Hydrophobic modified hydroxyethyl cellulose (HEC) is a kind of derivative modified by introducing hydrophobic groups (such as long-chain alkyl, aromatic groups, etc.) to hydroxyethyl cellulose (HEC). This type of material combines the hydrophilic properties of hydroxyethyl cellulose with the hydrophobic properties of hydrophobic groups and is widely used in coatings, detergents, cosmetics and drug carriers.

1. Synthesis method of hydrophobically modified hydroxyethyl cellulose
The synthesis of hydrophobically modified hydroxyethyl cellulose is usually carried out by the following methods:

1.1 Esterification reaction
This method is to react hydroxyethyl cellulose with hydrophobic chemical reagents (such as long-chain fatty acids, fatty acid chlorides, etc.) to introduce hydrophobic groups into cellulose molecules through esterification reaction. Esterification reaction can not only effectively introduce hydrophobic groups, but also adjust the hydrophobicity and thickening effect of polymers. The reaction conditions of the synthesis process, such as temperature, time, reaction solvent and catalyst, will affect the performance of the final product.

1.2 Substitution reaction
In this method, the hydroxyl group of hydroxyethyl cellulose is replaced by a hydrophobic group (such as alkyl, phenyl, etc.). The advantage of this method is that the synthesis conditions are relatively mild, the structural characteristics of hydroxyethyl cellulose can be well preserved, and the modified product usually has good solubility and thickening effect.

1.3 Copolymerization reaction
By copolymerizing with other monomers (such as acrylic acid, acrylate, etc.), a new polymer with hydrophobicity can be prepared. This method can achieve precise control of the thickening performance of cellulose by adjusting the ratio of different monomers.

1.4 Intercalation reaction
Hydrophobic compounds are chemically embedded into the structure of hydroxyethyl cellulose to form hydrophobic blocks or segments. This method can enhance the thermal stability and surface activity of hydrophobically modified hydroxyethyl cellulose, which is suitable for specific high-performance requirements.

2. Thickening mechanism of hydrophobically modified hydroxyethyl cellulose
The thickening mechanism of hydrophobically modified hydroxyethyl cellulose mainly consists of the following aspects:

2.1 Increase intermolecular interactions
The introduction of hydrophobic groups enhances the interactions between cellulose molecules, especially in the aqueous environment, where hydrophobic groups tend to aggregate together to form larger molecular aggregates. This aggregation effect leads to an increase in the viscosity of the solution, thus showing a strong thickening property.

2.2 Hydrophilic-hydrophobic interaction
The hydrophilic groups (such as hydroxyethyl) and hydrophobic groups (such as alkyl, phenyl, etc.) in hydrophobically modified hydroxyethyl cellulose work together to form a special hydrophilic-hydrophobic interaction. In the aqueous phase, the hydrophilic part interacts strongly with water molecules, while the hydrophobic part attracts each other through the hydrophobic effect, further increasing the structural density between molecules and thus increasing the viscosity.

2.3 Constructing the network structure of the solution
After hydrophobic modification, the structure of the molecular chain may change, forming a relatively tight three-dimensional network structure. This network structure can significantly improve the viscoelasticity and thickening ability of the solution through physical cross-linking between molecules.

2.4 Easy to form a gel-like structure
Due to the introduction of hydrophobic groups, hydrophobically modified hydroxyethyl cellulose has good gelation properties. Under appropriate conditions, such as changes in temperature, pH or concentration, hydrophobic modified groups may cause the formation of gel structures in the solution, which is also a manifestation of its thickening properties.

3. Application of hydrophobically modified hydroxyethyl cellulose
Hydrophobic modified hydroxyethyl cellulose is widely used in many industrial fields, especially in situations where thickening, rheological improvement and stability improvement are required:

3.1 Coatings and paints
In the coatings industry, hydrophobically modified hydroxyethyl cellulose can improve the rheological properties, suspension and construction performance of the coating, while improving the water resistance and stain resistance of the coating.

3.2 Cleaners and detergents
Adding hydrophobically modified hydroxyethyl cellulose to the detergent can effectively improve the viscosity of the detergent, making it more stable and easy to control during use.

3.3 Cosmetics
In the cosmetics field, hydrophobically modified hydroxyethyl cellulose is often used as a thickener and suspending agent, especially in lotions, creams and other products, which can improve the texture and feel of the product.

3.4 Drug carrier
Due to its good thickening and biocompatibility, hydrophobically modified hydroxyethyl cellulose has also been widely studied for use in drug controlled release systems, which can effectively control the release rate of drugs.

By introducing hydrophobic groups, hydrophobically modified hydroxyethyl cellulose not only gives the original hydroxyethyl cellulose a stronger thickening effect, but also makes it show excellent performance in a variety of applications. Its thickening mechanism mainly depends on the interaction between hydrophobic groups and hydrophilic groups, molecular aggregation effects and changes in solution structure. With the deepening of research, the synthesis method and application field of hydrophobically modified hydroxyethyl cellulose will be further expanded, with broad market prospects.