Tropical forests play a major role in global carbon (C) dynamics and maintain some of the highest biological complexity on Earth; however, little is known about how variation in wood chemical traits contributes to tropical forest structure and function. This research examines inter- and intraspecific patterns in wood chemical traits in order to understand 1) the role wood chemical traits play in tropical forest C dynamics, and 2) the adaptive significance of wood chemical traits in tropical trees. I found wood C concentration varies widely among co-occurring tropical tree species, with average C concentration (47.4 ± 0.33% w/w (S.E.)) being significantly lower than values assumed in prominent forest C accounting protocols. Failing to account for this variation leads to overestimates of ~3.3 – 5.3% in tropical forest C accounting, an error that compounds significantly at larger spatial scales. I also show that oven drying samples prior to elemental analysis underestimates wood C concentration by 2.5 ± 0.17%, due to the loss of the “volatile C fraction”. Counter to expectations, I found wood C concentration is not ii phylogenetically conserved nor correlated to species demography or life history traits. Wood chemical traits showed consistent size-dependent patterns: wood C (in 16 of 24 species) and lignin (in 15 of 16 species) was higher in saplings vs. conspecific canopy trees. These patterns, complimented by phylogenetic analyses, suggest saplings require wood chemical traits that confer greater pathogen defense. When analyzed across a continuous size spectrum, I found wood C concentration (and leaf structural traits) increases linearly, while wood starch concentration (and leaf traits associated with C gain) shows “hump-shaped” patterns with peak values closely preceding reproductive onset; the latter result suggests C may limit growth in larger trees. Overall, my dissertation provides one of the first comprehensive examinations of wood chemical trait variation in tropical trees. In doing so it provides novel, timely, and critical insights into how wood chemical traits contribute to tropical forest structure and function.

The environmental factors affecting wood property formation of Eucalyptus spp. trees in two distinct geographic areas within South Africa were studied. Wood prop~rty data for trees from 43 sites (26 in Zululand and 17 in Mpumalanga) were collected from work conducted at the Forest and Forest Products Research Centre (FFPRC) at the CSIR (Council for Scientific and Industrial Research) in Durban. The wood properties considered included screened pulp yield, fibre length, wood density and active alkali chemical consumption during pulping. The effect of environmental factors on growth rate (expressed as Site Index at a base age of 5 years) was also measured. A detailed site description for each forest compartment was carried out. Detailed annual and monthly rainfall and minimum and maximum temperature estimates were calculated for each site by interpolating long term means of these variables by splining using the software package Anusplin. These estimates of climatic factors were validated by comparison to the data published in the South African Atlas of Agrohydrology and -Climatology. The outputs of the Anusplin model were used to derive surrogate bioclimatic parameters for each site using the computer program Bioclim. These parameters are considered as better descriptors of the energy-water balance experienced by the plant than normal measures of climate such as mean monthly or annual precipitation. Soil characteristics were measured on samples taken from the individual sites. The effects of these environmental and bioclimatic variables on wood properties were analysed using appropriate statistical techniques. Multiple regression models were used to predict wood properties and it is suggested that this approach could form part of a fibre management system. Wood property prediction models incorporating climate (and bioclimate) alone were preferred to those including soil data as no further site data are required. The effect of edaphic factors was considered to describe any further variation not accounted for by bioclimate alone. Particle size distribution of the soil, as an indication of the water holding capacity of that soil, was not found to effect wood properties or growth significantly. A weak influence of organic matter content in the topsoil on wood density was noted in Mpumalanga. In Zululand, a multiple linear regression using both rainfall of the wettest quarter and mean diurnal temperature range as inputs yielded the best predictive model for growth rate. In this region a combination of precipitation seasonality and mean diurnal temperature range gave the best linear regressi'o,n model describing variation in screened pUlp' yield and fibre length. In Mpumalanga effective rooting depth was found to have a pervasive effect on plant development. Solar radiation (as a measure of energy supply), calculated from a function of latitude, aspect, slope and time of year, was also found to significantly affect the growth rate and SPY of plant material in Mpumalanga. Measures of temperature in both geographic regions were found to significantly affect wood density. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Made available in DSpace on 2014-06-11T19:35:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-12-17Bitstream added on 2014-06-13T20:25:43Z : No. of bitstreams: 1 souza_se_dr_botfca.pdf: 819772 bytes, checksum: f7cd95ae9d4f5c4dc21861b150059d3e (MD5) / Em três povoamentos de Eucalyptus grandis na região norte do Estado de São Paulo, foi realizado um estudo com objetivo de conhecer a dinâmica espaço-temporal do cancro basal, quantificar os danos no volume e efeito na qualidade da madeira. Foram instaladas nove parcelas de 7500 m², com 1000 árvores de E. grandis, procedência Santa Rita do P. Quatro-SP, origem Coffs Harbour, dos plantios seminais em solos de areia franca AQ1, AQ3 (10 a 15% de argila) e textura franco-argila-arenosa LEm2 (26 a 35% de argila). As avaliações foram realizadas em nove mil árvores com idade de dois anos. A incidência foi monitorada individualmente de acordo com a presença ou ausência da doença e a severidade, mediante o uso de uma escala diagramática de notas. Foram feitas avaliações nos anos 2000, 2001 e 2002, o que gerou 26 mapas de evolução da doença. Os resultados permitiram concluir que: (1) A incidência média do cancro basal foi influenciado pelo tipo de solo AQ3 (0,25%), AQ1 (0,21%) e LEm2 (0,09%); (2) Os valores do índice de dispersão (ID) foram > 1, para os tamanhos de quadrat 2x4, 5x2, 5x4 e 5x10; os valores de log (A) = log (Vobs) e log de (b) = log (Vbin) foram maiores que 1 e diferentes de zero, sugerindo uma tendência à agregação independente do tipo de solo; (3) 54,6% dos focos foram unitários, indicando que o cancro basal inicia-se com focos de apenas uma árvore; 80,8% dos focos apresentam maior comprimento na direção entre as linhas de plantio do que na direção da linha; focos maiores ocorreram no solo AQ3, que apresentaram-se menos compactos; a disseminação do cancro nesses povoamentos parece ter sido via sementes através das mudas; 89,1% dos mapas apresentaram focos com tamanho médio inferior a 10 árvores, no solo AQ3 em 10,9% dos focos o tamanho variou entre 11 a 30 árvores e nenhum foco foi formado acima de 30 árvores;... / A study was carried out in three Eucalyptus grandis stands in the northern region of the State of São Paulo, in order to provide information on the spatio-temporal dynamics of eucalyptus canker, evaluate volume losses, and determine the effect of the disease on wood quality. Nine 7500 m² plots (10×100) containing 1000 E. grandis trees from Santa Rita do P. Quatro-SP (origin: Coffs Harbour), in seed plantations on soils classified as loamy sands, AQ1 and AQ3 (10 to 15% clay), and on a silty-clay-loam-textured soil, LEm2 (26 – 35% clay). Evaluations were made in nine thousand two-year-old trees. Incidence was monitored individually according to the presence or absence of the disease. Severity was evaluated through the use of a diagrammatic rating scale. Evaluations were made in 2000, 2001, and 2002, and 26 disease progress maps were generated. The results allowed us to conclude that: (1) The mean incidence of eucalyptus canker followed a trend that matched the soil types:AQ3 (0.25%), AQ1(0.21.%), and LEm2 (0.09%); (2) The ID values were > 1 for quadrat sizes equal to 2×4, 5×2, 5×4, and 5×10; The log (A) = log (Vobs) and log (b) = log (Vbin) values were higher than 1 and different from zero, suggesting a tendency for aggregation, regardless of soil type; (3) 54.6% of the foci were single-unit, indicating that eucalyptus canker starts with single-tree foci; 80.8% of the foci had greater lengths between planting rows than along the rows; larger foci occurred in the AQ3 soil, which were less compact; canker dissemination in those stands seemed to have occurred via seeds through the seedlings; 89.1% of the maps had foci with mean sizes smaller than 10 trees in the AQ3 soil; in 10.9% of the foci the size ranged between 11 and 30 trees, and no focus formed at sizes above 30 trees; the ICF and ICFNU values were not close nor very far from ...(Complete abstract click electronic access below)

Esta pesquisa tem por objetivo analisar os procedimentos e os resultados de métodos de ensaios propostos para a identificação da resistência ao cisalhamento de madeiras no sentido paralelo as fibras. Almeja-se observar as imperfeições dos métodos existentes, com intuito de propor um novo método de ensaio em que algum dos problemas apresentados possam ser minimizados ou reduzidos. O método proposto pela norma NBR 7190/97 utiliza um corpo de prova prismático retangular com um dente para impedir sua rotação, causada pela assimetria na aplicação da força que promove o cisalhamento. O método proposto por SANTOS NETO (1999) utiliza também um corpo de provas prismático longelíneo com interrupções parciais alternadas nas seções transversais, as quais promovem solicitações de cisalhamento em regiões pré-escolhidas. Como alternativa, o presente estudo apresenta dois métodos: o primeiro método de ensaio sugerido é análogo ao ensaio da norma, porém aplicando a carga simetricamente a duas seções cisalhantes, de modo a evitar a rotação do corpo. Esse método evidenciou problemas ocorridos em razão das proporções entre as tensões de cisalhamento e tensões de esmagamento por compressão na superfície de aplicação das cargas e da antecipação da ruptura de cisalhamento por ruptura de tração na face inferior do corpo de provas. Um segundo procedimento é proposto, induzindo o esforço de cisalhamento através de puncionamento de um corpo de prova prismático simples e sem recortes, com distribuição da seção cisalhantes simetricamente em relação a um ponto. Para tanto, desenvolve-se uma ferramenta de macho e fêmea adaptado a uma prensa universal de ensaios para aplicação dos esforços. Verificada a validade do método, realiza-se um conjunto de ensaios com três espécies de madeiras, diferenciadas entre si pelas suas resistências mecânicas e, valendo-se dos métodos propostos pela norma NBR 7190/97, por SANTOS NETO (1999) e o cisalhamento por puncionamento, analisa-se e discute-se o desempenho dos três processos. / This research aims to examine the procedures and results of test methods proposed for the identification of the shear strength of wood fibers in parallel direction. Aims to observe the imperfections of existing methods, aiming to propose a new test method in which some of the problems shown can be minimized or reduced. The method proposed by NBR 7190/97 uses a rectangular prismatic body of evidence with a tooth to prevent its rotation caused by asymmetry in the application of force that causes the shear. The method proposed by SANTOS NETO (1999) also uses a prismatic body of evidence with alternating partial interruptions in cross sections, which provide requests shear at pre-selected regions. Alternatively, the paper presents two methods: the first test method suggested is analogous to the standard test, but applying the load symmetrically to shear two sections so as to prevent rotation of the body. This method revealed problems that occurred because of the proportions between the shear stresses and strains of crushing by compression on the surface of application of loads and the anticipation of breaking the shear rupture of traction on the underside of the body of evidence. A second procedure is proposed, leading to shear stress by punching a simple prismatic body of evidence and without cutouts, with the distribution of shearing section symmetrical about a point. To this end, it develops a tool of male and female adapted to press a universal test for application of effort. Verified the validity of the method, takes place a series of tests on three wood species, differentiated from each other by their mechanical stregth, and, drawing on the methods proposed by NBR 7190/97, and by SANTOS NETO (1999) and by punching shear, analyzes and discusses the performance of the three cases.

Esta pesquisa tem por objetivo analisar os procedimentos e os resultados de métodos de ensaios propostos para a identificação da resistência ao cisalhamento de madeiras no sentido paralelo as fibras. Almeja-se observar as imperfeições dos métodos existentes, com intuito de propor um novo método de ensaio em que algum dos problemas apresentados possam ser minimizados ou reduzidos. O método proposto pela norma NBR 7190/97 utiliza um corpo de prova prismático retangular com um dente para impedir sua rotação, causada pela assimetria na aplicação da força que promove o cisalhamento. O método proposto por SANTOS NETO (1999) utiliza também um corpo de provas prismático longelíneo com interrupções parciais alternadas nas seções transversais, as quais promovem solicitações de cisalhamento em regiões pré-escolhidas. Como alternativa, o presente estudo apresenta dois métodos: o primeiro método de ensaio sugerido é análogo ao ensaio da norma, porém aplicando a carga simetricamente a duas seções cisalhantes, de modo a evitar a rotação do corpo. Esse método evidenciou problemas ocorridos em razão das proporções entre as tensões de cisalhamento e tensões de esmagamento por compressão na superfície de aplicação das cargas e da antecipação da ruptura de cisalhamento por ruptura de tração na face inferior do corpo de provas. Um segundo procedimento é proposto, induzindo o esforço de cisalhamento através de puncionamento de um corpo de prova prismático simples e sem recortes, com distribuição da seção cisalhantes simetricamente em relação a um ponto. Para tanto, desenvolve-se uma ferramenta de macho e fêmea adaptado a uma prensa universal de ensaios para aplicação dos esforços. Verificada a validade do método, realiza-se um conjunto de ensaios com três espécies de madeiras, diferenciadas entre si pelas suas resistências mecânicas e, valendo-se dos métodos propostos pela norma NBR 7190/97, por SANTOS NETO (1999) e o cisalhamento por puncionamento, analisa-se e discute-se o desempenho dos três processos. / This research aims to examine the procedures and results of test methods proposed for the identification of the shear strength of wood fibers in parallel direction. Aims to observe the imperfections of existing methods, aiming to propose a new test method in which some of the problems shown can be minimized or reduced. The method proposed by NBR 7190/97 uses a rectangular prismatic body of evidence with a tooth to prevent its rotation caused by asymmetry in the application of force that causes the shear. The method proposed by SANTOS NETO (1999) also uses a prismatic body of evidence with alternating partial interruptions in cross sections, which provide requests shear at pre-selected regions. Alternatively, the paper presents two methods: the first test method suggested is analogous to the standard test, but applying the load symmetrically to shear two sections so as to prevent rotation of the body. This method revealed problems that occurred because of the proportions between the shear stresses and strains of crushing by compression on the surface of application of loads and the anticipation of breaking the shear rupture of traction on the underside of the body of evidence. A second procedure is proposed, leading to shear stress by punching a simple prismatic body of evidence and without cutouts, with the distribution of shearing section symmetrical about a point. To this end, it develops a tool of male and female adapted to press a universal test for application of effort. Verified the validity of the method, takes place a series of tests on three wood species, differentiated from each other by their mechanical stregth, and, drawing on the methods proposed by NBR 7190/97, and by SANTOS NETO (1999) and by punching shear, analyzes and discusses the performance of the three cases.

Le bois est un tissu plurifonctionnel permettant la conduction de la sève brute, le stockage de l’eau et des sucres ainsi que le soutien mécanique de la plante. L’arbre au cours de son développement expérimente différentes contraintes liées à son environnement et à sa taille croissante. En réponse à ces contraintes, les performances fonctionnelles du bois sont ajustées par des variations de valeurs de propriétés, elles-mêmes dépendantes du produit de la xylogénèse. Cependant les extrais chimiques déposés lors du processus de duraminisation, entraine la modification des propriétés du bois. Les propriétés du duramen sont le fruit de la xylognénése et de la duraminisation ainsi que de leurs interactions. Ce travail de thèse a donné naissance au terme ‘profil ligneux’, désignant l’ensemble des variations des propriétés du bois à différentes échelles et dans une dimension ontogénique résultant des deux processus cités précédemment. La diversité de tempéraments vis-à-vis de la lumière (héliophilie à sciaphilie) des essences tropicales suggère une diversité d’expressions du profil ligneux. La description de ces différentes expressions serait gage d’une meilleure compréhension du tempérament. Comprendre et caractériser le profil ligneux et la variation de la quantité de bois de cœur dans l’arbre, représentent également un enjeu économique puisque l’industrie du bois Guyanaise a été identifiée comme une filière d’avenir. L’analyse de la diversité du profil ligneux—par une approche ascendante, de l’échelle individuelle à l’échelle interspécifique—a prouvé son efficacité dans la discrimination du degré d’affinité à la lumière. La variation de densité est particuliérment pertinente. Néanmoins, sa pertinence réside dans (1) la combinaison du gradient radial et vertical et (2) la prise en compte du duramen qui modifie parfois, l’amplitude et la direction du gradient ainsi que la forme du profil.L’effet de la duraminisation sur la variation de densité devient alors évocateur du tempérament de l’espèce au même titre que la qualité et/ou la quantité d’extraits chimique mis en jeu. La pertinence du profil ligneux dans la caractérisation du tempérament écologique est due à son aspect intégrateur de divers processus et propriétés. En regard du changement l’allocation de croissance (i.e. du tronc vers la couronne) observée chez Dicorynia guianensis et de travaux précédents sur la croissance des arbres, un lien potentiel entre la diversité du profil ligneux et la stratégie d’allocation de la croissance pourrait exister. / Wood is a multifunctional tissue involved in sap conduction, storage of water and reserves as well as mechanical support. Tree during its development experiments various constraints due to its environment and its growing size. In response to these constraints, wood functional performances are adjusted by variations of property values, which are dependent on the xylogenesis product. However, wood properties may be modified by the deposition of chemical extractives during heartwood formation. Thus heartwood properties are the result of xylogenesis, heartwood formation and their interactions. This work gave rise to the term 'wood profile', designating all variations of wood properties at different scales and in an ontogenetic dimension, resulting from both processes described above. The diversity of shade tolerance (heliophilic to sciaphilic) strategies species suggests a diversity of wood profile expressions. The description of these different expressions could be a way to better understand plant strategies. Understanding and characterizing wood profile and variations in heartwood quantity in tree, is an economical issue since the Guyanese timber industry has been identified as a promising sector. The analysis of the diversity of wood profile—using a bottom-up approach, from the individual level to the interspecific level—proves to discriminate shade tolerance strategies efficiently. Wood specific gravity variation is especially relevant. However, its relevance is based on (1) combinations of both radial and vertical variations and (2) integration of heartwood that may impact range and direction of the gradient and shape of the profile as well. Effect of heartwood formation on wood specific gravity variations is suggestive of shade tolerance strategy as well as quality and/or quantity of chemical extractives. Relevant characterization of shade tolerance strategies by wood profile is the result of the integration of diverse processes and properties. To the view of growth allocation shift (from trunk to crown) observed in Dicorynia guianensis and of previous studies on tree growth, a potential link between wood profile diversity and growth allocation strategies may exist.

Rapporten presenterar en studie där tre trätyper, balsa, ask och björk, fabriceras genom en förutbestämd metod till transparent trä. Detta material har många möjliga applikationer, inklusive energieffektiva byggnader, förpackningar, solceller och elektroniska apparater. Syftet med studien är att jämföra de erhållna proverna av transparent trä utifrån morfologi och optiska egenskaper samt koppla dessa resultat till mikrostruktur. Detta för att avgöra huruvida den specifika fabriceringsmetoden lämpar sig för trätyperna och vilken som är mest lämpad. Den valda fabriceringsmetoden består av tre steg, delignifiering, tvätt med lösningsmedel samt polymerinfiltration. Syftet med det första steget i processen, delignifieringen, är att ta bort lignin, beståndsdelen i trä som ger träet dess färg. Detta skedde genom kemikaliebehandling med acetatbuffer och natriumklorit i sur miljö under uppvärmning, varvid träproverna blev vita. Proverna placerades därefter i en vakuumdesickator där de tvättades med etanol och därefter aceton. Etanol hindrar fibrerna från att krympa och acetonet tar bort de sista kemikalieresterna i trästrukturen. Inför det sista steget, polymerinfiltrationen, polymeriserades monomerer av metylmetakrylat till oligomerer, varpå dessa pressades in i träproverna med vakuum där de polymeriserades till polymetylmetakrylat (PMMA). PMMA har ett liknande brytningsindex till trä, vilket minskar ljusspridningen och ökar transparensen i provet. Vidare placerades träproverna mellan två glasplattor och lindades in i aluminiumfolie. Proverna värmdes i ugn där polymeriseringen slutfördes och det transparenta träet erhölls. Träprovernas optiska egenskaper och morfologi karakteriserades. För att bestämma optiska egenskaper uppmättes transmittans och haze. Transmittansen anger hur mycket ljus som kan passera genom provet, medan haze anger hur mycket ljusspridning som sker i förhållande till transmittansen. Dessa parametrar uppmättes enligt ASTM D1003 “Standard Method for Haze and Luminous Transmittance of Transparent Plastics”. Provernas morfologi karakteriserades med ett svepelektronmikroskop (SEM) och resultaten presenterades med högupplösta bilder. Från dessaanalyserades mikrostrukturen i träproverna och graden av delignifiering och polymerinfiltration bedömdes. Resultaten från mätningarna av de optiska egenskaperna visade att balsa har den högsta transmittansen (81–87%), följt av björk (74–83%) och sedan ask (66–78% för sommarved och 74–83% för vårved). Vidare uppmättes haze till ca 65–70% för balsa, ca 70–75% för björk och 74-80% för ask. Genom analys av SEM-bilderna bedömdes graden av delignifiering som högst i balsaträet. För att avgöra detta studerades mellanrummet mellan fibrerna som i obehandlat trä är ligninfyllda. Det observerades då att dessa mellanrum var mest tomma i det delignifierade balsaträt, vilket antydde på att graden av delignifiering var högst för denna trätyp. Graden av polymerinfiltrering ansågs likvärdig för de tre träsorterna då det förekom luftfickor i samtliga träprov. Sammanlagt ledde detta till att balsa blev mest transparent av de tre träsorterna, och är den mest lämpade träsorten för denna fabriceringsmetod.

In 1997, a phytoremediation program began at a creosote-contaminated former railroad tie yard in Oneida, Tennessee with the planting of over 1000 hybrid poplar trees onsite. Creosote, a mixture of hazardous chemicals composed of 85% polycyclic aromatic hydrocarbons (PAH) had entered the site soil and ground water. After planting, a seasonal ground water testing program began that monitored the progress of remediation by measuring the concentration of the 10 predominant PAHs in the contaminant plume: naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, and benzo(b)fluoranthene. The concentrations of these compounds steadily decreased over time, but the role the trees played in the remediation was unclear. In order to gain a clearer understanding of the role the trees played in contaminant remediation, chemical analysis of tree tissue began. It was not known whether the trees were taking up PAH contaminants or their metabolites or if the rhizosphere zone created by the trees simply enhanced the ability of the site microflora to degrade the PAH. The objectives of this research were to (1) develop a suitable method for the chemical analysis of tree tissue collected from a field site, (2) determine if there were any chemicals not usually found in poplar trees that occurred in the trees growing over contamination, (3) determine if bud, bark, and twig tissue differed in their ability to predict ground water contamination, and (4) determine if a spatial correlation existed between the aromatic compounds in the tree tissue and the ground water total PAH plume. Two types of tree tissue/ground water comparisons were performed: spatial distribution of isoeugenol concentration in tree tissue with spatial distribution of total PAH in ground water over the area of interest; and the spatial distribution of the quantity of aromatic compounds in tree tissue with the spatial distribution of total PAH concentration in ground water. Due to unit discrepancies between the quantities of interest, all comparisons were made on a percentile basis. Initial tree sampling revealed that several compounds not usually present in poplar trees occurred only in those trees growing over contamination. In the first part of this study, the concentration of one of these chemicals, the substituted phenol isoeugenol, was compared with the concentration of total PAH in ground water from samples collected from February-March 2002. The bark tissue percentiles fell within 20 percentiles of ground water total PAH concentrations in 60% of the study area. The twig tissue showed slightly better agreement, with 67% of the study area differing from ground water by twenty percentiles or less. The second comparison took place over three sampling events: March 2001, July 2001, and February-March 2002. The number of unique aromatic compounds in bark, bud, and twig tissue was compared with the total PAH concentration in ground water. Twig tissue aromatic compound content was the most accurate predictor of ground water contamination among the tissue types. After excluding those chemicals likely to be interferences from consideration, twig tissue aromatic content agreed with ground water total PAH concentration to within 20 percentiles over 2/3 or more of the study area during each sampling event, suggesting the potential uptake of PAHs or their microbial metabolites as a mechanism of phytoremediation at the site. / Master of Science

Free radicals are produced in lignin during mechanical treatment and irradiation with light of various wavelengths. During mechanical treatment, the lignin macromolecule is degraded severely as revealed by ESR and viscosity measurements. Several types of mechano-radicals are produced in lignin during the mechanical process. Among these the phenoxy radicals are rather stable, where carbon-radicals are labile at ambient conditions. Transient mechano-radicals reacted readily with oxygen molecules to produce peroxy radicals even at 77°K, but they decayed rapidly at ambient temperature. Photodegradation of lignin was observed when macromolecule was irradiated with light of λ<3500 Å as revealed by ESR, viscosity, and weight loss. Phenoxy radicals are the predominant intermediates in the photoirradiated lignin as shown by ESR studies. Elimination of side chains of lignin phenyl propane units took effect in α-carbonyl group bearing molecules. By contrast, β aryl ether substituents adjacent to α-carbonyl groups caused ether cleavage under identical conditions of photoirradiation. This is attributed to energy transferred from excited α-carbonyl groups to the ether bonds. The α-carbonyl groups also functioned as photosensitizers accelerating photochemical reactions of lignin. Termination and decomposition reactions of mechano-radicals and photoinduced free radicals in lignin ultimately lead to the formation of para- and ortho-quinones, carbonyl groups, and double bonds which cause the color of lignin. These potential choromophoric groups can be partially removed from lignin by using ultraviolet light of λ> 4000 Å; and they can be completely removed by irradiation of lignin in the presence of dioxane-water with light of λ>3500 Å. Experimental findings suggest chat chromophoric groups in lignin were being trapped or blocked by dioxanyl radicals resulting in brightening. However, the photoreduced lignin-adduct suffered color reversion. This adverse effect can be prevented by using 2-hydroxy-4-methoxy-benzophenone as a photostabilizer. The feasibility of applying photoreduction techniques to high- yield pulps was demonstrated. However, optimal experimental conditions for photoreduction of lignin in high-yield pulps have not been established yet. / Ph. D.

No description available.