Classification and characterization of cellulose

1, methyl cellulose (MC) molecular formula \[C6H7O2(OH)3-h(OCH3)n]x refined cotton after alkali treatment, with chlorinated methane as etherification agent, after a series of reactions to make cellulose ether.Generally, the degree of substitution is 1.6~2.0, and the solubility varies with the degree of substitution.Nonionic cellulose ether.
1.Methylcellulose is soluble in cold water, which is difficult to dissolve in hot water, and its aqueous solution is very stable in the pH range of 3~12.It has good compatibility with starch, guar gum and many surfactants.Gelation occurs when the temperature reaches the gelation temperature.
2.The water retention of methyl cellulose depends on its additive amount, viscosity, particle fineness and dissolution rate.Generally large amount of addition, small fineness, viscosity, water retention rate is high.The amount of addition has the greatest influence on the water retention rate, and the viscosity is not proportional to the water retention rate.The dissolution rate mainly depends on the degree of surface modification and fineness of cellulose particles.In the above cellulose ether, methyl cellulose and hydroxypropyl methyl cellulose water retention rate is higher.
3.The change of temperature will seriously affect the water retention rate of methyl cellulose.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 mortar construction.
4.Methyl cellulose has obvious influence on the construction and adhesion of mortar.The "stickiness" here refers to the adhesive force felt by the workers between the smudge tool and the wall substrate, that is, the shear resistance of the mortar.The adhesion is big, the shear resistance of mortar is big, the strength that the worker needs in the use process is big also, the construction sex of mortar is bad.In cellulose ether products, the adhesion of methyl cellulose is at a medium level.
Hydroxypropyl methyl cellulose (HPMC)\[C6H7O2(OH)3-m-n(OCH3)m,OCH2CH(OH)CH3\ n\]x hydroxypropyl methyl cellulose (HPMC) is a cellulose variety whose yield and dosage are increasing rapidly in recent years.It is a kind of non-ionic cellulose mixed ether made by a series of reactions after the alkalization treatment of refined cotton with propylene oxide and methane chloride as etherification agent.The degree of substitution is generally 1.2~2.0.Its property is affected by the proportion of methoxy content and hydroxypropyl content is different, and have difference.
1.Hydroxypropyl methyl cellulose soluble in cold water, hot water solution will encounter difficulties.However, its gelation temperature in hot water was significantly higher than that of methyl cellulose.The dissolution in cold water, compared with methyl cellulose also has a great improvement.
2.The viscosity of hydroxypropyl methyl cellulose is related to its molecular weight.Temperature will also affect its viscosity, temperature increases, viscosity decreases.But the effect of high viscosity and temperature is lower than that of methyl cellulose.The solution is stable when stored at room temperature.
3.The water retention of hydroxypropyl methyl cellulose depends on its addition amount, viscosity, and so on.
4.Hydroxypropyl methyl cellulose is stable to acid and alkali, and its aqueous solution is very stable in the range of pH=2~12.Caustic soda and lime water have little effect on its properties, but alkali can accelerate its dissolution rate and improve the viscosity pin.Hydroxypropyl methyl cellulose has stability to general salts, but when the salt solution concentration is high, hydroxypropyl methyl cellulose solution viscosity has the tendency to increase.
5.Hydroxypropyl methyl cellulose can be mixed with water soluble polymer compounds into a uniform, higher viscosity solution.Such as polyvinyl alcohol, starch ether, plant gum, etc.
6.Hydroxypropyl methyl cellulose has better resistance to enzymes than methyl cellulose, the possibility of degradation of the solution enzyme is lower than methyl cellulose, hydroxypropyl methyl cellulose to mortar construction adhesion is higher than methyl cellulose.
Iii. Hydroxyethyl cellulose (HEC) is prepared from refined cotton treated with alkali and reacted with ethylene oxide as etherification agent in the presence of acetone.The degree of substitution is generally 1.5~2.0.With strong hydrophilic, easy to absorb moisture.
1.Hydroxyethyl cellulose soluble in cold water, hot water solution is more difficult.The solution is stable at high temperature and does not gel.It can be used for a long time under high temperature in mortar, but its water retention is lower than that of methyl cellulose.
2.Hydroxyethyl cellulose for general acid and base have stability, alkali can speed up its dissolution, and slightly improve the viscosity, its dispersibility in water than methyl cellulose and hydroxypropyl methyl cellulose slightly worse.
3.Hydroxyethyl cellulose has a good performance in mortar anti-hanging, but the slow setting time of cement is longer, some domestic enterprises produced hydroxyethyl cellulose, due to the large water content, high ash content and its performance is significantly lower than methyl cellulose.
Carboxymethyl cellulose (CMC) \[C6H7O2(OH)2och2COONa\]n by natural fiber (cotton, etc.) after alkali treatment, using sodium chloroacetate as etherification agent, after a series of reactions to make ionic cellulose ether.Its degree of substitution is generally 0.4~1.4, and its performance is greatly affected by the degree of substitution.
1.Carboxymethyl cellulose hygroscopicity is bigger, general condition store can contain bigger moisture.
2.Carboxymethyl cellulose solution will not produce gel, with the rise of temperature and viscosity decline, temperature more than 50℃, viscosity irreversible.
3.Its stability is greatly affected by pH.Generally can be used in gypsum - based mortar, can not be used in cement - based mortar.At high alkalinity, viscosity is lost.
4.Its water retention is much lower than methyl cellulose.It can slow the setting of gypsum mortar and reduce its strength.But the price of carboxymethyl cellulose is significantly lower than that of methyl cellulose.


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