Views:0 Author:Site Editor Publish Time: 2020-07-23 Origin:Site
Functions of HPMC in Cement Based and Gypsum Based Products
Hydroxypropyl methylcellulose, abbreviated as: HPMC or MHPC. The appearance is white or almost white powder; the main purpose is as a dispersant in the production of polyvinyl chloride, and is the main auxiliary agent for the preparation of PVC by suspension polymerization. In the construction process of the construction industry, it is mainly used in mechanized construction such as wall masonry, plastering, caulking, etc.; especially in decorative construction, it is used for pasting tiles, marble, and plastic decoration, with high bonding strength and reducing cement consumption. . Used as a thickener in the coating industry, it can make the layer bright and delicate, without powdering, and improve the leveling performance.
In cement mortar and gypsum-based slurry, hydroxypropyl methyl cellulose mainly plays a role of water retention and thickening, which can effectively improve the adhesion and sag resistance of the slurry.
Factors such as air temperature, temperature and wind pressure will affect the volatilization rate of water in cement mortar and gypsum-based products. Therefore, in different seasons, the water retention effect of the product with the same amount of hydroxypropyl methylcellulose is different.
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 index to distinguish the quality of methyl cellulose ether.
Excellent hydroxypropyl methyl cellulose 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 free water becomes bound water, thereby effectively controlling the evaporation of water caused by high temperature weather, and achieving high water retention.
In order to set cementitious materials such as cement and gypsum, water is required for hydration. The correct amount of HPMC can maintain the moisture in the mortar for a long enough time so that the setting and hardening process can continue.
The amount of HPMC required to obtain sufficient water retention capacity depends on:
1. The absorbency of the base layer
2. Composition of mortar
3. The layer thickness of mortar
4. Water demand of mortar
5. Setting time of cementitious material
High-quality hydroxypropyl methyl cellulose can be uniformly and effectively dispersed in cement mortar and gypsum-based products, and wrap all solid particles, and form a wetting film. The water in the base is gradually released over a long period of time , And the hydration reaction occurs with the inorganic cementing material 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, it is necessary to add high-quality HPMC products 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.
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