Redispersible polymer powder
Redispersible polymer powder is a spray-dried dispersion that can form a stable dispersion when added to water. It has the same properties as the original emulsion and is a commonly used dry powder mortar additive in putty.
1. The role of the flexibility of the polymer powder
Redispersible polymer powder is needed in the production of putty powder for architectural coatings. A reasonable formulation can increase the bond strength with a small amount of latex powder.
In practical terms, the strength of the putty used as a transition layer between the external thermal insulation and the coating should not be higher than that of the rendering mortar, otherwise cracking is likely to occur. The flexibility of the putty should be higher than that of the substrate throughout the insulation system. This allows the putty to better adapt to the deformation of the substrate and buffer its own deformation under the influence of external environmental factors, relieving stress concentration and reducing the possibility of cracking and peeling of the coating.
2. The role of a continuous film after drying
Redispersible polymer powder is used to produce putty powder. During the production process, the latex powder can be redispersed and then remixed. Due to the continuous consumption of water in the mortar (part of it is absorbed by the base layer and part of it participates in the internal reaction of the mortar), and the strongly alkaline environment provided by the cement, the latex particles form a continuous film that is insoluble in water after drying in the mortar. This continuous film is formed by the fusion of the single dispersed particles in the latex into a homogeneous body.
During the process of applying putty, the latex powder can improve the workability, thereby increasing the scratch resistance and flexural strength of the mortar, giving the mortar plasticity and reducing its setting time.
3. The polymer powder has a high degree of compatibility with the cement base
When the dispersible polymer powder is stirred evenly in the putty powder and mixed with water, it forms a polymer emulsion in contact with water. Gradually, a cement gel is formed through the initial hydration of the cement. The liquid phase is saturated by Ca(OH)2 formed during hydration, while the latex powder is dispersed into fine polymer particles and deposited on the surface of the cement gel/unhydrated cement particle mixture. As the cement further hydrates, the water in the capillaries decreases, and the polymer particles are gradually gradually become confined in the capillaries, forming a tightly packed layer on the surface of the cement gel/unhydrated cement particle mixture and the filler; as a result of the hydration reaction, base absorption and surface evaporation, the moisture content is further reduced. During the drying process, the emulsion is dehydrated again, and the formed packed layer aggregates into a film, which bonds the hydration reaction products together to form a complete network structure. The combined effect of the cement hydration and the composite system formed by the emulsion film formation improves the dynamic crack resistance of the putty.
4. Powdered polymer can increase overall strength
Adding dispersible polymer powder to putty powder can increase its strength and greatly improve its hardness. It has outstanding waterproofing properties, good adhesion strength, and can also increase the elasticity of the mortar and provide a longer open time. It also gives the mortar excellent alkali resistance, and can improve the adhesion/bonding, flexural strength, abrasion resistance and workability of the mortar. In addition, it has greater flexibility in flexible crack-resistant mortars.
