Biaxially stretched polyamide 6/ethylene vinyl alcohol copolymer films with improved oxygen barrier and mechanical properties

Polyamide 6 (PA6) and PA6/ethylene vinyl alcohol copolymer (EVOH) films were prepared through extrusion casting process, followed by uniaxial and biaxial stretching on a laboratory biaxial stretcher. The crystallization properties, mechanical properties, and barrier properties of PA6/EVOH films before/after stretching were investigated. It is found that the crystallinity of the stretched PA6/EVOH film is increased with the increase in EVOH content and stretching ratio. Notably, the oxygen barrier property of biaxially stretched PA6/EVOH films is 3 times higher than that of neat PA6 due to the strong interaction of two polymers and increased crystallinity. The modulus, tensile strength, and elongation at break of biaxially stretched PA6 films are also enhanced with the incorporation of EVOH. The crystal orientation of stretched PA6/EVOH films was investigated according to the wide-angle X-ray scattering analysis. The degree of orientation is increased with the stretching ratio. With the increase in the orientation degree, the stretched films show increased tensile strength whereas decreased toughness. Furthermore, the biaxially stretched films present balanced mechanical properties, and the stretching ratio of 3 × 3 shows excellent comprehensive mechanical properties.