In-situ Preparation, Characterization And Properties Of Nylon 11/Silica Nanocomposites

Polyamide 11(PA 11)is an engineering plastics with excellent performance, such as low water absorption and high low-temperature impact strength. PA11 was mostly used as automobile pipe-laying and municipal gas pipe as well as offshore oilfield application.But with the increasing request of low cost and high mechanical properties,pure PA11 resin can not fully satisfy various usages.To solve these above-mentioned problems, PA11/silica nanocomposites(PSN-X, where X represent the weight percentage of silica) were in-situ polymerized using 11-amino undecanoic acid and wet silica as raw materials, and their morphology structure, thermal stability, rheological behavior,crystallization properties, mechanical properties and barrier properties were investigated by scanning electron microscopy (SEM), fourier-transform infrared spectroscopy (FTIR),thermo-gravimetric analyzer (TGA),capillary rheometer, differential scanning calorimeter (DSC) and polarizing microscopy (POM),respectively.The main results were listed as following:1.Silica of small particle size and narrow distribution was prepared by oil-in-water microemulsion, and was uniformly dispersed in PA 11 matrix during in-situ polymerization. Strong interaction was observed between PA11 and silica. With the increasing silica content, the inherent viscosity gradually decreased and the initial temperature of weight loss improved slightly.The addition of silica contributed to improve the tensile strength, flexural strength, thermal stability and barrier property of PA11,while it also led to reduce the impact strength and elongation at break.2.Rheological properties of PA11/silica nanocomposites were investigated by capillary rheometry. The experimental results showed that both PA 11 and PA11/silica nanocomposites were pseudoplastic fluid and exhibited shear-thinning behavior. Non-newtonian index increased with the silica content increasing.In case of a constant shearing rate, apparent viscosity of all PA11/silica nanocomposites except PSN-5 was lower than that of pure PA11.The reduction of the viscous activation energy with the increasing shearing stress indicated that nanocomposites can be processed over a wide temperature at a constant shearing stress.3.Crystallization and melting behavior of PA 11 and PA11/silica nanocomposites were investigated by differential scanning calorimeter. It was found that silica acted as the nucleating agent of PA11,the Avrami equation was suitable to describe the isothermal crystallization of PA11 and its nanocomposites,while both the Avrami equation modified by Jeziorny and Mo's method well described the nonisothermal crystallization kinetics. 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.