Synthesis and characterization of waterborne polyurethane dispersions with different chain extenders for potential application in waterborne ink

• Actual maximum chain extension degree is approximately 60%.
• Diethylene triamine (DETA) is an effective chain extender and crosslinker.
• Chain extenders of ethylene diamine and DETA with a mole ratio of 2:3 are optimal.
• Stable waterborne polyurethane is obtained without removing the organic solvent.
• Synthesized waterborne polyurethane can be directly used as an aqueous ink binder.

Waterborne polyurethane (WPU) dispersions with different amine chain extenders, including ethylene diamine (EDA), diethylene triamine (DETA), and triethylene tetramine (TETA), were synthesized, and the effects of these chain extenders and the NCO/OH molar ratio on the properties of WPU dispersions were investigated. The results revealed that the chain extension mainly occurred on the particle surface and the actual maximum chain extension degree was approximately 60%. All the synthesized WPUs had a lower degree of crystallinity, and the post-chain extension promoted phase separation between soft and hard segments in polyurethane. The trifunctional DETA chain-extended WPU had better thermal stability and adhesion strength, which indicates that DETA is an effective chain extender that can be used for the performance improvement of WPU. Moreover, the chain-extended WPU by EDA and DETA with a mole ratio of 2:3 showed excellent properties. It was also revealed that the NCO/OH molar ratio of 1.6 was appropriate for the preparation of stable WPU dispersion with solid content of about 40 wt% and organic solvent content of 5 wt%. The obtained WPU dispersion could be directly used as a waterborne ink binder without removing the organic solvent, which is conducive to the industrialized production of WPU dispersion and avoids the cost of organic solvent recovery.