Enabling multifunctional bio-based waterborne polyurethane through polyphenol-mediated assembly of zirconium phosphate nanoplatelets for patternable coating

Sustainable bio-based waterborne polyurethane (WPU) has been widely used in a wide range of industrial applications owing to its favorable environmental safety and excellent properties. However, achieving superior mechanical properties and favorable multifunctionalities in bio-based WPU remains a considerable challenge. In this work, we proposed a facile and effective interfacial engineering strategy which was synergistically enabled via phosphoric acid-assisted exfoliation and polyphenol-mediated assembly of zirconium phosphate nanoplatelets (ZrP NPs) to prepare multifunctional castor oil-based supramolecular WPU composites for patternable leather coating. Tunable ZrP based supramolecular assemblies with the weight ratio of TA to pZrP NPs of 2.0 wt.% and pH > 5.0 were fabricated to manipulate the assembly of the WPU molecules. Active TA molecules bound on the interfaces of ZrP NPs can function as organic junctions through the formation of hydrogen-bonding interactions between the phenolic groups of TA molecules and the functional groups of WPU molecules. Benefiting from this hydrogen-bonding-driven co-assembly, the resultant supramolecular WPU composite films not only exhibited excellent transparency and reinforced mechanical strengths, thermal stability, and flame-retardant properties, but also possessed photoluminescent properties suitable for patternable leather coating. For example, the peak heat release rate (PHRR) was decreased from 389.45 kW/m² to 199.75 kW/m², and the total heat release (THR) was from 15.49 MJ/m² to 13.58 MJ/m². We envision that this study contributes to the development of sustainable multifunctional bio-based WPU coatings with significant potential for advanced applications in information encryption and displays, etc.