Effect of polyether soft segments on structure and properties of waterborne UV-curable polyurethane nanocomposites

Waterborne UV-curable polyurethane (WUPU)/silica nanocomposites were prepared using three types of polyether (PEO-PPO-PEO, PPG, and PTMG) and aqueous colloidal silica by phase-inversion emulsification. The PEO-PPO-PEO and PPG-WUPU nanocomposite dispersions exhibited smaller particles and higher viscosity than their pure WUPU dispersions, whereas PTMG-WUPU nanocomposite dispersion exhibited larger particles and higher viscosity than its pure WUPU dispersion. The SEM analysis indicated that the continuous silica clusters network was distributed in the PEO-PPO-PEO-WUPU matrix, whereas the separate silica clusters were dispersed in the PPG and PTMG-WUPU matrix, respectively. The DMA analysis demonstrated that a slight narrowing of the peak in tan delta and a shift in T-g toward lower temperature were observed for the WUPU nanocomposite films with PEO-PPO-PEO and PPG. Conversely, the PTMG-WUPU nanocomposite film showed the insensitivity of the soft segment glass transition (T-g) peak positions, supporting preferential attraction of the silica nanoparticles to the highly polar hard segments. The WUPU nanocomposite films showed increased storage modulus, Young' modulus, and tensile strength. However, for toughness, only the PTMG-WUPU nanocomposite film exhibited great improvement when compared to its pure film due to the silica nanoparticles preferential, but not exclusive, interaction with the hard segment of WUPU.