In protective apparels, there is no one-size-fits-all solution for all situations, and rather selection of these apparels should be based both on risk assessment and an evaluation of the workers' specific tasks and work environments, state S Sakthivel, Valarmathi Shravanthi, M Vinothini and E Rajadurai.

Protective textiles are a fragment of technical textiles, demarcated as encompassing all those textile-based products that are used predominantly for their performance and functional characteristics rather than their aesthetic and decorative characteristics. It includes protection against cuts, scuff, ballistic and other types of severe impact including stab wounds and explosions, fire and extreme heat, hazardous dust and particles, nuclear, biological and chemical hazards, high voltages and static electricity, foul weather, extreme cold and poor visibility.

Materials
Textile materials in the form of woven, knitted, nonwoven and braided erections or a combination of these structures are being used for protective textiles. Furthermost fabrics are two-dimensional but an increasing number of three-dimensional protective textile structures are being developed and produced. The properties of fabrics depend on the characteristics of the component yarns or fibres and on the geometry of the formed structure.

Method

Nonwovens are produced in two distinct steps:

1. Web formation: arrangement of fibres into a 2D sheets, which includes dry-laid, spun-laid and wet-laid processes, and
2. Consolidation: bonding the fibres together to create a nonwoven fabric, which includes into mechanical, chemical, thermal and stitch bonding processes. Braided textile structures are manufactured with mutual inter-wining of yarns in a tubular form. There are three typical braid structures: diamond, regular and hercules.

Classification:
Personal protective textiles can be classified as:

• Fire Protection
• Heat and cold protection
• Mechanical impact protection
• Biological Protection
• Electrical Protection
• Radiation Protection

Fire protection
It would have been impossible for humans to survive the primitive age without the use of fire. Conversely, fire could be perilous. Fire disasters occur frequently resulting in non-fatal and fatal fatalities. In most of the fire accidents most recurrently ignited materials were the textiles, especially upholstery and furnishings. Human tissue (skin) is very sensitive to heat. It is reported that, at 45°C, the sensation of pain is experienced. The purpose of fire protective clothing is to reduce the rate of heating of human skin in order to provide the wearer enough time to react and escape. Fibres commonly used for textiles are easily burnt.

Protective clothing designed for flame protection must have two functions, ie, be flame-resistant and form a heat barrier. The latter is a very important factor if the wearer needs to stay near flames for a fairly long time. Using inherently flame-retardant materials such as Kevlar, Nomex, applying a flame-retardant finish or a combination of these methods are commonly used to make clothing and textiles flame retardant.

Heat and cold protection
Normally, human bodies are comfortable to heat in a very narrow temperature range of 28 - 30°C. Heat stress may be defined as the situation where the body cannot dissipate its excess heat to the environment is a serious problem especially during physical working. Basically, heat is transferred either as conductive, convective, radiant heat or a combination of these modes depending on the source of heat, the atmosphere, the heat absorbing material is in and the protection available against heat. Any heat transfer will have at least one of these modes and heat protection is the method to decrease or increase the rate of heat transfer.

For protection from conductive heat, the fabric thickness and density are the major considerations, since air trapped between fibres has the lowest thermal conductivity of all materials. For protection from convective heat, the flame retardant properties of the fabric are important. As for radiant heat protection, metallised fabrics such as aluminised fabrics are preferred, since metallised fabrics have high surface reflection and also electrical conductivity.

Ideal clothing for protection from heat transfer are fabrics with thermo regulating or temperature adaptable properties. Phase change materials (PCM) are one such example that can absorb heat and change to a high-energy phase in a hot environment, but can reverse the process to release heat in cold situations. The preferred fabric has core-spun yarns with a flame and high heat resistant filament core covered by a layer of flame retardant fibres consisting of at least 35% melamine.

Specifically designed protective clothing is necessary to survive and operate in temperatures below -30°C. Such low-temperature conditions are aggravated in the presence of wind, rain or snow leading to cold stress that may be fatal. The most effective method of cold protection is to avoid or decrease conductive heat loss. Clothing designed to protect from cold is usually multi-layered, consisting of a nonabsorbent inner layer, a middle insulating layer capable of trapping air but transferring moisture, and an outer layer that is impermeable to wind and water.

Mechanical impact protection
Ballistic protection is generally required for soldiers, policemen and general security personnel. Ballistic protection devices were made from metals and were too heavy to wear. Textile materials provide the same level of ballistic protection as metals but have relatively lower weight and are therefore comfortable to wear. High-performance clothing designed for ballistic protection dissipates the energy of the fragment/shrapnel by stretching and breaking the yarns and transferring the energy from the impact at the crossover points of yarns. The ballistic protection of a material depends on its ability to absorb energy locally and on the efficiency and speed of transferring the absorbed energy. Fibres like Kevlar, and ultra high modulus polyethylene are used for ballistic protection.

Ballistic protective helmet:
An advanced bomb suit and helmet that offers highest ballistic protection has been designed. The suit is constructed from Kevlar with an outer antistatic cover of 50/50 Nomex/Kevlar .The suit itself is light weight in comparison with other suits and this reduces operator fatigue and increases operator effectiveness.

Biological protection
Most natural textile fibres such as wool, silk and cellulosic are subject to biological degradation by bacteria, dermatophytic fungi, etc. Textiles designed for biological protection have two functions: first, protecting the wearer from being attacked by bacteria, yeast, dermatophytic fungi, and other related microorganisms, which cause aesthetic, hygienic or medical problems. Secondly, protecting the textile itself from bio-deterioration caused by mold, mildew and rot-producing fungi and from being digested by insects and other pests.

Fabrics designed for microbial protection should act as barriers to bacteria and other microorganisms that are believed to be transferred from one location to another by carriers such as dust or liquids. Films generally have high barrier properties against microbes and chemicals. However, films when used with fabrics to provide antimicrobial properties make fabrics impermeable to airflow leading to heat stress and other physiological problems that may be fatal. New membrane structures called ‘perm-selective' or breathable membranes have been developed that can prevent airflow through the fabric layer but have high water-vapour permeability. Using these membranes with fabrics provides effective protection from hazardous materials or microbes without causing heat stress.

Electrical protection
Electrostatic charges accumulate easily on ordinary textile materials, especially in dry conditions. Charges once accumulated are difficult to dissipate. The dissipation of an electrostatic charge occurs through shocks and sparks, which can be hazardous in a flammable atmosphere. Therefore, the presence of a static charge in textiles can be a major hazard in explosives, papers, printing, electronics, plastics, and the photographic industry. The basic principle of making an antistatic garment is to decrease the electrical resistivity or the chance of electrostatic accumulation in a fabric increases.

Radiation protection
Nuclear Radiation Protection
Special clothing to prevent exposure to radiation is needed for people working in radioactive environments. Woven cotton, polyester/cotton or nylon/polyester fabrics with a twill and sateen weave are the major types of fabric forms used for nuclear protective clothing.

UV Radiation Protection
An appropriate amount of sun bath promotes the circulation of blood, invigorates the metabolism and improves resistance to various pathogens. Penetration of UVR into the top layer of the skin leads to damage in the lower layer and produces premature aging of skin and other effects including roughening, blotches, sagging, wrinkles, squamous cells and basal cell cancer. Many people love sunbathing, thereby extending the long-term risk to their health. Persons working in the open atmosphere are also prone to keratose, the precursor of skin cancer. Terms such as near UV (290 - 400 nm), far UV (180 - 290 nm) and vacuum UV (below 180 nm) have been coined by physicists based on the properties of the radiation.

Applications

They have got a wide range of applications starting from the use in garment interlinings, tarpaulins, tents & coverings, flexible bulk/liquid containers, conveyer belts, sails, air balloons, filter products, geo membranes and tyres & hoses. Automotive applications include seat covers, interior coverings, air bags, safety belts and linings. It finds its applications in building and construction industry such as fabric coverings, tents coated roofing materials (black out/UV proof) and curtains. Household products have got a variety of uses, which include furniture upholstery, mattresses, shower curtains, curtain linings, blackout curtains, wipe clean table cloths, baby pant fabrics, ironing board covers and carpets. Life jackets, camouflage materials (Visible light, UV, Radar, IR) and extreme weather clothing systems are the few military applications. A few other applications include packaging fabrics, agricultural applications andecological applications

Conclusion

When did man became aware of safety and protection? No one can predict the exact time, but one indisputable fact is he has already taken efforts to protect himself from various vulnerabilities and he has been constantly making efforts to safeguard himself. There is no one best solution for all situations; rather selection of these apparels should be based both on risk assessment and an evaluation of the workers' specific tasks and work environments.

References

1. N Gokarneshan: Textile Asia, July 2007, 48 - 50.
2. G Demboski, and G B Gaceva: Bulletin of the Chemists and Technologists of Macedonia, 2005, 24, 77 - 86.
3. A R Horrocks, and S C Anand: Handbook of Technical Textiles, Woodhead Publishing, Cambridge, 2000.
4. D J Spencer, Knitting Technology, Pergamon Press, Oxford, UK, 1986.
5. A Book on Technical Textiles—Wood House Publication.
6. Perkin S W: Functional Finishes and High Performance Textiles, Textile Chemists and Colourists and American Dyestuff Reporter 32 (4) 2000.
7. Achwal W B: UV Protection by Textiles Colourage 2000.
8. Mallik S K, Arora T: UV Radiations -- Problems and Remedies, Man made Textiles in India 2003 (5).
9. Singh M K: Sun Protective Clothing, Asian Textile Journal 2005 (1 - 2).

Note: For detailed version of this article please refer the print version of The Indian Textile Journal June 2012 issue.

S Sakthivel
Department of Fashion Technology,
Angel College of Engineering and Technology,
Tirupur, Tamil Nadu 641 665.
M: 090479 2363.
Email: sakthi.texpsg@gmail.com.

Valarmathi Shravanthi
Department of Fashion Technology,
Angel College of Engineering and Technology,
Tirupur, Tamil Nadu 641 665.

M Vinothini
Department of Fashion Technology,
Angel College of Engineering and Technology,
Tirupur, Tamil Nadu 641 665.

E Rajadurai
Department of Fashion Technology,
Angel College of Engineering and Technology,
Tirupur, Tamil Nadu 641 665.