FORMALDEHYDE LIBERATION AND CURE BEHAVIOR OF UREA-FORMALDEHYDE RESINS

The cure behavior of several urea-formaldehyde resins containing different catalyst systems and potential acid-neutralizing additives was followed by differential scanning calorimetry (DSC). Catalysts included ammonium chloride, ammonium sulfate, zinc nitrate, and an amine hydrochloride. Additives included powdered aluminium, glass, and magnesium oxide. The DSC results were employed to guide and interpret formaldehyde liberation testing of the cured systems. Large differences in both cure and formaldehyde liberation behavior were seen among the various resins cured with a given catalyst and as a consequence of using different catalysts and different potential acid neutralizers. In general, for a given resin the more acidic catalyst-additive systems cure the resins more completely and at lower temperature. However, the more acidic systems also exhibit greater postcure formaldehyde liberation. Assuming the observed formaldehyde liberation arises from resin hydrolysis, the results confirm the desirability of neutralizing an acidic cure catalyst after wood bonding to reduce formaldehyde liberation and increase bonded product durability. © 1990, Walter de Gruyter. All rights reserved.