Hydroxypropyl Methylcellulose (HPMC)

Cellulose ether utilized as an emulsifier and thickening agent for colloid dispersion in water.

"HPMC" also relates to other uses; for detailed usage, refer to HPMC (disambiguation).

Chemical compound.

Hypromellose (INN), which stands for hydroxypropyl methylcellulose (HPMC), is a semi-synthetic, inert, viscoelastic polymer commonly found in eye drops and employed as an excipient and controlled-release component in oral medications. This compound appears in a variety of commercial products.^[1][2]

As an additive in food, hypromellose acts as an emulsifier and as a thickening and suspending agent, also serving as a substitute for animal gelatin.^[3] Its Codex Alimentarius code (E number) is E464.

Chemistry

Hypromellose exists as a solid, appearing as a slightly off-white to beige powder and can be formed into granules. It creates colloids when dissolved in water. This ingredient is non-toxic but can combust and react aggressively with oxidizing agents.^[4]

In aqueous solutions, hypromellose, similar to methylcellulose, shows thermal gelation properties—when heated to a specific temperature, it solidifies into a semi-flexible mass. The critical temperature for this reaction is inversely related to both the concentration of HPMC and the methoxy group within its molecular structure. The higher the methoxy concentration, the lower the critical temperature. In contrast, the inflexibility/viscosity of the mass correlates directly with methoxy concentration—higher concentration leads to increased viscosity and reduced flexibility.

Uses

Hypromellose has diverse applications, including:

• Tile adhesives
• Cement renders
• Gypsum products
• Pharmaceuticals
• Paints and coatings
• Food products
• Cosmetics
• Detergents and cleaners
• Eye drops
• Contact lenses
• Polyvinyl Chloride (PVC)^[6]

Use in Whole Grain Breads

Research conducted by Agricultural Service scientists explores the potential of using plant-derived HPMC as a gluten substitute in making all-oat or other grain breads. Gluten is present in wheat and barley but absent in oats, thus gluten-like properties might be achieved with HPMC, trapping air bubbles during fermentation to help the dough rise.

Use in Construction Materials

HPMC is extensively used in the construction sector, especially in tile adhesives and renders, acting as a rheology modifier and water-retaining agent. It performs similarly to Hydroxy Ethyl Methyl Cellulose (HEMC) and is available under trade names like Methocel and Walocel. The leading global manufacturer is DuPont, previously produced by Dow Wolff Cellulosics GmbH.^[8]

Ophthalmic Applications

Hypromellose solutions serve as semi-synthetic substitutes for tear film.^[9] Its molecular configuration, derived from cellulose, is highly soluble in water, thus enhancing visual clarity. Once applied, it swells and absorbs water, thickening the tear film, leading to a prolonged lubricant presence on the cornea and mitigating dryness-related irritation in various environments.^[10]

Because it is a vegetarian alternative to gelatin, hypromellose is slightly costlier to produce due to its semi-synthetic manufacturing process. Despite this, it is widely available over the counter in multiple products, and hypromellose 2% solution has proven effective during surgical procedures for corneal protection.

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Excipient/Tableting Ingredient

Beyond ophthalmic solutions, hypromellose is utilized as an excipient in oral tablet and capsule formulations, where it functions as a controlled-release agent to delay the medicinal ingredient’s release into the digestive tract.^[11] Additionally, hypromellose serves as a binder^[12] and contributes to tablet coatings.^[13][14]

Testing Methods

To qualify hypromellose, various benchmark tests are employed:

• Viscosity
• Degree of Substitution (DS)
• Molar Substitution (MS)
• Salt Content
• Moisture

Viscosity Test Methods

Hypromellose solution is a non-Newtonian fluid exhibiting pseudoplasticity, specifically thixotropic behavior. Different test methods may yield varying results, so viscosity is generally reported as a mean or range. Typical viscosity tests include:

• Solution Concentration (1%, 2%, etc.)
• Viscometer Type (e.g., Brookfield, RheoSense)
• Viscometer Spindle Numbers
• Solution Temperature

Degree of Substitution

The degree of substitution refers to the average level of methoxy substitution on the cellulose chain, measured as a real number between 0 and 3. This value is often represented as a percentage.

Molar Substitution

Molar substitution indicates the average level of hydroxypropoxy substitution on the cellulose, potentially exceeding 3 due to side-chain attachments, but typically expressed as a percentage.

Moisture

Cellulose ethers are hygroscopic and absorb moisture from their environment when unsealed. Hence, moisture content must be measured and adjusted to ensure the adequacy of dry active components. This is typically assessed by weighing a sample, heating it, and re-measuring its weight.

See Also

References

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