A novel method to prepare conductive nanocrystalline cellulose/graphene oxide composite films L. Valentini a,n , M. Cardinali a , E. Fortunati a , L. Torre a , J.M. Kenny a,b Q1 a Dipartimento di Ingegneria Civile e Ambientale, Università di Perugia, UdR INSTM, Pentima 4, 05100 Terni, Italy b Institute of Polymer Science and Technology, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain article info Article history: Received 16 January 2013 Accepted 6 April 2013 Keywords: Nanocomposites Coatings Nanocrystalline cellulose Graphene oxide Electrical properties abstract In this study nanocrystalline cellulose (CNC)/graphene oxide (GO) composite films were prepared by drop casting water dispersion of GO in the presence of CNC and their nanostructures, surface and electrical properties were investigated. It was found that pristine hydrophilic GO presents a good dispersion when mixed with CNC along with a decrease of the composite electrical resistivity. The surface properties of the composite film indicated a poorer wettability with respect to that measured for separated materials. By applying an electric current through the CNC/GO composite a transition from an electrically insulating material to a conductive one was observed along with an improved wettability. The obtained results open an easy route for paper electronic based on the integration of nanocrystalline cellulose onto graphene devices. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Cellulose, one of the world's most abundant, natural and renewable biopolymer resources, is widely present in various forms of biomasses, such as trees, plants, tunicate and bacteria and it finds applications in many spheres of modern industry. Cellulose has been shown to be a long-chain polymer with repeating units of D-glucose, a simple sugar [1]. In plant cell walls, approximately 36 individual cellulose mole- cule chains connect with each other through hydrogen bonding to form larger units known as elementary fibrils, which are packed into larger microfibrils with 5–50 nm in diameter and several micrometers in length. These microfibrils have disordered (amor- phous) regions and highly ordered (crystalline) regions. When the start materials, as lignocellulosic biomass, fiber plant, trees, tunicates, etc., are subjected to pure mechanical shearing, and a combination of chemical, mechanical and/or enzymatic treatment, the amorphous regions of cellulose microfibrils are selectively hydrolyzed under certain conditions [2,3]. Consequently, these microfibrils break down into shorter crystalline parts with high crystalline degree, which are generally referred to as nanocrystal- line cellulose or cellulose nanocrystals (CNC) [4]. Nanocrystalline cellulose, is typically a rigid rod-shaped monocrystalline domain with 1–100 nm in diameter and from 10 to 100 nm in length depending on the resources of cellulose. CNC have a crystalline structure, a very high aspect ratio (length/diameter around 70), and a large surface area (ca. 150 m 2 /g) [5]. During the past decade, CNC have attracted considerable attention attributed to their unique features. First, CNC have nanoscale dimensions and excellent mechanical properties. The theoretical value of Young's modulus along the chain axis for perfect native CNCs is estimated to be 167.5 GPa [6]. Due to abundance of hydroxyl groups on surface of CNC, reactive CNC can be modified with various chemical groups to accomplish expected surface modification, such as esterification, etherification, oxidation, silylation, or polymer grafting, which could successfully functionalize the CNC and facilitate the incorporation and dispersion of CNC into different polymer matrices [4]. In addition, high aspect ratio, low density, low energy consumption, inherent renewability, biodegradability and biocompatibility are also the advantages of environmentally-friendly CNC [7,8]. Graphene oxide (GO) is a water soluble insulating material that can be obtained by oxidizing graphite [9]. The main disadvantage of this material is that the charge carrier transport (i.e. electrons) observed in nearly ideal graphene is absent in GO, but at the same time the easy processing and the versatile properties of GO make the reduction methods for such material attractive for fundamen- tal research as well as for applications. Paper, an organic-based material, is universally available: the high demand and the mass production of paper has made it one of the cheapest materials. The possibility to integrate electronic and optoelectronic functions within the production methods of the paper industry is of current interest to enhance and to add new functionalities to paper. Thus, composites prepared from aqueous GO solution with CNC represents a method for manufacturing cellulose nanocrystal/ graphene oxide composites. Nevertheless, an unavoidable drawback of this approach is that the resistance of such composite films is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 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.2013.04.034 n Corresponding author Q2 . Tel.: +39 0744492924. E-mail address: mic@unipg.it (L. Valentini). Please cite this article as: Valentini L, et al. A novel method to prepare conductive nanocrystalline cellulose/graphene oxide composite films. Mater Lett (2013), http://dx.doi.org/10.1016/j.matlet.2013.04.034i Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎