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Effect of EPDM as compatibilizer on mechanical properties and morphology of PP/LDPE blends

Development of new material with broader application is possible by blending polymers, which will give an enhance properties then individual polymer. Producing new materials by blending two homopolymer is economical acceptable, but also from ecological view. Polyolefins represent most of post-consumer plastics waste, so one of the ways of commingled waste management is forming the polyolefin blends from recycled plastic waste. Polypropylene (PP) and polyethylene (PE) represent most of the waste streams, thus a study was focused on preparing and characterization of PP and low density polyethylene (LDPE) blends. Since most of the polymers are incompatible and immiscible, the resulting PP/LDPE blends will exhibit poor mechanical properties as a consequence of low interfacial adhesion. To improve their compatibility ethylene-propylene-diene terpolymer (EPDM) as compatibilizer was added in PP/LDPE blends, in two different amounts (5 and 7 %). Pure homopolymers and PP/LDPE blends with and without EPDM as compatibilizer were prepared by extrusion in twin screw extruder. The specimens were prepared by injection molding. Mechanical properties, tensile strength at break, elongation at break, Izod impact strength, were chosen to estimate the compatibilization efficiency of EPDM in PP/LDPE blends. Phase structure and stiffness of PP/LDPE blends with and without EPDM were studied by Dynamic Mechanical Analyzer (DMA). The glass transitions of each component were determined from loss modulus (E'') in DMA spectra and interactions between phases were valued through glass transition shifts. The morphology of the blends was investigated by means of scanning electron microscopy. Tensile strength at break was reduced by adding LDPE to PP. EPDM decreased a tensile strength at break. The higher amount of EPDM did not have influence on tensile strength at break except for PP/LDPE 80/20 where the tensile strength at break was increased after addition of higher amount of EPDM. For blends PP/LDPE 80/20 and 20/80 the elongation at break was between values of pure homopolymers. Blends PP/LDPE 60/40 and 40/60 had lower values of elongation at break comparing with pure homopolymers. Additions of EPDM improve elongation at break in all blends. The higher amount of added EPDM did not have larger effect of elongation at break value, except in 80/20 blend. Izod impact test showed low values of noncompatibilized blends. Addition of EPDM improved Izod impact strength. This effect was more pronounced in LDPE– rich phase blends and with higher EPDM content. Storage modulus (E’ ) was decreased by LDPE addition to PP, as well as by EPDM addition in PP/LDPE blends. The shifting of glass transition in PP/LDPE blends with and without EPDM was determined. SEM micrographs of PP/LDPE/EPDM blends showed better compatibility comparing with noncompatibilized PP/LDPE blends.

blends; mechanical properties; morphology; dynamic mechanical analysis

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