3 Applications in the construction industry
HPMC and HEMC have similar roles in construction materials.
They can be used as dispersants, water retaining agents, thickeners and binders, etc. They are mainly used in cement mortars and in the forming of plaster products. It is used in cement mortars to increase their adhesion, workability, reduce flocculation, improve viscosity and shrinkage, retain water, reduce water loss on the concrete surface, increase strength, prevent cracks and weathering of water-soluble salts.
It is widely used in cement-based plasters, gypsum plasters, gypsum products, masonry mortars, panel caulks, caulks, tile adhesives, self-levelling floor materials, etc. In coatings it can be used as a film-forming agent, thickener. Emulsifier and stabiliser in emulsion coatings and water-soluble resin coating components. Giving the coating film good abrasion resistance, uniformity and adhesion. And improving surface tension, stability to acids and bases and compatibility with metal pigments. Due to the good viscosity storage stability, it is particularly suitable as a dispersant in emulsified coatings. All in all, although used in very small quantities in the system. They are very useful and have a wide range of applications.
The gel temperature of cellulose ethers determines their thermal stability in application.
The gel temperature of HPMC is usually between 60°C and 75°C, depending on the type, group content and the production process of different manufacturers. In practice, under very hot construction conditions in summer. The water retention of HEMC in wet mix mortar with the same viscosity and dosing has a greater advantage than HPMC. Especially in the south, the mortar will sometimes be constructed at high temperatures. The gel temperature is too low for the cellulose ether, which will lose its thickening and water retention properties at high temperatures. Thus accelerating the cement solidification and hardening of the mortar. Directly affecting the constructability and anti-cracking properties.
HEMC has a better hydrophilicity due to the more hydrophilic groups in its structure. So the water retention rate of HEMC in mortar is slightly higher than that of HEMC for the same viscosity and the same admixture. Therefore, HEMC is more effective when used in tile adhesives.
Reprinted from< Science & Wealth> No. 7, 2018