Water vapour transmission rate of Ethylene Vinyl Acetate (EVA): Encapsulant with different curing levels

Water vapour transmission rate of EVA sheets with different curing levels is investigated under a various temperature and relative humidity levels. The gravimetric cup method is used to measure the transmission rate. EVA samples’ thermal and structural properties are measured and results confirm that the curing level does not affect material VAc contents or crystallinity, though their degrees of crosslinking are significantly different. For the EVA studied in this work, lower degrees of crosslinking (gel content <60%) show water transmission rate at about 35 g/m2/day under 23°C and 1 bar. The transmission rate reduces with the increasing crosslinking degree and reaches about 10 g/m2/day for samples of gel content >80%. Results also show the water transmission is able to be accelerated by temperature with an activation energy of about 7.5kJ/mol.