Hot Press Interior Plywood Adhesives

A history is given of the development of adhesives used on the West Coast for manufacturing interior-type Douglas-fir plywood. After beginning with hot animal glue and progressing through starch, vegetable, and casein adhesives, the first advance in glueline quality was found with cold-press soya-bean glues. Later these were modified for hot-press use or blended with blood for similar curing. In 1934, the first exterior-type plywood was made in a hot press with phenolic resin adhesive. Present interior hot-press adhesives for plywood are protein and phenol-formaldehyde adhesives. The protein type includes blood glues, blood-soya glues, and fortified blood or blood-soya or phenol modifications. Phenol-formaldehyde adhesives include bark flour extended, furafil extended, and walnut-shell flour extended glues. General manufacturing and handling descriptions are given for phenol-formaldehyde and blood-soya hot-press interior adhesives, as are the typical ingredients, mixing procedures, and costs for the two types. Both types are reported capable of meeting Commercial Standards requirements for interior type plywood, and advantages of each are described in detail. The blood-soya systems are lower cost and may be used with veneer dried to a higher moisture content, resulting in savings in dryer capacity. Mixing times and press times are shorter for the blood-soya. Curing of protein adhesives is by formation of insoluble proteinate compounds and is rapidly accomplished at inner glueline temperatures of 170? to 200?F. Phenolic systems cure by polymerization and condensation and require more time and higher glueline temperatures. Furafil-extended phenolic adhesives provide superior bond quality over protein types. Phenolic glues have a pot life of up to a week or more as opposed to 3 or 4 hours for proteins. Also, hot-press phenolic bonded plywood contains less moisture than protein bonded panels, which reduces the shipping weight. Phenolic bonded plywood can tolerate greater closed assembly times than protein glues which provides a safety factor against dryout of the glueline.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member