Rheology, phase morphology and processing of polymer blends

The development of phase morphology. Theological properties, and processing behavior of mechanical blends of a polystyrene (PS) and three different high density polyethylenes (PE), high density polyethylene and nylon 6 (N6), high density polyethylene and polycarbonate were studied. Phase morphologies were determined by scanning-electron microscopy for: (a) products prepared in a screw extruder/ static mixer system, (b) samples removed from a cone-plate viscometer, (c) extrudates from capillary dies, (d) melt spun fibers, and (d) biaxially stretched films. Disperse phase dimensions were measured. The values varied from 1-5μ in the products from static mixers. The dimensions of the dispersed phase in the blend products from the cone-plate and capillary die were of the same order. The melt spun fibers exhibited disperse phase dimensions as low as 0.35y. Polystyrene was extracted from the blend fibers to produce small diameter, PE fibrils, or mini-fibers.

Both initial melts and the blends were Theologically characterized. The shear viscosity n and principal normal stress difference N₁. exhibit maxima and minima when plotted as a function of composition. The phenomena were interpreted using the observed two-phase morphologies, i.e., droplets, lamellae, and fibers. An attempt was made to predict the observed dependence using hydrodynamic theories of dispersed two-phase liquids. Studies of elongational flow indicated that the PE/PS blend behavior was similar to the characteristic of pure PE whose failure was due to ductile necking.

The characteristics of extrudates and isothermal and non-isothermal melt spinning behavior of the PE/PS blends were investigated. Wide-angle x-ray diffraction studies have been carried out on blend fibers and the orientation of the crystalline polyethylene regions determined as a function of process conditions. This orientation decreases rapidly with addition of polystyrene when the melt spun filaments are compared at the same spinline stress.

The characteristics of biaxially stretched films of PE/PS blends were studied. The dispersed phase was stretched biaxially and have the appearance of multi-layered sheets.