Effects of processing parameters on the preparation of nylon 6 nanocomposites

An experimental study was carried out to investigate the effects of the following parameters: (1) organic modifier and nylon 6 molecular weight, (2) processing conditions, and (3) pressure, with and without supercritical fluids, on the dispersion of clays for nylon 6/montmorillonite nanocomposites. A novel experimental setup was designed that physically separated the melting and mixing unit operations, and allowed control of the pressure using a pressure adjustable die. Exfoliated clay morphology was realized using a wide angle X-ray diffraction technique when both requirements of (1) selecting an organic modifier that was thermodynamically compatible with the polymer matrix and (2) applying sufficient degree of shear stress were fulfilled. Keeping the organic modifier constant, either longer residence time or the same level of shear stress did not improve the state of clay dispersion once a critical morphology was established. In the absence of supercritical fluids, pressure improved the clay delamination by reducing the free volume of the polymers and thereby increasing the interaction between the chains, and ultimately increasing the viscosity and, therefore, the level of wall shear stress. Using supercritical fluids such as either carbon dioxide or 1,1,1,2-tetrafluoroethane did not improve the clay dispersion for 95/5 N6-L/20A due to its role in increasing the free volume and decreasing the melt viscosity.