Water‐based polyurethanes for sustainable advanced manufacture

Abstract Polyurethanes (PUs) are a class of versatile polymers; their structure and morphology can be readily tailored to exhibit various mechanical, physical, chemical, and biological properties. PUs have been employed in a variety of industrial applications including foams, coatings, textiles, machinery, sporting, transportation, vehicles, and construction. Water‐based PU was developed to reduce the usage of volatile organic compounds (VOCs) in the synthesis of conventional solvent‐based PU, and exhibits advantages of superior material properties (eg, flexibility, stretchability, elasticity, mechanical strength), processability (eg, 3D printing, inkjet printing, screen printing, spray coating, moulding), and sustainability (eg, low VOCs, degradable). Water‐based PU combines the superior mechanical properties of PU with the excellent stability of colloids. The current research trend of PU is shifting from traditional industrial applications to state‐of‐the‐art fields such as soft and wearable electronics, energy storage devices, biosensors, actuators, photovoltaic devices, and stimuli‐responsive materials. Due to the existence of a variety of functional groups such as urethane, aliphatic or aromatic hydrocarbons, esters, ethers, amides, and urea, water‐based PU can be physically or chemically incorporated with functional materials to form PU colloidal composites towards various applications. This paper summarizes the fundamentals of water‐based PU and their colloidal properties and reviews the advanced printing manufacture and the latest explorations of water‐based PU for emerging flexible and stretchable electronics.