Hydroxypropyl methyl cellulose is in recent years, the rapid increase in the amount of yield of cellulose varieties. It is a non-ionic cellulose mixed ether made from refined cotton by alkalization and treated with epoxy propane and methyl chloride as etherification agent through a series of reactions. The degree of substitution is generally 1.2~2.0. its properties by methoxy content and hydroxypropyl content in different proportion.
(1) the water holding capacity of hydroxypropyl methyl cellulose depends on its amount and viscosity, and its water retention rate is higher than that of methyl cellulose under the same amount of addition.
(2) hydroxypropyl methyl cellulose soluble in water, soluble in hot water will encounter difficulties. But it is in the hot water in the gelation temperature was higher than that of methyl cellulose. Dissolved in cold water, is also a big improvement in methyl cellulose.
(3) the viscosity and molecular weight of hydroxypropyl methyl cellulose on the size of molecular weight, high viscosity. The temperature will affect the viscosity, temperature, viscosity decreased. But the impact of high viscosity temperature low than methyl cellulose. The solution is stable at room temperature.
(4) hydroxypropyl methylcellulose has better enzyme resistance than methyl cellulose, and the possibility of enzymatic degradation is lower than that of methylcellulose.
(5) hydroxypropyl methyl cellulose with stability to acid and alkali, its water solution is very stable in the range of pH=2~12. Hydroxypropyl methyl cellulose has stability to general salts, but the viscosity of hydroxypropyl methyl cellulose solution tends to increase when the concentration of salt solution is high.
(6) hydroxypropyl methyl cellulose can be mixed with water-soluble polymers to become homogeneous and higher viscosity solution. Hydroxypropyl methyl cellulose adhesive on mortar construction is higher than that of methyl cellulose.
The purified cotton was treated with alkali, and chlorinated methane was used as etherification agent to produce cellulose ether through a series of reactions. The general degree of substitution for 1.6~2.0, different degrees of substitution have different solubility. It belongs to non-ionic cellulose ether.
(1) water on methyl cellulose from its content, viscosity, fineness and dissolution rate. The general amount of large, small fineness, high viscosity, water retention rate is high. The amount of water retention rate is the greatest impact, the viscosity and the level of water retention rate is not proportional to the. The dissolution rate mainly depends on the surface modification of cellulose particles and the degree of fineness.
(2) seriously affect the water retention rate of methyl cellulose will be affected by temperature. The higher the temperature is, the worse the water holding capacity is. Methyl cellulose is difficult to dissolve in cold water and hot water, and its aqueous solution is very stable in the range of pH=3~12. When the temperature reaches the gelation temperature, gel phenomenon will appear.
(3) have obvious effect of methyl cellulose on mortar and bonding. The "cohesiveness" here refers to the cohesive force between the applicator and the wall material, that is, the shear resistance of the mortar. Adhesion is large, mortar shear resistance is large, the use of force in the use of workers is also large, the construction of mortar is poor.
The purified cotton was treated with alkali and then reacted with ethylene oxide as etherification agent in the presence of isopropyl alcohol. The degree of substitution is generally 1.5~2.0. has strong hydrophilic, easy to absorb moisture.
(1) have good performance of mortar anti vertical hanging hydroxyethyl cellulose, but for the long time retarded cement. The denaturation of hydroxyethyl cellulose in aqueous solution is serious, and the mildew can occur in 3~5 days at 40 or so, which affects its performance.
(2) hydroxyethyl cellulose is soluble in cold water, hot water is difficult to dissolve. The solution is stable under high temperature, has no gel. In the mortar under high temperature can be used for a long time, but the water is low methyl cellulose.
(3) hydroxyethyl cellulose has stability to general acid base, alkali can accelerate its dissolution, and slightly increase viscosity, and its dispersion in water is slightly worse than methyl cellulose and hydroxypropyl methyl cellulose.
An ionic cellulose ether was prepared by a series of reaction treatment with natural fiber (cotton, etc.) after alkali treatment, with sodium chloroacetate as etherification agent. The degree of substitution is generally 0.4~1.4, its performance is affected by the degree of substitution effect.
(1) the water retention of carboxymethyl cellulose is far lower than that of methyl cellulose. A retarding effect of gypsum mortar, and reduce its strength. But the price is significantly lower than that of carboxymethyl cellulose methyl cellulose.
(2) carboxymethyl cellulose aqueous solution does not produce gel, and viscosity decreases with the increase of temperature. When the temperature is above 50, the viscosity is irreversible. The hygroscopicity of carboxymethyl cellulose is large, the general conditions will contain large water storage.
(3) the stability of carboxymethyl cellulose was affected by pH. General can be used for gypsum mortar, cement mortar can not be used. It loses viscosity when it is high alkaline.
In the above several cellulose ether, methyl cellulose and hydroxypropyl methyl cellulose water retention rate is higher.