DSC characterisation of urea-formaldehyde (UF) resin curing

Purpose - The purpose of this paper is to investigate the effects of various catalyst contents, resin solid contents, catalyst species and wood extract on urea-formaldehyde (UF) curing by differential scanning calorimetry (DSC) technique. The finding obtained would benefit the manufacturers of UF-bonded composite panels. Design/methodology/approach - The UF curing rate under each condition in terms of DSC peak temperature was measured by high-pressure DSC at a heating rate of 15 degrees C/min; the correlations of peak temperature with catalyst content, resin solid content, catalyst species and wood extract, respectively, were regressed via a model equation, which described the curing characteristics of the UF bonding system. Findings - A model equation, T-p = A.EXP(-B.CC per cent) + D-1 was proposed to characterise the DSC peak temperatures or the rate of UF curing with regressing coefficients greater than 0.97 (commonly greater than 0.99). The constants A and B in the model equation were found to correspond to kinetic characteristics of UF resin curing reaction. The constant D in the model equation is believed to be associated with the utmost peak temperature, which implies that the DSC peak temperature will finally reach a maximum with catalyst content increasing. it was also found that the wood extracts having higher pH value and base buffer capacity had stronger catalyses on UF curing. Research limitations/implications - The catalysts commonly used in medium density fibreboard plants or particleboard plants are those having the utmost peak temperature of about 90-95 degrees C; the catalyses of wood extracts were much weaker than that of catalyst NH4Cl. Practical implications - The model equation could be used to predict the peak temperature or the curing rate of UF resin, and to quantify the effects of wood extracts on UF curing. Originality/value - The study developed a model equation that can well characterise the UF curing, and quantified the effects of wood extracts on UF curing.