Synthesis, Structure And Properties Of Silica/mc Nylon6 In-Situ Nanocomposites

In this thesis, after homogeneously dispersing nano-silica in ε -caprolactam melt, silica/MC nylon6 in-situ nanocomposites possessing evenly dispersed silica were successfully obtained via anionic polymerization. The influence of silica on the monomer conversion and intrinsic viscosity of composites during polymerization was investigated in detail. The mechanisms for the dispersion and stabilization of silica in ε -caprolactam melt were discussed, and the subsequent dispersing behavior of silica in MC nylon6 was also characterized. Furthermore, the crystallization, melting behaviors, mechanical properties as well as thermal stability of the composites were systematically studied. At the same time, the dependence of structure and properties of composites on silica and its dispersion was also elucidated. The main results are summarized as follows:1. The results of anionic polymerization showed that silica had little influence on the polymerization of ε -caprolactam. The strong interaction between nano-silica and caprolactam/sodium-caprolactam (hydrogen bonds and chemical bonds) accelerated the homogeneous dispersion of silica in the medium by the assistance of energy produced from ultrasonic cavitation effect. Sequentially the in-situ polymerized nanocomposites were readily obtained. TEM photographs showed that silica dispersed rather well in MC nylon6 matrix and appeared to be ca .30nm in diameter when the load of silica was lower than 2.0%.2. For the composites with lower silica load (0.5%), silica hindered the crystallization of MC nylon6. In contrast, silica promoted crystallization of polymer matrix with the increase of its load. The corresponding melting behaviors of composites were attributed to recrystallization and reorganization.3. Based on the results of WAXD, the crystalline structure appeared merely in a form in both MC nylon6 and nanocomposites, while nothing more than γ form presented in samples quenched in liquid nitrogen from melt. The quenched samples possessed a form and γ form after annealed at 200℃ for 10hr, however, the strong interaction between silica and MC nylon6 hindered the transition of y form to a form.4. For nanocomposites with homogeneously dispersed silica, due to the interaction between silica and MC nylon6, silica acted as "physical crosslinked points", thus simultaneously enhanced the strength and toughness of MC nylon6.5. Owing to the strong interaction between silica and MC nylon6, silica dramatically enhanced the thermal stability of MC nylon6.