THE KINETICS OF FLOW-INDUCED CRYSTALLIZATION FROM SOLUTION

In situ birefringence measurements of the seeded growth in a tubular flow geometry of 0.01 wt% solutions of a polyethylene fraction in xylene have been used to determine the flow-induced crystallization kinetics as a function of temperature and flow rate. In contrast to earlier reports on higher molecular weight polyethylene and polypropylene systems, orientational properties of the crystallized fibers do not show a clear correlation with growth conditions (i.e., temperature and flow rate). The combined kinetic data from these experiments and our earlier studies of higher molecular weight polyethylene-xylene and polypropylene-tetralin systems are analyzed in terms of a modified form of the Avrami equation which provides a basis for separately correlating temperature and flow rate effects. The observed temperature dependency of the crystallization process can be interpreted in terms of nucleation and growth models while the flow rate dependency can be interpreted on the basis of entanglement formation arguments. Results showing liquid phase precursor formation in an atactic polystyrene system are also presented to further document the liquid-phase separation which can be induced in polymers under flow.