Investigation of UV aging influences on the crystallization of ethylene-vinyl acetate copolymer via successive self-nucleation and annealing treatment

Influences of UV aging on the crystallization of ethylene-vinyl acetate copolymer (EVA) were researched via successive self-nucleation and annealing (SSA) treatment. During the aging process, the polar vinyl acetate (VAc) units in the amorphous region were the most vulnerable structure. FTIR results demonstrated that, VAc units were initially attacked by the UV radiation, which further resulted in chain scission of molecules. Degradation expanded from the amorphous region to the crystal region gradually. Chain scission reaction freed crystallizable ethylene sequences from inter-/intra-molecular tanglement and confinement of neighboring VAc units. Although the crystallinity decreased after aging, newly freed crystallizable sequences preferentially arranged into more densely packed lamellae, leaving less residual fraction to arrange into loosely packed crystal region. WAXD patterns showed that the predominant orthorhombic crystal phase did not vary during aging. Simultaneously, re-arrangement in crystallization also resulted in the growth in lateral crystal size of EVA.