Cellulose Ether-Cellulose ether products for high performance tile adhesives
Cement-based tile adhesive is an excessive use of special dry-mixed mortar today. It is also a kind of organic or inorganic admixture with cement as an important cementing material and supplemented with graded aggregates, water-retaining agents, early strength agents, latex powders, etc. mixture. In general application, it only needs to be mixed with water. Compared with ordinary cement mortar, it can greatly improve the bonding strength between the facing material and the substrate. It has good slip resistance and good water resistance, heat resistance and other properties. Freeze-thaw cycle resistance and other advantages, suitable for adhering interior and exterior wall tiles, floor tiles and other decorative materials, widely applicable to interior and exterior walls, floors, shower rooms, restaurant kitchens and other building decoration venues, is currently widely used Tile bonding material.
Generally, when judging the characteristics of tile adhesive, in addition to its actual operating characteristics and anti-slip ability, it also cares about its mechanical strength and opening time. In addition to affecting the rheological properties of the tile adhesive, cellulose ether has a strong influence on the mechanical properties of the tile adhesive, such as the actual operation smoothness, sticking condition, etc.
1. Influence on the opening time of tile adhesive
When rubber powder and cellulose ether coexist in wet mortar, some data models show that rubber powder has a stronger kinetic energy to adhere to cement hydration products, and cellulose ether exists in a large amount in the interstitial liquid, and a large amount of It affects the viscosity and setting time of the mortar. The surface tension of cellulose ether is larger than that of rubber powder, and the accumulation of a large amount of cellulose ether on the mortar interface will facilitate the formation of hydrogen bonds between the basal plane and the cellulose ether.
In the wet mortar, the water in the mortar volatilizes, and the cellulose ether is enriched on the surface layer, which will form a film on the surface layer of the mortar in 5 minutes, which will reduce the subsequent volatilization rate, and then a large amount of water will flow from the thicker part of the mortar to the mortar. The thin layer migrates, and the initially formed film is partially dissolved, and the migration of water will bring a large amount of cellulose ether to the surface of the mortar.
The film formation of cellulose ether on the surface of the mortar has a great influence on the properties of the mortar. 1) The film formed is too thin and will be dissolved again, which cannot limit the volatilization 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, and it is not easy to break the surface film when the tiles are pasted. From this, it can be seen that the film-forming properties of the cellulose ether have an excessive influence on the opening time. 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, as well as the hardness and toughness of the film.
2. Influence on the pull-out strength
In addition to imparting various beneficial properties to the mortar, cellulose ethers also slow down the hydration kinetics of the cement. This type of retardation effect 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 C-S-H and calcium hydroxide. On the isohydration product, it is not much adsorbed on the original mineral phase of the clinker. In addition, cellulose ethers reduce the mobility of ions (Ca2+, SO42-, …) in the pore solution in view of the increase in the viscosity of the pore solution, which further slows down the hydration process.
Viscosity is another important main parameter, which shows the chemical properties of cellulose ethers. As mentioned above, the viscosity has an important influence on the water retention capacity, and also has a significant influence on the workability of the fresh mortar. However, experimental research found that the viscosity of cellulose ether has basically no effect on the hydration kinetics of cement. The influence of molecular weight on hydration is small, and the excessive difference between different molecular weights is only 10mln. Therefore, molecular weight is not an important main parameter for controlling cement hydration.