A whole-procedure solvent-free route to CO2-based waterborne polyurethane by an elevated-temperature dispersing strategy
An elevated-temperature dispersing (ETD) strategy was developed to disperse prepolymers at 80 °C for producing waterborne CO2-based polyurethane (CO2-WPU) in a whole-procedure organic solvent-free route. The obstacle of high viscosity challenging the traditional prepolymer-dispersing process was overcome, and the concern of significant NCO loss at high temperature was eliminated because prepolymer dispersion ensured >90% NCO retention. The particle size of the typical CO2-WPU emulsion lay between 45 nm and 70 nm, and it showed excellent stability even after centrifugation for 30 min at 3000 rpm. The dried CO2-WPU film showed not only good mechanical performance with a tensile strength of 54.3 MPa and elongation at break of 641%, but also excellent hydrolysis resistance owing to the unique structure of the CO2-polyol. This ETD strategy showed clear feasibility for commercial polyether or polyester oligomerols. It avoids the cooling step and solvent-removal procedure required in a traditional prepolymer-dispersing process, thereby greatly shortening the preparation period and reducing energy consumption.