Experimental set-up and characterization of a mLLDPE-PP co-extruded bilayer system

Abstract

The rheological behavior of the bilayer system mLLDPE (metallocene linear low density polyethylene)-PP (polypropylene) obtained by a coextrusion process has been investigated in this work. Metallocene polyethylenes are characterized by a superior toughness, heat sealing, and optical properties when compared with conventional polyethylenes. The purpose of the addition of PP in a two layer structure is to confer a better process facility and an enhanced rigidity to the structure itself. A rheological characterization of the two polymers was performed in order to study the flow behavior in each resin, and to verify their compatibility in a coextrusion process. Films, containing different percentages of metallocene polyethylene, were produced by a cast coextrusion process. Moreover, a mathematical modeling of the process was done in order to predict the die pressure gradient, the relative thicknesses, and the shear stress distributions as function of working conditions and rheological properties in the individual polymers. A preliminary investigation on the effect of film composition on the performance of the coextruded bilayers was realized by performing some mechanical tests. POLYM. ENG. SCI. 46:874–881, 2006. © 2006 Society of Plastics Engineers