press information

24-Jul-2012 | 410-EN

High tech textiles for security personnel

More function and comfort

BÖNNIGHEIM (dd/ri) Workwear has many requirements to fulfil, including a uniform appearance and consequently a high degree of memorability. Police officers for example can always be recognised by the well-known colours and shapes of their uniform. In addition to a flawless appearance, workwear also has to provide the wearer with a high level of wearing comfort and should be suitable for industrial cleaning. But functionalised textiles have a lot more to offer!

Special textiles are the ideal solution for effective protection against harmful UV radiation.
©Hohenstein Institute

Textiles as UV protection

Clothing with integrated sun protection is an example for this. The textile fibres contain titanium dioxide which is also used in sun protection creams, providing the wearer with a particularly high level of UV protection. Because clothing covers most of the body, it is predestined for protection from harmful UV radiation.

Different measurement methods exist for determining the UV protection factor UPF (Ultra Violet Protection Factor) which corresponds to the sun protection factor in creams. The measurements according to UV Standard 801 are particularly realistic as they take into account factors such as the change in UV protection of textiles through wearing and cleaning. For clothing textiles the UPF is therefore not only determined on the new item but also after stretching, when wet and after mechanical wear through wearing and textile care. It furthermore assumes the worst case scenario of the highest UV radiation level (sun spectrum in Melbourne, Australia at the height of the Australian summer).

Textiles with dirt and odour protection

Nature's so-called lotus effect has been known for some time. Dirt on the leaves of the lotus plant can easily be washed off with water. The basic principle has also been used for textiles for some time. Until now, the surfaces of the materials were additionally finished with hydrophobic (water-repellent) micro and nano structures. Researchers have now developed the lotus effect further: The nano particles are directly incorporated during production of the fibre, making the dirt-repellent effect resistant to intensive wear.

Another option for the use of nano particles is to embed silver into materials. The antimicrobial effect of silver has been known for centuries; one of its uses is water purification. It can be embedded into the fibres or applied by vapour-depositing. The electrically charged particles (ions) of the silver are effective against a multitude of micro-organisms, preventing the transmission of germs through textiles or the increase of (body) odours. Today, modern test methods even allow quantitative measuring of the effect of textiles against formation of odours and the adhesion of odour molecules to the fibres.

Textiles for (in)visibility

The functionalisation of textiles can achieve many other remarkable properties. A current example from textile research are textile materials which effectively shield infrared radiation (IR) and are intended for use in the uniforms of armed forces. Until now, IR-absorbing vat dyes in camouflage print ensured that the wearers were mostly “invisible” to the CCD sensors (charge-coupled device – a light sensitive electronic component) of night vision devices. The absorption capacity of the dye particles quickly reaches its limits, though. Dotation (embedding) or coating of chemical fibres with indium tin oxide nano particles (ITO) allows significantly more efficient absorption of heat radiation, achieving a higher shielding effect than conventional camouflage prints.

ITOs are transparent semiconductors which are also used e.g. in touch screens for smartphones. The challenge for many researchers was to fuse the ITO particles with the textiles in a way that does not negatively affect their other properties such as the physiological comfort. Furthermore it has to be ensured that the textile finish is resistant to washing, scrubbing and weathering.

Based on the results of the research of the scientists from the Hohenstein Institute in Bönnigheim and the ITCF Denkendorf, the IR-absorbing textiles are to be further optimised with regard to heat and perspiration management in future projects. The aim is to prevent the formation of telltale near and mid IR radiation in the form of emitted body heat, impeding detection even further. Optimum support of the physiological processes in the human body also ensures unrestricted capacity and ability of the wearers even under extreme climate conditions or during physical exertion.

Especially in road traffic, however, textiles are not meant to aid camouflage but rather to improve visibility for others. Fluorescent materials are particularly important for visibility during the day. During dusk and dawn and at night, good visibility is mainly provided by reflective materials. Retroreflective materials reflect most of the oncoming light back in the direction of the light source (car headlights etc.), regardless of their orientation.

By contrast materials which are only labelled as “reflective” will reflect light evenly in all directions, but less intensely in the direction of the light source. With regard to visibility for other road users this can be a disadvantage. High-quality high-visibility warning clothing as stipulated for the personal protective clothing (PPC) of police and fire services therefore uses a combination of retroreflective and fluorescent materials. It is important that the requirements of DIN EN 471 regarding the warning effect of the textiles are not only met by new textiles but – with regard to economic efficiency – also by textiles having undergone as many processing cycles in a commercial laundry as possible.

Spectroscopic testing can be used to determine how much radiation textiles absorb or reflect, fulfilling functions such as UV protection, warning effect or IR absorption.
©Hohenstein Institute

Textiles influence capability

Science has been examining the connection between clothing and human physical capability for several decades. Today, standardised laboratory tests can be used to objectively evaluate the physiological comfort of textile materials, garments and clothing systems. Textile products can therefore be optimised to optimally support the body functions of the wearer and prevent the serious effects of lack of comfort. It is important here that heat and moisture management as well as the sensation on the skin (sensory skin functions) are adapted to the climate at the place of use and to the intensity of the physical strain for the wearer. Sports science has found that physical fitness can be effectively increased by clothing with high physiological comfort. A lack of comfort however correlates to a decrease in concentration and condition, physical deficits and even lasting damage to the wearer's health. The scratchy feeling of stiff materials on the skin alone can be distracting and affect the wearer's acceptance of the garments.

Scientists from the Hohenstein Institute have examined in how far clothing can actually influence the mental capacity of the wearer in a current research project. Test subjects had to fulfil a demanding task with high concentration in a specially developed “stress box”, wearing clothing of different qualities. After the stress phase the mental capacity of the test subjects was tested with a new software test system comprising international standards of occupational psychology. Testing included the undivided concentration as well as the multitasking capability of the test persons.

The results of the study prove that under constant environmental conditions test subjects wearing high-quality clothing had better overall results than test subjects in clothing of lower quality. In addition to fast reactions the lowest possible error rate was the main focus of testing. The researchers can now measure this error rate depending on work situation and clothing. The new test system will help to improve selection and adaptation of workplace-specific clothing to the mental capacity and the work result in the future, allowing manufacturers of clothing for health service, military or civil defence (police, fire brigade) to benefit from the new method.

The use of different textile materials takes into account the spatial distribution of temperature and moisture emission to different body areas during the so-called comfort mapping process. Wind-proof textile material in the chest and back area wards off e.g. cold wind while an especially breathable and moisture-wicking textile material in the underarm area ensures a drier climate.

Comfort mapping combines textiles with different properties to achieve best possible functionality: For example UV protection and durability in the shoulder area, UV protection and elasticity in the back and sleeve area as well as breathability in the underarm and stomach area.
©Hohenstein Institute

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