Synthesis of black natural dye from locally available, sustainable and commercially viable ingredients

Abstract

The textile industry, ranked as the second-largest polluter globally, significantly contributes to water pollution by using synthetic dyes and other chemicals in textile treatment processes. In response to the growing global interest in green chemistry and sustainability, leading multinational companies are urging textile industries to adopt more sustainable practices. As a solution to this issue, there is a shift towards replacing synthetic dyes with natural dyes, which offer greater sustainability, biodegradability, and environmental friendliness. Among various color shades, obtaining a natural black dye poses a greater challenge, making it a focal point of interest for industries seeking alternatives. In this research study, the objectives were to identify locally available, sustainable, and commercially viable sources capable of producing black shade, to check the affinity of the dye with the fabrics, and to compare the colour strength of natural black dye with synthetic black dye. The focus was on using the obtained natural black dye to dye synthetic fabrics such as Nylon. The combination of Terminalia chebula and Caesalpinia sappan, along with Ferrous sulphate (FeSO4) as the mordant was employed in the production of the natural black dye. Moreover, the exhaust dyeing method was employed at 98 ºC for 90 minutes, at pH value of 5.5 for maximum extraction and absorption of dye to the Nylon fabric. In the research study, Terminalia chebula and Caesalpinia sappan were found to produce a blueish-black colour which closely resembled the shade of synthetic black dye. Although natural dyes are typically recommended for use with natural fabrics, the produced natural black dye exhibited good performance on synthetic Nylon fabric which was tested using ISO standard methods. The natural black dye that was produced showed excellent colorfastness in terms of colour change and colour staining, while exhibiting moderate colorfastness in relation to wet and dry rubbing which was indicated that the black dye had satisfactory colour fastness properties on Nylon. To ensure sustainable measures, the exhaust dyeing technique was employed with minimal usage of resources, chemicals, and energy. Comparative analysis using Data colour spectroscopy confirmed that the natural black dye developed in this study closely resembled the synthetic black dye commonly used in industry. The attempt of industry to find natural black shade, which is a challenging colour to achieve, exhibited promising results and replacing synthetic black dye in industry with natural black is somewhat succeeded. To improve adhesion and shade of the dye, the following methods are recommended; such as, to treat the produced natural black dye with alkali reduction methods to improve adhesion to fabric surface, and to isolate the chebulic acid from Terminalia chebula and to isolate brazilin from Caesalpinia sappan.