Flow-induced crystallization in polymer melts: how Winter's gelation concept fits into the picture

Nobody could expect that gelation times of many hours, which were observed in quiescent polymer melts below the melting temperature of the spherulites, would play a role in flow-induced crystallization. However, this role became obvious for an iPP, when special polarization optics were employed in the well-known arrangement of the Linkam CSS450 apparatus (parallel glass plate rheometer). With the aid of a lambda-plate, the interference color red of first order was created in white polarized light. This sensitive interference color changes quickly into blue, when a small phase difference is added (with subtraction a yellow color is obtained). With the aid of the great number of blue halos, which came up at 145 A degrees C after the cessation of flow, an oriented gelation was identified. It spreads faster over the sample than the spherulites. The unwieldy gelation times, which have been found in quiescent melts, seem to be the consequence of a shortage of nuclei.