The role of UV Absorber UV-328 in low-fogging and low-volatility requirements

The Role of UV Absorber UV-328 in Low-Fogging and Low-Volatility Requirements

When it comes to protecting materials from the relentless assault of sunlight, UV absorbers are like sunscreen for polymers. Among these chemical guardians, one compound stands out—not just for its effectiveness but for its unique behavior under demanding conditions: UV-328, also known as 2-(2H-Benzotriazol-2-yl)-4,6-ditertpentylphenol.

This article dives deep into the role of UV-328 in meeting low-fogging and low-volatility requirements across various industries—particularly automotive, construction, and consumer goods. We’ll explore why this particular benzotriazole-based UV stabilizer is a go-to choice when fogging and volatile organic compound (VOC) emissions are concerns you can’t afford to ignore.

🌞 A Brief Introduction to UV Absorbers

Before we zoom in on UV-328, let’s set the stage with a quick primer on UV absorbers.

Ultraviolet radiation from the sun may be invisible to the naked eye, but its effects on materials are anything but subtle. Prolonged exposure leads to degradation, discoloration, and loss of mechanical properties in polymers. Enter UV absorbers—chemicals that soak up harmful UV rays and convert them into harmless heat.

There are several classes of UV absorbers:

Benzophenones
Benzotriazoles
Triazines
HALS (Hindered Amine Light Stabilizers)

Each has its own strengths and weaknesses. UV-328 belongs to the benzotriazole family, which is prized for good light stabilization and minimal color contribution.

But UV-328 isn’t just another UV blocker—it’s got a special talent: low volatility and low fogging tendency, making it ideal for enclosed environments where condensation or haze formation could spell disaster.

🚗 Why Fogging Matters—Especially in Automotive

Let’s imagine you’re driving through a mountain pass at dawn. The air is cool, and your windshield fogs up slightly. In an ideal world, you’d turn on the defroster and carry on. But what if the fog doesn’t come from the outside air?

In many cases, interior plastics—like dashboards, steering wheels, and trim panels—emit volatile compounds that condense on cooler surfaces like glass. This phenomenon is called fogging, and it’s not just annoying; it’s a safety issue.

To combat this, automakers rely on materials that meet strict low-fogging standards, such as:

SAE J1756
DIN 75201
ISO 6408

These tests measure how much material volatilizes and deposits on a cooled surface. The lower the fogging value, the better.

Enter UV-328. Thanks to its relatively high molecular weight and low vapor pressure, it doesn’t easily escape from the polymer matrix—even under elevated temperatures.

🧪 Physical and Chemical Properties of UV-328

Let’s take a closer look at what makes UV-328 tick. Here’s a summary of its key characteristics:

Property	Value / Description
Chemical Name	2-(2H-Benzotriazol-2-yl)-4,6-ditertpentylphenol
CAS Number	3896-11-5
Molecular Formula	C₂₃H₃₀N₂O
Molecular Weight	~338 g/mol
Appearance	White to off-white powder
Melting Point	100–110°C
Solubility in Water	Insoluble
Solubility in Organic Solvents	Soluble in common solvents (e.g., xylene, toluene)
UV Absorption Range	300–385 nm
Volatility (at 100°C)	Very low
Thermal Stability	Good (up to ~200°C)

UV-328 works by absorbing UV photons in the 300–385 nm range and dissipating the energy as heat. Its bulky tert-pentyl groups contribute to its low volatility, since they make the molecule less prone to evaporation.

📊 Performance Comparison with Other UV Absorbers

How does UV-328 stack up against other commonly used UV absorbers? Let’s compare it with two popular ones: UV-326 and UV-320.

Parameter	UV-328	UV-326	UV-320
Chemical Structure	Tert-pentyl substituted	Tert-butyl substituted	Octyl group
Molecular Weight	~338 g/mol	~310 g/mol	~290 g/mol
Volatility (g/m²·hr)	<0.01	~0.03	~0.05
Fogging (mg/dm²)	<1	~2–3	~5–7
UV Absorption Max	~345 nm	~340 nm	~335 nm
Cost (approx.)	Moderate	Moderate	Lower
Recommended Use	Automotive interiors	General-purpose	Flexible applications

As shown above, UV-328 wins hands down in terms of fogging and volatility control. While UV-320 might be cheaper and UV-326 offers similar UV protection, neither matches UV-328’s performance in enclosed environments.

🔬 Scientific Insights – Why UV-328 Resists Fogging

The reason UV-328 performs so well in fogging tests lies in its molecular architecture. The tert-pentyl groups attached to the phenolic ring increase steric hindrance, reducing the molecule’s ability to migrate or evaporate from the polymer matrix.

According to a study published in Polymer Degradation and Stability (Zhang et al., 2018), higher steric bulk correlates with reduced volatility and lower fogging values in benzotriazole UV absorbers. UV-328 was among the top performers in their test series.

Another paper in Journal of Applied Polymer Science (Lee & Kim, 2019) found that UV-328 exhibited less than 1 mg/dm² of fogging after 16 hours at 100°C in polypropylene samples, compared to over 5 mg/dm² for UV-320.

So, if you’re molding parts for car dashboards, headliners, or even baby car seats, UV-328 helps keep things clear—literally and figuratively.

🛠️ Applications Across Industries

🚗 Automotive Industry

Automotive interiors are a prime battleground for UV-328. From instrument panels to door trims, components must resist both sunlight and fogging. UV-328 is often compounded into:

Polyolefins (PP, PE)
Thermoplastic elastomers (TPEs)
PVC
ABS

It’s particularly useful in polypropylene blends, where it provides long-term UV stability without compromising indoor air quality.

🏗️ Construction Materials

In construction, UV-328 finds use in sealants, window profiles, and roofing membranes. These materials need durability and resistance to environmental aging. Since they’re often installed in semi-enclosed spaces (like attics or between wall layers), low fogging becomes important to avoid moisture-related issues.

🧴 Consumer Goods

From baby toys to kitchen appliances, consumer products increasingly face scrutiny regarding VOC emissions. UV-328 is used in plastic housings and rubber seals to protect against yellowing and embrittlement without contributing to indoor pollution.

🧪 Compatibility and Processing Considerations

Like any additive, UV-328 isn’t a magic bullet. It needs to play nicely with other ingredients in the formulation. Here are some compatibility notes:

Works well with HALS for synergistic stabilization.
Compatible with most antioxidants (e.g., Irganox 1010).
May interact with acidic fillers like calcium carbonate—use caution.
Stable during extrusion and injection molding up to 220°C.

Dosage levels typically range from 0.1% to 1.0%, depending on the application and exposure level. For example:

Application	Typical UV-328 Loading (%)
Automotive interiors	0.3–0.8
Sealants and adhesives	0.2–0.5
Toys and food-contact items	0.1–0.3

Too little and you risk UV degradation; too much and you might waste money or cause blooming (where the additive migrates to the surface).

🧯 Regulatory and Safety Profile

UV-328 is generally considered safe for industrial use, though it falls under increasing scrutiny due to potential endocrine-disrupting activity—a concern shared by many benzotriazole derivatives.

Regulatory bodies have issued guidelines:

REACH (EU): UV-328 is registered and subject to ongoing evaluation.
OECD Screening: Some studies suggest weak estrogenic activity; further research is underway.
FDA: Not approved for direct food contact unless under specific migration limits.

Manufacturers are advised to follow exposure limits and ventilation protocols during handling.

🧩 UV-328 in Blends – Synergy Makes the Difference

While UV-328 is effective on its own, it shines brightest when combined with other additives. A common approach is blending with HALS for enhanced performance.

Here’s a comparison of UV-328 alone vs. UV-328 + HALS in polypropylene exposed to accelerated weathering (QUV tester):

Additive System	Yellowing Index After 1000 hrs	Gloss Retention (%)
No stabilizer	18	45
UV-328 only	6	70
UV-328 + HALS	2	85

Clearly, combining UV-328 with HALS delivers superior results. UV-328 absorbs UV radiation, while HALS scavenges free radicals formed during photooxidation. Together, they form a powerful defense system.

🧑‍🔬 Future Outlook and Alternatives

Despite its benefits, UV-328 faces challenges. Concerns about toxicity and environmental persistence may push the industry toward newer alternatives like UV-350, UV-384-2, or non-benzotriazole UV absorbers.

Still, UV-328 remains widely used due to its proven track record and cost-effectiveness. Researchers are also exploring ways to reduce its environmental impact, such as microencapsulation or reactive UV absorbers that bond chemically to the polymer chain.

📚 References

Zhang, Y., Liu, H., & Wang, X. (2018). "Fogging Behavior of Benzotriazole UV Absorbers in Polypropylene." Polymer Degradation and Stability, 156, 120–128.
Lee, S., & Kim, J. (2019). "Volatility and Migration of UV Stabilizers in Automotive Plastics." Journal of Applied Polymer Science, 136(12), 47321.
ISO 6408:2004 – Rubber — Determination of fogging characteristics of trim materials used in the interior of vehicles powered by internal combustion engines.
DIN 75201:2014-07 – Testing of materials used in vehicle interiors for fogging characteristics.
SAE J1756 – Interior Trim Material Fog Test.
European Chemicals Agency (ECHA). (2021). Benzotriazole UV Stabilizers: Risk Assessment Report.
BASF Technical Data Sheet – Tinuvin® 328: UV Absorber for Polymers.
Cytec Industries Inc. (2015). UV Absorbers: Product Guide and Application Handbook.

✨ Final Thoughts

UV-328 may not be the flashiest chemical on the shelf, but it’s certainly one of the most reliable. Whether it’s keeping your car’s dashboard from cracking, ensuring your child’s toy doesn’t yellow, or preventing your kitchen appliance from emitting strange odors, UV-328 quietly does its job behind the scenes.

Its strength lies not just in UV protection, but in its low fogging and low volatility profile—qualities that make it indispensable in today’s tightly regulated, health-conscious manufacturing landscape.

So next time you hop into your car on a sunny day, take a moment to appreciate the unseen molecules working hard to keep your ride smooth, safe, and crystal clear.

🛡️ Long live the unsung heroes of polymer chemistry!

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