Research On Epoxy Resins Modified By Flexible Segments And Functionalized Graphene Nanosheets

The epoxy resins (EP) have been widely applied in many industrial fields, such ascoatings, composite materials, high-performance adhesives, electrical insulatingmaterials owing to its unique mechanical and thermal properties, outstanding adhesionproperties, high chemical and corrosion resistance, and so on. However, due to theirhigh crosslink density, epoxy resins have some disadvantages such as brittle and notchsensitive, which limit their application in high-tech world. Therefore, lots of effortshave been devoted to improve the fracture toughness and impact resistance of theepoxy resins. In terms of the problems existed in traditional modification of epoxyresins, in our work flexible segments and functionalized graphene nanosheets wereprepared to modify epoxy resins. The main contents and conclusions are described asfollows:(1) Reactive modifier diglycidyl ether of diethylene glycol (DGEG) with aviscosity of25mpa s and epoxy value of0.508had been synthesized from diethyleneglycol (DEG) and epichlorohydrin (ECH). The DGEG/EP composites were prepared byintroducing different contents of DGEG into EP. The tensile and impact tests resultsshowed that the addition of flexible DGEG generally improved the elongation at breakand impact strength.28wt.%of DGEG was observed to increase the elongation atbreak of pure epoxy resin by175.0%and the impact strength by120.3%.(2) The graphite oxides (GO) were obtained by modified Hummers method.Through sonication and mechanical stirring the graphite oxides were exfoliated intographene oxide nanosheets and then introduced into the epoxy resin matrix to preparethe GO/EP composite. Unfortunately, the tensile test showed that the tensile strength ofthe GO/EP composite were inversely proportional to the content of DGEG, thedifferential scanning calorimetry (DSC) anslysis showed that the glass transitiontemperature (Tg) decreased with increasing the DGEG content.(3) The m-xylylenediamine (m-XDA) was covalently anchored on grapheneoxides, via the amidation reactions of terminal amines with carboxy groups attached tothe GO. The derivation was donated as m-GN and used as novel nanofillers of epoxyresin matrix. The m-GN/EP composite with different amounts of m-GN werefabricated by sonication and mechanical stirring. The tensile results demonstrated thatcompared to the pure epoxy resins the addition of only0.1wt.%m-GN yielded a~17% increase in tensile strength from55.8MPa to65.3MPa, and~262.2%increase intensile toughness from0.71MPa/m to3.3MPa/m. The thermal properties presented thatthe Tg of m-GN/EP composite showed a little decrease, while the peak temperature ofmaximum rate of weight loss (Tp) increased compared with that of EP.(4) Long chain polyether amine D400and D2000were grafted onto the grapheneoxides through the amidation reactions of terminal amines with carboxy groupsattached to the GO. The derivations were respectively donated as D400-GN andD2000-GN, and used as tougheners of epoxy resins. Based on the sonication andmechanical stirring, the D400-GN/EP and D2000-GN/EP composites were obtained.The mechanical results demonstrated that by addition of only0.1wt.%of D400-GN thecomposites showed a~25.3%increase in tensile strength,252.1%increase in tensiletoughness. In the same case the D2000-GN/EP composite presented a~21.6%increasein tensile strength,67.6%increase in tensile toughness.