Property Investigation Of Graphene Modified Epoxy And Its Composites

Graphene,a monolayer of sp² carbon atoms,is a novel two dimensional nano-materials with exceptional high strength,modulus,electrical and thermal properties,which has gained much attention in both academia and industrial fields.Graphene shows promising potential applications in various fields,such as capacitor,actuator,battery and composites.One of the most promising applications of graphene is fabrication of composites with polymers since incorporation of graphene into polymers can significantly improve the properties of polymers.However,the application of graphene was limited by weak interface between graphene and polymer as well as its poor dispersion due to its high specific surface area and strong Van der Waals force;moreover,single layer graphene can not be produced in large quantity and the fabrication cost is high.Multi-layer graphene have a good balance between properties and cost.Therefore,the commercially available multi-layer graphene with thickness of 5-7 nm was used in this study,and the fabrication technique of graphene/epoxy composites and the effect of graphene on the morphology,fracture toughness,mechanical,thermal and electrical properties of the resulting composites were investigated.The main work and detailed results are summarized as follows:Nanocomposites of epoxy with 3 wt%and 5 wt%graphene nanoplatelets?GnPs?were fabricated with GnP sizes of⁵?m?GnP-5?and<1?m?GnP-C750?dispersed within an epoxy resin using a sonication process followed by three roll milling.The morphology,fracture toughness,mechanical and thermal properties of the composites were investigated.Scanning electron microscopy?SEM?analysis shows that GnP-5were uniformly dispersed in the epoxy resin;although some agglomerates were observed in the GnP-C750/epoxy composites,most GnP-C750 were also found to be well dispersed within the matrix.Tensile and flexural property measurements indicated higher modulus and strength with increasing concentration of GnP-C750.In contrast,the incorporation of GnP-5 significantly improved the tensile and flexural modulus but reduced the strength of the resulting composites.The effects of different platelet sizes of the GnPs reinforcement on the damage mechanisms of these nanocomposites were studied by scanning electron microscopy.At 35oC,the dynamic storage modulus of GnP-5/epoxy composites increased with increasing platelet concentration,and improved by 12%at 3 wt%and 23%at 5 wt%.The smaller GnP-C750 increased the storage modulus by 5%at 3 wt%loading but only 2%at 5wt%loading.The glass transition temperatures?T_g?of the composites increased with increasing platelet concentration regardless of the GnPs particle size.A marked improvement in thermal conductivity and fracture toughness was measured with the incorporation of 5 wt%GnP-5,reaching 115%and 76%,respectively.Carboxyl terminated butadiene acrylonitrile?CTBN?was added to an epoxy resin to improve the fracture toughness,and then two different lateral dimensions of graphene nanoplatelets in diameter?GnP-C750 and GnP-5?were individually incorporated into the rubber modified epoxy to fabricate multi-phase epoxy based composites.The study showed that GnP-5 are more favorable for reinforcing most properties of CTBN/epoxy.The decreased tensile,flexural and storage modulus of epoxy after the addition of CTBN at ambient temperature were found to be improved and recovered with further addition of 3 wt%GnP-5.The fracture toughness of CTBN/epoxy was further improved by the addition of GnPs;meanwhile,good thermal conductivity was obtained,and larger platelets are easier to form thermal conductivity network.The fracture toughness and thermal conductivity of 10 wt%CTBN modified epoxy containing 3 wt%GnP-5 were significantly enhanced by about108%and 145%,respectively,compared to that of the pure epoxy.Investigations on fracture surfaces disclosed failure and toughening mechanisms;the interactions between cracks and GnPs/CTBN were studied in detail,and a schematic explaining the crack propagation in CTBN/epoxy and GnPs/CTBN/epoxy composites was proposed.To improve the interfacial adhesion,GnPs were treated by concentrated H₂SO₄/HNO₃ mixed acid?Oxygen functional groups were introduced after the acid treatment.The acid treated GnPs were further modified by a liquid rubber amine-terminated poly?butadiene-co-aocrylonitrile??ATBN?,Raman and XPS analysis show that GnPs were successfully functionalized with ATBN.Different amount of ATBN-GnPs and pristine GnPs were individually incorporated into epoxy resins to fabricate epoxy composites.The flexural and storage modulus increases with increase of filler content.Compared with the pristine GnPs,ATBN-GnPs demonstrated stronger ameliorating effects due to an enhanced GnPs-epoxy inter-facial adhesion.At 5 wt%GnPs content,the flexural modulus of GnPs/epoxy composite increased by 18.1%,whereas,the ATBN-GnPs improved the flexural modulus by 22.1%at the same fraction.The flexural strength of ATBN-GnPs/epoxy composites is higher than that of the non-modified GnPs/epoxy composite due to the enhanced interface adhesion between ATBN-GnPs and matrix.A remarkable enhancement of quasi-static fracture toughness(K_IC)was obtained at 5 wt%GnP and5 wt%ATBN-GnPs with 76.2%and 92.8%increase,respectively.Incorporation of 5wt%ATBN-GnPs improved thermal conductivity of the neat epoxy by 133.6%,and the thermal conductivity of 5 wt%ATBN-GnPs/epoxy is about 16%higher than that of the pristine GnPs/epoxy.GnPs were first dispersed in a water-based solution with the aid of polyethylenimine.A thin GnPs film?paper?having highly in-plane aligned platelets was produced by using a vacuum-assisted self-assembly?VASA?technique.After heat treatment,the GnPs paper was immersed in an epoxy/acetone bath at room temperature under vacuum to produce an epoxy impregnated composite.After removal of the acetone,nanocomposites consisting of multiple layers of the GnPs paper with up to 27.2 wt%GnPs were fabricated and thermally cured.Scanning electron microscopy?SEM?examination showed that the GnPs paper was fully impregnated with epoxy resin,the GnPs were well dispersed and aligned,and a good thermal and electrical conductivity network was formed.At 30 ^oC,dynamic mechanical analysis?DMA?results showed that the storage modulus of the resulting nanocomposites with 27.2 wt%GnPs reached 10.2 GPa,a 300%increase compared to the neat epoxy.The resulting composites also exhibited electrical conductivity as high as 35 Siemens per centimeter?S/cm?.This research demonstrates that the VASA processing technique is capable of fabricating well aligned,high GnPs content nanostructured polymer composites with high electrical conductivity.GnPs modified epoxy were combined with fibers to prepare fiber reinforced composites.First,3 wt%and 5 wt%of GnP-C750 and GnP-5 were individually integrated into epoxy suspension,glass fibers were then impregnated with the modified epoxy resins by hand lay-up method.GnPs/epoxy/glass composites were fabricated using the vacuum bag-autoclave curing process.The results showed that the flexural modulus of the GnPs/epoxy/glass composites increases with the increasing GnPs contents,and was improved by 11.5%and 26.3%with the addition of 5 wt%GnP-C750 and GnP-5,respectively.At the same filler content,the storage modulus of epoxy/glass composites incorporated with GnP-C750 and GnP-5 at 30oC was enhanced by 10.2%and 28.2%,respectively.The flexural strength of the 3 wt%GnP-5 reinforced glass fiber/epoxy composite is 16.2%higher than that of the glass fiber/epoxy composite.The dispersion results of GnPs in the composites and the interfacial interactions between fibers and modified matrix were observed with SEM.