石墨片对环氧树脂的热学、力学和电学性能影响

文章编号:1007-8827(2015)05-0432-06石墨片对环氧树脂的热学㊁力学和电学性能影响Subhra Gantayat1,2,Gyanaranjan Prusty1,Dibya Ranjan Rout2,Sarat K Swain1(1.Department of Chemistry,Veer Surendra Sai University of Technology,Burla,Sambalpur768018,India；2.School of Applied Science(Physics),KIIT University,Bhubaneswar751024,India)摘要:采用溶液技术制备出膨胀石墨增强环氧树脂复合材料㊂对石墨进行化学改性以提高与环氧树脂的相容性㊂采用XRD﹑FE-SEM和HR-TEM对环氧树脂/膨胀石墨复合材料进行表征㊂与环氧树脂相比,添加质量分数9%膨胀石墨后,该复合材料的热分解温度从340ħ升高至480ħ,抗张应力提高30%,导电率由10-15增加至10-5数量级㊂热学﹑力学和电学性能的显著提高,主要归因于膨胀石墨纳米片在环氧树脂基体中的良好分散性,从而可用于广泛的应用领域㊂关键词:膨胀石墨；扫描电镜；透射电镜；导电率中图分类号:TB332文献标识码:A通讯作者：Sarat K Swain.E-mail：swainsk2＠yahoo.co.inExpanded graphite as a filler for epoxy matrix composites toimprove their thermal,mechanical and electrical propertiesSubhra Gantayat1,2,Gyanaranjan Prusty1,Dibya Ranjan Rout2,Sarat K Swain1（1.Department of Chemistry,Veer Surendra Sai University of Technology,Burla,Sambalpur768018,India；2.School of Applied Science（Physics）,KIIT University,Bhubaneswar751024,India）Abstract:Expanded graphite(EG)-reinforced epoxy composites were prepared by a solution mixing method.The structure and morphology of the EG/epoxy composites were investigated by XRD,FE-SEM and HR-TEM.The EG prepared by acid oxidation and thermal expansion shows good compatibility with the epoxy resin that enters the EG layers to decrease their thickness to60-70nm,owing to its abundant oxygen-containing functional groups.With the addition of9wt%EG,the thermal decomposition temperature of the composite increases from340to480ħ,the electrical conductivity from10-15to10-5S/cm and the tensile stress is increased by more than30%.These improvements are attributed to the good dispersion of EG sheets in the epoxy matrix. Keywords: Expanded graphite；FE-SEM；HR-TEM；ConductivityReceived date:2015-03-05； Revised date:2015-10-08Corresponding author:Sarat K Swain.E-mail:swainsk2＠yahoo.co.inEnglish edition available online ScienceDirect(http:／／／science／journal／18725805).DOI:10.1016/S1872-5805(15)60200-11 IntroductionPolymer matrix composites are multi-phase mate-rials produced by combining polymer resins with rein-forcing fillers having improved properties in compari-son with the matrix materials.Hence,different fillers are used to enhance the physical and mechanical prop-erties of composites.Polymer matrix composites are of scientific and industrial interest because of their en-hanced properties arising from the reinforceing func-tion of nanofillers[1-4].Different conducting fillers such as carbon nanotubes and graphite have been ex-tensively studied because of their ability to increase the mechanical,thermal and electrical properties of the native polymers[5,6].Epoxy resins are a class of thermoset materials available in various forms from low viscosity liquid to high melting solids,which are widely used as poly-mer matrices in composites,owing to their high strength,low shrinkage,excellent adhesion to sub-strates,chemical resistance and low cost.Most of polymers are generally electrical insulators with very low concentrations of free charge carriers.Thus they are non-conductive and transparent to electromagnetic radiations.This property made them incapable for the use as enclosures for electronic equipments.Hence, these limitations are the causes of growing research activities for electrically conducting polymers.Con-ducting polymers can be either inherently conductive or insulating polymers composited with conductive fillers.Conductive composites are used in light emit-ting devices,batteries,electromagnetic shielding and第30卷第5期2015年10月新型炭材料NEW CARBON MATERIALS Vol.30 No.5 Oct.2015other functional applications[7-9].Conductive fillers such as carbon black,carbon nanotubes and graphite have been extensively investigated[10-16].These fillers effectively improve the electrical conductivity of the polymers.The significant increase in electrical con-ductivity with the filler content has been observed for most composites,which could be explained by the percolation transition from the formation of the con-ductive network[17].In comparison to carbon nanotubes,graphite continues to attract considerable attentions because of their mechanical and electrical properties,low densi-ty,easy processing and low cost.Graphite exists as a layered material and the layers are packed closely by Van der Waalsᶄforce.For an efficient utilization of graphite as filler in a polymer composite,its layers must be partly separated to obtain expanded graphite that is dispersed throughout the polymeric matrix. Also in its natural form,little reactive groups exist on the graphite and as a result,it is difficult to intercalate monomers into the graphite interlayer to form a com-posite.If the raw graphite is used as reinforcement,it is not possible to disperse graphite layers in epoxy matrix.The EG is prepared when raw graphite ex-posed to strong oxidizers such as nitric acid(HNO3), sulphuric acid(H2SO4)or potassium permanganate (KMnO4).In comparison to raw graphite,the EG sheets are heavily oxygenated having hydroxyl and epoxide functional groups on their basal planes,in ad-dition to carbonyl and carboxyl groups located at the sheet edges.The presence of these functional groups makesthem strongly hydrophilic.EG can be readily dispersed in water and incorporated into polymer ma-trices with a help of these functional groups for the preparation of composites.Chen et al.[18]measured the tensile strength of the EG/polystyrene composite and found that its tensile strength is a little higher that of the pure polystyrene.Kim et al.[19]compared the thermal property of virgin polylactic acid withthat of the EG/polylactic acidcomposites,and found that the thermal stability of the composites increased with the EG content.Xiao et al.[20]measured the thermal property of the polystyrene/graphite composite and reported a thermal degradation temperature of the composite20ħhigher than that of pure polystyrene.Though graphite was extensively investigated as filler in polymer matrix composites,EG was paid less attention.In the present study,the dispersion of EG in epoxy matrix to prepare EG/epoxy composites was investigated to reveal its influence on the mechanical, thermal and electrical properties of EG/epoxy com-posites.2 Experimental2.1 MaterialsEpoxy resin was purchased from Merck,India. Concentrated H2SO4and HNO3were analytical grade chemicals and used directly without any further purifi-cation.Graphite fine powder with an average diame-ter of500μm was purchased from Loba chemical Pvt.Ltd.,India for preparing the EG.2.2 Preparation of EGRaw graphite was first dried in a vacuum oven for24h at100ħ.Then a mixture of concentrated H2SO4and HNO3with a volume ratio of4：1was add-ed slowly to a glass flask containing graphite powder with vigorous stirring.After24h of reaction,the acid treated graphite powder was filtered and washed with deionised water until the pH value of the filtrate reached6.4.After drying at100ħfor24h,the re-sulting graphite intercalation compound was subjected to a thermal shock at900ħfor one minute in a fur-nace to form the EG.2.3 Synthesis of EG/epoxy compositesEG/epoxy composites were synthesized to have different contents of EG(3,6,and9wt%based on epoxy weight)by a solution mixing method.Calcu-lated amount of epoxy and EG were separately dis-persed in deionised water at ambient temperature via stirring for0.5h.The EG suspension was added to the epoxy solution and stirring was continued for3h. The resulting solution was centrifuged for15min and the resulting sample was dried in an oven at50ħ. The detail synthetic process is illustrated in Fig.1.Fig.1 Schematic representation for the preparationof EG/epoxy composite.2.4 CharacterizationX-ray diffraction(XRD)of the composites was carried out by a Rigaku X-ray diffractometer(Model No.P.DD966)with Cu Kαradiation at40kV and 150mA.The morphology and dispersion of the EG in epoxy resin were investigated by using a field emis-sion scanning electron microscope(JEOL-JSM-5800).A high resolution transmission electron micro-scope(Tec-nai12,Philips)operating at120kV was used to study the dispersion of EG in epoxy matrix.㊃334㊃第5期Subhra Gantayat et al:Expanded graphite as a filler for epoxy matrix composites to improve theirMechanical properties of the EG/epoxy composites were measured with ASTM-D-638-00using an Instron testing machine(Model-5567)and the test was per-formed at a rate of50mm/min with a load of0.5 ton.The five specimens for each composition were used for measurement and average values are repor-ted.The TGA analysis was carried out by taking the sample in the pan(8-10mg)and the temperature was increased by10ħper minute and heated up to 800ħ.Conducting measurment was carried out using LCR-Hi Tester,HOIKI after the sample being pro-cessed into petlet form.3 Results and discussion3.1 Structural AnalysisThe XRD patterns of raw graphite(RG),epoxy and the EG/epoxy composites are shown in Fig.2. The raw graphite exhibits a sharp diffraction peak at 2θvalue of26.36ᶄ.The peaks at2θvalues of77ᶄ, 54ᶄand44ᶄbelong to epoxy resin and the peak at2θvalues of26.36ᶄis ascribed to graphite.All the above peaks of epoxy and graphite are present in the EG/epoxy composites confirm the formation of com-posites.Similarly,the FE-SEM image of EG is shown in Fig.3a.It is found that the EG changes in-to sheets with thickness about60-70nm.Fig.3b,c and d show the FE-SEM images of the EG/epoxy composites at3%,6%and9%of EG respectively. In all these micrographs,the white spots indicate the epoxy matrix,whereas,the dark spots represent the EG sheets.The good dispersion of EG sheet in epoxy matrix directly correlates with its effectiveness for im-proving mechanical,thermal and electrical properties, which is another indirect evidence for a better interfa-cial adhesion between epoxy resin and EG.The simi-lar results have been reported in the earlier litera-tures[21,22].Due to the delamination nature of EG lay-ers,epoxy molecules easily enter into the graphite layers to form an exfoliated structure.Fig.4a shows the HR-TEM image of the EG.The dispersion state of EG sheets in the HR-TEM of epoxy resin is shown in Fig.4b.Further,it is noticed that the EG sheets are distributed in the epoxy resin with some local ag-glomerations.3.2 Thermal propertiesThermogravimetric analysis(TGA)is used to study the thermal properties of EG,epoxy and the EG/epoxy composites as shown in Fig.5.It is found that the thermal decomposition temperatures of the composites in all samples shift towards high tempera-tures as compared with that of virgin epoxy.The ther-mal degradation temperature for epoxy resin is340ħwhile those of the EG/epoxy composites are360,440 and480ħat3%,6%and9%of EG respectively. So the addition of EG lowers the thermal degradation rate of epoxy matrix.The residual weight of the EG/ epoxy composites is higher than that of epoxy resin. The residual weight of the EG/epoxy composites are 8%,24%and30%for the composites containing 3%,6%and9%of EG respectively,whereas,in case of epoxy no residue is left.The high residual mass of the composites is due to strong compatibility and interaction of EG with epoxy resin.Thus,the in-creased thermal degradation temperature for the EG/ epoxy composites indicate the enhancement of thermal stability of epoxy resin by EG.Otherwise,EG is act-ing as a thermal stabilizer[23-25]for epoxy resin,which could have a wide range of potential applications.Fig.2 XRD patterns of Epoxy and EG/epoxy composite at different percentage of EG concentration and XRD of raw graphite(Inset).3.3 Mechanical propertiesMechanical properties including extension at break,load at break,tensile stress and tensile strain of epoxy resin and its composites with different EG percentages are compared in Fig.6.The extension at break of the EG/epoxy composites decreases with the EG percentages(Fig.6(a)).It is interesting to note that extension at break is reduced by3times with an addition of3%of EG.The load at break of the com-posites increases monotonically with the EG percenta-ges.From Fig.6(b),load at break of the compos-ites increases by approximately6times as compared with that of raw epoxy resin.It may be due to strong interfacial adhesion between EG and epoxy matrix. Further,it is observed that tensile stress increases with ithe EG percentages(Fig.6(c)).However,the ten-sile strain of the EG/epoxy composite at9%of EG is reduced by9times in comparison with that of epoxy resin.A sudden fall of tensile strain of the composites is noticed by an addition of3%of EG(Fig.6(d)). It may be due to the uniform dispersion of EG sheets within the epoxy matrix.Hence due to the rigidity of epoxy,EG sheets cannot be deformed by external stress㊃434㊃新型炭材料第30卷in the composite specimen but act as stress concentration during the deformation process of the composites.From the results of mechanical properties,it is remarked that the dispersion state of EG sheetsin epoxy matrix played a vital role in decreasing the strain at break and increasing the tensile strength of the composites.Fig.3 FE-SEM images of(a)expanded graphite and EG/epoxy composite at graphite concentration of(b)3%,(c)6%,(d)9%.Fig.4HR-TEM images of(a)expanded graphite(b)EG/epoxy composite at9%of EG concentration.Fig.5 TGA curves of(a)epoxy,(b)EG/epoxy,3% (c)EG/epoxy,6%(d)EG/epoxy,9%(e)expanded graphite.3.4 Electrical conductivityElectrical conductivity of a composite generally depends upon the particle size,extent of dispersion and structure of conducting nanofillers as well as the properties of host polymers.The addition of conduc-tive nanofillers to an insulating polymer can result in an electrically conductive composite,if the filler con-centration exceeds the percolation threshold,which is defined as the minimum amount of filler required for the formation of a three dimensional conductive net-work within the polymer matrix.The EG/polymer composites exhibit a very low percolation threshold for electrical conductivity because of a large aspect㊃534㊃第5期Subhra Gantayat et al:Expanded graphite as a filler for epoxy matrix composites to improve theirFig.6 Mechanical properties of EG/epoxy composites as a function of EG concentration for study of(a)extension at break(b)load at break(c)tensile stress at break(d)tensile strain at break. ratio and the nanoscale dimension of the EG in poly-mer matrix.Fig.7shows the variation of the electrical con-ductivity of the EG/epoxy composites as a function ofEG content.The addition of EG within epoxy im-proves its conductivity significantly with a sharp tran-sition from an electrical insulator to an electrical con-ductor.The conductivity as a function of EG contentis plotted at constant frequency and it is found that theconductivity increases with the EG content from3%to9%.The increase in conductivity with EG contentfrom3%to6%is used to determine the percolationthreshold,a critical value at which a three dimension-al conductive network is formed.The conductivity of epoxy is about2.3ˑ10-15S/cm in the initial stage, which is regarded as a typical insulator.The conduc-tivity of the composites is about2.1ˑ10-5S/cm at 9%of EG,which is nearly a typical conductor. Hence,an incorporation of EG into epoxy resin in-creases the electrical conductivity significantly due to a good dispersion.The observations in this paper are in good agreement with those of our earlier re-ports[26,27].The epoxy resin composites reinforced by EG are good antistatic materials(conductivity~ 10-5S㊃cm-1).Fig.7 Electrical conductivities of the EG/epoxy compositesas a function of EG content.4 ConclusionsA series of EG/epoxy composites were prepared by a solution mixing method.The interaction of EG with epoxy matrix was investigated.The structure and morphology of the composites were studied by XRD and electron microscopy.The thermal,mechanical and electrical properties of epoxy resin are improved with increasing EG contents.In the EG/epoxy com-posites,EG sheets plays a vital role in decreasing the strain at break and increasing the tensile strength of the composites as compared with those of epoxy res-㊃634㊃新型炭材料第30卷in.The thermal stability of epoxy resin is enhanced with increasing the EG percentages.The mechanical and thermal properties of epoxy are improved due to the strong interfacial adhesion of the EG with epoxy matrix.Moreover,the epoxy resin is converted into electrically conductive materials by dispersing EG sheets into epoxy matrix. AcknowledgementsThe authors are thankful to Department of Atom-ic Energy,BRNS,and Government of India for pro-viding financial support under Grant OM＃2008/20/ 37/5/BRNS/1936.Authors are also thankful to Dr.D.Das of Inter University Consortium,Kolkata,In-dia for analysis of XRD.References[1] Swain S K,Isayev A I.PA6/clay nano-composites by continu-ous sonication process[J].Appl Polym Sci,2009,114:2378-2387.[2] Sahoo P K,Samal R,Swain S K,et al.Synthesis of poly(bu-tyl acrylate)/sodium silicate nanocomposite fire retardant[J].Eur Polym J,2008,44:3522-3528.[3] Lapshine S,Swain S K,Isayev A I.Ultrasound aided extrusionprocess for preparation of polyolefin-clay nanocomposites[J].Polym Eng Sci,2008,48:1584-1591.[4] Swain S K,Isayev A I.Effect of ultrasound on HDPE/clay nano-composites:Rheology,structure and properties[J].Polymer, 2007,48:281-289.[5] Prusty G,Swain S K.Synthesis and characterization of conduc-ting gas barrier polyacrylonitrile/graphite nanocomposites[J].Polym Compos,2011,32:1336-1342.[6] Prusty G,Swain S K.Dispersion of expanded graphite as nano-platelets in a copolymer matrix and its effect on thermal stability, electrical conductivity and permeability[J].New Carbon Materi-als,2012,27:271-277.(Prusty G,Swain S K.纳米石墨片/共聚物复合材料及其耐热﹑导电和气密性[J].新型炭材料,2012,27:271-277.) 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[27] Ma P C,Siddiqui N A,Marom G,et al.Dispersion and func-tionalization of carbon nanotubes for polymer-based nanocom-posites:A review[J].Composites:Part A,2010,41:1345-1367.㊃734㊃第5期Subhra Gantayat et al:Expanded graphite as a filler for epoxy matrix composites to improve theirpp.425-431Preparation and oil absorption performance of sponge-like activated carbon/organic compositesMA Wei,XU Sai-nan,CHEN Ke,GUO Yu-qiang,ZHAO Feng-hui,CHEN YongCoconut shell activated carbons were modified to increase their oil-absorption ability and a3D sponge-like activa-ted carbon/organic composite was then prepared through polymerization of polyvinyl alcohol with formalin in the presence of a foaming agent and the modified activated carbon.pp.432-437Expanded graphite as a filler for epoxy matrix composites to improve their thermal,mechanical and elec-trical propertiesSubhra Gantayat,Gyanaranjan Prusty,DibyaRanjan Rout,Sarat K SwainExpanded graphite(EG)-reinforced epoxy composites were prepared by a solution mixing method.With the ad-dition of9wt%EG,the thermal decomposition temperature of the composite increases from340to480ħ,the electrical conductivity from10-15S/cm to10-5S/cm and the tensile stress is increased by more than30%.石墨片对环氧树脂的热学、力学和电学性能影响作者：Subhra Gantayat， Gyanaranjan Prusty， Dibya Ranjan Rout， Sarat K Swain，Subhra Gantayat， Gyanaranjan Prusty， Dibya Ranjan Rout， Sarat K Swain作者单位：Subhra Gantayat,Subhra Gantayat(Department of Chemistry, Veer Surendra SaiUniversity of Technology, Burla, Sambalpur 768018, India;School of AppliedScience (Physics), KIIT University, Bhubaneswar 751024, India)， GyanaranjanPrusty,Sarat K Swain,Gyanaranjan Prusty,Sarat K Swain(Department of Chemistry,Veer Surendra Sai University of Technology, Burla, Sambalpur 768018, India)，Dibya Ranjan Rout,Dibya Ranjan Rout(School of Applied Science (Physics), KIITUniversity, Bhubaneswar 751024, India)刊名：新型炭材料英文刊名：New Carbon Materials年，卷(期)：2015,30(5)引用本文格式：Subhra Gantayat.Gyanaranjan Prusty.Dibya Ranjan Rout.Sarat K Swain.Subhra Gantayat. Gyanaranjan Prusty.Dibya Ranjan Rout.Sarat K Swain石墨片对环氧树脂的热学、力学和电学性能影响[期刊论文]-新型炭材料 2015(5)。