Polystyrene foams with dispersed catalyst for a design of recyclable plastics
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Polystyrene foams with dispersed catalyst for a design of recyclable plastics Tamaki Hirose, Yoshifumi Takai, Naoto Azuma, Yoshio Morioka, and Akifumi Ueno Department of Materials Science, Faculty of Engineering, Shizuoka University, Jyohoku, Hamamatsu, Shizuoka 432, Japan
Mitsunori Okada Yokohama Institute, Furukawa Electric Co., Okano, Nishi-ku, Yokohama, Kanagawa 220, Japan (Received 13 January 1997; accepted 2 July 1997)
The present authors have already reported that barium oxide is the most effective catalyst for the conversion of waste polystyrene into styrene including both monomer and dimer. Around 85 wt. % of waste polystyrene was converted into styrene when it was degraded at 623 K in the presence of barium oxide as catalyst. In this paper, the preparation and the thermal degradation of polystyrene films with dispersed catalyst are described for a design of recyclable plastics for better environment. More than 85 wt. % of the films was degraded into styrene at 623 K without addition of other catalytic compounds. Techniques for foaming the films using either nitrogen or carbon dioxide are discussed. It was found that the polystyrene foams with dispersed catalyst are well converted into styrene when they are simply degraded at 673 K.
I. INTRODUCTION
Recycling of waste plastics has been of current interest in the field of chemical engineering, since a catalytic degradation process was successfully commercialized in Japan using solid acid catalysts for the recycling of waste polyolefins into fuel oils.1 Three kinds of recycling methods for waste plastics have been proposed. First, there is energy recovery, e.g., conversion into fuel oils. A second method is material recycling, where the waste plastics are washed, crushed, and molded for the production of plastics, albeit of lower quality. Some have thought, however, that material recycling is not a longterm solution to the present problems.2 The third method is called chemical recycling, where the waste plastics are converted into the corresponding monomer or advanced chemicals. Among these three recycling methods, chemical recycling is the most attractive and has been studied extensively.3 DuPont has developed techniques to decompose waste PET (polyethylene terephthalate) into ethylene glycol and dimethyl terephthalate, which can be used for the reproduction of pure PET resin, in the presence of an excess amount of methanol and a small amount of catalytic compound.4 We also have reported that about 85 wt. % of waste polystyrene was degraded into styrene monomer and dimer at 623 K in the presence of solid base catalysts.5 Recently, studies of the design of recyclable plastics have been conducted so as to consider recycling the material in the course of its design. For example, automobile bumpers consisting of polypropylene and a small amount of liquid crystal fibrils are produced,6 and J. Mater. Res., Vol. 13, No. 1, Jan 1998
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these fibrils work as fillers
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