The influence of hematite nano-crystals on the thermal stability of polystyrene Milena Marinovic´-Cincovic´, Zoran V. S ˇ aponjic´, Vladimir Djokovic´, Slobodan K. Milonjic´, Jovan M. Nedeljkovic´ * Institute of Nuclear Sciences Vinc ˇa, Laboratory for Radiation Chemistry, P.O. Box 522, 11001 Belgrade, Serbia and Montenegro Received 3 February 2005; received in revised form 26 April 2005; accepted 28 April 2005 Available online 14 July 2005 Abstract A synthetic procedure based on thermal hydrolysis of iron(III) chloride solutions for the preparation of hematite (a-Fe 2 O 3 ) sol consisting of nano-crystals (NCs) is described. The a-Fe 2 O 3 NCs were characterized by transmission electron microscopy and X-ray diffraction measurements. Incorporation of a-Fe 2 O 3 NCs into polystyrene (PS) was based on the transfer of a-Fe 2 O 3 NCs from the aqueous phase to the organic solvent. A significant shift in the glass transition temperature of PS by 17  C towards higher temperatures was observed after incorporation of a-Fe 2 O 3 NCs. Also, the thermal stability of PS was improved by about 100  C in the presence of 3.6 wt% of a-Fe 2 O 3 NCs. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Hematite; Polystyrene; Nanocomposite; Thermal stability 1. Introduction The usage of nano-crystals (NCs) as polymer fillers relates to the strong current interest in development and application of new materials [1,2]. These, so-called, polymer nanocomposites take advantage of large spe- cific surface area and size-dependent properties of NCs as well as desired properties of host polymers such as possibility to be designed in various shapes, long-term stability and reprocessability. The resulting properties of nanocomposites are mostly a simple combination of the properties of the inorganic and organic components, although the appearance of completely novel character- istics sometimes can take place due to synergistic effects. Recently, significant progress has been made in the preparation of a large number of metal oxide colloids consisting of particles of different chemical composi- tions, shapes and sizes. Ferric oxide, in its own right, has been studied because of its applications in catalysis, gas sensing, magnetic storage, ferrofluids, magnetic refriger- ation and colour imaging. However, hematite (a-Fe 2 O 3 ) NCs have not been extensively used as polymer fillers. Recently, improvement in the mechanical properties of polystyrene (PS) matrix has been observed after in- corporation of a-Fe 2 O 3 NCs [3], as well as improvement in its thermal stability after incorporation of significantly larger a-Fe 2 O 3 particles (size range from 0.2 to 0.5 mm) [4]. On the other hand, stabilizing effects in poly(vinyl chloride), chlorinated poly(vinyl chloride) and in blends of these with acrylonitrileebutadieneestyrene were observed in the presence of flame retarding/smoke- suppressing iron(III) compound FeOOH [5e8]. The PS is a hydrophobic polymer frequently used as a matrix for a variety of fillers such as organoclays [9,10], metals [11,12], oxides [3,4,13], metal chalogenides [14e16], and graphite [17]. Due to their high surface to * Corresponding author. Tel.: C381 11 2453 986; fax: C381 11 444 5966. E-mail address: jovned@vin.bg.ac.yu (J.M. Nedeljkovic´ ). 0141-3910/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2005.04.044 Polymer Degradation and Stability 91 (2006) 313e316 www.elsevier.com/locate/polydegstab