Hydroxypropyl methyl cellulose ( HPMC)

Details:

Hydroxy Propyl Methyl Cellulose

Basic chemical information

• Hydroxy Propyl Methyl Cellulose (HPMC for short) is a non-ionic cellulose ether. It is obtained by chemically modifying natural cellulose (such as cotton linter or wood pulp). From a chemical structure perspective, it introduces hydroxypropyl (-CH?CH(OH)CH?) and methyl (-CH?) ether bonds onto the cellulose molecular chain.

• This chemical structure endows it with many unique properties. Its molecular formula can be roughly expressed as, where and represent the degree of substitution, and their values will vary according to the specific specifications of the product.

Physical properties

• Appearance: Usually a white or off-white powder or granular substance. The uniformity of its appearance helps in uniform dispersion in various applications.

• Solubility: It has good water solubility and can form a transparent viscous solution in water. This is because the polar groups such as hydroxyl groups in its molecular structure can form hydrogen bonds with water molecules. It can swell and dissolve in cold water, but the dissolution speed is relatively slow; in hot water, its dissolution process may be hindered by the formation of a gel layer, but proper stirring can promote dissolution.

• Viscosity: The viscosity of HPMC varies depending on the product model and concentration. It can provide multiple choices from low viscosity to high viscosity to meet the needs of different application scenarios. For example, in the construction industry, higher viscosity HPMC can be used to increase the consistency of cement mortar; in some coating applications, lower viscosity products may be used to adjust the rheological properties of coatings.

Chemical properties

• Stability: It has good chemical stability and is relatively stable under general acidic and alkaline environments. However, under strong acidic or alkaline conditions, its molecular chain may undergo hydrolysis reactions, resulting in a decrease in its performance. It also has a certain degree of thermal stability, but at high temperatures, degradation may occur over time.

• Reactivity: Due to the functional groups such as hydroxyl and ether bonds in its molecular structure, it can react with some chemical reagents. For example, it can undergo condensation reactions with aldehyde substances to prepare materials with special properties.

Uses

• Construction industry: It is an important additive for construction materials. In cement mortar, it can play roles such as water retention, thickening, and retardation. The water retention function can prevent cement mortar from losing water too quickly during construction, thereby improving its bonding strength and construction performance; the thickening function can make the mortar have good plasticity and sag resistance, facilitating construction operations. In gypsum products, it can also improve the setting time and strength of gypsum and other properties.

• Paint industry: Used as a thickener, rheology modifier, and stabilizer for coatings. It can adjust the viscosity and rheological properties of coatings, making coatings have good stability during storage and construction. For example, it can prevent precipitation and stratification of coatings during storage, and at the same time, it can make coatings evenly coated on the surface of objects during construction.

• Pharmaceutical industry: In pharmaceutical preparations, it can be used as a binder and coating material for tablets. As a binder, it can bind drug powders into solid tablets; as a coating material, it can control the release rate of drugs, play a sustained-release role, and also protect drugs from the influence of the external environment, such as preventing drugs from being oxidized or dampened.

• Food industry: It is an allowed food additive, mainly used as a thickener, emulsifier, and stabilizer. For example, in some sauces, jellies and other foods, it can increase the viscosity of products and improve the taste; in ice cream and other products, it can prevent the formation of ice crystals and improve the stability and taste of products.

Production method

• It is mainly produced through alkalization-etherification reaction. First, natural cellulose raw materials are alkalized with alkali solution (such as sodium hydroxide) to activate the hydroxyl groups on the cellulose molecules. Then, methylation reagents (such as chloromethane) and hydroxypropylation reagents (such as propylene oxide) are added, and etherification reaction is carried out under certain temperature, pressure and reaction time conditions to introduce methyl and hydroxypropyl groups into the cellulose molecular chain. Finally, HPMC products are obtained through post-treatment (such as neutralization, washing, drying, etc.).