Urethane Bonded Particleboard

Formaldehyde emissions from wood products which utilize a urea-formaldehyde (UF) resin have become a public concern. This paper reviews the various alternatives to UF adhesives tor particleboard. Many of these alternatives indicate the use of isocyanates, either alone or in combination with other resins. From a consideration of the stoichiometry and kinetics of the isocyanate-water reaction, it appears that practically no isocyanate is available to react with hydroxyl groups on the cellulose molecule if an isocyanate is the sole adhesive. Since the uncatalyzed reaction of isocyanates and poly(oxypropylene)polyols is relatively slow at temperatures below 40?C, advantage was taken of these reaction kinetics to prepare a series of urethane adhesives for blending with wood chips and thus form a urethane bonded particleboard. The isocyanate-polyol reaction occurs in the press. Sticking of the board to the platen is avoided by using a nearly stoichiometric quantity of isocyanate and polyol. Lower molecular weight polyols give better physical properties than those of higher molecular weight. An economic comparison shows that several urethane systems are competitive with UF resin, assuming hand-mix layup practice and test results can be transferred to an industrial scale.

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