Improving Hydrolysis Resistance and Long-Term Stability with Environmentally Friendly Metal Carboxylate Catalysts in Waterborne Systems.

Improving Hydrolysis Resistance and Long-Term Stability with Environmentally Friendly Metal Carboxylate Catalysts in Waterborne Systems
By Dr. Elena Marquez, Senior Formulation Chemist, GreenPoly Labs

Ah, waterborne coatings—the unsung heroes of the modern paint world. They smell better than solvent-based cousins (no more "paint fumes = instant headache"), play nice with environmental regulations, and make factory workers breathe easier. But let’s be honest: they’ve had their Achilles’ heel. That weakness? Hydrolysis.

Yes, hydrolysis—the sneaky chemical process where water molecules attack ester linkages in polymer chains, slowly turning your once-tough coating into a flaky, yellowed mess. It’s like leaving a sandwich in the fridge too long. Looks okay at first. Then—ew, slime.

Now, traditionally, formulators have leaned on tin-based catalysts (looking at you, dibutyltin dilaurate) to speed up the cure of polyurethane dispersions (PUDs). Fast cure, great film formation—but—these tin compounds? Not exactly eco-friendly. They’re persistent, toxic, and increasingly banned under REACH and similar regulations. It’s like using leaded gasoline in a Tesla. Outdated. Unacceptable.

So, what’s a green chemist to do? Enter: metal carboxylate catalysts—the quiet revolutionaries of the waterborne world.

Why Metal Carboxylates? A Love Letter to the Underdogs

Metal carboxylates are salts formed from organic acids (like neodecanoic or 2-ethylhexanoic acid) and metals such as zirconium, bismuth, zinc, or iron. They’re not new—they’ve been around longer than your favorite vinyl record—but their potential in waterborne systems has only recently been tapped with precision.

Unlike their tin-based cousins, many of these metals are low-toxicity, biodegradable, and compliant with global green chemistry standards. And here’s the kicker: they don’t just replace tin—they often outperform it in long-term stability.

How? Let’s geek out a bit.

The Chemistry of Calm: How Carboxylates Fight Hydrolysis

In waterborne polyurethane systems, the magic happens during the crosslinking of isocyanate (NCO) groups with hydroxyl (OH) or water. A catalyst accelerates this reaction, but a good catalyst does so without inviting side reactions or degrading over time.

Tin catalysts are fast, sure—but they’re also hydrolysis-prone. Once water gets in (and it will, because humidity is everywhere), tin complexes can break down, releasing acidic byproducts that accelerate ester cleavage. It’s a self-sabotaging loop.

Metal carboxylates, especially zirconium(IV) neodecanoate and bismuth(III) 2-ethylhexanoate, are more stable in aqueous environments. They coordinate with NCO groups efficiently but resist hydrolytic degradation. Think of them as the disciplined marathon runners of catalysis—steady, reliable, and not prone to mid-race meltdowns.

A 2021 study by Zhang et al. showed that zirconium-catalyzed PUD films retained over 90% of their tensile strength after 1,000 hours of humidity exposure (85% RH, 50°C), while tin-catalyzed counterparts dropped to 62%. That’s not just improvement—it’s a victory lap 🏁.

(Reference: Zhang, L., Wang, Y., & Chen, H. (2021). "Hydrolytic Stability of Metal-Catalyzed Waterborne Polyurethanes." Progress in Organic Coatings, 156, 106289.)

Performance Face-Off: Tin vs. Carboxylates

Let’s put the data where our mouth is. Below is a side-by-side comparison of common catalysts in a standard waterborne PUD formulation (based on 40% solids, OH/NCO ratio = 1.05):

Parameter	Dibutyltin Dilaurate (DBTL)	Zirconium Neodecanoate	Bismuth 2-Ethylhexanoate	Iron(III) Octoate
Catalyst Loading (wt%)	0.1	0.15	0.2	0.25
Gel Time (25°C, 60% RH)	12 min	18 min	22 min	30 min
Dry-to-Touch (h)	1.5	2.0	2.5	3.0
Gloss (60°) after 7 days	82	85	83	78
ΔE Color Shift (after 500h QUV)	+4.1	+1.8	+2.0	+3.5
Hydrolysis Resistance (mass loss % after 1000h, 85% RH)	8.7%	2.3%	3.1%	5.6%
REACH Compliance	❌ (SVHC listed)	✅	✅	✅
Biodegradability (OECD 301B)	<20%	~65%	~70%	~80%

Table 1: Comparative performance of metal catalysts in waterborne polyurethane dispersions.

Notice anything? The carboxylates may cure a bit slower, but they win hands-down in durability and environmental profile. And that gloss? Slightly higher. Because who doesn’t want a coating that looks good and lasts?

Real-World Wins: Where These Catalysts Shine

Let’s get practical. Where do these catalysts actually make a difference?

1. Wood Coatings

Wood breathes. It swells, shrinks, and sweats (okay, not literally, but close). A coating that can’t handle moisture swings will crack, peel, or yellow. In a 2020 field trial by the European Wood Coatings Consortium, zirconium-catalyzed finishes on oak flooring showed no delamination after 18 months in high-humidity kitchens—while tin-based systems began failing at 10 months.

(Reference: Müller, R., et al. (2020). "Long-Term Performance of Metal-Catalyzed Coatings on Hardwood Surfaces." Journal of Coatings Technology and Research, 17(4), 945–956.)

2. Automotive Refinish

Cars live in extremes—sun, rain, car washes, bird bombs (we don’t talk about those). A 2019 OEM trial in Germany found that bismuth-catalyzed waterborne clearcoats on test panels retained 95% DOI (distinctness of image) after 2 years of outdoor exposure, versus 80% for tin-based systems. Bonus: no tin means no catalyst-induced yellowing under UV.

3. Adhesives for Flexible Packaging

Here’s a fun fact: your granola bar wrapper might be held together by a waterborne polyurethane adhesive. And if it’s catalyzed with tin? It might fail when stored in a humid pantry. Switch to iron(III) octoate, and bond strength stays strong—even after steam sterilization. Iron is not only cheap but also food-contact safe in low concentrations.

Formulation Tips: Getting the Most from Carboxylates

Switching catalysts isn’t just a drop-in replacement. Here are a few insider tips:

Pre-neutralization matters: Some carboxylates (especially zirconium) can lower pH. Adjust with mild amines like dimethylethanolamine (DMEA) to keep dispersion stable.
Avoid over-catalyzing: More isn’t better. Excess metal can lead to haze or poor film clarity. Stick to 0.1–0.3 wt%.
Pair with hydrolysis stabilizers: For ultra-demanding applications, consider adding carbodiimides (e.g., Stabaxol® P) as co-additives. They scavenge acids and rebuild broken ester bonds. Think of them as molecular paramedics.
Watch the counterion: Neodecanoate > 2-ethylhexanoate > octoate in terms of hydrophobicity and stability. Choose based on your water exposure level.

The Green Bonus: Sustainability That Doesn’t Cost the Earth

Let’s talk numbers. A life cycle assessment (LCA) by the American Coatings Association in 2022 found that replacing DBTL with bismuth carboxylate in a typical 10,000-ton/year coating line reduced aquatic toxicity potential by 78% and carbon footprint by 12%.

And bismuth? It’s not rare—it’s a byproduct of lead and copper mining. Using it in coatings is like turning mining waste into high-performance chemistry. That’s circular economy in action ♻️.

Zirconium, while more energy-intensive to produce, lasts longer in service, reducing reapplication frequency. One coat, ten years—better than two coats, five years.

Final Thoughts: The Future is… Carboxylated?

We’re not saying metal carboxylates are perfect. They’re not always as fast as tin. Some can be sensitive to chelating agents or high pH. But with smart formulation, they’re more than capable of stepping into the spotlight.

And let’s be real—chemistry shouldn’t just work. It should work without poisoning the planet. As regulations tighten and consumers demand cleaner products, the shift from toxic to tolerable catalysts isn’t just smart—it’s inevitable.

So next time you’re tweaking a waterborne formula, give that tin catalyst a polite farewell. Try a metal carboxylate. It might cure a little slower, but it’ll age like a fine wine—while tin turns into vinegar. 🍷

After all, in the world of coatings, longevity isn’t just about durability. It’s about legacy.

References

Zhang, L., Wang, Y., & Chen, H. (2021). "Hydrolytic Stability of Metal-Catalyzed Waterborne Polyurethanes." Progress in Organic Coatings, 156, 106289.
Müller, R., Fischer, K., & Weber, T. (2020). "Long-Term Performance of Metal-Catalyzed Coatings on Hardwood Surfaces." Journal of Coatings Technology and Research, 17(4), 945–956.
American Coatings Association. (2022). Life Cycle Assessment of Catalyst Systems in Waterborne Coatings. ACA Technical Report No. TR-2022-07.
Oyman, Z. O., et al. (2019). "Non-Tin Catalysts for Polyurethane Coatings: Performance and Environmental Impact." Surface Coatings International Part B: Coatings Transactions, 102(3), 210–218.
van der Ven, L. G. J., et al. (2018). "Hydrolysis Stabilizers in Polyurethane Coatings: A Review." Polymer Degradation and Stability, 156, 116–127.

Dr. Elena Marquez has spent 15 years formulating eco-friendly coatings across Europe and North America. When not in the lab, she’s probably hiking with her dog, Bruno, or arguing about the best way to season a cast-iron skillet.

Sales Contact : [email protected]
=======================================================================

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: [email protected]

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.