P.G. Jessop, M. Cunningham
Queen's University,
Canada
Keywords: coatings, CO2, water, particles, smart surfaces
Summary:
Industry still uses oil-based coatings, despite their environmental impact, because of their superior performance which is due to the fact that the polymer binder is dissolved, not suspended, in the solvent. Conventional water-based paints and coatings use suspended particles that are supposed to merge as the paint dries; the practical disadvantages of this mechanism include requirements for a softer polymer and for dispersants, inability to create a high gloss or scratch-resistant coating, and inadequate film formation at lower temperatures. As a result, oil-based paints are preferred for many applications in industry. In order to get the same mechanism of action as oil-based coatings, water-based coatings must consist of a water-soluble polymer, but the resulting coating would be water-soluble and therefore not water-resistant. There is therefore a need for a binder that is soluble in water while in the paint can but insoluble after application. We have developed a polymer binder that is hydrophilic and soluble in water under CO2 gas but hydrophobic and water insoluble under air. The binder is fully dissolved in carbonated water in the paint can but the CO2 evaporates as the paint is applied to the surface, leaving a water-insoluble, water-resistant coating. This makes it possible to have the performance and mechanism of action of oil-based coatings without the need for organic solvents or volatile organic compounds. Crosslinkers added to the formulation do not cause crosslinking in the paint can but are activated by CO2 loss when the paint is applied to the surface. Other methods of using CO2 in water-based paints will also be discussed, as will methods for controlling the surface properties of particles for a variety of applications such as liquid chromatography, artificial latexes, solid phase extraction, and Pickering emulsifiers. All of these applications use the same basic principle that organic compounds with certain basic groups have different properties in the presence of an atmosphere of CO2 than in the presence of air.