Study of the Effect of EPDM Structure on the Compatibility of PP/LDPE Blends

Abstract

Melt-blending of polymers of dissimilar properties is an attractive route for producing new products of optimal properties if compatibility can be assured. This study is to assess the effectiveness of five types of ethylene-propylene-diene terpolymers (EPDM) as compatibilizers for enhancing the compatibility of polypropylene (PP)/low density polyethylene (LDPE) blend. The EPDM used differ in the type of the diene, the ethylene content, and two of them are grafted with maleic anhydride (MA) with different grafting density. The blends are characterized by mechanical testing, advanced rheometrics expansion system testing, differential scanning calorimeter (DSC), and scanning electron microscopy (SEM). The EPDM loading and the PP/LDPE mass ratio are fixed at 5 wt% and 30/70, respectively. Mechanical testing shows that EPDM of all structures enhances considerably the elongation at break of the blend but with some drop in the elastic modulus and tensile strength. However, EPDM-g-MA is better than the other compatibilizers for enhancing significantly the ductility of the blends without severely compromising the stiffness property. Rheological testing shows the increase in the viscosity and storage modulus of the PP/LDPE melt upon the addition of EPDM of all structures, with undistinguished differences between EPDM structures themselves. The melting points of the blend components are not affected by the addition of EPDM of all structures, as revealed by DSC. SEM results confirm the finer morphology obtained, relative to the unfilled blend, upon the addition of EPDM of different types, and this could be directly relevant for the improvement of the elongation at break property.