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Eastman Cellulose Esters Uses and Benefits in Wood Coatings
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Benefits of Cellulose Esters in Wood CoatingsWith rising pressure on VOC emission controls and 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 be incorporated due to safety concerns. Nitrocellulose can also compromise the quality of coatings compared to higher-performing coating ingredients, such as cellulose esters. Eastman’s cellulose esters are engineered to meet today's safety and regulatory requirements and ensure that quality in wood coating formulations will never be compromised. |
Issues with Nitrocellulose
Nitrocellulose is a commonly used cellulose derivative in wood coating formulations and is preferred for its low cost and good compatibility with other coating formulation components. However, its hazardous safety profile and performance limitations are challenging.
Safety
Nitrocellulose is a highly flammable and reactive material prone to cause accidents that endanger the safety of coating formulators and manufacturers. This causes issues and concerns for storage, transport, and material handling.
Performance
In addition to the safety issues cited above, nitrocellulose tends to yellow and become weathered from UV exposure. Wood coatings are extensively used in structural applications and furniture that can be exposed to sunlight, so the visual appearance of coatings formulated with nitrocellulose may be compromised. This is especially detrimental for wood coatings applied to light-colored wood substrates, where the appearance will be compromised.Eastman Cellulose Esters
Eastman's cellulose esters are a family of polymers that offer superior performance in coatings used on wood without many of the health and safety risks associated with nitrocellulose. They are supplied as free-flowing powders that can be easily dissolved in various solvents. Compared to nitrocellulose, which is prone to yellowing and weathering from UV exposure, Eastman's cellulose esters have excellent UV stability, allowing coatings to preserve the natural beauty of wood surfaces. The table below summarizes the advantages wood coating formulators and formulations gain from using cellulose esters over nitrocellulose.Performance Comparison of Eastman Cellulose Esters vs. Nitrocellulose
| 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 ✔ |
How Can Eastman Cellulose Esters Improve Your Wood Coatings?
Eastman's cellulose esters can provide solutions to quality issues for coating formulations, whether or not they use nitrocellulose. The table below offers insights into how Eastman's cellulose esters solve these coating issues.
| Coating Problem/Difficulty | Benefit of Using Eastman's Cellulose Esters |
|---|---|
Yellowing of lacquers |
Nonyellowing under exposure to UV; improved weathering resistance |
Poor adhesion |
High-butyryl CABs provide improved intercoat and substrate adhesion in UV-cured systems |
High drying time |
Faster cure and hardness development, leading to improved surface dry-to-touch time, allowing quicker stacking and processing of coated products |
Low viscosity control |
Balances optimum viscosity and solids content, allowing excellent wetting, better definition, and thinner films to be formed |
Surface defects |
Excellent flow and leveling properties, resulting in reduced surface defects, consistent gloss, and excellent quality appearance over the entire surface |
How to Select and Use Eastman Cellulose Esters for Wood Coatings
Eastman’s cellulose esters are used in wood coatings as the main film-forming resin or 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's cellulose acetate butyrates (CABs) are mixed cellulose esters with acetate and butyrate functional groups used to create wood coatings with diverse functionality. CABs are highly efficient resins and additives widely used in high-quality 2K acrylic urethane, thermoplastic, acid-curable coatings, and radiation-curable systems. A variety of CAB grades are available to provide key attributes to each formulation. Three main variables in CAB grades determine the best option for a given application: butyryl content, hydroxyl content, and viscosity.
Generally, a CAB grade with higher butyryl content will be more soluble in a wider range of organic solvents and more tolerable of diluents, have higher compatibility with other resins or coresins in the formulation, and lead to a softer coating film. CAB grades with lower butyryl content will have less solubility and compatibility but form harder coating films with better chemical resistance.
CAB grades with higher hydroxyl content have better reactivity and cross-linking ability with other coating resins. In addition, the formulation has better water tolerance, especially when polar organic solvents are present. Lower-hydroxyl-content grades will provide better water resistance and hydrophobicity to the cured coating.
CAB grades with a higher viscosity provide greater toughness and mechanical properties and are typically used as resins in coating formulations. CAB grades with a lower viscosity tend to be used as coating additives that 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 CAB 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.
Conclusion
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. Therefore, coatings formulated to protect and enhance the visual aesthetics of wood surfaces must use resins and additives that maximize longevity and quality. Eastman's cellulose acetate butyrate and Solus™ are cellulose esters that provide wood coating formulations with excellent resistance to abrasion, discoloration, and 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. It pales in its ability to provide the same visual quality as Eastman’s CAB and Solus™.
For more information on Eastman CAB and Solus™ or to request a sample to use in your coating formulation, contact us below.
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