Redispersible latex powder with other inorganic binders (such as cement, slaked lime, gypsum, etc.) and various aggregates, fillers and other additives (such as methyl hydroxypropyl cellulose ether, starch ether, lignocellulose, hydrophobic agent, etc.) for physical mixing to make dry-mixed mortar. When the dry-mixed mortar is added to the water and stirred, the latex powder particles will be dispersed into the water under the action of the hydrophilic protective colloid and mechanical shear. The time required for normal redispersible latex powder to disperse is very short, and this redispersion time index is also an important parameter to examine its quality. In the early mixing stage, latex powder has already begun to affect the rheology and workability of the mortar.
Due to the different characteristics and modifications of each subdivided latex powder, this effect is also different, some have a flow-aiding effect, and some have an increasing thixotropy effect. The mechanism of its influence comes from many aspects, including the influence of latex powder on the affinity of water during dispersion, the influence of different viscosity of latex powder after dispersion, the influence of protective colloid, and the influence of cement and water belts. Influences include the increase of air content in the mortar and the distribution of air bubbles, as well as the influence of its own additives and the interaction with other additives. Therefore, customized and subdivided selection of redispersible latex powder is an important means to affect product quality. The more common point of view is that the redispersible latex powder usually increases the air content of the mortar, thereby lubricating the construction of the mortar, and the affinity and viscosity of the latex powder, especially the protective colloid, to water when it is dispersed The increase of the concentration helps to improve the cohesion of the construction mortar, thereby improving the workability of the mortar. Subsequently, the wet mortar containing latex powder dispersion is applied on the work surface. With the reduction of water on three levels – the absorption of the base layer, the consumption of cement hydration reaction, and the volatilization of surface water to the air, the resin particles gradually approach , the interfaces gradually merge with each other, and finally become a continuous polymer film. This process mainly occurs in the pores of the mortar and the surface of the solid.
It should be emphasized that in order to make this process irreversible, that is, when the polymer film encounters water again, it will not be dispersed again, and the protective colloid of the redispersible latex powder must be separated from the polymer film system. This is not a problem in the alkaline cement mortar system, because it will be saponified by the alkali generated by cement hydration, and at the same time, the adsorption of quartz-like materials will gradually separate it from the system, without the protection of hydrophilicity Colloids, which are insoluble in water and formed by one-time dispersion of redispersible latex powder, can function not only under dry conditions, but also under long-term water immersion conditions. In non-alkaline systems, such as gypsum systems or systems with only fillers, for some reason the protective colloid still partially exists in the final polymer film, which affects the water resistance of the film, but because these systems are not used for In the case of long-term immersion in water, and the polymer still has its unique mechanical properties, it does not affect the application of redispersible latex powder in these systems.
With the formation of the final polymer film, a framework system composed of inorganic and organic binders is formed in the cured mortar, that is, the hydraulic material forms a brittle and hard framework, and the redispersible latex powder forms a film between the gap and the solid surface. Flexible connection. This kind of connection can be imagined as being connected to the rigid skeleton by many small springs. Since the tensile strength of the polymer resin film formed by latex powder is usually an order of magnitude higher than that of hydraulic materials, the strength of the mortar itself can be enhanced, that is, cohesion be improved. Since the flexibility and deformability of the polymer are much higher than that of the rigid structure such as cement, the deformability of the mortar is improved, and the effect of dispersing stress is greatly improved, thereby improving the crack resistance of the mortar.
Post time: Mar-07-2023