Preparation,Stucture And Mechanism Research Of Graphene And Typical Polymer-based Nanocomposites

Graphene, a monolayer of sp2carbon atoms with many unique properties, has gained much attention from various areas, such as the physics, chemistry, material, electron, energy, biology and information technique fields. One of the most promising applications of graphene is the graphene/polymer nanocomposite (GPNC), in which graphene causes significant improvements in various properties. There are still challenges in the academic research and practical application of GPNC:1) preparation of graphene with high efficiency;2) preparation of GPNC with good dispersion and in large quantities;3) investigation of the relationship between the structure and properties as well as the mechanism for the enhanced properties. In order to overcome those challenges, this paper mainly focused on three aspects:1) high efficient preparation of graphite oxide (GO) and graphene;2) a masterbatch-melt blending method to prepare GPNC;3) investigations of the structure, properties and mechanism of the improved properties in GPNC. In order to clarify the roles of the physical barrier effect of graphene, the high thermal conductivity of graphene and the interface interaction between graphene and polymer matrix on the thermal stability and fire safety properties of GPNC, poly(lactic acid)(PLA), poly(vinyl alcohol)(PVA) and polystyrene (PS) was choosen as the polymeric matrix of GPNC. By the compoarisons between GO, graphene and the three kinds of polymers, the mechanism of the improved thermal stabilitiy and fire safety propeties was studied.A pressurized oxidation and an ammonia-hydrazine-based multiplex reduction were developed to prepare GO and graphene, respectively. The pressurized oxidation was carried out in reactor with three steps:adding react agents, low temperature treatment (<5℃,>1hr) and high temperature reaction (60-160℃,>1hr). GO was prepared by the pressurized oxidation with fairly easy operation and controllable morphology and size. The ammonia-hydrazine-based multiplex reduction prepared graphene which can be easily observed by atomic force microscopy with a thickness (0.4-0.6nm) which is fairly closed to the ideal value.A masterbatch-melt blending was employed to prepare graphene/PLA nanocomposites. The graphene was well dispersed and exfoliated in the PLA, and the crystallinity, electrical conductivity, mechanical properties and fire safety performance of the nanocomposites were obviously improved. The mechanism of the improved properties were investigated:1) the graphene started to form a conducting network at the loading content of0.08%;2) the graphene reinforced the mechanism properties of the nanocomposites, but it also cut down the interaction among the PLA molecules and hence reduced the mechanical properties, competition of the reinforcing and the reducing caused inflexions at0.08%-0.2%;3) the high thermal conductivity of graphene was the main reason for the decreased thermal degradation temperature and ignition time, and the mass barrier effect of graphene is the cause of the reduced degradation rate and heat release rate.In the earlier literature, the hydrogen bonding between graphene (or GO) and PVA was regarded as the causes of property enhancements. GO/PVA and graphene/PVA nanocomposites were studied in order to investigate the mechanism of the improved properties. GO and graphene caused obvious property enhancements such as storage modulus and electrical conductivity. There are mainly four conclusions:1) graphene presented a poorer dispersion than GO but caused more property enhancements;2) the hydrogen bonding mainly contributed to the dispersion of the graphene (or GO) layers;3) the main cause of the improved properties was the completeness of graphene (or GO) structure;4) the mass barrier effect was the main reason for the improved thermal stability; when the loading amount was small, the thermal degradation temperature was decreased due to the high thermal conductivity of graphene; when the loading amount was large, the mass barrier effect dominated so the thermal degradation temperature was increased.PS-based nanocomposites were prepared based on GO, graphene, ZrO2-loaded graphene and Ni(OH)2-loaded graphene (joint title:Gs). The Gs were well dispersed and exfoliated due to two reasons:1) the PS in the masterbatch prevented the Gs from aggregation during drying and processing;2) the shearing effect during the melt blending further improved dispersion and exfoliation. The thermal degradation was increased with2%Gs (10.8℃with GO,14.0℃with graphene,10.5℃with ZrO2-loaded graphene and17.5℃with Ni(OH)2-loaded graphene). The peak heat release rate of the above four kinds of nanocomposites was reduced by23%,34%,42%and41%, respectively. There were three conclusions:1) the master-melt blending was feasible for the industrial processing of GPNC, which pioneers a viable path to the practical producing and application of GPNC;2) the mass barrier and interface interaction were found to be the main reasons for the improved thermal stability;3) there was synergism effect between the loaded metal and graphene on the fire safety properties of the PS-based nanocomposites.The masterbatch-melt blending was feasible with thermoplastic polymers but was not available in thermosetting polymers such as epoxy resin. In order to obtain good dispersion and strong interface interaction, GO was modified with hexachlorocyclotriphosphazene and glycidol and then incorporated into epoxy by the in-situ curing. The storage modulus (131%), hardness (32%) and electrical conductivity (6.5magnitude orders) were obviously increased and the maximum degradation rate was decreased by27%.As compared to the tradition preparation methods, the pressurized oxidation, ammonia-hydrazine multiplex reduction and the masterbatch-melt blending were more convenient and efficient. The masterbatch-melt blending offered a feasible way toward the industrial processing of GPNC with good dispersion. The investigations of the properties and mechanism promoted the research of GPNC.