Tea Polyphenols Functionalized Graphene And The Rubber/Graphene Composites

Graphene, composed of single-layer sp~2hybridized carbon atoms, is a carbonaceousmaterial with two-dimensional honeycomb lattice structure. For it’s special single carbonatomic layer structure, graphene possesses a number of unique physical properties, such ashigh strength, high modulu, high thermal conductivity, high electron mobility, high specificsurface area and high barrier performance, and such exceptional performance makes grapheneespecially promising in the fabrication of the polymer composites. One of the key issues infabricating the polymer/graphene composites is the surface functionalization for graphene.While the reduction and decoration of graphene oxide (GO) is one of the most effectivemethods for the fabrication of the functionalized graphene. In this study, tea polyphenols (TP)which is the extract of natural green tea, was used as both reducer and modifier for GO topreparing the functionalized graphene (TPG). We have investigated the preparation process,functionalized mechanism and microstructure of TPG. Then, TPG was used to fabricate therubber/TPG composites. The mechanical properties and electrical conductivity of rubber/TPGcomposites were studied. These studies are believed to be of great importance theoreticallyand practically in view of the reinforcement and functionlization of the rubber materials.As a kind of plant-based tannin, the low cost and environmentally friendly TP wasverified to be effective reducer and modifier for GO. This method possesses many attractingcharacteristics such as facile process, scalable, low cost and environmentally friendly. TPGexhibits considerably high electrical conductivity and excellent dispersity in water, alcoholsand some other polar solvents. The reduction mechanism of TP towards GO was disclosed.The B ring and C ring in the galloyl units of TP are oxidized to orthoquinone through a twostep SN2nucleophilic reaction followed by one-step elimination. At the same time, the epoxygroups in GO are repaired to carbon-carbon double bond. The main stabilization mechanismsof TPG are disclosed to be the π-π interaction and the steric hindrance provided by the TP ongraphene layer.Through the Michael addition between orthoquinones on TPG and a thiol, STPG whichconsisting sulfide structures was prepared. The preparation condition, reaction mechanism and mircrostructure of STPG were investigated. The results show that STPG has a broaderspectrum of solubility than TPG. In addition, taking advantage of the polyphenol group onTPG, the Mannich condensation between TPG and Jeffamine/formaldehyde was performed.JTPG decorated with the Mannich condensate was accordingly resulted. Except for theexcellent solubility in both water and organic solvent, JTPG can also be fabricated intopaper-like materials by vaccum-assisted filtration. The resulted hybrid film exhibits superiorperformance combination. For example, the tensile strength, break strain and electricalconductivity were measured to be275MPa,8%and700S/m, respectively.Butadiene-styrene-vinyl pyridine rubber (VPR)/TPG composites and styrene-butadienerubber (SBR)/TPG composite were prepared by latex co-coagulation method. TPG wasdemonstrated to be very effective in strengthening the VPR and SBR. TPG was found to beespecially effective in endowing SBR with unusual abrasion resistance. Interestingly,VPR/TPG composites may be vulcanized in absence of additional curing agents. TheSBR/JTPG and NBR/JTPG composites were prepared by melt compounding the gums with aJTPG master batch which was prepared by mixing JTPG and NBR in acetone. TheNBR/JTPG composites could also be prepared by blending JTPG and NBR in acetone,followed by curing with peroxide or sulfur. The structures and properties of these compositeswere investigated. For the NBR/JTPG systems, the composites prepared by solution methodpossess much better dispersion of graphene and consequently much higher reinforcingefficiency. The solution processed NBR/JTPG composites cured with peroxide exhibitsignificantly increased electrical conductivity. The percolation threshold of these compositeswas determined to be as low as0.23vol%。...