Kristoffer Segerholm

Micromorphological studies of modified wood using a surface preparation technique based on ultraviolet laser ablation.

Abstract The objective of this paper is to demonstrate an ultraviolet (UV) laser ablation technique as a tool for sample preparation in microscopy studies of modified wood. Improved techniques for studying the microstructure of modified wood are crucial for a deeper understanding of many of their physical, mechanical and durability properties. The surface preparation technique is described in this paper. An illustration of micrographs of the micromorphology and polymer distribution in some examples of modified wood is also presented. It is clearly demonstrated that in contrast to conventional surface preparation techniques used for light microscopy and scanning electron microscopy, i.e. razor blade and microtome cutting techniques, UV laser ablation does not introduce any mechanically induced microcracks and redistribution of polymers or other mobile substances in the prepared surface. Results also show that, in particular, this technique seems to be suitable for studying polymer distribution in resin-impregnated wood, as well as detection of microcracks in modified wood cell walls.

Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst).

The objective of this work was to study the hygroscopicity and surface chemical composition of thermally modified (TM) spruce. An effort was also made to study if those features were influenced by a previous exposure to a significant increase in relative humidity (RH). TM and unmodified Norway spruce (Picea abies Karst) samples, both in solid and ground form, were prepared. Water vapour sorption characteristics of the ground samples were obtained by measuring sorption isotherms using a dynamic vapour sorption (DVS). The surface chemical composition of the solid samples, both acetone extracted and non-extracted, were analysed using X-ray photoelectron spectroscopy (XPS). The DVS analysis indicated that the TM wood exposed to the 75% RH revealed a decrease in isotherm hysteresis. The XPS analysis indicated a decrease of acetone extractable or volatile organic components and a relative increase of non-extractable components for the samples exposed to the increased RH condition.

Wettability of acetylated Southern yellow pine

Abstract The aim of this work was to achieve a better understanding of the wettability, i.e. liquids wetting and sorption characteristics (or penetrability), of acetylated Southern yellow pine (SYP) including probable differences in such characteristics between early- or latewood. Matched samples of acetylated and untreated SYP boards were prepared. The wettability of the samples were measured by the Wilhelmy technique using standard probe liquids as well as two different sample coatings, a cationic knot sealer and an acrylic based dye. The results showed that latewood regions of the acetylated wood had a noticeably lower uptake of the non-polar low surface tension liquid octane as well as the polar high surface tension liquid water compared with latewood of the untreated controls. Contact angle analysis based on the Lewis acid–base concept indicated that the acetylated wood is predominantly Lewis basic. A preferential wetting of the knot sealer was observed on the acetylated wood.

SURFACE ENERGY CHARACTERISTICS OF REFINED FIBRES AT DIFFERENT PRESSURES

Wood fibres were produced on the pilot scale refiner at the BioComposites Centre, Bangor University, from a commercially sourced mix of chipped wood. The fibres were produced at refiner pressure 4, 6, 8 and 10 bar and dried in the associated flash drier. Surface energy characterization of the refined fibres was performed using inverse gas chromatography (IGC). The dispersive part of the total surface energy was analysed for duplicates of fibre samples at the four different refiner pressures. Non-polar alkane probes were used for the dispersive surface energy analysis at different surface coverage. Results indicate that the processing pressure has an effect of the dispersive surface energy and IGC analysis could be developed as a tool both for process development and process control in refining fibres.