hydroxypropyl methylcellulose HPMC in Plastering MortarFebruary 2nd 2023
The shallow admixture, which plays a key role in improving the performance of building dry-mix mortar, accounts for more than 40% of the material cost in dry-mix mortar. Most additives in the domestic market are supplied by foreign manufacturers, and the reference dosage of products is also provided by the suppliers. As a result, the cost of dry-mixed mortar products is high, and it is difficult to promote large-scale and general masonry and plastering mortar. Products in the high-end market are controlled by foreign companies. Dry-mix mortar manufacturers have low profits and poor price tolerance. The application of admixtures lacks systematic and targeted research and blindly follows foreign formulations. Here, I would like to share with you what is the role of hydroxypropyl methylcellulose in the commonly used admixtures of dry-mix mortar?
Hydroxypropyl methylcellulose is a cellulose variety whose output and dosage have been increasing rapidly in recent years. Shandong SLEO Chemical Technology Co., Ltd. Hydroxypropyl methylcellulose is made of refined cotton after alkali treatment, using propylene oxide and methyl chloride are used as etherifying agents, a non-ionic cellulose mixed ether made by a series of reactions. The degree of substitution is generally 1.2~2.0. Its properties are different depending on the ratio of methoxy content and hydroxypropyl content. The characteristics of hydroxypropyl methyl cellulose are as follows:
1. Hydroxypropyl methylcellulose is easy to dissolve in cold water, and it will be difficult to dissolve 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 to methyl cellulose.
Second, the viscosity of hydroxypropyl methylcellulose is related to the size of its molecular weight, and the higher the molecular weight, the higher the viscosity. Temperature also affects its viscosity. As the temperature increases, the viscosity decreases. However, the effect of high viscosity and temperature is lower than that of methyl cellulose. The solution is stable when stored at room temperature.
3. The water retention of hydroxypropyl methylcellulose depends on its added amount, viscosity, etc. The water retention rate at the same amount is higher than that of methylcellulose.
4. Hydroxypropyl methylcellulose is stable to acid and alkali. Hydroxypropyl methylcellulose , 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 accelerate its dissolution rate and slightly increase the viscosity. Hydroxypropyl methylcellulose is stable to general salts, but when the salt solution concentration is high, the viscosity of the hydroxypropylmethyl cellulose solution tends to increase.
5. Hydroxypropyl methylcellulose can be mixed with water-soluble polymer compounds to form a uniform and higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
6. hydroxypropyl methylcellulose has better resistance to enzymes than methylcellulose, and the possibility of enzymatic degradation of its solution is lower than that of methylcellulose.
7. The adhesion of hydroxypropyl methyl cellulose to mortar construction is higher than that of methyl cellulose.