Effect Of Silicon Nitirde On The Crystallization Behavior And Mechanical Property Of Polypropylene

Polypropylene （PP） is one of the most commonly used plastics in industrial fields andin our daily lives, which can be attribute to its abundant in sources, good mechanicalproperties, easy processing property and outstanding chemical stability. However, the poorimpact resistance of isotactic polypropylene（iPP）, especially at low temperatures, restrictsits application as engineering plastics. While copolymerized with a few co-monomers（mainly ethylene）, the impact resistance of PP would be greatly improved. The copolymerpolypropylene（CPP） has very broad development prospects. Nano-sized siliconnitride（Si₃N₄） is a type of ceramic material with some special features such as hightemperature resistance, high strength, good hardness and excellent wearing resistance. Notonly can it be used as nucleating agents which can improve the crystallization properties ofpolypropylene, still can further enhance its mechanical properties and expand itsapplication field.The effect of Si₃N₄nanoparticles on the crystallization process of iPP was discussed inthis study. Polarized microscope, wide-angle X-ray diffraction（WAXD） and differentialscanning calorimeter were used for the characterization of iPP/Si₃N₄nanocomposites.Kissinger method and Flynn-Wall-Ozawa method were adopted to analyze thecrystallization kinetics. The results showed that Si₃N₄nanoparticles of different contentwould have different effect on the crystallization behavior of iPP. The Si₃N₄nanoparticlesof2wt%content could effectively accelerate the nucleation process, while Si₃N₄（5wt%）could help reduce the activation energy of crystals growing process. Kissinger equation wasslightly adapted and was used for analyzing the activation energy of nucleation and crystalgrowth. Satisfying results were obtained.The crystallization behavior of pure CPP and CPP/Si₃N₄nanocomposites was alsostudied in this paper. Polarized microscope was used to observe the isothermalcrystallization morphology of CPP/Si₃N₄nanocomposites. Avrami equation, Ozawa equation and Mo’s method were adopted in treatment of the nonisothermal crystallizationkinetics. And Flynn-Wall-Ozawa method was employed to analyze variation trend ofactivation energy during crystallizing process. The results showed that Si₃N₄nanoparticlescould effectively promote the crystallization of CPP.At last, the mechanical properties of CPP/Si₃N₄nanocomposites were studied, withdifferent content Si₃N₄nanoparticles and whiskers. The results showed that both Si₃N₄nanoparticles and Si₃N₄whiskers could obviously improve the mechanical properties ofCPP. Among them, Si₃N₄nanoparticles were better than Si₃N₄whisker in improving theimpact property, while for the tensile strength and bending strength, Si₃N₄whiskers werebetter than Si₃N₄nanoparticles.