A waterborne polyurethane–based leather finishing agent with excellent room temperature self-healing properties and wear-resistance

Water-based polymers have been widely used in coating materials, but their durability and service life are often greatly reduced due to macroscopic damage or cracking caused by external forces. In this paper, poly(propylene glycol) terminated with ortho-amiomethylphenyl diboronic acid (AMPBA-PPG) and cross-linked polymer containing boroxine (CLP-boroxine) were synthesized by nucleophilic substitution. Then the CLP-boroxine was introduced into waterborne polyurethane (WPU) to prepare AMPBA-PPG/WPU composite emulsion for leather finishing and CLP-boroxine/WPU composite film. The self-healing characterization results showed that the self-healing efficiency of the 15 wt% CLP-boroxine/WPU film was as high as 93.6% after only 4 h of water stimulation at room temperature. Compared with neat WPU finished leather, the leather samples finished with AMPBA-PPG/WPU exhibited more excellent wear-resistance. More importantly, the leather coating finished with AMPBA-PPG/WPU still showed nice wear-resistance even after wear and self-healing treatment. These results are attributed to that the hydrogen bonds between AMPBA-PPG and WPU, WPU, and WPU, and the dynamic reversible covalent bonds in AMPBA-PPG can improve/increase the self-healing efficiency of the composite coating. In addition, the boron hydroxyl groups in AMPBA-PPG could also react with the hydroxyl groups on the leather surface, thereby further improving the wear-resistance of the leather coating.Graphical abstractDynamic boronate ester bonds can not only endow WPU excellent self-healing properties but also improve wear-resistance of its leather coating.