The changes in the birefringence and the true stress-true strain behavior of cast nylon 6 and nylon 6-clay nanocomposite films are monitored online as they are stretched uniaxially below the peak melting temperature. The effects of draw temperature (100°-140°-180°C) and clay content (2 and 5 volume%) are investigated by means of online measurements and X-ray diffraction. The presence of nanoplatelets in the nylon matrix enhances the uniformity of stretching by suppressing the localized necking behavior at these essentially cold drawing temperatures. At a given stress, the birefringence decreases as the clay content increases. This is quite interesting and perhaps is related to reduction of structural connectivities by reducing the polymer entanglements in the presence of these very small nanoparticles. The development of birefringence correlates well with the strain rather than the clay content or the stretching temperature. The crystalline phase of the as-cast films is ?-form. Stretching promotes the formation of ?-crystals at all draw temperatures for nylon films. At low draw temperatures, the nanocomposite films also assume ?-phase, while at 180°C they display a mixture of ? and ? phases.
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