Influence of plasticized UHMWPE on melt processability and supercritical CO2-assisted microcellular foaming of HDPE/UHMWPE blends

The extent to which plasticization of ultrahigh molecular weight (UHMWPE) can modify the micro- as well as macro-structural properties of HDPE/UHMWPE blends as well as their foam characteristics are investigated in the present study by preparing blends using melt mixing and further foaming of the developed blends using supercritical CO2 (scCO(2)). Fischer-Tropsch (H5) olefin wax is added to prepare plasticized UHMWPE (p-UHMWPE) and incorporation of plasticized UHMWPE reduces the processing time for melt blending. The reduction in the percentage crystallinity with neat UHMWPE loading without affecting thermal transition temperatures indicates immiscibility of components. The tensile strength of similar to 3-14%, Young's modulus of similar to 33-36% and impact strength of similar to 77-175% of blends improve with plasticized UHMWPE content. Interestingly, the slit capillary rheology data on application of the power-law model establish the rheological percolation threshold to be at 20 wt.% of plasticized UHMWPE content. In addition, blends containing plasticized UHMWPE reveal immiscibility by improving shear-thinning behaviour as well as melt elasticity during the small amplitude oscillatory shear (SAOS) based frequency sweep tests. Further, blends of plasticized UHMWPE reflect a reduction in microcracks and fibrillated microstructures with a switch over to corrugated and island in-the-sea morphology from scanning electron microscopy (SEM) images. After batch foaming of the plasticized UHMWPE containing blends, optimum cell size and density, volume expansion ratio (VER), compressive strength, and improved crystalline characteristics are observed for the blend containing 20 wt.% plasticized UHMWPE. The above results suggest that the plasticized UHMWPE improves interfacial chains diffusion and acts as a nucleating agent to enhance the foamability of HDPE/p-UHMWPE blends.