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.