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Journal of Thermal Analysis and Calorimetry

, Volume 81, Issue 1, pp 169–177 | Cite as

Comparison of enthalpy relaxation between two different molecular masses of a bisphenol-A polycarbonate

  • Pearl Lee-Sullivan
  • M. Bettle
Article

Summary

The present work is an extension of an earlier study that compared the stress relaxation between two molecular masses of a bisphenol-A polycarbonate due to thermal aging. The enthalpy relaxation of the same materials has been characterized. First, by measuring the change in enthalpy loss (ΔHa) and fictive temperature (Tf) as a function of aging temperature (Ta) ranging from -25 to 120°C, using differential scanning calorimetry. For the limited aging time of 120 h, ΔHa and Tf changes were only appreciable for (Tg -70 K)<Ta<Tg . While the influence of molecular mass was somewhat discernible, enthalpy measurements were not as sensitive as stress relaxation tests in differentiating molecular mass effects. In a second investigation, the kinetics of enthalpy relaxation upon isothermal aging at 130°C was evaluated using the peak shift method and found to be comparable to literature values. The plot of ΔHa as a function of log (aging time) showed two distinct regions: a brief non-linear portion (less than 1 h aging) which is followed by a linear relationship as typically reported in the literature. In contrast to the linear region, the non-linear relaxation behaviour of the poorly aged state does not appear to be dependent on molecular mass.

fictive temperature physical aging annealing enthalpic relaxation heat-aging 

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Copyright information

© Springer-Verlag/Akadémiai Kiadó 2005

Authors and Affiliations

  • Pearl Lee-Sullivan
    • 1
  • M. Bettle
    • 2
  1. 1.Department of Mechanical Engineering, University of Waterloo
  2. 2.Department of Mechanical Engineering, University of New Brunswick

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