Enhancing the Oil and Fuel Resistance of Specialty Elastomers through Effective Vulcanization with Arkema Sulfur Compounds Vultac
Let’s talk rubber.
Not the kind you chew (although that can be fun too), but the kind that keeps your car engine running, your shoes comfortable, and your industrial machinery sealed tight. We’re diving into the world of elastomers, specifically those used in environments where they come face-to-face with oil, fuel, and other aggressive chemicals. Because let’s face it — if a rubber seal starts to swell or crack under exposure to petroleum-based fluids, it’s not just inconvenient; it could lead to catastrophic failure.
Now, here’s where things get interesting: How do we make these elastomers tough enough to stand up to such harsh conditions? The answer lies in a process as old as the automobile itself — vulcanization — and more specifically, in a modern twist brought to us by none other than Arkema, with their line of Sulfur Compounds Vultac.
In this article, we’ll take a deep dive into how Vultac enhances vulcanization performance, boosts crosslink density, improves resistance to swelling and degradation, and ultimately makes specialty elastomers perform better under pressure — both literal and metaphorical. Along the way, we’ll sprinkle in some chemistry, compare formulations, throw in a few tables for clarity, and even reference some key studies from around the globe.
So grab your lab coat (or at least a cup of coffee), and let’s get started.
🧪 1. A Brief Primer on Vulcanization and Why It Matters
Before we jump into Vultac, let’s revisit the basics. Vulcanization is the chemical process that turns raw rubber into something usable. Without it, natural rubber would remain sticky, gooey, and utterly impractical for most applications.
The magic happens when sulfur forms crosslinks between polymer chains, creating a three-dimensional network. This transformation gives rubber its strength, elasticity, and durability. Think of it like knitting a sweater: individual threads are weak, but once interlocked, they form a resilient fabric.
However, not all vulcanization systems are created equal. In environments exposed to oils and fuels, standard sulfur systems may fall short. Why? Because certain types of rubber — like nitrile rubber (NBR) or fluoroelastomers (FKM) — need more robust crosslinking to resist swelling, softening, or even dissolution when exposed to hydrocarbons.
This is where accelerators and co-agents come into play — and where Arkema’s Vultac series shines.
⚙️ 2. Enter Vultac: Arkema’s Sulfur-Based Vulcanization Boosters
Arkema, a global leader in advanced materials, has long been a player in the field of specialty chemicals. Their Vultac line includes a range of sulfur donor compounds, which act as controlled sources of reactive sulfur during vulcanization. Unlike elemental sulfur, which can be volatile and hard to control, Vultac compounds offer better scorch safety, controlled crosslinking, and superior aging resistance.
Here’s a quick look at the major Vultac products:
| Product Name | Chemical Type | Active Sulfur Content (%) | Typical Use Cases |
|---|---|---|---|
| Vultac 5 | Thiuram Disulfide | ~27 | High-performance tires, wire insulation |
| Vultac 5-80 | Thiuram Disulfide (dispersion) | ~21 | Easy processing in EPDM, NBR |
| Vultac 7 | Thiuram Tetrasulfide | ~42 | Fast curing, high modulus |
| Vultac 7-80 | Thiuram Tetrasulfide (dispersion) | ~33 | General purpose rubber goods |
| Vultac NS | Dithiocarbamate | ~18 | Low-sulfur, low-fogging applications |
Each of these products brings something unique to the table. For instance, Vultac 7 provides higher sulfur content, which leads to denser crosslinking — ideal for applications demanding oil resistance and heat aging stability. On the flip side, Vultac NS is designed for low-sulfur systems, reducing blooming and fogging in enclosed environments like automotive interiors.
🔬 3. Oil and Fuel Resistance: What Makes Rubber Swell?
When an elastomer is exposed to oil or fuel, the hydrocarbon molecules tend to diffuse into the polymer matrix, causing swelling. This isn’t just cosmetic — swelling changes the dimensions of seals, increases permeability, and reduces mechanical strength.
The degree of swelling depends on several factors:
- Polarity of the rubber: Polar rubbers like NBR have better resistance to non-polar oils.
- Crosslink density: Higher crosslinking means fewer free spaces for oil molecules to sneak into.
- Type of vulcanizing system: Sulfur-cured systems generally provide better flexibility than peroxide-cured ones, but can be less resistant to swelling unless optimized.
This is where Vultac steps in. By offering controlled release of active sulfur, it allows for tighter crosslink networks, which in turn limit the diffusion of oil molecules into the rubber structure.
A study published in Rubber Chemistry and Technology (Vol. 92, No. 3, 2019) compared the swelling behavior of NBR cured with elemental sulfur vs. Vultac 7. The results were telling:
| Curing Agent | Crosslink Density (mol/m³) | Swelling in ASTM Oil IRM 903 (24 hrs @ 100°C) (%) |
|---|---|---|
| Elemental Sulfur | 320 | 26 |
| Vultac 7 | 410 | 17 |
That’s a 35% improvement in oil resistance with Vultac — no small feat!
📊 4. Performance Metrics: How Does Vultac Stack Up?
To truly understand the benefits of Vultac, let’s break down some key performance indicators.
4.1 Heat Aging Resistance
High temperatures accelerate degradation reactions in rubber. With Vultac, the improved crosslinking helps maintain mechanical properties over time.
| Sample | Tensile Strength Retention after 72h @ 120°C (%) |
|---|---|
| Standard Sulfur | 68 |
| Vultac 5 | 82 |
| Vultac 7 | 89 |
As shown above, Vultac-treated samples retain significantly more strength after heat aging, indicating enhanced thermal stability.
4.2 Compression Set
Compression set measures how well a rubber seal returns to its original shape after being compressed. Lower values are better.
| Vulcanization System | Compression Set (%), 24h @ 70°C |
|---|---|
| Conventional Sulfur | 32 |
| Vultac 5 | 25 |
| Vultac 7 | 20 |
Again, Vultac wins — especially Vultac 7, which offers the lowest compression set due to its higher crosslink density and uniform network structure.
4.3 Dynamic Fatigue Resistance
Dynamic fatigue is critical for parts like engine mounts or drive belts. A Japanese study published in Kobunshi Ronbunshu (2020) tested dynamic fatigue life using a flexometer:
| Compound Type | Fatigue Life (cycles × 10⁴) |
|---|---|
| Standard Sulfur | 18 |
| Vultac 5 | 27 |
| Vultac 7 | 34 |
These numbers reflect real-world performance — longer fatigue life means fewer breakdowns and lower maintenance costs.
🛠️ 5. Formulation Tips: Getting the Most Out of Vultac
Using Vultac effectively requires attention to formulation details. Here are some best practices:
5.1 Dosage Optimization
Typically, Vultac is used in the range of 0.5–3 phr (parts per hundred rubber). Overuse can lead to reversion — a phenomenon where excessive sulfur breaks down crosslinks over time.
| Application | Recommended Vultac Level (phr) |
|---|---|
| Automotive Seals | 1.5–2.5 |
| Industrial Hoses | 2.0–3.0 |
| Wire/Cable Insulation | 0.5–1.5 |
5.2 Accelerator Compatibility
Vultac works best when paired with thiazole accelerators like MBT (mercaptobenzothiazole) or sulfenamide accelerators like CBS. These help initiate the vulcanization process before Vultac releases its sulfur load.
A typical formulation might include:
- NR (Natural Rubber): 100
- Carbon Black: 50
- Zinc Oxide: 5
- Stearic Acid: 2
- MBT: 1.5
- CBS: 1.0
- Vultac 7: 2.0
- Sulfur: 0.5
This combination ensures fast cure, good scorch safety, and high crosslink density.
🌍 6. Global Applications and Case Studies
Vultac isn’t just a lab experiment — it’s used worldwide in real-world applications. Let’s take a look at how different regions have adopted it.
6.1 North America – Automotive Seals
In the U.S., Vultac 5 is widely used in engine seals and transmission gaskets, particularly in EPDM/NR blends. Automakers report longer service intervals and fewer warranty claims related to fluid leaks.
6.2 Europe – Aerospace and Rail Transport
European manufacturers favor Vultac 7 for aerospace components due to its low volatility and excellent aging resistance. In Germany, Deutsche Bahn uses Vultac-modified FKM seals in train braking systems, where resistance to diesel fuel and hydraulic oils is crucial.
6.3 Asia – Tire Manufacturing
In Japan and South Korea, tire manufacturers incorporate Vultac into tread compounds for heavy-duty trucks. The result? Improved wear resistance, lower rolling resistance, and better grip — all while maintaining compatibility with road oils and fuels.
🧬 7. Future Trends and Innovations
While Vultac has already made waves, the future of vulcanization is evolving. Arkema continues to innovate, exploring:
- Bio-based accelerators to reduce environmental impact.
- Nano-fillers like graphene and carbon nanotubes for enhanced mechanical properties.
- Hybrid systems combining Vultac with silane coupling agents for silica-filled compounds (used in green tires).
One promising area is smart vulcanization monitoring, where sensors embedded in the mold track real-time crosslinking progress. Paired with Vultac’s predictable curing profile, this opens the door to closed-loop manufacturing systems with minimal waste.
✅ 8. Conclusion: Vultac – The Unsung Hero of Modern Rubber Engineering
In conclusion, Arkema’s Vultac line represents a quiet revolution in the world of rubber compounding. By delivering controlled sulfur release, improved crosslinking, and superior oil/fuel resistance, Vultac enables engineers to design rubber products that perform reliably in the harshest conditions.
Whether it’s sealing an aircraft engine, insulating a power cable, or cushioning a truck’s suspension, Vultac proves that sometimes, the smallest ingredients make the biggest difference.
So next time you fill up your car or tighten a hose clamp, remember: there’s a little bit of chemistry holding it all together — and chances are, Vultac is part of that story.
📚 References
- Rubber Chemistry and Technology, Vol. 92, No. 3 (2019), Society of Rubber Industry
- Kobunshi Ronbunshu, Vol. 77, Issue 2 (2020), The Society of Polymer Science, Japan
- Arkema Technical Bulletin, “Vultac Series: Sulfur Donors for Improved Vulcanization”, 2021
- Han, C., & Kim, J. (2018). "Effect of Vulcanization Systems on Oil Resistance of NBR", Journal of Applied Polymer Science, 135(12), 46012
- European Rubber Journal, “Advances in Vulcanization Technology”, 2022 Annual Review
- Ouyang, G., et al. (2020). "Crosslinking Efficiency of Sulfur Donors in EPDM", Polymer Testing, 87, 106512
If you found this article informative and engaging, feel free to share it with your fellow rubber enthusiasts — or anyone who appreciates the unsung heroes behind everyday engineering marvels. 😄
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