redispersible latex powder RDP for tile adhesivesDecember 7th 2023
As for the particle size, the finer the particle, the better the water retention. After large particles of cellulose ether are touched with water, the surface will immediately dissolve to form a gel, which wraps the material to prevent the continuous entry of water molecules. Sometimes, it cannot be evenly dissolved after long-term mixing, forming a turbid flocculent solution or caking. It greatly affects the water retention effect of its cellulose ether, and solubility is one of the factors for selecting cellulose ether. Fineness is also a functional index of cellulose ether. HPMC for dry powder mortar needs to be powder with low water content, and the fineness also needs 20% – 60% of the particle size less than 63um. Fineness affects the solubility of hydroxypropyl methyl cellulose ether. The coarse HPMC is usually granular, which is easily dissolved in water without caking, but the dissolution rate is very slow, so it is not suitable to be used in dry powder mortar. In the dry powder mortar, HPMC is scattered between the cementation materials such as aggregate, fine filler and cement. As long as the fine powder is satisfied, the agglomeration of methyl cellulose ether can be prevented when mixing with water. When HPMC is dissolved with water, it is difficult to dissolve in laxity. HPMC with coarser fineness not only wastes, but also reduces part of the strength of the mortar. When such dry powder mortar is constructed in a large area, the curing speed of some dry powder mortar is significantly reduced, showing cracks formed due to different curing times. As for the selection of eruption mortar for mechanical construction, because the mixing time is short, the demand for fineness is higher.
Generally speaking, the higher the viscosity, the better the water retention effect. However, the higher the viscosity is, the higher the molecular weight of HPMC is, and its dissolution function will be reduced accordingly, which has a negative impact on the strength and construction function of mortar. The higher the viscosity is, the more significant the thickening effect on mortar is, but it is not proportional. The higher the viscosity, the more sticky the wet mortar will be, which is reflected in the high adhesion of the scraper and the substrate during construction. However, it is not helpful to increase the structural strength of wet mortar itself.
During construction, the anti sag function is not significant. On the contrary, some modified methyl cellulose ethers with medium and low viscosity have excellent performance in improving the structural strength of wet mortar.
The greater the increase of hydroxypropyl methyl cellulose ether in mortar, the better the water retention function. The higher the viscosity, the better the water retention function.
The fineness of HPMC affects its water retention. Generally speaking, for methyl cellulose ethers with the same viscosity but different fineness, the finer the fineness, the better the water retention effect under the same increase.
The water retention of HPMC is also related to the application temperature. The water retention of methyl cellulose ether decreases with the increase of temperature. However, in the actual application of data, dry powder mortar is often applied to hot substrates under high temperature (higher than 40 ℃), such as external wall putty plastering under the sun in summer, which usually accelerates the curing of cement and the hardening of dry powder mortar. The reduction of water retention rate has significantly affected the constructability and cracking resistance,
Under such conditions, it becomes particularly crucial to reduce the influence of temperature factors. Although methyl hydroxyethyl cellulose ether extender is currently considered to be at the forefront of technological development, its influence on temperature will still weaken the function of dry powder mortar. Although the amount of methyl hydroxyethyl cellulose (summer formula) has been improved, its workability and cracking resistance still cannot meet the needs of application. After some treatment of HPMC, such as improving the degree of etherification, it can make its water retention function adhere to a better role in the case of high temperature, so that it can better reflect the supply under adverse conditions.