Rheology of PBT-layered silicate nanocomposites prepared by melt compounding

The rheological behaviour of poly(butyleneterephthalate) (PBT) based clay nanocomposites processed by melt compounding is investigated and related to the morphology of the samples. Hybrids at three weight percentages (3, 6 and 9 wt-%) of a commercial organo-modified montmorillonite were prepared by means of a twin screw extruder, using two different extrusion rates (90 and 150 rev min ^-1). The samples produced were submitted to structural and rheological investigations. X-ray and TEM analyses were carried out to provide information on the morphology (i. e. clay dispersion, degree of exfoliation, orientation) of the hybrids, whereas rheological tests in the low and high shear region (dynamic frequency sweep, steady rate sweep and stress relaxation tests) were performed to evaluate the effect of both hybrid composition and extrusion rate on the flow behaviour of the nanocomposites. Both structural and rheological results showed that a good dispersion and a high degree of silicate exfoliation in the PBT matrix are obtained under the experimental conditions. As a consequence, hybrids having clay fractions higher than 6 wt-% show a pseudo-solidlike flow behaviour at long times, as a result of the occurrence of strong polymer–silicate interactions that slow the relaxation times of the PBT chains.