Totally Renewable Nanocomposite Plastics Made Possible with Carbon Nanospheres

Three scientists have developed a laser pyrolysis method for producing carbon nano-spheres that could lead to totally renewable plastics made from corn. According to U.S. Patent 7,601,321, Prof. J. Thomas McKinnon, (Boulder, CO), Colorado School of Mines Prof. Andrew M. Herring (Nederland, CO) and Bryan D. McCloskey (Austin, TX) have manufactured carbon nanospheres by pyrolyzing chars at high temperatures. The chars are doped with selected metals/metal salts which serve as templates for creating the nanospheres. The pyrolysis heating may take place using a laser, other intense light sources, or other energy sources capable of heating a solid to temperatures in excess of 2000 K.

The size of the carbon nanospheres may be optimized by adjusting the amount and type of metal catalyst used, the temperature, pressure, temperature ramp rate, and other conditions used to create the char; and the temperature, pressure, temperature ramp rate, and other conditions used to pyrolyze the char. The methods may also be used to create metal nanoparticles, which can be isolated from the carbonaceous material, and carbon nanospheres filled with metal, each of which has independent utility in various applications. The carbon nanospheres have various applications such as in fuel cell electrode supports, nanoreaction chambers, blending agents for polymers, and strengthening agents for high temperature glasses.

Their discovery provides improved methods and apparatus for synthesizing carbon nanospheres from a charable, carbonaceous substrate material. The char may be prepared from cellulose or other carbon substrate materials. Nanospheres produced in accordance with this invention will prove to be extremely useful in at least three technology areas: fuel cell electrode catalyst supports; high-temperature glass additives; and polymer blending agents.

Fuel Cell Electrocatalyst Supports:

The electrocatalyst support of a proton exchange membrane fuel cell must perform four separate operations. First, it must provide a means of efficiently dispersing the expensive platinum (or other precious metal) electrocatalyst, i.e., disperse the platinum in the smallest crystallites possible in order to maximize the effective surface area. Second, it must provide continuous bulk transport pathways for the fuel or oxidant to the electrocatalyst. Third, it must be electrically conductive to allow transport of the electrons. Finally, the electrocatalyst support must allow proton transport to the membrane. The properties of carbon allow the first three electrocatalyst support operations to be desirably carried out without additives. The simple addition of a proton conductor, such as Nafion®, to an electrocatalyst support based on carbon nanospheres prepared in accordance with this invention thereby allows a nearly ideal electrocatalyst support to be formed. To create these materials, the surface of the nanosphere product was modified by a mild oxidation using 4M HNO3 to convert the anhydride surface functionalities to carboxylic acid groups. The resultant black powder was refluxed with cholorplatinic acid in ethylene glycol for 6 hours followed by washing and drying in air.

High Temperature Stable Glasses:

Carbide and nitride based ceramic glasses (e.g., SiCN, SiOC, SiOCN) have shown the greatest potential for structural applications in high temperatures and harsh environments. Unfortunately, many of the carbides and nitrides processed through traditional powder consolidation and sintering are unstable in oxygen-containing environments due to passive and active oxidation. Polymer-derived carbide and nitride glasses, on the other hand, have shown excellent resistance to oxidation at temperatures up to 1450.degree. C. Although the exact mechanism is not yet well understood, it is believed that free carbon incorporated into the glass network structure is inherently less prone to oxidation and corrosion than polycrystalline ceramics. The addition of hollow carbon nanospheres prepared in accordance with this invention provides a promising method to further enhance the properties of these glass compositions by introducing additional free carbon into the O-, N-based glasses in an effort to prevent crystallization at temperatures up to 1700.degree. C. and yield a lightweight, creep-resistant, HT-stable glass.

Totally Renewable Nanocomposite Plastics:

The field of polymers produced from corn-based polylactic acid (PLA) is a rapidly exploding area both in terms of research and commercial interest. However, the current PLA materials have morphological and performance problems that must be addressed before they make widespread market penetration. Blending PLA plastics with carbon nanospheres shows promise in both addressing the plastic performance issues and producing a material based entirely on renewable resources.

J. Thomas McKinnon, Ph.D., is a professor of chemical engineering at the Colorado School of Mines and is also the founder and CTO of Novare Biofuels, Inc, a company developing technology to produce low-cost gasoline from cellulosic feedstocks. Dr. McKinnon’s expertise is in fuels, combustion chemistry, and pyrolysis.