Comparative study of Kenaf varieties and growing conditions and their effect on kraft pulp quality

Kenaf (Hibiscus cannabinus L.) is an annual plant which produces a very high fiber yield per hectare and has demonstrated to be a suitable material for pulping. The crop conditions influence fiber production, but there is no information about their effect on pulp quality. The aim of this work was to study the effect of kenaf varieties and crop conditions (watering dose and harvesting time) on sulfate pulp quality. The study has been made on bast fiber sulfate pulps due to their high added value. The quality criteria were fiber dimensions, chemical composition and pulp quality. Kenaf variety or crop conditions have significant effect on fiber dimensions, holocellulose content, kappa number and breaking strength. To obtain high fiber yield and good delignified pulps it is recommended to grow the Salvador variety and to employ advance harvesting. Received: 20 January 1999     

Acetic acid pulping of wheat straw under atmospheric pressure

Atmospheric acetic acid pulping of wheat straw was carried out. Pulping conditions and their effects on pulp properties were investigated in detail, and a comparison between acetic acid (AcOH) pulp and soda-anthraquinone (AQ) pulps of wheat straw was made of the chemical composition, strength, and fiber morphology of the pulps. Wheat straw was successfully pulped and fractionated into pulp (cellulose), acetic acid lignin, and sugars (monosaccharides from hemicellulose), making it easy to utilize them. It was found that among the pulping conditions the dosage of H₂SO₄ as catalyst was the most notable, and the extent and rate of delignification could be controlled by varying the amount of the catalyst. The results also showed that acetic acid pulp was quite different from soda-AQ pulp. About 70% of the ash or 90% of the silica in wheat straw were kept in AcOH pulp. The ash might function as filler and be beneficial to the printability of paper. It was known that many epidermal cells existed in AcOH pulp in bundles or in single cells. These ash-rich nonfiber cells seemed to hinder the bonding between fibers. AcOH pulp had lower strength than soda-AQ pulp, which might result mainly from the chemical damage of fibers caused by acid, not from the depolymerization of cellulose.Part of this paper was presented at the 65th Pulp and Paper Research Conference of Japan TAPPI, Tokyo, June 1998     

Steam explosion pretreatment used to remove hemicellulose to enhance the production of a eucalyptus organosolv dissolving pulp

The steam explosion (SE) pretreatment associated with the organosolv process was investigated to produce dissolving pulp from eucalyptus. Prehydrolysis Kraft (PHK) pulping was also done to produce viscose and acetate grade pulps as reference. The organosolv pulps were delignified in two steps with sodium chlorite. Viscose and acetate grade PHK pulps were bleached by OD₀(EH)D₁P and OD₀(EP)D₁PCCE sequences, respectively. Dilute acid-catalyzed (with acid addition) SE pretreatment dissolved more xylan than auto-catalyzed (no acid addition) SE pretreatment. Steam-exploded unbleached organosolv pulps showed lower residual lignin content and screened yield than unbleached organosolv pulps without SE pretreatment. Steam explosion pretreatment helped to decrease lignin content and damaged fiber length of unbleached organosolv pulps. The 1.0% H₂SO₄ organosolv pulp (organosolv dissolving pulp at bioconversion conditions) showed the highest reactivity. Even showing low viscosity for some applications, in general, the organosolv dissolving pulps produced in this study can be used for making lyocell fibers.     

On the selectivity of ozone delignification of softwood kraft pulps

Summary Ozonation of kraft pulp and oxygen-delignified kraft pulp in acetic acid/water mixtures has been studied at different pulp consistencies with and without an inhibitor to obtain information about the limitations of the selectivity of the ozone treatment. The experiments have been performed according to a full factorial design and data have been analysed by stepwise regression analysis. The results show that a better delignification selectivity can be achieved when ozone is applied in acetic acid media instead of conventional aqueous media. By combining conventional oxygen delignification and ozonation in acetic acid, pulps with equal strength properties and better optical properties compared to those of conventional O(DC)E prebleached pulps can be obtained. This study has also revealed that the reagent is utilized far more efficiently in ozonation at high pulp consistency (35%) than in ozonation at low consistency (1%), and that a similar selectivity can be achieved in both types of ozonation by choosing appropriate conditions. The greater selectivity of ozonation in acetic acid than in water is interpreted in terms of different stabilities of the oxidant in these reaction media. The relation between the formation of hydroxyl radicals and the extent and selectivity of delignification during ozonation has been investigated. The final bleaching of pulps prebleached with ozone in acetic acid medium has been studied. Two final bleaching sequences are presented, by which pulps with ISO brightness levels of 79% and 90% can be produced.The authors are indebted to the Swedish National Board for Technical Development (Styrelsen för Teknisk Utveckling) for financial support for this work and to STORA Technology for pulp tests and analyses     

The influence of acetosolv pulping conditions on the enzymatic hydrolysis of Eucalyptus pulps

Eucalyptus globulus wood was subjected first to HCl–catalysed delignification with 70% acetic acid under conditions realizing an incomplete 3 × 3 × 3 factorial design (HCl concentration 0, 0.025 or 0.05%; temperature 120, 140 or 160 °C; reaction time 1, 2.5 or 4 h), and then to enzymatic hydrolysis. The hydrolysis kinetics conformed to both Ghose's empirical model and a biexponential equation. The biexponential fit implies the presence of both readily and reluctantly hydrolysed cellulose fractions, and the fitted coefficients show hydrolysis yield to depend largely on the digestibility of the latter. Multiple regression of performance variables on pulping conditions showed that neither the rate nor the extent of hydrolysis is greatest for pulps with minimum lignin or xylose contents; we attribute this circumstance to the condensation and precipitation of lignin under severe pulping conditions, which protects the cellulose of the pulp from enzymatic attack. Received 20 June 1998     

Sulfuric acid bleaching of kraft pulp 1: Bleaching of hardwood and softwood kraft pulps

To develop a new nonchlorine bleaching technology, hardwood and softwood kraft pulps, before and after oxygen-alkali predelignification, were treated with dilute sulfuric acid solutions (pH 1.0-1.8) at 100°C for 1 h and then extracted with aqueous sodium hydroxide at 70°C for l h. Hardwood kraft pulp was successfully bleached. The delignification selectivity was similar to that seen with oxygen-alkali bleaching; and it was greatly enhanced by the addition of sodium nitrate and sodium nitrite. The sulfuric acid bleaching can replace the presently adopted oxygen and chlorine stages if the additives are allowed. This bleaching process was also effective for oxygen-bleached hardwood kraft pulp, but it was less effective for softwood kraft pulp and oxygen-bleached softwood kraft pulp. The effectiveness of the addition of sodium nitrate and sodium nitrite was more apparent for softwood kraft pulp than for hardwood kraft pulp.Part of this report was presented at the 7th International Symposium on Wood and Pulping Chemistry, Beijing, July 1993     

Residual extractives in aspen kraft pulps and their impact on kappa number and Klason lignin determination

We investigated the impact of residual extractives on lignin determination by lignin content difference between unextracted and extracted pulps, residual extractives analysis, and lignin content contribution from model extractive compounds. There were two different kinds of extractives in aspen kraft pulp. The extractives impacting on kappa number determination were well removed in oxygen delignification; these were mainly unsaturated fatty acids. However, the extractives impacting on Klason lignin determination were largely resistant to oxygen delignification; these were mainly saturated fatty acids, sterols, and hydrocarbons. Oxidation of unsaturated fatty acids was the main reaction in oxygen delignification. These trends were confirmed by simulation of lignin content determination with three model extractive compounds (β-sitosterol, linoleic acid, and palmitic acid). The publication of this article was made possible by an Emachu Research Fund. The authors are grateful for the fund.     

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     

Oxidative cleavage of lignin aromatics during chlorine bleaching of kraft pulp

Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted chlorine water (pH 5.7), by which chlorination under oxidation-favorable conditions was achieved, strongly supported the importance of the oxidation reaction by chlorine during delignification and lignin degradation. It was also suggested that methanol can be produced not only via catalytic hydrolysis by chlorine but via oxidative cleavage of the ether bond as well. The infrared spectrum of chlorolignins suggested that chlorine oxidation can open aromatic rings to muconic acid derivatives without cleaving ether bonding of the methoxyl group. No straight relation between the methoxyl content and the kappa number of chlorinated pulps was shown. The methoxyl content of bleached kraft pulps subjected to successive chlorination and alkali extraction showed a good relation with the kappa number. This means that almost all the portions of the oxidatively modified lignin structure were successfully removed during these treatments, and the aromatic structures of residual lignin in chlorinated and alkali-extracted pulps were thought to remain intact.Part of this paper was presented at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996; the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June 1999; and the 67th Pulp and Paper Research Conference, Tokyo, June 2000     

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。     

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.     

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.     

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     

p-TsOH对稻草的组分分离动力学及分离产物性质

在当前资源短缺和能源危机问题的背景下,用稻草等非木质纤维素原料制备生物质基材料等的研究备受重视。使用质量分数20%～60%的对甲苯磺酸,在60～80℃的反应温度、15～60 min的时间内对稻草进行组分分离,得到的纤维固体产物的得率基本在60%以上,灰分含量在10%以上。通过固体产物与废液等的化学成分分析,得到组分分离的脱木质素反应动力学曲线、半纤维素降解动力学曲线和反应动力学方程相应的参数值。分析了反应的联合脱木质素因子(CDF)跟固体产物的纤维组成、形态和表面电荷等之间的关系。根据反应剧烈程度,把CDF曲线分成3部分:当CDF值小于3 000 min·mol/L时,纤维分离不彻底;当CDF值为3 000～6 000 min·mol/L时,纤维分离程度较好;当CDF值大于6 000 min·mol/L时,纤维虽分离良好,但纤维断裂较多,碎片化严重。CDF因子越高,纤维表面Zeta电位绝对值越高,但红外光谱和羧基含量结果显示纤维的官能团类型没有变化。CDF曲线转折点附近的P30T80t30和P45T70t60条件下的纤维得到了有效的分离,并较好地保持了纤维形态,适用于造纸。     

Oxidation of bleached wood pulp by TEMPO/NaClO/NaClO2 system: effect of the oxidation conditions on carboxylate content and degree of polymerization

Oxidation of bleached wood pulp by the TEMPO/NaClO/NaClO₂ system was carried out at pH 3.5–6.8 and 25°–60°C with different amounts of NaClO, and investigated in terms of effects of the reaction conditions on carboxylate content and degree of polymerization (DP) of the oxidized pulp. Oxidation was accelerated by the addition of NaClO, when carried out at pH 6.8 and 40°–60°C. Addition of NaClO of more than 0.5 mmol per gram of the pulp was effective to accelerate the oxidation. Carboxylate content of pulp oxidized under such conditions increased to approximately 0.6 mmol/g within 6 h. Although DP of the oxidized pulp gradually decreased with oxidation time, no significant differences in DP of oxidized pulps were found at oxidation temperatures between 25° and 60°C, and DP values of more than 900 were maintained after oxidation for 54 h at 60°C.     

Industrial utilization of tobacco stalks II: preparation and characterization of tobacco pulp by steam explosion pulping

Our previous paper showed tobacco stalks to posses the characteristics of a raw material for pulp and paper application. It contains the major biomass constituents and cell components common to wood species. In this study, preparation and characterization of tobacco stalk pulp by steam explosion (SE) pulping at two chemical pretreatments were attempted. Chemical pretreatment prior to SE pulping improved the brightness, yield, and strength properties of the resulting tobacco SE pulps in the order: 6% Na₂SO₃ + 1% NaOH > 6% Na₂SO₃ > control (untreated). The 6% Na₂SO₃ + 1% NaOH-impregnated tobacco stalks produced SE pulps of good fiber length distribution and considerable properties that compare well with pulps from other raw materials obtained from previous studies, and the nonimpregnated ones showed strength properties superior to those of their poplar counterpart. Prior to bleaching, pretreating the tobacco stalk SE pulps with two stages, 2% NaOH at 90°C, improved the initial pulp brightness by about 5 points. Two-stage 6% H₂O₂ bleaching gave a comparable effect with hypochlorite bleaching for both tobacco and poplar, giving a 29–34 brightness point increase for tobacco SE pulp and 61 for the poplar samples. The differences in the bleaching responses for untreated tobacco and poplar SE pulps were attributed to the differences in their lignin structure, as shown in the total yield of their respective nitrobenzene oxidation products and FT-IR spectra. Tobacco SE pulps contain more of the guaiacyl-type lignin and poplar the syringyl-type lignin.This paper was presented in part during the 1998 CORESTA (Cooperation Centre for Scientific Research Relative to Tobacco) Congress, Brighton, UK, October 1998     

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。     

Effects of temperature on mechano-sorptive creep of delignified wood

The effects of temperature on mechano-sorptive (MS) creep of delignified hinoki wood (Chamaecyparis obtusa Endl.) were investigated using longitudinal (L) and radial (R) specimens during adsorption and desorption over the temperature range of 20°–80°C. The results were compared with those of stepwise delignified specimens tested at a constant temperature of 20°C. It was found that the effects of temperature on the MS creep of delignified specimens are more remarkable than for untreated specimens. The tendencies of increasing MS creep with temperature, delignification, and their combination were observed. The increase in MS creep for L specimens was relatively small and almost equal in both adsorption and desorption processes, while for R specimens the MS creep was small in desorption, but significantly different in adsorption. In addition, good correlation was observed between the MS coefficient (K) and instantaneous compliance (J ₀). The increase in MS creep occurs as a result of temperature increase or decrease in lignin content, or their interacting effects. However, in the case of desorption for R specimens, the increase of MS creep was unexpectedly small due to a remarkably increased J ₀. Part of this report was presented at the 15th Annual Meeting of the Chubu Branch of the Japan Wood Research Society in Fukui, October 2005     

Modeling of sapwood and heartwood delignification kinetics of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> using consecutive and simultaneous approaches

Eucalyptus globulus sapwood and heartwood were delignified at 130°, 150°, or 170°C by kraft pulping. Pulp yields of heartwood were lower than those of sapwood (46.5% vs. 50.4% at 170°C). Delignification was modeled using consecutive and simultaneous kinetic models. The modeling was similar for heartwood and sapwood, and either approach could be used, with both yielding good correlations between experimental and model data. The consecutive model identified two delignification phases with similar reaction rates and activation energies for heartwood and sapwood at 150° and 170°C. At 130°C only one phase was identified. Three reactive types of lignin fractions were identified using the simultaneous model, without differences between heartwood and sapwood. Their reaction rates were 0.152, 0.138, and 0.003 min⁻¹ at 170°C, and the activation energies were 132, 119, and 102 kJ.mol⁻¹. The presence of heartwood did not influence the kinetic development of delignification. The negative impact of heartwood in pulping is related to the higher content of extractives (9.8% vs. 3.9% in heartwood and sapwood) and to their influence on the process, namely in the heating-totemperature phase when a substantial mass loss occurs (30% vs. 20% for heartwood and sapwood).     

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007