Supercritical CO2 technology in resource-effectiveproduction of functional and smart textiles

Abstract: The demand for functional and smart textiles has risen nowadays due to the lifestyle change of human beings. Along with this, the production of functional and smart textiles is consistently increasing. However, the conventional dyeing and finishing methods used to produce the functional textiles have issues such as the requirement of a large amount of fresh-water, energy, and chemicals and the associated wastewater pollution which poses harmful effect to humans, animals, and the environment. Moreover, due to the stringent environmental legislation on effluent release and hence the necessity of wastewater treatment, it has also become an economic problem for the textile industry. Thus, the textile industry has nowadays focused on alternative green technologies and eco-friendly chemical agents to minimize these problems. In this regard, supercritical carbon dioxide (scCO2) dyeing technique is a promising alternative to conventional aqueous-based methods as it avoids the use of water, uses less energy, and fewer chemicals minimizing the waste generation which is important to improve the ecological footprint and reduced production cost. Owing to these important attributes, scCO2 dyeing has been investigated in the last three decades as an environmentally benign process and now it is commercially successful in an industrial scale for dyeing polyester fibres. Thus, employing this technique to textile functionalization can bring additional economic and environmental benefits for the textile dyeing and finishing industry. Nevertheless, only a few attempts have been made so far in using this technology for textile finishing despite having promising potentials.This thesis used scCO2 dyeing technology intending to explore its potential to the production of functional and smart textiles. To fulfil this, firstly, different functional dyes and functional finishing agents of interest suitable for scCO2 media were selected based on literature data and some screening experiments. Based on this, chitosan very low molecular weight and lactate derivatives, curcumin natural dye, and two commercial photochromic dyes based on spirooxazine and naphthopyran dye classes were selected. Secondly, these agents were incorporated into the polyester fabric using scCO2 impregnation technique to impart range functionalities such as antimicrobial, antioxidant, UV protecting and smart UV-sensor fabrics. Moreover, the functional and colour performances of these functional textiles and the effects of the processing variables on the functional/colour properties were explored. Besides, the thesis includes the production of pH sensing functional fabric with a halochromic molecule using photo grafting technique as an alternative resource-efficient method.The results showed that scCO2 is a viable technique for the production of functional polyester fabric in a resource-efficient and eco-friendly way. Dyed polyester fabric with additional functionalities such as antimicrobial, antioxidant, UV protection, and UV sensing properties were realised in a single step. The fabrics developed have demonstrated desirable colour and functional properties without affecting each other confirming compatibility. Moreover, the functional fabrics exhibited the required durability and fastness properties sufficient for various applications. This thesis contributes towards widening the application of supercritical CO2 dyeing technique further and paves a way for sustainable production of functional and smart textiles in a resource-efficient and eco-friendly way. Moreover, the functionalization of cotton fabric with a pH indicator dye using the photo-grafting technique was successful and exhibited good halochromic property towards different pH environments with potential application in several smart textile areas.