Role and mechanism of formic acid in stripping of paint comprising epoxy primer and polyurethane topcoat

Previous practice indicates that formic acid can play a significant role in the process of paint stripping. The results of this work explain how formic acid promotes degradation of both the topcoat and primer, and how proper use of a solvent can accelerate this process. To understand the role of acidic components in the method and develop a neutral or mildly acidic remover, we investigated this process using qualitative research methods. The degradation mechanism of topcoat and primer by formic acid in various solvent systems was studied to promote development of neutral or mildly acidic paint remover for use in this field. Fourier transform infrared (FTIR) spectra indicated that the polyurethane topcoat was degraded to aliphatic alcohol while carbamate was rapidly degraded to carbon dioxide and primary amine. At the same time, the epoxy primer was degraded to phenolic substances and aldehydes. X-ray photoelectron spectroscopy (XPS) results confirmed the proposed mechanism of this process.