HPMC full name is HydroxyPropyl Methyl Cellulose ether.
HEMC full name is HydroxyEthyl Methyl Cellulose ether.
In construction industry, both can be used as water retention agent, at the same time to improve the wetting, open time, bonding and workability of diverse mortars.
Theoretically, the hydroxyethoxy group in HEMC exhibits higher polarity than the hydroxypropoxy group in HPMC, resulting in better hydrophilicity and stronger water molecule binding capacity for HEMC. However, in practical applications, it’s difficult to assert that HEMC produced in any given plant is definitively superior to HPMC. This uncertainty stems from variations across manufacturing plants in equipment, raw materials, process flows, reaction pressure, and reaction time.
Especially, it is very difficult to say, HEMC has a better water retention effect than HPMC, because viscosity of cellulose ether can directly and obviously affect water retention rate when testing.
But one difference is very clear that the gelation temperature of HEMC(75-90℃, normally >80℃) is higher than HPMC(58-75℃), and due to the production cost issue, the HPMC with around 75℃ gelation temperature is less and less for the construction industry.
Hence if in tropical zone or in summer season, HEMC maybe a good choice for your mortars.