HEC (hydroxyethyl cellulose) is a commonly used non-ionic water-soluble polymer, which is widely used in water-based coatings. Its water retention property is one of the keys to achieve excellent performance of coatings. The water retention principle of HEC in water-based coatings is discussed in detail from three aspects: its molecular structure, mechanism of action and practical application.
1. Molecular structure characteristics of HEC
HEC is made by introducing hydroxyethyl groups into the cellulose main chain through chemical modification. Its molecular structure includes a long-chain cellulose skeleton and hydroxyethyl groups on the side chains. This structure gives HEC the following properties:
Hydrophilicity: The hydroxyethyl group has extremely strong hydrophilicity and can form hydrogen bonds with water molecules, thereby significantly improving KimaCell®HEC’s ability to adsorb and retain water.
Thickening: HEC molecules swell in water and form a high-viscosity solution, which can enhance the rheological properties of water-based coatings and slow down the evaporation of water.
Stability: HEC is a non-ionic polymer, not easily affected by pH and electrolytes, and has good chemical stability in coatings.
2. HEC’s water retention mechanism
The water retention effect of HEC in water-based coatings is mainly achieved through the following mechanisms:
Formation of a water molecule network:
When HEC is dissolved in water, the molecular chain stretches and forms a hydrogen bond network with water molecules. This network structure can capture a large number of free water molecules, reduce the evaporation rate of water, and thus achieve water retention function.
Enhance the adhesion and ductility of coatings:
During the construction process, the thickening effect of HEC can improve the adhesion of the coating, allowing it to adhere evenly to the surface of the substrate, while avoiding excessive water loss during construction. Especially on porous substrates (such as concrete and gypsum board), KimaCell®HEC can effectively reduce excessive penetration of moisture into the substrate.
Adjusting the rheological properties of waterborne coatings:
HEC optimizes the storage stability and construction performance of coatings by thickening and rheology adjustment. For example, under high shear conditions (brushing, spraying), the coating exhibits good fluidity, while in a static state it exhibits a higher viscosity, thereby delaying water evaporation.
3. Application examples of HEC in actual coatings
Improve coating cracking performance:
In wall paint, rapid evaporation of water may cause the paint film to crack. After adding HEC, the volatilization rate of water is slowed down, which helps the coating to dry evenly and reduces the occurrence of cracks.
Improve coating application performance:
During the spraying or rolling process, HEC can ensure that the paint has proper fluidity and anti-sagging properties, while preventing moisture from volatilizing due to high temperature or excessive wind speed, thus maintaining the paint’s workability and final effect.
Extended opening hours:
In two-component coatings, HEC can extend the open time of the coating through its water retention ability, providing construction workers with sufficient operating time, thereby improving construction efficiency.
4. Factors affecting HEC water retention performance
The water retention performance of HEC is affected by many factors, including its molecular weight, degree of substitution (DS and MS values) and addition amount.
Molecular weight: High molecular weight KimaCell®HEC has higher viscosity and water retention capacity, but may increase the flow resistance of the coating; low molecular weight HEC is more suitable for low viscosity coatings.
Degree of substitution: The higher the degree of substitution, the better the solubility and hydrophilicity of HEC, and the stronger the water retention effect.
Addition amount: The right amount of HEC can significantly improve the performance of the coating, but too much HEC may make the coating too viscous and affect the workability.
Post time: Jan-15-2025