Synthesis and Characterization of Polymer Nanocomposites with Improved Physical Properties Using Graphene Derivatives as Fillers for Various Applications

Abstract

Polymer nanocomposites containing graphene have drawn much attention for scientific interests and industrial purposes over the past few years because they can have much improved performance. However, the poor compatibility of graphene with polymers limits the practical application for the polymer nanocomposites. Therefore, the modification of graphene is strongly needed to increase the miscibility with the polymer. In addition to the improved compatibility with the polymer, surface modification of GO with a unique functional moiety can be also very advantageous for the polymer nanocomposites with desired functionality, because the functional moiety on GO can impart the special functionality to the polymer nanocomposites. Therefore, various approaches to prepare graphene-derivatives modified with various kinds of chemical moieties including polymers for the improved compatibility with the polymers were introduced in this study. The physical properties of polymers were much improved by using such graphene derivatives as the fillers of polymer nanocomposites. Firstly, polyketone (PK) nanocomposites were prepared by a solution casting method using 1,1,1,3,3,3-hexafluoro-2-propanol as a solvent and polyamide 6 grafted graphene oxides (PA 6-GOs) as filler materials. PA 6-GOs were obtained by in-situ polymerization of ε-caprolactam using GOs having different amounts of oxygen functional groups. The PK nanocomposites containing only an extremely small amount of the PA 6-GOs (~ 0.01 wt%) showed much improved mechanical properties compared to PK. This could be ascribed to the homogeneous dispersion of the graphene-based filler materials in the polymer and specific interactions such as dipole-dipole interactions and/or the hydrogen bonds between the fillers and polymer matrix. For example, when 0.01 wt% of PA 6-GO having less oxygen functional groups was used as a filler for the composite, the tensile strength, Youngs modulus, and elongation at break of the composite increased by 35, 26, and 76 %, respectively. When 0.01 wt% of PA 6-GO having larger content of oxygen functional groups and PA 6 was used, Youngs modulus decreased, while the tensile strength increased by 37 %, and the elongation at break increased tremendously by 100 times, indicating that very tough polymeric materials could be prepared using a very small amount of the graphene-based fillers. Secondly, PK nanocomposites were prepared by a polymer powder coating method using carbon nanomaterials, such as carbon nanotube (CNT), graphene oxide (GO), and antioxidant grafted GOs as filler materials. The antioxidant grafted GOs were obtained by grafting hindered amine and hindered phenol, respectively, onto the surface of the GOs. The PK nanocomposites containing the carbon nanomaterials showed much improved thermal stabilities and mechanical properties compared to PK. In particular, we found that the antioxidant grafted GOs are more effective in increasing the thermal properties of PK than CNT and GO without any antioxidant moieties. The enhanced thermal stability and mechanical property by the antioxidant grafted GOs can be explained by the combined antioxidant ability of the antioxidant functional groups and the rigid conjugated carbon units in the GOs having the ultrathin sheet shapes. Finally, poly(vinyl alcohol) (PVA) nanocomposites were prepared by a solution casting method using a reduced graphene oxide coated with tannic acid (rGO-TA) as a filler. The rGO-TA was simply prepared by mixing tannic acid (TA) with graphene oxide (GO). The simple mixing process was found to be effective to reduce GO and to produce covalently-grafted TA layers on the reduced GO. The mechanical properties of PVA were much improved by the addition of rGO-TA because the TA layers increased the compatibility of the reduced GO with PVA matrix. For example, Youngs modulus and elongation at break values of PVA were increased by 34.0 and 56.9%, respectively, by adding 1.0 wt% of rGO-TA. In addition, the PVA nanocomposites showed excellent humidity sensing properties over the wide relative humidity range and the long-term stability due to the conductive property of the reduced GO and the enhanced mechanical strength by the effective incorporation of rGO-TA into the PVA matrix.