Effects of ionizing radiation on epoxy, graphite fiber and epoxy/graphite fiber composites. Part I: Surface energy changes

Surface energy changes of an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T-300 graphite fiber, and T-300/5208 (graphite fiber/epoxy) composites have been investigated after irradiation with 0.5 MeV electrons. The surface energy of TGDDM-DDS epoxy increases monotonically with radiation doses up to 1,000 Mrad mainly due to increased concentration of polar groups. IR and ESCA spectral evidence indicates that carbonyl groups are formed, probably from the tertiary hydrogen at the carbon where the OH group is attached in the cured epoxy. The polarity of the graphite fiber and the graphite fiber/epoxy interface also increases with radiation dose. These results and the roles of oxygen are discussed in connection with mechanical properties of epoxy/graphite fiber composites exposed to ionizing radiation.