Properties of bacterial cellulose transparent film regenerated from dimethylacetamide–LiCl solution R. Yudianti a *, A. Syampurwadi a , H. Onggo a , M. Karina a , H. Uyama b and J. Azuma b Excellent transparent films were prepared from bacterial cellulose (BC) sheets by solubilization of its defibrillated freeze-dried specimens in a solvent of dimethylacetamide (DMAc) containing 8.0% (w/w) lithium chloride (LiCl), and their properties were compared with those of the native BC. Fibrillar structure of the native BC disappeared after dissolution, and the film formed after dissolution also loose this structure. Occurence of structural transformation from crystalline to amorphous state was also evidenced by X-ray diffraction, solid state cross polarization/magic an- gle spinning 13 C-NMR and attenuated total reflectance–Fourier transform infrared spectroscopic analyses. In addi- tion, excellent 3D uniform structure of the transparent BC film was further evidenced by X-ray micro computed tomography. Plastic-like characteristic was enhanced by film formation after dissolving the BC specimens in the DMAc–LiCl solution as shown by changing mechanical properties, a slight decrease in tensile strength (67.2 to 59.6 MPa) and breaking stress (67.2 to 58.4 MPa) but significant increase in elongation at break from 3.4 to 10.5%, and improvement of work of fracture from 5.8 to 21.2 kJ/m 2 . Copyright © 2016 John Wiley & Sons, Ltd. Keywords: bacterial cellulose; transparent film; DMAc–LiCl solution INTRODUCTION Bacterial cellulose (BC) is a typical natural cellulose which has a unique gel-sheet structure having I α crystalline polymorph in comparison with plant cellulose rich in I β crystalline poly- morph. [1,2] Because of high crystallinity, tensile strength and elas- tic modulus, its compatibility, and mixing ability with other materials are becoming promising factors for its use as a func- tional material. Previously, various kinds of modification of BC were tried [3] and bio-compatible films was also prepared. [4] We have succeeded to prepare a new type BC sheet modified selec- tively at one side of the sheet with introduction of aldehyde groups at O-6, and suggested the importance of the surface structure for its mechanical strength. [5] Potential of BC as a functional material could further be in- creased by its solubilization to make transparent film. Yano et al. discovered that BC nanofiber had very promising character- istic as reinforcing material for optically transparent plastic. [6] Dissolution of cellulose in solvent is a keyprocess for making composite with other materials. For further application, conduc- tive transparent BC could be able to contribute for many optical- electronic devices such as organic light emitting diodes, organic photovoltaic solar cells, liquid crystal display panels, and touch panels. The most critical requirements for transparent conduc- tive film or glass are low sheet resistance and high transparency. [7] Recently, Zhang et al. developed a method for preparation of amorphous cellulose films with excellent transparency from dimethylacetamide (DMAc)–lithium chloride (LiCl) solutions by using acetone as the regeneration solvent. [8] Although applica- bility of this method to BC is briefly mentioned in this report, no detailed description was explained by using the BC sheets usually prepared in Southeastern Asia countries including Indonesia. Matsumoto et al. also reported that the solution of BC in the DMAc–LiCl exhibits optical anisotropy and has a differ- ent viscosity behavior from plant origin celluloses, [9] but did not refer to the film formation. On account of dissolution mechanism of cellulose in the DMAc–LiCl solution, a lot of works [10–18] have been performed since the first report of this solvent by McCormick and Lichatowich. [19] A generally accepted dissolution process was demonstrated as formation of [DMAc n + Li] + macrocation by in- teraction of Li + cation with carbonyl group oxygens of DMAc molecules, with concomitant formation of strong hydrogen bonds between hydroxyl protons of cellulose and Cl À anion ac- companied by splitting of hydrogen bonded networks of cellu- lose, followed by dispersion of cellulose chains. Notable characteristics of this solvent are in that the solvent does not form chemical bonds with the cellulose molecule and Li + and Cl À ions behave as an ion pair. Previously, the process for activa- tion of cellulose from paper substrates by solvent exchange nec- essary to solubilize it was also optimized to follow with a * Correspondence to: Rike Yudianti, Indonesian Institute of Sciences, Research Center for Physics, Jalan Cisitu No. 21/154D, Bandung, West Java, 40135, Indonesia. E-mail: rikeyudianti@yahoo.com; rikeyudianti@gmail.com a R. Yudianti, A. Syampurwadi, H. Onggo, M. Karina Research Center for Physics, Indonesian Institute of Science, Bandung, Indonesia b H. Uyama, J. Azuma Graduate School of Applied Chemistry, Osaka University, Osaka, Japan Research article Received: 11 November 2015, Revised: 11 January 2016, Accepted: 28 January 2016, Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pat.3782 Polym. Adv. Technol. (2016) Copyright © 2016 John Wiley & Sons, Ltd.