Hydroxyethyl Cellulose (HEC) is an important nonionic water-soluble polymer belonging to the cellulose ether class of compounds. It is obtained by etherification reaction of natural cellulose with ethylene oxide (Ethylene Oxide) under alkaline conditions. Hydroxyethyl cellulose is a linear polysaccharide chain composed of glucose units of cellulose in chemical structure, and some or all of the hydroxyl groups on its glucose units are replaced by hydroxyethyl groups to form hydroxyethyl cellulose.

Ingredients and chemical structure
The molecular structure of hydroxyethyl cellulose mainly includes the following parts:

Cellulose backbone: Cellulose is a natural polysaccharide, the main component of which is a linear chain of glucose units connected by β-1,4-glycosidic bonds. This structure of cellulose gives it high crystallinity and physical strength.

Hydroxyethyl substituent: In the glucose unit of the cellulose backbone, there are three hydroxyl groups (–OH), located at the C2, C3 and C6 positions respectively. Hydroxyethyl cellulose is produced by introducing hydroxyethyl (–CH2CH2OH) groups on the hydroxyl groups through an etherification reaction between these hydroxyl groups and ethylene oxide. The introduction of these substituents reduces the crystallinity of cellulose, improves its water solubility, and makes it exhibit good thickening and viscoelasticity in aqueous solution.

Molecular weight and degree of substitution: The molecular weight and degree of substitution (i.e., the number of hydroxyl groups substituted on each glucose unit) of hydroxyethyl cellulose are two important factors affecting its properties. Generally, hydroxyethyl cellulose with a higher molecular weight has better viscosity and thickening ability, while a higher degree of substitution enhances its water solubility and stability.

Physicochemical properties of hydroxyethyl cellulose
Due to its unique structure, hydroxyethyl cellulose exhibits a series of excellent physicochemical properties:

Water solubility: Hydroxyethyl cellulose is easily soluble in cold and hot water to form a clear or slightly turbid colloidal solution. Its dissolution process is not significantly affected by pH value and remains stable over a wide pH range (usually between 2 and 12).

Thickening: Hydroxyethyl cellulose has a good thickening effect in aqueous solution, and its thickening ability is affected by molecular weight, degree of substitution and solution concentration. As the concentration increases, the viscosity of the solution increases exponentially, so it is widely used in industrial fields that require thickeners.

Surface activity: Since the hydroxyethyl cellulose molecule contains hydrophilic groups and hydrophobic skeletons, it can reduce the surface tension of water in the solution and show a certain surface activity. This property makes it used in coatings, inks and other fields, and can improve the fluidity and coating properties of the product.

Stability: Hydroxyethyl cellulose has good stability in aqueous solution, can resist the influence of general oxidants and light, and is relatively stable under acid and alkaline conditions. It will not be degraded by most microorganisms in aqueous solution, so it is not easy to deteriorate during storage.

Biocompatibility and safety: Hydroxyethyl cellulose is widely used in food, cosmetics and medicine because it is derived from natural cellulose and still maintains good biocompatibility and low toxicity after chemical modification. For example, it is used as a thickener and stabilizer in food, as a humectant and emulsifier stabilizer in cosmetics, and as a binder and controlled release matrix for tablets in pharmaceutical preparations.

Preparation and application
The preparation of hydroxyethyl cellulose is usually divided into three steps: alkalization of cellulose, etherification reaction, purification and drying. First, cellulose is treated under alkaline conditions to activate the hydroxyl groups of cellulose, and then reacted with ethylene oxide to produce hydroxyethyl cellulose. Finally, the final product is obtained through steps such as neutralization, purification and drying.

Hydroxyethyl cellulose is widely used in building materials (such as cement mortar and coatings), daily chemicals (such as detergents and cosmetics), medicine (such as drug controlled release systems) and food industry (such as thickeners and stabilizers).

Hydroxyethyl cellulose is widely used in various fields due to its excellent physical and chemical properties and versatility. The uniqueness of its structure and composition enables it to play an important role in thickening, emulsification, suspension, film formation and stabilization, and is an irreplaceable important chemical material.