Effect of Process Variables on the Foaming of Phenolic Resins

Resols prepared with a formaldehyde/phenol molar ratio equal to 1·5, and different reaction agents, were foamed with the addition of a chlorofluorocarbon blowing agent (R 113), a commercial surfactant, and a mixture of phosphoric and sulphuric acids. The curing of the resol followed second-order kinetics as determined with the adiabatic temperature rise method. Temperature evolution and the expansion rate during the foaming process were predicted by using a thermal energy balance together with constitutive equations for the crosslinking kinetics and the blowing agent solubility. Both the blowing agent and formaldehyde contribute to the foam expansion. Fixing the resol type and the initial temperature (or acid catalyst amount), an optimum amount of acid catalyst (or initial temperature), related to the maximum foaming extent, was found. The structure of the resulting foams was examined with scanning electron microscopy.