The effects of 4-acetamido-TEMPO-mediated oxidation on the extraction components of thermomechanical pulp

Abstract

4-Acetamido-TEMPO-mediated oxidation was carried out on thermomechanical pulp (TMP) to further investigate the extraction components of the oxidized pulp. Successive extractions on non-oxidized, bleached and oxidized TMP have shown that components were easier to extract from the oxidized pulp. The pulp lignin content demonstrated that the highest content of lignin was removed by sodium hydroxide extraction. Moreover, more than two times the amount lignin was extracted from oxidized pulp compared to non-oxidized pulp. The measured carboxylic groups showed that the highest amounts of the oxidized components were removed after the first extraction. However, after each extraction, reduced but still significant amounts of carboxylic groups were present in the extracted material. Thermogravimetric analysis showed that 4-acetamido-TEMPO oxidation treatment induced a decrease in the fibre degradation temperature caused by a weakening in the fibre structure. The results also demonstrated that some components of the highly oxidized pulp were more easily dissolved because of the critical extraction conditions. Furthermore, the recovered precipitate in the extraction solvent had different XPS characteristics according to the initial pulp treatment. The analysis of the oxidized TMP precipitate showed that the precipitate from hot water extraction was the most highly oxidized, while the precipitate from sodium hydroxide extraction approached pure lignin characteristics.