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Posted: Jun 12, 2006

Novel use of polymer nanofibers as filters for chemical warfare defense

(Nanowerk Spotlight) Researchers in Singapore functionalized a polymer nanofiber membrane to capture chemical warfare agents such as nerve agents. The nanofibers in the membrane act as a substrate on which the nerve agents get physically adsorbed followed by chemical decomposition.
Among chemical warfare agents, organophosphorus (OP) nerve agents are of particular interest due to their acute neurotoxicity. Protection against these agents can be achieved through protective suits and face masks.
The problems with this chemical warfare protection are the disposal issues of toxic agents and the weight considerations of the protective garment. Current protection techniques include usage of activated carbon as adsorbent. The activated carbon is functionalized with various metal oxides to facilitate chemisorption of warfare agents. However, nerve and blister agents just get physically adsorbed onto activated carbon, resulting in disposal hazards of the used suits and masks.
Tackling these issues, Seeram Ramakrishna, Professor of Mechanical Engineering and Bioengineering at National University of Singapore (NUS), and also head of the Nanobioengineering Labs at the NUS Faculty of Engineering, together with several colleagues, published a recent paper titled "Functionalized polymer nanofiber membranes for protection from chemical warfare stimulants" in the May 30, 2006 online edition of Nanotechnology.
Among the techniques used to decompose OP nerve agents, enzyme degradation is the most selective, fast and simple approach but is associated with a lot of limitations, such as cost, enzyme stability, and large scale production. The researchers at NUS try to mimic the enzyme functionalities using certain chemical molecules to achieve comparable kinetics, selectivity and performance for the decontamination reaction.
Ramakrishna explained the benefits of their novel filter material to Nanowerk: "We synthesized a new compound, which is a derivative of β-cyclodextrin, and found it to possess the capacity to hydrolyze nerve agent simulants. This catalyst, 3-carboxy-4-iodosobenzyl)oxy-β-cyclodextrin, was blended with Polyvinylchloride (PVC) and electrospun into nanofibers. The functionalized nanofibers had a better detoxification ability compared to other powerful nucleophiles such as Iodobenzoic acid. "
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Schematic showing the potential for replacing conventional filters by functionalized polymer nanofibers. (Source: Seeram Ramakrishna, NUS)
As a result, this new synthesized catalyst will help in complete hydrolysis of nerve agents into non-toxic products. The nanofibers act as a substrate on which the nerve agents get physically adsorbed followed by chemical decomposition. By replacing the activated charcoal laminate layer from current protective gear with functionalized nanofiber laminates, a considerable (50-70%) reduction in weight can be achieved. An added advantage in using polymer nanofiber laminates is that they allow for very good moisture and vapor transport in and out of the fabric. These factors considerably increase wearer comfort.
"We have also fabricated in our lab, nanofibers functionalized with silver nanoparticles and have proved their anti-bacterial ability" Ramakrishna says. "These nanofibers could be used as filter linings in face masks not only for military use but also for health care personnel for protection from bacterial and other biological agents of concern. These fibers when manufactured in large scale make good HEPA filters for hospitals, clean rooms and other sterile places where bacterial contamination is to be prevented."
Building on this work, Ramakrishna and his team are synthesizing catalysts for oxidation of blister agents. "We hope that these catalysts could be functionalized onto polymer nanofibers and used as filters to capture and effectively decontaminate chemical and bacterial warfare agents" he says.
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