Influence of molecular parameters on the miscibility of metallocene LLDPE and HDPE blends: Rheological and molecular dynamics simulation investigation

The melt miscibility of linear high-density polyethylene (HDPE) and octene-based metallocene linear low-density polyethylene (m-LLDPE) was investigated by rheological and molecular dynamics (MD) simulation techniques. The effects of molecular parameters, like branch content (BC), composition distribution (CD), and molecular weight (M_w) were studied. In the MD simulation study, branch content of m-LLDPE was varied in the range 10 to 80 branches/1000 C. Both Rheology and MD simulation suggest a strong influence for BC on blend miscibility, and blends start to phase separate when the branch content of LLDPE is 40 branches/1000C. The separation becomes sharper at higher branch content of 60 branches/1000C. At high-BC, mismatch of the molecular conformation of highly branched m-LLDPE and HDPE was observed. Interlayer morphology was suggested by rheology and observed in MD simulations. Also, Ziegler-Natta LLDPE was found to be more miscible than m-LLDPE of the same M_w and BC However, increasing the M_w of m-LLDPE from 70 to 100 kg/mol is of insignificant effect on its miscibility with HDPE. This research suggests the strong influence of molecular parameter of BC, and CD on miscibility of LLDPE/HDPE blends.