Study On Fabrication And Heat-Radiation/Waterproof And Breathable Performance Of PVDF Electrospun Nanofibrous

Nano-fiberswaterproof-breathablemembranesisthecoreof waterproof-breathable layer in multi-layer structure firefighter uniform.It can make water vapor and air pass freely and prevent liquid water droplets from passing through.Therefore,it can adjust the micro-environment of human body,improve the wearing comfort of users,and make the protection function and thermal-wet comfort of firefighter uniform unified.On the other hand,because the diameter of nano-fibers is close to the radiation wavelength and has special optical properties,it is a well thermal insulation material.For the heat-transfer mechanism of nano-fibers thermal insulation materials,the current research shows that it mainly includes three parts:the heat transfer of the fiber material itself,the heat conduction of the air inside the fiber material and the radiation heat propagated in the form of electromagnetic waveform.Among them,the radiative transfer takes a large proportion in the whole heat transfer process,so for firefighter uniform,improving its nano-fibers waterproof-breathable membranes thermal radiation protection performance is an effective way to improve its thermal protection performance.Therefore,it is necessary to develop waterproof-breathable membranes with thermal radiation protection function and waterproof-breathable function for a new generation of high-performance multi-layer structure fire fighter uniform.Electrospinning technology is one of the best methods to prepare nano-fibers at present.The prepared nano-fibers have the advantages of three-dimensional space network structure,large specific surface area,small diameter and high porosity.It can be used to prepare multifunctional waterproof-breathable membranes with high barrier propterty and comfortable propterty.At the same time,electrospinning technology also has the advantages of low price,simple equipment and easy operation.It is easy to combine functions and other technical advantages.However,in the process of combining electrospun nano-fibers with the field of waterproof-breathable of firefighter uniform,there are still some problems such as poor strength of nano-fibers membrane,contradiction between hydrostatic pressve and water vapor transmission.Therefore,in this paper will focus on the process optimization,poor mechanical strength,thermal radiationprotection,waterproof-breathable of electrospun nano-fibers membrane.Firstly,response surface analysis?RSA?was used to optimize the electrospinning process.Then,the strength,thermal radiation protection,waterproof-breathable permeability of nano-fibers were studied by introducing graphene?RGO?and opacifier.Some progress was made in the following aspects:?1?Single factor experiment and RSA were used to optimize the electrospinning process,the results showed that the optimum spinning process was 18%spinning solution concentration,21.06 KV voltage,15.8 cm spinning distance and 0.6 mL/h feed speed.Finally,the optimized process is verified,and the experimental results are similar to the predicted values of the model,combined with variance analysis,it is found that the established model is in good agreement with the actual values.Therefore,it is feasible to optimize the spinning process by RSA.?2?In view of the poor strength of pure PVDF nano-fibers membranes,graphene with high aspect ratio,high strength,high stiffness and high conductivity was used as additive to prepare RGO/PVDF nano-fiber composite membranes.It was found that the diameter of nano-fibers in the composite membranes was larger than that of pure PVDF,and RGO existed in four forms in the PVDF matrix,including encapsulation,lapping,adhesion and extension.At the same time,it was found that the thermal stability and thermal radiation protection?RPP?of the composite membranes were not as good as that the pure PVDF,and the RPP value decreased with the increase of RGO concentration.In terms of mechanical properties,the tensile strength and breaking elongation of the RGO/PVDF nano-fibers composite membranes were better than the pure PVDF.The breaking strength of the pure PVDF nano-fibers membranes was 6.7 MPa,the breaking elongation was 8.3%,and the breaking elongation of the composite membranes was 9.1?17.9%,the breaking strength is 13.2?19.8 MPa.?3?In order to improve the thermal radiation shielding efficiency of nano-fibers,Ag/PVDF composite membranes were prepared by adding the after redox nano-silver particles into PVDF spinning solution by one-step redox method.It was found that nano-silver particles formed a uniform porous protuberant composite structure on the surface of nano-fibers,the thermal stability of the composite membrane decreased slightly,but its thermal radiation protection performance was significantly improved.Its RPP value increased from 162.57 of pure PVDF membrane to 304.31 of silver nitrate at 0.5 wt%.In terms of mechanical properties,with the increase of nano-silver particles concentration,the tensile strength of the composite membranes decreases,but the elongation at break increases,indicating that the strength of the composite membranes decreases,but its flexibility increases.The breaking strength and elongation at break of composite membranes respectively were 1.4?2.7 MPa and 29.1?63.2%.?4?In order to improve the practical application value of nano-fibers membrane in the field of firefighter uniform,RGO/opacifier@PVDF nano-fibers composite membrane was prepared with graphene and various opacifier?Ag,TiO₂,Al₂O₃?as additives.It was found that the opacifier particles would form a layer sparse and porous protuberant composite structure on the surface of nano-fiber composite membrane,in which Al₂O₃ and TiO₂ composite membrane were heated and cracked.The pyrolysis temperature decreases,but the mass retention rate after pyrolysis is higher than that of pure PVDF,while the pyrolysis temperature of Ag particle composite membrane remains basically the same as that of PVDF.On the other hand,the thermal radiation protection?RPP?and mechanical properties of RGO/opacifier@PVDF nano-fibers composite membrane are better than those of pure PVDF,which shows that the application value of PVDF electrospun nano-fibers film in the field of firefighter uniform can be effectively improved by RGO and opacifier.