Design And Preparation Of Electrospun Fibrous Membranes With Waterproof And Breathable Performance For Protective Clothing

Protective clothing with excellent water resistance and moisture permeability can provide effective protection and good comfort for people in bad weather such as heavy rain and snow,or keep safety and comfort in some special working environment with toxic and harmful danger.Heretofore,there are three types of fabric for preparing protective clothing,including high density fabric,coated fabric and laminated fabric.However,the high density fabric and coated fabric were insufficient to achieve the balance of waterproof and breathable performance due to their structure.Only for,the laminated fabrics,which using functional membrane material with waterproof and moisture permeability as their core layer to offer both excellent waterproof and moisture permeable performance,involuntary,this type of fabrics has aroused widespread concern in the current market.In 1962,R.W.Gore developed a waterproof and breathable polytetrafluoroethylene?PTFE?macroporous membrane with good waterproof and moisture-permeable function,and then prepared a kind of protective fabric by laminating PTFE macroporous membrane with traditional textile fabrics,which is the well known Gore-Tex fabric.Subsequently,a new era of research on waterproof and breathable membranes have developed.At present,commercial waterproof and moisture permeable membranes are mainly divided into two categories,including hydrophilic non-porous membranes and hydrophobic macroporous membranes.For hydrophilic porous membranes,the water permeability pressure is generally high,but their defects such as lower low permeability flux and easy to adhesion to human body,have restrained its extensive application in clothing.The hydrophobic macroporous membranes composed with a great number of controllable interconnected pore structure could transfer water vapor effectively,resulting in excellent water permeability.Therefore,hydrophobic non porous membrane materials have became the main types of waterproof and moisture permeable membranes.Electrospinning is a new kind of technology for preparing nanofibrous membranes using high voltage electrostatic field.Nanofibrous membranes prepared by electrospinning technology have some interesting advantages,such as fibers and pores with small diameter,high porosity and interconnected pores.Up to now,a large number of works have reported the preparation of fiber-based waterproof and moisture permeable membrane by electrospinning technology.Nevertheless,here are still some shortcomings for waterproof and breathable fibrous membranes,including shortage of hydrophobic polymer as raw materials,unclear relationship between the pore structure and waterproof and breathable performance,inherent poor mechanical properties of the nanofibrous membranes,which have severely restricted their application in fabricating protective clothing.In order to solve the above problem,the present work mainly studied the effect of electrospinning parameters on the structure of fibrous membranes and the relationship between structure and waterproof,breathable and mechanical properties.Specifically,a new kind of fluorinated polyurethane?FPU?was synthesized as the additive for hydrophobic modification of commercial polyurethane?PU?.Then,a series of FPU/PU fibrous membranes with various fibers structure,adhesion structure,and porous structure were prepared simply by regulated the relative humidity?RH?during electrospinning process.Furthermore,performances of fibrous membranes were also researched,such as the relationship between surface wettability,porous structure,adhesion structure and hydrostatic pressure,water vapor transmission rate,mechanical property was discussed.The detail contents are summarized as follows:?1?Synthesis of the linear double ended fluorinated polyurethane.A new type of fluorinated polyurethane?FPU?was synthesized by four-step synthesis process using 4,4'-diphenylmethane diisocyanate as hard segment,polytetrahydrofuran ether glycol as soft segment,tetraethylene glycol as chain extender and perfluorooctyl ethyl alcohol as fluorinated sealing agent.Then,fourier transform infrared spectrum,nuclear magnetic resonance spectroscopy and gel liquid chromatography were used to analysis the molecular structure of FPU.The as-synthesized FPU confirmed to be with linear molecular chains without dendrite structure,and the fluorocarbon segment were all located at the end of the chains.What's more,after adding of FPU,the hydrophobic property of the electrospun FPU/PU fibrous membranes could be effectively improved.?2?Research of the water permeation mechanism through FPU/PU fibrous membranes.A series of electrspun FPU/PU fibrous membranes with different pore size were prepared by regulating the RH during electrospinning.In order to clarify the relationship between the RH and membranes structure,the phase diagram of DMF-FPU/PU-water ternary system was achieved by cloud point titration,then the influence of RH on the structure of FPU/PU fibrous membranes was investigated.Subsequently,the mechanism of liquid water permeated through the PU/PU fibrous membranes was explored.All above results confirmed that the relationship between the hydrostatic pressure,maximum pore size and advancing water contact angle were perfectly accorded with the Young-Laplace equation.?3?Study on the water vapor transmission process of FPU/PU fibrous membranes.FPU/PU fibrous membranes with various porosity were prepared by regulating the RH.Then we further investigated the transportation process of the water vapor in fibrous membranes,demonstrating that the water vapor transported through the interconnected pores by Fick diffusion.According to Fick diffusion law,porosity and thickness of the FPU/PU fibrous membranes were the most important factors that influenced the water vapor transmission rate.Meanwhile,the ambient temperature would also effect the breathable performance.In addition,FPU/PU fibrous membranes have extremely low wet resistance value,indicating that FPU/PU fibrous membranes have outstanding breathable performance.?4?Research of mechanical performance of FPU/PU fibrous membranes.A series of FPU/PU fibrous membranes with different fiber structure and adhesion structure were prepared.In order to illustrate the tensile-fracture mechanism,tensile stretching was used to test the mechanical performance of FPU/PU fibrous membranes.It was found that the fracture process of FPU/PU fibrous membranes conformed to the two-step fracture mechanism.The fracture strength and elongation at break were mainly affected by fiber and adhesion structure.At the same time,the stress-strain curves of FPU/PU fibrous membrane conformed to the"Marlins effect"when it is stretched by external force,demonstrating that the FPU/PU fibrous membrane could exhibit high elasticity similar to rubber in the range of breaking elongation.In addition,1000 cycles stretching and recovering test with elongation of 100%was processed,which results showed that FPU/PU fibrous membranes could exhibit excellent fatigue durability under longterm cyclic deformation.?5?Carbon nanotubes enhanced fluorinated polyurethane macroporous membranes for waterproof and breathable applicationWaterproof and breathable macroporous membranes that are both completely resistant to liquid water penetration and easily allowable to vapor transmission would have significant implication for numerous applications,however,fabrication of such materials has proved to be tremendously challenging.Herein,we reported novel electrospun composite fibrous membranes with high waterproof and breathable performance,which consisted of polyurethane?PU?,terminal fluorinated polyurethane?FPU?and carbon nanotubes?CNTs?.Benefiting from the utilization of FPU and CNTs,the fibrous membranes were endowed with superhydrophobic surface,optimized pores size and porosity,along with enhanced fibers,which resulted in excellent waterproof,breathable and mechanical properties.Significantly,the relationship among waterproofness,pore structure and surface wettability has been confirmed finely accordance with Young-Laplace equation.Ultimately,the resultant membranes presented high waterproofness with hydrostatic pressure up to 108 kPa,good breathability with water vapor transmission rate over 9.2 kg m^-2 d^-1,as well as robust mechanical properties with bursting strength of 47.6 kPa and tensile strength of 12.5 MPa,suggesting them as promising alternatives for a number of potential applications such as protective clothing.