Polyurethane based anti-graffiti coatings have been developed by incorporating varying amounts of OH-functional Silicone modified polyacrylate. Optimization of Silicone polyacrylate concentration in neat PU was done by testing its performance for graffiti resistance. Tests which include static contact angle measurements with water and spray paint, visual inspection of stain removal and color change measurements were performed. It was observed that 5 wt % of Silicone polyacrylate in the neat PU showed 95% stain removability. These coatings showed excellent graffiti resistance but poor mechanical properties. Hence modification of these coatings was done by nano-particle incorporation. Nano-silica particle concentration was optimized for surface mechanical properties such as surface hardness, elastic modulus and scratch resistance. FEG-TEM revealed that nano-silica particles were uniformly distributed over the surface. 5 wt % nano-silica particle additions in PU-5 wt % silicone polyacrylate base showed superior mechanical properties than other concentrations. Color change measurements showed that nano-silica particle addition had no effect on its graffiti resistance. Hence PU-5 wt % silicone polyacrylate, 5 wt % nano-silica showed excellent graffiti resistance and mechanical properties.

The components of automobile bodies have been manufactured primarily from steel since cars were first made. With the goal of energy savings, light-weighting is being adopted by substituting steel with a variety of light metals and composite materials. A DOE sponsored project in collaboration with PPG and Ford studied the use of automotive closure panels comprising an inner carbon fiber reinforced polymer (CFRP) sheet and an outer aluminum alloy (AA) sheet. The ends of closure panels are sealed with hem flange joints. A major concern is the formation of a galvanic cell within the joint wherein CFRP is the cathode that will accelerate the corrosion of the AA sheet. Various combinations of AA6xxx alloys with CFRP having two different orientations of carbon fiber, i.e., random and twill, are studied in this work. CFRP can only exert a galvanic driving force on a coupled AA panel by electrical connection at cut edges where sheared carbon fibers are exposed, or if carbon fibers are exposed on the CFRP panel surface by lack of coverage of the insulating epoxy matrix. It is believed that processing and curing variables lead to varied epoxy cover on the surfaces of CFRP. Electrochemical measurements such as the measurement of oxygen reduction limiting current density during cathodic polarization show that as-fabricated surfaces of CFRP panels exhibit some extent of electrochemical activity, indicating some lack of coverage of C fibers. It is of interest to characterize the epoxy cover on the CFRP surfaces in terms of the nature of the active sites (e.g., whether C fibers are totally uncovered or covered by a very thin layer of epoxy) and the density and distribution of the sites. A technique was developed to identify the exact locations of active sites on both random and twill CFRP by electrodeposition of small amounts of Cu. If the amount of deposited copper is small, the deposits indicate the location and number of the active sites on the CFRP surface. These deposits were also analyzed by serial sectioning using Focused Ion Beam/Scanning Electron Microscope. High resolution images of the deposit/epoxy interfaces provide a description of the nature of the defective/conductive regions on CFRP surfaces. Rotating disk electrode experiments were also performed to determine the oxygen reduction reaction (ORR) limiting current densities of CFRP at different electrode rotation rates i.e., different diffusion boundary layer thicknesses. These aspects are related to the overall mass transport in the electrolyte, which provides a deeper understanding of the kinetics on CFRP and the nature of active sites behaving as microelectrodes. The observations from the copper electrodeposition study and rotating disk electrode experiments will be correlated and the role of CFRP as a cathode contributing to the corrosion of AA in the galvanic couple will be presented. This work was supported by the U.S. Department of Energy through award DE-EE0007760, in collaboration with PPG Industries and Ford Motor Company.

Structures made from a combination of aluminum alloy (AA) and carbon fiber reinforced plastic (CFRP) are susceptible to galvanic corrosion of the AA in harsh atmospheric conditions, such as might exist for closure panels in automotive applications. It is important to understand the galvanic corrosion behavior of these materials under laboratory conditions as that might allow prediction of performance in real environments. This work tested specially designed AA6×××-CFRP coupons, including AA6111 and AA6022, connected to CFRP made from two different carbon fiber fabrics (twill and random) with the aim of understanding the corrosion behaviors in a laboratory cyclic exposure chamber and during on-road exposure. The extent of corrosion was assessed by galvanic current measurements, optical profilometry (OP), cross-sectional area analysis and microscopic analysis. Based on the results, it was determined that the corrosion susceptibilities and morphologies observed in CFRP/AA couples tested in environmental chamber for 12 weeks were in correspondence with those of the coupons subjected to on-road testing for 1 year in Columbus, OH.

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