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Morphology and Properties of polypropylene/low density polyethylene blends compatibilized by ethylene-propylene –diene terpolymer

Processing and compatibilization effects on the phase morphology and thermal properties of polypropylene (PP) and low density polyethylene (LDPE) blends were investigated. Ethylene-propylene–diene terpolymer (EPDM) was used as compatibilizer. The influence of blends composition and EPDM content on the rheological behavior of the blends in the melt during processing, morphological structure and thermal behavior were studied. Processing characteristics were followed by torque (TQ) and melt pressure in twin screw extruder, while the thermal behavior of extruded and molded samples was measured with differential scanning calorimetry (DSC). Morphological structure were investigated by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) and compared with processing properties and thermal behavior. The addition of PP into LDPE increased torque values of the blends. The torque values of PP/LDPE blends were between the TQ values of the pure homopolymers. With EPDM addition the values of TQ and back pressure are lower in comparison with noncompatibilized blends, what indicated better processibility. The degree of crystallinity (χc) of PP phase was decreased and χc of LDPE phase was increased with higher LDPE content in PP/LDPE blends with and without EPDM. The higher content of EPDM decreased χc of PP phase in comparison with χc of PP phase in PP/LDPE blends without EPDM and in PP/LDPE blends with lower EPDM content. The higher influence of EPDM was obtained on the χc of PP phase then on χc of LDPE phase in all investigated blends. SEM and STEM micrographs of EPDM compatibilized PP/LDPE blends with compositions 80/20 and 20/80 showed particulate morphology, whereas in the blends with compositions 60/40 and 40/60 the morphology was co-continuous. The EPDM compatibilizer was localized mostly on the interface in all cases. The increase in compatibilizer concentration from 5 pph to 7 pph did not have an important impact on the phase morphology.

polypropylene/low density polyethylene blends; compatibilization; morphology; rheological behavior; thermal behavior

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