Polypropylene random copolymer in pipe application: Performance improvement with controlled molecular weight distribution

The performance of polypropylene random copolymer (PP-R) for pipe applications, including their processibality and final mechanical properties, can be balanced by finely controlling the molecular weight distribution (MWD). In this study, two representative samples chosen from a material optimization design procedure were analyzed. Rheology tests showed that broadening MWD will improve the processability of PP-R. The samples were then fractionated according to molecular weight and studied by isothermal and non-isothermal crystallization kinetics as well as self-nucleation and annealing (SSA) technique. The results indicated that the ultra high molar mass component resulting from a broader MWD can act as nucleation agent, which might decrease the spherulite size and increase the tie-chain content of PP-R. Finally, polarized optical microscope (POM) and tensile tests were carried out to ascertain these speculations. It appears that finely controlling the MWD has a synergetic effect on the processability and mechanical properties of PP-R. (C) 2014 Elsevier B.V. All rights reserved.