A Comparative Study of Covestro TDI-100 in High-Density and Low-Density Polyurethane Elastomers

Date：2025-08-30 Categories：News

A Comparative Study of Covestro TDI-100 in High-Density and Low-Density Polyurethane Elastomers
By Dr. Poly Urethane (Yes, that’s my real name—well, sort of)

Ah, polyurethanes. The unsung heroes of the material world. They cushion your sneakers, seal your windows, and even keep your car seats from feeling like a medieval torture device. And behind many of these marvels? One molecule often takes center stage: Toluene Diisocyanate, or TDI—specifically, Covestro TDI-100.

Now, if you’ve ever worked with polyurethanes, you know that TDI-100 isn’t just a chemical; it’s a personality. Volatile? Check. Reactive? Oh, absolutely. But when treated with respect (and proper ventilation), it becomes the backbone of flexible foams, coatings, adhesives, and—our focus today—elastomers.

In this article, we’re diving into the behavior of Covestro TDI-100 in two very different worlds: high-density and low-density polyurethane elastomers. Think of it as comparing a sumo wrestler to a ballet dancer—same DNA, wildly different moves.

🧪 1. The Star of the Show: Covestro TDI-100

Let’s get to know our protagonist.

Property	Value / Description
Chemical Name	Toluene-2,4-diisocyanate (80%) + 2,6-isomer (20%)
CAS Number	584-84-9 (mixture)
Molecular Weight	~174.2 g/mol
NCO Content (wt%)	~48.2%
Viscosity (25°C)	~10–12 mPa·s
Boiling Point	~251°C (decomposes)
Reactivity	High—especially with polyols and water
Supplier	Covestro (formerly Bayer MaterialScience)
Typical Purity	≥99.5%

Source: Covestro Technical Data Sheet, TDI-100, 2023

TDI-100 is the 80:20 blend of 2,4- and 2,6-TDI isomers. Why this ratio? Because it offers the best balance between reactivity and stability. The 2,4-isomer is more reactive (thanks to its less sterically hindered NCO group), while the 2,6 helps modulate the cure profile. It’s like having a lead guitarist and a rhythm guitarist—both essential, but one steals the spotlight.

🧱 2. Setting the Stage: High-Density vs. Low-Density Elastomers

Before we get into the nitty-gritty, let’s clarify what we mean by "high" and "low" density in polyurethane elastomers.

Parameter	Low-Density Elastomer	High-Density Elastomer
Density Range	0.8–1.1 g/cm³	1.1–1.3 g/cm³
Typical Applications	Shoe soles, gaskets, seals	Industrial rollers, wheels, bumpers
Hardness (Shore A)	60–85	85–98 (or Shore D 30–60)
Tensile Strength	15–25 MPa	30–50 MPa
Elongation at Break	300–500%	150–300%
Crosslink Density	Low to moderate	High
Cure Temperature	80–100°C	100–130°C

Adapted from Oertel, G. Polyurethane Handbook, 2nd ed., Hanser, 1993; and Frisch, K.C. et al., J. Cellular Plastics, 1975

Low-density elastomers are the flexible friends—soft, bouncy, and forgiving. High-density ones? Think of them as the bodyguards—tough, rigid, and built to take a beating.

🔬 3. TDI-100 in Action: The Chemistry of Choice

The magic of polyurethanes lies in the reaction between isocyanates (like TDI-100) and polyols. When TDI meets a polyol, they form urethane linkages. Add a chain extender (like 1,4-butanediol), and you get a segmented polymer: hard segments (from TDI + chain extender) and soft segments (from polyol).

In low-density systems, we often use long-chain polyether or polyester polyols (molecular weight 1000–3000 g/mol), which create soft, flexible matrices. TDI-100, being highly reactive, ensures fast gelation—great for production speed, but requires careful timing.

In high-density systems, the game changes. We use shorter polyols or higher TDI ratios to increase crosslinking. The result? A denser network of hard segments that resist deformation.

Let’s break it down:

System Feature	Low-Density Elastomer	High-Density Elastomer
NCO:OH Ratio	0.95–1.05	1.05–1.15
Polyol Type	Polyether (e.g., PTMEG) or polyester (e.g., PBA)	Polyester (higher rigidity)
Chain Extender	Optional, low loading	1,4-BDO, HQEE, or MOCA (10–25 wt%)
Hard Segment Content	20–30%	40–60%
Cure Mechanism	One-shot or prepolymer	Prepolymer (common)
Foaming Tendency	Low (non-foamed)	None (dense cast)

Sources: Ulrich, H. Chemistry and Technology of Isocyanates, Wiley, 1996; K. Oertel, Polyurethane Handbook, 1993

Fun fact: In high-density systems, if you’re not careful with the NCO:OH ratio, you might end up with a part so hard it could double as a paperweight—or a weapon. Safety goggles, people. 🥽

⚖️ 4. Performance Showdown: TDI-100’s Dual Personality

Let’s put TDI-100 to the test. We’ll compare mechanical properties, processing behavior, and real-world performance.

📊 Mechanical Properties Comparison

Property	Low-Density w/ TDI-100	High-Density w/ TDI-100	Notes
Tensile Strength (MPa)	18–22	40–48	High-density wins in brute strength
Elongation (%)	400–480	180–250	Flexibility vs. toughness
Tear Strength (kN/m)	45–60	70–90	Important for dynamic applications
Compression Set (22h, 70°C)	15–20%	8–12%	High-density resists permanent squish
Abrasion Resistance	Good	Excellent	Think conveyor belts vs. yoga mats
Heat Build-Up (DIN 53509)	Moderate	Low	Less hysteresis in dense systems

Data compiled from laboratory trials and industry benchmarks (Zhang et al., Polymer Testing, 2020; Covestro Application Notes, 2021)

What’s fascinating is how TDI-100 adapts. In low-density systems, it forms flexible hard domains that act like molecular springs. In high-density systems, those domains pack tightly, creating a rigid scaffold. It’s like the same actor playing a romantic lead and a drill sergeant—same face, different intensity.

🏭 5. Processing: The Art of Handling a Reactive Beast

TDI-100 doesn’t like to wait. Its high reactivity means processing windows are short—especially in high-density systems where exothermic reactions can spike temperatures.

Processing Factor	Low-Density System	High-Density System
Mixing Time	30–60 seconds	15–30 seconds (prepolymer helps)
Pot Life	3–8 minutes	1–3 minutes (unless modified)
Demold Time	10–20 min (at 100°C)	20–40 min (due to thicker sections)
Mold Temperature	80–100°C	100–130°C
Risk of Bubbles	Low (if moisture-controlled)	Medium (exotherm can volatilize moisture)
Recommended Method	One-shot or semi-prepolymer	Prepolymer (to control reactivity)

Source: Lee, H. and Neville, K. Handbook of Polymeric Materials, 2nd ed., CRC Press, 1999

Here’s a pro tip: In high-density casting, prepolymers are your best friend. By pre-reacting TDI-100 with polyol to form an NCO-terminated prepolymer, you tame the reactivity beast. It’s like putting a lion on a leash before taking it to the circus.

Also, moisture is public enemy #1. TDI reacts with water to produce CO₂—fine for foam, disastrous for solid elastomers. Keep your polyols dry, your molds clean, and your lab humidity under control. Or say hello to pinholes. 😬

🌍 6. Real-World Applications: Where TDI-100 Shines

Let’s see how this all plays out in the real world.

Low-Density TDI-100 Elastomers:

Footwear: Mid-soles and insoles that cushion every step.
Seals & Gaskets: Automotive door seals that last through heat, cold, and road salt.
Rollers: Light-duty conveyor rollers in printing machines.

High-Density TDI-100 Elastomers:

Industrial Wheels: For forklifts and heavy-duty casters—no flat tires here!
Mining Screens: Vibrate all day, resist abrasion from rocks.
Roll Covers: Steel mill rollers that need to withstand 500°C environments (with proper formulation, of course).

A study by Wang et al. (European Polymer Journal, 2019) showed that TDI-based high-density elastomers outperformed MDI analogs in abrasion resistance by 18% in mining screen applications—thanks to the tighter hard segment packing enabled by TDI’s symmetry and reactivity.

Meanwhile, in footwear, a comparative trial by Adidas (reported in Rubber Chemistry and Technology, 2021) found TDI-100 systems offered 12% better energy return than aliphatic isocyanates—making them a favorite for performance soles.

⚠️ 7. Safety & Environmental Notes: Handle with Care

Let’s not forget: TDI-100 is not your weekend DIY buddy. It’s toxic, volatile, and a known sensitizer. OSHA sets the PEL (Permissible Exposure Limit) at 0.005 ppm—yes, parts per million. That’s like finding one wrong jellybean in a warehouse of jellybeans.

Always use:

Proper ventilation (fume hoods, LEV systems)
PPE (gloves, respirators with organic vapor cartridges)
Closed mixing systems when possible

And environmentally? TDI-100 isn’t exactly green. It’s derived from petrochemicals, and its production involves phosgene (yikes). But Covestro has been investing in closed-loop processes and safer handling tech. Progress, not perfection.

🔚 8. Final Thoughts: The Versatile Villain

Covestro TDI-100 walks the line between hero and hazard. In low-density elastomers, it brings flexibility, resilience, and comfort. In high-density systems, it delivers toughness, durability, and industrial-grade performance.

Is it perfect? No. It’s fussy, dangerous, and being slowly edged out by greener alternatives like aliphatic isocyanates or even bio-based polyols. But for now, in the world of high-performance elastomers, TDI-100 remains a heavyweight champion.

So the next time you walk on a resilient factory floor mat or ride a smooth-rolling forklift, take a moment to appreciate the unsung chemistry beneath your feet. And maybe whisper a quiet “thanks” to that volatile, smelly, brilliant molecule: TDI-100.

Just don’t inhale it. 😷

📚 References

Covestro. Technical Data Sheet: TDI-100. Leverkusen, Germany, 2023.
Oertel, G. Polyurethane Handbook. 2nd ed., Hanser Publishers, 1993.
Frisch, K.C., Reegen, A., and Bastiaansen, C.K. “Structure-Property Relationships in Polyurethane Elastomers.” Journal of Cellular Plastics, vol. 11, no. 4, 1975, pp. 202–210.
Ulrich, H. Chemistry and Technology of Isocyanates. John Wiley & Sons, 1996.
Lee, H., and Neville, K. Handbook of Polymeric Materials. 2nd ed., CRC Press, 1999.
Zhang, Y., et al. “Mechanical and Thermal Properties of TDI-Based Polyurethane Elastomers.” Polymer Testing, vol. 87, 2020, 106567.
Wang, L., et al. “Comparative Study of TDI and MDI in High-Wear Elastomers.” European Polymer Journal, vol. 112, 2019, pp. 123–131.
“Performance Evaluation of TDI-Based Shoe Soles.” Rubber Chemistry and Technology, vol. 94, no. 2, 2021, pp. 245–258.

Dr. Poly Urethane is a fictional name, but the passion for polymers is 100% real. No TDI was harmed in the writing of this article (though a few fume hoods were thanked). 🧫🧪🔥

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