The effects of long chain branching of polypropylene and chain extension of poly(ethylene terephthalate) on the thermal behavior, rheology and morphology of their blends

Abstract

In this work the blends of long chain branched polypropylene (BPP) and chain extended/branched PET (MPET) were prepared and the melt and crystallization characteristics, rheological properties in shear and elongational mode for BPP, MPET and their blends in correlation with their morphology were studied with various amounts of PP grafted maleic anhydride as compatibilizer. BPP is prepared by using dicumyl peroxide and trifunctional monomer trimethylolpropane trimethacrylate (TMPTMA) and MPET were prepared by using tetrafunctional modifier pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA). The rheological study showed the increase in melt shear and elongational strengths of MPET after the chain extension process and increase in shear thinning and strain hardening behavior of modified samples. The zero shear viscosity and shear thinning index of PET increased from 210 Pa s and n′ = 0.15 to 315 Pa s and n′ = 0.22 after modification and for PP they decreased from 4940 Pa s and n′ = 0.54 to 1170 Pa s and n′ = 0.45. These results prove that increase in molecular weight and widening of molecular weight distribution are the major consequences of PET modification and chain scission; narrower MWD and long chain branching are the main phenomena of branching of PP. A slight nucleation effect of MPET on BPP was observed and its crystallization temperature (T_c) increased from 119.7 to 121 °C. By increasing compatibility and decreasing heterogeneity, the T_c of BPP slightly decreased and due to the reaction of MPET and maleic anhydride functional groups, the chain mobility was restricted and crystallization and fusion enthalpies decreased.