Hobbs, C B; Ferriss, D H; Roberts, S; Gnaniah, S J P; Brown, C S (2001) Thermal properties of polymer melts at elevated pressure from compression heating and differential scanning calorimetry. NPL Report. MATC(A)25

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Abstract

A novel method has been developed to assess the thermal properties of polymer melts by compression heating at elevating pressure. The energy input and the resulting temperature rise are measured which can then be used to determine the specific heat capacity under pressure. A sample of polymer is heated to the test temperature within a cylindrical pressure vessel. The pressure is controlled through a piston fitted with PTFE seals. The temperature increases with increases in pressure.
Measurements of a high-density polyethylene (HDPE) at 208ºC, showed an increase in temperature of 3ºC as the pressure was increased from 20 MPa to 80 MPa. The sample was found to cool back to a temperature approximately equal to the initial temperature after a delay of about 1000 seconds. During subsequent release of the pressure a further cooling occurred before the whole system returned to equilibrium again. The duration of the pressure ramp and the cooling were of the same order. A mathematical model was developed which described both the temperature rise from the work done in compression heating and the heat transfer from the polymer melt to its surroundings. The model correctly predicted the experimentally measured time temperature behaviour.
A system was developed that can track changes in temperature due to compression heating down to ± 0.01ºC.
An elevated pressure DSC was also commissioned to provide thermal data up to about 7 MPa. These were compared with the above measurements.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MATC(A)25
Keywords:	polymer, thermal conductivity, thermal diffusivity, specific heat
Subjects:	Advanced Materials Advanced Materials > Thermal Analysis of Materials
Last Modified:	02 Feb 2018 13:17
URI:	http://eprintspublications.npl.co.uk/id/eprint/2100

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