novel electrically conductive … properties of insulating matrix ... fillers were dried in a...

1 IntroductionSince its discovery in the late 1970s the scientificinterest in understanding physical and chemicalproperties of the intrinsically conducting polymers(ICPs) has been increasing due to their potential invarious technological applications Among ICPspolypyrrole (PPy) is a particularly promising mate-rial because of its high electrical conductivity chem-ical and environmental stability in the oxidized statelow ionization potential electrorheological proper-ties electrochromic effect and relatively easy of syn-thesis [1ndash6] In fact PPy can be potentially used in

new advanced technology areas including elec-tronic and optoelectronic nanodevices [7] sensors [8ndash13] supercapacitors [14 15] energy storage devices[1 7 16] surface coatings for corrosion protection[17] electromagnetic shielding applications [18ndash20]smart textiles [21 22] and even in medical applica-tions [4 23ndash26]However the poor mechanical performances and thedifficult processability (insolubility and infusibility)[2 3 19 20 27 28] have hampered the use of PPyfor technological applications Intensive investiga-tions have been carried out to solve these problems

945

Novel electrically conductivepolyurethanemontmorillonite-polypyrrole nanocompositesS D A S Ramoa1 G M O Barra1 C Merlini1 S Livi2 B G Soares3 A Pegoretti4

1Universidade Federal de Santa Catarina Departamento de Engenharia Mecacircnica Florianoacutepolis SC Brazil2Universiteacute de Lyon Ingeacutenierie des Mateacuteriaux Polymegraveres CNRS UMR 5223 F-69003 Lyon France INSA LyonF-69621 Villeurbanne France

3Universidade Federal do Rio de Janeiro Departamento de Engenharia Metaluacutergica e de Materiais Rio de Janeiro RJ Brazil4Department of Industrial Engineering University of Trento 38123 Trento Italy

Received 3 April 2015 accepted in revised form 8 June 2015

Abstract This work describes the production of electrically conductive nanocomposites based on thermoplastic polyurethane(TPU) filled with montmorillonite-dodecylbenzenesulfonic acid-doped polypyrrole (Mt-PPyDBSA) prepared by meltblending in an internal mixer The electrical conductivity morphology as well as the rheological properties of TPUMt-PPyDBSA nanocomposites were evaluated and compared with those of TPU nanocomposites containing different conduc-tive fillers such as polypyrrole doped with hydrochloride acid (PPyCl) or dodecylbenzenesulfonic acid (PPyDBSA) ormontmorillonite-hydrochloride acid-doped polypyrrole (Mt-PPyCl) prepared with the same procedure The TPUMt-PPyDBSA nanocomposites display a very sharp insulator-conductor transition and the electrical percolation threshold wasabout 10 wt of Mt-PPyDBSA which was significantly lower than those found for TPUMt-PPyCl TPUPPyCl andTPUPPyDBSA Morphological analysis highlights that Mt-PPyDBSA filler was better distributed and dispersed in theTPU matrix forming a denser conductive network when compared to Mt-PPyCl PPyCl and PPyDBSA fillers This mor-phology can be attributed to the higher site-specific interaction between TPU matrix and Mt-PPyDBSA The present studydemonstrated the potential use of Mt-PPyDBSA as new promising conductive nanofiller to produce highly conductivepolymer nanocomposites with functional properties

Keywords nanocomposites polymer composites rheology

eXPRESS Polymer Letters Vol9 No10 (2015) 945ndash958Available online at wwwexpresspolymlettcomDOI 103144expresspolymlett201585

Corresponding author e-mail gbarraufscbrcopy BME-PT

One approach to possibly overcome the above limi-tations is blending PPy with commercial insulatingpolymers to produce conductive polymer blends orcomposites [3 11 27 29ndash33] Among the methodsmentioned in the scientific literature melt mixingoffers the advantages of large-scale production andreduced cost which are the bases for any industrialapplication However this process has been reportedto be less efficient on the dispersion of PPy or otherICPs within insulating polymer matrices In fact theproduction of conducting polymer mixtures withelectrical conductivity less than 10ndash7 Smiddotcmndash1 perco-lation threshold about 30 to 60 wt of ICP andpoor mechanical properties has been reported [34ndash38] Therefore a great challenge is how to producea conducting polymer mixture through melt blend-ing process with higher electrical conductivity atlow percolation threshold of ICP Some works inthe literature have demonstrated that montmoril-lonitepolypyrrole (Mt-PPy) nanocomposites arepotential fillers for improving the electrical andmechanical properties of insulating matrix [27 3638] According to Boukerma et al [36] the exfolia-tion of Mt-PPy promotes a conductive network for-mation in the insulating matrix with lower PPy con-centration when compared with that found for neatPPy Mravaacutekovaacute et al [38] have reported interest-ing results concerning the preparation of polypropy-leneMt-PPy composites On the other handPeighambardoust and Pourabbas reported that per-colation threshold of Nylon-6Mt-PPy compositeswas 15 wt of Mt-PPy [27]In this context thermoplastic polyurethane (TPU)is an interesting insulating matrix for developingflexible conductive Mt-PPy composites with highelectrical conductivity at low percolation thresholdTPU is among the most versatile engineering ther-moplastics since it associates the properties of ther-moplastic polymers with those of vulcanized rubberswithout vulcanizing agents [39 40] Moreover tothe best of our knowledge there are no studies con-cerning the preparation of TPU composites withMt-PPy through melt blending methodBased on the above considerations the main objec-tive of this study is to investigate TPUMt-PPyDBSAnanocomposites produced by melt blending and con-taining various filler contents In particular the atten-tion has been focused on obtaining good electricalconductivity at low filler concentration For compar-ison purpose three different conductive fillers such

as polypyrrole doped hydrochloride acid (PPyCl)or dodecylbenzenesulfonic acid (PPyDBSA) andmontmorillonite-polypyrrole doped hydrochlorideacid (Mt-PPyCl) were separately added into TPUmatrix under the same processing conditions Themorphology electrical and rheological properties ofnanocomposites were experimentally investigated

2 Experimental21 MaterialsSodium bentonite Vulgel CN 45 (Alianccedila LatinaInduacutestrias e Comeacutercio Ltda Uruguaiana Rio Grandedo Sul Brazil)) was kindly supplied by Ioto Interna-tional (Brazil) Pyrrole 98 (Aldrich Germany)was purified by distillation under reduced pressureand stored in a refrigerator before use Iron(III) chlo-ride hexahydrate FeCl3middot6H2O analytical grade(Vetec Duque de Caxias Rio de Janeiro Brazil) andthe surfactant dodecylbenzenesulfonic acid DBSA(Aldrich Italy) were used as received Commer-cially available TPU (Elastollanreg 1180 A10 extrusiongrade Shore A hardness = 80 density = 111 gmiddotcmndash1)based on polyether was purchased from BASF(Mauaacute Satildeo Paulo Brazil)

211 Synthesis of conducting nanocomposites(MtPPy)

The preparation procedure of the conducting nano -composites Mt-PPy with or without a surfactantwas based on the method described in our previousreport with some modifications [41] In a typical pro-cedure Mt (25 g) was dispersed into 250 mL ofwater or aqueous solution containing the DBSA andstirred for 2 h at room temperature The molar ratioof the surfactantPy used in the polymerization was15 The dispersion was sonicated with 35 power(263 W) for 20 min with a Sonics VCX 750 ultra-sonic processor (Sonics amp Materials Inc USA)FeCl3middot6H2O (02542 mol) dissolved in 125 mL of dis-tilled water was added in the aqueous MMT disper-sion under stirring at room temperature 50 mL of a026 molmiddotLndash1 aqueous dispersion of Py (01105 mol)were added dropwise in 15 min The polymeriza-tion proceeded for 1 h under stirring at room tem-perature After 24 h the conducting fillers (Mt-PPyCl and Mt-PPyDBSA) were filtered washedwith distilled water and dried at 60degC The PPy withor without surfactant denoted as PPyDBSA andPPyCl respectively were also prepared using asimilar procedure

Ramoa et al ndash eXPRESS Polymer Letters Vol9 No10 (2015) 945ndash958

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212 Preparation of TPUMt-PPynanocomposites

Before processing both TPU pellets and conductingfillers were dried in a circulating-air oven at 100degCfor 3 h and vacuum oven at 60degC for 12 h respec-tively TPU were melt blended with different amountsof conducting fillers (5 10 15 20 25 and 30 wt)in an internal mixer (Haake Polylab QC Thermo Sci-entific USA) at 170degC with a rotor speed of 50 rpmand mixing time of 15 min The specimens were com-pression-molded at 170degC for 5 min under 12 MPapressure and air cooled to room temperature

22 CharacterizationThe elemental analysis was used to determine thecomposition of conducting mixtures Elementalanalysis was performed on a CHN 2400 analyzer(Perkin-Elmer USA) The combustion process wascarried out at 925degC using oxygen with a puritylevel of 99995The electrical conductivity of the conducting fillersand low-resistivity TPU composites were measuredusing the four probe standard method with a Keith-ley 6220 (USA) current source to apply the currentand a Keithley Model 6517A (USA) electrometer tomeasure the potential difference For neat TPU andhigh-resistivity composites the measurements wereperformed using the two probe standard methodwith a Keithley 6517A (USA) electrometer con-nected to Keithley 8009 (USA) test fixture All meas-urements were performed at room temperature andrepeated at least five times for each sampleFracture surfaces of composites were observed by afield emission scanning electron microscope(FESEM) JEOL model JSM-6701F (JEOL USA)The specimens were fractured in liquid nitrogenand coated with gold and then the cross-section wasobserved at an accelerating voltage of 10 kVTransmission electron microscopy (TEM) observa-tions were performed by a Phillips CM120 micro-

scope (Phillips Germany) (located at the Center ofMicrostructure University of Lyon) at 80 kV Spec-imens consisting of 60 nm-thick ultrathin sectionswere obtained by a Leica Ultracut UCT ultramicro-tome (Leica Germany) equipped with a diamondknife and deposited on copper gridsFourier transform infrared (FTIR) spectra wereobtained through the attenuated total reflectance(ATR) method using a spectrometer Bruker Tensor27 (Bruker USA) with a resolution of 4 cmndash1 Thewavenumbers were in the range of 2000ndash600 cmndash1

for conducting fillers and 4000ndash600 cmndash1 for neatTPU and TPU compositesThe X-ray diffraction (XRD) patterns of all sampleswere obtained on an Philips XrsquoPERT (Philips Ger-many) X-ray diffractometer with CuK ( =0154 nm) radiation source operating at a voltage of40 kV and 30 mA current The samples were evalu-ated in a 2$deg range from 2 to 50deg at steps of 005degand a time step of 1 s Mt PPy and Mt-PPy sampleswere analyzed in powder form while neat TPU andrelative composites were in the form of compres-sion molded disksThe rheological properties of TPU and their physi-cal mixtures were analyzed using dynamic oscilla-tory rheometry in the molten state through an AntonPaar MCR302 rheometer (Anton Paar GmbH Ger-many) Dynamic frequency sweep test were con-ducted at 170degC with angular frequency range from01 to 100 Hz in an oscillatory shear mode by usinga 25 mm parallel plate with a gap around 1000 microm

3 Results and discussion31 Characterization of conductive fillersThe composition of samples electrical conductivityand PPy content inserted in the Mt are summarizedin Table 1 Mt-PPyDBSA and Mt-PPyCl displayhigher PPy content (approximately 90 wt of PPy)than those found by our recent study due to thehigher Py amount used in the in situ polymerization


947

Table 1 Elemental analysis PPy content and electrical conductivity of conductive filler (PPyCl PPyDBSA MtPPyCland MtPPyDBSA)

Calculated from elemental analysis

SamplesCompositiont PPy content

[wt]Electrical conductivity

[Smiddotcmndash1]C H NMt 008 193 000 000 (426plusmn034)middot10ndash6

PPyCl 5504 352 1614 10000 015plusmn002PPyDBSA 6620 635 990 10000 439plusmn102Mt PPyCl 4497 301 1348 8352 426plusmn014MtPPyDBSA 5675 581 892 9010 1003plusmn089

process [41] As expected the electrical conductivityof PPyDBSA (44 Smiddotcmndash1) is higher than that foundfor PPyCl (02 Smiddotcmndash1) due to the doping effect ofDBSA molecules [41 42] In fact the PPyCl samplewas prepared in absence of protonic acid and theHCl that participates on the doping process wasprovided by the FeCl3 used as an oxidantThis condition should be responsible for the lowerconductivity value found for the PPyCl sampleThe electrical conductivity values found for Mt-PPyDBSA and Mt-PPyCl samples are seven andsix orders of magnitude higher than that of neat Mtrespectively Furthermore Mt-PPyCl nanocompos-ite shows an increment in the electrical conductivityof one order of magnitude higher than that foundfor neat PPy-Cl probably due to the doping effectof the Mt [41]

32 Characterization of TPUMt-PPyDBSAnanocomposites

TPUMt-PPyDBSA nanocomposites show a verysharp insulator-conductor transition and the electri-cal conductivity increased significantly with increas-ing the Mt-PPyDBSA content as observed in Fig-ure 1 This behavior can be attributed to the forma-tion of a continuous conductive Mt-PPyDBSA net-work in the insulating polymer On the other handthe electrical conductivity of the systems containing30 wt of Mt-PPyCl PPyCl and PPyDBSA showelectrical conductivities of 13middot10ndash4 54middot10ndash11 and43middot10ndash10 Smiddotcmndash1 respectively which were muchlower than the value found for TPUMt-PPyDBSAnanocomposites(15middot10ndash2 Smiddotcmndash1) at the same con-ductive filler content

For electrically percolating systems the electricalconductivity of a filled material follows a power-law relationship in the form of Equation (1)

(1)

where 0 is a constant f is the content of conductingfiller fp is its percolation threshold and t is the criti-cal exponent The values of parameters fp and t asdetermined through the plot of log versus log(f ndash fp)of TPUMt-PPyDBSA nanocomposites resulted tobe ~10 wt and 22 respectively A critical expo-nent in the range from 2 to 4 is in agreement withthe classical theory for tridimensional systems Onthe other hand TPUMtPPyCl nanocompositesshow a percolation threshold of 225 wt Thelower fp value and higher electrical conductivity ofTPUMt-PPyDBSA nanocomposites with respectto TPUMtPPyCl and TPUPPy samples probablyreflects the good dispersion of the conductive filler(Mt-PPyDBSA) in the polymer matrix These resultsare consistent with the morphological features ofthese materials as it will be discussed laterFESEM micrographs of cryogenically fracturedsamples with 20 wt of conductive filler are shownin Figure 2 The microstructure of the TPUPPyCland TPUPPyDBSA blends revealed typical phaseseparation morphology with the presence of iso-lated PPy agglomerates in the TPU matrix This mor-phology can explain the low electrical conductivityfor these samples On the other hand TPUMt-PPyCl and TPUMt-PPyDBSA nanocompositespresent disperse agglomerates composed of con-ducting pathways in which the disperse phase isbetter interconnected than in the case of TPUPPyCland TPUPPyDBSA blends Furthermore TEMimage of TPUMt-PPyDBSA nanocomposite (Fig-ure 3) reveals a denser network formation of Mt-PPyDBSA in the TPU matrix when compared withthat found for Mt-PPyCl The morphological dif-ference of TPUMt-PPyCl and TPUMt-PPyDBSAnanocomposites indicates that DBSA was able toinduce the formation of conductive pathways in theTPU matrix and consequently enhancing the elec-trical conductivity This morphology can be attrib-uted to the higher site-specific interaction betweenTPU matrix and Mt-PPyDBSAThe infrared spectra of neat TPU TPUPPy blendsand TPUMt-PPy nanocomposites filled with 20 wt

s 5 s01f 2 fp 2 ts 5 s01f 2 fp 2 t


948

Figure 1 Effect of the conducting fillers content on electri-cal conductivity


949

Figure 2 FESEM micrographs of cryogenically fractured samples with 20 wt conductive for TPUPPyCl (a) TPUPPyDBSA (b) TPUMt-PPyCl (c) and TPUMt-PPyDBSA nanocomposites (d)

Figure 3 TEM images of TPUMt-PPyC (a) and Mt-PPyDBSA (b)

of conductive filler are shown in Figure 4 The absorp-tion bands of neat TPU in the region of 3320 cmndash1 andat around 2900 (2939 and 2852 cmndash1) are assignedto the NndashH and CH2 absorption bands respectivelyThe distinct bands that overlap intensively at 1730and 1703 cmndash1 are related to the free carbonyl andhydrogen-bonding absorption of the neat TPU mol-ecules respectively The absorption band at 1526 cmndash1

is attributed to ndashNH group of urethane while thebands at 1219 and 1105 cmndash1 are assigned to the ethergroup [43ndash50]The spectra of the TPUPPy and TPUMt-PPy exhib-ited overlapped absorption bands of PPy and TPUThe band centered at 3320 cmndash1 related to the bondedndashNH was red-shifted to 3300 cmndash1 for nanocom-posites (Figure 4b) [51] Furthermore the band at3435 cmndash1 assigned to the free ndashNH group practi-cally disappeared with the addition of the Mt-PPyDBSA or Mt-PPyCl in the TPU matrix Theseresults suggest that the specific interaction betweenTPU and Mt-PPyDBSA or Mt-PPyCl groups ishigher than that observed for TPU and PPyDBSAor PPyCl An in-depth analysis of the infrared spec-tra in the range 1800 to 1650 cmndash1 for neat TPU andits physical blends was carried out as shown in Fig-ure 5 The spectra with Gaussian deconvolution ofabsorption bands centered at 1730 and 1703 cmndash1

are assigned to the free and site-specific interac-tions of the carbonyl group As shown in Table 2the absorption area ratio between free and bondedcarbonyl groups (A1730A1703) reduces signifi-cantly with increasing of PPyDBSA Mt-PPyCland Mt-PPyDBSA content except for the PPyClThe observed shifts in the ndashNH region (1350 to1300 cmndash1) and the reduction of the free carbonyl

absorption bands (A1730A1703) provide direct sup-port for the fact that site-specific interaction betweenthe NndashH and C=O functional groups are operative inblends andor nanocomposites containing PPyDBSAMt-PPyCl and Mt-PPyDBSA These data alsoreveal that there are considerable fractions of bothfree and bonded carbonyl amine groups even whenTPU is the dominant (80 wt) component More-over the observed shifts and reduction of free car-bonyl groups for TPUMt-PPyDBSA are higher thanthose found for others blends andor nanocompos-ites suggesting higher interaction of TPU and Mt-PPyDBSA These results are consistent with thosediscussed in sections on morphology and electricalconductivityXRD curves of the neat TPU (Figure 6) exhibits alarge and intense diffraction peak centered at 2$ =1998deg assigned to the reflection plane (110) with d-value of 045 nm This diffraction pattern can beattributed to the irregular segments of the amor-phous phase and chains arranged on short-range ofthe TPU rigid phase respectively [52 53] Accord-ing to Ramocirca et al [41] the neat Mt used in this studymanifests a crystalline peak at 63deg (2$) assigned tothe periodicity in the (001) direction of neat Mt andd-value is 14 nm The Mt diffraction peak and basal


950

Figure 4 FTIR spectra of (a) pure TPU and physical mixtures with 20 wt loading of conductive filler and (b) free andhydrogen bonded NndashH stretching region

Table 2 Ratio of the area under the peak of C=O groups(free (A1730) and hydrogen bonded C=O (A1703))with 20 wt loading of conductive filler

Sample A(17301703)

TPU 046TPUPPyCl 048TPUMt-PPyCl 035TPUPPyDBSA 034TPUMt-PPyDBSA 030

distance d(001) for the TPUMt-PPyCl nanocompos-ites are shifted to 46deg (19 nm) respectively indi-cating an intercalation of Mt-PPyCl in the TPUmatrix However the peak at 63deg practically disap-peared for TPUMt-PPyDBSA nanocompositesThe storage (G) and loss moduli (G) as a functionfrequency are shown in Figure 7 for neat TPU and its

composites At the lowest frequencies neat TPUpresents a liquid-like behavior (GgtGamp) Furthermorethere is a transition from liquid to solid-like behav-ior (GltGamp) at a frequency of 318 Hz while forTPUPPyCl and TPUPPyDBSA composites con-taining 5 wt of PPyCl this transition was observedat 817 and 815 Hz respectively For both TPUPPy


951

Figure 5 Deconvolution on the FTIR spectra in the free and hydrogen bonded carbonyl peaks (C=O and HndashC=O) of pureTPU (a) and TPU composites with 20 wt loading of conductive filler PPyCl (b) PPyDBSA (c) Mt-PPyCl (d)Mt-PPyDBSA (e)

blends Gamp and G values decrease with increasingthe amount of PPy suggesting a certain degree ofpolymer matrix degradation On the other handTPUMt-PPyCl and TPUMt -PPyDBSA nano -composites show a quite different behavior when

compared with those found for TPUPPy blendsFor both TPUMt-PPy nanocomposites Gamp and Gvalues increase with increasing the Mt-PPy contentin the TPU matrix The significant increase in the stor-age modulus indicates that TPUMt-PPy nanocom-posites exhibit a pseudo-solid-like behavior More-over TPUMt-PPy nanocomposites with 5 wt ofMt-PPy content show a transition from liquid tosolid-like behavior at frequencies higher than 318 Hzwhich is the same value observed for the neat TPUwhile the values of Gamp becomes almost independentat lower frequency for nanocomposites containing15 wt of Mt-PPy This behavior can be attributedto the percolative network formation in which theconductive filler reduces the mobility of the TPUchain The rheological percolative network increasesthe number of interfaces between conductive fillersand thus an enhancement of the both elastic and vis-cous components is observedThe loss tangent (tan) curves as a function of fre-quency reported in Figure 8 can provide an insight


952

Figure 6 XRD patterns of pure TPU and TPU nanocompos-ites containing 20 wt loading of conductivefiller

Figure 7 Storage modulus (Gamp full points) and loss modulus (G empty points) versus frequency (() at a temperature of170degC for pure TPU and its composites containing 0 5 15 and 30 wt of various conductive fillers PPyCl (a)PPyDBSA (b) Mt-PPyCl (c) Mt-PPyDBSA (d)

on the site-specific interactions between the poly-mer matrix and conducting fillers [54 55] Accord-ing to Han et al [56] for a composite system withhigh-level of conducting phase agglomeration alarger and more intense tan curve with respect ofneat insulating polymer can be observed TPUPPyCland TPUPPyDBSA blends have shown this behav-ior suggesting PPy agglomeration into TPU matrixOn the other hand with increasing conducting fillerthe TPUMt-PPyCl and TPUMt-PPyDBSA nano -composites show lower tan intensities when com-pared with the neat TPU while for nanocompositescontaining 15 and 30 wt of Mt-Py tan values arepractically frequency independent In addition TPUMt-PPyDBSA composites exhibit lower tan val-ues than TPUMt-PPyCl indicating better distribu-tion and dispersion of Mt-PPyDBSA in the TPUmatrix According to Poumltschke et al [57] this behav-ior supports the idea that site-specific interactions atthe interface of insulating polymer matrix and con-ductive filler could be operative

Figure 9 shows the storage modulus Gamp as a functionof loss modulus G with frequency as a parameterfor neat TPU and relative composites These curveshave been extensively used to investigate modifica-tions in the structure of several polymeric systems ata fixed temperature [57ndash59] According to McCloryet al [60] any change in the curve behavior of thecomposite compared with the neat PPy is an indica-tion of network formation It is observed that withincreasing PPyDBSA or PPyCl content the varia-tion of Gamp as a function of G for TPUPPyDBSAand TPUPPyCl blends at lower frequency region(terminal zone) is different from that found for neatTPU This behavior is characteristic of a system withheterogeneous structure On the other hand in thehigh frequency region (rubbery plateau) these curvesare overlapped to that found for the neat TPU whichhighlights the occurrence of a homogeneous struc-ture As expected these mixtures should present aheterogeneous system behavior for all frequencyregions


953

Figure 8 Loss tangent (tan) versus frequency (() at a temperature of 170degC for pure TPU and its composites containingvarious percentages and types of conductive fillers PPyCl (a) PPyDBSA (b) Mt-PPyCl (c) Mt-PPyDBSA (d)

According to Barick and Tripathy [59] the differentbehavior observed for TPUPPyCl and TPUPPyDBSA blends at higher and lower frequenciescould be assigned to the difference of the dynamicrelaxing processes for the neat TPU and mixturesIn addition according to Han et al [56] for a partic-ular polymer system the applied shear stress at lowfrequency is not sufficient to disrupt the structure ofthe interconnected network due to the strong inter-actions between insulating polymer chains and con-ductive filler resulting in a heterogeneous structurebehavior below a critical shearing force Above thiscritical point with increasing the frequency theshear stress is able to separate the conductive net-work structure and a homogeneous system behavioris observed TPUMt-PPyCl and TPUMt-PPyDBSAnanocomposites containing conductive filler load-ing up to 5 wt show similar trend to those foundfor TPUPPyCl and TPUPPyDBSA blends How-ever above 10 wt of Mt-PPyDBSA and 15 wtof Mt-PPyCl content the curve slope of nanocom-

posites is higher than those observed for neat TPUfor all the investigated frequencies This result indi-cates that TPUMt-PPyDBSA and TPUMt-PPyClcomposites are more heterogeneous when comparedto TPUPPyCl and TPUPPyDBSA blends due tothe presence of a strong three-dimensional conduc-tive network which is not disrupted with the shearforce These changes in the curve slope of Mt-PPyDBSA nanocomposites suggest that the inter-phase interaction of the TPU matrix and Mt-PPyDBSA are higher in descendent order of thatfound for Mt-PPyCl PPyDBSA and PPyCl fillers[57 61]

4 ConclusionsA new electrical conductive nanocomposite based onthermoplastic polyurethane and montmorillonitedodecylbenzenesulfonic acid-doped polypyrrole(TPUMt-PPyDBSA) with an electrical conductiv-ity as high as 005 Smiddotcmndash1 was successfully preparedthrough melt mixing process using an internal mix-


954

Figure 9 Han plot of storage modulus (Gamp) versus loss modulus (G) at a temperature of 170degC for pure TPU and its com-posites containing various percentages and types of conductive fillers PPyCl (a) PPyDBSA (b) Mt-PPyCl (c)Mt-PPyDBSA (d)

ing chamber The structure and properties of the mix-tures were strongly dependent on the site-specificinteractions between the conductive filler and TPUchains TPUMt-PPyDBSA exhibits higher electricalconductivity and lower percolation threshold thanTPUMt-PPyCl TPUPPyCl and TPUPPyDBSAmixtures This behavior can be attributed to thestrong interaction of Mt-PPyDBSA particles andTPU matrix which induces a better conductive net-work formation than those found for Mt-PPyClPPyCl and PPyDBSA fillers Furthermore this syn-ergistic effect can also be assigned to the presenceof Mt that acts as a template for the PPyDBSAfacilitating the formation of Mt-PPyDBSA networkin the TPU matrix The results reported in this studyprove that the morphology and electrical conductiv-ity are significantly influenced by the composition ofthe conductive filler used in the melt mixing processespecially in the case of Mt-PPyDBSA Moreoverthe present work reveals the potential use of Mt-PPyDBSA as a new promising conductive filler forproducing highly conductive polymer nanocompos-ites to be applied in several technological applica-tions

AcknowledgementsThe authors gratefully acknowledge the financial support ofthe Conselho Nacional de Desenvolvimento Cientiacutefico eTecnoloacutegico ndash CNPq processo 4001552014-1 Coordenaccedilatildeode Aperfeiccediloamento de Pessoal de Ensino Superior ndash CAPESand Fundaccedilatildeo de Amparo agrave Pesquisa e Inovaccedilatildeo do Estadode Santa Catarina ndash FAPESC We are also very grateful toCentral Electronic Microscopy Laboratory (LCME-UFSC)for the microscopy analysis (FESEM)

References [1] Yang C Liu P Zhao Y Preparation and characteriza-

tion of coaxial halloysitepolypyrrole tubular nanocom-posites for electrochemical energy storage Electro -chimica Acta 55 6857ndash6864 (2010)DOI 101016jelectacta201005080

[2] Yanilmaz M Kalaoglu F Karakas H Sarac A SPreparation and characterization of electrospun poly -urethanendashpolypyrrole nanofibers and films Journal ofApplied Polymer Science 125 4100ndash4108 (2012)DOI 101002app36386

[3] Pojanavaraphan T Magaraphan R Fabrication andcharacterization of new semiconducting nanomaterialscomposed of natural layered silicates (Na+-MMT) nat-ural rubber (NR) and polypyrrole (PPy) Polymer 511111ndash1123 (2010)DOI 101016jpolymer200907003

[4] Lee J-W Serna F Nickels J Schmidt C E Car-boxylic acid-functionalized conductive polypyrrole asa bioactive platform for cell adhesion Biomacromole-cules 7 1692ndash1695 (2006)DOI 101021bm060220q

[5] Omastovaacute M Trchovaacute M Kovaacute)ovaacute J Stejskal JSynthesis and structural study of polypyrroles preparedin the presence of surfactants Synthetic Metals 138447ndash455 (2003)DOI 101016S0379-6779(02)00498-8

[6] Reung-u-Rai A Prom-Jun A Prissanaroon-Ouajai WSynthesis of highly conductive polypyrrole nanoparti-cles via microemulsion polymerization Journal of Met-als Materials and Minerals 18 27ndash31 (2008)

[7] Gurunathan K Murugan A V Marimuthu R MulikU Amalnerkar D Electrochemically synthesised con-ducting polymeric materials for applications towardstechnology in electronics optoelectronics and energystorage devices Materials Chemistry and Physics 61173ndash191 (1999)DOI 101016S0254-0584(99)00081-4

[8] Jiang L Jun H-K Hoh Y-S Lim J-O Lee D-DHuh J-S Sensing characteristics of polypyrrolendashpoly(vinyl alcohol) methanol sensors prepared by in situvapor state polymerization Sensors and Actuators BChemical 105 132ndash137 (2005)DOI 101016jsnb200312077

[9] Merlini C dos Santo Almeida R DrsquoAacutevila M ASchreiner W H de Oliviera Barra G M Developmentof a novel pressure sensing material based on polypyr-role-coated electrospun poly(vinylidene fluoride) fibersMaterials Science and Engineering B 179 52ndash59(2014)DOI 101016jmseb201310003

[10] Li M Li H Zhong W Zhao Q Wang D Stretch-able conductive polypyrrolepolyurethane (PPyPU)strain sensor with netlike microcracks for human breathdetection ACS Applied Materials and Interfaces 61313ndash1319 (2014)DOI 101021am4053305

[11] Hosseini S H Entezami A A Conducting polymerblends of polypyrrole with polyvinyl acetate poly-styrene and polyvinyl chloride based toxic gas sen-sors Journal of Applied Polymer Science 90 49ndash62(2003)DOI 101002app12492

[12] Brady S Diamond D Lau K-T Inherently conduct-ing polymer modified polyurethane smart foam forpressure sensing Sensors and Actuators A Physical119 398ndash404 (2005)DOI 101016jsna200410020

[13] Tjahyono A P Aw K C Travas-Sejdic J A novelpolypyrrole and natural rubber based flexible large strainsensor Sensors and Actuators B Chemical 166ndash167426ndash437 (2012)DOI 101016jsnb201202083


955

[14] Xu J Zhu L Bai Z Liang G Liu L Fang D Xu WConductive polypyrrolendashbacterial cellulose nanocom-posite membranes as flexible supercapacitor electrodeOrganic Electronics 14 711ndash718 (2013)DOI 101016jorgel201309042

[15] Mi H Zhang X Ye X Yang S Preparation andenhanced capacitance of corendashshell polypyrrolepoly -aniline composite electrode for supercapacitors Journalof Power Sources 176 403ndash409 (2008)DOI 101016jjpowsour200710070

[16] Olsson H Nystroumlm G Stroslashmme M Sjoumldin M NyholmL Cycling stability and self-protective properties of apaper-based polypyrrole energy storage device Elec-trochemistry Communications 13 869ndash871 (2011)DOI 101016jelecom201105024

[17] Armelin E Pla R Liesa F Ramis X Iribarren J IAlemaacuten C Corrosion protection with polyaniline andpolypyrrole as anticorrosive additives for epoxy paintCorrosion Science 50 721ndash728 (2008)DOI 101016jcorsci200710006

[18] Haringkansson E Amiet A Nahavandi S Kaynak AElectromagnetic interference shielding and radiationabsorption in thin polypyrrole films European PolymerJournal 43 205ndash213 (2007)DOI 101016jeurpolymj200610001

[19] Yavuz Ouml Ram M K Aldissi M Poddar P SrikanthH Polypyrrole composites for shielding applicationsSynthetic Metals 151 211ndash217 (2005)DOI 101016jsynthmet200505011

[20] Kim S H Jang S H Byun S W Lee J Y Joo J SJeong S H Park M J Electrical properties and EMIshielding characteristics of polypyrrolendashnylon 6 com-posite fabrics Journal of Applied Polymer Science 871969ndash1974 (2003)DOI 101002app11566

[21] Wallace G G Campbell T E Innis P C Putting func-tion into fashion Organic conducting polymer fibresand textiles Fibers and Polymers 8 135ndash142 (2007)DOI 101007BF02875782

[22] Gasana E Westbroek P Hakuzimana J De Clerck KPriniotakis G Kiekens P Tseles D Electroconductivetextile structures through electroless deposition of poly -pyrrole and copper at polyaramide surfaces Surfaceand Coatings Technology 201 3547ndash3551 (2006)DOI 101016jsurfcoat200608128

[23] Xu H Holzwarth J M Yan Y Xu P Zheng H Yin YLi S Ma P X Conductive PPyPDLLA conduit forperipheral nerve regeneration Biomaterials 35 225ndash235 (2014)DOI 101016jbiomaterials201310002

[24] Otero T F Corteacutes M T Artificial muscles with tactilesensitivity Advanced Materials 15 279ndash282 (2003)DOI 101002adma200390066

[25] Hara S Zama T Takashima W Kaneto K Polypyr-rolendashmetal coil composite actuators as artificial musclefibres Synthetic Metals 146 47ndash55 (2004)DOI 101016jsynthmet200406021

[26] Smela E Conjugated polymer actuators for biomed-ical applications Advanced Materials 15 481ndash494(2003)DOI 101002adma200390113

[27] Peighambardoust S J Pourabbas B Preparation andcharacterization of nylon-6PPyMMT composite ofnanocomposite Journal of Applied Polymer Science106 697ndash705 (2007)DOI 101002app26709

[28] Peighambardoust S J Pourabbas B Synthesis andcharacterization of conductive polypyrrolemontmoril-lonite nanocomposites via one-pot emulsion polymer-ization Macromolecular Symposia 247 99ndash109 (2007)DOI 101002masy200750112

[29] Sevil B Zuhal K Synthesis and characterization ofpolypyrrole nanoparticles and their nanocomposites withpoly(propylene) Macromolecular Symposia 295 59ndash64 (2010)DOI 101002masy200900164

[30] Ashraf S M Ahmad S Riaz U Pseudothermosetblends of poly (methyl methacrylate) and polypyrrolemorphological thermal and conductivity studies Jour-nal of Applied Polymer Science 93 82ndash91 (2004)DOI 101002app20404

[31] Mahmud H N M E Kassim A Zainal Z Yunus WM M Fourier transform infrared study of polypyrrolendashpoly(vinyl alcohol) conducting polymer compositefilms Evidence of film formation and characteriza-tion Journal of Applied Polymer Science 100 4107ndash4113 (2006) DOI 101002app23327

[32] Kotal M Srivastava S K Paramanik B Enhance-ments in conductivity and thermal stabilities of polypyr-rolepolyurethane nanoblends Journal of Physical Chem-istry C 115 1496ndash1505 (2011)DOI 101021jp1081643

[33] Muller D Garcia M Salmoria G V Pires A T NPaniago R Barra G M O SEBSPPyDBSA blendsPreparation and evaluation of electromechanical anddynamic mechanical properties Journal of AppliedPolymer Science 120 351ndash359 (2011)DOI 101002app33141

[34] Omastovaacute M Koina S Pionteck J Janke A Pavli-nec J Electrical properties and stability of polypyr-role containing conducting polymer composites Syn-thetic Metals 81 49ndash57 (1996)DOI 1010160379-6779(96)80228-1

[35] Omastovaacute M Pionteck J Koina S Preparation andcharacterization of electrically conductive polypropy-lenepolypyrrole composites European Polymer Jour-nal 32 681ndash689 (1996)DOI 1010160014-3057(95)00206-5

[36] Boukerma K Piquemal J-Y Chehimi M M Mrav-aacutekovaacute M Omastovaacute M Beaunier P Synthesis andinterfacial properties of montmorillonitepolypyrrolenanocomposites Polymer 47 569ndash576 (2006)DOI 101016jpolymer200511065


956

[37] Zhu D Bin Y Oishi K Fukuda Y Nakaoki T Mat-suo M Conductive composite materials of polyethyleneand polypyrrole with high modulus and high strengthMacromolecular Symposia 214 197ndash216 (2004)DOI 101002masy200451014

[38] Mravaacutekovaacute M Omastovaacute M Poumltschke P Pozsgay APukaacutenszky B Pionteck J Poly(propylene)montmo-rillonitepolypyrrole composites Structure and con-ductivity Polymers for Advanced Technologies 17715ndash726 (2006)DOI 101002pat765

[39] Boubakri A Haddar N Elleuch K Bienvenu YImpact of aging conditions on mechanical properties ofthermoplastic polyurethane Materials and Design 314194ndash4201 (2010)DOI 101016jmatdes201004023

[40] Fernaacutendez-drsquoArlas B Khan U Rueda L Coleman JN Mondragon I Corcuera M A Eceiza A Influenceof hard segment content and nature on polyurethanemultiwalled carbon nanotube composites CompositesScience and Technology 71 1030ndash1038 (2011)DOI 101016jcompscitech201102006

[41] Ramocirca S D A S Barra G M O Merlini C Schrei-ner W H Livi S Soares B G Production of montmo-rillonitepolypyrrole nanocomposites through in situoxidative polymerization of pyrrole Effect of anionicand cationic surfactants on structure and propertiesApplied Clay Science 104 160ndash167 (2015)DOI 101016jclay201411026

[42] Mravaacutekovaacute M Omastovaacute M Olejniacutekovaacute K Pukaacuten-szky B Chehimi M M The preparation and proper-ties of sodium and organomodified-montmorillonitepolypyrrole composites A comparative study Syn-thetic Metals 157 347ndash357 (2007)DOI 101016jsynthmet200704005

[43] Menes O Cano M Benedito A Gimeacutenez E CastellP Maser W K Benito A M The effect of ultra-thingraphite on the morphology and physical properties ofthermoplastic polyurethane elastomer composites Com-posites Science and Technology 72 1595ndash1601 (2012)DOI 101016jcompscitech201206016

[44] Bistrii+ L Baranovi+ G Leskovac M Bajsi+ E GHydrogen bonding and mechanical properties of thinfilms of polyether-based polyurethanendashsilica nanocom-posites European Polymer Journal 46 1975ndash1987(2010)DOI 101016jeurpolymj201008001

[45] Russo P Lavorgna M Piscitelli F Acierno D DiMaio L Thermoplastic polyurethane films reinforcedwith carbon nanotubes The effect of processing on thestructure and mechanical properties European PolymerJournal 49 379ndash388 (2013)DOI 101016jeurpolymj201211008

[46] Pattanayak A Jana S C Properties of bulk-polymer-ized thermoplastic polyurethane nanocomposites Poly-mer 46 3394ndash3406 (2005)DOI 101016jpolymer200503021

[47] Petcharoen K Sirivat A Electrostrictive properties ofthermoplastic polyurethane elastomer Effects of ure-thane type and softndashhard segment composition CurrentApplied Physics 13 1119ndash1127 (2013)DOI 101016jcap201303005

[48] Ferry A Jacobsson P van Heumen J D Stevens JR Raman infra-red and DSC studies of lithiumcoordination in a thermoplastic polyurethane Poly-mer 37 737ndash744 (1996)DOI 1010160032-3861(96)87248-X

[49] Yilgor I Yilgor E Guler I G Ward T C Wilkes G LFTIR investigation of the influence of diisocyanate sym-metry on the morphology development in model seg-mented polyurethanes Polymer 47 4105ndash4114 (2006)DOI 101016jpolymer200602027

[50] Van Heumen J D Stevens J R The role of lithiumsalts in the conductivity and phase morphology of a ther-moplastic polyurethane Macromolecules 28 4268ndash4277 (1995)DOI 101021ma00116a030

[51] Barick A K Tripathy D K Effect of organoclay onthe morphology mechanical thermal and rheologicalproperties of organophilic montmorillonite nanoclaybased thermoplastic polyurethane nanocomposites pre-pared by melt blending Polymer Engineering and Sci-ence 50 484ndash498 (2010)DOI 101002pen21556

[52] Barick A K Tripathy D K Preparation and charac-terization of carbon nanofiber reinforced thermoplasticpolyurethane nanocomposites Journal of Applied Poly-mer Science 124 765ndash780 (2012)DOI 101002app35066

[53] Barick A K Tripathy D K Preparation characteriza-tion and properties of acid functionalized multi-walledcarbon nanotube reinforced thermoplastic polyure -thane nanocomposites Materials Science and Engi-neering B 176 1435ndash1447 (2011)DOI 101016jmseb201108001

[54] Pistor V Lizot A Fiorio R Zattera A J Influence ofphysical interaction between organoclay and poly(eth-ylene-co-vinyl acetate) matrix and effect of clay con-tent on rheological melt state Polymer 51 5165ndash5171(2010)DOI 101016jpolymer201008045

[55] Hyun Y H Lim S T Choi H J John M S Rheol-ogy of poly(ethylene oxide)organoclay nanocompos-ites Macromolecules 34 8084ndash8093 (2001)DOI 101021ma002191w

[56] Han S-I Lim J S Kim D K Kim M N Im S S Insitu polymerized poly(butylene succinate)silica nano -composites Physical properties and biodegradationPolymer Degradation and Stability 93 889ndash895 (2008)DOI 101016jpolymdegradstab200802007

[57] Poumltschke P Fornes T D Paul D R Rheologicalbehavior of multiwalled carbon nanotubepolycarbon-ate composites Polymer 43 3247ndash3255 (2002)DOI 101016S0032-3861(02)00151-9


957

[58] Di Y Iannace S Di Maio E Nicolais L Nanocom-posites by melt intercalation based on polycaprolactoneand organoclay Journal of Polymer Science Part BPolymer Physics 41 670ndash678 (2003)DOI 101002polb10420

[59] Barick A K Tripathy D K Nanostructure morphol-ogy and dynamic rheological properties of nanocompos-ites based on thermoplastic polyurethane and organi-cally modified montmorillonite Polymer Bulletin 661231ndash1253 (2011)DOI 101007s00289-010-0395-6

[60] McClory C McNally T Baxendale M Poumltschke PBlau W Ruether M Electrical and rheological perco-lation of PMMAMWCNT nanocomposites as a func-tion of CNT geometry and functionality European Poly-mer Journal 46 854ndash868 (2010)DOI 101016jeurpolymj201002009

[61] Lee D Lee S-H Kim S Char K Park J H Bae Y HMicro-phase-separation behavior of amphiphilic poly -urethanes involving poly(ethylene oxide) and poly(tetramethylene oxide) Journal of Polymer SciencePart B Polymer Physics 41 2365ndash2374 (2003)DOI 101002polb10504


958

One approach to possibly overcome the above limi-tations is blending PPy with commercial insulatingpolymers to produce conductive polymer blends orcomposites [3 11 27 29ndash33] Among the methodsmentioned in the scientific literature melt mixingoffers the advantages of large-scale production andreduced cost which are the bases for any industrialapplication However this process has been reportedto be less efficient on the dispersion of PPy or otherICPs within insulating polymer matrices In fact theproduction of conducting polymer mixtures withelectrical conductivity less than 10ndash7 Smiddotcmndash1 perco-lation threshold about 30 to 60 wt of ICP andpoor mechanical properties has been reported [34ndash38] Therefore a great challenge is how to producea conducting polymer mixture through melt blend-ing process with higher electrical conductivity atlow percolation threshold of ICP Some works inthe literature have demonstrated that montmoril-lonitepolypyrrole (Mt-PPy) nanocomposites arepotential fillers for improving the electrical andmechanical properties of insulating matrix [27 3638] According to Boukerma et al [36] the exfolia-tion of Mt-PPy promotes a conductive network for-mation in the insulating matrix with lower PPy con-centration when compared with that found for neatPPy Mravaacutekovaacute et al [38] have reported interest-ing results concerning the preparation of polypropy-leneMt-PPy composites On the other handPeighambardoust and Pourabbas reported that per-colation threshold of Nylon-6Mt-PPy compositeswas 15 wt of Mt-PPy [27]In this context thermoplastic polyurethane (TPU)is an interesting insulating matrix for developingflexible conductive Mt-PPy composites with highelectrical conductivity at low percolation thresholdTPU is among the most versatile engineering ther-moplastics since it associates the properties of ther-moplastic polymers with those of vulcanized rubberswithout vulcanizing agents [39 40] Moreover tothe best of our knowledge there are no studies con-cerning the preparation of TPU composites withMt-PPy through melt blending methodBased on the above considerations the main objec-tive of this study is to investigate TPUMt-PPyDBSAnanocomposites produced by melt blending and con-taining various filler contents In particular the atten-tion has been focused on obtaining good electricalconductivity at low filler concentration For compar-ison purpose three different conductive fillers such

as polypyrrole doped hydrochloride acid (PPyCl)or dodecylbenzenesulfonic acid (PPyDBSA) andmontmorillonite-polypyrrole doped hydrochlorideacid (Mt-PPyCl) were separately added into TPUmatrix under the same processing conditions Themorphology electrical and rheological properties ofnanocomposites were experimentally investigated

2 Experimental21 MaterialsSodium bentonite Vulgel CN 45 (Alianccedila LatinaInduacutestrias e Comeacutercio Ltda Uruguaiana Rio Grandedo Sul Brazil)) was kindly supplied by Ioto Interna-tional (Brazil) Pyrrole 98 (Aldrich Germany)was purified by distillation under reduced pressureand stored in a refrigerator before use Iron(III) chlo-ride hexahydrate FeCl3middot6H2O analytical grade(Vetec Duque de Caxias Rio de Janeiro Brazil) andthe surfactant dodecylbenzenesulfonic acid DBSA(Aldrich Italy) were used as received Commer-cially available TPU (Elastollanreg 1180 A10 extrusiongrade Shore A hardness = 80 density = 111 gmiddotcmndash1)based on polyether was purchased from BASF(Mauaacute Satildeo Paulo Brazil)

211 Synthesis of conducting nanocomposites(MtPPy)

The preparation procedure of the conducting nano -composites Mt-PPy with or without a surfactantwas based on the method described in our previousreport with some modifications [41] In a typical pro-cedure Mt (25 g) was dispersed into 250 mL ofwater or aqueous solution containing the DBSA andstirred for 2 h at room temperature The molar ratioof the surfactantPy used in the polymerization was15 The dispersion was sonicated with 35 power(263 W) for 20 min with a Sonics VCX 750 ultra-sonic processor (Sonics amp Materials Inc USA)FeCl3middot6H2O (02542 mol) dissolved in 125 mL of dis-tilled water was added in the aqueous MMT disper-sion under stirring at room temperature 50 mL of a026 molmiddotLndash1 aqueous dispersion of Py (01105 mol)were added dropwise in 15 min The polymeriza-tion proceeded for 1 h under stirring at room tem-perature After 24 h the conducting fillers (Mt-PPyCl and Mt-PPyDBSA) were filtered washedwith distilled water and dried at 60degC The PPy withor without surfactant denoted as PPyDBSA andPPyCl respectively were also prepared using asimilar procedure


946








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(1)


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Sample A(17301703)





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Sample A(17301703)





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(1)


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Sample A(17301703)





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novel electrically conductive … properties of insulating matrix ... fillers were dried in a...

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