Melt processing of thermoplasticclay nanocomposites

Polymer/clay nanocomposites are materials composed of a polymer matrix and nanometer size clay particles. They exhibit significant improvements in tensile modulus and strength, reduced permeability to gases and liquids, compared to the pure polymer. These property improvements can be realized while retaining clarity of the polymer without a significant increase in density (typical clay loading is 2--5%). The aim of this research was to achieve maximum exfoliation of the clay and property enhancement in the nanocomposite by melt processing.The components of the Hansen solubility parameters and the Hamaker constants of the constituents were used to establish the compatibility between the polymer matrix and nanoclay. A mathematical model was formulated to study the mechanism of exfoliation of clay platelets in the polymer matrix. The mechanism of size reduction of clay particles was shown to be by erosion or surface peeling. A novel continuous process (System A) was developed and implemented to produce nanocomposites. The process incorporates chaotic mixing, efficient shearing and stretching of the melt, frequent changes in flow direction and higher residence time, in order to enhance exfoliation.The efficiency of the process was demonstrated, using transmission electron microscopy, wide angle X-ray diffraction, viscosity measurements, tensile and highspeed impact testing, and oxygen permeability measurements. Polyamide nanocomposites prepared with System A show a higher degree of exfoliation and better enhancements in mechanical and barrier properties than those prepared using conventional twin-screw extrusion (System C). Polystyrene nanocomposites show higher increase in the d-spacing of organoclay and improvement in barrier properties for System A than for System C, indicating higher specific surface area for the filler particles. The Pukanszky parameter was negative for PS nanocomposites, indicating poor polymer/clay adhesion.The crystallization kinetics of PA-6 nanocomposites were studied using high pressure dilatometry. The nanoclay seems to act as nucleating agent, increasing the rate of crystallization of PA-6 in the nanocomposite. The effect of the clay on the kinetics of formation of different PA-6 crystalline phases was evaluated and explained