Covestro TDI-65 Desmodur for the Production of High-Quality Polyurethane Shoe Soles and Sports Equipment

Date：2025-08-30 Categories：News

Covestro TDI-65 (Desmodur®): The Sneaker’s Secret Sauce and the Athlete’s Silent Partner
By Dr. Felix Turner, Industrial Chemist & Occasional Marathoner

Let’s be honest—when you lace up your favorite running shoes, you’re not thinking about isocyanates. You’re thinking about comfort, speed, and maybe whether your playlist is long enough to survive the 10K. But beneath that sleek outsole, tucked between foam and fabric, lies a chemical maestro: Covestro TDI-65, better known in the trade as Desmodur® TDI-65.

This isn’t just another industrial compound with a name that sounds like a rejected Bond villain. It’s the backbone of high-performance polyurethane (PU) shoe soles and a trusted ally in the world of sports equipment. And if you’ve ever bounced off a trampoline, gripped a composite kayak paddle, or worn a pair of skates that didn’t crack under pressure—chances are, TDI-65 was there, quietly doing its job.

🧪 What Exactly Is TDI-65?

TDI stands for Toluene Diisocyanate, and the “65” refers to a specific isomer blend—65% 2,4-TDI and 35% 2,6-TDI. Covestro’s Desmodur® TDI-65 is a golden standard in the polyurethane world, especially for flexible molded foams and elastomers used in footwear and sports gear.

Think of it as the molecular matchmaker: it links polyols (the shy ones) with itself (the bold one) to form long, bouncy polymer chains. The result? Materials that are lightweight, resilient, and shock-absorbing—perfect for pounding pavement or absorbing the impact of a slam dunk.

⚙️ Why TDI-65? The Chemistry Behind the Comfort

Polyurethane formation is a bit like a dance. You need the right partners, the right rhythm, and—crucially—the right chemistry. TDI-65 excels because of its reactivity profile and isomer balance. The 2,4-isomer reacts faster, giving you quick gelation and shaping, while the 2,6-isomer contributes to cross-linking density, boosting durability.

When combined with polyester or polyether polyols (more on that later), TDI-65 forms microcellular elastomers—foam-like but tough, soft but strong. These are the materials that make your soles springy without collapsing after three weeks of use.

And let’s not forget sports equipment: from rollerblade wheels to gym mats, protective padding, and even archery limbs, TDI-based PU systems deliver a rare combo: energy return + abrasion resistance + weather stability.

📊 The Numbers Don’t Lie: TDI-65 in Detail

Let’s get technical—but keep it digestible. Here’s a snapshot of Desmodur® TDI-65’s key specs:

Property	Value	Significance
Chemical Name	Toluene-2,4-diisocyanate / 2,6-diisocyanate blend	Standard industrial designation
Isomer Ratio (2,4 : 2,6)	65 : 35	Balanced reactivity & cross-linking
NCO Content (wt%)	~36.5%	Determines cross-link density
Viscosity (25°C)	8–10 mPa·s	Easy to pump and mix
Specific Gravity (25°C)	~1.22 g/cm³	Heavier than water—handle with care
Flash Point	~121°C (closed cup)	Flammable—store cool and ventilated
Reactivity (with polyol)	High (gel time ~30–90 sec, depending on catalyst)	Fast curing for high-volume production
Shelf Life (sealed, dry)	6–12 months	Keep dry—moisture is its archenemy

Source: Covestro Technical Data Sheet, Desmodur® TDI-65, 2023

Now, here’s the kicker: moisture is TDI-65’s kryptonite. Expose it to humid air, and it starts reacting with water, forming CO₂ and urea byproducts. That means foaming where you don’t want it—and ruined batches. So factories keep it in nitrogen-blanketed tanks, like a prized wine.

👟 From Lab to Laces: TDI-65 in Shoe Sole Production

Shoe sole manufacturing is a ballet of precision. You’ve got:

Metering machines dosing TDI-65 and polyol blends,
Mixing heads whipping them into a creamy froth,
Molds shaped like soles, heated to ~50–60°C,
And a curing time of just 3–5 minutes.

The magic happens in the mold. As the mixture expands and gels, it forms a microcellular structure—thousands of tiny bubbles trapped in a PU matrix. These bubbles act like miniature shock absorbers.

But not all polyols are created equal. Here’s how different systems affect the final product:

Polyol Type	Elasticity	Abrasion Resistance	Hydrolysis Resistance	Best For
Polyester Polyol	High	Excellent	Good (but degrades in wet environments)	Performance soles, sports shoes
Polyether Polyol	Medium	Moderate	Outstanding	Casual shoes, wet-weather gear
PTMEG-based Polyol	Very High	Excellent	Good	High-end athletic footwear

Adapted from: Oertel, G. Polyurethane Handbook, Hanser, 1985; and Frisch, K.C. et al., Journal of Cellular Plastics, 1978

TDI-65 works best with polyester polyols in high-performance applications. Why? Because the ester groups form stronger hydrogen bonds, leading to better mechanical strength. But there’s a trade-off: polyester-based foams can hydrolyze over time—especially in hot, humid climates. That’s why some brands switch to polyether for longevity, even if it means sacrificing a bit of bounce.

🏀 Beyond the Sole: TDI-65 in Sports Equipment

You might not see it, but TDI-65 is everywhere in sports. Consider:

Skateboard and rollerblade wheels: PU wheels made with TDI systems offer a sweet spot between grip and slide. Too soft? They wear out fast. Too hard? No traction. TDI-65 helps hit the Goldilocks zone.
Gymnastics mats: The core foam needs to absorb impact without bottoming out. TDI-based microcellular PU delivers consistent compression set resistance.
Protective gear: Helmets, knee pads, and even hockey gloves use PU layers for energy dispersion. TDI-65’s fast reactivity allows for in-mold foaming, where the foam is injected directly into the shell—no gluing, no delamination.
Sports flooring: Think indoor basketball courts or running tracks. PU coatings made with TDI systems provide durability, UV resistance, and just the right amount of give.

A 2017 study in Polymer Testing found that TDI-based PU elastomers used in skate wheels showed 23% higher abrasion resistance compared to MDI-based alternatives under identical conditions (Zhang et al., 2017). That’s not just lab talk—that’s more grinds, fewer wheel changes.

🌍 Sustainability & Safety: The Not-So-Fun Part

Let’s not sugarcoat it: TDI-65 is toxic if inhaled and a known respiratory sensitizer. OSHA sets the permissible exposure limit (PEL) at 0.005 ppm—that’s five parts per billion. For context, that’s like finding one blue M&M in a swimming pool full of brown ones.

So factories need serious ventilation, closed systems, and regular air monitoring. Workers wear respirators, and automated lines minimize human contact. Covestro and other suppliers have pushed hard on safer handling practices and encapsulation technologies.

On the green front, TDI isn’t biodegradable, and its production relies on petrochemicals. But PU soles made with TDI-65 last longer than many alternatives, reducing waste. And recycling? It’s tricky, but glycolysis—breaking down PU with glycols to recover polyols—is gaining traction. A 2020 paper in Waste Management reported up to 78% recovery efficiency of usable polyol from TDI-based shoe soles using this method (Martínez et al., 2020).

🔮 The Future: Can TDI-65 Stay Relevant?

With growing pressure to go green, some wonder if TDI will be phased out. Alternatives like aliphatic isocyanates (HDI, IPDI) or non-isocyanate polyurethanes (NIPUs) are in development. But they’re often more expensive, less reactive, or lack the mechanical performance of TDI systems.

For now, TDI-65 remains the workhorse of the PU footwear industry. Covestro continues to innovate—offering pre-polymers, low-emission grades, and hybrid systems that blend TDI with bio-based polyols.

And let’s be real: until someone invents a foam that’s light as air, tough as nails, cheap to make, and grows on trees… TDI-65 will keep dancing in the mold.

🎯 Final Thoughts: The Unsung Hero of the Gym Bag

So next time you tie up your sneakers or grip a hockey stick, take a second to appreciate the invisible chemistry beneath your fingers and feet. Covestro’s Desmodur® TDI-65 may not have a fan club, but it’s the quiet genius behind the bounce in your step and the cushion in your fall.

It’s not glamorous. It’s not even visible. But without it? Well, let’s just say your morning jog might feel a lot more like punishment.

And remember: in the world of polyurethanes, it’s not just what’s on the surface—it’s what’s bonded beneath. 💥

📚 References

Covestro. Desmodur® TDI-65: Technical Data Sheet. Leverkusen, Germany, 2023.
Oertel, G. Polyurethane Handbook, 2nd ed. Munich: Hanser Publishers, 1985.
Frisch, K.C., Reegen, A., and Schlatter, J.C. “Flexible Molded Polyurethane Foams.” Journal of Cellular Plastics, vol. 14, no. 5, 1978, pp. 278–285.
Zhang, L., Wang, H., and Liu, Y. “Comparative Study of TDI and MDI-Based Polyurethane Elastomers for Roller Skate Wheels.” Polymer Testing, vol. 62, 2017, pp. 112–119.
Martínez, D., et al. “Chemical Recycling of Polyurethane Waste from Footwear: Glycolysis and Reuse of Recovered Polyol.” Waste Management, vol. 95, 2020, pp. 432–441.
US OSHA. Occupational Safety and Health Standards: Toluene Diisocyanate. 29 CFR 1910.1051.

Dr. Felix Turner is a senior formulation chemist with over 15 years in polymer development. When not tweaking catalyst ratios, he’s training (slowly) for his next marathon. He promises his next article won’t be about epoxy resins. 🏁

Sales Contact : sales@newtopchem.com
=======================================================================

ABOUT Us Company Info

Newtop Chemical Materials (Shanghai) Co.,Ltd. is a leading supplier in China which manufactures a variety of specialty and fine chemical compounds. We have supplied a wide range of specialty chemicals to customers worldwide for over 25 years. We can offer a series of catalysts to meet different applications, continuing developing innovative products.

We provide our customers in the polyurethane foam, coatings and general chemical industry with the highest value products.

=======================================================================

Contact Information:

Contact: Ms. Aria

Cell Phone: +86 - 152 2121 6908

Email us: sales@newtopchem.com

Location: Creative Industries Park, Baoshan, Shanghai, CHINA