DILATOMETRY OF WOOD .1. LONGITUDINAL DILATOMETRY OF WOOD UNTREATED AND TREATED WITH AMMONIUM PHOSPHATE

In order to obtain information about the dimensional changes of wood at high temperatures, dilatometry of untreated and ammonium phosphate-treated Japanese cedar wood (25 x 5.0 x 0.2 mm) under constant tensile loads was carried out with uniform heating rates in a vacuum. The untreated sample first underwent elongation, due probably because of scission of linkages in the lignin network and then shrinkage due to bond formation in cellulose, such as cross-linking and grafting. With high heating rates or large loads the shrinkage was followed by another stage of elongation and then shrinkage which could be ascribed to the chain scission of cellulose accelerated by the increase in tensile stress and to bond formation in cellulose. The dimensional changes of ammonium phosphate-treated wood were first elongation due to the scission of cellulose and then shrinkage due to bond formation in cellulose. With large loads, the elongation stage progressed through two steps which were ascribable to the scission of linkages in lignin and cellulose, respectively. The activation energies for the dimensional changes were obtained and the effects of tensile loads on them are discussed. Also the activation energies of weight loss are determined.