Proceedings of the 2nd IEEE InternationalConference on Nano/Micro Engineered and Molecular Systems

January 16 - 19, 2007, Bangkok, Thailand

EVOH/Montmorillonite Intercalation Nano-compositesLijun Dai'*, Lei Li2, and Yujun Zhang2

2Logistics School, Harbin University ofCommerce, P.R. China'School ofMaterials Science and Engineering, Harbin University ofScience and Technology, P.R. China

Abstract- The montmorillonite (MMT) was treated by polyvinylpyrrolidone and hexadecyl quaternary ammonium saltrespectively to get two kinds of montmorillonite with goodintercalation written as PVP-MMT and HD-MMT, and then theethylene-vinyl alcohol copolymer (EVOH) / PVP-MMT or HD-MMT nano-composites were prepared by dynamic melt blending.The phase morphology and the crystallization behavior of thenano-composites were characterized by using X-ray diffraction(XRD), scanning electron microscopy (SEM) and atomic forcemicroscope (AFM). XRD indicate that EVOH intercalate into thegalleries of montmorillonite, the less content of PVP-MMT, thelarger of interlamellar spacing will be. When the content of PVP-MMT is below 8%, the exfoliated nano-composites are produced,and the intercalated nano-composites could be prepared as thecontent is 8%-15%. Additionally, the interlamellar spacing hasno clear changes after PVP-MMT content exceeds 15%. SEMimages show that the PVP-MMT has an irregular distributionwhen there is only a small amount PVP-MMT in nano-composites in certain content. On the contrary, PVP-MMT willexhibit regular distribution at higher content. The waterresistance of the nano-composites with 5%-10% MMT increase3.3% compared with that of neat EVOH.

Keywords-montmorillonite; ethylene-vinyl alcohol copolymer;nano-composite; intercalation

I. INTRODUCTION

Recently, polymer/layered silicate nano-composites havestimulated great interest in many researchers due to theirimproved tensile strength and modulus, decreased thermalexpansion, gas permeability [1], increased swelling resistance[2], and enhanced ionic conductivity [3] when compared withtheir micro- and macro-composite counterparts and the pristinepolymer matrix. The enhanced properties of polymer-layeredsilicate nano-composites are presumably because of thenanoscale structure of the hybrids, the large aspect ratio (100-1000) of the layer silicate and large surface area (760m2 g),able to contact with the polymer matrix to a great extent. Theunprecedented mechanical properties of polymer/layeredsilicate nano-composites were first demonstrated by a group atthe Toyota research center in Japan by using nylon as apolymer matrix. Since then, many polymer/layered silicatenanocomposites have been synthesized for variousapplications. The characteristic property of polymer/layeredsilicate nano-composites is the fact that these 1 nm thin silicatesheets (the primary particles) are individually dispersed in thepolymer matrix [4]. To achieve this fine dispersion, onlymechanical forces are not enough; there should be athermodynamic driving force as well to separate the layers intothe primary silicate sheets [5]. This thermodynamic drivingforce is introduced by inserting a certain coating of surfactantson each individual layer. These surfactant molecules increase

This work was carried out under grant No.QC04CO8 from HeilongjiangYoung's Foundation Program and grant No. 10551078 from HeilongjiangEducation Bureau Scientific Foundation, Peoples Republic ofChina

*Contact author: Liun. Dai is with Logistics School, Harbin Universityof Commerce, P.R. China (phone: +86 45186392586; email:dljl969@126.com; Address: P. 0. Box. 33. Tongda Street 138, Daoli District,Harbin 150076, P. R. China

the layer distance, improve the compatibility with the polymerand can give an increase in entropy because they can mix withthe polymer [6]. To enable each layer to be coated with thesurfactant, the layers should be accessible for the surfactantmolecules from the solution, and for this reason the clay layersneed to swell of exfoliate in the solvent (usually water). Thestructures of layer silicates consist of two fused silicatetrahedral sheets sandwiching an edge-shared octahedral sheetof either aluminum or magnesium hydroxide. The Na+ or Ca"residing in the interlayers can be replaced by organic cationssuch as alkylammonium ions via an ion-exchange reaction torender the hydrophilic layered silicate organophilic. Moreover,the functional groups provided by alkylammonium cations canreact with the polymer or initiate polymerization of monomersto improve the strength of the interface between the inorganicand the polymer [7].

Ethylene-vinyl alcohol copolymers known as EVOH arewidely used as barrier materials. The presence of hydroxylgroups suggests that the polymer have the potentials forforming covalent linkages with other polymers containingactive chemical functions. A nano-composite EVOH would beexpected to provide even better barrier performance and otherpotential applications, so it is important to investigate theEVOHIMMT nano-composites. The present study focuses onthe change of interlamellar spacing, phase morphology,crystallization behavior and relative water adsorption ofEVOHIMMT nano-composites and the XRD, SEM, AFM wereused to study these behaviors.

II. EXPERIMENTAL

A. Organic-MMA' andEVOHIMMA' nano-compositessynthesisEVOH (70mol% vinyl alcohol) was purchased from Japan

STS. A montmorillonite with an ion-exchange capacity (CEC)of 100mmol/1OOg were ion-exchanged by using polyvinylpyrrolidone and hexadecyl quaternary ammonium saltfollowing a standard procedure according to Usuki'S document[8], respectively, to get two kinds of montmorillonite withgood intercalation written as PVP-MMT and HD-MMT, andthen EVOHIPVP-MMT or EVOHIHD-MMT nano-compositeswith different MMT contents were prepared by dynamic meltblending.

B. Structure Characterization of the EVOHIMM]' nano-compositesX-ray diffraction is a conventional method to characterize

the gallery height in layered silicates. In this thesis, a Rigaku(Japan) D/max-RB X-ray diffraction (XRD) was used tocharacterize the crystallization behavior and the interlamellar

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spacing. The operation parameters were CuKo radiation at agenerator voltage of 50Kv and current of 1OOmA. The scanningrate was 80/min at an interval of 0.020. Furthermore, the phasemorphology in the nano-composites was investigated by usingAFM.

The surface morphology of nano-composites as well as thedistribution of MMT was observed on a high-resolutionscanning electron microscope (SEM) (Phillip FEI Sirion).Samples for SEM were mounted on metal sample stubs bymeans of double-sided adhesive tapes, and sputter-coated withgold for 2-3 min with a CressingtonR 208HR sputter-coater.The SEM measurements were performed at an acceleratingvoltage of 1OkV.

C. Water adsorption ofEVOHIMMT nano-compositesThe water resistance was studied by immersing the nano-

composites and polymer matrix into distilled water at 60°C,and determining the water relative adsorption in different timesshown as Figure.5. The relative adsorption is calculated by theflowing equation:

Wi-WOQ = W x100%(

Here, Q is the relative water adsorption, Wi, WO are the wet anddry mass of the nano-composites, respectively.

20(0)Figure 1. XRD patterns ofMMT, HD-MMT, PVP-MMT

TABLE I. INTERLAMELLAR SPACING OF THE MMT

Samples

MMT

HD-MMT

PVP-MMT

20/ (0)

8.260

7.020

3.660

dool/nm

1.070

1.258

2.412

III. RESULTS AND DISCUSSION

A. XRD characterizationXRD was used to research the interlamellar spacing and

crystallization behavior and the results are shown in Fig. 1 andFigure.2. Figure.la), lb), ic) are the XRD patterns of MMT,HD-MMT, PVP-MMT while Figure.2a), 2b), 2c) are thepatterns of the nano-composites with MMT content of 8%,15% and 20%, respectively. The interlamellar spacing ofMMTand nano-composites gained by Bragg equation is shown inTable. 1 and Table.2. The HD-MMT, PVP-MMT interlamellarspacing is larger than that of pure MMT due to the organictreatment, and HD-MMT interlamellar spacing is smaller thanPVP-MMT likely for the more methylene in polyvinylpyrrolidone. In Figure.2a) characteristic peaks of nointercalation and exfoliation as well as keeping accumulationappeared, so EVOHIPVP-MMT8% belongs to partiallyexfoliation nano-composites. Comparing the interlamellarspacing of PVP-MMT and EVOHIPVP-MMT we found thatEVOH intercalate into the galleries of montmorillonite for theincreased interlamellar spacing, the less content of MMT, thelarger of interlamellar spacing will be. When the content ofMMT is below 8%, the exfoliated nano-composite is produced,and the intercalated nano-composites could be prepared as thecontent in 8%-15%. Additionally, the interlamellar spacing hasno clear change after the MMT content exceeds 15%. There isan phenomenon that each system exhibits characteristic peak at20=10.80which belongs to the characteristic peak of MMTwithout intercalation and exfoliation, and the PVP-MMT'sinterlamellar spacing calculated here is smaller than that of neatMMT due to the large specific surface and high specific

4 6 8 10 1220(0 )

Figure 2. XRD patterns ofEVOH/ PVP-MMT

TABLE II. INTERLAMELLAR SPACING OF THE NANO-COMPOSITES

Constitution

EVOH/PVP-MMT 8%

EVOH/PVP-MMT 15%

EVOH/PVP-MMT 20%

20/(°)

10.803.62010.803.62010.803.700

dool/nm8.1852.4398.1852.4398.1852.386

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was found, and the nano-composites exhibit large-scaleordering structure due to the crystallization of EVOH withPVP-MMT as nucleus, and then the adding ofMMT makes thetendency of forming ordering structure easier.

D. Water adsorption ofEVOHIMMT nano-compositesThe water resistance was studied by immersing the nano-

composites and polymer matrix into distilled water at 60°C,and determining the water relative adsorption in different timesshown as Figure.5. The relative adsorption is calculated by theformula (1). A phenomenon was found that the Q changes as

the HD-MMT content change. The water resistance of thenano-composites with 5%, 10% HD-MMT increase 3.3%compared with that ofneat EVOH, What is over, the Q have a

a)

c). EVOH/8% PVP-MMT d). EVOH/15% PVP-MMT

Figure 3. SEM micrographs ofEVOH/MMT nano-composites

200am0Q

surface energy of itself, these make the self-aggregationhappens easily.

B. SEM characterizationSEM was used to examine the surface morphology as well

as the distribution of MMT in nano-composites shown as

Figure.3. The white segment belongs to the polymer matrixEVOH while the black is MMT. Significant phase separationand no winding are found between the polymer matrix andMMT in Figure.3a) because the polymer matrix EVOH was

not intercalated into the galleries of montmorillonite. FromFigure.3b), 3C) random distribution of MMT in nano-scale innano-composites was obtained although some aggregated HD-MMT particles are also found. In Figure.3d) PVP-MMTdistribute regularly within the polymer matrix in singledirection. When Figure.3a) is compared with Figure.3b), c), d),it was regarded that treated MMT have a good intercalationthan that of neat MMT. In a conclusion, the relationshipbetween the MMT distribution and its content was gained thattreated MMT have an irregular distribution when there is onlya small amount MMT in nano-composites, and MMT couldexhibit regular distribution with a bigger amount in certaincontent.

C. AFM characterizationThe phase morphology in the nano-composites was

investigated by AFM. Figure.4 is the AFM micrographs andpartially amplified micrographs of EVOHIPVP-MMT nano-

composites with 8% and 20% PVP-MMT, in the AFM imagesthe white segment belongs to the polymer matrix and the blackto the PVP-MMT. The nano-composites with 8% PVP-MMThave a more uniform distribution and smooth surface thannano-composites with 20% PVP-MMT. The morphologybetween polymer matrix and MMT observed in nano-scale isshown in Figure.4 from which the analogical crystallization

a). EVOH/8% PVP-MMT

rm

600

b). EVOH/8% PVP-MMT

rm

c). EVOH/20% PVP-MMT d). EVOH/20% PVP-MMT

Figure 4. AFM micrographs and partially amplified micrographs ofEVOH/PVP-MMT nano-composites

10-

0 8-

0

ct 6-

ct

4-2-4ct

2-

I**

O 20 40 60 80 100Tirm(h)

Figure 5. Relative water adsorption ofEVOH/HD-MMT nano-composites

115

rim

2E00

200

aS v ~~A..........zZZ/~~~~~~~~~,---0 ------------ ------t

1A' , -*-EVOHE,,--H--LVUHIAL-NIIW 5%

* --- EVOH/HD-N/IW10%- - EVOH/ID-fv'VIW20%

little change when the HD-MMT content reach 20% in nano-composites. The developed water resistance is good for thebarrier property as the EVOH/[D-MMT nano-compositeswould be used as packing materials in the end use.

IV. CONCLUSION

In this thesis, the montmorillonite (MMT) was treated bypolyvinyl pyrrolidone and hexadecyl quaternary ammoniumsalt respectively to get two kinds of montmorillonite with goodintercalation written as PVP-MMT and HD-MMT, and thenEVOH / PVP-MMT or HD-MMT nano-composites wereprepared by dynamic melt blending. The phase morphologyand the crystallization behavior of the nano-composites werecharacterized by using XRD, SEM and AFM. XRD indicatethat EVOH intercalate into the galleries of montmorillonite, theless content of PVP-MMT, the larger of interlamellar spacingwill be. When the content of PVP-MMT is below 8%, theexfoliated nano-composites are produced, and the intercalatednano-composites could be prepared as the content is 8%-15%.Additionally, the interlamellar spacing has no clear changesafter PVP-MMT content exceeds 15%. SEM images show thatthe PVP-MMT has an irregular distribution when there is onlya small amount PVP-MMT in nano-composites in certaincontent. On the contrary, PVP-MMT will exhibit regulardistribution at higher content. The study on water adsorption

of the polymer/layered silicate nano-composites show that thewater resistance of the nano-composites with 5%010% MMTincrease 3.3% compared with that ofneat EVOH.

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