TEMPO-mediated oxidation of bacterial cellulose in a bromide-free system
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ORIGINAL CONTRIBUTION
TEMPO-mediated oxidation of bacterial cellulose in a bromide-free system Chen Lai & Shujiang Zhang & Liyuan Sheng & Shibo Liao & Tingfei Xi & Zhixiong Zhang
Received: 2 April 2013 / Revised: 17 June 2013 / Accepted: 15 July 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract A partially C6-carboxylated bacterial cellulose (BC) with a high carboxylate content was prepared in a bromide-free system by using 2,2,6,6-tetramethylpyperidine1-oxyl (TEMPO) as a catalyst. ART-FTIR, X-ray diffraction, solid 13C-NMR, TEM analysis, and reaction kinetics measurements were performed to investigate the oxidation reaction of BC. Results show that C6 carboxylate was formed selectively on the microfiber surface without disrupting its highly ordered nanocrystalline structure. Given the extremely low accessibility of hydroxyl groups in D-anhydroglucopyranose units, the reaction can be described by second-order kinetics with very low reaction rate constants. pH exhibited a significant influence on the oxidation of BC and a higher activity at C6 was observed in a neutral medium. Keywords Bacterial cellulose . Oxidation . Bromide free
Introduction Bacterial cellulose (BC) is a form of cellulose that is produced by bacteria [1, 2], including Gluconacetobacter (also named Acetobacter), Acanthamoeba, Achromobacter, Zoogloea, and Shujiang Zhang contributed equally to the manuscript and is also a cofirst author. C. Lai (*) : L. Sheng : S. Liao : T. Xi : Z. Zhang Shenzhen Key Laboratory of Human Tissue Regeneration and Repair, Shenzhen Institute, Peking University, Shenzhen 518057, China e-mail: [email protected] C. Lai National Engineering Research Center for Biomaterials, Sichun University, Chengdu 610064, China S. Zhang The First Affiliated Hospital of Guangzhou Medical College, Guangzhou 510120, China
others. In particular, Acetobacter xylinum has a high yield of commercial BC [3] which has been used in the food industry for applications such as low-calorie desserts, salad, and fabricated foods [4]. As a cellulosic polymer, BC is a linear syndiotactic homopolymer composed of D-anhydroglucopyranose units (AGU), which are linked together by β-(1→4)-glycosidic bonds (Fig. 1). This kind of cellulose has unique mechanical and physical properties, which are accounted for their threedimensional network of microfibers with diameters of approximately 30 nm or a hundred times thinner than those from common cellulose in plants. The individual BC chains aggregate into fibrils, forming ribbons. The tensile strength of BC single fibers is equivalent to steel and Kevlar [5]. In contrast to native cellulose from plants [6], BC has higher purity, crystallinity, thermal stability (250 to 300 °C), biocompatibility, water-holding capacity, tensile strength, and Young's modulus [7, 8]. BC has a strong nanofibril architecture resembling that of collagen, but it exhibits no immunological reactivity and has been investigated for biomedical applications. It can be used to fabricated excellent wound dressings that promote rapid and vi
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