Comparing HPMC with MC, HEC, CMC

Hydroxypropyl Methyl Cellulose (HPMC)

Methyl cellulose (MC)

Methyl cellulose is refined cotton treated with alkali and then made into cellulose ether through a series of reactions using methylene chloride as the etherifying agent. The general degree of substitution is 1.6~2.0, and the solubility varies with the degree of substitution. It belongs to non-ionic cellulose ether.

1. Methyl cellulose is soluble in cold water, hot water solubility will encounter difficulties, and its aqueous solution is very stable in the range of pH=3~12. It is compatible with starch, guanidinium gum, etc. and many surfactants. When the temperature reaches the gelation temperature, gelation will occur.
2. The water retention of methyl cellulose depends on its addition amount, viscosity, particle fineness and dissolution speed. Generally the larger the addition amount, the smaller the fineness and the larger the viscosity, the higher the water retention rate. The viscosity is not directly proportional to the water retention rate. The dissolution rate mainly depends on the degree of surface modification of cellulose particles and particle fineness. Among the several cellulose ethers introduced in this paper, methyl cellulose and hydroxypropyl methyl cellulose have higher water retention rates.
3. Changes in temperature can seriously affect the water retention of methyl cellulose. Generally the higher the temperature, the worse the water retention. If the mortar temperature exceeds 40 ℃, the water retention of methyl cellulose will be significantly worse, seriously affecting the constructability of mortar.
4. Methyl cellulose has a significant impact on the construction and adhesion of mortar. The “adhesion” refers to the adhesion between the applicator and the wall substrate, i.e. the shear resistance of the mortar. Adhesion is large, the shear resistance of the mortar is large, the force required by the workers in the process of application is also large, and the constructability of the mortar is poor. In the cellulose ether products methyl cellulose adhesion is at a medium level.

Hydroxyethyl cellulose (HEC)

1. Hydroxyethyl cellulose can be dissolved in cold water, hot water is more difficult to dissolve. Its solution is stable at high temperature and does not have gelation. It can be used for a longer time in mortar under high temperatures, but the water retention is lower than methyl cellulose.
2. hydroxyethyl cellulose has the stability to general acid and alkali, alkali can accelerate its dissolution, and can slightly increase viscosity, its dispersion in water than methyl cellulose and hydroxypropyl methyl cellulose is slightly worse.
3. Hydroxyethyl cellulose has good performance on mortar anti-hanging, but the retardation time of cement is longer.
4. The performance of hydroxyethyl cellulose produced by some Chinese enterprises is significantly lower than that of methyl cellulose due to high water content and high ash content.

Carboxymethyl cellulose (CMC)

Carboxymethyl cellulose is made from natural fiber (cotton, etc.) after alkali treatment, with sodium monochloroacetate as the etherifying agent, after a series of reaction processing and made of ionic cellulose ether. Its substitution degree is generally 0.4~1.4, and the performance is greatly affected by the substitution degree.

1. Carboxymethyl cellulose is more hygroscopic and will contain more water when stored in general conditions.
2. Carboxymethyl cellulose aqueous solution will not produce gel, with the increase in temperature and viscosity decline, the temperature exceeds 50 ℃, the viscosity will be irreversible.
3. The stability of carboxymethyl cellulose is greatly affected by pH. Generally it can be used in gypsum-based mortar, not in cement-based mortar. At high alkalinity, it will lose viscosity.
4. The water retention of carboxymethyl cellulose is much lower than methyl cellulose. It has retardation effect on gypsum-based mortar and reduces its strength. However, the price of carboxymethyl cellulose is significantly lower than methyl cellulose.

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