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and similar chemical substances. The coating consists of a multi-layer, 500 nm composite
coating with incorporated immobilized enzymes in polycationic/polyanionic polymer
layers. The reactive layers benefit from high stability and can destroy hazardous
chemicals for long periods of time. Pesticide tests using natural and synthetic textile
fibres coated with the NRL catalytic enzyme system demonstrate its high neutralization
capability and robustness in comparison with traditional chemical decontamination
systems. Substantial R&D efforts are currently striving towards an additional increase in
the stability of the system and the realization of suitable industrial procedures for the
coating of various fibre materials and the consequent mass production of protective
clothing.
Figure 3.5 From left to right: A cotton thread coated with the NRL enzyme catalytic system (A)
and woven into a piece of textile fabric (B). Following contact with a pesticide solution, the textile
takes on a yellowish colour (C) that is characteristic of the completed neutralization process
(source: Naval Research Laboratory)
At the Nanotech Institute of the University of Texas in Dallas, researchers have
developed a method for creating a multi-layer, tear-proof yarn from multi-walled carbon
nanotubes. The yarn has a tensile strength of more than 460 MPa and has cushioning
properties that approach those of materials used for bullet-proof vests, such as Kevlar.
The nanotubes, which are grown individually on a substrate in a ‘nanotube forest’, are
mechanically extracted and twisted into yarn at the same time (see Figure 3.6). Unlike
normal fibres and yarns, the strength of these nanotube yarns is not decreased by
knotting, and their flexibility and strength is retained even after heating them to 450°C
for an hour or immersing them in liquid nitrogen. The mechanical properties of the
nanotube fibres can be further improved by combining them with polymer fibres —
without impeding electrical conductivity. The main focus of further development efforts is
on the production of longer yarn lengths for industrial production. To date, yarn lengths
have reached 50 m with a diameter of 2 µm at a production speed of 80,000 turns per
minute. In comparison, conventional textile fibres with a diameter 80 times larger have a
production speed of 1,000 turns per minute.
Figure 3.6 Dry spinning of a carbon nanotube yarn from the edge of a multi wall carbon
nanotube forest (source: Baughman/University of Texas)
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