This work has studied the effect of shear on the melt crystallization behavior of three poly(1-butene) materials at several shear rates and degrees of undercooling. The poly(1-butene) samples investigated varied in number average molecular weight from 35,000 to 105,000. Crystallization was carried out using a parallel plate rotary shearing apparatus mounted on the stage of an optical microscope. Photographic techniques were used to record nuclei formation and size during crystallization over a shear rate range of 0 sec('-1) to 12 sec('-1). The data was analyzed in light of classical nucleation theory and Avrami kinetics. The imposition of shear during crystallization generally accelerated the transformation process through increased nucleation rates. The process was also characterized by a reduction in induction times which generally showed a saturation effect with shear. The negative temperature coefficient of the nucleation rate becomes less negative for shear crystallization over the range studied. Shear stresses of the crystallizing melt were measured on a separate instrument and were found to increase rapidly with the onset of crystallization. The rise in shear stress paralleled the rise in nuclei formation. The corresponding increase in viscosity could be accounted for by using an effective nuclei volume concept during the early stages of crystallization. Morphological studies of sheared samples show deformed spherulites and row-nucleated structures. The observations here lead to the conclusion that the shear stress in the system induce a certain amount of molecular orientation which greatly accelerates the overall crystalline transformation process. The large increase in the nucleation process which is believed to be directly related to the orientation in the system, is the main contributing factor to the rapid crystallization as well as the decrease in induction period.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-5804 |
| Date | 01 January 1983 |
| Creators | WOLKOWICZ, MICHAEL DOMINIC |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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