NW Advanced Apparel Systems Centre Report:
The Agency (DCTA) is developing and supporting the diverse clothing and textiles interests of Army, Navy, Airforce and Civilian defence activities. The products specified result in about £100 million per year of contracts. The dominant expenditure is for uniforms and specialist clothing.
The Agency designed and developed the 1995 release of combat clothing. This comprised 19 articles that can be combined by the user in whatever way is deemed appropriate. The kit issued provides for personnel to operate effectively in difficult environments (Arctic winters to European summers), to be camouflaged (visually and from sensors), to have body armour and to gain some nuclear/biological and chemical protection. The layer principle is used to achieve an integrated clothing system. The articles were designed to last 60 days in combat.
The popularity of this kit has been such that "durability" has emerged as a major area for enhancement. Several other issues have been identified affecting the development of the next generation of clothing: the need to be effective in extreme climatic conditions; the need for reduced bulk and weight; and a reduction in the number of layers.
The main development project at present is to specify a new combat clothing system in 2005. Fabric development work is undertaken by textile technologists and the research is carried out by an interdisciplinary team that has been chosen to bring ideas from other sectors into textiles. A major emphasis of the Agency is that the discipline of textiles can benefit from cross-sectoral learning and technology transfer. Lateral thinking is encouraged. During the course of their research, the Textiles’ Team has identified a number of potentially exploitable technologies and those described below are in the public domain.
1. Variable Pile Fabrics
The thinking here is based on the principle that insulation is dependent primarily on still air. By altering the insulation thickness, the tog value of the fabric can be adjusted.
A fabric has been devised that has two sides linked by monofilament struts. The gap can be closed up (2 mm thickness) or opened (8 mm thickness) by a shearing action (initiated by a drawthread). The patent reference is GB 2 234 705A.
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Illustration 1: Fabric cross-section showing closed and opened scenarios.
The wearer can then adjust the insulation provided by the clothing to maximise personal comfort.
An alternative design has an inflatable fabric, using bladders. This design permits the use of pores in the fabric that allow moisture to pass.
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Illustration 2: Fabric cross-section showing collapsed and inflated scenarios.
2. Shaped Memory Materials
The context for this development has been protection from intense heat, allowing extra time for the wearer to escape. The main barrier to heat is still air (insulation) but this leads to heavy garments and to discomfort due to the wearer overheating. DCTA have explored ways of rapidly and automatically enhancing the insulation provided by the garment.
Shape memory alloy (SMA) strips have been sandwiched between two enclosing fabrics. (For some technical input on the SMA principle, see http://www.brunel.ac.uk/~dtsrjdc/SMA.html). In the passive state, the Ni/Ti alloy strip lies flat and the fabric is about 1 mm thick. When exposed to intense heat, the fabric thickness is increased very quickly to 8 mm. This doubles the escape time available to the wearer.
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Illustration 3: Fabric cross-section showing passive and active scenarios.
3. "Smart Pore" Fabrics
The objective here has been to produce shower and wind-proof breathable materials. Some existing breathable materials are waterproof by virtue of being gas impermeable. The problem for these fabrics is that vigorous exertion leads to discomfort, because although moisture is transmitted away from the body, the skin is hot and there is no opportunity for convective cooling.
The "smart pore" concept sacrifices waterproofness for an automatic breathability. This is achieved by locating hydrophilic molecules on the inside of the fabric and hydrophobic molecules on the outside, and by creating numerous pores in the fabric. When the fabric encloses warm, high humidity air, the attached molecules exert a force on the fabric that opens the pores and allows convective cooling to take place.
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Illustration 4: Fabric cross-section showing closed and open scenarios.
4. Intumescent coated fabrics
Intumescent materials are widely used in fire doors (when heated, intumescent strips expand to seal off air gaps and protect from smoke, as described (for example) in http://www.swindonweb.com/swindondoorservices/comm/comm02.htm). Intumescent paint is often found covering the steel supports of large buildings (as described in http://www.jotun.co.uk/intumescent.htm). When exposed to heat, the paint expands and provides an insulating layer that reduces damage.
Considerable work has taken place at DCTA to find materials that will be activated rapidly at lower temperatures of about 100°C (with the protection of humans in mind). Current research is considering how intumescent materials can be applied to textiles to yield a lower-weight protective fabric with an enhanced fire-resistant performance.
Companies interested in this area of technology will find it
useful to contact the Textiles Flammability Group at Bolton
Institute. During a previous ESPRC research project (1993-1997),
it has been observed that if selected intumescents are combined
with certain flame-retardant textile fibres in a suitable fabric,
unexpectedly high flame and heat barrier properties are observed.
A flexible textile composite barrier fabric produced on this
principle has already been patented by Professors Horrocks and
Anand in association with the British Technology Group. Further
research into flame retardant composites is underway. News
postings on this research are at:
http://www.bolton.ac.uk/technology/news/flamin.html
http://www.bolton.ac.uk/technology/news/flaming2.html
Partnering with DCTA
Development work is expensive, and DCTA are seeking partners who will bring these and related technologies to where they can be commercially exploited and, at the same time, further DCTA interests. The preference is to work with both textile and clothing companies.
Looking forward to 2005, when the next combat uniform will be specified, it is already clear that the materials and the garment construction will require a significantly higher technological competence on the part of suppliers. The North West Advanced Clothing Web (NWACW) sees this as an an opportunity for UK companies to recapture some of the business that is currently being sourced overseas. By participating in development projects now, UK companies will be in a better position to submit tenders for bulk defence work in 2005 and beyond.
Through previous work on new product development, NWACW is equipped to offer facilitation to companies wanting to work on projects that aim to exploit DCTA research. For further information, contact David Tyler at d.tyler@mmu.ac.uk or Tel: 0161-247-2636.
Report by David Tyler
August 2000
North West Advanced Apparel Systems Centre
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