Special Issue "Entropies of Polymers"

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List of Related Papers

See a list of related papers on configurational entropy compiled by Shu-Kun Lin

Title: Entropy Change and Physical Ageing in Polymers

Author: T. Vu-Khanh

Affiliation: Université du Québec - École de technologie supérieure, Department of Mechanical Engineering, 1100 Notre-Dame Street West Montreal, Quebec, Canada, H3C 1K3

E-mail: toan.vu-khanh@etsmtl.ca

Abstract: This paper discusses the influence of ageing, at room temperature, and for different ageing times, on the entropy change in polymers having different morphologies. Compressive tests were performed over various loading rates to analyze the effect of ageing on the yielding kinetics and Ree-Eyring’s model was used to analyze the entropy change in the material. Ageing only slightly affects the yielding stress, but it causes a significant variation in the pre-exponential factor values. The results suggest that plastic deformation implies more cooperative segmental motions for higher crystalline content, which result in higher values of the pre-exponential factor containing the entropy term. The parameters related to the β-process did not undergo any significant change during ageing, suggesting that ageing at room temperature does not affect localized molecular motions.

Dielectric spectroscopy was conducted in the frequency domain using a broadband dielectric spectrometer for the lowest and highest crystalline morphologies in both aged and unaged states. The results showed significant changes in the dissipation factors of the primary relaxations with ageing time, for both low and high crystallinity samples. On the other hand, no change in the secondary relaxation was observed in either case. DSC measurements did not show any effect of ageing at room temperature the degree of crystallinity as well as the melting temperature of polypropylene.
Keywords: Polymers, Entropy, Ageing, Crystallity, Yielding, Plasticity, Microstructure, Molecular Relaxation.