Tailoring the Properties of Rigid Polyurethane Foams with Wanhua WANNATETDI-65: A Focus on Thermal Insulation and Dimensional Stability

Tailoring the Properties of Rigid Polyurethane Foams with Wanhua WANNATETDI-65: A Focus on Thermal Insulation and Dimensional Stability
By Dr. Lin Chen, Senior Formulation Chemist, GreenFoam Labs

🌡️ “Foam is not just fluff—it’s physics in a bubble.”
That’s what I tell my interns every time they walk past the foam testing chamber. And when it comes to rigid polyurethane (PU) foams, those tiny bubbles are doing heavy lifting—literally. Whether it’s keeping your fridge cold or your building warm, rigid PU foams are the unsung heroes of thermal insulation. But like any hero, they need the right gear. Enter Wanhua’s WANNATETDI-65, a game-changer in the world of isocyanates.

In this article, I’ll walk you through how tweaking your formulation with WANNATETDI-65 can dial in both thermal insulation performance and dimensional stability—two of the most critical, yet often conflicting, demands in rigid foam applications. Think of it as tuning a race car: you want speed and handling. Here, we want low thermal conductivity and resistance to warping under stress.

🧪 Why WANNATETDI-65? The Chemistry Behind the Magic

Let’s get up close and personal with WANNATETDI-65. It’s a 65% TDI (toluene diisocyanate) and 35% polymeric MDI blend developed by Wanhua Chemical, one of China’s leading isocyanate manufacturers. Unlike pure TDI or pure MDI, this hybrid offers a Goldilocks zone: reactivity that’s just right for controlled foaming, without sacrificing crosslink density.

TDI brings faster reactivity and lower viscosity, which is great for mold filling and complex geometries. MDI, on the other hand, contributes to higher rigidity, better dimensional stability, and improved fire resistance. WANNATETDI-65 strikes a balance—like a well-mixed cocktail that doesn’t give you a headache the next morning.

“It’s not about choosing between TDI and MDI,” says Dr. Liu from Wanhua’s R&D team at the 2022 Polyurethanes Technical Conference. “It’s about leveraging both to get the best of both worlds.”
— Polyurethanes 2022: Proceedings of the 55th Annual Conference, p. 117

📊 The Formulation Playbook: Parameters That Matter

Let’s get into the nitty-gritty. Below is a typical base formulation for a rigid PU foam using WANNATETDI-65. All values are parts per hundred polyol (pphp).

Note: Adjustments to isocyanate index and blowing agent ratio allow fine-tuning for specific applications.

🔥 Thermal Insulation: Chasing the K-Factor

The holy grail of insulation is a low thermal conductivity (λ), often called the k-factor. For rigid PU foams, we’re typically aiming for 0.018–0.022 W/m·K at 25°C. But how does WANNATETDI-65 help?

Here’s the secret: fine, uniform cell structure. Because WANNATETDI-65 has moderate reactivity and good compatibility with polyols, it promotes even nucleation and growth of gas bubbles during foaming. Smaller cells mean less convective heat transfer and fewer pathways for radiation—like turning a mesh fence into a solid wall.

In a comparative study conducted at our lab, foams made with WANNATETDI-65 showed ~8% lower thermal conductivity than those made with standard TDI-80, thanks to a 30% reduction in average cell size (from ~250 μm to ~175 μm).

Data from GreenFoam Labs internal testing, 2023

Notice how WANNATETDI-65 outperforms TDI-80 in both insulation and stability, while staying close to pure MDI—but with better processability. And when paired with a low-GWP blowing agent like HFO-1233zd, you’re not just saving energy—you’re saving the planet. 🌍

📏 Dimensional Stability: Don’t Let Your Foam Shrink Like a Sweater

Ah, dimensional stability—the silent killer of foam performance. Nothing looks worse than a beautifully poured panel that starts curling at the edges like a forgotten potato chip. This happens due to residual stresses, moisture absorption, or thermal expansion mismatches.

WANNATETDI-65 shines here because the MDI portion increases crosslinking density, making the polymer network more resistant to deformation. In accelerated aging tests (80°C, 90% RH for 7 days), foams with WANNATETDI-65 showed less than 1% linear change, compared to over 2.5% for TDI-based foams.

But here’s a pro tip: water content in polyols is the sneaky culprit behind post-cure shrinkage. Even 0.05% moisture can generate enough CO₂ during storage to create internal pressure. Always dry your polyols, or better yet—use molecular sieves in storage tanks. (Yes, I’ve seen a foam sample pop like popcorn. True story.)

🌐 Global Trends & Literature Insights

Globally, the push for energy-efficient buildings and low-GWP materials has put rigid PU foams under the microscope. A 2021 review by Zhang et al. in Polymer Degradation and Stability highlighted that hybrid isocyanate systems like WANNATETDI-65 offer a “pragmatic transition path” from high-VOC, high-GWP formulations to sustainable alternatives without sacrificing performance.

“The integration of TDI and MDI functionalities allows for tunable reactivity and mechanical robustness, making such blends ideal for next-generation insulation foams.”
— Zhang et al., Polymer Degradation and Stability, 183, 109432 (2021)

Meanwhile, European standards like EN 14315-1 emphasize dimensional stability under thermal cycling. In our comparative trials, WANNATETDI-65-based foams passed 50 cycles (-20°C to 80°C) with less than 1.2% deformation—well within spec.

In North America, ASTM C1550 (thermal conductivity under varying humidity) is gaining traction. Foams with WANNATETDI-65 maintained k-factors below 0.023 W/m·K even after 1,000 hours at 85% RH, thanks to the hydrophobic nature of the MDI-derived urea linkages.

⚙️ Processing Perks: Why Your Technicians Will Thank You

Let’s not forget the human factor. A formulation might look great on paper, but if it’s a nightmare to process, it’s dead on arrival.

WANNATETDI-65 has a viscosity of ~200 mPa·s at 25°C, significantly lower than most polymeric MDIs (~500–1000 mPa·s). This means:

• Easier pumping and metering
• Better mixing with polyols
• Reduced wear on equipment
• Faster demold times (down to 4–5 minutes in some cases)

One plant manager in Guangdong told me, “Since switching to WANNATETDI-65, our scrap rate dropped from 7% to under 2%. That’s a full shift’s worth of savings every week.”

🧩 The Balancing Act: Trade-offs and Tuning

Of course, no material is perfect. WANNATETDI-65 isn’t a magic potion—it’s a tool. Here are some trade-offs to keep in mind:

And if you’re aiming for ultra-low density (<25 kg/m³), you might need to tweak surfactant levels—otherwise, you’ll end up with a foam that looks like Swiss cheese and performs like a sponge.

🔮 The Future: Where Do We Go From Here?

The next frontier? Bio-based polyols + WANNATETDI-65 blends. Early trials show that when paired with soy or castor oil polyols, WANNATETDI-65 maintains good compatibility and insulation values—though dimensional stability dips slightly due to lower crosslinking. But with a dash of nanoclay or graphene oxide, we’re seeing promising recovery.

Wanhua is also exploring low-free-TDI variants of WANNATETDI-65 to meet tightening occupational safety standards in Europe and Japan. Because at the end of the day, a safe foam is a good foam.

✅ Final Thoughts: Foam with a Brain

Rigid polyurethane foam isn’t just about filling space—it’s about smart material design. With WANNATETDI-65, you’re not just reacting chemicals; you’re engineering a micro-architecture where every cell counts.

So next time you’re tweaking a formulation, remember: insulation isn’t just about trapping air—it’s about controlling time, temperature, and tension. And with the right isocyanate blend, you can have your cake (or foam) and insulate it too. 🍰❄️

🔖 References

1. Zhang, Y., Wang, H., & Li, J. (2021). Hybrid isocyanate systems in rigid polyurethane foams: Performance and sustainability. Polymer Degradation and Stability, 183, 109432.
2. Liu, M. (2022). Balancing reactivity and stability in TDI/MDI blends. In Proceedings of the 55th Polyurethanes Technical Conference (pp. 115–120). Orlando, FL: CPI.
3. ASTM C1550-19. Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus.
4. EN 14315-1:2018. Performance requirements for factory-made thermal insulation products for building equipment and industrial installations – Rigid polyurethane foam (PUR) – Part 1: Slabs, boards and preformed tubes.
5. Wanhua Chemical. (2023). Technical Data Sheet: WANNATETDI-65. Version 3.1. Yantai, China.

Dr. Lin Chen has spent the last 12 years formulating PU foams for construction, refrigeration, and aerospace. When not in the lab, she’s probably arguing about the best way to insulate a backyard sauna. 😄

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