Sustainable and cleaner microwave-assisted dyeing process for obtaining eco-friendly and fluorescent acrylic knitted fabrics

Abstract

Synthetic garments pose significant environmental and human risks, which are further increased by the presence of synthetic dyes. As synthetic fibers cannot be eliminated, steps need to be taken in order to improve their sustainability. The paper presents a sustainable and cleaner microwave (MW)-assisted process of dyeing acrylic knitted fabrics with natural dyes based on curcumin extracted from turmeric powder (TP). The process is a novelty because it leads to fluorescent acrylic fabrics. The curcumin was extracted from TP, with or without 0.1 mL solvent. Based on the absorption curves in the ultraviolet–visible domain, the analysis indicates that 100 g of TP contains 3.6 g of pure curcumin. The factors influencing the MW-assisted extraction are presented and discussed. The eco-friendly dyeing was performed in the presence of MW, using only freshly extracted dyes, no additives. The research investigates the effects of the concentration of natural dyes (5–20%), presence of solvents, dyeing time (2–15 min), temperature gradient and nature of the textile support on color intensity (K/S) and CIELab measurements. Spectroscopy analyses highlight the effects of the MW treatment on the Melana and Dralon L samples and on two pretreated samples subjected to grafting and saponification. The presence of MW modifies the internal structure of the fibers, while the chemical pretreatments generate chemical modifications/functionalizations. The advantages of the cleaner MW-assisted process refer to the ease of application, eco-friendly process, shorter duration, low consumption of chemicals, leading to uniform dyeing and high fluorescence, to a level that was never before obtained with natural dyes. The use of natural dyes improves the sustainability of the process in terms of recycling.