mortar additive hpmcMay 11th 2023
Usually, when we say the performance of a tile adhesive is good or not, in addition to its operational performance and anti-slip ability, we also pay attention to its mechanical strength and open time. In addition to affecting the rheological properties of the tile adhesive, cellulose ethers have strong influence on the mechanical properties of the tile adhesive, such as operating smoothness, workability,open time, etc.
Influence on Tile Adhesive Open Time
When the redispersible polymer powder(RDP) and cellulose ether(HPMC MHEC) coexist in the wet mortar, the RDP has stronger energy to adhere to the cement hydration product, and the HPMC and MHEC exists more in the interstitial liquid, which affects the viscosity and time of coagulation for the mortar.The surface tension of HPMC is larger than that of RDP, and more cellulose ether enriched on the mortar interface will be beneficial to the formation of hydrogen bonds between the basal plane and the cellulose ether.
In wet mortar, the water in the mortar evaporates and the cellulose ether is enriched on the surface. A film will be formed on the surface of the mortar within 5 minutes, which will reduce the subsequent evaporation rate. As more water evaporates from the thicker mortar Part of it migrates to the place where the mortar layer is thinner, the film formed at the beginning is partially dissolved, and the migration of water will bring more cellulose ethers to concentrate on the surface of the mortar.
Therefore, the film formation of cellulose ether on the mortar surface has a great influence on the mortar properties.
Effect on pull-out strength
In addition to imparting the above-mentioned beneficial properties to the mortar, cellulose ethers also retard the hydration kinetics of cement. This retardation is mainly due to the adsorption of cellulose ether molecules on various mineral phases in the hydrating cement system, but in general, the consensus view is that cellulose ether molecules are mainly adsorbed on water such as C-S-H and calcium hydroxide. On the chemical products, it is rarely adsorbed on the original mineral phase of the clinker. In addition, cellulose ethers reduce the mobility of ions (Ca2, SO42-, …) in the pore solution due to the increase in the viscosity of the pore solution, which further retards the hydration process.
Viscosity is another important parameter, which shows the chemical properties of cellulose ethers. As mentioned above, the viscosity mainly affects the water retention capacity and also has a significant effect on the workability of the fresh mortar