Effect of short chain branching of LDPE on its miscibility with linear HDPE

The influences of short chain branching (SBC) on the melt miscibility of low-density polyethylene (LDPE) with linear high-density polyethylene (HDPE) were investigated by rheological methods. Two LDPE resins with different branch contents were blended with the same linear HDPE. Dynamic and steady shear measurements were carried out using a Rheometrics ARES rheometer at 190°C. The rheology of the low-SCB LDPE (9 CH₃/1 000 C) blends with HDPE can be predicted by the linear additivity rule. Hence blends were suggested to be completely misicible at all compositions. However, blends of the high branch content LDPE (SCB = 19 CH₃/1 000 C) were completely immiscible. Also, the different viscous and elastic properties of all the immiscible blends were much higher than the corresponding values for the more viscous and elastic blend component. The ratio of interfacial tension to droplet radius was estimated from Scholz et al. model as ≈1 500 N · m^-2. The leve] of SCB in LDPE was found to have a strong influence on its miscibility with linear HDPE.