Preparation of waterborne polyurethane coatings with enhanced mechanical properties and superhydrophobic surface

Waterborne polyurethane (WPU) coatings are recognized for their environmental friendliness and non-toxic nature. However, the presence of abundant hydrophilic groups within their polymer networks often restricts their hydrophobicity and mechanical performance. In this study, we utilized two distinct diols to design the molecular structure of WPU, aiming to enhance its mechanical properties by optimizing microphase separation and crystallinity, achieving a tensile strength of 24.13 MPa and a strain of 1350 %. The resultant WPU exhibited high cohesion and abundant hydrogen bonding sites, which contributed to its strong adhesion of 8.31 MPa. Moreover, inspired by the self-cleaning function of lotus leaf-micro-nipples, we made the surface superhydrophobic by micro-nano structure. The irregularly embedded structure was formed between the WPU and SiO2@hbp. The surfaces of WPU coatings formed the peak-valley structure similar to the lotus leaf, achieving a water contact angle of 162 degrees and a sliding angle near 1 degrees. Additionally, the self-cleaning property of the coatings was preserved after 200 cycles of friction, each with a single friction distance of 40 cm. The environmental friendliness and excellent self-cleaning capabilities of the coating highlight its potential for practical applications and provide a valuable reference for developing waterproof self-cleaning coatings.