Fillers and Extenders in Plywood Production–U.S. and Foreign Practices

This study on plywood glue fillers and extenders was prompted by the rapid worldwide growth in plywood production, reports of dwindling supplies of satisfactory softwood plywood glue filler, and the need for viable alternatives under present conditions. In a 1977 tour of non-U.S. plywood plants the authors obtained formula and application information related to the study. Plywood glue filler and extender factors considered important in formulating adhesive resin mixes are discussed. Formulas from many countries are presented that reveal combinations of different fillers and extenders. The filler-extender requirements and practices are treated separately, as pertaining either to urea resin mixes used principally in hardwood plywood applications, or to phenolic resin adhesives used mostly in gluing the softwood plywood. Protein-starch extender qualities and characteristics are reviewed and the possibilities noted for much larger extender inclusions since adoption of the APA Adhesive Policy Change in 1977. Plywood filler and extender factors considered important in formulating efficient adhesive resin mixes arc discussed. Filler and extender raw material sources are identified and evaluated by methods including physical and proximate chemical analyses. Characteristics related to production efficiency, marketing advantage, liability reduction, regulatory compliance, and panel quality are noted. Effects on bond quality, resin conservation, pollution control, flame spread, working conditions, and quality control are related to the economy of proper filler and extender selection. The authors question whether knowledge of filler and extender technology is being transferred in an adequate and timely manner. Never the less, there is an increasing recognition of the relationship between quality glue ingredients and satisfactory plywood products, sales, and profits.

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