Conductive polymer passivates iron and other metals / DECHEMA test results extremely positive
Zipperling Kessler & Co, a medium-sized company based in Ahrensburg near Hamburg, currently leads the field in a basic research marathon against major enterprises and renowned research institutions around the world. For more than 12 years a group in the 35-strong R+D department of this plastics compounder, which has a total of 230 employees, has been conducting research into "conductive polymers”, a new category of plastics that exhibit many unusual metallic properties.
Whereas most research institutes and major companies severely curtailed or discontinued their programmes some years ago in the face of extremely difficult research problems and uncertain market prospects, this SME under the leadership of its chief chemist and managing partner Dr. Bernhard Wessling did not give up the struggle. The reward: the development of a processable conductive polymer by the name of polyaniline (PANI), a commercialisable polymerisation process, a pre-commercial pilot plant, first marketable products - albeit still in "homoeopathic quantities” - and a major breakthrough in corrosion prevention.
As long as five years ago, Zipperling submitted a first patent application for the use of polyaniline for corrosion prevention, though at the time the effects were difficult to reproduce. "At that time we had not yet understood why PANI had an anti-corrosive effect, but now we have succeeded in answering that question,” says Dr. Wessling, explaining why such a long time elapsed after the first discovery. "Our discovery was noted in other places too, for example at the Los Alamos Laboratories in the USA, but we are evidently the only ones at present who understand how it works.”
This paved the way for Zipperling to develop and test effective preparations and coatings over the past two years. Rival work, e.g. in Los Alamos, has yet to progress beyond the laboratory stage.
The company has now issued this interim report in connection with the publication of an official test report by DECHEMA (Frankfurt/Main). As a leading European corrosion research institute DECHEMA was commissioned by Zipperling to test the corrosion prevention properties of a coating containing PANI by comparison with a tried-and-tested coating system. The material used for comparison was selected by DECHEMA itself.
The new polyaniline coating passed all the tests and out-performed the conventional coatings. The tests investigated crevice and pitting corrosion and galvanic corrosion. In parallel with the test, an outdoor weathering test ran from December 1993 to June 1994. (A summary of the test results is given at the end of this press release.)
At present the company is making preparations for the launch of a first product in limited test markets. The intention is to put a new "rust stopper” on the market on a regional basis. "This will be the first coating that really stops rust, because PANI passivates the iron/steel surface by forming a dense, firmly adhering oxide layer.”
Further products are in preparation, and protection for copper and aluminium is also possible.
In cooperation with the University of Arlington, Texas, and more recently with the technical faculty of the University of Kiel, further exploration of the fundamental nature of the action mechanism is being undertaken in parallel with the market-oriented development work.
"We were naturally overjoyed when Prof. Elsenbaumer in Texas, a long-standing expert and research colleague in the field of polyaniline, confirmed our research findings in an independent study. In our ongoing joint work we have found that the corrosion rate is reduced by at least a factor of 10, and in some systems by a factor of as much as 1,000 to 10,000.”
A polyaniline primer (coating) plus epoxy topcoat (Wilckens Eposist 2000) on steel (ST 37) was compared with specimens coated either with the epoxy topcoat only or with a zinc-rich primer (Wilckens Epoxid Zinkstaubfarbe EPB 7601) plus the same epoxy topcoat.
Only the steel specimen passivated with polyaniline primer plus epoxy satisfied the requirements of the crevice corrosion test (with injury to the topcoat). Without injury, all systems passed the test.
On the specimens passivated with PANI primer virtually no traces of rust were detectable at the injury sites, and certainly no undermining.
This test was performed with a cruciform injury in each case. In the first test design the joining screw was insulated from the copper and the cruciform injury was made through the epoxy film only. In this test the specimen passivated with polyaniline exhibited virtually no signs of rust, whereas the control specimens displayed heavy rust formation.
The second test design tested galvanic corrosion with a short circuit and involved a cruciform injury penetrating to the surface of the metal. The galvanic current was also measured. The specimen passivated with polyaniline primer registered a current of ca. 1 mA, the control specimens with and without zinc-rich primer 2.5 - 3 mA.
While the tests at DECHEMA were in progress, specimens with the same coatings underwent an outdoor test at Zipperling with 90 days' exposure to weathering. Here injuries to the anti-corrosion coating were made on all specimens in the form of horizontal cuts.
The specimen passivated with polyaniline displayed little or no rust formation at the site of the injury to the anti-corrosion coating. Both the straight epoxy coating and the one with zinc-rich primer exhibited heavy rust formation.
In a further test over the same period, Chemetal bonders (untreated steel plates) were each passivated over half their area and coated with a not very efficient topcoat (Hagebau Flüssigkunststoff). The topcoat was transparent to allow observation of changes at the surface of the metal and in the coating. In addition, horizontal cuts were made through the coating, extending from the unpassivated half across the boundary into the passivated half.
This test involved comparison of phosphate-coated and non-phosphate-coated specimens and also of specimens where after passivation with polyaniline primer the polyaniline primer coating had been carefully removed.
It was found that in all specimens the extent of the undermining at the site of the cut injury to the topcoat was several millimetres in the unpassivated area, whereas in the passivated half it was virtually undetectable. In some cases it was not even possible to detect any rust formation at the injury site.
The outdoor weathering results show a clear correlation with the findings of the DECHEMA corrosion test.
Ahrensburg, 14 September 1994
Dr. Bernhard Wessling
