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Soft Matter and Biological Physics

Eur. Phys. J. E 2, 335-341

Ageing of natural rubber under stress

S.M. Clarke - F. Elias - E.M. Terentjev

Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK

Received 22 November 1999 and Received in final form 18 January 2000

Abstract
We report a dynamical-mechanical study of stress relaxation at small deformation in a natural (polyisoprene) rubber well above its glass transition temperature $T_{\rm g}$. We find that an almost complete relaxation of stress takes place over very long relaxation periods, even though the elastic network is retained. The relaxation rate and the long-time equilibrium modulus are sensitive functions of temperature which do not follow time-temperature superposition. Many characteristic features of non-ergodic ageing response are apparent at both short and very long times. We interpret the observed behaviour in terms of the nature of rubber cross-links, capable of isomerisation under stress, and relate the results to recent models of slow glassy rheology.

PACS
61.41.+e Polymers, elastomers and plastics. - 62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances. - 83.50.By Transient deformation and flow; time-dependent properties: star-up, stress relaxation, creep, recovery, etc.

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