Water retention of HPMC

The water retention effect of HPMC depends on the water absorption of the base course, the composition of the mortar, the thickness of the mortar layer, the water demand of the mortar, and the setting time of the setting material. The water retention of HPMC itself comes from the solubility and dehydration of HPMC itself.

It is well known that although cellulose molecular chain contains a large number of OH groups with strong hydration, it is not soluble in water itself, because the cellulose structure is highly crystalline. The hydration ability of hydroxyl alone is not enough to pay for the strong intermolecular hydrogen bond and van der Waals force. Therefore, it only swells and does not dissolve in water. When a substituent is introduced into the molecular chain, not only the substituent destroys the hydrogen chain, but also the hydrogen bond between chains is destroyed due to the wedged substituent between adjacent chains. The larger the substituent, the greater the distance between molecules.

The greater the hydrogen bond breaking effect is, after the cellulose lattice is expanded, the solution enters, and HPMC becomes water-soluble, forming a high viscosity solution. When the temperature rises, the polymer hydration is weakened, and the water between chains is expelled. When the dehydration is sufficient, the molecules begin to gather and form a three-dimensional network structure gel. The factors affecting the water retention of mortar include the viscosity of HPMC, the amount of HPMC added, the particle fineness and the service temperature.