Researchers at Iowa State University in the US experimented with the use of used coffee grounds as a sustainable textile dye.

The textile industry uses more than 2 million US tons of chemicals and synthetic dyes annually, which often contain toxic compounds that pollute water. Natural dyes offer a sustainable alternative for the colouring of textiles and fabrics.

Daily, billions of cups of coffee are consumed worldwide, which means coffee grounds are available in abundance.

Working with leftover coffee grounds from local coffee shops, the researchers dried the grounds and then left them boiling for three days in purified water to extract the dye. The coffee dye was tested on cotton, linen, rayon, silk, and polyester mixed with various mordants, which help the dye bond to the fabric and reduce fading. They used copper [II] sulphate, ferrous sulphate, and aluminium potassium sulphate. The various mordants resulted in a greater variety in shades of brown.

Natural dyes, as opposed to synthetic dyes, have as downside (or upside, depending on your point of view) that it is very difficult to produce the same colour in the next batch. For the coffee dye, the coffee grounds available could come from different beans or the coffee could be brewed twice, which influences the resulting colour.

The researchers are currently experimenting with the coffee dye and cellulosic fibre from kombucha tea to make shoes.

Photos: Iowa State University / Needpix