Thermo Scientific

Making and AnalyzingPolymer Nanocomposites

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APPLICATION NOTE

AuthorsAuthorsAuthorsAuthorsAuthorsMatthias Jährling, Dirk Hauch and Fabian MeyerThermo Fisher Scientific, Karlsruhe, Germany

Producing high-performance polymer-compositesby embedding nanoparticles using twin screwextrusion

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IntroductionIntroductionIntroductionIntroductionIntroductionCarbon nanotubes are graphite sheets rolled into seam-less tubes, with diameters of just a few nanometersand lengths up to centimeters. Nanotubes have receiv-ed much attention because of their unique mechanical,electrical and thermal properties.

There are a large number of potential applications forCNTs, especially in the field of polymer compounds,where they are used to improve mechanical and electri-cal properties. Polymer nanocomposites are frequentlyused in the automotive and aviation industries, as wellas in construction materials for windmill blades.

Key to unleashing the unique properties of the polymernanocomposites is dispersion of the CNTs thoroughlyin the polymer matrix. Only when the CNT particles aredispersed homogeneously within the polymer and theformation of larger clusters is avoided, can the desiredproperty improvements be achieved. The improvedmechanical properties of the final compound can betested by means of dynamic mechanical thermal analysis(DMTA) which can be performed, for instance, with arotational rheometer [1].

One approach that can lead to a homogeneous distri-bution of the CNT particles within the polymer matrix isthe use of CNT suspensions for the extrusion process.For this the CNTs are functionalized first (i.e. by amina-tion) and dispersed afterwards in a carrier liquid likeethanol by means of high shear mixing or ultra sonictreatment. The obtained CNT suspension is then feedinto the extrusion process. Using CNT suspensions inthe extrusion process also avoids the formation of CNTdust in the laboratory environment.

The aim of this report is to demonstrate that CNT sus-pensions can be used to produce polymer nanocompo-sites by means of twin screw extrusion. With the described

procedure a homogeneous distribution of the CNTs inthe polymer matrix can be achieved in order to obtainthe desired property improvements for the polymernanocomposite.

Material and methodsMaterial and methodsMaterial and methodsMaterial and methodsMaterial and methodsTTTTTest materest materest materest materest materialialialialial- Base Polymer: Polypropylene Metocene HM562S (LyondellBasell)- Two CNT-Ethanol suspensions with different functiona- lization (Rescoll/France)

TTTTTest equipmentest equipmentest equipmentest equipmentest equipment- Torque rheometer system Thermo ScientificTM HAAKETM

PolyLab OS System- Co-rotating twin screw extruder Thermo ScientificTM

HAAKETM Rheomex PTW16 OS System (L/D = 40)- Gravimetric RotoTube feeder for pellets- Liquid feeding pump for the suspensions- Vacuum pump- Strand line with Varicut pelletizer

TTTTTest conditionsest conditionsest conditionsest conditionsest conditions- Screw speed: 250 rpm- Temperature profile: 20°/230°/250°/250°/230°/220°/ 220°/200°/200°- Feed rate PP: 0.919 kg/h- Feed rate CNT-suspension: 0.114 kg/h (equivalent to 0.5 % CNT in PP)

TTTTTest prest prest prest prest procedurocedurocedurocedurocedureeeeeThe complete extruder and screw configuration is present-ed in Fig. 1. In the first stage (zone 1) the polypropylenewas added and molten in the first mixing section (zone 2). The CNT suspension was dosed into the second feedingport (zone 3) into the polypropylene melt by means ofa liquid feeding pump. The ethanol of the suspensionwas removed from the extruder using an atmosphericventing port in zone 4 and a vacuum venting in zone 9.

Key wordsKey wordsKey wordsKey wordsKey wordsCompounding, Carbon nanotubes, Composites,Twin screw extrusion

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Fig. Fig. Fig. Fig. Fig. 11111: : : : : Extruder- and screw configuration.

The CNTs and the polypropylene were thoroughly mixedand sheared in two mixing sections in zones 5/6 andzone 8.

ResultsResultsResultsResultsResultsDuring the test, the melt pressure at the die was measured.Fig. 3 shows this melt pressure as an overlay of threedifferent extrusion tests. One test was done with the purepolypropylene, one test with the addition of CNT sus-pension “1“ and one with CNT suspension “4“.

It can be clearly seen that the pressure increased whena CNT suspension was added. The pressure differencebetween the two different suspen-sions itself was notsignificant. The extruded material was then formed intoa strand, which was cooled down in a water bath andcut into pellets by a pelletizer.

Using our mini injection moulding machine, the ThermoScientificTM HAAKETM MiniJet System those pellets wereinjection moulded into specimens like disks and DMTAbars for further investigation.

Fig. 4 shows a microscopic picture taken from specimensmade from the PP compound containing 0.5% CNT fromsuspension “1“.

In this picture no agglomeration can be seen and the CNTsseem to be evenly distributed in the polymer matrix.Fig. 5 shows a microscopic picture taken from the PPcompound containing 0.5% CNT from suspension “4“.This picture shows a large amount of agglomerates.The dispersion seems to be much worse than theresult we got from suspension “1“.

Fig. Fig. Fig. Fig. Fig. 22222: : : : : Extrusion conditions.

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Fig.Fig.Fig.Fig.Fig. 3 3 3 3 3::::: Pressure at Die-Had.

Fig.Fig.Fig.Fig.Fig. 4 4 4 4 4::::: PP with 0.5% of CNT “1“.

Fig.Fig.Fig.Fig.Fig. 5 5 5 5 5::::: PP with 0.5% of CNT “2“.

ConclusionConclusionConclusionConclusionConclusionThe PolyLab System with the lab scale twin screw com-pounder, Rheomex PTW16, can be used to prepare com-pounds from polymers and CNTs using CNT suspensions.

The result of these tests shows significant differencesbetween the compounds made with the differentlyfunctionalized CNTs.

AcknowledgementAcknowledgementAcknowledgementAcknowledgementAcknowledgementWe would like to thank the Fraunhofer Institute for Manu-facturing Engineering and Automation IPA in Stuttgart,Germany for their input and the Research CompanyRESCOLL in Pessac, France for their kind co-operationand supplying the CNT-suspensions. We also thankVolker Räntzsch from the Karlsruhe Institute of Technologyin Germany for providing the microscopic images.

ReferenceReferenceReferenceReferenceReference[1] Thermo Scientific Application note V241 “Dynamic mechanical thermal analysis (DMTA) on polymer nanocomposites“ Fabian Meyer, Klaus Oldörp and Frits de Jong

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APPLICATION NOTE

AuthorsAuthorsAuthorsAuthorsAuthorsFabian Meyer, Klaus Oldörp and Frits de JongThermo Fisher Scientific, Karlsruhe, Germany

Dynamic mechanical thermal analysis (DMTA)on polymer nanocomposites

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IntroductionIntroductionIntroductionIntroductionIntroductionPolymer nanocomposites (PNC) are materials that consistof a polymer matrix with embedded particles with a sizeof 100 nanometers or smaller. Typical nanoparticles arenanoclays, carbon nanotubes or nanofibers and graphen-es. Compared to unfilled polymers, polymer nanocom-posites show improved properties that make them in-teresting for various technical applications. In particular,the greater mechanical strength of polymeric materialscombined with low weight are desired properties. Addi-tionally the incorporation of nanocomponents can leadto an improved heat and chemical resistance as well aselectric conductivity. Nowadays, polymer nanocompositesare frequently used in the automotive and aviation in-dustries, as well as in construction materials for windmillblades.

Polymer nanocomposites can be produced by mixingthe nanoparticles into the molten polymer matrix usingextrusion. One way to achieve proper mixing during theextrusion process is to use nanoparticles that are pre-dispersed in a carrier liquid and to feed the dispersioninto the extruder. Only when the particles are distributedhomogeneously inside the polymer matrix and no largerclusters are formed, the composite material exhibit thedesired properties.

For testing the mechanical properties of a polymernano-composite, dynamic mechanical thermal analysis(DMTA) can be used. DMTA can be performed in torsionwith a rotational rheometer. The material is exposed tooscillatory shear while the temperature is changing con-tinuously. The obtained data is used to identify charac-teristic phase changes such as the glass transition orthe occurring of melting and crystallization. In additionto this, DMTA is used to determine the solid material’smechanical performance with important application re-

lated properties such as stiffness, brittleness, dampingor impact resistance. The rheological parameters storagemodulus (G’), loss modulus (G’’) and the loss or damp-ing factor (tan δ) are obtained from DMTA. The storagemodulus represents the elastic, and the loss modulusrepresents the viscous properties of a material. For so-lids, the storage modulus is larger than the loss modulusand vice versa for fluids. The loss factor is the ratio ofG’’ and G’ and is also a measure for the damping pro-perties of a material. Fig. 1 shows the schematic diagramfor DMTA on a semi-crystalline polymer. The glass tran-sition can be identified using different approaches. Themost common approach for rheological tests uses themaximum of the loss modulus (Fig.1). The onset of thedecrease of the storage modulus or the maximum in thetan δ (G’’/G’) are two alternative methods. At room tempe-rature, polymer nanocomposites are usually in the glassystate and show high values for G’, indicating the high stiff-ness of the material. Compared to the unfilled polymers,polymer nanocomposites show higher G’ values in theglassy state indicating their greater mechanical strength.

Key wordsKey wordsKey wordsKey wordsKey wordsDMTA, Solids clamping tool, Glass transtion

Fig. 1:Fig. 1:Fig. 1:Fig. 1:Fig. 1: Schematic drawing of dynamic mechanical thermal analysisresults of a semi-crystalline polymer.

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Smaller phase transitions at temperatures way below themain glass transition can occur for copolymers and po-lymers that carry side chains. The additional peak inthe damping factor can improve the impact resistanceof a polymer. An example for such a material would behigh impact polystyrene (HIPS), an engineering plasticwith a polystyrene backbone and rubber side chains.

Fig. Fig. Fig. Fig. Fig. 22222: : : : : Solids clamping tool with carbon fiber enforced compositesample.

Material and methodsMaterial and methodsMaterial and methodsMaterial and methodsMaterial and methodsTo extend its range of testing methods into the field ofcomposites and other solids, the Thermo ScientificTM

HAAKETM MARSTM rheometer can be equipped with asolids clamping tool [1]. The temperature control forthis setup is provided by the Controlled Test Chamber(CTC) (Fig. 2).

The patented design of the CTC, which uses a combi-nation of radiation heating and convection heating, createsa large uniform heating zone inside its gold plated testchamber (see Fig. 2) thus allowing testing of largersamples under uniform temperature conditions. Thesolids clamping tool can be equipped with special jawsfor soft, medium or hard samples.

With the latter, the jaws are even able to fix hard compo-site materials with smooth surfaces during oscillatorytesting. Due to the unique design with two moving jaws,the solids clamping tool automatically positions thesample in the axis of the rheometer, which is mandatoryto avoid any error from eccentric placement.

Two different composite materials were tested using theHAAKE MARS rheometer, CTC and solids clamping tool.

The first sample was a lightweight carbon fiber enforcedmaterial, which could be used, for instance, in airplaneconstruction. The second sample was a glass fiberenforced polyphenylene-sulfide (PPS). Such materialsare used for applications where a high mechanical andthermal stability are required.

DMTA was performed with both samples. The carbonfiber enforced material was tested in a temperaturerange between -100 °C and +240 °C. A constant oscilla-tory deformation γ of 0.1% was applied with a frequencyof 1 Hz. During the entire test, a constant axial force of-1 N (pulling force) was applied.

The glass fiber enforced PPS was tested from 30 °C to250 °C. A constant oscillatory deformation of 0.01% wasapplied at a constant frequency of 1 Hz. The axial forcewas kept constant at zero Newton during the tests.All tests were performed with a heating rate of 2 °C/min.

Results and discussionResults and discussionResults and discussionResults and discussionResults and discussionFig. 3 shows the results of the DMTA tests with the carbonfiber enforced sample. The data reveals the high stiff-ness of the material at room temperature, with a storagemodulus G’ of more than 3 x 109 Pa. The results alsoshow three transition temperatures of the sample repre-sented by the local maxima of the loss modulus G’’. Thebiggest change of the rheological properties occurs bet-ween 80 and 150 °C. The two maxima of G’’ at 99 °Cand 115 °C indicate the glass transitions of two differentcomponents in this temperature range. The excellentreproducibility of the test results was shown by com-paring the results of two independent tests run with twodifferent specimens of the same material. The two sets ofcurves shown in Fig. 3 are almost perfectly identical.

During the measurement, the rheometer applied a cons-tant small pulling force on the sample to compensatefor any thermal expansion or contraction (see black curvein Fig. 4). This results in a lift motion of the rheometer,that reacts to any change in sample length. This infor-mation can be used to check whether the clamps wereable to hold the sample or might have lost their grip. Ina plot of the sample length as a function of temperature,any slipping of the sample between the jaws of theclamps would show as a step-change. The smoothprogression of the orange curve in Fig. 4 documents theclamp’s steady grip even on such a hard material.

Apart from its diagnostic value, the data shown in Fig. 4contains valuable information about the sample itself.The length decrease with increasing temperature reflectsthe negative temperature expansion coefficient (α) somecarbon fiber enforced materials show in fiber direction.One can even see from the change in slope, that thematerial’s α changes around the major transition tempe-ratures starting at 80°.

Fig. 5 shows the results of the DMTA tests with the glassfiber enforced material. Also this material shows a highstiffness at room temperature with a storage modulus G’of above 3 x 109 Pa. The glass transition temperature,

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HAAKE RheoWin 4.69.0021

HAAKE RheoWin 4.69.0021

Fig. 3: Fig. 3: Fig. 3: Fig. 3: Fig. 3: Storage modulus G’ (red), loss modulus G“ (blue) andtan (δ) (green) as a function of temperature for the carbon basedsample. The glass transition temperature TG is indicated by thegreen line. The results of 2 independent tests (open and filledsymbols) run on fresh samples each, show the excellent repro-ducibility of the results.

Fig. 4: Fig. 4: Fig. 4: Fig. 4: Fig. 4: Constant normal force (black) and decreasing samplelength (orange) during a temperature increase from -100 °C to240 °C on the carbon fiber enforced sample.

indicated by the maximum in the loss modulus G’’, wasoccurring at 101 °C. At temperatures above the glasstransition, the material transformed into a rubber elasticcondition, where the moduli data changed less withincreasing temperature.

Also for this measurement, the sample length overtemperature plot shows the perfect grip of the solidsclamping tool. Compared to the carbon fiber enforcedsample, this material has a positive thermal expansioncoefficient, which does not change around the glasstransition temperature. From the data in Fig. 5, aconstant coefficient of approximately α = 3.3 × 10-6 K-1

can be calculated.

HAAKE RheoWin 4.69.0021

Fig. 5: Fig. 5: Fig. 5: Fig. 5: Fig. 5: Storage modulus G’ (red), loss modulus G“ (blue) andtan (δ) (green) as a function of temperature for a glass fiberenforced PPS sample. The glass transition temperature TG isindicated by the black line.

HAAKE RheoWin 4.69.0021

Fig. 6: Fig. 6: Fig. 6: Fig. 6: Fig. 6: Constant normal force (black) and increasing sample length(orange) during a temperature increase from 30 °C to 250 °C onone of the glass fiber enforced PPS samples.

SummarySummarySummarySummarySummaryThe special design of the solids clamping tool acces-sory for the HAAKE MARS rheometer combines easyhandling with high precision and perfect reproducibilityof test results. Different composite samples with veryhard and smooth surfaces have been tested with bothyielding very good results.

Using the rheometer’s lift and normal force sensor incombination with the solids clamping tool provides aneasy way to verify the perfect grip on the sample andthus the reliability of the data collected. Due to the uniqueprecision of both lift and normal force sensor, importantdata about the thermal expansion of the samples can becollected simultaneously. This allows, for example, thecalculation of the sample’s thermal expansion coefficient.

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With the Controlled Test Chamber and solids clampingtool, the HAAKE MARS rheometer is able to extend itsrange of testing capabilities into the field of dynamicmechanical thermal analysis. In combination with aclassical rheological setup like a Peltier temperaturecontrol module and cone & plate geometries, theHAAKE MARS rheometer is an ideal and cost-effectivesolution for testing polymer composites and their liquidbase materials on one instrument.

ReferenceReferenceReferenceReferenceReference[1] Thermo Scientific Product Information P004 “Solids clamping tool for Dynamic Mechanical Thermal Analysis (DMTA) with HAAKE MARS rheometers“ Cornelia Küchenmeister-Lehrheuer, Fabian Meyer and Klaus Oldörp

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