HPMC VS HEMC: Their Different Characteristics
Aug. 26, 2021
HPMC and HEMC have similar functions 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. Here hpmc manufacturer LISTAL shows you their differences.
The raw material for HPMC production can be refined cotton or wood pulp, which is partly methyl and partly polyhydroxypropyl ether of cellulose. The cellulose is alkalized and then etherified with propylene oxide and chloromethane-reaction system.
The production of HEMC is slightly different from HPMC. After alkalinization of cellulose, it is produced by replacing propylene oxide with ethylene oxide, which replaces the hydroxyl group on the glucose ring group.
The methoxy on HPMC chloromethane replaces the hydroxyl group on the glucose ring group. HPMC has thermal gel properties, its solution does not carry ionic charge, does not interact with metal salts or ionic compounds, has strong mold resistance, has good dispersion, emulsification, thickening, bonding, water retention and glue retention properties.
Compared with HPMC, the chemical structure of HEMC has more hydrophilic groups, so it is more stable at high temperature and has good thermal stability. Compared with common HPMC cellulose ether, it has higher gel temperature, which is more advantageous in high temperature use environment. Like HPMC, HEMC has good mold resistance, dispersibility, emulsification, thickening, adhesiveness, water retention and glue retention.
Gel temperature is an important indicator of cellulose ethers. Aqueous solutions of cellulose ethers have thermal gelation properties. As the temperature increases, the viscosity continues to decrease. When the solution temperature reaches a certain value, the cellulose ether solution is no longer uniform and transparent, but forms a white gel and eventually loses its viscosity. the overall gel temperature of HEMC is slightly higher than that of HPMC. generally the gel temperature of HPMC is 60℃~75℃ and that of HEMC is 75℃~90℃.
The ratio of methoxy and hydroxypropyl content of HPMC can negatively affect the water solubility, water retention capacity, surface activity and gel temperature of the product. Appropriate increase of hydroxypropyl content and decrease of methoxy content can improve the gel temperature, but too high hydroxypropyl content will lower the gel temperature and make the water solubility and surface activity worse.
Applications of tile adhesives
The gel temperature of cellulose ethers determines their thermal stability in applications. the gel temperature of HPMC is usually between 60°C and 75°C, depending on other manufacturers' models, group content and different production processes. Due to the nature of the HEMC moiety, it has a higher gel temperature, usually above 80°C, and therefore its stability at high temperatures is better than that of HPMC.
HEMC has better hydrophilicity because it has more hydrophilic groups in its structure. the water retention of HEMC in mortar is slightly higher than HPMC in the same viscosity and at the exact dosage. in addition, HEMC has relatively better anti-sagging ability.
Reasons to add HPMC to tile adhesives
Significantly improve the water retention capacity, so that the tile adhesive has sufficient water hardening process, improve the bonding strength of the tile adhesive, and further improve the anti-slip performance of the tile adhesive.
Good opening time and workable time, easy for workers to adjust the tiling error.
HPMC makes the dry powder components easy to mix without causing caking, saving working time. It also increases construction efficiency, improves work performance and reduces costs.
HPMC makes tile adhesive with better plasticity and flexibility.
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