Hydroxypropyl methyl cellulose (abbreviated as HPMC), the raw material for production can be refined cotton or wood pulp, which is part of the methyl and part of the polyhydroxypropyl ether of cellulose, and the cellulose undergoes alkali It is prepared by etherification with propylene oxide and methyl chloride. The methoxy group on methyl chloride replaces the hydroxyl group on the glucose ring group, and the hydroxyl group is replaced by hydroxypropoxy group and chain polymerization occurs. HPMC has thermogel characteristics, its solution has no ionic charge, does not interact with metal salts or ionic compounds, has strong anti-mildew properties, and has good dispersion, emulsification, thickening, adhesion, water retention, and gel retention properties.
Hydroxyethyl methyl cellulose (HEMC) is slightly different from HPMC in production and production. After the cellulose is alkalized, it is prepared by replacing propylene oxide with ethylene oxide and replacing hydroxyl groups on the glucose ring. Compared with HPMC, the chemical structure of HEMC has more hydrophilic groups, so it is more stable at high temperatures and has good thermal stability. Compared with common HPMC cellulose ethers, it has a relatively high gel temperature, which is more advantageous in high-temperature use environments. Like HPMC, HEMC also has good anti-mildew properties, dispersion, emulsification, thickening, cohesion, and water and glue retention properties.
2 Physical and chemical properties
The physical and chemical properties of the vitamin ether industry test standards include: appearance, fineness, weight loss on drying, sulfate ash, solution pH, solution transmittance, solution viscosity, gel temperature, group content, etc. Appearance, fineness, weight loss on drying, sulfate ash, solution pH and light transmittance, viscosity, etc. are related to the product's model and function. Different manufacturers have different levels, so we won't discuss them here.
2.1 Content of cellulose ether groups
Generally, the methoxyl content of HPMC is 16% to 30%, and the hydroxypropoxyl is 4% to 32%. The oxygen content is between 22% and 30%, and the hydroxyethoxy group is between 2% and 14%.
2.2 Gel temperature
Generally, HPMC gel temperature is between 60 ° C and 75 ° C, and HEMC is between 75 ° C and 90 ° C.
3 Applications in the construction industry
HPMC and HEMC have similar roles in building materials. It can be used as dispersant, water-retaining agent, thickener and binder, etc. It is mainly used in the molding of cement mortar and gypsum products.
Used in cement mortar to increase its cohesiveness, workability, reduce flocculation, improve viscosity and shrinkage, and have water retention, reduce concrete surface moisture loss, increase strength, prevent cracks and weathering of water-soluble salts.
It is widely used in cement-based plasters, gypsum plasters, gypsum products, masonry mortars, sheet joints, joints, tile adhesives, and self-leveling flooring materials. In coatings, it can be used in latex coatings and water-soluble resin coating components as film-forming agents, thickeners, emulsifiers and stabilizers, so that the coating film has good abrasion resistance, uniformity and adhesion, and improves Surface tension, stability to acids and bases, and compatibility with metallic pigments.
Due to its good viscosity storage stability, it is particularly suitable for use as a dispersant in emulsion coatings. All in all, although the amount is small in the system, it has a great effect and is widely used. Because there are more hydrophilic groups in the structure of HEMC, it has better hydrophilicity.
Under the same dosage of products with the same viscosity, the water retention of HEMC in mortar is slightly higher than HEMC. In addition, HEMC's ability to resist downflow is also relatively good. So HEMC will be more effective when applied to tile adhesive.
However, the mainstream cellulose ether in the domestic construction industry is still HPMC. Because of its many types and low prices, it can be freely selected at comprehensive costs. High-quality HPMC is not worse than HEMC.
With the development of the domestic construction market, especially the increase in the degree of mechanized construction and the increase in requirements for building quality, the consumption of HPMC in the construction field will continue to increase.