MC is methyl cellulose, which is obtained by subjecting refined cotton to alkali treatment and then using MC as an etherifying agent to form a cellulose ether through a series of reactions. The degree of substitution is generally 1.6 to 2.0, and the degree of substitution differs depending on the solubility. It belongs to nonionic cellulose ether.
(1) The water retention of MC depends on the amount of addition, viscosity, particle fineness and dissolution rate.
Generally, The addition amount has the greatest influence on the water retention rate, and the viscosity level is not proportional to the water retention rate. The rate of dissolution depends mainly on the degree of surface modification of the cellulose particles and the fineness of the particles.
Among the above cellulose ethers, methylcellulose and hydroxypropylmethylcellulose have a high water retention rate.
(2) MCis soluble in cold water, and it is difficult to dissolve in hot water.
The aqueous solution is very stable in the range of pH=3~12. It has good compatibility with starch, guar gum and many other surfactants.
(3) The change of temperature will seriously affect the water retention rate of MC.
Generally, the higher the temperature, the worse the water retention. If the temperature of the mortar exceeds 40 ℃, the water retention of methyl cellulose will be significantly deteriorated.
(4) MC has a significant effect on the workability and adhesion of the mortar.
“Adhesiveness” herein refers to the adhesive force felt between the worker’s application tool and the wall substrate, MC adhesion is intermediate in cellulose ether products.
HPMC is hydroxypropyl methyl cellulose, which is a nonionic cellulose mixed ether prepared by a series of reactions using acetal oxide and methyl chloride as an etherifying agent after alkalization of refined cotton. The degree of substitution is generally 1.2 to 2.0.
Its properties are different depending on the ratio of methxyl content and hydroxypropyl content.
(1) The dissolution in cold water is much better than MC.
Hydroxypropyl methyl cellulose is easily soluble in cold water, and it may be difficult to dissolve in hot water. However, its gelation temperature in hot water is significantly higher than that of methyl cellulose.
(2) The viscosity of HPMC is related to the molecular weight thereof,
when the viscosity is high and the molecular weight is large. The temperature also affects its viscosity, the temperature rises, and the viscosity decreases. However, its viscosity has a lower temperature than methyl cellulose.
(3) Hydroxypropyl methyl cellulose is stable to acids and bases, and its aqueous solution is very stable in the range of pH=2~12.
Caustic soda and lime water do not have much effect on their properties, but alkali accelerates their dissolution rate and increases viscosity. Hydroxypropyl methyl cellulose has stability to general salts, but when the concentration of the salt solution is high, the viscosity of the hydroxypropyl methyl cellulose solution tends to increase.
(4)The water retention rate under the same amount is higher than that of MC.
The water retention of hydroxypropyl methyl cellulose depends on the amount of addition, viscosity, etc.,
(5) HPMCcan be mixed with a water-soluble polymer compound to form a uniform, higher viscosity solution.
Such as polyvinyl alcohol, starch ether, vegetable gum and the like.