The influence of modified zeolites as nucleating agents on crystallization behavior and mechanical properties of polypropylene

Polypropylene (PP) composites with unmodified and modified zeolites were prepared by melt blending in single-screw extruder. The modified zeolites, diethoxy (distearoyl) silane (DDS)–zeolite 13X (DDS-13X) and diethoxy (distearoyl) silane–zeolite 5A (DDS-5A), were obtained by grafting diethoxy (distearoyl) silane onto zeolite 13X and 5A, respectively. The influence of the unmodified and modified zeolites as nucleating agents on properties of polypropylene was investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarized light microscopy (PLM), Vicat softening temperature (VST) and mechanical properties test. The XRD results revealed that zeolite 13X and DDS-13X had a great influence on nucleation of PP compared to zeolite 5A and DDS-5A. The DSC results showed that the addition of small amount of modified zeolites lead to increase in crystallization temperature (Tc), initial crystallization temperature (Tonset) and crystallinity (Xc) of PP composites compared to unmodified zeolites, especially, DDS-13X was more effective than DDS-5A, and the highest crystallinity Xc (50.48%) was observed in PP/0.3 wt.% DDS-13X, which was responsible to the higher tensile strength and flexural strength of PP/DDS-13X. The PP/DDS-5A, however, exhibited evident increase in flexural strength and a little change in tensile strength compared to pure PP. Moreover, as the addition amount of DDS-5A or DDS-13X up to 1 wt.%, the impact strength of both PP/DDS-5A and PP/DDS-13X reached 43 kJ/m2, which was about 2.8 times greater than that of the pure PP (11.3 kJ/m2). These results were in good agreement with the spherulite morphology observed from PLM micrographs.