Polymer/graphene nanocomposites have generated intensive interest due to their unique properties. Dispersion and interface interactions between graphene and the polymer matrix are two key factors to obtain property enhancements. According to the open literature, in poly(vinyl alcohol) (PVA) nanocomposites, graphene usually obtains more significant property enhancements than graphite oxide (GO), although GO can much more easily form a good dispersion and strong interaction in the PVA matrix because of its oxygenated functionalities, and the reason has not been well documented yet. In this work, graphene and GO were successfully incorporated into PVA; the properties and the mechanism for the property enhancements were investigated. GO formed better dispersion and exfoliation while graphene caused more property enhancements including mechanical properties, electrical conductivity and thermal stability. The mechanical strength of the graphene/GO nano-layers is attributed to be the fundamental cause for the enhancements in crystallinity and mechanical properties; the hydrogen bond among the PVA molecules is the key factor to influence the glass transition temperatures; the hydrogen bond between the graphene/GO nano-layers and PVA matrix is the decisive factor for the exfoliation and dispersion of graphene/GO; the conducting network is the explanation for the increased electrical conductivity; the physical barrier effect of graphene nano-sheets is the main cause for improved thermal stability. This work investigates the mechanisms for property enhancements, clarifies the roles of the hydrogen bond and the mechanical strength of the graphene/GO nano-layers, and explains why graphene usually achieves more property enhancements than GO.

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In order to obtain homogeneous dispersion and strong filler-matrix interface in epoxy resin, graphene oxide was functionalized via surface modification by hexachlorocyclotriphosphazene and glycidol and then incorporated into epoxy resin to obtain nanocomposites via in situ thermal polymerization. The morphology of nanocomposites was characterized by scanning electron microscopy and transmission electron microscopy, implying good dispersion of graphene nano-sheets. The incorporation of functionalized graphene oxide effectively enhanced various property performances of epoxy nanocomposites. The storage modulus of the epoxy nanocomposites was significantly increased by 113% (2% addition) and the hardness was improved by 38% (4% addition). Electrical conductivity was improved by 6.5 orders of magnitude. Enhanced thermal stability was also achieved. This work demonstrates a cost-effective approach to construct a flexible interphase structure, strong interfacial interaction and good dispersion of functionalized graphene in epoxy nanocomposites through a local epoxy-rich environment around graphene oxide sheets, which reinforces the polymer properties and indicates further application in research and industrial areas.

Starting from expandable graphite (EG), graphene, graphite oxide (GO), and organic phosphate functionalized graphite oxides (FGO) were prepared and incorporated into epoxy resin (EP) matrix via in situ polymerization to prepare EP based composites. The structure of the composites was characterized by transmission electron microscopy to show good dispersion without large aggregates. The thermal behavior investigated by thermogravimetric analysis indicated the EP/graphene composites show the highest onset temperature and maximum weight loss temperature compared with those added with GO and FGO. The flame retardant properties investigated by micro combustion calorimeter illustrate that both EP/graphene and EP/FGO composites perform better than EP/GO composites in flame retardant properties with a maximum reduction of 23.7% in peak-heat release rate when containing 5 wt % FGO and a maximum reduction of 43.9% at 5 wt % loading of graphene. This study represents a new approach to prepare functionalized GO with flame retardant elements to improve the flame retardancy of polymer and gives a way of application of graphene in enhancing thermal stabilities of polymer.

Graphene is promising for the fire safety applications of polymers, but the ease of burn out limits further developments. A novel strategy based on functionalized graphene oxide (FGO) is developed to overcome this challenge. Graphene oxide is functionalized with char-catalyzing agents and reactive compounds and incorporated into polystyrene. When FGO-polystyrene composites are degraded or burned, FGO catalyzes the char formation from polystyrene (Char A). Char A protects FGO from burning out and then FGO acts as a graphitic char (Char B). Because of the combination of Char A, Char B, the physical barrier effects of FGO, and the strong interfacial interactions of FGO and polymers, the fire safety properties of the FGO-polystyrene composites are improved, including decreased peak CO release rate (66% decrease), decreased peak CO 2 release rate (54% decrease), decreased peak heat release rate (53% decrease), decreased thermal degradation rate (30% decrease), decreased total heat release (38% decrease), and increased char formation (7 times), etc. This strategy combines several condensed phase flame retardant strategies such as the nanocomposite technique, intumescent flame retardant systems and phosphorus-nitrogen synergism systems, and hence results in more significant improvements as compared with prior work.

Graphite oxide, graphene, ZrO 2 -loaded graphene and b-Ni(OH) 2 -loaded graphene (joint appellation: Gs) were prepared and incorporated into polystyrene so as to improve the fire safety properties of polystyrene. By the masterbatch-melt blending technique, Gs nanolayers were well dispersed and exfoliated in polystyrene as thin layers (thickness 0.7-2 nm). The fire safety properties were visibly improved, including an increased thermal degradation temperature (18 C, PS/Ni-Gr-2), decreased peak heat release rate (40%, PS/Zr-Gr-2) and reduced CO concentration (54%, PS/Ni-Gr-2). The mechanism for the improved thermal stability and fire safety properties was investigated based on this study and previous works. The physical barrier effect of graphene, the interaction between graphene and polystyrene, and the synergistic effect of the metal compounds are the causes for the improvements.

A novel phosphorus- and nitrogen-containing compound (POPHA) has been synthesized by allowing phosphorus oxychloride to react with piperazine and 2-hydroxyethyl acrylate (HEA). Its structure was characterized by FTIR, 1H NMR, and 31P NMR. A series of UV-curable flame-retardant resins were obtained by blending POPHA with EA in different ratios. The flame-retardant properties were characterized by the limiting oxygen index (LOI) and microscale combustion calorimeter (MCC). The results showed that the incorporation of POPHA into EA can improve the flame retardancy of EA dramatically. The thermal properties of the resins were investigated by thermogravimetric analysis (TGA) in air atmosphere. Moreover, the thermal degradation mechanisms of the EA/POPHA were investigated by real-time Fourier transform infrared spectra (RTIR), thermogravimetric analysis/infrared spectrometry (TG-IR), and direct pyrolysis/mass (DP-MS). The morphologies of the formed chars were observed by scanning electron microscopy (SEM) demonstrating the most effective amount of POPHA is 20 wt %.

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