Influence of microwave plasticization, areal compression and high-temperature treatment on equilibrum moisture content and shrinkage of Spruce (Picea abies (L.) Karst.)

Abstract

MERENDA, L., NASSWETTROVÁ, A.: Infl uence of microwave plasticization, areal compression and high-temperature treatment on equilibrum moisture content and shrinkage of Spruce (Picea abies (L.) Karst.). Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 1, pp. 107-114 The wood is heterogenous material compound from substance of cell walls and air. It is colloidal capil la ry-cellular material with ortogonal anisotropy (Babiak, 1976). The wood has possibility to bound liquids and gases into the structure. Due to this the wood is hygroskopic material leads to changes in dimensions and volume of wood generating at adsorption and desorption of water molecules into the wood. The dimentional changes evoked by changes in moisture content (bounded water) during shrinkage and sweeling have the biggest importance. Shrinkage is making the linear dimensions, area and volume shorter and smaller (Požgaj a kol., 1997). Hygroscopicity and dimensional instability is possible to aff ect by drying or modifi cation (Horáček, 2004). Wood modifi cation is a process where it causes improvement in material properties. Aimed changes in chemical structure of wood leads to change in material properties. The aim of modifi cation is to reduce negative properties and to improve positive properties. Wood with changed properties has different parameters which it is necessary to investigate. Plasticization as temporary modifi cation of material properties leads to so er wood due to release of intercellular bonds mainly in middle lamela. It makes subsequent processing as areal compression possible (Bouajila et al., 2006). To ther plasticization is necessary to heat up the wood on the certain temperature. The microwave heating is very useful for this heating. It has smaller expenses and time consumption. Pressing or areal compression perpendicular to the gain in radial direction presses the wood and makes it's density bigger. Areal compression is responsible for changes in submicroscopic, microscopic and makroscopic levels of wood structure. Changes in wood structure leads to changes in linear directions during shrinking. Plasticizated and compressed wood has many of excellent properties, but it has some negative proper ties too that high temperature treatment reduces. The aim of this article is to fi nd and compare equilibrium mositure content, linear shrinkage in radial, tangential and longitudinal direction of the native spruce wood (Picea abies L. Karst.) with the same values of microwave plasticizated, areal compressed in radial direction perpendicular to the gain and high temperature treated Spruce wood.Picea abies (L.) Karst., microwave plasticization, pressing of wood, high temperature treatment, linear schrinkage, equilibrium moisture content Dřevo představuje heterogenní materiál složený z hmoty buněčných stěn a vzduchu. Má charakter koloidního kapilárně-pórovitého materiálu s ortogonální anizotropií (Babiak, 1976). Z ontogeneze elementů dřeva plyne jeho schopnost poutat těmito stavebními látkami buněčné stěny kap...