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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.
Supervisor(s):Jenkins, Mike and Kukureka, Stephen N.
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and Materials
Additional Information:

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

Subjects:TN Mining engineering. Metallurgy
Institution:University of Birmingham
ID Code:7299
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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