Crystalline modifications of ethylene-vinyl acetate copolymers induced by a tensile drawing: effect of the molecular weight

The influence of a tensile drawing on the crystalline organisation of ethylene-vinyl acetate copolymers (EVA) of different molecular weights has been investigated by differential scanning calorimetry (d.s.c.). The consequence of the crystalline organization changes on the mobility of the amorphous phase has been also investigated, through the study of the glass transition. The results show that more disorganized crystals appear after the tensile test, specially for the higher molecular weight. These more disorganized crystals constitute physical ties reducing the mobility of the amorphous chains which link them, as shown by the significant increase of the glass transition temperature of these high molecular weight EVA after tensile drawing.