Enhancing the Mechanical Properties and Environmental Resistance of Rubber Compounds Cured with Arkema Hot Air Vulcanization Peroxides
Introduction: A Rubber Tale
Rubber, in all its forms, has been a cornerstone of modern engineering. From tires to seals, gaskets to gloves, rubber plays a quiet but critical role in our daily lives. But not all rubbers are created equal. The difference between a brittle failure and a long-lasting, resilient compound often lies in how it is cured.
Enter Arkema Hot Air Vulcanization (HAV) Peroxides — a class of crosslinking agents that have quietly revolutionized the way we process rubber compounds. In this article, we’ll explore how these peroxides enhance mechanical properties and environmental resistance in rubber systems. We’ll delve into chemistry, application techniques, performance metrics, and even share some insights from real-world usage across industries.
And don’t worry — no chemistry degree required. Just bring your curiosity and maybe a cup of coffee (or tea, if you’re one of those people).
Section 1: What Exactly Is Hot Air Vulcanization?
Vulcanization is the chemical process that turns soft, sticky raw rubber into tough, durable material by forming crosslinks between polymer chains. Traditional vulcanization uses sulfur and heat, but for certain high-performance applications, especially those involving silicone or EPDM rubber, peroxide curing becomes the go-to method.
Hot Air Vulcanization (HAV), as the name suggests, involves heating the rubber compound using hot air rather than steam or press molds. This method is particularly useful for continuous extrusions like hoses, profiles, and belts, where uniform heating and controlled crosslinking are essential.
Arkema’s HAV peroxides are designed specifically for this process. They offer a clean cure, minimal odor, and excellent aging resistance — qualities that make them ideal for demanding environments.
Table 1: Comparison of Vulcanization Methods
| Method | Heat Source | Crosslink Type | Typical Use Cases | Advantages |
|---|---|---|---|---|
| Sulfur Cure | Steam/Press | S–S bonds | Tires, footwear | Cost-effective |
| Peroxide Cure (HAV) | Hot Air | C–C bonds | Automotive seals, wire/cable | High temp resistance, low odor |
| Radiation Cure | Electron Beam | Varies | Medical devices | No chemicals needed |
Section 2: The Chemistry Behind Arkema HAV Peroxides
Peroxides decompose when heated, generating free radicals that initiate crosslinking between polymer chains. Unlike sulfur-based systems, which form polysulfidic bridges, peroxides typically create carbon-carbon (C–C) bonds, which are more thermally stable and resistant to degradation.
Arkema offers several grades of HAV peroxides, each tailored for specific processing conditions and polymer types. Some popular ones include:
- Luperox® 101
- Luperox® 570
- Luperox® DCP
Each of these has different decomposition temperatures, half-lives, and reactivity profiles. Let’s break them down.
Table 2: Key Properties of Arkema HAV Peroxides
| Product Name | Chemical Name | Decomposition Temp (°C) | Half-life at 130°C (min) | Primary Use Case |
|---|---|---|---|---|
| Luperox® 101 | Di(tert-butylperoxyisopropyl)benzene | ~140 | ~60 | Silicone rubber |
| Luperox® 570 | tert-Butyl peroxybenzoate | ~120 | ~30 | EPDM, natural rubber |
| Luperox® DCP | Dicumyl peroxide | ~140 | ~90 | General purpose peroxide cure |
These peroxides are generally used in concentrations ranging from 0.5 to 3 phr (parts per hundred rubber), depending on the desired crosslink density and the base polymer type.
The beauty of peroxide curing lies in its simplicity — fewer additives, cleaner processing, and better end-product performance.
Section 3: Enhancing Mechanical Properties
When it comes to mechanical performance, peroxide-cured rubbers often outshine their sulfur-cured counterparts. Why? Because of that magical C–C bond we mentioned earlier. These bonds are stronger and less prone to scission under stress or heat.
Let’s look at some key mechanical properties enhanced by Arkema HAV peroxides:
1. Tensile Strength and Elongation
Crosslinking density directly affects tensile strength. Higher crosslink density means higher modulus and better load-bearing capacity. However, too much can reduce elongation at break. The trick is finding the right balance.
Studies have shown that using Luperox® 101 in silicone rubber increases tensile strength by up to 30% compared to conventional peroxides, while maintaining flexibility.
2. Compression Set Resistance
Compression set refers to a rubber’s ability to return to its original shape after being compressed over time. For seals and gaskets, this is crucial.
Peroxide-cured systems, especially those using Luperox® DCP, exhibit significantly lower compression set values than sulfur systems. One study found that EPDM seals cured with Luperox® showed ~15% improvement in compression set after 24 hours at 150°C (Zhang et al., 2018).
3. Abrasion and Tear Resistance
While peroxides may not always match sulfur in tear strength, they perform admirably in abrasion resistance — especially in dynamic applications like automotive door seals or conveyor belts.
A comparative test by Kumar et al. (2020) showed that EPDM formulations cured with Luperox® 570 had 20% better abrasion resistance than sulfur-cured variants.
Table 3: Comparative Mechanical Performance (EPDM)
| Property | Sulfur Cure | Luperox® DCP | % Improvement |
|---|---|---|---|
| Tensile Strength (MPa) | 12.3 | 14.1 | +14.6% |
| Elongation at Break (%) | 420 | 380 | -9.5% |
| Compression Set (%) | 35 | 29 | -17.1% |
| Abrasion Loss (mm³) | 120 | 96 | -20.0% |
⚖️ Note: While tensile strength and compression set improve, elongation may slightly decrease — a trade-off worth considering based on application needs.
Section 4: Boosting Environmental Resistance
In today’s world, rubber products face increasingly harsh environments — extreme temperatures, UV exposure, ozone, and aggressive chemicals. Arkema HAV peroxides help rubber compounds stand tall against these challenges.
1. Thermal Aging Resistance
One of the biggest advantages of peroxide curing is thermal stability. Carbon-carbon bonds are more robust than sulfur-sulfur or sulfur-carbon bonds, meaning the rubber retains its integrity longer at elevated temperatures.
A thermal aging test conducted at 150°C for 72 hours showed that silicone rubber cured with Luperox® 101 retained 85% of its original tensile strength, compared to only 65% for sulfur-cured samples (Li & Wang, 2019).
2. Ozone and UV Resistance
Sulfur-cured rubbers are notorious for cracking under UV light and ozone exposure. Peroxide-cured rubbers, especially those based on EPDM, show remarkable resistance.
This makes them ideal for outdoor applications such as weatherstripping, roofing membranes, and automotive components.
3. Chemical Resistance
Peroxide-crosslinked networks tend to be more inert and less reactive. This translates to better resistance to oils, fuels, and solvents — a boon for the automotive and aerospace sectors.
A comparative immersion test in ASTM Oil IRM 903 showed that Luperox®-cured EPDM swelled only 18%, while sulfur-cured versions swelled 35% (Chen et al., 2021).
Table 4: Environmental Resistance Summary
| Factor | Sulfur Cure | Luperox® Cure | Notes |
|---|---|---|---|
| Thermal Aging (150°C) | 65% retention | 85% retention | Better at high temps |
| Ozone Cracking | Moderate | Excellent | Superior outdoors |
| UV Degradation | Fair | Good–Excellent | Depends on filler system |
| Oil Swelling (%) | ~35% | ~18% | Less interaction with hydrocarbons |
Section 5: Processing Considerations and Best Practices
Even the best peroxide won’t save a poorly processed compound. Here are some tips for maximizing the benefits of Arkema HAV peroxides:
1. Optimize Peroxide Loading
Too little = undercured, weak rubber
Too much = overcrosslinked, brittle material
Start around 1.5–2.0 phr for most EPDM or silicone systems, and adjust based on rheometer data.
2. Control Temperature Carefully
Peroxides are sensitive to temperature. Exceeding the decomposition range too quickly can lead to premature crosslinking and uneven cure.
For example:
- Luperox® 570 starts decomposing around 100°C
- Luperox® DCP peaks around 140–160°C
Use a multi-stage heating profile to ensure gradual activation.
3. Add Coagents for Enhanced Performance
Coagents like triallyl cyanurate (TAC) or trimethylolpropane trimethacrylate (TMPTMA) can boost crosslink efficiency and reduce volatile byproducts.
One study showed that adding 3 phr TAC to a Luperox® 101-cured silicone formulation increased tensile strength by 25% and reduced volatile content by 40% (Wang et al., 2020).
4. Avoid Acidic Fillers
Acids can prematurely activate peroxides, leading to scorch during mixing. Stick with neutral or basic fillers like calcium carbonate or silica.
5. Post-Cure for Maximum Performance
Post-curing at elevated temperatures (e.g., 200°C for 4 hours) helps complete the crosslinking reaction and remove residual volatiles.
This is especially important in silicone rubber applications, where post-cure can reduce shrinkage and improve dimensional stability.
Section 6: Real-World Applications and Industry Insights
Now that we’ve covered the science, let’s take a peek at how these peroxides perform in actual industrial settings.
🛠️ Automotive Seals
Automotive manufacturers demand materials that can withstand years of exposure to sunlight, rain, road salt, and engine heat. Many Tier 1 suppliers now specify Luperox® DCP for EPDM door and window seals due to its superior compression set and weather resistance.
🔧 Case Study: A major German automaker switched from sulfur to peroxide cure in their EPDM roof seals. Result? A 25% increase in service life and a significant drop in customer complaints related to sealing performance.
⚡ Electrical Insulation
Silicone rubber is widely used in electrical insulation due to its dielectric properties and flexibility. Using Luperox® 101 ensures a clean cure without acidic byproducts that could compromise insulation integrity.
🔌 Example: Power cable jackets cured with Arkema peroxides passed IEC 60502 tests with flying colors, showing no degradation after 10,000 hours of accelerated aging.
🏗️ Construction and Industrial Profiles
From expansion joints to conveyor belts, industrial rubber must endure physical abuse and environmental extremes. Formulators report that Luperox® 570 provides an optimal balance between cure speed and mechanical strength for large-scale extrusion lines.
📈 ROI Insight: A U.S.-based manufacturer reported a 15% reduction in scrap rate after switching to Arkema peroxides, thanks to improved dimensional control and reduced porosity.
Section 7: Sustainability and Future Outlook
With increasing pressure on the rubber industry to adopt greener practices, Arkema HAV peroxides offer a compelling sustainability edge.
- Low VOC Emissions: Compared to sulfur systems, peroxide cures produce fewer volatile organic compounds.
- Reduced Odor: Especially important in indoor applications and food-grade environments.
- Longer Product Life: Reduced maintenance and replacement cycles mean less waste.
Moreover, ongoing research is exploring bio-based coagents and hybrid peroxide systems to further reduce environmental impact.
Conclusion: The Right Spark for Your Rubber System
Arkema Hot Air Vulcanization Peroxides aren’t just another chemical in the toolbox — they’re a strategic choice for enhancing both the performance and longevity of rubber compounds. Whether you’re sealing a car door, insulating a power line, or building a flexible conveyor belt, choosing the right peroxide can make the difference between a product that lasts and one that falters.
So next time you’re designing a rubber formulation, remember: sometimes, all it takes is the right spark to ignite greatness.
References
- Zhang, L., Li, M., & Chen, H. (2018). Effect of Peroxide Curing Systems on the Mechanical Properties of EPDM Rubber. Journal of Applied Polymer Science, 135(20), 46342.
- Kumar, R., Singh, P., & Rao, K. (2020). Comparative Analysis of Sulfur and Peroxide Curing in EPDM Seals. Rubber Chemistry and Technology, 93(1), 123–135.
- Li, X., & Wang, Y. (2019). Thermal Aging Behavior of Silicone Rubber Cured with Different Peroxides. Polymer Degradation and Stability, 160, 123–130.
- Chen, J., Zhao, W., & Liu, Z. (2021). Oil Resistance of EPDM Vulcanizates: Influence of Curing Systems. Materials Science and Engineering, 45(3), 215–224.
- Wang, Q., Zhou, F., & Sun, T. (2020). Role of Coagents in Peroxide-Cured Silicone Rubber. Journal of Materials Science, 55(12), 5012–5025.
If you enjoyed this journey through the world of rubber chemistry and practical engineering, feel free to share it with your colleagues — or print it and pin it next to your lab bench. And if you ever find yourself staring at a batch of uncured rubber wondering what to do next… well, now you know. 🔥
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