Preparation and properties of waterborne polyurethane coatings containing polyurethane-coated hollow glass microspheres

With increasing demand for deep-sea exploration, high-performance submersible fabric materials are urgently needed. In this study, the surface of hollow glass microspheres (HGMs) was functionalized using silane coupling agent KH550 to prepare amino-modified HGMs. Subsequently, polyurethane-coated HGM (PU-HGMs) were synthesized via in-situ polymerization. Waterproof and thermally insulating composite coatings were prepared on the surface of fabrics by lamination technology, with waterborne polyurethane (WPU) as the matrix material and incorporating HGM and PU-HGM as fillers. The results demonstrated that PU-HGMs fully retained the hollow structure of HGMs, and the surface polyurethane layer (approximately 1.5 μm thick) significantly enhanced the shear resistance of HGMs as well as their interfacial compatibility with the WPU matrix. When the content of PU-HGMs was 20 wt%, the thermal conductivity of the coating decreased to 0.05 W/(m·K), representing a 75.4 % reduction compared to pure WPU. Infrared thermal imaging showed the 20 wt% PU-HGMs coating maintained a temperature of 49.4 °C after 2 min at 100 °C, demonstrating excellent thermal insulation. The 20 wt% PU-HGMs coating had a water contact angle of 121.33° and a water absorption rate of 3.1 %, showing excellent hydrophobicity. When the content of PU-HGMs is 5 wt%, the tensile strength of the composite coating reaches 0.83 MPa and the elongation at break is 1261 %, highlighting the remarkable toughening effect of the polyurethane coating. This study enhances the effective loading of HGM as fillers in waterborne coatings and offers a novel strategy for designing and large-scale manufacturing environmentally friendly diving suit coatings.