Characterization of pre-curing behavior of urea-formaldehyde resin affected by different temperatures

Differential scanning calorimetry (DSC) was applied to investigate the thermal behavior of pre-curing urea-formaldehyde (UF) resin as affected by different temperatures; the activation energies (Ea) in different stages during the pre-curing course were analyzed by Kissinger method. The results indicated that the curing time was decreased with temperature increasing. Under isothermal temperature, the DSC curves of pre-curing UF resin shifted to shorter time, the conversion increased with increasing temperature. In dynamic scanning, with the pre-curing degree increasing, the DSC curves shifted to lower temperature, while both the onset and peak temperature decreased due to the cross-linking degree increased. The Ea and Z value decreased obviously firstly due to the concentration and reactivity of the reactants increased with water evaporation in the first stage, and then the increasing cross-linking degree and the formation of the network structure lead to both the Ea and Z value increasing in the second stage, indicating that the pre-curing behavior appeared.