Mussel-Inspired Polydopamine-Enhanced Polyimide for Ultrahigh Toughness and Ultraviolet Shielding Applications

A series of polyimide (PI)-based ultraviolet (UV) shielding nanocomposites were prepared with size-controlled polydopamine (PDA) nanoparticles. Two typical sizes of 120 and 200 nm were chosen to mainly investigate the influence of PDA on the structures, thermal stability, mechanical performance, and UV shielding properties of PI nanocomposites. The results revealed that the PI nanocomposites containing 120 nm PDA nanoparticles showed continuously improved mechanical properties with a maximum tensile strength of 94.1 MPa and a maximum elongation at break of 103.6%, respectively, which were 1.33 and 7.50× those of pure PI due to the strong adsorption between the PDA and PI molecules. Meanwhile, the PI nanocomposites with 200 nm PDA nanoparticles exhibited a maximum tensile strength of 78.9 MPa and an elongation at break of 83.5% when the content of PDA was 0.5 wt %. When the content of 200 nm PDA nanoparticles increased to 1 wt %, the PI nanocomposites exhibited a regressive tendency in mechanical properties due to the decrease in the number of adsorption sites and the expanded distance between the PI molecules caused by the increase in the PDA size. UV–vis tests exhibited that the PI nanocomposites were transparent to visible light at low PDA loadings and maintained a superior UV shielding performance and durability, especially for PI nanocomposites with 120 nm PDA nanoparticles, which was ascribed to the absorption of UV light by the PI matrix and PDA filler. Moreover, the PI nanocomposites with smaller PDA nanoparticles had a better thermal stability. The initial degradation temperatures of the PI nanocomposites containing 120 nm PDA were above 510 °C, which endow them the possibility to serve as flexible UV shielding materials in high temperatures and intense UV radiation.