Harris, Luke (2011)
M.Res. thesis, University of Birmingham.
The two main objectives of the current work were: 1) Isothermally crystallise samples of Carbon-Filled PEEK and Unfilled PEEK at a range of temperatures above the Tg and analyse them using the Conventional Avrami method and the Differential Avrami method. The results were then compared and conclusions drawn. 2) Characterise the crystallisation process by the use of two methods of determining polymer crystallinity. ATR-FTIR and Hyper-DSC were both used to determine sample crystallinity and correlations were drawn between the two methods to provide non-destructive crystallinity data of the samples.
The isothermal crystallisation behaviour of the filled samples showed that at lower isothermal crystallisation temperatures, carbon inclusions hindered the nucleation process compared to that of neat PEEK. However, at higher crystallisation temperatures the carbon inclusions could be said to act as stress initiators that increase polymer nucleation and subsequent growth. It could also be seen that the use of the Differential Avrami approach to analyse the Isothermal crystallisation process gave a more accurate determination of the Avrami exponent n. It was found that the Differential approach gave a higher value of n, closer to the integer 4. This therefore shows a shift in crystallisation growth mechanism and is conclusive with other literature findings.
FTIR and Hyper-DSC techniques can conclusively characterise crystalline presence within semi-crystalline PEEK. The crystalline fingerprint bands found within the FTIR spectra conclusively determined crystalline changes within pre-conditioned samples of PEEK, strongly correlating to other literature findings. Hyper-DSC results also showed that higher heating rates for determining crystallinity should be used in order to produce more accurate results and prevent any molecular melt and recrystallisation within the polymer samples.
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