Swelling of Paint Films in Water: IX–Effects of Temperature During Soaking and Film Formation and Repeated Soaking and Drying

Five single-pigment paints made with unbodied linseed oil and a pigment volume of 0.30 were used in the test. The five pigments were l) basic carbonate white lead, 2) antimony oxide, 3) rutile titanium dioxide, 4) zinc oxide, and 5) magnesium silicate. The first two make paints that are low and the last three high in absorption and swelling. Most paint films, both before and after weathering, absorb more water and swell more when soaked in warm water (119?F.) and absorb and swell less when soaked in cold water (33?F.) than when soaked in water at 70?F. Absorption at 119?F. was from l.9 to 8.4 times the absorption at 33?F. For unweathered films, the quantity of soluble material extracted from the films was nearly proportionate to the temperature of the soak water. The temperature coefficient of solubility fo unweathered films ranged from 0.051 to 0.087 grams per cubic centimeter of film for each degree of temperature Fahrenheit. At 70?F. the ratio of solubility to loss in volume indicates the soluble material for white lead films has a density of l.2 compared with 1.1 for antimony oxide or magnesium silicate. None of the paints tested absorbed more than 10.2 percent water when the coating was formed at 160?F.; this is less than 1/6th of their absorption when formed at 70 to 80?F. Antimony oxide is not significantly improved by formation at high temperature. The formation of coatings at low temperature (36?F.) increases the absorption and swelling of unweathered films markedly for zinc oxide and magnesium silicate paints, and slightly for titanium dioxide, white lead, and antimony oxide. After weathering, the effect of low temperature during formation is no longer observable. Repeated soaking and redrying of unweathered and weathered coatings of zinc oxide gave evidence of a disruption of the internal structure and development of porosity from the stresses involved. Unweathered coatings of white lead, antimony oxide, titanium dioxide, and magnesium silicate withstood 15 cycles of soaking and redrying without evidence of serious impairment of structure. The weathered coatings began to show disruption of structure and porosity if the cycles were repeated often enough.

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