Sang Xiankui,Qin Chengrong,Tong Zhangfa,Kong Song,Jia Zhuan,Wan Guangcong,Liu Xinliang
2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO) can selectively oxidize primary hydroxyl groups of cellulose to carboxyl groups. However, the depolymerization also occurs during the process. The kinetics and mechanism of carboxyl group formation on the surface of cellulose fiber oxidized by TEMPO/NaClO 2 /NaClO were discussed. The oxidization and depolymerization of cellulose occurred simultaneously, according to analysis of FTIR and 13 C CP/MAS NMR. The glucuronic acid and some small molecular fragments, formed by hydrolysis or β-elimination during the oxidation, are also discussed. The crystallization index increased and crystal size decreased, as shown by X-ray analysis. The degradation steps in the TEMPO/NaClO 2 /NaClO system was discussed, according to carbon conversion analyzed by 13 C CP/MAS NMR. The oxidation of cellulose can be described well by the kinetics model established based on the degradation of cellulose. It was found that temperature is one of the key parameters for controlling the oxdation and degradation level. The possible mechanism for oxidation of cellulose was composed.
There is a challenge to find an effective and eco-friendly method to achieve the modification of fibers. The effect of laccase-TEMPO system on the properties of the bleached eucalyptus kraft pulp was investigated in this work. The results were demonstrated by the decreases in curl values and kink index. In addition, carboxyl and aldehyde groups were introduced in this reaction system. Compared with initial pulp, the contents of aldehyde and carboxyl groups of the treated pulp were increased from 42.6 μmol/g, 8.4 μmol/g to 125.4 μmol/g, 26.3 μmol/g respectively. However, the treatment had a detrimental effect on the thermal stability of pulp fibers. Moreover, the crystallinity index was slightly increased (from 82.1 % to 83.8 %) after the TEMPO-mediated oxidation, but the native crystalline structure was nearly unchanged. Furthermore, after the oxidation treatment, the relatively smooth film surface became textured, the carbon and oxygen bonds were changed, which were investigated by scanning electron microscope and X-ray photoelectron spectroscopy.
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