Microscopy of Abrasive-Planed and Knife-Planed Surfaces in Wood-Adhesive Bonds

Abstract

Fluorescence microscopy (FM) disclosed no differences in wood cell structure between abrasikeand knife-planed Douglas-fir joints under constant conditions.However, after a one-cycle soak-dry exposure, formation of checks along the rays were visible in both abrasive-and knife-planed samples by fluorescence microscopy.For this same exposure, scanning electron microscopy revealed many radial cracks in the S, layer and ruptures between the S, and S, layers in abrasive-planed samples.Knife-planed samples had few ruptures between the S, and S, layers and very few cracks in the S, layer.Previous work showed that, although knife planing gave much smoother surfaces at the ccllular level than did abrasive planing, both surfaces resulted in high strength bonds.When those bonded samples were subjected to it soak-dry treatment, however, strength of abrasive-planed samples was much lower than that of knife-planed samples.The substantially intact S, layers in knife-planed samples, as revealed here, apparently retail1 considerable strength, while rupturing and cracking in the abrasive-planed samples explain the loss @sf bond quality reported in earlier work.