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UBC Theses and Dissertations

Photo-resistance of alkylammonium compound treated wood 2003

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P h o t o - r e s i s t a n c e o f A l k y l a m m o n i u m C o m p o u n d T r e a t e d W o o d by X U E Y U A N Z H A N G 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 SC IENCE IN T H E F A C U L T Y OF G R A D U A T E STUDff iS (Department of Wood Science, Faculty of Forestry) We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y OF BR IT ISH 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) A B S T R A C T The potential of alkylammonium compounds (AACs) as wood preservatives, was recognized during the 1970s. The problems associated with AAC-treated wood, particularly treated with didecyldimethylammonium chloride (DDAC) , are severe surface degradation and discoloration compared to untreated wood. The aims of this study were to assess the performance of A A C based chemically treated wood to ultraviolet (UV) irradiation and also determine photo-resistance of wood treated with a combination of 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 in the treated and untreated wood sections were examined using Fourier transformed infrared spectroscopy (FTIR), which provides a rapid and nondestructive analysis of the wood during U V irradiation. The relative l ignin degradation and the formation o f carbonyl groups were quantitatively analyzed based on the peaks at 1510 and 1730 cm"1 in the FTIR spectra. The studies showed that only the new biocides containing the cobiocide copper, slowed wood photodegradation by inhibiting the formation of carbonyl groups and delignification compared to the untreated wood and wood treated with only organic biocide formulations. D D A C treatment accelerates delignification and demethoxylation via the formation of free radicals. In order to increase the photo-resistance of D D A C treated wood, additives including butylated hydroxytoluene (BHT), lignosulfonic acid (LSA) , 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 . FTIR was used to examine the effectiveness of the additives in slowing the photodegradation of D D A C treated wood during U V irradiation. The FTIR 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" 1 which presents aromatic skeletal vibrations in lignin. A quantitative analysis of the FTIR spectra was used to assess the lignin degradation and the formation of carbonyl groups. The results showed that the addition of Douglas-fir extractives, and tannic acid to D D A C reduced lignin degradation. Douglas-fir and cedar extractives also reduced the formation of i i 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 of the additives slowed the oxidation process of lignin in the wood during U V exposure by terminating the formation of free radicals from lignin, generated by U V light. A washing study showed that the action of washing might wash off the additives and D D A C in the wood sections, because their FTIR 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 Minolta 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 of wood sections treated with additives plus D D A C by U V irradiation and washing showed that the action of 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. i i i TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES viii LIST OF FIGURES ix LIST OF ABBREVIATIONS xviii ACKNOWLEDGMENTS xix CHAPTER 1 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 CHAPTER 2 LITERATURE REVIEW 7 2.1. Photodegradation of wood by light 7 2.1.1. Phenomena of wood exposed to light 10 2.1.2. Physical changes 10 2.1.3. Chemical changes 11 2.1.4. Discoloration of wood by light 12 2.1.5 Chemistry of wood photodegradation 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. Painting 18 2.4.2. Inorganic treatment 18 iv 2.4.3. Organic chemical protections 19 CHAPTER 3 METHODOLOGY 22 3.1. Wood sample preparation 22 3.2. Chemicals 22 3.2.1. Biocides 22 3.2.2. Additives 25 3.2.3. Extraction of wood extractives 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. Theory 32 4.1.3. Methodology 33 CHAPTER 4 PHOTO-RESISTANCE OF ALKYLAMMONIUM COMPOUND TREATED WOOD TO UV IRRADIATION 35 4.1. The photodegradation of sapwood treated with amine oxide or QAC compounds 35 4.1.1. Effect of the treatment 35 4.1.2. Overview of the FTIR during photoexposure 38 4.1.3. Effect of the washing 39 4.2. Treatment of QAC related chemicals containing copper 50 4.2.1. Effect of copper chemicals as observed by FTIR 50 4.2.2. Effect of Q A C related chemicals containing copper on wood photodegradation by U V irradiation 51 4.2.3. Effect of copper concentration on the FTIR spectra 52 4.2.4. Effect of sample washing after photoexposure, on the FTIR spectra 52 4.3. The relative delignification rate and the formation of carbonyl groups 59 4.4. Conclusions 64 CHAPTER 5 PHOTODEGRADATION OF WOOD TREATED WITH DDAC PLUS ADDITIVES 66 5.1. FTIR studies 66 5.1.1. Effect of B H T on photodegradation of D D A C treated wood 66 5.1.2. Effect of l,4-diazabicyclo(2,2,2)octane on photodegradation of D D A C treated wood 66 5.1.3. Effect of wood extractives on photodegradation of D D A C treated wood — 69 5.1.4. Effect of lignosulfonic acid on photodegradation of 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 95 5.4.1. The relative delignification rate 95 5.4.2. Explanation for the differences observed 103 5.4.3. Formation of carbonyl groups 104 5.5. Conclusions 105 CHAPTER 6 COLOR CHANGES OF DDAC PLUS ADDITIVES TREATED WOOD DURING UV IRRADIATION 112 6.0. Introduction 112 6.1. Results and Disscusion 113 6.1.1. Effect of 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 ( LSA) + D D A C 117 6.1.2. Effect of additives on brightness of 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 of additives on the color and brightness of 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 (LSA) + 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 v i 6.1.3.2.3. Scots pine extractives + D D A C 136 6.1.3.2.4. Lignosulfonic acid + D D A C 136 6.1.4. A comparison of the effect of additives on their ability to retard color changes and brightness of D D A C treated wood 141 6.1.4.1. The effect of additives and D D A C on color changes 141 6.1.4.2. The effect of additives and D D A C on the brightness changes 143 6.2. Conclusions 145 6.2.1. Discoloration of the treated wood by U V irradiation 145 6.2.2. Discoloration of the treated wood by U V irradiation and washing 145 CHAPTER 7 SUMMARY AND RECOMMENDATIONS 1 4 6 7.1. Summary 146 7.2. Recommendations 147 R E F E R E N C E S 1 4 8 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 x i i 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 x i i i 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 xv i LIST OF ABBREVIATIONS A A C s Alkylammonium compounds A C Q Ammoniacal copper quaternary ammonium compound B H T Butylatedhydroxytoluene C C A Chromated copper arsenate Cu -EA Copper ethanolamine C u - M E A H Copper monoethanolamine D D A C Didecyldimethyl ammonium chloride DF Douglas-fir FTIR Fourier transform infrared spectroscopy IR Infrared spectroscopy L S A Lignosulfonic acid Q A C Quaternary ammonium compounds U V Ultraviolet WGs Weight gains xv i i A C K N O W L E D G M E N T First of 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. Phi l Evans and Dr. Simon El l is, for their invaluable advice and help on my research work and also in preparation of 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. xv i i i Chapter 1 Background 1.1. Trends in use of treated wood Wood possesses numerous attractive properties, such as an aesthetic appeal, low 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 of 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 of treated lumber produced in Canada was $547 mil l ion, and the value of the total volume o f treated wood installed in Canada was in excess o f $10 bi l l ion (Stephens et al., 1994). The wood preservation industry is therefore an important contributor to the Canadian economy. In a recent review of the evolution of the wood preservation industry, it was noted that profound changes have occurred (Preston, 2000). During the first half of the 20 t h century treated wood was mainly used for ground-contact applications (e.g., cross-ties, piles, and poles) whereas today a greater proportion of treated wood is used for above ground applications (e.g., decks). While the volume of 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, in contrast to the merits needed for industrial wood products, the appearance of 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 (CCA) (Micklewright, 1998). In 2000, the production of treated lumber in North America was estimated to be about 15 mil l ion 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 of 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 of bleeding after the treatment; and 4) it is relatively inexpensive. However, pressure is increasing to abandon the use of C C A because of its negative influence on the environment, and the increasing cost o f disposal of treated wood when its service life is over. These pressures have led to the development and use of alternative wood preservatives, in Europe and Japan for example, of alkaline ammoniacal copper quat (ACQ), or copper azole which are more environmentally friendly wood preservatives than C C A . In Apr i l 2002, both the U S A and Canadian producers decided to move towards the use of such alternative wood preservatives for the consumer purchased treated wood market. It is anticipated that no pressure-treated wood that contains arsenic wi 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, play- structures, picnic tables, landscaping timbers, residential fencing, patios and walkways/boardwalks. The environmental concerns that led to the industry abandoning the marketing of C C A have been the major driving forces behind the development of new wood preservatives in recent years. 2 1.3. QAC wood preservatives Quaternary ammonium compounds (QACs) have received considerable attention in recent years because of their potential as biocidal agents in wood preservatives. Didecyldimethylammonium chloride (DDAC) , which is a component of A C Q - type B and D, is stable, colorless, water or solvent soluble, and is relatively inexpensive. Also, it exhibits low mammalian toxicity and creates few environmental problems. D D A C belongs to the group of chemicals that are commonly used in 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 of the treated wood at the end of its service life is relatively straightforward compared to the problems associated with disposal of 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. As mentioned above, the resistance of 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 of wood. They confirmed that wood treated with 2% D D A C showed significantly increased lignin 3 degradation compared to untreated wood. The consequence of this accelerated delignification was undesirably rapid changes in the wood's appearance, i.e., discoloration, loss of gloss and lightness, roughening, considerable latewood defibration and severe early wood erosion, and checking of surfaces (Jin et al., 1991). 1.4. Objectives Clearly there is a need to find ways of preventing or slowing the deleterious effects of D D A C on the weathering of wood. The experiments in this thesis examined the photodegradation of treated wood and untreated controls under laboratory conditions. The first phase focused on measuring the relative photo-resistance of wood treated with selected novel biocidal. formulations based on Q A C or related co-amine components together with triazoles. The second phase of the thesis concentrated on determining the effectiveness of selected additives in improving the photodegradation resistance of wood treated with QACs (in particular DDAC ) . The specific aims of the research reported in this thesis were: • To measure the relative weatherability of wood treated with selected novel biocidal formulations based on Q A C or related co-amines together with triazoles. • To determine the effectiveness of selected additives in improving the photodegradation resistance of 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 of 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, FTIR spectroscopy and colorimetry) used to analyze the photo-resistance of treated and untreated wood during U V irradiation. Chapter 4 examines the photo-resistance of wood treated with alkylammonium compounds that have been developed by Lonza Inc. Such components may be used as components of new wood preservatives for above ground application (e.g., decks). It is important therefore, to obtain information on how they affect the photo-resistance of wood. The resistance of the treated wood was compared with that of untreated wood using FTIR spectroscopy. The rate of lignin degradation and the formation of carbonyl groups, as determined by FTIR spectroscopy, were used quantitatively to compare the effect of alkylammonium compounds on photo-resistance. Quantitative analysis of the FTIR spectra were made based on the lignin peak at 1510 cm"1 and the carbonyl groups 5 peak at 1730 cm" 1. Chapter 5 examines the ability of certain additives to improve the photo- resistance of D D A C treated wood. Wood extractives (Douglas-fir, cedar and pine extractives), tannic acid and butylated hydroxytoluene (BHT) (an antioxidant commonly used in the food industry) were selected as photostabilizing additives. FTIR 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 C I E L A B parameters) of D D A C and additives treated wood during U V irradiation. The color stability and brightness of extractives plus D D A C treated wood were determined using a spectrophotometer. Finally, Chapter 7 gives an overview of the findings of the study. Conclusions and recommendations for future research on improving the photo-resistance of 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 Wood is a complex biopolymer composed of principally cellulose and the aromatic polymer, lignin. Because of the chromophoric groups present in wood, for example phenolic hydroxyl groups, aromatic skeletons, double bonds and carbonyl groups, l ignin strongly absorbs ultraviolet (UV) 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 of cellulose and lignin make up the absorption curve of wood. According to Norrstrom (1969), lignin contributes 80-95% of the absorption coefficient, while the carbohydrates contribute 5-20%, and the extractives about 2%. Because of lignin's predominant light-absorption properties, it absorbs more light, resulting in more degradation, than cellulose. Moreover, because of lignin's phenolic based structure, the photon energy absorbed by cellulose is l ikely to delocalize and transfer to lignin, so the presence of l ignin wi 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 of the sunlight spectrum are more than sufficient to break many of the chemical bonds present in wood constituents, namely, cellulose, hemicellulose, and particularly lignin (Figure 2.2). The functional groups of lignin responsible for the photodegradation process have been identified. The carbonyl chromophore was shown to be one of the most effective reaction centers (L in and 7 Kringstad, 1970b; and Forsskahl, 1984a). Free phenolic hydroxyl groups are the major source of protons to be donated for the hydrogen abstraction reaction, and they are further oxidized in the presence of molecular oxygen (L in and Kringstad, 1970 and 1971; Gellerstedt and Peterson, 1977; and Forsskahl, 1984a). Visible light of 400-700 nm is insufficient to cleave chemical bonds in any of 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 of Radiata pine veneers (85 um in thickness) initially decreased rapidly over the first five days of 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 of wood, absorption due to carbonyl groups at 1720 cm"1 and 1735 cm"1 increased, whereas the absorption for lignin at 1265 cm"1 and 1510 cm"1 gradually decreased. The enhanced carbonyl groups were the result of oxidation of cellulose and lignin. The reduction in the amount of l ignin was due to its degradation by light (Feist and Hon, 1984). 8 ooo 1 ' 1 1 1 1 ' 1 1 1 1 200 250 300 350 400 450 Wavelength, nm Figure 2.1. Ultraviolet spectra of (a) wood, (b) lignin, and (c) cellulose (after Hon, 1991a). 105 - i 65-I 1 1 1 1 1 1 1 1 1 250 300 350 400 450 Wavelength, nm Figure 2.2. Approximate bond energy of chemical bonds in woods (after Hon, 1991a). 9 2.1.1. Phenomena of wood exposed to light The interaction of wood and U V light is essentially a surface reaction, in which the U V light does not penetrate wood deeper than 75 um (Hon and Ifju, 1978). When wood is exposed to daylight or U V irradiation, the first sign of change at the wood surface is yellowing. According to Hon (1981b), the changes in wood color fol low a pattern of 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 of the color changes is due to the chemical conversion and degradation of 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 of aesthetic appearance, which is an important criterion to customers, followed by the loosening of wood fibers. Rain washes the degraded woody materials from the surfaces, causes dimensional changes, and accelerates the surface erosion. 2.1.2. Physical changes The effects of photo-induced degradation on the structure and chemical composition of wood are superficial in nature. They do not affect mechanical properties of the wood significantly. Photodegradation of wood and stresses generated by cyclical wetting and drying result in the formation of 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 of longitudinal surfaces are the formation of microchecks originating in bordered and half-bordered pits and the degradation of ray tissues (Evans, 2001). 2.1.3. Chemical changes Photodegradation and photooxidation of wood result in changes in chemical and physical properties. Discoloration, loss of lightness, roughening of surfaces, damage to the microstructure, and loss of weight, as a result of U V irradiation, indicate that severe chemical modification of the structure of wood components, especially l ignin, 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 of exposure (Leary, 1967 and 1968; Kringstad, 1969). During photo-irradiation, in the initial stages up to 1 h, only CO, 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 of 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). Hon and Chang (1984) also used U V visible spectroscopy to analysis water- soluble fragments collected from U V irradiated wood. They found that the low molecular weight, water-soluble products were derived mostly from lignin. The degradation products contained carbonyl-conjugated phenolic hydroxyl groups and had a weight- average 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"1 became low in intensity, but did not disappear, until after 40 days of U V irradiation. This observation indicated that the structure of l ignin molecules had been subjected to significant photochemical degradation. The lignin content of 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"1 increased after U V irradiation, thus indicating an increase in the concentration of carboxylic and /or carbonyl groups that were derived from the lignin. 2.1.4. Discoloration of wood by light Wood is an excellent material for light absorption and light reflection. The color characteristics depend on the chemical components of wood that interact with light. Hence, the reaction of wood components to light, heat, and chemicals wi l l change the color of wood. Extensive studies and observations have shown that most, i f not all, wood species of 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 in above ground applications. Ultraviolet light plays an important role in the discoloration of wood. The color of unprotected wood surface changed rapidly, because of the degradation of lignin and the formation of 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 of U V light by lignin and photolysis and fragmentation of l ignin resulting in the formation of aromatic and other radicals (Feist and Hon, 1984). Research has shown that the aromatic lignin component of 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 in the polymer through the cleavage of molecular bonds (photolysis) resulting in the formation of a free radical. Because of the complexity of the lignin structure, identifying the free radical sites formed is extremely difficult. However, several aspects of the photochemical reactions have been determined and can be summarized as follows: • L ignin is degraded relatively easily by light of wavelength shorter than 350 nm, while photobleaching or whitening of lignin can be observed when it is exposed to light of wavelength longer than 400 nm. • Reduction of the methoxyl content of lignin occurs. • Phenoxy radicals are produced readily from phenolic hydroxy groups. • Carbon-carbon bonds adjacent to a-carbonyl groups are photodissociated v ia 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 of lignin (Feist, 1984). Because of 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 of the guaiacyl unit of lignin to produce o-quinonoid structures (Figure 2.4). Leary (1968) suggested that o- quinone is the end product of the reaction. Consequently, quinonoid moieties formed in wood are apparently the major chromophoric groups contributing to the discoloration of 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 (DDAC) in accelerating the weathering of wood was reported in the early 1990's by Jin et al. (1991). L i u and Ruddick (1993) reported the FTIR spectroscopic study of D D A C treated wood during U V exposure. The IR spectra of D D A C treated earlywood sections showed that the bands at 1267, 1510 and 1600 cm" 1, which represent benzene ring skeletal vibrations, were decreased faster than untreated controls. However, a band at 1735 cm" 1, indicative of 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"1 are related to delignification and demethoxylation which contribute to the discoloration of 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 of wood, as demonstrated by the spectra of FeCb-treated wood. The sensitization takes place via the DDAC- l i gn in 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 D D A C impact on the formation and decay of the phenoxy free radicals, based on the influence of D D A C leaching and retention on the free radical formation and decay. 15 2.3. FTIR spectral analysis of photo-exposed wood FTIR spectroscopy is a useful method for a rapid and convenient characterization of a thin wood sample and its major components. The FTIR technique has four important characteristics that contribute to its usefulness in detecting compositional changes of 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 of mixtures are additive and the absorption of the key peaks is proportional to the concentration of the chemical studied; and d) the IR spectra can be obtained non-destructively. The FTIR spectrum is obtained by passing a beam of infrared radiation of constantly varying frequency through a sample o f the compound. A detector generates a plot of percent transmission of radiation vs. the wavenumber. The bonds in the irradiated molecules are constantly vibrating. A stretching vibration is a vibration occurring along the axis of the bond, while a bending vibration occurs out of the axis of the bond. Each stretching and bending vibration of 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 of one of its bonds, the vibrating bond wi l l absorb energy and generate an absorption peak in the FTIR spectrum. The wavenumber range of interest lies between 4000 cm"1 to 400 cm" 1. The fingerprint region (1800 cm"1 to 1000 cm"1) contains many complex signals generally resulting from bond bending that are unique for each compound. The IR spectrum of wood is due to the combined absorption of individual components, namely, cellulose, hemicellulose, and lignin and extractives. The absorption bands in the 1740-1720 cm"1 region are due primarily to the carbonyl stretching 16 vibrations of carboxylic and acetyl groups. Several characteristics bands at 1600, 1510, and 1265 cm"1 are due to the C=C stretching vibrations of the benzene ring presented in lignin. The changes noted in the IR spectra of wood after irradiation with U V light are indicative of changes in chemical compositions at exposed surfaces. One indication of chemical changes in wood surfaces is an increase in cellulose content and a decrease of lignin content of the weathered wood surfaces (Evans et al., 1992; Wang and L i n 1991; Hon 1994). The photodegradation process is initiated by the formation of free radicals, presumably with oxidation of phenolic hydroxyl groups (Hon 1981). Free radicals generated in wood are known to react readily with oxygen to produce hydroperoxides (Hon and Chang 1984; Hon and Feist 1992). The wood photodegradation results in a decrease in methoxyl and lignin content and an increase in carboxyl in wood (Evans et al., 1992). IR absorbance of carbonyl groups at 1720 and 1735 cm"1 was also observed to be reduced because o f the washing o f the carbonyl rich components by rain (Feist and Hon 1984). 2.4. Wood protection against photodegradation Because photo-induced discoloration and deterioration of wood are undesirable, much work has been done to protect wood and woody material surface from photodegradation in outdoor applications. One or a combination of the fol lowing methods may be adopted to prevent photo-induced degradation (Hon, 1991b). • Cutting off the U V light, • Modify ing 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 lm 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 of weathering on wood. However, paints are less effective in 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 in 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 of application (Evans, 1991). In order to enhance the performance o f clear finishing on wood, a pretreatment with photostabilizers or U V absorbers is often required. 2.4.2. Inorganic treatment The protection of 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 (ACQ) and chromated copper arsenate (CCA) 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 (Cu- M 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" 1. Treatment with water- soluble salts of chromium, iron and copper were also used and effectively increased the weathering resistance of wood (Feist, 1979; Feist, 1983; Feist and Wil l iams, 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 of photochemical reactions (Hon and Chang, 1985; Ross and Feist, 1991). 2.4.3. Organic chemical protections A large number of organic chemicals have been used to modify wood (L in and Kringstad, 1970b; Gierer and L in, 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 photo- induced oxidation. If spruce milled wood lignin is first reduced with sodium borohydride, followed by catalytic hydrogenation of the conjugated double bonds, it is completely stable towards U V light (Lin and Kringstad, 1970b). The effect of acetylation on the 19 weathering performance of Scots pine wood veneers was studied by Evans et al. (2000). Scots pine wood veneers were acetylated to different weight gains (WGs) up to 20% and then exposed to nature weathering. It was found that acetylation of wood veneers to low WGs of 5 and 10% increased the susceptibility of lignin to degradation and also the depolymerisation of cellulose during weathering. At acetylation to higher WGs (20%), holocellulose was protected, but lignin was not protected. They suggested that the substitution of lignin phenolic hydroxyl groups, which occurs preferentially at low WGs, reduces the photostability of wood. Acetylation at low WGs may open up the wood matrix and increase the accessibility of 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 of wood to high weight gains (~70%) was effective at protecting wood from photodegradation and stabilizing lignin. Benzoylation reduced the quantity of 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 of U V absorbers to wood can also retard the photo-induced discoloration of wood (Will iams, 1983; Grelier et al., 1997). However, this system has a number of limitations in that it requires the synthesis of a functionalised U V absorber and the use of 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 of free radicals to be produced under the exposure of the wood to U V light. The generation of 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 of these free radicals. The strategies include the use of 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 mm (tangential) x 10 mm (radial) x 40 mm (longitudinal) (3-4 annual rings) were vacuum pressure impregnated with distilled water to soften them. Earlywood sections approximately 60 um (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 of new alkylammonium compound ( A A C ) based biocides formulated for wood protection in above ground applications. As mentioned preciously, it is important for treated wood to resist photodegradation when used in outdoors. Therefore, this study examined the ability o f these new A A C compounds to prevent the photodegradation of wood. The chemicals provided by Lonza Inc are listed in Table 3.1. The concentrations of chemical used in the treatment o f wood samples are listed in Table 3.2. 22 Table 3.1: Chemicals supplied by Lonza. Code Names (w/w), % WP-40 Alkyl(Ci 2Ci 4Ci6)dimethylamine oxide 5.2 Propiconazole 0.5 Inerts 94.3 WP-41 Didecyldimethylammonium chloride 4.78 Propiconazole 0.45 Inerts 94.7 WP-42 Alky l (C 1 2 Ci 4 Ci 6 )d imethy lamine oxide 5.8 copper carbonate, basic 8.4 Inerts 85.8 WP-43 *Alkylbenzylhydroxyethylimidazolinium 5.7 chloride 8.4 copper (II) carbonate, basic 85.9 Inerts WP-46 Alkyl(Ci 2Ci 4C| 6)dimethylamine oxide 5.2 Cyproconazole 0.1 Inerts 94.7 WP-47 Didecylmethylpoly(oxyethyl)ammonium 4.7 Propionate 0.1 Cyproconazole 95.2 Inerts WP-48 Alky l(C i 2 Ci 4 Ci 6 )d imethylamine oxide 9.0 Cyproconazole 0.5 Inerts 90.5 WP-62 Didecyldimethylammonium carbonate 16 Inerts 84 WP-63 Didecyldimethylammonium chloride 16 Inerts 84 WP-64 Didecyldimethylammonium chloride 16 Propiconazole 1.5 Inerts 82.5 * 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, % Concentrations of active components in formulated products (copper as copper oxide) Benzyldimethyldodecyl 77 1%, 2% ammonium chloride D D A C 80 2% Wp-40 5.2 2% Wp-41 4.78 2% Wp-42 8.4 0.25%, 0.5%, 1%, 2% Containing copper Wp-43 8.4 2% Containing copper 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% 24 3.2.2. Additives Butylated hydroxytoluene (BHT) (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 of 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 of 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 BHT , 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 of such chemicals for the photoprotection of wood is also attractive. The antioxidant activity of 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 of 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 Douglas- fir (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 in 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 of butylated hydroxytoluene (BHT). 26 Figure 3.2: Structure of 1,4-diazabicyclo (2,2,2) octane. Figure 3.3: Structure of lignosulfonic acid. Table 3.3: The solutions of the additives into D D A C prepared for the research. Treating solution Additives, 2%* B H T 1,4- diazabicyclo (2,2,2) octane Douglas- fir bark extractives western red cedar extractives Scots pine extractives LSA Tannic acid D D A C 2% V A/ A/ V 5% A/ y1 A/ Solvents Methanol Distilled water Methanol Methanol Methanol Distilled water Distilled water *based on air-dried weight, for wood extractives 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 Wi ley mil l , until the sawdust passed through a 20 mesh screen. About 8.0 g of 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 in 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 mL of 50:50 methanol-water solvents, at a minimum rate of 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 in 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 mL 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 in lignosulfonic acid or tannic acid solution for 2 hours. For 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 FTIR measurements. Untreated sections treated with distilled water (as above) were used as controls. 3.4. Leaching To examine whether the photoprotectants were soluble, a leaching study was done. After U V irradiation, treated samples and untreated controls were soaked in distilled water for 15 minutes. They were then air-dried before examination by FTIR 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 of a photoreactor chamber from A C E G L A S S 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. Fol lowing each period of U V irradiation, the samples were collected and placed in a cardboard holder for FTIR measurements. The FTIR spectra were obtained at a resolution of 8 cm"1, 64 scans per sample over the range 400-4000 cm"1 using a Perkin-Elmer FT IR 1600 series instrument. In the plots of combined spectra, the transmission scale of the offset spectra is omitted for the sake of clarity. 30 3.6. Quantitative analysis of FTIR spectra FTIR spectra were examined quantitatively to more precisely determine the effects of treatment and exposure on the photodegradation of wood during exposure to U V light. Since a large number of the FTIR 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"1 was used as an internal reference (Segal et al., 1960). The typical l ignin characteristic peak at 1510 cm"1 (C=C ring stretching in aromatic l ignin units) was chosen to monitor l ignin degradation in the wood, and the peak at 1730 cm"1 was used to evaluate the formation of carbonyl groups (Hon and Feist, 1986). Peak areas of interest were calculated by drawing a baseline from the point of transmittance at the beginning of the peak to its end using the spectrometer software for peak area determination (IR Spectra v2.0 ™) . Changes in areas of the peaks at 1510 and 1730 cm"1 relative to the internal reference peak at 1162 cm"1 were used to quantify delignification and the formation of carbonyl groups during U V irradiation, respectively. The delignification rate of treated and untreated wood after U V irradiation was also expressed by subtracting relative absorption areas of treated wood from the initial relative absorption areas. Because of changes in the spectra when copper was present in the formulation, the relative changes in the areas of the peaks due to the lignin (1510 cm"1) or carbonyl (1730 cm"1) compared to the internal standard were used. For the second phase of research where additives were combined with D D A C , the percentage changes in the areas o f the l ignin peak compared to that before irradiation were calculated. 31 3.7. Color and brightness measurement 3.7.1. Theory The surface color of wood was determined according to the ISO 2470 standard and the CIE 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 of color used a D65 light source, as recommended by CIE 1976 (Billmeyer and Saltzman, 1981). Color parameters were used to calculate the color change AE* as a function of the UV-irradiation period according to Eqs. (5), (6), (7), and (8). AL* = L f* - L|* (5) Aa* = af* - a;* (6) Ab* = b f* - bi* (7) AE* =VAI*2 +Aa*2 +Ab*2 (8) Where, AL*, Aa*, and Ab* are the changes between the initial (i) and final (f) values. L*, a* and b* contribute to the color change AE*. A low AE* corresponds to a low color change or a stable color. 32 Figure 3.6: Representation of C LELAB color system. 3.7.2. Methodology The surface color and brightness of 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 of the wood sections, of the color and brightness of the wood surfaces. Each measurement represented the average of 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 Hon (2000), it wi 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 C M - 2 6 0 0 d 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"1 is often used to monitor lignin in wood, arising from the C=C stretching vibrations of the aromatic ring present in lignin (Table 4.1). This peak usually appears in the region o f 1515-1500 cm" 1 depending on the ring substituents. It was noticed that the peak intensity at 1510 cm"1 was reduced 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 in intensity of this peak after the treatment implied that the substituents of the aromatic rings have been changed by the chemical bonding of the biocides. L i u (1997) reported the decrease in the peak intensity of the phenolic hydroxyl group following D D A C or A C Q treatment and suggested that an interaction of the hydroxyl group with D D A C and A C Q had taken place. The FTIR results confirmed that a cation exchange reaction took place between D D A C and the protons in the carboxylic acid and phenol in wood (Jin and Preston, 1992 and Doyle, 1995). Compared with untreated controls an increase in the peak intensity at 1730 cm" 1, which represents carbonyl groups, was observed after wood sections treated with 2% wp- 40, 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 of - O H groups in secondary alcohol in lignin and forming carbonyl groups. 35 Examination of the FTIR spectra of treated samples showed a new peak at 1460 cm" 1, which represents the C-N stretching vibration, occurred in the FTIR spectra after 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 of the bound or absorbed chemicals. 36 Table 4.1: The assignments of absorption peaks in IR spectra of southern pine- Frequency, cm' 1 Group or class Assignments & remarks 2860 O H in wood H-bonded O H stretching vibration - C H 3 attached to O & N C H stretch 1720-40 C=0 in unconjugated ketones C=0 stretching aldehydes & carboxyl compounds 1645-60 C=0 in para-OH substituted aryl Same ketone, quinone C=C in alkenes, etc. C=C stretching 1600-1610 C=C in aromatic ring in lignin Aromatic skeletal vibration COO" COO" 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 C 0 2 " Symmetrical stretching vibration 1370 C-H in all components in wood C -H deformation (bending) 1315 CH2 in cellulose C H 2 wagging 1267 CO in lignin and hemicellulose Guaiacyl ring breathing with CO - stretching 1162 C-O-C in cellulose Antisymmetrical bridge oxygen stretching 1035 Aromatic C-H C-H in plane deformation 37 4.1.2. Overview of the FTIR during photoexposure In evaluating the weathered wood, attention was focused on the changes of absorption peaks at 1720-40, 1600, 1510, 1267, and 1162 cm" 1. The peaks at 1720-1740 cm"1 are associated with the carbonyl group (C=0) stretching vibrations of esters and carboxylic acids. The peaks at 1600 and 1510 cm"1 are due to the C=C stretching vibration from the benzene ring (from lignin) (Sarkanen et al., 1967). The peak at 1162 cm"1 (C-O-C) is the antisymmetrical bridging oxygen stretching vibration in cellulose. It w i l l al low changes in cellulose to be monitored. The intensity o f these peaks is considered important, since they can be correlated to changes in functional groups and chemical structure of wood components. The infrared spectra of 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 FTIR spectra were noticed after 6 days of U V irradiation. Firstly, the intensities of the peaks at 1600, 1510, and 1267 cm"1 were decreased. Secondly, the peak at 1720-1740 cm"1 increased in area and broadened. For the wood sections treated with 2% wp-40, 2% wp-41, 2% wp-46, 2% wp-47, 5% wp-48, 5% wp-62, 5% wp-63, 5% wp-64, didecyldimethylammonium chloride (DDAC) , 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 of the peaks at 1600, 1510, 1267, and 1730 cm"1 to those observed in the untreated wood (Figure 4.1.1a). This suggested that none of these chemicals are able to prevent degradation of lignin. However, while the lignin in the wood sections treated with 5% wp-48 was clearly degraded based on the reduction in the intensity of the peaks at 1510 and 1600 cm" 1, there was no corresponding increase in the peak at 1730 cm"1 which arises from the resulting quinone, suggesting that the treatment 38 of wood with wp-48 (Figure 4.1.6a) prevented the formation of 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" 1, when compared with those in the untreated control. These changes at peaks 1510, 1600 and 1267 cm"1 are 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 iu et al, 1994). 4.1.3. Effect of the washing Whi le the photodegradation action was monitored on samples after periods of 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) of the leached and unleached wood samples were in the changes to the transmission peaks at 1730 and 1460 cm" 1. The peak at 1730 cm" 1, which is related to the C=0 group stretching 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" 1, which represents the 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 soireuiujsirejx | < 8 * c •g .2 CO a •2 «« 8 T J . a <o s s _•» co • is -Q c 8 O u a. g H > s L-> srf — H S f £ SoNO N XI 30irettimsuB.il T3 c o ts a> T J o o o ee) i cS a o I T J E • —H i~ 4> CC T3 C CO C O '5 -a 2 -3 ^ RJ T J C IS * .. * cs T  0 3 o c 43 •a .2 ~ t C - o « O «S C O ^ _ C O - co 0 G >> £ .3 -g «g I o 1 * « J 9! .5 "2 aouBHiujsueji — : » 00 . . « ° M 90UBUILUSU6JJ, T3 .2 4 - * C O +3 <C O «3 -a at .a « S 0 5 CO -o o o C M O ca fa CX ! | c2 CO T3 03 -O E T3 3 O -C 00 CO H 00 » v> J> aOUBHILUSUBJ l -o .2 * J co cO ^ 2 cO ° fc cn • — C •_ o 1> '& <c U CO <U —• oo "O C o o o O CO g a '-S --̂ ea co T3 • g § i H <& to « oo .. ts CO O r - v vq| * o OO co e f * 0 N / t U «/̂  .£> 45 o 90UBUIUJSUBJ1 CO eoueniwsueJi r- fa 1 <s •o .2 w co CO E i 0) ea T J eS O - co O R >. CO CO T J §.5-2 « > S « b co PS 8 3 H <S -e » oo CO ^ ^ £2 (N a. 5 3 JS +5 .Q 90UBJJ!UJSUBJ1 — CO c o 1 1) co T3 O O -o 0 3 t X) 03 i > T3 £ .2 g r. CO 03 o 03 .a ^3 03 — I o to ^ co p T3 s H [I* JO 00 3 O oo C M S 5b N O t- m 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 FTIR were noted when the wood sections were treated with the copper containing formulations wp-42 and wp-43. Firstly the absorption at 1730 cm' 1 became weaker (Figures 4.2.1a and 4.2.5a). Secondly, a peak around 1630 cm" 1 sharply increased, and also a new band around 1320 cm"1, assigned to the COO" 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"1 were noted before photoexposure. They did not show significant change even after 6 days of U V irradiation. The reduction of the peak at 1730 cm"1 during treatment indicated that copper reacted with the carbonyl containing groups in wood. The carbonyl peak at 1730 cm"1 was shifted to around 1630 cm"1, which sharply increased after treatment. It has been suggested by several authors that basic copper preservatives can react with carboxylic and groups in 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 QAC related chemicals containing copper on wood photodegradation by UV irradiation The IR 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 of l ignin at 1600 and 1510 cm" 1 and the peak associated with lignin at 1267 cm" 1. In the spectra the peaks at 1510 and 1267 cm"1 observed in the untreated 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 of U V irradiation. Also, the absorption peak at 1730 cm"1 that represents carboxylic and carbonyl groups, 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 of 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 of 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 of 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 of 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"1 in the treated sections became weaker (Figures, 4.2.1a to 4.2.4a, 4.2.6), while the absorption around 1630 cm"1 became more intense (Figures 4.2.1a to 4.2.4a, 4.2.6). During photo exposure the peak at 1510 cm"1 decreased less than in untreated wood (Figures 4.2.1a to 4.2.4a). This confirms a beneficial effect of copper on slowing lignin degradation. A peak around 1320 cm"1, due to the COO" symmetrical stretching vibration, formed during 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" 1, which is observed when conjugated alpha-carbonyl groups 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"1 could be due to hydrolysis of a carboxylate salt formed in the wood and which resulted in the increase o f the peak at 1600 cm" 1. Secondly, the peak at 1460 cm' 1 , arising from the C -N stretching vibration in the A A C , 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"1 almost disappeared (Figure, 52 4.2.1a, 4.2.2a, and 4.2.5a) suggesting that the action of washing leached out water soluble carboxylate salt formed during the treatment. 53 54 — 90UBHJUJSUBJJ. % cn <U o cn *~ C >-< O « t> cd 8-2 d •9 S.2 * -2 c .2 o "S O cS u s; 9 a. i cn i H 03 CM CM ^ ' s 3 .1 .1 c3 cn OJ CCS CM 3 00 N O 1 = o 00 CM   eoueniujsueji f £ * a T> .2 fi -s ^ CO Ca ' — at ~ t -o co g ~ - -5 O <U 2 O (!) r O „ co 0 d • - *° 1 i » 00 . . - ° <N £ ^1? <N rn of * t i M D 90UBUIOISUBJ1 -o td 1 CO C O tS to -o O o O a S3 O ' I TJ o o 8-! i g <0 m ed -o e Cd _r <*> C >> O ed I *° ed v£) ed T3 fc T3 H t i - ed 'ed 3 O J3 00 5 ? CO u. 3 O JS 58 Figure 4.2.6: FTIR spectra o f wood sections treated with different concentrations o f wp- 42 after 6 days of 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 of the lignin peak area at 1510 cm"1 in chemically treated wood, and untreated wood, during photo-exposure. Based on the relative peak area changes in the spectra of 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. Wood 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 of lignin. Figures 4.3.4 to 4.3.6 allow the formation of 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 of carbonyl groups comparing with the untreated controls (Figures, 4.3.5 and 4.3.6). 60 0.5 0.4 0 -•— untreated wp-40, 2% 50 100 U V irradiation, hours -m-B,2% - * - w p - 4 1 , 2 % 150 DDAC , 2% •wp-46, 2% Figure 4.3.1: The relative ratios of delignification of different chemical treated wood. Figure 4.3.2: The relative ratios of delignification of different chemical treated wood. 0.6 0 50 100 150 U V irradiation, hours | -•—untreated - " - w p - 4 2 , 2 % wp-43,2% | wp-42, 1% - * - wp-42, 0.5% wp-42, 0.25% I Figure 4.3.3: The relative ratios of delignification of different chemical treated wood. 3.5 2 I I 1 : .—J 0 50 100 150 U V irradiation, hours -•-untreated - " - B , 2% DDAC , 2% - * - wp-40, 2% - * - wp-41, 2% - • - wp-46, 2% Figure 4.3.4: The relative ratio of the formation of carbonyl groups of U V irradiated wood: the effect o f various treatments. 62 Figure 4.3.5: The relative ratio of the formation of carbonyl groups of U V irradiated wood: the effect o f various treatments. 0.5 1 3 1 1 1 0 50 100 150 U V irradiation, hours untreated -m- wp-42, 2% wp-43,2% - x - w p - 4 2 , 1% - * - wp-42, 0.5% wp-42, 0.25% Figure 4.3.6: The relative ratio of the formation of carbonyl groups of U V irradiated wood: the effect o f solution concentrations. 63 4.4. Conclusions From the quantitative analysis o f the FTIR spectra (Figures 4.3.1 to 4.3.6), the degree of degradation of l ignin in the treated and untreated sections increased after 6 days o f U V 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 of 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 of the provided formulations showed significant resistance to photodegradation. As observed by previous researchers the inclusion of 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 of 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 of 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'1 that can be 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: FTIR of untreated and chemically treated wood sections before and after 6 days of 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: FTIR of untreated and chemically treated wood sections before and after 6 days of 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 FTIR 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 FTIR peaks at 1510 and 1730 cm" 1. The effectiveness of 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 of Douglas-fir extractives, comprising up to 12% in Douglas-fir bark (Rydholm, 1965). OH O Figure 5.1.3: Structure of taxifolin. Western red cedar extractives FT IR spectra of 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 of carbonyl groups in wood sections treated with cedar extractives alone and in combination with 2% or 5% D D A C . The effectiveness of western red cedar extractives in reducing the delignification process may be due to the high concentration of 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). Wood sections treated with 2% tannic acid showed less lignin degradation than untreated controls and prevented the formation of 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 FTIR peak at 1510 cm*1 (Figures 5.1.10 and 5.1.11). This may be due to 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: 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% D D A C treated, UV irradiated; and e) 2% D D A C treated, irradiated. 72 1800 1600 1400 1200 1000 800 Wavenumbers, cm-1 Figure 5.1.5: FT IR of untreated and chemically treated wood sections before and after 6 days of 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 800 Wavenumbers, crrr1 Figure 5.1.6: FTIR of untreated and chemically treated wood sections before and after 6 days of 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 1000 800 Wavenumbers, crrr1 Figure 5.1.7: FTIR of untreated and chemically treated wood sections before and after 6 days of 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: FTIR of untreated and chemically treated wood sections before and after 6 days of 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: FTIR of untreated and chemically treated wood sections before and after 6 days of 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 800 Wavenumbers, cm 1 Figure 5.1.10: FTIR of untreated and chemically treated wood sections before U V irradiation and after 6 days of 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 800 Wavenumbers, crrr1 Figure 5.1.11: FTIR of untreated and chemically treated wood sections before U V irradiation and after 6 days of 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 FTIR peaks at 1510, 1267 and 1600 cm" 1. When wood sections were treated with 2% lignosulfonic acid 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: FTIR of untreated and chemically treated wood sections before and after 6 days of 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 1000 800 Wavenumbers, crrr1 Figure 5.1.13: FTIR of untreated and chemically treated wood sections before and after 6 days of 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 of the removal o f the soluble by-products o f photodegradation by washing, is shown in 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 FT IR 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"1 (which are related lignin peak concentrations), and also at 1730 cm"1 (which reflects the carbonyl groups), after 6 days of U V irradiation. The results confirmed the known solubility o f the by-products of photodegradation. 83 \ 1162 I I i I i I i I i v I i i 1800 1600 1400 1200 1000 800 Wavenumbers, crrr1 Figure 5.2.1: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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 1000 800 Wavenumbers, cm-1 Figure 5.2.2: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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 1000 800 Wavenumbers, crrr1 Figure 5.2.6: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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 800 Wavenumbers, crrr1 Figure 5.2.7: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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 c CD -4—' 1800 1600 1400 1200 1000 800 Wavenumbers, crrr1 Figure 5.2.8: FTIR of untreated and chemically treated wood sections before U V irradiation and washed after 6 days of 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 FTIR spectra of untreated wood sections and wood sections treated with Douglas-fir, western red cedar and Scots pine extractives, before U V irradiation. Examination of 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 FTIR spectra of untreated wood sections, as wel l as sections treated with 5% lignosulfonic acid and 5% tannic acid. For 5% lignosulfonic acid treated wood there was no discernible difference in the FT IR spectra of the treated and untreated wood. In the spectrum of 5% tannic acid treated wood sections, peaks were observed due to the presence of the carboxylic functional groups at 1600 and 1320 cm"1 and the 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"1 absorption peak areas o f weathered (Af) and unweathered (A;) samples relative to the unweathered peak areas (A)- The delignification of 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 in Table 5.1. They show that the relative delignification as indicated by the reduction in the absorption at 1510 cm"1 increased rapidly during the first 7 hours of U V exposure, and then more slowly during the next 21 hours of 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 of D D A C treated wood. The relative delignification rates of 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 of untreated wood. The relative delignification rates of 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 of 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 of tannic acid treated wood was 31.8% after 6 days o f U V irradiation. For 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"1, % Samples Additives 2% additives 2% additives + 2% DDAC + 5% DDAC ( antral DFext', 2% 47 0 ^ *' i , DF'ext;2% + DDAC 2% 48 6 Douglas-fir 7 DFext, 2% +DDAC i 50 1 DDAC, 2% 71 3 v ^ , 4 ' r D D A C ; V/o 83 4 Control 60.8 Cedar ext., 2% 53.4 Cedar ext., 2% + DDAC, 2% 54.9 Cedar Cedar ext., 2% + DDAC, 5% 59.0 DDAC, 2% 70.2 DDAC, 5% 84.1 Control 56 9 5 ^.^Pinie!ext». 2% 53 4 Pine c\t »2°/o + DDAC 2% 55 0 Scots pine Pine c\t. 2% + DDAC S% SA 7 DDAC; 2% 08 o : DDAC? 5 % f V s r-" ' «W*79*2- ' Control 56.9 Tannic acid, 2% 31.8 Tannic acid, 2% + DDAC, 2% 45.3 Tannic acid Tannic acid, 2% + DDAC, 5% 47.4 DDAC, 2% 68.6 DDAC, 5% 79.2 Control 59 7 LSA, 2% 55 8 LSA, 2% +DDAC, 2% 52 1 LSA LSA*2% + DDAC,5% 55 1 DPAC 2% 71 3 DDAC, 5% / >'\ 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 of (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 DF ext., 2% - ^ D F ext., 2% +DDAC, 5% - * - 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 Control Cedar ext., 2% + DDAC, 2% Cedar ext., 2% DDAC, 2% 20 40 60 80 100 120 140 UV irradiation, hours Figure 5.4.3: The relative ratios o f delignification of (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 of (a) untreated; (b) Cedar extractives treated; (c) Cedar extractives + D D A C treated; and (d) D D A C treated wood. 99 0 0 20 40 60 80 100 UV irradiation, hours — i — • 1— 120 140 - • - 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 -i 1 1 1 1 1 1 — 0 20 40 60 80 100 120 140 UV irradiation, hours ; -•— Control -*— Tannic acid, 2% ! Tan. acid, 2% + DDAC, 2% - * - DDAC, 2% Figure 5.4.7: The relative ratios o f delignification of (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 of (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 of delignification of (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 of 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 of phenoxy free radicals (Feist and Hon, 1984; Gierer and L in , 1972; Hon, 1975a, b, and c; Hon and Feist, 1981.). These free radicals may then cause further degradation of 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 in the performance could also due to the polyphenolic structure of tannic acid or polyphenols present in Douglas-fir extractives, e.g. taxifolin. In addition to acting as sacrificial molecules in place of 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» RO« + 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 of the propagation route by reacting with other free radicals (Shahidi, 1992): ROO» + PP« -> ROOPP 103 R O + PP« -> ROPP 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, 3- diphenols have antioxidant characteristics, which increase with the substitution o f hydrogen atoms by ethyl or n-butyl groups (Shahidi, 1992). This may explain why Douglas-fir and cedar extractives retard more lignin degradation than pine extractives. Tannic acid which is a gallotannin consisting of 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 of the FTIR carbonyl absorption at 1730 cm"1 with that o f the relatively stable cellulose absorption peak at 1162 cm"1 after various periods of U V irradiation. Based on a quantitative analysis after 6 days o f U V irradiation, more carbonyl containing chemicals were formed in wood impregnated with D D A C than in either untreated wood, or wood treated with any of 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 of 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 l ikely that the antioxidants in 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 in 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 of 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. As expected, tannic acid reduced lignin degradation but not the formation of 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 wi l l increase the FTIR peak at 1730 cm" 1. It should be noted that more carbonyl groups were formed in 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 (BHT), 1,4-diazabicyclo (2,2,2) octane were found not to reduce delignification in D D A C treated wood, during photo-exposure. They also had no impair on delignification of wood when used alone. Wood treated with Douglas-fir extractives and exposed to a U V source, showed reduced delignification and also there was less change in the formation of 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 in the additive treated wood and also when combined with D D A C during wood treatment. 105 The addition of pine extractives to the treating solution appeared to reduce the delignification of 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 U V irradiation, hours 150 Control DF ext., 2% + DDAC , 2% -*— DF extractives, 2% -* - DDAC , 2% 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% D D A C ; (c) 2% D D A C . 0.2 4 1 1 1 0 50 100 150 U V irradiation, hours —•— Control —•— DF extractives, 2% DF ext., 2% + DDAC , 5% - * - DDAC , 5% 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% D D A C ; (c) 5% D D A C . 107 0.2 4 1 1 1 0 50 100 150 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% - * - DDAC , 2% 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% D D A C ; (c) 2% D D A C . <N o en 1.8 1. 1. 1. 6 4 2 1 0.8 0.6 0.4 0. 2 1 0 50 100 U V irradiation, hours Control — C e d a r extractives, 2% Cedar ext., 2% + D D A C , 5% - * - DDAC , 5% 150 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% 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% i Pine ext., 2% + D D A C , 2% DDAC , 2% 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% D D A C ; (c) 2% D D A C . 1.4 0 50 100 150 U V irradiation, hours i —•— Control -*— Pine extractives, 2% Pine ext., 2% + D D A C , 5% D D A C , 5% Figure 5.4.16: The relative formation of 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% - * - DDAC , 2% 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% D D A C ; (c) 2% D D A C . 0 50 100 150 U V irradiation, hours —•— Control —•— Tannic acid, 2% Tannic acid, 2% + DDAC , 5% - * - DDAC , 5% 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% D D A C ; (c) 5% D D A C . 110 0.2 J 1 1 1 0 50 100 150 U V irradiation, hours - • - C o n t r o l - » - L S A , 2 % LSA, 2% + DDAC , 2% - * - DDAC , 2% 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% D D A C ; (c) 2% D D A C . UV i r r a d i a t i o n , hours Control - * - L S A , 2 % LSA, 2% + DDAC , 5% - * - DDAC , 5% 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% D D A C ; (c) 5% D D A C . I l l 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 of carbonyl groups of D D A C treated wood. Photodegradation is essentially a surface phenomenon, which results in the discoloration of the wood as well as the degradation of 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 IE L*, a*, b* color coordinate system. Zhang and Kamdem (2000) studied the weathering of copper-famine treated wood using a Q U V Weathering Tester. Southern pine treated with copper ethanolamine (Cu- E A ) was exposed to 2 hours U V irradiation followed by 18 minutes o f water spray for a total time of 1200 hours. FTIR studies showed that Cu -EA treated wood retarded lignin degradation and formation of carbonyl groups based on the peaks at 1510 and 1730 cm' 1 . The color changes (AE*) of untreated and treated wood showed that 1.5% Cu-EA treatment of wood effectively reduced the color change compared with untreated controls, which was about 5 for Cu -EA treated wood and 18.6 for the controls after 1200 112 hours of 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 in A C Q treated wood because the later is colored. In this Chapter the color changes of 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 of 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 in Chapter 5) and color changes. 6.1. Results and Disscusion The color changes (AE*) of untreated and treated samples versus the irradiation time are shown in 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 FTIR results in Chapter 5, which showed that a high proportion o f lignin was degraded resulting in the formation o f carbonyl groups. The AE* for the untreated exposed controls was about 14 after 6 days o f U V exposure, which is a clear indication of 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 in Chapter 5 that lignin degradation and formation of carbonyl groups were greater in D D A C treated wood sections during irradiation than in untreated wood sections. The differences, however, are not large, and clearly color was affected by the dramatic loss o f lignin in 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 of additives on the brightness of 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 of the effects o f additives on their ability to retard color changes and brightness of 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 of 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 of 2% Douglas-fir treated and 2% D D A C plus 2% Douglas-fir extractives treated wood sections were much lower than those of the D D A C and untreated sections clearly suggesting that Douglas-fir extractives are able to improve the color stability of wood in the presence of 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 in 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 of 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 of 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 of 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. Wood 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 of 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 of 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 of wood treated with 2% cedar extractives +5% D D A C (Figures 6.1.1.2a and 6.1.1.2b). The color change of 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 of 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 of 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 in reducing loss of color (Figure 6.1.1.3a) suggesting that Scots pine extractives are not effective additives for protecting the discoloration of 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 of the treatment of 2% pine extractives + 2% D D A C (Figure 6.1.1.3b) The difference in color o f wood treated with D D A C and 2% 116 pine extractives and that of the untreated control was 3 units, which is considered unacceptable for industrial applications (Hon and Feist, 1986). This is in accord with FTIR results, which showed pine extractives not preventing lignin degradation and the formation of 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 of wood treated 2% D D A C . The difference of 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 of wood treated with 2% L S A + 2% D D A C (Figures 6.1.1 4a and 6.1.1 4b). The value of AE* 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 -*— DF extractives, 2% DDAC , 2% + DF ext., 2% - * - DDAC , 2% Figure 6.1.1.1a: Changes in color of treated and untreated wood sections before and after U V irradiation. 0 50 100 150 U V irradiation, hours | —•— Control —•— DF extractives, 2% - ± - DDAC , 5% + DF ext., 2% - * - DDAC , 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% DDAC , 2% + cedar ext., 2% - * - DDAC , 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 Cedar ext, 2% DDAC , 5% + cedar ext., 2% - * - DDAC , 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 -•— Pine extractives, 2% D D A C , 5% + pine ext., 2% - * - DDAC , 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 ignosu l fon ic acki,2% DDAC , 2% + LSA, 2% DDAC , 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 - « — Lignosulfonic acid,2% DDAC , 5% + LSA, 2% - * - DDAC , 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 in brightness of 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 of untreated and wood sections treated with 2% DF extractives, 2% DF extractives + 2% D D A C , and 2% D D A C versus U V irradiation time are shown in Figure 6.1.2.1a. The brightness o f the wood is clearly reduced as a result of exposure to U V light, possibly because of the accumulation of unsaturated lignin photodegradation products on the surface o f the wood (Hon, 1981). The brightness of 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 in brightness (AL*) for wood sections treated with 2% Douglas-fir extractives + 2% D D A C after 6 days of 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 AL* 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*) of 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 of D D A C treated wood. 2% cedar extractives + 5% DDAC The AL* for 2% cedar extractives + 5% D D A C treated wood was also less than 1 unit after 6 days of 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 of wood. 6.1.2.3. Scots pine extractives + DDAC The brightness changes of 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 FTIR studies, which showed that Scots pine extractives did not prevent the formation of carbonyl groups. 123 6.1.2.4. Lignosulfonic + DDAC The AL* 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 of D D A C treated wood. 6.1.2.5. General observation From the data plotted in 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 of the wood surfaces even though lignin degradation and the formation o f carbonyl groups was higher in 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 of brightness. 124 0 50 100 150 U V irradiation, hours Control — D F extractives, 2% DDAC , 2% + D F ext., 2% - * - D D A C , 2% Figure 6.1.2.1a: Changes in brightness of treated and untreated wood sections before and after U V irradiation. Js 72 00 £ 70 CO 68 66 64 0 50 100 U V irradiation, hours 150 -•-Contro l DDAC , 5% + DF 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 - Cedar ext., 2% D D A C , 2% + cedar ext., 2% - * - D D A C , 2% Figure 6.1.2.2a: Changes in brightness of treated and untreated wood sections before and after U V irradiation. 0 50 100 150 U V irradiation, hours 4— Control Cedar ext, 2% DDAC , 5% + cedar ext., 2% - * - DDAC , 5% Figure 6.1.2.2b: Changes in brightness of treated and untreated wood sections before and after U V irradiation. 126 70 1 1 1 1 0 50 100 150 UV irradiation, hours —•— Control - * - Pine extractives, 2% DDAC, 2% + pine ext., 2% - x - DDAC, 2% Figure 6.1.2.3a: Changes in brightness of treated and untreated wood sections before and after U V irradiation. 80 i 78 1 I 76 ? 74 m 72 70 . i i ( ) 50 100 150 U V irradiation, hours —•—Control - "—Pine extractives, 2% - A - DDAC, 5% + pine ext., 2% - * - DDAC, 5% Figure 6.1.2.3b: Changes in brightness of treated and untreated wood sections before and after U V irradiation. 127 0 50 100 150 UV irradiation, hours Control DDAC, 2%+LSA, 2% -m— Lignosulfonic acid, 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 DDAC, 5% +LSA, 2% LigiosvJfonic acid, 2% DDAC, 5% Figure 6.1.2.4b: Changes in brightness of treated and untreated wood sections before and after UV 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 of 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 in color with increasing exposure to U V irradiation, and at the end of 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 of AE* 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 of 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 of wood treated with D D A C solutions containing western red cedar extractives, the color change after 6 days of U V irradiation increased in 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). FTIR 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 of 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 of 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 (LSA) + 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 of 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 of D D A C plus L S A treated sections (Figure 6.1.3.1.4a). The difference in color changes of 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 AE* 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. As suggested earlier this might be due to the reaction of 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 —•— Control DF extractives, 2% —*— DDAC , 2% + DF ext, 2% - ^ D D A C , 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 - •— DF extractives, 2% DDAC , 5% + DF ext, 2% DDAC , 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 U V irradiation, hours 150 Control DDAC,2% + cedar ext.,2% Cedar ext., 2% DDAC , 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% | DDAC ,5% + cedar ext,2% - * - DDAC , 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 Control DDAC , 2% + pine ext., 2% Pine extractives, 2% -* - DDAC , 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% - * - DDAC , 5% Figure 6.1.3.1.3b: Changes in color of treated and untreated wood sections before U V irradiation and with washing after treatment and U V irradiation. 133 DDAC , 2% + LSA , 2% - * - DDAC , 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 ignosu l fon ic acid, 2% —A— DDAC , 5% + LSA , 2% - K - DDAC , 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 of 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 of 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 of exposure period their brightness approached that of 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 of 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 of the untreated and D D A C treated sections decreased as a result of 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 of the cedar extractives. After leaching some of the cedar extractives washed 135 out, so increases in brightness were observed, particular during the early stages of the exposure trial. 6.1.3.2.3. Scots pine extractives + D D A C The brightness changes of 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 of leaching. 6.1.3.2.4. Lignosulfonic acid + D D A C The brightness changes of treated and untreated sections during U V irradiation were quite similar. The wood sections treated with 2% LSA , 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—; , , = l h 0 50 100 150 U V irradiation, hours »— Control - » DF extractives, 2% DDAC , 2% + DF ext, 2% - * - DDAC , 2% Figure 6.1.3.2.1a: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after U V irradiation. 0 50 100 150 U V irradiation, hours — C o n t r o l » - DF extractives, 2% -nkr- DDAC , 5% + DF ext., 2% - * - D D A C , 5% Figure 6.1.3.2.1b: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after U V irradiation. 137 80 , 78 ' at | 76 •g> 74 1 03 72 f - » - »— 70 _i i ' 0 50 100 150 UV irradiation, hours — C o n t r o l Cedar ext., 2% DDAC, 2% + cedar ext., 2% - * - DDAC , 2% Figure 6.1.3.2.2a: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation. 0 50 100 150 UV irradiation, hours | - • -Con t r o l - » - Cedar ext., 2% DDAC , 5% + cedar ext., 2% - * - DDAC , 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 UV irradiation, hours —•— Control —•— Pine extractives, 2% DDAC, 2% + pine ext., 2% - x - DDAC, 2% Figure 6.1.3.2.3a: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation. UV irradiation, hours —•— Control — P i n e extractives, 2% DDAC, 5% + pine ext., 2% - x - DDAC, 5% Figure 6.1.3.2.3b: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after treatment and U V irradiation. 139 50 100 150 U V irradiation, hours Control D D A C , 2% +LSA , 2% Lignosulfonic acid, 2% DDAC , 2% Figure 6.1.3.2.4a: Changes in brightness of treated and untreated wood sections before U V irradiation and washed after U V irradiation. 0 50 100 U V irradiation, hours Control D D A C , 5%+LSA , 2% -»— Lignosulfonic acid, 2% •*- D D A C , 5% Figure 6.1.3.2.4b: Changes in Brightness of 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, in 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 of cedar extractives and D D A C were the most effective at restricting color changes; 4) the combination of pine extractives and D D A C did not restrict color changes of the wood. 16 Figure 6.1.4.1.1: The effect of combinations of additives and D D A C on the color change of treated and untreated wood after 6 days of U V irradiation. 141 Figure 6.1.4.1.2 shows the color change o f treated and untreated wood after 6 days of 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 of 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 of additives and D D A C on the color change of treated and untreated wood after 6 days of 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 of brightness of 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 on the loss o f brightness of treated and untreated wood after 6 days of U V irradiation. 143 The loss of brightness of untreated and treated wood sections after 6 days of U V irradiation and leaching is shown in Figure 6.1.4.2.2. As was the case for sections subjected to U V irradiation in the absence of leaching, sections treated with cedar and Douglas-fir extractives retained their brightness. The loss of brightness of 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 of 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 of treated and untreated wood after 6 days of 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 in restricting loss of brightness of wood sections subjected to U V irradiation. However, the initial brightness o f the wood was lower because the Douglas- fir and cedar extractives colored the treated wood 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 LSA , leaching may have washed off most of the chemicals. Discoloration o f pine extractive and L S A treated wood was the same as that observed in untreated and D D A C treated wood. 145 CHAPTER 7 Summary and Recommendations 7.1. Summary Based on the observations in this study, the following can be summarized: 1. The new alternative formulations, which are based on alkylammonium compounds (AACs) together with organic cobiocides do not slow down photodegradation of the treated wood based on the FTIR spectra of the peak at 1510 cm"1 compared with the untreated control. 2. Wood treated with alkylammonium compounds (AACs) together with copper as cobiocide effectively resists lignin degradation and also the formation of carbonyl groups based on the FTIR observation bands at 1510 and 1730 cm" 1. This is due to copper reacting with phenolic hydroxy group, which is a main photoreaction site, in 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 of D D A C accelerates the wood photodegradation process. This process could be slowed down by using additives, which are antioxidants. Douglas- fir 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 of Douglas-fir extractives or western red cedar extractives together with D D A C greatly retarded the color change of wood during U V irradiation. The treatment also improves the brightness stability o f wood. 146 6. Wood treated with Douglas-fir extractives plus D D A C or western red cedar extractives plus D D A C after 6 days of U V irradiation and subsequent washing showed excellent brightness stability. 7.2. Recommendations 1. Selection of wood samples: the wood sample thickness should be measured and samples with the same thickness should be selected. 2. Long 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 of treated and untreated wood can be determined by exposing vertical panels in outdoor field trials. This wi l l confirm the effectiveness of the selected chemicals against weathering. The change of 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 of D D A C treated wood. It is necessary to clarify the roles of polyphenols in reducing lignin degradation when they are used alone or together with D D A C . 5. Since it has been suggested that taxifolin possesses high antioxidant property, Douglas-fir extractives that contain high concentration of taxifolin have also shown their effectiveness in reducing lignin degradation during U V irradiation. This may be confirmed using pure taxifolin or chemicals with a similar structure. 6. Since a two-step treatment is not commercially acceptable, a one-step treatment for use of L S A or tannic acid with D D A C wil l be studied. 147 References Ahmed, A., A. Adnot and S. Kaliaguine. 1987. 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