Description
Hydroxypropyl methylcellulose, commonly known as HPMC, is a semisynthetic polymer derived from cellulose. It is a non-toxic, off-white to beige powder that is widely used in various industries due to its excellent thickening, binding, and film-forming properties.
Chemical Properties and Structure
| Property | Details |
| Product Name | Hydroxypropyl Methylcellulose (HPMC) |
| Chemical Type | Semi-synthetic cellulose ether |
| Chemical Formula | [(C₆H₇O₂(OH)₃₋ₓ(OCH₃)ₓ(OCH₂CH(OH)CH₃)ᵧ)ₙ] |
| CAS Number | 9004-65-3 |
| Molar Mass | Variable (polymeric compound) |
| Appearance | White to off-white powder or granules |
| Odor | Odorless |
| Taste | Tasteless |
| Solubility | Soluble in cold water; insoluble in hot water |
| pH (2% solution) | 5.5 – 8.0 |
| Density (bulk) | ~0.30–0.50 g/cm³ |
| Moisture Content | ≤ 5% (typical) |
| Thermal Gelation | Forms gel upon heating (reversible on cooling) |
| Decomposition Temperature | > 200 °C (decomposes, no true melting point) |
| Viscosity | Varies by grade (e.g., 3–100,000 mPa·s at 2% solution, 20 °C) |
| Stability | Stable under normal storage conditions |
| Compatibility | Compatible with many salts, surfactants, and polymers |
Uses
HPMC’s versatility makes it a valuable ingredient in a wide range of products across several industries.
Pharmaceutical and Medical
Oral Medications: HPMC is a common excipient (inactive substance) in tablets and capsules. It acts as a binder to hold the ingredients together and can be used as a controlled-release agent to delay the release of a drug into the digestive tract.
Film Coatings: It is used to coat tablets to protect the active ingredients, mask unpleasant tastes, and make them easier to swallow.
Ophthalmic Products: HPMC is the main ingredient in many artificial tears and eye drops, where it acts as a viscosity enhancer to keep the product on the eye’s surface longer, providing lubrication for dry eyes.
Construction
Mortars and Adhesives: In building materials like tile adhesives and cement mortars, HPMC acts as a water retention agent and rheology modifier. This improves the workability, adhesion, and strength of the materials by preventing water from evaporating too quickly during curing.
Gypsum Products and Plasters: It enhances the consistency, spreadability, and anti-sag properties of plasters and joint compounds.
Food and Cosmetics
Food Additive: HPMC is used as a thickener, emulsifier, and stabilizer in various food products, including sauces, dressings, and gluten-free baked goods, where it can act as a gluten substitute.
Personal Care Products: In lotions, creams, shampoos, and detergents, it functions as a thickening agent and emulsifier, improving the texture and stability of the final product.
HPMC (hydroxypropyl methylcellulose) is available in a variety of grades, which are primarily differentiated by their viscosity, degree of substitution (DS), and application. These properties are precisely controlled during manufacturing to suit specific industrial needs.
Viscosity Grades
Viscosity is a key differentiator for HPMC grades. It is measured in millipascal seconds (mPa·s) or centipoise (cP) at a specified concentration (e.g., a 2% solution). Different viscosity grades are used for different purposes:
Low Viscosity (LV): Grades with a viscosity below 500 mPa·s. They are used in applications where a thin, fluid solution is required, such as tablet coatings and self-leveling compounds in construction. They provide binding without significantly increasing the final product’s thickness.
Medium Viscosity (MV): Grades with a viscosity from 500 to 20,000 mPa·s. These provide a balance between thickening and flow properties. They are common in tile adhesives, cement plasters, and many food and cosmetic products like sauces and lotions.
High Viscosity (HV): Grades with a viscosity above 20,000 mPa·s. They are powerful thickening and water-retention agents, making them ideal for applications requiring substantial body and structure. Examples include dry-mix mortars, joint fillers, and controlled-release pharmaceutical tablets.
Application-Specific Grades
In addition to viscosity and substitution, HPMC is often categorized by its intended application to meet specific regulatory and performance standards.
Pharmaceutical Grade: This grade must adhere to strict pharmacopoeia standards (e.g., USP, EP) and is highly purified. It is used in tablet binders, controlled-release matrices, and capsule coatings.
Food Grade: Approved as a food additive (E464 in the EU), this grade is used as a thickener, emulsifier, and stabilizer in foods like gluten-free baked goods, ice cream, and salad dressings.
Construction Grade: Designed to enhance the performance of building materials, this grade focuses on properties like water retention, workability, and anti-sagging for products such as mortars, adhesives, and plasters.
Personal Care Grade: Used in cosmetics and personal care products like shampoos, lotions, and detergents as a thickener, emulsifier, and film-former.
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