fire and materials performance

7/30/2019 Fire and Materials performance

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Flame resistant performance of nanocomposites coated withexfoliated graphite nanoplatelets/carbon nanofiber

hybrid nanopapers

Jinfeng Zhuge1, Jihua Gou1,*, and Christopher Ibeh2

1Composite Materials and Structures Laboratory, Department of Mechanical, Materials and Aerospace Engineering,

University of Central Florida, Orlando, FL 32816 USA2

Center for Nanocomposites and Multifunctional Materials, Pittsburg State University, Pittsburg, KS 66762 USA

SUMMARY

Exfoliated graphite nanoplatelets (xGnPs) were used to improve thefl

ame resistant performance of glassfiberreinforced polyester composites. Along with xGnP, traditional intumescentfire retardant ammoniumpolyphosphate (APP) was introduced into the polymer matrix as the dominant additive to reduce the heatrelease rate (HRR) and total heat released (THR) of the composites. The cone calorimeter test resultsIndicate that the optimal weight ratios of xGnP and APP were 3% and 17% by weight, respectively. Atsuch weight ratio, a synergistic effect between xGnP and APP was demonstrated. The flame resistantperformance of the nanocomposites was further improved by applying xGnPdominant carbon nanofiber(CNF)/xGnP hybrid nanopaper onto the surface of the samples. Compared with the control sample, theintegration of the HRR (THR) from 0 to 100 s of the sample coated with the nanopaper of CNF/xGnP=1/3 shows more than 30% decrease in THR. Based on the results of mass loss, the nanopaper coating isalso shown to enhance the structural stability of the samples under fire conditions, which affects themechanical properties of the composites. The results show that the thermal properties, permeability ofcomposites, and char formation play important roles in determining the fire behavior of the composites.Copyright 2011 John Wiley & Sons, Ltd.

Received 25 October 2010; Revised 21 March 2011; Accepted 26 April 2011

KEY WORDS: exfoliated graphite nanoplatelets; nanopaper; nanocomposites; permeability; synergistic effect

1. INTRODUCTION

Fiber reinforced polymers (FRP) have excellent physical and mechanical properties, such as high specificstrength, light weight, good fatigue, and corrosion resistance. They have become viable alternatives toconventional metallic materials in many industries such as aircraft, marine structures, ships, buildings,transportation, electrical and electronics components, and offshore structures. However, since FRPcontains polymer matrix, the composites and their structures are combustible. FRP will degrade,

decompose, and sometimes yield toxic gases at high temperature or subject to fire conditions. Due to theircombustible nature, fire safety and fire protection of FRP are of great concern. Consequently, improvingthe flame resistance of polymers is crucial to increase the utilization of FRP.

Understanding the combustion process of composite laminates has led to the knowledge that fireresistant performance can be improved chemically and physically in both vapor phase and condensedphase of the combustion process by controlling the heat and/or fuel to keep it below a critical level. In

*Correspondence to: Jihua Gou, Department of Mechanical, Materials and Aerospace Engineering, University of CentralFlorida, Orlando, FL 32816, USA.

Email: [email protected]

Copyright 2011 John Wiley & Sons, Ltd.

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short, fire can be prevented if the concentration of gaseous mixture and autoignition temperature aremaintained below a critical value [1, 2].

For the analysis of the fire resistance performance of polymer composites, open literature primarilyfocuses on parameters such as heat release rate (HRR), peak heat release rate (PHRR), and time toignition. If the evaluation on materials fire performance is based solely on these data, however, it runsthe risk of oversimplification and, possibly, misleading [3]. For example, when analyzing the flame

resistant performance of structural materials, their capability to sustain loading under combustionconditions is also extremely important [46]. Whereas the glass transition temperature Tg is anintrinsic material property that cannot be modified without changing the molecular structure of thepolymer, it is possible to control the mass loss and mass loss rate during combustion. In this case, it isimportant to determine the parameters such as mass loss and mass loss rate of the material, whichwould otherwise have been ignored.

In this study, exfoliated graphite nanoplatelets (xGnPs) were introduced into the polymer matrix toenhance the flame resistance of the composites. The selection of xGnP was to take advantage of theiranisotropic thermal conductivity (K =3000W/m; K = 6 W/m), so the heat could be easily dissipatedduring heat transfer process. Additionally, their planar structure is such that the permeability [7] of thecomposites would be lowered down and the path of decomposed polymer (fuel) would become moretorturous, which will be discussed in the later section [810]. However, it must be noted that theaddition of nanofillers alone into the polymer will often not satisfy the requirements offire regulations.The traditional additives still need to be used to satisfy them [11, 12]. Therefore, when preparingsamples, APP particles were used as major additives to satisfy this need with a weight ratio of 1:4.Under this ratio, 25, 15, 10, and 5 wt% of APP particles were incrementally replaced by xGnPs, andthe samples were then characterized by Xray diffraction (XRD) and cone calorimeter tests.

In previous research, a papermaking technique that combined carbon nanofiber, nanoclay, andpolyhedral oligomeric silsesquioxanes into a selfstanding nanopaper was developed. Thosenanopapers successfully improved the flame resistant performance of FRP [1315]. To attempt afurther improvement of the flame resistant efficiency of the nanocomposites, xGnp/CNF hybridnanopapers were developed and coated onto the surfaces of the laminates. xGnP and APP were alsomixed into the polymer matrix at a given ratio of xGnP/APP/resin = 2/18/80. The samples coated withhybrid nanopapers were characterized by cone calorimeter tests, and their chars collected after testingwere examined by scanning electron microscopy (SEM).

2. EXPERIMENTAL

2.1. Materials

Vapor grown carbon nanofibers (Polygraf III PR25HHT) were supplied by Applied Sciences, Inc.(Cedarville, OH, USA), with an average diameter of 80nm and average surface area of about 50m2/g.xGnP Graphene Nanoplatelets were supplied from XG Sciences (Lansing, MI, USA), and APP(AP423) was supplied from Clariant International Ltd (Charlotte, NC, USA). The glass fiber wassupplied by Composites One, Inc. (Lakeland, FL, USA) with a surface density of 800g/m2. Theunsaturated polyester resin (product code: 7126117, Composites One) was used as matrix materialfor laminated composites with the methyl ethyl ketone peroxide as a hardener at a weight ratio of

100:1.

2.2. Processing of nanocomposites containing exfoliated graphite nanoplatelets and

ammonium polyphosphate

Prior to mixing with the unsaturated polyester, xGnP was rinsed with acetone to improve itswettability with respect to the resin. Specifically, xGnP powders were suspended in acetone, and thenthe mixture was sonicated using a Misonix S3000 sonicator with a power of 90 W for 20 min. Theacetone was then drained using a vacuum system; finally, the treated xGnP and asreceived APP weremixed into the unsaturated polyester by a mechanical shear mixer (Model 5000230; manufactured byColeParmer Instrument Company, Vernon Hills, IL, USA) with a speed of 1400 rounds per minute

242 J. ZHUGE, J. GOU AND C. IBEH

Copyright 2011 John Wiley & Sons, Ltd. Fire Mater. 2012; 36:241253

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for 2.5 h. After preparing the matrix, a resin transfer molding process was used to manufacture glassfiberreinforced nanocomposites. The polymer was injected into an aluminum mold containing eightlayers of glass fiber mats at a pressure of 80 psi. After the resin was allowed to cure in the mold atroom temperature overnight, the composites were postcured at 120C in an oven for 2h. Table Ishows the compositions of the xGnP nanocomposite samples.

2.3. Processing of hybrid nanopapers and nanocomposites

The asreceived CNF and xGnP were dispersed in distilled water with the aid of surfactant TritonX100. Then, the mixture was sonicated with the S3000 for 30 min at a power of 3050 W. After thesuspension was well dispersed, the nanopaper was fabricated by filtering the suspension with a highpressure compressed air system (see Figure 1) at a pressure of 80psi. The nanopaper was then appliedto the surface of the nanocomposite during the resin transfer molding process. The compositions of thehybrid nanopapers and nanocomposites are shown in Table II.

2.4. Characterization and evaluation

2.4.1. Cone calorimeter tests. The fire retardant performance of the nanocomposites with andwithout nanopaper coatings was evaluated by cone calorimeter (manufactured by Fire TestingTechnology Ltd, UK) with an incident heatflux of 50 kW/m2 in accordance with ISO 56601 standard.The under and side edges of the composite samples were wrapped in an aluminum foil prior to thecone calorimeter test. All the samples were evaluated in a horizontal position with the surfaces coatedwith nanopapers, when applicable, directly exposed to the heatflux during cone calorimeter tests. Thethickness of the samples is about 8 mm, with a resin volume and weight fraction of 70% and 50%,respectively. The experiments were repeated three times for each sample, and the results werereproducible to within 10%. The cone calorimeter data reported in this study represent an average ofthree replicated tests.

Table I. Composition of exfoliated graphite nanoplatelet nanocomposites.

Sample ID* Contents (wt%) Weight ratios of GnP/APP/resin (%)

GF Resin AdditivesxGnPAPP0 laminates 51.75 48.25 0.00 0/0/100xGnPAPP15 laminates 48.23 41.41 10.35 5/15/80xGnPAPP17 laminates 49.18 40.66 10.16 3/17/80xGnPAPP18 laminates 47.30 42.16 10.54 2/18/80xGnPAPP19 laminates 49.78 40.18 10.04 1/19/80xGnPAPP20 laminates 50.71 39.43 9.86 0/20/80

GnP, graphite nanoplatelets; APP, ammonium polyphosphate; GF, glass fiber.*For the purpose of simplification, the above sample IDs are called control, APP15, APP17, APP18, APP19, and

APP 20 later, respectively.

Figure 1. High pressure system for papermaking.

FLAME RESISTANCE OF XGNP/CNF NANOPAPERCOATED NANOCOMPOSITES 243


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2.4.2. Xray diffraction. Xray diffraction analysis was carried out for the mixing samples (withoutnanopaper coating) using a Rigaku D/MAX Xray diffractometer (45kV, 30mA) equipped withcopper Xray tube (wavelength of 1.54 ) at a scanning rate of 0.06 and 7 s per step.

2.4.3. Scanning electron microscopy. The hybrid nanopapers and char materials of the samplescoated with nanopapers after cone calorimeter test were sputter coated with a conductive gold layer.They were analyzed by a Zeiss Ultra 55 SEM machine at an EHT of 5 kV.

3. RESULTS AND DISCUSSION

3.1. Cone calorimeter test of nanocomposites containing exfoliated graphite nanoplatelets and

ammonium polyphosphate

Figure 2 shows the HRRs of the samples containing different weight ratios of polyester, APP, andxGnP. Compared with the control sample, the HRRs of the samples containing APP and/or xGnP were

Table II. Composition of hybrid nanopapers and nanocomposites.

Nanocompositessample ID*

Composition (wt%) Weight ratios inthe nanopaper

GF Resin xGnP APP Nanopaper

GAL 49.83 40.14 1.00 9.04 0.00 No paper C0G1GAL 50.17 38.91 1.10 9.84 1.20 CNF/xGnP = 0/1

C1G3GAL 49.16 39.73 1.11 9.99 1.17 CNF/xGnP = 1/3C1G5GAL 49.10 39.81 1.10 10.00 1.16 CNF/xGnP = 1/5C1G1GAL 48.12 40.59 1.13 10.17 1.15 CNF/xGnP = 1/1C3G1GAL 48.85 39.99 1.12 10.04 1.17 CNF/xGnP = 3/1C5G1GAL 48.88 40.01 1.11 10.00 1.17 CNF/xGnP = 5/1C1G0GAL 48.27 40.46 1.13 10.14 1.15 CNF/xGnP = 1/0

GF, glass fiber; xGnP, exfoliated graphite nanoplatelets; APP, ammonium polyphosphate; CNF, carbon nanofiber.*For the purpose of simplification, the above sample IDs are called GA, C0G1, C1G5, C1G3, C1G1, C3G1,

C5G1, and C1G0 later, respectively; GA is the control sample.

Figure 2. Heat release rate of the samples with different weight ratios of ammonium polyphosphate andexfoliated graphite nanoplatelets.



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visibly lower. The sample APP17 labeled as composed of 80% of resin, 17% of APP, and 3% of xGnPshows the lowest HRR curve. However, the other samples with the content of APP greater than 17%(xGnP is lower than 3%) or lower than 17% (xGnP is higher than 3%) show a higher HRR. With thisinformation, it is inferred that there is an optimized weight ratio between APP and xGnP. A model forthese results is one where the APP particles serve to reduce the HRR of the samples by acting as blowagents to generate air bubbles, which are expected to lower the thermal conductivity in the thickness

direction (Figure 3). Simultaneously, the presence of xGnP would impair the thermal isolation abilityof the protective char layer because of its platelet structure, high thermal conductivity, and heatabsorption ability [16]. Therefore, there is a competing mechanism associated with introducingxGnPstheir high heat absorption and thermal conductivity will stimulate the pyrolysis of the polymer;conversely, the high thermal conductivity and the stimulation of polymer pyrolysis will accelerate theheat dissipation and rate of char creation, respectively. In addition, the platelet structure of xGnP mightserve as barrier to prevent the decomposed fuel to feed the flame as shown in Figure 4 where it isproposed that the underlying mechanism that the platelet structure of xGnP will decrease thepermeability of the samples, inhibiting the diffusion of the decomposed resin (fuel). This mechanism issupported by the mass loss rate of the samples. Figure 5 shows the mass loss rates of the control sampleand sample containing 3% of xGnP and 17% of APP within its matrix. (Other samples were observed tohave similar results but are excluded in this figure for ease of reading.) It can been seen that the curvesclosely line up with the HRR curves, which suggests that the reduced HRR is the consequence ofreduced mass loss rate. In other words, the xGnPs effectively slow down the migration of thedecomposed fuel, and it can be presumably concluded that under an optimized ratio, the synergisticeffect between APP and xGnP is revealed.

Figure 3. Air bubbles trapped in the char structure of the exfoliated graphite nanoplateletsAPP17 laminatesafter cone.

Figure 4. The presence of exfoliated graphite nanoplatelets (xGnP) particles inhibits the diffusion of thedecomposed resin.



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From the cone calorimeter tests results shown in Table III, it can be seen that the variations inweight ratios of xGnP and APP among these samples yield only differences in total HRR and charyielding. This indicates that the relatively large amount of traditional intumescent flame retardant,APP, has a dominant effect. With the exception of APP15, the PHRR of APP17, APP18, APP19, andAPP20 are very close, as shown in Table III, suggesting that the addition of small amounts ofthese nanoparticles into the polymer would not significantly affect the thermal properties of thesamples that already have a high concentration of APP additives, unless the concentration of xGnPis very high (5% in this case).

The HRRs of those samples coated with xGnP/CNF hybrid nanopapers are shown in Figure 6. As

shown in Figure 6(b), the PHRR of C0G1 is 11% less than that of the control sample GA, and PHRRsof the sample C1G5, C1G3, C1G0, C3G1, C1G1, and C5G1 are 7%, 11%, 28%, 33%, 39%, and 100%higher than that of the control sample, respectively. Such a high PHRR is undesirable for the purposeof fire retardancy, and a more sophisticated material design is needed. However, it can be seen inFigure 6(a) that immediately following the peaks of the papercoated samples, there is the dramaticdecrease of the HRR. It is unlikely that the drop is due to the complete consumption of the compositematerial but rather is likely due to the formation of a protective char layer, considering long high HRRafter the peak. In fact, it is intended that the introduction of the hybrid nanopaper should serve as a pre existed char layer and to prompt the formation of the protective char. In terms of analyzing the longterm heat release behavior, the total HRR during different periods can be calculated by

THR tt0 HRR dt (1)

Figure 5. Mass loss rate (MLR) of the samples.

Table III. A summary of the cone calorimeter test data of the mixing group.

Sample ID Control APP15 APP17 APP18 APP19 APP20

Total mass (g) 55 58.0 58.0 57.0 57.0 56.0Char yielding (wt%) 0 17.8 14.6 10.9 15.9 14.1Total heat released (MJ/m2) 135 111.0 115.0 115.0 118.0 116.0Peak heat release rate (kW/m2) 410 389.0 281.0 310.0 295.0 270.0Total smoke release (m/m2) 6063 6455.0 5270.0 5677.0 6104.0 4948.0

The thickness of all the samples is about 8 mm.



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By integrating the HRRs from 0 to 100 s, the total heat released (THR) before 100 s is shown in

Table IV. The THR before 100s of the samples coated with C0G1, C1G5, and C1G3 papers are,respectively, 33%, 16%, and 31% less than that of the GA sample. The differences between the GAsample and the rest of the samples are within 10%. During the major burning stage (100350 s) wheremost of the mass has been consumed, Figure 7 shows that the samples coated with xGnP dominated

Table IV. A summary of cone calorimeter test data of the papercoated group.

Sample ID GA C0G1 C1G5 C1G3 C1G1 C3G1 C5G1 C1G0

Total mass (g) 57.0 57.0 57.0 57.0 59.0 58.0 59.0 57.0Char yielding (wt%) 10.9 18.3 18.9 11.1 19.9 19.1 19.3 18.9Peak heat release rate (kW/m2) 310.0 276.0 331.0 344.0 430.0 411.0 621.0 396.0Total heat released (MJ/m2) 114.0 110.0 115.0 112.0 117.0 113.0 122.0 114.0Heat released (MJ/m2) (0100s) 17.1 11.5 14.4 11.8 17.3 16.7 18.9 18.1

Heat released (MJ/m2) (100350s) 69.3 60.3 62.0 57.2 60.7 60.6 59.0 67.5Total smoke release (m/m2) 5677.0 4811.0 5582.0 5765.0 5760.0 5578.0 5670.0 6011.0

The thickness of all the samples is about 8 mm.

Figure 6. Heat release rate of the samples coated with exfoliated graphite nanoplatelets CNF hybridnanopapers. (a) 0800s; (b) 0100s.

Figure 7. Heat release rate between 100s and 350 s.



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hybrid nanopapers exhibit lower heat release. By integrating the curve, it can be seen that the samplecoated with C1G3 has the lowest THR (as listed in Table IV). The difference of THR between thissample and the GA sample is more than 17%. Only the sample coated with a pure CNF nanopaper hassimilar THR value with that of the GA sample. This is attributed to the fact that the pure CNFnanopaper has much higher permeability, thermal conductivity, and heat absorption ability than thenanopapers containing xGnP.

The above results demonstrate the improvement in the THR of the composites achieved by coatingwith the hybrid nanopapers. The contents of the hybrid nanopapers that are dominated by xGnP havebetterflame retardancy than those of the CNFdominant hybrid papers. Similar to the fire retardantmechanism previously discussed (Figure 4), it is reasonable to conclude that the xGnP dominantnanopapers have much lower permeability, thereby slowing the evaporation of the decomposedpolymer that feeds the flame above the surface of the nanopaper. In addition, despite resulting in ahigher PHRR, the CNF/xGnP hybrid nanopaper accelerates the char formation process. This fireretardancy mechanism is further confirmed by the analysis of the smoke production rate data, as shownin Figure 8; these curves are highly similar to the HRR curves. Most of the smoke generated before350 s, with the peaks of the GA samples (a in Figure 8) and the sample coated with CNFdominatednanopapers (c, d, g, and h in Figure 8) occurring before 150 s, whereas those of the samples coatedwith xGnPdominated nanopapers (b, e, and f in Figure 8) occurring near 350 s with rates before 150 sbeing much less than those of the GA sample.

Although HRR is an important parameter to evaluate the fire performance of polymer [3], otherparameters such as mass loss are useful in regards to the materials postfire mechanical properties.Figure 9 shows the change of mass percentage of matrices during fire tests, mathematically, defined asthe change in the mass percentage of matrices obtained by normalizing the total mass of matrix duringcone calorimeter test. Because the mass of glass fiber remains stable during the whole testingprocedure, the matrix weight of a sample can be obtained as the difference of the mass of glass fiberand the total mass.

Mass percentage of matrix MtMGMiMG

(2)

where Mt is the mass of the sample recorded during test, MG is the mass of the glass fiber that equals

800 g/m

2

Asample 8, and Mi is the initial mass of the sample.As shown in Figure 9(a), the polymer matrix of the control sample has been almost completelyconsumed, whereas the samples containing APP and xGnP within their polymer show an improvedability to retain their matrices during fire testing. The sample containing 17% of APP and 3% of xGnPexhibits similar effectiveness as the sample where 20% of pure APP has been incorporated into thematrix. For the nanopapercoated samples, as shown in Figure 9(b), all the samples show an improved

Figure 8. Smoke production rate of the samples coated with the nanopapers. (a) 0700 s; (b) 0350s.



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capability in preventing the mass loss compared with the control sample. In addition to the lower

permeability of CNF/xGnP hybrid nanopaper that will effectively slow down the diffusion of thedecomposed resin, another possible explanation is that carbonbased material might accelerate theprocess of forming the protective char layer on the surface of the samples. Thermally, a carbon basedcoating layer would stimulate the decomposition of APP to form a foaming char layer, with thenanopaper itself structurally serving as a preexisted char layer.

3.2. Xray diffraction results of the samples containing different concentrations of ammonium

polyphosphate and exfoliated graphite nanoplatelets

As shown in Figure 10(a), there is no peak for the sample only composed of glass fiber and polyesterresin, whereas the peaks for APP powder (curve b in Figure 10) and the sample only containing APP

Figure 9. Mass percentage of matrices during cone calorimeter tests. (a) Direct mixing samples; (b) papercoated samples.



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are similar, only differencing in their intensity, which is due to the fact the concentration of APP in thecomposite sample is lower than that of pure APP powder. Figure 10(b) shows the XRD pattern ofxGnP powder, the sample containing APP only, and the samples containing both APP and xGnP onthe same axes. It can be seen that the peak for xGnP is around 26.5. When the particles are mixed intothe polymer with APP, the XRD patterns of the mixed samples are simply the combination of thepatterns of APP and xGnP. For example, there are two peaks around 26 for the samples containing2% and 3% (curves d and e, respectively, in Figure 10) of xGnP. The lower angle peak is attributed to

APP, and the higher angle peak comes from xGnP. When the concentration of xGnP is increased to5%, the contribution from xGnP around 26 becomes more obvious. These curves indicate that themixing of xGnP into the polymer using mechanical mixer at room temperature will not result in asignificant change of intercalated distance between xGnP.

As shown in Figure 10(c), it is interesting to note that there is no peak for the sample matrixcomposed of 1% of xGnP, 19% of APP, and 80% of polyester. If the xGnP particles had beenexfoliated, there should be peaks for APP. The possibility of significant experiment errors for theAPP19 samples XRD data is highly unlikely, because the test for this sample was repeated four timeswith different locations, yielding the same results. This might have resulted from the APP and xGnPparticles becoming amorphous at such a ratio. However, the phenomenon needs further investigationto determine its exact reason.

Figure 10. Xray diffraction results of the samples with different concentrations of ammoniumpolyphosphate and exfoliated graphite nanoplatelets.



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3.3. Morphology of the nanopapers and char materials of the paper coating samples after cone

calorimeter tests

3.3.1. Morphology of the nanopapers. The morphology of the nanopaper before coating onto thesurface of FRP is shown in Figure 11. SEM images Figures 11(a) and 11(b) indicate that xGnP

Figure 11. Scanning electron microscopy images of nanopapers. (a) C1G3, (b) C3G1, (c) C0G1, and(d) C1G0.

Figure 12. Scanning electron microscopy images of char materials of the sample C0G1 GAL.



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particles are well dispersed and entangled within the CNF networks. When the loading of xGnP isincreased within the hybrid nanopapers, the permeability of the nanopapers decreases because of morexGnP particles filling into the pores of CNF networks. As shown in Figures 11(c) and (d), the purexGnP and CNF nanopapers should have the lowest and highest permeability, respectively.

3.3.2. Morphology of chars after cone calorimeter tests. Figures 12 and 13 show the charcharacteristics of the composite samples coated with the nanopapers after cone calorimeter tests. Thereare three types of char formed during combustion reaction, labeled as A type, B type and C type. It isclear that A type char is the most compact, while the C type char has the lowest density. Generally, asample that generates more compact char demonstrates improved flame retardancy [17]. The sampleC0G1 shows a largest amount of A type chars in the surface and also shows good flame resistance(Figure 12). However, most of the chars from the sample C1G0 are composed of types B and C(Figure 13), and the sample shows a higherflammability than even the control sample.

4. CONCLUSIONS

Through the analysis of cone calorimeter test data and char characteristics, it was found that the thermalproperties and permeability of composites and char materials play important roles in determining the

flammability of the materials. xGnP particles, used as an alternative to clay, show an excellent barriereffect when they are mixed in polymers and incorporated into CNFbased nanopapers. Specifically, withan addition of 3% xGnP and 17% by weight APP into the polymer matrix, the fire performance of thesample is the best of those tested, suggesting that there is an optimized weight ratio between xGnP and

Figure 13. Scanning electron microscopy images of char materials of the sample C1G0 GAL.



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APP that uses their synergistic effect. By coating hybrid nanopapers onto the surfaces of those samples,the fire resistance performance of the composite is further enhanced, both thermally and structurally,with the traditional flame retardant APP proving to be important to control the overall heat release of thecomposite materials during combustion reaction process.

ACKNOWLEDGEMENTS

The materials presented here are based upon the work supported by the Office of Naval Research undergrant no. N000140910429 managed by Program Manager Dr Ignacio Perez. In addition, this work ispartially funded by the National Science Foundation Nanomanufacturing Program under grant no. CCMI 0757302. Any opinions, findings, and conclusions or recommendations expressed in this material are thoseof the authors and do not necessarily reflect the views of the Office of Naval Research and the NationalScience Foundation.

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