Preliminary Microscopic Studies of Wood Structure and Adhesion in Plywood

This paper describes the structure of the glue line and the mode of contact between the glue and the wood cell walls of veneer by means of electron microscopy. The plywood was made from silvertop ash, glued with phenol-formaldehyde containing coconut shell flour filler. Shear tests on standard plywood specimens were made according to Australian Stand Spec. AS No. K88 (1952). Optical examination showed that large holes or cavities existed in the glue line of all plywood specimens. The presence of shell flour in the glue line was shown using the optical microscope. it is assumed that the holes in the glue line arose from air bubbles which formed during the process of spreading the glue on the veneer surface. In ultra-thin sections no cracks appeared in the glue line and phenol-formaldehyde resin was shown to make very good contact with shell flour added as filler. Within the range of electron microscopic resolution, there was good contact between the glue and the wood surface.

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