Comparison of Curing and Bonding Properties of Particleboard and Waferboard Type Phenolic Resins

Differential scanning calorimetry (DSC) was used to compare the curing reactions of a powdered novolac and a powdered resol phenolformaldehyde resin, and the results were applied to composite board production. By comparing the heating rate curves of boards pressed at 205?C press temperature with the heating rate influence on DSC plate temperature, optimum pressing-time predictions were developed which corresponded closely to maximizing strength and dimensional properties of particleboard and waferboard. Curing mechanisms for novolacs and resols were found to be different, with the novolac reaching thermosetting properties only after the 160? to 180 C exotherm peak was reached. The resol needed only to reach the endothermic peak temperature at 150?C to attain thermosetting properties. This difference in curing properties between the two resins was not clearly evident from particleboard or waferboard dry IB strength or vacuum-pressure-soak dimensional stability tests; however, the boil test provided differentiating trends. The resol boards showed strength and dimensional property changes up to a cure temperature of 160?C, while the novolac boards showed changes in these properties up to 190?C cure temperature after a 2-hour boil. For this reason, a boil test is necessary to determine the degree of cure of boards made with novolac phenolic resin.

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