3D spacer fabrics for protection against heat

As part of the HEATex research project, a functionalised, three-dimensional underwear is being developed for use under conventional protective clothing at heat-exposed workplaces, say Lukas Lechthaler, Marie-Isabel Popzyk, Christoph Peiner, Thomas Gries and Markus Tutsch.

In Germany, around 10 per cent of the workforce is exposed to high temperatures in their workplaces (metal, glass, ceramics and steel production as well as forges, foundries, fire brigades, etc.) [1]. At these workplaces, employees are exposed to extreme heat due to the working and environmental conditions. In addition to intense physical exertion, an increased ambient temperature can lead to an increase in body temperature (regularly 37° ± 0.5°C) and thus to life-threatening heat shocks (from 40°C). This danger can be countered by using suitable protective clothing. [2; 3; 4]

Concerning conventional protective clothing, the protection is mainly provided by the outer layers of adhesive. In contrast to this, the current research project “Development of heat-exposed industrial safety textiles” (HEATex) focuses on the deeper layers of clothing. Usually conventional cotton underwear is used here to absorb moisture, while the outer layers protect against heat radiation and burns. The cotton is in direct contact with the skin and can absorb and store large amounts of moisture from the body due to its good absorption behaviour. The stored moisture is heated up from the outside, which is not absorbed by the outer layer of the protective clothing. This can lead to scalding and overheating due to the workers’ own body sweat. Pressure-loaded areas are critical in particular, as they hinder air circulation and thus a possible cooling effect. If the layers of clothing are compressed due to the pressure load, the skin comes into direct contact with the underwear, so that moisture is prevented from being removed and scalding is intensified.

Functionalised 3D textile
The share of all occupational accidents caused by overheating and scalding is around 50 per cent for heat-experienced jobs in Germany. The aim is to reduce this proportion to 10 per cent by using this innovative, functionalised 3D underwear. The solution lies in the use of specially designed and developed underwear for high temperatures. A locally reinforced 3D spacer fabric is used. On the one hand, this prevents scalding by avoiding direct skin contact and, on the other hand, protects against overheating by removing moisture. Pressure-loaded areas in particular are locally reinforced to reliably prevent contact between the skin and the overlying layer of protective clothing.

The layers of the 3D spacer fabric are designed, produced and validated. Spacer fabrics generally consist of two parallel layers of knitted fabric which are held apart by a third layer of thread (pile threads, usually rigid monofilaments). An insulation layer is created by the air entrapment between these layers. To prevent scalding, this insulation layer must be maintained throughout the entire use. In highly stressed areas (knees, elbows, shoulders, back), local reinforcements must therefore be used via stiffer, distancing pile threads. According to current research, there is no possibility of changing the stiffness of the pile yarn during the process.

Approach
The basic concept of protective clothing is a structure consisting of different layers. The various layers include, on the one hand, the spacer fabric and, on the other, layers that can absorb and reflect heat flows via various physical mechanisms.

The layer structure must transport water absorbed by the body (sweat) to the outside (high diffusibility) without absorbing water itself or conducting too much heat to the skin (low thermal conductivity). Here there is a conflict of objectives between high contact area between textile/skin (better moisture removal, but also higher heat conduction) and low contact area (better insulation effect, but lower moisture absorption). Good ventilation and diffusion properties are ensured by a large cross-section and an open mesh structure. In addition, the contact between the upper layers and the skin is reliably suppressed by a high resilience of the spacer fabric. The layer structure provides a shielding against heat radiation from the heat source by means of a low transmissivity and a high degree of reflection. In addition, a latent heat accumulator based on a phase-change material (PCM) can be used to compensate for the heat input into the deeper layers. In addition, there is a reflective layer through which heat radiation is reflected and thus absorbed together with less heat.

Acknowledgement
The research project is funded by the German Federal Ministry of Economics and Energy within the framework of the Central Innovation Programme for SMEs (ZIM) on the basis of a resolution of the German Bundestag. Within the scope of this project, ITA would like to thank its research partner STS Textiles GmbH, Grünbach, for the constructive cooperation.

References
[1]TÜV Rheinland: Hitze-Check am Arbeitsplatz H.E.A.T Analyse – Objective Klimamessung nach DIN EN 27243 und Beurteilung der Hitzebelastung am Arbeitsplatz URL: http://www.presseportal.de/pm/31385/2279470 Zugriff am 24.11.2016

[2]Atemschutzunfälle: URL: http://www.atemschutzunfaelle.de/unfaelle/eu/ Zugriff am 01.09.2015

[3]Kales, S. N.; Soteriades, E. S.; Christophi, C. A., Christiani, D. C.: Emergency Duties and Deaths from Heart Disease among Firefighters in the United States The New England Journal of Medicine, Vol. 356, no. 12; 22. März 2007

[4]NN: Unfallstatistik der Feuerwehr-Unfallkassen FUK Mitte und HFUK Nord Der Sicherheitsbrief, 37, H.1/2015, S. 6-8

Lukas Lechthaler, Marie-Isabel Popzyk, Christoph Peiner and Thomas Gries are from the Institut für Textiltechnik of RWTH Aachen University. Markus Tutsch is with STS Textiles GmbH & Co. KG, Grünbach.