固化环氧树脂中制备聚合物粘土矿物纳米复合材料文库.pdf

《固化环氧树脂中制备聚合物粘土矿物纳米复合材料文库.pdf》由会员分享，可在线阅读，更多相关《固化环氧树脂中制备聚合物粘土矿物纳米复合材料文库.pdf（9页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、Preparation of polymer/clay mineral nanocomposites via dispersion ofsilylated montmorillonite in a UV curable epoxy matrixA.Di Giannia,E.Amerioa,O.Monticellib,R.Bongiovannia,aPolitecnico di Torino,Dipartimento di Scienza dei Materiali e Ingegneria Chimica,C.so Duca degli Abruzzi 24,10129 Torino,Ital

2、ybUniversit di Genova,Dipartimento di Chimica e Chimica Industriale,V.Dodecaneso 31,16146 Genova,ItalyReceived 11 May 2007;received in revised form 21 December 2007;accepted 28 December 2007Available online 17 January 2008AbstractSurface modification of clay minerals plays an important role for thei

3、r application as fillers for polymeric materials.Among the manymodification reactions,the silanization reaction uses alkoxysilanes and exploits the OH reactive sites of the montmorillonite structure.We foundthat using an excess of silane it is possible to functionalize the clay mineral and,at the sa

4、me time,to intercalate some monomers or oligomers intothe clay mineral galleries,greatly enhancing the interlayer distance.The montmorillonite modified in this way has been then used in thepreparation of nanocomposite coatings by mixing it with a photocurable epoxy matrix.After UV irradiation the co

5、atings obtained were submittedto morphological,thermal and mechanical analysis.The photopolymerization kinetics was also investigated.The introduction of the modifiedmontmorillonite allowed to obtain transparent nanocomposite coatings characterized by a mixed intercalated/exfoliated structure and be

6、tterthermal and scratch resistance performances in comparison with the montmorillonite free coatings.2008 Elsevier B.V.All rights reserved.Keywords:Silylation;Montmorillonite;Epoxides;Nanocomposites1.IntroductionNanocomposite materials based on polymeric matricescontaining inorganic nano-objects hav

7、e been intensively studiedinthelastdecadesbecausetheintroductionofaninorganicphasedispersed at a nanoscale inside the polymer allows to obtain afinal product with enhanced performances.Among the possiblefillers,2:1 clay minerals are some of the most studied,since theycan lead to the preparation of n

8、ovel materials characterized byimproved thermal,mechanicalandbarrier properties(Alexandreand Dubois,2000;Ray and Okamoto,2003).Polymer/clay mineral composites can be classified in threedifferent types:conventional microcomposites where stacks ofsilicate layers are dispersed at a microscale inside th

9、e matrix,intercalated nanocomposites in which some polymeric chainsare able to insert between the platelets maintaining a long rangeorder,exfoliated nanocomposites in which the platelets are notordered any more but separately and homogeneously dispersedinto the matrix as single platelets.In many cas

10、es a mixture ofintercalated and exfoliated structure is obtained,thus singleplatelets and tactoids are both present in the material.The bestfinal properties are achieved when the clay mineral platelets arefully exfoliated and well dispersed(Messersmith and Giannelis,1993;Yano et al.,1993;Giannelis,1

11、996).In order to achieve a good dispersion of the clay mineralsinto the polymer it is often necessary to modify them in order tomake them more organophilic and compatible to the polymer.Moreover a suitable modification can enhance the interlayerdistance of the clay mineral and,thus,facilitate a bett

12、er swellingof the clay mineral itself in an organic polymer or monomer.Inthe case of montmorillonite,the modification reaction that hasbeen mostly exploited for this purpose is the cationic exchangebetween the metal ions present in the structures of the clayminerals and a quaternary ammonium salt:di

13、fferent organicmoieties can be used(Jordan,1949;Lagaly,1986;Vaia et al.,1994;Hackett et al.,1998;Xie et al.,2001;Xie et al.,2002;Park and Jana,2003).This organophilic modification,whichAvailable online at Applied Clay Science 42(2008) author.Tel.:+39 011 5644619;fax:+39 011 5644699.E-mail address:ro

14、berta.bongiovannipolito.it(R.Bongiovanni).0169-1317/$-see front matter 2008 Elsevier B.V.All rights reserved.doi:10.1016/j.clay.2007.12.011depends on the cation exchange capacity of the clay mineral(Moraru,2001),can be tailored depending on the polymericmatrix used to prepare the composites.Recently

15、 it has been studied the possibility of grafting somesilanemoleculesonthesurfaceoftheclayminerallayers(Herreraet al.,2004;Park et al.,2004b).In fact,reactive OH groups arepresent in the clay minerals at the edges and at the structuraldefects(Lee and Jang,1996;van Olphen,1997;He et al.,2005).Therefor

16、e,thefunctionalizationoftheclaymineralcantakeplaceat three possible sites:at the interlayer space,at the externalsurface(Herrera etal.,2004)andatthe edges(Parketal.,2004b).The silanization at the interlayer and at the edges can increase thedistance between the layers(Isoda and Kuroda,2000;Park et al

17、.,2004a).The effect of the solvent on the grafting reaction(Schanmugharajetal.,2006),aswellastheclaymineralstructure(Heetal.,2005)andthekindofsilane,arereportedinliterature.Insomecases,thesilanizationreactionhasalsobeenconductedontoorganophilicclaymineralstoenhancetheircompatibilitywiththepolymer:th

18、ese twice functionalized organo-clay minerals aredescribed by Chen(Chen and Yoon,2005a,b,c).The intercalation oreventually theexfoliation ofclayminerallayers after modification can be achieved by different methods.Some of them request the melting of the polymer and can affectits stability;others are

19、 solvent-based,thus releasing largeamounts of volatile compounds.In situ intercalative polymer-isation is also proposed:in this process,which is often solvent-based,thekindofguestspeciestobeintercalatedarethereactivemonomers.In situ crosslinking photopolymerisation of solventfree curable systems is

20、interesting:the procedure,whichinvolves the use of UV light and is called UV-curing,guaranteesthe building up of polymeric thermoset matrices via a fast andenvironmental friendly process with low energy consumptionand no emission of volatile organic compounds(Fouassier andRabek,1993).The first resul

21、ts on clay minerals based hybrids,obtained by UV-curing oligomers in the presence of organo-philic clay minerals have been recently published(Decker et al.,2004;Benfarhi et al.,2004).In previous works,we have prepared different intercalatednanocomposites by in situ photopolymerization of multifunc-t

22、ional monomers in the presence of pristine or organophilic clayminerals(Bongiovanni et al.,2006;Malucelli et al.,2007a,b).The monomers swell the clay minerals and,upon irradiation,yield the nanocomposite.Using an epoxy monomer,for whichthe photoinduced process follows a cationic mechanism,weachieved

23、 intercalation with a widely used organophilic mon-tmorillonite:Cloisite 30B.An original modification of this claymineral by reaction with maleinized polybutadiene was alsosuccessful,leading to a quasi exfoliated structure in an epoxyUV-cured matrix(Malucelli et al.,2007a,b).Pursuing this topic in o

24、rder to achieve even better results,wethought interestingly to use silanization as a modification ofnatural sodium montmorillonite.The silane employed isglycidyl-propyl-triethoxysylane(GPTS)as it bears an epoxygroup which could react during the photopolymerization of theepoxy monomer(Takimoto,1993).

25、The paper describes thepreparation of the GPTS functionalized montmorillonite and itscharacterization by FT-IR,TGA,DSC and XRD analysis.Thenit discusses the photopolymerization kinetics of the epoxy resinmonitored by FT-IR in real time and reports on the morphology,the thermal and mechanical propert

26、ies of the nanocompositesobtained.2.Materials and methods2.1.MaterialsThe clay mineral employed was a sodium montmorillonite(Cloisite Na+)obtained from Southern Clay Products(USA).As a solvent for the modification,a mixture of ethanol(supplied by Fluka)and deionized water was used.TheFig.1.Chemical

27、structure of the epoxy resin CE,the GPTS molecule and thephotoinitiator.Scheme1.Schematic representation of the hydrolysisof the alkoxysilanegroupsand of the condensation between them and the montmorillonite OH groups.117A.Di Gianni et al./Applied Clay Science 42(2008)116124silane employed was the g

28、lycidyl-propyl-triethoxysilane(GPTS)purchasedfrom Aldrich whose chemical structure is reported in Fig.1 as well as thestructure of the epoxy resin 3,4-epoxy-cyclohexylmethyl-3,4-epoxy-cyclohex-ylcarboxylate(CE),supplied by Cytec.As photoinitiator a commerciallyavailable triphenyl phosphate sulfonium

29、 salt(UVI 6990,Fig.1)was used whichwas supplied by DOW as solution in propylene carbonate(50 wt.%).2.2.Functionalization of the sodium montmorillonite400 ml of a mixture of EtOH/H2O(75:25)were introduced in a flask.1.5 gof sodium montmorillonite were then added to the solvent together with a largeex

30、cess of silane GPTS(5 g).The mixture was heated at 80 C and kept understirring for about 4 h.Then the clay mineral was filtered and washed carefullywith ethanol.The resulting product was dried in oven at 80 C overnight.2.3.Preparation of nanocomposite coatingsDifferent amounts of the modified montmo

31、rillonite(5 to 10 wt.%)wereintroduced into the liquid monomer CE and dispersed by ultrasounds for 8 h atroom temperature.The mixtures obtained were then added of 4 wt.%of the photoinitiator andcoatedontoglasssubstratesorpolypropylenesubstrates(filmthickness=100m).Fig.2.FT-IR of the unmodified montmo

32、rillonite(a)and of the modified montmorillonite(b).Fig.3.X-rays diffraction patterns of the pristine and of the modified montmorillonite.118A.Di Gianni et al./Applied Clay Science 42(2008)116124The coatingswere then irradiatedwith a mediumpressureHg lamp atthe intensityof 25 mW/cm2at the sample leve

33、l.2.4.CharacterizationX-rays diffraction analysis(XRD)were carried out on the clay mineralpowder and on the dispersion of the montmorillonite in the CE resin.XRD were performed using a Philips XPert-MPD diffractometer(CuKradiation;2 range:230;2 step:0.02;step time:2 s).X-ray diffractionfrom liquid d

34、ispersions of the clay minerals was carried out on the specimenlocated on a concave hemispherical glass container,in such a way that the liquidsurface was higher than the rim.The surface of liquid was then brought in thediffraction plane required by parafocalization geometry by sliding the trimmingb

35、lock.TEM analysis was performed using a Philips 2010 microscope onmicrotomized sample without any specific staining.The FT-IR measurements were performed using a Thermo-Nicolet 5700instrument:the clay mineral powder was mixed with KBr and,by pressing themixture in vacuum,a disk was obtained and used

36、 as sample.The kinetics of the photopolymerization was determined by real time(r.t.)FT-IR spectroscopy,employing the same instrument mentioned above.Theepoxy group conversion was followed in real time upon UVexposure followingthe decrease of the absorbance peak due to the epoxy group in the area 730

37、760 cm1.A Hamamatsu Lightningcure LC8 lamp equipped with an opticalguide was used to induce the photopolymerization(light intensity on the surfaceof the sample of about 25 mW/cm2).All the conversion curves reported in thepaper were performed on the same day and under the same conditionsin order toav

38、oid any variation of light intensity,humidity and temperature that can induceslight differences in the kinetic curves.The cured samples were stored at room temperature for 24 h before anytesting.DSC measurements were performed using a Mettler DSC30(Switzerland)instrument,equippedwithalowtemperaturep

39、robe,attheheatingrateof20C/minin nitrogen.Thermogravimetric analysis(TGA)was performed with a METTLERTGA/SDTA 851 instrument at a heating rate of 10 C/min in air.Scratch resistance tests were done by means of an open platform from CSMinstruments equipped with an optical microscope and a Rockwell dia

40、mondmicro-indenter having a radius of 200 m.A pin-on-flat method is employed inwhich the indenter(pin)and the substrate surface(flat)are both moving withrespect to each other.The test was performed for a length of 3 mm starting froma load of 100 mN to a load of 25000 mN at the load rate of 8333 mN/m

41、m.3.Results and discussion3.1.Modification of the montmorilloniteSome OH groups are present at the edges of the montmor-illonite layers,as well as at the structural defects.These OHgroups are active sites which can be used to obtain afunctionalization of the clay mineral platelets surface(Eket al.,2

42、004;He et al.,2005).The reaction is the same used inmany studies reported in literature about the functionalization ofsilica particles(Luechinger et al.,2005)and their compatibiliza-tion with organic matrices:an alkoxysilane is typicallyemployed for this purpose.In the present study the glycidyl-pro

43、pyl-triethoxysilane(GPTS)was used so that,while thetrialkoxysilane moiety can react with the active sites on the claymineral surface,the epoxy ring can take part into the UV-curingFig.5.1st and 2nd scan DSC thermograms of the modified montmorillonite.Fig.4.TGA thermograms of the unmodified and the m

44、odified montmorillonite.119A.Di Gianni et al./Applied Clay Science 42(2008)116124of the epoxy resin(CE)employed to build up the polymericmatrix.The functionalization of the clay mineral by means of GPTSis made in two steps:the hydrolysis of the silane compound andthe condensation between the silanol

45、s or the alkoxysilanegroups as schematically shown in Scheme 1.The powderobtained after washing and drying was analyzed by FT-IRspectroscopy.Fig.2 shows the comparison between thespectrum of the pure Na+montmorillonite and the spectrumof the clay mineral after the modification with GPTS.A firstsign

46、that the modification reaction actually took place is thedecrease of the intensity of the peak at 3600 cm1correspond-ing to the AlOH and MgOH groups.At the same time,afterthe silanization,the clay mineral shows an absorption bandbetween 30502700 cm1due to the vibrations of the CHbonds introduced by

47、the organic modifier.The high intensity ofthis band suggests that,not only the GPTS has been covalentlybonded to the clay mineral,but it has also been intercalated in itshydrolyzed form interacting with water molecules present in theclay mineral through hydrogen bonding.This fact is confirmedScheme

48、2.Different possible interactions between the hydrolyzed GPTS and the pristine montmorillonite.120A.Di Gianni et al./Applied Clay Science 42(2008)116124by the broadening of the peak centred at 3400 cm1and thedecrease in intensity of the peak at 2630 cm1in the modifiedclay mineral.The broad and stron

49、g peak between 900 and2300 cm1is attributed to the vibration of the SiO groups:thispeak should be modified after the treatment with GPTS,howeveritisso intense inthe spectrumofthe unmodifiedmontmorillonitethat it is very difficult to evidence any change.It is at leastpossible to detect two new peaks

50、at 1200 and 1000 cm1due toRSiO groups and SiOSi coming from oligomers eitherbonded to the surface of the clay mineral or intercalated.The intercalation of the GPTS is confirmed by the X-raysdiffraction patterns(Fig.3).The pristine sodium montmorillo-nite exhibits a sharp reflection at 2=7.29,corresp