Development of plasticied pvc/clay nano-composites

An effective stabilizing system for PVC/clay composites has been established in this work. Different types of stabilizers i.e. organo-tin, calcium/zinc, barium/zinc stabilizers and an epoxy co-stabilizer were investigated. It was found that the combination of the organo-tin stabilizer and the epoxy co-stabilizer was the most effective stabilizing system for PVC/clay composites. Different grades of Cloisite nano-clays supplied by Southern Clay Products Inc. were investigated. It was found that natural montmorillonite (Cloisite Na) did not cause premature degradation of PVC, however it was difficult to disperse in the PVC matrix due to its hydrophilicity. Ammonium modified nano-clays such as Cloisite lOA and Cloisite 30B were compatible with PVC, and both nano-clays were much easier to disperse in PVC than Cloisite Na. Cloisite lOA seriously accelerated the degradation of PVC, but PVC/Cloisite 30B system showed much better thermal stability. The effects of processing conditions on PVC/clay composite structure were investigated. The composite structure was characterized by both TEM and XRD. PVC/Cloisite Na nano-composites could not be successfully prepared no matter what processing conditions were used. Partially exfoliated and intercalated PVC/Cloisite 30B nano-composites could be prepared by melt compounding. The particulate structure of PVC resin affected the distribution of clay, which could be improved by increasing the processing temperature. Almost fully exfoliated PVC/Cloisite 30B nano-composites were successfully prepared by a solution process in tetrahydrofuran, and the plasticizer migration resistance ofthis composite was significantly improved. Phosphonium modified clays were also prepared successfully. They showed better thermal stability than ammonium modified clays, but the drying conditions still need to be optimized to produce a dispersable clay powder. Other commercial fillers for PVC such as calcium carbonate and hydrotalcite were compared with Cloisite 30B. It was found that Cloisite 30B provided the best improvement in plasticizer migration resistance, but decreased the tensile properties. Possible mechanisms were proposed. It is interesting to find that PVC crystallization in the clay galleries can occur during annealing that increased the clay gallery spacing. There seemed to be orientation of the newly formed crystallites, and two types of orientation have been proposed.