Electron beam initiated modification of ethylene vinyl acetate using trimethylolpropane trimethacrylate

Abstract

Electron beam initiated crosslinking of ethylene vinyl acetate (EVA), containing 12% vinyl acetate with trimethylolpropane trimethacrylate (TMPTMA), has been carried out over a range of radiation doses (2–20 Mrad) and concentrations of TMPTMA (0.5 to 5 parts by weight). The residual concentration of carbonyl groups due to oxidation and incorporation of TMPTMA into the crosslinked EVA, as determined from i.r. difference spectra increases with the radiation dose and with the TMPTMA level in the initial stages. The gel content increases with the radiation dose, though the increase is marginal with the TMPTMA level. X-ray studies indicate that there are two peaks at 10.8–10.9° and 11.8–11.9° and that the corresponding interplanar distances are 4.07 Å and 3.73 Å. With an increase in the radiation dose or TMPTMA level, the crystallinity increases in the initial stage and then decreases. The interplanar and interchain distances of the modified polymer do not change. Differential scanning calorimetry (d.s.c.) studies also support the X-ray results. Tensile properties increase with the radiation dose and the TMPTMA level up to 5 Mrad at 1 part TMPTMA level, and 1 part at a 5 Mrad dose, because of the formation of a large network structure. Beyond a 5 Mrad radiation dose and 1 part TMPTMA level, the tensile properties decrease due to a breakdown of the network structure.