Functionalized Graphene Sheet / Polyurethane Nanocomposites

Abstract

One of an integral aspect of polymer nanotechnology is precise synthesis of polymer nanocomposites. [1-6] Small insertion of nanosized inorganic compounds usually improves the properties of polymers in a great deal, which makes many of the most important application areas possible depending on the inorganic material present in polymers. [7] Specially, polymer composites which contain electrically conducting inorganic fillers, such as natural graphite, carbon black and metal powders, have been extensively investigated in the past few decades for their potential applications in antistatic coatings, electromagnetic shielding and corrosion-resistant coatings, etc. [8-10] Sometimes, in order to obtain an electrical conductivity of 10−4 S cm−1 required for commercial uses, these composites often contain as much as 15 wt% filler, which in turn causes deterioration of mechanical properties and poor processability. It is, therefore, important to use a small amount of filler to retain the stretchability or transparency of a matrix polymer. Graphene is essentially an isolated atomic plane of graphite, which is composed of a single layer sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice with large specific surface area. [11,12] Single-layer graphene sheet have been of great interest for their unique properties, including not only excellent mechanical properties but thermal conductivity and stiffness. Given these unique properties, graphene has been considered as an ideal reinforcing agent for high strength polymer composites. [13,14] In addition, the elusive two-dimensional structure of graphene has a number of unusual electronic and robust transport properties that may be useful in the electronics or in the related regions. [15-17] The properties of polymer nanocomposites depend strongly on how well inorganic fillers are dispersed in the polymer matrix. A great deal of nanocomposite research using carbon nanotubes (CNT) as nanosize conductive fillers has focused on finding better methods for dispersing nanotubes into polymers since pristine carbon nanotubes have poor compatibility with most organic solvents and polymers. For this reason, additional surface treatment is necessary for CNT based nanocomposites to allow better compatibility. [18] Though surface modification via acid modification and polymer grafting improves solubility of CNT in solvents and polymers somehow, the extent of disentanglement of the CNT bundles into polymers is low, and severe sonication often leads to disruption of the CNT. In case of graphene, during the synthesis of graphene from graphite oxide (GO)[19] some epoxide and hydroxyl groups remain, which greatly facilitate dispersion. [20] There