Mechanism of Redispersible Emulsion Powder in Dry Powder Mortar

Release time:

2022-03-04

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Mechanism of Redispersible Emulsion Powder in Dry Powder Mortar

Redispersible emulsion powder and other inorganic adhesives (such as cement, hydrated lime, gypsum, clay, etc.) and various aggregates, fillers and other additives [such as hydroxypropyl methyl cellulose, poly (starch ether), cellulose fiber, etc.] are physically mixed to make dry mortar. When the dry mortar is added to water and stirred, under the action of hydrophilic protective colloid and mechanical shear force, the latex powder particles can be quickly dispersed into water, and sufficient to make the redispersible latex powder fully film. The composition of different rubber powder, respectively, on the rheology of mortar and a variety of construction performance impact: latex powder re-dispersion of water affinity, latex powder after dispersion of different viscosity, on the mortar air content and bubble distribution, powder and other additives interaction, so that different latex powder respectively with increased fluidity, increase thixotropy, increase viscosity and so on. It is generally believed that the mechanism of redispersible latex powder to improve the workability of fresh mortar is: the affinity of latex powder to water, especially when the protective colloid is dispersed, increases the viscosity of the slurry and improves the cohesion of the construction mortar.

After the fresh mortar containing latex powder dispersion is formed, with the absorption of water on the base surface, the consumption of hydration reaction, and the volatilization to the air, the water gradually decreases, the resin particles gradually approach, the interface gradually becomes blurred, the resin gradually fuses with each other, and finally polymerizes into a film. The process of polymer film formation is divided into three stages. In the first stage, the polymer particles are free to move in the form of Brownian motion in the initial emulsion. With the evaporation of water, the movement of particles is naturally more and more restricted, and the interfacial tension between water and air causes them to gradually arrange together. In the second stage, when the particles begin to contact each other, the network-like moisture evaporates through the capillary, and the high capillary tension applied to the surface of the particles causes the deformation of the latex spheres to fuse them together, the remaining moisture is filled in the pores, and the film is roughly formed. The third, final stage allows diffusion (sometimes referred to as self-adhesive) of the polymer molecules into a truly continuous film. During film formation, isolated mobile latex particles consolidate into a new film phase with high tensile stress. Obviously, in order to make the re-dispersible latex powder can re-harden mortar film, it is necessary to ensure that the minimum film-forming temperature (MFT) is lower than the curing temperature of the mortar.