| Addition of nucleating agents and additives is a simple and useful method to optimize PP. Generally speaking, addition of nucleating agents increase crystallization rate, reduce spherulite size and shorten product circles, which affect the physics and chemical properties of polymer materials.In this paper, precious studies on the modification of polyoxymethylene (POM) and polypropylene (PP) have been reviewed. Small amount of Polyvinylidene Fluoride(PVDF) as a polymer nucleating agent has been added into POM and PP, respectively, then mixed in a twin-screw extruder and followed by injection moulding into standard samples for property tests. The influence of addition and content of PVDF on the crystal structure morphology and crystallization behavior of POM and two different brands of PP were investigated by means of polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD) and differential scanning calorimeter (DSC). Thermal-gravity analysis (TGA), heat treatment and illumination in natural sunshine for long period were also performed to study the mechanical properties,thermal stability of POM/PVDF blends and the ageing resistance of PP/PVDF blends.The crystal structure and morphology of POM/PVDF and PP/PVDF blends were investigated by PLM. The results showed that the size of spherulites of POM and PP decreased with small amount of PVDF. The PVDF has a nucleaing role on the crystallization of POM and PP, resulting in diminishing the size of spherulite and size distribution of crystallite. In this experiment, the size of POM spherulites decreased with the addition of PVDF till the composition of POM/PVDF was 100/4, and then, the spherulites of POM began to increase with higher content of PVDF. The spherulites size of PP had no obvious changes with the further increase of PVDF content.The influence of PVDF on crystallization performance of POM and PP were investigated. DSC and WAXD measurements showed that the addition of PVDF had no obvious effect on hexagonal system of POM crystal andα-monoclinic crystal of PP. PVDF acts as a nucleation agent in POM and PP, and heterogeneous nucleation domains during crystallization, thus upgrades the crystal temperature and nucleation rate.The DSC thermograms of POM/PVDF blends at different cooling rates were recorded to estimate their non-isothermal crystallization kinetics. Several equations were used to analyze the crystallization kinetic data of the samples. The kinetic analysis indicated that the applicability of the modified Avrami equation and Ozawa equation failed to provide an adequate description of the non-isothermal crystallization of POM and POM/PVDF blends because of the comparisons of different stages of crystallization at different cooling rates. However the combined Avrami and Ozawa equation can successfully describe the crystallization processes .The effects of PVDF on mechanical properties of POM and PP were investigated. The results showed that the impact strength of POM/PVDF and PP/PVDF increased with the addition of PVDF, when the composition was POM(PP)/PVDF=100/4, POM/PVDF and PP F-401/PVDF blends got the maximum impact strength, further increasing of PVDF content resulted a slight weakening of their impact strength, but it always higher than that of pure PP.The thermal stability tests showed that the residual mass percent and the degradation temperature of POM/PVDF blends were higher than that of pure POM, which means that the addition of PVDF improved the thermal stability of POM. After the long period illumination in natural sunshine, light oxygenolysis took place in PP, the mechanical properties and melt flow rate (MFR) of PP/PVDF blends all depressed. From the mechanical properties maintenance of PP/PVDF, it's obvious that the addition of PVDF could improve the light-oxygen ageing resistance of PP.
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