Phase segregation in multi-component polymer systems

grantor: University of TorontoThe phase segregation investigated in this work is the migration of dispersed particles or droplets to preferred locations in a polymer melt. An understanding of this area can lead to polymer processing directed at de-mixing polymer blends for recycling purposes and at the formation of multi-layer structures of polymers without co-extrusion. Although it is now recognized that viscosity ratio is an important factor in achieving phase segregation in polymer melts, non-Newtonian and elastic effects complicate the situation. This thesis is an investigation of these effects. The thesis centers on testing four hypotheses: (1) phase segregation does not take place in a Newtonian fluid; (2) in a shear thinning fluid having negligible elasticity, migration of the dispersed phase will be towards the high shear rate region of the flow; (3) in a significantly elastic fluid having negligible variation of viscosity with shear rate, migration of the dispersed phase will be towards the low shear rate region of the flow and; (4) in a fluid which is both shear thinning and elastic, the direction and extent of migration will depend upon the relative "strength" of the shear thinning and elastic effects. The validity of these hypotheses was tested using three types of experiments (all conducted at 250°C): melting and shearing a rod of the polymer containing the particles at well defined positions in a Couette apparatus (Couette-Rod Experiments); shearing of a polymer melt containing dispersed phase, which was extruded into the Couette apparatus (Couette-Extrusion Experiments) and; flow of a polymer melt containing the dispersed particles in a very long tube (Tube Experiments). Experiments were performed using both rigid particles (Glass beads) and deformable droplets (Polyamide 612 (PA612) droplets) as the dispersed phase. Polycarbonate (PC) was used as the Newtonian fluid for testing the first hypothesis. Poly(acrylonitrile butadiene styrene) copolymer (ABS) melt served as the test fluid in validating the remaining three hypotheses due to its particular dependence of rheological characteristics upon the shear rate. (Abstract shortened by UMI.)Ph.D