Sunlight contains harmful ultraviolet (UV) radiation, particularly in the wavelength range of 290–460 nm, which can degrade polymers, plastics, and coatings through oxidative reactions. Over time, this leads to color fading, loss of mechanical strength, and surface deterioration. To counteract these effects, UV absorbers—a type of light stabilizer—are added to materials to absorb and dissipate UV radiation before it causes damage.
This article explores the types of UV absorbers, their mechanisms of action, industry standards, and applications in coatings, plastics, and other polymer-based materials.
1. What Are UV Absorbers?
UV absorbers are chemical compounds that selectively absorb high-energy UV radiation and convert it into harmless heat or low-energy wavelengths. Unlike pigments or fillers that block UV light by scattering or reflecting it, UV absorbers function at a molecular level, making them ideal for transparent or lightly colored materials.
Key Properties of an Effective UV Absorber
- Strong UV absorption (especially 290–400 nm).
- Thermal stability—must withstand polymer processing temperatures.
- Chemical stability—should not react with other additives or degrade over time.
- Good compatibility—should not migrate, bloom, or leach out of the material.
- Photostability—should not decompose or discolor under prolonged UV exposure.
- Low toxicity and odor—suitable for food-contact and medical applications.
- Cost-effectiveness—affordable for industrial-scale use.
2. Industry Standards for UV Absorbers
Several national and international standards regulate the use and testing of UV absorbers in coatings and plastics:
A. Product Standards
- HG/T 5084-2016 (2023) – Specifies requirements for 2-hydroxy-4-n-octoxybenzophenone (UV-531), a widely used UV absorber in plastics and coatings.
B. Testing Methods
- SN/T 5258-2020 – Uses High-Performance Liquid Chromatography (HPLC) to detect UV-320 and UV-328 in coatings.
- SN/T 5259-2020 – Employs Gas Chromatography-Mass Spectrometry (GC-MS) to measure UV-320, UV-327, UV-328, and UV-350 in coatings.
These standards ensure quality control, safety, and performance consistency in industrial applications.
3. Classification of UV Absorbers
UV absorbers are categorized based on their chemical structure and absorption range:
| Benzophenones | UV-9, UV-531 | 270–330 | Broad compatibility, used in PVC, PE, PP |
| Benzotriazoles | UV-327, UV-328 | 270–380 | High photostability, good for polyolefins |
| Triazines | UV-1164 | 300–380 | Superior heat stability, often used with HALS |
| Hindered Amine Light Stabilizers (HALS) | UV-622 | N/A (radical scavenger) | Works synergistically with UV absorbers |
A. Benzophenones (e.g., UV-531)
- Absorb 270–330 nm UV light.
- Applications: Polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC).
- Advantages: Good solubility in organic solvents, low volatility.
B. Benzotriazoles (e.g., UV-327, UV-328)
- Absorb 270–380 nm UV light.
- Applications: Automotive coatings, packaging films, outdoor plastics.
- Advantages: Excellent chemical stability, minimal color impact.
C. Triazines (e.g., UV-1164)
- Absorb 300–380 nm UV light.
- Applications: High-performance polymers, automotive parts.
- Advantages: Exceptional thermal stability, often combined with HALS for enhanced protection.
D. Hindered Amine Light Stabilizers (HALS, e.g., UV-622)
- Not a UV absorber but a radical scavenger.
- Synergistic effect: When combined with UV absorbers, HALS significantly improves long-term stability.
4. Common UV Absorbers and Their Applications
A. 2-Hydroxy-4-Methoxybenzophenone (UV-9)
- Appearance: Light yellow or white crystalline powder.
- Melting Point: 62–66°C.
- Solubility: Soluble in acetone, benzene, ethanol; insoluble in water.
- Applications: PVC, PMMA, unsaturated polyesters, coatings.
- Advantages: Low visible light absorption, ideal for transparent products.
B. 2-Hydroxy-4-n-Octoxybenzophenone (UV-531)
- Appearance: Light yellow or white powder.
- Melting Point: 48–49°C.
- Solubility: Soluble in acetone, benzene; slightly soluble in water.
- Applications: PE, PP, PS, ABS, polycarbonates.
- Advantages: Low volatility, excellent compatibility with polymers.
C. 2-(2′-Hydroxy-3′,5′-Di-tert-Butylphenyl)-5-Chlorobenzotriazole (UV-327)
- Appearance: Pale yellow powder.
- Absorption Range: 270–380 nm.
- Applications: Polyolefins, PVC, polyurethane, coatings.
- Advantages: High resistance to extraction, minimal migration.
D. Monobenzoate Resorcinol Ester
- Appearance: White crystalline powder.
- Melting Point: 132–135°C.
- Applications: PVC, cellulose resins, polystyrene.
- Advantages: Similar performance to benzophenones, suitable for transparent films.
5. Synergistic Effects and Best Practices
A. Combining UV Absorbers with HALS
- HALS (e.g., UV-622) does not absorb UV but neutralizes free radicals generated during UV exposure.
- Triazine + HALS blends provide superior long-term stability in outdoor applications.
B. Optimal Loading Levels
- 0.1–1.5% is typical for most polymers.
- Higher concentrations may lead to migration or reduced transparency.
C. Selection Criteria
- Polymer type (PE, PP, PVC, etc.).
- Processing temperature (must withstand extrusion/molding).
- End-use environment (outdoor vs. indoor).
UV Absorber: 4-Chloro-4′-hydroxybenzophenone (CAS 42019-78-3)
4-Chloro-4′-hydroxybenzophenone (CAS 42019-78-3) is a benzophenone-based UV absorber that effectively protects polymers and coatings from ultraviolet (UV) degradation. It absorbs harmful UV radiation (290–350 nm) and converts it into harmless thermal energy, preventing yellowing, embrittlement, and loss of mechanical properties in materials.
Key Properties & Applications
- Chemical Formula: C₁₃H₉ClO₂
- Appearance: Light yellow crystalline powder
- Melting Point: ~140–145°C
- Solubility: Soluble in organic solvents (acetone, ethanol), low water solubility
- Applications:
- Plastics (PVC, polyesters, polycarbonates)
- Coatings & adhesives
- Photostabilizer in packaging films
Advantages
✔ Strong UV absorption in critical wavelengths
✔ Good thermal stability for processing
✔ Low volatility, reducing migration risks
This UV absorber is particularly useful in transparent or thin-film applications where UV protection is essential without compromising clarity. For technical specifications or sourcing, consult chemical suppliers specializing in polymer additives.
6. Future Trends in UV Stabilization
- Bio-based UV absorbers – Sustainable alternatives derived from natural sources.
- Nano-enhanced stabilizers – Improved dispersion and efficiency.
- Smart coatings – UV-responsive materials that adapt to sunlight intensity.
Conclusion
UV absorbers play a critical role in extending the lifespan of polymers, coatings, and plastics by preventing UV-induced degradation. The choice of UV absorber depends on material compatibility, absorption range, and environmental conditions. Industry standards such as HG/T 5084 and SN/T 5258-5259 ensure quality and performance consistency.
For optimal results, combining UV absorbers with HALS provides a synergistic effect, enhancing durability in harsh environments. As technology advances, eco-friendly and high-efficiency UV stabilizers will continue to evolve, meeting the demands of modern applications.
References & Further Reading
- HG/T 5084-2016 (2023) – UV-531 specifications.
- SN/T 5258-2020 – HPLC method for UV-320/UV-328.
- SN/T 5259-2020 – GC-MS method for multiple UV absorbers.
For technical inquiries or material sourcing, contact: info@hubeiteyer.com.
Would you like additional details on any specific UV absorber or application? Let us know in the comments!