Structure-property correlation of polyvinyl alcohol films fabricated by different processing methods

Abstract

Polyvinyl alcohol (PVA) films prepared by solution casting method or thermal processing techniques have been widely used in industrial applications. However, the relationship between processing methods and structural properties is still unclear. In this study, three film-forming techniques, namely solution casting, blown film extrusion and extrusion casting, were adopted to prepare PVA films and the influence of processing methods on the structural and physical properties of the films was studied. The results showed that blown film (BF) prepared under biaxial elongational flow had higher crystallinity, larger crystallite size and greater in-plane orientation compared to solution cast film (SCF) and extruded film (ETF). SCF showed the smallest crystallite size, slowest melting temperature, fewer defects, evident skin-core structure and in-plane orientation ascribing to its slow film forming process, stratified solidification and low initial macromolecular concentration. ETF displayed the lowest degree of crystallinity and orientation owing to the fast cooling outside the slit die and the absence of strong flow field. Hence, BF and SCF were endowed with high tensile strength (152.8 and 134.5 MPa), good puncture resistance (245.0 and 245.7 N/mm) and excellent oxygen barrier property (PO2 = 3.07 × 10−19 and 2.33 × 10−18 cm3 cm/(cm2·s·Pa)) while ETF exhibited inferior mechanical properties and oxygen barrier performance. These findings are of significance for building relationships between processing techniques, structural characteristics and practical properties of PVA films and help match appropriate film forming technology to the production of films for different application scenarios.