Cellulose is a natural polymer found in plant cell walls. It is the most abundant organic polymer on Earth. It is found in cotton, wood, and other types of plants. Cellulose ethers are used as thickeners and binders in daily chemical industrial. Typical consumer products that contain cellulose ethers include toothpaste, detergent, and cosmetics. (From: www.epa.gov: https://www.epa.gov/stationary-sources-air-pollution/cellulose-products-manufacturing-national-emission-standards)
Appearance
Generally, cellulose ether is white or milky white, odorless and non-toxic, fluid powder, easy to absorb moisture, and dissolves in water into a transparent viscous stable colloid.
Film formation and adhesion
The etherification of cellulose ether significantly influences its characteristics and performance, such as solubility, film-forming ability, bonding strength, and salt resistance. It has high mechanical strength, flexibility, and heat resistance, and has good compatibility with various resins and plasticizers，suitable for manufacturing plastics, films, varnishes, adhesives, latex, and drug coating materials.
Solubility
Methyl cellulose is soluble in cold water, insoluble in hot water, and soluble in some solvents; methyl hydroxyethyl cellulose is soluble in cold water-insoluble in hot water or organic solvents. However, aqueous solutions of methyl cellulose and methyl hydroxyethyl cellulose will precipitate when heated. Methyl cellulose precipitates at 45°C to 60°C, while the precipitation temperature of mixed etherified methyl hydroxyethyl cellulose increases to 65°C to 80°C. When the temperature drops, the precipitate redissolves. Hydroxyethyl cellulose and sodium carboxymethyl hydroxyethyl cellulose are soluble in water at any temperature but insoluble in organic solvents (with a few exceptions).
Thickening
Cellulose ether is dissolved in water in colloidal form, and its viscosity depends on the degree of polymerization of cellulose ether. The solution contains hydrated macromolecules. Due to the entanglement of macromolecules, the fluidity of the solution is different from that of Newtonian fluids. Instead, it shows that as the shear force increases, the hydrogen bond between the cellulose molecules in the solution is destroyed, and the viscosity decreases. When the shear force is removed, the viscosity of the system will gradually recover. This feature is of great significance in thickening toothpaste, cosmetics, and detergents. Due to the macromolecular structure of cellulose ether, the viscosity of the solution increases rapidly with the increase of concentration and decreases quickly with the rise of temperature.
Degradability
Cellulose ether is generally used in the water phase. The presence of water will promote the growth of bacteria. The development of bacteria leads to the production of mold. The mold breaks the bonds of the adjacent unsubstituted anhydroglucose unit of the cellulose ether, reducing the molecular weight of the polymer. Therefore, if the cellulose ether aqueous solution is to be stored for a long time, it is necessary to add a preservative, even if the antibacterial cellulose ether is used.
Toothpaste thickener
CMC has always been one of the essential raw materials for toothpaste production. Its function is to evenly mix the liquid raw materials and reliable raw materials of the toothpaste to give the toothpaste molding fluidity and appropriate viscosity, and an individual brightness and fineness. Purified CMC may be used as a thickener in toothpaste, as an adhesion promoter in denture adhesives (From: www.usitc.gov: https://www.usitc.gov/publications/701_731/pub4225.pdf )
Ordinary toothpaste without special functional additives can use CMC as a binder. However, anionic CMC is more sensitive to high concentrations of ions. The combination of carboxyl groups and metal ions will reduce CMC’s water solubility and affect its thickening effect. CMC is limited to high-quality toothpaste with special effects. Using non-ionic HEC as a binder can enhance the binder’s resistance to high-concentration ions, significantly improve the storage stability of the paste and prolong the storage time of toothpaste. Toothpaste manufacturers can combine CMC and HEC in high-salt toothpaste so that the product’s cost does not change much, but the toothpaste quality is greatly improved.
Emulsifying, dispersing and anti-redeposition agent for detergents
The shower gel with soap base as the main active ingredient does not have the slippery feeling of available surfactants after use, is easy to clean, and protects the skin’s natural luster. HEC has excellent solubility resistance to electrolytes, and its solution contains a high concentration of salts and is stable. It is the best choice to use HEC as a thickener for soap-based shower gel. The solubility of the disinfectant and the disinfectant added to the hand sanitizer in the aqueous solution is very different, and the use of HEC can form a uniform and stable emulsification system. In detergents, CMC can be used as an anti-soil redeposition agent, and its soil diffusion ability, especially for hydrophobic synthetic fiber fabrics, is beneficial.
Cosmetic thickener and stabilizer
In cosmetics, HPMC is used to improve the viscosity of various cosmetics, improve dispersion and foam stability, and improve the viscosity and fluidity of various creams. In oil/water or water/oil cream skincare products, HEC can play a role in emulsifying, thickening, and stabilizing.
Cellulose is an essential renewable resource on the earth. So far, the application range of cellulose and cellulose ether is extensive, and it has a high research value. With the deepening of cellulase research, especially cationic cellulose ethers and amphoteric cellulose ethers have functions such as sterilization and thickening, and cellulose ethers will undoubtedly play an increasing role in the field of daily chemistry.
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