PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci. 2005; 18: 11–20Published online 29 November 2004 in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/pts.670
A Study on Montmorillonite/PolyethyleneNanocomposite Extrusion-coated Paperboard
By M. Krook,1 M. Gällstedt1 and M. S. Hedenqvist2*1 STFI-Packforsk AB-Packaging and Logistics Box 5604, SE-114 86 Stockholm, Sweden2 Royal Institute of Technology, Department of Fibre and Polymer Technology, SE-100 44 Stockholm, Sweden
*Correspondence to: M. S. Hedenqvist, Royal Institute of Technology, Department of Polymer Technology, SE-100 44 Stockholm, Sweden.Email: [email protected]/grant sponsor: Swedish National Board of Industrial and Technical Developmental (Vinnova)
Polymer nanocomposites are becoming an increas-ingly large class of new hybrid materials. Since the introduction of the concept in the late 1980s,research has increased enormously and com-mercial products are being introduced onto themarket.1–3 Two major findings have triggered inter-est in these materials. First, a report from theToyota research group4 showed an improvement in the thermal and mechanical properties of apolyamide 6–montmorillonite composite; andsecond, Vaia et al.5 reported that it is possible to
melt-mix polymers with silicates. The melt-mixingprocess involves the mixing of clay and a polymerat a temperature above the softening point of thepolymer. When the polymer is being annealed,chains diffuse from the bulk polymer melt into thegalleries between the silicate layers.5–9 Vaia et al.10
have also applied a mean-field statistical latticemodel to the polymer melt intercalation process.Their model suggests that the interplay of entropicand energetic factors determine the outcome ofpolymer intercalation. According to Vaia et al.,10 theentropy loss associated with polymer intercalationmay be compensated for by the entropy gain
associated with the layer separation. Thus, theestablishment of many favourable polar polymer–surface interactions is the prime factorthat promotes melt intercalation.
Since polyethylene (PE) is non-polar, the disper-sion of nanoparticles is difficult. However, byincorporating a compatibilizer into the system, itis possible to achieve an exfoliated system. Usukiet al.11 were the first to report the preparation of(PP)–clay nanocomposites, using a polyolefinoligomer with polar telechelic OH-groups as com-patibilizer. The hydrogen bonding between theOH-groups of the oligomer and the oxygen in thesilicates promoted intercalation. When the modi-fied clay and the polyolefin oligomer were mixedwith PP, a clay layer exfoliation was obtained.
The preparation of an exfoliated PP–montmoril-lonite nanocomposite using a maleic anhydride-grafted polypropylene oligomer as compatibilizerwas first reported by Kawasumi et al.12 Almostcompletely exfoliated composites were obtained.Hasegawa et al.9 observed that the nanoparticlesbecame smaller and were more uniformly dis-persed as the content of the polypropyleneoligomer was increased.
Wang et al.13 prepared a maleic anhydride-grafted PE–clay nanocomposite by melt mixing.They showed that the hydrophilicity of themaleated PE and the hydrophobicity of the organ-ically modified clay are important factors to obtainan exfoliated PE–clay nanocomposite. The prepa-ration of PE–clay nanocomposites directly fromNa+-montmorillonite by melt intercalation hasbeen reported.14 Intercalated nanocomposites werealso obtained by adding cationic or anionic sur-factants as compatibilizers.15
The thermal stability of the intercalated silicatesis important because of the elevated temperaturesexpected during the extrusion and in the polymerprocessing in general.16 Studies show that silicateswith polyvinylpyrrolidone (PVP) intercalated inthe galleries can endure high temperatures, with aconsiderable capacity to keep the silicate structureexpanded.17 According to Hlavat et al.17 the majordegradation process starts at 370°C.
Several reports discuss the preparation, charac-terization and properties of PE–clay nanocom-posites.14,18–21 However, to our knowledge, theproblems and possibilities of applying a singleclay–PE (nano)composite layer on paperboard, e.g.through extrusion-coating, have not been reported.
However, the interest in using clay (nano)compos-ites on paper and board increases. In the quest toreduce the amount of material in packagings, it isof interest to increase the barrier properties andmechanical strength of the plastic coating.22 Clay inplastic layers for paperboard purposes has beenreported in patents. A patent considers differenttype of laminate solutions where the clay (particlesize 0.04–2.0mm) is incorporated in the ethyl-ene–vinyl alcohol co-polymer (clay–EVOH) or thepolyamide-6 (clay–PA6) layers.23 The improve-ments in barrier properties of the individualclay–polymer layers were in general modest, considering the large clay loadings (20–40 wt.%).However, the results seemed more promisingwhen the clay layer was located in the middle ofthe plastic coating on paperboard. The degree ofclay exfoliation was not investigated in the patent.In another patent the clay particles are delami-nated in a water-based poly(vinyl alcohol) binder.The binder may subsequently be applied to thepaperboard and the increase in barrier propertiesis achieved by the delaminated clay.24
This paper reports studies on the properties of amontmorillonite–polyethylene extrusion-coatedpaperboard. A low-density polyethylene (LDPE)was extruded with a commercial de-agglomeratedNanomer® LDPE master batch with a clay loadingof 32 wt.% montmorillonite. It also contained amaleated polyethylene compatibilizer (MaPE).PVP was choosen as clay intercalator due to its high temperature stability. The compatibilizationbetween clay and MaPE was considered to be facil-itated through the polarity and hydrogen bondingability of the carbonyl oxygen and the carbonyl orcarboxyl groups of MaPE. Properties important formaterials used in packaging applications, includ-ing interlaminate adhesion, creasability, barrierproperties (H2O and O2) and mechanical proper-ties, were determined. The influence of extrusiontemperature was studied. The characteristics of thecoating were assessed by X-ray diffraction andtransmission electron microscopy.
EXPERIMENTAL
Materials
Nanocor Inc. kindly supplied a commerciallyavailable master batch (C.30PE). The master batch
M. KROOK, M. GÄLLSTEDT AND M. S. HEDENQVISTPackaging Technologyand Science
contained 32 wt.% montmorillonite, which wasintercalated with PVP (I.30P). It also containedmaleated polyethylene (MaPE) and a LDPE with amelt flow index of 4g/10min. Infrared spec-troscopy revealed that the anhydride in the masterbatch was either in the form of maleic acid (peakat ~1710cm-1) or as an ester (peak at ~1740cm-1).25
Consequently, at least parts of MaPE had con-nected to PVP with hydrogen bonds through themaleic acid hydroxyl groups. The density of puremontmorillonite is 2608kg/m3.26 Borealis kindlysupplied a LDPE (CA 7230). The polymer had a density of 923kg/m3 and a melt flow rate of 4.5g/10min. Iggesund Paperboard provided theInvercoate Polyboard (ICPB) paperboard. Thepaperboard was delivered in rolls with a diameterof 800mm and a width of 400mm. The grammageof the paperboard was 230g/m2 (±4%), with athickness of 290mm (±5%).
Sample preparation
The master batch (C.30PE) and the LDPE (CA7230)were mixed at 220°C. The compounding was done with a twin-screw extruder from Werner &Pleiderer, with a diameter of 57mm at a melt-temperature of 220°C. Two compounds weremade, containing 4 wt.% and 8.3 wt.% montmoril-lonite as measured by TGA.
The extrusion coating was performed using anextrusion coating pilot plant built by Extron,Finland. The extruder was equipped with a singlestandard screw with a diameter of 25mm. Thewidth of the die was 400mm, with a gap of 0.5mm.The compounds were extruded onto paperboard attwo different melt temperatures, 305°C and 325°C.The surface temperature of the polymer meltleaving the die was measured with a RaytekMinitemp laser. The temperature of the meltsurface was approximately 212°C and 223°C. Thepressure in the extruder was set to 260 bar and thescrew speed at 175rpm for both extrusion temper-atures. The distance from the die outlet to the chillroll nip was 11cm. The nip pressure was set to 20N/cm. The line speed of the paperboard was 12m/min. A chill roll with a matt surface was used.The temperature of the chill roll was 15°C. Prior toextrusion, the compounds were dried at 60°C for 2h in a Piovan hopper (Model T 50 IX) coupled to aPiovan drying control (Model DS605HE), with a
maximum dew point of -50°C. The dryer wasplaced onto the extruder. Prior to being coated, thepaperboard was in-line corona-treated using aSherman Treaters (GX20) corona station with aneffect of 2kV. The throughput time of the polymerwas measured by timing the passage of redpigment granulates from the barrel inlet to the dieoutput. The throughput time was 130s for the meltwith a temperature of 305°C and 145s for the meltwith a temperature of 325°C. Before measuringsome of the properties, the coating was strippedfrom the paperboard by immersing samples in 5 lwater containing 75g NaOH. The temperature ofthe solution was 45°C and the samples were left inthe solution for 2min.
Characterization
Tensile tests. The fracture strain, fracture stressand Young’s modulus were determined using a Zwick Z010 tensile tester, controlled by the testXpert 7.1® computer program supplied fromZwickRoell and Lambda Instrument AB. Tendumbbell-shaped specimens (thickness, 18–25mm;length of narrow section, 40mm; width of narrowsection, 6.5mm; width of ends, 25mm) werepunched out using a stamping knife. A strain rateof 100mm/min and a clamp distance of 70mmwere used. All specimens were conditioned andtested at 23°C and 50% relative humidity.
Adhesion. The adhesion was determined on thesame tensile tester as that described in the tensiletest section. The adhesion test was performedaccording to a method developed by Packforsk(Figure 1). Before the coating, sheets of paper wereplaced on the paperboard. These acted as releaseagents and enabled the coating to be ripped off andinserted in the tensile tester clamp. Specimens witha dimension of 50 ¥ 50mm were punched out fromthe coated paperboard using a Deltron samplecutter. To avoid straining the coating during theadhesion test, the coated paperboard was lami-nated on the coating side with a reinforcing tape.The adhesion strength was measured by drawingthe coating off the paperboard at an angle of 180°from its original position on the board. The initialstrength (N/m), at the point of separation wasrecorded. The adhesion data were averages of 10measurements.
Water vapour transmission rate. The watervapour transmission rate (WVTR) was measuredon two replicates of each sample, using a MoconPermatran-W Twin at 23°C and 100% relativehumidity, as described in ASTM F 1249-90. Thespecimens were tightly sandwiched between twoaluminium foils, providing a 50cm2 exposure areafor the WVTR measurements. They were mountedin isolated diffusion cells with deionized waterand conditioned to a steady state in a ConditionRack for the Permatran-W Twin. The WVTR wasnormalized with respect to coating thickness toyield water vapour permeability.
Thermogravimetric analysis (TGA). Isothermalthermogravimetric measurements were made on aMettler-Toledo thermobalance (TGA/SDTA 851e).Samples with a mass of 250 ± 1mg were insertedin an aluminium oxide cup and the weight wasmeasured in air at 305°C, 325°C and 850°C during10min. The latter temperature was also used toassess the content of montmorillonite in the com-posites. Dynamic measurements were made on 250± 1mg specimens by heating from 30°C to 850°C(at a rate of 20°C/min) in air. All data are based onduplicate specimens.
Viscosity measurements. Viscosity data wereobtained with a plate-to-plate Rheometrics RDA IIusing a frequency of 0.126–300rad/s and strains of5% and 15%. The temperature was 190°C and thepre-heating time was 200s. The plate diameter was25mm and the gap was 1.2mm.
X-ray. X-ray diffractograms were obtained in aSiemens D5000 diffractometer with Cu radiation(50kV, 40mA). The scanning speed and the stepsize were 0.15°/min and 0.02°, respectively. Thespecimen rotation speed was 15rpm. The sampleswere taken directly from the melt coming out ofthe die before coating onto the paperboard. Thesesamples had an average thickness of 1mm andwere cut into a shape of 10 ¥ 10mm.
Transmission electron microscopy (TEM). Theclay–polymer structure was studied by transmis-sion electron microscopy (TEM) using a PhilipsTecnai 10 electron microscope. The coating wasfirst ripped off the paperboard, and was thenchlorosulphonated for a few days at room tem-perature, washed with ethanol and water and subsequently immersed in a 0.7% uranyl acetatesolution for at least 12h. After being washed withwater and dried, the film was embedded in epoxyand sectioned into approximately 50nm thick sec-tions using an RMC ultramicrotome.
Creasability testing. The creasability was deter-mined in a clamshell press, Econo cut model 20 ¥27. Five specimens, 100 ¥ 400mm in size, from eachof the coated paperboards, were tested. Each spec-imen was creased in both the machine and thetransverse directions on the coated side. The spec-imens were visually studied to determine thequality of the crease.
Pinholes. A dye solution (74-Service kit-224) wasused to assess the number of pinholes. The dyesolution consisted of Crocein Scarlet MOO powderand aerosol OT wetting agent. It was applied witha soft brush onto four randomly selected coatedpaperboard sheets (200 ¥ 250mm2) and left for 15min. After removal of the dye solution using awet cloth, the paperboards was turned upsidedown and the spots where the solution had penetrated the paperboard were counted.
Scanning electron microscopy. The laminatestructure was assessed using a JEOL JSM-5400scanning electron microscope. The specimens werecut into 50 ¥ 10mm2 pieces and freeze-fractured.They were subsequently sputtered for 30 + 30swith Au/Cd (60%/40%) using a Desk II sputterfrom Denton Vacuum.
M. KROOK, M. GÄLLSTEDT AND M. S. HEDENQVISTPackaging Technologyand Science
Infra-red (IR)-spectroscopy. A Perkin-Elmer 2000FTIR-spectrophotometer, equipped with a GoldenGate accessory from Grasseby Specac, was used toobtain reflection-IR spectra.
RESULTS AND DISCUSSION
Structure and processing
Extrusion process parameters were chosen toachieve a high extruder pressure, and thus ensurethe presence of high shear forces that would assistin the mechanical delamination of the silicatelayers.
The surface of the 4 wt.% composite was almostas smooth as the surface of the unfilled PE,although a small amount of what was believed tobe clay agglomerates was detected in the film.Figure 2a shows a SEM micrograph of a clayagglomerate in the surface of a sample extruded at305°C with 8.3 wt.% filler. The PE with the higherfiller content (8.3 wt.%) had a rougher surface witha larger amount of visible clay agglomerates. TEMshowed that the agglomerates contained numer-ous clay layers (Figure 2b).
The material extruded at 325°C had a highercontent of agglomerates than that extruded at305°C. A more effective destruction of agglomer-
ates and a better mixing was thus achieved at thelower extrusion temperature.
Adhesion
The air gap between the die outlet and the nip onthe pressure rolls was optimized to obtain suffi-cient adhesion between the unfilled polymer andthe paperboard at 305°C. The adhesion betweenthe PE–clay nanocomposite and the paperboarddecreased with increasing filler content andincreasing extrusion temperature (Figure 3).
The adhesion depends on the ability of thecoating to wet and penetrate into the paperboard.The wetting depends on the polarity/surfaceenergy and viscosity of the coating. The viscositydetermines the extent of coating penetration intothe board. The polarity should increase withincreasing melt temperature because of moreextensive oxidation. The melt temperature at theoutlet of the die was 10°C higher for the PEextruded at 325°C but, as mentioned previously,the adhesion not higher for the 325°C sample. IR,which covers a few microns into the film, did notreveal any signs of oxidation in any of the extrudedsamples. This suggested that oxidation was mildand was probably located to the outermost filmsurface (within a layer significantly less than 1mmthick). The viscosity decreases with increasing
Figure 2. (a) SEM micrograph of a large clay agglomerate (indicated bythe arrow). (b) TEM micrograph of a smaller clay agglomerate.
process temperature, and this should lead to abetter adhesion through a more extensive penetra-tion into the board. Thus, as in the case of polarity, this could not explain the trend inadhesion.
It was pointed out by Gervason et al.27 that thecoating thickness can influence the adhesion. Athicker coating cools more slowly and it may bespeculated that the slower cooling permits adeeper polymer penetration into the board beforesolidification. Figure 4 shows that the 305°C coat-ings were thicker than the 325°C coatings. This difference in thickness is the only explanation
available for the stronger adhesion at the lowertemperature.
SEM micrographs showed that the penetrationof PE into the paperboard was negligible (Figure5). It was observed visually, during adhesiontesting, that fibre-tear did occur for the unfilledsample extruded at 305°C but it was negligible inthe other samples. It was observed that thepolymer penetration was also low in a commercialPE–paperboard laminate.
The decrease in adhesion with increasing fillercontent was due to viscosity effects. Figure 6shows that the viscosity increased markedly with
M. KROOK, M. GÄLLSTEDT AND M. S. HEDENQVISTPackaging Technologyand Science
Figure 3. Adhesion of the coating to the paperboard,extruded at 305°C (�) and extruded at 325°C (�).
Figure 4.Thickness of the polymer layer. Extruded at305°C (�), extruded at 325°C (�).
Figure 5. SEM micrograph of unfilled PE extruded at325°C.
100
1000
104
105
106
0.01 0.1 1 10 100 1000
Com
plex
vis
cosi
ty (
Pa
s)
Shear rate (rad/s)
Figure 6. Complex viscosity as a function of shear rate forthe PE (thick line) and the 32 wt.% filler master batch
(thin line) at 190°C.
the incorporation of clay particles, even though theshear thinning effect was also greater in the filledpolymer. The dramatic effect of the increase in viscosity was shown in burning tests over an openflame. The droplet formation was heavy for thepure polymer and decreased very rapidly withincreasing filler content. The 8.3 wt.% compositedid not form any droplets at all.
Neck-in
The neck-in of the polymer melt increased withincreasing filler content. Compared to the unfilledpolyethylene, the neck width of the 8.3 wt.% fillersample was 2cm less at a melt temperature of305°C. At 325°C the decrease was 2.7cm. The neckwidth of the 4 wt.% filler sample was the same as that of the pure polymer and independent ofextrusion temperature.
Pinholes
The most highly filled composite (8.3 wt.%)extruded at 305°C showed the largest number ofpinholes. The average number was 80 holes/m2
and the number at 325°C was 40 holes/m2. In thecase of the pure PE and the PE with 4 wt.% filler,pinholes were absent. Pinholes may have beeninduced at the agglomerates, as was discussedearlier. In the most strongly filled samples, the red dye solution stained the agglomerates to some extent, particularly at the higher extrusiontemperature.
Morphology
TEM on the 4 and 8.3 wt.% systems revealed agood dispersion of the clay layers. They werelocated mainly in small entities containing a fewclay layers (Figures 7a, b). It also seemed as thoughthe layers were orientated preferentially along the extrusion direction. Voids were frequentlyobserved next to the layers, especially along thewidth of the layer. These voids were induced bythe diamond knife in the cutting operation, by thestaining operation or by delamination during the extrusion-coating process. Voids have beenobserved between clay layers in a previous study
on extruded and compression-moulded clay–poly-esteramide,28 but not to the same extent as wasobserved here. A study of the orientation of thevoids in relation to the cutting direction suggestedthat they were not caused by the knife. Moreover,voids were located only in the PE and not in the adjacent epoxy embedding. Interestingly, the
Figure 7. (a) TEM micrograph of the 4 wt.% filler sampleextruded at 325°C.The upper and lower arrows indicate,respectively, a void and clay layers. Scale bar: 2000nm. (b)TEM micrograph of the 8.3 wt.% filler sample extruded
at 325°C.The upper and lower arrows indicate,respectively, clay layers and a void. Scale bar: 1000nm.
chlorosulphonation fragmented the films differ-ently. The films with clay sustained the chloro-sulphonation better, which indicated that the voidswere probably not a consequence of chloro-sulphonation. Thus, it appears that the voids weregenerated by the mechanical action in the extru-sion-coating process. Indeed, it seems difficult toproduce non-covalently bonded clay–thermoplas-tic systems without any polymer–clay separationduring ‘severe’ melt processing, as in film blowingand extrusion-coating. Wang et al.29 observed thatthe impact strength decreased with increasing clay loading in film-blown PE. Although notstated, these changes were presumably due toclay–polymer delamination/void formation.
An X-ray study showed that the clay layers wereintercalated. The average d-spacing was 31.5Å,which was approximately 10Å larger than that in the pure PVP–montmorillonite (Figure 8). Nodifference was detected between the samplesextruded at 305°C and those extruded at 325°C.
Thermal analysis
In order to assess whether the PVP–clay surfacecould endure the necessary extrusion times andtemperatures, isothermal TGA measurements
were performed. Figure 9 shows the relativeweight vs. time for PVP-montmorillonite. At305°C, the decrease in weight was approximately5.5% over a period of 10 minutes. At 325°C and850°C, the decrease was 10% and 30% respectively.This indicated that PVP was to a large extent un-affected at the relevant processing temperaturesand extrusion times (approximately 2.5min).
As reported earlier, it has been noted thatpolyvinylpyrrolidone withstands high tempera-tures and has the ability to keep the clay layerstructure expanded.17 According to Hlavaty et al.,17
the major degradation process starts at 370°C.Non-isothermal TGA analysis at a heating rate
of 20°C/min from 30°C to 850°C (Figure 10)showed that the degradation temperature for thefilled PEs increased with increasing filler content.The difference in degradation temperature wasobtained by normalizing the TGA curves withrespect to the content of organic material anddefining the degradation temperature as the tem-perature corresponding to a 50% loss in weight.This yielded a degradation temperature for thefilled PEs which was 7.5°C higher than that of theunfilled PE at 4 wt.% and 12°C higher at 8.3 wt.%.This was probably due to limited absorption ofoxygen and to a reduction in the migration ofvolatile decomposition products from the compos-ite in the filled polymers. Gilman et al.30 proposethat a high-performance carbonaceous silicate charbuilds up on the surface during burning. This clay-
M. KROOK, M. GÄLLSTEDT AND M. S. HEDENQVISTPackaging Technologyand Science
Figure 8. X-ray diffractograms of the coatings extruded at305°C. (A) 8.3 wt.% filler; (B) 4 wt.% filler; (C)
PVP/montmorillonite; (D) Unfilled PE.The maximum peaks correspond to d-spacings of 31.5Å (A and B) and
22Å (C).
0.7
0.9
1.1
0 100 200 300 400 500 600
Rel
ativ
e w
eigh
t
Time (s)
305°C
325°C
850°C
Figure 9. Relative weight of PVP–clay vs. time at 305°C (upper curve), 325°C (middle curve) and 850°C
(lower curve).
reinforced surface char becomes an excellent insu-lator and an effective mass transport barrier, andthus slows both the oxygen supply and the escapeof combustion products generated during thedecomposition.
Mechanical properties
The variation in the grammage of the paperboard(230 ± 9g/m2) was too large to detect any signifi-cant contribution of the coating to its mechanicalproperties. In addition, the paperboard wasapproximately 15 times thicker (290 ± 14mm) thanthe coating (18–25mm). However, tensile measure-ments performed on the isolated polymer–claycoating shows that the films became stiffer andexhibited a lower fracture strain with increasingfiller content (Figure 11). The fracture straindecreased from 116% to 52% with increasing fillercontent for the samples extruded at 325°C. For thesamples extruded at 305°C, even the filled PE werevery ductile.
The ductility is important in several aspects, notleast in the creasing operation. The creasing knifeexposes the film to extensive bending and com-pressive stresses, and here a visual inspection ofthe creasing properties was made. The pure andfilled samples showed excellent creasability andno signs of cracking at the creases were observed.
Transport properties
The transport properties were affected byvoids/pinholes in the coatings. This was mostevident when the oxygen transmission rate wasmeasured. The filled polyethylenes showedextremely high values. Due to the high surfacetension of water, the water vapour transmissionwas, as expected, less sensitive to the presence ofvoids/pinholes. The water vapour permeabilitywas approximately independent of filler contentand at a level typical of PE (~0.34gmm/m2/day/atm).31 Thus, it seemed that the negative effectof the voids/pinholes was compensated for by theblocking effect of the clay.
CONCLUSIONS
The powerful melt mixing in the extrusion-coatingprocess evidently triggered the separation of theclay stacks into small evenly distributed entities. Italso seemed that the same process yielded voidsand pinholes. X-ray studies showed that the layerswithin small entities or large agglomerates wereintercalated. Even though clay agglomerates werevisible to the naked eye in the filled coating, itsuniform light brownish colour, its low drippingover an open flame and its high degradation
Figure 10. Relative weight vs. temperature for unfilled PE(solid line), 4 wt.% filler sample (dotted line) and 8.3 wt.%
filler sample (dashed line).
40
60
80
100
120
140
0 2 4 6 8 10
Fra
ctur
e St
rain
(%
)
Filler content (wt.%)
Figure 11. Fracture strain vs. filler content. Extruded at305°C (�), extruded at 325°C (�).
temperature suggested that the clay was relativelywell distributed.
Because of the higher viscosity, the lower extru-sion temperature yielded fewer agglomerates butmore pinholes. The presence of voids and pinholesaffected the barrier properties negatively. The coat-ings were, however, always ductile and the creas-ing properties were unaffected by the presence ofclay. Adhesion and neck-in were, for viscosityreasons, negatively affected.
Even though it is certainly a difficult task tocompletely eliminate void formation in severeprocesses such as extrusion-coating, it is possiblethat lower shear forces and covalent clay–polymerbinding can be possible routes. Future studies will elucidate whether this is possible. It may also turn out that lower shear rates will preventexfoliation and that covalent bonding induces brittleness.
ACKNOWLEDGEMENTS
B. Lindskog, STFI-Packforsk, Stockholm, is thanked forvaluable help. Mr S. Kahl, Royal Institute of Technology,is gratefully acknowledged for his kind help and valu-able comments. Special thanks are extended to Per Watleat Borealis for helping with the polymers and generat-ing the viscosity data, and Chris Bonnerup at IggesundPaperboard for help with the paperboard material. RonGartner of Nanocor Inc. is thanked for assistance regard-ing nanoparticles. Finally, the Swedish National Boardfor Industrial and Technical Development (VINNOVA)is thanked for financial support.
2. Mitsubishi Gas Chemical Co. Inc. Multilayer con-tainers featuring nano-nylon MXD6 barrier layerswith superior performance and clarity. Nanocor. Mitsubishi: 2003.
3. Leaversuch R. Plastics Technol., 2001; October, 64–69.4. Okada A, Kawasumi M, Kurauchi T, and Kamigaito
O. Polym. Prep. 1987; 28: 447–448.5. Vaia RA, Ishii H and Giannelis EP. Chem. Mater.
1993; 5: 1694–1696.6. Vaia RA, Jandt KD, Kramer EJ and Giannelis EP.
8. Laus M, Francescangeli O and Sandrolini F. J. Mater.Res. 1997; 12: 3134–3139.
9. Hasegawa N, Kawasumi M, Kato M, Usuki A andOkada A. J. Appl. Polym. Sci. 1998; 67: 87–92.
10. Vaia RA and Giannelis EP. Macromolecules 1997; 3:7990–7999.
11. Usuki A, Kato M, Okada A and Kurauchi T. J. Appl.Polym. Sci. 1997; 63: 137–139.
12. Kawasumi M, Hasegawa N, Kato M, Usuki A andOkada A. Macromolecules 1997; 30: 6333–6338.
13. Wang KH, Choi MH, Koo CM, Choi YS and ChungIJ. Polymer 2001; 42: 9819–9826.
14. Wang S, Hu Y, Tang Y, et al. J. Appl. Polym. Sci. 2002;89: 2583–2585.
15. Wang S, Hu Y, Zhongkai Q, Wang Z, Chen Z, Fan W. Mater. Lett. 2003; 57: 2675–2678.
16. Xie W, Gao Z, Liu K, Pan W-P, Vaia R, Hunter D,Singh A. Thermochim. Acta 2001; 367–368: 339–350.
17. Hlavaty V and Fajnor S. J. Therm. Anal. Calor. 2002;67: 113–118.
18. Wang KH, Xu M, Choi YS and Chung IJ. Polym. Bull.2001; 46: 499–505.
19. Gopakumar TG, Lee JA, Kontopoulou M and ParentJS, Polymer 2002; 43: 5483–5491.
20. Koo CM, Ham HT, Kim SO, Wang KH and ChungIJ. Macromolecules 2002; 35: 5116–5122.
21. Alexandre M, Dubois P, Sun T, Garces JM andJérôme R. Polymer 2002; 43: 2123–2132.
22. Association of Plastics Manufacturers in Europe.Environmental challenges: prevention. Report.APME: Brussels, 2001.
23. Adur AM, Volpe RA and Shih KS. United StatesPatent No. 6,358,576, 1998. International PaperCompany: Purchase, NY, USA, 1998.
24. Cavagna GA and Claytor RC. United States PatentNo. 5,153,061, 1992. Westvaco Corporation: NewYork, NY, USA.
25. Yoo SI, Lee TY, Yoon J-S, Lee I-M, Kim M-N, Lee HS.J. Appl. Polym. Sci. 2002; 83: 767–776.
26. Grim RE. Clay Mineralogy. McGraw-Hill: New York,1968.
27. Gervason G and Ducom J. Br. Polymer J. 1989; 21:53–59.
28. Krook M, Albertsson A-C, Gedde UW and Hedenqvist MS. Polym. Eng. Sci. 2002; 42: 1238–1246.
29. Wang KH, Koo CM and Chung IJ. J. Appl. Polym. Sci.2003; 89: 2131–2136.
30. Gilman JW, Kashiwagi T, Morgan AB, Harris R,Brassel L, Van Landingham M, Jackson CL. Flam-mability of Polymer Clay Nanocomposites Consortium:Year One Annual Report. National Technical Infor-mation Service (NTIS), Technology Administration,U.S. Department of Commerce, Springfield, IL,2000.
31. Plastics Design Library Staff. Permeability and OtherFilm Properties of Plastics and Elastomers. WilliamAndrew Publishing, Plastics Design Library: NewYork, 1995.
M. KROOK, M. GÄLLSTEDT AND M. S. HEDENQVISTPackaging Technologyand Science
