Multi-scale Green Construction Strategy Of Self-healing Ultra-tough Bionic Hybrid Fibers And Material

Advanced structural materials inspired by natural biological materials are promising to be the next generation of engineering materials.The development of fibers with synergistic mechanical properties,particularly combining high strength（to resist deformation）and toughness（to resist fracture）,is an everlasting target in designing and fabricating high-performance fiber.In recent years,inspired by nature（e.g.shell nacre,arthropod shell,spider silk）,researchers have constructed biomimetic multistage structural materials with high strength and toughness.It has always been the goal of researchers to study some fiber materials with high fracture energy with green and scalable preparation concept.Although there has been some progress in the research of high fracture energy materials inspired by the structure of spider silk fibers in recent years,it is still a great challenge to produce artificial fibers with extremely high toughness using simple green processes.In recent years,the rapid development of self-healing materials makes it possible for people to provide timely and effective feedback on material damage under a brand new technological means:self-healing according to the properties of materials and external intervention.However,most self-healing processes require high temperatures,solvents,or long healing times,which greatly limits their application.Based on the design concept of green and efficient self-healing materials and the understanding of the multi-scale and cross-scale construction of bionic strong and tough materials（macro-micro-nano-sub-nano-atomic scale）,the following specific research work is carried out in this paper:（1）Using subnanometer（<1nm）CaP oligomers were assembled with WPU at the molecular level.The biomimetic hybrid fibers with high strength（167-442 MPa）and super strength(362-640 MJ m^-3)were successfully prepared by traditional paper string preparation technology.It is as strong as steel and has a super high toughness more than three times of spider silk.In addition,CaP-WPU hybrid material has excellent self-healing properties,at room temperature,under certain pressure（1 Kg）,in a very short time（30 s）.（2）TOCNF-WPU hybrid film materials with water-vapor induced self-healing and shape-preserving properties were prepared by strong hydrogen bonding between pure green waterborne polyurethane（WPU）and Tempo-oxidized cellulose nanofiber（TOCNF）.In addition,various high-strength and high-toughness structural materials from one to three dimensions were successfully assembled by utilizing the water-vapor induced self-healing performance and wet draft shape retention performance of TOCNF-WPU hybrid materials,including fiber materials,plate materials,tube materials,sphere materials,rod materials,etc.Compared with traditional materials processing and forming methods,this material assembly and preparation strategy does not need expensive,complex machines and energy consumption,only uses water,the process is simple and environmentally friendly.（3）WPU-TOCNF nanocomposites（films and fibers）were fabricated by molecular and nanoscale engineering and novel wet drafting（twisting）and ion crosslinking strategies.The strength and toughness of the optimized WPU-TOCNF-15%film can reach 323 MPa and110 MJ m^-3,and the strength and toughness of the fiber can reach 715 MPa and 186 MJ m^-3.This toughness is the highest of all cellulosic materials reported to date.