Many families are now starting to use moisture-regulating building materials to help with home dampness. So, what is the principle behind moisture-regulating building materials and moisture-regulating boards?
The absorption and release of water vapor by moisture-regulating building materials and moisture-regulating boards depends on the water vapor partial pressure on their surface and the water vapor partial pressure of the surrounding air. As long as the moisture-regulating building materials are applied to the inner surface of the enclosure structure, it can automatically adjust the indoor humidity, and the moisture regulation process is continuous and energy-free.
The porous layer filler has a large specific surface area and is rich in internal channels. It adsorbs water through capillary action, providing a "channel" for water to enter and exit the coating. The solvent for moisture-regulating building materials can be an organic solvent and water, acting as a coating medium, or it can be solvent-free, made into powder coatings or photocurable coatings. Additives include emulsifiers, wetting dispersants, defoamers, thixotropic agents, thickeners, film-forming aids, etc., which can improve the coating state, improve certain properties of the coating, or impart certain special functions. The film-forming substance in the moisture-regulating coating acts as a binder or carrier, making the coating form a continuous phase, determining the film-forming method and the main properties of the coating, and playing an important role in moisture transmission. VanderWel, et al. [38] believe that when polymers come into contact with water, water molecules form hydrogen bonds with —O—, —S—, —N—, etc. in the polymer, enhancing the hygroscopicity. The greater the polarity of the polymer, the stronger the water absorption capacity. The water absorption of non-polar polymers is almost zero. The type and quantity of polar groups on the molecular chain determine the hygroscopicity; the hygroscopicity is also related to the polymer structure. The more regular the molecule, the less favorable it is for hygroscopicity; the density of the film will also affect the hygroscopicity of the coating. The better the continuity, the denser the film, the less favorable it is for water molecule penetration. The worse the continuity, the stronger the capillary action, and the more favorable it is for water molecule penetration. The structure and surface properties of the moisture-regulating building material coating determine the moisture absorption and release capacity. Inorganic polymers contain many polar groups and have a less dense film, which is conducive to moisture regulation. In the drying process of solvent-based coatings, the polymer resin used forms a continuous and dense network polymer film through self-drying or crosslinking as the solvent evaporates, and its hygroscopicity is poor. The film formation of polymer emulsions is achieved through capillary action, causing the latex particles to gradually approach and merge into a macroscopically continuous and microscopically discontinuous film. When encountering water, hydrogen bonds, diffusion, and capillary penetration occur. When the types and amounts of monomers are the same, the film formed by the emulsion has stronger water absorption than the film formed by the organic solvent polymer. The surface state, pore structure, and pore surface active sites of the porous layer filler in the moisture-regulating coating determine the water absorption capacity of the coating, which can be analyzed from the aspects of capillary condensation adsorption and surface adsorption. The adsorption of water molecules on the outer surface and the inner surface of the large pores of the multi-layer porous filler can be explained by the BET multi-molecular layer adsorption theory, and the behavior of water penetration into mesopores and micropores can be explained by the capillary condensation theory. Additives are used to improve the wetting dispersibility, sedimentation, leveling, and viscosity of the coating, and most of them contain hydrophilic components, such as hydrophilic resins, modified oils, surfactants, high-boiling alcohols or alcohol ether solvents. The polar groups in them form hydrogen bonds with the polar groups in the resin and filler, which helps to improve the water absorption of the coating.
In summary, everyone should have a preliminary understanding of moisture-regulating building materials.
