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12 POWDER COATING, August 2018 Powder Coatings Clinic Marek W. Urban, Ph.D. Clemson University Ying Yang, Ph.D. Clemson University Electrically conductive powder coatings bon single and double bonds along a polymer backbone). e classic ex- amples are polypyrrole, polyaniline, and polythiophene based polymers which exhibit both good stability and high conductance. To induce conductivity, doping is often re- quired to render conductivity reach- ing 103 to 105 S/cm levels. When an electrical potential is applied, the dopants, which are able to carry out charges, interact with the polymer by disrupting the electrical balance, and electrons begin to jump along the backbone and between the chains to conduct charges. Like conventional inorganic fillers, the conductive polymers can be incorporated into resins to impart desirable degrees of conductivity. They may also offer electroluminescence and photovol- taic effects as a second generation of conductive polymers. In summary, a combination of high s t r e n g t h - t o - w e i g h t r a t i o c a r - bon-based conductive fillers and conductive resins may offer powder coatings not only enhanced electrical conductivity, but also a superior combination of mechanical, thermal, and optical properties. PC Editor's note For further reading, visit Powder Coat- ing magazine's website at www.pcoat ing.com and search the Article Archive by keyword, subject, organization, author, or issue date. All articles listed in the archive are available for free download to registered users. Polymeric coatings typically do not conduct electricity. For example, the electrical conductivity of Teflon is 10 - 18 S/cm (Siemens per centimeter) whereas metallic silver and copper are in the 105 to 106 S/cm range. How- ever, by incorporating conductive fillers into nonconductive resins, or- ganic coatings can become electrically conductive. When they are utilized in powder coatings, a number of func- tions can be achieved such as corro- sion inhibition, electrostatic dis- charge, and shielding of electronic components (communication equip- ment, antenna, sensors, and con- sumer electronics) from electromag- netic and radio frequency interfer- ence (EMI/RFI). erefore, combin- ing conductive fillers with resins may create an opportunity for the develop- ment of a broad spectrum of applica- tions for military, industrial, and consumer sectors. A number of conductive coating products are available on the market, and they are commonly derived from a standard coating filled with inor- ganic conductive metal powders such as nickel, copper, and silver, or car- bon black. Among them, silver offers the highest electrical conductivity, but it is also costly. Recently, car- bon-based conductive nanomaterials, including graphene, carbon nano- tubes, and carbon fibers, have at- tracted more attention due to their significantly enhanced strength-to- weight ratios. Of particular interest is carbon nanotubes with electrical con- ductivity values of 104 to 105 S/cm. Dispersing a 3 wt% of multi-wall car- bon nanotubes in a commercial paint can increase the electrical conductiv- ity by up to 10 - 2 S/cm. Notably, most of the formulations are based on the weight percentage (wt%) of each component. However, structure-property relationships in polymeric coatings are determined by volume fractions (vol%) of pig- m e n t s , w h i c h i s k n o w n a s p i g - ment-volume concentration (PVC). The PVC of a coating system is de- fined as the vol% of pigments to the total solid content in a coating after film formation (solidified coating): PVC = (V p + V f )/(V p + V f + V nv ) x 100% Where: V p is a total volume of all pigments in a coating; V f is a total volume of other nonvolatile fillers; and V nv is the total volume of nonvolatile binder components Keep in mind that the occupied threshold volume, not the wt%, is re- sponsible for conductivity and many other coatings properties. erefore, PVC values need to be taken into con- sideration when optimizing coating formulations, especially for the high aspect ratio phases such as carbon nanotubes. Aside from PVC, conduc- tivity levels can also be impacted by the levels of percolation, uneven dis- tribution, and incompatibility. Another opportunity for incorporat- ing conductivity into polymeric coatings is to utilize conductive polymers. Discovered in 1977, the key property of a conductive poly- mer is the presence of conjugated backbone (alternating carbon-car-