Miscibility and rigid amorphous phase in blends of polypropylene with poly(propylene‐co‐ethylene)

Abstract

AbstractThermal and mechanical properties of binary blends of polypropylene (PP) with a statistical copolymer (85 wt% propylene and 15 wt% ethylene, abbreviated here as VM) have been investigated. Both components were found to be miscible in the melt in the whole range of compositions. No separate domains of VM have been detected by polarizing optical microscopy, and the size of spherulites is going down with increasing VM content. The crystallization temperature of PP as detected by DSC, is going down to 83°C, for PP/VM blends 10:90. This is another evidence for miscibility in the melt. Viscoelastic properties of the melt were measured. Regarding the solid state, the melting enthalpy is exactly proportional to the PP content in the blend. The DSC step height at the glass transition is exactly proportional to the VM content. These results are suggesting a three‐phase model (crystalline, rigid amorphous, and mobile amorphous phase), where the VM component is mainly located in the mobile amorphous regions, while the amorphous part of PP is in the rigid amorphous regions. Stress–strain curves show a systematic increase of elongation at break with increasing VM%, to be extended from 7.8% to more than 550%.