Effect of Siloxane Crosslinking on Colloidal, Mechanical, and Thermal Properties of Self-curable Waterborne Polyurethane Dispersions

Self-curable waterborne polyurethane (WPU) dispersions were prepared via acetone process. The effects of (3-aminopropyl) triethoxysilane (APTES) content as crosslinking agent on the properties of WPUs were investigated. To confirm the polymer structure and the presence of alkoxysilane groups, 1H nuclear magnetic resonance and fourier transform infrared spectroscopy were used. Gel content of the sample containing 10 wt% APTES was reported 90.5% which were revealed highly crosslinking network of the WPU film. Although the particle size went up from 36.5 to 63 nm by introducing 10 wt% APTES, narrow particle size distributions (PDI < 0.2) and the absolute value of zeta potentials greater than 40 mV were obtained. Furtheremore, atomic force microscopy showed that the introduction of siloxane crosslinking increased microphase-separation of the polyurethane films. In the presence of 10 wt% APTES, excellent enhancement in water resistance (water absorption < 5%), mechanical properties (Young’s modulus=420 MPa and tensile strength=46.7 MPa), and thermal stability (Tmax1=321 ºC and Tmax2=407 ºC) made this type of crosslinking highly suitable for WPUs in coating applications.