10 Questions About Hydroxypropyl Methylcellulose (HPMC)

Industrial grade hydroxypropyl methylcellulose used in mortar is divided by viscosity. The following grades are commonly used (unit is viscosity).

Low viscosity: 400 is mainly used for self-leveling mortar, but it is generally imported.Reason: Low viscosity, although the water retention is poor, but the leveling property is good, and the mortar has high density.

Medium and low viscosity: 20000-40000 is mainly used for tile adhesive, caulking agent, anti-cracking mortar, thermal insulation bonding mortar, etc. Reason: Good construction performance, less water addition, and high mortar density.

Q1. What is the main use of hydroxypropyl methylcellulose (HPMC)?

A：HPMC is widely used in building materials, coatings, synthetic resins, ceramics, medicine, food, textiles, agriculture, cosmetics, tobacco and other industries. HPMC can be divided into: construction grade, food grade and pharmaceutical grade according to its use. At present, most of the domestic products are construction grade. Among the construction grade, the amount of putty powder is very large, about 90% is used to make putty powder, and the rest is used for cement mortar and glue.

Q2. How many types of hydroxypropyl methylcellulose (HPMC) are there and what are the differences in their uses?

A：HPMC can be divided into instant and hot-soluble types. Instant products disperse quickly in cold water and disappear in the water. At this time, the liquid has no viscosity because HPMC is only dispersed in the water and not really dissolved. After about 2 minutes, the viscosity of the liquid gradually increases, forming a transparent viscous colloid. Hot-soluble products clump together in cold water and can disperse quickly and disappear in hot water. When the temperature drops to a certain temperature, the viscosity slowly appears until a transparent viscous colloid is formed. Hot-soluble products can only be used in putty powder and mortar. In liquid glue and paint, they will clump together and cannot be used. Instant type has a wider range of applications. It can be used in putty powder and mortar, as well as liquid glue and paint, without any taboos.

Q3. What are the dissolution methods of hydroxypropyl methylcellulose (HPMC)?

A：Hot water dissolution method: Since HPMC does not dissolve in hot water, HPMC can be evenly dispersed in hot water at the beginning, and then quickly dissolve when cooled. Two typical methods are described as follows:

1) Put the required amount of hot water in the container and heat it to about 70℃. Add hydroxypropyl methylcellulose gradually under slow stirring. HPMC will float on the surface of the water at first, and then gradually form a slurry. Cool the slurry under stirring.

2) Add 1/3 or 2/3 of the required amount of water to the container and heat it to 70℃. Disperse HPMC according to method 1) to prepare hot water slurry; then add the remaining amount of cold water to the hot water slurry, stir and cool the mixture.

Powder mixing method: Mix HPMC powder with a large amount of other powdered ingredients with a mixer, and then add water to dissolve. At this time, HPMC can be dissolved without agglomeration, because there is only a little HPMC powder in each tiny corner, which will dissolve immediately when it encounters water. ——Putty powder and mortar manufacturers use this method. [ Hydroxypropyl methylcellulose (HPMC) is used as a thickener and water-retaining agent in putty mortar. ]

Q4. What is the appropriate viscosity of hydroxypropyl methylcellulose (HPMC)?

A：Generally, 100,000 is enough for putty powder, but 150,000 is required for mortar. Moreover, the most important function of HPMC is water retention, followed by thickening. In putty powder, as long as the water retention is good, a lower viscosity (70,000-80,000) is also acceptable. Of course, the higher the viscosity, the better the water retention. When the viscosity exceeds 100,000, the viscosity has little effect on water retention.

Q5. What are the main technical indicators of hydroxypropyl methylcellulose (HPMC)?

A：Hydroxypropyl content and viscosity, most users are concerned about these two indicators. The higher the hydroxypropyl content, the better the water retention. The higher the viscosity, the better the water retention, relatively (not absolutely), and the higher the viscosity, the better it is to use in cement mortar.

Q6. What is the main role of HPMC in putty powder? Does it cause any chemical reaction?

A：HPMC plays three roles in putty powder: thickening, water retention and construction. Thickening: Cellulose can thicken and suspend the solution, keep it uniform and consistent, and resist sagging. Water retention: Make the putty powder dry slower and assist the lime calcium to react under the action of water. Construction: Cellulose has a lubricating effect, which can make the putty powder have good construction properties. HPMC does not participate in any chemical reaction, but only plays an auxiliary role. Putting water on the putty powder and putting it on the wall is a chemical reaction because new substances are generated. If the putty powder on the wall is taken off the wall and ground into powder, it will not work because new substances (calcium carbonate) have been formed. The main components of lime calcium powder are: a mixture of Ca(OH)2, CaO and a small amount of CaCO3, CaO+H2O=Ca(OH)2—Ca(OH)2+CO2=CaCO3↓+H2O. Under the action of water and CO2 in the air, lime calcium generates calcium carbonate, while HPMC only retains water and assists lime calcium to react better, and it does not participate in any reaction itself.

Q7. What does the gel temperature of hydroxypropyl methylcellulose depend on?

A：The gelation temperature of HPMC is related to its methoxy content. The lower the methoxy content, the higher the gelation temperature.

Q8. How to choose the appropriate hydroxypropyl methylcellulose (HPMC) for different uses?

A：Application of putty powder: The requirements are relatively low, and a viscosity of 100,000 is sufficient. The important thing is to retain water well. Application of mortar: The requirements are relatively high, and high viscosity is required. 150,000 is better. Application of glue: Instant products are required, and the viscosity should be high.

Q9. What is the formula for interior and exterior wall putty powder?

A：Interior wall putty powder: heavy calcium 800KG, gray calcium 150KG (starch ether, pure blue, penrun clay, citric acid, polyacrylamide, etc. can be added appropriately) Exterior wall putty powder: cement 350KG, heavy calcium 500KG, quartz sand 150KG, latex powder 8-12KG, cellulose ether 3KG, starch ether 0.5KG, wood fiber 2KG.

Q10. What is the relationship between the viscosity and temperature of HPMC? What should be paid attention to in practical applications?

A：The viscosity of HPMC is inversely proportional to the temperature, that is, the viscosity increases as the temperature decreases. When we usually say the viscosity of a product, we mean the test result of its 2% aqueous solution at a temperature of 20 degrees Celsius. 

In practical applications, in areas with large temperature differences between summer and winter, it should be noted that it is recommended to use a relatively low viscosity in winter, which is more conducive to construction. Otherwise, when the temperature is low, the viscosity of cellulose will increase, and it will feel heavy when scraping. Medium viscosity: 75000-100000 Mainly used for putty Reason: good water retention High viscosity: 150000-200000 Mainly used for polystyrene particle insulation mortar glue powder and glass bead insulation mortar. Reason: high viscosity, mortar is not easy to fall or sag, which improves construction. But generally speaking, the higher the viscosity, the better the water retention. Therefore, many dry mortar factories use medium viscosity cellulose (75000-100000) instead of medium and low viscosity cellulose (20000-40000) to reduce the amount added due to cost considerations.