Changes in the crystallite size distribution during the isothermal crystallization of linear polyethylene fractions were studied using low frequency Raman spectroscopy. Increases in the crystallite size and broadening distributions were observed as a function of time for all molecular weights studied. Large increases in size occurred even after most of the isothermal crystallinity had formed. The rate of increase was faster for higher crystallization temperatures, while the process was retarded for higher molecular weights. The existing theories for crystallite thickening were found to be insufficient to explain all of the experimental results. These experimental observations could be rationalized if the thickening occurred by a partial melting process. The observed increases in thickness were found to correlate very well with increases in calorimetric melting points. The extrapolation of this thickness-melting point data to obtain an equilibrium melting point was complicated by the possibility of changes in the crystallite's surface free energy. The use of melting temperature-crystallization temperature plots was found to be a better method of extrapolation. The best estimate of the equilibrium melting point of polyethylene was determined to be 146(DEGREES)C. / Source: Dissertation Abstracts International, Volume: 44-06, Section: B, page: 1847. / Thesis (Ph.D.)--The Florida State University, 1983.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75119 |
| Contributors | STACK, GARY MICHAEL., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 415 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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