Effect of cellulose ethers on tile adhesives
Cement-based tile adhesive is the largest current application of special dry-mix mortar, which is a mixture of cement as the main cementitious material. Cement-based tile adhesive is supplemented by a mixture of graded aggregates, water retention agents, early strength agents, emulsion powder and other organic or inorganic admixtures.
When used, cement-based tile adhesive is simply mixed with water and, compared to ordinary cement mortars. Cement-based tile adhesive can substantially increase the bond strength between the finishing material and the substrate. Cement-based tile adhesive has good anti-slip properties and has excellent resistance to water, heat and freeze-thaw cycles. It is mainly used for pasting wall tiles, floor tiles and other decorative materials inside and outside the building. So it is widely used in the decoration of internal and external walls, floors, bathrooms, kitchens and other buildings. Cement-based tile adhesive is currently the most widely used tile bonding material.
Usually when we judge how well a tile adhesive performs, in addition to its operational performance and resistance to slippage. We also pay attention to its mechanical strength and open time. Cellulose ether in tile adhesive in addition to influence the rheological properties of tile adhesive, such as operating slip performance, sticky knife situation, etc. It also has a strong influence on the mechanical properties of tile adhesive.
1.Opening time
When gum powder and cellulose ether are present together in wet mortar, some data models show that gum powder has stronger kinetic energy to adhere to cement hydration products. Cellulose ether is more present in the interstitial fluid, affecting the viscosity and setting time of the mortar more. The surface tension of cellulose ethers is greater than that of gum powder. And the greater enrichment of cellulose ethers at the mortar interface will facilitate the formation of hydrogen bonds between the substrate and the cellulose ethers.
In wet mortars, the water in the mortar evaporates and the cellulose ether is enriched on the surface. Within 5 minutes a film is formed on the mortar surface, which reduces 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 initially is partially dissolved and the migration of water leads to more enrichment of the cellulose ether on the mortar surface.
The film formation of cellulose ether on the mortar surface has a great influence on the mortar properties.
One, the film formed is too thin. It will be secondarily dissolved and cannot limit the evaporation of water, reducing the strength.
Second, the film formed is too thick. The concentration of cellulose ether in the mortar interstitial liquid is high. The viscosity is large, when the tile paste is not easy to break the surface of the film.
It can be seen that the film-forming properties of cellulose ether have 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.
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