Process And Performance Aid For Carbon Nanotubes

The primary methods of increasing the electrical conductivity of plastics have been to fill them with conductive additives such as metallic powders, metallic fibers, intrinsically conductive polymeric powder, e.g., polypyrrole, or carbon black. The most common method involves carbon black. However, each of these approaches has some shortcomings. Metallic fiber and powder enhanced plastics have diminished mechanical strength. Further, cost is high and their density makes high weight loadings necessary.

 Intrinsically conductive polymers have high costs and are often not stable in air. Thus, their use is frequently impractical. It has been recognized that the addition of carbon nanotubes to polymers in quantities less than that of carbon black can be used to produce conductive end products and/or to modify the mechanical properties of the product.

Encapsulation of carbon nanotubes is known. Multi-walled carbon nanotubes (MWCNT's) are marketed as nanotubes compounded in a resin matrix. The resin matrix is formed depending upon customer needs. For example, if the customer is interested in compounding MWCNT's into polyamide-6, a resin matrix of carbon nanotubes in polyamide-6 is prepared. The MWCNT's concentration in such matrixes typically ranges from approximately 2% to approximately 20%. These matrices are called master batches. This process requires a distinct master batch for each end use. Such a process is costly and inefficient.

According to U.S. Patent Application 20100210781, Arkema inventors discovered that incorporation of carbon nanotubes into a resin matrix simplifies melt processing in polymer matrixes and/or addition into polymer matrixes and provides a polymer matrix having higher electrical conductivity and/or improved mechanical properties. Generally the resin matrix comprises chains containing aromatic groups, oxygen and/or nitrogen atoms, has a low melting temperature (less than about 200.degree. C.), and a molecular weight such that melt viscosity is low (less than about 5000 centipoise). 

A preferred resin matrix is cyclic butylene terephthalate (CBT). The concentration of carbon nanotubes in the resin matrix is preferably between about 0.1 and 50% by weight, more preferably between about 5 and 33% by weight and most preferably about 25% by weight. Unless otherwise specified, all percentages herein are percentages by weight and all temperatures are in degrees Centigrade (degrees Celsius). 

The use of carbon nanotubes in polymer technology is very important. One reason is that carbon nanotubes can increase the electrical conductivity of a polymer matrix at relatively low concentration. In many cases, less than 5% by weight, and often less than 2% by weight. This makes the polymer matrix suitable for numerous applications, such as electrostatic painting, static charge dissipation, and electromagnetic interference shielding. Metals can be used in these applications, but conductive polymers offer a lower-cost, lighter-weight, alternative. 

Carbon black can provide a conductivity effect in polymers. However, with carbon black, much higher concentrations are required, typically 10-20% by weight. Such a level of additives, while providing good electrical conductivity, reduces other properties of the polymer, such as mechanical strength, impact resistance, gas/liquid permeability, etc. Carbon nanotubes provide good electrical conductivity while also maintaining other desirable polymer properties. Some examples of applications where a polymer/nanotube composition could be advantageous are: conductive polymer fuel handling components of automobiles, electrostatically paintable thermoplastic automotive body/interior components, coatings to shield electronic equipment, etc.

Another property of importance in the use of carbon nanotubes is an increase in mechanical properties of a polymer matrix at a relatively low concentration of carbon nanotubes. This makes the polymer matrix suitable for applications where otherwise, heavier, more expensive materials are needed, such as metals. Some examples of carbon nanotube--containing composites are tennis rackets, baseball bats, golf clubs, bicycle components and possibly automotive and aeronautical components.
 

Still more applications for carbon nanotube containing composites, with carbon nanotubes properly dispersed in a polymer matrix include, but are not limited to: membranes employed for selective separation of gases, composites displaying enhanced flame retardancy, coatings or composites showing enhanced resistance to UV degradation, coatings showing enhanced absorption of visible light, coatings and composites showing enhanced wear resistance, coatings showing enhanced scratch resistance, coatings and composites having enhanced chemical resistance to dissolving/swelling agents, composites in which stress/strain/defects can be detected easily, composite acoustic sensors and actuators, electrode materials in capacitors, fuel cells, rechargeable batteries, electrically conductive and injury-resistant fabric, composites in a variety of electronic devices, such as glucose sensors, LED displays, solar cells, pH sensors
 

There is significant worldwide interest in carbon nanotubes (multi walled, double walled, single walled). Nanotubes are known to be composed either of a single sheet, in which case they are called single-walled nanotubes (SWNTs), or made up from several concentric sheets, when they are called multi-walled nanotubes (MWNTs). Carbon nanotubes can be formed from petroleum-based sources or form biological-based sources.