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Silver coated vapor-grown-carbon nanofibers for effective reinforcementof polypropylene–polyaniline

Guy Nesher, Maéva Serror, David Avnir ⇑, Gad Marom ⇑Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

a r t i c l e i n f o

Article history:Received 14 April 2010Received in revised form 4 November 2010Accepted 10 November 2010Available online 17 November 2010

Keywords:A. Particle-reinforced compositesA. Carbon fibersA. MetalsB. Mechanical propertiesB. Electrical conductivity

a b s t r a c t

This work utilizes a modification of our process of polymer entrapment in silver to deposit silver crystalson carbon nanofibers at different relative concentrations. The experimental procedure and the character-istics of silver coated nanofibers are presented in detail. The resulting nanofibers are then melt-mixedwith a polypropylene–polyaniline blend to form a uniform dispersion that is finally extruded to producecontinuous monofilament composites of high axial orientation. The reinforcement effect of the silvercoated nanofibers, manifested in the mechanical properties of the monofilament composites, is 3–5 foldshigher than that of the pristine nanofibers due to the improved stress transfer mechanism of the former.Additional attractive properties of the new system may result from its anisotropic crystalline structure,enhanced thermal stability, potential electrical conductivity and antibacterial behavior.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Strong interfacial interaction is an essential prerequisite in fiberreinforced composites for an effective stress transfer mechanism.This interaction can either be chemo-physical, based on chemicalcovalent bonding and or physical attraction, or of mechanical nat-ure, wherein the fiber surface provides the matrix with anchoringpoints to increase the friction. For nano-reinforcement such as car-bon-nanotubes this requirement is additional to that of uniformdispersion of the fully exfoliated nanoparticles. Thus, an efficientsurface treatment can first facilitate mixing and dispersion andthen enhance nanoparticle–matrix interactions for more effectivestress transfer in the composite. In that respect, our previous workon polymers embedded in silver would be a good starting point, asfollows. A recently developed methodology allows the formation ofmetal–organic alloys by entrapping organic or biological compo-nents within tightly aggregated metallic matrices. Such com-pounds offer a significantly wider property spectrum comparedwith pure metallic alloys, resulting from their composite structurethat reflects simultaneously their organic and metallic nature.Using this principle, it was shown that organic compound dopedmetals comprise an interesting family of materials, which can leadto various useful applications [1–12]. Among the properties thatcan be achieved with these materials are superior metallic cata-

lysts [5,10,11], acidic metals [1], chiral metals [2,7], and conductivepolymer@metal composites [9]. The methodology of preparation ofthose metal matrix composites is based on the reduction of a metalsalt in the presence of the selected organic molecule which isentrapped in the nascent metallic matrix. This reductive entrap-ment can be carried out either homogenously [1–4,8,9], heteroge-neously [6], or electrolytically [12]. The composites are obtained ina powder form, which can be hot-pressed to create films or plates.

In the present study the methodology is extended to the entrap-ment of nanoparticles, such as carbon-nanotubes, to form nanopar-ticle@metal composites. The resulting nanocomposite materialsare of potential use in a wide range of applications such as sensors,catalysis, energy storage and reinforcement.

Of the various reduction processes of metal cations, one methodemerged as particularly attractive, namely, the use of N,N-dimeth-ylformamide (DMF) as an excellent solvent for the carbon nanofil-lers, and as a reducing agent [13,14].

Of the family of carbon nanofillers, the most appealing for rein-forcement applications is the vapor grown carbon fibers (VGCF)due to their high aspect ratio and low cost [15–17]. VGCF also haveexcellent electrical, thermal and mechanical properties, whichmake them compatible with metals. In this work VGCF–Ag wasused as nanofiller to reinforce a polymeric matrix, the idea beingto deposit silver crystals on the surface of the nano-reinforcementand to roughen it in a similar manner to that proposed by Simonand Prosen [31], who grew carbon whiskers on the surface ofcarbon fibers to improve the grip of the latter by the matrix.

Melt-mixing is probably the most suitable technique for indus-trial production of thermoplastic composites. By this technique,

0266-3538/$ - see front matter � 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.compscitech.2010.11.005

⇑ Corresponding authors. Tel.: +972 2 6585898; fax: +972 2 6586068 (G. Marom),tel.: +972 2 6585332; fax: +972 2 6520099 (D. Avnir).

E-mail addresses: david@chem.ch.huji.ac.il (D. Avnir), gadm@vms.huji.ac.il (G.Marom).

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the dispersion of nanofillers in a polymer is achieved through sub-jecting the polymer blend to high shear stresses. Specifically, in thisstudy, blends of nanoparticle@metal in polyaniline/polypropylene(PANI/iPP) were prepared by melt-mixing, aiming at inventing anew family carbon-nanoparticles@metal reinforced polymers.

2. Results

2.1. Characterization the VGCF–Ag nanofillers

Fig. 1a shows SEM image of 5 wt.% VGCF–Ag sample. It is seenthat the VGCF are fully exfoliated and embedded in the silver ma-trix. It is also noted that the presence of VGCF affects the silvercrystal size, so that the average particle size is smaller than that

of neat silver formed under similar conditions [8,9]. A typical highmagnification of 5 wt.% VGCF–Ag sample is presented in Fig. 1c.Density measurements confirm this observation, as seen at Table1. Whereas the density of pure silver is 10.5 g/cm3, those of allthe carbon-nanoparticle@Ag compositions are significantly lower.In particular, the density of the 30 wt.% VGCF–Ag is approximatelyhalf of that of pure silver, reflecting both the contribution of the or-ganic component and the interstitial porosity between thenanocrystals.

Fig. 2a shows a SEM image of 5 wt.% VGCF–Ag sample and a cor-responding electron disperse spectroscopy (EDS) scan along themarked arrow (Fig. 2b). On the basis of these observations, it isapparent that the particle seen to be attached to the carbon nano-fiber surface is of silver.

The thermal stability results are presented in Fig. 3. They reveala significant catalytic effect of silver in the oxidation reactions,(probably due to the fact that silver can support a thin surfaceoxide like structure under those conditions) [18] which results inlowering of the decomposition temperature. Specifically, basedon the first derivatives of the TGA traces, the reaction temperaturefor the free VGCF sample is �600 �C, for the 30 wt.% VGCF–Ag sam-ple is �500 �C and for the 5 wt.% VGCF–Ag sample is �350 �C. It hasbeen shown that a strong catalytic effect is indicative of effectiveentrapment, i.e. a close interaction between the silver and the or-ganic material [9].

Further analysis of the temperature stability results (Fig. 3) basedon the two VGCF concentrations, underlines the concentrationdependent catalytic effect. It is evident that a stronger catalytic ef-fect is attained at higher silver concentration. Specifically, the oxida-tion temperature peak is shifted from �350 �C to �500 �C as theVGCF concentration decreases from 30 wt.% to 5 wt.%. This observa-tion correlates well with the density and the surface area values(Table 1) of the two composites. It is seen that the composite withthe higher VGCF content has significantly higher surface area andlower density, which implies that the properties of VGCF (low den-sity and high surface area) become dominant in the composite.

The N2-adsorption–desorption BET measurements (Fig. 4) showa lower location of the P/P� hysteresis loop and a bigger hysteresisloop for the 30 wt.% VGCF–Ag sample, which also corroborates theformation of a better mesoporous material.

The effect of VGCF concentration can be analyzed also in view ofSEM images in Fig. 1. It is seen that the coverage of the nanofibersby the silver matrix depends strongly on the concentration, so thatin the 5 wt.% VGCF–Ag composite the nanofibers are almost en-tirely covered by the metal matrix, whereas in the 30 wt.%VGCF–Ag composite only small spots of silver can be seen on theirsurfaces. In terms of atomic concentration [19], based on themolecular weights of C and Ag, the concentrations of the carbonfraction in the composites can be converted to �25 atom-% and�80 atom-%, respectively.

This leads to the conclusion that the VGCF/Ag proportion notonly determines the extent of embedment of the nanofibers inthe silver matrix, but more importantly, it determines themorphology of the silver clusters attached to the surface of thenanofibers [20–22].

Fig. 1. SEM pictures of the nanofillers: (a) 5 wt.% VGCF–Ag; (b) 30 wt.% VGCF–Ag;(c) high magnification of 5 wt.% VGCF–Ag.

Table 1Porosities, surface areas and densities of the composites.

Sample Average poresize (nm)

Pore volume(cm2 g�1)

Surface areaa

(m2 g�1)Densitya

(g cm�3)

5 wt.% VGCF–Ag 61 0.060 0.02 8.4730 wt.% VGCF–Ag 29 0.093 9.8 5.865 wt.% CNT-Ag 31 0.032 4.9 8.495 wt.% GNP-Ag 50 0.006 0.63 9.55

a Pure silver prepared by the same method has a very low surface area of0.003 m2 g�1 and a density of 10.41 g cm�3.

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The mechanism of silver attachment to the carbon nanofiber’ssurface involves some interaction between the metal cationswith surface defects, possibly with –COO� groups that arepresent there (the presence of oxidation products at defects ofvarious graphitic structures has been shown by a number ofstudies [23,24], and confirmed by our EDS analyses – not shown).As a result, silver is nucleated at the defects with subsequentpreferential attachment of silver particles to surface defects(see Fig. 2a).

2.2. Characterization of iPP–PANI filaments reinforced by VGCF–Ag

VGCF and VGCF–Ag nanofillers (Fig. 1c) were mix-blended withthe iPP–PANI matrix to produce continuous monofilaments. Fig. 5shows SEM images of filament cross-sections, comparing betweenthe unfilled iPP–PANI matrix (Fig. 5a), and the same with the addi-tions of VGCF (Fig. 5b) and VGCF–Ag (Fig. 5c). It is seen that theVGCF are uniformly and individually dispersed and oriented byand large perpendicular to the cross-section of the filament. It isalso evident that VGCF generate sporadically transcrystallinitywhich appears to nucleate at their surfaces (Fig. 5b, this is also truefor the VGCF–Ag case), whereas only vague signs of crystallinitycan be traced in the unfilled matrix (Fig. 5a). It is also apparent(Fig. 5c) that the silver particles remain attached strongly to theVGCF despite their processing history which subjected them tohigh shear rates during the mix-blending with iPP–PANI. In fact,no difference at all can be seen between the VGCF–Ag nanofillersin Figs. 1c and 5c.

The thermal properties of the monofilaments analyzed by DSCare discussed next. Fig. 6 shows DSC traces of the different systems,comparing the reference iPP–PANI monofilaments with those con-taining VGCF and 5 wt.% VGCF–Ag, for small and large draw-downratios (DDR), before and after annealing. In all the systems, a singleendothermic process is observed at approximately 165 �C, whichcorresponds to the melting temperature of the iPP component.An additional exothermic process is observed at 230 �C, which cor-responds to the cross-linking of PANI [25]. It seems that the DDRhas no effect on the thermal behavior (Fig. 6a and b), however,the annealing process eliminates the cross-linking exothermic

Fig. 2. High resolution SEM image with EDS scan: (a) SEM image of a 5 wt.% VGCF–Ag sample; (b) A line EDS scan of C and Ag atom intensity, corresponding to the arrow in(a).

Fig. 3. The thermogravimetric analysis in air (a) and its first derivative (b) of the original carbon nano-filler and the entrapped one: VGCF (i) vs. VGCF–Ag 5 wt.% (ii) and30 wt.% (iii).

Fig. 4. Adsorption–desorption BET isotherms of N2 for 5 wt.% VGCF–Ag sample (i)and 30 wt.% VGCF–Ag sample (ii).

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peak, except in the high DDR iPP–PANI filaments (Fig. 6c and d).This implies that most of the cross-linking reaction occurs duringthe annealing process. The degrees of crystallinity of the varioussystems are summarized in Table 2. The main effect on crystallinityis that of annealing which increases the degree of crystallinity froman average of 34–41%.

The interactions between PANI, VGCF and silver were investi-gated by FTIR. All the fibers showed a very similar absorption spec-trum comprising the characteristic vibrational modes of PANI andiPP. Fig. 7 presents the spectrum around 1450 cm�1 assigned to theC–N stretching in the benzenoid diimine unit of the PANI (there is asmall contribution from the C–H deformation in the benzenoid ring

[26,27]). The absorption peak shifts from 1460 cm�1, in the iPP–PANI monofilament, to �1455 cm�1 in the VGCF–Ag containingmonofilaments. This shift is attributed to the interaction betweenthe C–N moiety of PANI and silver [8,9,28]. This can also be takenas evidence that the presence of the silver particles improves thedispersion of PANI in the iPP and concurrently – the contact ofPANI and VGCF. Recalling that the Ag is connected to the VGCF italso indicates that the PANI is near the VGCF.

WAXD analyses were performed to understand the influence ofthe nanofillers on the crystalline orientation of the iPP matrix.Fig. 8 shows the structural analysis of the monofilaments whereeach diffraction pattern presents six different reflections. The ringindexing of the reflections is consistent with the a polymorph ofthe iPP [29]. To evaluate the crystalline orientation of the differentsystems, both the width at half height (whh) and Herman’s factorwere calculated utilizing an azimuthal scan of the (0 4 0) reflection(for a detailed procedure see Ref. [29]). This particular reflectionhas been shown to be highly sensitive to different process condi-tions [29]. Based on the two orientation parameters in Table 3,the following conclusions can be attained: comparing the referenceiPP–PANI monofilament with the same monofilament containingVGCF, reveals that the orientation of the iPP crystallites wasincreased by the VGCF, an observation that had already been con-firmed by the SEM images (Fig. 5b). However, the use of VGCF–Agnanofillers, decreases the orientation of the iPP crystallites in rela-tion with the concentration of silver, an observation that will bediscussed in the next paragraph. Evidently [30], an additionalparameter that influences the orientation is the DDR. From the2D WAXD patterns of the same system containing 3 wt.% ofVGCF–Ag with different DDR, before and after annealing, it is seenthat the orientation of the iPP crystallites increases with the DDR,expressed by a difference of �30 a.u. in the whh values regardlessof the annealing process (Table 3). Moreover, it seems that theannealing process tends to reduce the orientation but only to a lim-ited extent.

2.3. Enhancement of mechanical properties

The WAXD results show that under the effect of VGCF–Agnanofillers the iPP crystalline orientation decreases. We attributethis effect to the silver particles on the VGCF surface which nucle-ate crystallization and interfere with the orientated crystal growth.

Fig. 9 presents the Young’s modulus and the ultimate strengthas a function of DDR for the different systems. It is seen that rein-forcing the iPP–PANI matrix with VGCF leads to a small enhance-ment in the Young’s modulus (Fig. 9a). However, reinforcing thesame matrix with VGCF–Ag nanofillers, enhances the Young’smodulus dramatically (Fig. 9a). For the two VGCF–Ag systems pre-sented in Fig. 9a, the Young’s modulus increases by more than300%. The tensile strength reveals similar results (Fig. 9b). Typi-cally, an increase in crystalline orientation causes an increase inthe mechanical properties of polymers [30]. Here also, the ultimatetensile strength and the apparent Young’s modulus of the differentsystems (presented in Fig. 9, as a function of DDR) reveal a similarbehavior.

The fact that the mechanical properties increase through thepresence of silver in spite of the observation that its presence inter-feres with the structural orientation of the matrix (shown by theWAXD results) is worth noting. It can be explained on the basisof the classical stress transfer mechanism in composite materials,where a strong interfacial interaction between the matrix andthe reinforcing fiber is an essential attribute [31,32]. Clearly, thesilver particles that nucleate on the surface of the VGCF providethe matrix with anchoring points that facilitate a much betterinterfacial interaction and result in improved mechanical proper-ties. Hence, the improved reinforcing effect of the strongly

Fig. 5. SEM pictures of: (a) fibers containing iPP–PANI, (b) fibers containing iPP–PANI with 1 wt.% VGCF, (c) fibers containing iPP–PANI with 1 wt.% VGCF–Ag.

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anchored VGCF overrules that of un-oriented matrix due to itsnucleation by silver particles.

2.4. Electrical properties

The use of conductive fillers is of great interest for conductivefibers, films and coatings. The electrical conductivity of the filledpolymers depends on the inherent conductivity of the filler, itsgeometry, concentration and dispersion within the polymer [33].In particular, a threshold percolation concentration should beachieved to utilize effectively the contribution of the conductivefiller. Table 4 presents the electrical measurements for three differ-ent systems studied here. It is seen that the conductivity values arerelatively low and that all the filled systems are below the percola-tion concentration even for relatively high filler concentration of12% of PANI and VGCF–Ag combined, for which a value of

1.2 � 10�7 X cm was observed. Based on the literature [34], thepercolation threshold of VGCF is around 5% which is above thatof 3% in the filled systems here. Apparently, attaining the percola-tion threshold of the VGCF is a prerequisite for high electrical con-ductivity, while the presence of PANI is anticipated to increaseconductivity beyond percolation [35–37].

2.5. Antibacterial activity

Silver is known for its effective antibacterial qualities and hasbeen utilized accordingly in a broad range of applications [38].Here, its embedment in a polymeric matrix may provide it withadvantageous handling properties, as long as its efficacy is not

Fig. 6. DSC traces and degree of crystallinity for: matrix with no nanofiler (i), VGCF, 1 wt.% in the matrix (ii) and VGCF–Ag, 1 wt.% in the matrix (iii); (a) large diameter notannealed (b) small diameter not annealed, (c) large diameter annealed, (d) small diameter annealed.

Table 2Table of degree of crystallinity for the fibers.

Sample % Crystallinitybefore annealing

% Crystallinityafter annealing

iPP–PANI matrix – no nanofiller 37 46Low DDRiPP–PANI matrix containing: 37 451 wt.% of VGCF, low DDRiPP–PANI matrix containing: 36 431 wt.% of VGCF–Ag, low DDRiPP–PANI matrix – no nanofiller 32 37High DDRiPP–PANI matrix containing: 32 381 wt.% of VGCF, high DDRiPP–PANI matrix containing: 31 361 wt.% of VGCF–Ag, high DDR

Fig. 7. Fourier transform infrared spectrum of: matrix with no nanofiler (i). VGCF,1 wt.% in the matrix (ii). 30 wt.% of VGCF–Ag, 1 wt.% in the matrix (iii), 5 wt.% ofVGCF–Ag, 1 wt.% in the matrix (iv), 30 wt.% of VGCF–Ag, 3 wt.% in the matrix (v).

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hindered by a potential blocking effect of the polymer. Fig. 10shows pictures of Petri dishes in which filament segments layamidst Escherichia coli cultures. In Fig. 10a the iPP–PANI filamentsegment contains 1 wt.% of VGCF and that in Fig. 10b contains1 wt.% of VGCF–Ag. The antibacterial effect of the silver containingsystem is obvious: whereas in the first dish the bacteria (identifiedby the white shine) are at close contact with the filament, in thesecond the filament is protected by a barrier zone due to the rejec-tion effect of silver. It is noted however that this rejection effect is

considered to be relatively mild, which is attributed to the hydro-phobic nature of the iPP containing matrix.

Fig. 8. Room temperature 2D WAXD patterns of extruded monofilaments of: (a) iPP–PANI matrix with no nanofiler. (b) VGCF, 1 wt.% in the matrix. (c) 5 wt.% of VGCF–Ag,1 wt.% in the matrix. (d) 30 wt.% of VGCF–Ag, 1 wt.% in the matrix. (e1) to (e4): 30 wt.% VGCF–Ag, 3% in the iPP–PANI matrix: (e1) low DDR, not annealed, (e2) low DDR,annealed, (e3) high DDR, not annealed, and (e4) high DDR, annealed. The X-Ray beam was directed perpendicular to the filament, which was held vertically.

Table 3Table of widths at half height (whh) and Herman’s factors for the fibers.

Sample Width at half height(whh)

Herman’sfactor (Hf)

iPP–PANI matrix 22 0.45iPP–PANI matrix containing: 1 wt.%

of VGCF16 0.50

iPP–PANI matrix containing: 1 wt.%of VGCF–Ag

30 0.50

Low VGCF content in the nanofilleriPP–PANI matrix containing: 1 wt.%

of VGCF–Ag18 0.45

High VGCF content in the nanofilleriPP–PANI matrix containing: 3 wt.%

of VGCF–Ag49 0.25

Low DDR, not annealediPP–PANI matrix containing: 3 wt.%

of VGCF–Ag66 0.30

Low DDR, annealediPP–PANI matrix containing: 3 wt.%

of VGCF–Ag30 0.30

High DDR, not annealediPP–PANI matrix containing: 3 wt.%

of VGCF–Ag35 0.40

High DDR, annealed

Fig. 9. Young’s modulus (a) and tensile strength (b) vs. the draw-down ratio of:iPP–PANI matrix with no nanofiler (black, squares). VGCF, 1 wt.% in the matrix (red,circles). 5 wt.% of VGCF–Ag, 1 wt.% in the matrix (blue, up-triangles). 30 wt.% ofVGCF–Ag, 1 wt.% in the matrix (green, dawn-triangles). (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version ofthis article.)

Table 4Resistivity of a film of iPP matrix containing PANI and nanofiller.

Sample q (X cm)

iPP matrix containing: 2 wt.% of PANI and 3 wt.% of VGCF–Ag 1.3 � 10�11

iPP matrix containing: 3 wt.% of PANI and 9 wt.% of VGCF–Ag 1.2 � 10�7

iPP matrix containing: 9 wt.% of PANI and 3 wt.% of VGCF–Ag 0.9 � 10�8

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3. Conclusions

We have demonstrated a relatively simple procedure by whichcarbon nanofibers can be coated by silver that is generated in situby a reduction reaction of a silver salt and which can crystallizeon the fiber surface. The resulting VGCF–Ag nanofibers can thenbe melt-mixed with a polymer blend of iPP–PANI to form auniform dispersion, which is then extruded to produce continu-ous monofilaments of high axial orientation. The reinforcementeffect of the VGCF–Ag nanofibers, manifested in the mechanicalproperties of the monofilaments, is 3–5 folds higher than thatof VGCF alone due to the improved stress transfer mechanismof the former. Additional attractive properties of the new systemmay result from its anisotropic crystalline structure, enhancedthermal stability, potential electrical conductivity and antibacte-rial behavior. (For experimental details see in the Supplementaryinformation file).

Acknowledgments

This study was supported by the Israeli Ministry of Science andTechnology, Tashtiot (Grant # 3-6474). We thank Hagay Shpais-man and Ellen Wachtel from the Weizmann Institute, EstelleKalfon-Cohen from the Hebrew University of Jerusalem, Avi Ben-Hurand Vladimir Uvarov from the Unit for Nanoscopic Characteriza-tion of the Hebrew University of Jerusalem. G.N. thanks the Clorefoundation for their support.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.compscitech.2010.11.005.

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Supplementary Information

Instrumentation: SEM was carried on a Sirion (FEI) HR-SEM instrument (operating

voltage is indicated for each picture). Thermogravimetric thermal analysis (TGA) was

preformed on a Mettler TC10A/TC15 TA controller from 25 to 800°C at a heating

rate of 10 °C/min in flowing dry air. Surface area and porosity were determined from

nitrogen adsorption/desorption isotherms with a Micromeritics ASAP-2020

physisorption instrument. Density was determined from weight/volume analysis using

Micromeritics AccuPyc 1340 gas pycnometer instrument using helium as a displacing

gas. DSC (Mettler 822e Toledo, Switzerland) of the thermograms were measured in

the temperature range 30-300°C at a heating rate of 10°C/min under a nitrogen flux of

50 mL/min. Tensile testing was performed on an universal testing machine (Instron,

Model 4502) at a gage length of 10 mm and loading rate of 10 mm-min with cell

force ranges from 10N to 1kN in respect with the fiber diameter. Different mechanical

characteristics of fibers were measured: the stress at maximum load (MPa) and the

Young's Modulus (MPa) as a function of diameter. FTIR spectra of the drawn fibers

were measured with a Bruker α Alpha-P in ATR mode (Germany), with wavenumber

ranges from 400 to 4000 cm-1. XRD measurement were carried out with Philips

automated powder diffractometer (with PW1830 generator, PW1710 control unit,

PW1820 vertical goniometer, 40 KV, 35 mA, Cu Kα (1.5405 Å)). WAXD

measurements were carried out on an X-ray generator Elliott GX-6 rotating anode

with copper target operating at 1.2 kW, focus 200 microns. The X-ray camera is

manufactured by Searle, and includes two Franks mirrors. The detector is a Fuji

imaging plate, which we scan with a He-Ne laser on a home made scanner. The

conduction measurements were carried out on films that were prepared by pressing

the fibers at 180 °C with a pressure of 4.4 MPa for 15 sec. The current density-voltage

characteristics were collected in the voltage scan mode, ranging from -10V to 10V by

a Keithley 6430 picoampermeter, and the resistivity was calculated from the graph.

The antibacterial activity measurements were conducted by putting the extruded fibers

in Petri dishes containing low concentration of E. Coli for 24h.