- Effect of Viscosity on Water Retention
Viscosity is an important parameter of cellulose ether performance. At present, different cellulose ether manufacturers use different methods and instruments to measure the viscosity of cellulose ether. The main methods are Haake Rotovisko, Hoppler, Ubbelohde, DNJ and Brookfield. For the same product, the viscosity results measured by different methods vary greatly, therefore, when comparing viscosity, it must be carried out between the same test methods, including temperature, rotation speed, etc. The water retention of cellulose ether increases with the increase of viscosity. Generally speaking, the higher the viscosity, the better the water retention effect. However, the higher the viscosity, the higher the molecular weight of cellulose ether, and its solubility will be reduced accordingly, which has a negative impact on the strength and construction performance of mortar. The higher the viscosity, the more obvious the thickening effect on mortar, but it is not a proportional relationship. The higher the viscosity, the stickier the wet mortar will be, that is, during construction, it will show high adhesion to the spatula and the substrate.
- Effect of Fineness on Water Retention
Fineness is also an important performance indicator of cellulose ether. Cellulose ether used in ordinary dry-mix mortar is required to be powder with low water content and fineness, with 20%~60% of the particle size less than 63μm. Fineness affects the solubility of cellulose ether. Coarser cellulose ether is usually granular and can be easily dispersed and dissolved in water without agglomeration, but the dissolution rate is very slow and it is not suitable for use in ordinary dry-mix mortar. In ordinary dry-mix mortar, cellulose ether is dispersed between aggregates, fine fillers and cement and other binder materials. Only sufficiently fine powder can avoid agglomeration of cellulose ether when adding water and stirring. When cellulose ether is dissolved and agglomerated by adding water, it is difficult to disperse and dissolve it again. Coarser cellulose ether is not only wasteful, but also reduces the local strength of the mortar. When such dry-mix mortar is constructed over a large area, the curing speed of the local dry-mix mortar is significantly reduced, and cracks caused by different curing times appear. For spray mortar constructed by machinery, due to the short stirring time, the fineness requirement is higher. The fineness of cellulose ether has a certain influence on its water retention. Generally speaking, for methyl cellulose ethers with the same viscosity but different fineness, the finer one has better water retention than the coarse one under the same addition amount.
- Effect of addition amount on water retention
The water retention of cellulose ether increases with the increase of addition amount.
- Effect of temperature on water retention
The water retention of cellulose ether is also related to the temperature of mortar. The water retention of cellulose ether decreases with the increase of temperature. In actual production and application, ordinary dry mortar often has a high mortar temperature (above 70°C) due to continuous production, which reduces the water retention rate of mortar. The decrease in water retention affects both construction performance and crack resistance. In this case, it is particularly important to reduce the influence of temperature factors. As the temperature increases, the water retention rate of cellulose decreases to varying degrees.