HPMC manufacturer-Problems with cellulose ethers used in cement-based materials
Cellulose ethers are increasingly used in cement-based materials, especially in dry mortar, due to their excellent water retention and thickening effects. Therefore, the properties and formation mechanism of cellulose ether-modified cement-based materials and the interaction between cellulose ether and cement slurry have gradually become the focus of attention in the field of building materials and engineering in recent years. Many research results have been achieved. Combined with the research progress at home and abroad, there are still the following problems in the research and application of cellulose ether-modified cement-based materials.
1. There are many types of cellulose ethers. Even cellulose ethers used in cement-based materials are classified into many types such as MC, HEC, HEMC and HPMC due to their degree of substitution. The same type of cellulose ethers have many differences in molecular structure, molecular weight, degree of substitution or content of substituents. At present, most researches at home and abroad focus on one or several cellulose ethers. The choice of cellulose ethers is limited to their respective fields of application. The molecular structure of cellulose ether is not indicated, and its representation is not representative. The conclusion is the inevitable result of “partial substitution”, and there are contradictions and disputes between the test results. Therefore, it is necessary to systematically study the classification and structural properties and mechanisms of different species of cellulose ether-modified cementitious materials.
2. The influence of cellulose ether on various properties of cementitious materials has been studied in the existing literature, and its formation mechanism has been analyzed to some extent, but the relationship between the molecular structure of cellulose ether and the performance of modified cement slurry has not been determined. In the cellulose ether-modified cement-based materials, there are few studies on materials with different molecular structures, and the formation mechanism of various properties of cellulose ether-modified cement-based materials cannot be fundamentally explained. . Although some literatures found that cellulose ethers with different molecular structures have different effects on the hydration of cement, the underlying reasons have not been further elucidated.
3. The effect mechanism of cellulose ether on cement hydration kinetics needs to be further studied. At present, regarding the delayed cement hydration mechanism of cellulose ethers, although Pourchez believes that adsorption is the real reason for the delayed hydration of cellulose ethers, it is found that the stronger the adsorption capacity between hydration products and cellulose ethers, the more delayed hydration of cement. However, the adsorption mechanism between cellulose ethers and cement hydration products, and the reasons for the different adsorption capacities of different cellulose ethers and hydration products have not been further studied.
4. The existing literature shows that cellulose ethers can significantly affect the pore structure of cement-based materials. The cellulose ethers are also believed to be surface active and have an air-entraining effect on the fresh grout, thereby increasing the porosity of the hardened grout. However, the effect of cellulose ether on the regularity and formation mechanism of the pore size distribution of cement slurry is rarely discussed.
5. Rheological properties are an important aspect of the application of cellulose ethers in cement-based materials. Unfortunately, there are few studies on the rheological properties of cellulose ether-modified cement slurries at home and abroad.