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 ensuring the mechanical properties of the mortar. HPMC is especially beneficial to thin-layer 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 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, the water retention rate increases, the trend of increase is slow.
As 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 ethers with lower degrees of substitution have better water retention properties.
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. The mutual diffusion between water molecules and cellulose ether molecular chains makes water molecules enter the interior of cellulose ether chains and receives a strong binding force, thus forming free water and entangled water, improving water retention.
Hydroxypropyl methylcellulose improves the rheological properties, porous network structure and osmotic pressure of fresh cement paste or the film-forming properties of cellulose ether hinders the diffusion of water.
Landcel’s hydroxypropyl methylcellulose (HPMC) has good water retention and improves the operability of construction.