Hydroxypropyl Methylcellulose (HPMC) is a common semi-synthetic polymer material and a cellulose derivative. It is a non-ionic water-soluble polymer made by chemically modifying natural cellulose. The preparation process of HPMC usually includes the following steps: alkalizing cellulose by alkali treatment, and then reacting with propylene oxide and methyl chloride under alkaline conditions to generate hydroxypropyl and methyl substituents to form HPMC.

Chemical structure and properties of HPMC
The basic structural unit of HPMC is β-D-pyranose glucose, which is also the basic structural unit of cellulose. In HPMC, some hydroxyl groups (-OH) are replaced by methoxy groups (-OCH?) and hydroxypropoxy groups (-OCH?CHOHCH?), so its structure is different from that of natural cellulose. This substitution improves the solubility of HPMC in water and certain organic solvents, and has good stability and low hygroscopicity.

When HPMC is dissolved in water, it can form a stable colloidal solution. Its solubility is related to the type and degree of substitution of the substituent. Generally speaking, HPMC with a higher content of methyl substituents has better solubility in cold water, while HPMC with a higher content of hydroxypropyl has better solubility in warm water. In addition, HPMC solutions have reversible thermogel properties, that is, they gel when heated and dissolve again when cooled.

Application fields of HPMC
Due to its unique chemical structure and physicochemical properties, HPMC has been widely used in many fields.

Building materials: In building materials, HPMC is usually used as a thickener and water retaining agent to improve the construction performance of cement and gypsum-based materials and the quality of the final product. It can also improve the adhesion, crack resistance and durability of mortar.

Medicine: The application of HPMC in the pharmaceutical field mainly includes controlled release coating materials, capsule shells and thickeners for tablets. Because HPMC is non-toxic, non-irritating and has good biocompatibility, it is widely used in sustained-release and controlled-release preparations of tablets.

Food: In the food industry, HPMC is used as a thickener, stabilizer and emulsifier in the production of a variety of foods, such as ice cream, jelly, yogurt, etc. It can improve the texture and taste of food and extend the shelf life of food.

Cosmetics: In the field of cosmetics, HPMC is often used as a thickener for emulsions, creams and gels. It not only provides a good texture, but also forms a moisturizing film on the skin surface, thereby playing a moisturizing and protective role.

Coatings: HPMC is used as a thickener, dispersant and emulsifier in coatings, which can improve the construction performance of coatings and improve the leveling and gloss of coatings.

Advantages and limitations of HPMC
HPMC has many advantages, such as good water solubility, chemical stability, non-toxicity and biocompatibility. These characteristics have made it widely used in many fields. However, HPMC also has some limitations. For example, under high temperature environment, the viscosity of HPMC will drop significantly, which may become a problem in some applications. In addition, HPMC has poor stability in high concentration salt solutions, which also limits its application in some special environments.

HPMC is a very important functional polymer. With its unique physical and chemical properties and good application performance, it has been widely used in construction, medicine, food, cosmetics and coatings. Although it has some limitations, the application field of HPMC is still expanding through continuous research and improvement. With the development of science and technology, HPMC is expected to play an important role in more emerging fields.