碳纤维增强树脂基复合材料中的碳纤维与树脂之间界面改.pdf

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1、Short CommunicationInterface properties of carbon fiber/epoxy resin composite improvedby supercritical water and oxygen in supercritical waterYongping Baia,Zhi Wangb,*,Liqun FengaaSchool of Chemical Engineering and Technology,Harbin Institute of Technology,Harbin 150001,ChinabCenter for Composite Ma

2、terials,Harbin Institute of Technology,Harbin 150001,Chinaa r t i c l ei n f oArticle history:Received 20 June 2009Accepted 2 September 2009Available online 6 September 2009a b s t r a c tThe interface properties between the carbon fibers and epoxy resin were improved by the supercriticalwater and o

3、xygen in supercritical water because the surface roughness and the functional groups con-taining oxygen were increased obviously compared with that of untreated carbon fibers.This was favor-able to improvement of the adhesive strength between the carbon fibers and the resin.The maximal IFSSof the ca

4、rbon fiber/epoxy resin composite treated by the supercritical water and the oxygen in supercrit-ical water were 58.3 and 92.8 MPa,respectively,which increased by approximately 10%and 75%for52.9 MPa of the untreated carbon fiber/epoxy resin composite.?2009 Elsevier Ltd.All rights reserved.1.Introduct

5、ionCarbon fibers have a unique combination of outstandingmechanical,physical and chemical properties,such as highstrength,high modulus and thermal resistance 1.The carbon fi-bers reinforced resin matrix composites have been used in aircraftand space structures 2,3.The performance of these composites

6、strongly depends on the quality of the fibermatrix interface,which determines the way loads can be transferred from the poly-mer to the fiber and interfacial characteristics are often quantifiedin terms of the so-called interfacial shear strength(IFSS)4,5.Interfacial strength between the fiber and t

7、he matrix is dependentto a great extent on carbon fiber surfaces.As surface of the carbonfibers is inert and smooth,untreated carbon fiber-reinforced com-posites exhibit weak fiber/matrix interface bonding.Therefore,numerous methods concerning surface treatment of the carbon fi-bers,such as chemical

8、 method,electrochemical method,and plas-ma treatment have been developed to increase the quantities ofsurface functional groups and roughness,thus enhance the abilityto establish strong interactions between fibers and matrix 57.Moreover,it is very important to design and introduce the suitablesurfac

9、e functional groups on the carbon fibers for different resinmatrices.Since most carbon fibers are utilized with epoxy matricesin the form of composites,their surfaces are oxidized in order toobtain adequate adhesion to epoxy resins 6.The supercritical water is in the supercritical state at tempera-t

10、ures above 374.15?C and pressures above 22.1 MPa 8.In recentyears,the supercritical water oxidation technique has been widelyapplied to the process of decomposition of stable toxic organicwastes because the supercritical water has a high solubility forboth organic compound,and oxygen and water can f

11、orm a singleand homogeneous phase,which allows oxidation to proceed rap-idly by an elimination of the potential interface mass transportlimitations 912.Nevertheless,up to date,there are only a fewpapers devoted to the investigation of the supercritical water treat-ment of the carbon fiber surface,si

12、nce supercritical water oxida-tion technique is generally considered as a method that is onlysuitable for the process of decomposition of stable toxic organicwastes 912.In the present work,the effect of the supercritical water on thesurface properties of carbon fibers was investigated.Furthermore,th

13、e low-cost oxygen was added into the water in order to increasethe oxidation ability of the supercritical water.The surface micro-structure and element compositions of the carbon fibers wereinvestigated using atomic force microscopy(AFM)and X-ray pho-toelectron spectroscopy(XPS).The interface proper

14、ties betweenfibers and resin matrix in composites were evaluated by the inter-facial shear strength(IFSS).2.ExperimentalCommercially available T-300TMcarbon fibers with a diameter ofabout 67lm,purchased from Japan Toray,was used as reinforcefillerinthepresentwork.E-51epoxyresinwasobtainedfromYuey-an

15、g Chemical Co.Ltd.,China.The pressure and temperature in thereactor was maintained at 30 3 MPa and 440 10?C.The mass ra-tio of the carbon fibers to water was below 10%.The carbon fiberswere treated in supercritical water and the oxygen in supercriticalwater for 530 min.The surface microstructure of

16、the carbon fibers0261-3069/$-see front matter?2009 Elsevier Ltd.All rights reserved.doi:10.1016/j.matdes.2009.09.003*Corresponding author.Tel./fax:+86 451 86413711.E-mail address:(Z.Wang).Materials and Design 31(2010)16131616Contents lists available at ScienceDirectMaterials and Designjournal homepa

17、ge: examined on a Russian solver P47 atom force microscopy(AFM).The surface functional groups of the carbon fibers weremeasured using the X-ray photoelectron spectroscopy(XPS)alongwithanX-rayphotoelectronspectrometer(PerkinElmer,PHI 5300)equipped with magnesium X-ray source.Thephthalic anhydride was

18、 chosen as curing agent.Epoxy resin/phtha-lic anhydride/benzyl dimethylamine were 100,70 and 1 parts byweight,respectively.For the further investigation of interfacialproperties between the fiber and the resin,a single fiber compositetest was carried out to determine the interfacial shear strength(I

19、FSS)of the carbon fiber/epoxy resin composite.The single fibercomposite specimens were prepared in paper frames with dimen-sions of 20 mm?100 mm.The free fiber length was approximately30 mm.Some resin droplets were placed against a monofilamentand cured(Fig.1A).A single fiber pull-out test was carri

20、ed out usingan interfacial micro-bond evaluation instrument made by ToheiSanyonCorporationofJapan(Fig.1B).Thecureprocedureofthesin-glefibercompositewasusedasfollows:heatingfrom25to90?Cfor15 min;holding at 90?C for 2 h;heating from 90 to 120?C for10 min;holding at 120?C for 2 h;heating from 120 to 15

21、0?C for10 min;holding at 150?C for 4 h;then cooling to 25?C naturally.To measure IFSS,a specially designedmicro-tensile testingmachinewas used with AE system and a polarized-light microscope.Afterthetestingspecimenwasfixedinthemicro-tensiletestingmachine,the composite was strained incrementally and

22、the fiber was brokeninto small fragments embedded in the matrix until no longer fiberfracture occurred.The classical relationship between fiber tensilestrength,rfcriticalfragmentlengthtodiameterratio(i.e.,aspectra-tio,lc/d)and IFSS,swas expressed typically by KellyTyson 13 as,srf?d2?lc1The IFSS,swas

23、 determined using Eq.(2)that was modified fromKellyTyson equation.(1).sFpdl2where F is the tensile force,d is the fiber diameter,and l is theembedded length.A minimum number of 120 specimens weretested for each treatment condition.3.Results and discussion3.1.Surface morphologiesThe typical surface m

24、icrostructures of commercially availableT-300TMcarbon fibers before and after the supercritical water treat-ment are shown in Fig.2A and B,respectively.The resin protectioncoatings on the surface of the carbon fiber were readily observed asshown in Fig.2A.As the treatment time increased,the resin pr

25、otec-tion coatings on the surface of the carbon fiber were gradually re-moved.The surface roughness of carbon fibers was measured byAFM.For treatment of 30 min,the resin protection coatings werefully removed and the surface roughness of carbon fibers as highas 158.2 nm was obviously increased compar

26、ed with 104.8 nm ofthe carbon fibers treated by acetone extraction,which is attributedto the oxidative etching of the supercritical water.This reveals thatthe supercritical water not only has high solubility for the resinprotection coatings but also has oxidative etching action 14.In comparison with

27、 the hydrogen peroxide reported in the liter-ature 15,the low-cost oxygen relative to the hydrogen peroxidewas added into water in order to increase the oxidation ability ofthe supercritical water.The mass ratio of oxygen to water was1.5%,which was equivalent to 3%hydrogen peroxide in supercrit-ical

28、 water containing oxygen content.Fig.3 shows the typical sur-face microstructures of the carbon fibers treated by oxygen insupercritical water for different times.The resin protection coat-ings on the surface of the carbon fibers were fully removed fortreatment time of 5 min,which reveals that the o

29、xygen in super-critical water is more effective to removing resin protection coat-ings than the supercritical water.The surface roughness of thecarbon fibers increased obviously with increasing treatment time,which would enhance the wettability and mechanical interlockingbetween fiber and resin in t

30、he composites 5.Moreover,theamount of the surface grooves increased as the treatment time in-creased and many grooves on the surface of the carbon fibers wereincorporated into a deep furrow when the treatment time wasmore than 15 min.3.2.Surface functional groupsTable 1 summarizes the surface elemen

31、t compositions mea-sured by XPS analysis.From these data,it was found that the sur-faceelementsoftheuntreatedcarbonfibersweremainlycomposed of the carbon,oxygen and nitrogen.The carbon and oxy-gen contents of the untreated carbon fibers were 91.07%and 7.35%and the O/C ratio was 0.0807.The carbon fib

32、er treated in supercrit-ical water,the carbon and oxygen contents of the carbon fiberswere 86.12%and 12.50%,respectively,and the O/C ratio of0.1451 was significantly higher than that of the untreated carbonfibers.This also revealed that the supercritical water has slightability to the oxidation of t

33、he carbon fibers.The carbon and oxygencontents of the carbon fibers treated in oxygen in supercriticalwater were 70.11%and 28.39%,respectively,and the O/C ratio of0.4049 was significantly higher than that of the untreated carbonfibers due to the surface oxidation of the carbon fibers.The O/C ra-tio

34、of 0.4049 was also higher than that of the carbon fibers treatedby hydrogen peroxide in supercritical water 15,which indicatedthat the oxygen in supercritical water has stronger ability to oxida-tion of carbon fibers.From these results,it could be detected thatfunctional groups containing oxygen for

35、 the carbon fibers treatedin oxygen in supercritical water were significantly increased,which was favorable to adhesion between the carbon fibers andthe resin.This also indicated that the oxygen in supercritical watertreatment was better than hydrogen peroxide in supercriticalwater treatment for inc

36、reasing surface functional groups contain-ing oxygen of the carbon fibers.3.3.Mechanical propertiesThe increase in the surface functional groups containing oxygenof the carbon fiber is favorable to the improvement in interfacestrength between fibers and resin along with enhancement in theFig.1.Schem

37、atic drawing of IFSS test.1614Y.Bai et al./Materials and Design 31(2010)16131616mechanical properties of the fibers reinforced resin matrix com-posites,so that IFSS of the carbon fiber/epoxy resin composite weremeasured and listed in Table 2.For treatment of 30 min in super-critical water,IFSS of tr

38、eated carbon fiber/epoxy resin compositewas 58.3 MPa,which was higher than 52.9 MPa of untreated car-bon fiber/epoxy resin composite.The increase in IFSS of carbon fi-ber/epoxy resin composite was attributed to the increase in thesurface functional groups containing oxygen and roughness ofthe carbon

39、 fibers 5.This reveals that the supercritical water treat-ment of the carbon fibers is favorable to increase the interfacialstrength between fibers and resin.IFSS of carbon fiber/epoxy resincomposite treated by oxygen in supercritical water increased shar-ply from 59.1 to 92.8 MPa as treatment time

40、increased from 5 to15 min.Although,IFSS of treated carbon fibers/epoxy resin com-posite for treatment of 30 min was reduced to 60.9 MPa,it was stillFig.2.The AFM micrographs of the surface of the carbon fibers:(A)before treatment and(B)after the supercritical water treatment.Fig.3.The AFM micrograph

41、s of the surface of the carbon fibers treated in oxygen in supercritical water for different times.(A)5 min;(B)10 min;(C)15 min;(D)30 min.Table 1XPS element content results of untreated and treated carbon fibers for 30 min.Carbon fibersElement content(%)O/CCONUntreated91.077.351.560.0807Treated in s

42、upercritical water86.1212.501.380.1451Treated in oxygen in supercritical water70.1128.391.490.4049Y.Bai et al./Materials and Design 31(2010)161316161615higher than that of untreated carbon fiber/epoxy resin composite,which was presumably ascribed to the degradation of the carbonfiber strength becaus

43、e the deep furrow on the surface of the carbonfibers resulted in the damage of the carbon fibers due to the exces-sive oxidation.4.ConclusionThis study clearly displayed that the interface properties be-tween the carbon fibers and resin were improved by the supercrit-ical water and oxygen in supercr

44、itical water because the surfaceroughness and the functional groups containing oxygen were in-creased obviously compared with that of untreated carbon fibers.This was favorable to improvement of the adhesive strength be-tween the carbon fibers and resin.Furthermore,this study also dis-played that th

45、e oxygen in supercritical water treatment was betterthan hydrogen peroxide in supercritical water treatment forincreasing surface functional groups containing oxygen of thecarbon fibers along with enhancement in the interfacial strengthbetween fibers and resin matrix.The maximal IFSS of the carbonfi

46、ber/epoxy resin composite treated by the supercritical waterand the oxygen in supercritical water were 58.3 and 92.8 MPa,respectively,which increased by approximately 10%and 75%for52.9 MPa of the untreated carbon fiber/epoxy resin composite.References1 Tang YP,Liu HZ,Zhao HJ,Liu L,Wu YT.Friction and

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