Rapid preparation of waterborne polyurethane dispersions using continuous-flow microreaction technology†

This paper provides a strategy for the preparation of waterborne polyurethane (WPU) dispersions by continuous-flow microreaction technology. The strategy starts with the preparation of polyurethane prepolymers in a continuous-flow reactor, followed by emulsification and post-chain expansion reaction in a high-speed disperser to produce M-WPU. Compared with B-WPU preparation in a traditional batch reactor, the continuous-flow microreaction technology can shorten the polymerization time from several hours to several minutes, which greatly improves the production efficiency. Meanwhile, the optimal process conditions were determined by investigating the effects of solvent dosage, catalyst type and dosage, reaction temperature, reaction residence time, total flow rate, and reactor configuration on the extent of reaction of polyurethane prepolymers as well as the effects of neutralization residence time and neutralization temperature on the particle size of WPU. Finally, the films of M-WPU and B-WPU were characterized and tested, and it was found that the M-WPU film exhibited higher molecular weight, tensile strength, hardness, larger water contact angle, better heat resistance, and lower water absorption compared with the B-WPU film prepared by the traditional batch process. This suggests that the continuous-flow microreactor process provides an efficient and promising method for the preparation of WPU.