The shallow admixture, which plays a key role in improving the performance of building dry-mixed mortar, accounts for more than 40% of the material cost in dry-mixed mortar. Most of the admixtures in the domestic market are supplied by foreign manufacturers, and the reference dosage of the products is also provided by the suppliers. The cost of dry-mixed mortar product remains high thus, and it is difficult to popularize common masonry and plastering mortar with a large amount and a wide range. High-end market products are controlled by foreign companies, and dry-mixed mortar manufacturers have low profits and poor price affordability; the application of admixtures lacks systematic and targeted research, and blindly follows foreign formulas. Here, what we share with you is, what is the role of hydroxypropyl methylcellulose in the common admixtures of dry-mixed mortar?
Hydroxypropyl methylcellulose is a cellulose variety whose output and consumption have been increasing rapidly in recent years. Hydroxypropyl methylcellulose is made of refined cotton after alkalization treatment, using propylene oxide and methyl chloride as etherification agents , a non-ionic cellulose mixed ether made through a series of reactions. The degree of substitution is generally 1.2~2.0. Its properties are different depending on the ratio of methoxyl content and hydroxypropyl content. The characteristics of hydroxypropyl methylcellulose are as follows:
1. Hydroxypropyl methylcellulose is easily soluble in cold water, and 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 solubility in cold water is also greatly improved compared with methyl cellulose.
2. The viscosity of hydroxypropyl methylcellulose is related to its molecular weight. The larger the molecular weight, the higher the viscosity. Temperature also affects its viscosity, as temperature increases, viscosity decreases. However, the influence of its high viscosity and temperature is lower than that of methyl cellulose. Its solution is stable when stored at room temperature.
3. The water retention of hydroxypropyl methylcellulose depends on its addition amount, viscosity, etc., and its water retention rate under the same addition amount is higher than that of methyl cellulose.
4. 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 slightly 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.
5. Hydroxypropyl methylcellulose can be mixed with water-soluble polymers to form a uniform and higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
6. Hydroxypropyl methylcellulose has better enzyme resistance than methylcellulose, and the possibility of enzymatic degradation of its solution is lower than that of methylcellulose.
7. The adhesion of hydroxypropyl methylcellulose to mortar construction is higher than that of methylcellulose.
Post time: May-09-2023