Effect of pimelic acid on the crystallization, morphology and mechanical properties of polypropylene/wollastonite composites

The pimelic acid (PA) was used as a new surface modifier for wollastonite. The effects of PA treatment on the crystallization, morphology and mechanical properties of polypropylene/wollastonite composites were investigated. The Fourier transform infrared spectroscopy analysis revealed that the PA bonded to the wollastonite's surface and formed the calcium pimelate after reacting with the wollastonite. The results of wide angle X-ray diffraction, differential scanning calorimetry and polarized light microscopy proved that the PA treated wollastonite induced more β-crystalline form and decreased the spherulites sizes of polypropylene. The results of scanning electron microscopy showed that the PA treatment enhanced the interfacial adhesion between the filler and the matrix, indicating the improvement of the compatibility between polypropylene and wollastonite. The toughness of the composites was improved by the more ductile β-form spherulites. When 2.5 wt% of PA treated wollastonite was added, the Izod notched impact strength reached its maximum, a value of 17.33 kJ/m², which was 3.19 times greater than that of the blank polypropylene.