Preparation of High‐Solid‐Content and Highly Water‐Resistant Waterborne Polyurethanes via Combined Internal‐External Emulsification and <scp>KH560</scp> Crosslinking

ABSTRACT Conventional waterborne polyurethanes (WPUs) are often limited by low solid content, poor water resistance, and reliance on organic solvents in their synthesis. In this study, a series of crosslinked high‐solid‐content WPUs (CHWPUs) with different external emulsifier and crosslinker contents were synthesized. The synthesis was conducted using a combined internal‐external emulsification approach, wherein a carboxylate‐sulfonate type WPU served as the matrix and 3‐glycidoxypropyltrimethoxysilane (KH560) was incorporated as a crosslinker. The results showed the introduction of the external emulsifier significantly enhanced the solid content and stability of the WPU emulsion, attributable to its amphiphilic (hydrophilic–lipophilic) structure. Fourier transform infrared (FTIR) spectroscopy confirmed the successful formation of Si–O–Si crosslinked networks in CHWPUs. The crosslinking strategy significantly improved the water resistance of the CHWPU films. At optimal external emulsifier and crosslinker contents of 1.5 and 3.0 wt% (based on total solid mass), the solid content of the CHWPU emulsion was increased to 51.41%, and the water absorption rate of the CHWPU film was reduced to 10.94%. This work can provide useful references for the research and development of high‐performance HWPUs.