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1.
Behavior of lignin in supercritical methanol (250–270°C, 24–27 MPa) was studied by using lignin model compounds at the tin bath temperature of 270°C with a batch-type reaction vessel. Guaiacol and veratrole were selected as a guaiacyl type of aromatic ring in lignin, while 2,6-dimethoxyphenol and 1,2,3-trimethoxybenzene as a syringyl one. In addition, biphenyl and β-O-4 types of dimeric lignin model compounds were, respectively, studied as condensed and ether linkages between C6-C3 phenyl propane units. As a result, both guaiacyl and syringyl types of aromatic rings were very stable, and the biphenyl type was comparatively stable under supercritical conditions of methanol. However, β-ether linkage in the phenolic β-O-4 model compound was cleaved rapidly into guaiacol and coniferyl alcohol, which was further converted to its γ-methyl ether. Non-phenolic β-O-4 model compound was, on the other hand, converted initially into its α-methyl ether and degraded further to produce guaiacol. These lines of evidence imply that in lignin macromolecules, the new phenolic residues are continuously formed and depolymerized repeatedly in supercritical methanol into the lower molecular products, mainly by the cleavage of the dominant β-ether structure in lignin.  相似文献   

2.
Rigid polyvinyl chloride–wood flour composite lumber containing either pine or maple wood flour and pine and maple lumber was subjected to accelerated weathering according to the ASTM Standard G 53 protocol. Non-weathered and weathered surfaces of all specimens were analyzed using colorimetric methods, reflectance infrared Fourier transform and Raman spectroscopic techniques. In the FT-IR spectra, conjugated ketones (1,744 cm?1) of lignin as evidenced by their skeletal vibrations (1,560–1,500 cm?1) and stretching (1,440–1,500 cm?1) were reduced in weathered specimens. Cellulose was largely unaffected by weathering. C–O bending vibrations at 1,040 cm?1 from holocellulose in pine specimens and intensity bands at 1,125–1,090 and 1,360 cm?1 (C–O stretching and O–H bending from cellulose) in the maple and wood–plastic composite (WPC)-maple specimens were unaffected. A band at 1,650 cm?1 became prominent after weathering of both pine and maple WPC specimens which is due to C=C–C=C stretching vibration of weathered PVC portion of the specimen. Raman shifts at 530 and 840–900 cm?1 are attributed to C–O and C–C–O stretching in cellulose (remain unchanged). The role of extractives in weathering of pine is shown by the disappearance of Raman shifts at 392 and 434 cm?1 (C=C deformations in pine extractives) in weathered pine. One-Way ANOVA, between-group designs showed significant effect on brightness (L*), redness (a*) and yellowness (b*) for all treatments.  相似文献   

3.
The dioxygen consumption by kraft lignin and several lignin model compounds during oxygen-alkali treatments were directly analyzed using a dioxygen fl owmeter. The average dioxygen consumption by 200 g of kraft lignin was about 3 moles. Because this value was as much as those obtained for monomeric phenolic lignin model compounds, guaiacol and vanillyl alcohol, it was postulated that not only phenolic but also nonphenolic moieties in kraft lignin are extensively oxidized. The dioxygen consumption by 0.5 moles (one equivalent of aromatic units) of a dimeric lignin model compound, guaiacylglycerol-β-guaiacyl ether (GG), was also similar to that for 1 mole of guaiacol and vanillyl alcohol, regardless of the type of the aromatic moiety, which supports the above postulation. The most plausible mechanism for the oxidation of nonphenolic moieties is the oxidation of side chains of residual β-O-4 substructures by active oxygen species. By this mechanism, nonphenolic moieties in kraft lignin and GG are converted into corresponding phenolic moieties, and the oxidation by dioxygen progresses. Part of this article was presented at the 13th International Symposium on Wood, Fiber, and Pulping Chemistry (13th ISWFPC), Auckland, New Zealand, May 2005  相似文献   

4.
Pyrolysis reactions of various lignin model dimers   总被引：1，自引：0，他引：1  
Primary pyrolysis reactions and relative reactivities for depolymerization and condensation/carbonization were evaluated for various lignin model dimers with α-O-4, β-O-4, β-1, and biphenyl substructures by characterizing the tetrahydrofuran (THF)-soluble and THF-insoluble fractions obtained after pyrolysis at 400°C. Reactivity was quite different depending on the model structure: depolymerization: α-O-4 [phenolic (ph), nonphenolic (nonph)], β-O-4 (ph) > β-O-4 (nonph), β-1 (ph, nonph) > biphenyl (ph, nonph); condensation/carbonization: β-1 (ph) > β-O-4 (ph) > α-O-4 (ph) > β-O-4 (nonph), biphenyl (ph, nonph), α-O-4 (nonph), β-1 (nonph). Major degradation pathways were also identified for β-O-4 and β-1 model dimers: β-O-4 types: Cβ-O cleavage to form cinnamyl alcohols and phenols and Cγ-elimination yielding vinyl ethers; β-1 types: Cα-Cβ cleavage yielding benzaldehydes and styrenes and Cγ-elimination yielding stilbenes. Relative reactivities of these pathways were also quite different between phenolic and nonphenolic forms even in the same types; Cβ-O cleavage (β-O-4) and Cγ-elimination (β-1) were substantially enhanced in phenolic forms.  相似文献   

5.
Vanillin is one of the industrially important compounds that can be produced from lignin. This study presents production of vanillin and vanillic acid (oxidized form of vanillin) through aerobic oxidation of Japanese cedar (Cryptomeria japonica) at 120 °C for 72 h in aqueous alkali solutions with several Bu4N+ and OH? concentrations (1.25, 2.50, and 3.75 mol/L), where Bu4N+ is an enhancer of the vanillin formation reported in our previous study. The concentrations of Bu4N+ and OH? were adjusted by the additions of Bu4NCl and solid NaOH into the base medium Bu4NOH·30H2O, which forms 1.25 mol/L aqueous solution of Bu4NOH at the elevated temperature. Vanillin and vanillic acid were produced with the maximum yields of 21.0 and 1.7 wt% (lignin-base), respectively, at the 1.25 mol/L Bu4N+ and 3.75 mol/L OH? concentrations. This vanillin yield is close to that obtained by the alkaline nitrobenzene oxidation (26.5 wt%), indicating significantly high selectivity of our lignin degradation with Bu4N+ toward vanillin formation. We also proposed a novel Bu4NOH·30H2O-free reaction medium, where Bu4NOH·30H2O as the base medium were substituted with an aqueous solution of Bu4NCl and NaOH to avoid using expensive Bu4NOH·30H2O. The treatment of the Japanese cedar with this alternative medium exhibited the moderately decreased vanillin yield of 14.6 wt%, which is, however, much higher than the vanillin yield obtained with a simple 1.25 mol/L NaOH solution.  相似文献   

6.
A discolouration that appeared on the surfaces of a European white birch (Betula pubescens) board during vacuum drying was studied by means of colour measurements (CIEL*a*b*), elemental analysis and the analysis of extractives. The discoloured surface layer of the dried board contained substantially more methanol-soluble extractives than did the light-coloured part (50.7 mg g−1 vs. 26.7 mg g−1 dry wood), and the colour difference (ΔE* ab 20.0) between the two extracts was notable. Characterization by means of GC and 13C NMR spectroscopy showed that the extracts contain sugars (mainly glucose and fructose), low-molecular-weight phenolic compounds, proanthocyanidins, Brauns’ lignin and fatty acid esters. Concentrations of sugars, low-molecular-weight phenols, proanthocyanidins and Brauns’ lignin were higher in the discoloured surface layer than in the light-coloured part. The yellowness of the surface layer was associated with the accumulation of low-molecular-weight phenolic extractives, and the redness with Brauns’ lignin and possibly proanthocyanidins.  相似文献   

7.
Lignin containing substantial aromatic rings and high content of carbon has been employed as carbonizing agent to investigate the flame retardancy in the lignin/ammonium polyphosphate (APP) intumescent flame retardant (IFR) system. In addition, owing to the abundant phenolic and aliphatic hydroxyl groups, lignosulfonate, which is considered as a renewable aromatic macropolyols, substituted part of diethylene glycol (DEG) and copolymerized with isocyanate to produce lignosulfonate-based rigid polyurethane (LRPU) foams. Thermal stability was characterized by thermogravimetric analysis (TGA), and flame retardancy was investigated by limiting oxygen index (LOI) and cone calorimetry testing (CCT). Lignosulfonate increases thermal stability of LRPU foams and LRPU containing 15 wt% of lignosulfonate based on DEG (L15RPU) give rise to the best thermal stability. When 15% of lignosulfonate incorporated in the LRPU, reduced the heat release rate (HRR) and total heat release (THR) value 21 kW/m2 and 13 MJ/m2, respectively, and postponed 96 s time-to-peak carbon monoxide production than that of pure DEG rigid polyurethane (RPU) foam, the LOI values increased progressively with lignosulfonate content increasing. These results showed that lignosulfonate polyol may substitute polyol to produce lignosulfonate-based RPU foam and the presence of lignosulfonate could improve the flame retardancy. The mass loss gradually decreases with increasing APP addition, and the highest char yield was obtained from LRPU5 foam which at the lignosulfonate-to-APP ratio is 1:5. At the lignosulfonate-to-APP ratio of 1:5, the LOI value increased over 30%, and the HRR value reduced and the time-to-peak HRR postponed significantly. In addition, LRPU5 foams give rise to the lowest effect heat combustion (EHC) value, less smoke, and carbon monoxide (CO) production. Lignosulfonate acts as carbonizing agent in the lignosulfonate/APP IFR system, and the best fire retardancy is obtained at 1:5 of lignosulfonate-to–APP ratio.  相似文献   

8.
Rhizosphere-induced changes of Pinus densiflora (S. and Z.) grown at elevated atmospheric temperature and carbon dioxide are presented based on experiments carried out in a two-compartment rhizobag system filled with forest soil in an environmentally controlled walk-in chamber with four treatment combinations: control (25°C, 500 μmol mol?1 CO2), T2 (30°C, 500 μmol mol?1 CO2), T3 (25°C, 800 μmol mol?1 CO2), and T4 (30°C, 800 μmol mol?1 CO2). Elevated temperature and atmospheric carbon dioxide resulted in higher concentration of sugars and dissolved organic carbon in soil solution, especially at the later period of plant growth. Soil solution pH from the rhizosphere became less acidic than the bulk soil regardless of treatment, while the electrical conductivity of soil solution from the rhizosphere was increased by elevated carbon dioxide treatment. Biolog EcoPlate? data showed that the rhizosphere had higher average well color development, Shannon–Weaver index, and richness of carbon utilization compared with bulk soil, indicating that microbial activity in the rhizosphere was higher and more diverse than in bulk soil. Subsequent principal component analysis indicated separation of soil microbial community functional structures in the rhizosphere by treatment. The principal components extracted were correlated to plant-induced changes of substrate quality and quantity in the rhizosphere as plants’ response to varying temperature and atmospheric carbon dioxide.  相似文献   

9.
The present study contributes to the controversial discussion in the literature whether Si–O–C bonds in wood–silica–gel composites exist. 13C NMR is a suitable method to proof such bonds. Because of the low concentration of 13C isotopes in natural wood, 13C cellulose was used as 13C-enriched substitute. A tailored sol for the impregnation of that cellulose was chosen by liquid 29Si NMR pre-investigations of various sols whose reactivity and stability were time-dependently analysed. It is based on a sub-stoichiometric hydrolysis of tetraethoxysilane (TEOS) with 1 mol water per mol TEOS. Thermal analyses were performed to show a comparability of the thermal behaviour of wood–silica–gel and cellulose–silica–gel composites. There are two strong hints of the existence of stable Si–O–C bonds: (1) by thermal analysis, a shift in the fire behaviour of 100 K can be observed with a change in pyrolysis behaviour of the composite and (2) the proof by REDOR NMR that a dipolar coupling between 29Si and 13C nuclei exists.  相似文献   

10.
To learn more about lignin formation in response to wounding in trees, we adopted two complementary approaches: (1) microscopic and histochemical studies of the wound response in 3.5‐month‐old Eucalyptus gunnii plantlets and (2) biochemical investigations of hydroxycinnamyl alcohol dehydrogenase activities in wounded 6‐year‐old, field‐grown E. gunnii trees. The first approach revealed that a barrier zone was formed in response to wounding in both ground tissues (cortex barrier and pith reaction zone) and vascular tissues. The barrier zone was barely detectable after 24 h but well‐developed 7 days after wounding. Microscopic analyses indicated that the barrier zone was formed by the reinforcement of cell walls with ‘lignin‐like material’ in both ground tissues and vascular tissue, and that, in addition, the lumen of certain xylem cells (vessels and fibres) were blocked by the deposition of polymeric phenolic material. Histochemical characterization revealed that the lignin‐like material (‘defence lignin’) deposited in ground tissue cell walls and xylem cell blockages was poor in syringyl (S‐type) lignin units and therefore differed from the usual mixed guaiacyl–syringyl (G–S) lignin unit composition of E. gunnii developmental lignin. In contrast, S‐type lignin appeared to be deposited in the cell walls of immature developing secondary xylem cells at a stage when the cell walls of comparable cells from unwounded control stems contained lignin poor in syringyl units. The second approach indicated that two different types of cinnamyl alcohol dehydrogenase activity are induced, and apparently regulated differentially, in response to wounding in E. gunnii trees. Coniferyl alcohol dehydrogenase activity was induced immediately and continued to increase throughout the first 15 days of the 17‐day experimental period, while sinapyl alcohol dehydrogenase activity was first detected at 8 days after wounding and continued to increase throughout the experimental period. The biological roles of the two alcohol dehydrogenase activities are discussed in relation to the formation of defence lignin versus developmental lignin in trees.  相似文献   

11.
Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by 1H and 13C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol−1) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol−1). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red; between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood.  相似文献   

12.
Thermoplastic processing of lignin is restricted by its high glass transition temperature (T g). In this study, lignin was modified with polyethylene glycol (PEG) during steam explosion to improve its thermoplastic properties, and the effects of steam explosion and PEG on the chemical structure and thermal properties of lignin were investigated. Structure characterization using Fourier transform infrared spectroscopy showed that hydroxyl and ether functional groups increased and the activity of lignin was improved by steam explosion. In addition, steam explosion treatment was more effective than heat treatment for promoting the reaction of PEG with lignin. Solid-state 13C NMR revealed that PEG was grafted onto lignin. The T g of raw lignin was 164.1 °C; after steam explosion, lignin exhibited more than one T gs. The T g of lignin was reduced when the steam explosion temperature increased and decreased further, to around 60 °C, when PEG was used to modify lignin. Therefore, this work provides an effective approach to reducing the high T g of lignin.  相似文献   

13.
Chemical changes in cell wall components of bamboo internode during steam explosion process were analyzed to investigate self-binding mechanism of binderless board from steam-exploded pulp. More than 30% of xylose on initial mass, which is a major hydrolyzate of bamboo hemicelluloses, was lost after steam explosion treatment. Bamboo lignin is characterized by the presence of ester- and/or ether-linked p-coumaric acid to lignin. The content of phenolic hydroxyl groups of lignin isolated from steam-exploded pulp was characterized 2.3 times higher than those of the extract-free bamboo internode due to the cleavage of β-O-4 linkages. Alkaline nitrobenzene oxidation of the bamboo lignin gave vanillin, syringaldehyde and p-hydroxybenzaldehyde as major products. The content of p-hydroxybenzaldehyde decreased after steam explosion treatment, indicating the cleavage of ester- and/or ether-linked p-coumaric acid. The total yield of erythronic and threonic acids in ozonation products of the extract-free bamboo internode lignin was 268 mmol (200 g lignin)−1, while those of lignins in the steam-exploded pulp and powdery fraction were 96 and 129 mmol (200 g lignin)−1, respectively, suggesting the significant cleavage of β-O-4 linkages during steam explosion treatment. The cleavage of β-O-4 linkages was also confirmed by 1H- and 13C-NMR spectroscopic observations.  相似文献   

14.
为了解木质素的热解机理,利用密度泛函理论B3LYP方法,在6-31++G(d,p)基组水平上对含有C_α位羰基的β-O-4型木质素二聚体模型化合物(3-羟基-1-(4-羟基苯基)-2-苯氧基-1-丙酮)的热解过程进行了理论计算和分析。结果表明,C_α位上的羰基取代基可大大降低C_β—O的键解离能,提高C_α—C_β的键解离能,使得C_β—O的键解离能比C_α—C_β低91.5 k J/mol,因此该二聚体主要通过C_β—O键均裂的方式发生热解反应,其主要酚类热解产物是苯酚和4-羟基苯甲醛,次要产物是4-羟基苯乙酮,生成4-羟基苯甲醛的动力学最优路径是R7-a,其反应能垒为236.6 k J/mol。  相似文献   

15.
To elucidate the decomposition behaviors of lignin from different taxonomic groups, five different lignocellulosics were treated with hot-compressed water (230 °C/10 MPa/15 min) to fractionate lignins into water-soluble portions, precipitates, and insoluble residues. The lignin-derived products in each fraction were characterized and compared. The delignification of monocotyledons [nipa palm (Nypa fruticans) frond, rice (Oryza sativa) straw, and corn (Zea mays) cob] was more extensive than that achieved for Japanese cedar (Cryptomeria japonica, gymnosperm) and Japanese beech (Fagus crenata, dicotyledon angiosperm). The water-soluble portions contained lignin monomers like coniferyl alcohol and phenolic acids, while the precipitates contained higher molecular weight lignin with high content of ether-type linkages. Lignin in the insoluble residues was rich in condensed-type structures. In all five lignocellulosics, ether-type linkages were preferentially cleaved, while condensed-type lignin showed resistance to hot-compressed water. In the monocotyledons, lignin–carbohydrate complexes were cleaved and gave lignins that had higher molecular weights than those eluted from the woods. These differences would facilitate the delignification in monocotyledons. Such information provides useful information for efficient utilization of various lignocellulosics.  相似文献   

16.
To examine whether non-phenolic lignin moiety is converted into the new phenolic counterpart by the participation of active oxygen species (AOS) under oxygen bleaching conditions, a β-O-4 type dimeric lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (I), 2-(3,5-difluorophenoxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol (III), or 2-(3,5-difluorophenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (IV), was treated under conditions similar to those for oxygen bleaching. A phenolic compound, 4-hydroxy-3-methoxybenzyl alcohol, was added together to generate AOS in the reaction of compound I or IV. The results obtained suggested that AOS attack the side chains of compounds I, III, and IV accompanied by the β-O-4 bond cleavages and the liberations of the corresponding phenolic compounds, 2-methoxyphenol (II), 3,5-difluorophenol (V), and compound V, respectively. However, the rapid liberation of compound V in the oxygen-alkali treatment of compound III may mainly be caused by alkaline-induced reactions and/or some oxidation reactions of the primary degradation product of compound III, a muconic acid derivative.  相似文献   

17.
Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and chemical changes in spruce (Picea abies L.) and oak wood (Quercus robur F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the L*a*b* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-O-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.  相似文献   

18.
To examine why green liquor (GL) pretreatment of lignocellulosic materials effectively facilitates enzymatic saccharification under conditions milder than those of a common alkaline cooking process, dimeric β-O-4 type lignin model compounds with and without free phenolic hydroxyl group were reacted in several alkaline solutions including a model solution of GL, which mainly contains Na2CO3 and Na2S. The β-O-4 bond of the phenolic model compound was cleaved with a sufficient rate in the model solution of GL. The β-O-4 bond cleavage of the non-phenolic model compound was more frequent in the model solution of GL than in other alkaline solutions. These results suggest that β-O-4 bonds present in lignocellulosic materials are effectively cleaved in a GL pretreatment. It was also suggested that HS? and CO3 2? synergistically contribute to the β-O-4 bond cleavage of the non-phenolic model compound under GL pretreatment conditions.  相似文献   

19.
 The reaction behavior and kinetics of lignin model compounds were studied in supercritical methanol with a batch-type supercritical biomass conversion system. Guaiacol, veratrole, 2,6-dimethoxyphenol, and 1,2,3-trimethoxybenzene were used as model compounds for aromatic rings in lignin. In addition, 5-5, β-1, β-O-4, and α-O-4 types of dimeric lignin model compounds were used as representatives of linkages in lignin. As a result, aromatic rings and 5-5 (biphenyl)-type structures were stable in supercritical methanol, and the β-1 linkage was not cleaved in the β-1-type structure but converted rapidly to stilbene. On the other hand, β-ether and α-ether linkages of β-O-4 and α-O-4 lignin model compounds were cleaved rapidly, and these compounds decomposed to some monomeric compounds. Phenolic compounds were found to be more reactive than nonphenolic compounds. These results indicate that cleavages of ether linkages mainly contribute to the depolymerization of lignin, whereas condensed linkages such as the 5-5 and β-1 types are not cleaved in supercritical methanol. Therefore, it is suggested that the supercritical methanol treatment effectively depolymerizes lignin into the lower-molecular-weight products as a methanol-soluble portion mainly by cleavage of the β-ether structure, which is the dominant linkage in lignin. Received: December 19, 2001 / Accepted: April 30, 2002 Acknowledgments This research has been done under the research program for the development of technologies for establishing an ecosystem based on recycling in rural villages for the twenty-first century from the Ministry of Agriculture, Forestry and Fisheries, Japan; by a Grant-in-Aid for Scientific Research (B)(2) (no.12460144, 2001.4–2003.3) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; and under the research program from Kansai Research Foundation for Technology Promotion, Japan. The authors thank them for their financial support. This study was presented in part at the 45th Lignin Symposium, Ehime, Japan, October 2000 and the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002 Correspondence to:S. Saka  相似文献   

20.
To determine the independent decomposition rates of lignin and cellulose of decayed woody debris, a technique for the rapid analysis of lignin and cellulose is required. We applied a near-infrared spectroscopy (NIRS) technique to measure the lignin and holocellulose content in decayed wood. We succeeded in creating partial least-squares (PLS) models to estimate the lignin and holocellulose content in the decayed wood of five species using NIR spectra. Although the accuracy was acceptable for the estimation of a five-species mixed model (R 2 = 0.970 for lignin and R 2 = 0.962 for holocellulose), it was further improved when the model was applied to each species independently. This combination of NIRS and a PLS model is a valuable tool for the determination of the lignin and holocellulose content in decayed wood. The technique is time efficient (3 min per sample) and non-hazardous (no acid treatment is required).  相似文献   

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