Waste PET bottles are recycled into various articles by melt recycling processes. However, the heat of melting causes thermal cracking and reduces the strength of the articles. Resin flakes of virgin PET are added to preserve the molecular weights of the articles, but the effect of this addition on the retention of strength had not been clarified.
The relationship between molecular weight and the strength of PET was examined using models of waste PET prepared by blending low-molecular-weight PET and high-molecular-weight PET. The following results were obtained.
(1) The yield strength of PET is maintained when high-molecular-weight PET is used to form a frame for the cross section of the resin. Consequently, it is not necessary to increase the amount of high-molecular-weight PET to form the frame in order to maintain the yield strength of recycled articles.
(2) The breaking elongation rate of PET drops when low-molecular-weight PET produces voids.
(3) The Ionomer method of joining low-molecular-weight PET can maintain the breaking elongation of recycled articles.

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Refractories, including chromium trioxide, exhibit excellent corrosion resistance, making them suitable for use in waste melting furnaces. However, there is some concern that hexavalent chromium compounds may be formed in such high-temperature environments. Therefore, in the present study, heating tests were carried out at different temperatures for various mixing ratios of CaO, SiO₂, Al₂O₃ and Cr₂O₃ powders, and the resulting compounds, following quenching in water, were analyzed using x-ray diffraction (XRD). The XRD analysis results indicated that Ca₄Al₆CrO₁₆was present in water-cooled samples following heating for two hours at temperatures in the range 1300-1500°C. It is suggested that this compound may be stabilized by the presence of Al₂O₃ at temperatures above 1300°C and that it has elution characteristics. Electron probe microanalyser (EPMA) analysis of a section of the slag obtained by a rotary corrosion test was carried out. The results indicated that Al₂O₃ and CaO migrated to the surface of a Cr₂O₃ aggregate that was separated from the refractory. It is possible that the Ca₄Al₆CrO₁₆ formed at the surface of the Cr₂O₃ aggregate. Although the amount of Cr(VI) elution from the slag does not currently pose a problem, it is necessary to improve this to prevent the separation of Cr₂O₃ aggregate to hold stably Cr(VI) elution concentration at the level lower than its elution standard level.

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Design for disassembly (DfD) has the potential to reduce environmental burdens by promoting the recovery of materials and subassemblies in products at the end of their lives and reducing waste management processes. Many researchers have developed decision-making methodologies that determine how to maximize the economical and environmental benefits of end-of-life processing under variable end-of-life situations. However, the potential reductions of environmental burdens associated with introducing DfD have rarely been evaluated. In this paper, we developed a method to estimate the potential reductions of environmental burdens and to visualize changes for the optimal disassembling sequence by using an AND/OR graph when DfD is incorporated. We assumed the optimal sequence was the one that has the highest total economic value among the possible sequences. Environmental burdens associated with the optimal disassembly sequence before and after the introduction of DfD were evaluated for the potential reduction. The processes evaluated include dismantling, shredding and mechanical sorting, mechanical recycling, and landfill. Using the method we developed, a case study was conducted on an electrical hot-water pot. The optimal sequence was obtained, and it indicated 200 yen profit and 7.6kg CO₂ reduction potential. The introduction of DfD could further reduce the CO₂ emissions by 0.3kg.

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