Preparation of polymer-clay nanocomposites and their properties

Preparation of Polymer–ClayNanocomposites and TheirProperties

QUANG T. NGUYEN, DONALD G. BAIRDDepartment of Chemical Engineering, Virginia Polytechnic Institute and State University,Blacksburg, VA 24061-0211

Received: November 27, 2005Revised: December 24, 2006

ABSTRACT: An overview of the progress in polymer nanocomposites ispresented in this paper with an emphasis on the different methods used forpreparing polymer-layered silicate (PLS) nanocomposites and the extent to whichproperties are enhanced. Other related areas that are also discussed include thetypes of polymers used in PLS nanocomposites preparation, the types of PLSnanocomposites morphologies that are most commonly achieved, the structureand properties of layered silicates, and the most common techniques used forcharacterizing these nanocomposites. C© 2007 Wiley Periodicals, Inc. Adv PolymTechn 25: 270–285, 2006; Published online in Wiley InterScience(www.interscience.wiley.com). DOI 10.1002/adv.20079

KEY WORDS: Clay, Composites, Nanocomposites, Processing, SupercriticalCO2

Introduction

D uring the last decade, interest in polymer-layered silicate (PLS) nanocomposites has

rapidly been increasing at an unprecedented level,both in industry and in academia, due to their poten-

Correspondence to: Donald G. Baird; e-mail: [email protected].

tial for enhanced physical, chemical, and mechan-ical properties compared to conventionally filledcomposites.1−6 They have the potential of beinga low-cost alternative to high-performance com-posites for commercial applications in both theautomotive and packaging industries. The earli-est motivation for the use of nanoparticles seemsto have been stimulated by the Toyota researchgroup, where the first practical application of nylon-6–montmorillonite (MMT) nanocomposite was

Advances in Polymer Technology, Vol. 25, No. 4, 270–285 (2006)C© 2007 Wiley Periodicals, Inc.

PREPARATION OF POLYMER–CLAY NANOCOMPOSITES

commercialized. With only a small MMT loading(4.2 wt%), the modulus doubled, the tensile strengthincreased more than 50%, the heat distortion tem-perature increased by 100◦C, and combustion heatrelease rate decreased by up to 63%.7−9 However,in general, all the promises and claims that theaddition of nanoparticles to polymer matrices willmiraculously lead to exceptional mechanical prop-erties have not been completely fulfilled becausethe improvements in properties seem to plateau atlevels of about 4 wt%. In nylon-6 (N6), levels of7 wt% have been reached because of hydrogen bond-ing between the amide groups and the nanoclayparticles.

Polymer nanocomposites are two-phase materialsin which the polymers are reinforced by nanoscalefillers. The most heavily used filler material is basedon the smectite class of aluminum silicate clays, ofwhich the most common representative is montmo-rillonite (MMT). MMT has been employed in manyPLS nanocomposite systems because it has a poten-tially high-aspect ratio and high-surface area thatcould lead to materials which could possibly exhibitgreat property enhancements. In addition, it is envi-ronmentally friendly, naturally occurring, and read-ily available in large quantities. Layered silicates intheir pristine state are hydrophilic. Most of the engi-neering polymers are hydrophobic. Therefore, dis-persion of native clays in most polymers is not eas-ily achieved due to the intrinsic incompatibility ofhydrophilic-layered silicates and hydrophobic engi-neering polymers.10 In order to have a successful de-velopment of clay-based nanocomposites, it is neces-sary to chemically modify a natural clay so that it canbe compatible with a chosen polymer matrix. Gen-erally, this can be done through ion-exchange reac-tions that replace interlayer cations with quarternaryalkylammonium or alkylphosphonium cations.11−13

It is well established that when layered silicates areuniformly dispersed (exfoliated) in a polymer ma-trix, the composite properties can be improved to adramatic extent. These improvements may includeincreased strength,14 higher modulus,15−20 thermalstability,21−23 barrier properties,24,25 and decreasedflammability.26−30 Hence, in order to capitalize onthe potential offered by nanoparticles in areas suchas reinforcement, barrier, and electrical conductiv-ity, higher loadings of fully dispersed nanoparti-cles must be obtained. In this article, we review thetechniques that have been used to date to exfoliatenanoparticles and we describe initial attempts at im-proving the degree of exfoliation using supercriticalcarbon dioxide.

Polymer–Clay Nanocomposites:Structures and Polymers

In general, the degree of dispersion of the clayplatelets into the polymer matrix determines thestructure of nanocomposites. Depending on the in-teraction between the clay and the polymer ma-trix, two main idealized types of polymer–clay mor-phologies can be obtained: namely, intercalated andexfoliated (Fig. 1). The intercalated structure resultsfrom penetration of a single polymer chain into thegalleries between the silicate layers, resulting in for-mation of alternate layers of polymer and inorganiclayers. An exfoliated structure results when the indi-vidual silicate layers are completely separated anddispersed randomly in a polymer matrix. Usually ex-foliated nanocomposites are preferred because theyprovide the best property improvements.31

Since the remarkable improvements in the ma-terial properties in a nylon-6/clay nanocompositedemonstrated by the Toyota research group,33

numerous other polymers have been investigatedby many researchers around the world. Theseinclude, but are not limited to, polypropylene,34−79

polyethylene,80a−89 polystyrene,90−96

poly(ethylene oxide),97−101 polycaprolactone,102,103

polyimides,104−121 polyamides,122−129 poly(ethyleneterephthalate),130−136 polycarbonate,137,138

polyurethane,139 and epoxy resins,140−144 Thereare other polymers that have been reported in theliterature, but it is not feasible to cite them all here.Additional information can be found in a paperby Sur et al.145 who had cited many referencesregarding other polymers.

Structure and Propertiesof Layered Silicates

To understand the complex morphologies thatoccur in the polymer-layered silicate nanocompos-ites, it is important to review the structural de-tails of layered silicates and their properties. Themost heavily used filler materials in the fabrica-tion of PLS nanocomposites are based on the 2:1layered structure also known as phyllosilicates, ofwhich the most common representative is montmo-rillonite (MMT).146 Although MMT is most com-monly used, other layered silicates in the same

Advances in Polymer Technology DOI 10.1002/adv 271


FIGURE 1. Schematic illustrations of two types of polymer-layered silicate morphologies: (left) intercalated and (right)exfoliated (after Sinha-Ray and Okamoto32).

general family are also used, such as hectorite,saporite, mica, talc, vermiculite.147,148 The MMTcrystal structure is made up of a layer of alu-minum hydroxide octahedral sheet sandwiched be-tween two layers of silicon oxide tetrahedral sheets(Fig. 2).149 The nominal composition of MMT isNa1/3(Al5/3Mg1/3)Si4O10(OH)2.150 The layer thick-ness of each platelet is on the order of 1 nm, andthe lateral dimension is approximately 200 nm.150

FIGURE 2. Structure of 2:1 layered silicate showing two tetrahedral sheets of silicon oxide fused to an octahedral sheetof aluminum hydroxide (after Sinha-Ray and Okamoto32).

These clay platelets are stacked on each otherand held together through van der Waal forcesand are separated from each other by 1 nm gaps(galleries).146 These galleries are usually occupiedby cations, normally alkali and alkaline-earth cationssuch as Na+ and K+, which counterbalance the neg-ative charges generated from isomorphic substitu-tion within the layers (for montmorillonite, Al3+

replaced by Mg2+).146 It is well established that the

272 Advances in Polymer Technology DOI 10.1002/adv


key in preparing PLS nanocomposites is to obtain ex-foliation of the large stacks of silicate nanoplateletsinto individual layers.151,152 By analogy with poly-mer blends, the physical mixture of silicate lay-ers and polymer matrix may not form a nanocom-posite due to the unmatched chemical affinity be-tween the two. Thus, in order to have a success-ful development of clay-based nanocomposites, itis necessary to chemically modify a naturally hy-drophilic silicate surface to an organophilic one sothat it can be compatible with a chosen polymermatrix. Generally, this can be done through ion-exchange reactions by replacing interlayer cationswith quarternary alkylammonium or alkylphospho-nium cations (Fig. 3).153−155 Ion-exchange reactionswith cationic surfactants such as those mentionedabove render the normally hydrophilic silicate sur-face organophilic, thus making it more compatiblewith nonpolar polymers. These cationic surfactantsmodify interlayer interactions by lowering the sur-face energy of the inorganic component and improvethe wetting characteristics with the polymer.153,154

Furthermore, they can provide functional groupsthat can react with the polymer or initiate poly-merization of monomers and thereby improve thestrength of the interface between the polymer andinorganic component.150,153,154

FIGURE 3. Schematic representation of acation-exchange reaction between the silicate and analkylammonium salt (after Zanetti et al.146).

Techniques Used forCharacterization ofNanocomposites

In developing and optimizing nanocomposites,one needs to know the degree of exfoliation of aparticular sample and compare it to other sam-ples. A number of methods have been reportedin the literature for this purpose.156−169 Wide an-gle X-ray diffraction (WAXD) analysis and trans-mission electron microscopy (TEM) observation aregenerally the two methods that have been used totypically establish the structure of nanocomposites.WAXD is most commonly used to probe nanocom-posite structure.170 The nanocomposite structure,namely, intercalated or exfoliated, may be identi-fied by monitoring the position, shape, and inten-sity of the basal reflections from the distributed sil-icate layers. WAXD can offer a convenient methodto determine the interlayer spacing of the silicatelayers in the original layered silicates and in in-tercalated nanocomposites, but not much can beconcluded about the spatial distribution of the sil-icate layers.149 In addition, because some layeredsilicates initially do not exhibit well-defined basalreflections, peak broadening and intensity decreasesare very difficult to study systematically. Thus,conclusions based solely on WAXD patterns areonly tentative when concerning the mechanism ofnanocomposite formation and their structure. Tosupplement the deficiencies of WAXD, TEM can beused. TEM allows a qualitative understanding of theinternal structure, spatial distribution of the variousphases, and views of the defect structure throughdirect visualization.149 Together, TEM and WAXDare essential tools for evaluating nanocompositestructure.156 TEM is time consuming and gives qual-itative information on selected regions of the sample,whereas low-angle peaks in WAXD allow quantifica-tion of changes in layer spacing. Occasionally, smallangle X-ray scattering (SAXS) can also be used tocharacterize the structure of nanocomposites. SAXSis useful when layer spacings exceed 6–7 nm inintercalated nanocomposites or when the layers be-come relatively disordered in exfoliated nanocom-posites. Recent simultaneous SAXS and WAXDstudies yielded quantitative characterization ofnanostructure and crystallite structure in nylon-6based nanocomposites.157



Methods Used for the Synthesisof Polymer–ClayNanocomposites

The key to the successful development of clay-based nanocomposites is to achieve exfoliation ofthe layered silicate in the polymer matrix. A numberof PLS nanocomposite preparation methods havebeen reported in the literature. The three most com-mon methods to synthesize PLS nanocompositesare intercalation of a suitable monomer and subse-quent in situ polymerization, intercalation of poly-mer from solution, and polymer melt intercalation.In the in situ polymerization method (Fig. 4), themonomer is used directly as a solubilizing agentfor swelling the layered silicate. Subsequent poly-merization takes place after combining the silicatelayers and monomer, thus allowing formation ofpolymer chains between the intercalated sheets.146

The second method involves intercalation of poly-mer from solution (Fig. 5). This method requires asuitable solvent that can both solubilize the poly-mer and swell the silicate layers. When the layeredsilicate is dispersed within a solution of the poly-mer, the polymer chains intercalate and displace thesolvent within the gallery of the silicate.146 A PLSnanocomposite is obtained upon the removal of thesolvent, either by solvent evaporation or polymerprecipitation.174−176 The drawbacks in these two pre-viously mentioned methods are the requirement ofsuitable monomer/solvent or polymer solvent pairsand the high costs associated with the solvents, theirdisposal, and their impact on the environment. Thelast method, melt intercalation (Fig. 6), does not re-quire the use of a compatible solvent or suitablemonomer. In this method, a polymer and layered sil-icate mixture is heated under either batch or contin-

FIGURE 4. Schematic representation of PLSnanocomposite obtained by in situ polymerization (afterZanetti et al.146).

FIGURE 5. Schematic representation of PLSnanocomposite obtained by intercalation of polymer fromsolution (after Zanetti et al.146).

uous shear (in an extruder) above the softening pointof the polymer.146 During the heating process, poly-mer chains diffuse from the molten polymer into thesilicate galleries to form either intercalated or exfo-liated depending on the degree of penetration.177,178

This method has become the mainstream for the fab-rication of PLS nanocomposites in recent years179,180

because it is simple, economical, and environmen-tally friendly. However, melt mixing seems to beonly partially successful since concentrations of ex-foliated silicates greater than about 4 wt% have notbeen possible.

METHOD OF IN SITU INTERCALATIVEPOLYMERIZATION

The field of PLS nanocomposites gained tremen-dous attention recently due to the accomplishmentswith a N6/MMT nanocomposite from the Toyota re-search group,80b even though the method of in situpolymerization has long been known.153,154 Theirfindings showed that with only very small amountsof layered silicate loadings, the thermal and mechan-ical properties had improved remarkably. They firstdiscovered the ability of ε-caprolactam monomerto swell α,ω-amino acids (COOH (CH2)n − 1 NH+

2 ,with n = 2,3,4,5,6,8,11,12,18) modified Na+-MMTat 100◦C and subsequently to initiate its ring-opening polymerization to obtain N6/MMT



FIGURE 6. Schematic representation of nanocompositeobtained direct melt intercalation (after Zanetti et al.146).

nanocomposites.181 They chose the ammoniumcation of ω-amino acids for the intercalation ofε-caprolactam because these acids catalyze ring-opening polymerization of ε-caprolactam. Theyshowed that the swelling behavior of ω-amino acidmodified MMT is strongly affected by the numberof carbon atoms in the α,ω-amino acids, suggest-ing that the extent of intercalation of ε-caprolactammonomer is high when the number of carbon atomsin the ω-amino acid is high. A more detailed descrip-tion of the process can be found in Usuki et al.182 Theauthors also demonstrated that intercalative poly-merization of ε-caprolactam could be achieved evenwithout the organic modification of MMT. However,it was proven that the degree of intercalation of ε-caprolactam seemed to be sensitive to the nature ofthe acid used.

Messersmith and Giannelis183 utilized thismethod in the preparation of poly(ε-caprolactam)-based nanocomposites. They modified MMT usingprotonated aminolauric acid and dispersed the mod-ified MMT in liquid ε-caprolactone before polymer-izing at high temperature. The nanocomposites wereprepared by mixing up to 30 wt% of the modi-fied MMT with ε-caprolactone for a few of hours,followed by ring-opening polymerization with stir-ring at 170◦C for 48 h. Wang and Pinnavaia184 usedthis poly(ε-caprolactone) (PCL) based nanocom-posites synthesis technique for the preparation ofpolyurethane–MMT nanocomposites. WAXD anal-yses of these nanocomposites showed the formationof an intercalated structure.

Polystyrene-based nanocomposites were pre-pared using this in situ intercalative polymerization

technique by Akelah and Moet.185,186 Modified Na+-MMT and Ca2+-MMT with vinylbenzyltrimethylammonium cation were used for the preparationof these nanocomposites. First, modified clays weredispersed in various solvent and cosolvent mixturessuch as acetonitrile, acetonitrile/toluene, and ace-tonitrile/THF by stirring for 1 h under a N2 at-mosphere. Then N-N′-azobis(isobutyronitrile) wasadded to the stirred solution, and finally, polymer-ization of styrene was carried out at 80◦C for 5 h. Theresulting nanocomposites were obtained after pre-cipitation of the colloidal suspension in methanol,filtered off, and dried. In this approach, interca-lated polystyrene/MMT nanocomposites were pro-duced. The degree of intercalation completely de-pends upon the nature of the solvent used. Althoughthe polystyrene (PS) is well intercalated, one draw-back in this procedure is that the macromoleculeproduced is not a pure PS, but rather a copolymer be-tween styrene and vinylbenzyltrimethylammoniumcations.

In a similar approach, Doh and Cho187 preparedPS-based nanocomposites with several differentquaternary alkylammonium cations incorporated inNa+-MMT. They found the resulting materials, evenwith MMT loading as low as 0.3 wt%, showed an ex-pansion of interlayer distance. Also, they exhibitedhigher thermal stability compared with the virginpolystyrene. In addition, they found that the struc-tural affinity between styrene monomer and the or-ganically modified MMT plays an important role inthe final structure and properties of the nanocom-posites. Weimer et al.188 also used this concept in thepreparation of PS/MMT nanocomposites. WAXDanalyses together with TEM observations showedexfoliation of the layered silicate in the PS matrix.No other properties, such as mechanical properties,were reported.

Polyethylene/layered silicate nanocompositeshave also been prepared by in situ intercalative poly-merization of ethylene using the polymerization-filling technique.86 WAXD and TEM analysesshowed the formation of exfoliated nanocompos-ites with up to 3.4 wt% MMT. In the absence ofa chain transfer agent, the tensile properties ofthese nanocomposites were poor and essentiallyindependent of the nature and content of the sil-icate. Upon chain transfer agent addition, the re-sulting nanocomposites exhibited improvements inmechanical properties. With about 3.4 wt% MMTloading, Young’s modulus increased roughly 85%.

Polyethylene terephthalate (PET) has also beenstudied using this technique. There are many



literature reports on the preparation and character-ization of PET/clay nanocomposites,130−136 but noreports give a detailed description of the prepara-tive method. For example, one report presents thepreparation of a PET nanocomposite by in situ poly-merization of a dispersion of organoclay in water.However, characterization of the resulting compos-ite was not reported.130 In this report, the authorsclaim that water serves as a dispersing aid for theintercalation of monomers into the galleries of theorganoclay.

INTERCALATION OF POLYMERFROM SOLUTION

Aranda and Ruiz-Hitzky101 reported the firstpreparation of polyethylene oxide (PEO)/MMTnanocomposites by this method. They conducteda series of experiments to intercalate PEO(Mw = 105 g/mol) into Na+-MMT using differ-ent polar solvents including water, methanol, ace-tonitrile, and mixtures (1:1). The nature of thesolvents, with polarity of the medium being a de-termining factor, is critical in facilitating the in-sertion of polymers between the silicate layers inthis method.154,189 The high polarity of water causesswelling of Na+-MMT. Methanol is not suitable asa solvent for high-molecular weight (HMW) PEO,whereas water/methanol mixtures appear to be use-ful for intercalation, although cracking of the re-sulting materials is frequently observed. Wu andLerner190 reported the intercalation of PEO into Na+-MMT and Na+-hectorite using this method in ace-tonitrile. Diffusion of one or two polymer chains inbetween the silicate layers was observed and theintersheet spacing increased from 0.98 to 1.36 and1.71 nm, respectively. In another study, Choi et al.191

prepared PEO/MMT nanocomposites by a solvent-casting method using chloroform as a cosolvent.Intercalated structure was observed for the result-ing nanocomposites as confirmed by WAXD analy-ses and TEM observations. Other authors192,193 havealso used the same method and same solvent for thepreparation of PEO/clay nanocomposites.

Jeon et al.80a applied this technique to thepreparation of nanocomposites of nitrile-basedcopolymer and polyethylene-based polymer withorganically modified MMT. A partially exfoliatedstructure was obtained as revealed by the TEManalysis, where both stacked intercalated and ex-foliated silicate layers coexist. This observation wasconfirmed by the WAXD analysis, which reveals abroad diffraction peak that has been shifted toward

a higher d-spacing. The same authors also presentedHDPE-based nanocomposites prepared by dissolv-ing HDPE in a mixture of xylene and benzonitrilewith dispersed organically modified layered sili-cates (OMLS).80a Syndiotactic polystyrene (s-PS) or-ganically modified clay nanocomposites have alsobeen prepared by the solution intercalation tech-nique by mixing pure s-PS and organophilic claywith adsorbed cetyl pyridinium chloride.195 TheWAXD analyses and TEM observations showed anearly exfoliated structure of these nanocomposites.

Sur et al.196 applied this solvent-based techniqueto the preparation of polysulfone (PSF)-organoclaynanocomposites. PSF/organoclay nanocompositeswere obtained by mixing the desired amount ofthe organoclay with PSF in DMAC at 80◦C for24 h. WAXD and TEM analyses indicated exfoliationof the organoclay in the nanocomposites. Polylac-tide (PLA) or poly(ε-caprolactone)-based nanocom-posites have also been produced197,198a using thistechnique, but neither intercalation nor exfolia-tion was obtained as the clay existed in the formof tactoids, consisting of several stacked silicatemonolayers.

In another report,119 polyimide/MMT nanocom-posites were prepared using solutions of poly(amicacid) precursors and dodecyl-MMT using N-methyl-2-pyrrolidone as a solvent. FTIR, TEM, and WAXDshowed exfoliated nanocomposite structures at lowMMT content (<2 wt%) and partially exfoliatedstructures at high-MMT content. Polyimide hybridsin thin-film form display a 10-fold decrease in per-meability toward water vapor at 2 wt% clay loadingcompared to the neat polyimide film.

Zhong and Wang198b studied the exfoliation ofsilicate nanoclays in organic solvents such as xyleneand toluene. In particular, they exposed the solu-tions of clay loadings from 1 to 10 wt% to ultrasoundfor several hours. When the clay particles were ex-foliated, the solutions became transparent and ex-tremely viscous. The exfoliation was confirmed byX-ray diffraction measurements, where a peak asso-ciated with diffraction from the silicate layers dis-appeared. Furthermore, they observed that solventssuch as tetrahydrofuran (THF) did not lead to ex-foliation as evidenced by a low-viscosity turbid so-lution. Hence, the importance of the compatibilitybetween the dispersing medium and the modifiedclay for exfoliation was established. Although theycarried out an extensive study of the rheology ofthe exfoliated clay solutions, they did not considerhow this information would be used in generatingthermoplastic composites.



In another study, Avella et al.198c investigated thecrystallization behavior and properties of exfoliatedisotactic polypropylene (iPP)/organoclay nanocom-posites prepared by a solution technique. From theXRD results, it was shown that the nanocompositefilled with 1 wt% of organoclay possesses exfoliatedstructure, whereas the sample with 3 wt% containsboth exfoliated and intercalated structures. Above3 wt%, clay aggregates were observed. Young’smoduli increased with increasing clay content andreached the maximum at 3 wt% filler content. Above3 wt%, tensile moduli actually decreased due tothe agglomeration and collapse of the clay layers.Regarding the crystallization behavior, the authorsobserved spherulites with positive birefringence inthe optical microscope images for the crystallizediPP filled with 1% of organoclay. Also, the nucle-ation density increased with increasing nanopar-ticle content, indicating that the nanoparticles be-have as nucleating agents. While a lot of interest-ing observations were presented, this study wasonly able to achieve exfoliated and stable structuresonly up to 1 wt% clay content. Also, it would beuseful to conduct rheological experiments to deter-mine the nanocomposites’ behavior of the exfoli-ated and nonexfoliated structures. This study, alongwith other studies using solvent-based technique,requires a suitable polymer/solvent pair, which canbe expensive and environmentally unfriendly dueto the use of organic solvents.

MELT INTERCALATION

This method was first demonstrated by Vaiaet al.199 in 1993, which stimulated the revival of in-terest in PLS nanocomposites. In recent years, thismethod has become mainstream for the fabricationof PLS nanocomposites179,180 because it is simple,economical, and environmentally friendly.

Vaia and Giannelis200,201 applied a mean-field sta-tistical lattice model to study the thermodynamic is-sue associated with nanocomposite formation. Theyreported that calculations based on this mean-fieldtheory agree well with the experimental results.Details regarding this model and explanation arepresented in Vaia and Giannelis.200 The authorsclaimed that from their theoretical model, entropicand energetic factors primarily determine the out-come of nanocomposite formation via polymer meltintercalation. General guidelines may be establishedfor selecting potentially compatible polymer/OMLSsystems based on the Vaia and Giannelis study.200

According to the authors, polymers containing po-lar groups capable of associative interactions, suchas Lewis-acid/base interactions or hydrogen bond-ing, lead to intercalation. The greater the polarizabil-ity or hydrophilicity of the polymer, the shorter thefunctional groups in the OMLS should be in orderto minimize unfavorable interactions between thealiphatic chains and the polymer.200

Vaia et al.199 were the first to apply the melt inter-calation technique in the preparation of polystyrene(PS)/OMLS based nanocomposites. The resultinghybrid shows a WAXD pattern corresponding tothat of the intercalated structure. These authorsalso carried out the same experiment under thesame experimental conditions using nonmodifiedNa+-MMT, but WAXD patterns did not show anyintercalation of PS into the silicate galleries, em-phasizing the importance of polymer/OMLS inter-actions. Vaia et al.202 and Shen et al.203 also ap-plied the same technique to the preparation ofPEO/Na+-MMT and PEO/OMLS nanocomposites,respectively.

Liu et al.204a first applied melt intercalation tech-nique in the preparation of a commercially availablenylon-6 with octadecylammonium-MMT nanocom-posites, using a twin-screw extruder. WAXD pat-terns and TEM observations indicate exfoliatednanocomposite structures with MMT less than5 wt%. At a loading of 4.2 wt% MMT, the yieldstrength increased from 68.2 to 91.3 MPa, the ten-sile modulus increased from 3.0 to 4.1 GPa, and theheat distortion temperature increased from 62◦C to112◦C.

Fornes et al.204b investigated the effect of organ-oclay structure on nylon-6 nanocomposite morphol-ogy and properties. To study this effect, a series of or-ganic amine salts were ion exchanged with sodiummontmorillonite (Na+-MMT) to form organoclaysvarying in amine structure or exchange level relativeto the starting clay. Each organoclay was melt-mixedwith a high-molecular grade of N6 (Capron B135WP,with Mn = 29,300) using a twin-screw extruder.Figure 7 summarizes the structure and correspond-ing nomenclature of various amine compounds usedfor the modification of Na+-MMT using the ion-exchange method. Figure 8 summarizes WAXD pat-terns and TEM observations for one representativenanocomposite. From the WAXD analysis, the au-thors observed that the galleries of the organoclaysexpand in a systematic manner to accommodate themolecular size and the amount of amine surfactantexchanged for the Na+-MMT. They also identifiedthree distinct surfactant structural effects that led to



FIGURE 7. (a) Molecular structure and nomenclature of amine salts used to organically modify Na+−MMT by ionexchange. The symbols M: methyl, T: tallow, HT: hydrogenated tallow, HE: 2-hydroxy-ethyl, R: rapeseed, C: coco, and H:hydrogen designate the substitutents on the nitrogen. (b) Organoclays used to evaluate the effect of structural variationsof the amine cations on nanocomposite morphology and properties (after Fornes et al.204b).

greater extents of exfoliation, higher stiffness, and in-creased yield strengths for the nanocomposites: de-creasing the number of long alkyl tails from two toone tallow, use of methyl rather than hydroxy-ethylgroups, and finally, use of an equivalent amountof surfactant on the clay as opposed to an excessamount.

Gilman et al.205 reported the preparation ofpolyamide-6 (PA6) and PS-based nanocompositesof MMT modified with trialkylimidazolium cations.WAXD analyses and TEM observations showed anexfoliated structure for a PA6-based nanocomposite,whereas for a PS/MMT system, mixed intercalatedand exfoliated structures were obtained.

In another study, Huang et al.137 reported thesynthesis of a partially exfoliated bisphenol polycar-bonate nanocomposite prepared by using carbonatecyclic oligomers and dimethylditallowammonium-exchanged MMT. WAXD patterns indicated that ex-foliation of this OMLS occurred after mixing withthe cyclic oligomers in a Brabender mixer for 1 hat 180◦C. Subsequent ring-opening polymerization

of the cyclic oligomers converted the matrix into alinear polymer without disruption of the nanocom-posite structure. TEM imaging revealed that partialexfoliation was obtained, although no indication oflayer correlation was observed in the WAXD.

Lee and Huang et al. prepared poly(etherimide)(PEI)/MMT nanocomposites by melt-blendinghexadecylamine-modified MMT and PEI at 350◦C toobtain thermoplastic poly(etherimide) (PEI)-basednanocomposites.206,207a The dispersion of the MMTlayers within the PEI matrix was verified usingWAXD and TEM. From WAXD patterns, it wasassumed that exfoliation was achieved because ofthe lack of diffraction peaks. However, TEM ob-servations revealed stacked silicate layers heteroge-neously dispersed in the polymer matrix.

Finally, in a different study, Liu and coworkersinvestigated the effects of clay concentration andprocessing-induced clay dispersion on the struc-ture and properties of PA6/clay nanocomposites.207b

The PA6/clay nanocomposites were prepared viaa melt-compounding method using a Brabender



FIGURE 8. Morphological analysis of nanocompositesbased on HMW nylon-6 and the organoclays M3(HT)1and M2(HT)2-95. (a) WAXD patterns and TEM images of(b) M3(HT)1 and (c) M2(HT)2-95 based nanocomposites.The concentration of MMT in the M3(HT)1 andM2(HT)2-95 nanocomposites are 2.9 and 3 wt% (afterFornes et al.204b).

twin-screw extruder. The nanostructure and mor-phology of PA6/clay nanocomposites were exam-ined using XRD, TEM, and optical microscopy.By combining XRD and TEM studies, the au-thors observed mostly exfoliated structure in thenanocomposites at low concentration (<5 wt%),

while above it intercalated clay aggregates wereobserved. Young’s moduli and tensile strength ofthe PA6/clay nanocomposites were seen to increasewith increasing clay concentration up to 5 wt%.Above 5 wt%, yield strength actually dropped. Theauthors also made another interesting observationregarding an uneven clay distribution resulting frominjection molding, which affected the crystallinestructure of PA6. It would be useful to know howthese PA6/clay nanocomposites behave rheologi-cally at different clay concentrations. Regarding theprocessing conditions, the processing temperatureof PA6/clay nanocomposites was a bit high, so itmight be interesting to find out whether there wasany degradation in the organic modifiers and how itcould have affected the final structure and propertiesof the nanocomposites.

Different processing machinery, conditions, andclay modifiers can significantly affect the result-ing nanocomposites. A paper by Dolgovskij et al.shows the effect of different mixer types on the ex-foliation of polypropylene (PP) nanocomposites.207c

The mixers examined in this study were DACA mi-crocompounder corotating twin-screw, Haake inter-nal mixer, DSM corotating twin-screw, KWP ZSK30twin-screw, and a two-step multilayer extrusionusing a Prism 16 mm corotating twin-screw ex-truder followed by a Davis–Standard single-screwextruder. The best dispersion of clay, thus the bestmechanical and thermal properties, was achieved byusing the DACA mixer. This effectiveness could bedue to the right balance of shear rate and residencetime in the DACA mixer. Another paper by Dennis etal. also shows the important impact of extruder typeson the delamination and dispersion of layered sili-cate nanocomposites.207d Although not an exhaus-tive study of mixer types, they included enough va-riety to demonstrate the importance of the processfor making nanocomposites. The extruders includedin that study were a Leistritz 34 mm modular in-termeshing, counterrotating twin-screw extruder, aLeistritz 34 mm modular nonintermeshing, coun-terrotating twin-screw extruder, a Killion 25.4 mmsingle-screw extruder outfitted with a high-intensitymixing head, and a Japan Steel Works 30 mm modu-lar self-wiping corotating twin-screw extruder. Thenonintermeshing twin-screw extruder was provento yield the best delamination and dispersion ofthe clay, hence the most property improvement.Other processing conditions, such as temperatureand screw speed, can also affect the propertiesof nanocomposites as demonstrated by Modestiet al.207e In this study, the authors demonstrated



the influence of varying the processing temperatureand screw speed on the enhancement of mechanicalproperties of polypropylene nanocomposites. UsingXRD, SEM, TEM, and a dynamometer as character-ization methods, the authors observed the best re-sults at high-screw speed (350 rpm) and low-barrelprofile temperature (170◦C–180◦C). At these process-ing conditions, maximum shear stress exerted on thepolymer was achieved, which helped shearing andbreaking the clay platelets apart more effectively.Clay types can also have critical effects on the mor-phology and physical properties of the nanocom-posites. Thus, depending on the polymer matrix, theright clay surface modifier must be selected in orderto achieve the best delamination and dispersion. Leiet al. studied the effect of clay types on the process-ing and properties of polypropylene nanocompos-ites and showed that the surface treatment of claycan improve the clay dispersion in the PP matrix.207f

The clays included in the study were Cloisite 15A,Cloisite 20A, Nanocor I30E, and Nanocor I31PS.Cloisite 15A and 20A were modified by long-alkylchains with quaternary ammonium groups, whereasI30E and I31PS were modified by long-alkyl chainswith amine groups. It was found that nanocompos-ites with alkyl-onium ion treated clays have highermoduli and better thermal stability than the oneswith alkyl amine treated clays. A similar study byDan et al. also shows the effect of clay modifierson the morphology and properties of thermoplasticpolyurethane/clay nanocomposites.207g This is notan exhaustive list of work that studied the effectsof processing machinery, conditions, and clay mod-ifiers on the resulting nanocomposites. However,it includes enough to show the importance manyprocessing factors have on the melt compound-ing of nanocomposites. Therefore, when preparingnanocomposites using the melt-compounding tech-nique, careful selection of mixer type, clay modifier,and processing conditions must be made in orderto have a successful development of good qualitynanocomposites.

NANOCOMPOSITE SYNTHESIS WITH THEAID OF SC-CO2

Supercritical fluids have been receiving atten-tion recently in various applications such as in thefood and pharmaceutical industries as well as inthe plastics industry. Particularly, supercritical car-bon dioxide (sc-CO2) has been used widely in manyapplications because it is environmentally friendly,nontoxic, relatively low cost, and nonflammable

compared to other supercritical fluids.208 High vis-cosity is usually a major problem in the process-ing of high-molecular weight polymers or complexmixtures of particle-filled polymers. To overcomethis problem, sc-CO2 can be used as a plasticiz-ing agent to lower the viscosity of various poly-mer melts.209−211 Under ambient conditions, CO2 isa gas that makes its removal from the polymericproduct easy. At near critical conditions, as Berensand Huvard212 point out, CO2 behaves like a po-lar, highly volatile organic solvent, which swellsand plasticizes polymers when it interacts withthem. Montmorillonite is a typical swellable mineralbecause it contains alkali metal ions between thesilicate sheets, and, therefore, it can be swollen inpolar solvents such as water and sc-CO2.150 In po-lar solvents, the basal distance of the silicate sheetsexpands and finally the silicate sheets come to ex-foliate into individual sheets. These concepts can beutilized in the fabrication of PLS nanocomposites asa few authors have reported.213,214 However, the ex-tent of success is questionable and further research isneeded because most authors did not investigate orreport quantitatively the improvements in the mate-rials’ properties.

To date, there are only a few papers that have re-ported on the use of supercritical carbon dioxide asan alternative route for the preparation of polymer–clay nanocomposites.213,214 Zerda et al.214 usedsc-CO2 for the synthesis of poly(methylmethacrylate)-layered silicate intercalatednanocomposites. The authors presented a syn-thetic route to produce nanocomposites withsignificantly high concentrations of OMLS. OMLSused in this experiment were Cloisite 15A, 20A,and 25A from Southern Clay Products, Gonzales,Texas. At high levels of OMLS (>20 wt%), theviscosity was apparently high and was overcome byusing sc-CO2 as a reaction medium. Homogeneousdispersion of monomer, initiation, and subsequentpolymerization all occur under a significantlyreduced viscosity in this medium. The detailedexperiments can be found in Caskey and Lesser.215

The authors reported a homogeneous morphology,which was aided by sc-CO2, in the intercalatednanocomposites containing as high as 40 wt% ofOMLS. At this loading, only a 50% increase inmodulus was observed.

In a different approach, Wingert et al.216 investi-gated the effect of nanoclay and sc-CO2 on polymermelt rheology in an extrusion process. Polystyreneand organophilic montmorillonite (Cloisite 20A)were used in the fabrication of the nanocomposite.



An extrusion slit die rheometer with backpressureregulator was used to measure the shear viscosityof polystyrene/CO2/nanoclay melts. The authorsobserved that, without the presence of sc-CO2, theviscosity of the nanocomposite (<5 wt% OMLS) in-creased with nanoclay loading. With the presenceof sc-CO2, the nanocomposite melt is swollen, andthe nanoclay acts to reduce viscosity compared tothe pure polystyrene/CO2 system. No satisfactoryexplanation of why the nanoclay lubricates the flowwas given by the authors. No information regard-ing nanocomposite structures nor material proper-ties was reported.

Recently, another approach to prepare polymernanocomposites using sc-CO2 in the melt intercala-tion process was reported by Lesser and Manuel.213

Here, a study of the effect of sc-CO2 on the melt inter-calation process and on the final structure and mor-phology of polymer–clay nanocomposites is pre-sented. sc-CO2 was absorbed into the nanoclay par-ticles and pellets in a pressurized hopper. Hence,mixing of the nanoclays with sc-CO2 was done bymeans of diffusion, which may limit the amounts ofCO2 absorbed. High-density polyethylene (HDPE)and unmodified montmorillonite (Cloisite Na+) andsurface-modified montmorillonite (Cloisite 15A)were used in the preparation PLS nanocompos-ites. Details of the processing system can be foundin Garcia-Leiner and Lesser.217,218 WAXS and TEMwere used to analyze the resulting nanocomposites.In summary, the authors found that, regardless of theclay nature (modified or unmodified), the presenceof sc-CO2 promotes significant increase in the basalspacing of the clay, and thereby may enhance theease of the polymer intercalation into the galleries ofthe clay. The increases in the clays’ d-spacings werereported to be as much as 100%. Properties of thenanocomposites were not reported.

Conclusions

There are certain limitations and drawbacks toeach of the techniques used to disperse nanoparti-cles in polymer matrices. For the methods of inter-calation of polymer from solution and in situ poly-merization, the drawback is the requirement of asuitable solvent. It has, in fact, been shown that inter-calation only occurs for certain polymer/solvent ormonomer/solvent pairs. Application of these meth-ods in the production of industrially significant poly-

mers may, thus, be impracticable, especially in viewof the high costs associated with solvents them-selves, their disposal and their environmental im-pact. Furthermore, the extent of intercalation com-pletely depends upon the nature of solvent used.For the melt intercalation technique, the drawbackis its dependence on the processing conditions, andfavorable interactions between the polymer and theclay are required. Thus far in most studies, only ex-foliated nanocomposite structures with up to 5 wt%MMT can be achieved. In order to capitalize on thepotential offered by nanoparticles in areas such asreinforcement, barrier, and electrical conductivity,higher levels of fully dispersed nanoparticles mustbe reached. The use of supercritical CO2, if appro-priately used, may lead to higher concentrations ofexfoliated nanoclay particles.

References

1. Usuki, A.; Kojima, Y.; Kawasumi, M.; Okada, A.; Fukushima,Y.; Kurauchi, T.; Kamigaito, O. J Mater Res 1993, 8, 1185.

2. Kojima, Y.; Usuki, A.; Kawasumi, M.; Okada, A.; Kurauchi,T.; Kamigaito, O. J Polym Sci, Part A: Polym Chem 1993, 31,983.

3. Kojima, Y.; Usuki, A.; Kawasumi, M.; Okada, A.; Kurauchi,T.; Kamigaito, O. J Polym Sci, Part A: Polym Chem 1993, 31,1755.

4. Liu, L.; Qi, Z.; Zhu, X. J Appl Polym Sci 1999, 71,1133.

5. Lan, T.; Kaviratna, D.; Pinnavaia, J. Chem Mater 1994, 6, 573.6. Gilman, W.; Morgan, A.; Giannelis, P.; Wuthenow M.;

Manias, E. In Flame Retardancy 10th Annual BBC Confer-ence Proceedings, 1999; p. 1.

7. Okada, A.; Kawasumi, M.; Usuki, A.; Kojima, Y.; Kurauchi,T.; Kamigaito, O. Mater Res Soc Symp Proc 1990, 171, 45.

8. Usuki, A.; Kawasumi, M.; Kojima, Y.; Okada, A.; Kurauchi,T.; Kamigaito, O. J Mater Res 1993, 8, 1174.

9. Fornes, D.; Yoon, J.; Keskkula, H.; Paul, R. Polymer 2001, 42,9929.

10. LeBaron, P.; Wang, Z.; Pinnavaia, T. Appl Clay Sci 1999, 15,11.

11. Blumstein, A. J Polym Sci, Part A: Polym Chem 1965, 3, 2665.12. Theng, B. K. G. Formation and Properties of Clay–Polymer

Complexes; Elsevier: Amsterdam, 1979.13. Krishnamoorti, R.; Vaia, A.; Giannelis, P. Chem Mater 1996,

8, 1728.14. Giannelis, P. Appl Organomet Chem 1998, 12, 675.15. Okada, A.; Kawasumi, M.; Usuki, A.; Kojima, Y.; Kurauchi,

T.; Kamigaito, O. Mater Res Soc Symp Proc 1990, 171, 45–50.16. Giannelis, P. Adv Mater 1996, 8, 29.17. Giannelis, E. P.; Krishnamoorti, R.; Manias, E. Adv Polym

Sci 1999, 138, 107.



18. LeBaron, P. C.; Wang, Z.; Pinnavaia, T. J Appl Clay Sci 1999,15, 11.

19. Vaia, R. A.; Price, G.; Ruth, P. N.; Nguyen, H. T.; Lichtenhan,J. Appl Clay Sci 1999, 15, 67.

20. Biswas, M.; Sinha, S. Adv Polym Sci 2001, 155, 167.21. Gilman, J. W. Appl Clay Sci 1999, 15, 31.22. Bins & Associates. Plast Addit Compd 2002, 4(1), 30–33.23. Lan, T.; Kaviratna, P. D.; Pinnavaia, T. J. Chem Mater 1994,

6, 573.24. Sall, K. Eur Plast News March 14, 2002.25. Messersmith, P. B.; Giannelis, E. P. J Polym Sci, Part A: Polym

Chem 1995, 33, 1047.26. Gilman, J. W.; Kashiwagi, T.; Lichtenhan, J. D. SAMPE J 1997,

33, 40.27. Gilman, J. W. Appl Clay Sci 1999, 15, 31.28. Dabrowski, F.; Bras, L.; Bourbigot, S.; Gilman, J. W.;

Kashiwagi, T. In Proceedings of the Eurofillers ’99, Lyon-Villeurbanne, France, 1999; pp. 6–9.

29. Bourbigot, S.; LeBras, M.; Dabrowski, F.; Gilman, J. W.;Kashiwagi, T. Fire Mater 2000, 24, 201.

30. Gilman, J. W.; Jackson, C. L.; Morgan, A. B.; Harris, R.;Manias, E.; Giannelis, E. P.; Wuthenow, M.; Hilton, D.;Phillips, H. Chem Mater 2000, 12, 1866.

31. Masenelli-Varlot, K.; Reynaud, E.; Vigier, G.; Varlet, J. JPolym Sci, Part B: Polym Phys 2002, 40, 272.

32. Sinha-Ray, S.; Okamoto, M. Macromolecules 2003, 36,2355.

33. Okada, A.; Fukoshima, Y.; Inagaki, S.; Usuki, A.; Sugiyama,S.; Kurashi, T.; Kamigaito, O. U.S. Patent 4,739,007 (1998).

34. Kato, M.; Usuki, A.; Okada, A. J Appl Polym Sci 1997, 66,1781.

35. Kawasumi, M.; Hasegawa, N.; Kato, M.; Usuki, A.; Okada,A. Macromolecules 1997, 30, 6333.

36. Hasegawa, N.; Kawasumi, M.; Kato, M.; Usuki, A.; Okada,A. J Appl Polym Sci 1998, 67, 87.

37. Liu, X.; Wu, Q. Polymer 2001, 42, 10013.38. Nam, P. H.; Maiti, P.; Okamoto, M.; Kotaka, T.; Hasegawa,

N.; Usuki, A. Polymer 2001, 42, 9633.39. Kurokawa, Y.; Yasuda, H.; Oya, A. J Mater Sci Lett 1996, 15,

1481.40. Furuichi, N.; Kurokawa, Y.; Fujita, K.; Oya, A.; Yasuda, H.;

Kiso, M. J Mater Sci 1996, 31 4307.41. Tudor, J.; Willington, L.; O’Hare, D.; Royan, B. Chem Com-

mun 1996, 2031.42. Kurokawa, Y.; Yasuda, H.; Kashiwagi, M.; Oya, A. J Mater

Sci Lett 1997, 16, 1670.43. Nyden, M. R.; Gilman, J. W. Comput Theor Polym Sci 1997,

7, 191.44. Kato, M.; Usuki, A.; Okada, A. J Appl Polym Sci 1997, 66,

1781.45. Usuki, A.; Kato, M.; Okada, A.; Kurauchi, T. J Appl Polym

Sci 1997, 63, 137.46. Kawasumi, M.; Hasegawa, N.; Kato, M.; Usuki, A.; Okada,

A. Macromolecules 1997, 30, 6333.47. Hasegawa, N.; Kawasumi, M.; Kato, M.; Usuki, A. Okada,

A. J Appl Polym Sci 1998, 67, 87.48. Oya, A. In Polymer–Clay Nanocomposites; Pinnavaia, T. J.;

Beall, G. W. (Eds.); Wiley: London, 2000; pp. 151–172.

49. Hasegawa, N.; Okamoto, H.; Kato, M.; Usuki, A. J ApplPolym Sci 2000, 78, 1918.

50. Oya, A.; Kurokawa, Y.; Yasuda, H. J Mater Sci 2000, 35, 1045.51. Lee, J. W.; Lim, Y. T.; Park, O. O. Polym Bull 2000, 45, 191.52. Zhang, Q.; Fu, Q.; Jiang, L.; Lei, Y. Polym Int 2000, 49,

1561.53. Garces, J. M.; Moll, D. J.; Bicerano, J.; Fibiger, R.; McLeod,

D. G. Adv Mater 2000, 12, 1835.54. Hasegawa, N.; Okamoto, H.; Kawasumi, M.; Kato, M.;

Tsukigase, A.; Usuki, A. Macromol Mater Eng 2000, 280/281,76.

55. Hambir, S.; Bulakh, N.; Kodgire, P.; Kalgaonkar, R.; Jog, J. P.J Polym Sci, Part B: Polym Phys 2001, 39, 446.

56. Zanetti, M.; Camino, G.; Reichert, P.; Mulhaupt, R. Macro-mol Rapid Commun 2001, 22, 176.

57. Galgali, G.; Ramesh, C.; Lele, A.; Macromolecules 2001, 34,852.

58. Solomon, M. J.; Almusallam, A. S.; Seefeldt, K. F.;Somwangthanaroj, A.; Varadan, P. Macromolecules 2001, 34,1864.

59. Gloaguen, J. M.; Lefebvre, J. M. Polymer 2001, 42, 5841.60. Garcia-Martinez, J. M.; Laguna, O.; Areso, S.; Collar, E. P. J

Appl Polym Sci 2001, 81, 625.61. Schmidt, D.; Shah, D.; Giannelis, E. P.; Curr Opin Solid State

Mater Sci 2002, 6, 205.62. Reichert, P.; Hoffman, B.; Bock, T.; Thomann, R.; Mulhaupt,

R.; Friedrich, C. Macromol Rapid Commun 2001, 22,519.

63. Nam, P. H.; Maiti, P.; Okamoto, M.; Kotaka, T.; Hasegawa,N.; Usuki, A. Polymer 2001, 42, 9633.

64. Liu, X.; Wu, Q. Polymer 2001, 42, 10013.65. Nam, P. H.; Maiti, P.; Okamaoto, M.; Kotaka, T. In Proceeding

Nanocomposites, June 25–27, 2001, Chicago, IL, USA; ECMPublication: San Diego, CA, 2001.

66. Manias, E. Mater Res Soc Bull 2001, 26, 862.67. Okamoto, M.; Nam, P. H.; Maiti, P.; Kotaka, T.; Hasegawa,

N.; Usuki, A. Nano Lett 2001, 1, 295.68. Okamoto, M.; Nam, P. H.; Maiti, M.; Kotaka, T.; Nakayama,

T.; Takada, M.; Ohshima, M.; Usuki, A.; Hasegawa, N.;Okamoto, H. Nano Lett 2001, 1, 503.

69. Hambir, S.; Bulakh, N.; Kodgire, P.; Kalgaonkar, R.; Jog, J. P.J Polym Sci, Part B: Polym Phys 2001, 39, 446.

70. Sun, T.; Garces, J. M. Adv Mater 2002 14, 128.71. Maiti, P.; Nam, P. H.; Okamoto, M.; Kotaka, T.; Hasegawa,

N.; Usuki, A. Macromolecules 2002, 35, 2042.72. Maiti, P.; Nam, P. H.; Okamoto, M.; Kotaka, T.; Hasegawa,

N.; Usuki, A. Polym Eng Sci 2002, 42, 1864.73. Nam, P. H.; Maiti, P.; Okamoto, M.; Kotaka, T.; Nakayama,

T.; Takada, M.; Ohshima, M.; Usuki, A.; Hasegawa, N.;Okamoto, H. Polym Eng Sci 2002, 42, 1907.

74. Hambir, S.; Bulakh, N.; Jog, J. P. Polym Eng Sci 2002, 42,1800.

75. Kaempfer, D.; Thomann, R.; Mulhaupt, R. Polymer 2002, 43,2909.

76. Lele, A.; Mackley, M.; Galgali, G.; Ramesh, C. J Rheol 2002,46, 1091.

77. Zhang, Q.; Wang, Y.; Fu, Q. J Polym Sci, Part B: Polym Phys2003, 41, 1.



78. Somwangthanaroj, A.; Lee, C.; Solomon, J. Macromolecules2003, 36, 2333.

79. Morgan, B.; Harris, D. Polymer 2003, 44, 2113.80. (a) Jeon, G.; Jung, T.; Lee, W.; Hudson, D. Polym Bull 1998,

41, 107; (b) Okada, A.; Kawasumi, M.; Usuki, A.; Kojima, Y.;Kurauchi, T.; Kamigaito, O. Mater Res Soc Symp Proc 1990,171, 45–50; (c) Usuki, A.; Kawasumi, M.; Kojima, Y.; Okada,A.; Kurauchi, T.; Kamigaito, O. J Mater Res 1993, 8, 1174; (d)Fornes, T. D.; Yoon, P. J.; Keskkula, H.; Paul, D. R. Polymer2001, 42, 9929.

81. Heinemann, J.; Reichert, P.; Thomson, R.; Mulhaupt, R.Macromol Rapid Commun 1999, 20, 423.

82. Privalko, V. P.; Calleja, F. J. B.; Sukhorukov, D. I.; Privalko,E. G.; Walter, R.; Friedrich, K. J Mater Sci 1999, 34, 497.

83. Bergman, J. S.; Chen, H.; Giannelis, E. P.; Thomas, M. G.;Coates, G. W. J Chem Soc, Chem Commun 1999, 21, 2179.

84. Rong, J.; Jing, J.; Li, H.; Sheng, M. Macromol Rapid Commun2001, 22, 329.

85. Wang, K. H.; Choi, M. H.; Koo, C. M.; Choi, Y. S.; Chung, I.J Polymer 2001, 42, 9819.

86. Alexandre, M.; Dubois, P.; Sun, T.; Graces, J. M.; Jerome, R.Polymer 2002, 43, 2123.

87. Gopakumar, T. G.; Lee, J. A.; Kontopoulou, M.; Parent, J. S.Polymer 2002, 43, 5483.

88. Jin, Y.-H.; Park, H.-J.; Im, S.-S.; Kwak, S.-Y.; Kwak, S. Macro-mol Rapid Commun 2002, 23, 135.

89. Bafna, A.; Beaucage, G.; Mirabella, F.; Mehta, S. Polymer2003, 44, 1103.

90. Vaia, R. A; Isii, H.; Giannelis, E. P. Chem Mater 1993, 5, 1694.91. Vaia, R. A.; Jandt, K. D.; Edward, J. K.; Giannelis, E. P. Macro-

molecules 1995, 28, 8080.92. Weiner, M. W.; Chen, H.; Giannelis, E. P.; Sogah, D. Y. J Am

Chem Soc 1999, 122, 1615.93. Moet, A.; Akelah, A. Mater Lett 1993, 18, 97.94. Hasegawa, N.; Okamoto, H.; Kawasumi, M.; Usuki, A. J

Appl Polym Sci 1999, 74, 3359.95. Alexandre, M.; Dubois, P. Mater Sci Eng 2000, 28, 1.96. Lincoln, D. M.; Vaia, R. A.; Wang, Z. G.; Hsiao, B. S. Polymer

2001, 42, 1621.97. Strawhecker, K. E.; Manias, E. Chem Mater 2003, 15, 844.98. Messersmith, P. B.; Giannelis, E. P. J Polym Sci, Part A: Polym

Chem 1995, 33, 1047.99. Hackett, E.; Manias, E.; Giannelis, E. P. Chem Mater 2000,

12, 2161.100. Kuppa, V.; Manias, E. Chem Mater 2002, 14, 2171.101. Aranda, P.; Ruiz-Hitzky, E. Chem Mater 1992, 4, 1395.102. Lan, T.; Kaviratna, P. D.; Pinnavaia, T. J. Chem Mater 1994,

6, 573.103. Messersmith, P. B.; Giannelis, E. P. J Polym Sci, Part A: Polym

Chem Ed 1995, 33, 1047.104. Yano, K.; Usuki, A.; Okada, A.; Kurauchi, T.; Kamigaito, O.

Polym Prepr (Jpn) 1991, 32(1), 65.105. Lan, T.; Kaviratna, P. D.; Pinnavaia, T. J. Chem Mater 1994,

6, 573.106. Yano, K.; Usuki, A.; Okada, A. J Polym Sci, Part A: Polym

Chem 1997, 35, 2289.107. Zhu, Z.-K.; Yang, Y.; Yin, J.; Wang, X. Y.; Ke, Y. C.; Qi, Z. N. J

Appl Polym Sci 1999, 73, 2063.

108. Yang, Y.; Zhu, Z. K.; Yin, J.; Wang, X. Y.; Qi, Z. E. Polymer1999, 40, 4407.

109. Tyan, H. L.; Wei, K. H.; Hsieh, T. E. J Polym Sci, Part B: PolymPhys 2000, 38, 2873.

110. Yano, K.; Usuki, A.; Okada, A. Polym Prepr (201 ACS) 1991,32, 65.

111. Gu, A.; Chang, F.C. J Appl Polym Sci 2001, 79, 289.112. Gu, A.; Kuo, S. W.; Chang, F. C. J Appl Polym Sci 2001, 79,

1902.113. Hsiao, S. H.; Liou, G. S.; Chang, L. M. J Appl Polym Sci 2001,

80, 2067.114. Tyan, H. L.; Leu, C. M.; Wei, K. H. Chem Mater 2001, 13,

222.115. Huang, J. C.; Zhu, Z. K.; Ma, X. D.; Qian, X. F.; Yin, J. J Mater

Sci 2001, 36, 871.116. Agag, T.; Koga, T.; Takeichi, T. Polymer 2001, 42, 3399.117. Morgan, A. B.; Gilman, J. W.; Jackson, C. L. Macromolecules

2001, 34, 2735.118. Leu, C. M.; Wu, Z. W.; Wei, K. H. Chem Mater 2002, 14, 3016.119. Magaraphan, R.; Lilayuthalert, W.; Sirivat, A.; Schwank, J.

W. Compos Sci Technol 2001, 61, 1253.120. Delozier, D. M.; Orwoll, R. A.; Cahoon, J. F.; Ladislaw, J. S.;

Smith, J. G.; Connell, J. W. Polymer 2003, 44, 2231.121. Liang, Z.-M.; Yin, J.; Xu, H.-J. Polymer 2003, 44, 1391.122. Dabrowski, F.; Bourbigot, S.; Delbel, R.; Bras, M. L. Eur

Polym J 2000, 36, 273.123. Ding, Y.; Jones, D. J.; Maireles-Torres, P.; Roziere, J. Chem

Mater 1995, 7, 562.124. Reichert, P.; Kressler, J.; Thomann, R.; Mulhaupt, R.;

Stoppelmann, G. Acta Polym 1998, 49, 116.125. Hoffman, B.; Kressler, J.; Stoppelmann, G.; Friedrich, C.;

Kim, G. M. Colloid Polym Sci 2000, 28, 629.126. Giza, E.; Ito, H.; Kikutani, T.; Okui, N. J Polym Eng 2000, 20,

403.127. Kim, G. M.; Lee, D. H.; Hoffmann, B.; Kresler, J.;

Stoppelmann, G. Polymer 2001, 42, 1095.128. Nair, S. V.; Goettler, L. A.; Lysek, B. A. Polym Eng Sci 2002,

42, 1872.129. Liu, X.; Wu, Q.; Zhang, Q.; Mo, Z. J Polym Sci, Part B: Polym

Phys 2003, 44, 6367.130. Ke, Y. C.; Long, C.; Qi, Z. J Appl Polym Sci 1999, 71,

1139.131. Sekelik, D. J.; Stepanov Enazarenko, S.; Schiraldi, D.; Hiltner,

A.; Baer, E. J Polym Sci, Part B: Polym Phys 1999, 37, 847.132. Matayabas, J. C., Jr; Turner, S. R.; Sublett, B. J.; Connell,

G. W.; Barbee, R. B. Int Appl WO 1998, 98, 29499.133. Takekoshi, T.; Khouri, F. F.; Campbell, J. R.; Jordan, T. C.;

Dai, K. H.; US Patent 5,530.052 (General Electric Co.); June25, 1996.

134. Tsai, T. Y. In Polymer–Clay Nanocomposites; Pinnavaia,T. J.; Beall, G. W. (Eds.); Wiley: Chichester, England, 2000;pp. 173–189.

135. Davis, C. H.; Mathias, L. J.; Gilman, J. W.; Schiraldi, D. A.;Shields, J. R.; Trulove, P. J Polym Sci, Part B: Polym Phys2002, 40, 2661.

136. Imai, Y.; Nishimura, S.; Abe, E.; Tateyama, H.; Abiko, A.;Yamaguchi, A.; Aoyama, T.; Taguchi, H. Chem Mater 2002,14, 477.



137. Huang, X.; Lewis, S.; Brittain, W. J.; Vaia, R. A. Macro-molecules 2000, 33, 2000.

138. Mitsunaga, M.; Ito, Y.; Ray, S.; Okamoto, M.; Hironaka, K.Macromol Mater Eng 2003, 288, 543.

139. Zilg, C.; Thomann, R.; Mulhaupt, R.; Finter, J. Adv Mater1999, 11, 49.

140. Usuki, A.; Mizutani, T.; Fukushima, Y.; Fujimoto, M.;Fukumori, K.; Kojima, Y.; Sato, N.; Kurauchi, T; Kamigaito,O. U.S. Patent 4,889,885 (1989).

141. Wang, M. S.; Pinnavaia, T. J. Chem Mater 1994, 6, 468.142. Lan, T.; Pinnavaia, T. J. Chem Mater 1994, 6, 2216.143. Lan, T.; Kaviratona, P. J.; Pinnavaia, T. J. Chem Mater 1995,

7, 2214.144. Kelly, P.; Akelah, A.; Qutubuddin, S.; Moet, A. J Mater Sci

1994, 29, 2274.145. Sur, G. S.; Sun, H. L.; Lyu, S. G.; Mark, J. E. Polymer 2001,

42, 9783.146. Zanetti, M.; Lomakin, S.; Camino, G. Macromol Mater Eng

2000, 279, 1.147. Bridley, S.; Brown, G. Crystal Structure of Clay Minerals

and Their X-ray Diffraction; Mineralogical Society: London,1980.

148. Pinnavaia, T. Science 1983, 220, 365.149. Yalcin, B.; Cakmak, M. Polymer 2004, 45, 6623.150. Pinnavaia, T.; Beall, G. Polymer-Clay Nanocomposites;

Wiley: New York, 2000.151. Giannelis, E. P. Adv Mater 1996, 8, 29.152. Fornes, T. D.; Yoon, P. J.; Keskkula, H.; Paul, D. R. Polymer

2001, 42, 9929.153. Blumstein, A. J Polym Sci A 1965, 3, 2665.154. Theng, B. K. G. Formation and Properties of Clay–Polymer

Complexes; Elsevier: Amsterdam, 1979.155. Vaia, R. A.; Giannelis, E. P. Chem Mater 1996, 8, 1728.156. Morgan, A. B.; Gilman, J. W. J Appl Polym Sci 2003, 87, 1329.157. Mathias, L. J.; Davis, R. D.; Jarrett, W. L. Macromolecules

1999, 32, 7958.158. Roe, R. Methods of X-Ray and Neutron Scattering in Poly-

mer Science; Oxford University Press: New York, 2000;p. 199.

159. Bafna, A.; Beaucage, G.; Mirabella, F.; Skillas, G.;Sukumaran, S. J Polym Sci, Part B: Polym Phys 2001, 39,2923.

160. Bafna, A.; Beaucage, G.; Mirabella, F.; Mehata, S. In Proceed-ings Nanocomposites, Sept. 23–25, 2002; ECM Publication:San Diego, CA.

161. Alexander, L. X-Ray Diffraction Methods in Polymer Sci-ence; Wiley: New York, 1970.

162. VanderHart, D. L.; Asano, A.; Gilman, J. W. Macromolecules2001, 34, 3819.

163. Bensimon, Y.; Deroide, B.; Zanchetta, J. V. J Phys Chem Solid1999, 60, 813.

164. Yang, D. K.; Zax, D. B. J Chem Phys 1991, 110, 5325.165. Blumberg, W. E. Phys Rev 1960, 119, 79.166. Abragam, A. (Ed.). The Principles of Nuclear Magnetism;

Oxford University Press: New York, 1961; Chap. V.167. VanderHart, D. L.; Asano, A.; Gilman, J. W. Chem Mater

2001, 13, 3796.

168. Sahoo, S. K.; Kim, D. W.; Kumar, J.; Blumstein, A.; Cholli,A. L. Macromolecules 2003, 36, 2777.

169. Hou, S. S.; Bonagamba, T. J.; Beyer, F. L.; Madison, P. H.;Schmidt-Rohr, K. Macromolecules 2003, 36, 2769.

170. Park, C. I.; Park, O. O.; Lim, J. G.; Kim, H. J. Polymer 2001,42, 7465.

171. Wu, H. D.; Tseng, C. R.; Chang, F. C. Macromolecules 2001,34, 2992.

172. Loo, L. S.; Gleason, K. K. Macromolecules 2003, 36, 2587.173. Nascimento, G. M.; Constantino, V. R. L.; Temperini, M. L.

A. Macromolecules 2002, 35, 7535.174. Jimenez, G.; Ogata, N.; Kawai, H.; Ogihara, T. J Polym Sci,

Part B: Polym Phys 1997, 35, 389.175. Ogata, N.; Kawakage, S.; Ogihara, T. J Appl Polym Sci 1997,

66, 573.176. Ogata, N.; Jimenez, G.; Kawai, H.; Ogihara, T. J Polym Sci,

Part B: Polym Phys 1997, 35, 389.177. Vaia, R. A.; Giannelis, E. P. Macromolecules 1997, 30,

8000.178. Vaia, R. A.; Giannelis, E. P. Polymer 2001, 42, 1281.179. Vaia, R. A.; Ishii, H.; Giannelis, E. P. Chem Mater 1993, 5,

16946.180. Nam, P. H.; Maiti, P.; Okamoto, M.; Kotaka, T.; Hasegawa,

N.; Usuki, A. Polymer 2001, 42, 9633.181. Usuki, A.; Kawasumi, M.; Kojima, Y.; Okada, A.; Kurauchi,

T.; Kamigaito, O. J Mater Res 1993, 8, 1174.182. Usuki, A.; Kojima, Y.; Kawasumi, M.; Okada, A.; Fukushima,

Y.; Kurauchi, T.; Kamigaito, O. J Mater Res 1993, 8, 1179.183. Messersmith, P. B.; Giannelis, E. P. Chem Mater 1993, 5, 1064.184. Wang, Z.; Pinnavaia, T. J. Chem Mater 1998, 10, 3769.185. Akelah, A. In Polymers and Other Advanced Materials;

Prasad, P. N.; Mark, J. E.; Ting, F. J. (Eds.); Plenum Press:New York, 1995; pp. 625–630.

186. Akelah, A.; Moet, M. J Mater Sci 1996, 31, 3589.187. Doh, J. G.; Cho, I. Polym Bull 1998, 41, 511.188. Weimer, M. W.; Chen, H.; Giannelis, E. P.; Sogah, D. Y. J Am

Chem Soc 1999, 121, 1615.189. Rausell-Colom, J. A.; Serratosa, J. M. In Chemistry of Clays

and Clay Minerals; Newman, A. C. D. (Ed.); Wiley: NewYork, 1987; p. 371.

190. Wu, J.; Lerner, M. M. Chem Mater 1993, 5, 835.191. Choi, H. J.; Kim, S. G.; Hyun, Y. H.; Jhon, M. S. Macromol

Rapid Commun 2001, 22, 32025.192. Hyun, Y. H.; Lim, S. T.; Choi, H. J.; Jhon, M. S. Macro-

molecules 2001, 34, 8084.193. Lim, S. K.; Kim, J. W.; Chin, I.; Kwon, Y. K.; Choi, H. J. Chem

Mater 2002, 14, 1989.194. Liao, B.; Song, M.; Liang, H.; Pang, Y. Polymer 2001, 42,

10007.195. Tseng, C.-R.; Wu, J.-Y.; Lee, H.-Y.; Chang, F.-C. Polymer 2001,

42, 10063.196. Sur, G. S.; Sun, H. L.; Lyu, S. G.; Mark, J. E. Polymer 2001,

42, 9783.197. Ogata, N.; Jimenez, G.; Kawai, H.; Ogihara, T. J Polym Sci,

Part B: Polym Phys 1997, 35, 389.198. (a) Jimenez, G.; Ogata, N.; Kawai, H.; Ogihara, T. J Appl

Polym Sci 1997, 64, 2211; (b) Zhong, Y.; Wang, S. Q. J Rheol



2003, 47(2), 483; (c) Avella, M.; Cosco, S.; Volpe, G. D.; Errico,M. E. Adv Polym Technol 2005, 24(2), 132.

199. Vaia, R. A.; Ishii, H.; Giannelis, E. P. Chem Mater 1993, 5,1694.

200. Vaia R. A.; Giannelis, E. P. Macromolecules 1997, 30,7990.

201. Vaia, R. A.; Giannelis, E. P. Macromolecules 1997, 30,8000.

202. Vaia, R. A.; Vasudevan, S.; Krawiec, W.; Scanlon, L. G.;Giannelis, E. P. Adv Mater 1995, 7, 154.

203. Shen, Z.; Simon, G. P.; Cheng, Y. B. Polymer 2002, 43, 4251.204. (a) Liu, L. M.; Qi, Z. N.; Zhu, X. G. J Appl Polym Sci 1999, 71,

1133; (b) Fornes, T. D.; Yoon, P. J.; Hunter, D. L.; Keskkula,H.; Paul, D. D. Polymer 2002, 43, 5915.

205. Gilman, J. W.; Awad, W. H.; Davis, R. D.; Shields, J.; Harris,R. H.; Davis, C.; Morgan, A. B.; Sutto, T. E.; Callahan, J.;Trulove, P. C.; DeLong, H. C. Chem Mater 2002, 14, 3776.

206. Lee, J.; Takekkoshi, T.; Giannelis, E. P. Mater Res Soc SympProc 1997, 457, 513.

207. (a) Huang, J. C.; Zhu, Z. K.; Qian, X. F.; Sun, Y. Y. Polymer2001, 42, 873; (b) Liu, T.; Tjiu, W. C.; He, C.; Na, S. S.; Chung,T. S. Polym Int 2004, 53, 392; (c) Dolgovskij, M. K.; Fasulo,P. D.; Lortie, F.; Macosko, C. W.; Ottaviani, R. A.; Rodgers,W. R. In SPE ANTEC 2003; p. 2255; (d) Dennis, H. R.; Hunter,D. L.; Chang, D.; Kim, S.; White, J. L.; Cho, J. W.; Paul, D. R.Polymer 2001, 42, 9513; (e) Modesti, M.; Lorenzetti, A.; Bon,D.; Besco, S. Polymer 2005, 46, 10237; (f)Lei, S. G.; Hoa, S. V.;Ton-That, M.-T. Compos Sci Technol 2006, 66, 1274; (g) Dan,

C. H.; Lee, M. H.; Kim, Y. D.; Min, B. H.; Kim, J. H. Polymer2006, 47, 6718.

208. Tomasko, D. L.; Li, H.; Liu, D.; Han, X.; Wingert, M. J.;Lee, L. J.; Koelling, K. W. Ind Eng Chem Res 2003, 42,6431.

209. Chiou, J. S.; Barlow, J. W.; Paul, D. R. J Appl Polym Sci 1985,30, 2633.

210. Garg, A.; Gulari, E.; Manke, C. W. Macromolecules 1994, 27,5643.

211. Lee, M. H.; Tzoganakis, C.; Par, C. B. Adv Polym Technol2000, 19(4), 300.

212. Berens, A. R.; Huvard, G. S. In Supercritical Fluid Sci-ence and Technology; Johnston, K. P.; Penninger, J. M. L.(Eds.); American Chemical Society: Washington, DC, 1989;p. 208.

213. Garcia-Leiner, M.; Lesser, A. J. In SPE ANTEC 2004;pp. 1528–1532.

214. Zerda, A. S.; Caskey, T. C.; Lesser, A. J. Macromolecules 2003,36, 1603.

215. Caskey, T. C.; Lesser, A. J. Polym Eng Sci 2001, 84,134.

216. Wingert, M. J.; Han, Z.; Zeng, C.; Li, H. In SPE ANTEC 2003;pp. 986–990.

217. Garcia-Leiner, M.; Lesser, A. J. In 225th ACS National Meet-ing PMSE Proceedings, New Orleans, LA, 2003.

218. Garcia-Leiner, M.; Lesser, A. J. In 226th ACS National Meet-ing PMSE Proceedings, New York, 2003.


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Preparation of polymer-clay nanocomposites and their properties

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