Insight into the less β-phase induction by calcium pimelate in polypropylene random copolymer

Abstract

Although calcium pimelate (CaPim) is recognized as an efficient β-nucleating agent for polypropylene with nucleating ability solely for the β-phase, it was found to induce less β-phase in polypropylene random copolymer (PPR) compared to polypropylene homopolymer (PPH). Generally, this reduction is attributed to unfavorable β-growth. Besides growth, here, nucleation behavior was also investigated in detail. With nucleation barrier determined through fractionated crystallization, the relative β-nuclei proportion induced by CaPim was calculated to be 96.6 % for PPH and 79.1 % for PPR with 7.3 mol% ethylene inserted. This fewer β-nuclei induction may be linked to a decreased proportion of isometric sequences exceeding the critical length required for β-nucleation. As expected, the relative growth rate of the β- to α-phase (G_β/G_α) is lower in PPR indicating unfavorable β-growth. These results indicate that diminished β-nuclei induction and subsequent unfavorable β-growth jointly result in less β-phase induction in PPR.