Macromol. Chem. Phys. 2001, 202, 2239–2246 2239

Metallocene Catalyzed Polymerization of Ethylene inthe Presence of Graphite, 1

Synthesis and Characterization of the Composites

Michael Alexandre,1 a Miroslaw Pluta,2 Philippe Dubois,1 a Robert JØrôme* 1

1 University of Liege, Center for Education and Research on Macromolecules (CERM), Sart-Tilman,B6, 4000 Liege, BelgiumFax: +32/(0)4/3663497; E-mail: rjerome@ulg.ac.be

2 Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112,90-363 Lodz, Poland

IntroductionMost composites that consist of a thermoplastic matrixand a particulate filler are commonly prepared by mechan-ical mixing of the components above the melting tempera-ture of the polymer or sometimes by solution blending.Mechanical kneading is however unable to promote fineand homogeneous dispersion of the filler, particularly athigh filler content. Above ca. 60 wt.-% filler, the particleaggregation results in extremely brittle materials.[1–4]

When the solution blending is concerned, the filler is pre-

dispersed in a solution of the polymer, followed by the sol-vent evaporation which sometimes allows the filler to befinely dispersed within the polymer.[5] However, in thespecific case of polyolefin matrices, the polymer is insolu-ble in conventional low boiling point solvents. Xylene orhigh boiling point chlorinated aromatic solvents have to beused which addresses the question of their completeremoval and the possible modification of the polymerproperties by residual solvent (e.g. plasticization).

The polymerization-filling technique (PFT), mainlydeveloped in the case of polyolefin matrices, is muchmore efficient in dispersing the filler in a homogeneousfashion.[6–10] The composite results from the direct olefin

Full Paper: Polyethylene/graphite composites have beenprepared by two different methods. In a first approach, theethylene polymerization has been catalyzed by metallo-cene in the presence of neat graphite particles (NGC com-posites). A second series of composites (TGC) has beenprepared by the polymerization-filling technique, whichrequires that the metallocene/methylalumoxane catalyst isfixed onto the graphite surface prior to the ethylene poly-merization. The two series of composites exhibit signifi-cantly different morphology and thermal properties. Thefiller distribution is very heterogeneous in the NGC series.The morphology changes from an intimate mixture of PEand filler particles at low graphite content to graphite cov-ered by patches of PE at high filler loading. The graphitedistribution is much more homogeneous in the TGC sam-ples, and the morphology consists of particles covered bya layer of PE in the whole composition range. Differencesin the thermal properties are discussed in relation to themorphology.

Macromol. Chem. Phys. 2001, 202, No. 11 i WILEY-VCH Verlag GmbH, D-69451 Weinheim 2001 1022-1352/2001/1107–2239$17.50+.50/0

a Present address: University of Mons – Hainaut, Laboratory ofPolymeric and Composite Materials, Place du Parc 20, 7000Mons, Belgium.

SEM micrograph of TGC9 (30 wt.-% PE, tp = 1 min).

2240 M. Alexandre, M. Pluta, P. Dubois, R. JØrôme

polymerization from the filler surface onto which thecoordination catalyst has been previously deposited. Thismethod leads to so-called “homogeneous” compo-sites,[11, 12] as result of the deagglomeration of the fillerparticles when treated by the constitutive components ofthe polymerization catalyst. Because the polymer chainsgrow from the filler surface (including pores open to thesurface), they are in intimate contact with it, and thiseffect is reinforced by the propensity of the polyolefinchains to precipitate from the polymerization medium, asthey grow. In contrast to other techniques in which thepolymer chains are chemically grafted onto the filler par-ticles (polymerization initiated by pre-grafted initiators,or chain grafting in reactive processing), there is no cova-lent bonding between the filler surface and the polyolefinmatrix when the polymerization filling technique isimplemented. The characteristic features of this in-situtechnique compared to conventional mechanical meltblending leads to a much more uniform filler distributionand a considerably enhanced interfacial adhesion, even athigh filler content,[7] as a result of the extended deagglo-meration of the filler particles and their intimate coatingby the polymer.

The purpose of this paper is to report on polyethylene/graphite composites prepared by using polymerizationcatalysts,[12–14] and to compare the morphology and ther-mal properties of the composites prepared by the poly-merization-filling technique and by the direct polymeri-zation of ethylene catalyzed by a metallocene-based solu-ble catalyst in the presence of a suspension of pristinegraphite particles. It must be noted that Kaminsky etal.[16] have prepared aluminum and zinc-based compositesby using metallocene-mediated PFT.

Experimental Part

Materials

Methylaluminoxane (MAO, 10 wt.-% solution in toluene,1.65 m in Al) was purchased from Witco GmbH. (tert-Butyl-amido)dimethyl(tetramethyl-g5-cyclopentadienyl)silane tita-nium dimethyl (CGC) was provided by DOW Benelux N.V.as a 0.153 m solution that was diluted ca. 30 times in driedheptane before use. Ethylene (Air Liquide, 99.95%) wasdried by passing through a molecular sieve 4 � column. Gra-phite EP1002 (S.A.Contimet N.V., Brussels) was kindly pro-vided by the supplier. Heptane and toluene were refluxedover sodium and CaH2, respectively, and distilled prior touse.

In-Situ Polymerization in the Presence of UntreatedGraphite

A given amount of neat graphite was placed in the 250 mlpolymerization flask and dried overnight at 1058C underreduced pressure (10–2 mmHg). The graphite was dispersedin 100 ml dried heptane under nitrogen followed by the addi-

tion of 1.5 ml MAO and 1.1 ml CGC (5.5 N 10–3m). MAO

was added before CGC in order to prevent CGC from beingdeactivated by the functional groups on the graphite surface,the dimethyl titanium species used as catalyst being verysensitive towards protic compounds. The stirred mixture wasthen heated up to 708C for 15 min. The reactor was purgedby ethylene (0.5 min) in order to remove nitrogen. The poly-merization then proceeded under continuous pressure of 1.7bar at 708C under vigorous stirring for 5 min or 1 h. Thefinal composite was dried at 858C for ca. 18 h under reducedpressure. These composites will be referred to as NGC (Non-treated-Graphite Composites).

Polymerization-Filling Technique

i) Graphite Activation

25 g of EP1002 graphite powder, previously dried overnightat 1058C under reduced pressure (10–2 mm Hg) were addedunder nitrogen with 175 ml of dried and deoxygenated hep-tane and 125 ml of MAO. The mixture was stirred for 2 h atroom temperature so allowing MAO to react with the gra-phite surface. Solvents were then distilled off at 708C underreduced pressure. The solvents together with any volatileorganoaluminium compounds were trapped in a flask cooleddown by liquid nitrogen. The recovered organoaluminiumcompounds were hydrolyzed by HCl and titrated by colori-metry with 9-hydroxyquinoline (Aldrich). Treated graphitewas heated up at 1508C under reduced pressure for 2 h. TheMAO excess was removed by washing off the graphite withdried toluene (26100 ml) at 708C. The collected MAO washydrolyzed by addition of 100 ml aqueous HCl (ca. 2 m), andAl was titrated by colorimetry (9-hydroxyquinoline). 20 mlof the acidic solution were diluted 50 times and 5 ml of thissolution was buffered at pH = 5.5 with 3 ml of an ammoniumacetate buffer. 2 ml of a chloroform solution of 9-hydroxy-quinoline (0.141 m) was added to extract the aqueous alumi-num cations in the organic phase. The absorbance of the yel-low aluminum complex in chloroform was measured at410 nm with a Phillips PU8700 UV-visible spectrophoto-meter. A calibration curve was set up with standard solutionsof 9-hydroxyquinoline complexed by Al3+ in the concentra-tion range from 2.45 N 10–4 to 2.45 N 10–5 mol N l–1. Theamount of the Al eliminated during the solvent evaporationand the graphite washing was calculated from the colori-metric titration of Al.

ii) Polymerization Step

The treated graphite was transferred into a 250 ml glass-reac-tor in a glove-box. Approximately 2 g of the treated graphitewere dispersed in 100 ml dried heptane and added with0.8 ml of CGC (6.633 N 10–3

m). The synthesis was carriedout at 708C under 1.7 bar of ethylene pressure. The final gra-phite content in the composites was controlled by the poly-merization time. The polymerization was stopped by adding3 ml of concentrated hydrochloric acid, and the final materialwas precipitated in 1 l acetone. The final composite wasdried at 858C for ca. 18 h under reduced pressure. Thesecomposites will be referred to as TGC (Treated-GraphiteComposites).

Metallocene Catalyzed Polymerization of Ethylene in the Presence of Graphite, 1 2241

Composite Characterization

Thermogravimetric analysis (TGA) was performed under airflow, with a DuPont 51 thermogravimetric analyzer at aheating rate of 208C N min–1. In addition to the thermal stabi-lity of the polymer matrix, the graphite content was calcu-lated from the weight loss at 6008C, at which temperaturethe sample mass remained constant.

Thermograms of compression molded and annealed sam-ples (heated at 2008C then slowly cooled down to room tem-perature) were recorded with a DuPont 910 differential scan-ning calorimeter. Samples were heated from –1508C to2008C, under nitrogen, at a heating rate of 108C N min–1. Thedegree of crystallinity, Xc,was calculated from the meltingenthalpy of 100% crystalline PE,[17] i. e., 2.93 N 10–5 J N kg–1,and from the heat of melting (DHm, in J N gPE

–1) of the samplesextracted from the area under the peak between 08C to1908C. The melting temperature (Tm) was reported as thetemperature at the maximum of the melting endotherm.

Scanning electron micrographs were recorded with aJEOL JSM-840A Scanning Microscope on gold-palladiummetallized specimens. The same microscope coupled withDe-Excitation X-ray Analysis (EDAX) was used in order toidentify the elements on the surface of treated graphite.

Results and Discussion

Polymerization with Neat Graphite (NGC)

In this series of experiments, ethylene has been polymer-ized in the presence of non treated graphite particles dis-persed in the polymerization medium. The prepared com-posites have been collected after a one-hour polymeriza-tion time, the graphite weight fraction being controlledby the initial amount of graphite added to the reactor(Table 1).

Although a large range of composition can be covered,it is difficult to correlate the amount of polyethylene pro-duced (evaluated as the mass difference between theengaged graphite and the recovered composite) to the

initial load of graphite. The production of polyethyleneafter 1 h, averaged over the whole range of compositeproduced, was found to be 3.6 l 1.4 g N cm–3. The notice-able scattering of the data makes it difficult to knowwhether graphite has an effect on the polymerization pro-cess or not. Moreover, the discrepancy between the theo-retical graphite content and the experimental value esti-mated by TGA for small sample amounts (between 10and 20 mg) might reflect a large heterogeneity in thecomposite composition. It must be noted that the color ofthe composite changes from deep black (for NGC 8) tolight gray (for NGC 1) consistently with an intimate mixof black platelets (graphite) and white PE particles.

The DSC curves for the NGC composites are shown inFigure 1, and the melting temperature (Tm) and degree ofcrystallinity (Xc) are listed in Table 2. With increasinggraphite content, the melting temperature and the half-width of the main melting peak decreased, and the lowtemperature endotherm (onset at ca. 08C) is more pro-nounced. The change in Tm can be related to differencesin the thermal conductivity for composites of differentgraphite contents. Indeed, when the thermograms forNGC 1 and NGC 8 are recorded at a rate of 28C N min–1

instead of 108C N min–1, the same Tm value is observedand the melting endotherms have a more comparableshape. A high graphite content is favorable to the heat

Table 1. Composition of HDPE/graphite composites contain-ing untreated filler (NGC) (polymerization in 100 ml heptane,catalyst: 6.06 N 10–6 mol, Tpolym. = 70 8C, pethylene = 1.7 bar, tpolym. =1 h).

Composite mgaÞ

gmPE

bÞ

gwt.-% graphite Dwt.-% graphite

code calc.c) meas.d) (calc. – meas.)

NGC1 0.41 4.71 8.0 12.4 –4.6NGC3 0.75 3.05 19.7 23.7 –4.0NGC5 2.4 5.4 30.8 35.1 –4.7NGC6 3.5 3.61 49.2 49.4 –0.2NGC7 5.5 3.9 58.5 57.2 +1.3NGC8 12 2 85.7 83.0 +2.7

a) mg = mass of untreated graphite in the reactor.b) mPE = mass of PE produced as determined (weighing of the

recovered composites).c) Calculated from mg and mPE.d) By TGA (see Experimental Part).

Figure 1. DSC traces for untreated graphite composites (NGC)of various graphite contents (1 h polymerization time), normal-ized to the unit mass of polyethylene.

2242 M. Alexandre, M. Pluta, P. Dubois, R. JØrôme

transfer through the sample, so that the melting tempera-ture is observed at an as low temperature as the heatingrate is high. The change in the melting peak half-widthand shape can be attributed to a complex interplay ofthermal conductivity of the samples, molecular character-istics of the polyolefin (MW, MWD), and interaction ofPE with the graphite particles, which all influence thecourse of the crystallization. The melting domain from 0to 1008C tends to be more pronounced as the graphiteloading is increased, thus as the crystallinity (Xc) isdecreased. This observation suggests that the graphite fil-ler has a deleterious effect on the ordering, and thus stabi-lity of the PE crystallites.

In order to have a better insight into the interaction ofthe catalytic system with the graphite, the polymerizationtime has been decreased in the presence of variousamounts of graphite (Table 3). At short polymerizationtimes, the increase in the amount of graphite drasticallydecreases the PE production, indicating that graphite (i.e.,the functional groups on the surface) is a poison for thecatalyst. There is again a large discrepancy between thetheoretical graphite content and the value estimated byTGA, which is consistent with a heterogeneity in thecomposite composition.

The morphology of these composites has beenobserved by scanning electron microscopy (SEM). SEMmicrographs for the powdery NGC9 and NGC11 samplesare shown in Figure 2a and 2b, respectively and are dee-ply different one from each other. At the lower graphite

content (NGC 9; 65.2 wt.-% filler), graphite plateletscoexist with typical PE particles (Figure 2a). In the caseof NGC11 (91 wt.-% graphite), deposition of PE on gra-phite surface is clearly observed and confirms that MAOhas reacted with the surface and drives the ethylene poly-merization from it. The DSC traces for these compositesare shown in Figure 3. As previously observed, there is asmall endothermic effect (from 08C to 1258C), ahead ofa sharp endotherm at ca. 1358C. This contribution in thelow temperature range is the signature of the less orderedPE crystallites, and it decreases with the graphite content,thus with the improved ordering of the polyethylene crys-talline phase. This characteristic feature could indicatethat the crystallization of PE is adversely affected by theclose vicinity of the graphite surface. An additional con-firmation has to be found in the degree of crystallinity(Table 4), which decreases from 65.2% for NGC9 downto only 32.4% for NGC11.

Further information can be retrieved from thermogravi-metric analysis (Figure 4). This technique shows thatpolyethylene in the composites is less thermally stablecompared to polyethylene produced under the very sameconditions but in the absence of graphite. The composites

Table 2. Degree of crystallinity (Xc) and melting temperature(Tm) for the untreated graphite composites (See Table 1).

Compositecode

Graphite contentwt:-%

Xc

%

Tm

�C

NGC1 12.4 80.4 139.0NGC3 23.7 73.9 143.5NGC5 35.1 80.5 139.0NGC6 49.4 78.6 136.5NGC7 57.2 79.5 137.5NGC8 83.0 62.3 135.0

Table 3. Composition of HDPE/graphite composites contain-ing untreated filler (polymerization in 100 ml heptane, catalyst:6.06 N 10–6 mol, Tpolym. = 70 8C, pethylene = 1.7 bar, tpolym. = 5 min).

Composite mgaÞ

gmPE

bÞ

gwt.-% graphite Dwt.-% graphite

code calc.c) meas.d) (calc. – meas.)

NGC9 1 0.62 61.7 67.5 –5.8NGC10 3 0.37 89.0 88.4 +0.6NGC11 5 0.3 95.0 91.0 +4.0

a) mg = mass of untreated graphite in the reactor.b) mPE = mass of PE produced as determined (weighing of the

recovered composites).c) Calculated from mg and mPE.d) By TGA (see Experimental Part).

Figure 2. SEM micrographs of composites collected after5 min polymerization in the presence of different amounts ofneat graphite. (a) 1 g (NGC9), (b) 5 g (NGC11).

Metallocene Catalyzed Polymerization of Ethylene in the Presence of Graphite, 1 2243

start to degrade above 2008C with a sharp weight loss at3008C, in contrast to pure polyethylene which mainlydegrades between 400 and 5008C. This observation indi-

cates that the degradation of PE in the NGC9, 10 and 11composites is activated by the graphite. The same thermalinstability was also observed for the composites of thefirst series (NGC1-NGC8).

Polymerization-Filled Composites (TGC)

In contrast to the NGC samples, the catalytic system isimmobilized onto the filler surface in the polymerization-filling technique. The graphite particles are first treatedwith methylaluminoxane, at 1508C, in order to attach thecatalyst.

The colorimetric titration of the alkylaluminium resi-dues left after graphite washing and the solvent evapora-tion (see experimental) allows the actual amount of alu-minum immobilized onto the graphite particles to be esti-mated. The experimental value (3.6 N 10–3 mol of Al per gof graphite), shows that a relatively high amount of MAOcan be fixed onto graphite because of possible interac-tions between the Lewis acid Al centers of MAO and theelectron rich surface of graphite. The MAO deposition(and distribution) on the MAO-treated graphite particlessurface has been analyzed by electron de-excitation x-rayanalysis (EDAX). As a rule, the EDAX analysis confirmsthe presence of MAO homogeneously spread out on thegraphite surface, since the sharp maxima observed in theEDAX mapping are characteristic of the constitutiveatoms of the aluminoxane derivatives, i.e., O and Alatoms at 0.55 and 1.5 keV, respectively.

This MAO treated graphite is then contacted with thepolymerization precatalyst to form the active polymeriza-tion species by the known cationization mechanism. Cat-alytic species are therefore immobilized onto the surfacethrough electrostatic interactions between the cationiccatalytic Ti center and the surface-anchored MAO-basedanion. Because the chains are growing from the cationicspecies, the polymer is formed in very close contact withthe filler surface.

The composition of the polymerization-filled compo-sites (TGC) is controlled by the ethylene polymerizationtime (tp) as shown in Figure 5 and Table 5. The productiv-ity, calculated from the mass of PE produced for a givenand fixed amount of catalyst (5.31 N 10–6 mol) shows adrastic loss in activity with time. Two major factorsexplain this observation, i.e., the deactivation of theactive species with time and a decrease in the polymeriza-tion rate, as result of the continuously reduced diffusionof the monomer (ethylene) to the active polymerizationsites as more and more PE is produced.

The time dependence of the morphology is exemplifiedby TGC9 (1 min, 30 wt.-% PE) and TGC6 (6.5 min, 60.5wt.-% PE) composites. SEM micrographs (Figure 6a and6b) clearly show that a PE layer, whose the thicknessincreases with time, closely encapsulates the filler parti-cles. The polymer directly grows from the activated sur-

Figure 3. DSC traces for untreated graphite composites (NGC)of various graphite contents (5 min polymerization time), nor-malized to the unit mass of polyethylene.

Table 4. Degree of crystallinity (Xc) and melting temperature(Tm) for the untreated graphite composites (see Table 3).

Compositecode

Graphite contentwt:-%

Xc

%

Tm

�C

NGC9 67.5 65.2 136.6NGC10 88.4 58.8 135.4NGC11 91.0 39.5 133.9

Figure 4. TGA traces for NGC9, NGC10 and NGC11 com-pared with pure polyethylene.

2244 M. Alexandre, M. Pluta, P. Dubois, R. JØrôme

face of the filler particles. Some particles are connectedone to each other by polymer threads. This techniqueleads to composites, in which the filler is encapsulatedand thus totally isolated from the neighbor particles. Amuch more homogeneous filler distribution is alsoobserved as shown in Table 5, where the discrepancybetween the graphite content estimated from the directweighing of the as-recovered composites and from TGAare in close agreement. Note that the high value forTGC9 results from the weighing of the only partly recov-ered composite.

The DSC melting thermograms for the TGC samplesof different content of treated graphite are shown in Fig-ure 7. When the graphite content exceeds 50 wt.-%, therelative importance of the low temperature endotherm inbetween 0–1008C increases. As previously suggested,the melting of the less ordered and thus, less thermallystable polyethylene regions is at the origin of this effect.Since this contribution is related to the graphite content,these regions are thought to be formed by the polymerclose to the filler surface. This can be rationalized by theimmobilization of the polymer chains on the surface of

the treated particles and/or by their physical entanglementaround the filler which results in limitation for the chaincrystallization and defects in the crystalline structure.This effect is further confirmed by the values of Xc inTable 6 which are essentially independent of the graphite

Table 5. Composition of HDPE/graphite composites containing treated filler (polymerization in 100 ml heptane, catalyst:5.31 N 10–6 mol, Tpolym. = 70 8C, pethylene = 1.7 bar).

Composite mgaÞ

gmT

bÞ

gtp

cÞ

minwt.-% graphite Dwt.-% graphite

code calc.d) meas.e) (calc. – meas.)

TGC1 1.96 22.91 320 8.5 8.1 0.4TGC2 1.94 11.31 80 17.2 16.5 0.7TGC3 2.14 9.20 42 23.3 22.1 1.2TGC4 2.02 6.33 15 31.9 32.1 –0.2TGC5 1.82 4.95 8 36.8 38.0 –1.2TGC6 1.98 4.74 6.5 41.8 39.5 2.3TGC8 2.3 3.84 3.0 59.9 58.0 1.9TGC9 2.04 2.61f) 1.0 78.2 70.0 8.2

a) mg = mass of untreated graphite in the reactor.b) mT = mass of composite produced as determined (weighing of the recovered composite).c) tpolym. = time of polymerization.d) Calculated from mg and mT.e) By TGA (see Experimental Part).f) Partial sample recovery.

Figure 5. PE content (in wt.-%) and productivity of the poly-merization vs. time for the treated graphite composites (TGC).

Figure 6. SEM micrographs of (a) TGC9 (30 wt.-% PE, tp =1 min), (b) TGC6 (60.5 wt.-% PE, tp = 6.5 min).

Metallocene Catalyzed Polymerization of Ethylene in the Presence of Graphite, 1 2245

content up to 50 wt.-% (samples from TGC1 to TGC6)and then decrease for the samples TGC8 (58 wt.-%) andTGC9 (70 wt.-%) with the graphite content.

The thermal degradation analyzed by TGA qualita-tively confirms the observations reported for the NGCsamples. The graphite is responsible for the thermaldegradation at a lower temperature than for neat PE.

ConclusionTwo different methods for the preparation of polyethyl-ene/graphite composites based on the in-situ polymeriza-tion of the matrix have been compared, which leads to

composites of different morphology and thermal proper-ties.

Composites prepared by polymerization of ethylene inthe presence of unmodified graphite (NGC) have a mor-phology that changes with the graphite content. At lowcontent, graphite particles are intimately mixed withpolyethylene particles. At high graphite content, the poly-ethylene chains which grow away from the graphite sur-face are clearly observed, supporting that the MAO co-catalyst has extensively reacted with the graphite surface.This difference in morphology has a direct effect on themelting behavior of the PE matrix, in apparent relationwith the polymer/graphite surface interaction. Moreover,it is difficult to control precisely the amount of polymerproduced in this case.

The polymerization-filling technique that has beenused to produce the TGC series provides a much bettercontrol of the PE production by tuning the polymerizationtime. The morphology of these composites shows that thefiller has been encapsulated, even at high graphite con-tent, so leading to better defined materials. The closeinteraction of the matrix with the filler surface perturbsthe melting behavior, the degree of crystallinity decreas-ing when the filler content is increased. TGA has shownthat the graphite filler has a detrimental effect on the ther-mal stability of the two sets of composites. However, thedegradation appears beyond 2008C, thus above the tem-perature of PE melting and melt processing of the mate-rial which is quite acceptable. The difference in the mor-phology of the two series of composites is expected toaffect the macroscopic properties of the composites, par-ticularly their electrical conductivity,[18] which will be thetopic of a forthcoming paper.

Acknowledgement: M. A., P. D. and R. J. are indebted to theServices FØdØraux des Affaires Scientifiques, Techniques et Cul-turelles for general support to CERM in the frame of the “Pôlesd’Attraction Interuniversitaires: Supramolecular Catalysis andSupramolecular Chemistry-PAI(4–11)”, and for a postdoc stayof M. P. at CERM. They are also grateful to DOW Europe (Ter-neuzen, The Netherlands) for financial support and to Dr M.Garcia Marti for fruitful scientific discussions.

Received: August 28, 2000Revised: December 1, 2000

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Figure 7. DSC traces for selected treated graphite composites(TGC) of various graphite contents.

Table 6. Degree of crystallinity (Xc) and melting temperature(Tm) for the treated graphite composites (see Table 5).

Compositecode

Graphite contentwt:-%

Xc

%

Tm

�C

TGC1 8.1 70.0 141.0TGC2 16.5 69.3 141.0TGC3 22.1 70.0 141.0TGC4 32.1 68.8 141.0TGC5 38.0 69.8 141.5TGC6 39.5 70.1 140.5TGC8 58 66.2 140.0TGC9 70.0 61.4 136.5

2246 M. Alexandre, M. Pluta, P. Dubois, R. JØrôme

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