Donald Rivin

Transport properties of porous membranes based on electrospun nanofibers

Abstract Electrospinning is a process by which high voltages are used to produce an interconnected membrane-like web of small fibers (10–500 nm in diameter). This novel fiber spinning technique provides the capacity to lace together a variety of types of polymers, fibers, and particles to produce ultrathin layers. Of particular interest are electrospun membranes composed of elastomeric fibers, which are under development for several protective clothing applications. The various factors influencing electrospun nonwoven fibrous membrane structure and transport properties are discussed. Performance measurements on experimental electrospun fiber mats compare favorably with transport properties of textiles and membranes currently used in protective clothing systems. Electrospun layers present minimal impedance to moisture vapor diffusion required for evaporative cooling. There may be special considerations in the application of elastomeric membranes for protective clothing. Effects of membrane distortion upon transport behavior of the structure might be significant. Preliminary measurements have found that changes in elastomeric membrane structure under different states of biaxial strain were reflected in measurements of air flow through the membrane. Changes in membrane structure are also evident in environmental scanning electron microscope (SEM) images of the pore/fiber rearrangement as the membrane is stretched. Experimental measurements and theoretical calculations show electrospun fiber mats to be extremely efficient at trapping airborne particles. The high filtration efficiency is a direct result of the submicron-size fibers generated by the electrospinning process. Electrospun nanofiber coatings were applied directly to an open cell polyurethane foam. The air flow resistance and aerosol filtration properties correlate with the electrospun coating add-on weight. Particle penetration through the foam layer, which is normally very high, was eliminated by extremely thin layers of electrospun nanofibers sprayed on to the surface of the foam. Electrospun fiber coatings produce an exceptionally lightweight multifunctional membrane for protective clothing applications, which exhibits high breathability, elasticity, and filtration efficiency.

An Automated Water Vapor Diffusion Test Method for Fabrics, Laminates, and Films

An automated apparatus has been developed to measure the transport of water vapor through coated and uncoated fabrics, fabric laminates, thin foams, and solid films under a variety of conditions. The apparatus is more convenient to use than the traditional test methods for textiles and clothing materials; it allows one to use a wider variety of test conditions to investigate the concentration-dependent and nonlinear transport behavior of many of the semipermeable membrane laminates that are now available. The dynamic moisture permeation cell (DMPS) has been auto mated to permit multiple setpoint testing under computer control and to facilitate in vestigation of transient phenomena. Results generated with the DMPC are in agree ment with and of comparable accuracy to those from the ISO 11092 (sweating guarded hot plate) method of measuring water vapor permeability.

Humidity-Dependent Air Permeability of Textile Materials1:

Changes in fabric structure as hygroscopic fibers swell at high humidities can have a large influence on the measured air permeability of fabrics such as cotton, wool, silk, and nylon. The variation of air permeability as a function of relative humidity is of practical importance in ranking and evaluating candidate textiles for protective clothing applications. This paper describes a test method used to determine the relative humidity dependence of the air permeability of hygroscopic woven textile fabrics. The instru mentation also permits dynamic measurements during a step change in relative humid ity. Typical results are shown for woven fabrics, nonwoven battings, and novel elec trospun fiber mats.

A Test Method to Determine the Relative Humidity Dependence of the Air Permeability of Woven Textile Fabrics

This paper describes a test method used to determine the relative humidity dependence of the air permeability of hygroscopic woven textile fabrics. Changes in fabric structure as hygroscopic fibers swell at high humidities can have a large influence on the measured air permeability of materials such as cotton, wool, silk, and nylon fabrics. The method is sensitive enough to show sorption hysteresis effects in the relative humidity versus air permeability curve. The instrumentation also permits dynamic measurements during a step change in relative humidity. Typical results are shown for seven fabrics, covering a range of fiber hygroscopic properties and air permeabilities.

An Automated Dynamic Water Vapor Permeation Test Method

Abstract : This report describes an automated apparatus developed to measure the transport of water vapor through materials under a variety of conditions. The apparatus is more convenient to use than the traditional test methods for textiles and clothing materials, and allows one to use a wider variety of test conditions to investigate the concentration-dependent and nonlinear transport behavior of many of the semipermeable membrane laminates which are now available. The dynamic moisture permeation cell (DMPC) has been automated to permit multiple setpoint testing under computer control, and to facilitate investigation of transient phenomena. Results generated with the DMPC are in agreement with and of comparable accuracy to those from the ISO 11092 (sweating guarded hot plate) method of measuring water vapor permeability.

Convection/diffusion test method for porous textiles

Reports on an automated apparatus and test procedure to determine the convective and diffusive gas and vapor transport properties of small pieces of woven and nonwoven fabrics, membranes, and foams. The apparatus allows measurement of these properties in the very small quantities typical of material development programs, where the largest sample available may only be 1‐10cm2 in area. The convection/diffusion test method is useful for determining the gas flow resistance property and water vapor diffusion properties from a single experimental run. This eliminates the need for two separate tests, which is the usual procedure. The apparatus may also be used to perform separate tests for the diffusion property or the air permeability property, which may have some advantages when materials exhibit strongly concentration‐dependent transport properties. The convection/diffusion test method is well‐suited for rapid screening and comparison of the properties of a large number of materials with widely‐varying transport properties.

Measurement of Water Vapor Diffusion Through Polymer Films and Fabric/Membrane Laminates Using a Diode Laser Spectroscope

A spectroscopic system based on vapor-phase absorption of infrared radiation produced by a diode laser is shown to be useful for measuring water vapor diffusion rates through materials in sheet form. Measurements of water vapor diffusion through four polymer membranes and membrane laminates show an excellent correlation with an existing water vapor transport apparatus that uses hygroscopic polymer-film capacitance sensors. The diode laser spectroscope eliminates sorption hysteresis artifacts present in the capacitance sensors.