Chemistry Reference
In-Depth Information
by the random chemical structure of silk (only a limited number of amino
acids in the sequence are able to adsorb nickel), resulting in areas that
contain nickel while other areas are nickel-free. Secondly, variation of the
relative amounts of carboxylic, cyanide and keto groups in the structure of
the PAN resulted in an increased uptake of nickel. This observation also
indicates that the presence of functional groups and their distribution in the
chemical sequence of the polymeric fibre affects the uptake and distribu-
tion of nickel. A non-uniform distribution of the functional groups able to
coordinate with nickel in the silk structure probably explains a non-uniform
nickel distribution at the surface of and in the fibre, which explains the rel-
atively high specific electrical resistance.
From the above results, it can be concluded that PAN fibres resulted in
the desired conductive behaviour and will be used further in this investi-
gation. Microscope images of the cross-section of PAN fibres treated with
NiCl
2
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.
11.2.3 Optimisation of the PAN-fibre production
PAN fibres are produced mainly from acrylonitrile copolymers processed
in water-rhodanate, dimethylformamide or other solvents. It was found that
fibres produced by the first of these methods show the highest porosity
(higher capacity for metal uptake) and, as this process is performed in
water, there is less pollutant. Therefore, it was chosen to use this type of
processing for parameter optimisation. Mainly three parameters of the pre-
cipitation bath determine the structure of the PAN fibres: concentration of
NaCNS, temperature and plasticisation drawing. The formation of the fibre
itself, before entering the precipitation bath is performed on a laboratory
wet-spinning device using a 12% solution of co-polymer (92.4% acryloni-
trile, 6% methylacrylate and 1.6% itaconic acid) in 51.5% NaCNS. In order
to determine the optimal values for the parameters of the precipitation
bath, PAN fibres were produced under different conditions and were sub-
sequently treated with a 1.0 mol l
-1
NiCl
2
or CoCl
2
solution, containing
1.5 mol l
-1
of rongalite. The treatment process was interrupted at different
times, an excess of liquor was removed, and the fibre was dried, thermofix-
ated at 413 K for 20 min and washed until negative reaction was observed
against metal ions of Ni or Co.
