Gallic acid derivatives as stabilizers in cellulose solutions: analysis by 31 P NMR spectroscopy

Lyocell dopes for cellulosic fiber manufacture, i.e., cellulose solutions in N -methylmorpholine- N -oxide monohydrate, are commonly stabilized by propyl gallate, or alternatively by recently proposed gallic acid amide derivatives. In this study, the analysis of the stabilizer and its major degradation products, ellagic acid and ellagoquinone, is investigated. The stabilizer-derived compounds are readily extracted from the dopes with polar aprotic solvents without solvent or cellulose interference. This is followed by the derivatization of the OH groups with a phosphitylation agent and subsequent 31 P NMR analysis—an approach frequently used to differentiate and quantify OH groups in lignins. The chemical shifts of the resulting phosphites are reported and structures of the stabilizer derivatives are discussed. The 31 P NMR approach offers a straightforward way to analyze the stabilizer chemistry in the Lyocell process. Graphical abstract