Synthesis Of Graphene And Its Application In Polymer Composites

Graphene is a novel two-dimensional inorganic nano-materialdeveloped recently, it has great promise applications in the fields ofchemistry, physics, material science, electronics, and so on, since its firstsuccessful fabrication. Especially, it is because of its ultrahigh mechanicalproperty, excellent electrical and thermal conductivity, and abundantresources (graphite) that graphene shows promise as an ideal reinforcingagent for reinforcement of polymer composite materials. However, thefabrication of graphene based materials, the homogeneous incorporation ofgraphene into polymer matrix and optimizing the interfacial interactionsbetween them are still obstacles to be resolved in both academia andindustry. With the aim of addressing these problems, this dissertationfocuses on and realizes the preparation of graphene and fuctionalizedgraphene by employing a number of novel methods, and has successfullyfabricate several kinds of high-performance graphene/polymer composites.The details of research are as follows:(1) Poly-p-phenylene terephthalamide (PPTA) oligomerfunctionalized graphene (FGS) was prepared by simple grafting ofamino-terminated PPTA oligomer on the surface of graphene oxide (GO)followed by reducing with hydrazine hydrate. By using FGS as fillers, Poly(methyl methacrylate)(PMMA) and Polyimide (PI) composites werefabricated. High-level reinforcement of both PMMA and PI was observedwith low content of FGS (≤0.2wt%), but no further improvement wasobtained as the content of FGS further increased. The mechanism of thereinforcement was discussed based on morphological characterizations of the composites. Moreover, the glass transition temperature and thermalstability of PMMA were also increased with the addition of FGS.(2) Homogenous organic dispersion of graphene oxide (GO) wasprepared by a solvent-exchange method. This method enabled thesimultaneous achievement of full exfoliation and high concentration of GOin several high boiling-point organic solvents, overcoming the problem ofpoor dispersion of GO in organic solvent. Then, poly[2,2'-(p-oxydiphenylene)-5,5'-bibenzimidazole](OPBI)/GO compositeswere fabricated by a solution-casting method. Morphologicalcharacterization taken of the fracture surface of composites revealed that thestructure of composites changed to quasi-layered structure as the addition ofsmall amounts of GO. The incorporation of GO also showed profoundeffects on the mechanical and thermal properties of OPBI. The mechanismof reinforcement was explained based on the special morphology of thecomposites.(3) Taking graphene oxide (GO) as a precursor, a green and facilestrategy was developed for the fabrication of soluble graphene. This methodwas based on the reduction of GO sheets in green tea solution by makinguse of tea polyphenol (TP) that contained in tea solution as both reducingagent and stabilizing agent. The measurements of the resultant grapheneconfirmed the efficient removal of the oxygen-containing groups in GO. Theπ-π interactions between the reduced graphene and the aromatic TPguaranteed the good dispersion of the reduced graphene in both aqueous anda variety of organic solvents. This green approach shows great potential inthe field of bio-related materials, especially for high-performancebio-materials as demonstrated in this section of chitosan/graphenecomposites.(4) Graphene was fabricated by a simple liquid-phase exfoliation ofgraphite in methanesulfonic acid (MSA) with the aid of sonication. Raman,XPS and FT-IR spectroscopy revealed that the obtained graphene was withlow defect density and low degree of oxidation. TEM and AFM measurements further confirmed that the resultant graphene was inwell-exfoliated state. Using the graphene/MSA solution as a reaction solventmedium, graphene/OPBI composites were fabricated by in situpolymerization. The assessment of the mechanical and thermal properties ofthe composites revealed high reinforcement efficient of the high-qualitygraphene. All these features make this simple procedure a potential route forthe fabrication of low-cost and high-performance polymer composites.(5) Graphite oxide (GO) with different oxidation degrees were preparedby a modified Hummers method with different amounts of oxidant. Themeasurements conducted on the samples showed that the amount of oxidanthad significant effects on the composition, structure and morphology of GO.Compared to traditional GO nanosheets (GONS), the GONS exfoliated fromlow-oxidation-degree GO were high-quality with low-level oxygenfunctionalities and low density of defects, which might provide possibilityfor large-scale fabrication of high-quality graphene. Meanwhile, we alsodemonstrated the superior reinforcement effect of this high-quality GONSover traditional ones.(6) Graphene oxide nanoribbon (GONR) was prepared by oxidativeunzipping of multiwalled carbon nanotube (MWNT), which involved thelengthwise cutting and exfoliation of the walls of MWNT. During unzippingprocess, different amounts of oxidant were used to obtain GONR withdifferent oxidation and unzipping degrees. The surface functionalities,morphologies and structures of GONRs with different unzipping degreewere characterized by several measurements. The mechanical test of theresultant poly(vinyl alcohol)-based composites confirmed that the GONRwas more effective than pristine MWNT in terms of reinforcing polymers instrength and modulus, and the GONR prepared by400%oxidant showedthe highest reinforcement effect.