Macromolecular Nanotechnology Estimation of interphase thickness and properties in PP/layered silicate nanocomposites Zita Dominkovics, József Hári, János Kovács, Erika Fekete, Béla Pukánszky ⇑ Laboratory of Plastics and Rubber Technology, Budapest University of Technology and Economics, P.O. Box 91, H-1521 Budapest, Hungary Institute of Materials Science and Environmental Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary article info Article history: Received 29 December 2010 Received in revised form 10 June 2011 Accepted 13 June 2011 Available online 29 June 2011 Keywords: Nanocomposites Layered silicates Polypropylene Interphase Thickness abstract Nanocomposites were prepared from sodium montmorillonite (NaMMT) and organoclays (OMMT) with different particle sizes as a function of silicate content. Composite structure was characterized by various methods including X-ray diffraction (XRD), scanning electron microscopy (SEM) and rheology. Model calculations were carried out to estimate the thick- ness and yield stress of the interphase forming in the composites. The results proved the formation of an interphase, but the determination of interphase properties was hampered by several factors. First of all, the particle size of the filler changed quite considerably in PP/ OMMT composites in spite of earlier observations and expectations. Particle characteristics changed even further when a relatively small amount (5 vol.%) of functionalized polymer (MAPP) was added to the composite. As a consequence, the estimation of the contact sur- face between the silicate and the polymer became extremely difficult. In spite of the uncer- tainties overall values of interphase properties were obtained using the results of all composites prepared. The prediction for the average thickness of the interphase is 0.23 lm and we obtained 51.2 MPa for interphase yield stress, but this estimate neglects the different interactions developing in composites containing the uncoated and the mod- ified silicate, respectively. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The basic idea of polymer/layered silicate nanocompos- ites is to create large interfaces through the complete or al- most complete exfoliation of the silicate and thus to render extraordinary properties to the composites. The expected and often claimed benefits of such composites is large rein- forcement at small silicate content, i.e. large stiffness and strength, increased heat deflection temperature, improved barrier properties and decreased flammability [1–4]. A clo- ser scrutiny of results published in the literature clearly prove that the expected properties are rarely achieved and the long awaited breakthrough in the application of polymer/layered silicate nanocomposites has not occurred yet. Among others, one of the main reasons for the lack of success is the complex nature of composite structure developing in these materials. The large extent of exfolia- tion constituting the basis of the original idea is rarely achieved and the composites usually contain four struc- tural units: individual platelets, intercalated stacks (tac- toids), but also large particles and a silicate network, instead of the usually claimed intercalated/exfoliated structure [5]. The relative amount of these structural units is not known and structure is rarely characterized quanti- tatively, although recently several attempts have been done to do this [6–8]. Even less is known about interactions developing in lay- ered silicate nanocomposites, although strong interactions are necessary to achieve the desired goal, i.e. large extent of reinforcement at small silicate content. Interactions are usually addressed in very general and undefined terms, 0014-3057/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2011.06.010 ⇑ Corresponding author at: Laboratory of Plastics and Rubber Technol- ogy, Budapest University of Technology and Economics, P.O. Box 91, H- 1521 Budapest, Hungary. Tel.: +36 1 463 2015; fax: +36 1 463 3474. E-mail address: bpukanszky@mail.bme.hu (B. Pukánszky). European Polymer Journal 47 (2011) 1765–1774 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj MACROMOLECULAR NANOTECHNOLOGY