Thursday, September 24

Protective clothing systems composed of permselective polymer film laminates are an alternative to standard air-permeable garments based on activated carbon. These polymer layers are designed with high water vapor permeation rates and low permeation of chemical warfare agents. Polymer films that have a significant water vapor flux usually also have an affinity for water, and will hydrate and swell significantly at high humidity levels. The polymer film_s increase in water content has the potential to affect the transport rate of chemical warfare agents in vapor and liquid form, and usually also has a large effect on the intrinsic water vapor permeability of the membrane. Test methods developed for air-permeable sorptive layers are not designed to probe the effect of different hydration levels of a polymer film. In particular, testing with a dry gas sweep on one side of the membrane can dry out the film so much on one side that the membrane becomes a significant barrier to water transport. Examples of misleading test results and appropriate sample conditioning and testing will be discussed along with implications for comparative selection criteria for advanced protective fabrics.

As an ongoing research on silver antimicrobials, this report delineates measurements of the diameters of swollen silver antimicrobial dressings and commercially available calcium-sodium alginate dressings (controls) in water and in 0.9% sodium chloride solution after 8 hours and after one week of immersing in the solution. The swelling characteristics are measured (Olympus BH2 with Ocular Micrometer), and correlated with the absorption of saline g/g. At the SRRC, we have developed antimicrobial silver-sodium-carboxymethylated (CM)-cotton printcloth from the sodium salt of CM-cotton, and silver-Ca-Na alginates from commercially available four alginate moist wound dressings. These silver dressings have high absorption of saline solution, and in vitro data show 99.5% reduction in both gram positive (Staphylococcous aureus) and gram negative (Klebsiella pneumoniae ) bacterial growth, suggesting that such dressings containing silver may protect wound surfaces from microbial invasion and effectively suppress bacterial multiplication.

Nonwoven fabrics have been used extensively in industrial and single-use applications. The next phase of research in the nonwovens field should be to bring nonwovens into apparel sector. Characteristics such as breathability; measured as Moisture Vapor Transport Rate (MVTR), softness, non-plastic feel, etc., play important roles in determining the suitability of synthetic nonwovens for apparel use. Research that enhances these characteristics in spunmelt nonwovens is very critical and will help with creating new markets for nonwovens. Most recently, the use of atmospheric pressure plasma treatment has been considered as a promising technology to functionalize textile materials as it overcomes some of the disadvantages with the earlier version of plasma technology such as the low pressure/vacuum plasma treatment. The low pressure/vacuum plasma treatment is inefficient at commercial scale due to its low pressure requirement for operation. To overcome this, atmospheric pressure plasma functionalization has been recently developed, which can be carried out at atmospheric pressure. Since it is operated at atmospheric pressure, it is feasible for commercial scale operations and enables to impart a myriad of functionalities to textile materials. More importantly, research on the use of atmospheric pressure plasma on nonwovens and technical textiles is at its infancy and not much information is available in the public domain.

This paper which evolved out of collaboration between academic institution and industry will present recent results on the enhancement of moisture vapor transport characteristics of polypropylene spunbonded nonwovens via two routes of plasma functionalization. In one method, spunbonded nonwoven fabrics have been just treated in the plasma chamber with oxygen pulled from the atmosphere. In the second route, spunbonded nonwovens were treated with nitrogen gas in oxygen atmosphere so that the surface gets etched intensively which may lead to more transport of moisture through the filaments. MVTR was evaluated using the standard method BS7209. Spunbonded samples of three different weights (20, 50, 75 g/m2) respectively) were used in this study to examine the effect of fabric weight on atmospheric plasma functionalization. Results showed that both oxygen and combined gas functionalization resulted in more moisture vapor transport characteristics. In addition, lighter fabrics were more susceptible to atmospheric pressure plasma treatment which is reflected in higher MVTR values.

In a general sense, the MVTR was enhanced by 95% in lightweight fabrics. Statistical analysis carried out in _R_ environment showed that MVTR values of plasma treated fabrics irrespective of their weights were significantly different from those of untreated spunbonds. This robust analysis proves that the atmospheric pressure plasma process in the presence of gases like nitrogen can serve as a viable method to enhance the breathability and cotton-like characteristics of synthetic nonwovens. This paper will also present SEM characterization of plasma enhanced nonwovens and other apparel related characteristics.

These materials would be used to coat a fabric, which would then be used as a barrier ply in an article of clothing. As you might guess, the Army is interested in barrier fabrics that repel chemical warfare agents but also transmit perspiration moisture.

Elastomeric block copolymers, poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid), with potential applications in protective clothing for soldiers were synthesized and their properties were evaluated. These polymers were synthesized using a combination of carbocationic polymerization and atom transfer radical polymerization. They were designed to provide barrer properties against chemical warfare agents and enhanced transmission rates for perspiration moisture. Structural and molecular weight characterization indicated that targeted molecular weights of the various blocks were achieved. Transmission electron microscopy, supported by other techniques, indicated triphasic morphology. Attenuated total reflectance Fourier transform infrared spectroscopic analysis showed high water permeability due to enhanced solubility of water in the hydrophilic poly(acrylic acid) domains.

Chemical modifications of polyolefin fibers were produced by using radical graft polymerization in extruders, and several acyclic and cyclic halamine precursors were successfully grafted onto polypropylene and polyethylene. The chemically modified fibers could be converted to biocidal N-halamine polymers by rinsing with a diluted chlorine bleach solution. The final products exhibited powerful antimicrobial properties against Escherichia coli and Staphylococcus aureus, and the functions are refreshable and durable. The structures and performance of the modified fibers are characterized and evaluated by using different instrumentation methods. The modified polymers can be meltblown to nonwoven structures and the products can be applied in antibacterial wipers, air and water filters, and respirators.

Infrared thermography and high speed photography were used to take on-line measurements of PP fiber temperature and diameter for both the melt spinning and melt blowing process. In melt spinning, the fibers cooled slightly faster with increase in spinning speed. In melt blowing, the fiber temperature at any downstream location showed a slight increase with an increase in the mass throughput of the polymer over the range of mass flow rates studied. In parallel with the experimental studies, a numerical model was used to predict the fiber diameter profiles for both melt spinning and melt blowing. These predictions were very close to the actual experimental measurements. Thus, the model can be used to predict and optimize the operation of commercial melt spinning and melt blowing.

There has been continuing interest in nanofibers for filtration and related applications . Although tremendous amount of research has been done on electrospinning, it has seen only a limited commercial success. Melt blowing has been known to produce nonwoven webs from with fiber diameters in the range of a few microns. With recent advances in technology, it has been possible to produce nonwoven webs with diameters in the range of few nanometers. Such an approach will allow the production of nanofiber webs from thermoplastic polymers with reasonable production rate. Results form the research being done at UTNRL to produce and evaluate nanofiber filter media by melt blowing will be presented.

Nonwovens are subjected to compressive stress in many applications in a broad variety of industries including biotechnology, household, healthcare, filtration, paper, and power source. The performance of nonwovens in such applications is determined by the pore structure of the nonwovens under application environments. Therefore, determination of pore volume, pore size, and pore volume distribution of nonwovens under compressive stress is important. None of the currently available pore structure characterization devices is capable of measuring such pore structure characteristics of nonwovens as a function of compressive stress. Innovative technology has been developed to measure pore vole, pore size, and pore volume distribution of nonwoven as a function of desired compressive stress applied on the nonwovens. The sample of the nonwoven wetted with a wetting liquid and supported on a membrane with pores smaller than the pores of the nonwoven is placed on the bottom of the sample chamber. A computer controlled pneumatic device is used to apply pressure independently on o-ring seals and on the sample. Compressive stress on the sample is adjusted to any desired amount. Pressure of a nonreacting gas is increased on the sample to displace the wetting liquid from the mpores of the sample. The displaced liquid flowing out through the pores of the membrane are accurately measured. Applied gas pressure and volume of liquid yield pore volume, pore diameter and pore volume distribution. The technique has been successfully used to measure pore volume of nonwovens. The results will be presented and critically examined.

Discussions on the need for pre-discharge conditioning as a necessary step to conform to test standards continues to be a topic of discussion, both within the industry and specific committees focused on testing standards. In this presentation, different methods of preconditioning will be reviewed and experimentally investigated on their impacts on fiber or media structural properties and filter performance. The research is based on literature review, lab testing, and actual field measurement.