Investigation On The Preparation Of PA6/POE/OMMT Ternary Nanocomposites By Two-step Melting Blend And Its Structure-properties Relationship

As an engineering plastic, Nylon 6(PA6) shows excellent abrasion resistance, self-lubrication, heat resistance, good oil resistance and high mechanical strength, etc. However, PA6 also posseses some disadvantages such as high water absorption, low heat distortion temperature and low impact strength. Generally, the addition of elastomer can significantly improve the toughness of nylon, but it also results in the loss of strength, stiffness as well as heat distortion temperature. The application of montmorillonite(MMT) in nylon/elastomer blends leads usually to a certain compromise. At present, many studies focus on nylon/elastomer binary blends and nylon/MMT nanocomposites.However, there are few reports of nylon/elastomer/MMT ternary blends.This paper aims at improving their comprehensive performance two-step melting blend method was used to prepare PA6/POE/OMMT ternary nanocompites.We systematically investigated the structure, mechanical and barrier properties as well as rheology, melting behavior and crystallization kinetics.The main research work related to the content and results are listed as following:(1)Preparation and characterization of PA6/POE/OMMT nanocompositesToughened PA6/POE blends were prepared by in situ compatibilization in twin-screw extruder, and then PA6/POE/OMMT ternary nanocomposite was prepared by melt intercalation of the compatibilized PA6/POE blends and organic-modified montmorillonite.Their structer were characterized by Fourier transform IR (FT-IR) spectroscopy, wide angle X-ray diffraction(WAXD) and scanned electron microscope (SEM); the thermal properties were investigated using Differential scanning calorimetry(DSC) and thermal gravity(TG);The mechanical properties, water absorption and oil absorption were also analyzed. These experimental results showed that the mechanical and barrier properties as well as thermal stability of the ternary nanocomposite were improved in comparison with the neat PA6.(2) Investigation on the rheological behaviors of PA6/POE/OMMT nanocompositesNon-Newtonian indexes(n) of the selected temperature is less than 1 in the range of the experimental shear rate,which indicated that the melt of ternay nanocomposites were pseudo-plasitc and exhibited shear-thinning behavior. The n values were also decreased with the increasing montmorillonite content.In the case of constant shear stress and shear rate, the maximum apparent viscosity was obtained at the 3% loading level of OMMT. It was also found that the addition of the OMMT led to reduce the viscous activation energy.(3) The melt behaviors and crystallization kinetics of PA6/POE/OMMT nanocompositesThe crystallization process and melting behaviors of PA6/POE/OMMT nanocomposites were investigated by DSC and POM (Polarized Optical Microscopy). It was found that the Avrami equation described well the isothermal crystallization of nanocomposites.The OMMT served as nucleating agent and did not change the crystal forms of PA6 matrix;The Ozawa equation was not suitable to describe the non-isothermal crystallization process, while the modified Avrami and Mo equations took great advantages over treating the non-isothermal crystallization kinetics. Although the incorporation of OMMT increased the crystallization nucleating rate of PA6, it didn't change the mechanism of nucleation and the growth of crystallites. The data calculated from the Hoffman-Lauritzen theory and its deduction revealed that the addition of POE decreased the absolute values of effective activation energy and the effective activation energy of non-isothermal crystallization. Some important parameters for the crystallization kinetics were obtained. Additionally, the equilibrium melting temperature and the activation energy of nonisothermal crystallization for nanocomposites were calculated from Hoffman-Weeks equation and Hoffmann-Lauritzen theory.The results of POM showed that the size of PA6/POE/OMMT blends crystal ball decreased, while the number increased.