Study on rheological behaviour of poly(butylene terephthalate)/montmorillonite nanocomposites

Poly(butylene terephthalate)/montmorillonite composites (PBT/MMT) were prepared by melt intercalation and then investigated using X-ray diffractometer (XRD) and transmission electron microscope (TEM) as well as parallel plate rheometer. It was found that the composites had various phase morphologies with nanoscales and distinct behaviours of a percolation network structure under certain conditions. The linear viscoelastic region of the composites is much narrower than that for PBT matrix, the percolation threshold of the composites is near 3 wt.%, and the percolation network structure is not stable under a shear as well as in a quiescent annealing process. Moreover, PBT/MMT presents the nature of temperature independence of G′ versus G″ whether the internal percolated tactoids network formed or not. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which could be inferred that the ruptured network is reorganized under the quiescent annealing process. Furthermore, PBT/MMT shows a strain-scaling stress response to the startup of steady shear, indicating that the formation of the liquid crystalline-like phase structure in the nanocomposites may be the major drive force for the reorganization of the internal network.