Enhanced mechanical strength and water resistance in waterborne polyurethanes through hydroxyl-functionalized MQ silicone resin modification

Abstract

As an alternative to solvent-based polyurethane, waterborne polyurethane (WPU) uses water as dispersants and can significantly reduce VOC. However, dispersing polyurethanes with hydrophobic backbones in water requires hydrophilic groups, which undermine the water resistance. It remains a challenge to simultaneously improve water resistance and mechanical properties. Here we report a polyurethane with superior mechanical properties and water resistance through the introduction of an organic-inorganic hybrid material, MQ silicone resin. Hydroxyl functionalized MQ silicone resin increases chemical crosslinking and improves the microphase separation and hydrogen bonding strength of polyurethanes. When the MQ-OH content was 10.1 wt%, the tensile strength increased from 27 MPa to 37.3 MPa, and the toughness increased from 74.8 MJ/m3 to 97.4 MJ/m3. Si-O-Si backbones with low surface energy can migrate to the film surface, increasing the surface hydrophobicity. WPU films with MQ silicone resin exhibited remarkable tensile strength retention, with 84.7 % after 40 h hydrolysis in 80 °C water, while WPU retained only 24.6 %. MQ silicone resin offers a novel approach to enhance the hydrophobic properties of WPU without compromising the mechanical properties.