Regenerated cellulose – zinc oxide nanocomposite filaments obtained from the dissolution of cotton waste in ionic liquid/cosolvents

Abstract Cotton waste from textile processes is often disposed of in landfills, resulting in environmental and resource losses. In this context, the objective of this study was to develop regenerated cellulose filaments from textile waste, processed in systems composed of ionic liquid (IL) in combination with different proportions of the cosolvents dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). Furthermore, the reinforcement of the filaments with different concentrations of zinc oxide (ZnO) nanoparticles was evaluated. The cotton was dispersed in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) for 2.5 h at 110 °C, with the addition of DMSO or DMF at 15%, 30%, and 50% (g cosolvent/g IL). The resulting filaments were characterized for degree of polymerization (DP), morphology, mechanical properties, and thermal stability. The optimized condition was obtained with 30% DMSO, resulting in the highest DP values and best mechanical performance. The incorporation of ZnO was confirmed by XRD and FTIR analyses, promoting significant improvements in mechanical properties, up to 15%. However, the 20% ZnO concentration showed a tendency towards agglomeration, reducing the reinforcement efficiency. Thermal analysis indicated variations associated with the inorganic content, but no substantial gain in thermal stability. Among the conditions tested, the filament with 10% ZnO presented the best balance between mechanical performance, ZnO-cellulose interaction, and thermal stability. The regenerated filaments show potential for technical textiles and biodegradable composites, combining enhanced mechanical performance and sustainable reuse of textile waste.