Research paper Organoclay polypropylene nanocomposites under different electric field strengths Zbigniew Rozynek a, ⁎ ,1 , Suédina Maria de Lima Silva b , Jon Otto Fossum a, ⁎, Geraldo José da Silva c , Eduardo Novais de Azevedo d , Henrik Mauroy e , Tomás S. Plivelic f a Department of Physics, NTNU, Høgskoleringen 5, NO-7491 Trondheim, Norway b Departamento de Engenharia de Materiais, Universidade Federal de Campina Grande, 58429900 Campina Grande, PB, Brazil c Instituto de Física, Universidade de Brasília, 70.919-970, Brasília, DF, Brazil d Núcleo de Tecnologia, Centro Acadêmico do Agreste, Universidade Federal de Pernambuco, 55002-970 Caruaru, PE, Brazil e Physics Department, IFE, P.O. Box 40, N-2027 Kjeller, Norway f MAX IV Laboratory, Lund University, Box 118, SE-22100 Lund, Sweden abstract article info Article history: Received 31 October 2013 Received in revised form 1 February 2014 Accepted 18 March 2014 Available online 18 April 2014 Keywords: Clay mineral Alignment Polymer Nanocomposite Electric field Exfoliation Functionalities of clay-polymer nanocomposites (CPN) are related to the degree of clay particle exfoliation and orientation within the polymer matrix. Exploration of new physical methods for such CPN processing is currently an active field of research. In the present work, organoclay polypropylene nanocomposites were prepared by melt intercalation and subsequently exposed to an electric field (E) and studied in-situ by means of synchrotron X-ray scattering. Experiments were performed both at room temperature, and in the melted state (up to 200°C) and during solidification (cooling down to room temperature). Structural changes and time evolution of the alignment of the layered silicates at different E-field strengths, as well as, the final degree of their orientation is discussed. Despite many efforts, i.e. applying different E-field strengths, frequencies, and temperatures; E-field-induced clay particle exfoliation was not observed. The final state of the solidified sample is a semi-crystalline polymer matrix with embedded aligned clay particles having intercalated morphologies. E-field-assisted control of clay layers exfoliation in polymer matrices remains challenging. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In this work clay mineral particles are added as nano-fillers to poly- mer matrices. The increase in separation of the layered structure of the clay mineral in part or in whole, known respectively as intercalation and exfoliation, produces layers, which have large specific surface area, and this in turn allows for efficient load transfer from the matrix, and en- hancement in stiffness and strength. Dispersed layers also act as barriers to diffusion increasing the tortuosity of the path and inhibiting the flow of gases (Wang et al., 2006). Several chemical approaches have been uti- lized to prepare clay-polymer nanocomposites (CPN), including in-situ polymerization (Sun and Garces, 2002; Mauroy et al., 2013a,b) and direct melt intercalation. For the polypropylene (PP) matrix, a proper compatibility between the polymer and the clay mineral surface requires modification of the polymer with maleic anhydride (MAPP) or hydroxyl groups (HOPP) (Liu and Wu, 2001; Nam et al., 2001). It would be beneficial if the dispersion and alignment of exfoliated clay layers within polymeric matrices were achieved without chemical modification. Therefore other methods have been investigated includ- ing mechanical shearing (Okamoto et al., 2001; Murata and Haraguchi, 2007). A relatively novel idea was explored (Kim et al., 2003) using the effect of an external electric field to assist the penetration the polymer chains into the interlayer spaces that led to clay mineral exfoliation. An electric field (AC-60 Hz, 1 kVmm -1 ) is applied on clay PP melts between the parallel layers of a rheometer, resulting in the increase of the rheological properties and exfoliation (Kim et al., 2003). However, the explanation for this behaviour was not provided within the article. Further measurements performed by the same group led to the conclusion that the exfoliation process prevails in the AC field due to the imbalance between the van der Waals attraction and the electrostatic repulsion, originating from the dissociation of the bound ions from the clay mineral surfaces (Kim et al., 2006; Park et al., 2006). In these two latter reports the clay PP nanocomposites were investigated by means of X-ray scattering in the presence of both DC and AC electric fields without any mechanical shear. Thus, a time-dependent clay exfoliation in the AC case was reported to occur purely due to the electric effects. The clay mineral alignment was also studied by the same group. They found a very strong DC electric field de- pendence on the clay mineral alignment, while for the AC electric fields; Applied Clay Science 96 (2014) 67–72 ⁎ Corresponding authors. E-mail addresses: zbigniew.rozynek@ntnu.no (Z. Rozynek), jon.fossum@ntnu.no (J.O. Fossum). 1 Present address: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland. http://dx.doi.org/10.1016/j.clay.2014.03.011 0169-1317/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay