The Importance of Water Retention of HPMC
April 24th 2024
Water retention of hydroxypropyl methyl cellulose ether
The water retention of dry mortar refers to the ability of the mortar to retain and lock moisture. The higher the viscosity of hydroxypropyl methyl cellulose ether, the better the water retention. Since the cellulose structure contains hydroxyl and ether bonds, the oxygen atoms on the hydroxyl and ether bond groups associate with water molecules to form hydrogen bonds, so that free water becomes bound water, entangles the water, and plays a role in water retention.
Solubility of hydroxypropyl methyl cellulose ether
1 Coarse cellulose ether is easy to disperse in water without agglomeration, but the dissolution rate is very slow. The cellulose ether below 60 mesh dissolves in water for about 60 minutes.
2Fine-particle cellulose ether is easily dispersed in water without agglomeration, and the dissolution rate is moderate. The cellulose ether above 80 mesh dissolves in water for about 3 minutes.
3 Ultra-fine particles of cellulose ether disperse quickly in water, dissolve quickly, and form viscosity quickly. The cellulose ether above 120 mesh dissolves in water for about 10-30 seconds.
The finer the particles of hydroxypropyl methyl cellulose ether, the better the water retention. The surface of the coarse particles of cellulose ether dissolves immediately after contact with water and forms a gel phenomenon. The mortar wraps the material to prevent the water molecules from continuing to penetrate, and sometimes it is not evenly dispersed and dissolved after a long time of stirring, forming a turbid flocculent solution or agglomerate. The fine particles are dispersed and dissolved immediately after contacting with water to form a uniform viscosity.
PH value of hydroxypropyl methyl cellulose ether (retarding or early strength effect)
The pH value of hydroxypropyl methyl cellulose ether manufacturers at home and abroad is basically controlled at about 7, showing an acidic state. Because there are still a large number of anhydroglucose ring structures in the molecular structure of cellulose ethers, anhydroglucose rings are the main group that causes cement retardation. The anhydroglucose ring can make calcium ions in the cement hydration solution generate sugar calcium molecular compounds, reduce the concentration of calcium ions in the induction period of cement hydration, prevent the formation and precipitation of calcium hydroxide and calcium salt crystals, thereby delaying the hydration of cement process. If the PH value becomes alkaline, the mortar will appear early strength. Now most factories use sodium carbonate to adjust the pH value. Sodium carbonate is a kind of quick-setting agent. Sodium carbonate improves the surface performance of cement particles, promotes the increase of cohesion between particles, and further improves the viscosity of mortar. At the same time, the sodium carbonate quickly combines with the calcium ions in the mortar to promote the formation of ettringite, and the cement quickly sets. Therefore, the PH value should be adjusted according to different customers in the actual production process.
Air-entraining properties of hydroxypropyl methyl cellulose ether
The air-entraining effect of hydroxypropyl methyl cellulose ether is mainly because cellulose ether is also a kind of surfactant. The interfacial activity of cellulose ether mainly occurs at the gas-liquid-solid interface, firstly by introducing bubbles, and secondly by dispersion and Wetting effect. Cellulose ether contains alkyl groups, which significantly reduces the surface tension and interfacial energy of water, making it easy to produce many tiny closed bubbles in the aqueous solution during stirring.
Gel properties of hydroxypropyl methyl cellulose ether
After the hydroxypropyl methyl cellulose ether is dissolved in the mortar, the methoxy and hydroxypropyl groups on the molecular chain will interact with the calcium and aluminum ions in the slurry to form a viscous gel and fill it in the voids of the cement mortar. , Improve the compactness of the mortar, and play the role of flexible filling and reinforcement. However, when the composite matrix is compressed, the polymer cannot play a rigid supporting role, so the strength and crush ratio of the mortar decrease.
Film-forming properties of hydroxypropyl methyl cellulose ether
After the hydroxypropyl methyl cellulose ether is added for hydration, it forms a very thin latex film between the cement particles. This film has a sealing effect and improves the surface dryness of the mortar. Because the hydroxypropyl methyl cellulose ether has good water retention, enough water molecules are stored inside the mortar, thereby ensuring the hydration hardening of the cement and the complete development of the strength, improving the bonding strength of the mortar, and at the same time Improve the cohesiveness of the mortar, make the mortar have good plasticity and flexibility, and reduce the shrinkage and deformation of the mortar.
Tags:
