The advanges of HPMC & MHEC in dry mix mortar products
November 22nd 2024
EPS granular thermal insulation mortar is a lightweight thermal insulation material mixed with inorganic binders, organic binders, admixtures, additives and light aggregates in a certain proportion. Among the EPS granular thermal insulation mortars currently researched and applied, it can be recycled redispersible polymer powder has a great influence on the performance of mortar and occupies a high proportion in the cost, so it has been the focus of people’s attention. The bonding performance of the EPS particle insulation mortar external wall insulation system mainly comes from the polymer binder, and its composition is mostly vinyl acetate/ethylene copolymer. Redispersible latex powder can be obtained by spray drying this type of polymer emulsion . Due to the precise preparation, convenient transportation and easy storage of redispersible powders in construction, special loose polymer powder has become a development trend due to its precise preparation, convenient transportation and easy storage. The performance of EPS particle insulation mortar depends largely on the type and amount of polymer used. Ethylene-vinyl acetate rdp powder (EVA) with high ethylene content and low Tg (glass transition temperature) value has better performance in terms of impact strength, bond strength and water resistance.
The optimization of redispersible polymer powder on the performance of mortar is due to the fact that polymer powder is a high molecular polymer with polar groups. When RDP is mixed with EPS particles, the non-polar segment in the main chain of the polymer powder 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 fromhydrophobicity to hydrophilicity. Due to the modification of the surface of EPS particles by polymer 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.
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. To study the long-term performance of redispersible latex powder in mortar, it was observed by SEM that after 10 years, the microstructure of the polymer in the mortar has not changed, maintaining stable bonding, flexural and compressive strength and good water repellency. The formation mechanism of the tile adhesive strength was studied on the redispersible latex powder, and it was found that after the polymer was dried into a film, the polymer film formed a flexible connection between the mortar and the tile on the one hand, and on the other hand, The polymer in the mortar 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 favorable influence on the hydration process and shrinkage of the cement in the binder, All of these will help to improve the bond strength.
Adding redispersible polymer powder to the mortar can significantly improve the bonding strength with other materials, because the hydrophilic polymer 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.
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