Covalently grafted carbon nanotube on bacterial cellulose composite for flexible touch screen application K. O-Rak a , S. Ummartyotin b , M. Sain c , H. Manuspiya a,n a The Petroleum and Petrochemical College, Centre of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Bangkok 10330, Thailand b Faculty of Pharmaceutical Science, Burapha University, Chonburi, 20131, Thailand c Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Canada M5S 3B3 article info Article history: Received 5 April 2013 Accepted 25 May 2013 Available online 2 June 2013 Keywords: Bacterial cellulose Carbon nanotube Polarization effect Touch screen feature abstract Carbon nanotube was successfully grafted on hydroxyl group of bacterial cellulose molecule by conventional synthetic method. The purpose of incorporated carbon nanotube on bacterial cellulose was to enhance the polarization effect on its composite. The appearant peak from Fourier transform infrared at 1730 and 1350 cm -1 exhibited that chemically modified bacterial cellulose by insertion of carbon nanotube was observed. Scanning electron microscope revealed that the structure of composite was designed as 3 stacks of grafted carbon on bacterial cellulose encapsulated on both sides by resin. In addition, significant enhancement on dielectric properties can be remarkably observed, suggesting bacterial cellulose composite exhibited superiority on polarization effect and it may initially be developed as electroactive macterials. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Due to the growing environmental awareness and concerns over reliable availability of petrochemicals in the future, the polymer industry and academia have been pressed to design and produce polymers and composites based on renewable natural resources. In the past decades, the push towards flexible electronic device based on “Green composite materials” has been evident. Achievement of this new promising concept can easily lead to flexible displays and optoelectronics, as well as more novel ideas such as smart textiles, photovoltaic cells, and building lighting. Among the flexible electronic displays, organic light emitting diode (OLED) [1] is a versatile platform system that has attracted worldwide attention. OLED has been traditionally fabricated on rigid glass sheet substrates. Although flexible polymer substrates have been expected as potential alternatives in replacing the glass substrate, the use of conventional polymer substrates has been limited by their coefficient of thermal expansion (CTE). Okahisa [2] and Choi et al. [3] suggested that the CTE of the substrate should be restricted to 20 ppm/K at most, as the thermal expansion of the substrate can lead to the destruction of functional materials of the OLED circuit during the temperature fluctuation in OLED assembly and mounting processes. To overcome the CTE limitation of the flexible polymer substrate, our previous works have focused on the exploitation of the composite of nano-sized cellulose and polymeric matrices [4]. Bacterial cellulose, which is a nano-sized extracellular product of the bacteria strain Acetobacter xylinum, has the CTE of as low as 0.1 ppm/K. The incorporation of bacterial cellulose into polymeric matrix can be expected to yield a composite film with much decreased CTE to be less than 20 ppm/K. In addition, bacterial cellulose has the typical thickness and width of 10 and 50 nm. Its nano-entity will allow the fabrication of optically transparent OLED substrate as any element with size smaller than one-tenth of visible light wavelength is free of visible light-scattering. Moreover, up to the present time, in order to prolong the service lifetime of electronic device, this bacterial cellulose composite was further developed for water vapor transmission barrier [5] and surface smoothness [6], respectively. Recently, on the other hand, small amount of carbon nanotube (CNT) incorporated on cellulose composite has been pioneered to re-discover as a smart material that can be utilized for sensors and actuators, so-called electro-active paper (EAPap). It commonly offered numerous advantages including lightweight, dryness, large deformation as well as minimal on power consumption. Due to this achievement on electro-active properties on cellulose modified by carbon-based material, not only elastic modulus and mechanical properties can be improved, but also, it can open to the wide vision on the development of successfully transparent and flexible cellu- lose composite with additional feature of touch screen character- istic. However, as the structure of cellulose was strongly evident as Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$- see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.126 n Corresponding author. Tel.: +66 2 2184125; fax: +66 2 218 4145. E-mail address: hathaikarn.m@chula.ac.th (H. Manuspiya). Materials Letters 107 (2013) 247–250