Effects of polymerization parameters on the slow crack growth resistance and rheological properties of bimodal polyethylene resins

In this paper, using a comprehensive study, we have investigated the effect of various polymerization parameters during the synthesis of bimodal polyethylene resins on their rheological and mechanical properties. Bimodal polyethylene resins were synthesized in two subsequent stages in a lab-scale reactor by manipulating a set of parameters such as C-2/H-2 ratios in the first and second stages, the split value, and the comonomer type. The results showed that the comonomer type and C-2/H-2 ratio of the second stage of the polymerization are the most critical parameters that control the final resins' slow crack growth resistance properties. On the other hand, the shear-thinning behavior of the resins is mainly controlled by the first-stage polymers. Although the C-2/H-2 ratio of the first stage results in a moderate effect on the rheological properties of the final resins, its split value governs the flow characteristics of the final molten polymers under high shear rates.