Methyl cellulose (MC) and hydroxypropyl methyl cellulose (HPMC) are two cellulose derivatives widely used in industry, construction, pharmaceuticals, food and other fields. Although they are similar in structure, they have different properties and There are significant differences in applications and production processes.
1. Differences in chemical structure
Methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) are both derived from natural cellulose and are chemically modified cellulose ether compounds. But their difference mainly lies in the type and number of substituent groups.
Methyl cellulose (MC)
MC is produced by replacing the hydroxyl groups on cellulose with methyl groups (i.e. -OCH₃). The chemical structure of MC mainly consists of methyl substituent groups on the cellulose main chain, and its substitution rate affects its solubility and properties. MC is generally soluble in cold water but not in hot water.
Hydroxypropyl methylcellulose (HPMC)
HPMC is further modified on the basis of methylcellulose, by replacing part of the hydroxyl groups with methyl (-CH₃) and hydroxypropyl (-CH₂CH(OH)CH₃). Compared with MC, the molecular structure of HPMC is more complex, its hydrophilicity and hydrophobicity are well balanced, and it can be soluble in both cold and hot water.
MC: Methylcellulose generally has good solubility in cold water, but will form a gel when the temperature rises. In hot water, MC becomes insoluble, forming a thermal gel.
HPMC: Hydroxypropyl methylcellulose can be dissolved uniformly in cold and hot water, has a wide dissolution temperature range, and its solubility is more stable than MC.
Thermal gelability
MC: MC has strong thermal gelling properties. When the temperature rises to a certain level, it will form a gel and lose its solubility. This characteristic makes it have special uses in the construction and pharmaceutical industries.
HPMC: HPMC also has certain thermal gelling properties, but its gel formation temperature is higher and the gel formation speed is slower. Compared with MC, HPMC’s thermal gel properties are more controllable and therefore more advantageous in applications requiring higher temperature stability.
Surface activity
MC: MC has low surface activity. Although it can be used as a certain emulsifier or thickener in some applications, the effect is not as significant as HPMC.
HPMC: HPMC has stronger surface activity, especially the introduction of hydroxypropyl group, which makes it easier to emulsify, suspend and thicken in solution. Therefore, it is widely used as an additive in coatings and building materials.
Salt tolerance and pH stability
MC: Methylcellulose has poor salt tolerance and is prone to precipitation in high-salt environments. It has poor stability in acid and alkali environments and is easily affected by pH value.
HPMC: Due to the presence of hydroxypropyl substituent, HPMC’s salt tolerance is significantly better than MC, and it can maintain good solubility and stability in a wide pH range, so it is suitable for various chemical environments.
Production of MC
Methylcellulose is produced through the methylation reaction of cellulose, usually using methyl chloride to react with alkaline cellulose to replace the hydroxyl groups in the cellulose molecules. This process requires control of reaction conditions to ensure the appropriate degree of substitution, which affects the solubility and other physicochemical properties of the final product.
Production of HPMC
The production of HPMC is based on methylation and adds hydroxypropylation reaction. That is, after the methylation reaction of methyl chloride, propylene oxide reacts with cellulose to generate a hydroxypropyl substituent. The introduction of hydroxypropyl group improves the solubility and hydration ability of HPMC, which also makes its production process more complex and slightly higher cost than MC.
Building materials field
MC: MC is often used in building materials, especially as thickener, water retaining agent and adhesive in dry mortar and putty powder. However, due to its thermal gelling properties, MC may fail in high-temperature environments.
HPMC: HPMC is more widely used in the construction field. Because it also has good stability in high temperature environments, it is more suitable for scenarios that require higher temperature tolerance, such as tile adhesives, insulation mortars and self-leveling floors. .
Pharmaceutical and food fields
MC: Methylcellulose is commonly used as a disintegrant and thickener for tablets in pharmaceutical preparations. It is also used in some foods as a thickener and fiber supplement.
HPMC: HPMC has more advantages in the pharmaceutical field. Because of its more stable solubility and good biocompatibility, it is often used in sustained-release film materials and capsule shells for drugs. In addition, HPMC is also widely used in the food industry, especially in the manufacture of vegetarian capsules.
Coatings and paints sector
MC: MC has better thickening and film-forming effects, but its stability and viscosity adjustment ability in solution are not as good as HPMC.
HPMC: HPMC is widely used in the paint and paint industry due to its excellent thickening, emulsification and film-forming properties, especially as a thickener and leveling agent in water-based coatings, which can significantly improve the construction performance and surface of the coating. Effect.
5. Environmental protection and safety
Both MC and HPMC are modified from natural cellulose and have good biodegradability and environmental protection properties. Both are non-toxic and harmless in use and comply with environmental protection requirements, so they are very safe to be used in the fields of food, pharmaceuticals and cosmetics.
Although methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) are similar in chemical structure, due to different substituent groups, their solubility, thermal gelability, surface activity, production process and application are different. There are obvious differences in fields and other aspects. MC is suitable for low temperature environments and simpler thickening and water retention requirements, while HPMC is more suitable for complex industrial, pharmaceutical and construction applications due to its good solubility and thermal stability.