What are the factors that affect the water retention of HPMC ?

Viscosity is an important parameter of HPMC performance. At present, different HPMC manufacturers use different methods and instruments to determine the viscosity of HPMC. The main methods are HaakeRotovisko, Hoppler, Ubbelohde, and Brookfield.

For the same product, the viscosity results measured by different methods are very different, and some are even doubled. Therefore, when comparing the viscosity, it must be carried out between the same test methods, including temperature, rotor, etc.

Generally speaking, the higher the viscosity, the better the water retention effect. However, the higher the viscosity, the higher the molecular weight of MC, and its solubility will be reduced accordingly, which has a negative impact on the strength and construction performance of the 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, which is manifested by the sticking of the scraper and the high adhesion to the substrate during construction. But it does not help much to increase the structural strength of the wet mortar itself. The performance of anti-sagging performance is not obvious during construction. On the contrary, some medium and low viscosity but modified methyl cellulose ethers have excellent performance in improving the structural strength of wet mortar.

The fineness of HPMC also has a certain effect on its water retention. Generally speaking, for methyl cellulose ethers with the same viscosity but different fineness, in the case of the same addition amount, the finer the better the water retention effect.

The water retention of HPMC is also related to the temperature of use, and the water retention of methyl cellulose ether decreases with the increase of temperature. However, in actual material applications, dry powder mortar is often applied to hot substrates under high temperature (above 40 degrees) conditions in many environments, such as exterior wall putty plastering under the sun in summer, which often accelerates the curing of cement and the hardening of dry mortar. The decrease in water retention rate has led to the obvious feeling that both workability and crack resistance are affected. Under such conditions, reducing the influence of temperature factors becomes particularly critical. Although the methyl hydroxyethyl cellulose ether additive is currently considered to be at the forefront of technological development, its temperature dependence will still cause the performance of dry mortar to weaken. Although the amount of methyl hydroxyethyl cellulose in summer is increased, the workability and crack resistance still cannot meet the needs of users. Through some special treatments for MC, such as increasing the degree of etherification, it can maintain its water retention effect at higher temperatures and make it perform better under harsh conditions.

Milacell® is a trademark for Michem’s cellulose ether products and derivatives Michem HPMC is widely used in various fields, including Tile adhesive Grouts, Skim coats, Wall putty, Gypsum plasters, Mortar, Render, EIFS, etc. Milacell® HPMC can improve its good water retention, extend the operation time and improve adhesive strength and flexibility. Milacell® HPMC substantially reduces the loss of water into absorbing substrates in formulations like cement renders, tile cement, gypsum plasters, etc. The water retention ability of Milacell® also strongly enhances the adhesion strength of thin-bed mortars. This is because the binders in the mortar such as the cement and gypsum have enough time for hydration and at the same time do not lose water. Milacell® Improve construction efficiency and mechanical application to save time on materials.

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