Structural evolution and properties of polyamide‐6/poly(ether block amide) films during the simultaneous biaxial stretching

The purpose of this study was to investigate the structural evolution and properties of simultaneously biaxially stretched polyamide‐6/poly(ether block amide) copolymer (PA6/PEBA) films. The results showed the melting temperature of PA6 increased from 220.02°C to 225.56°C when the stretching ratios increased from 1 × 1 to 3.5 × 3.5, suggesting the occurrence of β → α crystal transformation. Meanwhile, the increase of stretching ratios increased the crystallinity of the films due to the molecular orientation, which could create a more tortuous path for the diffusion of oxygen molecules through the films. As a result, the oxygen barrier performance of the stretched PA6/PEBA film was increased after biaxial stretching. The morphological observation showed that spherical or slightly ellipsoidal PEBA particles were dispersed in the PA6 matrix. The thermal shrinkage of the stretched film increased as the stretching ratios increased, and no significant difference of the shrinkage between machine direction (MD) and transition direction (TD) was observed in the stretched films. It was also found that the tensile strength of the stretched films in MD and TD exhibited the highest value at a stretching ratio of 3.5 × 3.5, which was about 1.7 times and 2.1 times higher than that of the unstretched PA6/PEBA film, respectively.