Re-Dispersible Polymer Powder Rdp for Construction Chemicals Tile AdhesiveDecember 5th 2023
In the use of hydroxypropyl methyl cellulose HPMC, we usually find that it is basically divided into two types: immediate and slow dissolution. Let us understand the difference between quick dissolution and slow dissolution of hydroxypropyl methyl cellulose.
Instant HPMC refers to the use of cross-linking agent for surface treatment in the production process, so that HPMC can be quickly dispersed in cold water, but not a real solution, through uniform stirring, viscosity slowly rise, that is, dissolution;
Slow soluble HPMC can also be called hot melt products. When cold water is encountered, it can be quickly dispersed in hot water. By stirring evenly, the temperature of the solution will drop to a certain temperature. (The temperature of our gel is about 60°C), the viscosity will appear slowly until a transparent and sticky gel is formed.
Here is the distinction between immediate solution and slow solution. If you have any questions about this knowledge, you can also consult us.
Adding hydroxypropyl methyl cellulose to cement slows down its hydration. So what do you know about how it works? Let’s look at hydroxypropyl methyl cellulose to delay cement hydration. Principle.
1. Ion movement disorder hypothesis
We hypothesized that hydroxypropyl methyl cellulose would increase the viscosity of pore solutions, hinder the rate of ionic movement, and delay the hydration of cement. However, the lower viscosity cellulose ethers in this test had a stronger ability to delay cement hydration. Therefore, this assumption is invalid. Pourchez et al. also doubt this hypothesis. In fact, the time of ion migration or migration is very short, apparently not dissimilar to the delay of cement hydration.
2. Alkaline degradation
Polysaccharides readily degrade under alkaline conditions to produce hydroxyl carboxylic acids that delay cement hydration. Therefore, the delayed hydration of hydroxypropyl methyl cellulose may be due to its degradation in alkaline cement slurries to form hydroxycarboxylic acids. cellulose ethers were very stable under alkaline conditions, degraded only slightly, and the degradation products had little effect on the delay of cement hydration.
3, the adsorption
Adsorption can be hydroxypropyl methyl cellulose block cement hydration the real reason is that many organic additives will be adsorbed on cement particles and hydration products, prevent the dissolution of cement particles and the crystallization of hydration products, so as to delay the hydration and condensation of cement. cellulose ethers readily adsorbed on the surfaces of hydration products such as calcium hydroxide, C.S.H gel and calcium aluminate hydrate, but not readily adsorbed by ettringite and unhydrated phases. Moreover, in the case of cellulose ether, the adsorption capacity of HEC is stronger than that of swelling MC. The lower the content of hydroxyethyl in HEC or hydroxypropyl in HPMC, the stronger the adsorption capacity: as for hydration products, the adsorption capacity of calcium hydroxide is stronger than that of CSH. Further analysis also shows that the adsorption capacity of hydration products and cellulose ether is related to the delay of cement hydration: the stronger the adsorption, the more obvious the delay, but ettringite adsorption of cellulose ether is weak, but its formation, but this is significantly delayed. cellulose ether of tricalcium silicate and its hydration products has a strong adsorption, it obviously delay the hydration process of silicate phase, the adsorption amount of ettringite is very low, but delayed ettringite formation is obvious, because of delayed ettringite formation is affected by Ca 2 + balance in the solution, it is an extension of the cellulose ether. Late silicate hydration continued.
These are hydroxypropyl methyl cellulose delay cement hydration principle. We hope that this knowledge will enable everyone to understand how the product works and use it better.