Microfibers that slough off so-called “machine washable” wool biodegrade three times faster in marine environments than those from untreated wool, a new study commissioned by Australia’s largest wool-grower trade group has found.
To prevent felting and shrinkage, machine-washable wool is typically treated with chlorine and coated with Hercosett, a polyamide-epichlorohydrin resin that prevents the barbed scales on the fiber surface from interlocking when moisture and heat are applied.
Scientists from AgResearch, a state-run research institute in New Zealand, claimed there was no evidence that the resin, which is essentially a plastic, added to burgeoning problem of marine microplastics, which have been uncovered in the gastrointestinal tracts of fish, turtles and whales, in most drinking water, in the majority of table salt, in the Antarctic and even human stool.
Both types of wool broke down more readily than synthetic fibers such as polyester, nylon and polypropylene, according to the study, which was funded by Australian Wool Innovation, a not-for-profit that represents more than 24,000 Australian woolgrowers.
To measure fiber degradation after washing, researchers employed scanning electron microscopy and energy-dispersive X-ray spectroscopy. Kraft paper pulp, which breaks down rapidly in water, was used as a point of comparison.
Compared to paper, which was assigned a score of 100, machine-washable wool scored 67. Viscose rayon made from cellulosic fibers earned 64 and untreated wool 20. Polyester made from fossil fuels, unsurprisingly, racked up a meager 6.3.
“Both types of wool biodegrade to a high degree, as does the cellulose-based viscose rayon,” the researchers wrote in a paper. “Synthetic fibers show little or no biodegradation.”
They surmised that the polyamide-epichlorohydrin treatment caused the wool to biodegrade more rapidly because it removes some of the fiber’s cuticle, making it more susceptible to microorganisms in the ocean that target keratin, a structural protein found also in hair, nails, feathers and horns.
The scientists referred to water-logged archaeological deposits, where human hair and woolen textiles are sometimes preserved because of lower microbial activity.
“Based on observations from soil biodegradation we expect that over a relatively short time wool will biodegrade completely in the marine environment,” they added. “The rate of biodegradation for untreated wool is likely to increase to be similar to that of machine-washable wool once its cuticle is broken down.”