Changes in Solubility and Removability of Varnish Resins With Age

A series of mixtures based on cyc1ohexane, toluene and acetone have been employed to investigate the solvent power needed to remove various varnish resins in the course of photochemical deterioration. Under ordinary conditions of exposure, dammar and mastic resins tend to reach a maximum degree of oxidation at which time mixtures of no greater solvent power than 60/40 v/v toluene/acetone are needed to remove the aged coatings. Polycyc1ohexanone polymers tend to lose their solubility more slowly than the two natural resins but may in time require solvents of higher solvent power to remove them. In contrast, the two highly stable polymers, polyviny1acetate and Acryloid ®B-72 essentially maintain their solubility and removability in the solvents in which they were originally soluble, mixtures of lower solvent power than toluene.An investigation of the actual percentage of the resins dissolved by the various solvent mixtures indicates that, in the case of po1yviny1acetate and Acryloid ®B-72, solubility and removability are closely related. In contrast, solubility of the natural and po1ycyc1ohexanone resins changes more gradually with changes in solvent power, implying that their ease of removal depends more on rate of attack than upon the amount of resin dissolved.