HPMC (hydroxypropyl methylcellulose) and HEC (hydroxyethyl cellulose) are cellulose derivatives widely used in industry and medicine, but they have some significant differences in chemical structure, properties, application fields, etc. difference.

1. Differences in chemical structure
HPMC and HEC are both cellulose ethers processed from natural cellulose (such as cotton or wood pulp), but they differ in the substituents:

HPMC (hydroxypropyl methylcellulose): HPMC is obtained by partially or completely replacing some of the hydroxyl groups (-OH) of cellulose with methyl (-CH?) and hydroxypropyl (-CH?CH(OH)CH?) Cellulose derivatives. The degree of substitution of methyl and hydroxypropyl groups determines the properties of HPMC.
HEC (Hydroxyethyl Cellulose): HEC is a cellulose ether made by replacing part of the hydroxyl groups of cellulose with hydroxyethyl groups (-CH?CH?OH), primarily hydroxyethylation.
These differences in chemical structure directly affect their solubility, viscosity, and other physical and chemical properties.

2. Solubility and dissolution conditions
HPMC: HPMC has excellent water solubility and can be dissolved in cold water to form a transparent viscous solution. It can also be dissolved in organic solvents such as ethanol, acetone, etc., but the dissolution speed and degree vary depending on the specific substituent content. An important feature of HPMC is that it dissolves in cold water, whereas during heating the solution undergoes thermal gelation (turns into a gel when heated and dissolves when cooled). This property is very important in fields such as construction and coatings.

HEC: HEC also dissolves in cold water, but unlike HPMC, HEC does not gel in hot water. Therefore, HEC can be used over a wider temperature range. HEC has strong salt tolerance and thickening properties and is suitable for use in solutions containing electrolytes.

3. Viscosity and rheological properties
The viscosity of HPMC and HEC varies with their molecular weight, and both have good thickening effects at different concentrations:

HPMC: HPMC exhibits high pseudoplasticity (i.e., shear-thinning properties) in solution. The viscosity of HPMC solutions decreases when shear increases, making them suitable for applications that require easy spreading or brushing, such as paints, cosmetics, etc. The viscosity of HPMC decreases with increasing temperature, and a gel will form at a certain temperature.

HEC: HEC solutions have higher viscosity and better thickening properties at low shear rates, exhibiting better Newtonian flow properties (i.e. shear stress is proportional to shear rate). In addition, HEC solutions have small viscosity changes in environments containing salts and electrolytes, and have good salt resistance. They are widely used in fields that require salt resistance, such as oil extraction and mud treatment.

4. Differences in application fields
Although both HPMC and HEC can be used as thickeners, adhesives, film formers, stabilizers, etc., their performance in specific application areas differs:

Applications of HPMC:
Construction industry: HPMC is used as a thickening agent and water-retaining agent in the fields of building materials such as cement mortar, gypsum products, and ceramic tile adhesives. It improves the workability of the mortar, resists sagging, and prolongs the open time of the mortar.
Pharmaceutical and food fields: In medicine, HPMC is often used as coating materials for tablets and framework materials for sustained-release preparations. In the food industry, HPMC is used as a food additive, mainly as an emulsifier, thickener, and stabilizer.
Daily chemical industry: HPMC is used as an emulsion stabilizer, thickener, and protective film-forming ingredient in cosmetics and personal care products.

Applications of HEC:
Oil extraction: Since HEC has strong tolerance to salts, it is particularly suitable for use as a thickening agent for drilling fluids and fracturing fluids in environments with high salt content to improve the rheological properties of the mud.
Coating industry: HEC is used as a thickener and stabilizer in water-based coatings. It can improve the fluidity and construction performance of the coating and prevent the coating from sagging.
Papermaking and textile industry: HEC can be used for surface sizing in papermaking and slurry treatment in the textile industry to thicken, stabilize and adjust rheological properties.

5. Environmental stability and biocompatibility
HPMC: HPMC is commonly used in the pharmaceutical and food fields due to its good biocompatibility and biodegradability. Its thermal gelling properties also give it unique advantages in certain temperature-sensitive pharmaceutical formulations. Furthermore, HPMC is nonionic, unaffected by electrolytes, and has good stability to pH changes.

HEC: HEC also has good biocompatibility and biodegradability, but it exhibits greater stability in high-salt environments. Therefore, HEC is a better choice where salt resistance and electrolyte resistance are required, such as oil exploration, offshore engineering, etc.

6. Cost and Supply
Since both HPMC and HEC are derived from natural cellulose, the supply of raw materials is stable, but due to different production processes, the production cost of HPMC is generally slightly higher than that of HEC. This makes HEC more widely used in some cost-sensitive applications, such as construction materials, oil field chemicals, etc.

HPMC and HEC are both important cellulose derivatives. Although they are different in chemical structure, they both have functions such as thickening, stabilization, water retention and film-forming. In terms of specific application selection, HPMC occupies an important position in the construction, pharmaceutical preparation and food industries due to its special thermal gelling properties; while HEC plays an important role in the petroleum industry due to its excellent salt tolerance and wider temperature adaptability. More advantageous in mining and water-based coatings. According to different application requirements, selecting appropriate cellulose derivatives can improve product performance and economic benefits.