We present an experimental investigation on the creep behavior of molten polypropylene organically modified clay nanocomposites. The nanocomposite hybrids were prepared by melt intercalation in an extruder in the presence or absence of a compatibilizer. They were subsequently annealed and simultaneously characterized using high-temperature wide-angle X-ray diffraction and controlled stress rheometry. The creep resistance of compatibilized hybrids was significantly higher than that of uncompatibilized hybrids and also increased with annealing time. The microstructure of the nanocomposites as investigated by TEM and high-temperature WAXD showed the presence of clay crystallites dispersed within the polymer matrix. The creep data together with the microstructural investigation are probably indicative of a small amount of exfoliation from the edges of the clay crystallites during extrusion and annealing. The zero shear viscosity of the compatibilized nanocomposites containing greater than 3 wt % clay was at least 3 orders of magnitude higher than that of matrix resin and the uncompatibilized hybrids. Importantly, the large increase in zero shear viscosity was not accompanied by any increase in the flow activation energy compared to the matrix polymer. The compatibilized hybrids also showed an apparent “yield” behavior. We conclude that the solidlike rheological response of the molten nanocomposite originates from large frictional interactions of the clay crystallites. Compatibilizer has a significant influence in modifying the rheological behavior.

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The crystallization of nylon-6 from the melt was monitored in situ by X-ray diffraction. The nylon-6 was found to crystallize into a high-temperature R′-phase as indicated by the two-peak nature of the diffractogram. On cooling from the crystallization temperature to room temperature, nylon-6 retained the two-peak nature. However, data analysis indicates a change from high-temperature (HT) R′-phase to low-temperature R-phase at ∼180 °C. On heating, the R-phase transformed into the R′-phase at about 190 °C and melted in the R′-phase. The transition took place over a temperature range where both phases coexisted. However, samples crystallized from the melt at temperatures 140 and 180 °C showed the R-phase at room temperature, but on heating the R-phase first transformed into a pseudohexagonal phase and before melting the pseudohexagonal phase further transformed into the R′-phase. The R-phase was transformed into the γ-phase, by potassium iodide-iodine treatment, and the behavior of the γ-phase with temperature had been studied for the first time. The γ-phase was very stable and did not show any crystalline transition below the melting point.

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