Using Isocyanate-Free Crosslinked PUDs in High Performance Wood Coating Applications

Posted by Performance Coatings Team on 02/21/2023

Developing new coating components requires prioritizing both performance and environmental impact, including the need to eliminate or drastically reduce any toxic ingredients. To balance these different priorities means developing innovative approaches, taking into account sustainability considerations, such as using recycled/renewable content, extending the service life of the coating to reduce the substrate footprint, and reducing or eliminating hazardous substances (formaldehyde, crosslinking additives like isocyanates and adipic acid dihydrazide, fungicides, VOCs, etc.).

Developing a urethane dispersion for a sustainable, user-friendly and high-performance wood coating requires this innovative approach – like creating polyurethane dispersions (PUDs) that enable coating formulations to be free from isocyanate crosslinkers.

In high-performance applications, two-component coatings are widely used. That means an external crosslinker will be needed. The most common are isocyanates, aziridines, hydrazides and carbodiimides, which all have strengths and weaknesses.

Higher Reactivity. Higher Toxicity.

Isocyanates, aziridines and hydrazides are common crosslinkers due to their highly reactive nature and their efficiency in covalently connecting functional groups in coating compositions. They might only represent a small percent in a formulation, but they often significantly increase the hazard level of coatings because of the ongoing chemical reaction they trigger at the time of the application and in the proximity of the individual applying the coating.

Carbodiimides have a low toxicity, which significantly reduces hazardous components when used as a crosslinker in PUDs. But, carbodiimides are less reactive than other common crosslinkers, which negatively impacts crosslinking efficiency and performance. To use carbodiimides as effective crosslinkers, reactivity issues have to be overcome.

Lubrizol’s Carbodiimide Solution

Lubrizol developed novel polymer technology for two-component water-borne urethane dispersions that address the reactivity issue by improving the reactive nature of the functional groups on the resin side. This was accomplished by transferring the carboxylic groups to the surface, so they are more available to react. By doing so, the technology works more efficiently with environmentally compliant polymeric carbodiimide crosslinkers, providing similar crosslinking performance as isocyanates or aziridines as well as a long pot life, but with a much better toxicity and regulatory profile.

The new resin technology has a renewable carbon content of up to 34% and can be formulated to a low VOC1 content. A high solids content (≥ 45 %) improves dry time and reduces paint application workload due to a higher film build. High solids content also reduces freight and packaging costs because more resin and less water are shipped, while also reducing CO2 emissions in freight and manufacturing. The novel polymer technology also uses amine neutralizers that are alternatives to triethylamine (TEA), which contributes negatively to indoor air quality.

Lubrizol’s polyamide PUD technology was formulated into coatings and tested along with three other commercial products, which are good representatives of demanding interior and exterior wood coating applications. For testing against these 1K and 2K wood coatings, the Lubrizol polymer technology was used in clear wood coatings on maple boards. All coatings passed ambient temperature coalescence and low temperature coalescence at 4.4 °C. The dry coatings were estimated to be 76 μm thick for all the coatings. All coatings passed one-hour sandability checks. Both the polymer and paint also exhibited stability in 60 °C oven testing at greater than 8 weeks.

The novel high solid, TEA-free, water-borne polyamide-based PUD technology with high bio-based content for low VOC 12K isocyanate-free wood coating and protective coating applications outperformed the array of commercial coatings in multiple testing areas. These areas included aesthetic qualities and protective features, including gloss, hardness, chemical and abrasion resistance, and weatherability.

Explore additional information about Lubrizol's polyurethane dispersions or contact us to learn more about our environmentally compliant two-component water-borne urethane dispersions.


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