石墨片对环氧树脂的热学、力学和电学性能影响_图文

1、文章编号 :1007-8827(201505-0432-06石墨片对环氧树脂的热学 力学和电学性能影响 Subhra Gantayat 1, 2, Gyanaranjan Prusty 1, Dibya Ranjan Rout 2, Sarat K Swain 1(1. Department of Chemistry , Veer Surendra Sai University of Technology , Burla , Sambalpur 768018, India ；2. School of Applied Science (Physics , KIIT University , Bh

2、ubaneswar 751024, 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 对石墨进行化学改性以提高与环氧树脂的相容性 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 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 340 升高至 480 , 抗张应力提高 30%, 导电率由 10-15增加至 10-5数量级 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 关键词 :膨胀石墨 ；扫描电镜 ；透射电镜 ；导电率中图分类号

3、:TB 332文献标识码 :A通讯作者 ：Sarat K Swain. E-mail ：swainsk 2yahoo. co. inExpanded graphite as a filler for epoxy matrix composites to improve their thermal , mechanical and electrical properties Subhra Gantayat 1, 2, Gyanaranjan Prusty 1, Dibya Ranjan Rout 2, Sarat K Swain 1（1. Department of Chemistry, Vee

4、r Surendra Sai University of Technology, Burla, Sambalpur 768018, India；2. School of Applied Science （Physics）,KIIT University, Bhubaneswar 751024, India）Abstract :Expanded graphite (EG -reinforced epoxy composites were prepared by a solution mixing method. The structure and morphology of the EG /ep

5、oxy 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 to 60-70nm , owing to its abundant oxygen-containing functional groups. With the ad

6、dition of 9wt%EG , the thermal decomposition temperature of the composite increases from 340to 480 , the electrical conductivity from 10-15to 10-5S /cm and the tensile stress is increased by more than 30%.These improvements are attributed to the good dispersion of EG sheets in the epoxy matrix. Keyw

7、ords : Expanded graphite ；FE-SEM ；HR-TEM ；ConductivityReceived date :2015-03-05； Revised date :2015-10-08Corresponding author :Sarat K Swain. E-mail :swainsk 2yahoo. co. inEnglish edition available online ScienceDirect (http :www.sciencedirect. comsciencejournal18725805 .DOI :10. 1016/S 1872-5805(15

8、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 compo

9、sites. 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 i

10、ncrease 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

11、, 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 incap

12、able 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 compo

13、sites 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

14、 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 net

15、work 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 Waals force. For a

16、n 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 inter

17、calate 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 (HNO 3, sulphuric acid (H 2SO 4 or p

18、otassium permanganate (KMnO 4 . 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 strong

19、ly 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. 18measured the tensile strength of the EG /polystyrene composite and found that its tensile strength is a little higher t

20、hat of the pure polystyrene. Kim et al. 19compared 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. 20measured the thermal property of the polystyrene /grap

21、hite composite and reported a thermal degradation temperature of the composite 20 higher 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 pre

22、pare 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 H 2SO 4and HNO 3were analytical grade chemicals and used directly

23、without any further purifi-cation. Graphite fine powder with an average diame-ter of 500m 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 for 24h at 100. Then a mixture of concentrated H 2SO 4and HNO 3with a

24、volume ratio of 4：1was add-ed slowly to a glass flask containing graphite powder with vigorous stirring. After 24h of reaction , the acid treated graphite powder was filtered and washed with deionised water until the pH value of the filtrate reached 6. 4. After drying at 100 for 24h , the re-sulting

25、 graphite intercalation compound was subjected to a thermal shock at 900 for one minute in a fur-nace to form the EG.2. 3 Synthesis of EG /epoxy composites EG /epoxy composites were synthesized to have different contents of EG (3,6, and 9wt%based on epoxy weight by a solution mixing method. Calcu-la

26、ted amount of epoxy and EG were separately dis-persed in deionised water at ambient temperature via stirring for 0. 5h. The EG suspension was added to the epoxy solution and stirring was continued for 3h. The resulting solution was centrifuged for 15min and the resulting sample was dried in an oven

27、at 50. The detail synthetic process is illustrated in Fig. 1.Fig. 1 Schematic representation for the preparation of EG /epoxy composite.2. 4 CharacterizationX-ray diffraction (XRD of the composites was carried out by a Rigaku X-ray diffractometer (Model No. P. DD 966 with Cu K radiation at 40kV and

28、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-nai 12, Philips operating at 120kV was used to study the dispersion of EG in epoxy matrix.

29、 334Mechanical 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 of 50mm /min with a load of 0. 5 ton. The five specimens for each composition were used for measurement and average values are repo

30、r-ted. The TGA analysis was carried out by taking the sample in the pan (8-10mg and the temperature was increased by 10 per minute and heated up to 800. Conducting measurment was carried out using LCR-Hi Tester , HOIKI after the sample being pro-cessed into petlet form.3 Results and discussion 3. 1

31、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 2value of 26. 36. The peaks at 2values of 77 , 54 and 44 belong to epoxy resin and the peak at 2values of 26. 36 is ascribed to grap

32、hite. 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 about 60-70nm. Fig. 3b , c and d show the FE-SEM images of

33、 the EG /epoxy composites at 3%, 6%and 9%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 ,

34、 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 graph

35、ite 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 propert

36、iesThermogravimetric 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. T

37、he ther-mal degradation temperature for epoxy resin is 340 while those of the EG /epoxy composites are 360, 440 and 480 at 3%, 6%and 9%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 o

38、f epoxy resin. The residual weight of the EG /epoxy composites are 8%, 24%and 30%for the composites containing 3%, 6%and 9%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 resi

39、n. 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 23-25for epoxy resin , which could have a wide range of potential applications.Fig. 2 XRD patte

40、rns 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 perce

41、ntages 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 by 3times with an addition of 3%of EG. The load at break of the com-posites increases monotonically with the EG

42、 percenta-ges. From Fig. 6(b , load at break of the compos-ites increases by approximately 6times 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.

43、6(c . However , the ten-sile strain of the EG /epoxy composite at 9%of EG is reduced by 9times in comparison with that of epoxy resin. A sudden fall of tensile strain of the composites is noticed by an addition of 3%of EG (Fig. 6(d . It may be due to the uniform dispersion of EG sheets within the ep

44、oxy matrix. Hence due to the rigidity of epoxy , EG sheets cannot be deformed by external stress 434 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 dispersi

45、on 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 g

46、raphite (b EG /epoxy composite at 9%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 str

47、ucture 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 o

48、f 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 aspect 534Fig. 6 Mechanical properties of EG /epoxy composites as a function of

49、 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.

50、 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

51、 from 3%to 9%.The increase in conductivity with EG contentfrom 3%to 6%is used to determine the percolationthreshold , a critical value at which a three dimension-al conductive network is formed. The conductivity of epoxy is about 2. 310 -15S /cm in the initial stage , which is regarded as a typical

52、insulator. The conduc-tivity of the composites is about 2. 1 10-5S /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

53、 with those of our earlier re-ports 26,27. The epoxy resin composites reinforced by EG are good antistatic materials (conductivity 10-5S cm -1 .Fig. 7 Electrical conductivities of the EG /epoxy composites as a function of EG content.4 ConclusionsA series of EG /epoxy composites were prepared by a so

54、lution 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

55、-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- 634 新 型 炭 材 料 第 30卷第5 期 Subhra Gantayat et al: Expanded graphite as a filler for epoxy matrix composites to improve their Polym Compos,

56、 2008, 29: 125 -132 . 104: 697-709. 437 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

57、 electrically conductive materials by dispersing EG sheets into epoxy matrix. Acknowledgements The authors are thankful to Department of Atomic Energy, BRNS, and Government of India for providing financial support under Grant OM 2008 / 20 / 37 / 5 / BRNS / 1936 . Authors are also thankful to Dr. D.

58、Das of Inter University Consortium, Kolkata, India for analysis of XRD. References 1 2 3 4 5 6 Swain S K, Isayev A I. PA6 / clay nano-composites by continu2387 . Sahoo P K, Samal R, Swain S K, et al. Synthesis of poly ( butyl acrylate / sodium silicate nanocomposite fire retardant J . Eur Polym J, 2

59、008, 44: 3522 -3528 . process for preparation of polyolefin-clay nanocomposites J . Polym Eng Sci, 2008, 48: 1584 -1591 . 2007, 48: 281 -289 . Lapshine S, Swain S K, Isayev A I. Ultrasound aided extrusion Swain S K, Isayev A I. Effect of ultrasound on HDPE / clay nanoous sonication process J . Appl Polym Sci, 2009, 114: 2378 - tive e