Influence of the ion content of CaCl2-ionised polyamide-66 nucleator on the crystalline nucleation of poly(ethylene terephthalate) through ion–dipole interactions

Abstract

Polyamide (PA)-66 is successfully ionised with various weight fractions of CaCl₂ to prepare PA-66 ionenes bearing different ion contents (ICs). The PA-66 ionenes against PA-66 are incorporated as heterogeneous nucleators into poly(ethylene terephthalate) (PET) to effectively promote PET crystallisation. Compared to the PET/PA-66 (95/5 wt/wt), the PET/PA-66 ionenes (95/5) markedly improve the crystallisation rate and degree of crystallinity. Notably, as the IC of the PA-66 ionene rises from 0 to 11.4 mol%, the nucleation efficiency first increases and then decreases. This may be attributed to the introduction of strong ion–dipole interactions between the CaCl₂-coordinating amides of the PA-66 ionenes and the esters of the PET matrices as the IC increases, which gradually boosts the PET/PA-66 ionene interfacial compatibility to create finer nucleator crystals with a denser distribution, thereby steadily enhancing the nucleation efficiency. However, once the IC exceeds 6.5 mol%, the dramatically improved interfacial compatibility causes greatly more and thicker amorphous interphase, which inhibits PET crystallisation. The results indicate that the PA-66 ionene containing 6.5 mol% of Ca²⁺ is a promising nucleator to maximise the crystallisation acceleration of PET due to the moderate interfacial compatibility by medium-concentration ion–dipole interactions.