Fire retardancy effect of migration in polypropylene nanocomposites induced by modified interlayer Gy. Marosi a, *,A.Ma´rton a ,A.Sze´p a , I. Csontos a , S. Keszei a , E. Zimonyi a ,A.Toth b , X. Almeras c ,M.LeBras c a Budapest University of Technology and Economics, Department of Organic Chemical Technology, H-1111 Mu ˆ egyetem rkp.3, Budapest, Hungary b Research Laboratory of Materials, Environmental Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1025 Budapest, Pusztaszeri u ´ t 59-67, Hungary c Ecole Nationale Superieure de Chimie Lille, USTL.BP 108.F-59658-4-2 Villeneuve d’Ascq Ce ´dex, France Received 6 November 2002; received in revised form 15 February 2003; accepted 20 February 2003 Abstract Montmorillonite nanoparticles were found to be inefficient in polypropylene because of the lack of a heat insulating char layer and the decomposition of the compatibilising surfactant layer on their surface. Combination with an ammonium polyphosphate- based intumescent system showed some synergism due to modified rheology. The effect of surface and interface modification was analysed using Raman microscopy and X-ray photoelectron spectroscopy. Forming a heat resistant coating layer of low surface energy around the nanoparticles promotes their migration to the surface and formation of a flexible barrier layer, and thus leads to better performance. # 2003 Elsevier Ltd. All rights reserved. Keywords: Nanoparticles; Flame retartdant 1. Introduction In recent years nanocomposites became the most widely studied subject of flame retardant research. The flame retardant efficiency of nanoparticles and the mechanism of their action, especially when applied with other flame retardant (FR) additives, is, however, still not satisfactorily clarified. The development of nanocomposites reflects the advancement in the technology of interface modifi- cation. The first methods applied the steps of organo- phillisation with cationic surfactant and a subsequent polymerisation to form polymer-intercalated clay nano- layers [1–3].Inthemeantimeinlinemethodsforforming multilayer interphase in polymer composites have been developed including the method for formation of a thin surfactant layer and a thicker polymer (elastomer) layer around inclusions to be embedded into a polymer matrix [4–7]. The need for economic production of nanocomposites required the development of similar interface modification methods for nanocomposites [8,9]. The synthesis and application of reactive surfac- tants for composites provided an advancement in com- posite technology [10–12]. The first application of reactive surfactant in nanocomposites appeared recently [13]. Formation of a polymer interfacial layer (like PP–g–MA) is also needed for achieving an exfoliated or intercalated nanocomposite structure. The method of intercalation with poliorganosiloxanes before embed- ding into the polymer matrix has been also proposed proving the nanocomposite structure by wide and small angle XRD method [14]. The research for finding the most suitable interfacial structures for various types of nanocomposites has accelerated in the last years and is still not finished. The role played by interface modifi- cation of nanoparticles in their fire retardant efficiency and in their synergistic interaction with other additives is also not yet clarified. The synergism between various inorganic additives (including nanoparticles) and other flame retardants has been explained by different mechanisms. The advanta- geous effect of phosphorus flame retardants for example with TiO 2 was explained by formation of a coherent 0141-3910/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0141-3910(03)00223-4 Polymer Degradation and Stability 82 (2003) 379–385 www.elsevier.com/locate/polydegstab * Corresponding author. Fax: +36-1-463 3648. E-mail address: gmarosi@mail.bme.hu (Gy. Marosi).