Polyester-amide hyperbranched polymer as an interfacial modifier for graphene oxide nanosheets: Mechanistic approach in an epoxy nanocomposite coating

Graphene Oxide nanosheets (GO) are synthesized through modified Hummer's method using expandable graphite. Consequently, the synthesized GO is surface functionalized by the aid of a polyester-amide hyperbranched polymer (HB) possessing hydroxyl end-groups. The characteristics of the surface modified GO are assessed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV-VIS spectroscopy and thermogravimetric analysis (TGA). The results show that HB molecules have been adsorbed on the GO surface and the dspacing of the GO lamellae has been increased from 11.058 angstrom to 13.763 angstrom. Subsequently, the modified GOs are impregnated into an epoxy resin at various loadings and dispersed utilizing mechanical agitation and complementary sonication process. The d-ispersions are mixed and cured with stoichiometric amount of a poly-amidoamine-based curing agent and applied on glass substrates to form 75-100 mu m thick free-standing films. Viscoelastic behavior are then evaluated by dynamic mechanical analysis (DMA). The results show that storage (E') modulus is enhanced and the glass transition temperatures (T-g) increases as GO and its modified counterparts are impregnated. Also, among the nanocomposites, coatings prepared by HB/GO = 0.5 and HB/GO = 1 show better improved properties indicating there exists an optimum ratio of GO/HB in which maximum surface modification has occurred.