AVS 45th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS-WeA

Paper AS-WeA9
Evaluation of the Degradation Mechanism(s) Associated with Acid Rain Exposure of Acrylic Melamine Based Automotive Clearcoats

Wednesday, November 4, 1998, 4:40 pm, Room 307

Session: Polymer Surfaces, Films and Interfaces
Presenter: P.J. Schmitz, Ford Motor Company
Authors: P.J. Schmitz, Ford Motor Company
J.W. Holubka, Ford Motor Company
L.F. Xu, Ford Motor Company
Correspondent: Click to Email
Environmental exposure of clearcoats to ambient conditions of low pH can result in visible surface pitting. The degradation phenomenon associated with this localized loss of material is thought to occur primarily through crosslink hydrolysis as a result of acid rain exposure. Although this phenomenon has been studied quite extensively, limited chemical data has been presented that confirms the mechanism(s) of the degradation process. Most conclusions that have been made are largely based on empirical considerations involving observations that degradation is most prevalent in areas having low pH rain, and the results of field exposure studies that indicate the sensitivity of a particular coating to environmental degradation is directly associated with the ease of hydrolysis of the crosslink. In this study, we have used XPS to monitor changes occurring at the clearcoat surface as a result of field exposure, to attempt to more clearly define degradation products, and therefore the mechanism(s) associated with the degradation phenomenon. Changes were observed in the N, C, and O core level spectra after field exposure, and were found to be consistent with the modification of melamine crosslinkers following laboratory acid treatment. Bulk elemental analysis and XPS core level results, obtained from sulfuric acid treated crosslinkers, were found to be consistent with melamine salt (sulfate) formation. The confirmation of residual melamine sulfate on the clear coat surface following field exposure, strongly suggests that the prominent degradation pathway is acid rain induced crosslink hydrolysis. The identification of degradation products associated with environmental exposure could prove useful in the development of laboratory testing for the evaluation of clearcoat hydrolysis resistance, to verify that exposure conditions reproduce field degradation pathways.