Other Functions of Cellulose Ether in Cement-Based Materials
Other Functions of Cellulose Ether in Cement-Based Materials
In addition to its water retention and thickening effects, cellulose ether also influences other properties of cement mortar, such as retardation, air entrainment, and increased bonding strength. Cellulose ether slows down the setting and hardening process of cement, thereby extending the working time. For this reason, it is sometimes used as a setting regulator. The retardation effect is not significantly related to the molecular weight of cellulose ether but is closely linked to the degree of alkyl substitution. A lower degree of alkyl substitution corresponds to a higher hydroxyl content, resulting in a more pronounced retardation effect. This pattern is observed in the three most commonly used cellulose ethers—HEC, MHEC, and MHPC.
The enhancement of bonding strength is reflected in the improved adhesion of cement paste containing cellulose ether to non-absorbent substrates such as steel mesh and glass. This is primarily attributed to the adhesive properties provided by the long polymer chains of cellulose ether.
The introduction of alkyl groups lowers the surface energy of cellulose ether-containing aqueous solutions, giving cellulose ether an air-entraining effect in cement mortar. With the addition of cellulose ether, liquid more readily entrains air bubbles, and the bubble membranes exhibit greater toughness compared to pure water bubbles, reducing drainage effects. As a result, the entrained bubbles remain stable and are less likely to be expelled. The air-entraining effect of cellulose ether negatively impacts mechanical strength, as it may introduce harmful bubbles that reduce compressive strength. However, when used as a foam stabilizer in the production of foamed concrete, it enhances foam stability. If bubble elimination is required, defoamers can be added.
