Transparent blown films from poly(lactide) and poly(ethylene-co-vinyl acetate) compounds: Structure and property

摘要

The application range of poly(lactide), PLA, films is limited due to the brittleness and notch-sensitivity. In this work, thin films with balanced properties were fabricated by melt blowing of PLA and poly(ethylene-co-vinyl acetate) (EVA) blends. The film thickness is dependent on the taken-up speed and reached to around 10 nm at the taken-up speed over 14 m/min. The presence of EVA not only significantly enhanced the tensile toughness and notch-resistance of the PLA films but also retained high transmittance. The films exhibited anisotropic mechanical performances which were correlated to the micro-morphology differences between the take-up direction (DD) and the transversal direction (TD) as characterized by atomic force microscope. In addition, the EVA with 80 wt% VA units showed better overall modification effect on the PLA films than the EVA with 60 wt% VA units. Superior mechanical properties of PLA/EVA (80/20) blends such as tensile strength of 50-60 MPa, elongation at break up to 230% and tear strength of 85 kN/m were achieved in the DD direction. Meanwhile, balanced properties were also achieved in TD direction. Moreover, a transmittance of around 90% was obtained for the PLA/EVA films which are comparable to neat PLA films. A high enough VA unit content is crucial for superior mechanical properties and high transparency.