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Monitoring clay exfoliation during polymer/clay compounding using fluorescence spectroscopy

A fluorescent probe molecule, Nile blue perchlorate, was used to monitor the compounding of nylon 11 with clay filler. Prior to compounding, Nile blue was incorporated into the gallery region between silicate layers of the clay by an ion-exchange process. While residing in the gallery, fluorescence from Nile blue was quenched because of fluorescence resorption in a high dye concentration environment. However, when clay is compounded with the nylon, clay exfoliation allowed the dye to escape the gallery region and to become dispersed in the resin matrix. During batch mixing, we observed that fluorescence increased with time indicating that dye molecules were migrating from the gallery. Experiments carried out using a twin-screw extruder to compound resin and clay showed that twin-screw compounding was much more efficient in producing clay exfoliation than was the batch mixer.