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# Characterisation of crystallisation and melting in thermoplastic polymers using chip calorimetry

Marsh, Joseph Jack (2017)
Ph.D. thesis, University of Birmingham.

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## Abstract

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.

Type of Work: Ph.D. thesis. Jenkins, Mike and Kukureka, Stephen N. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Metallurgy and Materials Publication resulting from research: Murphy, S.H., Marsh, J.J., Kelly, C.A., Leeke, G.A. and Jenkins, M.J., 2017. Co2 Assisted blending of poly(lactic acid) and poly(ε-caprolactone). European Polymer Journal. 88: 34–43. http://dx.doi.org/10.1016/j.eurpolymj.2016.12.013 TN Mining engineering. Metallurgy University of Birmingham 7299
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