Degradation and Removal of Acrylic/Alkyd Hybrid Paint Using Soybean Oil-Derived Methyl Esters as Bio-Based Solvents

Abstract Acrylic/alkyd hybrid coatings effectively combine the superior adhesion and gloss of alkyd resins with the chemical and mechanical resilience of acrylic polymers. However, their removal typically necessitates the use of hazardous petroleum-derived solvents. This study evaluates the application of vegetable oil methyl esters (VOMEs)─synthesized via alkaline transesterification of soybean oil─as a biobased and efficient alternative for paint degradation and removal. Commercial acrylic/alkyd paint films were exposed to VOMEs for varying durations (15–120 min) and characterized using mass change analysis, Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), thermogravimetric analysis (TGA), and elongation testing. Mass change analysis indicated a maximum film mass increase of 10.51% after 120 min, due to the sorption of VOMEs into the paint film. The TGA data revealed an additional mass loss between 150 and 260 °C in the treated films, attributed to the thermal release of sorbed VOMEs. Furthermore, the FTIR-ATR spectra demonstrated that this solvent uptake disrupted the cross-linking and aromatic structures of the paint film. Mechanical characterization confirmed significant structural weakening, as evidenced by a 97% reduction in time to failure. Practical assays on glass, carbon steel plates and cladding stone substrates achieved complete paint removal within 55 min. Thermogravimetric analysis confirmed that these biobased VOMEs remain thermally stable up to 150 °C, preventing premature thermal release during stripping operations and positioning them as promising, environmentally friendly alternatives to conventional stripping agents. Hansen solubility parameters and relative energy difference values indicate that the main VOMEs components drive the stripping action by weakening interchain forces, which promotes blistering, curling, and swelling and thereby facilitate coating removal.