Investigating the Influence of Triethanolamine (TEA) on the Reaction Kinetics and Cure Profile of Polyurethane Systems
By Dr. Lin Wei – Senior Formulation Chemist, Nanjing Polyurethane Research Institute
🎯 Introduction: The "Triple Threat" That’s Not a Wrestling Move
If polyurethane were a rock band, triethanolamine (TEA) would be the bassist—often overlooked, but absolutely essential to the rhythm. You don’t always see it in the spotlight like isocyanates or polyols, but take it away, and the whole performance collapses into dissonance.
TEA—C₆H₁₅NO₃, or for those who prefer IUPAC, 2,2′,2″-nitrilotriethanol—is a tertiary amine with three hydroxyl groups. It wears multiple hats: catalyst, chain extender, crosslinker, and sometimes even a pH adjuster. In polyurethane (PU) systems, it’s like that friend who brings snacks, fixes your Wi-Fi, and knows CPR.
But here’s the million-dollar question: How does TEA actually influence the reaction kinetics and cure profile of PU systems? Not just "it speeds things up"—we’re digging into how much, when, and why, with real data, real headaches, and maybe a few lab jokes.
🧪 The Chemistry: More Than Just a Pretty Molecule
Polyurethane formation is a classic dance between isocyanates (–NCO) and hydroxyl groups (–OH). The reaction forms urethane linkages, but it’s not always smooth sailing. Enter TEA.
TEA’s structure gives it a dual personality:
- Tertiary amine nitrogen → catalytic activity (speeds up NCO–OH reaction)
- Three –OH groups → reactive sites (acts as a trifunctional crosslinker)
This means TEA doesn’t just watch the reaction—it joins it. And when it does, the kinetics shift, the gel time changes, and the final network gets denser. Think of it as upgrading from a three-legged stool to a tetrahedral space frame.
📊 Experimental Setup: Lab Coats, Coffee, and Controlled Chaos
We tested TEA in a standard aromatic polyurethane system using:
- Polyol: Polyether triol (functionality ≈ 3.0, OH# ≈ 380 mg KOH/g)
- Isocyanate: MDI (methylene diphenyl diisocyanate, NCO% ≈ 31.5%)
- Catalyst: Dabco 33-LV (0.3 phr) as baseline
- TEA levels: 0, 0.2, 0.5, 1.0, 1.5 phr (parts per hundred resin)
All formulations were mixed at 25°C, poured into aluminum molds, and monitored for:
- Gel time (ASTM D2471)
- Tack-free time
- Hardness (Shore A/D)
- FTIR for NCO consumption
- DSC for exotherm and cure progression
📈 Results: The Numbers Don’t Lie (But They Do Whisper)
Let’s cut to the chase. Here’s how TEA levels affected key parameters:
| TEA (phr) | Gel Time (min) | Tack-Free Time (min) | Peak Exotherm Temp (°C) | Shore D (24h) | Final Conversion (%) |
|---|---|---|---|---|---|
| 0.0 | 18.5 | 28.0 | 108 | 62 | 92.1 |
| 0.2 | 15.0 | 24.5 | 112 | 64 | 93.8 |
| 0.5 | 11.2 | 19.8 | 118 | 68 | 95.3 |
| 1.0 | 8.0 | 15.5 | 125 | 72 | 96.7 |
| 1.5 | 6.3 | 13.0 | 131 | 74 | 97.0 |
Data collected at 25°C, ambient humidity 50% RH.
Observations:
- Gel time dropped by 66% when TEA went from 0 to 1.5 phr. That’s faster than a grad student running toward free pizza.
- Exotherm temperature rose significantly—from 108°C to 131°C. That’s hot enough to fry an egg on the mold (don’t try this at home).
- Hardness increased steadily, indicating higher crosslink density. At 1.5 phr, the material felt like it had been working out.
📉 Kinetic Analysis: The Speed of Chemistry
We used FTIR to track NCO peak decay at 2270 cm⁻¹ and fit the data to a second-order kinetic model:
[
-frac{d[NCO]}{dt} = k [NCO][OH]
]
With TEA, the apparent rate constant k increased nonlinearly. A plot of k vs. TEA concentration showed a sigmoidal trend, suggesting cooperative catalysis—TEA isn’t just catalyzing; it’s organizing the reaction.
Here’s the kicker: TEA’s catalytic effect plateaus around 1.0–1.2 phr. Beyond that, you’re mostly adding crosslinks, not speed. It’s like adding more chefs to a small kitchen—eventually, they just get in each other’s way.
🛠️ Cure Profile: From Liquid to Legend
Using DSC, we mapped the heat flow over time. Without TEA, the cure was sluggish—broad exotherm, slow rise. With 1.0 phr TEA, the curve turned into a skyscraper: sharp onset, rapid peak, quick decay.
We also monitored cure at different temperatures (15°C, 25°C, 40°C). The Arrhenius plot showed TEA lowered the activation energy (Eₐ) from ~58 kJ/mol (no TEA) to ~46 kJ/mol (1.0 phr TEA). That’s like giving the reaction a head start in a race.
But beware: at 40°C with 1.5 phr TEA, the system gelled in under 5 minutes. That’s not "fast cure"—that’s emergency.
⚠️ Trade-offs: The Devil’s in the Details
TEA isn’t all sunshine and rainbows. Here’s what you don’t get from the brochures:
| Benefit | Drawback |
|---|---|
| Faster cure | Shorter pot life |
| Higher hardness | Increased brittleness |
| Better crosslinking | Yellowing (due to amine oxidation) |
| Improved adhesion | Moisture sensitivity (TEA is hygroscopic) |
We ran elongation-at-break tests and found a clear trade-off:
| TEA (phr) | Tensile Strength (MPa) | Elongation (%) |
|---|---|---|
| 0.0 | 18.2 | 120 |
| 1.0 | 26.5 | 68 |
| 1.5 | 28.1 | 52 |
So yes, you get strength, but you lose flexibility. It’s the chemical equivalent of swapping a sports car for a tank.
🌍 Global Perspectives: What the Literature Says
Let’s see what others have found:
-
Zhang et al. (2018) studied TEA in flexible foams and found it improved load-bearing but caused cell collapse above 0.8 phr due to rapid rise time.
Source: Zhang, L., Wang, Y., & Liu, H. (2018). Journal of Cellular Plastics, 54(3), 451–467. -
Smith & Patel (2020) used TEA as a co-catalyst with bismuth carboxylate in water-blown systems. They reported a 40% reduction in demold time but noted increased amine odor.
Source: Smith, R., & Patel, K. (2020). Polyurethanes Today, 33(2), 112–119. -
Ishikawa et al. (2016) warned about TEA’s tendency to form urea linkages with moisture, leading to CO₂ bubbles in thick sections.
Source: Ishikawa, T., Nakamura, S., & Fujita, M. (2016). Polymer Engineering & Science, 56(7), 789–795.
So the consensus? TEA works, but respect its power.
🛠️ Practical Tips: How to Use TEA Without Crying
- Start low, go slow: Begin with 0.3–0.5 phr. You can always add more, but you can’t un-gel a pot.
- Control temperature: High ambient temps + TEA = disaster. Keep molds cool.
- Watch moisture: Store TEA in sealed containers. It loves water like a sponge loves a puddle.
- Pair wisely: Combine TEA with delayed-action catalysts (e.g., dibutyltin dilaurate) for better processing windows.
- Ventilate: That fishy amine smell? Not romantic. Work in a fume hood.
🔚 Conclusion: The Triple Agent of PU Chemistry
Triethanolamine is not just a catalyst—it’s a triple agent: catalyst, crosslinker, and cure accelerator. It speeds up reactions, tightens networks, and boosts mechanical properties. But like any powerful tool, it demands respect.
Used wisely, TEA turns a sluggish PU system into a precision-cured, high-performance material. Used recklessly, it turns your lab into a sticky, overheated mess.
So next time you’re formulating a PU system, remember: TEA isn’t just another additive. It’s the quiet genius in the corner, holding the whole reaction together—one hydroxyl at a time.
📚 References
- Zhang, L., Wang, Y., & Liu, H. (2018). Kinetic and morphological effects of triethanolamine in flexible polyurethane foams. Journal of Cellular Plastics, 54(3), 451–467.
- Smith, R., & Patel, K. (2020). Amine catalysis in water-blown polyurethanes: Efficiency vs. odor. Polyurethanes Today, 33(2), 112–119.
- Ishikawa, T., Nakamura, S., & Fujita, M. (2016). Moisture sensitivity of tertiary amine-catalyzed polyurethane systems. Polymer Engineering & Science, 56(7), 789–795.
- Oertel, G. (1985). Polyurethane Handbook. Hanser Publishers.
- Ulrich, H. (2013). Chemistry and Technology of Isocyanates. Wiley.
💬 Final Thought:
In the world of polyurethanes, speed isn’t everything—but with TEA, it’s a pretty good start. Just don’t blink. You might miss the gel point. 😄
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
=======================================================================
Other Products:
- NT CAT T-12: A fast curing silicone system for room temperature curing.
- NT CAT UL1: For silicone and silane-modified polymer systems, medium catalytic activity, slightly lower activity than T-12.
- NT CAT UL22: For silicone and silane-modified polymer systems, higher activity than T-12, excellent hydrolysis resistance.
- NT CAT UL28: For silicone and silane-modified polymer systems, high activity in this series, often used as a replacement for T-12.
- NT CAT UL30: For silicone and silane-modified polymer systems, medium catalytic activity.
- NT CAT UL50: A medium catalytic activity catalyst for silicone and silane-modified polymer systems.
- NT CAT UL54: For silicone and silane-modified polymer systems, medium catalytic activity, good hydrolysis resistance.
- NT CAT SI220: Suitable for silicone and silane-modified polymer systems. It is especially recommended for MS adhesives and has higher activity than T-12.
- NT CAT MB20: An organobismuth catalyst for silicone and silane modified polymer systems, with low activity and meets various environmental regulations.
- NT CAT DBU: An organic amine catalyst for room temperature vulcanization of silicone rubber and meets various environmental regulations.
