MC is methyl cellulose: is refined cotton after alkali treatment, methane chloride as etherifying agent, through 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. Belongs to nonionic cellulose ether.
(1) The water retention of methyl cellulose depends on its addition amount, viscosity, particle fineness and dissolution rate. Generally add large amount, small fineness, viscosity, water retention rate is high. The amount of additives has a great influence on the water retention rate, and the viscosity is not proportional to the water retention rate. The dissolution rate mainly depends on the surface modification degree and particle fineness of cellulose particles. In the above several cellulose ethers, methyl cellulose and HPMC hydroxypropyl methyl cellulose water retention rate is higher.
(2) Methyl cellulose is soluble in cold water, which is difficult to dissolve in hot water. Its aqueous solution is very stable within the pH=3~12. It has good compatibility with starch, guanidine gum and many surfactants. Gelation occurs when the temperature reaches gelation temperature.
(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 temperature of mortar exceeds 40℃, the water retention of methyl cellulose will be significantly worse, which seriously affects the constructability of mortar.
(4) Methyl cellulose has obvious influence on the constructability and adhesion of mortar. “Adhesion” here refers to the adhesion felt by the worker between the tool and the wall substrate, namely the shear resistance of the mortar. Adhesion is large, the shear resistance of mortar is large, the strength required by workers in the process of use is also large, and the construction of mortar is poor. In cellulose ether products, the adhesion of methyl cellulose is at a moderate level.
HPMC is hydroxypropyl methyl cellulose: it is made of refined cotton after alkali treatment, with propylene oxide and chloromethane as etherifying agent, through a series of reactions and made of non-ionic cellulose mixed ether. The degree of substitution is generally 1.2~2.0. Its properties vary with the proportion of methoxy and hydroxypropyl content.
(1) HPMC hydroxypropyl methyl cellulose is easily soluble in cold water, which is difficult to dissolve in hot water. However, its gelation temperature in hot water is obviously higher than that of methyl cellulose. The solubility of methyl cellulose in cold water was also improved greatly.
(2) The viscosity of HPMC hydroxypropyl methyl cellulose is related to its molecular weight, and the higher the molecular weight, the higher the viscosity. Temperature also affects viscosity. Viscosity decreases as temperature increases. But its viscosity high temperature effect is lower than that of methyl cellulose. The solution is stable when stored at room temperature.
(3) HPMC hydroxypropyl methyl cellulose is stable to acid and base, 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. HPMC hydroxypropyl methyl cellulose is stable to general salts, but when the concentration of salt solution is high, the viscosity of HPMC hydroxypropyl methyl cellulose solution tends to increase.
(4) The water retention of HPMC hydroxypropyl methyl cellulose depends on its dosage and viscosity, and the water retention rate of HPMC hydroxypropyl methyl cellulose is higher than that of methyl cellulose at the same dosage.
(5) HPMC hydroxypropyl methyl cellulose can be mixed with water-soluble polymer compounds to become uniform, higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable glue and so on.
(6) The adhesion of HPMC hydroxypropyl methyl cellulose to mortar construction is higher than that of methyl cellulose.
(7) HPMC hydroxypropyl methyl cellulose has better enzyme resistance than methyl cellulose, and its solution enzyme degradation possibility is lower than that of methyl cellulose.
Post time: May-26-2022