Chemical Structure and Properties
Chemical Structure: Microcrystalline Cellulose is a pure depolymerization product of cellulose. Its chemical structure mainly consists of D - glucose units connected through β - 1,4 - glycosidic bonds to form a linear high - molecular - weight compound. The arrangement of these glucose units forms the basic framework of cellulose. The "microcrystalline" part of microcrystalline cellulose refers to the fact that during the hydrolysis process of cellulose, some regions form a highly ordered crystalline structure, and these crystalline regions are intertwined with amorphous regions.
Physical Properties: It is a white, odorless, and tasteless crystalline powder. It has good fluidity and can flow relatively easily in powder form, which makes it convenient for handling and processing in industrial production. Microcrystalline cellulose is insoluble in water, dilute acids, organic solvents, and oils. However, it can swell in alkaline solutions such as sodium hydroxide under certain conditions. Its density is approximately 1.5 - 1.6 g/cm³, and it has a relatively high melting point, starting to decompose only when the temperature exceeds 260°C.
Chemical Properties: It has relatively stable chemical properties and is not prone to chemical reactions in a general chemical environment. However, due to the presence of a large number of hydroxyl groups (-OH), under specific chemical conditions, these hydroxyl groups can participate in esterification, etherification, and other reactions. For example, it can react with organic or inorganic acids to form cellulose esters and react with halogenated hydrocarbons to form cellulose ethers.
Production Process
Raw Material Selection: The main raw materials are plants rich in cellulose, such as wood and cotton. These plant - based raw materials have a high cellulose content and good quality, making them ideal choices for the production of microcrystalline cellulose. Taking wood as an example, usually, wood varieties with a lower lignin content and higher cellulose purity are selected.
Pretreatment: The raw materials first need to be pretreated, including steps such as cleaning and crushing. Cleaning is to remove impurities, dirt, etc. on the surface of the raw materials; crushing is to turn the raw materials into smaller particles to increase the reaction surface area and facilitate subsequent chemical treatment. For example, wood needs to be cut into wood chips, and cotton needs to be dispersed into cotton fibers.
Hydrolysis Process: This is a crucial step. The cellulose is partially hydrolyzed through acid hydrolysis or enzymatic hydrolysis. Acid hydrolysis generally uses dilute acids, such as dilute hydrochloric acid or dilute sulfuric acid, and is carried out under certain temperature and pressure conditions. Enzymatic hydrolysis utilizes cellulase, and this method is relatively mild and has less impact on the environment. The hydrolysis process causes the long - chain molecules of cellulose to break and form a microcrystalline structure.
Post - treatment: The products after hydrolysis need to undergo post - treatment steps such as filtration, washing, and drying. Filtration is to separate the solid microcrystalline cellulose. Washing can remove residual acids, enzymes, or other impurities. Drying is to produce microcrystalline cellulose in powder form. Common drying methods include spray - drying and vacuum - drying.
Application Fields
Pharmaceutical Industry: It is widely used in the pharmaceutical industry. It can be used as an excipient for tablets, capable of increasing the hardness and friability of tablets, making tablets less likely to be damaged during production, packaging, and transportation. At the same time, microcrystalline cellulose can also be used as a filler to increase the volume of tablets without affecting the active ingredients of drugs, facilitating tablet formation. For example, it is used in the production of various tablets such as vitamin tablets and cold - medicine tablets. In addition, it can also be used in drug - sustained - release preparations. By controlling the particle size and structure of microcrystalline cellulose, drugs can be slowly released, prolonging the drug's action time.
Food Industry: As a food additive, it can be used to increase the stability and texture of food. In baked goods such as bread and cake, microcrystalline cellulose can increase the toughness and elasticity of the dough, prevent the dough from collapsing, and at the same time, can improve the volume and taste of the baked products. In dairy products, it can be used as a thickening agent and stabilizer to prevent whey separation and product precipitation. In some low - calorie foods, microcrystalline cellulose can also be used as a dietary fiber supplement to increase the fiber content of food without increasing the calorie content.
Cosmetics Industry: In cosmetics, microcrystalline cellulose can be used as a thickening agent, stabilizer, and adsorbent. For example, in skin - care products such as lotions and creams, it can increase the viscosity of the products, making them easier to apply and maintaining the stability of the products to prevent emulsion stratification. In powdered cosmetics such as loose powder and powder compacts, microcrystalline cellulose can adsorb oils and absorb sweat, making the makeup more long - lasting.
Product Specifications and Quality Standards
Product Specifications: The product specifications of microcrystalline cellulose usually include parameters such as particle size, crystallinity, and purity. The particle size can range from a few micrometers to dozens of micrometers. Different particle - sized microcrystalline celluloses are suitable for different application scenarios. For example, microcrystalline cellulose with a smaller particle size may have an advantage in drug - sustained - release preparations because it can provide a larger specific surface area. The crystallinity is generally between 50% and 80%. The level of crystallinity will affect the physical and chemical properties of microcrystalline cellulose. A relatively high purity is required, and generally, the purity of pharmaceutical - grade and food - grade microcrystalline celluloses is above 97%.
Quality Standards: Quality standards vary depending on the application field. In the pharmaceutical industry, it must comply with strict drug quality standards, such as meeting the microbiological limits, heavy - metal content, and other indicators specified in the pharmacopoeia. In the food industry, it must comply with national food - safety standards, with clear regulations on the use range and maximum usage amount of additives. The cosmetics industry also has corresponding quality requirements, such as requirements for product safety and stability.
Safety and Precautions
Safety: Microcrystalline cellulose is considered a safe substance. Under normal usage doses in industries such as pharmaceuticals, food, and cosmetics, it does not cause obvious harm to the human body. It is not absorbed by the human digestive system but is excreted as dietary fiber and can, in some cases, promote intestinal peristalsis.
Precautions: During storage, it is necessary to keep it dry and avoid moisture because microcrystalline cellulose is prone to absorbing water and caking, which will affect its performance. During use, especially in pharmaceutical and cosmetic production, it is necessary to strictly follow the formula and operating procedures to ensure product quality and safety. At the same time, for microcrystalline celluloses from different sources and with different specifications, appropriate pretreatment or quality testing may be required to meet specific application requirements.
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