Cement-based ceramic tile adhesive is currently the largest application of special dry mixing mortar, which is a kind of cement as the main cementing material and supplemented by gradation of aggregate, water retention agent, early strength agent, latex powder and other organic or inorganic admixtures. Usually used only with water mixing, compared with ordinary cement mortar, can greatly improve the bonding strength between the finishing material and the base material, has good anti-slip and has excellent water resistance, heat resistance and freezing-thawing cycle advantages, mainly used for pasting building interior and exterior wall tiles, floor tiles and other decorative materials, It is widely used in the decoration of walls, floors, bathrooms, kitchens and other buildings. It is the most widely used ceramic tile bonding material.
Usually when we judge the performance of a ceramic tile adhesive, in addition to paying attention to its operating performance, anti-sliding ability, but also pay attention to its mechanical strength and open time. Cellulose ether on ceramic tile adhesive in addition to affect the rheological properties of porcelain glue, such as smooth operation performance, stick knife situation, but also on the mechanical properties of ceramic tile adhesive has a strong influence
1. Open time
When rubber powder and cellulose ether co-exist in wet mortar, some data models show that rubber powder has stronger kinetic energy to adhere to cement hydration products, and cellulose ether exists more in the gap fluid, which affects the viscosity and setting time of mortar more. The surface tension of cellulose ether is larger than that of rubber powder, and the enrichment of more cellulose ether at mortar interface is beneficial to the formation of hydrogen bonds between the base plane and cellulose ether.
Moisture evaporation from in the wet mortar, mortar, cellulose ether in the surface enrichment, 5 minutes can form a membrane on the surface of the mortar, will reduce the evaporation rate of follow-up, with more water from the slurry thick part of the move to the mortar layer is thinner, open points partly dissolved when the initial formation of the membrane, the migration of water can bring more enrichment of cellulose ether in the mortar on the surface.
The film formation of cellulose ether on the surface of mortar has a great influence on the properties of mortar:
First, the film formed is too thin, will be dissolved twice, unable to limit the evaporation of water, reduce the strength.
Two, the formation of the film is too thick, cellulose ether in the mortar gap liquid concentration is high, viscosity, when the ceramic tile paste is not easy to break the surface of the film.
It can be seen that the film forming performance of cellulose ether has a great influence on the opening time. The type of cellulose ether (HPMC, HEMC, MC, etc.) and degree of etherification (degree of substitution) directly affect the film forming performance of cellulose ether, to the hardness and toughness of the film.
2, drawing strength
Cellulose ether not only endows mortar with all the above beneficial properties, but also delays the hydration kinetics of cement. This retarded effect is mainly due to the adsorption of cellulose ether molecules on various mineral phases in the cement system being hydrated, but it is generally agreed that cellulose ether molecules are mainly adsorbed on hydration products such as C-S-H and calcium hydroxide, and rarely adsorbed on the original mineral phase of clinker. In addition, cellulose ether reduces ions (Ca2+, SO42-,…) due to increased viscosity of pore solution. Activity in pore solution, which further retards the hydration process.
Viscosity is another important parameter, which represents the chemical properties of cellulose ether. As mentioned above, viscosity mainly affects water retention capacity, and also has a significant impact on the workability of fresh mortar. However, the experimental study found that the viscosity of cellulose ether had almost no effect on the hydration kinetics of cement. Molecular weight has little influence on hydration, and the largest difference between different molecular weights is only 10min. Therefore, molecular weight is not the key parameter to control cement hydration.
“Cellulose ether in cement based dry mix mortar products in the application” clearly pointed out that cellulose ether delay depends on its chemical structure. The general trend is that for MHEC, the higher the degree of methylation, the smaller the retarding effect of cellulose ether. In addition, hydrophilic substitution (such as substitution of HEC) has a stronger retarding effect than hydrophobic substitution (such as substitution of MH, MHEC and MHPC). The retarding effect of cellulose ether is mainly affected by the two parameters of the type and number of substituted groups.
Our systematic experiment also found that the content of substituents plays an important role in the mechanical strength of ceramic tile adhesive. We evaluated the performance of HPMC with different degrees of substitution in ceramic tile adhesive, and tested the influence of cellulose ether containing different groups under different curing conditions on the mechanical properties of ceramic tile adhesive. Influence of the content of DS and MS on the drawing strength of ceramic tile adhesive at room temperature.
HPMC is a composite ether, so to put the two figures together, for HPMC, there needs to be a degree of supply, in order to ensure its water solubility and transmittance, we know that the content of substituents also determines the gel temperature of HPMC, which is to determine the use of HPMC environment, In this way, the group content of HPMC is framed in a range. In this range, how to combine methoxy and hydroxypropoxy to achieve the best effect is the content of our study. In a certain range, the increase of methoxy content will lead to a downward trend of drawing strength, while the increase of hydroxypropoxy content will lead to an upward trend of drawing strength. There is a similar effect on open time.