Sulfuric acid bleaching of kraft pulp II: Behavior of lignin and carbohydrate during sulfuric acid bleaching

The purpose of this study was to investigate the behavior of lignin and carbohydrates in kraft pulps during sulfuric acid bleaching. Beech kraft pulp and red pine kraft pulp were bleached with dilute sulfuric acid at pH 1.3 with addition of sodium nitrate and sodium nitrite at 100°C for 1 h. The pulps were then extracted with aqueous sodium hydroxide solution at 70°C for 1 h. Lignin and carbohydrates in the acid effluents and the alkali effluents were analyzed. The carbohydrate compositions of unbleached and bleached kraft pulps were also determined. The residual lignin in kraft pulp was degraded to a molecular size similar to that of milled wood lignin during sulfuric acid bleaching without additives, and it was further degraded to a much smaller molecular size during sulfuric acid bleaching with additives. It was found that the amount of carbohydrate dissolved in the bleach effluents were only about 1 of the dry weight of the kraft pulp under these bleaching conditions. The carbohydrates dissolved during bleaching were mostly of hemicellulose origin.Part of this report was presented at the 8th International Symposium on Wood and Pulping Chemistry, Helsinki, July 1995     

Influence of carboxyl group on the acid hydrolysis of cellulose

Cellulose isolated from wood is more susceptible than cotton cellulose to homogeneous hydrolysis in phosphoric acid. The influence of carboxyl group introduction at the C6 position on the hydrolysis rate of cellulose in 82.5% phosphoric acid was studied as a model of the oxidation of cellulose during pulping. The rate constant of hydrolysis for dissolving pulp was larger than that of cotton cellulose at temperatures of 25°–35°C. Mercerized cotton cellulose was partially oxidized regioselectively at the C6 position by a free radical system using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The oxidized cellulose was obtained at a range of 1.7–12.7 mEq carboxyl content per 100 g of cellulose. The hydrolysis rate of the oxidized cellulose samples accelerated with increasing carboxyl content in the samples.Part of this work was presented at the 5th Annual Meeting of the Cellulose Society of Japan, Kyoto, July 1998     

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.     

Influence of the chemical composition of kenaf bast and core on the alkaline pulping response

The bast and core of kenaf,Hibiscus cannabinus L., have markedly different chemical components and alkaline cooking responses. The bast had about double the hot-water extractives content and only about half the lignin content of the core. The core contained a large amount of hemicellulose, mostly composed of xylan. The lignin structures of bast and core were also quite different: The former had a significant abundance of syringyl structures. Evidence showed that the bast was much more easily delignified than the core. When the bast and core were cooked together in alkaline condition, the pulp yields at the same kappa number were higher than those of the individual pulpings of bast and core. The bast-core pulping gave a positive effect on the yield of bast pulp in the sodaanthraquinone and kraft pulpings. On the other hand, kenaf was abundant in the hot water extractives. These extractives consumed alkali during cooking to a relatively large extent but acted as a protector of hemicellulose and slightly increased the pulp yields.Part of this paper was presented at the 48th and 49th Annual Meetings of the Japan Wood Research Society, Shizuoka, April 3–5, 1998 and Tokyo, April 3–5, 1999     

Thermo-mechano-chemical pretreatment of wood in a process development unit

Summary Continuous thermo-mechano-chemical pretreatment of wood (particle size: 0.25–0.50 mm) was conducted by steam injection for rapid heating-up of slurry (170–215°C), flow through homogenization valves (mechanical effects), and autohydrolysis in a plug flow reactor (90–95 s) (thermochemical reactions). The process was carried out in aqueous phase without addition of any chemicals. Residues resulting from the pretreatment were characterized by thermal and elemental analyses. The extent and selectivity (hemicellulose removal and delignification) of the wood solubilization were analyzed as a function of pretreatment temperature and the thermal severity factor, the goal being the optimization of hemicellulose dissolution. Experimental results were compared with those previously obtained in a batch cascade reactor system.Thanks are due to the Natural Science and Engineering Research Council (NSERC) of Canada and the Fonds pour la formation de chercheurs et l'aide à la recherche (FCAR) of Quebec for financial support. The author wishes to express his gratitude to the Université de Sherbrooke, Canada, where experimental trials were carried out     

Wood-to-bark adhesion of subalpine fir (<Emphasis Type="Italic"> Abies lasiocarpa</Emphasis>) in extreme temperatures

Wood-to-bark adhesion strengths were tested at 25 to –78°C under moisture contents of 0–200%. The freezing temperature of the cambium appeared to be between –20 and –40°C. The low freezing temperature was assumed to be due to the high pectin and protein contents in the cambium cells. At temperatures above the freezing point of the cambium (–20 to 25°C), the adhesion strength was curvilinearly and negatively related to moisture content. At temperatures below the freezing point of the cambium (–40 to –78°C), adhesion strength was not correlated with moisture content. For practical application, maintaining logs at high moisture content and temperatures above –20°C would assure a good debarking and yield high quality wood chips for pulping, with less wood loss to hog fuel.     

Enzymatic hydrolysis of wood with alkaline treatment

Pulverized samples of wood, cedar and eucalyptus were treated with 5 N NaOH solutions at 25–150 °C. Hemicellulose and lignin content in the samples decreased with increasing treatment temperatures, while the recovery of glucose was maintained at nearly 90 %. X-ray diffraction analysis showed that the content of the original cellulose I structure in the samples decreased with increasing temperature, and most of the cellulose in the sample treated at 150 °C was converted to cellulose II by mercerization. Enzymatic hydrolysis of the alkaline-treated samples was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The samples treated at higher temperatures showed better enzymatic degradability. Treatment with an alkaline solution of lower concentration (1 N NaOH) at 150 °C was also used. Despite significant quantities of hemicellulose and lignin being removed, mercerization was not induced. The enzymatic degradability was much lower than that of the sample treated with a 5 N NaOH solution at 150 °C. Thus, treatment with concentrated alkaline solution at high temperature led to not only the removal of hemicellulose and lignin, but also to modification of the cellulose structure, which resulted in high efficiency of enzymatic saccharification of the wood samples.     

Lignin-carbohydrate bonds in a residual soda spruce pulp lignin

Summary The behaviour of lignin-polysaccharide complex of spruce wood in soda pulping was studied by the characterization of lignin-saccharide fractions isolated from a series of soda pulps. The dioxane pulp lignins contain 8–14% of carbohydrates in which glucose was the predominant component. Its content increased with increasing degree of delignification indicating the formation of secondary lignin-carbohydrate linkage. Both glycosidic and ether type of bond between residual lignin and cellulose in pulp was proved by methylation analysis of the pulp dioxane lignin.The work was supported by the Slovak Academy of Sciences grant number 2/999389/92.     

Acid prehydrolysis of pinus pinaster bark with dilute sulfuric acid

Summary The influence of temperature (100–150°C) and acid concentration (0–5 wt%) on the prehydrolysis of pine bark and its alkaline-extracted residues was studied (the latter were obtained by vigorously stirring the bark for 15 min with a solid/liquid ratio of 1:10). Optimal prehydrolysis conditions were established by the sectioning method with a solid/liquid ratio of 1:10. For milled bark these conditions were: temperature 125°C, sulphuric acid concentration 2 wt%, duration of prehydrolysis 4.5 h; and for alkali-extracted residues, temperature 125°C, sulphuric acid concentration 3 wt%, duration of prehydrolysis 5 h. These treatments removed respectively 90% and 75% of non-glucose sugars in the hydrolysate while solubilizing less than 20% (respectively 10%) of the potential glucose yield. Enzymatic digestion of bark successively alkali-extracted and prehydrolysed under optimal conditions gave poor results, with yields similar to those obtained after other pretreatments.This work was supported by the CAICYT (Pr. 0030/85)     

Lignin distribution in spruce (Picea abies) determined by mercurization with SEM-EDXA technique

Summary The lignin distribution between the middle lamella and the cell wall of spruce fibers has been determined by a new technique based on a mercurization of the lignin and a concomitant determination of mercury by the SEM-EDXA technique. The ratio of lignin in the middle lamella at the cell corners to the lignin in the secondary wall was 2.5±0.6 for latewood and 2.4±0.6 for earlywood. This gives a lignin content of 55–58% in the true middle lamella in the cell corners. The reactivity to mercuric acetate of different wood elements was determined in separate experiments. Fractions enriched in ray cells, middle lamella, and compression wood all reacted at the same rate as the whole wood; about one mole of mercury was incorporated per mole of lignin (C₉-unit).     

Differential calometric analysis of wood and wood components

Summary The prolysis of cellulose, hemicelluloses, lignin preparations, and wood was studied by differential calorimetric analysis (DCA) for the range of 25° to 800° C. The test samples included powdered and filter paper celluloses; hardwood xylan; softwood galactoglucomannans, compression wood galactan, and arabinogalactan; a synthetic (DHP), sulfuric acid, Björkman, Brownell, and cellulase lignins; and unextracted and extracted hardwoods and softwoods. Heats of reaction were determined from the DCA thermal transition areas. Distinct differences were found between the thermograms of each hemicellulose and lignin sample. Although wood species could not be separated thermally, hardwood and softwood thermograms differed because of the hemicellulose degradation pattern.Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the U.S. Department of Agriculture.Formerly Research Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture. The Laboratory is maintained at Madison, Wis. 53705, in cooperation with the University of Wisconsin. Present address: The Pennsylvania State University, University Park, Pennsylvania 16802.     

Changes of chemical properties and the water vapour sorption of <Emphasis Type="Italic">Eucalyptus pellita</Emphasis> wood thermally modified in vacuum

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.     

Proportion of above-ground biomass in commercial logs and residues following the harvest of five commercial forest species in Australia

A significant factor influencing the contribution of wood products to carbon (C) storage is the proportion of above-ground tree biomass (AGB) recovered in commercial logs at harvest. This study examined the proportion of AGB in logs and residues at the harvest of radiata pine, cypress pine, blackbutt, spotted gum and messmate. Messmate and spotted gum had the highest variation in stem diameter and height. The average AGB ranged from 2000 to 3000 kg for the hardwoods and 220–1000 kg for the softwoods. Blackbutt had the overall lowest proportion of AGB recovered in commercial logs (45.5%) and radiata pine the highest (65%). The proportion of AGB in the bark of the hardwoods was significantly lower than in the softwoods. The proportion of the AGB in forest residues following harvest ranged from 30 to 55% depending on the species.The proportion of AGB recovered in high quality commercial logs ranged from 15% for spotted gum to 63% for radiata pine. The differences were due to the natural characteristics of the selected species and variations in regional market availability. The highest retention rates of AGB in high quality hardwood commercial logs were obtained for trees with DBH between 500 and 600 mm (messmate and blackbutt) and greater than 600 mm for spotted gum.The mean moisture content of the wood of the different species ranged from 35 to 50%. Messmate and radiata pine logs had the highest moisture content (48 and 50%, respectively).The C concentration of blackbutt, radiata pine and cypress pine was slightly higher than 50%. The softwoods had significantly higher C concentration than the hardwoods. The C concentration between positions (cross-section, sapwood and heartwood) also varied for the different species.The highest proportion of the above-ground C was in the debarked log for all species with the exception of blackbutt.The cellulose concentration of the wood ranged from 56 to 64% for hardwoods and 40–52% for the two softwoods. The lignin concentration of the wood ranged from 16 to 19% for the hardwoods and 25–35% for the two softwoods. The hardwood species could not be distinguished from one another based on the cellulose, hemicellulose and lignin concentration, but within the softwood species, cypress pine and radiata pine formed separate clusters.     

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin III: effects of sodium chlorite treatment

To obtain high-strength phenol–formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, we investigated the effects of sodium chlorite (NaClO₂) treatment on wood prior to low molecular weight PF resin impregnation. Sawn veneers of Japanese cedar (Cryptomeria japonica) were treated with 2% aqueous NaClO₂ solution at 45°C for 12 h to remove lignin, and the process was repeated up to four times, resulting in weight loss of 21%. NaClO₂ treatment has shown considerable potential for high compression of PF resin-impregnated wood at low pressing pressure, especially after adding moisture to a content of 10%–11%. This deformation is further enhanced during pressure holding by creep deformation. The density, Young’s modulus, and bending strength of PF resin-impregnated veneer laminated composites that were treated with NaClO₂ four times and compressed at 1 MPa, reached 1.15 g/cm³, 27 GPa, and 280 MPa, respectively. The values in untreated PF resin-impregnated wood reached 0.8 g/cm³, 16 GPa, and 165 MPa, respectively.     

Recent progress in the chemistry and topochemistry of compression wood

Summary A review of the chemistry and topochemistry of compression wood with 200 references. Compression wood contains on the average 30% cellulose, 35–40% lignin, 10% galactan, 9% galactoglucomannan, 8% xylan, and 2% of a 1,3-glucan (laricinan). The cellulose is less crystalline, and the xylan has fewer arabinose side chains than in normal wood. The lignin is composed of guaiacylpropane and p-hydroxyphenylpropane units. It is more condensed, has a higher proportion of carbon-carbon bonds, and contains fewer arylglycerol--aryl ether structures than a normal conifer lignin. The ray cells and the primary wall of the tracheids have the same chemical composition in normal and compression woods. The galactan is largely located in the outer region of the secondary wall. Only 5–10% of the lignin in compression wood tracheids is extracellular. The middle lamella is less lignified than in normal wood, while the S₁ and inner S₂ layers have a lignin concentration of 30–40% which is twice as high as in normal wood. The lignin content of the S₂ (L) layer is equal to or higher than that of the intercellular region along the wall. The review is concluded with a brief reference to areas where present information is incomplete or lacking.A portion of an Academy Lecture of the International Academy of Wood Science, presented at the International Symposium on Wood and Pulping Chemistry (Ekmandagarna 1981), held in Stockholm, Sweden, June 9–12, 1981. Reprints of the unabridged review, published under the title Recent Progress in the Chemistry, Ultrastructure, and Formation of Compression Wood in the preprints of the symposium (SPCI Report 38, Vol. 1, p. 99–147) are available from the author. I wish to express my gratitude to my colleague Professor Robert A. Zabel for generous travel assistance     

The optimum temperature–humidity combination for the feeding activities of Japanese subterranean termites

Two species of Japanese subterranean termite, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), were used in an investigation of the optimum temperature–relative humidity (RH) combination for their feeding activities. Daily wood consumption per worker and survivals were measured, and the protozoan fauna in the hindgut were observed under 15 temperature–RH combinations for 1 week. Five temperatures (20°, 25°, 30°, 35°, and 40°C) and three RH conditions (50%, 70%, and 90% RH) were examined. The activities of the workers were highest at around 30°C for both species, and workers died at 40°C within 5 days and 2 days for C. formosanus and R. speratus, respectively. The optimum RH condition for feeding activity was 90% RH for C. formosanus and 70%–90% RH for R. speratus. The optimum temperature–RH combinations for feeding activities were 30°C at 90% RH for C. formosanus and 30°C at 70%–90% RH for R. speratus.     

13C CP/MAS nuclear magnetic resonance study of the peroxide bleaching of ultra high yield chemimechanical pulp produced from sound and spruce budworm killed balsam fir

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     

Vibrational properties of Sitka spruce heat-treated in nitrogen gas

Sitka spruce (Picea sitchensis Carr.) wood was heated for 0.5–16.Oh at temperatures of 120°–200°C in nitrogen gas or air. The values for Young's modulus, shear modulus, and loss tangent were measured by free-free flexural vibration tests. X-ray diffractometry was carried out to estimate the crystallinity index and crystallite width. The results obtained are as follows: (1) Density decreased at higher temperatures and longer heating times. The specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width increased during the initial stage and were constant after this stage at 120°C and 160°C, whereas they increased during the initial stage and decreased later when the temperature was high. Loss tangent in the longitudinal direction increased under all conditions, whereas that in the radial direction increased at 120°C and decreased at 160°C and 200°C. (2) From the relation between Young's modulus and moisture content, it can be safely said that Young's modulus is increased by the crystallization and the decrement in equilibrium moisture content, and that crystallization (rather than degradation) is predominant at the initial stage of the heat treatment, whereas the latter is predominant as the heating time increases. (3) It is implied that the specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width decreased more in air than in nitrogen gas because of oxidation in air.This study was presented in part at the 43th Annual Meeting of Japan Wood Research Society at Morioka, August 1993, the 44th Annual Meeting of Japan Wood Research Society at Nara, April 1994, and the 45th Annual Meeting of Japan Wood Research Society at Tokyo, April 1995     

Mechanical properties of wood swollen in organic liquids with two or more functional groups for hydrogen bonding in a molecule

The modulus of elasticity and the modulus of rupture during static bending in the radial direction, and the viscoelastic properties in the radial direction in the temperature range 20°–100°C of hinoki (Chamaecyparis obtusa) swollen in organic liquids with two or more functional groups in a molecule were compared with those of wood swollen by moisture. The wood swollen in organic liquids in or near the swelling equilibrium, but not that swollen in organic liquids distant from the swelling equilibrium, showed higher moduli of elasticity and rupture than the wood swollen to a similar degree by moisture. This suggests that wood exists in an unstable state as it approaches the swelling equilibrium, rendering it highly flexible and weak. During the first viscoelastic measurements for wood swollen in various organic liquids, thermal softening was observed in 40°–60°C range and above 80°C, though this softening disappeared during the second measurement. The softening observed in the 40°–60°C range and above 80°C was thought to have been caused by the redistribution of liquid toward the equilibrium state at a higher temperature and the swelling accompanying an elevated temperature, respectively.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

草木半纤维素的研究进展

结合前人的研究成果综述了各种草木原料中半纤维素的类型、结构形式及制备方法,特别指出在造纸原料和纸浆中存在部分半纤维素与木质素发生化学键连接形成了木质素-碳水化合物复合体(LCC),还对纸浆中的半纤维素对浆性能所产生的影响加以阐述,针对半纤维素在造纸工业中所引起的"假木质素"问题总结出相应的应对策略.此外,还概述了从草木原料中制备粗半纤维素的分离方法以及对其进一步纯化的技术,对半纤维素的检测手段也做了介绍.