Polyamide-12 layered silicate nanocomposites by melt blending

Polyamide-12/tetrasilisic fluoromica (PA12-ME100) and polyamide-12/quaternary tallow ammonium chloride modified fluoromica nanocomposites (PA12-MAE) were prepared by melt compounding. The nanocomposite morphology and clay dispersion were investigated using wide angle X-ray diffraction (XRD), scanning electron microscopy (SEM), SEM-energy dispersive X-ray analysis (SEM-EDX), transmission electron miscroscopy (TEM), high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). A predominantly intercalated morphology was observed for PA12-ME100, and a very high degree of exfoliation for PA12-MAE. HRTEM showed that the polymer crystallites lie perpendicular to the clay surface. The tensile and flexural properties of the PA12-MAE nanocomposite were significantly enhanced compared to neat polyamide-12, even with the addition of only 4 wt% nanoclay. Furthermore, the elongation at break (%) increased from 180% for polyamide-12 up to >500% for the PA12-MAE nanocomposite. In situ measurement of the heat generated in the test specimens during uniaxial tensile deformation using infra-red thermal imaging showed that the temperature of the dumbbell samples increased from room temperature (23 °C) to as high as 70 °C regardless of the strain rate used. This is considerably above the glass transition temperature (T_g) of PA12-MAE (30 °C), as measured by dynamic mechanical thermal analysis (DMTA). The mechanism of deformation is partially explained in terms of microvoid formation. The shear viscosity of the PA12-MAE nanocomposite determined by dual capillary rheometry was lower than both neat polyamide-12 and PA12-ME100. The reduction in shear viscosity of the nanocomposites was shown, from gel permeation chromatography (GPC) studies, not to originate from polymer degradation during melt blending. The coefficient of thermal expansion, decomposition temperature, and melting and crystallisation temperatures and relative crystalline content of the nanocomposite materials were measured by thermo-mechanical analysis (TMA), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) respectively—properties which can be related to polymer nanoclay interactions.