First, cellulose nanocrystals were extracted from microcrystalline cellulose using the sulfuric acid hydrothermal method. Second, imine aromatic diol (Imine) was synthesized from p-hydroxybenzaldehyde and 4,4'-diaminodiphenylmethane as raw materials. Then the imine was introduced into the polyurethane, and the reversible covalent bond between the imine and the C = N group was used to endow the polyurethane with self-healing properties. Finally, cellulose nanocrystalline (CNC) was added into the self-healing polyurethane as the dispersed phase to prepare the composite. The experimental results show that with the increase of the amount of CNC, the properties of the composites increase first and then decrease, which is due to the physical cross-linking effect of proper CNC distribution in the self-healing polyurethane, it is beneficial to the mechanical properties, but the self-healing property is reduced by further increasing the content, which restricts the movement of the molecular chain. The mechanical properties of the composite with 0.049 g CNC are the best, with fracture strength reaching 20.59 MPa, approximately 1.56 times higher than that of pure self-healing polyurethane, and its elongation at break is 979%, and the self-healing efficiency reaches 84.7%, keeping an excellent level.

Keywords: self-healing polyurethane, imine bond, cellulose nanocrystal composites.