Methyl Red-loaded halloysite nanotubes-based silica coatings for durable dyeing of polyester fabrics

Since unmodified polyester fibres have no reactive groups like those in cellulose and protein fibres, they do not show an affinity for water-soluble acid, basic and direct dyestuffs. Only disperse dyestuff, a non-ionic dyestuff class with low molar mass molecules, proved to be useful for dyeing this man-made fibre following a solid–solid interaction; disperse dyestuffs do not form primary chemical bonds with polymer chains rather the dye colour is retained by H-bonds and Van der Waals forces. Herein, a new strategy for dyeing polyester fabrics with a direct dyestuff in a two-step strategy was designed and realized, using an organic–inorganic composite coating based on methyl red-loaded sol-gel modified halloysite nanotubes. In the first step two distinct reaction methods were compared to functionalize halloysite nanotubes with (3-Glycidyloxypropyl)trimethoxysilane, as a covalent crosslinker between the halloysite nanotubes and fibres, (i) in water and (ii) in ethanol, using BF3O(C2H5) and chloridric acid (HCl) as catalysts, respectively. In the second step, methyl red loaded GPTMS modified halloysite sols were applied onto polyester fabrics by impregnation. The amount of methyl red dyestuff was evaluated to be superior for the complex realized in ethanol than in water, thus promoting homogeneous nanocomposite coatings on treated polyester samples. Methyl red loaded sol-gel modified halloysite complex, as well as treated and untreated samples, were investigated to characterize their properties and morphology. NMR investigation confirmed the structure of the new complex, validating the successful dyestuff coordination reaction at GPTMS. The influence of treatments on the morphology of fibres surfaces was demonstrated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), and Atomic Force Microscopy (AFM) analyses, highlighting the influence of GPTMS-based composites on the microstructure of functionalized polyester fibres. To further confirm if the suggested approach offers a stable dyestuff loading on PE, diffuse reflectance spectroscopic studies, X-ray Photoelectron Spectroscopy (XPS) and colour fastness to rubbing and washing tests were carried out on the coated polyester. All findings make sol-gel based modification of halloysite a reliable and promising method for eco-friendly dyeing processes of polyester fabrics.