On the use of the model proposed by Leonov for the explanation of a secondary plateau of the loss modulus in heterogeneous polymer-filler systems with agglomerates
Résumé
The purpose of the presented work was to test the capability of the model proposed by Leonov (J Rheol 34:1039-1068, 1990) for the prediction of secondary plateaus on the storage and loss moduli during small-amplitude oscillatory shear flow experiments on filled or heterogeneous polymer melts. Though the occurrence of a plateau on the storage modulus can be well explained in the frame of a filler network, a plateau on the loss modulus can hardly be described with the classical models. In the Leonov model, the continuum of dissipative processes is attributed to the rupture of flocs of particles. Experiments with polyolefins filled with magnesium hydroxide show that there is a clear connection between the amount of agglomerates and the occurrence of a plateau on the loss modulus. However, the value of the critical strain for floc rupture that can be calculated from the experiment shows that the processes responsible for the low-frequency dissipation are rather changes of configuration within the agglomerates than floc rupture. These processes are not described by the Leonov model, and the predicted strain dependence of the plateau is not observed experimentally.