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Thermal Analysis of Liquid Phenol-Formaldehyde Resin Curing

The curing properties of phenol-formaldehyde resin were examined by use of differential thermal and thermal gravimetric analysis. The differential thermogram of the liquid adhesive showed two endothermic peaks in the regions 122° to I35°C and 145° to 170° C, the exact positions of these maxima depending on the heating rate. A heating rate of 6° to 9°C/min was found to be most suitable for obtaining good resolution of the thermogram. The thermal gravimetric analysis showed two transitions at 85° and I35°C. The former was associated with the weight loss of the liquid water, while the latter was related to the first endothermic reaction in the differential thermogram. The endothermic peaks were further related to the curing properties of resin by infrared plus ultraviolet spectroscopic and formaldehyde analysis. The first peak at 122° to I35°C was found to be most important to the initial curing of the adhesive while the peak in the region at 145° to 170° C probably relates to the final curing of the resin. The hydrolysis resistance, and hence the durability of the resin, was found to depend on the degree of cure of resin. Adhesive cured at a temperature greater than the second endothermic reaction (170° C) is substantially stable to hydrolysis.