A recent development of existing thermodynamic theory has been applied to the analysis of heat of fusion (ahf) data from both “dry” and “suspension” polyethylene (PE) single crystals. AHf for suspension crystals was found to be larger than any value previously reported for high molecular weight PE crystals: 60. 7 to 64.4 cal/g, depending on the crystallization temperature. Plots of AHf,/Wc versus a[(1/Wc) - 1] were constructed for suspension samples assuming various fold models. Irrespective of the model chosen, the perfect crystal heat of fusion was found to be approximately 72 cal/g. From analysis of the slopes of these plots it was concluded that a 10-carbon-atom fold model best fits the suspension AHf data. Melting points for suspension crystals were also obtained. Analysis according to the Hoffman-Weeks equation reveals that the equilibrium melting point is somewhat lower than the usual range of accepted values. The discrepancy between the value determined here and that reported by other authors is discussed. The magnitude of the derived surface free energy from melting point data also indicates that PE crystals consist of folds containing approximately 10 methylene units on average. This conclusion is in excellent agreement with the results from recent small-angle x-ray studies.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Polymers and Plastics
- Materials Chemistry