Objective In order to clarify the resin curing characteristics of the resin impregnated wood in different spatial layers during different drying stages, the effects of moisture content on resin solution curing process were studied.
Method The melamine-urea-formaldehyde (MUF) resin solution prepared in the laboratory was diluted to 20%, 30%, 40% and 50%, respectively. Then, they were analyzed by differential scanning calorimetry (DSC) method. Without the effect of heating rate, the optimum curing temperature was obtained by extrapolation method to clarify the effect of moisture on MUF resin curing characteristics qualitatively. The apparent activation energy of resin solution, which was diluted to 20%, 30%, 40% and 50%, was calculated by the Kissinger differential method and Flynn-Wall-Ozawa integral method, to quantify the effect of moisture on resin curing process.
Result The peak temperature (Tp) tended to shift to the higher temperature with the decrease of mass fraction of MUF resin solution. Under the heating rate of 15 and 20 ℃/min, the Tp of 20% resin solution shifted to the lower temperature region. The optimum curing temperatures of 20%, 30%, 40% and 50% MUF resin solution were 93.99, 90.71, 85.46 and 79.71 ℃, respectively. And their apparent activation energies calculated by Kissinger differential method were 92.94, 82.37, 65.93 and 50.68 kJ/mol, respectively, which were similar to those of the Flynn-Wall-Ozawa integral method.
Conclusion Generally, the moisture hinders the resin solution curing reaction in the absence of heating rate effect, and the blocking effect increases with the increase of moisture content. However, in the condition of higher heating rate (15 and 20 ℃/min), the DSC result of 20% resin solution shows that the moisture promotes the resin curing process, which might due to the drastic molecular movement.
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