Crosslinking and physical properties of poly (ethylene-co-vinyl acetate) produced by autoclave and tubular reactors

Four commercial poly (ethylene-co-vinyl acetate) grades, EVA, two produced by autoclave and two by tubular high-pressure reactors were selected to characterize the effect of molecular structure and long chain branching (LCB) onto the crosslinking performance, optical properties and thermal shrinkage of the converted films. HT-GPC and 13C NMR spectroscopy techniques were used to determine the molecular structure and degree of LCB on EVA resins. Blends of EVA resin with organic peroxide, co-agent and antioxidant were prepared and converted into flexible foils. The ordered comb-type structure of the tubular EVA showed lower molecular weight, narrower polydispersity index, lower degree of LCB and crystallinity degree at least 29 % higher when compared to autoclave EVA. It was assumed that the crosslinking kinetic is influenced by the ability of the radical species from the organic peroxides to easily abstract hydrogen from the terminal methyl groups of incorporated acetate units. Haze increases significantly with the presence of high content of LCB. Thermal shrinkage was found to be correspondent to the degree of LCB and inversely proportional to the degree of crystallinity.