Metallisation conductive fibres

A final method is metallisation11 of fibres, which is most related to the technology described in this chapter. In this method, metal salts are taken up by the fibre and reduced to their metallic conductive form. Metallisation can be achieved in different ways. A first way is by a vacuum metal spray. However, this results in very poor defined metallisation. In addition, galvanic coating is used in the production of conductive fibres, but this type of coating requires a fibre that is already conductive. 

Metallisation is a process in which a metal ion is absorbed by a conventional fibre, followed by chemical reduction of the absorbed metal ions to its metallic phase. In this case, conduction is also obtained through the entire fibre but with a limited rate, dependent on the density of metal ion absorbed in the fibre and adsorbed at the surface of the fibre. 

From the above results, it can be concluded that PAN fibres resulted in the desired conductive behaviour and will be used further in this investigation. Microscope images of the cross-section of PAN fibres treated with NiCl2 show that after thermofixation of the fibre, no swelling is obtained. Therefore thermofixation will be an important step in the production process and will also be taken into account in the following steps of this investigation. Finally, it should be pointed out that similar absorption behaviour of PAN fibres for Co and CoS was observed but, contrary to Ni, this led to much weaker electroconductive properties of the metallised fibres. 

The main purpose of middle layers is to provide additional (thermal) insulation. Nowadays, these layers are often made of fleece materials with good air entrapment properties. Their thermal conductivity (typically 0.03-0.04 W/mK) is near from air (0.026 W/mK). The thermal resistance of such layers is directly correlated with their thickness, provided that no air movement occurs within the fabric. Thermal conductivity and air permeability also are generally dependent on the fabric density (Yip and Ng, 2008). Conduction has been shown to be the main heat transfer mechanism through textile layers as long as the fibre volume fraction is higher than 9% (Woo et al., 1994). However, materials with very low density (like spacer materials) allow radiant and convective heat transfer. This was demonstrated by Das et al. (2012) who compared a spacer fabric middle layer with two non-woven middle layers and showed that the contribution of this spacer fabric to the overall insulation was higher than the two other samples in a non-convective mode, while it was the lowest in a forced convective mode. The positive effect of metallised interlayers with low emissivity on the reduction of... 

Synthetic fibres take a static charge because they are non-conductive and only absorb small quantities of water. This effect is reinforced by low air humidity, particularly in winter, and soiling may be increased. Antistatic finishings reduce the high electrical resistance of fibres. These consist of hydrophilic surface active polar compounds (tensids), carbon particles, electrically guiding polymers or salts. Textiles may also be made antistatic by incorporating metallic or metallised fibres or conductive carbon fibres which are coated with polyamide. 

Conductive additives Carbon black, carbon/graphite fibres, metals, metallised fibres/reinforcements... 

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