Application of the Flory-Rehner equation and the Griffith fracture criterion to paint stripping

Chemical paint stripping is a part of paint technology that is very necessary but for which quantitative understanding has been comparatively unexplored. Traditional paint strippers were based on very effective solvents, such as dichloromethane, that are now recognized as being dangerous for people and the environment. Optimal replacement by environmentally sound, and effective, paint strippers requires a better understanding of the action of the traditional materials. This communication links the stripping of cured paint films by aggressive solvents to the effect that swelling has on the cohesive and adhesive properties of a crosslinked polymer network. Swelling, described by the well-known Flory-Rehner equation, can be used to estimate the reduction in strength of the coating film. Thus, its resistance to fracture, described by the Griffith equation, is decreased so that the swelling stresses cause severe weakening and sometimes spontaneous removal. The equations lead to a description that fits well with common experience and so may be useful in selecting materials for future, less toxic, and more easily disposed, stripping formulations.