Ali Yadegari

In this study, the influence of line speed on the crystallinity of linear low-density polyethylene (LLDPE) stretch films manufactured in a cast extrusion line was examined using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The multilayer LLDPE films were prepared at a wide range of line speeds. The DSC results showed that there was an increase in the crystallinity of films at higher line speeds. The crystallinity increased from 24.5 to 39.8 % while the line speed changed from 200 to 1000 m/min. Evaluating melting endotherms showed that the size of crystals was more uniform as the line speed increased. The crystallinity of films obtained from WAXD analysis exhibited the similar trend of DSC results, though their values were different. Additionally, there was a reduction in the crystal size calculated from WAXD data upon increasing the line speed. The observed increase in crystallinity and decrease in crystal size were due to the enhanced flow induced crystallization (FIC) as a result of greater shear stresses the polymer melt encountered at higher line speeds.