Best Corrosion Protection Yet: Thin Film Polymers

The same polymers used in shampoos that leave hair feeling silky also can be used to prevent corrosion in pipelines because of a technique developed by a Florida State University researcher.

"Layering is the key to making polymers effective in protecting metals from corrosion," said materials chemist Joseph Schlenoff, who is the associate director of the FSU Center for Materials Research and Technology.

Shampoos leave a single layer of either positively or negatively charged polymers on the hair, Schlenoff said. However, by using multilayered polymers -- a thin film of both positively and negatively charged electrolytes layered one on top of the other -- a protective seal more effective than paints or resins alone is formed to exclude ions that promote corrosion, like salt.

"We start with a negatively charged metal surface and coat it with a positively charged liquid, or aqueous, polymer, then add a negatively charged aqueous polymer, and keep adding positive and then negative layers of polymers," Schlenoff said. "The postive and negative layers form a gel-like film that has a neutral charge because the positive and negative charges cancel each other. When they're bonded together, they really adhere to the surface. The film has about 10 or 20 layers, which is less that .1 micrometer thick."

Schlenoff said he has been contacted by a pipeline company that is interested in using the technique to help protect its pipeline from joint corrosion.

"It's a new way to solve an old problem," he said. "It is difficult to coat the inside of a pipeline once it has been built. We can pump aqueous polymers through a pipeline in turn, first the plus, then the minus, so that all the nooks and crannies and crevices are coated with this multilayer polymer. We can apply it in this way to the inside of a pipeline that is already in use."

Schlenoff and chemistry graduate student Tarek R. Farhat wrote a paper on the technique, "Corrosion Control Using Polyelectrolyte Multilayers," which was published in the March 2002 journal Electrochemical and Solid-State Letters (Vol. 5, page B13). The journal Science News featured an article on the technique in its April 13, 2002, issue.

The process of making thin films from aqueous polymers is a more environmentally friendly method than processes that use toxic, volatile organic compounds (VOCs), such as organic solvents, according to Schlenoff.

"Charged polymers, which are water soluble, have a low toxicity and are the same kinds of polymers as are used in shampoos," he said. "Because shampoos are mainly water, their manufacturers use aqueous polymers to make them thicker so they seem like gels. Some polymers stick to the hair and give it a certain feel, like a silky feel."

However, the polymers used in shampoos are either positively or negatively charged, not both, so their bond to hair isn't permanent, according to Schlenoff.

In addition to interest from the pipeline industry, Schlenoff also has been contacted by a well-known manufacturer of disposable razors.

"This technique can coat all metallic surfaces, including disposable razors, to prevent corrosive ions from reaching them and to provide a bit of lubrication."