Morphology,Thermal,and Mechanical Properties of Polypropylene/Polyaniline Coated Short Glass Fiber Composites
Rodolfo Cruz-Silva,1Jorge Romero-Garcı´a,2Sofı´a Vazquez-Rodriguez,2 Jo Luis Angulo-Sa´nchez2
1Centro de Investigacio´n en Ingenierı´a y Ciencias Aplicadas,UAEM.Av.Universidad1001, Col.Chamilpa,CP62210,Cuernavaca,Morelos,Me´xico
2Centro de Investigacio´n en Quı´mica Aplicada,Saltillo,Coah.Blvd.Enrique Reyna No.140, CP25100Saltillo,Coahuila,Me´xico
Received12June2006;accepted14November2006
DOI10.1002/app.26026
Published online8May2007in Wiley InterScience(www.).
ABSTRACT:Short glassfiber Type E was coated with electrically conducting polyaniline(PAn)by in situ chemical polymerization.The resulting PAn coated glassfiber,with surface conductivity of 3.3Â10À1S/cm,was melt-com-pounded with isotactic polypropylene(iPP).Polypropylene grafted with m
aleic anhydride was investigated as an adhe-sion promoter for the composites.Differential scanning calo-rimeter and polarized light microscopy indicates that the PAn coated glassfiber has a strong nucleating activity towards iPP. Scanning electron microscopy showed the improvement in the wetting and dispersion of thefibers when the adhesion promoter was added,although this also led tofiber encap-sulation and lowering the electrical conductivity of the com-posites.The adhesion promoter greatly improved the Young’s modulus of the composites,and a reaction between the maleic anhydride groups of the adhesion promoter and the PAn was propod.Composites with an electrical con-ductivity greater than10À9S/cm were achieved using a 30wt%of PAn coated glassfiber.Ó2007Wiley Periodicals, Inc.J Appl Polym Sci105:2387–2395,2007
安卓怎么刷机
Key words:electrically conductive composites;reinforced composites;nucleating agent;adhesion promotor;maleic anhydride copolymer
INTRODUCTION
Polyaniline(PAn),an intrinsically conductive poly-mer,has been increasingly employed in the prepara-tion of thermoplastic-bad composites for antistatic or electromagnetic shielding applications in the last years.1–7The great potential of this polymer in the aforesaid applications is due to its environme
ntal stability,relatively high electrical conductivity and low-cost synthetic route.8Compared with traditional electrically conductive metallicfillers,PAn has advantages such as lower weight,lower cost,and higher corrosion resistance.However,PAn is infusi-ble,and direct blending of PAn powder with ther-moplastics by melt processing techniques results in incomplete dispersion leading to composites with poor mechanical properties.Since the introduction of counter-ion induced processability,9blends of PAn and a wide range of thermoplastics have been pre-pared by extrusion or injection techniques,1–7,10but low interfacial adhesion has led to a decrea in the mechanical properties of the blends.For this reason, incorporation of reinforcements or adhesion pro-moters to PAn-thermoplastic blends is expected to improve the overall mechanical performance of the resulting composites.
The electrical conductivity of composites of insulat-ing and conducting phas is well described by the percolation theory.11When a certain amount of con-ductivefiller is gradually added to an insulating ma-trix,the conductivity of the composite remains clo to that of the matrix,but when the amount of conduc-tivefiller is high enough to form a continuum net-work,a drastic increa in the electrical conductivity is achieved.The fraction of conductivefiller at this point is called percolation threshold.Further addition of the conductivefiller has a less dramatic impact on electrical conductivity.
Not only the concentration but also the shape and aggregation behavior of the particles of the conductivefiller have strong influence to lower the percolation threshold.12,13Theoretical
the memory of Prof.Jo Luis Correspondence to:R.Cruz-Silva(). Contract grant sponsor:CONACYT;contract grant number: 46046.
刘佳璐
Contract grant sponsor:PROMEP;contract grant number: UAEMOR-PTC-151.
Journal of Applied Polymer Science,Vol.105,2387–2395(2007) V C2007Wiley Periodicals,Inc.
and experimental studies have shown that particles with aggregation behavior or high aspect ratio,such asfiber orflakes,achieve the percolation threshold at lower volume concentrations.13,14
It is expected that PAn-coatedfibers can achieve the percolation threshold at relatively low concentra-tion not only becau of its high aspect ratio but also due to a phenomenon called double percolation,com-mon in composites where the conducting pha is located between two nonconducting phas.15,16For instance,Taipalus et al.1found that in ternary compo-sites of polypro
pylene(PP)/glassfiber/PAn,location of PAn at the interface between thefibers and the matrix lowered the percolation threshold due to a double percolation mechanism.Nevertheless,upon PAn incorporation,a decrea in the mechanical properties was obrved.When conducting carbon fiber was employed instead of glassfiber,an improvement in electrical conductivity was achieved.4 In this ca,the PAn pha behaved as a‘‘bridge’’to connect the carbonfibers.A similar behavior was obrved in composites of nickelflakes coated with conductive polypyrrole.17Recently,glassfiber2and mica6coated with PAn were ud to prepare compo-sites with epoxy resin.In the cas,the PAn-coated particles help to develop a conductive network within the composite.However both composites were pre-pared in liquid media and the polymerization took place after mixing.In melt processing,it is possible that adhesion of physically adsorbed PAn on rein-forcements would not be strong enough to resist the high shear during processing.
Since the work done by Gregory et al.,18the sur-face modification of a wide range offibers with PAn has been extensively studied.19–22Geetha et al.23 studied different sulfonic acid in the surface modifi-cation of glassfibers by in situ chemical polymeriza-tion.However,grafting of PAn to silicon dioxide surfaces using silane coupling agents bearing aniline moieties wasfirst propod by Wu et al.24,25to improve the adhesion between the inorganic sub-strate and the PAn.Using a similar appro
ach,Li and Ruckenstein successfully grafted PAn on surface treated glassfiber.26However,this material has not been ud to preparefiber reinforced composites by melt processing techniques,and optimization of the surface modification process would be inter-esting.
The aim of this work was to investigate the me-chanical,thermal and electric properties of isotactic polypropylene(iPP)/PAn-coated short glassfiber (SGF)composites.The relation between the morphol-ogy and both the mechanical and electrical proper-ties was investigated.A PP–maleic anhydride copoly-mer,a widely ud adhesion promoter in PP/SGF composites,27was incorporated to the composites to improve their mechanical properties.In addition,a novel reactor design for PAn coating of SGF by in situ polymerization is prented.
EXPERIMENTAL
Materials
Aniline was acquired from Baker(Xalostoc,Mexico) and distilled under reduced pressure before u.SGF Type E was acquired from Vitro Group(Monterrey, Mexico).N-phenyl-g-aminopropyltrimethoxysilane was a commercial product from Sylquest(Y-9669TM). Polypropylene grafted maleic anhydride copolymer (PP-g MA)was acquired from Uniroyal Chemical under the trade
name of Polybond3200.The maleic anhydride content was of 1.0%as determined by FTIR spectroscopy.28iPP with a MFI of3.8and den-sity of0.9g/cm3,was acquired from Indelpro, Ball.All other reagents were of analytical grade and ud as received.
情不自禁Fiber modification
SGF was calcinated in a furnace at5008C for3h to eliminate the sizing and coupling agents,then washed with water and treated with10wt%hydro-chloric acid solution for3h at608C to increa the silanol groups concentration on the surface.After-wards,thefiber was thoroughly washed with dis-tilled water.After drying,silanization was done by immersion in a0.025wt%N-phenyl-g-aminopropyl-trimethoxysilane solution in methanol during24h. Then,thefibers were rind with methanol,dried under nitrogenflow,andfinally in a vacuum oven for3h at1008C.
Modification of silanized SGF by in situ polymer-ization of aniline was done in a5-L jacketed reactor (Fig.1),where1.5kg of SGF was packed,and4L of HCl1.0N and20mL of aniline were added.Nitro-gen was bubbled trough the packedfiber during2h and maintained during the polymerization.The reac-tion was initiated by adding56.4g of ammonium persulfate dissolved in250mL of degasd1.0N hy-drochloric acid.The reaction media was unstirred; however the liquid was recirculated through the pa
ckedfiber using a peristaltic pump at approxi-mately180mL/min.Temperature was kept clo to 08C by recirculating coolingfluid by the jacket. Three hours after the reaction was initiated deep green PAn-coated SGF was obtained.Thefibers were treated in a2.0wt%solution of sodium car-bonate and washed thoroughly with deionized water.The blue color of thefiber at this stage was indicative of dedoping.The PAn-coated SGF was redoped with p-toluenesulfonic acid,which unlike chlorine,has been reported to be thermally stable up to2008C as doping agent.29Afterwards thefiber was
2388CRUZ-SILVA ET AL. Journal of Applied Polymer Science DOI10.1002/app
dried in a convection oven at708C.This procedure afforded PAn-coated SGF,with a fractional PAn weight of4%,as determined by thermogravimetry. This value indicates that the organic coating is rather a complex of PAn and toluenesulfonic acid in excess; however it will be referred solely as PAn. Preparation of composites
Prior to mixing,PAn-coated SGF was dried in a vac-uum oven for4h at608C whereas the iPP and PP-g MA were dried in a vacuum oven for12h at908C. Blending was performed in a Banbury Type Mixer at 2008C using CAM rotors.iPP wasfirst melted at 25rpm for5min,PP-g MA was added at this point in some formulations.Then,the PAn-coated SGF was added gradually over a3-min period and
mixed for an additional4-min period.Then the blends were removed from the mixer,cooled to room tem-perature,and crushed using a mill equipped with a sieve.Finally,the composites were press molded under 2.45MPa in a steel mold obtaining square composites of20cmÂ20cm and2.6mm wide. Characterization
Differential scanning calorimetry
A differential scanning calorimeter(MDSC TA Instru-ments2920)was ud for thermal analys.Samples of about12mg were loaded in aluminum aled pans and heated at a rate of108C/min from20to 2008C,held in this temperature for3min to era pre-vious thermal history,and cooled to room tempera-ture at the same rate and held for3min.Then,a c-ond heating scan was performed from20to2008C. The temperatures at the maximum of the crystalliza-tion exotherm and the melting endotherm in the c-ond heating scan were taken as the melting(T m)and crystallization temperatures(T c),respectively.Calcula-tions of the crystalline fraction of the polymeric pha were done using a heat of fusion of209J/g.30 Optical and polarized light microscopy
Optical and polarized light microscopy obrvations of the composites were done in a Olympus BX90 microscope using small samples melted and presd to form afilm.For polarized light microsco
py obr-vation,model composites were prepared mixing individualfibers of PAn-coated SGF with melt iPP or PP/PP-g MA blends and obrved using a Metler-Toledo FP90heating stage.Samples were heated to 2008C and held in this temperature for3min and then cooled to room temperature at58C/min. Mechanical properties
Young’s modulus,elongation at break,and tensile strength of the composites were acquired using an Instron universal machine,according to ASTM D638. All samples were cut into dogbones samples and conditioned for48h at51%R.H.and228C.The test was run at a5.08mm/min deformation rate.
X-ray diffraction pattern
A Siemens D-5000X-ray diffractometer was ud to acquire the wide-angle X-ray diffraction patterns (WAXD)of the press-molded composites.Data acquisi-tion was done in the2y mode using a CuK a radiation source(intensity25mA,35kV acceleration voltage). Electrical resistance measurements
Single-fiber electrical conductivity measurements were done using a Keithley2400sourcemeter.Indi-vidualfibers were placed between two silver paint electrodes over a glass slide.The gap between the electrodes was measured by optical microscopy. The electrical resistance of the composites was mea-sured using a Keithley6517A electrometer/high resist-ance meter.Samples of2cmÂ2cmÂ0.26c
m were cut from the compression molded composites,and the insulating skin layer of the composites was carefully removed.Opposite sides of the sample were coated with silver paint to reduce the contact
resistance.
The electrical resistance was measured parallel and across the plane of compression.Each value is the average of three measurements.Scanning electron microscopy
SEM obrvations were done in a TopCom 510equip-ment.Composites samples and PAn-coated SGF were fractured under liquid nitrogen and coated with a thin layer of Au/Pd.
RESULTS AND DISCUSSION真石漆做法
SGF modification and composites formulation In Figure 2(a)is shown a photo of the PAn-coated SGF after being scratched.This image reveals that the coating is debonded as a free-standing thin film.The int shows an optical microscopy image of a single fiber that has a uniform coating,as indicated
by the homogeneous green color of the fiber.In Fig-ure 2(b),a SEM image of the PAn-coated SGF as obtained after the fiber modification is shown.The morphology of the PAn coating consists of a thin film with particles adhered onto its surface.The thin film is most probably grown from adsorbed aniline on the fibers,whereas the particles are grown in the liquid pha and later adhered on the gro牡丹赋
wing PAn film,in agreement with the growth mechanism of PAn films prepared by in situ chemical polymeriza-tion.31The conductivity of the fiber (3.3Â10À1S/cm)is similar to that reported by Li and Rucken-stein,26and is high enough to be obrved without metallic coating by scanning electron microscopy.Single-fiber conductivity measurements also pro-vided information on the homogeneity of the coat-ing.Electrical conductivity of veral fibers from a bundle fluctuates less than one order of magnitude,and less than two orders of magnitude from fibers from a different bundle.By using densities of both materials and the gravimetric results we were able to calculate the average PAn coating thickness ($300nm)and the electrical conductivity of the
bulk
Figure 2(a)SEM image of PAn coated SGF (PAn-coated SGF)after being scratched.A debonded thin film is obrved next to the fiber.The int shows an optical mi-croscopy image of a single fiber.(b)SEM image of the PAn-coated
SGF.
Figure 3Optical microscopy images of thin films obtained from iPP/PAn-coated SGF composites containing (a)10wt %of PAn-coated SGF and (b)30wt %of PAn-coated SGF.紫菀花
2390CRUZ-SILVA ET AL.
Journal of Applied Polymer Science DOI 10.1002/app
PAn of the coating($3.6S/cmÀ1).Optical micros-copy images revealed that most of the SGF kept the PAn coating after melt processing at10wt%with iPP[Fig.3(a)];however,some PAn particles were also prent becau of debonding of the coating. Increasing the amount of PAn-coated SGF led to a higher degree of debonding,due tofiber abrasion during compounding,but even at30wt%offiller load[Fig.3(b)]a large number offibers remain coated with PAn.
Effect of the PAn-coated SGF on iPP and
iPP/PP-g MA crystallization
The effect of the PAn-coated SGF on the thermal properties of iPP and iPP/PP-g MA blends was stu
d-ied by DSC.In Table I,the crystallization tempera-tures of the composites are shown.The T c of iPP is 1128C but after the addition of10wt%of PAn-coated SGF the T c increments to124.28C.This nucle-ating activity of PAn-coated SGF towards iPP was previously reported.32The thermal properties in prence of the adhesion promoter were also stud-ied.The addition of5.0wt%of PP-g MA to pure iPP incread the crystallization temperature to115.78C. This is attributed to the prence of C¼¼O groups from the maleic anhydride moieties that behave as nucleating points in the nonpolar iPP matrix.33The addition of10wt%of PAn-coated SGF to the iPP/ PP-g MA blend increments the T c to121.58C,indicat-ing that the nucleating activity of the PAn is main-tained in the prence of PP-g MA,contrasting with previous studies on nucleatingfibers,where the nucleating activity is suppresd after PP-g MA addi-tion to the composite due tofiber encapsulation.34 Further addition of PAn-coated SGF to the compo-sites caus only a slight increment in the T c,sug-
gesting that10wt%provides enough surface to the polymer matrix to nucleate,and conquently the crystal growth rate becomes limited above that con-centration of PAn-coated SGF.The development of transcrystalline zones around PAn-coated SGF in composites,with and without PP-g MA,is shown in Figure4(a,b),respectively.As previously reported, no transcrystallization is induced by the bare glass fiber,32,33which is show in Figure4(c).The width of the crystallization exotherm slightly sharpe
ns in all composites formulations[Fig.5(a,b)],as compared to the matrix,most likely due to the nucleating effect of the PAn-coated SGF.The crystalline fraction (Table I)slightly increments for the composites as the content of PAn-coated SGF does,indicating that transcrystallization propagate to the matrix. Surface treatment of SGF and some polymeric fibers can induce transcrystalline zones of different crystal type,such as the g or b form.35,36For this rea-son,we carried out a study of the composites by wide angle X-ray diffraction,shown in the Figure6. Nevertheless,the iPP and iPP/PP-g MA blend(Fig.6, curves a and b,respectively),as well as the compo-sites,showed only the characteristic peaks of a-type PP.The peaks appear at2y of14.18,16.98,18.58, 21.18,and21.88,and correspond to the(110),(040),
TABLE I
Composition and Thermal Properties of the Composites
Sample
Composition(wt%)
炒什么菜T c X c T m iPP PP-g MA
PAn-coated
处女座和什么座最配SGF
PP000010000112.20.45164.8 PP001090010122.40.47164.9 PP002080020123.60.49165.1 PP003070030123.90.51164.6 PP05009550115.70.46164.1 PP0510********.50.47164.7 PP052075520123.50.49164.9 PP0530********.60.48
164.3Figure4Polarized optical microscopy showing morphol-ogy of single PAn-coated SGF embedded in(a)iPP and (b)iPP/PP-g MA blend.A single uncoated glassfiber embed-ded in iPP during crystallization is shown in(c)for com-parison.
PP/PAn COATED SHORT GLASS FIBER COMPOSITES2391
Journal of Applied Polymer Science DOI10.1002/app
