Evaluation of three fillers in PF adhesives used to bond intermediate moisture content plywood: glueline durability and knife wear

Intermediate moisture content (MC) southern pine veneers (approx. 9%) were bonded into plywoods with phenol-formaldehyde (PF) adhesives containing one of three different fillers. The fillers were pecan shell flour and two furfural-process residues. The fillers and the ash of the fillers were analyzed for 18 chemical elements and compounds. The plywoods were tested for glueline durability by an accelerated-aging vacuum-pressure water-soak test. Knife-wear at the plywood gluelines was also tested for each filler-type adhesive. Satisfactory adhesive mixes and exterior-quality plywood were made with all three fillers. The pecan shell flour mix was the most stable in viscosity over a 24-hour period. The adhesive mixes showed gross differences in the level of knife wear; the pecan shell flour type had the least wear. Pecan shell flour also had the lowest ash content among the three fillers and had lower levels of chemical elements (e.g., sulfur, iron, aluminum, and silicon). The chemical elements probably contribute to abrasion and chemical attack on tool metal at high temperatures. These results are important to plywood and laminated veneer lumber (LVL) plants, which spray-apply adhesives and trim panels. Tool year data are also important to plants that process plywood and LVL products (e.g., furniture plants and LVL finger-jointing operations).

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