Abstract
AbstractThe crosslinked structure of irradiated ethylene‐vinyl acetate copolymer (EVA) film was examined by means of ESR, IR and pyrolysis‐gas chromatography. The ESR spectrum of 35 Mrad irradiated EVA film with 95g kg−1 vinyl acetate content consisted of a three‐line component with an intensity ratio of 1:2:1, a hyperfine structure coupling of 22.4 G and g factor of 2.0049. Therefore, the spectrum was assigned to the methylene radical with two α protons on the same plane; this radical is formed by loss of a hydrogen atom from the acetoxymethyl group.In pyrolysing EVA films at 500°C, the yield of acetic acid from 10 Mrad‐150 g kg−1 film significantly decreased compared with that of unirradiated film, and it decreased with increasing crosslinking density.By measuring the IR spectra of methanolysed EVA films, the following results were obtained: the absorbances at 1740, 1250 and 1050cm−1, attributed to the CO, OCOR and COC groups, respectively, had a marked decrease, whereas the three peaks for 20Mrad film were much stronger than those of unirradiated film. On the basis of these findings, it is suggested that the crosslinking reaction in electron beam irradiated EVA film with lower doses takes place between the acetoxy groups and the main chains.
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