Views: 3 Author: Site Editor Publish Time: 2022-11-03 Origin: Site
Hydroxypropyl methylcellulose and methylcellulose
1. Hydroxypropyl methylcellulose
Hydroxypropyl methylcellulose is a non-ionic cellulose mixed ether prepared by a series of reactions after alkali treatment of refined cotton, using propylene oxide and methyl chloride as etherifying agents. Its properties are differentiated by the ratio 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 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.
(3) The viscosity of hydroxypropyl methylcellulose is related to the size of its molecular weight. 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.
(4) Hydroxypropyl methylcellulose is stable to acid and alkali, and its aqueous solution is very stable in the range of pH=2~12. 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.
(5) The adhesion of hydroxypropyl methyl cellulose to mortar construction is higher than that of methyl cellulose.
(6) Hydroxypropyl methylcellulose has better resistance to enzymes than methylcellulose, and its solution enzymatic degradation possibility is lower than that of methylcellulose.
(7) Hydroxypropyl methylcellulose can be mixed with water-soluble polymer compounds to form a solution with a uniform and higher viscosity.
Methyl cellulose is made of cellulose ether by treating refined cotton with alkali, using methyl chloride as an etherifying agent, and 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 a great 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) 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.
(3) 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. When the temperature reaches the gelation temperature, the phenomenon of gelation occurs.
(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.
Usually only one type is used in dry powder mortar, which is usually added as a water-retaining agent, and the effect is basically the same. The specific effect should be tested by yourself.