Electron beam initiated grafting and crosslinking of ethylene vinyl acetate copolymer. Part II : Mechanical and electrical properties
Mechanical, dynamic mechanical and electrical properties of electron beam modified ethylene vinyl acetate (EVA) copolymer in presence of trimethylolpropane trimethylacrylate (TMPTMA) and triallyl cyanurate (TAC) as sensitizer have been described. The tensile strength of the TMPTMA modified EVA increases with increase in radiation dose up to a certain level due to the development of network structure, while it does not change significantly for the TAC based system due to poor stress transfer. The tensile strength deteriorates sharply at higher radiation doses because of the predominating effect of breakdown of the network structure. However, the tensile strength changes marginally with TMPTMA level and decreases with an increase in TAC level. DMTA studies indicate mainly two transitions (namely γ and α) in the order of increasing temperature for both TMPTMA and TAC based samples. The γ-transition temperature shifts to higher values and the α-transition shifts to lower values with an increase in radiation dose due to modification of the main chain and to a decrease in crystallinity. Dielectric analysis shows a sharp transition at around -20°C for all uncured and cured samples due to movement ofthe highly polar acetate groups present in EVA. The loss factor decreases sharply at high temperature with increase in radiation dose due to crosslinking.