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

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.Des essais sur des rev\ueatements de polystyr\ue8ne et de polyisobutyl m\ue9thacrylate coul\ue9s \ue0 partir de tolu\ue8ne ont indiqu\ue9 que la contrainte interne r\ue9siduelle n'est pas influenc\ue9e par l'\ue9paisseur du rev\ueatement sec ou par la concentration initiale de la solution. On pr\ue9sente une th\ue9orie selon laquelle on peut pr\ue9dire l'importance de la contrainte et stipulant que la contrainte ne d\ue9pend nullement de l'\ue9paisseur ou de la concentration initiale de la solution. La contrainte interne est calcul\ue9e selon le volume de solvant qui s'\ue9vapore apr\ue8s la solidification de rev\ueatement. Ce point de solidification s'identifie \ue0 la concentration de solvant n\ue9cessaire pour faire diminuer la temp\ue9rature de transition du polym\ue8re \ue0 l'\ue9tat vitreux \ue0 la temp\ue9rature d'essai. Il y a donc corr\ue9lation directe entre le volume de solvant perdu durant le s\ue9chage de la solution et le changement de volume de la pellicule de polym\ue8re.Peer reviewed: YesNRC publication: Ye