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Benefits of Cellulose Esters in Wood CoatingsWith rising pressure on VOC emission control paired with a fast-growing construction market, it has become even more challenging for wood coating formulators to find the right balance between meeting quality standards and complying with legislative restrictions. It is now more difficult than ever for traditional ingredients used in wood coating formulations, such as nitrocellulose, to meet regulatory requirements. Nitrocellulose can also compromise the quality of coatings when compared to higher-performing coating ingredients, such as cellulose esters. Eastman’s cellulose esters are engineered to ensure that today's safety and regulatory requirements are met and that quality in wood coating formulations will never be compromised. |
Nitrocellulose is a commonly used cellulose derivative in wood coatings and is preferred for its good compatibility with other coating formulation components and low cost. However, it presents challenges resulting from its hazardous safety profile and performance limitations.
Nitrocellulose is a highly flammable and reactive material that is prone to cause accidents that endanger the safety of coating formulators and manufacturers. This causes issues and concerns when it comes to storage, transport, and handling of the material.
| Properties | Cellulose Esters | Nitrocellulose |
|---|---|---|
Product form |
White Powder |
Flakes (damped) |
Hazard rating |
Low ✔ |
Highly flammable ⇩ |
Film former |
Excellent ✔ |
Excellent ✔ |
Coating clarity |
Excellent ✔ |
Excellent ✔ |
UV resistance |
Excellent ✔ |
Poor - strong yellowing ⇩ |
Pigment dispersion |
Excellent ✔ |
Excellent ✔ |
| Coating Problem/Difficulty | Benefit of Using Eastman's Cellulose Esters |
|---|---|
Yellowing of lacquers |
Non-yellowing under exposure to UV; improved weatherability resistance |
Poor adhesion |
High-butyryl CABs provide improved intercoat adhesion in UV cured systems |
High drying time |
Faster cure and hardness development, leading to improved dry-to-touch time, which allows quicker stacking and processing of coated products |
Low viscosity control |
Balances optimum viscosity and solids content, allowing excellent wetting, definition, and thinner films to be formed |
Finishing defects |
Excellent flow and leveling properties, resulting in reduced finishing defects, consistent gloss, and excellent quality appearance over entire surfaces |
Eastman’s cellulose esters benefit wood coatings as the main film-forming resin or as an additive to improve coating properties and enhance quality. Eastman’s cellulose acetate butyrate and Solus™ are two cellulose ester products introduced below in their significance to wood coating formulations.
Eastman Cellulose Acetate Butyrate (CABs) are mixed cellulose esters with both acetate and butyrate functional groups and are instrumental in creating wood coatings with diverse functionality. CABs are highly efficient resins and additives that are widely used in high-quality 2K acrylic urethane, thermoplastic, and acid curable coatings, as well as radiation-curable systems. A variety of CAB grades are available from Eastman that provide key attributes to formulations. Three main variables within CAB grades determine the best option for a given application: butyryl content, hydroxyl content, and viscosity.
Generally, a cellulose acetate butyrate grade with higher butyryl content will be more soluble in a wider range of organic solvents, be more tolerable of diluents, have higher compatibility with other resins or co-resins in the coating, and lead to a softer coating film. Cellulose acetate butyrate grades with lower butyryl content will have less solubility and compatibility but form harder coating films that have better chemical resistance.
For cellulose acetate butyrate grades with higher hydroxyl content, there is better reactivity and cross-linking ability with other coating resins. In addition, there is better tolerance to water in the formulation, especially when polar organic solvents are also present. Lower hydroxyl content grades will provide better water resistance and hydrophobicity to the cured coating.
Cellulose acetate butyrate grades with higher viscosity provide greater toughness and mechanical properties and are typically used as resins in coating formulations. Cellulose acetate butyrate grades with lower viscosity tend to be used as additives and permit higher solids concentrations in formulations at a given solution viscosity.
With these guidelines in mind, the diagram below can be used to select a cellulose acetate butyrate grade based on the needs of a specific formulation.
| Key Attribute | Grade Selection | Grade Examples |
|---|---|---|
Compatibility |
Higher butyryl content |
|
Solubility |
High butyryl or hydroxyl content |
|
Reactivity |
Higher hydroxyl content |
|
Toughness |
Higher viscosity |
|
Hardness |
Lower butyryl or hydroxyl content |
|
Chemical resistance |
Lower butyryl content |
|
Moisture resistance |
Lower hydroxyl content |
|
Adhesion |
Higher butyryl and hydroxyl content |
Eastman Solus™ performance additives are also cellulose esters ideal for wood coatings. They are the newest cellulose esters designed by Eastman for high-solids, solvent-borne systems to meet lower VOC levels through lower solvent demand. Eastman Solus™ grades are engineered with very low molecular weights and excellent solubility. This allows them to be loaded into formulations at high levels without a drastic increase in viscosity, solvent usage, or VOCs. Solus™ also has improved compatibility towards alkyd resins commonly used in wood coating formulations. Like the cellulose acetate butyrate grades introduced previously, they also are much safer and outperform nitrocellulose in providing excellent weathering resistance under UV exposure. In addition, they offer excellent adhesion, hardness development, and significantly improved dry-to-touch time.
Due to an increased focus on sustainability in today's world, wood will continue to be a material of choice to create buildings and furniture. Coatings formulated to protect and enhance visual aesthetics of wood must, therefore, use resins and additives that maximize longevity and quality. Eastman cellulose acetate butyrate and Solus™ 2100 are cellulose esters that provide wood coating formulations excellent resistance to abrasion, discoloration, chemical attack, and promote good adhesion and leveling. While nitrocellulose is commonly used in wood coating formulations, it poses serious safety risks and regulatory concerns and pales in its ability to provide the same visual advantages as those of Eastman’s cellulose acetate butyrate and Solus™ 2100.
For more information on Eastman cellulose acetate butyrate and Solus™ 2100 or to request a sample to use in your coating formulation, contact us below.
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