Effect of interphase and strain-rate on the tensile properties of polyamide 6 reinforced with functionalized silica nanoparticles

The effects of the polymer/nanofiller interphase as well as the strain-rate on the tensile behaviors of polyamide 6 (PA6) nanocomposites were studied. Two types of nano-silica with different surface modification (hexamethyldisilazane and 3-aminopropyltriethoxysilane, denoted as HMDZ and APTES) were used as filler. The tensile responses of all nanocomposites, under strain-rates of 1 × 10−3 and 3 × 102 s−1, were investigated. A Hopkinson Split Tensile Bar (SHTB) device was successfully applied to study the high speed tensile properties. The experimental results showed that nanocomposites tend to illustrate obviously increased tensile strength and dropped ductility under high speed loading in comparison with low speed cases. On the other hand, it is observed that the incorporation of amine-functionalized APTES–silica can yield simultaneous enhancement of both stiffness (modulus/strength) and ductility (failure strain) under high strain-rate. Further interfacial analysis using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) indicated that covalent binding of PA6 with amine-featured nano-silica constructs a strong and tough interphase and is the major contributor to the enhanced mechanical properties. Dynamic reinforcing mechanism was speculated as: the covalently-bonded nano-silica may inhibit the propagation of micro-cracks and even pin cracks, thus more energy can be absorbed and dissipated effectively.