Effect of Carbon Nanotube Functionalization on the Structure and Properties of Poly(3- Hydroxybutyrate)/mwcnt Biocomposites

Poly(3-hydroxybutyrate) (PHB) is a natural, linear, thermoplastic polyester synthesized by microorganisms as intracellular carbon reserves and ion sinks in response to limited nutrient availability and imposed stress conditions. The PHB has become one of the most interesting biomaterials for application in tissue engineering due to its excellent biodegradability and biocompatibility. Nanocomposites of biopolymers with carbon nanotubes (CNTs) offer significant potential for their increased utilization, as a result of the improvements in electric conductivity, mechanical and thermal properties. In regards to the fabrication of polymer/CNT composites, the most critical issue remains the development of methods to homogenously disperse the CNTs throughout the polymer matrices. Dispersion of CNTs is an important first step toward many potential applications that harness the unique electronic, thermal, optical, and mechanical properties of the individual tube. Furthermore, conventional applications such as the use of single wall carbon nanotubes (SWNTs) as conductive fillers in composites will benefit from a well-dispersed system that will exhibit the same conductivity with a smaller percentage of filler. Although high power ultra-sonication can make metastable solutions of nanotubes, it is found invariably that the nanotubes tend to aggregate when slow solvent evaporation is employed, leading to an inhomogeneous distribution of nanotubes throughout the polymer matrix. One of most frequently used techniques to improve the CNT solubility is to covalently functionalize CNT surface. Covalent functionalization can be accomplished by either modification of surface-bound carboxylic acid groups on the nanotubes or by direct reagents to the side walls of nanotubes. The amidation or esterification of oxidized CNTs has become one of the most popular ways of producing soluble materials in organic solvents or in polymers. Although nanocomposites of PHB/CNT have been studied by several groups, Attempt to utilize the covalently functionalized CNTs to obtain the better dispersion of CNTs within PHB matrix has not been made. The fundamental materials property, the electric conductivity of PHB/CNT nanocomposites has not also been reported, to our knowledge. In this paper we synthesized multiwall carbon nanotubes (MWNTs) and covalently functionalized MWNTs with alkyl group. The PHB and MWNTs functionalized with alkyl group were mixed in chloroform and the nanocomposite film was casted from the solutions. It was found that PHB composites of CNTs functionalized with alkyl groups showed a better solubility in PHB/chloroform solutions and casted films, which resulted in higher electric conductivity and higher mechanical properties compared to acid treated CNT.