Wilkie lab

 

 

Nanocomposite Technology

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.

 

Nanocomposite

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:

Our recent work has demonstrated that the presence of iron in a nanocomposite has an advantageous effect on both thermal stability, as assessed by TGA, and fire stability, determined from cone calorimetry. The suggested role by which this occurs is paramagnetic radical trapping by the substitutional iron which is naturally present in the clay. We have also, in conjunction with Jianqi Wang at the Beijing Institute of Technology, investigated nanocomposites using x-ray photoelectron spectroscopy, XPS, and have shown that, as the polymer undergoes degradation, the clay builds up at the surface of the nanocomposite and provides a barrier to mass transport from the polymer and to prevent the thermal radiation from causing further degradation.

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.

Research projects


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