Materials Chemistry and Physics 129 (2011) 932–938 Contents lists available at ScienceDirect Materials Chemistry and Physics jo u rn al hom epage : www.elsevier.com/locate/matchemphys Preparation and properties of chitosan nanocomposite films reinforced by poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) treated carbon nanotubes Tongfei Wu, Yongzheng Pan, Hongqian Bao, Lin Li ∗ School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore a r t i c l e i n f o Article history: Received 13 January 2011 Received in revised form 14 April 2011 Accepted 13 May 2011 Keywords: Biomaterials Composite materials Mechanical properties a b s t r a c t Carbon nanotube-based nanocomposites of chitosan were successfully prepared by a simple solution-evaporation method. Multiwalled carbon nanotubes (MWCNTs) were treated by poly(3,4- ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT-PSS) in water before mixed with a chitosan solution to improve the dispersion of MWCNTs and interfacial compatibility between MWCNTs and chitosan. The morphological and mechanical properties of the prepared PEDOT-PSS/MWCNT/chitosan nanocomposites have been characterized with field emission scanning electron microscopy (FESEM) and tensile tests. MWCNTs were observed to be homogeneously dispersed throughout the chitosan matrix. As compared with the neat chitosan, the tensile strength and modulus of the nanocomposite were greatly improved by about 61% and 34%, respectively, with incorporation of only 0.5 wt.% of MWCNTs into the chitosan matrix. The comparison of mechanical properties for PEDOT-PSS/MWCNT/chitosan and pris- tine MWCNT/chitosan nanocomposites has been made. The hardness of the nanocomposites was also evaluated by nanoindentation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) are promising reinforcing nanofillers for various polymeric matrices because of their unique physical properties [1–4], including the high length-to-diameter ratio and extraordinary strength [5–8]. However, to access these extraordi- nary properties, a number of technical issues must be addressed during the preparation of CNT/polymer composites. Of these issues, it is considered to be crucial to have a uniform dispersion of CNTs within a polymer matrix and strong interfacial adhesion between nanotubes and the polymer matrix [9]. The interactions of the polymeric molecular chains with the surface of CNTs would deter- mine the efficiency of loading transfer from the polymer matrix to the ultrastrong nanotubes [10]. Chemical bonding between the polymeric matrix and CNTs will greatly enhance their interfacial adhesion. A few polymers can directly bond to CNTs by grafting to methods [11]. One more flexible way is to introduce various func- tional groups on the surface of CNTs through a simple oxidation reaction. For example, by refluxing CNTs with sulphuric acid or mixed acids, some functional groups, such as carboxylic, carbonyl, and hydroxyl groups, can be introduced on the surfaces of CNTs [12,13]. With these reactive groups on CNTs, many other organic ∗ Corresponding author. E-mail address: mlli@ntu.edu.sg (L. Li). groups, including polymeric molecular chains, can be grafted on by routine chemical synthesis methods. [14–16] The functional groups or the organic groups grafted onto the CNTs will greatly increase their interactions with a variety of polymeric matrices, thus resulting in significant improvement in mechanical properties of CNT/polymer composites [15,17]. Besides the interfacial adhe- sion, the other issue is the aggregation of CNTs into bundles and/or entangled structures together because of the intrinsic van der Waals attraction of nanotubes. To get a homogeneous dispersion of CNTs in the polymer matrix, it is necessary to disaggregate CNT bundles in their suspensions. To this end, high-energy ultrasonica- tion is usually employed for uniform dispersion of CNTs [18,19]. The use of surfactants has been demonstrated to improve the disper- sion of CNTs in solvents [20]. Interestingly, a few polymers, such as polyvinyl pyrrolidene (PVP), polystyrene sulfonate (PSS), and poly(aryleneethynylene)s (PPE), are also known to effectively sol- ubilize a CNT dispersion [21,22]. As a natural polymer, amylase has also been used for the homogeneous dispersion of CNTs in water [23,24]. But it is noticed that high-energy ultrasonication can break CNTs into shorter ones which could reduce the reinforcement effect in comparison with individual longer CNTs. There must be a balance between disaggregation and length reduction of CNTs for an opti- mal effect of reinforcement. Therefore, the duration and strength (i.e. high-energy) of ultrasonication should be optimized in order to achieve the highest degree of CNT dispersion and the minimal reduction of CNT length. 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.05.030