Tool wear properties of five extender/fillers in adhesive mixes for plywood

Southern pine veneers were bonded into plywood with phenol-formaldehyde adhesives containing one of five different extender/fillers. The five fillers were 1) a 65/35 ratio blend of English walnut shell flour/oat hull furfural residue; 2) an oat hull furfural residue; 3) an imported Asian furfural residue; 4) an English walnut shell flour; and 5) a pecan shell flour. The fillers were analyzed for 16 chemical elements, ash, pH, and moisture content. An alder bark flour (West Coast, U.S. source) was also analyzed for elemental analysis for comparison. The plywood was tested for glueline durability by an accelerated-aging (vacuum-pressure water) test and with a two 4-hour boil test regime. The knife wear at the plywood gluelines was tested for each filler-type adhesive. Differences in knife wear were evident depending on the filler-type adhesive. The plywood with the 65 percent walnut shell flour/35 percent oat hull furfural residue filler had the lowest knife wear, and the plywood bonded with the Asian furfural residue had the highest knife wear. The Asian furfural residue had a low pH and a high presence of sulfur, chloride, iron, aluminum, and organic-type silicon (and generally ash) compared to the other fillers tested for knife wear.

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