Regenerated Cellulose Filaments from the Recycling of Textile Cotton Waste Using Ionic Liquids

In this study, cellulose filaments were obtained from the dissolution of an industrial cotton residue in the ionic liquids (ILs) 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) and 1-ethyl-3-methylimidazolium acetate ([Emim]OAc) using dimethyl sulfoxide (DMSO) as the cosolvent. Cellulose regeneration was carried out in water or ethanol coagulation baths, and the effect of IL and coagulant on the degree of polymerization (DP), morphology, crystallinity, and thermal and mechanical properties was evaluated. Both ILs promoted the complete dissolution of cellulose, with the process in [Emim]OAc occurring faster and with less fiber swelling. The obtained filaments exhibited a homogeneous appearance and a dense morphology, and it was noted that the optical brightener present in the cotton residue was maintained in the filament composition. The dissolution and regeneration processes promoted the depolymerization of cellulose, with significant differences between the ILs and the coagulant. The highest depolymerization was observed for the filaments resulting from the dissolution in [Emim]Cl. X-ray diffraction analysis indicated a change in the crystalline structure of cellulose I of the residue to an amorphous structure in the filaments, except for the filament from dissolution in [Emim]OAc and coagulation in ethanol, which presented a type II cellulose structure. Thermal stability was reduced for all filaments, with the lowest degradation temperature observed for the filament from dissolution in [Emim]Cl and coagulation in ethanol. This filament also obtained inferior mechanical properties as a result of low DP and crystallinity. The elastic modulus of the other filaments (10–13 GPa) was similar to that of regenerated fibers such as viscose and modal. Among the IL-coagulant systems evaluated, [Emim]OAc-ethanol resulted in the most promising mechanical, thermal, and morphological properties.