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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.