EFFECT OF PROCESSING PARAMETERS ON MECHANICAL PROPERTIES OF LINEAR LOW-DENSITY POLYETHYLENE FILM

Optimization of extrusion conditions is critical to the production of polyethylene films with good mechanical integrity. Yet past studies on the mechanical properties of polyethylene films have neglected the significant effect of critical extrusion conditions. Much of the research into the mechanical properties of polyethylenes, have been limited to the effect of conventional processing parameters such as temperature and pressure. The present study investigates the effects of blowup ratio (BUR), die gap and output rate on mechanical properties of blown Linear Low-Density Polyethylene (LLDPE) films. The mechanical properties examined were impact strength, tear strength and tensile modulus. It was observed that there was an increase in impact strength, while tensile modulus decreased with increasing BUR. The increase in impact strength was attributed to film orientation in the transverse direction which improved with increasing BUR. In contrast, the observed decrease in tensile modulus was due to poor film orientation in the machine direction which was more pronounced with increasing BUR. At the narrowest die gap (1.27mm) and lowest BUR (2.0), the transverse direction (TD) tear strength showed a decrease at high output rates, but increased sharply at high output rates for all the resins. However, at both the low and high output rates, no dependence of the transverse direction (TD) tear strength on the intermediate die gap (2.03mm) was observed. The results show that the extrusion parameters studied are critical factors that determine film orientation and ultimate mechanical properties and, should be carefully controlled when extruding films from Linear Low-Density Polyethylene (LLDPE) resin.