Poly(p-phenylenebenzobisoxazole) nanofiber layered composite films with high thermomechanical performance

Assembling nanoscale building blocks derived from ultrastrong polymer fibers into ordered architectures should offer an effectively alternative way to access high-performance nanocomposites with extremely high strength and heat resistance for advanced applications. Poly(p-phenylenebenzobisoxazole) (PBO) fibers possess outstanding mechanical and thermal properties among the synthetic organic fibers. Here, commercial PBO fibers have been disintegrated into uniform nanofibers with the diameter of ca. 20 nm by a mixed acid treatment, and then served as a polymeric building block to be assembled into layered architectures through layer-by-layer deposition. The resulting (PBO-PBO)₅₀ films exhibit superior mechanical and thermomechanical properties with the modulus of 3.29 GPa, the toughness of 2.1 MJ m⁻³, and the strength of 181.08 MPa. Through employing the poly(vinyl alcohol) (PVA) as a connecting layer in the deposition, the (PBO-PVA)₅₀ nanocomposite films possess remarkable mechanical properties demonstrated by the modulus of 6.48 GPa, the toughness of 4.6 MJ m⁻³, and the strength of 304.34 MPa, due to the synergistic interfacial interaction between the PBO nanofibers and the matrix. In addition, the (PBO-PBO)₅₀ films possess the thermal stability up to 625 °C and excellent fire retardancy.