Using liquid salts during the formation of smart textiles and conductive polymer composites instead of harsh chemicals can strengthen fibers that conduct electricity, according to a patent issued to a team of researchers at the University of Alabama (UA). The new method of crafting the fibers could enable normally flimsy materials, such as cotton, to conduct electricity in technologies normally reserved for stronger fibers, and could also make conductive polymer composites less expensive to prepare with fewer harmful environmental side-effects.
Conductive polymers have wide-ranging physical and electrical properties and are used in applications such as organic transistors, coatings for fuel cells, smart textiles and electromagnetic shielding. However, the process for making conductive polymer composites such as electrically-conductive cotton, wool or nylon is difficult since the mechanical properties are weakened during preparation.
The UA researchers worked with polypyrrole, a particularly useful conductive polymer that can be difficult to bind to fibers. To turn the base chemical, pyrrole, into a polymer that can conduct electricity, the pyrrole is put through a chemical process using methanol and ferric chloride. To bind the fibers with the polypyrrole, they are dipped in an acidic solvent that degrades the fiber to increase the surface area so the polypyrrole can stick. However, this degradation weakens the fiber.
The patented method developed at UA would retain much of the fiber’s strength by using ionic liquids, which are liquid salts at or near room temperature with low volatility that carry an electric charge. The ionic liquids do not degrade the fibers as much, and the process creates nanostructures that result in a stronger composite material that conducts electricity better. The ionic liquids can be used to fabricate conductive polymer composites as well as in place of other solvents to create the polypyrrole.
The process is potentially cheaper and environmentally cleaner since using ionic liquids results in much less harmful by-products from the chemical reaction. “A lot of effort has been made into making cellulose fibers conductive through chemical methods that, from a manufacturing standpoint, are not environmentally friendly,” says Dr. Anwarul Haque, associate professor of aerospace engineering at UA. “Our process does away with the use of methanol through the novel use of ionic liquids, which, by their very nature, have a low volatility that essentially eliminates environmental release pathways exhibited by methanol.”