THE INFLUENCE OF MOISTURE ON THE DIELECTRIC-PROPERTIES OF POLY(ETHYLENE-CO-VINYL ALCOHOL)

The influence of moisture on the dielectric properties of poly(ethylen e-co-vinyl alcohol) copolymer (EVA) has been investigated using a Seik o DES 100 dielectric spectrometer between 170 and 385 K in the frequen cy range 10-100 kHz. A scanning rate of 1 K min(-1) was used. Two peak s were observed. The a-relaxation is ascribed to the glass transition. The presence of water facilitates molecular motion, shifting the a-re laxation to lower temperatures. The beta-relaxation is due to the loca l-mode relaxation in the crystalline regions of the copolymer or to th e motion of hydroxyl groups. At low temperatures, water molecules may form mechanically stable bridges between the vinyl alcohol regions of the copolymer chains which inhibit molecular motion.