Preparation Of Silica Modified Polyurethane Nanofiber Membrane And Study On The Waterproof And Breathable Properties

Waterproof and breathable membrane is widely used in many fields,such as medical and health care,protective clothing,electronic equipment,household products and so on,because of its resisting the penetration of liquid water and allowing water vapor to penetrate.The electrostatic spinning technology has simple operation process with low cost,and the waterproof and moisture permeable membrane prepared by this technology has the characteristics of small pore size,high porosity and adjustable surface wettability,which has attracted extensive attention in waterproof and breathable research field.Polyurethane（PU）has gradually become an important raw material for preparing waterproof and breathable membranes because of its remarkable elasticity and resilience,but the hydrophilicity of PU fiber membranes limits its practical application in the field of waterproof and breathable.At the same time,with the development of society,the requirement of hydrophobic properties become higher and higher for waterproof and breathable membrane.Therefore,it is urgent to find a simple and efficient method to prepare PU nanofiber membranes with superhydrophobic properties.In this paper,the PU emulsion modified by 4,4’-methylenebis（phenyl isocyanate）（4,4’-MDI）and 3-aminopropyltriethoxysilane（APTES）was electrospun,and then silica（SiO₂）particles were grafted on the surface of modified PU nanofibers by hydrothermal assisted sol-gel process.Considering that different proportions of modifiers will affect the structure and properties of fiber membranes,this paper discusses the internal relationship between the content of modifiers and the microstructure and properties of PU nanofiber membranes,focusing on the changes of fiber morphology and properties of PU/SiO₂fiber membranes.The main research works are as follows:（1）PU was used as elctrospinning polymer,in which 4,4’-MDI and APTES were added to modify PU emulsion.On the basis of systematically regulating the modifiers content of in mixed emulsion,it was found that when the mass ratio of 4,4’-MDI to mixed emulsion was 0.4%,the fiber thickness was uniform,and the fiber diameter was mainly distributed between 180 nm～300 nm;The water contact angle of fiber membrane was 127°;The maximum pore size was 3.29μm;The breaking strength was4.76 MPa and the elongation at break was 183.6%.When the mass ratio of additive APTES to mixed emulsion was 2%,the fiber diameter distribution was concentrated,and the water contact angle of fiber membrane was 130°;The breaking strength and elongation at break were 3.64 MPa and 180%respectively.（2）TEOS was used as silicon source,and HDTMS was used as hydrophobic agent.Hydrophobic SiO₂particles were grafted on the surface of PU nanofiber membrane by hydrothermal assisted sol-gel process.The structural characteristics of PU/SiO₂nanofiber membrane were analyzed by scanning electron microscope（SEM）,Fourier infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.The infrared spectrum of PU nanofiber membrane grafted with SiO₂particles showed the characteristic peak vibration of Si-OH at 952 cm^-1,and the characteristic peak vibration of Si-O-Si at 800 cm^-1,which proved that SiO₂particles were successfully grafted on PU nanofiber membrane.The breaking strength of PU/SiO₂fiber membrane increased to 5.3 MPa,and the breaking elongation was 198%.（3）Due to the grafting of SiO₂particles,the fiber membrane with rough surface was obtained,and the surface energy of the fiber was reduced,which further improved the waterproof performance of the PU nanofiber membrane,even endowed membrane a superhydrophobility.The water contact angle of the PU/SiO₂nanofiber membrane reached 154°,and the hydrostatic pressure was 8.02 k Pa.At the same time,the air permeability of the membrane was 3.89 mm/s and a water vapor transfer rate was 8.12kg/m²/d.Meanwhile,the superhydrophobic PU/SiO₂nanofiber membrane presented good wear resistance.After ultrasonic cleaning for 36 h,the water contact angle could still be kept above 140°.In addition,under the irradiation of xenon lamp,the surface of PU/SiO₂nanofiber membrane could be kept at a low temperature.In conclusion,in this paper,super-hydrophobic,wear-resistant and light-resistant PU/SiO₂nanofiber membranes were prepared by combining emulsion electrospinning technology and hydrothermal-assisted sol-gel process.Compared with directly mixing inorganic nanoparticles in electrospinning solution,the spinnability of the solution and the mechanical properties of the fiber membrane was not affected by the agglomeration of nanoparticles.Importantly,the porous structure of the fiber membrane will not disappear due to the grafting of SiO₂particles,and the modified composite fiber membrane showed more excellent comprehensive properties.This study further broadens the application fields of waterproof and breathable textiles,and is expected to provide new design inspiration and ideas for the development of oil-water separation,thermal insulation,smart wearable,filter textiles and other fields through a simple and efficient chemical modification method.