Processability of polyethylene homopolymers and copolymers with respect to their molecular structure

摘要

The processability of commercial polyethylene homopolymers and copolymers, including both high and low density polyethylenes, was evaluated with respect to their molecular structure by measuring their melt rheological and thermodynamic properties. Short chain branching (SCB) mainly controls the density and thermodynamic properties, but it has little effect on the melt rheological properties. Long chain branching (LCB) has little effect on the density and the thennodynamic porperties, but it has drastic effects on the melt rheological properties. LCB increases the pseudoplasticity and the flow activation energy, reducing the viscosity in processing and thus improving the processability. Very small amounts of LCB in metallocene type low density polyethylenes very effectively reduce the viscosity and improve the flow stability in processing.