The effect of crystal water in calcium salt of hexahydrophthalic acid on nucleation efficiency in isotactic polypropylene

The calcium salt of hexahydrophthalic acid (HHPA-Ca), an effective nucleating agent for isotactic polypropylene (iPP), was synthesized through neutralization. The presence of crystal water in HHPA-Ca may significantly influence the processing and performance of iPP. In this study, HHPA-Ca was dehydrated to eliminate crystal water (HHPA-Ca-RCW), and its properties were compared to those of undehydrated HHPA-Ca (HHPA-Ca-CW). The structural characteristics of HHPA-Ca, both before and after the removal of crystal water, were analyzed using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The influence of crystal water on the nucleation of iPP was investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM), and mechanical property testing. The results demonstrate that HHPA-Ca-RCW exhibits higher nucleation efficiency in iPP, leading to an increase of 8.1 °C in the crystallization peak temperature (Tc) upon the addition of 0.04 mass%. This modification also promotes the rapid formation of a significant number of spherical crystals. Moreover, HHPA-Ca-RCW, when incorporated into nucleated iPP, maintains toughness of iPP while showing a modest enhancement in stiffness.