Lamellar orientation in the blends of linear low density polyethylene and isotactic polypropylene induced by dynamic packing injection molding

In this work, we have carried out 2 dimensional small and wide angle X-ray scattering experiments on the blends of linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) obtained by dynamic packing injection molding in which the melt was firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurred from the mold wall to the molding core part. iPP was found to form a shish-kebab structure with its lamellar stack oriented perpendicularly to the shear flow direction. Very interestingly, the lamellae of LLDPE were found tilted away from shear flow direction with molecular chain still along flow direction, and the tilted angle increases from the skin to the core part. This can be only understood if the intra-lamellar block slip in the chain direction is generally activated during shearing process achieved by dynamic packing injection molding. Our finding is important and seems to provide further support for the idea that the structure of the crystalline lamellae is not continuous but constructed of small building units with thin boundary in between.