International. For the first time, stable water-based polyurethane dispersions were prepared that led to mechanically strong polyurethane coatings without any chain extenders.
The elimination of this stage and the use of cross-linking with water result in promising applications of water-based polyurethane dispersions (PUDs) as biomaterials and industrial-scale production. The polyurethane (PU) coating system consists of macrodiol polycarbonate (PCD), propionic 2,2-bis (hydroxymethyl) acid (DMPA), 1,6-diisocyanatehexane (HDI) and N, N-diethylenetamine (TEA).
Fourier transformed infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA), static light scattering (SLS), dynamic light scattering (DLS) and atomic force microscopy (AFM) allowed to study the assembly of PU chains/nanoparticles in supramolecular structures in acetone and water. In acetone, the self-assembly chain of isocyanate-terminated prepolymeras occurs in the form of PU solutions (linear PUs) or PU dispersions (cross-linked PT). Due to an inversion phase, linear or cross-linked spherical PU dispersions are formed with water after the addition of water.
The ratio of total isocyanate-a hydroxyl is very important; a slight isocyanate excess (NCO) of 1.05 leads to linear rod-shaped nanoparticles in acetone, followed by a core-envelope structure after the addition of water. An isocyanate excess of 1.5 leads to compact spheres or microgel particles initially cross-linked by moisture in acetone, and final cross-linking and phase inversion occur after the addition of water.
The string lengths of linear PUs and mesh sizes in PU networks increase with the pcd range: DMPA. Therefore, the design of PU nanoparticles with desired sizes, shapes and cross-linking densities is possible. Unlike the substantially different shapes, sizes and compactness of PUs in acetone, all PUDs in water are spherical nanoparticles with an average diameter of 21 to 72 nm, a zeta potential of -40 to -65 mV and a size dispersion index of 0.05 to 0.22.
Source: www.sciencedirect.com
