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ALTERNATIVE TO CHROME ETCHING PROCESSES FOR METALS
Citation:
Bell, J. P. ALTERNATIVE TO CHROME ETCHING PROCESSES FOR METALS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-97/031 (NTIS 97-152698), 1997.
Impact/Purpose:
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Description:
Several industries, including the National Center for Manufacturing Science have initiated programs for chrome abatement. The programs, however, generally focus on chrome reduction by use of existing technologies and do not address the elimination of chrome in pretreatment processes by new technology development. It is proposed to evaluate polymeric coupling agents as replacements for chromium pretreatment processes on aluminum and steel. Polymeric coupling agents offer a practical alternative and improvements to chrome etching pretreatments presently utilized on aluminum and steel. Polymeric coupling agents are molecules which have the ability to chemically react with both the metal substrate and wide variety of polymer top coats, thus forming a "bridge" between them. The coupling agents can be tailored to specific systems, depending on the functionalities of the polymer top coat and the reactivity of the metal substrate. Bond failure caused by environmental factors (humidity, etc.) can be greatly reduced. In addition, polymeric coupling agents are able to distribute mechanical and thermal stresses near the metal interface thereby reducing internal stress concentrations which result in bond failure. A copolymer has been polymerized containing both b-diketone and epoxy functional groups. This copolymer is being evaluated as a potential polymeric coupling agent for bonding polymers to aluminum. X-ray Photoelectron Spectroscopy indicates interaction of the coupling agent with the aluminum oxide surface. Etched coupling agent treated joints exhibited improved joint strengths after immersion in water. Coupling agent treated aluminum substrates displayed improved corrosion resistance after ASTM B117 salt spray chamber exposure as compared to untreated controls. Quinone-amine polyurethanes (QAPs) are being evaluated as potential polymeric coupling agents for the steel-epoxy system. Infrared Spectroscopy and X-ray Photoelectron Spectroscopy indicate chemical interactions of the coupling agent with both the steel and epoxy surfaces. Quinone-amine treated steel substrates exhibited increased joint shear strengths as compared to untreated controls. Increases in both hot water stability and corrosion resistance were also observed for coupling agent treated substrates. X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy investigations suggest that failure is occurring within the epoxy layer. This report was submitted in fulfillment of Cooperative Agreement No. CR821875 by the University of Connecticut. This report covers a period of time from October 1993 to October of 1995.