Scratch behavior of low density polyethylene film: Effects of pre-stretch and aging

Highlights: • Three typical scratch damage modes: smoothing sliding, folding over and tension induced puncture are identified for LDPE film. • When scratched parallel to the pre-stretch direction, the scratch performance of LDPE film improves with increasing pre-stretch level. • Scratch resistance declines with the increase of residual stress when the pre-stretch direction is perpendicular to scratch. • Thermal aging causes poor scratch resistance, as well as diminishes the anisotropy. • A good correlation exists between the onset of tension induced puncture and the elongation at break of LDPE film. To investigate the influences of pre-stretch and aging on the scratch behavior of low density polyethylene (LDPE) film, the scratch tests were conducted with the linearly increasing normal load. The scratch process was recorded using a high-speed camera and the scratched surface morphology was microscopically investigated. Three typical film scratch deformation/damage modes, i.e., smooth sliding, folding over and tension induced puncture were identified. Their mechanisms and evolution processes were analyzed. It was found that the pre-stretch could improve the scratch performance of LDPE film in the same direction while the scratch resistance perpendicular to the pre-stretch direction declines. While the thermal aging tends to diminish this anisotropic scratch performance, a long thermal aging time causes poor scratch resistance. A good correlation was found between the critical load of tension induced puncture and the elongation at break of LDPE film. Thus, the elongation at break can be one of the good indexes to evaluate the scratch resistance. Those findings provide a fundamental insight for material scientists to design LDPE film with better scratch performance and longer service lifetime.