Gallic acid derivatives as stabilizers in cellulose solutions: analysis by 31P 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 P-31 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 P-31 NMR approach offers a straightforward way to analyze the stabilizer chemistry in the Lyocell process. [GRAPHICS] .

Automated summary

This study investigates the analysis of stabilizers and their major degradation products in Lyocell dopes. The stabilizer-derived compounds are easily extracted from the solution and analyzed using P-31 NMR after chemical derivatization of the hydroxyl groups.