Methylcellulose (MC)
The molecular formula of methylcellulose (MC) is:
[C6H7O2(OH)3-h(OCH3)n\]x
The production process is to make cellulose ether through a series of reactions after the refined cotton is treated with alkali, and methyl chloride is used as etherification agent. Generally, the degree of substitution is 1.6~2.0, and the solubility is also different with different degrees of substitution. It belongs to non-ionic cellulose ether.
Methylcellulose is soluble in cold water, and it will be difficult to dissolve in hot water. Its aqueous solution is very stable in the range of pH=3~12.
It has good compatibility with starch, guar gum, etc. and many surfactants. When the temperature reaches the gelation temperature, gelation occurs.
The water retention of methylcellulose depends on its addition amount, viscosity, particle fineness and dissolution rate.
Generally, if the addition amount is large, the fineness is small, and the viscosity is large, the water retention rate is high. Among them, the amount of addition has the greatest impact on the water retention rate, and the level of viscosity is not directly proportional to the level of water retention rate. The dissolution rate mainly depends on the degree of surface modification of cellulose particles and particle fineness.
Among the above cellulose ethers, methyl cellulose and hydroxypropyl methyl cellulose have higher water retention rates.
Carboxymethylcellulose (CMC)
Carboxymethyl cellulose, also known as sodium carboxymethyl cellulose, commonly known as cellulose, cmc, etc., is an anionic linear polymer, a sodium salt of cellulose carboxylate, and is renewable and inexhaustible. Chemical raw materials.
It is mainly used in detergent industry, food industry and oil field drilling fluid, and the amount used in cosmetics only accounts for about 1%.
Ionic cellulose ether is made from natural fibers (cotton, etc.) after alkali treatment, using sodium monochloroacetate as etherification agent, and undergoing a series of reaction treatments.
The degree of substitution is generally 0.4~1.4, and its performance is greatly affected by the degree of substitution.
CMC has excellent binding ability, and its aqueous solution has good suspending ability, but there is no real plastic deformation value.
When the CMC dissolves, depolymerization actually occurs. The viscosity starts to rise during dissolution, passes through a maximum, and then drops to a plateau. The resulting viscosity is related to depolymerization.
The degree of depolymerization is closely related to the amount of poor solvent (water) in the formulation. In a poor solvent system, such as a toothpaste containing glycerin and water, CMC will not completely depolymerize and will reach an equilibrium point.
In the case of a given water concentration, the more hydrophilic highly substituted CMC is easier to depolymerize than the low substituted CMC.
Hydroxyethylcellulose (HEC)
HEC is made by treating refined cotton with alkali, and then reacting with ethylene oxide as etherification agent in the presence of acetone. The degree of substitution is generally 1.5~2.0. It has strong hydrophilicity and is easy to absorb moisture.
Hydroxyethyl cellulose is soluble in cold water, but it is difficult to dissolve in hot water. Its solution is stable at high temperature without gelling.
It is stable to common acids and bases. Alkalis can accelerate its dissolution and slightly increase its viscosity. Its dispersibility in water is slightly worse than that of methyl cellulose and hydroxypropyl methyl cellulose.
Hydroxypropyl Methyl Cellulose (HPMC)
The molecular formula of HPMC is:
\[C6H7O2(OH)3-m-n(OCH3)m,OCH2CH(OH)CH3\]n\]x
Hydroxypropyl methylcellulose is a cellulose variety whose output and consumption are increasing rapidly.
It is a non-ionic cellulose mixed ether made from refined cotton after alkalization, using propylene oxide and methyl chloride as etherification agent, through a series of reactions. The degree of substitution is generally 1.2~2.0.
Its properties are different due to the different ratios of methoxyl content and hydroxypropyl content.
Hydroxypropyl methylcellulose is easily soluble in cold water, but it will encounter difficulty in dissolving in hot water. But its gelation temperature in hot water is significantly higher than that of methyl cellulose. The solubility in cold water is also greatly improved compared with methyl cellulose.
The viscosity of hydroxypropyl methylcellulose is related to its molecular weight, and the larger the molecular weight, the higher the viscosity. Temperature also affects its viscosity, as temperature increases, viscosity decreases. However, its high viscosity has a lower temperature effect than methyl cellulose. Its solution is stable when stored at room temperature.
The water retention of hydroxypropyl methylcellulose depends on its addition amount, viscosity, etc., and its water retention rate at the same addition amount is higher than that of methyl cellulose.
Hydroxypropyl methylcellulose 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 performance, but alkali can speed up its dissolution and increase its viscosity.
Hydroxypropyl methylcellulose is stable to common salts, but when the concentration of salt solution is high, the viscosity of hydroxypropyl methylcellulose solution tends to increase.
Hydroxypropyl methylcellulose can be mixed with water-soluble polymer compounds to form a uniform and higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
Hydroxypropyl methylcellulose has better enzyme resistance than methylcellulose, and its solution is less likely to be enzymatically degraded than methylcellulose
Post time: Feb-14-2023