Self-healing waterborne polyurethane nanocomposites with high strength and toughness based on ureidopyrimidinone-modified cellulose nanocrystals

Cellulose nanocrystals (CNCs), as a biomass resource, are mainly used as fillers to enhance the mechanical strength of materials. However, CNCs are prone to aggregation in an aqueous matrix due to their high hydroxyl group content. Nevertheless, preparing high-performance synthetic polymers or biopolymers to reinforce polymer nanocomposites is still a significant challenge. Herein, a strategy was developed to prepare high-performance waterborne polyurethane (WPU) nanocomposites via synergistic interaction of multiple hydrogen-bonded assemblies and disulfide bonding. First, 2-ureido-4-[1H]-pyrimidinone (UPy) motifs were grafted onto CNC to obtain UPy-CNC and alleviate the aggregation problem. Then, WPU nanocomposites containing aromatic and aliphatic disulfide bonds were reinforced by UPy-CNC. The tensile strength and toughness of the composites were tested. The tensile strength of the material reached 48.07 ± 2.45 MPa, and the toughness was as high as 142.72 ± 2.7 MJ m⁻³. Thus, these nanocomposites exhibited exceptional tensile strength as well as good elongation at break and self-healing properties. This simple and effective strategy to prepare WPU nanocomposites may have excellent application value in waterborne coatings.