(374b) Improving the Dispersion of Nanoclays in PET/Clay Nanocomposites

Thermally stable surfactants were used to modify clay nanoparticles for use in preparation of poly(ethylene terephthalate)/clay nanocomposites. Nanoclays with smaller particle size distributions were prepared with a two-step centrifugation method that removed large particles from commercial montmorillonite (MMT). Scanning electron microscopy of aqueous dispersions of MMT and centrifuged clay (CMMT) illustrated that the average particle size of CMMT in water was much lower than that of MMT in water. Both CMMT and MMT were modified with two different thermally stable surfactants (imidazolium and phosphonium surfactants). PET/clay nanocomposites with surfactant modified MMT and CMMT were prepared by using a twin screw extruder. Fourier transform infrared spectroscopy and X-ray diffraction results revealed that the surfactants were associated with the clay surface and that the gallery spacing of the layered silicates was expanded. Thermal gravimetric analysis results indicated that clays modified with thermally stable surfactants degraded above 300 ºC and could survive PET processing temperatures. Transmission electron microscopy revealed an improvement in the dispersion of centrifuged nanoclays (modified with both imidazolium and phosphonium surfactants) into the polymer matrix compared to non-centrifuged modified MMT with larger particle sizes. XRD indicated that particle size distributions have a significant effect on the dispersion of nanoclays modified with imidazolium surfactants. There was, however, a less important effect of centrifugation on the dispersion of nanoclays modified with phosphonium surfactants. DSC data also revealed that initial clay particle size distributions have a significant effect on the rate of crystallization of nanoclays modified with imidazolium surfactants.