A flexible membrane with sub-5 nm single-walled carbon nanotube (SWNT) pores is developed by F. Fornasiero and co-workers, as described on page 5871, for application as a key component of protective, yet breathable fabrics. The SWNTs are shown to enable exceptionally fast transport of water vapor under a concentration driving force. Thus, membranes having SWNTs as moisture-conductive pores feature outstanding breathability and provide a high degree of protection from biological threats by size exclusion.

Small-diameter carbon nanotubes (CNTs) are shown to enable exceptionally fast transport of water vapor under a concentration gradient driving force. Thanks to this property, membranes having sub-5 nm CNTs as conductive pores feature outstanding breathability while maintaining a high degree of protection from biothreats by size exclusion.

A computational clothing design tool is used to examine the effects of different clothing design features upon performance. Computational predictions of total heat and mass transfer coefficients of the clothing design tool showed good agreement with experimental measurements obtained using a sweating thermal manikin for four different clothing systems, as well as for the unclothed bare manikin. The specific clothing design features examined in this work are the size and placement of air-permeable fabric vents in a protective suit composed primarily of a fabric-laminated polymer film layer. The air-permeable vents were shown to provide additional ventilation and to significantly decrease both the total thermal insulation and the water vapor resistance of the protective suit.

Over the past decade, semi-permeable membranes that transfer heat and water vapor have been investigated and applied in air-to-air or liquid-to-air energy exchangers. The water vapor diffusion resistance and modulus of elasticity are two of the most important properties of membranes. These properties play significant roles on the design and performance of the membrane-based energy exchangers. In this study, measurement test methods for membrane properties are presented and important factors impacting the test results are evaluated using the test data. It is found that operating conditions and crystals or deposits in membranes influence the vapor diffusion resistances. The elastic modulus can be determined from the elastic deflection of a simply supported membrane subject to a normal pressure difference. Deflections of membranes are known to cause mal-distribution of flows in energy exchangers and this degrades their performance. Some effective methods to reduce deflections of membranes are presented.

The role of water in protective fabrics is critical to comfort and material performance. Excessive perspiration in clothing causes discomfort, and bound water can adversely affect the ability of carbon to adsorb chemicals. Yet the presence of water can also improve the moisture vapor transport of protective polymer films, and is essential for the hydrolytic destruction of nerve agents. Reported here are the findings of wicking and drying experiments conducted on various hydrophilic and hydrophobic cover fabrics that demonstrate the influence of wetting on permeation through fabrics. The influence of water content on reactive polymers capable of degrading nerve agent simulant is also discussed, and the importance of a novel “delivery system” for water to the reactive components through the use of a wicking fabric is introduced.

A series of different experimental techniques were applied to quantify the effects both steady and unsteady pressure differential across a fabric had on the flow through the fabric. Static permeability measurements were made on four common nylon parachute fabrics over a range of fix pressure differentials to provide a baseline for the other techniques. An examination of the effects humidity had on the permeability of the fabric showed that the permeability had no change or slight increase when exposed to flows with higher humidity. The permeability at high static pressure differentials was examined by applying a weak shock wave to a fabric specimen. The results of this experiment showed the flow resistance increased (i.e. permeability decreased) as the pressure levels increased in all the fabrics except for the low permeability fabric which showed the opposite effect. A computer numerically controlled, piston permeability apparatus was designed and applied to test the dynamic permeability of the low permeability fabric. The results from this investigation do indicate a small effect of unsteady pressure differential on the fabric permeability. The fabric permeability is slightly higher than the static permeability when the pressure differential is increasing with respect to time and the opposite is true when the pressure differential is decreasing. This change in permeability is more pronounced as the pressure is higher and the pressure changes more rapidly with respect to time, suggesting dynamic permeability likely affects highly unsteady phenomena such as parachute opening.

Closure systems for personnel protection applications, such as protective clothing or respirator face seals, should provide effective permeation barrier to toxic gases. Currently available mechanical closure systems based on the hook and loop types (example, Velcro) do not provide adequate barrier to gas permeation. To achieve hermetic sealing, we propose a nonmechanical, nanoscopic molecular closure system based on complementary polyelectrolyte multilayers, one with a polycation outermost layer and the other with a polyanion outermost layer. The closure surfaces were prepared by depositing polyelectrolyte multilayers under a variety of deposition conditions, on conformable polymer substrates (thin films of polyethylene teraphthalate, PET or polyimide, PI). The hermetic sealing property of the closures was evaluated by measuring the air flow resistance using the dynamic moisture permeation cell (DMPC) at different humidity conditions. The DMPC measurements show that the polyelectrolyte multilayer closures provide significantly large resistance to air flow, approximately 20-800 times larger than that possible with conventional hook and loop type closure systems, at all humidity levels (from 5 to 95% relative humidity). Hence, from the point of view of providing a hermetic seal against toxic gas permeation, the polyelectrolyte multilayer closures are viable candidates for further engineering development. However, the adhesive strength of the multilayer closures measured by atomic force microscopy suggests that the magnitude of adhesion is much smaller than what is possible with mechanical closures. Therefore, we envisage the development of a composite closure system combining the mechanical closure to provide strong adhesion and the multilayer closure to provide hermetic sealing.

Novel composite membranes with poly(vinyl alcohol-co-ethylene-g-diallylmelamine) (PVA-co-PE-g-DAM) nanofibers layered on poly(propylene-g-diallylmelamine) (PP-g-DAM) meltblown nonwoven fabric were successfully developed as lightweight and breathable protective materials with chemical and biological decontamination functions. By controlling levels of coated nanofibers, three nanofibrous membranes with similar surface morphology, hydrophilicity and transport properties were prepared. The N-halamine precursor moieties in the membrane matrices can be converted to active N-halamine structures with a diluted sodium hypochlorite solution, and the active chlorine content on the membranes is rechargeable and durable. The chlorinated nanofibrous membranes demonstrated very powerful and rapid biocidal effects against both E. coli and S. aureus by contact, as well as excellent disinfection effect to wet bacterial penetration through the membrane. Furthermore, the efficient chemical detoxification functions of the halamine nanofibrous membranes were also observed by a total decontamination of aldicarb, a carbamate pesticide, within 30 min. These PVA-co-PE-g-DAM nanofiber composite membranes can serve as ideal ultra-light filtering media for chemical and biological protective clothing materials.

This paper describes permeability measurements for porous fabrics as influenced by strain, humidity, air flow rate, and fabric elasticity. The focus is on standard parachute fabrics, where the fabric's porosity and air permeability influence the rate of steady-state descent, and also affect the complicated fluid-structure interactions taking place during parachute opening and deployment. High strength nylon parachute fabrics showed relatively small permeability changes due to strain, humidity, and flow rate. Comparative measurements on elastomeric fabrics showed much larger changes in air flow due to fabric dimensional changes at high pressures and flow rates. Elastomeric fabrics that stretch and change permeability in response to higher pressures and flow rates may be able to reduce the “opening shock” during the parachute deployment phase.

Garment materials that provide protection against exposure to toxic chemical warfare agents (CWAs) not only require the ability to block the passage of these toxic compounds in vapor form but also the ability to transport water vapor to allow cooling for the wearer. Only a very limited number of examples of such "breathable" CWA barrier materials are known. A new type of reactive organic/inorganic composite film material is presented that has a very high water vapor transport rate (>1800 g m(-2) day(-1) for a 220-mu m-thick film) and the ability to completely block penetration of the mustard agent simulant, 2-chloroethyl ethyl sulfide (CEES), after 22 h of continuous exposure. This new composite material is based on two components: (1) a cross-linked, diol-functionalized room-temperature ionic liquid polymer that serves as a dense, flexible hydrophilic matrix, and (2) a basic zeolite (sodium zeolite-Y (NaY)) that serves as an inexpensive, nucleophilic additive that chemically degrades the CEES as it enters the film. Preliminary FT-IR studies on this new reactive barrier material suggest that the OH groups on the ionic polymer not only facilitates water vapor transport but may also help activate mustard-type vapors for reaction with the imbedded NaY.

Experimental measurements of water vapor sorption and desorption in wool/polyester blend fabrics are used to assess associated changes in temperature and heat flux during varying relative humidity levels. The results aid further development and adoption for military applications of cold-weather wool blend fabrics that are more flame resistant and warmer than 100% polyester garments. Two types of bi-sided fabrics were tested: 1) thin knit fabrics designed to be worn next to the skin, usually as undergarments, and 2) thick fleece mid and outer layers with 100% wool on the outer face and 100 % polyester on the inner surface. The following issues were addressed: 1) the effect of wool content on the knit fabrics, 2) the effect of fabric orientation on both the knit and the fleece fabrics, and 3) the effect of durable water-repellent treatment on the fleece fabrics.

Breathable chemical and biological detoxifying protective fabrics are obtained via functionalization of electrospun fiber mats using a layer-by-layer electrostatic assembly technique. The chemically reactive polyanion, poly(N-hydroxyacrylamide) or poly(hydroxamic acid) (PHA), and bactericidal polycation, poly(N-vinylguanidine) (PVG), were synthesized and assembled electrostatically to generate multifunctional coatings on prefabricated polyacrylonitrile (PAN) fiber mats. Reactivity of PHA in the hydrolysis of diisopropyl fluorophosphate (DFP), a close analog of the chemical warfare agent sarin, was demonstrated. The DFP degradation rate with PHA is comparable to that with compounds such as isonicotinhydroxamic acid methiodide, an efficient catalyst of organophosphate ester hydrolysis. Protective fabrics functionalized with PVG/PHA layers are able to degrade DFP mists, with DFP hydrolysis rates 60-fold higher than those with unmodified fabrics under identical conditions. Fabrics modified with PVG/PHA layers are bactericidal against E. coli and S. epidermidis. Breathability of functionalized fiber mats as protective fabrics was evaluated versus standard reference fabrics.

Protective clothing systems composed ofpermselective polymer film laminates are analternative to standard air-permeable garments basedon activated carbon. These polymer layers aredesigned with high water vapor permeation rates andlow permeation of chemical warfare agents. Polymerfilms that have a significant water vapor flux usuallyalso have an affinity for water, and will hydrate andswell significantly at high humidity levels. Thepolymer film’s increase in water content has thepotential to affect the transport rate of chemicalwarfare agents in vapor and liquid form, and usuallyalso has a large effect on the intrinsic water vaporpermeability of the membrane.

Fabric-covered cylinders are convenient analogs for clothing systems. The geometry is well defined and includes many of the effects that are important in garments. Fabric-covered cylinder models are used in conjunction with laboratory measurements of material properties to calculate heat and mass transfer properties of clothing under specific conditions of environmental wind speed, temperature, and relative humidity.

Nanocomposite films consisting of amphiphilic ionic polyacetylenes (P2EPy-R) and layered aluminosilicates (saponite) have been prepared through electrostatic layer-by-layer assembly. The water vapor barrier properties of the nanocomposite films coated on Nafion™ film have been studied. The Nafion film coated with poly(N-octadecyl-2-ethynylpyridinium bromide) (P2EPy-C18) and aluminosilicates showed 22 times higher diffusion resistance to water vapor and 95% reduction in water vapor permeability when compared with the pristine Nafion control film. The X-ray diffraction data, UV–vis absorption spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM) suggest a strong tendency of micellization of P2EPy-C18 polymer and ordered structure on the surface of aluminosilicate nanosheets compared to short alkyl side chains, C12, C6, and C0. The micellized and ordered structure of P2EPy-C18 between aluminosilicate could explain the improved hydrophobic barrier properties of P2EPy-C18/aluminosilicate nanocomposites.

Cost-effective nanotechnology-based water-repellent treatments for clothing fabrics are now commercially available. The effectiveness of these durable water repellent (DWR) fabric treatments are evaluated for application to military uniforms. The addition of a non-wicking finish to clothing fabric negatively impacts comfort in hot and humid environments. Clothing comfort may be improved by refining the DWR fabric treatment process to retain wicking properties on the fabrics inner surface.