Mordant-free Natural Dyeing of Cotton Fabric

Natural dyes, while biodegradable, are usually used together with mordants to enhance dye uptake due to natural dyes’ poor affinities with textiles. However, mordants may contain heavy metals that cause severe contamination of water sources. To address this issue, this project has developed a mordant-free natural dyeing method.

An Innovative Natural Dyeing Solution

The project uses metal organic frameworks (MOFs) to functionalise the fabric surface, making dyeing more effective. The process begins by dipping the fabric in an ultrasonic bath or a padder containing a metal ion solution and a ligand ion solution. This facilitates the formation of MOFs, a class of compounds consisting of metal ions and ligand with pores in between, on the fabric surface.

After that, the functionalised fabric is processed with natural dye in a water-based bath. The pore size in the MOFs can be optimised to permit adsorption of various dyes, thereby enhancing dye uptake without the use for mordants.

The porous structure of MOFs allows the adsorption of various dyes, thereby enhancing dye uptake

MOF-functionalised cotton fabric (top) show more notable dyeing performance

 

Enhancing Dyeing Performance

This mordant-free dyeing method offers at least a 50% higher dye uptake than the conventional natural dyeing method. MOF-modified fabrics also meet four AATCC standards of colourfastness at a level no lower than 3.5. Additionally, fabrics dyed by this mordant-free dyeing method have excellent antibacterial properties, notable biodegradability and cause no skin irritation.

Project video

Showcasing the project in the International Exhibition of Inventions Geneva

 

The modification of fabric surfaces using MOFs has great potential to replace the use of mordants as fixatives of natural dye, while encouraging the use of natural dye as an alternative to synthetic dye. This method mitigates pollution in effluent and greatly reduces the cost of wastewater treatment. The project received a Gold Medal in the International Exhibition of Inventions Geneva 2023, highlighting its innovative and environmental significance.

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