ELECTRON-BEAM INITIATED MODIFICATION OF ETHYLENE-VINYL ACETATE USING TRIMETHYLOLPROPANE TRIMETHACRYLATE

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 Mr ad) and concentrations of TMPTMA (0.5 to 5 parts by weight). The resid ual concentration of carbonyl groups due to oxidation and incorporatio n of TMPTMA into the crosslinked EVA, as determined from i.r. differen ce spectra increases with the radiation dose and with the TMPTMA level in the initial stages. The gel content increases with the radiation d ose, though the increase is marginal with the TMPTMA level. X-ray stud ies indicate that there are two peaks at 10.8-10.9 degrees and 11.8-11 .9 degrees and that the corresponding interplanar distances are 4.07 A ngstrom and 3.73 Angstrom. With an increase in the radiation dose or T MPTMA level, the crystallinity increases in the initial stage and then decreases. The interplanar and interchain distances of the modified p olymer do not change. Differential scanning calorimetry (d.s.c.) studi es also support the X-ray results. Tensile properties increase with th e radiation dose and the TMPTMA level up to 5 Mrad at 1 part TMPTMA le vel, 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 le vel, the tensile properties decrease due to a breakdown of the network structure.