Fast scanning chip-calorimetry was used to explore the crystallisation and melting of three semi-crystalline polymers. The heating and cooling rates required to prevent crystallisation on cooling (from above Tm) and on re-heating (from below T\(_g\)) were determined as: 3,000 and 8,000˚C/s respectively in PCL, 75 and 250˚C/s respectively in PEEK and 10 and 100˚C/s respectively in PLA. The effect of the thermal lag was considered using indium as a standard and corrections of >5˚C were required at rates in excess of 5,000˚C/s. As readily observed in conventional DSC (CDSC), PEEK exhibited a double melting endotherm and this was attributed to a melting-recrystallisation-melting process. The absence of recrystallisation above 250˚C allowed a Hoffman-Weeks analysis to be carried out over a broader temperature range than is general possible in CDSC. The interplay between thermal lag and re-crystallisation was analysed using heating rates covering 5 orders of magnitude. At an optimum heating rate of 1,500 ˚C/s, an equilibrium melting temperature of 359˚C was determined. The consideration of thermal lag led to the measurement of diffusivity using the technique of laser flash apparatus (LFA). The high measurement speed in the LFA allowed a time and temperature resolved study of diffusivity in PLA. LFA, chip-calorimetry and CDSC were used in parallel to explore the cold-crystallisation kinetics of PLA and the development of the relatively unstable α’ crystals. A good correlation between chip-calorimetry and LFA was found, showing an Avrami exponent of 2 and nucleation constant of 6.58 x10\(^5\) and 6.87 x10\(^5\) respectively, corresponding to regime III.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:707652 |
| Date | January 2017 |
| Creators | Marsh, Joseph Jack |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.bham.ac.uk//id/eprint/7299/ |
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