Bihe Yuan

Functionalized reduced graphene oxide (FRGO) wrapped with a phosphorus and nitrogen-containing flame retardant (FR) was successfully prepared <italic>via</italic> a simple one-pot method and well characterized.

Graphene is prepared from graphite by pressurized oxidation and multiplex reduction. The pressurized oxidation is advantageous in easy operation and size-control, and the multiplex reduction, based on ammonia and hydrazine, produces single-atom-thick graphene (0.4–0.6 nm thick) which can be directly observed by atomic force microscopy. A masterbatch strategy, which is feasible in “soluble” thermoplastic polymers, is developed to disperse graphene into poly(lactic acid) by melt blending. The graphene is well dispersed and the obtained nanocomposites present markedly improved crystallinity, rate of crystallization, mechanical properties, electrical conductivity and fire resistance. The properties are dependent on the dispersion and loading content of graphene, showing percolation threshold at 0.08 wt%. Graphene reinforces the nanocomposites but cuts down the interactions among the polymer matrix, which leads to reduced mechanical properties. Competition of the reinforcing and the reducing causes inflexions around the percolation threshold. The roles of the heat barrier and mass barrier effects of graphene in the thermal degradation and combustion properties of the nanocomposites are discussed and clarified.

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.