Tuning the hydrophobicity of bio-based waterborne polyurethane by leveraging a diol derived from oleic acid

Vegetable oils containing long aliphatic chains are widely used to obtain polyols and further produce eco-friendly bio-based waterborne polyurethanes (BWPU). However, the effect of the long aliphatic chains on the properties of BWPU, especially hydrophobicity, has been awfully neglected in previous works. Here, we have successfully prepared a series of linear anionic BWPU by incorporating an oleic-based primary glycol (OPG) with long aliphatic chains into polytetrahydrofuran ether glycol (PTMG) in different proportions. Firstly, the optimized reaction conditions for efficient synthesis of OPG via the thiol-ene photo-click reaction are: 2 wt% photoinitiator 1173, molar ratio of -SH to -CC- of 2:1, and reaction time of 1 h. Then, the effect of incorporating OPG on BWPU’s properties, especially the intrinsic hydrophobicity, was extensively investigated. Specifically, due to the long hydrophobic aliphatic chain, the particle size of the BWPU dispersions increased with the increase of OPG content, and correspondingly the absolute value of zeta potential decreased. Additionally, the water contact angle of the BWPU films increased from 60.8° to 90.3°, and their water absorption decreased from 7.88% to 3.21%, exhibiting enhanced hydrophobicity and water resistance. This work demonstrates the designed and synthesized vegetable oil-based diol with a long aliphatic chain plays a positive role in tailoring the hydrophobicity of bio-based WPU, which holds great promises for applications in waterproof and self-cleaning coatings.