Abstract:

A series of high melt flow index(MFI) polypropylene(PP) in-reactor alloys with different contents of hexane soluble fraction was prepared by bulk-gas phase polymerization process using spherical Ziegler-Natta catalyst(phosphate as internal electron donor). The mechanical properties and microcosmic morphology of the obtained PP in-reactor alloys were investigated. It was found that the impact strength increased with the increase of hexane soluble fraction. Impact strength increased from 4.4 kJ/m2 to 52.7 kJ/m2. While the flexure strength and tensile strength slightly decreased, tensile strength decreased from 28.6 MPa to 19.5 MPa, the flexure strength decreased from 37.2 MPa to 21.5 MPa. According to the micrographs of FESEM, the ethylene-propylene rubber(EPR) phase was evenly dispersed in PP matrix and formed “core-shell” structure.

Key words: PP in-reactor alloy, Bulk-gas phase polymerization, Ziegler-Natta catalyst, ‘Core-shell&rsquo, structure