Study on Quality Deterioration Mechanisms and Impurity Removal Methods for Waste PET Bottles

概要

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Melted waste PET bottles that have been spun into polyester fibers cause coloration and thread breakage problems. The causative chemical agents and process had not been identified because analytical methods for waste PET bottles contaminated with several impurities had not been developed. We examined the relationships between the chemical cleaning and melting processes, the quality deterioration of the recycled products, and impurity removal processes including the polishing of waste PET bottles. We obtained the following results.<BR>Sb in the residual polymerization catalyst and Na compounds in the cleaning agent and the impurities are oxidized in the melting process, causing the coloration of polyester fibers. Moreover, contaminated inorganic matter causes blockages in the spinning filter that cause thread breakage.<BR>Selective physical polishing of impurities that are difficult to remove with chemical cleaning decreases the contamination of inorganic matters. The impurities are removed uniformly when the polished amount is increased, reducing the formation of coloring precursors. However, the balance of impurity removal effect and the amount of polishing should be considered because the amount is inversely proportional to the selective removal of impurities.<BR>The prospect of producing high quality recycled PET products is enhanced through the introduction of polishing into existing recycling processes.