Probing tensile properties of LLDPE stretch films prepared in cast extrusion process

Linear low-density polyethylene (LLDPE) cast stretch films were fabricated at broad range of line speeds (200–1000 m/min) to investigate the relationship between tensile properties of films and line speed of cast extrusion process, particularly high line speeds as a matter of scientific and economic interest. In addition, tensile experiments were carried out at low and high drawing speeds as well as in both machine and transverse directions (MD and TD). The results illustrated an enhancement of MD modulus (more than 100%) and strength (about 22%) with increasing the line speed from 200 to 1000 m/min, indicating a more pronounced increase for modulus values. Changing the drawing speed, generally, affected the high strain behavior of films. Nevertheless, at the lower strains, the drawing speed influences particularly the modulus of lower line speed films. It was observed that increasing the line speed in the cast film line has stronger effects on the film elongation behavior than the drawing speed in tensile tests. The tensile properties along TD showed greater deviations from MD tensile behaviors as line speed increased. The variations of tensile properties by line speed were due to chain orientation and extension especially in the amorphous phase. Furthermore, the surface morphology of the LLDPE films were also observed, and it was found that increasing the line speed leads to reduction of surface roughness.