Abstract
Stress relaxation behavior of wood treated with alkaline aqueous solution was investigated to clarify the efficiency of alkaline as a plasticizer of wood. Torsional stress relaxation of wood specimens treated with three kinds of alkali, namely, lithium hydroxide (LiOH), sodium hydroxide (NaOH) and potassium hydroxide (KOH), was measured in water at 30°C over a wide range of alkali concentration. Relaxation rigidity Gr at 104 sec decreased remarkably in the concentration of 5-10% of the NaOH solution, while the corresponding decrease of Gr treated with the KOH solution occurred at somewhat higher concentrations compared with those of NaOH. The coefficient of longitudinal shrinkage of the treated wood under water-saturated condition showed similar dependence on alkali concentration. Furthermore, a peak in relaxation spectrum of the treated wood shifted toward shoter time range above the concentration of 10% for NaOH and above 18% for KOH. It has been inferred from the results that slipping and loosing motions of the microfibrils in the wood cell being shrinked by the alkali treatment give rise to the stress relaxation phenomena. The wood plasticized by the present method has been found to be easily bent and molded, which indicates the versatility of the present method.
