Non-isothermal crystallization kinetics and morphology of wollastonite-filled β-isotactic polypropylene composites

To obtain wollastonite-filled beta-iPP composites, the wollastonite with beta-nucleating surface (beta-wollastonite) was prepared through chemical reaction between wollastonite with alpha-nucleating surface (alpha-wollastonite) and pimelic acid. The formation of calcium pimelate on the surface of wollastonite was proved using Fourier transform infrared spectrometry and scanning electron microscopy. The crystallization behavior, melting characteristics, non-isothermal crystallization kinetics, and crystalline morphologies of alpha- and beta-wollastonite-filled iPP composites were studied by differential scanning calorimetry and polarizing optical microscopy. It is found that the crystallization peak temperatures of beta-wollastonite-filled iPP composites were higher than that of alpha-wollastonite-filled iPP composites, which indicated that wollastonite with beta-nucleating surface has stronger heterogeneous nucleation than that of wollastonite with alpha-nucleating surface. Although the crystallization temperatures of iPP and iPP composites decreased with increasing cooling rates, alpha-wollastonite-filled iPP composites mainly crystallized in alpha-spherulite and beta-wollastonite-filled iPP composites formed beta-spherulite. In addition, the spherulite size of beta-wollastonite-filled iPP composites was smaller than that of alpha-wollastonite-filled iPP composites. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of wollastonite-filled iPP composites. The activation energy (a dagger E) and the nucleation efficiency (EN) of non-isothermal crystallization were calculated by Kissinger method and the equation proposed by Fillon, respectively. The beta-wollastonite-filled iPP composites exhibited higher crystallization rate, activation energy, and EN than that of alpha-wollastonite-filled iPP composites.