Cellulose ether is an important class of polymer compounds, widely used in construction, medicine, food and other fields. Among them, HPMC (hydroxypropyl methylcellulose), MC (methylcellulose), HEC (hydroxyethyl cellulose) and CMC (carboxymethyl cellulose) are four common cellulose ethers.
Methyl cellulose (MC):
MC is soluble in cold water and difficult to dissolve in hot water. The aqueous solution is very stable in the range of pH=3~12, has good compatibility, and can be mixed with a variety of surfactants such as starch and guar gum. When the temperature reaches the gelation temperature, gelation occurs.
The water retention of MC depends on its addition amount, viscosity, particle fineness and dissolution rate. Generally, the water retention rate is high when the addition amount is large, the particles are fine and the viscosity is high. Among them, the addition amount has the greatest impact on the water retention rate, and the viscosity level is not proportional to the water retention rate. The dissolution rate mainly depends on the surface modification degree and particle fineness of the cellulose particles.
Temperature changes will seriously affect the water retention of MC. Generally, the higher the temperature, the worse the water retention. If the mortar temperature exceeds 40°C, the water retention of MC will be significantly reduced, seriously affecting the construction performance of the mortar.
MC has a significant impact on the construction performance and adhesion of the mortar. Here, “adhesion” refers to the adhesion between the worker’s construction tools and the wall substrate, that is, the shear resistance of the mortar. The greater the adhesion, the greater the shear resistance of the mortar, the greater the force required by the worker during use, and the poor construction performance of the mortar. The adhesion of MC is at a medium level among cellulose ether products.
Hydroxypropyl methylcellulose (HPMC):
HPMC is easily soluble in water, but may be difficult to dissolve in hot water. However, its gelation temperature in hot water is significantly higher than that of MC, and its solubility in cold water is also better than that of MC.
The viscosity of HPMC is related to the molecular weight, and the viscosity is high when the molecular weight is large. Temperature also affects its viscosity, and the viscosity decreases as the temperature increases, but the temperature at which its viscosity decreases is lower than that of MC. Its solution is stable at room temperature.
The water retention of HPMC depends on the addition amount and viscosity, etc. The water retention rate at the same addition amount is higher than that of MC.
HPMC is stable to acids and alkalis, and its aqueous solution is very stable in the pH range of 2~12. Caustic soda and lime water have little effect on its performance, but alkali can accelerate its dissolution rate and increase viscosity. HPMC is stable to general salts, but when the concentration of salt solution is high, the viscosity of HPMC solution tends to increase.
HPMC can be mixed with water-soluble polymer compounds to form a uniform, higher viscosity solution, such as polyvinyl alcohol, starch ether, vegetable gum, etc.
HPMC has better enzyme resistance than MC, and its solution is less susceptible to enzymatic degradation than MC. HPMC has better adhesion to mortar than MC.
Hydroxyethyl cellulose (HEC):
HEC is soluble in cold water and difficult to dissolve in hot water. The solution is stable at high temperature and has no gel properties. It can be used in mortar for a long time at high temperature, but its water retention is lower than MC.
HEC is stable to general acids and alkalis, alkali can accelerate its dissolution and slightly increase viscosity, and its dispersibility in water is slightly inferior to MC and HPMC.
HEC has good suspension performance for mortar, but the cement has a longer retarding time.
HEC produced by some domestic enterprises has lower performance than MC due to its high water content and ash content.
Carboxymethyl cellulose (CMC):
CMC is an ionic cellulose ether prepared by a series of reaction treatments after natural fibers (such as cotton) are treated with alkali and chloroacetic acid is used as an etherifying agent. The degree of substitution is generally between 0.4 and 1.4, and its performance is greatly affected by the degree of substitution.
CMC has thickening and emulsification stabilization effects, and can be used in beverages containing oil and protein to play an emulsification stabilization role.
CMC has a water retention effect. In meat products, bread, steamed buns and other foods, it can play a role in tissue improvement, and can make water less volatile, increase product yield, and increase taste.
CMC has a gelling effect and can be used to make jelly and jam.
CMC can form a film on the surface of food, which has a certain protective effect on fruits and vegetables and prolongs the shelf life of fruits and vegetables.
These cellulose ethers each have their own unique properties and application areas. The selection of suitable products needs to be determined according to specific application requirements and environmental conditions.
Post time: Oct-29-2024