Progress and Problems in the Southern Pine Plywood Industry

The southern plywood industry faces a number of challenging problems today. The greatest is that of dried-out gluelines, the result of long periods of high ambient temperatures combined with the high absorptivity of pine springwood. Temperature extremes also affect the gluability of southern pine. Summertime mill temperatures of 100? to 120?F. are not uncommon, while winter temperatures may be as low as 50?F. To compensate for these extremes, at least two phenolic resin formulations may be required to maintain production on a year-round basis. Pine wood appears to be more difficult to glue than West Coast softwood for several reasons. Southern pine is characteristically of faster growth and exhibits wide bands of springwood and summerwood on the surface of the veneer. Such wood peels rough and loose and is uneven in thickness. Adhesive spread must therefore be increased. There is wide variation in specific gravity range within a single piece of veneer, and differences in the amount of wood failure are likely to vary within a plywood panel. The likelihood of gluing areas of summerwood to summerwood is very high, and such bonds often show high shear values but low wood failure. It is felt that dynamic growth of the southern pine plywood industry will continue to spur the development of better adhesives, more efficient equipment, and improved techniques.

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