Hydroxypropyl methyl cellulose HPMC is a non-ionic cellulose ether made from natural polymer material cellulose through a series of chemical processing. They are an odorless, tasteless and non-toxic white powder that swells into a clear or slightly turbid colloidal solution in cold water. It has the characteristics of thickening, bonding, dispersion, emulsification, film formation, suspension, adsorption, gelation, surface activity, moisture retention and protective colloid. Hydroxypropyl methylcellulose can be used in building materials, coating industry, synthetic resin, ceramic industry, medicine, food, textile, agriculture, daily chemical industry and other industries.
Water retention function and principle: cellulose ether HPMC mainly plays a role of water retention and thickening in cement mortar and gypsum-based slurry, which can effectively improve the bonding force and sag resistance of the slurry. Factors such as air temperature, temperature and wind pressure speed will affect the volatilization rate of water in cement mortar and gypsum-based products. Therefore, in different seasons, there are some differences in the water retention effect of the same amount of HPMC products. In the specific construction, the water retention effect of the slurry can be adjusted by increasing or decreasing the amount of HPMC added.
The water retention of methyl cellulose ether under high temperature conditions is an important indicator to distinguish the quality of methyl cellulose ether. Excellent HPMC series products can effectively solve the problem of water retention at high temperatures. In high temperature seasons, especially in hot and dry areas and thin-layer construction on the sunny side, high-quality HPMC is required to improve the water retention of the slurry.
High-quality HPMC has very good uniformity. Its methoxy and hydroxypropoxy groups are evenly distributed along the cellulose molecular chain, which can improve the ability of the oxygen atoms on the hydroxyl and ether bonds to associate with water to form hydrogen bonds. , So that the free water becomes bound water, thereby effectively controlling the evaporation of water caused by high temperature weather, and achieving high water retention.
High-quality cellulose HPMC can be uniformly and effectively dispersed in cement mortar and gypsum-based products, and wrap all solid particles, and form a layer of wetting film. The water in the base is gradually released over a long period of time. The condensed material undergoes hydration reaction, so as to ensure the bonding strength and compressive strength of the material. Therefore, in the high-temperature summer construction, in order to achieve the effect of water retention, high-quality HPMC products must be added in sufficient quantities according to the formula, otherwise, insufficient hydration, reduced strength, cracking, hollowing and falling off will occur due to excessive drying. Problems, but also increase the difficulty of construction workers. As the temperature decreases, the amount of HPMC added can be gradually reduced, and the same water retention effect can be achieved.
The water retention of HPMC is affected by the following factors:
1. Homogeneity of cellulose ether HPMC
In the homogeneously reacted HPMC, the methoxy and hydroxypropoxy groups are evenly distributed, and the water retention rate is high.
2. Thermal gel temperature of cellulose ether HPMC
Thermal gel temperature is high, the water retention rate is high; on the contrary, the water retention rate is low.
3. Viscosity of cellulose ether HPMC
When the viscosity of HPMC increases, the water retention rate also increases; when the viscosity reaches a certain level, the increase in the water retention rate tends to be flat.
4. Addition of cellulose ether HPMC
The greater the amount of cellulose ether HPMC added, the higher the water retention rate and the better the water retention effect. In the range of 0.25-0.6% addition, the water retention rate increases faster with the increase of the addition amount; when the addition amount further increases, the increasing trend of the water retention rate slows down.