Solid-State Foaming of Epoxy Resin

Abstract

A new foaming process has been developed for epoxy resins. Uncured epoxy tablets are fabricated by pressing commercial powders in a steel mold at room temperature and used as foam precursors. The tablets foam when heated in a muffle at high temperature. No blowing agent was added because the foaming mechanism depends on the uncured resin boiling point. The foaming temperature is set to be high enough to rapidly produce the resin boiling but not excessive to avoid the thermal degradation. During boiling, the epoxy resin polymerizes and the bubbles freeze in the final structure. Epoxy foams are obtained by heating the compacted tablets in cylindrical copper molds, having internal diameter equal to the tablet diameter. Several process parameters have been changed in the experiment to understand their correlation with the foaming efficiency. However, the foaming ratio (expressed in terms of the ratio between the final and the initial tablet height) is found to be mainly dependent on the initial tablet density. In optimal conditions, the foaming ratio can rise up to 6. Thermal tests have been performed to evaluate the epoxy powder behavior during the cure, whereas mechanical compression tests were used to evaluate the final performances of the foams.