Curing characteristics of urea-formaldehyde resin in the presence of various amounts of wood extracts and catalysts

The characteristics of urea-formaldehyde (UF) resin curing in the presence of wood extracts and a catalyst [ammonium chloride (NH4Cl)] were investigated by differential scanning calorimetry (DSC). The effects of extracts from 16 wood species on resin curing behaviors were evaluated. A model developed in this study, T-p = 53.296 exp(-9.72C) + 93.104, could be used to predict the resin curing rate in terms of the DSC peak temperature (Tp) as influenced by the NH4Cl content (C). The results indicated that the curing rate of UF resin increased as the catalyst content increased and reached a maximum when the catalyst content ranged from 0.5 to 1.0% (solid basis over liquid UF resin weight). Further increases in the catalyst content had no effect on the resin curing rate. The curing rates of UF resin in the presence of wood extracts increased with decreased pH values or increased base buffer capacities. It was also discovered that the activation energy could not fully explain the resin curing behavior when some species of wood extracts were present, and therefore, the pre-exponential factor had to be taken into account. The concept of the equivalent catalyst content (ECC) of wood extracts to the NH4Cl content was introduced in this study; ECCs ranged from 0.0022 to 0.0331% among the 16 wood species. (c) 2007 Wiley Periodicals, Inc.