Synthesis And Properties Of The In-situ Surface-Modified Nano-SiO₂/Nylon 1010 Composites

The PA1010-based nanocomposites containing different surface-modified nano-SiO₂ were prepared by melt blending method and in-situ Polymerization. The nylon 6 /nano- SiO₂ composites were prepared by in-situ polymerization. The mechanical properties of nanocomposites were investigated in detail. The mechanisms of reaction between the different surface-modified nano-SiO₂ and the nylon matrix were presumed and discussed, and the subsequent dispersing behavior of silica in nylon matrix was also characterized. Furthermore, the microstructure, crystallization, melting behaviors as well as thermal stability of the composites prepared by melt blending were systematically studied. At the same time, the effect of diferent surface-modified nano-SiO₂ on the structure and properties of composites was also elucidated. The main results are summarized as follows:1. For the nano- SiO₂ /nylon1010 composites prepared by melt blending, the results of mechanical testing showed that the addition of reactable nano-SiO₂ (RNS) could reinforce the tensile strength, impact strength,break elongation and Yong's modulus of nanocomposites. It could improve the mechanical prorerties and had good effects on the reinforcement and toughening of the composites. The incorporation of dispersible nano-SiO₂ (DNS) could increase the notched impact strength and break elongation of nanocomposites in the case of holding the Yong's modulus of material; but it would produce a negative influence on the tensile property of nanocomposites. For composites prepared by in-situ polymerazition, the addition of nano-SiO₂ (whether RNS or DNS) could enhance the toughness and stiffness of composites, but the change of material tensile strength was not obvious.2. In order to farther analyse more deeply the interaction between different surface-modified nano-SiO₂ and PA1010 matrix during the preparation of nanocomposites, the extraction treatment of nanocomposites was used, and extraction products were investigated by Fourier-transform infrared spectroscopy. The results showed that there was a strong interaction at the interface of RNS and PA1010 matrix, which promoted the formation of interface structure based on hydrogen bonding and covalent bonding. The interfacial interaction of DNS and PA1010 matrix is not very strong, which was connected each other only by few hydrogen bonding and intertwist of chains segments. When mechanical properties of RNS / PA1010 and DNS / PA1010 nanocomposites are compared, it is found that different surface structure of nanoparticles would produce different influences on the mechanical properties of nanocomposites. In addition, based on the result of TGA the addition of nano-SiO₂ could enhance the thermal stability of composites, but the effect of RNS on the thermal stability of material was more than that of DNS. The results showed that thermal properties of nanocomposites were closely correlated with the different surface structure of nano-SiO₂.3. Melt and crystallization behavior of DNS / PA1010 and RNS / PA1010 nano-composites prepared by melt blending were also investigated. The results showed that the addition of DNS and RNS had the different effect on the melt and crystallization behavior of the composites. The addition of RNS increased the melt temperature and decreased the crystallization temperature of nanocomposites, promoted the crystallization of PA1010. At the same time the RNS increased the crystallinity of PA1010. While as a nucleating agent, DNS reduced the melt tempreature and increased the crystallization tempreature of composites. But it made the crystallinity of nanocomposites decreased a little. In the study of crystallization structure of nanocomposites, it was found that the addition of RNS and DNS did not change the crystal form of nylon 1010.4. The microstructure of nano-SiO₂ / nylon1010 composites prepared by in-situ polymerization was characterized by scanning electron microscopy (SEM), X-ray Diffraction (XRD) and Differential scanning calorimetry (DSC). The results indicated that RNS and DNS could disperse rather well in nylon matrix. The addition of RNS and DNS changed the crystal form, hindered the formation of theγ-crystalline of nylon 1010. Nano-SiO₂ made the melt temperature of nylon1010 increased 4⁵ oC and the crystallization temperature increased 5⁸ oC. These indicated that the filling of SiO₂ acted as the heterogeneous nucleation spot of the crystallizing induced and made crystallizing process easier at higher temperature. At the same time, it is found that the effect of the nano-SiO₂ added by in-situ polymerization on the melt and crystallization behavior of nylon1010 was much more than that of it added by melt blending.5. The MC PA6 / nano-SiO₂ composites were prepared by in-situ polymerization and their properties were investigated. The results showed that nano-SiO₂ had little influence on the polymerization ofε-caprolactam when the load of nano-SiO₂ was low. The strong interaction between nano-silica and caprolactam/sodium- caprolactam (hydrogen bonds and chemical bonds) accelerated the homogeneous dispersion of silica in the medium. Sequentially, this strong interaction made the tensile and impact strength increased, which indicated that in-situ surface-modified nano-SiO₂ not only could strengthen but also toughen the nylon matrix. The results of XRD indicated that both MC nylon 6 and its RNS and DNS nanocomposites showed a typicalαcrystalline form diffraction peak. This meaned nano-SiO₂ did not change the crystal modality of nylon 6. The TGA results showed that nano-SiO₂ increased thermal stability of composites and the effect of RNS was much more than that of DNS, which were closely correlated with the different surface structure of nano-SiO₂.