Mechanical Interlocking of Adhesive Bonds to CCA-Treated Southern Pine—A Scanning Electron Microscopic Study
Keywords:
Phenolic adhesives, mechanical interlocking bonds, CCA preservative, southern pine, delamination resistance, SEM (scanning electron microscopy)Abstract
New adhesively bonded products made from lumber, veneer, flakes, and fibers that are protected from biological deterioration can play a prominent role in the marketplace if difficulties in bonding preservative-treated wood can be overcome. The purpose of this study was to demonstrate that bonds of extraordinary integrity can be developed in southern pine treated with chromated copper arsenate (CCA) preservative if a durable adhesive penetrates deeply enough to mechanically interlock within the cellular structure of the wood. Scanning electron microscopy and elemental analysis by energy dispersive spectrometry were used to explore the interfacing of adhesive with the cellular structure of wood treated with CCA preservative. The surfaces of cell lumens were thoroughly covered with hemispherically shaped deposits consisting of mixtures of chromium, copper, and arsenic. The micrographs support physicochemical theories of bonding of metals to microfibrils in cell walls. The presence of insoluble metallic deposits was so pervasive that most opportunities for molecular forces of attraction to act between normally polar wood and adhesive were physically blocked. Our results nevertheless show that adhesion by mechanical interlocking of a phenolic adhesive deep in the cellular structure of CCA-treated southern pine can produce delamination-resistant bonds even after severe cyclic aging.References
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