| Nano-silicon nitride (SisN4) powder is a high performance structural ceramic material and it has been widely used in the preparation of polymer nanocomposites. However, the high surface energy and large specific surface area of nano-Si3N4easily leads to aggregation when it is used in the materials. So the powder can not reach nanometer scale dispersion in the polymer matrix. By adding modifier, the compatibility between polymer matrix and nano-particles as well as the dispersion of nano-particles can be improved effectively. A lot of literatures have described the methods of developing novel polymer-based nanocomposites with special properties using high performance inorganic nano-particles, but it is not clearly explained on how the nano-particles affecting the crystallization behavior of semi-crystalline polymer matrix. In this paper, the surface modification of nano-SisN4, the dispersion behavior of nano-Si3N4in the semi-crystalline polymer matrix, the crystallization behavior of the polymer matrix and the impact of nano-Si3N4on the crystallization process of the polymer matrix are deeply investigated.1. According to the chemical structure characteristics of the crystalline polymer and the experience of our laboratory, low molecular modification agent KH570is used to modify the surface of nano-Si3N4and improve the compatibility between nano-Si3N4and the polymer matrix as well as to prevent the happening of the aggregation. The structure of modified nano-Si3N4is investigated by IR,TGA, TEM and settlement experiment, The results show that modifier KH570is already successful bonded on the surface of nano-Si3N4, the best percentage is33wt%and the chemical coating rate is13.05wt%, the modified nano-Si3N4has reached nanometer scale dispersion in the polymer matrix.2. The composites of PCL/nano-Si3N4and PEO/nano-Si3N4were prepared by solution blending. The crystallization behavior of polycaprolactone (PCL) and PCL/Si3N4nanocomposites is measured by DSC, polarizing microscope (POM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and how the cooling rate, the content of nano-Si3N4, the surface properties of nano-Si3N4and other factors’effect on the crystallization process are explained too. The results show that nano-Si3N4has nucleation effect and can reduce the dependence of the polymer on the cooling rate, while the crystal structure of PCL is not changed during the process. With the increasing content of nano-Si3N4, the crystallization temperature Tc and the initial crystallization temperature Tstart of polymer matrix are improved when the content of nano-Si3N4reaches5wt%, Tc and Tstart can reach maximum. The spherocrystal growth rate of PCL are16.46×10-3μm/s and12.83×10-μm/s when the isothermal crystallize are at44℃and48℃, respectively, while the spherocrystal growth rate of PCL/Si3N4composite is3.87×10-3μm/s when the isothermal crystallize is at48℃. The slower the spherulite growth rate, the bigger the spherocrystal radius is.3. The crystallization curve and the molten curve of PEO and PEO/Si3N4nanocomposites are measured by DSC. The changing of the crystallization temperature Tc and melting temperature Tm and AH with different molecular weight and are summarized. Further data processing is made to get the curve of the relative crystallinity Xt with crystallization time and the data is simulated by using Avrami equation. The plots of the spherocrystal radius to the crystalline time and the crystalline nucleation density to the crystalline time are investigated by analyzing the PEO photos. The changing of the spherocrystal radius and the crystalline nucleation density with different molecular weight are explained. The crystal structure of the polymers is studied by using TEM and XRD, and the results show that the crystal structure of PEO is independent on the molecular weight. But the PEO with low molecular weight has a better crystallinity and more perfect crystal structure. |
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