Hydroxypropyl methylcellulose (HPMC) is a chemical substance widely used in the pharmaceutical, food, cosmetic and construction industries. It is mainly made of methylcellulose and hydroxypropyl cellulose through chemical reactions, and has the functions of thickening, stabilization, film formation and lubrication.

Basic characteristics of HPMC
Chemical structure: The chemical structure of HPMC contains two substituents, methyl and hydroxypropyl, which are connected to the cellulose molecule through etherification reaction. The presence of methyl and hydroxypropyl groups makes it have good water solubility and surface activity.

Solubility: HPMC can dissolve quickly in cold water to form a transparent or slightly turbid solution, but it is insoluble in hot water. This property makes it advantageous in many applications, such as as a sustained-release agent and thickener in pharmaceutical preparations.

Viscosity: The viscosity of HPMC solution is affected by temperature, concentration and degree of substitution. HPMC products with different degrees of substitution can provide different viscosities at various temperatures to meet the needs of different applications.

Difference between S-free HPMC and ordinary HPMC
In some applications, especially in the pharmaceutical and food industries, the purity and impurity content of the product are very critical indicators. Sulfur (S) may be considered an impurity in some cases, so some application scenarios require the use of S-free HPMC.

Higher purity: S-free HPMC undergoes a more rigorous purification step during the production process to remove sulfur and its compounds. This high-purity HPMC is suitable for applications that are sensitive to impurities, such as advanced pharmaceutical preparations and high-end cosmetics.

Stronger stability: Because sulfur may participate in redox reactions under certain conditions, resulting in changes or degradation in product performance. S-free HPMC can maintain the stability of its physical and chemical properties under a wider range of environmental conditions and extend the shelf life of the product.

Higher safety: In the food and pharmaceutical industries, sulfur and its compounds may cause allergic reactions or other adverse reactions in some people. Therefore, S-free HPMC is considered safer in these fields and is suitable for a wider range of consumer groups.

Expansion of application areas: Due to its high purity and safety, S-free HPMC can be used not only for conventional thickening and stabilization applications, but also for special applications that require high standards, such as ophthalmic drugs, fine cosmetics, and specific food additives.

Differences in production processes
The production of S-free HPMC usually involves the following steps:

Raw material selection: Select high-purity cellulose raw materials to ensure that the raw materials contain no or very little sulfur.

Refining process: During the etherification reaction, sulfur-free catalysts and additives are used to avoid the introduction of sulfur.

Post-treatment: During the washing and drying process of the product, pure water sources and sulfur-free equipment are used to further reduce the sulfur content in the product.

S-free hydroxypropyl methylcellulose (HPMC) is similar to ordinary HPMC in basic properties such as chemical structure, solubility and viscosity, but due to its higher purity, stronger stability and better safety, it has significant advantages in some high-end application fields. Through more stringent production processes and quality control, S-free HPMC provides a reliable choice for applications that require high purity and low impurities.