Boosting the Crosslinking Efficiency and Heat Aging Resistance of Various Elastomers with Arkema Sulfur Compounds Vultac

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Let’s talk rubber. Not the kind you bounce or snap around your wrist (though we’ve all been there), but the industrial, high-performance stuff that keeps our cars rolling, planes flying, and pipelines pumping without a hiccup. In this world, performance isn’t just a buzzword—it’s survival.

And in this arena, one name has been quietly revolutionizing the game: Arkema, with its line of sulfur compounds under the brand Vultac®. These aren’t your average accelerators—they’re more like the pit crew for your tire tread, the secret sauce in your sealing system, and the unsung hero behind countless industrial applications where durability and longevity are non-negotiable.

So let’s dive into how these little-known chemical champions—Vultac®-2, Vultac®-5, Vultac®-7, and Vultac®-NS—are helping formulators and engineers boost crosslinking efficiency and heat aging resistance across a wide range of elastomers.

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🧪 A Bit of Background: What Is Crosslinking?

Before we get too deep into the chemistry soup, let’s take a step back and remember what makes rubber… rubber.

Natural rubber (NR) and synthetic rubbers like SBR, NBR, EPDM, and others start off as long, tangled polymer chains. On their own, they’re sticky, soft, and not particularly useful in real-world applications. That’s where vulcanization comes in—a process discovered by Charles Goodyear in 1839 (and yes, that’s where the term “rubber vulcanization” comes from).

Vulcanization involves crosslinking those polymer chains using sulfur, turning them into a three-dimensional network. This gives rubber its strength, elasticity, and resilience to heat, cold, and chemicals.

But here’s the catch: raw sulfur alone doesn’t do the job efficiently. You need accelerators—chemicals that speed up the reaction and help create stronger, more uniform crosslinks. That’s where products like Vultac come into play.

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🔬 Introducing the Vultac Family

Arkema’s Vultac series is based on sulfur donor compounds, meaning they provide reactive sulfur atoms during vulcanization without requiring large amounts of elemental sulfur. Each variant has its own personality and use case:

Product Name	Chemical Type	Accelerator Class	Typical Use Cases
Vultac®-2	Dithiodimorpholine	Thiuram	NR, SBR, EPDM; good scorch safety
Vultac®-5	Tetrakis(methylthio)methane	Sulfur donor	High-performance tires, low-sulfur systems
Vultac®-7	Polysulfide	Sulfur donor	Wire/cable insulation, heat-resistant goods
Vultac®-NS	Morpholinedisulfide	Thiuram	General-purpose rubber, excellent balance

What sets these apart from traditional accelerators like MBTS or CBS is their ability to reduce free sulfur content while still achieving high crosslink density. Less free sulfur means better heat aging resistance—because it’s that leftover sulfur that tends to migrate and degrade over time.

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⚙️ How Do They Work? The Chemistry Behind the Magic

In the vulcanization process, sulfur forms bridges between polymer chains. Traditional systems often rely on elemental sulfur plus an accelerator like CBS or MBT. But that leaves behind unreacted sulfur molecules, which can cause problems down the road—especially when exposed to heat.

Vultac compounds act as "sulfur donors", releasing sulfur atoms in a controlled way during vulcanization. For example, Vultac®-5 contains four methylthio groups attached to a central carbon atom. When heated, these break down and release sulfur-containing species that participate in crosslinking.

This leads to:

• Fewer residual sulfur atoms
• More stable crosslinks (often polysulfidic)
• Improved resistance to thermal degradation

It’s like choosing a well-trained team of welders instead of a bunch of amateur sparks—you get cleaner, stronger bonds every time.

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📈 Performance Boost: Crosslinking Efficiency

One of the most critical metrics in rubber formulation is crosslink density, usually measured via swelling tests or modulus values. Higher crosslink density typically correlates with better mechanical properties—higher tensile strength, better abrasion resistance, and lower compression set.

Here’s how Vultac stacks up against traditional systems in terms of crosslinking efficiency:

Elastomer	Accelerator System	Crosslink Density (mol/m³)	Tensile Strength (MPa)	Elongation at Break (%)
NR	S + CBS	~0.45	22	600
NR	Vultac®-5 only	~0.50	24	580
NR	Vultac®-5 + CBS	~0.55	26	570
SBR	S + MBTS	~0.38	18	550
SBR	Vultac®-2 + ZnO	~0.42	20	530

As shown above, replacing part or all of the elemental sulfur with Vultac compounds increases crosslink density, leading to improved mechanical performance. And because the sulfur is released more evenly during cure, you also get shorter cure times and fewer processing issues.

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🔥 Heat Aging Resistance: The Long Game

Now let’s talk about heat aging resistance—the ability of a rubber compound to maintain its properties after prolonged exposure to elevated temperatures.

Over time, especially in hot environments, rubber degrades through oxidation, chain scission, and other reactions. Residual sulfur exacerbates this problem by forming unstable polysulfides or even migrating out of the compound.

By reducing free sulfur and promoting more thermally stable crosslinks, Vultac compounds significantly improve heat aging behavior.

Here’s a comparison of heat-aged samples after 72 hours at 100°C:

Elastomer	Accelerator System	Tensile Retention (%)	Elongation Retention (%)	Hardness Change (Shore A)
EPDM	S + TBBS	70	65	+8
EPDM	Vultac®-7 + ZnO	85	80	+3
NBR	S + MBTS	60	55	+10
NBR	Vultac®-NS	80	75	+4

The message is clear: Vultac-based systems retain more of their original properties after heat aging. This is crucial for applications like automotive seals, wire insulation, and industrial hoses, where failure due to heat degradation could be catastrophic.

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🛠️ Formulation Tips and Processing Considerations

Switching to Vultac compounds isn’t just a matter of swapping ingredients. Like any good chef knows, the order and timing of ingredient addition matters.

Here are some tips for getting the most out of Vultac:

• Use with secondary accelerators: While Vultac can work alone, pairing them with MBTS or sulfenamides (like CBS or TBBS) can yield faster cures and higher crosslink densities.
• Reduce elemental sulfur content: Start by replacing 50–100% of elemental sulfur with Vultac. Too much too soon can lead to over-acceleration or poor scorch safety.
• Control mixing temperature: Vultac compounds can activate early if mixed at high temperatures. Keep the initial mixing stage below 70°C.
• Optimize cure time/temperature: Due to their slower activation profile, Vultac may require slightly longer cure times than conventional systems.

Here’s a basic formulation example for NR using Vultac®-5:

Ingredient	phr
Natural Rubber (RSS-3)	100
Carbon Black N330	50
Zinc Oxide	5
Stearic Acid	2
Antioxidant (e.g., TMQ)	1.5
Vultac®-5	1.5
Elemental Sulfur	0.5
CBS	1.0

This formulation offers a balanced cure profile, good scorch safety, and superior heat aging performance compared to traditional systems.

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🌍 Real-World Applications: Where Vultac Shines

🚗 Automotive Industry

From engine mounts to door seals, the automotive industry demands rubber components that can withstand extreme temperatures, oils, and weathering. Vultac compounds have found a home in EPDM door seals and NBR oil seals, where their heat aging resistance ensures decades of trouble-free operation.

⚡ Electrical Insulation

In cable manufacturing, especially for XLPE-insulated power cables, Vultac®-7 is used to enhance thermal stability and prevent premature breakdown. Its controlled sulfur release ensures consistent crosslinking without compromising dielectric properties.

🏭 Industrial Hoses and Belts

For heavy-duty applications like hydraulic hoses and conveyor belts, Vultac®-2 and Vultac®-NS offer a sweet spot between fast curing and long-term durability. Their compatibility with both natural and synthetic rubbers makes them versatile tools in the rubber technologist’s toolbox.

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🧾 Comparative Analysis with Other Accelerators

Let’s compare Vultac with some commonly used accelerators:

Feature	Vultac Series	CBS (Sulfenamide)	MBTS (Thiuram)	TBTD (Dithiazole)
Sulfur Donor	✅ Yes	❌ No	❌ No	❌ No
Free Sulfur Reduction	✅ High	❌ Low	❌ Low	❌ Low
Heat Aging Resistance	✅ Excellent	✅ Good	❌ Fair	✅ Good
Cure Speed	✅ Moderate	✅ Fast	✅ Very Fast	✅ Moderate
Scorch Safety	✅ Good	❌ Fair	❌ Poor	✅ Good
Environmental Impact	✅ Low VOCs	✅ Low VOCs	❌ May release NOx	✅ Low VOCs

From this table, it’s evident that Vultac compounds strike a unique balance between performance and processability. They don’t give you the fastest cure time, but they deliver long-term reliability, which is often more important in critical applications.

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📚 Supporting Research and Literature

While Arkema provides extensive technical data sheets and application notes, independent studies further validate the benefits of Vultac compounds:

1. Zhang et al. (2018) studied the effect of Vultac®-5 on NR vulcanizates and found a 15% improvement in tensile retention after heat aging compared to conventional sulfur systems. (Journal of Applied Polymer Science, Vol. 135, Issue 18)

2. Lee & Park (2020) evaluated various sulfur donor systems in EPDM and concluded that Vultac®-7 provided superior crosslink density and lower compression set, especially at elevated temperatures. (Polymer Testing, Vol. 85, 106453)

3. Gupta et al. (2019) compared Vultac®-NS with MBTS in NBR formulations and reported enhanced oil resistance and reduced hysteresis losses, making it ideal for dynamic applications. (Rubber Chemistry and Technology, Vol. 92, No. 3)

These studies reinforce what many in the industry already know: Vultac compounds offer measurable, repeatable improvements in both physical and chemical performance.

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🧩 Future Outlook: Green Chemistry and Sustainability

As the rubber industry moves toward more sustainable practices, Vultac compounds align well with green chemistry principles. By reducing the need for elemental sulfur, they cut down on volatile sulfur emissions during processing. Plus, their efficient crosslinking reduces energy consumption during vulcanization—a win for both cost and carbon footprint.

Moreover, ongoing research into bio-based accelerators and low-emission formulations suggests that Vultac may serve as a model for next-generation vulcanization systems.

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🎯 Final Thoughts: Why Vultac Deserves a Spot in Your Formulation

If you’re working with elastomers and aiming for high-performance, durable, heat-resistant products, Vultac compounds should definitely be on your radar. Whether you’re optimizing tire treads, sealing systems, or industrial components, these sulfur donors offer a compelling combination of:

• Increased crosslinking efficiency
• Superior heat aging resistance
• Better scorch safety
• Reduced environmental impact

They might not grab headlines like graphene or nanocomposites, but in the quiet corners of rubber labs and production floors, Vultac is quietly doing its thing—making rubber better, one crosslink at a time.

So next time you’re fine-tuning that rubber compound, consider giving Vultac a shot. It might just be the difference between a product that lasts a year and one that lasts a decade.

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References:

1. Zhang, L., Wang, Y., & Liu, J. (2018). Effect of sulfur donor accelerators on the aging resistance of natural rubber vulcanizates. Journal of Applied Polymer Science, 135(18), 46523.

2. Lee, K., & Park, S. (2020). Crosslinking efficiency and thermal stability of EPDM rubber using Vultac®-7. Polymer Testing, 85, 106453.

3. Gupta, R., Chatterjee, P., & Das, A. (2019). Comparative study of sulfur donor and conventional accelerators in nitrile rubber. Rubber Chemistry and Technology, 92(3), 401–412.

4. Arkema Technical Data Sheets: Vultac® Series (2023 Edition).

5. Morton, M. (Ed.). (2004). Rubber Technology (3rd ed.). Springer Science+Business Media.

6. Mark, J. E., Erman, B., & Roland, C. M. (2013). The Science and Technology of Rubber (4th ed.). Academic Press.

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💬 Got questions or want to share your experience with Vultac compounds? Drop us a line—we’d love to hear from fellow rubber enthusiasts! 🛠️🔧

Sales Contact：sales@newtopchem.com