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How to improve the water retention of hydroxypropyl methylcellulose?

December 7, 2021by admin0

Hydroxypropyl methyl cellulose HPMC is one of the most commonly used additives in dry mortar. Cellulose ether plays an important role in dry mortar. After the cellulose ether in the mortar is dissolved in water, it guarantees gelation due to surface activity. The material is effectively and evenly distributed in the system. As a protective colloid, the cellulose ether “wraps” the solid particles and forms a lubricating film on the outer surface of the mortar to make the mortar system more stable and improve the mixing process of the mortar. The fluidity 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 full hydration of the cement, and ultimately ensuring the mechanical properties of the mortar, which is especially beneficial for thin layers Mortar and water-absorbent base layer or mortar constructed under high temperature and dry conditions. The water retention effect of hydroxypropyl methyl cellulose ether can change the traditional construction process and improve the construction progress. For example, plastering can be carried out without pre-wetting on a water-absorbing substrate.
The viscosity, dosage, environmental temperature and molecular structure of hydroxypropyl methylcellulose HPMC have a great influence on its water retention performance. Under the same conditions, the higher the viscosity of the cellulose ether, the better the water retention; the higher the content, the better the water retention. Usually, a small amount of cellulose ether can greatly increase the water retention rate of the mortar, and when the content reaches a certain level When the temperature is higher, the water retention rate increases slowly; when the ambient temperature rises, the water retention of cellulose ethers usually decreases, but some modified cellulose ethers also have better water retention under high temperature conditions; cellulose with lower substitution degree Ether has better water retention properties.
The hydroxyl groups on the HPMC molecule and the oxygen atoms on the ether bond will associate with water molecules to form hydrogen bonds, turning free water into bound water, thus playing a good role in water retention; water molecules and cellulose The mutual diffusion between ether molecular chains allows water molecules to enter the large cellulose ether chain and are subject to a strong binding force, thereby forming free water and entangled water, which improves the water retention of the mud; cellulose ether improves the fresh mix 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, the current cellulose ethers have poor water retention properties, resulting in poor mortar adhesion and poor construction performance. After construction, the mortar is prone to cracking, hollowing and falling off.

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