polymers

Article Fabric: A Promising Reinforcement for Polymer Composites

Sergio Neves Monteiro 1, Foluke Salgado de Assis 1, Carlos Luiz Ferreira 1, Noan Tonini Simonassi 1, Ricardo Pondé Weber 1, Michelle Souza Oliveira 1, Henry A. Colorado 2 and Artur Camposo Pereira 1,*

1 Materials Science Program, Military Institute of Engineering, IME, Praça General Tibúrcio 80, Urca, Rio de Janeiro 22290-270, ; [email protected] (S.N.M.); [email protected] (F.S.d.A.); [email protected] (C.L.F.); [email protected] (N.T.S.); [email protected] (R.P.W.); [email protected] (M.S.O.) 2 CCComposites Laboratory, Universidad de Antioquia, UDeA, Calle 70, No. 52-21, Medellin 050010, Colombia; [email protected] * Correspondence: [email protected]; Tel.: +55-22-999-290-508

Received: 6 February 2018; Accepted: 24 February 2018; Published: 28 February 2018

Abstract: A relatively unknown natural fiber extracted from the leaves of the fique , native of the South American Andes, has recently shown potential as reinforcement of polymer composites for engineering applications. Preliminary investigations indicated a promising substitute for synthetic fibers, competing with other well-known natural fibers. The fabric made from fique fibers have not yet been investigated as possible composite reinforcement. Therefore, in the present work a more thorough characterization of fique fabric as a reinforcement of composites with a matrix was performed. Thermal mechanical properties of fique fabric composites were determined by dynamic mechanical analysis (DMA). The ballistic performance of plain woven fique fabric-reinforced polyester matrix composites was investigated as a second layer in a multilayered armor system (MAS). The results revealed a sensible improvement in thermal dynamic mechanical behavior. Both viscoelastic stiffness and glass transition temperature were increased with the amount of incorporated fique fabric. In terms of ballistic results, the fique fabric composites present a performance similar to that of the much stronger KevlarTM as an MAS second layer with the same thickness. A cost analysis indicated that armor vests with fique fabric composites as an MAS second layer would be 13 times less expensive than a similar creation made with ™.

Keywords: fique fabric; composites; polyester matrix; thermal dynamic mechanical behavior; ballistic performance

1. Introduction The beginning of this new century witnessed a surge in research works dedicated to the use of fibers extracted from in engineering applications. Several specialized and review articles [1–15] emphasized the use of these natural lignocellulosic fibers and their fabrics as reinforcements of polymer composites, competing with synthetic fibers. Environmental sustainability goals associated with lower cost, societal benefits, and some technical advantages favor the substitution of natural fiber and fabric for glass fiber [16] and fabric [17]. Industrial components, mainly in automobile fabrication [18–20], increasingly employ natural fiber and fabric composites. A specific industrial sector in which fibers and fabrics are of relevance is that of armor vests. Originally, fiber glass was extensively used [21,22] and carbon fiber-reinforced polymer composites were also considered [23]. Today, synthetic aramid fabrics such as Kevlar™ (Du Pont, Richmond, VA, USA) [24] and ™ (Teijin Aramid, Conyers, GA, USA) [25] as well as ultra-high molecular weight fibers, such

Polymers 2018, 10, 246; doi:10.3390/polym10030246 www.mdpi.com/journal/polymers Polymers 2018, 10, 246 2 of 10 as Spectra™ (Spectra Energy Corporation, Houston, TX, USA) [26] and Dyneema™ (DSM Dyneema LLC, Stanley, NC, USA) [27], are major choices for personal armor vests. Recent publications [28–33] revealed that natural fibers as well as corresponding fabrics-reinforced polymer composites display comparable ballistic performance to KevlarTM. In spite of numerous publications dedicated to this subject, thePolymers growing 2018, 10 interest, x FOR PEER for REVIEW engineering applications is continuously demanding research2 of 10 works on less commonpolyethylene promising , such natural as Spectra™ fibers (Spectra and fabrics. Energy AnCorporation, example Houston, is the relativelyTX, USA) [26] unknown and fiber extractedDyneema™ from the leaves(DSM Dyneema of an AndeanLLC, Stanley, plant NC, (USA) [27], are andina major). choices This for fique personal fiber armor has vests. been brought to attentionRecent for publications its potential [28–33] as arevealed composite that natural reinforcement fibers as well [as34 corresponding–39]. Figure fabrics-reinforced1 illustrates: (a) fique TM plantationpolymer in Colombia composites and display (b) acomparable bundle ofballistic fique performance fibers extracted to Kevlar from. In spite the of leaves numerous of the plant. publications dedicated to this subject, the growing interest for engineering applications is For practicalcontinuouslyuse, the demanding fique fabric research is yearlong works on foundless common in the promising Colombian natural market fibers and and fabrics. largely An available for commonexample applications, is the relatively mostly unknown as sackclothfiber extracted for from agricultural the leaves of products. an Andean Owingplant (Furcraea to its national importance,andina the). This federal fique governmentfiber has been brought of Colombia to attention controls for its potential both the as a pricecomposite and reinforcement quality of the fique fiber, which[34–39]. is stored Figure and 1 illustrates: distributed (a) fique for industrial in Colombia processing, and (b)including a bundle of fique as a fibers . extracted The extraction from the leaves of the plant. For practical use, the fique fabric is yearlong found in the Colombian cost, frommarket plantation and largely to clean available fibers for common (see Figure applications,1a,b), ismostly around as sackcloth US$0.14, for agricultural while the products. consumer price varies fromOwing US$0.36 to its tonationalUS$0.45. importance, surfacethe federal modification government of [ 34Colombia] and thermalcontrols both degradation the price and [35 ] as well as bendingquality [36] andof thetensile fique fiber, [37, 38which] properties is stored and of fiquedistributed fiber-reinforced for industrial processing, composites including were as preliminarily a investigated.textile. Moreover, The extraction an cost, inverse from correlationplantation to clean between fibers (see the Figure density 1a,b), and is around the diameter US$0.14, while of fique fibers the consumer price varies from US$0.36 to US$0.45. Fiber surface modification [34] and thermal was establisheddegradation [39]. [35] As foras well fique as fabric,bending either[36] and woven tensile or [37,38] non-woven, properties characterization of fique fiber-reinforced and properties of polymeric-reinforcedcomposites were compositespreliminarily areinvestigated. still not Moreover, found in an the inverse scientific correlation literature. between In the particular, density thermal dynamic mechanicaland the diameter properties, of fique fibers which was are established important [39]. forAs for engineering fique fabric, either applications, woven or non-woven, were not mentioned for fique fabriccharacterization in the only and reviewproperties [40 of] polymeric-reinforc dedicated to polymered composites composites are still not reinforced found in the with scientific less common literature. In particular, thermal dynamic mechanical properties, which are important for engineering natural fiber-basedapplications, materials. were not mentioned These properties for fique fabric might in the be obtainedonly review by [40] dynamic dedicated mechanical to polymer analysis (DMA) andcomposites could providereinforced viscoelastic with less common behavior natural as fiber-based well as materials. temperature These effectproperties on might distinct be dynamic moduli. Anyobtained possible by dynamic engineering mechanical application analysis (DMA) of fiqueand could fabric-reinforced provide viscoelastic composites, behavior as well particularly as in personal armors,temperature will effect demand on distinct additional dynamic moduli. information Any possible on thermal engineering dynamic application mechanical of fique fabric- and ballistic reinforced composites, particularly in personal armors, will demand additional information on properties,thermal which dynamic is the objectivemechanical ofand the ballistic present properti work.es, which is the objective of the present work.

Figure 1. PlantationFigure 1. Plantation of fique of (Furcraea fique ( andin) ina) Colombia in Colombia (a ),(a bundle), bundle of of fique fique fibersfibers ( (bb),), and and as- as-received received piece of fique fabric (c). piece of fique fabric (c). 2. Materials and Methods 2. Materials and Methods 2.1. Materials Source and Process 2.1. Materials SourceFique fabric and Processcommercially available in Colombia was supplied by Compañia de Empaques, Itagüí, Antioquia, Colombia. A piece of as-received fabric is shown in Figure 1c. An average Fiqueequivalent fabric commercially diameter of 0.18 available mm and inan Colombiaaverage density was of supplied 667 kg/m3 byfor Compañiathe fique fiber, de Figure Empaques, 1b, Itagüí, Antioquia,were Colombia. reported elsewhere A piece [39]. of The as-received areal density fabric of theis plain-woven shown in fabric, Figure Figure1c. 1c, An investigated average in equivalent 2 diameter ofthis 0.18 work mm was and found an to average be 0.036 kg/m density. An isophtalic of 667 kg/m polyester3 for resin the hardened fique fiber, with Figure1% methyl-ethyl-1b, were reported ketone, fabricated by Dow Chemical and supplied by Resinpoxy, Rio de Janeiro, Brazil, was used as elsewherethe [39 composite]. The areal matrix. density Composites of the were plain-woven prepared by accommodating fabric, Figure the1c, previously investigated dried fabric in this (60 work was 2 found to be°C for 0.036 24 h) kg/m in a steel. mold, An isophtalic and then pouring polyester the still resin fluid resin-hardener hardened with mixture 1% between methyl-ethyl-ketone, fabric fabricatedlayers. by Dow In this Chemicalway, 120 × 150 and × 50 supplied mm3 plates byof laminate Resinpoxy, composites Rio with de 10, Janeiro, 20, and 30 Brazil, vol % fique was used as the composite matrix. Composites were prepared by accommodating the previously dried fabric (60 ◦C for 24 h) in a steel mold, and then pouring the still fluid resin-hardener mixture between fabric layers. In this way, 120 × 150 × 50 mm3 plates of laminate composites with 10, 20, and 30 vol % fique Polymers 2018, 10, 246 3 of 10 fabric associated with 4, 8, and 12 layers were respectively produced. These plates were kept under ◦ 3 MPaPolymers pressure 2018, 10 for, x 24FOR h, PEER at room REVIEW temperature (25 C), until complete solid cure. Test samples3 of were 10 cut from the laminate composite plates and standard flexural specimens with 10, 20, and 30 vol % fabric, as wellfabric as neatassociated polyester with for4, 8, control, and 12 layers were prepared.were respectively produced. These plates were kept under 3 MPa pressure for 24 h, at room temperature (25 °C), until complete solid cure. Test samples were 2.2. Dynamiccut from Mechanicalthe laminate Analysis composite (DMA) plates and standard flexural specimens with 10, 20, and 30 vol % fabric, as well as neat polyester for control, were prepared. DMA tests were performed in fique fabric composites, using flexural specimens according to standard.2.2. Dynamic All Mechanical analyses Analysis were conducted(DMA) in triplicate to evaluate the degree of dispersion in corresponding curves. Less than 10% difference was found between curves for identical conditions, DMA tests were performed in fique fabric composites, using flexural specimens according to basicallystandard. confirming All analyses the samewere results.conducted Therefore, in triplicate only to evaluate one typical the degree curve isof useddispersion to illustrate in eachcorresponding condition. curves. Less than 10% difference was found between curves for identical conditions, ◦ Eachbasically DMA confirming test was the carried same results. out in Therefore, the interval only fromone typical−20 tocurve 160 is usedC in to a illustrate model Q/800 each TA Instrumentscondition. (New Castle, DE, USA) in three-point flexural mode, 1 Hz frequency, and a heating rate of 3 K/minEach DMA (3 ◦ testC/min) was undercarried nitrogenout in the atmosphere. interval from The −20 storageto 160 °C modulus in a model (E0), Q/800 loss modulusTA (E”),Instruments and tangent (New delta Castle, curves DE, were USA) provided in three-point by the flexural equipment. mode, 1 Prismatic Hz frequency, standard and a heating specimens rate with dimensionsof 3 K/min of 50(3 °C/min)× 13 × under3 mm nitrogen were used atmosphere. for the tests. The storage modulus (E′), loss modulus (E″), and tangent delta curves were provided by the equipment. Prismatic standard specimens with dimensions 2.3. Ballisticof 50 × 13 Tests × 3 mm were used for the tests.

In2.3. addition Ballistic Tests to DMA, preliminary ballistic tests were carried out according to the NIJ 0101.06 × 2 standardIn using addition 7.62 to DMA,51 mm preliminaryNATO military ballistic ammunitiontests were carried with out a 9.7 according g projectile to the propelled NIJ 0101.06 from a gun barrel.standard The using tests 7.62 were × 51 conducted mm2 NATO at themilitary Brazilian ammunition Army shootingwith a 9.7 facility, g projectile CAEX, propelled in the Marambaiafrom a Peninsula,gun barrel. Rio The de tests Janeiro, were withconducted three at samples the Brazil ofian 10 Army and shooting 20 vol %facility, of fique CAEX, fabric in the for Marambaia each type of multilayeredPeninsula, armor Rio de system Janeiro, (MAS) with [three41,42 ].samples Figure of2a 10 shows and 20 the vol exploded % of fique view fabric of the for ballistic each type test of setup whilemultilayered Figure2b illustrates, armor system schematically, (MAS) [41,42]. the MASFigure composed 2a shows the of a exploded front ceramic view followedof the ballistic by a test layer of fiquesetup fabric while composites Figure 2b and illustrates, backed schematically, by an aluminum the MAS alloy composed sheet. The of a MASfront ceramic is set as followed a target by together a withlayer a block of fique of so-called fabric composites clay witness and that backed simulates by an aluminum a human bodyalloy sheet. and should The MAS only is set allow as a penetration target together with a block of so-called clay witness that simulates a human body and should only allow to a certain depth. According to the standard NIJ 0101.06, the measured depth of indentation is limited penetration to a certain depth. According to the standard NIJ 0101.06, the measured depth of to 44 mm in order to avoid lethal trauma to the MAS wearer. Measurements were performed with a indentation is limited to 44 mm in order to avoid lethal trauma to the MAS wearer. Measurements laserwere sensor performed caliper withwith a 0.01 laser mm sensor of precision. caliper with 0.01 mm of precision.

Figure 2. (a) Schematic exploded view of the ballistic experimental setup and (b) schematic illustration Figure 2. (a) Schematic exploded view of the ballistic experimental setup and (b) schematic illustration of the investigated multilayered armor system (MAS), as a target placed ahead of a clay witness block. of the investigated multilayered armor system (MAS), as a target placed ahead of a clay witness block. 2.4. Fracture Microscopy 2.4. Fracture Microscopy The ruptured surface of each MAS component after the ballistic test was analyzed by scanning Theelectron ruptured microscopy surface (SEM) of each in a model MAS componentQUANTA FE afterG250 the Fei ballistic(Thermo testFisher was Scientific, analyzed Hillsboro, by scanning electronOR, microscopyUSA) microscope (SEM) operating in a model with QUANTA secondary FEG250electrons Feiat 20 (Thermo kV. Fisher Scientific, Hillsboro, OR, USA) microscope operating with secondary electrons at 20 kV.

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3.3. ResultsResults andand DiscussionDiscussion

3.1.3.1. DynamicDynamic MechanicalMechanical AnalysisAnalysis (DMA)(DMA) FiguresFigures3 –3–55 respectively respectively show show the the DMA DMA storage storage modulus modulus (E 0), (E loss′), modulusloss modulus (E”), and(E″), tangent and tangent delta (tandeltaδ) curves(tan δ) forcurves the neat for polyesterthe neat resinpolyester and fiqueresin fabric-reinforced and fique fabric-reinforced composites. Figurecomposites.3 compares Figure the 3 variationcompares of the the variation storage modulus of the storage (E0) with modulus temperature (E′) forwith the temperature neat polyester for and the different neat polyester composites and investigated.different composites For all temperatureinvestigated. levels,For all fromtemper 25ature◦C up levels, to 70 from◦C, the25 °C E0 upvalues to 70 for°C, thethe fiqueE′ values fabric for compositesthe fique fabric aresignificantly composites are higher significantly than that higher of the th neatan that polyester of the resin.neat polyester In fact, the resin. value In fact, of E 0theis directlyvalue of related E′ is directly to the related material’s to the ability material’s to withstand ability mechanicalto withstand loads mechanical with recoverable loads withviscoelastic recoverable deformation.viscoelastic deformation. Consequently, Consequently, the results in the Figure results3 above in Figure room 3 temperatureabove room indicatetemperature a substantial indicate a raisesubstantial in the viscoelastic raise in the stiffness viscoelastic of the stiffness polyester of withthe polyester increasing with incorporation increasing of incorporation fique fabric, withoutof fique lossfabric, in recoverable without loss deformation. in recoverable Moreover, deformation. while Moreover, an accentuated while decrease an accentuated in stiffness decrease begins in tostiffness occur aroundbegins to 10 occur◦C for around the neat 10 polyester,°C for the neat the 30 polyester, vol % fique the 30 fabric vol % composite fique fabric remains composite stiffer remains up to 40 stiffer◦C. Asup the to 40temperature °C. As the increases, temperature there increases, is a rapid there decrease is a rapid in the decrease E0 value fromin the about E′ value 40 ◦ fromC until about a plateau 40 °C ofuntil less a than plateau 100 MPaof less is than reached. 100 MPa is reached.

. 0 FigureFigure 3. 3.Storage Storage modulus modulus (E (E)′) curvescurves forfor thethe neat neat polyester polyester resin resin andand for for the the composites composites reinforced reinforced withwith fique fique fabric. fabric.

FigureFigure4 4compares compares the the variation variation of of the the loss loss modulus modulus (E”) (E″) with with temperature temperature for for the the neat neat polyester polyester resinresin andand thethe investigatedinvestigated composites.composites. AllAll ofof thethe curvescurves ofof thisthis figurefigure gogo throughthrough aa well-definedwell-defined maximummaximum value value that that can can be be associated associated with with the the relaxation relaxation peak peakα [α43 [43].]. This This relaxation relaxation is attributed is attributed to theto the mobility mobility of theof the chains chains in in the the crystalline crystalline phase phase of of the the polymer, polymer, which which in in this this work work is is the the polyester polyester matrixmatrix [ 44[44].]. For For the the fique fique fabric fabric composites, composites, the the peaks peaksα inα thein the E” curvesE″ curves are are shifted shifted by aboutby about 15 ◦ C15 for °C higherfor higher temperatures. temperatures. Kalusuraman Kalusurama et al.n et [43 al.] suggested[43] suggested that that the α thepeaks α peaks in E” in could E″ could be related be related to the to onsetthe onset of the of glass the transitionglass transition temperature temperature (Tg) of ( theTg) polymericof the polymeric matrix. Therefore,matrix. Therefore, the results the in results Figure 4in revealedFigure 4 thatrevealed the incorporation that the incorporation of fique fabric of fique restrains fabric the restrains mobility the of themobility polyester of the chains polyester and retards chains theand formation retards the of formation an amorphous of an amorphous structure. This structure. mechanism This mechanism also explains also the explains relative the shift relative to higher shift temperatureto higher temperature (10 to 40 ◦C) (10 of to the 40 fique °C) of fiber the composites fique fiber viscoelasticcomposites softening, viscoelastic Figure softening,3, as compared Figure 3, to as thecompared neat polyester. to the neat polyester.

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. . FigureFigure 4. 4.Loss Loss modulusmodulus(E”) (E″) curvescurves forfor thethe neatneat polyesterpolyester resinresin andand forfor thethe compositescomposites reinforcedreinforced with with Figure 4. Loss modulus (E″) curves for the neat polyester resin and for the composites reinforced with fiquefique fabric. fabric. fique fabric. The variation of the tan δ with the temperature for the neat polyester resin and the composites TheThe variationvariation ofof thethe tantanδ δwith with the the temperature temperaturefor forthe the neat neat polyester polyester resinresin andand thethe composites composites incorporated with fique fabric is shown in Figure 5. It can be seen in this figure that the composites incorporatedincorporated withwith fiquefique fabricfabric isis shownshown inin FigureFigure5 .5. It It can can be be seen seen in in this this figure figure that that the the composites composites exhibit peaks with lower amplitude and shifted to relatively higher temperatures as compared to the exhibitexhibit peakspeaks with lower amplitude amplitude and and shifted shifted to to re relativelylatively higher higher temperatures temperatures as ascompared compared to the to neat polyester resin. This suggests, as also observed for the storage modulus in Figure 3 and loss theneat neat polyester polyester resin. resin. This This suggests, suggests, as also as alsoobse observedrved for the for thestorage storage modulus modulus in Figure in Figure 3 and3 and loss modulus in Figure 4, that the fique fabric effectively interacts with the polyester matrix chains, lossmodulus modulus in Figure in Figure 4, 4that, that the the fique fique fabric fabric effect effectivelyively interacts interacts with thethe polyesterpolyester matrixmatrix chains, chains, impairing their mobility and reducing their structural damping ability. The tan δ peaks are attributed impairingimpairing their their mobility mobility and and reducing reducing their their structuralstructural dampingdamping ability.ability. The The tan tanδ δpeaks peaksare areattributed attributed toto the the upper upper limit limit of ofT Tg [[43].43]. Moreover,Moreover, thethe decreasedecrease inin peakpeak amplitudeamplitude andand increaseincrease inin temperature,temperature, to the upper limit of Tgg [43]. Moreover, the decrease in peak amplitude and increase in temperature, Figure 5, also suggest a higher attenuation in internal vibration and a shift to higher temperature of FigureFigure5 ,5, also also suggest suggest a highera higher attenuation attenuation in internalin internal vibration vibration and and a shift a shift to higher to higher temperature temperature of T ofg withTg with the increasingthe increasing amount amount of fique of fabricfique fabric in the polyesterin the polyester matrix. matrix. Consequently, Consequently, the results the in results Figure 5in Tg with the increasing amount of fique fabric in the polyester matrix. Consequently, the results in Figure 5 indicate that the incorporation of fique fabric not only reduces the mobility of the polyester indicateFigure 5 that indicate the incorporation that the incorporation of fique fabric of fique not onlyfabric reduces not only the reduces mobility the of mobility the polyester of the chains, polyester but chains, but also prevents the disruption of their structural organization. Consequently, the end of the alsochains, prevents but also the prevents disruption the ofdisruption their structural of their organization. structural organization. Consequently, Cons theequently, end of the polyesterend of the polyester matrix transition from the glass to the rubbery state could occur at higher temperatures. matrixpolyester transition matrix fromtransition the glass from to the the glass rubbery to the state rubbery could state occur could at higher occur temperatures. at higher temperatures.

. . Figure 5. Tan δ curves for the neat polyester resin and for the composites reinforced with fique fabric. FigureFigure 5.5.Tan Tanδ δcurves curves for for the theneat neatpolyester polyesterresin resinand andfor forthe the compositescomposites reinforcedreinforced with withfique fique fabric. fabric. 3.2. Ballistic Tests 3.2. Ballistic Tests Table 1 presents the average depth measured in the clay witness for the different MAS targets Table 1 presents the average depth measured in the clay witness for the different MAS targets investigated. For application in armor vests, the fique fabric composite is lighter and significantly investigated. For application in armor vests, the fique fabric composite is lighter and significantly

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3.2. Ballistic Tests Table1 presents the average depth measured in the clay witness for the different MAS targets investigated.Polymers 2018, 10, For x FOR application PEER REVIEW in armor vests, the fique fabric composite is lighter and significantly6 of 10 cheaper than the Kevlar™. These are factors that are further discussed and might play practical cheaper than the Kevlar™. These are factors that are further discussed and might play practical advantages in considering the substitution of fique fabric composites for Kevlar™ in an MAS for advantages in considering the substitution of fique fabric composites for Kevlar™ in an MAS for personal protection against high velocity projectiles, such as the 7.62 × 51 mm projectile. personal protection against high velocity projectiles, such as the 7.62 × 51 mm projectile.

Table 1. Average depth of penetration in the clay witness backing different MAS of fique Table 1. Average depth of penetration in the clay witness backing different MAS of fique fabric fabric composites. composites.

IntermediateIntermediate Layer Layer Material Material DepthDepth of of Penetration Penetration (mm) (mm) 1010 vol vol % fique% fique fabric fabric 17 17± 3± 3 2020 vol vol % fique% fique fabric fabric 15 15± 3± 3 ± Kevlar™Kevlar™ 23 23 3± [345 [45]]

FigureFigure6 6aa illustratesillustrates thethe aspectaspect of the different MAS targets targets after after the the ballistic ballistic tests. tests. In In Figure Figure 6b,6b, it itcan can be be seen seen that that the the ceramic ceramic has has di disappearedsappeared by by complete complete shattering. shattering.

FigureFigure 6.6. TypicalTypical aspect aspect before before (a )(a and) and after after (b )( ballisticb) ballistic test test of MAS of MAS targets targets with with a second a second layer oflayer fique of fabric-reinforcedfique fabric-reinforced polyester polyester composite. composite.

AfterAfter ballisticballistic tests,tests, thethe fracturefracture surfacesurface ofof MASMAS componentscomponents werewere observedobserved byby SEM.SEM. FigureFigure7 7aa showsshows thethe expectedexpected inter-crystallineinter-crystalline brittlebrittle fracturefracture surfacesurface ofof aa collectedcollected macroscopicmacroscopic ceramicceramic particle,particle, which is almost splitting splitting into into microscopic microscopic fragments fragments associated associated with with grains. grains. As As indicated indicated by byMedvedovski Medvedovski [46], [46 a], 7.62 a 7.62 mm mm projectile projectile causes causes diff differenterent kinds kinds of of cracks cracks to to be formed during thethe impact.impact. Figure7 7bb showsshows thethe abilityability ofof thethe 2020vol vol% % fique fique fabric fabric composite compositesecond secondlayer, layer, in in an an MAS MAS withwith a ceramic front, front, to to collect collect fragments fragments generated generated from from the the ballistic ballistic impact impact shown shown in Figure in Figure 7a. This7a. Thisability ability does does not notrequire require stronger stronger fibers fibers but but mechanisms mechanisms of of mechanical mechanical incrustation incrustation as as well asas fragmentfragment attractionattraction byby VanVan derder WaalsWaals forcesforces andand staticstatic chargescharges onon thethe fiberfiber surface,surface, ofof eithereither syntheticsynthetic Kevlar™Kevlar™ [[47]47] oror naturalnatural fiber-basedfiber-based compositescomposites [[28–33].28–33].

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FigureFigure 7.7. (a) Fracture surface of a particleparticle fromfrom thethe ceramicceramic afterafter thethe ballisticballistic testtest andand ((bb)) fracturefracture surfacesurface ofof 2020 volvol %% fiquefique fabricfabric compositecomposite coveredcovered withwith ceramicceramic fragments.fragments.

3.3. Cost Comparison 3.3. Cost Comparison A cost model associated with the use of fique fabric composites in comparison to conventional A cost model associated with the use of fique fabric composites in comparison to conventional engineering composites is presented in Table 2. The basic costs were obtained from the literature for engineering composites is presented in Table2. The basic costs were obtained from the literature for polyester, epoxy, aramid laminates (Kevlar™), and [48], as well as for fique fiber/fabric polyester, epoxy, aramid laminates (KevlarTM), and glass fiber [48], as well as for fique fiber/fabric [49] [49] and for , , curaua, and piassava [50]. and for sisal, jute, curaua, and piassava [50].

Table 2. Cost model for different fabric composites. Table 2. Cost model for different fabric composites. Composite Material Cost (US$/Kg) Reference 64.8 vol %Composite aramid laminate/epoxy Material Cost (US$/Kg) 49.59 Reference [48] 7264.8 vol vol % % glass aramid fiber/epoxy laminate/epoxy 49.59 18.06 [48] [48] 30 vol72 % vol sisal % glass fiber/polyester fiber/epoxy 18.06 3.23 [48] [49] 30 vol % sisal fiber/polyester 3.23 [49] 30 vol30 vol% jute % jute fiber/polyester fiber/polyester 3.24 3.24 [50] [50] 30 vol30 vol% curaua % curaua fiber/polyester fiber/polyester 3.19 3.19 [50] [50] 30 vol30 vol% piassava % piassava fiber/polyester fiber/polyester 3.21 3.21 [50] [50] 20 vol20 vol% fique % fique fabric/polyester fabric/polyester 3.61 3.61 Present PresentWork Work 30 vol % fique fabric/polyester 3.26 Present Work 30 vol % fique fabric/polyester 3.26 Present Work

InIn thisthis table,table, isis itit shownshown thatthat KevlarKevlarTMTM (aramid(aramid fiber fiber laminate) is th thee most expensive composite, moremore thanthan 1313 timestimes thethe priceprice ofof anyany commoncommon naturalnatural fiberfiber composite,composite, includingincluding thethe presentlypresently investigatedinvestigated fiquefique composites.composites. EvenEven aa lessless expensive glass fiberfiber compositecomposite isis moremore thanthan fivefive timestimes asas costlycostly asas any natural fiberfiber composite. Therefore, the incorporation of any common -based fiber-based material,material, includingincluding fiquefique fabric,fabric, reducesreduces thethe priceprice ofof thethe composite.composite.

4.4. Summary and Conclusions •• TheThe introductionintroduction ofof fiquefique fabricfabric raisesraises thethe viscoelasticviscoelastic stiffnessstiffness levellevel andand tendstends toto shiftshift thethe curves 0 ofof thethe storagestorage modulusmodulus (E(E′)) toto higherhigher temperatures.temperatures. This This leads to a delay in the onsetonset ofof thethe thermalthermal softeningsoftening ofof thethe composite.composite. TheThe peakpeak αα ofof thethe lossloss modulusmodulus (E”)(E″) is also shifted to higher glassglass transitiontransition temperaturestemperatures ((TTg), indicating less mobility in the polyester resin chainschains ofof thethe matrixmatrix byby interactioninteraction withwith the the fique fique fabric. fabric. The The maximum maximum in in tan tanδ curves,δ curves, associated associated with with end end of Tofg ,T suffersg, suffers not not only only a reduction a reduction in its in amplitude its amplitude but alsobut also a shift a shift towards towards higher higher temperatures temperatures with thewith introduction the introduction of fique of fique fabric. fabric. Hence, Hence, a high a attenuationhigh attenuation of internal of internal vibration vibration and increase and increase in Tg occurin Tg occur with anwith increasing an increasing amount amount of fique of fabricfique fabric in the in polyester the polyester matrix. matrix. • A multilayered armor system (MAS), in which conventional Kevlar™ was replaced by a polyester matrix composite reinforced with 10 or 20 vol % of fique fabric as second layers,

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• A multilayered armor system (MAS), in which conventional Kevlar™ was replaced by a polyester matrix composite reinforced with 10 or 20 vol % of fique fabric as second layers, attended the NIJ trauma limit after ballistic tests with 7.62 mm ammunition. The depth of penetration into 20 vol % fique fabric composite, 15 mm, demonstrated this composite to be more efficient than conventional Kevlar™ with 23 mm as a second MAS layer. • More than ballistic performance, the significantly lower cost in association with the environmental and societal benefits of using a natural material favor the substitution of fique fabric composite as an MAS second layer. As an economical advantage, armor vests with fique fabric composites would be 13 times cheaper than similar ones made with Kevlar™.

Acknowledgments: The authors acknowledge the support to this investigation by the Brazilian agencies: Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES; and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, FAPERJ. Author Contributions: Sergio Neves Monteiro conceived and Artur Camposo Pereira designed the experiments; Noan Tonini Simonassi and Foluke Salgado de Assis performed the experiments; Ricardo Pondé Weber and Carlos Luiz Ferreira analyzed the data; Michelle Souza Oliveira contributed with specimen fabrication; Henry A. Colorado contributed with materials; Sergio Neves Monteiro wrote the . Conflicts of Interest: The authors declare no conflict of interest.

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