Relationship between bending creep behavior and structural factors of woodunder changing moisture conditions

To clarify the relationship between the bending creep behaviors under chang ing moisture conditions and structure of wood, the bending creeps of four s oftwoods and six hardwoods were measured under air-dry, high-moisture, mois ture-regain and moisture-loss conditions. The effects of structural factors [degree of crystallinity (Cr), lignin content (L) and degree of molecular orientation in amorphous area (F)] on the bending creep under each conditio n were investigated by the analysis of linear multiple regression, assuming that the creep compliance was inversely proportional to specific gravity. Judging from the standard regression coefficient and the partial correlatio n coefficients, the effects of structural factors on specific initial creep compliance and specific amount of creep under air-dry and high-moisture co nditions had similar tendencies that F had the greatest effect on them and the effect of Cr was greater than that of L, and the effect of L was larger under high-moisture condition than under air-dry condition. The amount of creep under moisture-regain and moisture-loss conditions were proportional to change in moisture content. For both the conditions, the c hange in moisture content decreased with increases in specific gravity and L, and the effect of specific gravity was greater than that of L. The speci fic amount of creep per unit change in moisture content varied remarkably w ith wood species. The partial correlation coefficients between the structur al factors and the specific amount of creep per unit change in moisture con tent had negative values and were in the order F > Cr > L. It was found that the structural factors had smaller effects on the specifi c amount of creep per unit change in moisture as well as the specific amoun t of creep under constant moisture conditions than the specific initial cre ep compliance, but effects of F, Cr, and L on them were similar in the orde r. From the above results, it can be concluded that wood whose specific gravit y, degree of molecular orientation, degree of crystallinity and lignin cont ent are higher has less creep under changing moisture conditions.