Views: 1 Author: Site Editor Publish Time: 2020-05-28 Origin: Site
Thickening and thixotropy of cellulose ethers : The role of cellulose ether-thickening depends on: the degree of polymerization of cellulose ether, solution concentration, shear rate, temperature and other conditions. The gelation characteristics of the solution are unique to alkyl cellulose and its modified derivatives. Gelation characteristics are related to the degree of substitution, solution concentration and additives. For hydroxyalkyl modified derivatives, the gel properties are also related to the degree of hydroxyalkyl modification. For MC and HPMC with low viscosity, 10% -15% concentration solution can be prepared, medium viscosity MC and HPMC can be prepared 5% -10% solution, while high viscosity MC and HPMC can only be prepared 2% -3% solution, and Generally, the viscosity classification of cellulose ether is also classified as a 1% -2% solution. High molecular weight cellulose ethers have high thickening efficiency. In the same concentration solution, different molecular weight polymers have different viscosities. The viscosity and molecular weight can be expressed as follows, [η] = 2.92 × 10-2 (DPn) 0.905, DPn is average polymerization Degree is high. The addition of low molecular weight cellulose ether can only achieve the target viscosity. Its viscosity has little dependence on the shear rate, high viscosity to reach the target viscosity, the required amount of addition is small, the size of the viscosity depends on the thickening efficiency. Therefore, to achieve a certain consistency, a certain amount of cellulose ether (concentration of the solution) and solution viscosity must be ensured. The gel temperature of the solution also decreases linearly as the concentration of the solution increases, and it gels at room temperature after reaching a certain concentration. The gelation concentration of HPMC at room temperature is higher.
The consistency can also be adjusted by selecting the particle size and selecting the cellulose ether with different degrees of modification. The so-called modification is to introduce a certain degree of substitution of hydroxyalkyl group to the skeleton structure of MC. By changing the relative substitution values of the two substituents, that is, the DS and ms relative substitution values of methoxy and hydroxyalkyl that we often say. By changing the relative substitution values of the two substituents, various performance requirements of cellulose ether are obtained.
Consistency and modification relationship:The addition of cellulose ether affects the water consumption of mortar. Changing the water-cement ratio of water to cement is the thickening effect. The higher the dosage, the greater the water consumption.