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

•Two PP-R samples were obtained from the material optimization design procedure.•The processibility was evaluated by rheology tests and theoretical calculations.•The crystallization behaviors were analyzed.•The ultra high molecular weight component acted as nucleation agent.•The long-term property was evaluated.

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.