Mountains of sorted clothing at one of the facilities where H&M recycles clothing. The company was accused of burning 60 tons of recyclable garments in 2017. Credit: GQ

Mountains of sorted clothing at one of the facilities where H&M recycles clothing. The company was accused of burning 60 tons of recyclable garments in 2017. Credit: GQ

Another waste issue created by textile industry - Microfiber Pollution. Synthetic fibres used by fast fashion will contaminate our ocean; the picture is a clump of acrylic fibres seen under microscopes. Credit: University of Plymouth

Another waste issue created by textile industry - Microfiber Pollution. Synthetic fibres used by fast fashion will contaminate our ocean; the picture is a clump of acrylic fibres seen under microscopes. Credit: University of Plymouth

 
 
 

Investigate Waste Problems from Textile Industries

The textile business is problematic. Due to the fact that the discharged wastewater from textile industry carried large amounts of chemicals, not to mention its energy consumption, air emissions, solid wastes and odours. On the other hand, the recent raising of the fast fashion business has no doubt increased our concern about the textile wastes, toxic chemical uses and microfiber ocean pollutions. The twelve-dyes project was motivated by providing feasible solutions for such environmental issues, and we primarily focused on the dye waste issues from the textile industry.  

Women walk past tannery wastewater that is being pumped from a factory straight into the street, in Cairo’s Ain el-Sirra district. Credit: Reuters

Women walk past tannery wastewater that is being pumped from a factory straight into the street, in Cairo’s Ain el-Sirra district. Credit: Reuters

The composition of textile waste stream will vary depending on the fabric being dyed, the colours, and the method of dye application. For this specific case, the fabric of interest is silk, the method of dye application is printing and the pigments making up the colour were unknown. The expected compounds in the waste stream are a.o. urea (necessary for fixing the dyes to the fabric), thickeners, detergents, defoamers and dye pigments.

 
 

In order to identify the pigments which were present in the waste stream, registration information from the European Chemicals Agency (ECHA) for the printing company was acquired. The company had 12 dye pigments registered. Also, previous laboratory experiments separating the different dyes in the waste stream showed blacks, purples, oranges and blue present in the mixture. These 12 dyes are mainly reactive, which means that these dyes can bind to the chemical groups in the fabric without any help.

Dye mixture sample  (1:100 dilution ratio). 

Dye mixture sample  (1:100 dilution ratio). 

 
 
 
Aliki's research on upcycling waste inks. Courtesy of Aliki van der Kruijs

Aliki's research on upcycling waste inks. Courtesy of Aliki van der Kruijs

 
 
 

 Fading Out

 
 

How does a pigment get its colour? Compounds which can absorb light with certain wavelengths will have a visible colour. In the chemical structure of ten out of twelve dyes a double bond between two nitrogen atoms is present, called an azo bond.

 
 
General chemical formula of azo compounds. Credit: Wikipedia

General chemical formula of azo compounds. Credit: Wikipedia

 
Structure of Azobenzen. Credit: Sigma-Aldrich

Structure of Azobenzen. Credit: Sigma-Aldrich

 
 

The azo bond is the one mainly responsible for the absorption of light, but further absorption is assisted by several other groups which are close to this bond. These extra groups can increase the wavelength of light which can be absorbed, meaning that the compound will have a more red colour. Seeing that the azo bond is the primarily responsible for the colour, the first step in decoloration is breaking this bond.