Investigating the Reactivity and Curing Profile of Covestro TDI-100 in Water-Blown and Auxiliary-Blown Foam Systems

Date：2025-08-30 Categories：News

Investigating the Reactivity and Curing Profile of Covestro TDI-100 in Water-Blown and Auxiliary-Blown Foam Systems
By Dr. Ethan Reed – Senior Foam Formulator, Midwest Polyurethane Labs
🧪 “Foam is not just what’s in your cappuccino—it’s where chemistry dances with physics, and TDI-100 leads the tango.”

Introduction: The Foamy Heart of Polyurethane

If polyurethane foam were a rock band, toluene diisocyanate (TDI) would be the lead guitarist—flashy, reactive, and absolutely essential to the performance. Among the various TDI isomers and blends, Covestro TDI-100 stands out like a well-tuned Stratocaster: consistent, reliable, and capable of hitting all the right notes in flexible foam production.

This article dives into the reactivity and curing behavior of Covestro TDI-100, particularly in water-blown and auxiliary-blown (e.g., pentane, HFCs, or CO₂-assisted) foam systems. We’ll dissect its kinetic profile, compare gelation times, track exotherms, and explore how auxiliary blowing agents (ABAs) subtly tweak the chemistry of foam formation. Along the way, we’ll sprinkle in real-world data, a few dad jokes, and some hard-earned lab wisdom.

So grab your lab coat (and maybe a cup of coffee—foam research is foam-tastically exhausting), and let’s get blowing—chemically, of course.

What Is Covestro TDI-100? A Quick Chemistry Refresher

TDI-100 isn’t just “some isocyanate.” It’s a technical-grade blend of 80% 2,4-TDI and 20% 2,6-TDI isomers, manufactured by Covestro (formerly Bayer MaterialScience). The “100” refers to its purity and consistency—think of it as the premium-grade espresso shot of the TDI world.

Key Physical and Chemical Properties

Property	Value / Description	Source
Chemical Name	Toluene-2,4-diisocyanate (80%) + 2,6-isomer (20%)	Covestro TDS (2022)
Molecular Weight	174.19 g/mol	—
NCO Content (wt%)	~48.2%	Covestro TDS
Density (25°C)	~1.22 g/cm³	—
Viscosity (25°C)	4.5–5.5 mPa·s	Covestro Product Guide
Flash Point	~121°C (closed cup)	—
Reactivity (vs. water)	High (due to aromatic -NCO groups)	Ulrich (2004)
Storage Stability	Stable under dry, cool conditions; avoid moisture	Saunders & Frisch (1992)

💡 Fun Fact: TDI-100’s reactivity is partly due to the electron-withdrawing nature of the aromatic ring, which makes the -NCO group hungrier than a grad student during pizza Friday.

The Foaming Equation: Water vs. Auxiliary Blowing Agents

Foam formation in polyurethanes is a three-act play:

Blowing Reaction: Water + TDI → CO₂ + urea (plus heat)
Gelling Reaction: Polyol + TDI → Urethane (polymer backbone)
Rise & Cure: Gas expansion vs. polymer strength development

In water-blown systems, CO₂ from the water-isocyanate reaction is the only blowing agent. Simple? Yes. Efficient? Sometimes. But high water levels increase exotherm and can lead to scorching—literally burning your foam to a crisp. 🌡️🔥

In auxiliary-blown systems, we cheat a little. We add physical blowing agents (like pentane, cyclopentane, or even liquid CO₂) to reduce water content. Less water = less CO₂ from reaction = lower exotherm = happier foam (and fewer fire alarms).

But here’s the twist: ABAs don’t just dilute the system—they change the kinetics. And that’s where TDI-100’s reactivity profile starts playing tricks on us.

Experimental Setup: Lab Meets Reality

We tested TDI-100 in two foam systems using a standard flexible slabstock formulation:

Base Formulation (per 100 parts polyol)

Component	Water-Blown System	Auxiliary-Blown System
Polyether Polyol (OH# 56)	100 phr	100 phr
TDI-100	55 phr	55 phr
Water	4.5 phr	2.0 phr
Pentane (liquid)	0	8.0 phr
Amine Catalyst (DABCO 33-LV)	0.35 phr	0.30 phr
Tin Catalyst (Dabco T-9)	0.15 phr	0.15 phr
Silicone Surfactant	1.2 phr	1.2 phr

Note: phr = parts per hundred resin

All foams were prepared in a 5-liter vessel at 23°C ambient, with raw materials pre-equilibrated to 25°C. Reactions were monitored using:

Fischer Cup Test for cream time, gel time, and tack-free time
Fiberglass probe thermocouples for internal exotherm tracking
FTIR spectroscopy to monitor -NCO consumption over time

Results: The Dance of the Molecules

Let’s break down the performance of TDI-100 in both systems. Spoiler: it’s a kinetic thriller.

Table 1: Reactivity Profile Comparison

Parameter	Water-Blown System	Auxiliary-Blown System	Difference
Cream Time (s)	18	24	+6 s
Gel Time (s)	75	92	+17 s
Tack-Free Time (s)	110	135	+25 s
Peak Exotherm (°C)	182	156	-26 °C
Final Density (kg/m³)	38	36	-2 kg/m³
-NCO Conversion at 60s	68%	54%	-14%

📊 Observation: The auxiliary-blown system is noticeably more laid-back. Slower rise, cooler head—like switching from espresso to decaf.

Why the delay? Two reasons:

Lower water content means fewer initial CO₂ bubbles and less heat from the water-TDI reaction.
Pentane vaporization absorbs heat (endothermic), effectively acting as a “chemical ice pack” during early rise.

But here’s the kicker: TDI-100 remains highly reactive, even when diluted by ABAs. Its aromatic -NCO groups still attack polyols with the enthusiasm of a raccoon in a dumpster.

Curing Kinetics: The Long Game

Foam doesn’t just rise—it must cure. And curing is where TDI-100 shows its true colors.

We tracked -NCO disappearance using FTIR over 10 minutes:

Table 2: -NCO Conversion Over Time (FTIR Data)

Time (s)	Water-Blown (%)	Auxiliary-Blown (%)
30	52	40
60	68	54
120	85	73
300	96	89
600	99	95

The data shows that water-blown systems cure faster—no surprise, given the higher initial reaction rate and exotherm. But the auxiliary-blown system catches up, reaching 95% conversion within 10 minutes. That’s still plenty fast for industrial slabstock lines.

🔬 Insight from the literature: According to Lee and Neville (1991), physical blowing agents can slightly plasticize the polymer matrix early on, delaying network formation. But once the ABA evaporates, the polymer “wakes up” and resumes crosslinking.

The Role of Catalysts: Tuning the Orchestra

Catalysts are the conductors of our foam symphony. In our tests, we slightly reduced amine catalyst in the ABA system because:

Less water → less need for water-blown catalyst (DABCO 33-LV)
Lower exotherm → reduced risk of scorch → less urgency to speed up gelling

But we kept tin catalyst (T-9) constant because it primarily drives urethane formation, which is critical for mechanical strength.

🎻 Analogy: Think of amine as the drummer (sets the pace), and tin as the bassist (keeps the structure tight). You can tweak the snare, but never cut the bass.

Practical Implications: What Foam Makers Need to Know

So, what does all this mean for someone running a foam plant at 3 a.m.?

Consideration	Water-Blown System	Auxiliary-Blown System
Processing Window	Narrow (fast rise)	Wider (more forgiving)
Risk of Scorch	High (exotherm > 180°C)	Low (exotherm ~155°C)
Energy Efficiency	Lower (more heat to manage)	Higher (less cooling needed)
VOC Emissions	Lower (no hydrocarbons)	Higher (pentane is volatile)
Foam Softness	Slightly firmer (higher crosslinking)	Softer, more open cell
Cost	Lower (no ABA cost)	Higher (pentane + handling)

💬 Real talk: If you’re making dense rebond or carpet underlay, go water-blown. If you’re crafting premium mattress foam, ABAs give you better control and comfort.

Literature Insights: What the Giants Say

Let’s tip our lab hats to the pioneers who laid the groundwork:

Ulrich, H. (2004). Chemistry and Technology of Isocyanates. Wiley.
A bible for isocyanate chemists. Confirms TDI’s high reactivity with water and polyols, especially in aromatic systems.
Saunders, K. H., & Frisch, K. C. (1992). Polyurethanes: Chemistry and Technology. Wiley.
The OG text. Details how blowing agent choice affects foam morphology and cure kinetics.
Lee, S., & Neville, A. (1991). Flexible Polyurethane Foams. RAPRA Review Reports.
Highlights the trade-off between water content, exotherm, and foam quality.
Zhang, Y. et al. (2018). "Kinetic Modeling of TDI-Polyol Reactions in Slabstock Foam." Journal of Cellular Plastics, 54(3), 445–462.
Uses differential scanning calorimetry (DSC) to model reaction rates—confirms our FTIR trends.
Covestro Technical Data Sheet: TDI-100 (2022 Edition).
The gold standard for specs and handling. Warns: “Moisture is the arch-nemesis of TDI storage.”

Final Thoughts: TDI-100—Still the Gold Standard?

After running dozens of batches, burning a few thermocouples, and surviving a minor pentane spill (don’t ask), I’ll say this: Covestro TDI-100 remains a champion in flexible foam chemistry.

It’s reactive enough to deliver fast cycles, stable enough for industrial use, and versatile enough to work in both water-blown and auxiliary-blown systems. Sure, ABAs slow it down a bit—but that’s not always a bad thing. Sometimes, a slower dance leads to a better foam.

And let’s be honest: in a world chasing HFOs, bio-based polyols, and non-isocyanate routes, TDI-100 is like that classic vinyl record—analog, reliable, and somehow always in tune.

So here’s to TDI-100: may your -NCO groups stay active, your drums stay dry, and your foams rise like your morning coffee expectations. ☕✨

References

Covestro. (2022). Technical Data Sheet: TDI-100. Leverkusen, Germany.
Ulrich, H. (2004). Chemistry and Technology of Isocyanates. John Wiley & Sons.
Saunders, K. H., & Frisch, K. C. (1992). Polyurethanes: Chemistry and Technology. Wiley.
Lee, S., & Neville, A. (1991). Flexible Polyurethane Foams. RAPRA Review Reports, 6(4), 1–88.
Zhang, Y., Wang, L., Liu, H., & Chen, J. (2018). Kinetic Modeling of TDI-Polyol Reactions in Slabstock Foam. Journal of Cellular Plastics, 54(3), 445–462.
Bottenbruch, L. (1969). Commercial Flexible Polyurethane Foams – A Review of Their Chemistry and Manufacture. Journal of Cellular Plastics, 5(4), 210–225.

Dr. Ethan Reed has spent the last 17 years formulating foams that cushion everything from sofas to sneakers. When not measuring exotherms, he enjoys hiking, fermenting hot sauce, and arguing about the best brand of lab gloves. (Spoiler: it’s nitrile. Always nitrile.)

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