Polymers replace chromates
3 Aug 2004
University of Rhode Island scientist Sze Yang has created a new group of non-toxic, corrosion-resistant polymers.
The polymers are designed as a replacement for chromates in paints and other coating systems. Chromates have been used commercially to protect metal from corrosion for 50 years but have recently been declared hazardous.
"There is now a worldwide push on to remove chromates because they are carcinogens," said Yang, a professor of chemistry. "Their use is gradually decreasing as replacements are found."
The new product is said to be a two-strand, conducting polymer that can emulate the most important functions of chromates. Rather than serve as a barrier coating, which is ineffective when damaged by scratches, the new URI polymers inhibit the process of corrosion and are "self-healing." They promote the formation of a protective layer and can resist scratch damage, pinholes, pitting, and stress cracking corrosion.
"Typical polymers are insulators, but conducting polymers allow electrons to move along the polymer chain," explained Yang, who collaborated on the research with Richard Brown, a URI professor of chemical engineering. "This ability to give and take electrons is essentially the same as what chromates do, interrupt the electro-chemical process of corrosion formation."
Unlike other efforts to develop single-strand, corrosion-resistant conducting polymers, this low-cost polymer has a second strand that provides space for a variety of modifications to its physical structure, making it more malleable and adaptable for many application processes, including spraying, dipping or spin coating.
Major potential markets are said to include coating of aluminium alloys for aircraft, aluminium and steel for the automotive industry, and concrete-reinforcing bars for bridges, highways and buildings. The polymers are effective as a low-cost, minor additive to paint, and can be soluble in commercial paint solvents and used in water-based epoxies. It also is effective for surface treatments, steel coil coating, and as a corrosion resistant primer under other resin-coating systems.
Corrosion is a chemical process that causes rust and the deterioration of metals and other materials. "We can usually see rust easily, but the bigger problem is the dangerous weakening effects of corrosion that we can't see," Yang said.
In addition to their anti-corrosive properties, the new polymers are also effective as a coating to prevent the build-up of electrostatic charges. They can be used in a wide variety of ways, from surgical wards and computer chip "clean rooms" where static can interfere with operations and production, to electrical appliances and many other products that naturally become charged with static electricity. They can also be useful in operations where combustible materials are in use, as discharges of static in these circumstances can be a significant hazard.
Yang and Brown have been issued two patents and have four others pending on various versions of the new conducting polymers. Laboratory studies have been completed on the polymer syntheses, on some test coating formulations, and corrosion tests of coatings on aluminium and steel. With the research complete, the co-inventors are now seeking collaborators to commercialise the polymers.
