Influence of film preparation procedures on the crystallinity, morphology and mechanical properties of LLDPE films

Abstract

Influence of various film preparation procedures on the crystallinity, morphology and mechanical properties of pure linear low-density polyethylene and its calcite filled composite films has been studied using differential scanning calorimeter (DSC), wide-angle X-ray diffractometer (WAXRD), atomic force microscope (AFM) and ultimate tensile testing machine (UTM). The film preparation procedures include variation in cooling rates such as quenching, force (fan) and natural cooling and in techniques such as extrusion followed by melt squeezing and compression molding. The heat of fusion (from DSC), the degree of crystallinity (from WAXRD) and the crystallite size (from WAXRD and AFM) are found to be the highest for naturally cooled specimen, followed by fan cooled and quenched ones. The AFM images of surface topology exhibit stacked lamellar morphology for forcefully cooled (fan cooled and quenching) samples and spherulitic ‘lozenges’ for naturally cooled ones. The Young’s modulus and yield stress (from UTM) are the highest for naturally cooled samples, followed by fan cooled and quenched ones. Amongst the calcite filled composites, the ‘base film’, which is prepared by extrusion followed by melt squeezing and natural cooling, exhibits the lowest heat of fusion, degree of crystallinity and Young’s modulus, but the highest yield stress, elongation at break and tensile strength compared to the compression molded ones.