Mr. Chuck Brunner from Smith Paint Products in Orlando, Florida, reported that a line of specialty paint formulas and coatings were failing. The failures appeared to be related to the water quality of the make-up water. The types of failures that were reported were that the paint would clump or form a precipitate and/or that it would not adhere to the surface to be painted. To be able to reproduce this condition, Mr. Brunner supplied a sample of water from Orlando, Florida. This source was one of the water sources that appeared to be too reactive with the coating. In addition, Mr. Brunner provided a second source of water from Colton, California. The scope of the preliminary evaluation was limited to these objectives:
1) Conduct a preliminary water quality characterization of these two water sources,
2) Attempt to reproduce the paint failure with the Orlando, Florida sample,
3) Evaluate possible chemicals related to specific cations or anions in the water; and
4) Make recommendations on potential engineering or management solutions.
After initiating the project, the scope of work was further modified to include a more detailed evaluation of the relationship between water hardness and sulfates on coating clumping. For the two water quality samples, the reaction formed small sand-size paint particles immediately upon mixing the water and chemicals. Overtime, the masses began to coagulate and form larger clumps that began to settle out of solution. With respect to the chemical matrix testing, positive clumping reactions occurred immediately when the fluid matrix contained calcium. Based on this result, it is likely that the reaction with hardness, i.e., multivalent cations like calcium, may be the cause of the paint clumping.
The samples from Florida and California have a total hardness ranging from 264 to 285 mg CaCO3/L. To test the hypothesis that the water hardness was responsible for the paint clumping, the water samples were treated using the following water treatment methods: deionization, cation removal, and anion removal. Deionization was accomplished by allowing the test solution to react with a deionization resin. The deionization resin removes cations and anions from the water and exchanges cations for hydrogen ions and anions for hydroxyl ions. The control solution was deionized water with a conductivity of < 1 umohms/cm with an estimated total dissolved solids of < 0.01 mg/L.
The cation exchange resin, C-100, is a water softening resin that was manufactured by The Purolite Company, 3620 “G” Street, Philadelphia, Pennsylvania, 19134 (purolite.com). The resin is made up of spherical beads that vary in diameter from 0.3 to 1.2 mm and that are manufactured using an inert co-polymer of polystyrene to which functional groups are added to the resin surface. The resins can be recharged using a brine or sodium chloride solution. The cation exchange resin exchanges divalent and multivalent cations, i.e., calcium, magnesium, iron, manganese, and aluminum for sodium, for hydrogen ions. The anionic-exchange resin removes negative ions from solution. This resin that was manufactured by The Purolite Company, 3620 “G” Street, Philadelphia, Pennsylvania, 19134 (purolite.com). The anionic resins retain all the ions with a negative charge, such as: sulfates, carbonate, bicarbonate, chloride, and nitrate and exchange them with hydroxyl ions (OH-). When both water samples and the control samples were deionized or treated with the cation resin, the mixed paint product does not clump, precipitate, or flocculate.
When the samples were only treated with the anion resin, the water samples and the calcium chloride solutions still caused a precipitate or clumping to occur. Therefore, it appears that deionization of the water would be excessive and only water softening would be required to prevent the clumping problem.
The next series of experiments were designed to determine at what point does the water hardness begin to cause problems with clumping and precipitation of the paint products. This preliminary assessment was conducted by preparing solutions of CaCO3 with concentrations of 0 mg/L, 5 mg/L, 25 mg/L, 30 mg/L, 40 mg/l, 50 mg/L, 75 mg/L, 100 mg/L, 150 mg/L, and 300 mg/L. The test solutions were prepared using a laboratory-grade calcium carbonate and the actual hardness concentrations were determined by a titration method. The test samples were prepared following the instructions provided by the manufacturer. Based on this preliminary laboratory experimentation, it appears that “clumping” does not occur when the total hardness is less than 30 mg CaCO3/L or 1.75 grains per gallon. Based on standard descriptions for hardness, it appears that waters classified as soft water with a hardness of less than 17 mg CaCO3/L, should not cause the paint product to clump.