hydroxypropyl methylcellulose HPMC in Plastering MortarFebruary 2nd 2023
Cellulose ethers are currently the commonly used polymer admixtures of the cement mortar used in construction. Cellulose ethers can be fully dispersed in water to form a transparent viscous liquid. With a small amount (the mass percentage of less than 1%) added to the cement, it can improve the flow and condensation characteristics of cement mortar, so it is widely used in the field of building materials.
In addition to water retention and thickening effects, cellulose ethers also have effects on other properties of the cement mortar, such as retarding, air entraining, increasing bonding strength.
Cellulose ethers make the cement slow down during the setting and hardening process, thus extending the operating time. The retarding effect has little to do with the molecular weight of cellulose ethers, but a lot to do with the degree of substitution of alkyl. The smaller the degree of substitution of alkyl is, the larger the content of hydroxyl will be and the more obvious the retarding effect will be. This law is present in the three most commonly used cellulose ethers— HPMC and MHEC.
The role of increasing the bonding strength is reflected in the improvement of the bonding capability of the cement slurry with the addition of cellulose ethers on steel mesh, glass and other non-absorbent base materials. This is mainly attributable to the bonding effect provided by the viscosity of long chain polymer substances, cellulose ethers.
After adding cellulose ethers, the liquid is not only easy to introduce bubbles, but also the toughness of bubble film is higher than that of pure water bubbles and it can reduce the drainage effect. Therefore, this helps to make the introduced air bubbles not broken, and make air bubbles not likely to be discharged. The air entraining effect of cellulose ethers is negative for the mechanical strength, since harmful air bubbles may be introduced and the compressive strength may be reduced. But when cellulose ethers are used as foam stabilizers for the preparation of foamed concrete, the foam stability can be improved. If air bubbles need to be removed, the defoamer can be added.