Effect of temperature on dimensional stability of wood with polyethylene glycol I. Bulking effect

Degrees of molecular weight of polyethylene glycol (PEG) being able to pene trate into cell wall of wood is important in the dimensional stabilization of wood treated with PEG. It have been generally recognized that although P EG having a lager molecular weight than 3000 could not penetrate into the c ell mall of wood, appreciable dimensional stabilities had been obtained by treating with PEGs having larger molecular weights in practice. These incon sistent results are probably stemmed from an effect of temperature. Conside ring these, temperature effect on the dimensional stability of wood treated with PEGs, and depolymerization of PEGs in aqueous solution by heat were s tudied with respect to molecular weight of PEG. Bulking effect of treated w ood increased with increasing temperature in the case of treatment and dryi ng, especially in the case of treatment with PEGs having higher molecular w eights. This is interpreted to be caused by increase in the amount of PEG p enetrated into the cell wall, which results from a solublization of PEG int o bound water in the cell wall because of relaxation of cohesive structure of the bound water by elevating temperature. Appreciable depolymerization o f PEG was found at elevated temperatures. The resulting lower molecular wei ght PEG may be able to penetrate into the cell wall, and possibly attribute s to the bulking effect of the treated wood. Considerable values of bulking effect obtained for the wood treated and dried at a low temperature (20 de grees C) with PEGs having molecular weight of 8500 and 21700 was probably c aused by the water which was remained in the cell wall because of coating b y PEG solidified during drying process.