Date of Award
Fall 2006
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Wilkie, Charles
Second Advisor
Reid, Scott
Third Advisor
Sem, Daniel
Abstract
The objective of this work was to answer one of the fundamental questions regarding polymer-clay nanocomposites, namely how does the clay act as a fire retardant in such materials. The present understanding of the problem states that the clay creates a physical barrier that slows the mass (fuel) transfer from the degrading polymer to the flame, and also slows the heat transfer from the flame to polymer. The implications of this simple mechanism are that, on one hand, for the same clay loading, assuming similar dispersion, every polymer-clay system should exhibit roughly the same fire retardant efficiency. On the other hand, since there appears to be no chemical interaction between the polymer and clay, one should expect to see no alteration of the degradation pathway of the nanocomposite as compared to the virgin polymer, and, subsequently, no changes in their degradation products. However, numerous cone calorimetric studies have shown that there is a difference between nanocomposites prepared with various polymeric systems in terms of the fire retardancy; earlier work from this laboratory has indicated that changes occur in the degradation of polyamide-6 and polystyrene-clay nanocomposites as compared to virgin polymer. Based upon these interesting findings, we have taken a closer look at what happens to the degradation products when clay was nano-dispersed in polymers such as ethylene-vinyl acetate copolymer, poly(methyl methacrylate), polyethylene and polystyrene. In addition, in order to check whether the chemical identity of the nanomaterial used as has an influence on the degradation chemistry, layered double hydroxides and carbon nanotubes were compared with clay in polymer nanocomposites. The second part of this work focused on synthesis of alkyl-benzimidazolium surfactants that show a high thermal stability. The need for such materials is justified by the fact that engineering polymers such as poly(ethylene terephtalate), polyamide 6, polyamide 6,6 and polycarbonate have processing temperatures of about 300°C, above the onset degradation temperature of the commonly used alkyl-ammonium halides, and therefore polymer-clay nanocomposites are difficult to prepare through melt blending (the industry-preferred method). Also, previously known, thermally stable quinolinium and oligomeric surfactants have been melt blended with poly(ethylene terephtalate), thus demonstrating the potential of such modified clays for nanocomposites formation with high temperature polymers. Finally, a wide range of potential fire retardants have been tested with polyurea, a polymer family that is becoming important for applications such as lining, coatings, and impact resistant liners and tiles.