Monohydrated hydrazine

The epoxy resin employed in this study was a difunctional diglycidyl ether of bisphenol A (DGEBA) with an equivalent weight of 175–180 g/equiv. and a hydroxyl/epoxy ratio of 0.03, supplied by Sigma-Aldrich (St. Louis, MI, USA). The hardener was a solid tetrafunctional aromatic amine, 4,4′-diaminodiphenylmethane (DDM), from Sigma-Aldrich, with a molecular weight of 198 g/mol and an amine equivalent weight of 49.5 g/mol.
Commercial powder graphite containing 99 wt % minimum of carbon, 0.8 wt % maximum of ash, and 0.05 wt % maximum of sulfur from Acros Organic was selected for the preparation of GO and rGO. For the oxidation of graphite, sodium nitrate was purchased from Acros Organic, whereas sulfuric acid (95–97%), potassium permanganate (extra pure) and hydrogen peroxide (30 wt %) were purchased from Scharlau. For the GO reduction, monohydrated hydrazine (64–65%) from Sigma Aldrich was used. Pure water by ELIX Advantages (type II) was employed in the current work. All reagents have been used without further purification.

Different reactants were used for synthesizing the waterborne poly(urethane urea) dispersions (PUDs). Dried polyadipate of 1,4-butanediol with molecular weight of 2000 Da—Hoopol F-501 (Synthesia, Barcelona, Spain)—was used as polyol. Isophorone diisocyanate (IPDI, 98 wt.% purity) was used. As internal emulsifier, 2,2 bis(hydroxymethyl) propionic acid (DMPA, 98 wt.% purity) was used, triethylamine (TEA, 99 wt.% purity) was used as neutralization agent, monohydrated hydrazine (HZ, 60 wt.% purity) was used as chain extender, and dibutyltindilaurate (DBTDL, 95 wt.% purity) was used as catalyst—all were supplied by Sigma Aldrich (Barcelona, Spain). Acetone (99.5 wt.% purity)—Sigma Aldrich, St. Louis, MO, USA—and de-ionized water were used.
Three different graphene oxide derivatives were used: Graphene oxide (GO), reduced graphene oxide (r-GO), and amine-functionalized graphene oxide (A-GO)—all were supplied by Graphenea (San Sebastián, Spain). A-GO was obtained by treatment of GO with dodecyl amine. Before use, all GO derivatives were dried in oven at 80 °C overnight and they were kept in oven at 80 °C until use.