The Effects of Miscibility on the Dynamic and Uniaxial Viscosity of HDPE/LDPE Blends

Low density polyethylene (LDPE) and high density polyethylene (HDPE) are two structurally different polyolefins with distinguishable rheological and mechanical properties. Commercial Ziegler Natta based HDPEs have narrow polydispersity with good mechanical properties while commercial LDPEs have hyper-branched structure which is the reason of showing strain hardening behavior during the extensional flows [1]. The present work investigates the effects of miscibility on the rheological behavior of polyethylene blends. In this regard, two commercial polyethylenes, LDPE 0200 and HDPE 0205 from Bandar Imam Petrochemical Co. Iran, were blended in 25, 50 and 75 percent of LDPE. The miscibility of blends is studied by Cole-Cole plot. It is found that HDPE/LDPE 25/75%, is miscible and immiscibility is observed for the other blends. The result is also verified by the logarithmic mixing rule of dynamic viscosity. It is also found that the zero shear viscosity of immiscible blends has higher value than that of the miscible and the pure materials. The uniaxial elongational viscosity of polymer blends and the pure material is also investigated; it is observed that, as expected for linear polyethylenes, HDPE does not show any strain hardening behavior. The strain hardening behavior manifests itself by the addition of LDPE to HDPE, the higher the LDPE percentage the more intense the strain hardening. It is seen that immiscibility of blends changes the shape of strain hardening behavior at high strain rates but has no effects at low rate of strains.

کلیدواژه ها:

LDPE ، HDPE ، Blending ، Cole-Cole Plot ، Miscibility