Types of cellulose ethers
Cellulose ethers are manufactured from wood, cotton, etc. as raw materials, in which the cellulose is alkaliated, ethoxylated, and reacted with chloroethane and chloromethane to form a variety of water-soluble cellulose ethers.
Cellulose ethers are non-ionic water-soluble polymers. They have a long history of use, spanning more than 30 years, and are available in many varieties. They are still used in almost all emulsion paints and are the main type of paint thickener.
The most commonly used cellulose thickeners in the paint industry are methyl cellulose ether (MC), hydroxyethyl cellulose ether (HEC), ethyl hydroxyethyl cellulose ether (EHEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), and hydrophobically modified hydroxyethyl cellulose (HMHEC).
Hydroxyethyl cellulose (HEC) is the most versatile polysaccharide thickener and is widely used to thicken matt and semi-gloss architectural emulsions. By controlling the molecular weight of the cellulose ether, thickeners with different viscosity grades can be obtained. Thickeners thickened with this cellulose ether have excellent colouring compatibility and storage stability. The leveling, anti-splashing, film-forming and anti-sagging properties of the coating film depend on the relative molecular mass of HEC.
The role of cellulose ethers in coatings
1. Thickening
Cellulose ethers are effective in thickening aqueous systems, whether they are high-PVC or low-PVC coating systems. Because they are water-soluble, they can form high-viscosity liquids.
2. Rheology control
Ethyl or hydrophobically modified cellulose ethers can produce a certain degree of association in emulsion paints, and when applied, such as rolling or brushing, they thicken upon shearing, which helps the paint level off.
3. In-can suspension stability
Prevents the settling of pigments during storage of the paint
4. Water retention
Cellulose ethers have a strong affinity for water, which slows down the evaporation of water. This prolongs the open time of water-based paints and reduces the risk of paint marks.
Cellulose ether is an essential raw material for multi-colour coatings
In the base paint, cellulose ether not only thickens the paint, but more importantly, the gel reaction between the cellulose ether and the protective glue affects the size, shape, hardness, colour bleeding resistance and storage stability of the colour particles. Choosing the right cellulose ether is crucial to the successful preparation of multi-colour paints.
Characteristics of cellulose ether application
Traditional cellulose ethers are high-molecular-weight polymers. Due to their high viscosity at low shear rates, they have poor leveling properties and affect the gloss of the coating film. At high shear rates, their viscosity is low, which results in poor anti-splash properties of the coating film when roller coating, and the fullness of the coating film is also not good.
Therefore, it can be used in combination with other types of thickeners such as polyurethane or alkali-soluble acrylic acid to reduce its disadvantages. In addition, cellulose ether is more susceptible to microbial attack and degradation than other thickeners, and a little more preservative needs to be added.