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Analytical Modeling of Stress Relaxation and Evaluation of the Activation Volume Variation: Effect of Temperature and
Laura Aliotta1,2, Vito Gigante1,2, Andrea Lazzeri1,2
1University of Pisa, Department of Civil and Industrial Engineering, Via Diotisalvi, 2, Pisa 56122, Italy.
Abstract:
In this study, stress-relaxation tests that have been carried out at different temperatures (quite below the heat deflection temperature) on a poly(3-hydroxybutyrate-3hydroxyvalerate) (PHB-HV) matrix containing different amounts of the acetyl tributyl citrate plasticizer (added at 5 and 10 wt %) are investigated. The analytical modeling of the stress relaxation behavior by the coupling of Eyring's approach and the Guiu and Pratt model is successful. The activation volume results achieved are very interesting; in fact, not only the dependence of the activation volume from temperature is confirmed (and it resulted in dependence from the α' relaxation temperature) but also, for the first time, the dependence of the activation volume from the plasticizer content is shown. In particular, the presence of a linear relationship between the activation volume and the plasticizer volume content is observed.
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