MC is methyl cellulose, which is obtained by treating refined cotton with alkali, using methyl chloride as an etherifying agent, and making cellulose ether through a series of reactions. Generally, the degree of substitution is 1.6~2.0, and the solubility is also different with different degrees of substitution. Belongs to non-ionic cellulose ether.
(1) The water retention of methyl cellulose depends on its addition amount, viscosity, particle fineness and dissolution rate. Generally, if the amount of addition 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 influence on the water retention rate, and the level of viscosity is not proportional to the level of water retention rate. 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 higher water retention rates.
(2) Methylcellulose is soluble in cold water, but difficult to dissolve in hot water, and 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, the phenomenon of gelation occurs.
(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 mortar temperature exceeds 40 °C, the water retention of methyl cellulose will be significantly worse, which will seriously affect the workability of the mortar.
(4) Methyl cellulose has a significant effect on the workability and adhesion of mortar. “Adhesion” here refers to the adhesion felt between the worker’s applicator 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, and the force required by the workers in the use process is also large, and the construction of the mortar is poor. Methylcellulose adhesion is at a moderate level in cellulose ether products.
HPMC is hydroxypropyl methyl cellulose, which is a non-ionic cellulose mixed ether made from refined cotton after alkali treatment, using propylene oxide and methyl chloride as etherifying agents, and through a series of reactions. The degree of substitution is generally 1.2 to 2.0. Its properties vary depending on the proportion of methoxyl content and hydroxypropyl content.
(1) Hydroxypropyl methylcellulose is easily soluble in cold water, but it will encounter difficulties in dissolving in hot water. But its gelation temperature in hot water is significantly higher than that of methyl cellulose. The dissolution in cold water is also greatly improved compared with methyl cellulose.
(2) The viscosity of hydroxypropyl methylcellulose is related to the size of its molecular weight, and the larger the molecular weight, the higher the viscosity. Temperature also affects its viscosity, as temperature increases, viscosity decreases. But its viscosity is less affected by high temperature than methyl cellulose. Its solution is stable on storage at room temperature.
(3) 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 the viscosity. 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.
(4) The water retention of hydroxypropyl methylcellulose depends on its addition amount, viscosity, etc. The water retention rate under the same addition amount is higher than that of methyl cellulose.
(5) Hydroxypropyl methylcellulose can be mixed with water-soluble polymer compounds to form a solution with uniform and higher viscosity. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
(6) The adhesion of hydroxypropyl methylcellulose to mortar construction is higher than that of methylcellulose.
(7) Hydroxypropyl methylcellulose has better resistance to enzymes than methylcellulose, and its solution enzymatic degradation possibility is lower than that of methylcellulose.
Post time: Apr-28-2024