Analysis Of Multiwalled Carbon Nanotube Agglomerate Dispersion In Polymer Melts

For the commercial success of polymer - multiwalled carbon nanotube (MWNT) composites the production of these materials on industrial scale by melt processing is of significant importance. The complete dispersion of primary MWNT agglomerates in a polymer melt is difficult to achieve, making it an important and challenging technological problem. Hence, it is necessary to understand the process of MWNT agglomerate dispersion in a polymer melt. Based on an intensive literature research on mechanisms and influencing factors on dispersion of other agglomerated nanostructured fillers (e.g. carbon black), the main dispersion steps were evaluated and investigated concerning the agglomerated MWNT.Consequently, systematic investigations were performed to study the effect of the melt infiltration on MWNT agglomerate dispersion and to analyse the corresponding main dispersion mechanisms, namely rupture and erosion. The states of MWNT agglomerate dispersion were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. Additionally, the composite’s electrical resistivity was determined. In the prevailing study, polycarbonates (PC) varying in molecular weight were used to produce composites containing 1 wt% MWNT (Baytubes C150HP) as model systems and a discontinuous microcompounder was applied as melt mixing device. The agglomerate structure of the used MWNT material made them especially suitable for the reported investigations. The step of melt infiltration into the primary nanotube agglomerates plays a crucial role for their dispersion in the PC melt. During melt mixing when low shear rates were applied, better state of MWNT dispersion was obtained in high viscosity matrices because applied shear stresses were high. On the contrary, if high shear rates were applied, similar states of MWNT dispersion were obtained in low and high viscosity matrices although significantly lower shear stresses were applied in the low viscosity matrix as compared to the high viscosity matrix. The results indicate that if the applied shear stress values are compared, with increasing matrix viscosity the agglomerate dispersion gets worsen. This is attributed to the fact that low viscosity matrices can infiltrate relatively faster than high viscosity matrices into the agglomerate making them weaker and reducing the agglomerate strength. Thus, at sufficient shear rates MWNT agglomerates disperse relatively faster in low viscosity matrix. This illustrates a balance between the counteracting effects of viscosity on agglomerate infiltration and agglomerate dispersion. Additionally, the effect of matrix molecular weight on the size of un-dispersed MWNT agglomerates was investigated. Under similar conditions of applied shear stress, the composites based on low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices. This again highlights the role of matrix infiltration as the first step of dispersion. Following the step of melt infiltration, agglomerate size gets reduced due to the dispersion mechanisms. To analyse the corresponding contributions of different dispersion mechanisms (rupture and erosion), the kinetics of MWNT agglomerate dispersion was investigated. If high mixing speeds are employed dispersion is quite fast and needs less time as compared to low mixing speed. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion based on the kinetic study in the discontinuous mixer. Under the employed experimental conditions, at high mixing speeds, the dispersion was found to be governed by rupture dominant mechanism, whereas at low mixing speeds the dispersion was controlled by both mechanisms. As far as electrical resistivity is concerned, for a given content of MWNT as the state of dispersion improves, the resistivity values decrease significantly but only up to a plateau value. The composites produced using low viscosity matrices have lower resistivity values as compared to high viscosity matrices. Additionally, composites were prepared using additives, whereas the additives were found to be useful for improving filler dispersion and electrical conductivity

Role of processing history on the mechanical and electrical behavior of melt-compounded polycarbonate-multiwalled carbon nanotube nanocomposites

This work investigates the effects of primary compounding temperature and secondary melt processes on the mechanical response and electrical resistivity of polycarbonate filled with 3 wt % multiwalled carbon nanotubes (CNT). Nanocomposites were melt compounded in an industrial setting at a range of temperatures, and subsequently either injection molded or compression molded to produce specimens for the measurement of electrical resistivity, surface hardness, and uniaxial tensile properties. Secondary melt processing was found to be the dominant process in determining the final properties. The effects observed have been attributed to structural arrangements of the CNT network as suggested by morphological evidence of optical microscopy and resistivity measurements. Properties were found to be relatively insensitive to compounding temperature. The measured elastic moduli were consistent with existing micromechanical models

Melt processing and properties of Polyamide 6/Graphene nanoplatelet composites.

Graphene, due to its outstanding properties, has become the topic of much research activity in recent years. Much of that work has been on a laboratory scale however, if we are to introduce graphene into real product applications it is necessary to examine how the material behaves under industrial processing conditions. In this paper the melt processing of polyamide 6/graphene nanoplatelet composites via twin screw extrusion is investigated and structure-property relationships are examined for mechanical and electrical properties. Graphene nanoplatelets (GNPs) with two aspect ratios (700 and 1000) were used in order to examine the influence of particle dimensions on composite properties. It was found that the introduction of GNPs had a nucleating effect on polyamide 6 (PA6) crystallization and substantially increased crystallinity by up to 120% for a 20% loading in PA6. A small increase in crystallinity was observed when extruder screw speed increased from 50 rpm to 200 rpm which could be attributed to better dispersion and more nucleation sites for crystallization. A maximum enhancement of 412% in Young's modulus was achieved at 20 wt% loading of GNPs. This is the highest reported enhancement in modulus achieved to date for a melt mixed thermoplastic/GNPs composite. A further result of importance here is that the modulus continued to increase as the loading of GNPs increased even at 20 wt% loading and results are in excellent agreement with theoretical predictions for modulus enhancement. Electrical percolation was achieved between 10-15 wt% loading for both aspect ratios of GNPs with an increase in conductivity of approximately 6 orders of magnitude compared to the unfilled PA6.</p

Establishment, morphology and properties of carbon nanotube networks in polymer melts

As for nanofillers in general, the properties of carbon nanotube (CNT) -polymer composites depend strongly on the filler arrangement and the structure of the filler network. This article reviews our actual understanding of the relation between processing conditions, state of CNT dispersion and structure of the filler network on the one hand, and the resulting electrical, melt rheological and mechanical properties, on the other hand. The as-produced rather compact agglomerates of CNTs (initial agglomerates, >1 μm), whose structure can vary for different tube manufacturers, synthesis and/or purification conditions, have first to be well dispersed in the polymer matrix during the mixing step, before they can be arranged to a filler network with defined physical properties by forming secondary agglomerates. Influencing factors on the melt dispersion of initial agglomerates of multi-walled CNTs into individualized tubes are discussed in context of dispersion mechanisms, namely the melt infiltration into initial agglomerates, agglomerate rupture and nanotube erosion from agglomerate surfaces. The hierarchical morphology of filler arrangement resulting from secondary agglomeration processes has been found to be due to a competition of build-up and destruction for the actual melt temperature and the given external flow field forces. Related experimental results from in-line and laboratory experiments and a model approach for description of shear-induced properties are presented

The influence of injection molding parameters on electrical properties of PC/ABS-MWCNT nanocomposites

[EN] The influence of injection molding parameters on electrical properties and morphology of PC/ABS-MWCNT nanocomposites is presented in this article. Investigation is based on the masterbatch of 5.0wt% carbon nanotubes obtained by melt-mixing. Further processing includes dilution of this nanocomposite to desired concentrations on twin-screw extruder and injection molding or direct dilution of masterbatch in injection molding. Additionally, reprocessing of materials formed by compression and injection molding is presented along with the change in electrical conductivity. Morphology differs strongly between the two processing paths showing change in agglomeration behavior between nanotubes concentrations. Electrical properties show dependence on injection velocity and melt temperature in both applied processing paths. Moreover, electrical conductivity recovery is proved after injection and compression molding.This work is funded by the European Community's Seventh Framework Program (FP7-PEOPLE-ITN-2008) within the CONTACT project Marie Curie Fellowship under grant number 238363. The authors would like to thank to Javier Gomez (SCIC, University Jaume I of Castellon) for support with electron microscopy measurements.Wegrzyn, M.; Juan Nadal, S.; Benedito, A.; Giménez Torres, E. (2013). The influence of injection molding parameters on electrical properties of PC/ABS-MWCNT nanocomposites. Journal of Applied Polymer Science. 130(3):2152-2158. https://doi.org/10.1002/app.39412S215221581303Pötschke, P., Dudkin, S. M., & Alig, I. (2003). Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites. Polymer, 44(17), 5023-5030. doi:10.1016/s0032-3861(03)00451-8Duong, H. M., Yamamoto, N., Bui, K., Papavassiliou, D. V., Maruyama, S., & Wardle, B. L. (2010). Morphology Effects on Nonisotropic Thermal Conduction of Aligned Single-Walled and Multi-Walled Carbon Nanotubes in Polymer Nanocomposites. The Journal of Physical Chemistry C, 114(19), 8851-8860. doi:10.1021/jp102138cLee, S. H., Kim, J. H., Choi, S. H., Kim, S. Y., Kim, K. W., & Youn, J. R. (2009). Effects of filler geometry on internal structure and physical properties of polycarbonate composites prepared with various carbon fillers. Polymer International, 58(4), 354-361. doi:10.1002/pi.2532Mari, D., & Schaller, R. (2009). Mechanical spectroscopy in carbon nanotube reinforced ABS. Materials Science and Engineering: A, 521-522, 255-258. doi:10.1016/j.msea.2008.09.102Krause, B., Pötschke, P., & Häußler, L. (2009). Influence of small scale melt mixing conditions on electrical resistivity of carbon nanotube-polyamide composites. Composites Science and Technology, 69(10), 1505-1515. doi:10.1016/j.compscitech.2008.07.007Villmow, T., Pegel, S., Pötschke, P., & Wagenknecht, U. (2008). Influence of injection molding parameters on the electrical resistivity of polycarbonate filled with multi-walled carbon nanotubes. Composites Science and Technology, 68(3-4), 777-789. doi:10.1016/j.compscitech.2007.08.031Richter, S., Saphiannikova, M., Jehnichen, D., Bierdel, M., & Heinrich, G. (2009). Experimental and theoretical studies of agglomeration effects in multi-walled carbon nanotube-polycarbonate melts. Express Polymer Letters, 3(12), 753-768. doi:10.3144/expresspolymlett.2009.94Pegel, S., Pötschke, P., Petzold, G., Alig, I., Dudkin, S. M., & Lellinger, D. (2008). Dispersion, agglomeration, and network formation of multiwalled carbon nanotubes in polycarbonate melts. Polymer, 49(4), 974-984. doi:10.1016/j.polymer.2007.12.024Park, D. H., Yoon, K. H., Park, Y.-B., Lee, Y. S., Lee, Y. J., & Kim, S. W. (2009). Electrical resistivity of polycarbonate/multiwalled carbon nanotube composites under varying injection molding conditions. Journal of Applied Polymer Science, 113(1), 450-455. doi:10.1002/app.29989Lellinger, D., Xu, D., Ohneiser, A., Skipa, T., & Alig, I. (2008). Influence of the injection moulding conditions on the in-line measured electrical conductivity of polymer-carbon nanotube composites. physica status solidi (b), 245(10), 2268-2271. doi:10.1002/pssb.200879619Tiusanen, J., Vlasveld, D., & Vuorinen, J. (2012). Review on the effects of injection moulding parameters on the electrical resistivity of carbon nanotube filled polymer parts. Composites Science and Technology, 72(14), 1741-1752. doi:10.1016/j.compscitech.2012.07.009Mahmoodi, M., Arjmand, M., Sundararaj, U., & Park, S. (2012). The electrical conductivity and electromagnetic interference shielding of injection molded multi-walled carbon nanotube/polystyrene composites. Carbon, 50(4), 1455-1464. doi:10.1016/j.carbon.2011.11.004Yang, L., Liu, F., Xia, H., Qian, X., Shen, K., & Zhang, J. (2011). Improving the electrical conductivity of a carbon nanotube/polypropylene composite by vibration during injection-moulding. Carbon, 49(10), 3274-3283. doi:10.1016/j.carbon.2011.03.054Li, S.-N., Li, B., Li, Z.-M., Fu, Q., & Shen, K.-Z. (2006). Morphological manipulation of carbon nanotube/polycarbonate/polyethylene composites by dynamic injection packing molding. Polymer, 47(13), 4497-4500. doi:10.1016/j.polymer.2006.04.051Chandra , A. Kramschuster , A. J. Hu , X. Turng , S. Proc Annual Technical Conference of the Society of Plastics Engineers 2007 3 2184Zhang, H., & Zhang, Z. (2007). Impact behaviour of polypropylene filled with multi-walled carbon nanotubes. European Polymer Journal, 43(8), 3197-3207. doi:10.1016/j.eurpolymj.2007.05.010Rios, P. F., Ophir, A., Kenig, S., Efrati, R., Zonder, L., & Popovitz-Biro, R. (2010). Impact of injection-molding processing parameters on the electrical, mechanical, and thermal properties of thermoplastic/carbon nanotube nanocomposites. Journal of Applied Polymer Science, 120(1), 70-78. doi:10.1002/app.32983Cipriano, B. H., Kota, A. K., Gershon, A. L., Laskowski, C. J., Kashiwagi, T., Bruck, H. A., & Raghavan, S. R. (2008). Conductivity enhancement of carbon nanotube and nanofiber-based polymer nanocomposites by melt annealing. Polymer, 49(22), 4846-4851. doi:10.1016/j.polymer.2008.08.05

Microwave heating of polymers: Influence of carbon nanotubes dispersion on the microwave susceptor effectiveness

"This is the peer reviewed version of the following article: Galindo, Begoña, Adolfo Benedito, Fernando Ramos, and Enrique Gimenez. 2016. Microwave Heating of Polymers: Influence of Carbon Nanotubes Dispersion on the Microwave Susceptor Effectiveness. Polymer Engineering & Science 56 (12). Wiley: 1321 29. doi:10.1002/pen.24365, which has been published in final form at https://doi.org/10.1002/pen.24365. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] Carbon nanotubes dispersion within the polymer matrix is a very important factor to take into account when developing new nanocomposites with optimized properties. In this article, dispersion studies have been carried out with polypropylene filled with 1% of multiwall carbon nanotubes. The nanocomposites were obtained by melt compounding in a corotative twin screw extruder. Processing parameters as screw speed, screw configuration and feeding technology were modified to analyse their effect onto carbon nanotubes dispersion. Developed nanocomposites were exposed to microwave heating (5.8 GHz, 700 W, 60 min) and heating temperature was monitored. The relation between dispersion level of carbon nanotubes and heating effectiveness was studied. Microwave heating efficiency of carbon nanotubes was increased as dispersion was improved. Electrical conductivity of nanocomposites was measured and used as indirect variable of microwave heating susceptor of carbon nanotubes nanocomposites. Higher electrical conductivity indicates a better microwave susceptor propertiy of the nanocomposite. (C) 2016 Society of Plastics EngineersGalindo-Galiana, B.; Benedito-Borrás, A.; Ramos, F.; Giménez Torres, E. (2016). Microwave heating of polymers: Influence of carbon nanotubes dispersion on the microwave susceptor effectiveness. Polymer Engineering & Science. 56(12):1321-1329. https://doi.org/10.1002/pen.24365S132113295612Ku, H. S., Siu, F., Siores, E., & Ball, J. A. R. (2003). Variable frequency microwave (VFM) processing facilities and application in processing thermoplastic matrix composites. Journal of Materials Processing Technology, 139(1-3), 291-295. doi:10.1016/s0924-0136(03)00238-3Ku, H. S., MacRobert, M., Siores, E., & Ball, J. A. R. (2000). Variable frequency microwave processing of thermoplastic composites. Plastics, Rubber and Composites, 29(6), 278-284. doi:10.1179/146580100101541076Williams, N. H. (1967). Curing Epoxy Resin Impregnates Pipe at 2450 Megahertz. Journal of Microwave Power, 2(4), 123-127. doi:10.1080/00222739.1967.11688661Antonio, C., & Deam, R. T. (2005). Comparison of linear and non-linear sweep rate regimes in variable frequency microwave technique for uniform heating in materials processing. Journal of Materials Processing Technology, 169(2), 234-241. doi:10.1016/j.jmatprotec.2005.03.024I. Gómez J. Aguilar Ciencia UANL 2005AGUILAR-GARIB, J. A., GARCÍA, F., & VALDEZ, Z. (2009). Estimating resistive and dielectric effects during microwave heating of Fe0.22Ni0.67Mn2.11O4. Journal of the Ceramic Society of Japan, 117(1367), 801-807. doi:10.2109/jcersj2.117.801Harper, J., Price, D., & Zhang, J. (2005). Use of Fillers to Enable the Microwave Processing of Polyethylene. Journal of Microwave Power and Electromagnetic Energy, 40(4), 219-227. doi:10.1080/08327823.2005.11688543Ling, Q., Sun, J., Zhao, Q., & Zhou, Q. (2009). Microwave absorbing properties of linear low density polyethylene/ethylene–octene copolymer composites filled with short carbon fiber. Materials Science and Engineering: B, 162(3), 162-166. doi:10.1016/j.mseb.2009.03.023Shim, H. C., Kwak, Y. K., Han, C.-S., & Kim, S. (2009). Enhancement of adhesion between carbon nanotubes and polymer substrates using microwave irradiation. Scripta Materialia, 61(1), 32-35. doi:10.1016/j.scriptamat.2009.02.060Xie, R., Wang, J., Yang, Y., Jiang, K., Li, Q., & Fan, S. (2011). Aligned carbon nanotube coating on polyethylene surface formed by microwave radiation. Composites Science and Technology, 72(1), 85-90. doi:10.1016/j.compscitech.2011.10.003Wadhawan, A., Garrett, D., & Perez, J. M. (2003). Nanoparticle-assisted microwave absorption by single-wall carbon nanotubes. Applied Physics Letters, 83(13), 2683-2685. doi:10.1063/1.1615679F. Naab M. Dhoubhadel O.W. Holland J.L. Duggan J. Roberts F.D. McDaniel Proceedings Of the International Conference on PIXE and its Analytical Applications Portoroz Slovenia 2004Mack, C., Sathyanarayana, S., Weiss, P., Mikonsaari, I., Hübner, C., Henning, F., & Elsner, P. (2012). Twin-screw extrusion of multi walled carbon nanotubes reinforced polycarbonate composites: Investigation of electrical and mechanical properties. IOP Conference Series: Materials Science and Engineering, 40, 012020. doi:10.1088/1757-899x/40/1/012020Castillo, F. Y., Socher, R., Krause, B., Headrick, R., Grady, B. P., Prada-Silvy, R., & Pötschke, P. (2011). Electrical, mechanical, and glass transition behavior of polycarbonate-based nanocomposites with different multi-walled carbon nanotubes. Polymer, 52(17), 3835-3845. doi:10.1016/j.polymer.2011.06.018Coleman, J. N., Cadek, M., Blake, R., Nicolosi, V., Ryan, K. P., Belton, C., … Blau, W. J. (2004). High Performance Nanotube-Reinforced Plastics: Understanding the Mechanism of Strength Increase. Advanced Functional Materials, 14(8), 791-798. doi:10.1002/adfm.200305200Krause, B., Pötschke, P., & Häußler, L. (2009). Influence of small scale melt mixing conditions on electrical resistivity of carbon nanotube-polyamide composites. Composites Science and Technology, 69(10), 1505-1515. doi:10.1016/j.compscitech.2008.07.007Prashantha, K., Soulestin, J., Lacrampe, M. F., Claes, M., Dupin, G., & Krawczak, P. (2008). Multi-walled carbon nanotube filled polypropylene nanocomposites based on masterbatch route: Improvement of dispersion and mechanical properties through PP-g-MA addition. Express Polymer Letters, 2(10), 735-745. doi:10.3144/expresspolymlett.2008.87Benedito, A., Buezas, I., Giménez, E., Galindo, B., & Ortega, A. (2011). Dispersion and characterization of thermoplastic polyurethane/multiwalled carbon nanotubes by melt mixing. Journal of Applied Polymer Science, 122(6), 3744-3750. doi:10.1002/app.34788Villmow, T., Pötschke, P., Pegel, S., Häussler, L., & Kretzschmar, B. (2008). Influence of twin-screw extrusion conditions on the dispersion of multi-walled carbon nanotubes in a poly(lactic acid) matrix. Polymer, 49(16), 3500-3509. doi:10.1016/j.polymer.2008.06.010Kasaliwal, G. R., Göldel, A., Pötschke, P., & Heinrich, G. (2011). Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion. Polymer, 52(4), 1027-1036. doi:10.1016/j.polymer.2011.01.007Krause, B., Boldt, R., & Pötschke, P. (2011). A method for determination of length distributions of multiwalled carbon nanotubes before and after melt processing. Carbon, 49(4), 1243-1247. doi:10.1016/j.carbon.2010.11.04

Characterization of the state of dispersion of carbon nanotubes in polymer nanocomposites

A practical overview of possibilities and limits to characterize the state of dispersion of carbon nanotubes (CNT) in polymer based nanocomposites is given. The most important and widely available methods are discussed with practical employment in mind. One focus is the quantitative characterization of the state of dispersion in solid samples using microscopy techniques such as optical microscopy or transmission electron microscopy. For dispersions of CNTs in aqueous media, solvents or monomers a sedimentation analysis is presented. This way dispersability and dispersion state of CNTs can be assessed. Indirect methods such as electrical conductivity measurements and rheological tests, dynamic differential scanning calorimetry and mechanical test are discussed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Effects of particle size and surface chemistry on the dispersion of graphite nanoplates in polypropylene composites

Carbon nanoparticles tend to form agglomerates with considerable cohesive strength, depending on particle morphology and chemistry, thus presenting different dispersion challenges. The present work studies the dispersion of three types of graphite nanoplates (GnP) with different flake sizes and bulk densities in a polypropylene melt, using a prototype extensional mixer under comparable hydrodynamic stresses. The nanoparticles were also chemically functionalized by covalent bonding polymer molecules to their surface, and the dispersion of the functionalized GnP was studied. The effects of stress relaxation on dispersion were also analyzed. Samples were removed along the mixer length, and characterized by microscopy and dielectric spectroscopy. A lower dispersion rate was observed for GnP with larger surface area and higher bulk density. Significant re-agglomeration was observed for all materials when the deformation rate was reduced. The polypropylene-functionalized GnP, characterized by increased compatibility with the polymer matrix, showed similar dispersion effects, albeit presenting slightly higher dispersion levels. All the composites exhibit dielectric behavior, however, the alternate current (AC) conductivity is systematically higher for the composites with larger flake GnP.This work was funded by National Funds through FCT-Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2013 and FEDER funds through the COMPETE 2020 Programme under the project number POCI-01-0145-FEDER-007688. We acknowledge Mrs. Uta Reuter from Leibniz-Institut für Polymerforschung Dresden e.V. for TEM specimen preparation and image acquisition for the composites.info:eu-repo/semantics/publishedVersio

Controlling the dynamic percolation of carbon nanotube based conductive polymer composites by addition of secondary nanofillers: The effect on electrical conductivity and tuneable sensing behaviour

In this paper, the electrical properties of ternary nanocomposites based on thermoplastic polyurethane (TPU) and multi-walled carbon nanotubes (MWCNTs) are studied. In particular two nanofillers - differing in shape and electrical properties - are used in conjunction with MWCNTs: an electrically conductive CB and an insulating needle-like nanoclay, sepiolite. The ternary nanocomposites were manufactured in a number of forms (extruded pellets, filaments and compression moulded films) and their morphological and electrical properties characterised as function of time and temperature. The presence of both secondary nanofillers is found to affect the formation of a percolating network of MWCNTs in TPU, inducing a reduced percolation threshold and tuneable strain sensing ability. These ternary nanocomposites can find application as conductive and multi-functional materials for flexible electronics, sensing films and fibres in smart textiles. (c) 2012 Elsevier Ltd. All rights reserved