The radiation resistance of thermoset plastics—IV. Melamine-formaldehyde plastics

Abstract Samples of two melamine-formaldehyde plastics, one filled with asbestos and the other filled with wood flour, were irradiated under two very different conditions. One set of samples was irradiated with electrons, under the exclusion of oxygen, using a high dose rate. The second set was irradiated with γ-rays, in an air environment, using a very low dose rate. This experiment lasted longer than 10 years. Mechanical properties of the asbestos-filled type, measured at room temperature, remained unchanged up to the highest dose and were independent of irradiation conditions. However, polymer deterioration was observed as evidenced by the heat deflection temperature at irradiation doses above 2MGy. The wood-filled samples were considerably deteriorated at doses above 0.1 MGy with the lower dose rate (13.8Gy/h) showing the more severe deterioration. Surface resistance was adversely affected by irradiation but other electrical properties remained unchanged.