Impact of Orientation Temperature and Resin Density in structural evolution and morphology of MDO-PE films

PE based mono material flexible packaging design presents a new alternative to conventional design as it can be efficiently mechanically recycled. The work focusing on outer structural layer of novel design addressed the impact of principle process parameter (Orientation Temperature) and resin parameter (Density) on the structural evolution and final morphology attained by MDO (Machine Direction Oriented)-PE films. 5 different PE resins and their blends chosen for study were processed in a lab scale setup to produce MDO-PE films. One selected resin was further processed at different orientation temperatures during stretching. Tensile tests were performed prior and after MD stretching. X-Ray scattering (SAXS and WAXS) were performed for the analysis of shape, size and orientation of the crystals. AFM (Atomic Force Microscopy) presented the surface morphology. Results showed that deformation and fibrillation of initial crystalline structure was relatively higher in high density resins and their blends. Crystallite dimension and long period increased with increase in orientation temperature indicating higher partial melting and strain induced re crystallization. Increase in apparent crystallinity was relatively higher for higher density resins and blends. Lower density resin and blends presented comparatively low roughness at the surface in the AFM analysis. Orientations quantified by Herman orientation factors combined with X-ray diffractograms presented highly oriented structure towards stretch direction. Our study revealed the structural evolution of PE films going through MDO process and concluded that enhancement in crystallinity due to fibrillation and re-crystallization of initial crystal structure at relatively higher orientation temperatures in combination with highly oriented structure in stretch direction leads to enhancement of stiffness of MDO-PE films which can be further used as outer layer in PE based design for flexible packaging applications.