Effect of damp-heat aging on the properties of ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer blends

The aim of this investigation is to evaluate the effect of damp-heat aging on properties of ethylenevinyl acetate (EVA) copolymer (14 wt % vinyl acetate units), ethylene-acrylic acid (EAA) copolymer (8 wt % acrylic acid units) and their blends. Attenuated total reflection Fourier transform infrared spectrum (ATR-FTIR), differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD), and mechanical tests are employed to investigate the changes of copolymer blends' structures and properties. ATR-FTIR tests show that increase of carbonyl index is owing to the incorporation of oxygen into the polymeric chain of EVA in the blends and has not much influence on the EAA. By DSC measurements, the low temperature endothermic peak (T _m2) of various EAA/EVA blends at about 43.7°C attributed to the secondary crystallization is increased with the aging time, which means the lamellar thickness of low temperature crystallite is increased. The increase of low temperature peaks probably derives from the interphase or even amorphous parts of both EVA and EAA components. The crystalline size detected by WAXD and degree of crystalline have both been improved by damp-heat aging. By mechanical tests, the sample has more hardness, more modulus at 100% extension ratio, more tensile strength with less elongation at break as the proportion of EAA increase. Aging influence will induce deterioration of mechanical properties, and increase of degree of crystallinity can make the hardness, the modulus at 100% extension ratio and tensile strength increase. The two factors will both have effect on the mechanical properties of EAA/EVA blends.