Overview
A polyurethane dispersion is a polyurethane or polyurethane-urea polymer dispersed as fine particles in water. Internal emulsifiers built into the polymer backbone keep the particles stable without large amounts of added surfactant. As water evaporates, particles coalesce into a film, much like an acrylic latex but with urethane toughness.
Key findings
- Main synthesis routes include the acetone process, the prepolymer process (traditionally using NMP as a co-solvent), modified prepolymer routes that avoid NMP, and emerging solvent-free variants.[1]
- Anionic internal emulsifiers such as DMPA, DMBA and sulfonates are the most widely used industrially; nonionic polyether segments give steric stabilization, while cationic systems tend to yellow.[1]
- Because NCO groups react with water during dispersion, processes aim to preserve most of the isocyanate for chain extension. The review also cites EU limits on NMP, free diisocyanate and paint VOC content.[1]
- PUD films can approach conventional polyurethanes in chemical resistance, flexibility and adhesion, and nanocellulose reinforcement substantially increased tensile strength in reported studies.[1]
- Batch production limits solids content and productivity; continuous processes have reached higher solids, and more hydrophilic content gives smaller particles and better storage stability.[2]
- Reviews cover applications from adhesives and fibers to metal primers and water-based inks, and newer polyols and controlled polymerization methods for tailoring properties.[3][4][5]
What it means in the field
For specifiersPUDs are strong options for low-VOC, low-odor primers, sealers and clear or pigmented topcoats on wood and concrete. Ask for NMP-free grades, and check water resistance and yellowing, which depend on the emulsifier type and ionic content.
References
- Santamaria-Echart A, Fernandes I, Barreiro F, et al. (2021). Advances in waterborne polyurethane and polyurethane-urea dispersions and their eco-friendly derivatives: a review. Polymers, 13(3), 409. doi:10.3390/polym13030409
- Liu X, Hong W, Chen X (2020). Continuous production of water-borne polyurethanes: a review. Polymers, 12(12), 2875. doi:10.3390/polym12122875
- Zhou X, Li Y, Fang C, et al. (2015). Recent advances in synthesis of waterborne polyurethane and their application in water-based ink: a review. Journal of Materials Science & Technology, 31(7), 708–722. doi:10.1016/j.jmst.2015.03.002
- Honarkar H (2018). Waterborne polyurethanes: a review. Journal of Dispersion Science and Technology, 39(4). doi:10.1080/01932691.2017.1327818
- Kim BK (1996). Aqueous polyurethane dispersions. Colloid and Polymer Science. doi:10.1007/BF00653056
Citations were checked against publisher, DOI or agency records. Summaries are paraphrased; read the original papers for full methods and data.