Chemical Control of Hot-Press Urea-Formaldehyde Glue Mixes

A plywood plant chemist can design new glue mixes or modify old ones in order to utilize a variety of raw materials and to make rapid adjustments to changing plant conditions. Eastern Canadian mills generally use feed-grade wheat flour as an extender in their urea-formaldehyde glue mix. Where blood meal is used with this high-protein flour in a highly extended mix, the pH-time curve is a better indicator of pot life than the viscosity-time curve. With a small percentage of soluble blood meal, thickening usually begins between pH 6.0 and 5.5. If flour alone is used, thickening may begin between pH 5.5 and 5.2. Soluble blood meal in extended mixes allows shorter press time, shorter closed assembly time, and better gluing of birch and low-density species. Pine oil, the normally used antifoam agent, is being replaced by more efficient and economical non-ionic detergents.

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