Fabrication Of Waterborne Polyurethane/Black Phosphorus Nanocomposites:Investigation On Flame Retardancy And Electromagnetic Interfere Shielding Performance

With the increasing attention to the ecological environment,waterborne polyurethane(WPU),a kind of polymer material with excellent performance,non-toxic and environmental protection,has been paid more and more attention.Like most polymer materials,waterborne polyurethanes are highly flammable,which limits their wide use in some areas.Therefore,flame retardant functionalization has become an important direction.The specific surface area of nanomaterials is more than one order of magnitude higher than that of traditional materials,and the interface area between nanomaterials and the enhanced phase is very large,which means that only a very small amount of addition can have a huge influence on the whole composite system.For example,adding less than 5 wt%of nanomaterials to the polymer can significantly change the conductivity,thermal conductivity,optical properties,mechanical properties,dielectric properties and thermal stability of the polymer.Therefore,the preparation of high-performance polymer-based nanocomposites can greatly expand the range of use of polymer materials and serve People's Daily life.Because of its two-dimensional morphology,inherent high strength and outstanding thermal properties,black phosphoene has the huge potential to be used as a nano additive to enhance the mechanical properties,thermal stability and flame retardant properties of polymer materials.Compared with other two-dimensional nanosheets,two-dimensional black phosphorus itself is all composed of "phosphorus"element,and phosphorus is a highly efficient flame retardant element.Therefore,we have reason to believe that black phosphorus nanosheets can enhance the mechanical properties,thermal stability and fire safety of polymer materials at the same time.However,in order to realize the large-scale application of 2D black phosphorus/polymer composites,the first thing we need to think about is how to prepare 2D black phosphorus in a simple and efficient way;secondly,the compatibility between inorganic nanosheets and polymer matrix is need to be solved.Also,black phosphorus will degrade and lose its structure under high temperature condition.Finally,the multi-function of polymer composites is explored on the premise of meeting the flame retardant properties.In this paper,the effects of electrolyte type,electrolyte concentration and electro-stripping voltage on the preparation of two-dimensional black phosphorus by electrolysis stripping were firstly explored,and the appropriate electro-stripping conditions were summarized based on the experimental data.Secondly,in order to improve the oxidation degree of two-dimensional black phosphorus prepared by anode electrostripping method,the polymer cationic electrolyte was used to peel and modify the black phosphorus by cathode exfoliation method.Moreover,in order to solve the problem that the two-dimensional black phosphorus will lose its structure when the polymer is burning,we prepared BP-Ti3C2 hybrid by double-electrode electrochemical exfoliation method and added it to the waterborne polyurethane,which significantly improved the gas toxicity while reducing the heat release.We prepared Ti3C2@PANI hybrid with high stability and good electrical conductivity by electrochemical deposition method,and prepared BP-WPU/Ti3C2@PANI conductive composites with flame retardant properties by building isolation structure.Finally,we use hydrothermal method and freeze-drying to prepare RGO-MXene aerogel,and then obtain a lightweight BP-WPU/RGO-MXene composite material through the infiltration method,which has low density,good electromagnetic shielding performance,heat insulation and good flame retardant performance and other advantages,meettinge the application of some high-end field.The main research work is as follows:(1)In view of how to obtain two-dimensional black phosphorus easily and efficiently,this paper adopts electrochemical stripping of black phosphorus,and studies the effects of different electrolyte,different electrolyte concentration and different stripping on the product.Based on the analysis of the test data,it is concluded that two-dimensional black phosphorus with lower oxidation degree can be obtained with higher yield by using high concentration and low voltage method when the size of anion and the spacing of black phosphorus layer are matched with each other.(2)In view of the problems of high oxidation degree of two-dimensional black phosphorus prepared by anodic electric stripping method and poor compatibility between two-dimensional black phosphorus and waterborne polyurethane interface due to inert surface,we adopted cathodic electrochemical stripping method,selected cationic polymer electrolyte,and peeled and surface modified black phosphorus at the same time.Thanks to the reductive atmosphere around the cathode,the oxidation degree of the black phosphorus nanosheets was significantly reduced.At the same time,the long polymer chain attached to the surface of black phosphorus can not only hinder the reaccumulation of black phosphorus nanosheets in solution,but also form hydrogen bond with the main chain of waterborne polyurethane,which improves the interfacial compatibility of two-dimensional black phosphorus and polymer.(3)In view of the problem that the oxidative degradation of two-dimensional black phosphorus in the polymer combustion cannot play the role of lamellar barrier,we prepared BP-Ti3C2 hybrid by double-electrode electrochemical stripping method.It's different from the black phosphorus in 500? when almost fully biodegradable,Ti3C2 nanosheets under the condition of oxygen would generate carbon nanosheets and TiO2.The carbon nanosheets have barrier effect during the whole process of polymer combustion and TiO2 have the effect of smoke suppression attenuated.This can have synergism effect with BP.(4)In order to broaden the application range of composite materials,PANI nanowires were grown on Ti3C2 nanosheets by electrochemical deposition method,which successfully solved the problem of easy oxidation deterioration of Ti3C2 nanosheets in the air environment.Then ethanol dispersion method was used to make Ti3C2@PANI evenly distributed on the waterborne polyurethane particles containing black phosphorus nanosheets.After hot pressing,flame-retardant electromagnetic shielding composites with isolation structure were obtained.(5)In order to meet the requirements of some high-end fields such as aerospace,aircraft preparation and the automotive industry for electromagnetic shielding materials such as light weight,good mechanical properties,heat insulation and high fire safety.Based on the preparation of RGO-MXene aerogel,WPU containing BP was attached to its skeleton by the infiltration method,and FBP-WPU/RGO-MXene composite material was obtained after drying.Due to the combination of the advantages of organic and inorganic materials,the density of the composite material is only one-tenth of that of WPU.Compared with RGO-MXene aerogel,the compressive strength is increased by 328.3%,and the peak heat release value and total heat release value are increased,and it also has good heat insulation and fire resistance.This design idea has proved to be a feasible method for preparing high-performance composite materials.