Selective oxidation of bacterial cellulose by NO2–HNO3

Bacterial cellulose (BC) needs to be selectively oxidized by different oxidants such as TEMPO–NaClO–NaBr and NaIO4 in order to control its degradability in vivo. However, both of these two oxidants are difficult to remove and the oxidation process is often accompanied by undesirable degradation of the material. In this work, a highly selective and efficient method for producing oxidized bacterial cellulose (OBC) has been developed in the reaction with NO2 in HNO3 solution. Systematic characterization of the structure and property of the resulting OBCs demonstrated that the oxidation process not only avoided the secondary reaction but also significantly enhanced its mechanical properties, controllability of biodegradability and protein absorbability. Nuclear magnetic resonance (NMR) testing and Fourier transform infrared spectroscopy (FTIR) proved that the selective oxidation of BC took place only at C6 where primary alcohol groups were quickly oxidized to carboxyl groups, with a maximum oxidation degree achieved up to 32.54% after 40 h. The oxidation process not only retained the crystal structure of BC, but slightly increased its degree of crystallinity, thus contributing to the improvement of its strength and toughness. At the same time, OBC manifested more controllable degradability and higher protein adsorption than the original BC as a function of the oxidation time.