Fabrication And Performance Of Poly(p-phenylene Benzobisoxazole) Nanofibrous Composites

Poly(p-phenylene benzobisoxazole)(PBO)fibers possess �Four Super� performance,namely ultrahigh strength,modulus,heat and flame resistance,and are known as a new generation of �Super Fiber�.However,due to the micro scale and the chemical inertness of their surface,PBO fibers are difficult to incorporate various nanomaterials,limiting their applications in the field of advanced functional nanocomposites.This paper focuses on the fabrication of PBO nanofibers with uniform size using commercial PBO fibers,then employing PBO nanofibers as building blocks.High-performance nanocomposites of two-dimension composite films and three-dimension aerogels based on PBO nanofibers are fabricated.Carbon nanotubes(CNTs),gold nanoparticles(Au NPs)and graphene are further employed to functionalize the PBO nanofiber films and aerogels.Application potential of PBO nanofiber nanocomposites in the fields of flame resistance,interfacial solar evaporation and soft actuator are investigated,which provides a solid theoretical and technological basis for the preparation and application of PBO nanofiber composites.Commercial PBO fibers are treated with a mixed acid to produce PBO nanofibers with a diameter of 19.2 � 2.8 nm.The PBO nanofibers doped CNT/poly(vinyl alcohol)(PVA)bilayer is then successfully fabricated by a vacuum filtration process.Results of the tensile mechanical test show tensile strength and modulus of the bilayer are 118.46 MPa and 5.67 GPa,respectively.Introduction of PBO nanofibers enhanced the mechanical performance of the CNT conductive film.Such PBO nanofiber-reinforced bilayer can spontaneously adsorb and desorb water.Resulting from the asymmetry of the bilayer structure,a reversible deformation is realized.Further investigation shows that such bilayer can be employed as a moisture-responsive soft actuator.More importantly,the conductivity of soft actuators significantly increases due to the deformation induced by moisture change.As an example of their application,the actuators can respond to increasing humidity by the deformation of shielding and report the humidity change in a visual manner.PBO nanofibers are further used to fabricate two kinds of(PBO-PBO)50 and(PBO-PVA)50 multilayered composite films by layer-by-layer deposition processes.Scanning electron microscope(SEM)images demonstrate that both kinds of films possess ordered and multilayered structures.Results of the tensile mechanical test and dynamic thermal mechanical test show that tensile strength,modulus and storage modulus of the as-prepared(PBO-PBO)50 multilayered composite film are 181.08 MPa,3.29 GPa,and 6.50 GPa,respectively.In contrast to the(PBO-PBO)50 film,the tensile strength and modulus of the(PBO-PVA)50 multilayered composite film are 304.34 MPa and 6.48 GPa,respectively.The strength and modulus of the composite film significantly increased due to the formation of hydrogen bonds between PVA and PBO nanofiber surface.In addition,the(PBO-PBO)50 multilayered composite film exhibits high thermal stability,and the decomposition temperature is 625 ?.The UL 94 vertical combustion test of the(PBO-PBO)50 film can reach V-0 level.The(PBOPBO)50 film is a self-extinguishing material.Such high-performance PBO nanofiber composite films have potential application in the field of fire-proofing.PBO nanofibrous aerogels are prepared by the sol-gel method and a supercritical drying process,transforming two-dimension films to three-dimension aerogels.Results of SEM show that as-prepared aerogels exhibit interconnected threedimensional frameworks and randomly oriented and continuous mesoporous structures,in which PBO nanofibers are connected through a large number of nodes.PBO nanofibrous aerogels possess comprehensive properties of low density of 32 mg/cm3,high porosity and specific surface area.Aerogels possess stable and high storage modulus of ca.2.2 MPa at 25-300 ?,which is better than the most of polymeric nanofibrous aerogels.Furthermore,PBO nanofibrous aerogels have a low thermal conductivity of 0.045 W/(m�K),a thermal expansion coefficient(close to zero),a thermal decomposition temperature of 692 ? and good flame retardancy.The thermal decomposition temperature of PBO nanofibrous aerogels is higher than any of previously reported polymeric aerogels(610 ?).AuNPs,graphene oxide(GO)and reduced graphene oxide(RGO)are introduced to functionalize PBO nanofiber composite films and aerogels.Robust porous Au NP/PBO nanofiber composite films,PBO nanofiber/GO and PBO nanofiber/RGO composite aerogels are prepared.The resulting composites exhibit mesoscopic and porous structure,and also possess high strength and Young's modulus,broad light absorption,high performance of photothermal conversion and low thermal conductivity.Evaporators based on both composite films and aerogels possess outstanding ability of steam generation,recycling stability and capacity to generate clean water from seawater and heavy metal-containing wastewater.Here we achieved the controllable fabrication of PBO nanofibers and their efficient composites with various nanomaterials.Combined with PBO nanofibers,nanocomposites possessing excellent strength,modulus,thermal stability are prepared.Such high-performance nanocomposites are suitable for different applications,given that PBO fibers have been employed in the field of aerospace and exhibited harsh space environment tolerance.These PBO nanofibrous composites feature a combination of high performance characteristics,and have potential applications in many fields such as aerospace,water treatment and smart devices.