Construction grade HPMC hydroxypropyl methylcellulose Advantages
December 23rd 2024
When mastic powder and cellulose ether are present together in wet mortar, some data models show that mastic powder has stronger kinetic energy to adhere to cement hydration products and cellulose ether is more present in the interstitial fluid, affecting the viscosity and setting time of the mortar more.
Effect on the opening time of tile adhesive
The surface tension of cellulose ethers is larger than that of gum powder, and more enrichment of cellulose ethers at the mortar interface will be beneficial to the formation of hydrogen bonds between the substrate and cellulose ethers. In wet mortar, the water in the mortar evaporates and the cellulose ethers are enriched on the surface, a film will be formed on the mortar surface within 5 minutes, which will reduce the subsequent evaporation rate, as more water migrates from the thicker part of the mortar to the thinner part of the mortar layer, the film formed at the beginning will be partially dissolved and the migration of water will bring more cellulose ethers enriched on the mortar surface.
Film formation of cellulose ether on mortar surface
1. The formed film is too thin, it will be dissolved twice and cannot limit the evaporation of water and reduce the strength.
2. The film formed is too thick, the concentration of cellulose ether in the mortar interstitial liquid is high and the viscosity is large, so it is not easy to break the film on the surface when the tiles are pasted. It can be seen that the film-forming property of cellulose ether has a greater influence on the opening time. And the type of cellulose ether (HPMC, HEMC, MC, etc.) and the degree of etherification (degree of substitution) directly affect the film-forming properties of cellulose ether to the hardness and toughness of the film.
Effect on pull-out strength
In addition to imparting various beneficial properties to mortar as mentioned above, cellulose ethers also retard the hydration kinetic process of cement. This retarding effect is mainly due to the adsorption of cellulose ether molecules on various mineral phases in the hydrating cement system, but the general consensus is that cellulose ether molecules are mainly adsorbed on hydration products such as C-S-H and calcium hydroxide, and rarely 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 increased viscosity of the pore solution, which further retards the hydration process.
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