In our previous studies on the relationships between lignin structure and hemicellulose composition in a wide range of hardwood species, we showed that the higher the syringyl ratio, the higher the xylan/mannan ratio. In this study, the relationship of the syringyl ratio and xylan/mannan ratio was further studied using fractions obtained by stepwise extraction of finely milled beech wood by use of aqueous dioxane and subsequent dimethyl sulfoxide (DMSO)/LiCl solvents with increasing LiCl concentration. Each soluble fraction obtained with a different LiCl concentration was compared with the corresponding insoluble residue, and it was shown that both the syringyl ratio and xylan/mannan ratio were always higher in the insoluble fraction. To analyze polysaccharides closely located with lignin, milled wood lignin (MWL), and cellulolytic enzyme lignin (CEL) obtained by enzyme treatment after DMSO/LiCl swelling were investigated. Although the xylan/mannan ratio of MWL was higher, that of CEL with more than 80% lignin yield was lower. 相似文献
Abstract A total of 17 softwoods and 48 hardwoods were analyzed by IR spectroscopy to examine if syringyl ratio (syringyl/(syringyl+guaiacyl)) calculated from nitrobenzene oxidation products can be precisely expressed by area ratios of characteristic peaks of lignin in IR spectrum. Area ratio of two peaks is referred to as that of two wavenumber domains, represented by “wavenumber 1/ wavenumber 2.” Examined peak area ratios were 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/(855+815). Among these ratios, log(1595/1509) and log(1275/1220) showed significant linear relationship with the syringyl ratios with a correlation coefficient of 0.98 for all 65 woods. These two ratios could also be used to distinguish all the hardwoods from the softwoods. 相似文献
The chemical characteristics of lignin, including the Klason lignin content, acid-soluble lignin content, proportion of the aromatic ring types [syringyl ratio = syringyl/(syringyl + guaiacyl)], and proportion of the diastereomeric forms for the β-O-4 structure [erythro ratio = erythro/(erythro + threo)], and pulpability were investigated for 28 wood samples belonging to the genera Acacia and Eucalyptus. Although the lignin characteristics of these 28 woods varied widely, the chemical characteristics of the two genera could be categorized in two clearly distinguished groups on the basis of the syringyl ratio. Clear negative correlations were observed between both the syringyl and erythro ratios and the total lignin content (sum of the Klason and acid-soluble lignin contents) within each genus. In addition, the syringyl ratio correlated positively with the erythro ratio and acid-soluble lignin content, regardless of the genus. The existence of a clear, high correlation between the syringyl and erythro ratios supports the hypothesis that the aromatic ring type (syringyl ratio) is a decisive factor for controlling the diastereomeric forms of the β-O-4 structure (erythro ratio). Each of the wood samples was also subjected to Kraft pulping, and it was demonstrated that the woods with higher syringyl ratios were easier to delignify. This tendency is reasonably attributed to the high reactivity of the erythro-rich and syringyl-rich β-O-4 structures, and the low lignin content of these syringyl-rich woods. 相似文献
The benzyl cation intermediate is believed to be primarily formed in the acid-catalyzed reaction of lignin, and the reaction route of the intermediate determines which reaction products are afforded and whether lignin undergoes depolymerization or condensation. This study aimed to examine the formation rate of the benzyl cation intermediate from phenolic (P) or non-phenolic (N) lignin model compounds with different types of aromatic nuclei, namely p-hydroxyphenyl (H), guaiacyl (G), or syringyl (S). The rate was in the order of H > G > S for both P- and N-type model compounds and of P > N for all H-, G-, and S- type model compounds. The orders were successfully explained by the electron-donating or electron-withdrawing properties of the hydroxy and methoxy groups at the para- and meta- of the benzyl position, which is the reaction center in the formation of the benzyl cation intermediate. 相似文献
Photoyellowed and control unbleached, borohydride bleached, and bleached and diimide-reduced spruce thermomechanical pulps (TMPs) were studied using near-IR excited FT Raman, DRIFT, and diffuse reflectance UV-Vis. spectroscopies. In addition, extracts of yellowed pulps were analyzed spectroscopically. FT Raman spectroscopy was used for the first time in the study of the photoyellowing phenomenon. Post color number data of the yellowed TMP handsheets suggested that α-carbonyl and ring-conjugated ethylenic groups did not play a significant role in the yellowing process. This suggestion was further supported by not only the similarity of the FT Raman and DRIFT spectra of the three yellowed pulps but by the similarity between the spectra of the pulps' yellow extracts. Raman spectra of the TMPs provided evidence for the following: (1) diimide-reduced TMP was indeed free of aromatic ring-conjugated ethylenic bonds; (2) photoexposure of unbleached TMP caused degradation of coniferaldehyde and coniferyl alcohol structures; and (3) photoexposure of bleached TMP caused the degradation of coniferyl alcohol structures. In addition, yellowing resulted in changes in the 1600 cm?1 Raman band and a new broad feature appeared at 1675 cm?1. In the IR spectra of pulp extracts, the latter vibrational mode was detected at 1673 cm?1. IR spectra of the yellowed pulps and their extracts showed increased absorption at 1727 cm?1. Upon yellowing, contribution to this band was primarily from the photoproducts of those lignin structures that did not contain a conjugatedethylenic bond. These results suggest that there are yellowing initiating structures, other than a-carbonyl and ethylenic groups, that are responsible for most of the yellowing in unbleached, borohydride bleached, and diimidereduced TMPs. 相似文献
Different softwood lignin O‐acyl derivatives, i.e., methacrylated, hexanoylated, benzoylated, methoxybenzoylated, and cinnamoylated lignin are synthesized and subjected to melt spinning. In the presence of spinning aids such as vanillin and ethylene glycol dimethacrylate, multifilament melt spinning is accomplished with spinning speeds up to 500 m min−1, which allowed for realizing uniform precursor fibers 17 μm in diameter. Out of all acyl‐derivatives of softwood lignin investigated, cinnamoylated softwood lignin (CL) turned out to be superior in terms of processability. CL‐derived precursor fibers are oxidatively thermostabilized and then carbonized applying carbonization temperatures up to 2200 °C. Carbon fiber structure formation is followed in detail by wide‐angle X‐ray scattering and Raman spectroscopy. An orientation ≤53% and a d 002 spacing of 0.353 nm is achieved. According to small angle X‐ray scattering, carbon fibers have a porosity of ≈38%. CL‐derived carbon fibers are also characterized in terms of mechanical properties. Tensile strengths up to 0.93 GPa (average 0.75 GPa) are obtained and follow Weibull statistics. Elastic moduli are ≤66.5 GPa (average 41.1 GPa).
To improve the mechanical properties of hemicellulose hydrogel, a green, adjustable mechanical property, high swelling ratio (SR) composite hydrogel was successfully prepared by using modified lignin as a reinforcing agent. The structure and characteristics of the composite hydrogels were investigated by TGA, FTIR, SEM, rheological analysis, and SR. It can be found that the modified lignin could significantly improve the mechanical properties of the composite hydrogels. The maximum compressive stress of unmodified lignin hydrogel was 61.72 kPa and the compressive deformation was 75%. Compared with the unmodified lignin hydrogel, the mechanical properties were significantly improved, with the maximum compressive stress of the modified lignin hydrogel was 145.2 kPa and the compressive deformation was up to 90%. After adding modified lignin, the SR of the as-prepared hydrogel was up to 155.17 g/g, which was much higher than that of unmodified lignin hydrogel (105.79 g/g). The composite hydrogel had good antioxidant properties, and the free radical removal rate can reach 85.3%, which is twice as much as that without the modified lignin. With cost-effective lignin as a reinforcing agent, the as-prepared hemicellulose hydrogel with adjustable mechanical properties is favorable for great application potential. 相似文献
Abstract The natural variation in wood and pulp fiber quality of 15 aspen (Populus tremuloides Michx) clones, represented by 47 trees, was assessed from 4 different sites in British Columbia, Canada. Kraft pulping trials revealed substantial variation in the pulping efficiencies, illustrated by differences of 6% in total pulp yield, ～30% differences in H‐factor required to attain a target kappa of 21, and differences of up to 2 ISO brightness units in bleachability of kappa 21 pulp. Clearly, enormous variation exists in the natural stands of aspen, and presents some exciting opportunities for selecting clonal aspen for targeted end‐product applications. A comprehensive characterization of wood chemical composition, wood density, and fiber properties indicated that pulp yield is directly related to syringyl lignin monomer composition, and not inherent wood density, regardless of geographic locations, whereas pulp bleachability and viscosity appear to be associated with the inherent cell wall thickness of the starting wood resources (fiber coarseness). These findings suggest that geographic location imparts influences on wood fiber coarseness traits, while substantial genetic variability exists on all sites. 相似文献
Rice hulls were treated using several sodium hydroxide concentrations and temperatures. The black liquor contents of silica, lignin and hemicelluloses increased with increase in temperature or sodium hydroxide concentration. Hexoses constituted the major part and pentoses the minor part of the black liquor hemicelluloses. The ratio of pentoses to hexoses increased slightly with the increase of treatment variables. The pentose content of the black liquor consisted of arabinose and xylose, while the hexose composition was mannose, galactose, rhamnose and glucose. On increasing the alkali concentration, the xylose and mannose concentrations increased greatly, while galactose and glucose increased only slightly. Using 10 soil samples several isolates of fungi and actinomycetes were obtained. These were identified as five species of the genus Aspergillus, three species of Paecilomyces, two species of Penicillium, one species each of Alternaria, Trichoderma, Chaetomium and Actinopolyspora. These fungi were cultivated on black liquor basal salts medium. The highest bioconversion rate of black liquor hemicelluloses into biomass and single-cell proteins was achieved by Aspergillus terreus, followed by Paecilomyces simplicissima then Actinopolyspora sp. 相似文献
In our previous studies, a method of quantitative analysis of lignin structure by IR spectroscopy with direct use of wood meal was developed which can be apply to a wide range of wood species. Lignin structure deposition in different fractions in the same wood sample also has characteristic diversity and differences. In this study, quantitative analysis of lignin structure by IR spectroscopy was used to determine whether it can be applied to different fractions in the same wood sample. Finely milled beech wood was fractionated by stepwise extraction using aqueous dioxane and followed by subsequent dimethyl sulfoxide (DMSO)/LiCl solvents with increasing LiCl concentrations. The results showed that fractions of the peak area ratio of log(1595/1509) fit a linear relationship with different wood species very well. Therefore, log(1595/1509) could be used not only with different wood species but also with different fractions from the same wood. For 1509/1460, log(1275/1220), 1130/1030 and 835/(835+815), different fractions deviated from the original relationship obtained from different wood species. 相似文献
