Hydroxypropyl Methyl Cellulose HPMC Powder for Cement Based Tile BondFebruary 23rd 2024
Usually when we judge the performance of a tile adhesive, in addition to its operating performance and anti-sliding ability, we also pay attention to its mechanical strength and open time. In tile adhesive, hydroxypropyl methyl cellulose(HPMC) not only affects the rheological properties of the porcelain adhesive, such as operating slip properties, sticking conditions, etc., but also has a strong influence on the mechanical properties of the tile adhesive.
1. Opening Time
When rdp powder and hydroxypropyl methyl cellulose(HPMC) coexist in the wet mortar, some data models show that the rdp powder has stronger kinetic energy to adhere to the cement hydration products, and the hydroxypropyl methyl cellulose exists in the interstitial fluid. , More influence the viscosity and setting time of the mortar. The surface tension of hydroxypropyl methyl cellulose is larger than that of vae powder, and more hydroxypropyl methyl cellulose is enriched at the mortar interface, which will be beneficial to the formation of hydrogen bonds between the base surface and hydroxypropyl methyl cellulose.
In the wet mortar, the water in the mortar evaporates, and the hydroxypropyl methyl cellulose 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 the water becomes thicker from the mortar The part migrates to the thinner part of the mortar layer, and the film splits formed at the beginning are partially dissolved. The migration of water will bring more hydroxypropyl methyl cellulose to be enriched on the surface of the mortar.
The film formation of hydroxypropyl methyl cellulose on the surface of the mortar has a great influence on the performance of the mortar:
1. The formed film is too thin and will be dissolved again, which cannot limit the evaporation of water and reduce the strength.
2. The formed film is too thick, the concentration of hydroxypropyl methylcellulose in the interstitial liquid of the mortar is high, and the viscosity is large, and it is not easy to break the surface film when the tiles are pasted.
It can be seen that the film-forming properties of hydroxypropyl methyl cellulose have a greater impact on the open time. The type of hydroxypropyl methyl cellulose (HPMC, HEMC, MC, etc.) and the degree of etherification (degree of substitution) directly affect the film-forming properties of hydroxypropyl methyl cellulose, and the hardness and toughness of the film.
2. Drawing strength
In addition to imparting the above-mentioned beneficial properties to the mortar, hydroxypropyl methyl cellulose(HPMC) can also delay the hydration kinetics process of cement. This retardation effect is mainly due to the adsorption of hydroxypropyl methyl cellulose molecules on various mineral phases in the cement system being hydrated, but generally speaking, the consensus is that the hydroxypropyl methyl cellulose molecules mainly adsorb The hydration products such as CSH and calcium hydroxide are rarely adsorbed on the original mineral phase of the clinker. In addition, due to the increase in the viscosity of the pore solution, hydroxypropyl methyl cellulose reduces the mobility of ions (Ca2+, SO42-, …) in the pore solution, thereby further delaying the hydration process.
Viscosity is another important parameter, which shows the chemical properties of hydroxypropyl methyl cellulose. As mentioned above, viscosity mainly affects water retention capacity and also affects the workability of fresh mortar. However, experimental studies have found that the viscosity of hydroxypropyl methyl cellulose has no effect on the kinetics of cement hydration. Molecular weight has little effect on hydration, and the biggest difference between different molecular weights is only 10 minutes. Therefore, molecular weight is not a key parameter to control cement hydration.
“The application of hydroxypropyl methyl cellulose in cement-based dry-mix mortar products” clearly pointed out that the retardation of hydroxypropyl methyl cellulose depends on its chemical structure. And the general trend summarized is that for MHEC, the higher the degree of methylation, the smaller the retarding effect of hydroxypropyl methyl cellulose. In addition, hydrophilic substitution (such as the substitution of HEC) has a stronger retarding effect than hydrophobic substitution (such as the substitution of MH, MHEC, and MHPC). The retardation effect of hydroxypropyl methyl cellulose is mainly affected by the two parameters of the type and number of substituent groups.