Effect of temperature on dimensional stability of wood with polyethylene glycol II. Temperature dependence of PEG adsorption and mechanical properties of treated wood

For the purpose of clarifying the mechanism of dimensional stabilization of wood treated with polyethylene glycol (PEG) having relatively high molecul ar weight, temperature dependence of the adsorption of PEG onto wood (Chama ecyparis obtusa Endl.) and the amount of preferentially sorbed water were i nvestigated. Some mechanical properties of wood treated with PEGs having va rious molecular weights were also studied for certifying penetration of PEG s into cell walls of wood. Amount of adsrbed PEGs (molecular weights : 1600 and 21700) increases with elevating temperature, and this tendency was mor e extensive for PEG of higher molecular weight. The amount of preferentiall y sorbed water decreases remarkably with elevating temperature in the case of the adsorption of PEG having higher molecular weight. Modulus of elastic ity (MOE) and modulus of rupture (MOR) in bending were larger than those of control wood (not including PEG) for wood treated at low temperature with PEG having molecular weight higher than 8500, the differences became smalle r with elevating temperature, and MOE and MOR of the wood treated at 80 deg rees C were smaller than that of the control. An extraordinal decrease in d ynamic moduli of elasticity (E') with elevating temperature and a peak or s houlder of dynamic losses (E ") were found in the temperature range higher than melting points of PEGs used, and this became more remarkable for wood treated with PEG at higher temperatures. These results indicate that larger amount of PEGs could penetrate into cell walls of wood at higher temperatu re. This can be interpreted from the view point that molecules of PEG havin g relatively high molecular weight can penetrate more easily into cell wall s of wood at higher temperature, resulted from relaxation of cohesive struc ture of water in the cell wall at higher temperature.