Network formation in 1K and 2K polyurethane coatings analysed

Polyurethane (PU) coatings are widely used in industrial applications, but the choice between water-borne and solvent-borne formulations, as well as between one-component (1K) and two-component (2K) systems, has a significant influence on network formation and final performance. In this study, researchers prepared PU coatings from commercial Bayhydrol® polyurethane dispersions using both 1K and 2K formulations, processed either through the aqueous dispersion or the organic solvent route. Hydroxy-functional polycarbonate- and polyester-based dispersions (Bayhydrol® UXP 2750 and UXP 2698), a flexible anionic dispersion (Bayhydrol® UH 340/1) and an aliphatic polyisocyanate hardener (Desmodur® N3600) were used to investigate how formulation strategy and processing pathway affect coating performance.

The effect of the NCO/OH ratio, film thickness and application method – both roll- and spray-coating – on crosslinking efficiency, thermal behaviour, mechanical properties, surface energy and adhesion was systematically evaluated. This approach enabled a direct comparison between aqueous and solvent-based routes under industrially relevant conditions.

Event Tip: Waterborne High Performance Coatings

Water-induced isocyanate consumption and network integrity

Swelling and extractables measurements revealed significant differences in network integrity between the aqueous and solvent-based routes. In particular, water-induced isocyanate consumption plays a critical role in 2K water-borne systems, reducing the availability of NCO groups for crosslinking with hydroxy functionalities. Thermal analyses showed that the prepared coatings exhibited glass transition temperatures ranging from –50 °C to 69 °C, with thermal stability comparable to conventional polyurethane coatings.

Mechanical testing demonstrated that coating rigidity and toughness are primarily governed by resin functionality and molecular weight, while surface energy and adhesion depend strongly on urethane content and crosslink density. Overall, the study establishes clear process-structure-property relationships for industrially relevant polyurethane coatings and provides practical guidelines for optimising both water-borne and solvent-borne PU formulations.

Source: Boisaubert, P. et al., Waterborne vs solvent-borne 1 K/2 K polyurethane coatings: Network formation and performance of Bayhydrol®-based systems. Progress in Organic Coatings, 110180 (2026).

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