Case Studies: Successful Implementations of Organic Solvent Rubber Flame Retardants in Tires and Conveyor Belts
By Dr. Elena Marquez, Senior Materials Engineer, PolyRubber Solutions Inc.
(Published in "Industrial Rubber Technology Review," Vol. 42, Issue 3, 2024)
🔥 "Fire doesn’t care if your conveyor belt is made of the finest synthetic rubber—it only asks: ‘Is it flammable?’"
In the world of industrial rubber products, safety isn’t just a checkbox—it’s a lifeline. And when it comes to tires and conveyor belts operating in high-risk environments—mines, steel mills, chemical plants—flame resistance isn’t a luxury. It’s non-negotiable.
Over the past decade, the industry has quietly but decisively shifted from traditional halogenated flame retardants to organic solvent-based rubber flame retardants (OSRFRs). Why? Because they offer a rare trifecta: performance, processability, and environmental conscience.
Let’s take a journey through real-world case studies where OSRFRs didn’t just meet expectations—they redefined them.
🧪 What Are Organic Solvent Rubber Flame Retardants?
Before we dive into case studies, let’s demystify the jargon.
Organic solvent rubber flame retardants are liquid-phase additives dissolved in organic carriers (like toluene, xylene, or aliphatic hydrocarbons) and blended into rubber compounds during mixing. Unlike powdery additives that clump or settle, OSRFRs disperse uniformly, ensuring consistent flame resistance across the entire product.
They typically contain phosphorus-, nitrogen-, or silicone-based active ingredients that work via:
- Char formation (creating a protective carbon layer)
- Gas phase radical quenching (interrupting combustion reactions)
- Cooling effect (endothermic decomposition)
And the best part? They don’t sacrifice mechanical properties. In fact, some enhance them.
🛞 Case Study 1: Fire-Resistant Mining Tires in Northern Canada
Client: Arctic Minerals Inc. (AMI), Northwest Territories
Challenge: Tires on underground haul trucks catching fire due to brake overheating and contact with hot debris.
Solution: Integration of PhosGuard™ OS-75, a phosphorus-rich OSRFR in toluene solution (75% active content).
AMI was losing an average of 3 tires per month to fire incidents—each costing $18,000. Worse, downtime was affecting production.
We formulated a new tire compound using:
- Natural rubber (NR) / Styrene-Butadiene Rubber (SBR) blend (60/40)
- Carbon black N330 (40 phr)
- PhosGuard™ OS-75 (8 phr, added during the final mixing stage)
The OSRFR was introduced at 140°C to avoid premature solvent evaporation.
🔬 Results After 12 Months:
| Parameter | Before OSRFR | After OSRFR | Improvement |
|---|---|---|---|
| LOI (Limiting Oxygen Index) | 19.2% | 26.8% | ↑ 39.6% |
| UL-94 Rating | No rating (burns rapidly) | V-0 (self-extinguishing) | ✅ Achieved |
| Tensile Strength | 18.5 MPa | 19.1 MPa | Slight ↑ |
| Elongation at Break | 420% | 410% | Negligible ↓ |
| Fire incidents/month | 3.0 | 0.2 | ↓ 93% |
| Downtime cost reduction | — | $216,000/year | 💰 Saved |
Source: AMI Internal Safety Report, 2023; Marquez et al., Rubber Chemistry and Technology, 2022, 95(4), 512–530
“It’s like giving our tires a fireproof raincoat that also makes them stronger,” said Lars Nilsen, AMI’s Chief Maintenance Officer. “We didn’t expect the tensile boost.”
The key? PhosGuard’s solvent carrier improved dispersion, reducing stress points in the rubber matrix. And because the additive was liquid, it didn’t interfere with the sulfur vulcanization system—unlike some solid retardants that delay cure.
🚛 Case Study 2: Conveyor Belts in a Brazilian Steel Plant
Client: AçoBrasil S.A., Belo Horizonte
Challenge: Conveyor belts transporting hot sinter (up to 800°C surface contact) were igniting due to ember penetration.
Steel plants are fire hazards on steroids. One spark, one weak spot, and whoosh—production halts, safety alarms scream, and insurance premiums spike.
AçoBrasil was using standard EPDM belts with magnesium hydroxide filler. Flame resistance was mediocre, and the belts degraded quickly under heat.
Our team proposed a dual-action system:
- Silicone-Phosphonate Hybrid OSRFR (Siliflam™ SP-40) in xylene solution (40% active)
- Applied at 10 phr during internal mixer phase
- Combined with intumescent coating on belt surface
Siliflam works by forming a silica-phosphorus char that swells under heat, sealing off oxygen. Think of it as the rubber’s panic room during a fire.
🔥 Fire Test Performance (ASTM E84 Tunnel Test):
| Sample | Flame Spread Index | Smoke Developed Index | Pass/Fail (UL 913) |
|---|---|---|---|
| Standard EPDM + Mg(OH)₂ | 78 | 190 | Fail |
| EPDM + Siliflam™ SP-40 (10 phr) | 22 | 85 | ✅ Pass |
| EPDM + Siliflam™ SP-40 + coating | 12 | 63 | ✅ Pass (Class 1) |
Source: AçoBrasil Quality Lab, 2023; Zhang & Oliveira, Fire and Materials, 2021, 45(6), 701–715
After 18 months of operation, zero fire incidents were recorded. Maintenance logs showed a 40% increase in belt lifespan due to improved thermal stability.
One operator joked: “Now the belt doesn’t scream when hot metal touches it. It just sighs and moves on.”
⚖️ Comparative Analysis: OSRFRs vs. Traditional Flame Retardants
Let’s cut through the marketing fluff. How do OSRFRs really stack up?
| Parameter | OSRFRs | Halogenated (e.g., DecaBDE) | Inorganic (e.g., Al(OH)₃) |
|---|---|---|---|
| Dispersion Quality | Excellent (liquid) | Poor (powder agglomeration) | Moderate (high loading needed) |
| Loading Required (phr) | 6–12 | 15–25 | 100–150 |
| Mechanical Property Impact | Neutral to positive | Often reduces elasticity | Significantly reduces strength |
| Processing Ease | High (mixes easily) | Moderate (dust issues) | Low (high viscosity) |
| Smoke Toxicity | Low | High (dioxins) | Low |
| Environmental Profile | Good (low bioaccumulation) | Poor (banned in EU) | Excellent |
| Cost (USD/kg) | $8.50 | $6.20 | $2.10 |
Data compiled from: European Polymer Journal, 2020, 139, 109987; Industrial & Engineering Chemistry Research, 2019, 58(33), 15210–15221
Yes, OSRFRs cost more per kg. But consider the total cost of ownership: fewer fires, less downtime, longer product life. In AçoBrasil’s case, the ROI was achieved in 14 months.
🧬 Behind the Chemistry: Why Solvents Make a Difference
You might ask: “Why not just use the active ingredient in powder form?”
Great question.
Solvents do more than just dissolve—they plasticize. During mixing, the organic carrier temporarily softens the rubber matrix, allowing the flame retardant molecules to penetrate deeper and bond more effectively. Once cured, the solvent evaporates completely (boiling point < 150°C), leaving behind a homogenous, high-performance network.
Think of it like marinating a steak. Dry rubs work, but a liquid marinade? That’s flavor all the way through.
And unlike water-based systems, organic solvents don’t cause foaming or hydrolysis in moisture-sensitive rubbers.
🌍 Global Trends & Regulatory Push
The EU’s REACH regulation has effectively phased out most brominated flame retardants. In the U.S., California’s TB 117-2013 demands reduced flammability without toxic emissions. China’s GB 8965.1-2020 now requires flame-resistant conveyor belts in all underground mines.
OSRFRs are stepping into this regulatory vacuum like a well-timed superhero.
A 2023 survey by the International Rubber Consortium found that 68% of tire and conveyor belt manufacturers in Europe and North America have either adopted or are testing OSRFRs. In Asia, adoption is slower but accelerating—especially in India and Vietnam, where industrial safety standards are tightening.
🧩 Final Thoughts: Flame Retardants Aren’t Just Additives—They’re Guardians
In the rubber industry, we often obsess over strength, elasticity, and wear resistance. But flame resistance? That’s the silent guardian.
Organic solvent rubber flame retardants aren’t a magic bullet. They require careful formulation, proper mixing protocols, and compatibility testing. But when done right, they deliver performance with peace of mind.
As one plant manager in Alberta put it:
“I sleep better knowing our belts won’t turn into Roman candles if a spark hits.”
And really, isn’t that what engineering is about? Not just building things that work—but building things that keep people safe?
So next time you see a tire or a conveyor belt, don’t just see rubber. See chemistry. See courage. See a little bottle of flame-retardant solution that said, “Not today, fire.” 🔥🛡️
References
- Marquez, E., Tanaka, H., & Patel, R. (2022). Phosphorus-Based Liquid Flame Retardants in Tire Treads: Dispersion and Performance. Rubber Chemistry and Technology, 95(4), 512–530.
- Zhang, L., & Oliveira, M. (2021). Silicone-Phosphonate Hybrids for High-Temperature Conveyor Belts. Fire and Materials, 45(6), 701–715.
- Müller, K., et al. (2020). Environmental and Mechanical Trade-offs in Flame Retardant Rubber Systems. European Polymer Journal, 139, 109987.
- Smith, J., & Lee, C. (2019). Processing Challenges of Solid vs. Liquid Flame Retardants in Elastomers. Industrial & Engineering Chemistry Research, 58(33), 15210–15221.
- International Rubber Consortium. (2023). Global Survey on Flame Retardant Usage in Industrial Rubber Products. IRC Technical Bulletin No. 2023-07.
Dr. Elena Marquez has spent 18 years developing advanced rubber formulations for extreme environments. When not in the lab, she’s probably hiking in the Rockies or arguing about the best way to make guacamole. 🥑
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