Unraveling wool yellowing

27 Jan, 2009 08:53 AM
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Scientists expect to identify why wool 'yellows' when exposed to sunlight for extended periods of time, and the role played by genetics, environments and trace minerals.

While wool has many valued qualities that are superior to other textile fibres, its intrinsic cream colour and tendency to yellow in sunlight are impediments to the production of bright white and pastel shades, which are so in-demand by today’s modern consumers.

Investigations being conducted under the Sheep CRC’s post-graduate research program aim to resolve the biological mystery and the consequent marketing issue.

Based at the CSIRO's Materials and Science and Engineering Division, Belmont, Victoria, Lee King says it makes sense to understand why wool yellows in the first instance.

"Fluorescent whitening agents can be applied to initially improve the colour. But they also cause significant yellowing of the wool upon exposure to sunlight," she says.

"The inability to produce bright white photostable wool products prevents it from being the fibre of choice for important market niches, such as baby wear, fashion knitwear and leisurewear."

In technical terms, wool yellowing involves the production of free-radicals which are generated as wool absorbs light.

These radicals react with the protein to yield yellow compounds and their production is significantly increased in the presence of trace metals - particularly copper, iron and manganese.

Ms King explains that trace metals are always present in wool and are not removed during processing.

They are bound within wool protein during fibre formation in the follicle and possibly via absorption from the environment. Their concentration in wool is expected to be related to the genetics, diet and the environment of the sheep.

"To understand how we might manage this costly problem, we'll source wool from the eight CRC Information Nucleus flocks spread across Australia," she says.

"They'll represent different genetic backgrounds and bloodlines, environments and soil types.

"Samples will be scoured, the colour measured and then rigorously cleaned.

"Trace metal contents, wool colour, fleece physical properties and genetic data will be evaluated.

"This will then provide insight into the genetics and biochemical mechanisms associated with wool colour and yellowing."

Sheep CRC Postgraduate co-coordinator, Dr Graham Gardner, says this research is one example of the Sheep CRC’s scholarship program to investigate key production issues and train tomorrow’s scientists.

PhD and Masters Degree projects are currently available at sites across the CRC network.

Sheep CRC

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