Fibers and Polymers 2008, Vol.9, No.4, 410-415 410 Improved Dispersion of Carbon Nanotubes in Chitosan Sukrut Ozarkar, Manjeet Jassal*, and Ashwini K. Agrawal** Department of Textile Technology, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India (Received November 16, 2007; Revised March 26, 2008; Accepted April 9, 2008) Abstract: Carbon nanotubes (CNT)/chitosan films and fibers can find use in specialized applications like the artificial mus- cles and other intelligent switching devices. The dispersion state of the single walled carbon nanotubes (SWCNTs) in chito- san matrix plays a major role in deciding the ultimate properties of composite. A suitable chemical treatment for purification and functionalization of SWCNTs is reported. Optimal conditions to prepare water soluble and stable, dispersion of SWCNT in chitosan are presented. The dispersion behavior of purified and functionalized SWCNT was characterized by visual obser- vations, transmission electron microscopy (TEM), and Raman spectroscopy. The dispersion obtained using functionalized SWCNT was stable, while the purified SWCNT dispersion showed limited stability. The better stability of functionalized SWCNT dispersion in chitosan was evidenced by improved interaction between chitosan and carboxyl functional groups of SWCNT. Keywords: SWCNT, Dispersion, Chitosan, Carbon nanotube, Raman spectra Introduction Single-wall carbon nanotubes (SWCNTs) have been of interest since their discovery because of their unique architecture and remarkable mechanical, thermal, and electrical properties. Carbon nanotubes have the potential applications in a broad range of technologies, in different fields including engineering, biology, chemistry, medicine, electronics, and material science [1]. As fillers in polymer matrix materials, SWCNTs promise an extraordinary opportunity for development of new products with desirable physical properties [2]. For example, the addition of well dispersed SWCNT in an insulating polymer matrix results in a conductive network that forms a polymer composite with dramatic improvement in electrical conductivity with low percolation threshold (0.05-0.3 % of SWCNT loading) [3]. The critical challenges related to achieving these superior properties lie in uniformly dispersing the nanotubes in the required polymer matrix. The carbon nanotubes tend to aggregate by virtue of very strong van der Waal’s forces of attraction. Their inherent chemical inertness makes it difficult to disperse them in any solvent or polymer matrices [4-7]. Another obstacle in dispersing the carbon nanotubes is the presence of various impurities including amorphous carbon and other metal catalyst particles. These impurities are responsible for the poor properties of carbon nanotube reinforced composites [8]. In recent years, research has been focused on achieving the highest possible degree of dispersion without altering the properties of the CNTs themselves. Ideally, individual nanotubes must be separated from the bundles to exploit the intrinsic properties of SWCNTs. Among various approaches reported for dispersing CNTs in aqueous medium, the use of surfactants is most popular and effective. New methods of chemical functionalization have been developed so as to enhance the dispersion of SWCNTs in the aqueous medium [9-17]. These functionalized CNTs showed improved solubility/dispersion in water and various common organic solvents/polymer matrices [18-21]. In this manuscript, we report a comparison of the dispersion behavior of SWCNTs and carboxyl functionalized SWCNTs in chitosan solution for the potential application of SWCNT/ chitosan composites in the area smart materials like the bio- actuators, where the carbon nanotubes provide a conducting reinforcement for the biocompatible chitosan matrix. The dispersion studies using TEM and Raman spectroscopy revealed a better dispersion of functionalized SWCNT in chitosan in comparison to non-functionalized SWCNT. Experimental Materials The SWCNTs used in this experiment were supplied by Carbolex Inc. Their average diameter was 4 nm and purity was 50 %. Chitosan polymer (degree of deacetylation~85 % and molecular weight~5×10 5 ) was obtained from Sigma- Aldrich. All other chemicals used were of high purity and used without further purification. Purification of Carbon Nanotubes The SWCNTs were purified using the following method. The SWCNT (2 mg) was Soxhlet extracted with 50 ml of toluene for 6 h. After Soxhlet extraction, the nanotubes were rinsed with acetone and finally dried in the air oven at 100 o C. The Soxhlet extracted and dried nanotubes were oxidized with 10 % hydrogen peroxide (H 2 O 2 ) solution under reflux for 1 h [8]. The sample was then filtered, washed with deionized water, followed by acetone, and dried in oven at 100 o C. **Corresponding author: manjeetjassal@gmail.com **Corresponding author: ashwini_agrawal@yahoo.com