Mechanism of hemicellulose-directed prebleaching of kraft pulps

Paice, Michael G.; Gurnagul, N.; Page, D. H.; Jurášek, L.

doi:10.1016/0141-0229(92)90150-m

Cited by 104 publications

(45 citation statements)

References 6 publications

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“…In the absence of lignin, z-strength appears to depend almost exclusively on cellulose, while f-strength is apparently determined by properties of both cellulose and hemicelluloses. Thus, treatment of kraft pulps with xylanase reduced the DP of xylans, but had no effect on the z-strength (Paice et al 1992). In the wood matrix, hemicelluloses cover cellulose microfibrils and bind them together to form fibril aggregates (Fengel and Wegener 1984).…”

Section: Effect Of Magnesium Chloride On Tensile Strengthmentioning

confidence: 99%

Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood

et al. 2007

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The thin-veneer strip technique was applied to investigate the modifying effects of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) on the tensile strength of wood. Pinewood veneers treated with solutions of DMDHEU alone and in combination with magnesium chloride (MgCl 2 ) as a catalyst showed considerable strength losses of up to 50% in zero-span and up to 70% in finite-span testing modes. The higher strength losses in the latter case are due to hemicellulose degradation, which cannot be assessed in zero-span testing. Strength loss observed after treatment with DMDHEU and MgCl 2 was approximately as high as the sum of the strength losses determined after individual treatments with MgCl 2 or DMDHEU. Micrographs of veneers after finite-span testing revealed that catalysed DMDHEU treatment changed the predominant failure mode from interfibre fracture (in controls) to intrafibre fracture. The mechanism of strength loss resulting from treatment with DMDHEU is discussed.

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Section: Effect Of Magnesium Chloride On Tensile Strengthmentioning

confidence: 99%

Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood

et al. 2007

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“…Hemicellulase activity may remove lignin-carbohydrate complexes (LCCs) from the pulp fibers. The extraction stage after enzymatic prebleaching facilitates the dissolution of lignin-carbohydrate complexes (LCC) in pulp that were previously modified by enzymes but still remained in pulp because of their large molecular weight (Lal et al 2012;Singh et al 2010;Paice et al 1992). AOX in combined effluent of XODED and XOD(E OP )DP was reduced by 41.43% and 40%, respectively, compared to their respective controls.…”

Section: Resultsmentioning

confidence: 94%

Ecf and TCF Bleaching of Saccharum Officinerum-Co89003 Bagasse Soda-Aq Pulp With Alkali-Thermo-Tolerant Crude Xylanase From Coprinellus Disseminatus Sw-1 Ntcc1165

Agnihotri¹,

Dutt²,

Vidyarthi³

2012

BioResources

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An alkali-thermo-tolerant crude xylanase from Coprinellus disseminatus SW-1 NTCC1165 produced under solid-state fermentation conditions improves the brightness of sugarcane bagasse soda-AQ pulp by 7.3, 4.7, 6.1, and 8.2% in XODED, XOD(E OP )DP, OX(E OP )P, and XO(E OP )P bleaching sequences, respectively, at an enzyme dose of 8IU/g, a reaction time of 120 min, a consistency of 10%, and a pH of 6.4 at 55 o C. An improvement in brightness by 2.1% for pulp bleached by XO(E OP )P compared to OX(E OP )P sequence validates that xylanase treatment is more effective for hydrolysing lignin-carbohydrates complexes before oxygen treatment. AOX after XODED and XOD(E OP )DP sequences is reduced by 41.43 and 40%, respectively, compared to controls, but an increase in COD and color in studied bleaching sequences is attributable to the hydrolysis of hemicelluloses and the release of lignincarbohydrates complexes after xylanase treatment. Xylanase treatment modifies fibre surface by introducing cracks, peelings, swelling, and external fibrillation, which facilitates faster penetration of bleach chemicals by disrupting physical barriers, as revealed by scanning electron microscopy.

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“…Paice et al (1992) have found that xylanases are much more effective than mannanases in enhancing the bleaching of both hardwood and softwood pulps, despite that fact that xylans constitute only a small fraction of the hemicellulose in softwoods. Moreover, the efficacy of enzyme treatment was associated with a drop in the average DP rather than with the solubilization of xylan as such.…”

Section: Discussionmentioning

confidence: 99%

Chromophore release from kraft pulp by purified streptomyces roseiscleroticus xylanases

Patel

Grabski

Jeffries

1993

Appl Microbiol Biotechnol

103

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Treating kraft pulps with the crude xylanase from Streptomyces roseiscleroticus followed by alkali extraction reduces the kappa number in a linear manner with enzyme doses up to about 3 IU/gm of oven-dry pulp. The enzyme complex consists of four isoenzymes designated Xyll, Xyl2, Xyl3 and Xyl4. Each can release chromophores when used alone and each can facilitate alkali extraction to reduce the kappa number, but their relative abilities are different. Of the four isozymes, Xyl4 releases the least color and 237-nm-absorbing material whereas Xyl3 releases the most. Xyl4 best enhances the ability of alkali to reduce the kappa number. The UV absorption spectrum of the material released by alkali extraction differs significantly from the spectral characteristics of that released during enzyme treatment. The alkali-solubilized material has a maximum absorptivity at 265 nm and relatively little absorptivity at 237 nm. The material released during enzyme treatment • absorbs strongly at 205 and 237 nm. UV/VIS spectroscopy of the enzyme-or alkali-released material does not show a characteristic lignin peak at 280 nm, nor does it reveal any notable peaks in the visible region. Analysis of the material released by enzyme treatment revealed more than 40 product peaks after fractionation by reversed-phase HPLC. We observed many products with strong UV absorption. These were relatively hydrophilic. Fewer products absorbed in the visible region. These were more hydrophobic. All four isoenzymes exhibit endo-action patterns; none forms xylose from oatspelt xylan. The action patterns fell into two groups: endo-1 enzymes (Xyll and Xyl3) formed xylotriose (X3) and other lower oligosaccharides as the predominant products; endo-2 enzymes (Xyl2 and Xyl4)formed roughly equimolar amounts of X3, xylotetraose (X4), and xylopentaose (Xs), and tended to leave larger amounts of undigested higher oligosaccharides.

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Mechanism of hemicellulose-directed prebleaching of kraft pulps

Cited by 104 publications

References 6 publications

Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood

Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood

Ecf and TCF Bleaching of Saccharum Officinerum-Co89003 Bagasse Soda-Aq Pulp With Alkali-Thermo-Tolerant Crude Xylanase From Coprinellus Disseminatus Sw-1 Ntcc1165

Chromophore release from kraft pulp by purified streptomyces roseiscleroticus xylanases

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