Hypromellose, also known as hydroxypropyl methylcellulose (HPMC), is a polymer derived from cellulose. Due to its multifunctional properties, it is commonly used in a variety of industries, including pharmaceuticals, food and cosmetics. An important property of hypromellose is its viscosity, which varies depending on the grade or type of hypromellose used.

Hypromellose viscosity grades are usually classified according to their molecular weight and degree of substitution. Molecular weight affects polymer chain length, while degree of substitution refers to the extent to which hydroxypropyl and methyl groups are substituted onto the cellulose backbone.

Here are some common viscosity grades of hypromellose and their properties:

1. Low viscosity grade:

Characteristics: Low molecular weight, shorter polymer chains.
Applications: These grades are commonly used as binders in tablet formulations where lower viscosity facilitates better flow and compression.

2. Medium viscosity grade:

Properties: Medium molecular weight, balanced between viscosity and solubility.
Applications: Widely used in pharmaceuticals as matrix formers in controlled-release drug delivery systems, and in the food industry for thickening and gelling.

3. High viscosity grade:

Characteristics: High molecular weight, long polymer chains.
Application: Commonly used in sustained-release preparations and ophthalmic solutions. They provide enhanced gel strength and viscosity.

4. Professional level:

Properties: Custom properties for specific applications.
Applications: Custom grades can be developed to meet the specific requirements of different industries such as ophthalmic formulations, topical applications and controlled release of drugs.

It is worth noting that viscosity is usually measured in units of centipoise (cP) or millipascal seconds (mPa·s). The specific viscosity grade selected for a specific application depends on the desired performance characteristics, such as release profile in pharmaceutical formulations or texture in food products.

When selecting a grade of hypromellose, manufacturers consider factors such as the intended application, desired viscosity, and compatibility with other ingredients. Additionally, regulatory standards and compendial requirements may influence the selection of hypromellose in drug and food formulations.

As with any material, it is critical to follow industry guidelines and specifications when using hypromellose in formulations to ensure product quality and compliance with relevant standards.