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1.
The use of calibrated near infrared (NIR) spectroscopy for predicting the chemical composition of Pinus taeda L. (loblolly pine) wood samples is investigated. Seventeen P. taeda radial strips, representing seven different sites were selected and NIR spectra were obtained from the radial longitudinal face of each strip. The spectra were obtained in 12.5 mm sections from pre-determined positions that represented juvenile wood (close to pith), transition wood (zone between juvenile and mature wood), and mature wood (close to bark). For these sections, cellulose, hemicellulose, lignin (acid soluble and insoluble), arabinan, galactan, glucan, mannan, and xylan contents were determined by standard analytical chemistry methods. Calibrations were developed for each chemical constituent using the NIR spectra, wood chemistry data and partial least squares (PLS) regression. Relationships were variable with the best results being obtained for cellulose, glucan, xylan, mannan, and lignin. Prediction errors were high and may be a consequence of the diverse origins of the samples in the test set. Further research with a larger number of samples is required to determine if prediction errors can be reduced.  相似文献   

2.
The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Bj?rkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by 1H NMR and 13C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of 1H NMR and 13C NMR of Bj?rkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Bj?rkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Bj?rkman lignins of bark may be rather low.  相似文献   

3.
The aim of this study was to evaluate the chemical composition and the dynamic water vapour sorption properties of Eucalyptus pellita wood thermally modified in vacuum. For this purpose, wood samples were thermally modified in a vacuum oven at 160–240 °C for 4 h. Chemical composition were investigated by wet chemical analysis, elemental analysis, as well as Fourier transform infrared (FTIR) analysis, and dynamic water vapour sorption properties were evaluated by dynamic vapour sorption apparatus. The results showed that holocellulose and alpha-cellulose contents decreased and lignin and extractives contents relatively increased during the heat process. Elemental analysis showed a reduction in hydrogen content and an increase in carbon content. FTIR analysis indicated that the degradation of hemicellulose and condensation reactions of lignin occurred. In addition, the thermo-vacuum resulted in a reduction in the equilibrium moisture content of wood during the adsorption or desorption process. And the sorption hysteresis had a decreasing trend with increasing treatment temperature. The development of the hygroscopicity was related to the increase in the relative content of lignin, the degradation of the carbonyl groups in xylan and the loss of carbonyl group linked to the aromatic skeleton in lignin after heat treatment.  相似文献   

4.
Ultraviolet resonance Raman spectroscopy (UVRRS) was used to study the formation of aromatic and/or lignin-carbohydrate (LC) structures at the reducing end groups of O-alkyl-substituted cellulose under conditions simulating the initial phase of kraft pulping. The derivatives studied were methyl cellulose (MC) with degree of substitution (DS) of 1.64–1.95, carboxymethyl cellulose (CMC) with DS ∼0.6, and a lignin model compound, creosol. The total alkali concentrations in the treatments were 0.1 M and 0.5 M and the sulfidities were 1%, 10%, and 30%. HS− ions and creosol are both strong nucleophiles and they compete for the hot-alkali-generated unsaturated electrophilic reaction sites in the reducing end groups of the polysaccharides. The results indicated that conditions similar to those in the initial phase of conventional kraft cooking (high OH− and low HS− ion concentrations) increased the aromatic nature of the end groups and conditions similar to those in the initial phase of super batch cooking (low OH− and high HS− ion concentrations) partly inhibited the formation of aromatic and LC end groups.  相似文献   

5.
The effects of the combined treatment of drying and heat treatment using superheated steam (SHS) were studied relative to the changes of the major chemical components in larch wood. The green lumber was dried and heat-treated in SHS conditions of 250 °C and 0.5 MPa for 18 h, and the relative percentage contents of sugars, lignin, and extractives were investigated and compared with the relative percentage contents in the lumber heat-treated in hot air conditions of 250 °C and atmospheric pressure for 18 h. After both heat treatment methods, the relative percentage contents of xylan, mannan, galactan, and arabinan were greatly decreased, whereas that of the Klason lignin was increased, additionally that of glucan and extractives remained almost unchanged. Lignin may bind with furan compounds decomposed from hemicellulose following heat treatment, thus contributing to the increase in the apparent relative percentage contents of the Klason lignin. In addition, the condensate collected in the condenser after combined drying and heat treatment using SHS was investigated qualitatively and quantitatively by high-performance liquid chromatography (HPLC). A large amount of furfural and acetic acid decomposed from hemicellulose was detected and some sugar components composed of cellulose and hemicellulose were detected in the liquid condensate.  相似文献   

6.
Wood samples of apitong (Dipterocarpus grandiflorua) and ilang-ilang (Ilang-Ilang C. dadloyi) and feces of termites [Cryptotermes brevis (Walker)] fed on these woods were collected from University of the Philippines, Los Baňos. Lignin of each sample was isolated by Björkman’s procedure. There was no significant difference in 1H nuclear magnetic resonance (NMR) spectra or in the methoxyl content between Björkman lignins from original woods and termite feces. Differences were detected in the contents of aliphatic and unconjugated phenolic hydroxyl groups, suggesting minor structural changes of lignin during digestion by termites. In addition, the ratio of syringyl to guaiacyl nuclei of Björkman lignin from termite feces determined by 1H NMR spectra was higher than those from the original woods. The molar ratio of syringyl to guaiacyl nuclei of termite feces was higher than those from the original woods as determined by alkaline nitrobenzene oxidation. These results suggest that the structural changes of lignin in the termite gut are due to the insignificant formation of C-C linkages in guaiacyl nuclei. It was concluded that there were minor changes in the structural features of lignin under mostly anaerobic conditions, in contrast to the significant changes that occur through biological modification under aerobic conditions.  相似文献   

7.
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   

8.
Structural characterization of lignin from wheat straw   总被引：1，自引：0，他引：1  
Enzyme/mild acidolysis lignin (EMAL) was isolated from wheat straw. The structural characterization of wheat straw EMAL was investigated by FT-IR, 1H NMR, quantitative 31P NMR and DFRC, and DEPT CH (θ = 135C°) techniques. The wheat straw EMAL was a GSH-lignin with β-O-4′ structures and several condensed units (β-5′, β-β′, β-1′, 5-5′) and vinyl ether moieties; the contents of DBDO substructures and total β-aryl ether in the wheat straw EMAL were 0.257 mmol·g−1 and 0.818 mmol·g−1, respectively. Meanwhile, the structure features of the hemicelluloses residues attached to lignin were also investigated using DEPT CH (θ = 135C°) spectra.  相似文献   

9.
Summary The chemimechanical pulping (CMP) of sound balsam fir and the subsequent peroxide bleaching of the CMP pulp were investigated using solid state 13C CP/MAS NMR. A parallel study was made of a CMP pulp produced from spruce budworm killed balsam fir. Changes in the lignin and hemicellulose components were readily evident. The residual lignin and carbohydrate macromolecules in dead balsam fir CMP appeared to be the same as those in the sound wood CMP, before and after bleaching.We are indebted to Mr. S. S. Johal and Dr. J. V. Hatton of PAPRICAN, Vancouver, B.C., for generously supplying the wood and pulp samples. We also appreciate the assistance of Dr. N. R. Jagannathan with the 13C CP/MAS NMR measurements. Financial support from NSERC, in the form of a Postdoctoral Fellowship (JMW) and operating grants (FGH), is gratefully acknowledged  相似文献   

10.
The correlation of structural assembly on a molecular level with macroscale properties such as accessibility and reactivity was investigated. A series of TCF-bleached E. globulus kraft dissolving pulps was prepared aiming at a specification suitable for viscose application. The removal of xylan to a comparable level was achieved by different pre- and post-treatments. Solid-state CP-MAS 13C NMR was used to determine the degree of order and the lateral fibril dimensions of cellulose fibrils. The results of the NMR measurements were related to the processability of these pulps during viscose manufacture, expressed in terms of filterability of the viscose dope and its amount of undissolved particles. The cellulose crystallinity did not affect the pulp reactivity. It was noticed that the cold caustic extracted (CCE) pulps revealed both large fibril aggregate width as determined from NMR data and low reactivity toward xanthation at the same time. These pulps exhibited significantly higher amounts of alkali-resistant xylan than those prepared by prehydrolysis kraft cooking.  相似文献   

11.
Summary 13C CP MAS NMR spectroscopy was used to characterize the structural changes of cell wall polymers in beech wood Fagus sylvatica during drying processes. The analysis of five wood samples, namely, untreated, untreated dried, pre-treated by steam and/or NaOH subjected to drying showed partial depolymerization of lignin component as well as the change of the ratio of the crystalline and of the amorphous parts of cellulose as the consequence of wood pre-treatment. In addition, T1ρ(1H) relaxation times were determined in beech wood sample pre-treated with steam at 135 °C and the lignin isolated from this sample. The magnitudes of the relaxation times were found comparable in both samples as well as in the lignin-cellulose model compound. These unique T1ρ (1H) values indicate that spin diffusion is complete and homogeneous due to spatial proximity of spins and confirmed the formation of lignin-cellulose complex during thermal treatment of wood. Received 30 June 1997  相似文献   

12.
Summary The in vitro decay of Aextoxicon punctatum and Fagus sylvatica wood by the fungi Trametes versicolor, Ganoderma australe, Phlebia chrysocrea and Lentinus cyathiformis was studied by the agar-block method, and then the decayed woods were analyzed by chemical and spectroscopic techniques. The results demonstrated the strong resistance of the A. punctatum wood to the brown-rot fungus L. cyathiformis; the resistance might be related to the low S/G lignin ratio in this Austral hardwood. Wood decay by the Austral white-rot fungi G. australe and P. chrysocrea was rather limited, and preferential degradation of lignin was not produced although all the fungi studied increased wood digestibility. The most characteristic white and brown-rot decay patterns were observed during the in vitro decay with T. versicolor and L. cyathiformis, respectively. Trametes versicolor caused high weight losses and reduced the lignin content of the wood, whereas L. cyathiformis produced a preferential removal of xylan. No important changes in the solid-state 13C NMR spectra were observed after wood degradation by T. versicolor, but this technique evidenced an increase in aromatic carbon by L. cyathiformis. This increase was higher than that found in the Klason lignin content, suggesting the presence of altered lignin fractions in the brown-rotted wood.The authors are indebted to Prof. H. D. Lüdemann for the facilities at the Institut für Biophysik und physikalische Biochemie (Regensburg), to A. Navarrete (INIA, Madrid) for her collaboration, and to C. F. Warren (ICE, Alcalá de Henares) for her linguistic assistance. The computer program for spectra treatment was developed by G. Almendros (Centro de Ciencias Medioambientales, CSIC, Madrid). This investigation has been funded by the Spanish Biotechnology Program (Grant BIO88-0185)  相似文献   

13.
In order to understand the structural characteristics of lignin in triploid clones of Populus tomentosa and its changes in the processes of pulping and bleaching, milled wood lignin (MWL), lignin carbohydrate complex (LCC) and the residual lignin from kraft pulp (KP) and sulfite pulp (SP) were isolated and analyzed by Fourier transform infrared (FTIR) spectrum and 13C nuclear magnetic resonance (NMR). The most diagnostic peaks were assigned and the differences were discussed. The spectral patterns reveal that triploid P. tomentosa shows the specific features of hardwood from temperate areas, but in the spectrum of FTIR, the strength ratio of A 1270 cm−1 to A1226 cm−1 is 0.88, higher than the average of hardwood from temperate areas, which will make the lignin delignification more difficult during pulping and bleaching. The LCC from triploid P. tomentosa is mainly composed of xyloglucan and glucuronic acid, and other glucides have much lower ratio. In LCC FTIR, there are three peaks at 1 427, 1 329 and 1 046 cm−1, indicating that both semi-cellulose and cellulose could exist in LCC, and that there might be relationships between cellulose and lignin. Compared with the residual lignin from KP and SP, the condensed structure in KP is more than that in SP.  相似文献   

14.
Elastic modulus of lignin as related to moisture content   总被引：5，自引：0，他引：5  
The Young's and shear moduli of two lignins have been measured at several moisture contents. Cylindrical test specimens moulded from periodate and Klason lignin powders were conditioned to the required moisture contents and tested in tension and torsion. The Young's modulus of periodate lignin increased linearly from 3.1x109 to 6.7x109 Pa, and the shear modulus from 1.2x109 to 2.1x109 Pa as the moisture content of the lignin decreased from 12 to 3.6%. Klason lignin showed similar behaviour but its moduli were always much lower. This was probably a consequence of the more drastic alteration undergone by the Klason lignin during its isolation from the wood cell wall.I am indebted to Messrs M. B. Forsyth and L. P. Lowe for assistance with the design and construction of the testing equipment used in this work.  相似文献   

15.
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   

16.
The improvement of lignin pyrolysis by biopretreatment of white-rot fungi was investigated in this study. Results showed that biopretreatment can decrease the final residue yields, increase the weight loss rates, and absorb less heat during the pyrolysis of lignin in the inert atmosphere. In addition, the activation energies of biopretreated lignin were lower with the pre-exponential factors much higher compared with unpretreated lignin during the whole pyrolysis procedure. Analyses by FTIR and 13C NMR indicated that the structural alterations caused by biopretreatment might significantly influence the pyrolysis characteristics of lignin. By using biopretreatment, it is possible to enhance the lignin pyrolysis.  相似文献   

17.
Coloring characteristics of in situ lignin during heat treatment   总被引：1，自引：0，他引：1  
To investigate the effects of lignin on the discoloration of Black locust (Robinia pseudoacacia) wood during heat treatment, chromatic indexes of the extractive-free wood samples are examined at different moisture contents (MC) under oxygen and nitrogen environment, respectively. The organic acids are produced during heat treatment, resulting in pH decrease in the samples. Components absorbing visible light are formed during heat treatment, and oxygen and moisture contents have obvious effects on the decrease in L*, increase in a* value, yellowness (b*) and total color difference (ΔE) of the samples. It is found that the β-5, C α C β unsaturated bond, the conjugated carbonyl group, quinones structures, α, β-unsaturated ketone and α-C?=?O in lignin increased after heat treatment. The formation of condensation products, the low-molecular-weight phenolic substances and the oxidation products in lignin result in the increment of the light absorption within the entire visible region.  相似文献   

18.
The occurrence and nature of acetate groups in the milled wood lignin (MWL) isolated from birch (Betula pendula Roth) has been addressed by spectroscopic (2D-NMR) and chemical degradative (derivatization followed by reductive cleavage, DFRC) methods. Considerable amounts of acetate groups were present in the MWL preparation. However, 2D-NMR analysis indicated that the lignin polymer is not extensively acetylated and that the major part of the acetate groups is attached to the xylan moieties present in the MWL preparation. Nevertheless, evidence of the presence of minor acetylation of the γ-carbon of the lignin side chain (<3% of both syringyl and guaiacyl lignin units) was provided by DFRC analysis.  相似文献   

19.
Sequential extractions of the mild ball-milled Eucommia ulmoides Oliv with 80% neutral dioxane, 75% dioxane containing 0.025 M HCl, 75% dioxane containing 0.1 M NaOH, 60% ethanol containing 0.5 M NaOH, 5% KOH, 5% NaOH, and 8% KOH at 75°C for 3 h released 91.3% of the original lignin. The results showed that the procedure for extracting lignin from the mild ball-milled wood with mild alkaline organic solvent was more efficient than the traditional method of neutral and mild acidic dioxane extractions. The structure of the seven lignin fractions were analysed using wet chemical analysis, such as alkaline nitrobenzene oxidation, FT-IR, and solution-state 1H, 13C, and 31P NMR techniques. It is clear that the sequential mild acidic and alkaline organic solvent extractions of the mild ball-milled E. ulmoides Oliv offered significant yield improvements over the traditional signal acidolysis procedure for isolating lignin from wood, and the alkaline organic solvent extraction led to more lignin release than that of the mild acidolysis. This new procedure proposed in this study could be used for the lignin structural analysis, whereby wood is mild ball-milled and successively extracted with both mild acidic and alkaline organic solvents as well as aqueous alkalis to produce lignin fractions with high yield and purity and representing the total lignin in wood.  相似文献   

20.
Wood from white spruce Picea glauca that had been preserved by rapid burial in lake sediments 10,000 years ago, was investigated and compared to a contemporary reference white spruce wood. The 10,000-year old sample appeared to have an intact primary cell wall and middle lamella, whereas the carbohydrate monomer distribution, and microscopic images showed that the secondary wall was at least partially removed, indicating that this structure had been selectively attacked by bacteria. The Klason lignin amount in the aged spruce was found to be 60%. The relative lignin monomer content in the aged spruce was 9% lower than that of the reference wood, showing that there were fewer β-O-4′ linkages in the aged sample. This finding was supported by SEC analysis of the thioacidolysed samples as a larger proportion of lignin oligomers were observed in the aged spruce than in the reference material. This indicates a somewhat greater number of condensed bonds in the aged spruce than in the reference spruce sample. Quantitative 13C NMR analysis and HSQC techniques applied on milled wood lignins (MWL) revealed no significant structural differences between the aged spruce and the reference.  相似文献   

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