HEC (Hydroxyethyl Cellulose) and HPMC (Hydroxypropyl Methylcellulose) are two commonly used cellulose derivatives, which are widely used in many industries. These materials have become important functional materials due to their unique physical and chemical properties.

1. HEC (Hydroxyethyl Cellulose)

1.1 Basic structure and properties
HEC is a non-ionic water-soluble polymer obtained by chemical modification of natural cellulose. Its basic structure is the introduction of hydroxyethyl substituents on the β-D-glucose skeleton of cellulose. Due to the hydrophilicity of the hydroxyethyl group in its structure, HEC has good solubility and thickening properties in water.

HEC exhibits good adhesion, film-forming and lubricity, and is also acid- and alkali-resistant and has good biocompatibility. These properties make it an extremely effective thickener, stabilizer and film-forming agent in aqueous systems. In addition, HEC solution has good thixotropy, which can show high viscosity under low shear force, and the viscosity drops rapidly under high shear force. This characteristic makes it have important application value in various fluid treatments.

1.2 Preparation process
HEC is mainly prepared by etherification reaction of natural cellulose. Commonly used raw materials include cellulose sources such as cotton and wood, which are reacted with ethylene oxide after alkalization to obtain hydroxyethyl cellulose. During the whole reaction process, the control of reaction conditions (such as temperature, pH value and time) has an important influence on the degree of substitution, solubility and viscosity of the final product.

1.3 Application fields
HEC is widely used in building materials, coatings, daily chemicals, medicine and food. In building materials, HEC is widely used in cement mortar and gypsum as an effective thickener and stabilizer to improve its operability and anti-sagging properties. In the coatings industry, HEC can be used as a thickener and rheology modifier for water-based coatings to improve the adhesion and smoothness of coatings. In daily chemicals such as shampoo and hand sanitizer, HEC is used as a thickener and moisturizer to give the product a good feel and stability. In addition, in the pharmaceutical and food industries, HEC is used as a binder for tablets, a film former for capsules, and a thickener and stabilizer for food due to its good biocompatibility and low toxicity.

2. HPMC (Hydroxypropyl Methylcellulose)

2.1 Basic Structure and Properties
HPMC is a non-ionic cellulose ether obtained by introducing hydroxypropyl and methoxy groups into the cellulose skeleton. Similar to HEC, HPMC has good water solubility, thickening, film forming properties and biocompatibility. Due to the methoxy and hydroxypropyl groups in its structure, HPMC not only has good solubility in water, but also exhibits strong surface activity and suspension properties.

The viscosity of HPMC solution is significantly affected by temperature. Within a certain temperature range, the viscosity of HPMC solution decreases with increasing temperature. In addition, HPMC also has good gel properties. When the solution temperature exceeds a certain value, a gel will be formed. This property has special application value in the fields of food and medicine.

2.2 Preparation process
The preparation of HPMC is similar to HEC, and is also carried out through the etherification reaction of cellulose. Usually, cellulose reacts with propylene oxide and methyl chloride under alkaline conditions to introduce hydroxypropyl and methoxy groups, respectively. The properties of HPMC (such as viscosity, solubility and gel temperature) can be precisely controlled by adjusting the degree of substitution and reaction conditions.

2.3 Application fields
HPMC has a wide range of applications in the fields of construction, medicine, food and daily chemicals. In building materials, HPMC is widely used in cement mortar and gypsum products as a thickener, water retainer and binder to improve the construction performance and durability of the material. In the field of medicine, HPMC is used as a controlled release agent, adhesive and capsule coating material for tablets, which can effectively control the release rate of drugs and improve the stability of drugs. In the food industry, HPMC is widely used as a thickener and emulsifier in baked goods, dairy products and condiments to improve the texture and taste of the products. In addition, HPMC is also widely used in daily chemicals such as shampoo, conditioner, facial cleanser, etc., giving the products excellent thickening effect and lubrication properties.

As two important cellulose derivatives, HEC and HPMC play a key role in many industries. HEC is widely used in construction, coatings, daily chemicals and medicine due to its excellent thickening, film-forming and biocompatibility. HPMC, on the other hand, plays an important role in the construction, medicine and food industries due to its unique gelling properties and wide application fields. With the advancement of technology, the preparation process and application fields of these two materials will continue to expand, bringing more possibilities for the development of related industries.