The differences between HPMC and MC, HEC, CMC
1, methyl cellulose (MC) (1) Methylcellulose is soluble in cold water, and it is difficult to dissolve in hot water. The aqueous solution is very stable in the range of pH=3~12. It has good compatibility with starch, guar gum and many other surfactants. When the temperature reaches the gelation temperature, a gelation phenomenon occurs. After the refined cotton is treated with alkali, methyl chloride is used as an etherifying agent, and a series of reactions are carried out to prepare a cellulose ether. The degree of substitution is generally 1.6 to 2.0, and the degree of substitution differs depending on the solubility. It belongs to nonionic cellulose ether. (2) The water retention of methyl cellulose depends on its addition amount, viscosity, particle fineness and dissolution rate. Generally, the amount of addition is large, the fineness is small, and the viscosity is large, and the water retention rate is high. The addition amount has the greatest influence on the water retention rate, and the viscosity level is not proportional to the water retention rate. The rate of dissolution depends mainly on the degree of surface modification of the cellulose particles and the fineness of the particles. Among the above cellulose ethers, methylcellulose and hydroxypropylmethylcellulose have a high water retention rate. (3) The change of temperature will seriously affect the water retention rate of methyl cellulose. Generally, the higher the temperature, the worse the water retention. If the temperature of the mortar exceeds 40 ° C, the water retention of methyl cellulose will be significantly deteriorated, which seriously affects the workability of the mortar. (4) Methyl cellulose has a significant effect on the workability and adhesion of the mortar. “Adhesiveness” herein refers to the adhesive force felt between the worker’s application tool and the wall substrate, that is, the shear resistance of the mortar. The adhesion is large, the shear resistance of the mortar is large, the force required by the worker during use is also large, and the workability of the mortar is poor. Methylcellulose adhesion is intermediate in cellulose ether products. 2, hydroxypropyl methylcellulose (HPMC) Hydroxypropyl methylcellulose is a cellulose variety that has been rapidly increasing in both production and dosage in recent years. It is a nonionic cellulose mixed ether prepared by a series of reactions using propylene oxide and methyl chloride as an etherifying agent after alkalization of refined cotton. The degree of substitution is generally 1.2 to 2.0. Its properties are different depending on the ratio of methoxyl content and hydroxypropyl content. (1) Hydroxypropyl methylcellulose is easily soluble in cold water, and it may be difficult to dissolve in hot water. However, its gelation temperature in hot water is significantly higher than that of methyl cellulose. The dissolution in cold water is also much better than methyl cellulose. (2) The viscosity of hydroxypropylmethylcellulose is related to the molecular weight thereof, and the viscosity is high when the molecular weight is large. The temperature also affects its viscosity, the temperature rises, and the viscosity decreases. However, its viscosity has a lower temperature than methyl cellulose. Its solution is stable at room temperature. (3) The water retention of hydroxypropylmethylcellulose depends on the amount of addition, viscosity, etc., and the water retention rate under the same amount is higher than that of methylcellulose. (4) Hydroxypropyl methylcellulose is stable to acids and bases, and its aqueous solution is very stable in the range of pH=2~12. Caustic soda and lime water do not have much effect on their properties, but alkali accelerates their dissolution rate and increases viscosity. Hydroxypropyl methylcellulose has stability to general salts, but when the concentration of the salt solution is high, the viscosity of the hydroxypropylmethylcellulose solution tends to increase. (5) Hydroxypropyl methylcellulose can be mixed with a water-soluble polymer compound to form a uniform, higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum and the like. (6) Hydroxypropyl methylcellulose has better enzymatic resistance than methylcellulose, and its solution is less likely to be enzymatically degraded than methylcellulose. Hydroxypropyl methylcellulose is more adhesive to mortar than methylcellulose. 3. Hydroxyethyl cellulose (HEC) It is prepared by subjecting refined cotton to alkali treatment and then reacting with ethylene oxide as an etherifying agent in the presence of acetone. The degree of substitution is generally 1.5 to 2.0. It has strong hydrophilicity and is easy to absorb moisture. (1) Hydroxyethyl cellulose is soluble in cold water, and it is difficult to dissolve hot water. The solution is stable at high temperatures and does not have gel properties. It can be used for a long time in the mortar at high temperature, but the water retention is lower than that of methyl cellulose. (2) Hydroxyethyl cellulose has stability to general acid and alkali, alkali can accelerate its dissolution, and slightly increase the viscosity, its dispersion in water is slightly worse than methyl cellulose and hydroxypropyl methyl cellulose. . (3) Hydroxyethyl cellulose has good performance against mortar hanging, but the retardation time for cement is longer. (4) Hydroxyethyl cellulose produced by some domestic enterprises has a performance lower than that of methyl cellulose due to its high water content and high ash content. 4, carboxymethyl cellulose (CMC) After the natural fiber (cotton, etc.) is treated with a base, sodium chloroacetate is used as an etherifying agent, and a series of reaction treatments are carried out to prepare an ionic cellulose ether. The degree of substitution is generally 0.4 to 1.4, and its performance is greatly affected by the degree of substitution. (1) Carboxymethyl cellulose has a large hygroscopicity and generally contains a relatively large amount of water during storage. (2) The carboxymethylcellulose aqueous solution does not produce a gel, and the viscosity decreases as the temperature rises. When the temperature exceeds 50 ° C, the viscosity is irreversible. (3) Its stability is greatly affected by pH. Generally used in gypsum-based mortar, it can not be used in cement-based mortar. When it is highly alkaline, it loses its viscosity. (4) Its water retention is much lower than that of methyl cellulose. It has a retarding effect on the gypsum-based mortar and reduces its strength. But the price of carboxymethyl cellulose is significantly lower than that of methyl cellulose.