Journal of Food Engineering 110 (2012) 262–268

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Journal of Food Engineering

journal homepage: www.elsevier .com/locate / j foodeng

Modification of cellulose acetate films using nanofillers based on organoclays

Francisco J. Rodríguez ⇑, María J. Galotto, Abel Guarda, Julio E. BrunaCenter for the Development of Nanoscience and Nanotechnology (CEDENNA), Food Packaging Laboratory (Laben-Chile), Department of Food Science andTechnology, Faculty of Technology, University of Santiago de Chile (USACH), Santiago, Chile

a r t i c l e i n f o a b s t r a c t

Article history:Available online 11 May 2011

Keywords:Cellulose acetateMontmorilloniteOrganoclayNanocomposites

0260-8774/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.jfoodeng.2011.05.004

⇑ Corresponding author. Address: Obispo Manuel Ude Alimentos, Estación Central, Santiago, Chile. Tel.: +

E-mail address: francisco.rodriguez.m@usach.cl (F

The present work has been oriented on the development of cellulose acetate films with nanofillers ofmontmorillonite/alkylammonium (hexa- and tetra-decyltrimethylammonium) and montmorillonite/chitosan which have been synthesized using a cationic exchange process. All synthesized organoclayshave been characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fouriertransform infrared spectroscopy (FTIR). These analyses confirmed the modification of clay structureswhich proved to be dependent on the chemical structure of chosen organic precursor. On the other hand,the different organoclays have been used to produce cellulose acetate nanocomposites by solvent-castingtechnique. The nanocomposite films have been characterized by XRD, TGA, Differential scanning calorim-etry (DSC), oxygen and water vapor permeability and scanning electronic microscopy (SEM). All nano-composites obtained showed the intercalation of polymer inside the clay structure and an importantreduction of oxygen transmission rate (OTR) compared to cellulose acetate films without nanofillers.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Plastic materials derived from petroleum become indispensablematerials to our society. Excellent mechanical performance, versa-tility, lightness, durability, low cost, and easy processing, are someimportant properties of these materials. Because of this, consump-tion of these materials has grown considerably in recent decades.One of the industries in which the impact of plastic materials has be-come decisive is the food packaging industry. Thus, thermoplasticlike polyolefins (polyethylene, PE, polypropylene, and PP), polyethy-len terephthalate (PET), polivinyl chloride (PVC), and poliamides arethe most used by this industry (Marsh and Bugusu, 2007).

Despite of advantages offered by traditional plastic materials aserious problem has risen in recent years. Due to excessive consump-tion of these materials a massive accumulation of plastic waste hasbeen disposed in the environment. Considering the poor degradationof traditional plastics in the environment, they have been classified ashighly polluting agents. To avoid this negative impact, the EuropeanUnion is promoting different strategies to confront this problem.According to the European Directive on Packaging and PackagingWaste the management of packaging and packaging waste should in-clude as a first priority the prevention of packaging waste and, asadditional fundamental principles, reuse of packaging, recyclingand other forms of recovering packaging waste which allow reducingof the final disposal of such wastes. However, so far these measures

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maña 050 (9170201), Edificio56 2 7184520.

.J. Rodríguez).

have failed to reduce significantly the amount of wastes (Rudnik,2008). Thus, the use of natural polymers has emerged as an alterna-tive to face up to this problem. Nevertheless, properties such as highpermeability to gases, poor mechanical properties, and low melt vis-cosity, have restricted their use in a wide range of applications.Regarding to this, technologies oriented to modify properties of nat-ural polymers has been of great interest in the materials field. In viewof the success of nanotechnology application on the use of nanofillersto modify the properties of traditional polymeric materials (Ray andOkamoto, 2003), nanocomposites based on natural polymers havebeen considered as the next generation of eco-friendly materials(Darder et al., 2003). Therefore, it has been suggested that a majorapplication of this bio-nanocomposites will be in the developmentof new food packaging systems (Sozer and Kokini, 2009).

According to nanocomposites preparation, nanoparticles usedas fillers or additives in polymers for various desired effects arereceiving an increased interest for research and development. So,nanoparticles like carbon nanotubes (CNTs), clays and metal oxideshave been used to modify the polymer performance (Esawi et al.,2010; Vladuta et al., 2009; Wang and Guo, 2010). Concerning clays,montmorillonite (MMT) has been the most commonly employedclay mineral in the preparation of polymer composites (Hasegawaet al., 2003; Morawiec et al., 2005). To ensure good compatibilitybetween the polymer and montmorillonite in composites, this lay-ered silicate has been modified with quaternary ammonium orphosphorous salts with long alkyl chains to produce organoclays(Patel et al., 2005; Yang et al., 2007). It has been recognized thatthe intercalation of an organic surfactant between the clay layersis required in order to change the intergallery structure and to

F.J. Rodríguez et al. / Journal of Food Engineering 110 (2012) 262–268 263

increase the distance between the layers (Paul et al., 2005). In thisway, the organoclays favor the nanoparticle–polymer interaction.

Considering cellulose as the most abundant natural polymer, itsapplication in the plastic area is attracting interest as a substitutefor traditional plastics. Studies applied to cellulose are centeredon cellulose derivates because these present better processabilitythan pure cellulose. Within cellulosic derivates, cellulose acetate(CA) is of particular interest because it is a biodegradable polymerand has excellent optical clarity and high toughness, therefore thiscellulose derivate can produce films either by solvent-casting(Meier et al., 2004) or melting techniques (Mohanty et al., 2003).

Studies oriented to develop nanocomposites from cellulose ace-tate are limited. Park et al. reported the effect of a compatibilizer(Park et al., 2004a) and plasticizer (Park et al., 2004b) on the nano-composite formation using a commercial organoclay by a melt pro-cess. In these studies, it has been observed an important reductionof water vapor permeability (WVP) according to clay and plasti-cizer content; therefore, the addition of compatibilizer based onmaleic anhydride grafted cellulose acetate butyrate (CAB-g-MA) al-lowed to produce the clay exfoliation which was attributed to bet-ter interaction between CA and organoclay. Wibowo et al. (2006)used cellulose acetate, triethyl citrate and organically modifiedclay nanofillers to produce a intercalated nanocomposite whichshowed important changes on the mechanical properties. Recently,Varsha et al. (2010) also reported the decrease of WVP of celluloseacetate films using filler based on nanosilver.

The aim of the present study is the development of organoclaysfrom different cationic organic components using an ionic inter-change process and the assessment of the effect of these organoc-lays on the nanocomposites properties based on cellulose acetate.

2. Experimental

2.1. Materials

Montmorillonite (Cloisite�Na+) with a cationic exchange capac-ity (CEC) of 92.7 meq/100 g and Cloisite�30B were obtained from

4000 3500 3000 2500

34353635

34343631

34343633

3410

3434

2852Tran

smitt

ance

, %

Wavenum

(a)

(b)

(c)

(d)

(e)

2927

28502927

28522927

3635

3635

Fig. 1. Fourier transform infrared spectra of (a) montmorillonite (MMT)

Southern Clay Products Inc. Hexadecyltrimethylammonium bro-mide (P97%) and tetradecyltrimethylammonium bromide (99%)were supplied by Merck and Sigma, respectively. Chitosan, lowmolecular weight (75–85% deacetylated) and Cellulose Acetate(39.8 wt.% acetyl content. Mn ca. 30,000) were supplied by Aldrich.

2.2. Modification of montmorillonite: preparation of organoclays(OMMT)

MMT (5.0 g) was dispersed in 150 mL of distilled water andstirred with a magnetic stirrer for 1 h at 60 �C. The suspensionwas then underwent an ultrasonic treatment (Elmasonic bathS60H, 50 Hz) for 30 min at 60 �C. Alkyltrimethylammonium bro-mide (1.5 CEC) was dissolved in 50 mL of distilled water and addedto clay suspension. The suspension obtained was stirred for 1 h at60 �C and placed inside of ultrasonic bath for 30 min at 60 �C. Thesolid phase was filtered, washed with distilled water and ethanoland dried at 70 �C for 12 h. The organoclay was purified by meansof Soxhlet extraction using ethanol as solvent during 3 h. After-ward the purified solid was dried at 70 �C for 12 h. Finally, theorganoclay was ground in an analytical mill (Cole Parmer 4301-02, 20,000 rpm) and the fraction under #200 Tyler screen(75 lm) selected.

Preparation of organoclays from chitosan was similar to thealkyltrimethylammonium. However, in this case it was necessaryfirst to determine the charge capacity of chitosan (meq –NH2/gchitosan) to determine the appropriate quantity of this biopolymerto modify the structure of montmorillonite according to the CECvalue of this. Thus, the charge capacity of chitosan was determinedby means of a potentiometric titration (Jiang et al., 2003). Basicallythis method is oriented to the determination of the deacetylationdegree of chitosan through acid–base titration of protonated aminogroup from polymer using a standardized NaOH solution; however,it also allows to determine the equivalents of amino group pergram of chitosan. Unlike the alkyltrimethylammonium/MMT, thechitosan quantity corresponding to 1.0 CEC of clay (0.89 g) was dis-solved in an acetic acid solution (2 v/v%).

2000 1500 1000 500

1034

1637

1036

1637

1637

1036

1637

1637

1036

1637

1051

1641

1475

1477

ber, cm-1

1536

1469

, (b) Cloisite�30B, (c) C14OMMT, (d) C16OMMT, and (e) ChOMMT.

Table 1Results of the TGA of organoclays.

MMT Cloisite�30B C14OMMT C16OMMT ChOMMT Process

Step 1 DehydrationMass loss (%) 7.2 2.1 2.0 1.8 7.0Temperature (�C)a 88 55 107 96 106Step 2 Decomposition of organic componentMass loss (%) – 14.2 15.6 18.6 8.9Temperature (�C)a – 282 and 354 289 and 436 300 and 441 267Step 3 DehydroxilationMass loss (%) 3.4 9.6 7.8 6.4 9.6Temperature (�C)a 682 622 674 682 655

a Obtained from the first derivative of the TGA curve.

264 F.J. Rodríguez et al. / Journal of Food Engineering 110 (2012) 262–268

2.3. Preparation of cellulose acetate/OMMT nanocomposites

Nanocomposites were prepared by means of casting techniqueusing acetone as solvent. All nanocomposites consisted of 5 wt.%of OMMT. 10 g of cellulose acetate were dissolved in 150 mL ofacetone under vigorous stirring for 1 h at ambient temperature.0.53 g of OMMT was dispersed in 50 mL of acetone and sonicatedfor 30 min at room temperature. Then, the cellulose acetate solu-tion was added on organoclay suspension under vigorous stirring.This mixture was stirred during 60 min and then sonicated during30 min at room temperature. After that the mixture was added onPetri disk and dried at 40 �C in oven for 4 h. Finally, the films wereremoved from the glass disk and stored in polyethylene bags toavoid contamination.

2.4. Characterization of organoclays and nanocomposites

2.4.1. Fourier transform infrared (FTIR)This spectroscopic analysis was carried out in a Bruker IFS 66 V

spectrometer. MMT and OMMT were crushed and blended withKBr. Spectra were taken with 4 cm�1 resolution in a wave-numberrange from 4000 to 400 cm�1 with 32 scans.

2.4.2. Thermogravimetric analysis (TGA)This thermal analysis was performed on a SDT 2960 DSC-TGA

instrument (TA Instruments) at a heating rate of 20 �C/min from

2 4 6 8 10

1,85 nm

1,80 nm

1,76 nm

1,65 nm1,32 nm

1,18 nm

Inte

nsity

(a.u

)

2theta (degree)

(a)

(b)

(c)

(d)

(e)

Fig. 2. X-ray diffraction pattern of (a) MMT, (b) Cloisite�30B, (c) C14OMMT, (d)C16OMMT, and (e) ChOMMT.

room temperature to 850 �C. All analyses were performed undera flow of air.

2.4.3. Differential scanning calorimetry (DSC)Differential scanning calorimetry analyses were conducted with

a Mettler DSC-822e calorimeter. Samples were heated from 25 �Cto 300 �C at a rate of 10 �C/min. The sample weight was about8 mg. All experiments were carried out under the purge of drynitrogen.

2.4.4. X-ray diffraction (XRD)XRD analysis was carried out in a Siemens Diffractometer

D5000 (30 mA and 40 kv) using CuKa (k = 1.54 Å) radiation at roomtemperature. All scans were performed in a 2h range 2–10� at0.02�/seg.

2.4.5. Oxygen transmission rate (OTR)The OTR of films was determined with an Oxygen Permeation

Analyzer (MOCON OX-TRAN� MS2/20), equipped with a Coulox�

oxygen sensor with a sensitivity of 0.1 [cc/(m2 day atm)]. Measure-ments were carried out at 23 �C and 0% RH until a steady-state oxy-gen transmission rate was achieved. Output values were expressedas the oxygen transmission rate in [cc/(m2 day)].

2 4 6 8 10

Inte

nsity

(a.u

)

2 theta (degree)

(a)

(b)

(c)

(d)

(e)

(f)

2,16 nm

2,15 nm

2,20 nm

3,11 nm

1,26 nm

Fig. 3. X-ray diffraction pattern of (a) cellulose acetate (CA), (b) CA + MMT, (c)CA + Cloisite�30B, (d) CA + C14OMMT, (e) CA + C16OMMT, and (f) CA + ChOMMT.

F.J. Rodríguez et al. / Journal of Food Engineering 110 (2012) 262–268 265

2.4.6. Water vapor transmission rate (WVTR)The WVTR of each tested film was determined using a MOCON

Permatran W 3/31 Tester. Measurements were carried out at37.8 �C and 100% RH until a steady-state water vapor transmissionrate. An infrared detector was used for quantification of the WVTRin the film. Output values were expressed as water vapor transmis-sion rate in [g/(m2 day)].

2.4.7. Scanning electronic microscopy (SEM)The SEM micrographs of nanocomposites films were obtained

from an JSM-5410 Jeol Scanning Microscope with accelerating volt-age at 10 kV. Samples were coated with gold palladium using aSputtering System Hummer 6.2. To the cross-section analysis, thesamples were previously fractured under liquid nitrogen.

3. Results and discussion

3.1. Organoclay characterization

Fig. 1 shows the FTIR spectra of different organoclays synthe-sized, a commercial organoclay (Cloisite�30B) and montmorillonite(Cloisite�Na+). The organoclays synthesized from alkyltrimethyl-ammonium bromides showed similar bands to those of commercialorganoclay, a clay modified with methyl, tallow (�65% C18, �30%C16 and �C14), bis-2-hidroxyethyl, quaternary ammonium chlo-ride. The exclusive bands observed between 3000–2800 cm�1

(–CH2– stretching band) and 1480–1450 cm�1 (–CH2– bending

Table 2Results of DSC and TGA of nanocomposite films.

Sample DSC TGA

Tg

(�C)aTm

(�C)aDHf

(Jg�1)aTStep1

b TStep2b TStep3

b

CA 182 216 1.90 55 371 550CA + Cloisite�30B 173 206 1.29 86 381 610CA + C14OMMT 180 215 1.91 98 377 612CA + C16OMMT 178 214 1.88 86 377 598CA + ChOMMT 184 216 1.67 9 376 568

a Obtained from second scan of the DSC thermogram.b Obtained from the first derivative of the TGA curve.

CA

CA+Cloi

site3

0B

CA+14O

MMT

0

200

400

600

800

1000

1200

OTR

(cm

3 /m2 d

ay)

Sampl

Fig. 4. Effect of nanofillers on oxygen and wate

band) to Cloisite�30B, hexadecyltrimethylammonium/MMT (C16OMMT) and tetradecyltrimethylammonium/MMT (C14OMMT)confirmed the presence of the long alkyl chain of ammonium surfac-tant (Vazquez et al., 2008; Zhao et al., 2003). On the other hand, thespectrum of organoclay from chitosan/MMT (ChOMMT) showed asignal at 1536 cm�1 which has been assigned to the deformationof the protonated amine group from polysaccharide (–NHþ3 ) (Darderet al., 2003). The rest of signals from different organoclays areaccording with vibrational band characteristic of the silicate miner-als, such as, �3630 cm�1 (Al–OH stretching), �3430 cm�1 (–OHstretching from interlayer water), �1640 cm�1 (–OH bending fromabsorbed water), �1050 cm�1 (Si–O stretching) (Patel et al., 2005;Yang et al., 2007).

The presence of organic component in clay was also determinedby means of a thermogravimetric analysis (TGA). Results of TGAanalysis are resumed at Table 1. MMT, C14OMMT, C16OMMT andChOMMT showed a dehydration process under 200 �C (Xie et al.,2001a) and dehydroxylation of the aluminosilicate from 620–680 �C (Xie et al., 2002). Water elimination was more importantfor MMT and ChOMMT because the most hydrophilic charactercompared with other organoclays where the organic ammoniumcomponent is characterized by a high hydrophobic character.Regarding commercial organoclay (Cloisite�30B) a mass loss of2.1% was observed at 55 �C. This process is observed in the dehydra-tion zone; however, it could also be attributed not only to the dehy-dration process, but also to other solvent which could be used tosynthesize the commercial organoclay. Therefore, all organoclayspresented an organic material decomposition zone between 200–500 �C which evidenced the presence of organic component in theclay structure (Xie et al., 2001b). In DTG, multiple peaks were ob-served in Cloisite�30B, C14OMMT and C16OMMT. These peakshave been assigned to decomposition process of different types ofbonding of surfactant molecules in the organoclay (Xi et al.,2005). On the other hand, the ChOMMT organoclay showed adecomposition process at 267 �C which has been assigned to degra-dation and deacetylation of chitosan (Wang et al., 2005). Therefore,the ChOMMT presented the lowest incorporation of organic compo-nent (8.9 wt.%). This result could be explained due to steric hin-drance of chitosan which difficults its incorporation inside theclay structure.

CA+16O

MMT

CA+ChO

MMT

OTR WVTR

e

0

200

400

600

800

1000

1200

WVT

R (g

/m2 d

ay)

r vapor transmission rate of different films.

Fig. 5. Scanning electronic microscopy analysis of the cross-sections (left) andsurface (right) of the different nanocomposites from cellulose acetate. 9a) CA, (b)CA + Cloisite�30B, (c) CA + C14OMMT, (d) CA + C16OMMT, and (e) CA + ChOMMT.

266 F.J. Rodríguez et al. / Journal of Food Engineering 110 (2012) 262–268

At difference of TGA and FTIR analysis, the X-ray diffraction(XRD) is the most important analysis to determine the incorpora-tion of organic component inside of interlayer zone in the clay.According to XRD results (Fig. 2), all synthesized organoclaysshowed an important shifted of d001 (d-spacing) characteristic peakof montmorillonite (2h = 7.50) to lowest 2h values. This effect isproduced by the larger size of cationic organic component than so-dium cation present in unmodified clay. Therefore, the interlayerdistance in organoclays modified with quaternary ammonium ionsincreased according to the length of alkylic chain of surfactant.Thus the interlayer distance to these organoclays increased in or-der: C14OMMT (1.76 nm) < C16OMMT (1.80 nm) < Cloisite�30B(1.85 nm). These results are in good agreement with moleculardynamics simulations performed by Zeng and Yu (2008). AboutChOMMT an increase of interlayer distance was also observed,however, the XRD pattern showed an irregular distribution withat least two maximums. Similar behavior was reported in the prep-aration of chitosan nanocomposites by Darder et al. (2003). This ef-fect could be explained due to polymeric nature of chitosan whichwould produce different dispositions of polymer chain inside ofinterlayer zone with a broad interlayer distance distribution incontrast with small molecules such as surfactants.

3.2. Nanocomposites characterization

Films of cellulose acetate nanocomposites were obtained bymeans of solvent-casting technique using a 5 wt.% of each organo-clay. Cellulose acetate films are characterized by a high transpar-ency; however, the incorporation of a low content of nanofillersignificantly affected this property.

To evaluate the type of nanocomposites obtained, the filmswere analyzed by XRD (Fig. 3). All nanocomposites showed a d001

diffraction plane which was shifted to lower 2h value respect tothe corresponding organoclay. These results confirmed that cellu-lose acetate has been intercalated inside the clay structure; how-ever, this intercalation was more important to ChOMMT. Thiseffect could be due to a greater affinity between cellulose acetateand chitosan (Liu and Bai, 2005). In contrast, films fabricated withcellulose acetate and pure montmorillonite presented a slightshifted of the d001 signal. Thus, these results confirmed the impor-tance of using modified clays to produce nanocomposites.

The nanocomposite films from cellulose acetate were also ana-lyzed by differential scanning calorimetry and thermogravimetricanalysis (Table 2).

Regarding DSC analysis, the cellulose acetate without nanofillershows a Tg value of 182 �C and Tm value of 216 �C which is consis-tent with other studies (Lui et al., 1999). Nanocomposites based onCloisite�30B showed the greatest decrease in Tg, Tm and fusion en-thalpy respect to other nanocomposites. This effect could be ex-plained by the presence of organic component with alcoholicgroups (2-hidroxyethyl) inside of polymer structure which couldbe acting as a plastizicer agent decreasing the Tg value and hinder-ing the polymer cristalization. This alcoholic component would bereleased by the introduction of cellulose acetate chains in theorganoclay structure. In addition, no changes in the shape of themelting points of cellulose acetate in presence of the differentorganoclays were observed, changes that could evidence a nucleat-ing effect on the crystallization process. On the other hand, ther-mogravimetric analysis showed three processes where masslosses were observed which are in concordance with other re-ported studies (Arthanareeswaran et al., 2004). The first processocurrs at a temperatures lower than 100 �C and it represents theloss of water. The second process corresponding to the main ther-mal degradation of cellulose acetate chains (�370 �C) and the lastone is identified as the carbonization of the degradaded productsto ash at 550 �C. This thermal analysis allowed to observe that

the thermal stability of cellulose acetate is slightly increased bythe presence of organoclay in the system which is according witha nanocomposites properties (Pavlidoua and Papaspyrides, 2008).

F.J. Rodríguez et al. / Journal of Food Engineering 110 (2012) 262–268 267

It has been well accepted that clays favors the char formationwhich hinders the out-diffusion of the volatile decompositon prod-ucts, as a direct result of the decrease in permeability of nanocom-posite (Leszczynska et al., 2007).

The effect of clay on the nanocomposites permeability wasdetermined for both oxygen and water vapor by means of oxygenand water vapor transmission rate determination, respectively(Fig. 4). All nanocomposites showed an important reduction ofOTR value compared with cellulose acetate alone; however, thisreduction was not dependent on the intercalation degree of poly-mer inside of clay structure. The effect of layered silicates on gaspermeability has mainly been attributed to its high aspect ratio.These properties facilities the generation of a tortuos path whichproduces an increase of path length for permeating solute mole-cules enhancing the barrier properties of nanocomposites (Solo-vyov and Goldmen, 2008). On the other hand, the effect of clayon WVTR was not significant. Here, the high water afinity of cellu-lose acetate by water would be more important than the barrier ef-fect of layered silicate.

Finally, the different films from nanocomposites were analyzedby SEM (cross-section and film surface). Fig. 5 (left) shows SEMmicrographs of the cross-section of different films. All samples pre-sented a homogenuos structure without an important presence ofpores on the film structure as other studies based on cellulose ace-tate (Gemili et al., 2009). This fact would explain that the perme-ability process is controled by difusion rather a capillaritymechanism in these films. Fig. 5 (right) shows the SEM micro-graphs of surface of films. Here it was possible to observe impor-tant differences between nanocomposites and cellulose acetatealone; the presence of organoclay modified the surface texturewhat was more important for organoclays with higher molecularweight of organic component.

4. Conclusion

It was possible to obtain different organoclays by means ofan interchange process between montmorillonite and alkylammonium salts or chitosan. The modification of layered silicatewas dependent on the molecular weight of different organicadditives.

On the other hand, the preparation of films using solvent-cast-ing techniques allowed the polymer intercalation inside of layeredstructure of montmorillonite. Regarding to the intercalation pro-cess was confirmed the importance of organoclays to producenanocomposites. Therefore, the highest level of intercalation wasobserved to organoclays modified with chitosan. Concerning theproperties of nanocomposites, all of them showed an importantdecrease of oxygen transmission rate but not water vapor. Micro-scopic analysis evidenced a non-porous structure of cellulose ace-tate nanocomposites which explain that the permeability processis controlled by a diffusion process rather a capillary mechanism.Finally, the hybrid structures present a slight effect on the thermaldecomposition of cellulose acetate.

Acknowledgements

The authors thank to Comisión Nacional de InvestigaciónCientífica y Tecnológica, CONICYT, for the financial support fromPrograma Bicentenario de Ciencia y Tecnología (Project PDA-22)and Programa de Financiamiento Basal para Centros Científicos yTecnológicos de Excelencia (Project FB0807). To Departamento deInvestigaciones Científicas y Tecnológicas, Universidad de Santiagode Chile, DICYT-USACH (Project 080971RM). Finally, the authorsthanks to Southern Clay Products by donation of Cloisite�Na+ andCloisite�30B.

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