| 1. |
- Ekblad, C., et al.
(författare)
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Enzymatic-mechanical pulping of bast fibers from flax and hemp
- 2005
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 39:02-jan, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- A technique for pulping of bast fibers of flax (Linum usitatissimum) and hemp (Cannabis sativa), based on treatment with cellulolytic and pectinolytic enzymes has been developed. Initially the bast fibers were mechanically separated from shieves and subjected to washing with diluted acid, followed by enzyme treatment, an alkaline hydrogen peroxide bleaching step that also inactivated the enzymes, and finally beating in a laboratory beater. Brightness, dewatering and strength of handsheets were comparable with the traditionally-made pulps. Fibers not treated with enzymes could not be beaten. The main pulping effect is related to cellulases, but the presence of pectinases influenced both brightness and strength properties.
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| 2. |
- Henriksson, Gunnar, et al.
(författare)
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Migrating electron holes in lignin during wood biosynthesis and biodegradation - A hypothesis
- 2005
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 39:04-mar, s. 189-200
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Tidskriftsartikel (refereegranskat)abstract
- An unsolved question in biodegradation is how ligninases can oxidize the lignin structures that are located so deep inside the compact woody cell walls, that they are inaccessible for the enzyme, due to sterical restrictions. One explanation may be that ligninases generate small diffusible agents, redox mediators, that in turn perform lignin oxidation. Parts of the cell wall structure may nevertheless be too compact even for these, and some enzymes seem to interact directly with the lignin. The present paper discusses the hypothesis that the enzymatically generated aromatic radicals in lignin can oxidize other aromatic structures within the polymer. A chain-reaction may be therefore created, that allows the electron-holes to migrate, probably facilitated by some flexibility of the lignin. Thus, the eventual depolymerization of lignin may possibly occur far apart from the initial oxidation site. The migrating electron hole theory might be also applied on lignin biosynthesis.
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| 3. |
- Krusa, Martin, et al.
(författare)
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Pre-treatment of cellulose by cellobiose dehydrogenase increases the degradation rate by hydrolytic cellulases
- 2007
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 41:2-3, s. 105-111
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Tidskriftsartikel (refereegranskat)abstract
- Cellobiose dehydrogenase (CDH) is an extra-cellular flavocytochrome with unknown biological function, produced by various wood degrading fungi. In the presence of Fe(III) and cellobiose, CDH produces hydroxyl radicals through a Fenton-type reaction. Treatment of cellulose with CDH, cellobiose, hydrogen peroxide and ferriacetate decreased cellulose's polymerization degree and increased its degradability for different functional types of hydrolytic cellulases, except for an exo-enzyme working from the reducing end. This suggests a biological role for CDH in fungal cellulose degradation, possibly by activating the cellulose for hydrolytic cellulases by depolymerization and disturbance of the hydrogen bonding pattern in cellulose.
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| 4. |
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| 5. |
- Ondaral, Sedat, et al.
(författare)
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FIXATION OF DISSOLVED AND COLLOIDAL SUBSTANCES ON FIBERS AND SILICON OXIDE SURFACES USING WATER SOLUBLE CROSSLINKED CATIONIC POLYMERS
- 2008
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 42:1-3, s. 61-69
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of water soluble crosslinked cationic polymers (CCP) in the fixation of dissolved and colloidal substances (DCS) onto fibers was investigated. Two different types of CCP were synthesized by dispersion polymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC), with N,N'-methylene-bis-acrylamide (MBA) as a crosslinker. Relative turbidity, zeta potential and average diameter of the colloidal particles were determined to monitor their performance in DCS fixation. The results indicated that both polymers were able to fix a maximum amount of DCS particles onto fibers around a zero zeta potential, most probably clue to a patch-type flocculation mechanism. The conclusion reached was that flocculation was significant while the particles still had a negative zeta potential. The aggregation mechanism of a fiber-free DCS suspension occurred as Charge neutralisation, changed, by the addition of 10 mM NaCl to a patch-type mechanism. The CCPI consumption necessary to attain a maximum DCS removal was lower than the CCP2 consumption, as ascribed to the higher charge density and higher molecular mass of this polymer. The experiments performed on a quartz crystal microbalance equipment with dissipation (QCM-D) showed that the adsorbed charge and layer thickness of the polymers significantly affected fixation of the DCS particles onto the pre-adsorbed polymer layers on the SiO2 surface.
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| 6. |
- Stevanic Srndovic, Jasna, et al.
(författare)
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The primary cell wall studied by dynamic 2D FT-IR : Interaction among components in Norway spruce (Picea abies)
- 2006
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 40:9-10, s. 761-767
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge on the interactions among the wood polymers, viz. cellulose, hemicellulose, pectin, lignin and protein, in the outer fibre wall layers is essential for understanding fibre separation in thermomechanical and chemithermomechanical pulping processes. For this reason, dynamic two-dimensional Fourier Transform Infra-Red (2D FT-IR) spectroscopy was applied to examine the interaction of these components in the primary cell wall of spruce fibres. Sheets made of an enriched primary cell wall material were used for studying the viscoelastic response to loading. The dynamic 2D correlation FT-IR spectra indicated the existence of strong interactions between lignin and protein, as well as among pectin, xyloglucan and cellulose, in the primary cell wall. This is in contrast to the picture for the secondary cell wall, in which cellulose-glucomannan and xylan-lignin interactions are prevailing.
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| 7. |
- Sundqvist, Bror, et al.
(författare)
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Cellulose degradation during hydrothermal treatment of birch wood (Betula pubescens Ehrh.)
- 2006
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 40:3-4, s. 217-221
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Tidskriftsartikel (refereegranskat)abstract
- Study of cellulose degradation during wood's heat treatment showed a considerable degradation in both commercially and laboratory heat-treated wood samples, probably due to the low pH induced by the heat treatment. Experimental series were performed for investigating cellulose degradation in birch wood, at different pH levels and times, during heat treatments performed at pH values of 4, 7 and 10, for 3 and 6 hours at 180°C. The results show that the selected span of pH and time of treatment clearly affects the size of the cellulose molecules. Study of cellulose degradation involved intrinsic viscosity measurements on α-cellulose from the samples. As a result of heat treatment, viscosity drops from 1430 mL/g (untreated wood) to less than or equal 700 mL/g and less than or equal 350 mL/g, for durations of 3 and 6 hours, respectively. The wood buffered in an aqueous solution at pH 4 showed a drop in intrinsic viscosity around 880 mL/g, while a sample of commercial "thermowood" yielded an intrinsic viscosity of 732 mL/g. For neutral and alkaline pH values, the drop in viscosity is considerably lower. At pH values of 7 and 10, a 3 hr treatment had almost no effect on the degree of polymerisation, while a 6 hr treatment gave intrinsic viscosities around 1000 mL/g and 1216 mL/g, respectively. There is a distinct relation between cellulose's molecular size and wood's strength properties. The decrease in cellulose length in unbuffered systems may affect the strength properties of the treated wood. The experiments show that pH is an important factor to consider.
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