Viscosity is an important property parameter of cellulose ether. Generally speaking, the higher the viscosity, the better the water-retaining effect of gypsum mortar. However, the higher the viscosity is, the higher the molecular weight of cellulose ether is, and the solubility of cellulose ether decreases accordingly. The higher the viscosity is, the more obvious the thickening effect is, but it is not proportional. The higher the viscosity, the more sticky the wet mortar will be, in the construction, the performance of sticking scraper and high adhesion to the substrate. But it is not helpful to increase the structural strength of wet mortar itself. In addition, during construction, the performance of the wet mortar anti-sagging performance is not obvious. In contrast, some modified Methyl cellulose with low to medium viscosity showed improvement in the structural strength of the wet mortar. Building wall materials are mostly porous structures, they have water absorption. And the gypsum building materials used for wall construction, after adding water modulation on the wall, the moisture is easy to be absorbed by the wall, causing the gypsum to lack the moisture necessary for hydration, causing difficulties in plastering construction and reducing the bond strength, thus there are cracks, hollow drum, spalling and other quality problems. Improving the water retention of gypsum building materials can solve the problem of construction quality and improve the bonding force with the wall. Therefore, water-retaining agent has become one of the important additives of gypsum building materials.
In order to facilitate the construction, the building powder materials such as plaster, adhesive plaster, jointing plaster and plaster putty are used, and the gypsum retarder is added in the production to prolong the construction time of plaster paste, because the hydration process of hemihydrate gypsum is restrained by adding retarder to gypsum, this kind of gypsum paste needs to remain on the wall for 1-2 hours before setting, and most of the walls have water absorption property, in particular, new lightweight wall materials such as brick walls, aerated concrete walls, perforated thermal insulation panels, so to carry out water-retaining treatment of gypsum slurry, to avoid the transfer of some of the water slurry to the wall, causes the gypsum paste hardens when the water shortage, the hydration is not complete, causes the gypsum and the wall surface joint place separation, the shell. Adding water-retaining agent is to keep the moisture contained in gypsum paste, to ensure the hydration reaction of gypsum paste at the interface, thus ensuring the bond strength. The common water-retaining agents are cellulose ethers, such as Methyl cellulose (MC) , hypromellose (HPMC) , hydroxyethyl methyl cellulose (HEMC) , etc. . In addition, polyvinyl alcohol, sodium alginate, modified starch, diatomite and rare earth powder can also be used to improve water retention.
Post time: Jul-26-2023