Traditional carpets consist of yarns stuck to a backing fabric by an adhesive – usually synthetic latex. As part of the production process, the latex is cured at high temperatures, but this creates a non-recyclable material as the latex is almost impossible to remove at the end of a carpet’s life. As a result, almost all carpets are disposed of by burning in an incinerator.
With a view to finding a more environmentally friendly solution to carpet disposal, Tzanko Tzanov and his team at the Polytechnic University of Catalonia in Barcelona, Spain, decided to replace the synthetic latex with an organic lignin-based adhesive to produce a renewable woollen floor covering.
Lignin is an aromatic polymer that reinforces cellulose fibres in plants and is readily available as a waste product of paper and biofuel production. It can be easily converted into an adhesive using laccase, an enzyme found in plants and fungi. ‘Lignin is transformed by an oxidative enzymatic process that activates the phenolic structures, which can then react chemically with the wool fibres and bind them to the backing,’ explains Tzanov. The process is carried out at much lower temperatures than in latex production – around 50°C rather than 150°C – making it much more environmentally friendly.
The laccase enzymes that convert lignin into an adhesive are also involved in its biodegradation, meaning that the carpets can be recycled at the end of their usable life. Instead of being incinerated, the carpets are shredded and returned to nature, where they degrade and can be used as a soil fertiliser.
Diego Moldes Moreira, an expert in natural products and bioprocesses at the University of Vigo in Spain is impressed by the innovative and sustainable solution. ‘We could expect to find the proposed biotech carpets in stores in the short–medium term,’ he says. In fact, Tzanov’s team are already working with Dutch companies, James and Best Wool Carpets, on an industrial scale-up.
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