Features of extrusion of films from blends of LDPE and LLDPE of modern grades

Abstract

The study of rheological and viscoelastic characteristics of modern grades of LLDPE and their mixtures with LDPE, intended for the production of fi lm products, as well as the evaluation of mechanical characteristics of films made of them have been carried out. As a result of studying the rheological properties of LLDPE and LDPE, it was found that polymer melts show behavior typical of pseudoplastic liquids. The flow index for all grades of LLDPE was 0.78–0.91, which indicates a narrow MWD of polymers; LDPE had a flow index of 0.56–0.57 and a higher activation energy for viscous flow than LLDPE.

The viscoelastic properties of the polymers were assessed by the value of swelling coefficient (Ks) at two test temperatures. It is shown that the Ks of LDPE significantly exceeded that of all studied LLDPE grades at the same shear rates or shear stresses. The increase in temperature had an insignificant effect on the Ks value for both LDPE and LLDPE. It has been found that an increase in the content of LDPE in mixtures with LLDPE leads to an increase in Ks.

The analysis of tensile properties of films obtained from the original polymers and their blends showed that the character of change in strength and elongation at break depends on the composition and type of LLDPE from different manufacturers. Films based on m-LLDPE of LUCENE brand had the maximum strength properties. The optimal content of LDPE in a mixture with LLDPE depends on the type of LLDPE and is no more than 10–20 wt.%.