Tuning the Mechanical and Dielectric Properties of Clay-containing Thermoplastic Elastomer Nanocomposites E. Helal, 1 L.G. Amurin, 1 D.J. Carastan, 2 R.R. de Sousa Jr, 2 E. David, 1 M. Fr  echette, 3 N.R. Demarquette 1 1 Mechanical Engineering Department,  Ecole de Technologie Sup  erieure, Montr  eal, Quebec, Canada 2 Center for Engineering, Modeling and Applied Social Sciences, Federal University of ABC, Santo Andr  e, Sao Paulo, Brazil 3 Institut de Recherche d’Hydro-Qu  ebec, Varennes, Quebec, Canada In this study, the mechanical strength and the AC short term breakdown strength of polystyrene-b-poly(ethylene- co-butylene)-b-polystyrene (SEBS) thermoplastic elasto- mer clay-containing nanocomposites have been investi- gated as function of their morphologies. The SEBS/clay nanocomposites with tailored morphologies were pre- pared previously by different processing techniques. They featured different orientations of clay platelets as well as polystyrene (PS) block nanodomains, namely: isotropic, oriented, and partially oriented morphologies. In unfilled SEBS matrices, the mechanical strength was mainly tuned by the orientation of PS block nanodomains. A good cor- relation between the dielectric breakdown strength and the mechanical stiffness was observed overall: the higher the mechanical strength was, the higher the breakdown strength was. In the nanocomposites, the orientation of clay platelets as well as the degree of order and the char- acteristic sizes of the block copolymer domains were seen to affect strongly the breakdown strength behavior in addition to the mechanical strength. In particular, the partially oriented morphology achieved by film blowing extrusion exhibited the maximum increase of the break- down strength by 25% with optimized mechanical stiff- ness evaluated between that of the oriented morphology as a lower limit and that of the isotropic morphology as an upper limit. POLYM. ENG. SCI., 00:000–000, 2018. VC 2018 Society of Plastics Engineers INTRODUCTION Block copolymers are a special class of materials composed of immiscible polymer blocks that are usually self-organized in well-ordered nanodomains. The morphologies adopted by these nanodomains depend on several parameters such as the affinity between the blocks, their molecular weights and their relative proportions [1, 2]. Besides, these morphologies can be easily tuned by different external forces that can be applied either during melt compounding or solvent casting fabrication pro- cesses [3–8]. Because of these features, block copolymers have been inves- tigated recently as templated multiphase matrices to tailor nano- particles dispersion in polymer nanocomposites [1, 9–14]. Currently, this approach is considered of high importance to develop techniques for designing an advanced generation of nanocomposites with prescribed morphologies and engineering properties. In this context, some recent studies investigated different morphologies of polystyrene-b-poly(ethylene-co-butylene)-b- polystyrene (SEBS) triblock copolymers and their clay- containing nanocomposites [15–20]. In fact, SEBS belongs to the class of styrenic thermoplastic elastomers. It is composed of two polystyrene (PS) blocks and one poly(ethylene-co-butylene) (PEB) elastomer midblock. It features in addition to its ordered nanostructure as a block copolymer, excellent combination of mechanical properties [21, 22], good resistance to water treeing [23, 24], good electromechanical coupling [25–30] and high compatibility with polyolefins and other polymers [31–34]. The studies performed on SEBS and SEBS/clay nanocompo- sites demonstrated that different morphologies with tailored spa- tial distributions and orientations of PS ordered nanodomains and clay nanoplatelets can be achieved by appropriate process- ing techniques [3, 15–19]. For instance, isotropic lamellar or cylindrical morphologies were obtained by solvent casting pro- cess when adequate thermal annealing procedures were applied, and appropriate fractions of PS blocks were present [19]. Besides, oriented morphologies where PS nanodomains and clay nanoplatelets are simultaneously aligned in the same direction were obtained by extensional and shear forces applied during a sheet die extrusion process [3, 15, 16]. In addition, more com- plex morphologies where PS domains and clay platelets have more than one preferential direction of alignment were achieved by film blowing extrusion. Furthermore, the abovementioned changes in spatial distribution of PS domains and nanoclays were correlated with changes in the mobility of elastomer chains located in the interfacial region. More details regarding these morphologies are available in the cited publications [17, 18]. The control of morphology of these materials ultimately resulted in changes in their dielectric properties. This behavior was partially expected due to the observed changes in the inter- facial region which usually governs the properties of nanocom- posites. In particular, increase of the breakdown strength was observed when SEBS-30 matrix (30 wt% PS domains) was filled with clay content equal to 5 wt% [19]. Moreover, the comparison between isotropic and oriented morphologies of this nanocomposite revealed that the maximum increase of Correspondence to: N.R. Demarquette; e-mail: nicoler.demarquette@etsmtl.ca L.G. Amurin is currently at MackGraphe Research Center, Mackenzie Presbyterian University, S~ao Paulo, Brazil M. Frechette is currently at State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, China Grant sponsors: The Natural Sciences and Engineering Research Council (NSERC); Hydro-Quebec, Canada; Coordenac¸~ao de Aperfeic¸oamento de Pessoal de Nıvel Superior (CAPES); Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (CNPq); Fundac¸~ao de Amparo a Pesquisa do Estado de S~ao Paulo (FAPESP), Brazil. DOI 10.1002/pen.24844 Published online in Wiley Online Library (wileyonlinelibrary.com). VC 2018 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2018