On the occasion of the “CBRNE protection symposium 2022” to be held in Malmö, we thought it would be useful to review the main principles on which protective textiles against nuclear, radiological, biological and chemical risks (NRBCe) are based and to see how these textiles are evolving.
What is it about?
The release of sarin gas in the Tokyo subway in 1995 was the first large-scale attack by a terrorist group using a toxic chemical weapon. In 2001, an attack by a biological agent, Bacillus anthracis spore powder (anthrax), was carried out by sending mail to U.S. government authorities. The terrorist threat exists and must be taken into account. We have already spoken in this blog about the use of chemical weapons in wartime, this state threat is still very real and the latest developments in the war in Ukraine will not deny us…
In addition, protection against TICs (industrial and chemical toxins) also requires specific protective clothing.
Combat personnel and first responders must therefore be equipped with PPE to protect them in their mission.
Clothing materials are now commonly used as personal protective equipment, and are classified as “technical or industrial textiles”. In addition, today’s protective textiles must protect against a wide range of hazards while meeting a wide range of functional needs: a good protective garment must provide protection from hazards while maintaining the wearer’s comfort and ability to perform vital tasks.
What are CBRN agents?
Chemicals (gases, vapors, liquids, particulates): chemical warfare agents, ICT/TIM (chemical toxic agent, toxic industrial equipment) ;
Biological (particulate): pathogenic micro-organisms, biological toxins;
Radiological (particulate): radiation-carrying particles spread by a radiological dispersal device (RDD) or a dirty bomb;
Nuclear (particulate): radiation-carrying particles dispersed by a detonation involving nuclear fuel or a nuclear weapon.
The mechanisms of CBRN protection
PPE includes protection for the whole person (usually a suit) and respiratory protection (mask).
Equipment must prevent the entry of hazardous materials through a variety of techniques: creating an impermeable barrier between the agent and the individual; filtering, adsorbing, or reacting with hazardous materials to remove them; and keeping contaminated air away from entry points using overpressure or directional airflow.
Barrier materials
CBRN clothing made of waterproof rubber prevents the absorption of toxic chemicals and is impermeable to air and water vapor. The old Soviet suit, for example, was made of waterproof canvas covered with rubber.
However, this type of suit quickly generates a lot of heat and is uncomfortable; they also reduce human performance to a very low level, which is incompatible with most military missions. Rubber suits have no adsorptive capacity; they are merely impermeable barriers to CBRN hazards. These garments were intended to provide sufficient protection against chemical warfare agents, but because they are impermeable and also because of perspiration, they are an unacceptable barrier to the natural cooling processes of the human body. Of this equipment only butyl rubber boots and gloves remain today.
Therefore, one of the most important characteristics of a functional protective suit is that it must allow for proper cooling of the body. Due to their open porosity, these materials must be permeable to air, to facilitate the evacuation of perspiration.
Selective permeability material
The selectively permeable material allows small molecules to pass through, while blocking larger toxic molecules. It has good protective characteristics and can resist hazardous chemicals such as liquids, gases, aerosols and high molecular weight solids. In addition, selectively permeable materials have good moisture permeability and comfort when worn, making them an excellent candidate for permeable protective suits.
While these materials are suitable for protection against biological and radioactive agents, they are not necessarily suitable for full CBRN protection because they are not impermeable to chemical or vapor permeation.
Microporous barriers such as super-expanded PTFE film (polytetrafluoroethylene, ePTFE) have been developed by GORE. A cast PTFE film is stretched at a high rate but without changing its outer dimensions. Millions of pores are formed in the structure instead of shrinking or thinning during stretching. The ePTFE material is hydrophobic in nature and has one of the lowest surface energies of any known material. Water vapor, on the other hand, can easily flow through the pores, while liquid water cannot.
Activated carbon adsorption technology
The primary method of protection against agent vapors is activated charcoal capable of adsorbing chemical warfare agents. To protect against liquids, activated charcoal and barrier materials are used (see Figure 3), and clothing often has water-repellent properties. When these protective garments are exposed to contaminated air, the toxic gases carried by the flow are adsorbed by the single layer of activated charcoal, allowing the purified air to flow freely through the protective garment, thus providing sufficient ventilation for the wearer.
For CBRN protection, two separate protective layers, a selective membrane layer over an activated carbon layer, can be coupled. The advantage of this combination is that any vapor that manages to enter the system, either by permeation or through the interfaces, is absorbed by the inner activated carbon layer, and the material as a whole resists liquid penetration.
New materials and technologies have improved this basic system in order to provide high performance, multi-functionality, lightness and comfort.
Ouvry’s Polycombi is based on this model: a filtering suit that protects against CBRN agents in liquid, vapor and aerosol form for 12 hours. Extremely light and ergonomic, it provides the user with comfort and optimal protection. It allows a quick evacuation of heat, and thus reduces the risks of heat stroke. It is certified CE PPE category III: type 4, 5 and 6.
Nanofiber-based multifunctional materials
Multifunctional materials based on nanofibers (e.g. electrospun) can be incorporated into protective clothing systems. Due to the tiny pore size and large surface area of nanofibers, nanofiber membranes have high aerosol filtration efficiency, good air permeability, low surface density, and low pressure drop. Nanofiber-based protective equipment can be lightweight while offering a wide range of capabilities and could lead to a new type of protective clothing.
Autodetoxifying electrospun fabrics could be a new type of textile designed to guard against chemical and biological warfare agents. Functional chemicals such as cyclodextrin, iodobenzoic acid, polyoxometalates, peroxides, oximes, and chloramines could significantly improve detoxification performance. This opens up new possibilities for the development of advanced systems capable of guarding against chemical and biological threats. Electrospun protective clothing is still under development and there are some constraints to commercial production.
On the other hand, metal oxide nanoparticles, such as MgO, CaO, ZnO, TiO2, Al2 O3, MnO2, Fe2O3, present capacities to degrade chemical agents but, their perennial fixation on the tissue is still a difficult problem to solve.
Smart second skin technology
These smart membranes, still under development, are called “switchable”. They close their pores in response to chemical substances, but remain open in the absence of contact.
There are currently three strategies for developing them:
Carbon nanotubes can efficiently accelerate the transfer of gas or liquid molecules due to their unique intrinsic cavity-like structure, monodisperse nanochannels, and transport properties, offering hope for the fabrication of extremely thin, ultra-light, super-breathable protective clothing.
The first strategy is to integrate aligned carbon nanotubes into highly breathable membranes that provide an effective barrier against biological threats and a thin sensitive functional layer grafted or coated onto the membrane surface. It either closes the pore entrance of the vertically aligned carbon nanotubes upon contact with a chemical warfare agent, or it self-exfoliates in the region of the pollutants after neutralizing the threat.
By closing the pore entrance or removing the contaminated surface layer, the fabric goes into protective mode.
The second method is to create a copolymer membrane incorporating an enzyme. These membranes expand and close when exposed to chemical agents as a result of an enzymatic reaction with the chemical agent, protecting the combatants wearing the garment.
A third method is to coat existing fabrics with electrically conductive elements. When subjected to a small electric current, this coating reacts by sealing the fabric against penetration. Within seconds, the pores close, forming a protective barrier that can last up to 24 hours. A different current can either open the membrane or keep it closed.
Metal-organic frame materials
Metal-organic frameworks (MOFs) are porous crystalline solids composed of metal ion units or clusters linked together by organic bridges held together by strong coordination bonds. Due to their excellent adsorption, reactivity, and catalytic ability towards chemical warfare agents, MOFs have been identified as one of the most important materials for the detection and detoxification of chemical warfare agents.
Techniques for self-repair of microcapsules
The self-repair mechanisms of the microcapsules help to establish a good physical barrier against deadly chemical agents, bacteria and viruses. This technology combines novel gap-closing techniques with healing microcapsules that activate when torn, allowing cuts and punctures to be repaired. The self-healing layer contains reactive compounds that neutralize harmful threats, such as deadly chemicals, while reforming the physical barrier against bacteria and viruses.
Conclusion
The CBRN threat is still very present but research on technical textiles is advancing rapidly to develop protective clothing that is increasingly effective in terms of protection and comfort.
References
1_M.A.R. Bhuiyan, L. Wang, R. A. Shanks and J. Ding , Advances and applications of chemical protective clothing system, J. Indus. Textile, 2019, Vol. 49, 97–138. DOI: 10.1177/1528083718779426
2_ Md. Khalilur Rahman Khan, CBRN Personal Protective Clothing, Kohan Textile Journal (2021), https://kohantextilejournal.com/category/all/technical-textile/
3_ X. ZHAO, B. LIU, Permeable Protective Suit: Status Quo and Latest Research Progress, Materials Reports 2018, Vol. 32
Issue (17): 3083-3089, http://www.mater-rep.com/EN/10.11896/j.issn.1005-023X.2018.17.022
4_ A Second Skin for the First Layer of Defense
5_ U.S. Army Investigates Self-Healing Protective Clothing