Prehydrolysis of beechwood

Summary The kinetics of the isothermal prehydrolysis of beechwood at 160°C and 170°C were investigated. It was shown that the hydrolysis of the hemicellulose portion was realised in two phases. The depth and rate of the first rapid prehydrolysis phase and the second slow phase depend on the temperature used. The lignin content in the prehydrolysed chips increased with the duration of the prehydrolysis due to the easily removable hemicellulose portion. The maximum amount of lignin extracted was gained after 45–60 minutes of isothermal prehydrolysis at 160°C with the yield decrease to 82–80 per cent and at 170°C with the yield decrease to 70–68 per cent. At the temperature of 160°C the amount of the lignin portion extracted was about 5 per cent and at 170°C at about 10 per cent of the whole lignin content in wood. The extraction of the whole hemicellulose portion present in wood was attained at 160°C after 5 hours prehydrolysis time, at 170°C after 80 minutes.By the prehydrolysis of hardwood to 30 per cent loss of the wood substance highly purified dissolving pulp was prepared by AQ catalysed sodium pulping. The pulp attained was characterised by a high alpha-cellulose content over 97 per cent and a low solubility in solutions of alkali. The sulphur-free delignification together with the low consumption of active chlorine (1.5–1.7 per cent) cause less environmental pollution.     

Delignification of cell walls of <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> during alkaline nitrobenzene oxidation

To clarify the behavior of whole lignins in wood cell walls during alkaline nitrobenzene oxidation, the delignification process from cell walls in normal and compression woods of Chamaecyparis obtusa Endl. (Cupressaceae) was observed using ultraviolet and transmission electron microscopies. The lignin content conspicuously decreased to around 10% after 35min in normal wood. The lignin content in compression wood finally leveled off at aroumd 10% after 50min. In gel filtration of oxidation products in ethyl acetate, a high molecular weight fraction was prominent in extracts from the early stage of the reaction. As the oxidation progressed, the high molecular weight fraction became less prominent in both normal and compression wood. Changes in the weights of cell wall residues during reaction indicated that approximately half of the components other than lignin were also removed from the cell walls. This shows that the majority of lignin with relatively high molecular weight is removed from the cell walls together with polysaccharides in the early stage of the reaction and that further oxidative degradation occurs in solution in later stages. Only a small amount of the lignin with low molecular weight could be analyzed by gas chromatography.Parts of this report were presented at the 47th (Kochi, April 1997) and 48th (Shizuoka, April 1998) Annual Meetings of the Japan Wood Research Society, and at the Lignin Symposium, Sapporo, October 1997     

Swelling of acetylated wood II: effects of delignification on solvent adsorption of acetylated wood

To clarify the role of lignin in the affinities of acetylated wood for organic solvents, the effects of delignification on the solvent adsorption of acetylated wood were investigated. Acetylated wood meals rapidly adsorbed organic solvents that were hardly adsorbed by unmodified wood. For nonpolar and low-polarity organic solvents, a clear positive correlation was observed between the amount of adsorption and the lignin content. This indicated that acetylated lignin was responsible for the excellent affinities of acetylated wood for hydrophobic organic solvents. On the other hand, for lower alcohols and water, the amount of adsorption reduced with an increase in the lignin content. It was suggested that the adsorption of such polar solvents was dominated by insufficiently acetylated hydrophilic polysaccharides.     

Non-isothermal autohydrolysis of Eucalyptus wood

Non-isothermal autohydrolysis treatments of Eucalyptus globulus wood were carried out in batch reactors in order to assess the kinetics of hemicellulose degradation, as well as the effects caused on cellulose and lignin. Experiments were carried out at a liquor to wood ratio of 8 g/g, and two heating profiles were explored. The maximum temperature considered was 224 °C, and the longest reaction time was 0.94 h. The experimental variables considered were solid residue yield, solid residue composition and composition of liquors. Up to 90.4% of the initial xylan was removed in treatments, which also caused some delignification (up to 13.8% of the initial lignin was removed), whereas cellulose was almost quantitatively retained in solid phase. The conversion of xylan into xylooligomers, with further hydrolysis to xylose and decomposition of this sugar into furfural was assessed by means of a kinetic model based on sequential, first order reactions involving kinetic coefficients with Arrhenius-type dependence on temperature. Received 23 November 1999     

Fractional isolation and structural characterization of mild ball-milled lignin in high yield and purity from <Emphasis Type="Italic">Eucommia ulmoides</Emphasis> Oliv

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.     

Characterization of lignin-derived products from Japanese beech wood as treated by two-step semi-flow hot-compressed water

Japanese beech (Fagus crenata) wood was treated by two-step semi-flow hot-compressed water (the first stage: 230 °C/10 MPa/15 min, the second stage: 270 °C/10 MPa/15 min), and produced lignin-derived products in the hot-compressed water-soluble portions at the first and second stages, and the final residue of the second stage was characterized with alkaline nitrobenzene oxidation method and gel permeation chromatographic analysis. As a result, the lignin-derived products at the first stage, where hemicellulose was also decomposed, consisted of lignin-based monomers and dimers and oligomers/polymers in the water-soluble portion. A large part of the oligomers/polymers was, however, recovered as the precipitate during 12 h setting after hot-compressed water treatment. By the analysis of nitrobenzene oxidation products, there were relatively higher contents of ether-type lignin in the precipitate at the first stage than in original beech wood. Since the ether linkages of lignin are more preferentially cleaved by this hot-compressed water, lignin-based polymeric fractions were flowed out from the porous cell walls from which hemicellulose was removed. On the other hand, at the second stage condensed-type lignin remained in the precipitate and residue. Based on these results, decomposition behavior of lignin in Japanese beech wood as treated by the two-step semi-flow hot-compressed water was discussed regarding the topochemistry of lignin structure.     

Cellular UV-microspectrophotometric investigations on pine wood ( Pinus taeda and Pinus elliottii) delignification during biopulping with Ceriporiopsis subvermispora (Pilát) Gilbn. & Ryv. and alkaline sulfite/anthraquinone tr

Scanning UV-microspectrophotometry was used to investigate the topochemistry of lignin removal from pine wood (Pinus taeda and P. elliottii) chips during biopulping involving wood treatment with Ceriporiopsis subvermispora (Pilát) Gilbn. & Ryv. followed by alkaline sulfite/anthraquinone delignification. A delignification front starting from the lumen towards the compound middle lamella was clearly observed in micrographs recorded from individual cell wall layers of wood samples biotreated for 30 days. Lignin was removed without cell wall erosion. UV-micrographs of wood samples cooked for a short time (90 min pulping) showed that the S2 of biotreated samples are more homogeneously delignified compared to the S2 of the undecayed controls. Similarly, the compound middle lamella and cell corners are also more delignified in biotreated samples. On the other hand, UV-micrographs of samples cooked for a long time (150 min pulping at 170°C) showed that there are no significant differences in the contents of residual lignin retained in the S2 of undecayed and biotreated wood samples.     

麦草碱性亚硫酸盐制浆生物炼制的研究(I) ——深度脱木质素及木质素磺化特性

提出了非木材木质纤维生物质碱性亚硫酸盐制浆(ASP)生物炼制的理念,研究了总用碱量、亚硫酸化度、温度和时间对麦草碱性亚硫酸盐法蒸煮深度脱木质素特性和木质素磺化的影响。结果表明:麦草ASP法具有高的深度脱木质素选择性;深度脱木质素延伸与木质素磺化度提高具有一致性;总用碱量、亚硫酸化度、最高温度和保温时间对深度脱木质素选择性和木质素磺化度都有重要的影响;在总碱用量18.0%,亚硫酸化度85.0%,液比值3.5,最高温度168℃,保温150 min的条件下,可制得卡伯值8.8,得率56.8%,黏度为33.3 mPa.s的优良纸浆,此时黑液中磺化木质素磺酸基含量达2.16 mmol/g(以固形物计)。从深度脱木质素选择性、木质素磺化和纸浆基本特性考虑,麦草ASP法具有制浆生物炼制的前景。     

Characteristic fragment ions from lignin and polysaccharides in ToF–SIMS

Different model compounds for lignin, hemicelluloses and pectins were studied by time-of-flight secondary-ion mass spectrometry (ToF–SIMS). Mass spectra of Klason lignin from normal and compression spruce wood, aspen wood and wheat straw were compared. Spectra of brominated spruce and aspen wood sections showed fragment ions attributed to brominated guaiacyl and syringyl units in lignin at m/z 215, 217, 229 and 231, and m/z 245, 247, 249 and 261, respectively. Spectra of mono-, oligo- and polysaccharides showed fragment ions at m/z 127 and 145 characteristic for hexose units, and ions at m/z 115 and 133 characteristic for pentose units. The same ions were detected in spectra of delignified spruce and aspen wood sections. Labelling of anionic groups by Sr²⁺ ions followed by ToF–SIMS analysis showed that pectins were present at specific locations on the surfaces of spruce and aspen wood sections still after delignification with hydrogen peroxide in acetic acid.     

A mathematical model of kraft pulping related to the alkali concentration in the cooking liquor

Summary A new mathematical model for checking and controlling the kraft pulping process has been derived. The model is based on the modified relationship between the lignin content and the alkali concentration of a cooking liquor expressed as the ratio of lignin/active alkali vs. concentration of the active alkali in a cooking liquor. The derived model characterizes the variation of the lignin content of the partially delignified wood or pulp with the concentration of the residual alkali in a cooking liquor during an entire pulping cycle, i.e. during the initial, transition, bulk and residual phases of the kraft delignification. The relationship between the lignin content of the partially delignified wood ships or pulp and the concentration of the residual alkali in a cooking liquor is expressed by the logarithmic straight line equation or its power form. The slope and intercept constants of the derived equation for the individual phase of delignification have different values. Received 5 June 1996     

Chemical reactivity of heat-treated wood

Chemical reactivity of heat-treated wood was compared with that of untreated wood. For this purpose, heat-treated pine or beech sawdust was reacted with different carboxylic acid anhydrides in pyridine or with phenyl isocyanate in dimethyl formamide. Compared to controls, weight gains obtained with heat-treated sawdust are smaller showing a lower chemical reactivity. FTIR analyses of lignin and holocellulose fractions, isolated after acidic hydrolysis of polysaccharides or delignification with sodium chlorite, indicate that both components are involved in the reactions. Compared to lignin, holocellulose exhibits important infrared absorptions of about 1,730 cm⁻¹, characteristic of ester or urethane linkages formed. Lower reactivity of heat-treated sawdust is explained by the decrease in free reactive hydroxyl groups in holocellulose due to the thermal degradation of hemicelluloses, considered more reactive than cellulose.     

Pressurized hot water extraction of Norway spruce hemicelluloses using a flow-through system

Norway spruce saw meal was extracted with pressurized hot water at 120–240°C using a flow-through system. Only small amounts of hemicelluloses were extracted at 120–160°C, but dissolution was significantly enhanced when higher extraction temperatures were applied. All hemicelluloses but only 15% of lignin were removed from wood at 220°C, and even less lignin was extracted at lower temperatures. Partial degradation of cellulose seemed to take place only at 240°C. Of the total amount of extracted hemicelluloses, 4–22% was hydrolyzed to monosaccharides. Although the average molar masses of extracted hemicelluloses decreased with increasing extraction temperature, even at 240°C the extracted carbohydrates occurred, on average, as polysaccharides. Polysaccharides with an average molar mass of 31 kDa were obtained at 170°C. The molecular-mass characteristics and yield of carbohydrates depend on the extraction temperature, which should be chosen based on the end use of the isolated hemicelluloses.     

Studies on the delignification of spruce wood by organosolv pulping using SEM-EDXA and TEM

Summary Samples of spruce wood derived from various stages of organosolv pulping were studied by SEM-EDXA and TEM. During the first stage (methanol-water) the lignin content of the secondary walls decreased slowly, whereas in the compound middle lamellae only the reactivity of lignin increased. During the subsequent stage (methanol-NaOH) the delignification proceeded fast in both layers but the residual lignin content in the compound middle lamellae remained higher than in the secondary walls.     

Lignin as a cross-linker of acrylic acid-grafted carboxymethyl lignocellulose

Cunninghamia lanceolata wood meal samples with different lignin contents after delignification with an acidic NaClO₂ system were carboxymethylated, and the degree of substitution (DS) and the distribution of the carboxymethyl (CM) groups were investigated by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Cellulose samples prepared from bleached kraft softwood pulp, food-grade konjac mannan, and commercial oat xylan (containing 10% arabinosyl and 15% glucosyl residues) were also investigated. The chemical shift of methylene protons in ¹H NMR spectra of CM groups of carboxymethyl konjac mannan and commercial oat xylan appeared in the same region as those of carboxymethylcellulose. The DS of carboxymethyl lignocellulose (CMLC) increased slightly from 1.36 to 1.48 with decreasing lignin content, but the water solubility of CMLC clearly increased with decreasing lignin content. It was suggested that the covalent linkages between lignin and cell-wall polysaccharides play the role of cross-linker in CMLC. Water absorbents were synthesized by graft-copolymerization of acrylic acid onto CMLC samples with different lignin contents. The highest level of water absorbency was obtained from CMLC containing 14% of lignin, suggesting the importance of lignin as the cross-linker.     

The ultrastructure of cellulose from wood

Summary During the delignification of wood several processes overlap one another. One of these is the penetration of the wood samples by the delignifying solution. Penetration tests under different conditions show that there is almost no difference in the penetration depth of wood samples penetrated by diffusion only and of wood samples treated with pressure. In both cases the pits are closed during the flow of fluids. Vacuum treated samples show better penetration and most of the pits in these samples remain open. The distribution of fluids within the cell walls takes place in the intercellular spaces, in small openings in the compound middle lamella and in the secondary wall 1 as well as in very fine pores in the secondary wall 2. The penetration of a wood sample is greatly facilitated if the sample is mechanically injured. A slowly proceeding delignification with ethylene sulphite shows that the delignification obviously starts in the S 1 layer and proceeds from there towards the compound middle lamella and the S 2 layer. In the first stages of lignin removal the compound middle lamella is also attacked, the attack beginning at the border of the pit chambers.     

Analysis of progress of oxidation reaction during oxygen-alkali treatment of lignin I: method and its application to lignin oxidation

A new method is applied to evaluate the progress of the oxidation reaction of lignin during oxygen-alkali treatment. This method employs the difference in permanganate consumption of the sample before and after the oxygen-alkali treatment as an indication for the lignin oxidation. When kraft lignin and residual lignin isolated from unbleached softwood kraft pulp were subjected to oxygen-alkali treatment up to 6000min, the progress of the oxidation expressed by this method was separated into clearly distinguished three phases. During the first and second phases, the progress of oxidation was well correlated to the loss of methoxyl group and to the decrease in the yield of nitrobenzene oxidation products. The addition of Mn⁺ to the oxygen-alkali treatment depressed oxidation during the second phase partly and that during the third phase almost completely. Calculations based on the change in the permanganate consumption revealed that the oxidation during the first phase corresponded to 4.2 electrons abstracted from one lignin structural unit on average. The oxidation process by oxygen-alkali treatment was hypothetically attributed to the direct reaction between molecular oxygen and the phenolic unit of lignin, which mainly took place during the first phase, and to the autooxidation-type oxidation during the second and third phases.Part of this paper was presented at the 9th ISWPC, Montreal, June 1997; and at the 42nd Lignin Symposium, Sapporo, October 1997     

马尾松硫酸盐浆两段氧脱木质素最佳工艺条件的研究

研究了马尾松硫酸浆两段氧脱木质素的最佳工艺条件。结果表明，第一段氧脱木质素的条件为：氧压0．6MPa，温度100℃，时间80min,NaOH 量5％，MgSO4用量0．5％，浆浓10％；第二段氧脱木质素的条件为：氧压0．4MPa，温度90℃，时间60min，NaOH用量3％，MgSO4用量0．5％，浆浓10％。在此条件下，OIOⅡ木质素脱除率达到72．5％，粘度775．2cm^3/g,得率90．5％。经过氧脱木质素后浆的裂断长5．8km，耐破指数5．3kPa.m^2/g，撕裂指数12．7mN.m^2/g。     

Impact of Ceratocystis wilt on eucalyptus tree growth and cellulose pulp yield

In this study, we determined the effects of Ceratocystis fimbriata wilt on volumetric growth and cellulose pulp yield of eucalyptus. Seven‐year‐old healthy and infected trees were separated into different classes of severity, and the individual volume of each whole tree with bark was determined. Volumetric losses were found regardless of the class of disease severity, resulting in reduction in volumetric growth of the trees from 65% to 87%, depending on the infection level. Two approaches were used for evaluating the effects of the disease on cellulose pulp yield: (i) evaluation of wood basic density and chemical composition, contents of ethanol/toluene extractives and Klason lignin, and the alkaline load and screen yield across Kraft pulping to kappa number 18 ± 0.5 for both healthy and discoloured materials; (ii) determination of the alkaline load and yield across Kraft pulping to kappa number 18 ± 0.5 of woods with different levels of discoloration (0, 25, 50, 75 and 100% of discoloured wood). Discoloured wood presented lower basic density, higher ethanol/toluene extractives and Klason lignin, higher alkaline load and lower pulp screened yield at kappa number 18 ± 0.5 compared with the healthy ones. Increasing the fraction of infected wood in chip furnishes resulted in proportionally increased alkaline load demand and decreased screen yields. Adding 50% of infected wood in the chip furnish resulted in 23.8% increase in the alkali load and 13.7% reduction in the pulp screen yield at kappa number 18 ± 0.5. The results obtained have proved that the disease reduces volumetric growth, increases wood consumption and reduces yield in eucalyptus pulp production.     

Enzymic isolation of lignin from wood and pulps

After enzymic hydrolysis of polysaccharides in milled wood or pulp the unhydrolysed lignin residue becomes soluble in certain polar solvents. Extensive disintegration of the wood is necessary to obtain a sufficient accessibility toward the enzyme. For milling a porcelain rotary ball mill is recommended. A relationship has been found between the milling energy, which is proportional to the size of the mill, the milling time, and the yield of ball-milled wood lignin (BMWL). Enzymatically isolated lignin (EIL) requires a critical milling time which is shorter than that for obtaining maximum yields of BMWL. A procedure for isolation of the total lignin content from wood and pulps in the form of three fractions has been developed, giving a water soluble, low molecular carbohydrate-lignin complex by water extraction of ball-milled wood, a BMWL-carbohydrate complex by subsequent extraction with dioxane, and a EIL-carbohydrate complex by dioxane extraction of the residue after enzymic hydrolysis.