Abstract
This paper studies alternative catalysts to ammonium sulfate for curing urea-formaldehyde (UF) resins. When using a latent catalyst like ammonium sulfate, hexamine is formed as by-product of curing reaction. It is believed that hexamine hydrolysis may contribute to formaldehyde release during the life-time of wood-based panels produced with UF resins. Orthophosphoric acid, on the other hand, catalyzes resin cure without by-product formation and was compared to ammonium sulfate. The pot-life of adhesives with both catalysts was evaluated at 40 °C with a Brookfield rheometer. Mechanical resistance tests performed with ABES (Automated Bonding Evaluation System) showed that orthophosphoric acid effectively catalyzes UF resin cure. Particleboards were produced using both catalysts and the most important properties evaluated, according to European Standards: formaldehyde content, internal bond, moisture content, thickness swelling and density. Particleboards cured with orthophosphoric acid and stored under forceful conditions of humidity and temperature presented similar internal bond and lower formaldehyde content than those produced with ammonium sulfate.
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