How to improve the water retention of hydroxypropyl methylcellulose

Hydroxypropyl methylcellulose is the most commonly used additive in dry powder mortar. Cellulose ether plays an important role in dry powder mortar. After the cellulose ether in the mortar is dissolved, the surface activity ensures that the cementitious material is The system is effectively evenly distributed, and cellulose ether, as a protective colloid, “wraps” solid particles and forms a layer of lubricating film on its outer surface, making the mortar system more stable and improving the flow of the mortar during the mixing process properties and smoothness of construction.

Hydroxypropyl methylcellulose HPMC has excellent water retention, which can prevent the moisture in the wet mortar from evaporating prematurely or being absorbed by the base layer, ensuring that the cement is fully hydrated, thereby finally ensuring the mechanical properties of the mortar, which is especially beneficial to thin layers Mortar and absorbent base or mortar applied under high temperature and dry conditions. The water retention effect of hydroxypropyl methylcellulose ether can change the traditional construction process and improve the construction progress. For example, plastering construction can be carried out on water-absorbing substrates without pre-wetting.

The viscosity, dosage, ambient temperature and molecular structure of hydroxypropyl methylcellulose HPMC have a great influence on its water retention performance. Under the same conditions, the greater the viscosity of cellulose ether, the better the water retention; the higher the dosage, the better the water retention. Usually, a small amount of cellulose ether can greatly improve the water retention of mortar. When the dosage reaches a certain When the degree is high, the water retention rate increases slowly; when the ambient temperature rises, the water retention of cellulose ether usually decreases, but some modified cellulose ethers also have better water retention under high temperature conditions; cellulose with a lower degree of substitution Ether retains water better.

The hydroxyl group on the HPMC molecule and the oxygen atom on the ether bond will associate with the water molecule to form a hydrogen bond, turning the free water into bound water, thus playing a good role in water retention; water molecules and cellulose The interdiffusion between ether molecular chains enables water molecules to enter the interior of the large chains of cellulose ether and is subject to strong binding forces, thus forming free water and entangled water, which improves the water retention of mud; cellulose ether improves the water retention of freshly mixed The rheological properties, porous network structure and osmotic pressure of cement paste or the film-forming properties of cellulose ether hinder the diffusion of water. However, due to the unsatisfactory water retention performance of the current cellulose ether, the mortar has poor cohesiveness and poor construction performance, and the mortar is prone to cracking, hollowing and falling off after construction.