In dry mortar, cellulose ether is a main additive that can significantly improve the performance of wet mortar and affect the construction performance of mortar. Methyl cellulose ether plays the role of water retention, thickening, and improvement of construction performance. Good water retention performance ensures that the mortar will not cause sanding, powdering and strength reduction due to water shortage and incomplete cement hydration; thickening effect The structural strength of the wet mortar is greatly increased, and the addition of methyl cellulose ether can significantly improve the wet viscosity of the wet mortar, and has good adhesion to various substrates, thereby improving the performance of the wet mortar on the wall and reducing waste; in addition, different The role of cellulose in products is also different, for example: cellulose in tile adhesives can increase the opening time and adjust the time; cellulose in mechanical spraying mortar can improve the structural strength of wet mortar; in self-leveling, cellulose plays a role in preventing settlement, Segregation and stratification.
The production of cellulose ether is mainly made of natural fibers through alkali dissolution, grafting reaction (etherification), washing, drying, grinding and other processes. The main raw materials of natural fibers can be divided into: cotton fiber, cedar fiber, beech fiber, etc. Their degree of polymerization is different, which will affect the final viscosity of their products. At present, major cellulose manufacturers use cotton fiber (a by-product of nitrocellulose) as the main raw material. Cellulose ethers can be divided into ionic and non-ionic. The ionic type mainly includes carboxymethyl cellulose salt, and the non-ionic type mainly includes methyl cellulose, methyl hydroxyethyl (propyl) cellulose, and hydroxyethyl cellulose. Su and so on. In dry powder mortar, because ionic cellulose (carboxymethyl cellulose salt) is unstable in the presence of calcium ions, it is rarely used in dry powder products such as cement slaked lime as cementitious materials.
The water retention of cellulose is also related to the temperature used. The water retention of methyl cellulose ether decreases with the increase of temperature. For example, in summer, when there is sunlight, the external wall putty is plastered, which often accelerates the curing of cement and mortar. The hardening and the decrease of water retention rate lead to the obvious feeling that both the construction performance and the anti-cracking performance are affected. In this case, it is particularly critical to reduce the influence of temperature factors. Sometimes it cannot meet the needs of use. Some treatments are done on the cellulose, such as increasing the degree of etherification, etc., so that the water retention effect can still maintain a better effect at a higher temperature.
Water retention of cellulose: The main factors affecting the water retention of mortar include the amount of cellulose added, the viscosity of cellulose, the fineness of cellulose, and the temperature of the operating environment.
Viscosity of cellulose: Generally speaking, the higher the viscosity, the better the water retention effect, but the higher the viscosity, the higher the molecular weight of cellulose, and the corresponding decrease in its solubility, which has a negative impact on the construction performance and strength of mortar . The higher the viscosity, the more obvious the thickening effect on the mortar, but it is not directly proportional. The higher the viscosity, the more viscous the wet mortar will be. During construction, it will stick to the scraper and have high adhesion to the substrate, but it will not help much to increase the structural strength of the wet mortar itself, and the anti-sag performance will not be obvious during construction.
The fineness of cellulose: The fineness affects the solubility of cellulose ether. Coarse cellulose is usually granular and easily dispersed in water without agglomeration, but the dissolution rate is very slow. It is not suitable for use in dry powder mortar. Domestically produced Some of the cellulose is flocculent, it is not easy to disperse and dissolve in water, and it is easy to agglomerate. Only a fine enough powder can avoid methyl cellulose ether agglomeration when adding water and stirring. But the thicker cellulose ether is not only wasteful but also reduces the local strength of the mortar. When such a dry powder mortar is constructed in a large area, the curing speed of the local mortar is obviously reduced, and cracks due to different curing times appear. Due to the short mixing time, the mortar with mechanical construction requires higher fineness.
Post time: Feb-13-2023