Supramolecular BioNanocomposites: Grafting of Biobased Polylactide to Carbon Nanoparticle Surfaces

Novel carbon nanostructures are attracting increasing interest and the combination of graphitic substrates with grafted biodegradable polymers may ultimately be of interest in a variety of biomedical and sensing applications. Here, a novel graphitic nanosubstrate, carbon nanospheres derived from cellulose, is functionalized with polylactides (PLA) using an established thionyl chloride intermediate scheme; the resulting supramolecular bionanocomposite is 97% from renewable resources. In addition, a direct ‘grafting from’ approach is utilized to grow polylactide chains on multi-walled carbon nanotubes (MWCNT). In the latter case, unlike previous approaches, the ring-opening polymerization is initiated directly from a hydroxyl bearing surface. Verification of the covalent attachment and characterization of the grafted layer are accomplished via a variety of techniques and methods. Even after repeated washing, thermal gravimetric analysis clearly shows the presence of a grafted layer, which decomposes at approximately 300°C, a value characteristic of PLA; it is found that 20 mg m–2 of PLA is grafted to the MWCNT and 3.9 mg m–2 of PLA is grafted to the carbon nanospheres. Solubility tests clearly show the graphitic structures have been fundamentally altered in their physiochemical properties; they become highly soluble in chloroform after the grafting reaction is complete. Transmission electron microscopy provides evidence of a 2–3 nm thick polymer layer. Finally, Fourier transform infrared spectroscopy shows several characteristic peaks of PLA including the ester group at 1760 cm–1.