A Study of Some Factors Affecting the Gap-Filling Properties of Wood Adhesives

One of the main considerations in evaluating adhesives for gap-filling properties relates to the shrinkage of the adhesive. Walnut shell flour filler, up to 30 percent of the resin, improved the thickness tolerance of a straight urea adhesive but not the rate of strength decline with time. The response to addition of walnut shell flour in a furfuryl alcohol modified urea was the same in a dowel type joint as the shimmed cross-lap specimen. The epoxy adhesive exhibited the best behavior under increasing time and film thicknesses; a furfuryl modified urea gave slightly higher strength but with a definite limitation on maximum thickness between 0.02 and 0.04 inch and with some strength loss with time; and a polyvinyl acetate emulsion gave the highest over-all strength.

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