Side-chain ether groups in lignin model compounds of the general structure 1-(3$ sp prime$,4$ sp prime$-dimethoxyphenyl)-1,2-diaryloxyethane exhibited hydrolytic cleavage (the extent depending on the substituents on the 1-aryloxy groups) in aqueous 2N NaOH at 150$ sp circ$C (i.e. under wood pulping conditions). The level of hydrolysis increased in phenylpropane models (i.e. with $ gamma$-CH$ sb2$OH). Thus the commonly accepted generalization that 1,2-diethers of 3$ sp prime$,4$ sp prime$-dimethyoxyphenylpropane are stable in hot alkali is valid only for 1-alkoxy compounds. The newly observed hydrolytic cleavage is influenced by a combination of steric effects, electronic effects and solubility parameters. These observations now make it possible to consider alkaline delignification in the light of gel-degradation theory. / A series of compounds of the general structure 1-(3$ sp prime$-4$ sp prime$,dimethoxyphenyl)-1-aryl-2-guaiacyloxyethane, where the 1-aryl group bore a hydroxy substituent, also exhibited alkaline hydrolysis, at 150$ sp circ$C, at the $ beta$-carbon. The extent was greater when the 1-aryl group bore an $o$-OH than when it bore a $p$-OH. Thus, the reaction was assisted by the nucleophilic attack of the $o$-phenoxide anion on the $ beta$-carbon. / A relatively high release of guaiacol occurred on treatment of 1-(3$ sp prime$,4$ sp prime$-dimethoxyphenyl)-1-thio-2-guaiacyloxyethane with 2N NaOH at 150$ sp circ$C, and the yield of guaiacol was increased when the terminal sidechain carbon bore a $-$CH$ sb2$OH group. Analogous $ alpha$-thioaryl and $ alpha$-thioalkyl compounds also exhibited greater ether cleavage than their oxy counterparts. The hydrolysis of the $ beta$-guaiacyl group was also enhanced by the presence of $ alpha$-seleno-containing groups.

Changes in wood chemistry could have significant impact on both environmental and economic aspects of the pulp and paper industry. Consequently, a considerable amount of effort has been devoted to altering lignin content and/or modifing lignin monomer composition, a cell wall component whose removal is a major part of the chemical pulping process. Analysis of poplar transformed with a cinnamate 4-hydroxylase (C4H):ferulate5-hydroxylase (F5H) construct confirmed significant increases in the mole percent syringyl lignin in transgenic lines. Further, this study demonstrated significant increases in pulping efficiency from greenhouse grown transgenic trees. Compared to wild-type pulp, decreases of 23 kappa units (residual lignin) and increases of >20 ISO brightness units were observed in tree lines exhibiting high syringyl monomer concentrations (93.5% mol S). These changes were associated with no significant change in total lignin content or observed phenotypic differences in the trees. Additionally, pulp yields were not affected by the enhanced removal of lignin.. Furthermore, transgenic lines exhibit reduced fibre coarseness and increased cellulose viscosity. These results suggest that C4H-F5H transformed trees could be used to produce pulp for paper with substantially less severe delignification conditions (lower chemical loading or less energy), and that the pulp produced is of comparable quality to that of the wild-type poplar. Consequently, the ecological footprint left on the environment, measured by the amount of deleterious pulping by-products released into the environment may be significantly reduced.

No description available.

No description available.

No description available.

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.

No description available.

No description available.

No description available.

No description available.