Polyethylene/starch blends with enhanced oxygen barrier and mechanical properties: Effect of granule morphology damage by solid-state shear pulverization

A mechanical process called solid-state shear pulverization (SSSP) was used to create blends or composites of polyethylene (PE) and starch that resulted in damaged granular structures. Because starch granules are unchanged when polymer/starch blends are made by melt mixing, this is the first time that damage (surface roughening, cracking, and clustering) to starch granule morphology has been reported in polymer/starch blends or composites. These morphological changes result in a 29% reduction in oxygen permeability for a 70/30 wt% PE/starch blend made by SSSP relative to neat PE; this compares with a 21% reduction in oxygen permeability when a similar blend is made by melt processing. In addition, relative to neat PE, the tensile modulus of a 70/30 wt% PE/starch blend is increased by 20% in the damaged starch case (vs. 10% in the blend made by melt mixing) while the reduction in tensile strength is significantly smaller than that found in melt-mixed blends.