Hydroxypropylmethylcellulose (HPMC) is a cellulose ether widely used in several industries such as pharmaceuticals, cosmetics, food, and construction. Due to its versatility and beneficial properties, HPMC has become a popular ingredient in various formulations. Currently, there are several types of HPMCs on the market, each with unique properties and applications.
HPMC is a chemically modified cellulose polymer obtained by reacting cellulose with methyl chloride and propylene oxide. This reaction introduces methyl and hydroxypropyl groups into the cellulose structure, forming a water-soluble, non-ionic and high-performance polymer. However, different HPMC types have different degrees of substitution (DS) of methyl and hydroxypropyl groups, which determine their physical and chemical properties.
Generally, HPMC products are classified according to viscosity and DS value. Viscosity is an important property of HPMC as it affects the product’s solubility, film forming ability and thickening ability. On the other hand, the DS value determines the degree of polymer substitution and thus the degree of hydrophobicity of the HPMC type. Therefore, different HPMC types are derived through variations in their viscosity and DS values. Below are the most common types of HPMC and how they differ.
1. Ordinary grade HPMC
Common grade HPMC has a methyl DS ranging from 0.8 to 2.0 and a hydroxypropyl DS ranging from 0.05 to 0.3. This type of HPMC is available in a wide range of viscosity grades from 3cps to 200,000cps. Common grade HPMC has good solubility in water and forms clear solutions, making it suitable for various applications in the food, pharmaceutical and cosmetic industries. Such HPMCs are commonly used as film formers, thickeners, emulsifiers and stabilizers in food and cosmetics.
2. Low substitution HPMC
Low-substituted HPMC has a lower degree of methyl and hydroxypropyl substitution than regular grade HPMC. This particular type of HPMC has a methyl DS ranging from 0.2 to 1.5 and a hydroxypropyl DS ranging from 0.01 to 0.2. Low substitution HPMC products have lower viscosity, usually between 3-400cps, and are highly resistant to salt and enzymes. These properties make low-substitution HPMC suitable for food products such as dairy, bakery and meat products. In addition, low-substituted HPMC is also used as a binder, disintegrant and tablet coating agent in the pharmaceutical industry.
3. High replacement HPMC
High degree of substitution HPMC has a higher degree of methyl and hydroxypropyl substitution than ordinary grade HPMC. This type of HPMC has a methyl DS ranging from 1.5 to 2.5 and a hydroxypropyl DS ranging from 0.1 to 0.5. Highly substituted HPMC products have higher viscosity, ranging from 100,000cps to 200,000cps, and have strong water retention properties. These properties make highly substituted HPMC ideal for use in the construction sector, such as cement-based products, coatings and adhesives. Highly substituted HPMC is also used as a binder, thickener and release agent in the pharmaceutical industry.
4. Methoxy-Ethoxy HPMC
Methoxy-Ethoxy HPMC is a specially designed type of HPMC with a high degree of ethoxy substitution. The ethoxy groups increase the hydrophobicity of HPMC, making it less soluble in water than regular grade HPMC. With a methyl DS ranging from 1.5 to 2.5 and an ethoxy DS ranging from 0.4 to 1.2, methoxy-ethoxy HPMC is ideal for use in oil-based products such as cosmetics, paints and coatings. This type of HPMC forms a stable and uniform film that provides a smooth, glossy finish to the final product.
5. Granular HPMC
Granular HPMC is a type of HPMC that has a small particle size, typically between 100-200 microns. Granular HPMC is used in the pharmaceutical industry as a tablet binder, disintegrant and sustained release agent. The small particle size of HPMC particles allows for an even distribution of ingredients, resulting in a consistent and reliable product. Granular HPMC has a methyl DS ranging from 0.7 to 1.6 and a hydroxypropyl DS ranging from 0.1 to 0.3.
Hydroxypropylmethylcellulose (HPMC) is a multifunctional polymer with a wide range of applications in various industries. HPMC types are classified according to viscosity and DS value, which determine their physical and chemical properties. Regular grade HPMC, low substitution HPMC, high substitution HPMC, methoxyethoxy HPMC and granular HPMC are the most common types of HPMC. Understanding the differences between these types will allow formulators to exploit the full potential of HPMCs to produce high quality and potent end products.