Polymeric nanocomposite materials: Preparation and characterization of star-shaped PbS nanocrystals and their influence on the thermal stability of acrylonitrile–butadiene–styrene (ABS) copolymer Mohammad Yousefi a,⇑ , Forozan Gholamian b , Davood Ghanbari c , Masoud Salavati-Niasari d,e,⇑ a Islamic Azad university, Shahre rey Branch, Tehran, P.O. Box 18155-144, Islamic Republic of Iran b Faculty of Chemistry, Malek Ashtar University, Tehran, Islamic Republic of Iran c Islamic Azad University, Arak Branch, Young Researchers Club, Arak, Iran d Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran e Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran article info Article history: Received 21 August 2010 Accepted 5 January 2011 Available online 1 February 2011 Keywords: ABS PbS Nanocrystals Nanocomposite materials Flame retardant abstract Star-shaped PbS nanocrystals were synthesized via a simple hydrothermal reaction between Pb(NO 3 ) 2 Á4H 2 O and thioglycolic acid at a relatively low temperature. The PbS nanostructures were then combined in a acrylonitrile–butadiene–styrene copolymer. The effect of the PbS nanostructures on the thermal stability of the nanocomposite products has been investigated. The nanostructures and nano- composite were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, thermogravimetric-differential thermal analysis and atomic force microscopy. Cone calorimeter measurements showed that the heat release rate significantly decreased in the presence of PbS. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, natural and synthetic polymer materials are used in ever increasing areas. However, one of the main disadvantages of most of these compounds is their inherent flammability, most often accompanied by the production of corrosive or toxic gases and smoke during combustion. Among the major markets where flame retardants are required, the industries dealing with construction, electronics components and transportation are of the greatest importance [1–5]. Various flame retardant additives, such as haloge- nated compounds, are limited with respect to environmental requirements [6]. Nanocomposite technology is the next great fron- tier of materials science, because by using minimal additive levels (<10 wt.%), one can achieve excellent mechanical properties, chem- ical resistance and thermal stability [7,8]. The use of flame retar- dants to reduce the combustibility of polymers becomes an important part of the development and application of new materials. The acrylonitrile–butadiene–styrene copolymer (ABS) is a com- mercial material with relatively low cost and good mechanical properties. It is widely used as an important engineering thermo- plastic because of its desirable properties; which include good mechanical properties, chemical resistance and good processing characteristics. ABS is a mixture of styrene, butadiene and acrylo- nitrile, which also provides strength, rigidity and toughness. ABS is composed of a styrene–acrylonitrile copolymer (SAN) matrix phase, with grafted polybutadiene particles [9,10]. One of the main drawbacks of ABS is its inherent flammability, and therefore there is a need to increase its thermal stability and flame retar- dant (FR) properties [11]. There are already various methods of improving the fire retardancy of this copolymer, such as ABS/clay [7,12], ABS/halogenated FR [13,14], ABS/phosphorous FR [15,16], ABS/intumescent FR [17], nitrogen–phosphorus FR [18], ABS/zinc stannate [19], ABS/ferric chloride [20], synergistic agent [21,22] and ABS/carbon nanotube [23]. We have been interested in the synthesis of Bi 2 S 3 [24], SnS [25], CdS [26–28] and ZnS [28–30] nanostructures, using thioglycolic acid, via hydrothermal method for a few years. In this work, addressing the above issue, we have used a thioglycolic acid assisted hydrothermal process to success- fully synthesize PbS nanostructures. This metal sulfide was then added to the ABS copolymer in order to increase its thermal stability. 0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2011.01.012 ⇑ Corresponding authors. Tel.: +98 21 552 29321 (M. Yousefi). Address: Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran. Tel.: +98 361 591 2383; fax: +98 361 555 29 30 (M. Salavati-Niasari). E-mail addresses: myousefi50@yahoo.com (M. Yousefi), salavati@kashanu.ac.ir (M. Salavati-Niasari). Polyhedron 30 (2011) 1055–1060 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly