Thermal and rheological properties of Fischer-Tropsch wax/high-flow LLDPE blends

Abstract

Waxes find use as processing aids in filled compounds and polyethylene-based masterbatches. In such applications, the thermal and physical property changes they impart to the polymer matrix are important. Therefore, this study details results obtained for blends prepared by mixing a Fischer–Tropsch (F–T) wax with a high-flow linear low-density polyethylene (LLDPE). The melting and crystallization behavior are studied using hot-stage polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The calorimetry results are consistent with partial cocrystallization of the two components. The melting and crystallization exo- and endotherms for the wax- and LLDPE-rich phases remained separate. However, they change in shape and shift toward higher- and lower temperature ranges, respectively. It is found that increasing the wax content delays the crystallization, decreases the overall crystallinity, and reduces the size of the crystallites of the polyethylene-rich phase. Rotational viscosity is measured at 170 °C in the Newtonian shear-rate range. The variation of the zero-shear viscosity with blend composition is consistent with the assumption of a homogeneous melt in which the chains are in an entangled state. Therefore, it is concluded that the wax and LLDPE are, in effect, miscible in the melt and partially compatible in the solid state.