Study On Polypropylene Composite Toughened By Surface Modified Needle-Like Nano-CaCO₃

As a functional filling material, nano-caleium carbonate (nano-CaCO₃) is widely used in many fields such as plastic, rubber, paint, pigment and paper.In this paper, needle-like nano-CaCO₃ was prepared by adding additives in the pilot-plant using bubbling carbonization method. The mean diameter of the product is 20～90nm with 10～15 aspect ratio and the specific surface area (BET) is about 20～70m²/g.Isomeric polypropylene (PP) is a most common commodity plastic; however, PP is notch sensitive and brittle under severe conditions of deformation, which has limited its wider range of engineering usage. Incorporation of rigid inorganic particles is a promising approach to improve both stiffness and toughness of plastic simultaneously, in which surface modifier is very important for the interface incorporation between PP and CaCO₃. In this study, best surface modifier was selected and PP/nano-CaCO₃ composites were prepared by melt blending method. The needle-like nano-CaCO₃ with average diameters of 70nm was used as filler from 0-9.60 wt%. The influence of surface modifier on the properties of PP/nano-CaCO₃ composites was studied. The experiments included tensile tests, impact tests, flexural tests, scanning electron microscopy, polarized optical microscopy and X-ray diffraction.By adding 4.21% of nano-CaCO₃ to PP with the selected surface modifier, the experimental results indicate that the impact strength, elongation at break increased by 49% and 339%, respectively, while the tensile was decreased 2.7%. The presence of surface modifier decreases the interfaeial interaction between nano-CaCO₃ particles and PP matrix. Based on Percolation theory, the essential condition occurring brittle-tough transition in this ternary system was L=Lc(≈0.034μm). The morphology of the impact fracture surface of composites was observed by SEM, nano-CaCO₃ were dispersed uniformly in the matrix. Acting as multi-nuclei, the presence of needle-like nano-CaCO₃ particles caused small and imperfect PP spheruliters and decreased the spherulite growth rate, however, not induced formation ofβ-form PP.