Investigation of LLDPE/LDPE blown films by response surface methodology

Film blowing is the most important method in producing polyethylene films. For years, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) blends have been used in blown film manufacture. In this paper basic mathematical models and response surface graphs have been used to illustrate the relationship between blown film fabrication variables and mechanical and optical properties of 50μm films made from LLDPE and LDPE blends. These films are currently used in various non-barrier packaging applications. Using a Box-Behnken statistical design experiment methodology, the effects of LLDPE/LDPE ratios (25-75%), blow up ratio (1.5-2.5), melt temperature (215-235°C) and frost line height (1-3D) were evaluated on the mechanical properties, e.g., tensile and tear properties in both machine direction (MD) and transverse direction (TD) and impact strength as well as optical property such as haze. The R2 values of all the responses of mathematical models are obtained to be more than 0.85 which is an indication of very good filing of the model with the experimental data of response surface method used. Although this study is confined to the equipment and resin types used, it can offer some curves and equations for predicting the properties of produced films. The processors can use these data to find the first approximation of the most important blown film parameters to achieve their favorite product properties.