| 1. |
- Buchert, J, et al.
(författare)
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Surface characterization of unbleached kraft pulps by enzymatic peeling and ESCA
- 1996
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 50, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- Specific enzymes hydrolyzing pulp carbohydrates can be used for characterization of pulp fibres. By combining enzymatic peeling of fibre hemicelluloses with novel techniques of surface analysis, such as ESCA, new information can be obtained on the location of different components, i.e. xylan, glucomannan and lignin on the fibre surfaces. In this work unbleached kraft pulps were selectively peeled with purified Trichoderna reesi xylanase and mannanase and the structural modifications caused by the removal of the hemicelluloses were analyzed with ESCA. The removal of the accessible portion of the pine kraft xylan increased the amount of surface lignin, whereas mannan removal had no effect on the amount of lignin on the surface. In the case of birch kraft pulp the removal of accessible xylan did not enhance the amount of lignin on the surface. However, in birch kraft pulp the removal of xylan decreased the amount of extractives covering the surface.
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| 2. |
- Carlsson, Peter, et al.
(författare)
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Optimization, a tool with which to create an effective drying schedule
- 1998
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 52:5, s. 530-540
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Tidskriftsartikel (refereegranskat)abstract
- A method for defining effective schedules for kiln drying of wood is presented. The method is designed in such a way that it proposes an optimized variation of temperature and humidity which yields the minimum total drying time, with the condition that the moisture content and the deformation not exceed specified limits after the drying and that the stress not exceeds a specified level at any time during the drying process in order to avoid crack development. To demonstrate the capability of the optimization method numerical results are presented. It should be noted that ill this first approach, drying starts from moisture content corresponding to the fibre-saturation point, i.e. approximate to 30%).
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| 3. |
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| 4. |
- Kifetew, G
(författare)
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The influence of the geometrical distribution of cell-wall tissues on the transverse anisotropic dimensional changes of softwood
- 1999
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 53:4, s. 347-349
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the geometrical distribution of cell-wall tissues on the transverse anisotropic dimensional changes of softwood has been studied using two isotropic models. A finite element model has been used to calculate the thermal expansion of two aluminium plates without and with holes in the two perpendicular directions. Moisture expansion measurements in the two perpendicular directions were conducted using a polyamide (PA6) plate containing several holes. No differences were found in either the thermal expansion of the aluminium plates or the moisture expansion of the PA6 plate between the two perpendicular directions. Thus, the investigation suggests that the geometrical distribution of cell-wall tissues has no effect on the transverse anisotropic shrinkage of softwood.
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| 8. |
- Oksman, Kristiina, et al.
(författare)
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Interaction between wood and synthetic polymers
- 1995
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 49:3, s. 249-254
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Tidskriftsartikel (refereegranskat)abstract
- The properties of wood composites consisting of low density polyethylene (LDPE) and wood flour (WF) were studied. In an attempt to improve the interfacial adhesion between hydrophobic LDPE matrix and the hydrophilic WF filler, a styrene-butadiene-styrene (SBS) copolymer was added as a compatibilizer. The interaction between LDPE and wood was investigated for PE/WF- and PE/WF/SBS-composites. The experimental measurements were conducted by conventional mechanical testing and Scanning Electron Microscopy (SEM). The interaction between polystyrene and wood in PS/WF composites was also studied by SEM and by Dynamic Mechanical Thermal Analysis (DMTA). PE/WF/SBS composites showed higher maximum tensile stress and strain at failure than the composites without SBS. SEM fractography confirmed better adhesion between the PE matrix and wood particles when SBS was present. DMTA measurements confirmed molecular interaction between PS and wood, the glass transition (Tg) peak of PS moved towards the Tg peak of cellulose
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| 9. |
- Oksman, Kristiina, et al.
(författare)
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The Influence of a SBS Compatibilizer in Polyethylene-Wood Flour Composites
- 1998
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 52:6, s. 661-666
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Tidskriftsartikel (refereegranskat)abstract
- A styrene-butadiene-styrene (SBS) block copolymer has been used as a compatibilizer in a low density polyethylene/wood flour (LDPE/WF) composite system. Dynamic mechanical thermal analysis (DMTA) and a transmission electron microscopy (TEM) were used to investigate the interfacial properties in the composites. A high resolution study of the composite microstructure, and especially of the interfaces between the wood particles and LDPE matrix, indicated that the SBS compatibilizer was located at the interface region between the wood particles and LDPE matrix and partially covered the wood particle surfaces. The SBS was also found in the LDPE matrix. The unsaturated part of the copolymer was stained with osmium(VIII)tetraoxide (OsO4) to enhance contrast and to allow it to be detectable in TEM. Dynamic mechanical measurements confirmed interaction between polystyrene (PS) and wood in the PE/PS/WF system. The tan d peak of PS was shifted about 10°C to a higher temperature and also broadened when wood flour was added in the LDPE/PS blend.
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| 12. |
- Rosenqvist, Marie
(författare)
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Localization of wood improvement compounds by microautoradiography and ESEM
- 1999
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 53:6, s. 648-654
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Tidskriftsartikel (refereegranskat)abstract
- Environmental-SvepElektronMikroskop, ESEM, har använts för att undersöka mikroautoradiogram av furusplint (Pinus silvestris L.) målad med en grundolja innehållande 14C-märkt alkyd. Mikroautoradiografi är en fotografisk metod som visar var ämnen märkta med radioaktiva isotoper finns i det undersökta materialet. De fotografiskt framkallade silverkornen i mikroautoradiogrammet visar var det märkta ämnet finns. Ej preparerade mikroautoradiogram undersöktes med ESEM, konventionella prepareringstekniker är tidsödande och kan orsaka oönskade artefakter. Det är bevisat att trästrukturen syns tydligt under den i huvudsak transparenta fotografiska filmen i mikroautoradiogrammet. Bilder framtagna med backscatter-detektorn hade hög kvalitet, silverkorn och trästruktur är synliga samtidigt och bilderna har nästan inga artefakter p g a uppladdningar, vilket inte är möjligt att uppnå med ett konventionellt SEM. Inträngning i trä undersökt med mikroautoradiografi kan sålunda enkelt utvärderas med ESEM.
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| 13. |
- Sandberg, Dick, 1967-
(författare)
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Weathering of Radial and Tangential Wood Surfaces of Pine and Spruce.
- 1999
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 53:4, s. 355-364
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Tidskriftsartikel (refereegranskat)abstract
- The development of cracks and changes in appearance have been investigated on radial and tangential surfaces of pine (Pinus silvestris L.) and spruce (Picea abies Karst.) which have been exposed outdoors for 33 months. The degradation of the surfaces has also been studied at the micro-level. Untreated samples, samples impregnated with a CCA-agent and samples surface treated with linseed oil have been tested. The annual ring orientation is the most important factor for crack development on weathering. The type of wood, impregnation treatment and surface treatment with linseed oil have only a marginal effect on the crack development. No relation has been found between the density of the samples and the crack development After 33 months of outdoor exposure, tangential surfaces of pine have 13 times more total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces is 6 times greater than on the radial surfaces. Tangential surfaces of both pine and spruce have a greater number of cracks per unit area and wider cracks than the corresponding radial surfaces. Tangential and radial surfaces show the same colour change in the surface as a result of weathering. On the micro-level, tangential surfaces have more and deeper cracks than radial surfaces. The cracks on the tangential surfaces occur frequently in both earlywood and latewood. On radial surfaces, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage. Decomposition of the cell wall takes place on both radial and tangential surfaces. Cracks arise which follow the S2 fibril orientation in the cell-wall. Delamination in the middle lamella is especially noticeable in the latewood on tangential surfaces. No differences have been observed regarding linseed oil treatment, impregnation or type of wood.
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