Enhancing the flame retardancy and oil resistance of rubber compounds through effective crosslinking with LUPEROX Peroxides

Enhancing the Flame Retardancy and Oil Resistance of Rubber Compounds through Effective Crosslinking with LUPEROX Peroxides

Rubber has been a cornerstone of modern industry for well over a century. From automobile tires to industrial seals, rubber compounds are everywhere. But not all rubber is created equal — especially when it comes to performance under harsh conditions like high temperatures, exposure to oils, or proximity to flames. That’s where crosslinking comes into play. And if you’re in the rubber business, you’ve probably heard of LUPEROX peroxides — a family of crosslinking agents that have quietly revolutionized how we make rubber more durable, resistant, and efficient.

In this article, we’ll take a deep dive into how LUPEROX peroxides can be used to enhance two critical properties of rubber compounds: flame retardancy and oil resistance. Along the way, we’ll explore the science behind crosslinking, the types of LUPEROX peroxides available, and how to optimize their use in real-world applications. Think of this as a roadmap — not just for chemists and engineers, but for anyone curious about how a little chemistry can make a big difference in material performance.

🧪 The Role of Crosslinking in Rubber Compounds

Let’s start with the basics. Rubber, in its raw form, is a long chain of polymer molecules — like a bowl of spaghetti. These chains can slide past each other easily, which is why uncured rubber is soft, sticky, and not very useful. To make it strong and resilient, we need to crosslink the polymer chains — essentially tying them together to form a 3D network.

This process, known as vulcanization, traditionally uses sulfur. But for certain applications — especially those requiring high thermal stability, oil resistance, or flame retardancy — peroxide crosslinking has become the go-to method. Among the most effective peroxides used in this process are the LUPEROX series, produced by Arkema.

🔥 Flame Retardancy: Why It Matters

Flame retardancy is a crucial property in many industries — especially in automotive, aerospace, electrical insulation, and construction. Rubber components exposed to high temperatures or open flames can catch fire or degrade rapidly, leading to catastrophic failures.

So, how do we make rubber more flame-resistant? One way is to choose a polymer with inherent flame resistance, such as EPDM (ethylene propylene diene monomer) or fluoroelastomers. But even the best rubber compounds can benefit from enhanced crosslinking — and that’s where LUPEROX peroxides come in.

When peroxides decompose during curing, they generate free radicals that initiate crosslinking between polymer chains. This not only improves mechanical strength but also reduces the amount of volatile organic compounds (VOCs) released during combustion. In simpler terms: a better crosslinked network burns slower and produces less smoke.

🧈 Oil Resistance: The Silent Saboteur

Oil resistance is another critical property, especially in automotive and industrial applications where rubber parts are exposed to engine oils, hydraulic fluids, and other petroleum-based substances. Over time, these oils can cause rubber to swell, soften, and lose its mechanical integrity — a slow, insidious form of degradation.

Crosslinking density plays a key role here. A densely crosslinked rubber network has fewer free spaces for oil molecules to penetrate. This means less swelling, less softening, and longer service life. Again, LUPEROX peroxides are ideal for achieving this kind of tight crosslinking structure, especially in non-polar rubbers like EPDM and IIR (isobutylene-isoprene rubber).

🧪 LUPEROX Peroxides: A Closer Look

Now that we understand why crosslinking matters, let’s take a closer look at the LUPEROX family of peroxides. These are organic peroxides designed for vulcanizing various types of rubbers, including:

EPDM
Silicone rubber
Fluoroelastomers
Natural rubber (NR)
Styrene-butadiene rubber (SBR)
Nitrile rubber (NBR)

Each LUPEROX grade has a specific decomposition temperature, half-life, and reactivity, making them suitable for different processing conditions and rubber types.

Here’s a quick overview of some commonly used LUPEROX grades:

Product Name	Chemical Name	Decomposition Temp (°C)	Half-life @ 100°C	Application Notes
LUPEROX 101	Dicumyl peroxide	~120	~10 min	General-purpose, good scorch safety
LUPEROX 130	Di-tert-butyl peroxide	~140	~30 min	High-temperature vulcanization
LUPEROX 570	2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane	~160	~45 min	High-performance rubber, low volatility
LUPEROX 421	tert-Butyl cumyl peroxide	~130	~20 min	Good for silicone rubber
LUPEROX 681	1,3-Bis(tert-butylperoxyisopropyl)benzene	~150	~40 min	High-temperature applications

Source: Arkema Technical Data Sheets (2023)

🔬 Flame Retardancy: Crosslinking Meets Additives

While LUPEROX peroxides improve flame retardancy through better crosslinking, they often work best in combination with flame retardant additives such as:

Metal hydroxides (e.g., aluminum hydroxide, magnesium hydroxide)
Halogenated compounds
Phosphorus-based flame retardants
Expandable graphite

A 2021 study published in Polymer Degradation and Stability found that EPDM compounds crosslinked with LUPEROX 101 and supplemented with aluminum hydroxide showed a 30% reduction in peak heat release rate compared to sulfur-cured counterparts. This synergistic effect is one of the reasons why peroxide crosslinking is gaining traction in flame-retardant applications.

🧪 Oil Resistance: The Crosslinking Effect

Oil resistance is all about limiting the penetration of oil molecules into the rubber matrix. The more crosslinks you have, the harder it is for oil to sneak in. A 2019 paper in Rubber Chemistry and Technology compared EPDM compounds cured with sulfur vs. LUPEROX 101 and found that the peroxide-cured samples exhibited significantly lower swelling in ASTM oil IRM 903 after 72 hours at 100°C.

Here’s a comparison from that study:

Cure System	Swelling in Oil (%)	Tensile Strength (MPa)	Elongation at Break (%)
Sulfur	42	10.2	320
LUPEROX 101	27	12.5	290

This shows that while elongation was slightly reduced (a common trade-off with peroxide curing), oil resistance and tensile strength improved significantly.

⚙️ Optimizing Peroxide Curing: Dos and Don’ts

Using LUPEROX peroxides effectively requires a bit of finesse. Here are some best practices:

Use the right dosage: Too little peroxide = undercured rubber. Too much = scorch risk and degradation. A typical dosage range is 1–4 phr (parts per hundred rubber) depending on the grade and application.
Control the temperature: Each peroxide has a specific decomposition temperature. Don’t rush the cure — let the peroxide work at its optimal rate.
Add co-agents for enhanced performance: Co-agents like triallyl cyanurate (TAC) or trimethylolpropane trimethacrylate (TMPTMA) can boost crosslink density and improve both flame retardancy and oil resistance.
Avoid moisture-sensitive environments: Some peroxides are sensitive to moisture, which can prematurely trigger decomposition.
Monitor scorch time carefully: Unlike sulfur systems, peroxides don’t offer much in terms of scorch delay. Use a scorch retarder if needed.

📈 Real-World Applications

Let’s bring this out of the lab and into the real world. Here are a few examples of how LUPEROX peroxides are being used to improve rubber performance:

1. Automotive Seals and Gaskets

In engine compartments, rubber parts are exposed to high temperatures, oils, and occasional sparks. EPDM seals crosslinked with LUPEROX 101 + TAC offer excellent oil resistance and moderate flame retardancy, making them ideal for long-term durability.

2. Electrical Cable Insulation

Cable jackets made from EPDM or silicone rubber and crosslinked with LUPEROX 570 provide low smoke emission, high thermal stability, and good resistance to oils and solvents — a must-have for fire safety in buildings and public transport.

3. Industrial Belts and Rollers

These components often run hot and come into contact with lubricants. NBR or ACM rubbers crosslinked with LUPEROX 130 deliver high crosslink density, low swelling, and long service life.

📚 References

Here are some of the key references that informed this article:

Arkema. (2023). LUPEROX Peroxides: Technical Data Sheets. Arkema Inc.
Zhang, Y., et al. (2021). "Synergistic Flame Retardancy in EPDM Rubber Cured with Organic Peroxides." Polymer Degradation and Stability, 187, 109523.
Kumar, R., & Singh, R. (2019). "Comparative Study of Sulfur and Peroxide Curing in EPDM Rubber: Mechanical and Swelling Behavior." Rubber Chemistry and Technology, 92(3), 456–469.
Li, J., et al. (2020). "Effect of Crosslinking Agents on Oil Resistance of Nitrile Rubber." Journal of Applied Polymer Science, 137(18), 48765.
Wang, X., et al. (2018). "Thermal and Flame Retardant Properties of Silicone Rubber Cured with Different Peroxides." Fire and Materials, 42(4), 410–419.

🧠 Final Thoughts

In the world of rubber compounding, the devil is in the details. And when it comes to achieving flame retardancy and oil resistance, the choice of crosslinking agent can make all the difference. LUPEROX peroxides offer a powerful, versatile, and reliable way to enhance rubber performance — especially when used thoughtfully and in combination with other additives.

So the next time you’re designing a rubber compound for a demanding application, remember: crosslinking isn’t just about making rubber harder — it’s about making it smarter. And with LUPEROX peroxides in your toolkit, you’re one step closer to creating a rubber that can stand up to the toughest conditions nature — or industry — can throw at it.

🛠️ Summary Table: LUPEROX Peroxides for Flame Retardancy & Oil Resistance

Property	Benefit of LUPEROX Crosslinking	Recommended Grades
Flame Retardancy	Reduces VOC release, improves char formation	LUPEROX 101, 570
Oil Resistance	Increases crosslink density, reduces swelling	LUPEROX 101, 130
Thermal Stability	Enhances heat resistance	LUPEROX 570, 681
Processing Ease	Good scorch safety with proper formulation	LUPEROX 101, 421
Mechanical Strength	Improves tensile strength and modulus	LUPEROX 130, 570

📝 A Note from the Author

If you’ve made it this far, congratulations — you’re officially a rubber enthusiast! Whether you’re a seasoned formulator or just rubber-curious, I hope this article has given you a fresh perspective on how crosslinking can transform a humble polymer into a high-performance material. And if you ever find yourself staring at a batch of uncured rubber wondering how to make it flame-resistant and oil-proof, just remember: there’s a LUPEROX for that. 🔥🧯

Let’s keep the rubber rolling — safely and efficiently.

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