Metal-free process makes plant dyes more durable for textiles

A study published in the International Journal of Materials and Product Technology describes a metal-free dye-fixing process that could make natural plant dyes more practical for high-performance textiles.

Natural plant dyes are biodegradable and generally produce less pollution than synthetic dyes, but they fade easily when worn, washed, or exposed to light, limiting their use in functional clothing such as antibacterial or insect-repellent fabrics.

The new method replaces conventional metal salts, known as mordants, which are major contaminants in wastewater from the textile dyeing sector.

The fixation system uses a modified form of chitosan, a biopolymer derived from sources such as crustacean shells, together with ellagic acid, a compound found in many plants.

Dyes are held in place through electrostatic attraction between electrically charged molecules and hydrogen bonding, stabilizing the dye without permanently altering the fabric.

Researchers also optimized dyeing conditions — including temperature, acidity, and steam treatment — to improve dye uptake while preserving the fabric's functional properties.

In tests on antibacterial fabrics, about 70% of the dye remained on the fabric after 25 washes, with water- and light-fastness remaining high even after many hours of exposure.

Antibacterial performance stayed above 90% after repeated washing, indicating the process maintains the fabric's intended function.