POLYMER MELT LUBRICATED ELONGATIONAL FLOW

Use of lubricated skin/core flow of a polymer melt and a hyperbolic sh aped converging die are shown to result in essentially pure elongation al flow at a constant elongational strain rate. This behavior is demon strated first by modeling a series of skin/core layered flows: power-l aw rectangular channel shearing flow; Newtonian fluid converging chann el elongational flow; and power-law fluid converging channel elongatio nal flow. Experimental measurements using tracer particles and an imag e analysis system confirm the predicted behavior and demonstrate the a bility to achieve a constant elongational strain rate in the core laye r. The constant value is controlled by the volumetric flow rate and di e geometry in this confined flow. The viscosity ratio of the core poly mer must be at least 100 times that of the core and the converging flo w channel must have a specific hyperbolic shape. A Dowex low-density p olyethylene skin and a Marlex polypropylene core were used for the exp erimental measurements and for the rheological parameters used in the modeling.