The process of polymer film formation is divided into three stages.
In the first stage, the polymer particles move freely in the form of Brownian motion in the initial emulsion. As the water evaporates, the movement of the particles is naturally more and more restricted. The interfacial tension between water and air causes them to line up gradually.
In the second stage, when the particles come into contact with each other, the water in the network evaporates through the capillary. The high capillary tension applied to the particle surface causes deformation of the latex spheres causing them to fuse together. The remaining moisture fills the pores. A film is roughly formed.
The third, final stage allows the diffusion (sometimes called self-adhesion) of the polymer molecules to form a true continuous film. During film formation, isolated mobile latex particles consolidate into a new film phase. The film has high tensile stress.
Obviously, in order to make the redispersible polymer powder can form a film in the hardening mortar. It must be ensured that the minimum film forming temperature (MFT) is lower than the curing temperature of the mortar.
Colloids – polyvinyl alcohol must be separated from the polymer film system.
This is not a problem in alkaline cement mortar systems. Because polyvinyl alcohol will be saponified by the alkali generated by cement hydration. At the same time, the adsorption of the quartz material makes the polyvinyl alcohol gradually separated from the system. There is no hydrophilic protective colloid. A film formed by primary dispersion of redispersible polymer powder which itself is insoluble in water is sufficient. Not only in dry conditions, but also in long-term water immersion conditions.
Of course in a non-alkaline system. Such as gypsum or only filler system. Since polyvinyl alcohol still partially exists in the final polymer film. Affect the water resistance of the membrane. Where these systems are not used for prolonged immersion in water. And the polymer still has its characteristic mechanical properties. Redispersible polymer powders can still be used in these systems.
Following the final formation of the polymer film, a structured system of inorganic and organic binders is formed in the cured mortar. That is, a brittle and hard skeleton composed of hydraulic materials. And the flexible network formed by the film formation of redispersible polymer powder in the gap and solid surface.