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     

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.     

Distribution of chemical components in the walls of kraft and bisulphite pulp fibres

Summary Fines removed from the surfaces of Pinus radiata fibres by beating were identified and characterised in terms of microfibril orientations in the surfaces of beaten fibres. Fines fractions subjected to chemical analyses were selected so that chemical component data could be related to specific layers or lamellae in fibre walls.Carbohydrate distributions within the walls of kraft fibres differed from those in bisulphite fibres. In the kraft fibres, glucomannan increased and other hemicelluloses decreased from the primary wall to the outer lamellae of the S₂ layer of the secondary wall. In the bisulphite fibres, hemicelluloses were uniformly distributed throughout the outer wall layers, i. e., the primary wall and the S₁ and outer lamellae of the S₂ layers of the secondary wall. More galactan but less arabinan, xylan, and glucomannan were found in the outer layers than in the inner layers of the bisulphite fibres. Carbohydrate distributions were determined for a range of bisulphite pulp yields (53 to 80 percent).The outer layers of the bisulphite fibres contained more Klason lignin than the inner layers. Acid-soluble lignin contents were similar in the inner and outer layers.Helpful discussions with Dr. V. D. Harwood are gratefully acknowledged.     

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     

Biobleaching of unbleached and oxygen-bleached hardwood kraft pulp by culture filtrate containing manganese peroxidase and lignin peroxidase fromPhanerochaete chrysosporium

Unbleached and oxygen-bleached hardwood kraft pulp (UKP and OKP), respectively, were bleached with a culture filtrate containing manganese peroxidase (MnP) and lignin peroxidase (LiP) fromPhanerochaete chrysosporium Burds. The brightness increases of UKP upon biobleaching with the culture filtrate with and without MnSO₄ were the same. The brightness increase of OKP with MnSO₄ decreased to about half that seen without MnSO₄. Changes in the brightness of UKP and OKP by treatment with the culture filtrate were determined. The brightness increased sharply by about eight points during the first 3h. The 3-h treatment was repeated seven times. The brightness increased linearly with the bleaching of UKP. On bleaching of OKP, the brightness increased slowly and stopped at about 78%.Part of this report was presented at the 62nd Pulp and Paper Research Conference of the Japan Tappi, Tokyo, June 1995     

Development of high-retention water absorbent from cellulosic materials: water absorbent from bleached kraft pulp

This paper describes the synthesis of highretention water absorbents from kraft pulp and examination of their properties. A bleached kraft pulp from mixed hardwoods (LBKP) was carboxymethylated, then crosslinked with polyethylene glycol diglycidyl ethers (PEGDGE) with different degrees of polymerization under different conditions. A crosslinking agent with longer chain length might be advantageous for preparing a water absorbent with high water retention, and water retention could be improved at lower molar ratio of the crosslinking agent to the glucose unit. Isolation of carboxymethylated LBKP before crosslinking was advantageous for higher water absorbence. A water absorbent with a water retention value of as high as 500 times its weight was obtained.Part of this paper was presented at the annual meeting of the Society of Fibre Science and Technology, Tokyo, June 22–24, 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     

Rapid estimation of kraft pulp yield and lignin in Eucalyptus camaldulensis and Leucaena leucocephala by diffuse reflectance near-infrared spectroscopy (NIRS)

Near-infrared spectroscopy has been used to develop calibration models for the rapid determination of kraft pulp yield (KPY) and lignin in Eucalyptus camaldulensis and Leucaena leucocephala. The correlation coefficient for cross-validation is 0.90 for KPY and 0.95 for lignin prediction, while the root mean square error for cross-validation for KPY and lignin prediction are 1.46 and 0.77, respectively. The method has been validated with 37 samples of E. camaldulensis and 18 samples of L. leucocephala. The root mean square error of prediction for KPY (1.53) is higher than for lignin (0.77). The method is rapid and can be used for screening a large number of samples.     

Degradation of pine kraft lignin by Coriolopsis gallica growing on a fibre-glass support

Summary Coriolopsis gallica was grown in static liquid cultures on an inert support consisting of fibre-glass impregnated with Indulin AT (pine kraft lignin). The fungus developed well in such conditions enabling the study with the SEM of the morphology and penetration of the fungus. The method also pemits the recovery of degraded lignin, the characteristics of which was monitored by direct analysis of its elementary composition, methoxyls groups, and by spectroscopic techniques and gel permeation. Degraded lignin differed from sound lignin by its higher percentages of oxygen, and lower percentages of C, H, and OCH₃ was richer in oxygen. The IR and vis-UV spectra as well as the fractionation by gel filtration showed that the structure of the lignin incubated in the presence of the fungus had been modified.     

Sulfuric acid bleaching of kraft pulp III: reactivity of kraft pulping-resistant structures under acidic conditions

To investigate the bleaching mechanism, a lignincarbohydrate complex (LCC) model compound, a vinyl ether-type lignin model dimer, and a hexeneuronic acid model compound were treated with dilute sulfuric acid of different pHs. Beech kraft pulp and red pine kraft pulp were also treated with dilute sulfuric acid and then extracted with aqueous alkali. The amount of hexeneuronic acid degradation products in acid effluents and lignin dissolved in alkali effluents were determined. It was found that the benzyl ether-type LCC bond and the vinyl ether bond in lignin were effectively cleaved under the pH where sulfuric acid bleaching of kraft pulp was effective. Hexeneuronic acid group was also effectively degraded during sulfuric acid bleaching. In beech kraft pulp bleaching, both lignin removal and hexeneuronic acid removal contributed to the kappa number reduction. In red pine bleaching, the contribution of hexeneuronic acid removal was negligible, and most of the kappa number reduction was achieved by the lignin removal.Part of this report was presented at the 9th International Symposium on Wood and Pulping Chemistry, Montreal, July 1997     

Screening of wood-rotting fungi for kraft pulp bleaching by the Poly R decolorization test and biobleaching of hardwood kraft pulp byPhanerochaete crassa WD1694

From among 419 wood-rotting fungi 10 were selected by the Poly R decolorization test, and their ability to bleach hardwood kraft pulp was assayed. Of the 10 selected, 6 fungi (i.e.,Phanerochaete crassa WD1694 and F150;Pleurotus pulmonarius PSC-H, PSC-M, and PSC-T;and Pleurotus species A119) showed much higher bleaching ability thanPhanerochaete chrysosponum BKMF1767 orTrametes versicolor WD1670, both of which are well-known high ligninolytic fungi.P. crassa WD1694 had the highest bleaching ability among the selected strains, and it increased the pulp brightness from 28 to 54, with a corresponding decrease in kappa number from 16 to 6 after 10 days of cultivation and alkali extraction. MnP was a predominant ligninolytic enzyme ofP. crassa WD1694 during the biobleaching.This research was presented in part at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Reduction of aluminum toxicity to radish by alkaline oxygen treated kraft lignin

To obtain a soil-conditioning agent for acid soil containing excess aluminum ions (AL), kraft lignin was modified by alkaline oxygen treatment. The growth of radish root in solution and in soil containing AL with or without addition of these lignins under controlled pH was examined. We concluded the following. Growth inhibition of radish roots by AL can be removed by adding alkaline oxygentreated lignins in the range of pH 4.5–4.8 in soil. A similar result was obtained at pH 4.5 in a culture solution. The reduction of AL toxicity to plant may be due to the aggregation between AL and the modified lignin at low concentrations of modified lignin because soluble AL could not be detected. On other hand, elongation of radish root was not obviously inhibited, although the soluble AL in the solution culture was at an extremely high level when the dosage of a modified lignin was high. This suggests that the reduction in AL toxicity to plants was due to formation of a complex between AL and acidic groups of the modified lignin.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999 and the 44th Lignin Symposium, Gifu, October 1999     

Empirical modeling of chlorine dioxide delignification of oxygen-delignified hardwood kraft pulp

Due to the complexity of delignification, it is still not accurate enough to describe the whole chlorine dioxide delignification system with mechanistic models such as kinetic studies. The simple aim of predicting and optimizing the process requires the use of economical empirical models, few of which are in the literature. In this study, principal component analysis was used to classify various bleaching response variables, including end pH, kappa number, viscosity, and optical properties such as brightness, into different categories. Statistical methods, including factorial design, multiple regression, and response surface methodology, were then used successfully to screen the importance of bleaching factors and their interactions. Models to control, predicate, and optimize the bleaching responses were established. In most cases, the results of empirical modeling coincided well with those from conventional research methods, but the empirical methodology was more economic or less laborious. The empirical models are robust enough to predicate and optimize the bleaching responses to chlorine dioxide delignification of oxygen-delignified hardwood kraft pulp.     

Modification of softwood kraft pulp with carboxymethyl cellulose and cationic surfactants

An elemental chlorine-free (ECF)-bleached soft-wood kraft pulp was treated first with a carboxymethyl cellulose (CMC, degree of substitution 0.3, 1% on pulp) and then with alkyltrimethylammonium bromides (alkyl chain lengths of C₁₀ to C₁₆). Surprisingly, the treatment with dodecyltrimethylammonium bromide (C₁₂TAB) markedly increased the internal and tensile strengths of the handsheets prepared from the modified pulp. Environmental scanning electron microscopy (ESEM) showed that these properties could be partly explained by the “rope/gum-like” bridges that were formed between the fibers.     

Mechanism of detoxification of aluminum ions by kraft lignin treated with alkaline oxygen

 Kraft lignins modified by radical sulfonation or alkaline oxygen treatment were rich in acidic groups, such as sulfonic acid, carboxylic acid, and phenolic hydroxyl groups, and were effective as soil-conditioning agents, especially because of their ability to trap aluminum ions eluted from soil under acidic conditions. Formation of complexes between aluminum ions and modified lignins was examined using potentiometric titration and ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Changes in the titration curve of a modified lignin by the addition of aluminum ions suggest the release of protons after the formation of complexes between them. Disappearance of ²⁷Al-NMR signals assigned to various aluminum ions by the addition of kraft lignin treated with alkaline oxygen was also attributed to the formation of complexes. The relative ease of proton release because of complex formation between a modified lignin and metal ions was as follows: Fe³⁺ > Al³⁺ > Cu²⁺ > Pb²⁺ > Mn²⁺ > Ca²⁺. This indicates that aluminum complexes are quite stable, and the aluminum ion is not exchanged with cations other than Fe³⁺. Received: October 24, 2001 / Accepted: January 16, 2002 Present address: Asian Natural Environmental Science Center, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan Tel. +81-3-5841-7506; Fax +81-3-5841-5230 e-mail: ukyoko@mail.ecc.u-tokyo.ac.jp Part of this study was presented at the 11th International Symposium on Wood and Pulping Chemistry, Nice, June 2001 Correspondence to:K.S. Katsumata     

Effects of site on fibre, kraft pulp and handsheet properties of Eucalyptus globulus

? Eight-year old trees from two Eucalyptus globulus Labill. clones planted across three different sites in Tasmania, Australia, were sampled for wood and kraft pulp/handsheet properties.

? Site had a significant effect on all measured properties. Compared with the poor site (Parkham) the wood from the good site (West Ridgley) had on average 11 % lower wood density. The poor site had also greater microfibril angles, shorter fibres at lower pulp yields.

? The handsheets produced with pulp from the poor site resulted in comparatively higher bulkiness, lower burst, lower tear and tensile indices, lower zero span tensile strength, but higher opacity, higher light scattering and higher surface roughness. Significant height effects were found with all wood properties, and also with tear index, zero span tensile strength and opacity.

? Discriminant analysis showed that for 76 out of 100 handsheets the raw material source, i.e. growth site, could be predicted correctly using a set of handsheet properties with tear index and bulk index being most prominent.

? This is unique evidence that site conditions are strongly reflected in handsheet properties produced from Eucalyptus pulp.

     

木质素合成关键酶基因与造纸植物转基因改良应用研究

木质素是自然界数量仅次于纤维素的自然有机物质,但在造纸业中是主要的污染来源。木质素生物合成过程十分复杂,涉及了大量酶体系。综述了木质素合成途径中的关键调控酶特性及其基因调控情况,从培育低木质素、易降解木质素的造纸植物为出发点,分析了这些关键基因在转基因造纸植物应用中的潜力和存在的主要问题,并提出了应从改变植物体内木质素含量、改变木质素单体构成比例这两个方面进行转基因的研究思路。     

Gremmeniella-infected Pinus contorta as raw material in the production of kraft pulp

Pinus contorta, logs with occluded cankers caused by the pathogen Gremmeniella abietina, as well as logs from unaffected trees were sampled from a 23-year-old plantation in Sweden and compared in terms of their paper properties. Damaged wood gave kraft pulp with poor paper properties: it required a larger amount of beating energy and resulted in paper with low tear strength, air permeability, tensile stiffness, burst strength, and poor light-scattering properties. However, small amounts of damaged wood mixed in with a large amount of healthy wood can pass almost unnoticed. The use of trees with a larger content of damaged wood will lead to serious processing problems and give a pulp with poor paper properties. Thus, wood damaged by Gremmeniella should be sorted out and classed as low-grade raw material.