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UV Technology: Applications in the Textile Industry

Most of the difficulties in applying conventional UV polymer curing technology to textiles are associated with the polymer systems, their constituents and the means of application to the textile surface.

One major problem is that most textiles are highly absorbent and capillary attraction of the fibres tends to draw the liquid polymer film away from the fabric surface and into the bulk textile. Since UV light cannot penetrate beyond the surface fibres, this results in uncured resin remaining inside the textile structure. Another problem is the effect of the cured polymer on the handle and drape of the fabric. The high level of crosslinking common for UV-cured polymers tends to produce rigid inflexible fabrics, unsuitable for apparel use.

An alternative approach has recently been developed by CSIRO using UV radiation to modify the fabric surface whilst leaving the bulk textile unaffected. Surface modification is particularly useful on natural fibres such as wool and cotton, where the engineering of fibre and fabric properties, now commonplace for synthetics, is precluded.

Applications for textiles

UV treatment can add value in colouration (dyeing and printing), since it is predominantly
surface fibres in a fabric that absorb, reflect and scatter light. Photomodification of the
surface fibres can allow :-
more dye or pigment to become fixed, producing deeper shades
more rapid fixation of dyes
dye fixation under less severe conditions (eg. lower temperature)
use of stencils before dyeing to produced intricate patterned effects
increased wettability of hydrophobic fibres to improve depth of shade in printing
for knitted wool and cotton fabrics, the problem of pilling (the formation of
unsightly balls of fibre on the fabric surface) can be eliminated.

Modifying dye affinities

There are two main commercial aims for studying the effect of UV radiation on the dye
uptake of various textiles. The first is to improve quality and production efficiency of fabrics dyed with heavy shades, especially black and navy blue. The second is to reduce the cost of producing patterned fabrics, which would normally be printed or colour woven, by selectively UV-irradiating the textile through a stencil and then dyeing. Using suitable dyes this process can produce large variations in shade between irradiated and unirradiated regions. Heavy black and navy shades on wool are important for formal business suits. Chrome dyes are preferred since they are inexpensive and have good evenness and fastness properties. However chrome dyeing requires long, energy intensive dyeing cycles which can cause significant fibre damage, colour matching is difficult and there are environmental concerns over the release of chromium residues in dyehouse effluent, particularly in the form of toxic Cr (VI). Recently deep black shades with excellent evenness have been achieved on UVtreated wool using dyes which require no Cr (VI) aftertreatment.

Preparation for printing on wool

Wool is a particularly difficult fabric to print, since each fibre is coated with a thin layer of hydrophobic lipid making the wettability of untreated wool similar to Teflon. To obtain good prints on wool it is essential to modify the fibre surface using a pretreatment, usually oxidative chlorination. Chlorination has limitations, both for the fabric (yellowing and poor evenness) and for the environment due to the release of adsorbable organohalogens (AOX) in effluent. The Siroflash process involves continuous UV exposure of wool, followed by a mild wet oxidative treatment with hydrogen peroxide. The fabric UV irradiation machine is shown below. Siroflash is a very even pretreatment, producing a bright, white base fabric for printing.

Prevention of pilling

The important factor in the mechanism of pilling is the existence of strong anchor fibres that bind individual pills to the fabric surface. By selectively<

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