HPMC manufacturer-Hydroxypropyl methylcellulose delays cement hydration
Adding hydroxypropyl methylcellulose to cement can slow down the hydration of cement. So what do you know about how it works? Let’s look at hydroxypropyl methylcellulose to retard cement hydration. principle.
1. The ionic dyskinesia hypothesis
We speculate that hydroxypropyl methylcellulose would increase the viscosity of the pore solution, hinder the speed of ionic movement, and delay the hydration of cement. However, the lower viscosity cellulose ethers in this test have a greater ability to retard cement hydration. Therefore, this assumption is invalid. Pourchez et al. also doubt this hypothesis. In fact, the time for ion migration or migration is very short, apparently not much different from the delay in cement hydration.
2. Alkaline degradation
Polysaccharides readily degrade under alkaline conditions to yield hydroxycarboxylic acids that delay cement hydration. Therefore, the reason for the delayed hydration of hydroxypropyl methylcellulose may be due to its degradation in alkaline cement slurries to form hydroxycarboxylic acids. However, Pourchez et al. found that cellulose ethers were very stable under alkaline conditions with only minor degradation, and the degradation products had little effect on the retardation of cement hydration.
Adsorption can be the real reason why hydroxypropyl methylcellulose hinders cement hydration. Many organic additives will adsorb on cement particles and hydration products, preventing the dissolution of cement particles and the crystallization of hydration products, thereby delaying the hydration of cement. and condensation. Pourchez et al. found that cellulose ethers were readily adsorbed on the surfaces of hydrated products such as calcium hydroxide, C.S.H gels, and calcium aluminate hydrates, but were not readily adsorbed by ettringite and unhydrated phases. Moreover, in the case of cellulose ethers, the adsorption capacity of HEC is stronger than that of swollen MC. The lower the content of hydroxyethyl in HEC or hydroxypropyl in HPMC, the stronger the adsorption capacity: in terms of the hydrated product, the adsorption capacity of calcium hydroxide is stronger than that of CSH. Further analysis also showed that the adsorption capacity of hydration products and cellulose ether was related to the delay of cement hydration: the stronger the adsorption, the more obvious the delay, but the adsorption of ettringite to cellulose ether was weak, but its formation, however, this significantly delayed. MUllert’s research also shows that cellulose ether has a strong adsorption effect on tricalcium silicate and its hydration products, which obviously delays the hydration process of the silicate phase. The adsorption capacity of ettringite is very low, but calcium The formation of alumite is significantly delayed because delayed ettringite formation is influenced by the Ca balance in solution, which is an extension of the cellulose ether. Late silicate hydration continues.
These are the principles by which hydroxypropyl methylcellulose retards cement hydration. We hope that the above knowledge will allow everyone to understand the mechanism of action of the product and make better use of it.