Cellulosic fibers spun from stabilized imidazolium ionic liquids: identification of chromophores in the fibers after accelerated ageing

Cellulosic fibers spun from 1,3-dialkylimidazolium ionic liquids are effectively stabilized against cellulose degradation by the addition of antioxidants, but this protective effect comes at the expense of chromophore generation from the degradation products of the stabilizers. In this study, we identified the oxidation and degradation products of four natural antioxidants, α-tocopherol, N-methyl-α-tocopheramine, propyl gallate, and hydroxytyrosol, formed upon accelerated ageing of the fibers. Ageing was performed according to standard protocols under either dry or moist conditions and the extraction was done with supercritical carbon dioxide. Chromophore formation in spinning dope, upon dry ageing and moist ageing were compared. In total, 16 different oxidation/degradation products were isolated, their structure confirmed by comprehensive analytical characterization with full NMR resonance assignment in the ¹H and ¹³C domains as well as by comparison with authentic samples, and their formation pathways discussed. Knowledge of the chemical structures of the degradation products originating from the stabilizers now provides a good starting point for optimization of the fiber bleaching stage.