| Waterproof and breathable fabric is a new functional membrane which has outstanding waterproofness,moisture permeable properties and warmth retention performances.It can prevent the certain pressure water and allow the transit of water vapor.In many harsh climatic conditions,it can prevent human from the body injury resulted from storm or fierce wind and timely transmit the water vapor to the outside environment in order to maintain a dry environment in clothes.At the same time,this clothes can also break off the direct contact with the liquid reagent for these people worked in medical and chemical industries,which could avoid toxic substances hurting human's bodies.Owing to its excellent performance,the demand of waterproof and breathable fabric is gradually increasing in domestic and foreign markets.Its application is also not limited to traditional military supplies and professional medical protective products,now it can be used in daily life like outdoor sports clothing.Although the development of waterproof and breathable fabric is fast and flourishing on domestic market,however,it has either excellent performance of waterproof but bad moisture permeability,or good moisture permeability but low waterproofness.Hydrostatic pressure and water vapor transmittance rate are a measure of waterproof breathable fabrics two fundamental and very important reference indexes.Therefore,it has an important significance for developing a new-style waterproof and breathable fabric.Electrospinning technique is often used to fabricate polymer fibers in diameters of tens of nanometers to micrometers.Such fibers tend to produce a stacked three-dimensional network structure whose small pores can provide many narrow passages that can allow the transmission of water vapor when there is pressure or humidity difference on both sides of the clothing.And its random porous structure does not allow water droplets to pass.In principle,the properties of electrospun nanofibrous membranes are highly dependent on the natures of the intrinsic polymers.Polyvinylidene fluoride(PVDF)is commonly used in waterproof materials because of its good hydrophobicity,resistant to abrasion,acid and alkali resistance.Therefore,we choose PVDF as the raw material for the preparation of waterproof breathable membranes.In this paper,PVDF fibrous membranes were prepared from different concentration(18 wt%,20 wt%,22 wt%,24 wt%)by electrostatic spinning.The role of concentration of electro-spinning solution on the morphology,wettability and mechanical property of PVDF membranes were discussed.In order to improve the performance of fiber membranes,the ratios of mixed solvents are further explored.Meanwhile fiber membranes have been characterized through the emission electron microscopy,optical contact Angle tester,pore size analyzer and so on.When the ratio of dimethylacetamide(DMAc)/Acetone is 7/3,the membranes exhibited relative good performance with water resistance(82 k Pa),air permeability(8.1 mm/s),water transmission vapor(11.5 kg/m2/d).In addition,the quantitative relationship between the hydrostatic pressure and the pore size of the fiber and the surface wettability was analyzed based on the equation of “Yang Laplasse” in this paper.In order to optimize the performance of fiber membranes,Li Cl was added into PVDF solution and obtained the finer f ibers.When the concentration of Li Cl was 0.003 wt%,the membranes exhibited high water resistance(110 k Pa),good air permeability(6.1 mm/s)and water transmission vapor(11.8 kg/m2/d).At the same time,the tensile strength increased from 8.6 MPa to 12.2 MPa.These parameters fully confirmed that electro-spinning technique can be made a good use to fabricate the waterproof and breathable fabric.Therefore,the PVDF fiber membrane has practical application value on the waterproof and moisture permeable fabric.Compared with the process complex waterproof and breathable films,its simple and convenient preparation method also provided a new way to design and develop waterproof and breathable films. |
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