Biobased polyurethane coatings with fast self-healing and tunable mechanical properties derived from curcumin and castor oil

Biobased thermosetting polymers have attracted interest owing to their renewable source materials, long service life, and properties comparable to those of petroleum-based materials. However, the fabrication of those that merge exquisite mechanical properties with fast self-healing performance has not been demonstrated to date. In this work, a biobased polyurethane coating was constructed using curcumin dioxime (CD), castor oil (CO), and isophorone diisocyanate (IPDI) to fulfill these features. The biobased CD monomer was prepared using curcumin and hydroxylamine hydrochloride and confirmed by nuclear magnetic resonance, flourier-transform infrared (FT-IR) spectra, and high-resolution mass spectrometry (HR-MS). To investigate the correlation between the mechanical properties and self-healing performance, a series of polyurethane coatings were fabricated by varying the ratio of CO to CD. The results showed that the crosslinking density (ve), glass transition temperature (Tg), and Young modulus of these coatings increased with the decrease in the ratio of CO to CD, leading to tunable mechanical properties. In particular, the tensile strength and elongation of the COPU-4 coating were as high as 17.2 MPa and 295 %, respectively. The stress relaxation experiments revealed that these coatings exhibited low activation energy (Ea), as low as 28.3 kJ/mol for COPU-5. Besides, all COPU-X coatings demonstrated self-healing efficiency higher than 71 % within 1 min at 90 °C, and some of them even reached >90 % after 8 min. The results demonstrate the promising tunable mechanical and excellent self-healing properties of these novel biobased polyurethane coatings and pave the way for the development of bioderived sustainable thermosetting polymers.