Carbon-based thermoplastic elastomer nanocomposites for electromagnetic interference shielding applications

Abstract

This thesis reports different approaches to obtaining flexible materials for electromagnetic interference (EMI) shielding. The relationship between structure, properties, processing, and performance of carbon nanotube (CNT), graphene (GnP), and GnP/CNT filled poly (styreneb-ethylene-ran-butylene-b-styrene) (SEBS) nanocomposites prepared by two different melt compounding methods was investigated. In a first step, SEBS/CNT nanocomposites were successfully prepared by melt compounding in a batch mixer followed by compression molding. SEBS/CNT nanocomposites exhibited low electrical percolation threshold with the formation of a three-dimensional conductive network starting at around 1 wt% of CNT. An electrical conductivity of 1 S.cm-1, which represents an increase of 17 orders of magnitude compared to the one of the matrix, was achieved with 8.0 wt% of CNT. The maximum electromagnetic interference shielding effectiveness (EMI-SE) reached with 15 wt% of CNT was 30.07 dB. This effectiveness corresponds to a reduction of 99.9 % of the incident electromagnetic radiation. In a second step, nanocomposites of SEBS/GnP and hybrid nanocomposites of SEBS/GnP/CNT were prepared using the same processing conditions used in the first phase. Morphological characterization showed that SEBS/CNT presented better dispersion of the carbon nanoadditives and higher filler-matrix interactions than SEBS/GnP. SEBS/GnP presented lower values of electrical conductivity and EMI-SE compared to SEBS/CNT prepared in the first phase. The maximum electrical conductivity was 2.6E-7 S.cm-1 and the higher EMI-SE was 8.63 dB achieved with 15 wt% of GnP. However, the addition of both CNT and GnP resulted in synergic effects regarding shielding properties when compared to both binary nanocomposites (SEBS/CNT and SEBS/GnP). The combination of both nanoparticles improved the connection of the electrical conductive network formed throughout the material, which resulted in an improvement of EMI-SE. The maximum EMI-SE of 36.47dB, which represents an attenuation of 99.98% of the incident radiation, was achieved for the SEBS/GnP/CNT nanocomposite with 5/10 wt% of GnP/CNT. In the last part of this project, SEBS/CNT and SEBS grafted maleic anhydride (SEBSMA)/ CNT nanocomposites were prepared by melt compounding and post-processed using two different techniques, extrusion and compression molding. Results showed that the CNT loading amount, the presence of MA in the matrix, and the molding technique affected the final morphologies, the electrical, mechanical and EMI shielding properties of nanocomposites. For the nanocomposites prepared by extrusion, electrical and mechanical properties suggested that CNT were aligned in the matrix. MA did not improve the interactions between CNT and the matrix. However, SEBS-MA presents a higher melt flow index, which affected the dispersion and alignment of the CNT and the final properties of the nanocomposites. Nanocomposites prepared by extrusion presented slightly higher values of Young’s modulus, tensile strength, and elongation at break compared to the ones prepared by compression. On the other hand, nanocomposites prepared by compression presented lower electrical percolation threshold, and much higher AC electrical conductivity and EMI-SE. The highest EMI-SE value was 56.73 dB, which represents a reduction of 99.9996% of the incident radiation, achieved by SEBS/CNT with 8 wt% of CNT prepared by compression. However, the nanocomposite of SEBS/CNT with 5 wt% of CNT prepared by extrusion presented the best balance between EMI-SE and mechanical properties.

Date	19 Jan 2018
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicole R. Demarquette (Supervisor) & Guilherme M.O. Barra (Co-supervisor)