Methyl Cellulose (MC) Molecular formula \[C6H7O2(OH)3-h(OCH3)n1] x Refined cotton is treated with alkali, and methyl chloride is used as etherification agent. After a series of reactions, cellulose ether treatment is carried out. Generally, the degree of substitution is 1.6~2.0, and the degree of substitution is different. It belongs to non-ionic cellulose ether.
1. Methylcellulose is soluble in cold water, hot water will encounter difficulties, and the pH range of the aqueous solution is very stable between 3/12. Starch, guar gum and many other surfactants are more compatible. Gelation occurs when the temperature reaches the gelation temperature.
The water retention of methylcellulose depends on its added amount, viscosity, particle fineness and dissolution rate. Generally enlarged, small, high viscosity, high water retention. Among them, the water retention has the greatest impact, and the viscosity level is not directly proportional to the water retention. The dissolution rate mainly depends on the degree of surface modification of the cellulose particles and the fineness of the particles. Among the above cellulose ethers, methyl cellulose and hydroxypropyl methyl cellulose have high water retention.
Temperature changes can seriously affect the water retention of methyl cellulose. – The higher the temperature, the worse the water retention. If the mortar temperature exceeds 40°C, the water retention of methyl cellulose will be significantly reduced, seriously affecting the construction of the mortar.
Methylcellulose has a significant effect on the workability and adhesion of mortar. The “stickiness” here refers to the adhesion between the worker’s applicator tool and the wall substrate, that is, the shear resistance of the mortar. Viscosity, mortar shear strength, and the strength required by workers in use are also very large, and mortar construction is not good. Methylcellulose adhered at moderate levels in cellulose ether products.
2. Hydroxypropyl methylcellulose (HPMC) [C 6 H 7 O 2 (OH) 3-mn (OCH 3 ) m, OCH 2 CH (OH) CH 3 ] n]] hydroxypropyl methyl cellulose In recent years, the types of cellulose have increased rapidly. It is a non-ionic cellulose mixed ether prepared by a series of reactions after alkalization of refined cotton alkali, in which propylene oxide and methyl chloride are used as etherification agents. The degree of substitution is typically 1.2/2.0. Its properties vary according to the ratio of methoxyl content and hydroxypropyl content.
1. Hydroxypropyl methylcellulose is divided into hot-melt type and instant type. Its gelation temperature in hot water is significantly higher than that of methylcellulose. It also shows a great improvement over methylcellulose when dissolved in cold water.
The viscosity of hydroxypropyl methylcellulose is related to the molecular weight, and the molecular weight is high. Temperature also affects its viscosity, as temperature increases, viscosity decreases. However, the influence of temperature on viscosity is lower than that of methyl cellulose. The solution is storage stable at room temperature.
3. The water retention of hydroxypropyl methylcellulose depends on its addition amount, viscosity, etc., and the water retention rate of the same amount is higher than that of methyl cellulose.
4. Hydroxypropyl methylcellulose is stable to acid and alkali, and its aqueous solution is very stable in the pH range of 2/12. The performance of caustic soda and lime water does not have much influence, but the alkali can accelerate its dissolution rate, and the viscosity is increased. Hydroxypropyl methylcellulose is stable to common salts, but when the concentration of the salt solution is high, the viscosity of the hydroxypropyl methylcellulose solution tends to increase.
Hydroxypropyl methylcellulose can be mixed with water-soluble polymers to form a uniform, high-viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
Hydroxypropyl methylcellulose has better enzyme resistance than methylcellulose, the possibility of enzymatic degradation of its solution is lower than that of methylcellulose, and the adhesion of hydroxypropylmethylcellulose to mortar construction is higher than that of methylcellulose. base cellulose.
Three, hydroxyethyl cellulose (HEC) is made from refined cotton treated with alkali, in the presence of acetone, and ethylene oxide as etherification agent. Its degree of substitution is usually 1.5/2.0. It has strong hydrophilicity and is easy to absorb moisture.
1. Hydroxyethyl cellulose is soluble in cold water, but it is difficult to dissolve in hot water. The solution is stable at high temperature and does not have gel properties. It can be used for a long time in high-temperature mortar, but its water retention is lower than that of methyl cellulose.
2. Hydroxyethyl cellulose is stable to general acid and alkali. Alkali accelerates its dissolution, and its viscosity increases slightly. Its dispersion in water is slightly worse than that of methyl cellulose and hydroxypropyl methyl cellulose.
3. Hydroxyethyl cellulose has good anti-hanging performance on mortar, but for a long time, some domestically produced hydroxyethyl cellulose has significantly lower performance than methyl cellulose due to its large water content and high ash content.
4. Carboxymethyl cellulose (CMC) \ [C6H7O2 (OH) 2och2COONa] (cotton, etc.) of natural fiber is treated with alkali, and sodium chloroacetate is used as etherification agent, after a series of reaction treatments, it is made into ionic cellulose ether. The degree of substitution is generally 0.4/1.4, and the degree of substitution has a greater impact on performance.
Carboxymethyl cellulose has high hygroscopicity, and the general storage conditions contain more water.
2. Carboxymethyl cellulose aqueous solution does not produce gel, the viscosity decreases when the temperature rises, and the viscosity is irreversible when the temperature exceeds 50°C.
Its stability is greatly affected by pH. Generally used for gypsum mortar, not for cement mortar. In the case of high alkalinity, it will lose its viscosity.
Its water retention is much lower than that of methyl cellulose. Gypsum mortar has a retarding effect, reducing strength. But the price of carboxymethyl cellulose is significantly lower than that of methyl cellulose.