Polymer Degradation and Stability 90 (2005) 78e85

www.elsevier.com/locate/polydegstab

Photooxidation of ethylene-propylene-diene/montmorillonitenanocomposites

Sandrine Morlat-Therias a, Benedicte Mailhot a, Jean-Luc Gardette a,*,Claude Da Silva b, Bassel Haidar b, Alain Vidal b

a Laboratoire de Photochimie Moleculaire et Macromoleculaire/UMR-CNRS 6505,

Universite Blaise Pascal - Ensemble Universitaire des Cezeaux, 63177 Aubiere Cedex, Franceb Institut de Chimie des Surfaces et Interfaces (CNRS UPR 9069), Universite de Haute Alsace,

15 rue Jean Starcky, BP 2488, 68057 Mulhouse Cedex, France

Received 13 January 2005; accepted 30 January 2005

Available online 11 April 2005

Abstract

The UV-light induced oxidation of ethylene-propylene-diene (EPDM)/montmorillonite nanocomposites obtained with syntheticmontmorillonite was studied. The nanocomposites were obtained by melt compounding EPDM-g-MA (EPDM grafted with maleicanhydride as compatibilising agent) and organophilic synthetic clays. Four different samples were prepared and fully characterised:

an EPDM grafted with maleic anhydride, an EPDM/Na-MMt microcomposite and two EPDM/MMt nanocomposites, one withintercalated MMt and the other with exfoliated MMt. The oxidation of the polymeric matrix was characterised by infrared andUVevisible spectroscopies. Special attention was given to the EPDM-g-MA sample in order to understand the complex modificationsof the infrared spectra resulting from the presence of the compatibiliser. The photoproducts were the same in all samples. The

formation of these oxidation products occurred after an induction period, explained by the presence of a residual processingantioxidant. The induction time was found to be reduced in the presence of MMt and the effect was enhanced in the case of theexfoliated nanocomposite. After the induction period, oxidation started with a rate that was independent of the presence of MMt.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Nanocomposite; EPDM; Photooxidation

1. Introduction

Nanocomposite materials have been the object of aconsiderable attention since a montmorillonite rein-forced Nylon nanocomposite was developed by Toyotagroup [1]. Because of the nanometer-size dispersedparticles, the simple addition of a small amount (lessthan 5%) of alkylammonium exchanged clays givesimproved mechanical, thermal and physicochemical

* Corresponding author. Tel.: C33 4 73 40 71 77; fax: C33 4 73 40

77 00.

E-mail address: luc.gardette@univ-bpclermont.fr (J.-L. Gardette).

0141-3910/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.polymdegradstab.2005.01.040

properties in comparison with pristine polymers or con-ventional microcomposites. Among the many propertiesthat are modified, the observed improvements includeincreased moduli and strength, heat resistance, anddecreased gas permeability and flammability with lowinorganic loadings [2e4].

The most commonly used clay is a smectite groupmineral, such as montmorillonite, which belongs to thegeneral family of 2:1 layered silicates. Its crystal latticeconsists of 1 nm thin layers, with a central octahedralsheet of alumina fused between two external silicatetrahedral sheets (oxygen atoms of the octahedral sheetalso belong to the silica tetrahedra) (Scheme 1).Isomorphic substitution within the layers (Al3C replaced

79S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

by Mg2C or Fe2C) generates a negative charge, which isbalanced by exchangeable cations (NaC, LiC or Ca2C).

The growing interest in applications of nanocompo-site materials in many industrial fields is the driving forcefor the development of new polymer matrix-nanofillerformulations. Among the tremendous literature devotedto nanocomposite materials, only very few papers [5e10]deal with the long-term ageing of polymer/clay nano-composites, and more particularly with the photo-degradation of these materials. These studies concernnanocomposites with montmorillonite and polymermatrices, such as polypropylene [5,8e10], polyethylene[6] and polycarbonate [7]. In all cases, these studies givethe same conclusion, which is that the nanocompositesdegrade faster than the pristine polymers. This relativeinstability of nanocomposites to UV ageing couldconstitute a major drawback for the applications ofthese materials in outdoor applications.

At first sight, this observation is quite unexpected, andfor that reason, the behaviour of nanocomposites whenexposed to light requires a much stronger attention. Inprevious papers published by our group concerningthe photooxidation of polypropylene/montmorillonitenanocomposites [8e10], a significant reduction in theinduction period of oxidation was observed in thepresence of MMt. This was explained by interactionsbetween the organo-clays and the antioxidants. Severalhypotheses were proposed in order to explain theseinteractions: adsorption of additives onto the clay,catalytic effect of iron impurities of the organo-mont-morillonite, and degradation of the alkylammoniumcations of MMt [10].

Depending on their mineral origin, natural mont-morillonites contain some impurities, such as iron,

Montmorillonite:

Nax(Al(2-x)Mgx)Si4O10(OH)2

x = 0,3

T Tetra Si, Al

O Octa Al, Mg

Compensation Cation Na+

T

O

T

d001

Scheme 1. Formula and structure of montmorillonite.

which are likely to modify the UV-light stability of theorganic polymeric phase. In the present paper, we reporton a study of the photooxidation mechanisms ofelastomeric (EPDM)/Montmorillonite nanocomposites(EPDM/MMt) obtained with synthetic montmorillon-ites prepared according to a hydrothermal process[11,12]. The study of these iron-free materials is expectedto give new elements that are likely to help inunderstanding the photodegradation mechanisms ofpolymer/MMt nanocomposites. A second point of ourinvestigation concerns the effect of the structure of thecomposites on their photochemical behaviour: micro-composites and nanocomposites are compared, with twodifferent morphologies in the case of the nanocompo-sites, either intercalated or exfoliated.

EPDM/MMt nanocomposites were obtained by meltcompounding EPDM-g-MA (EPDM grafted withmaleic anhydride as compatibilising agent) and organo-philic clays. Depending on the exchange conditions ofthe organo-montmorillonite, two nanomorphologieswere prepared:

- an intercalated structure, with well-ordered multi-layered structures where the extended polymerchains are inserted into the gallery space betweenthe silicate layers,

- an exfoliated (or delaminated) structure, where theindividual silicate layers are no longer close enoughto interact with the gallery’s cations.

In the elastomeric matrix, exfoliation/intercalation iscontrolled by the amount of alkyl chains introduced inthe clay structure by an organophilic treatment [11,12].

The dispersion and exfoliation of silicate layersof MMt in the nanocomposite were investigated usingX-ray diffraction (XRD) and transmission electronmicroscopy (TEM).

The nanocomposites were irradiated in conditions ofartificial accelerated weathering and the chemicalmodifications resulting from photooxidation were in-vestigated by infrared and UVevisible spectroscopies,which also permitted to follow the consumption of theadditives and to determine the kinetics of degradation.

2. Experimental

2.1. Materials

The elastomers used were functionalised commer-cial ethylene-propylene-diene monomer (EPDM).Maleic Anhydride grafted EPDM (EPDM-g-MA,MA wt content: 1%) was Royaltuf 498 by UniroyalChemicals (ethylidene-2,5-norbornene, E/PZ 55/45%,MwZ 110 000 g mol�1 determined by GPC). Polymerswere purified by dissolving them in cyclohexane,

80 S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

followed by centrifugation. Only the soluble superna-tant fractions were dried and used.

2.2. Organo-clay preparation

The clays were synthesised using commercial re-agents. Sodium form of montmorillonite-type clay wasprepared by hydrothermal synthesis in hydrofluoricmedium at 220 �C for 48 h in a stainless steel PTFElined autoclave. In order to convert such clay into anorganophilic silicate, it was treated by cation exchangewith an aqueous solution of octadecyltrimethyl-ammo-nium bromide (C18TMAC, Aldrich). The amount ofintercalated C18TMAC was controlled by the concen-tration of the treatment solution, which in turncontrolled the nanocomposite intercalated/exfoliatedstructure [11,12].

2.3. EPDM/clay nanocomposite preparation

The nanocomposites were prepared by direct com-pounding process of the layered silicate (4% w/w) withthe elastomer for 20 min at 80 �C and 30 rpm ina Brabender Plasticorder PLE851 internal blender[11,12]. Four samples were prepared with differentcompositions and structures (description in Table 1).The samples were compression-moulded in the form offilms (thickness of about 80e100 mm) between PTFEfilms at 200 bar for 1 min at 80 �C.

2.4. Characterisation

Infrared spectra were recorded with a Nicolet 5SX-FTIR spectrometer, working with OMNIC software.Spectra were obtained using 32 scans and a 4 cm�1

resolution. UVevisible spectra were recorded on aShimadzu UV-2101 PC spectrometer equipped with anintegrating sphere.

Wide angle X-ray Diffraction (XRD) data werecollected with a Philips X’Pert diffractometer usingCuKa radiation (1.54 A, 40 kV, 20 mA) in a Bragggeometry at room temperature. Transmission Electron

Table 1

Composition of the samples

Sample EPDM-

g-MA(%)

Clay (wt%)

EPDM-g-MA 100 0

Microcomposite

EPDM/Na-MMt

96 Na-Montmorillonite (4%)

Intercalated EPDM/MMt 94.7 C18-Montmorillonite

(inorganic 4%)

Exfoliated EPDM/MMt 92.3 C18-Montmorillonite

(inorganic 4%)

Microscopy (TEM) was performed with a PhilipsCM200, acceleration voltage of 200 kV.

2.5. UV irradiations

The samples were irradiated in the form of the filmsdescribed above. UV-light irradiations were carried outunder polychromatic light with wavelengths higher than300 nm in a SEPAP 12.24 unit, in presence of oxygen.This accelerated weathering device is equipped with fourmedium pressure mercury lamps (400 W) and thesamples are placed on a rotating carousel located inthe centre. The temperature is regulated at 60 �C andcontrolled by a Pt thermocouple (PT100 probe).

3. Results and discussion

3.1. Characterisation of the clay dispersion [11,12]

Wide angle X-ray diffraction technique is commonlyused to determine the clay-based composite structure.Characterisation is generally based on the comparisonbetween the diffraction peak position of the organo-claypowder and the organo-clay in the polymer matrix [11].At the low angle values, the position of the diffractionpeak d001, is related to the extent of the interlayerspacing. A shift of this diffraction peak toward a lowervalue reveals an increase of the interlayer spacing. It hasbeen shown in previous studies [12,13] that such a shiftdepends on the amount and the arrangement ofintercalated C18TMAC cations between clay platelets.

For the sample containing unmodified Na-MMt, theweak change of the basal diffraction peak observedupon mixing with EPDM-g-MA (d001 are 1.34 nm and1.43 nm for powder and microcomposite, respectively)suggests that nanocomposite structure was not achieved.This was also confirmed by TEM showing primary clayparticles in the matrix with, in the best case, goodmicroscale dispersion.

The basal diffraction peak for the organo-modifiedmontmorillonite with a low C18TMAC cations content,was shown to be shifted to lower angle values, correlatedwith an increase of the interlayer spacing (d001 increasesfrom 1.97 nm to 4.60 nm) due to the intercalation ofpolymer chain within the C18TMAC cations. TEM imagewas consistent with a morphology in which elastomericmacromolecules were most likely intercalated betweenclay layers forming an intercalated nanocomposite.

In the case of the highest organic C18TMAC cationcontent, the amount of intercalated polymer was highenough to split the platelets away from each other, thebasal diffraction peaks collapse (d001 which has beenestimated as 4.10 nm before polymer mixing was nolonger perceptible). These results were considered asa proof of the clay exfoliation in the rubbery matrix.

81S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

This nanocomposite morphology was confirmed byTEM, clay layers appeared was then well dispersed.

3.2. Photooxidation of EPDM-g-MA

3.2.1. Infrared analysisThe IR spectrum of EPDM-g-MA before irradiation

(Fig. 1a) shows the expected absorption bands corre-sponding to the EPDM backbone and additionalabsorption bands in the carbonyl domain due to the

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Fig. 1. FTIR spectra of an EPDM-g-MA film photooxidised at

lO 300 nm, 60 �C: (a) direct spectra in the domain 1900e1500 cm�1,

(b) subtracted spectra (Ft � F0), (c) subtracted spectra to the spectrum

at 6 h.

grafted anhydride with maxima at 1713 cm�1,1740 cm�1 and 1775 cm�1. The intense absorption bandat 1713 cm�1 is known to arise from the formation ofcarboxylic acid resulting from the hydrolysis of theanhydride groups. The absorption band at 1775 cm�1

[13e15] is characteristic of cyclic anhydrides anda second absorption band of the anhydride functionsshould be around 1850 cm�1 (respectively, due tosymmetric and asymmetric C]O anhydride stretching[14]). However, the absorbance is too weak to beobserved as the grafted anhydride is mainly present inthe acidic form [13]. The presence of both acid andanhydride groups results from the equilibrium of thehydrolysis of the anhydride to give acid functions. Theabsorption band at 1740 cm�1 can be attributed on onepart to the ester functions of a compounded phenolicantioxidant, which is also detected by UVevisiblespectrometry (antioxidants are indeed commonly addedto elastomers to prevent further oxidation during theirservice life), and for the other part to the ester functionformed by reactions that open the anhydride ring.

A careful examination of the modifications of the IRspectra coming from photooxidation of EPDM-g-MAfilms reveals that two successive steps occur. The firstphase of the modification (up to 6 h of irradiation) isa decrease of the nC]O band of the acid functions(1713 cm�1) (Fig. 1a and b, which shows the subtractedspectra Ft� F0; F0 and Ft corresponding, respectively, tothe IR spectra recorded before photooxidation and afterirradiation for a given time t). The shift of the nC]O bandof the anhydride from 1775 cm�1 to 1782 cm�1 after thefirst two hours of irradiation suggests a different structureof the anhydride ring. Before irradiation, the very weakabsorption band at 1775 cm�1 indicates that unsaturatedanhydride rings (as already reported in the literature forcitraconic anhydride [15]) are still present. The anhydridering restored by a thermal effect from dehydration of theacid form should correspond to poly(maleic anhydride)obtained by intramolecular reaction, which is graftedonto the polymer backbone with characteristic absorp-tion band at 1784 cm�1. Under exposure to UV-light inthe presence of oxygen, saturation of the double bonds islikely to occur very rapidly. In the mean time, it has beenshown that irradiation of the anhydride units is likely togenerate a ring opening and that further photochemicalreactions result in the formation of volatile products,which are not detected in the solid film. However, duringthis first phase, no absorption band develops in thehydroxyl domain (3800e3100 cm�1) and the absorbanceat 808 cm�1 corresponding to EPDM unsaturation isnearly unchanged (Fig. 2), which indicates that thepolymer has not been oxidised.

After 6 h of irradiation, the second phase ofphotooxidation occurs. Irradiation of EPDM-g-MA(Fig. 1c and Fig. 2) leads to important changes in theIR spectrum in three main domains. In the carbonyl

82 S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

region (Fig. 1c), the appearance of an absorption bandcharacterised by a main maximum at 1713 cm�1

indicates the presence of carboxylic acids. During thissecond phase, modifications also occur in the region ofthe CH wag of double bonds. A decrease of theabsorbance of the ethylidene units at 808 cm�1 (Fig. 2)is observed, as already reported in the case of EPDM[16e18]. The new bands at 910 cm�1 and 870 cm�1 canbe, respectively, assigned to vinyl-type unsaturationcoming from Norrish II type reactions and to CH wagof the other double bonds derived from hydrogenabstraction reactions on allylic positions during thephotooxidation [16e18]. In the hydroxyl domain, notshown here, the appearance of a broad band witha maximum at 3415 cm�1 can be attributed to hydrogen-bonded alcohols and hydroperoxides [16e18].

The modifications of the IR spectra can be moreeasily observed in Fig. 1c which shows the spectraresulting from the subtraction of F6.25. They aresomewhat similar to those reported above in the caseof the pure unmodified EPDM sample (Fig. 3a and b),showing the increase with irradiation time of a broadcarbonyl band with a maximum at 1713 cm�1 andshoulders at 1730 cm�1 and 1790 cm�1, respectively.

3.2.2. UVevisible characterisationThe UVevisible spectrum of an unexposed EPDM-g-

MA film (Fig. 4) shows an absorption band witha maximum at 280 nm. This band can be attributed toaromatic structure of the phenolic group of a residualprocessing antioxidant. The modifications of the UVevisible spectra (Fig. 4) follow the same fate as reportedabove in the case of the IR analysis. One observesindeed a progressive decrease of the absorbance at280 nm up to 6 h. This induction period of about 6 h ismost likely to be related to the consumption of theantioxidant. Thereafter, the effect of irradiation resultsin a progressive shift of the absorbance towards longerwavelengths without any defined maximum, which

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Fig. 2. FTIR spectra of an EPDM-g-MA film photooxidised at

l O 300 nm, 60 �C in the domain 1000e600 cm�1.

indicates the formation of conjugated photoproductsby photooxidation of the EPDM matrix.

3.3. Photolysis and thermolysis of EPDM-g-MA

In order to understand the behaviour of EPDM-g-MA during the first hours of exposure, irradiation of the

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Fig. 3. FTIR spectra of an EPDM film photooxidised at l O 300 nm,

60 �C: (a) direct spectra in the domain 1900e1500 cm�1, (b)

subtracted spectra (Ft � F0).

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Fig. 4. UVevisible absorption spectra of an EPDM-g-MA film versus

photooxidation time at lO 300 nm, 60 �C.

83S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

samples was also carried out in vacuum (photolysis)under similar conditions (lR 300 nm and 60 �C). TheIR spectrum of photolysed samples (Fig. 5) shows theformation of two absorption bands at 1785 cm�1 and1864 cm�1 that is accompanied by a decrease of theabsorbance at 1713 cm�1. These modifications suggestthat a dehydration of the carboxylic acids restored ascyclic anhydrides occurs, with the two characteristic IRbands of maleic anhydride grafted onto EPDM [13] at1785 cm�1 and 1864 cm�1, respectively, for the symmet-ric and asymmetric stretching C]O bands.

A similar behaviour is observed when the samples areheated under vacuum at 60 �C (thermolysis). Moreover,the IR spectrum of an EPDM-g-MA film heated for90 h at 60 �C under vacuum shows the same modifica-tions as those observed in the case of the photolysisexperiments.

These results confirm that the modifications of the IRspectra reported above for the samples irradiated in thepresence of oxygen result from an equilibrium betweenthe anhydride and acid forms of the grafted poly(maleicanhydride). These modifications are more readilyobserved in the first phase of the oxidation, before theoccurrence of the oxidation of the polymeric matrix.

3.4. Photooxidation of EPDM/MMt micro- andnanocomposites

3.4.1. Infrared and UVevisible analysisThe initial infrared spectra of EPDM/MMt micro-

composite and EPDM/MMt intercalated nanocompo-site are similar to that of pristine EPDM-g-MA (notshown). Conversely, the IR initial spectrum of theexfoliated nanocomposite (Fig. 6a) is quite different inthe carbonyl domain. A broad absorption band peakingat 1735 cm�1, a shoulder at 1710 cm�1 and a smallerband at 1690 cm�1 were observed. The weak absorptionband at 1775 cm�1, attributed to the anhydride is notmodified compared to the EPDM-g-MA sample (Fig. 1).

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Fig. 5. FTIR spectra of an EPDM-g-MA film (a) before and (b) after

30 h of photolysis at l O 300 nm, 60 �C.

These differences in the IR spectra indicate thatinteractions occur between the carboxylic acid and thealkylammonium cations of the organo-clay, which arepresent in higher amount in the case of the exfoliatedEPDM/MMt nanocomposite. These interactions resultin the disappearance of the carboxylic acid functions.

On exposure of the EPDM/MMt microcomposite,modifications of the infrared spectra of the intercalatedand exfoliated EPDM/MMt nanocomposite can beobserved. They are mainly characterised by an increaseof the absorbance in the hydroxyl and carbonyl regions(Fig. 6b) and a decrease in the absorbance of theunsaturation absorption bands. These modifications aresimilar to those observed for the EPDM-g-MA material.

3.5. Influence of MMt on the photooxidation rates

The kinetic curves of oxidation are given in Fig. 7a.Because the various films were of slightly differentthicknesses, the results had to be multiplied bya correcting factor in order to adjust the absorbance at720 cm�1.

The increase of absorbance versus irradiation time ismeasured at the maximum in the carbonyl domain(1713 cm�1) and reported in Fig. 7. All the obtained

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Fig. 6. FTIR spectra of an exfoliated EPDM/MMt nanocomposite

film photooxidised at l O 300 nm, 60 �C: (a) direct spectra in the

domain 1900e1500 cm�1, (b) subtracted spectra (Ft � F0).

84 S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

curves are characterised by an induction period, alreadydescribed above in the case of the EPDM-g-MAmaterial. As indicated previously, no oxidation of thepolymer is detected during this period, corresponding tomodifications of the anhydride/acid equilibrium andto the disappearance of the phenolic antioxidant. Asshown in Fig. 7a, the induction time is stronglydependent on the type of sample. It is similar in thecase of EPDM-g-MA and of EPDM/MMt micro-composite (about 6 h). No influence of the presence ofthe Na-MMt can be noted. The induction period isslightly reduced in the case of EPDM/MMt intercalatednanocomposite and it almost disappears in the case ofthe exfoliated EPDM/MMt nanocomposite. Thus, thedegradation of the material starts shortly after thebeginning of irradiation.

After the induction period, the kinetic curves(Fig. 7a) show that the oxidation rates are similar for

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50

Fig. 7. Variations of absorbance as a function of irradiation time for

films photooxidised at lO 300 nm, 60 �C for the pristine polymer,

microcomposite, intercalated and exfoliated nanocomposites: (a) at

1713 cm�1, (b) at 808 cm�1.

the four samples (almost the same slope). This indicatesthat the filler is inert towards oxidation of the polymericmatrix, despite the interaction observed with theantioxidant. The kinetics of oxidation can be alsocharacterised by the disappearance of the unsaturationsof the diene monomer, which fits the formation of theoxidation products. The results given in Fig. 7b showthe variations of the absorbance at 808 cm�1 with timeof irradiation. These results indicate a slight reduction ofthe induction time in the case of the EPDM/MMtintercalated nanocomposite and a rather completedisappearance for the exfoliated EPDM/MMt nano-composites, which confirm the conclusions deducedfrom the curves of Fig. 7a.

These results were confirmed by the changes of theUVevisible spectra of the samples on irradiation. Theyindeed show a very fast disappearance of the antioxidantabsorption band and a shift of the absorption fronttowards longer wavelengths. Fig. 8 shows the variationsof absorbance at 280 nm versus exposure time. At first,the decrease of the absorbance indicates the consump-tion of the antioxidant and then an increase due to theformation of the photoproducts resulting from theoxidation of EPDM is observed. Again one observesa dramatic shortening of the induction period in the caseof the exfoliated nanocomposite.

4. Conclusions

The results reported in this paper about thephotooxidation of EPDM/montmorillonite nanocom-posites show that the oxidation mechanism of thepolymeric matrix is not modified by the presence ofthe clay. However, the influence of the organo-clay onthe durability of the nanocomposite material is observed

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Fig. 8. Evolution of the absorbance at 280 nm of UVevisible spectra

versus irradiation time.

85S. Morlat-Therias et al. / Polymer Degradation and Stability 90 (2005) 78e85

through the disappearance of the processing antioxidantduring the first phase of oxidation before the detectionof the oxidation of the polymeric matrix. The inductiontime is similar in the case of EPDM-g-MA and EPDM/MMt microcomposite. It is slightly reduced in the caseof EPDM/MMt intercalated nanocomposite, and italmost disappears in the case of the exfoliated EPDM/MMt nanocomposites. These results confirm formerconclusions found in the case of other polymers [5e10].Conversely, no influence of the clay on the rate ofoxidation of the polymeric matrix, once started, can beevidenced.

As the montmorillonite used is of synthetic origin anddeprived of iron, the influence of the clay on the rate ofdegradation cannot be attributed to a catalytic effect ofiron. Therefore, the adsorption of the antioxidant andadditives is most likely to be the key factor behind thephotodegradation of the exfoliated nanocomposites.The tremendous increase of accessible clay surface uponexfoliation enhances the probability of additive adsorp-tion on the solid surface and, hence, would help reducedramatically its efficiency as antioxidant agent. Never-theless, the organic moiety of the modified clay can beinvolved in the degradation, the effect being morepronounced in the case of the exfoliated sample whichcontains a larger amount of the organic cations. Theexfoliated structure appears to be more sensitive to theoxidation with higher dispersion of the organo-clay anda higher amount of organic cations.

One has to consider that because of the dramaticdecrease of the induction period resulting from thepresence of residual antioxidant or even its almost totaldisappearance, the presence of the clay results in a fasterpolymer photodegradation.

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