Technical Note Alkaline hydrothermal treatment of brominated high impact polystyrene (HIPS-Br) for bromine and bromine-free plastic recovery Mihai Brebu 1 , Thallada Bhaskar, Akinori Muto, Yusaku Sakata * Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1 Tsushima Naka, Okayama 700-8530, Japan Received 4 November 2005; received in revised form 3 February 2006; accepted 3 February 2006 Available online 3 April 2006 Abstract A method to recover both Br and Br-free plastic from brominated flame retardant high impact polystyrene (HIPS-Br) was proposed. HIPS-Br containing 15% Br was treated in autoclave at 280 °C using water or KOH solution of various amounts and concentrations. Hydrothermal treatment (30 ml water) leads to 90% debromination of 1 g HIPS-Br but plastic is strongly degraded and could not be recovered. Alkaline hydrothermal treatment (45 ml or 60 ml KOH 1 M) showed similar debromination for up to 12 g HIPS-Br and plas- tic was recovered as pellets with molecular weight distribution close to that of the initial material. Debromination occurs at melt plastic/ KOH solution interface when liquid/vapour equilibrium is attained inside autoclave (280 °C and 7 MPa in our experimental conditions) and depends on the plastic amount/KOH volume ratio. The antimony oxide synergist from HIPS-Br remains in recovered plastic during treatment. A pictorial imagination of the proposed debromination process is presented. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Debromination; Alkaline hydrotreatment; HIPS-Br; Bromine recovery 1. Introduction Nowadays increasing plastic consumption leads to accu- mulation of huge amount of waste that poses serious envi- ronmental problems. There are many techniques to convert the plastic waste into valuable materials (Aguado and Ser- rano, 1999; Tukker, 2002). However special methods for treatment/recovery of plastic waste are needed, as plastic materials become more and more complex. High impact polystyrene (HIPS) is the main component of waste from electrical and electronic equipment (WEEE) being followed in amount by acrylonitrile–butadiene– styrene (ABS) (Tange, 1999). These polymers are widely found in TV housing, computers and office equipment. Brominated flame retardants (Br-FR) such as polybromi- nated diphenyls, polybrominated diphenyl oxides, tetra- bromo bisphenol-A or polybrominated epoxy resins (BSEF Report, 2000) are used in plastic materials to pre- vent combustion during accidental fires. Antimony oxide is widely used as synergist to enhance the flame-retardant effect (Ga ¨chter and Mu ¨ ller, 1990). The treatment methods for the recycling of plastics and recovery of Br-FR have been the topic of many research interests. Br-FR and antimony trioxide synergist remain in HIPS materials after five consecutive mechanical repro- cessing without debromination (Hamm et al., 2001). How- ever they create many problems during treatment/recovery of plastic waste due to formation of corrosive compounds such as hydrobromic acid as well as environmentally harm- ful polybrominated dibenzofurans, which appear during incineration or pyrolysis (Vehlow et al., 2001). Br-FR can 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.02.036 * Corresponding author. Tel./fax: +81 86 251 8082. E-mail addresses: bmihai@icmpp.ro (M. Brebu), yssakata@cc.okaya- ma-u.ac.jp (Y. Sakata). 1 Permanent address: ‘‘Petru Poni’’ Institute of Macromolecular Chem- istry, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania. www.elsevier.com/locate/chemosphere Chemosphere 64 (2006) 1021–1025