IntroductionIntroductionIntroductionIntroductionDue to the steady growth of communication technology and the adverse effects of electromagnetic radiations on the human body and electronic devices, it is critical to reduce the electromagnetic interference (EMI) and its impact on medical apparatus and electronic engineering. In that context, polymer/multi-walled carbon nanotubes (MWNT) nanocomposites are proposed for their high EMI shielding performance.1-11 The strategy is to render the polymer conductive by adding MWNTs and to promote wave absorption by foaming the polymer-based composite. These MWNT/PU polymeric foams thus show a promising EMI shielding efficiency due to their high capacity to absorb electromagnetic radiation at low MWNT content.

Foams of Polyurethane/MWNT Nanocomposites Foams of Polyurethane/MWNT Nanocomposites Foams of Polyurethane/MWNT Nanocomposites Foams of Polyurethane/MWNT Nanocomposites for Efficient EMI Reductionfor Efficient EMI Reductionfor Efficient EMI Reductionfor Efficient EMI Reduction

Y.Y. Chen,Y.Y. Chen,Y.Y. Chen,Y.Y. Chen,a,ba,ba,ba,b L. Urbanczyk,L. Urbanczyk,L. Urbanczyk,L. Urbanczyk,aaaa JJJJ----M. Thomassin, M. Thomassin, M. Thomassin, M. Thomassin, a C. Detrembleur,C. Detrembleur,C. Detrembleur,C. Detrembleur,aaaa C. JeromeC. JeromeC. JeromeC. Jeromeaaaaa Center for Education and Research on Macromolecules (CERM), University of Liege, Sart-Tilman, B6, 4000 Liege, Belgium.

b FAME, Institut Polytechnique de Grenoble, Grenoble 38031, France. C.Jerome@ulg.ac.be

4. Electrical propertiesHigh electrical conductivity is directly related to good EMI shielding effectiveness, while lowpermittivity is required in order to avoid wave reflection and promote wave absorption. Therefore,accurate foaming conditions must be found to reach both high conductivity and low permittivity.

2. Nanocomposite preparation1 and 2 wt% MWNT (NC7000, Nanocyl™, Belgium)/PU(Desmopan 2590A, Bayer, Germany) composites were prepared by melt blending in a twin-screw internal mixer (180°C, 60 rpm, 5 min) and then molded into 2mm thick sheets under a hot press (180°c) for 5min.

Fig 1: a) Behavior of nanocomposite foams under EMI radiation, b) difference between an EMI shield by reflection and by absorption.

The MWNT/polymer foam can effectively protect an electronic device from waves interference thanks to its capacity to absorb the waves instead of reflecting them.

Fig 2: Schematic representation of the two-steps batch foaming process with CO2.

Fig 3: Characterization of non-foamed MWNT/PU nanocomposites; a) homogeneous dispersion of MWNTs observed by TEM, b) rheological behavior of pure PU and PU/MWNT nanocomposites with an increasing MWNT content.

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� MWNTs are very well-dispersed within PU matrix.� The percolation threshold is reached with a low carbon nanotubes loading(1wt%), as proved by rheological analysis.In fact, the nanocomposites show solid-like behavior at low frequency range.

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3. Nanocomposite foams preparationThe nanocomposite is saturated in scC 2 for 24h at 40°C and 60-300bar. The vessel is then quicklydepressurized and the sample is transferred in a hot press (120°C) for 2min in order to allow cell

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Conclusions Conclusions Conclusions Conclusions MWNT/PU composites with an uniform porous structure have been successfully prepared by melt blending and accordingly foamed with scC 2. We have shown that the cellular morphology and foam density can be controlled by varying the foaming parameters. The electrical properties, which are directly related to EMI shielding effectiveness, are improved by adding MWNTs (conductivity) and foaming (permittivity). Although the results obtained here still need optimization in order to be competitive, these MWNT/PU polymeric foams are very promising EMI shielding materials due to their high capacity to absorb electromagnetic radiation at low MWNT content.References References References References 1 Thomassin, J.M. Pagnoulle, C. Bednarz, L. Huynen, I. Jerome, R. Detrembleur, C. J. Mater. Chem. 2008200820082008, 18, 2.

2 Yuen, S.M. Ma, C.C.M. Chuang, C.Y. Yu, .C. Wu, S.Y. Yang, C.C. Wei, M.H. Compos. Sci. Technol. 2008200820082008, 68, 63.

3 Huynen, I. Bednarz, L. Thomassin, J.M. Pagnoulle, C. Jerome, R. Detrembleur, C. in 2008 38th European Microwave Conference, IEEE, 2008200820082008, 5. 4 J r me, R. Pagnoulle, Detrembleur, C. Thomassin, J.-M. Huynen, I. Bailly, C. Bednarz, L. Daussin, R. Saib, A. Baudouin, A.-C. Laloyaux . PCT Int. Appl. 2008200820082008, W

2008068042.

5 Thomassin, J.M. Lou, . Pagnoulle, C. Saib, A. Bednarz, L. Huynen, I. Jerome, R. Detrembleur, C. J. Phys. Chem. C , 200200200200 , 111, 11186.

6 hang, C.S. Ni, . . Fu, S.Y. urashiki, . Compos. Sci. Technol. 200200200200 , 6 , 2 3.

Yang, Y.L. Gupta, M.C. Dudley, .L. Lawrence, R.W. J. Nanosci. Nanotechnol. 200200200200 , , 54 . 8 Saib, A. Bednarz, L. Daussin, R. Bailly, C. Lou, . Thomassin, J.M. Pagnoulle, C. Detrembleur, C. Jerome, R. Huynen, I. IEEE Trans. Microw. Theory Tech. 2006200620062006, 54, 2 45.

Yang, Y.L. Gupta, M.C. Dudley, .L. Lawrence, R.W. Adv. Mater. 2005200520052005, 1 , 1 .

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Fig. 4: Porous structure of a) pure PU and b) PU/2%MWNT observed by SEM. C) Cell size distribution of pure PU and nanocomposite foams.

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� The composites foams have smaller cell size and narrower cell size distribution compared to neat PU foam. �The nanofiller acts as a heterogeneous nucleating agent, increasing the cell density.

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Fig 6: a) Conductivity and b) permittivity of pure and nanocomposite foams (d~0.4 g/cm³) as a function of wave frequency.

Fig 7: a) Conductivity and b) permittivity of PU/2wt%MWNT foams as a function of foam density. Foams with lower density lead to low permittivity, high absorption, and low conductivity.

Decreasing the foam density leads to lower permittivity but also to lower conductivity (lower EMI shielding effectiveness). The carbon nanotube content as well as foaming conditions must therefore be optimized in order to find a compromise between high conductivity and low permittivity, which will result in excellent EMI shielding performance.

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depressurized and the sample is transferred in a hot press (120°C) for 2min in order to allow cellgrowth. The foam is finally quenched in an ice/water bath.

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Acknowledgements Acknowledgements Acknowledgements Acknowledgements The authors are grateful for the financial support to BELSPO, in the frame of network IAP 6/27 and to the “Région Wallonne” for its financial support in the frame of the MULTIMASEC project. Y-Y. Chen thanks the FAME program. C.D. is “Maître de Recherche” by F. R. S.-FNRS, Belgium and J-M. Thomassin is “Chercheur Scientifique Logistique post-doctoral” by F. R. S.-FNRS.

P (bar)Fig 5: a) cell diameter decreases with increase of saturation pressure and MWNT content, b) foam density decreases and then increases with the pressure and is higher for nanocomposite foams.

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