The origin of residual internal stress in solvent‐cast thermoplastic coatings

Abstract

Abstract Experiments on polystyrene and poly(isobutyl methacrylate) coatings cast from toluene have shown that residual internal stress is independent of dried coating thickness and initial solution concentration. A theory is presented that predicts the magnitude of the stress and shows that it has no dependence on thickness or initial solution concentration. Internal strain is calculated from the volume of solvent lost after the coating has solidified. This solidification point is identified with the solvent concentration that is sufficient to depress the glass transition of the polymer to the prevailing experimental temperature. A one‐to‐one correlation is confirmed between the volume of solvent lost from solution during drying and the volume change of the polymer film.