A Comparative Study of the Environmental Impacts of Standardized Dyeing Systems Using Natural and Synthetic Dyes on Knitted Cotton Fabric

Cotton apparel is universally accepted, comfortable to wear and remains in high demand. The 2016-17 global forecast for cotton consumption is 21.81million metric tons and has remained relatively stable since 2014-2015. Traditional manufacturing practices for cotton consumes large amounts of water, energy and chemicals as well as discharging large amounts of polluted effluent. Textile dyeing has been blamed for up to 20% of all global industrial wastewater pollution.;With cotton apparel, we are faced with the multi-faceted and complex balancing act of strong market demand for the end product versus the negative environmental impact resulting from old and traditional manufacturing technologies. The challenge is to find new synergies in dyes, colorants and manufacturing technology to apply color to cotton while reducing the negative environmental impact from manufacturing. The objective of the research is to identify select processing parameters for use in comparing the dyeing efficiency and environmental impact of various dyeing systems for cotton.;Cotton was originally dyed using natural colorants coupled with toxic heavy metal mordants. Synthetic versions of natural colorants were introduced and used before the introduction of direct dyes. Direct dyes provided the mills a more robust means of applying color using electrolyte and temperature. Early direct dyes were limited by their moderate to poor wet fastness and eventually were replaced with fiber reactive dyes. Fiber reactive dyes have evolved to provide satisfactory results using lower amounts of water and energy. A recent improvement in fiber reactive dyes increased the dyeing efficiency, which results in more color going on the fabric and less color going down the drain as waste.;Water usage, steam consumption, cycle time, impact of effluent, and dyestuff efficiency were the processing parameters selected for comparison using a Weighted Parameter Evaluation. A representative set of dyeings from the study was submitted for a limited panel of apparel fastness testing. Since fastness testing is not directly related to dyestuff efficiency and impact on the environment, the data from fastness testing was used only for relative comparison of the various types of colorants and dyes and was not included in the Weighted Parameter Evaluation.;When the Weighted Parameter Evaluation data for natural colorants was compared to data for synthetic dyes, the petroleum based, synthetic dyes produced the best overall scores, thus confirming the hypothesis.;When the petroleum-based synthetic dyes were compared to each other, the sequential improvements made over time were apparent. Direct dyes performed better than natural colorants. First generation fiber reactive dyes displayed improved performance and lower environmental impact than direct dyes. And finally, the newest iteration of fiber reactive dyes, poly-functional dyes, recorded the lowest amount of water usage, steam consumption, and cycle time, plus had the highest dyestuff yield of all systems evaluated.