Preparation of hyperbranched poly (amidoamine)-grafted graphene nanolayers as a composite and curing agent for epoxy resin

Highlights: • Improvement of epoxy resin's thermal stability was achieved by preparation of a curing agent containing graphene oxide (GO) and poly (amidoamine) (PAMAM) dendrimer. • Hyperbranched PAMAM-modified GO (GD) was prepared by a divergent dendrimer synthesis methodology. • Then, epoxy resin was cured in the presence of different amounts of GD and the final products were compared with ethylenediamine-cured epoxy resin (E) in their char contents. • Char residue and decomposition temperature are higher for composites compared with E which indicates higher thermal stability of composites. Thermal properties of epoxy resin were improved by preparation of a curing agent of poly (amidoamine) (PAMAM) dendrimer-grafted graphene oxide (GO). Hyperbranched PAMAM-modified GO (GD) was prepared by a divergent dendrimer synthesis methodology. Modification of GO with (3-Aminopropyl)triethoxysilane (APTES), Michael addition of methacrylic acid, and amidation reaction with ethylenediamine results in the curing agent of GD. Then, epoxy resin was cured in the presence of different amounts of GD and the final products were compared with ethylenediamine-cured epoxy resin (E) in their thermal degradation temperature and char contents. Functionalization of GO with APTES and hyperbranched dendrimer formation at the surface of GO were evaluated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and thermogravimetric analysis (TGA) results. TGA results showed that the weight loss associated with chemical moieties in GONH2, GOMA, and GD is estimated to be 10.1, 12.2, and 14.1%, respectively. Covalent attachment of dendrimer at the surface of GO increases its thermal stability. TGA also showed that decomposition temperature and char content are higher for composites compared with E. Scanning and transmission electron microscopies show that flat and smooth graphene nanolayers are wrinkled in GO and re-stacking and flattening of nanolayers is observed in GD.