Redispersible latex powder is a commonly used organic gelling material. It is a powder obtained by spray-drying a polymer emulsion with polyvinyl alcohol as a protective colloid. This powder can be evenly dispersed in water after meeting water. , forming an emulsion. Adding redispersible latex powder can improve the water retention performance of freshly mixed cement mortar, as well as the bonding performance, flexibility, impermeability and corrosion resistance of hardened cement mortar.
Effect of latexr powder on bond strength of cement-based materials
Emulsion and redispersible latex powder can form high tensile strength and bonding strength on different materials after film formation, they are used as the second binder in mortar to combine with inorganic binder cement, cement and polymer respectively Give full play to the corresponding strengths to improve the performance of the mortar. By observing the microstructure of the polymer-cement composite material, it is believed that the addition of redispersible latex powder can make the polymer form a film and become a part of the hole wall, and make the mortar form a whole through the internal force, which improves the internal force of the mortar. Polymer strength, thereby improving the failure stress of the mortar and increasing the ultimate strain. The long-term performance of the redispersible latex powder in the mortar was studied. It was observed by SEM that after 10 years, the microstructure of the polymer in the mortar has not changed, and the stable bonding, flexural and compressive resistance have been maintained. strength and good water repellency. The redispersible latex powder has studied the formation mechanism of the tile adhesive strength, and found that after the polymer is dried and formed into a film, the polymer film forms a flexible connection between the mortar and the tile on the one hand, and on the other hand, the fresh mortar The medium polymer increases the air content of the mortar and affects the formation and wettability of the surface, and subsequently during the setting process, the polymer also has a better influence on the hydration process and shrinkage of the cement in the binder, all These will help to improve the bond strength.
Adding redispersible latex powder to the mortar can significantly improve the bonding strength with other materials, because the hydrophilic latex powder and the liquid phase of the cement suspension penetrate into the pores and capillaries of the matrix, and the latex powder penetrates into the pores and capillaries. The inner film is formed and firmly adsorbed on the surface of the substrate, thus ensuring a good bond strength between the cementitious material and the substrate.
The optimization of latex powder on the performance of mortar is due to the fact that latex powder is a high molecular polymer with polar groups. When latex powder is mixed with EPS particles, the non-polar segment in the main chain of the latex powder polymer will Physical adsorption will occur with the non-polar surface of EPS. The polar groups in the polymer are oriented outward on the surface of the EPS particles, so that the EPS particles change from hydrophobicity to hydrophilicity. Due to the modification of the surface of EPS particles by latex powder, it solves the problem that EPS particles are easily exposed to water. Floating, the problem of large layering of mortar. At this time, when cement is added and mixed, the polar groups adsorbed on the surface of the EPS particles interact with the cement particles and combine closely, so that the workability of the EPS insulation mortar is significantly improved. This is reflected in the fact that EPS particles are easily wetted by cement paste, and the bonding force between the two is greatly improved.