- June 25, 2021
- Posted by: admin
- Category: News
The effection of HPMC in dry mixed mortar
In the production of building materials, especially dry mixed mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), is an indispensable and important part.
Water-soluble cellulose ether plays an important role in mortar in three aspects: first, its excellent water retention ability; second, its influence on mortar consistency and thixotropy; third, its interaction with cement.
The water-retaining effect of cellulose ether depends on the water absorption of the base, the composition of mortar, the thickness of mortar layer, the water demand of mortar, and the setting time of the setting material. The water retention of cellulose ether itself comes from the solubility and dehydration of cellulose ether itself. It is well known that although cellulose molecular chain contains a large number of highly hydrating OH groups, it is not soluble in water itself because of the high crystallinity of the cellulose structure. Hydroxyl hydration alone is not sufficient to pay for strong inter-molecular hydrogen bonds and van der Waals forces. Therefore, water can only swell and do not dissolve. When substituents are introduced into the molecular chain, not only the substituents destroy the hydrogen chain, but also the inter-chain hydrogen bond is broken due to the wedge of substituents between adjacent chains. The larger the substituents are, the greater the distance between molecules will be. The larger the effect of hydrogen bond destruction, the cellulose lattice expanded, the solution into cellulose ether becomes water soluble, the formation of high viscosity solution. As the temperature rises, the hydration of the polymer diminishes and the water between the chains is expelled. When dehydrating is sufficient, the molecules begin to assemble, forming a three-dimensional network of gels that fold out. The factors that affect the water retention of mortar include cellulose ether viscosity, additive amount, particle fineness and service temperature.