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Studies on the Wood Gluing. XIV. Effect of Chemical Activity of Wood Surface on Polypropylene Bonding

In order to clarify the adhesion mechanism, Hinoki wood specimens which differ in degree of surface activity were glued with nonpolar polypropylene and modified polypropylene, and the relative contribution of mechanical and specific adhesion on wood gluing was investigated. Further, the chemical interaction between wood and polypropylene was estimated from the accessibility of hydroxyl groups in wood and wood laminated with polypropylene by means of deuterium exchange. The glue-joint strengths of acetylated and silane treated wood glued with polypropylene were nearly constant regardless of the amounts of acetyl and silane in wood. On the other hand, with modified polypropylene the glue-joint strength decreased slightly with increasing acetyl content. The accessibilities of hydroxyl groups in controls and in polypropylene laminated wood sections were found to be about 53 and 51 percent, respectively, and that of modified polypropylene laminated wood sections was about 45 percent. It could be concluded on the basis of gluability and accessibility that wood gluing with nonpolar polypropylene was dominated by mechanical adhesion rather than specific adhesion, and that some specific adhesion contributed to the formation of glue-joints with modified polypropylene, although the mechanical adhesion was the main factor.