Fabracation Of Polyvinylidene Fluoride/Polyurethane Fibrous Membranes For Waterproof And Breathable Fabric

Waterproof and breathable fabric is a new functional fabric which has outstandingwaterproofness, moisture permeable properties and warmth retention properties. In many harshclimatic conditions, it can prevent human from the body injury resulted from storm or fierce windand timely transmit the water vapor to the outside environment in order to maintain a dryenvironment in clothes. And at the same time, this clothes can also break off the direct contact withthe liquid reagent for these people worked in medical and chemical industries, which could avoidtoxic substances hurting human’s bodies. Owing to its excellent performance, the demand ofwaterproof and breathable fabric is gradually increasing in market. Its application is also not limitedto traditional military supplies and professional medical protective products, now it can be used indaily life like outdoor sports clothing. In2012, the value of the United States outdoor fabrics marketreached$50billion, and the value of Chinese market was$2.3billion. Significantly, the Chinesemarket in this field was going to increase at the rate of the annual growth rate above40%, which isexpected to be over10billion in2020. However, the waterproof and breathable fabric on thedomestic market has either excellent performance of waterproof but bad moisture permeability, orgood moisture permeability but low waterproofness, which leads to people’s discomfort feelfor theclothing. Meanwhile, Gore, a leader company in the global waterproof and breathable fabric markets,take the full advantage of its unique waterproof and breathable membrane to make it superb high- end market for decades. Therefore, it has an important significance for developing a new-stylewaterproof and breathable fabric.Electro-spinning technique is often used to fabricate polymer fibers in diameters of tens ofnanometers to micrometers. Such fibers tend to produce a stacked three-dimensional networkstructure whose small pores can provide many narrow passages that can allow the transmission ofwater vapor when there is pressure or humidity difference on both sides of the clothing. And itsrandom porous structure does not allow water droplets to pass.Polyvinylidene fluoride is commonly used in waterproof materials because of its goodhydrophobicity, acid and alkali resistance. In this paper, PVDF fibrous membranes were preparedfrom different concentration (14、16、18、20wt%) by electrostatic spinning. The role of compositionof electro-spinning solution on the morphology, wettability and mechanical property of PVDFmembranes were discussed. To improve the spinnability of PVDF solution, we added the LiCl intoPVDF solution for the finer fiber, and these experiment proved adding0.010%LiCl is suitable. Inthis case, the membranes exhibited high water resistance (36.0kPa), good water transmission vapor(5965g/m2/d) measured by ASTM test method, excellent tensile strength (12.2MPa), and theoutstanding water contact angle (135°), but the elongation at break of this film is only30%.As a major outdoor sports clothes for the waterproof and breathable fabric clothing, thematerial itself should have good toughness and mechanical stretch. Polyurethane has excellentelasticity, abrasion resistance and resistance to hydrolysis. Thus, it was added spinning solution withPVDF spinning solution for the product of the polyvinylidene fluoride/polyurethane compositefibrous membranes. The study discussed the ratio of two different solutions for fibrous membraneproperties and also took into account the production efficiency. The final decision is that the ratioshould be4/1. By this way the elongation at break of this membranes increased to60%, its watertransmission vapor also raised to a higher level (6653g/m2/d) compared to ordinary Gore-Texfabrics (5674g/m2/d), while the most excellent GORE-Tex XCR’s is7513g/m2/d.Finally, in order to further enhance the performance of the composite fibrous membranes, westudied the changes of morphology, water resistance, moisture resistance, surface wettability andmechanical properties under different spinning voltage. The results showed that: the severalperformances of the fiber membrane has been further improved under50kV spinning voltage, whichare high water resistance (44.6kPa), good water transmission vapor (6573g/m2/d), excellent tensilestrength (16.2MPa), outstanding water contact angle (148°), and the finer elongation at break (70%).These parameters are fully confirmed that electro-spinning technique can be made a good use of thefabrication of the waterproof and breathable fabric.