Bondability of ipê (Tabebuia spp.) wood using ambient-curing exterior wood adhesives

Abstract

Ipê is an extremely difficult species to bond because of its high density, interlocking grain, and high volumetric swelling–shrinkage under prolonged wet conditions. Despite its difficulties, the wood is known to be extremely durable in exterior conditions because of its resistance to microbial and insect degradation. Therefore, investigating its bondability with exterior wood adhesives will broaden its use in applications in which fasteners are not feasible. In this study, ipê wood was bonded with five ambient-curing exterior-grade wood adhesives (epoxy, emulsion polymer isocyanate, two polyurethanes, and phenol-resorcinol formaldehyde). Tests for compression-shear using ASTM D 905 and percentage wood failure using ASTM D 5266 concluded that, of the five tested adhesives, phenol-resorcinol formaldehyde provided the most durable bonds and highest wood failure after cyclic vacuum pressure soaking. Fluorescence microscopy images showed that none of the five adhesives penetrated far into the ipê void volume. Transmitted-light microscopy (40× and 63×) showed that phenol-resorcinol formaldehyde traveled between surface fiber cells more effectively than did other adhesives. Phenol-resorcinol formaldehyde adhesive was probably able to encapsulate loose interfacial fibers and permeate microvoids between fibers, therefore acting as a stress reducer during moisture-induced swelling and shrinking.

Citation

Yelle, Daniel J. 2016. Bondability of ipê (Tabebuia spp.) wood using ambient-curing exterior wood adhesives. FPL–RP–689. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 6 p.