Structure build-up at rest in polymer nanocomposites: Flow reversal experiments

Evolution of the microstructure as well as the shear stress and the normal stress difference ofpolymer/layered silicate nanocomposites prepared by melt mixing of poly[butylene succinate-co-adipate] and organically modified montmorillonite are investigated in transient forward and reverse start-up shear flows at different clay loading and different shear rates. Special attention is paid to the structure build-up at rest and to the amplitude of the overshoots observed during the reverse start-up test in the shear stress and the normal stress difference. The model that we have developed previously is used to suggest an explanation for the observed phenomena. The model is able to capture observed behavior of the shear stress in both forward and reverse start-up flows. It fails, however, to predict experimentally observed overshoot in the normal stress difference. © 2009 Wiley Periodicals, Inc.