Design,Preparation And Performance Of Self-healing Polyurethane Composite

With the development of modern industry,the requirements for material properties are constantly increasing.Polyurethane（PU）is also developing towards the direction of intelligence and functionalization,among which the self-healing function of PU materials is one of the important topics to promote the direction of intelligence.At present,a series of remarkable achievements have been obtained in the self-healing PU materials.Among them,the introduction of thermally reversible Diels-Alder（DA）covalent bond into the molecular chain of PU materials and the nanocarbon materials（such as carbon nanotubes and graphene）added into traditional polyurethane materials have become the research hotspots.However,the thermal reversible DA self-healing polyurethane（DA-PU）still has some problems,such as poor mechanical properties,low self-healing efficiency and rapid decrease of self-healing efficiency,and the complex technological process of the carbon nanomaterials need to be modified.In this paper,the composite hybrid structures of silver nanowires（Ag NWs）and graphene were synthesized in situ by improved polyol-thermal method with silver nanowires the main conductive phase and graphene as the auxiliary conductive phase and were introduced into DA-PU to design and prepare DA-PU composite conductive films with the advantages of high conductivity,high self-healing efficiency and rapid multiple self-healing properties,etc.In addition,commercial graphene and graphene oxide（GO）as functional fillers respectively,were introduced into traditional thermoplastic polyurethane（TPU）through solution blending process to prepare self-healing PU,and the effects of functional fillers and TPU substrate on the electrical,mechanical,thermal and self-healing properties of the self-healing PU were investigated.The main research contents of this paper are as follows:（1）Silver nanowires-graphene composite hybrid structure materials were prepared by improved polyol method.The effects of the mass ratio of GO to silver nitrate,reaction temperature and reaction time on the morphology of the composites were investigated.The experimental results showed that when the mass ratios of GO to silver nitrate in the reaction system was less than 0.0210:0.6795,and as the reaction time and temperature increase,the degree of reduction of GO increases but the length of silver nanowires was decreased;When the mass ratios of GO to silver nitrate was more than 0.0927:0.6795,respectively,the synthesized products were mainly silver nanoparticles and graphene composites.When the mass ratio of GO to silver nitrate in the reaction system was0.0210:0.6795 and reacted at 150℃for 3 h,the average length of Ag NWs in the silver nanowires-graphene composite material was 41.81μm.（2）Thermally reversible DA-PU was prepared using furfurylamine and bismaleimide as DA reaction monomers by two-step synthesis method.The silver nanowire-graphene composite materials（Ag NWs-RGO）were mixed with DA-PU via solution blending method to prepare the Ag NWs-RGO-DA-PU composite film.The effects of the Ag NWs-RGO mass content on the electrical,thermal,mechanical and self-healing properties of the composite films were investigated.The experimental results show that the Ag NWs-RGO composite materials improve the electrical,thermal and self-healing properties（infrared photothermal and electrothermal self-healing）of DA-PU,but degrades the mechanical properties.When the mass content of Ag NWs-RGO was 25 wt%,The Ag NWs-RGO in the composite film was well dispersed and show good morphologies.The resistivity,thermal conductivity and tensile strength of the composite film were 0.544Ω?m,0.3039 W·m^-1·K^-1 and 9.05 MPa respectively.The infrared photothermal and electrothermal conversion temperatures of the composite film were 158.5℃（3450 lux for 1 min）and 108.5℃（30 V for 1 min）respectively,and the infrared photothermal self-healing and electrothermal efficiencies were 118%（3450 lux for 600 s）and 79%（30 V for 20 min）,respectively.Repeated thermal self-healing experiments showed that when the mass content of Ag NWS-RGO was 35 wt%,the first and the fifth self-healing efficiencies of infrared photothermal healing（3450 lux for 1205 s）were 105%,and 86%,respectively.The first and the fifth self-healing efficiencies of the electrothermal self-healing（30 V for 20 min）were 74%and 51%,respectively,indicating that the infrared photothermal self-healing was more conducive to improve the self-healing ability of the composite film.（3）G-TPU composite films were prepared with commercial graphene as functional fillers and four kinds of TPU masterbatch with different melting points were used as the matrix material by the solution blending method and casting process.The effects of the mass content of graphene,the initial concentration of TPU and characteristics of TPU materials on the electrical,thermal,mechanical and self-healing properties of G-TPU films were investigated.The experimental results show that graphene improves the electrical,thermal,mechanical,and repair efficiency of TPU,and the comprehensive performance of G-TPU with appropriate initial TPU concentration and low melting point TPU substrate was better.When the melting point of TPU was 163℃,the initial concentration of TPU was 20 wt%and the mass content of graphene was 2 wt%,the thermal conductivity and infrared photothermal transition temperature（3450 lux for 1min）of the G-TPU film was 0.3299 W·m^-1·K^-1and 143.2℃,respectively,and the infrared photothermal self-healing performance of G-TPU was the best.The first and the fifth self-healing efficiencies of infrared photothermal（3450 lux for 10 min）were 98%and 79%,respectively.When the initial concentration of TPU was 20 wt%and the mass content of graphene was 4 wt%,the resistivity of G-TPU was 1.08Ω?m,and the electrothermal self-healing efficiency of G-TPU was the best.The first and the fifth self-healing efficiencies of electrothermal（30 V for 10 min）were 90%and 70%,respectively.（4）GO-TPU composite films were prepared with commercial GO as functional fillers and four kinds of TPU masterbatch with different melting points were used as the matrix material.The effects of the mass content of GO,the initial concentration of TPU and characteristics of TPU materials on the thermal,mechanical and self-healing properties of GO-TPU films were investigated.The experimental results show that GO improves the electrical,thermal,mechanical,and repair efficiency of TPU,and the comprehensive performance of GO-TPU with appropriate initial TPU concentration and low melting point TPU substrate was better.When the melting point of TPU was 163℃,the initial concentration of TPU was 20 wt%and the mass ratio of GO was 2 wt%,the thermal conductivity and infrared photothermal conversion temperature（3450 lux for 1min）of GO-TPU film were 0.3471 W·m^-1·K^-1 and 124.3℃,respectively.The first and the fifth self-healing efficiencies of infrared photothermal（3450 lux for 10 min）of GO-TPU were 97%and 66%,respectively.