The effect of the acid/dithionite/peroxide treatments on reactively dyed cotton and indigo dyed denim and the implications for waste cellulosic recycling

Abstract

Previous studies have established that the application of crosslinking dyes and easy care finishes to cotton can significantly reduce the dissolution of waste cotton in swelling solvents and limit potential recycling of cellulosic materials through Lyocell fibre regeneration process. In this study, a sequential hydrolysis/reduction/oxidative treatment was investigated as a potential method to completely strip all types of reactive dye chromophores from cotton. It was established that the treatment could completely strip off colours from the reactively dyed fabrics and post-consumer denim jeans fabric resulting in a white, NMMO-dissolvable cellulosic material, which could be used as a feedstock for Lyocell fibre regeneration. The white cellulose had an acceptable degree of polymerisation and the regenerated fibres had structural and mechanical properties similar to those of fibres regenerated from conventional wood pulp. Blending conventional wood pulp and recycled cotton pulp allowed manufacturing of regenerated Lyocell-type fibres with acceptable properties.