Comparison of the effect of ethylene and hexene-1 co-monomers on the composition, microstructure, rheology, thermal and mechanical behaviour of randomized polypropylene hetero-phasic block co-polymers
In this work, ethylene and hexene-1 co-monomers were applied in the matrix preparation stage (MPS) of isotactic polypropylene (iPP) reactor alloys to compare the effect of the co-monomer type used in MPS on their interfacial interaction and impact strength. For this purpose, before ethylene–propylene gas phase co-polymerization to produce dispersed phase, propylene was co-polymerized by 0.5, 1.0, 1.5 and 3.0% wt of ethylene and hexene-1 co-monomers in two separate slurry procedures to produce the partially randomized iPP (PR-iPP). Dispersed phase content of reactor alloys was strongly affected by the amount of the co-monomers used in MPS, while ethylene–propylene segmented co-polymers (EPs), as the compatibilizer between the matrix and dispersed phase, were little changed for all samples. SEM micrographs of the modified reactor alloys displayed that matrix modification technique (MMT) improves the morphology of the dispersed phase insofar as a single-phase morphology was seen when an appropriate amount of hexene-1 was used in the MPS. Pal and Palierne rheological models were applied to determine the interfacial tension of reactor alloys and the results illustrated that MMT affects the interfacial tension of matrix-dispersed droplets. Next rheological studies revealed that the interfacial interaction of EPR with the matrix modified by hexene-1 is higher than the matrix modified by ethylene. Improvement of interfacial interaction reduced the degree of crystallinity and overspread the melting thermograms of PR-iPP reactor alloys. Also, the presence of ethylene through the growth of β crystalline forms and hexene-1 via changing the α-form distribution help to improve the toughness of PR-iPP reactor alloys.