HPMC Frequently Asked Questions

I. What are the types of hydroxypropyl methylcellulose (HPMC), and how do their applications differ?

Hydroxypropyl methylcellulose (HPMC) can be mainly divided into two categories: instant-dispersible and hot-melt-dispersible.

Instant-dispersible products can quickly disperse in cold water to form a homogeneous system. Initially, the liquid has no viscosity because it is not yet completely dissolved. After about two minutes, the viscosity of the system gradually increases, eventually forming a transparent, viscous colloid.

Hot-melt-dispersible products need to be dispersed in hot water. As the temperature drops to a specific range, the viscosity gradually forms, eventually resulting in a transparent colloid. This type is generally suitable for putty powder and mortar systems; it is prone to clumping in liquid adhesives or coatings, so it is not suitable for use.

Instant-dispersible types have wider applicability and can be used not only in putty powder and mortar but also in various liquid adhesives and coatings, with no usage restrictions.

II. What are the main application areas of hydroxypropyl methylcellulose (HPMC)?

HPMC is widely used in building materials, coatings, synthetic resins, ceramics, pharmaceuticals, food, textiles, agriculture, cosmetics, and tobacco industries. Based on its application grade, it can be divided into building grade, food grade, and pharmaceutical grade. Currently, building grade is the dominant grade in China. In building grade applications, putty powder accounts for the vast majority of usage (approximately 90%), with the remainder mainly used in cement mortar and adhesive products.

III. What are the common methods for dissolving hydroxypropyl methylcellulose (HPMC)?

Common dissolving methods include hot water dissolution and powder mixing:

Hot water dissolution: Utilizing the property that HPMC is insoluble but dispersible in hot water, it is first uniformly dispersed in hot water, and then dissolved upon cooling. The specific operation is as follows:

Take a portion of the required water (approximately 1/3 to 2/3), heat it to about 70℃, and slowly add HPMC while stirring to form a uniform slurry;

Continue to add the remaining cold water, stirring and cooling until completely dissolved.

Powder mixing: Premix HPMC with a large amount of other powdered raw materials (such as putty powder and fillers in mortar) until uniform, then add water and stir. This method effectively avoids clumping because HPMC is finely dispersed in the system and dissolves instantly in water. This method is commonly used in the production of dry-mix mortar and putty powder.

IV. How to initially judge the quality of HPMC from its appearance and properties?

Apparent density: Higher apparent density usually reflects a denser particle structure, generally indicating better quality.

Color: High-quality products are usually white, but it should be noted that the addition of whitening agents may affect the true quality; therefore, whiteness is only one of the reference indicators.

Fineness: Common fineness is 80 mesh and 100 mesh, with some products reaching 120 mesh. Higher fineness usually indicates better solubility.

Transmittance: After HPMC is dissolved in water to form a transparent colloid, higher transmittance indicates lower insoluble content and generally better purity. Transmittance is affected by the production process but is not the sole basis for judging the overall performance of the product.

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

Hydroxypropyl content and viscosity are two key indicators for evaluating the performance of HPMC. Higher hydroxypropyl content generally results in better water retention; viscosity directly affects the thickening and water retention effects of the system. Generally, higher viscosity indicates better water retention, especially noticeable in cement mortar.

VI. How should the viscosity of HPMC be selected for different applications?

For putty powder applications, a viscosity of approximately 100,000 mPa·s is generally recommended. For mortar, higher viscosity grades, such as 150,000 mPa·s, are suggested to ensure better workability and water retention. It should be noted that HPMC primarily functions as a water-retaining agent in the system, followed by thickening. For putty powder, lower viscosity (e.g., 70,000–80,000 mPa·s) can also be used as long as the water retention requirements are met. When the viscosity is too high, its effect on improving water retention gradually plateaus.

VII. What are the main raw materials used in the production of hydroxypropyl methylcellulose (HPMC)?

The main raw materials for HPMC production include refined cotton, chloromethane, and propylene oxide; auxiliary raw materials typically include caustic soda, acid, toluene, and isopropanol. The purity of raw materials and process control directly affect the performance and quality stability of the final product.