Turning a linear waterborne polyurethane into a crosslinked counterpart with improved water resistance and mechanical strength through a fast post metal-organic crosslinking

Covalent crosslinking can improve the water resistance of waterborne polyurethanes (WPUs), but the preparation time of WPUs will be greatly extended by the crosslinking process, and the long-term storage stability of WPU emulsions will decrease because the crosslinked molecular chains cannot disperse in any organic solvents or water. In this paper, a crosslinked WPU was prepared through a post metal-organic crosslinking toward a conventional linear WPU. This post crosslinking is quite fast since it is based on the ionic bond interaction between metal cations and organic anions. The crosslinked WPU emulsion has narrow particle size distribution and small average size, giving rise to excellent long-term storage stability. Additionally, the water absorptions of the crosslinked WPU at 25°C and 60°C are 6.3% and 8.6% respectively, which decrease by 47.9% and 39.4% compared with those of the linear counterpart, indicating that the post metal-organic crosslinking highly improves the water resistance of the WPU. The mechanical strength of the crosslinked WPU also improves compared with the linear WPU.