What are the differences between HPMC and HPC?

Hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) are both important nonionic cellulose ethers widely used in pharmaceuticals, food, daily chemicals, and building materials. Despite their similar names, they differ significantly in chemical structure, properties, and applications.

I. Differences in Chemical Structure Both are based on cellulose, but the core difference lies in the substituent groups:

HPMC: Both methyl (-CH₃) and hydroxypropyl (-CH₂CHOHCH₃) groups are introduced onto the cellulose glucose unit. The methyl group imparts hydrophobic properties, while the hydroxypropyl group provides hydrophilicity. The ratio of these two groups can be adjusted, resulting in a range of products with varying properties.

HPC: Only hydroxypropyl (-CH₂CHOHCH₃) is introduced as a substituent; it does not contain a methyl group. Therefore, its molecular structure is relatively simple, resulting in stronger hydrophilicity and significantly lower hydrophobicity than HPMC.

II. Comparison of Key Properties

Solubility

HPMC: Solubility is significantly affected by the degree and ratio of substitution. Generally soluble in cold water and undergoes thermal gelation at certain temperatures. Solubility in organic solvents is limited.

HPC: Excellent water solubility, dissolves quickly, produces clear solutions, and is less affected by temperature and pH. Also soluble in some polar organic solvents.

Thickening and Gel Properties

HPMC: Due to the presence of methyl groups, intermolecular forces are strong, resulting in high thickening efficiency, the formation of high-viscosity solutions, and unique thermogenic gelation properties.

HPC: Thickening ability is generally lower than that of HPMC of the same molecular weight; solution viscosity is relatively low, and it does not easily form strong gels, but it provides excellent flowability and film-forming properties.

Stability

HPMC: Good chemical stability, wide acid and alkali resistance range, and strong thermal stability.

HPC: Excellent biocompatibility and water retention, but relatively sensitive to high temperatures and extreme pH conditions; long-term exposure to strong acids, strong alkalis, or high temperatures may lead to degradation.

III. Main Application Areas

HPMC: Due to its strong thickening, film-forming, and thermogelating properties, it is widely used in sustained-release and controlled-release drug formulations, building mortars (as a water-retaining and thickening agent), polymer dispersants, and daily chemical creams.

HPC: Based on its excellent water solubility, film-forming properties, and lubricity, it is mainly used in immediate-release drug formulations, coating materials, cosmetics (such as shampoos and skin lotions), and specialty coatings.

IV. Other Considerations

Production Cost: HPMC involves a methylation reaction, making the process relatively complex and generally more expensive than HPC.

Biocompatibility: Both have good biocompatibility. HPC, due to its higher hydrophilicity and biodegradability, has advantages in certain biomedical applications.

Conclusion: The main difference between HPMC and HPC lies in the presence or absence of methyl groups, which directly leads to differences in solubility, thickening ability, gelation behavior, and stability. HPMC has stronger overall performance and is suitable for applications with high requirements for viscosity, gelation, and stability; while HPC excels in excellent water solubility and film-forming properties. In actual selection, a comprehensive judgment should be made based on specific dissolution requirements, rheological objectives, environmental conditions, and costs.