FLOW INDUCED CRYSTALLIZATION OF POLYPROPYLENE IN STRETCHED RIBBONS.

Flow during crystallization of polymer melt produces a material with structure and properties vastly different from those of samples crystallized from quiescent melts. Fiber spinning and film extrusion are two major processing techniques that may exploit flow-induced crystallization phenomena. This paper describes conditions and phenomena associated with the formation of PP films whose crystallization was induced by the prevailing melt flow. X-ray diffraction photographs of various PP samples are enclosed. Experimental data show that as multiaxial flow tends toward being uniaxial (simple tensile flow), there is an increase in both ″elasticcity″ and preferred crystallite orientation in the resulting solids. The temperature of air into which molten ribbons are extruded appears to have a strong control over the character of elongational flow that becomes established as the ribbon undergoes stretching.