Investigation On The Self-healing Of Damage On Graphene-carbon Nanotube Synergetic Reinforced Polyurethane Under Microwave Radiation

Thermoplastic polymers exhibit excellent performance in terms of abrasion resistance,radiation resistance and impact resistance,etc,which are widely used in national defense,aerospace,construction and other fields.However,due to the fact that the mechanical strength of this polymer is generally not high,and it can be easily damaged under the external fatigue loading and then lead to material failure.This severely harms the safety of the structure and hinders the application of thermoplastic polymer in some important engineering and cutting-edge fields.In order to broaden the application field of thermoplastic polymer,exploring this polymer with both excellent mechanical properties and the self-healing properties for further development and application of polymer materials is a top priority.In this paper,the thermoplastic polyurethane(TPU)was used as the research object.Graphene(G)and carbon nanotube(CNT)enhanced polyurethane(TPU)composite materials with self-healing under microwave induction and mechanical enhancement were prepared by solution mixing.The performance of composite materials was tested through mechanical properties test and material microstructure characterization(SEM).The mechanics performance and self-healing properties under microwave induction of TPU composites was studied from three perspective including the mesoscopic mechanics,electromagnetism,thermal.The main research contents are as follows:(1)In the study of mechanical properties : the G/TPU composites with different graphene content were prepared.The mechanical properties of G/TPU composites were studied.The result showed that the tensile strength of composites increased with the increase of graphene content(when the graphene content was 1.5%,the tensile strength is the best).The optimum tensile strength of G/TPU composites is about 35% higher than that of pure TPU.In order to further improve the tensile strength of the polyurethane materials,the G-CNTs packing were used to replace the graphene packing,and G-CNTs/TPU composites with different proportions of G-CNTs were prepared.The study of the mechanical properties of the composites found that: G-CNTs/TPU composites increased first and then decreased with the decrease of the mass ratio of graphene and carbon nanotubes.When the content ratio of graphene to CNTs equaled to 3:1,the mechanical properties of G-CNTs/TPU composites approached the optimum value.The tensile strength of G-CNTs/TPUcomposites increased by 67%,18%,25% when compared with that of pure TPU,G/TPU composites and CNTs/TPU composites.The mechanical strengthening mechanism of carbon nanotubes and graphene reinforced polyurethane composites was analyzed by combining the microscopic morphology and the micromechanical model based on shear lag theory of composites.The results show that the three-dimensional composite structure formed by graphene and carbon nanotubes will improve the dispersibility of the enhanced phase in the matrix,which have a positive effect in improving the stress transfer efficiency between the substrate and the tensile strength.(2)In terms of the self-healing of crack in the material under microwave radiation: In this paper,the self-healing properties of G/TPU,G-CNTs/TPU,CNTs/TPU composites were studied.The result showed that: three kinds of composite materials under microwave induction can achieve completely repair.When the ratio of G-CNTs was 3:1,the mechanical strength recovery rate of the composites was as high as 117%.This paper analyzes the phenomenon by referring to the conclusions of mechanics analysis.In addition,on account of the process of microwave treatment,the heat conduction process and the electromagnetic field distribution will directly affect the crack repair and mechanical properties.Therefore,the finite element software ANSYS was used to simulate the internal heat transfer.The simulation results show that the composites can achieve the macroscopic cracks uniformly,rapid heating by the microwave processing,and realized the self-healing of damage within materialquickly.The Ansoft HFSS software is used to simulate the distribution of the microwave field at the crack of the material.The results show that the microwave is focused at the crack of the material,which can effectively ensure the energy supply at the crack.The results of thermal conduction and electromagnetic field simulation provide theoretical support for the further improvement of the composite's rapid self-healing under microwave control and the overall mechanical properties of the material.The results of this study will have significant influence on the improvement the preparation process and enchantment of mechanical properties of thermoplastic self-healing materials,which will provide useful exploration in the fields of automobile,aerospace and architecture.