Influence of polymer characteristics on compatibility of PP-LDPE blends: Study of rheological, thermal and mechanical properties

Abstract

The influence of polymer characteristics on the miscibility of polypropylene/low density polyethylene (PP/LDPE) blends was investigated by rheological, thermal and mechanical technique. Commercial and research grade PP were used in this study. Two PP resins of different tacticity were separately blended with the same LDPE in a melt blender at different compositions. Degradation of pure polymers during melt blending was examined and adequate amounts of antioxidants were added, if necessary. Also, LDPE of different molecular weight (MW) and short chain branching (SCB) was blended with the commercial PP to examine the influence of MW and SCB of LDPE on the miscibility of PP/LDPE blends. In this study, melt rheology of all blends was measured in ARES rheometer and melt miscibility/immiscibility inferred from both viscous and elastic properties. The implications of melt miscibility or immiscibility on the thermal and mechanical properties of blends were measured in a TA Q1000 differential scanning calorimetry (DSC) and Instron machines, respectively. It was found that high tacticity resulted in immiscibility of PP-rich blends and it had no influence on the LDPE-rich blends. For SCB of LDPE, high SCB enhanced its miscibility with PP. The large strain behavior of all PP/LDPE blends at PP ≥ 30% is dominated by the brittle behavior of the PP component. In general, matching the conformations and MW is the key to miscibility of PP/LDPE blends.