A known contributor to the physical failure of a coating or adhesive is shrinkage stress, which occurs during the loss of volatile material during drying or aging.  High internal stresses in a film can cause a loss of adhesion or cracking or put it at risk of failure due to other stresses such as handling and environmental changes.  We have measured the stress development of films for various polymers, the effect of solvents and pigment loading on drying stresses, as well as evaluating the risk of stress failures in commercial artists’ paints and coatings.

The research focuses on:

• Measuring the internal stress in polymeric films cast from solutions.
• Examining the factors that most affect the magnitude of drying stresses  (pigment concentration or solvent type).
• Evaluating the risk of dangerous stress development in commercial art materials.

The magnitude of shrinkage stress, which develops in the film generally increases with the T_g of the polymer.  Thus harder resins (high T_g) tend to have large shrinkage stress, exacerbated by increasing pigment volume concentration, while softer resins and commercial products form relatively stress-free films.  Further, films formed from rapidly evaporating solvents develop greater stress than films formed from slowly evaporating solvents.  Possible treatments to relieve stress in coatings include mild heat, humidification, or exposure to solvent vapors, but it is not yet possible to identify highly stressed films that might be at risk.

For more information:
            Moran et al. Mat. Res. Soc. Symp. Proc., 352 (1995): 293-303. (Abstract) (pdf [428 KB])
            Whitmore et al. JAIC, 38 (1999): 429-441. (Abstract) (pdf [884 KB])

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