Comparison of the time-temperature superposition of the relaxation modulus and time-to-break of preswollen gels
It is well known that the viscoelastic functions measured at different temperatures can be superimposed by means of the WLF equation, thus yielding generalized curves which extend the experimental time scale. It has been found (1) that the WLF equation holds well for the reduction of the viscoelastic data of a great majority of polymers measured in the main transition region, approximately over the temperature range from T g to T g + 100°. The moduli of crosslinked polymers approach with increasing temperature and time a certain limiting value predicted by the kinetic theory of elasticity. In this region, the viscoelastic curves determined at different temperatures are almost parallel, and the superimposed data are often subjected to a considerable error and sensitive to the use of various correction factors.
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