| 1. |
- Lindblad, M. S., et al.
(författare)
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New hemicellulose-based hydrogels
- 2004
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Ingår i: HEMICELLULOSES: SCIENCE AND TECHNOLOGY. - WASHINGTON : AMER CHEMICAL SOC. - 0841238421 ; , s. 347-359
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Konferensbidrag (refereegranskat)abstract
- Different kinds of hemicellulose-based hydrogels have been made by radical polymerization using hydrosoluble hemicellulose from spruce chips with a number-average molecular weight and polydispersity of 2400 and 1.5 respectively. 80% of the hemicellulose was galactoglucomannan. and the remainder mainly 4-O-methylglucuronoxylan. Hemicellulose/poly(2-hydroxyethyl methacrylate) based hydrogels were prepared by polymerization in water of 2-hydroxyethyl methacrylate with hemicellulose modified with well-defined amounts of methacrylic functions. The chemical modification of hemicellulose was performed in dimethyl sulfoxide using 2[(l-imidazolyl) formyloxy]ethyl methacrylate as modifying agent. The kinetics of the modification reaction were monitored by H-1 NMR. The degree of modification of the hemicellulose used for the hydrogel synthesis varied from 10% to 40%. The ratio of modified hemicellulose to 2-hydroxyethyl methacrylate in the hydrogels was 1: 1 by weight. The resulting hydrogels were elastic, homogeneous, soft, transparent and easily swollen in water.
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| 2. |
- Paananen, A., et al.
(författare)
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Interaction between cellulose and xylan : An atomic force microscope and quartz crystal microbalance study
- 2004
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Ingår i: Hemicellulose. - 0841238421 ; , s. 269-290
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Konferensbidrag (refereegranskat)abstract
- The atomic force microscope (AFM) colloidal probe technique has been used to investigate forces between cellulose beads as well as cellulose beads and mica in aqueous solution, and the interaction between cellulose surfaces in xylan solutions. Several observations of the behaviour of the cellulose beads were made. Swelling of the beads in aqueous solutions is rather slow. Thus, it is important to let the beads equilibrate before measurements. The beads are somewhat compressed when forced together to constant compliance, but relax back to their original shape in a few minutes. A long-range electrostatic repulsion between cellulose and mica occurs on approach. The xylan concentration in solution affects the forces between two cellulose surfaces. When the concentration increases from 10-100 mg/l more xylan adsorbs slowly and irreversibly on the cellulose leading to an increasingly long-range and stronger repulsion between the surfaces on approach. Adhesion between the layers is very low and seems to be due to entanglement of polymer chains. Studies of the adsorption of xylan (100 mg/l) on cellulose films with a quartz crystal microbalance with dissipation (QCM-D) verify that a thick, water-swollen layer of xylan is formed by slow adsorption. It has been proposed that adsorbed xylan on fibre surfaces increases paper strength. We conclude that this must be associated with the behaviour of the adsorbed layers of xylan on drying.
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| 3. |
- Stålbrand, Henrik, et al.
(författare)
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Isolation, characterization, and enzymatic hydrolysis of acetyl-galactoglucomannan from spruce (Picea abies)
- 2004
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Ingår i: Hemicelluloses. Science and Technology (ACS Symposium Series). - 0097-6156. - 9780841238428 - 0841238421 ; 864, s. 66-78
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Water-soluble hemicelluloses were extracted from spruce chips by heat-fractionation using microwave treatment. A screening of conditions (pH, temperature and residence time) was performed for the extraction of O-acetyl-galactoglucomannan (AcGGM). The yield and the average molecular weight of the extracted mannan were analysed using HPLC, size-exclusion chromatography (SEC) and mass-spectrometry. The pH during heat fractionation influenced the yield and the structure of AcGGM. The highest yield (78%) of AcGGM (average molecular weight 3800) was achieved with heat-fractionation in water at 190degrees C for 5 minutes. With 0.025% NaOH, an average molecular weight of 9500 was obtained at a yield of 30%. AcGGM molecular weight standard molecules were prepared using SEC. The structure of the AcGGM was determined using H-1-NMR. The enzymatic hydrolysis of AcGGM was studied using beta-mannanase and alpha-galactosidase.
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