It is well-known that nanocomposites show enhanced mechanical properties relative to virgin polymers. A nanocomposite typically contains a nano-dispersed material, in this laboratory we work with clays, both montmorillonite (MMT) and layered double hydroxides (LDH), carbon nanotubes and graphite, together with a polymer. The work of the laboratory with MMT has had three goals, 1) understand the process by which the presence of a nanoclay enhances the fire retardancy of a polymer; 2) develop novel surfactants that will enable good dispersion of clays in polyolefins; and 3) combine nanoclays with conventional fire retardants to obtain synergistic combinations that are true fire retardant systems.
The goals with layered double hydroxides are similar. The layered double hydroxides can be tuned to a particular polymer since one can vary the identity of the divalent metal, the trivalent metal, the anion and the stoichiometry. Recent work has explored how the variations in the LDHs affect performance. A zinc-containing LDH is better dispersed in polyethylene (PE) than in poly(methyl methacrylate) (PMMA) and has better fire properties while a magnesium-containing material is better in PMMA. There has also been a large amount of work examining combinations of LDHs with conventional fire retardants.
With carbon nanotubes, the primary focus has been to evaluate combinations of CNT with conventional fire retardants to understand how these interact and how can one develop useful fire retardant systems.
Graphite as the nano-dimensional material has been studied with polystyrene and polyamide-6. Work on graphite has been largely replaced with carbon nanotubes.
We have studied the following nanocomposite systems:
These nanocomposites may be prepared by bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, solution mixing, and melt blending and all of these techniques are in use in these laboratories.
Our interests in the area include:
We have also been active in the quite new area of graphite nanocomposites. Here we have used the graphite intercalation compound potassium graphite, KC8, as the initiator for the bulk polymerization of polystyrene. This gives a polystyrene-graphite nanocomposite in which the d-spacing has increased from the 3.35D of graphite to 15 to 20D in the nanocomposite. Polyamide - graphite nanocomposites have been prepared by the melt blending of expanded graphite with polyamides.