Analysis of carboxylate groups in oxidized never-dried cellulose II catalyzed by TEMPO and 4-acetamide-TEMPO.

Abstract

In this report, never-dried regenerated celluloses, i.e. cellulose II, from their NaOH/urea/H2O solutions were subjected to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) or 4-acetamide-TEMPO-mediated oxidation. Water-soluble and -insoluble fractions of carboxyl cellulose (COC) were obtained and their DO were determined to be between 0.08 and 0.85. Apart from conductometric titration, complexometric titration with EDTA was used to analyze the DO of COC. The conductometric titration can be used for lowly or highly oxidized celluloses, while the complexometric titration with EDTA is only adequate for COC with DO lower than 0.6. FT Raman spectroscopy represents characteristic bands of carboxyl and carboxylate groups. It demonstrates the feasibility of establishing novel analyzing methods for DO of COC with high correlation coefficients of up to 0.9867. Moreover, long oxidation duration, high temperature and high amounts of oxidizing agents are important for the synthesis of COC with high DO and yields.