o f combinations o f additives and D D A C on the color change o f treated and untreated wood after 6 days o f U V irradiation and washed after U V irradiation.  142  6.1.4.2.  The effect of additives and DDAC on the brightness changes  Figure 6.1.4.2.1 shows the reduction o f brightness o f untreated and treated wood after 6 days o f U V irradiation. The Douglas-fir and cedar extractives plus D D A C appeared to enhance brightness stability. For examples, sections treated with 2% cedar extractives + 2% D D A C or 2% cedar extractives + 5% D D A C restricted brightness change to less than 1 compared to 6.5 for the untreated control.  Figure 6.1.4.2.1: The effect o f combinations o f additives and D D A C o n the loss o f brightness o f treated and untreated wood after 6 days o f U V irradiation.  143  The loss o f brightness o f untreated and treated wood sections after 6 days o f U V irradiation and leaching is shown in Figure 6.1.4.2.2. A s was the case for sections subjected to U V irradiation in the absence o f leaching, sections treated with cedar and Douglas-fir extractives retained their brightness. The loss o f brightness o f sections treated with Douglas-fir extractives + D D A C was less than 0.5 compared to 6.2 for the untreated control. Brightness control in sections treated with cedar extractives + D D A C was also better than was the case for sections subjected to U V irradiation in the absence o f leaching.  Figure 6.1.4.2.2: The effect o f combinations o f additives and D D A C on the loss o f brightness o f treated and untreated wood after 6 days o f U V irradiation and washed after U V irradiation.  144  6.2.  Conclusions  6.2.1. Discoloration of the treated wood by UV irradiation In conclusion, it was found that 1) Douglas-fir extractives and cedar extractives, when added to D D A C at concentrations o f 2% and used to treat wood, were effective at restricting color changes o f sections subjected to U V irradiation; 2) Douglas-fir extractives and cedar extractives were more effective additives for D D A C  than  lignosulfonic acid and pine extractives; 3) Douglas-fir and cedar extractives and D D A C were also effective i n restricting loss o f brightness o f wood sections subjected to U V irradiation. However, the initial brightness o f the wood was lower because the Douglasfir and cedar extractives colored the treated w o o d brown.  6.2.2. Discoloration of the treated wood by UV irradiation and washing The following conclusions can be drawrn: 1) the Douglas-fir and cedar extractives were able to enhance the color and brightness stability o f treated wood sections even when they were subjected to U V irradiation and leaching; 2) when wood treated with pine extractives or L S A , leaching may have washed o f f most o f the chemicals. Discoloration o f pine extractive and L S A treated wood was the same as that observed i n untreated and D D A C treated wood.  145  CHAPTER 7 7.1.  Summary and Recommendations  Summary Based on the observations in this study, the following can be summarized: 1.  The new alternative formulations, which are based on alkylammonium  compounds ( A A C s ) together with organic cobiocides do not slow down photodegradation o f the treated wood based on the F T I R spectra o f the peak at 1510 cm" compared with 1  the untreated control. 2.  W o o d treated with alkylammonium compounds ( A A C s ) together with  copper as cobiocide effectively resists lignin degradation and also the formation o f carbonyl groups based on the F T I R observation bands at 1510 and 1730 cm" . This is due 1  to copper reacting with phenolic hydroxy group, which is a main photoreaction site, i n lignin and blocking the main photoreaction site in wood. 3.  The washing study shows that the wood samples treated with A A C s  together with copper are still less susceptible to the photodegradation process compared with the untreated control. 4.  The treatment o f D D A C accelerates the wood photodegradation process.  This process could be slowed down by using additives, which are antioxidants. Douglasfir extractives, western red cedar extractives and tannic acid are effective at reducing the delignification process when they are used alone or combined with D D A C . This is probably due to the polyphenols in the extractives. 5.  The combination  o f Douglas-fir  extractives  or western red cedar  extractives together with D D A C greatly retarded the color change o f wood during U V irradiation. The treatment also improves the brightness stability o f wood.  146  6.  W o o d treated with Douglas-fir extractives plus D D A C or western red  cedar extractives plus D D A C after 6 days o f U V irradiation and subsequent washing showed excellent brightness stability.  7.2.  Recommendations 1.  Selection o f wood samples: the wood sample thickness should be  measured and samples with the same thickness should be selected. 2.  L o n g term natural exposure trials need to be conducted to confirm whether  Douglas-fir and cedar extractives can provide long term protection to wood in practice. 3.  Natural weathering test: the weathering resistance o f treated and untreated  wood can be determined by exposing vertical panels in outdoor field trials. This w i l l confirm the effectiveness o f the selected chemicals against weathering. The change o f color should also be monitored during natural weathering. Brush applied finishes on solid wood ' 1 x 4 ' lumber should be used. 4.  It was confirmed that natural polyphenols, that are antioxidants, could be  used to reduce lignin degradation o f D D A C treated wood. It is necessary to clarify the roles o f polyphenols in reducing lignin degradation when they are used alone or together with D D A C . 5.  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