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Influences of hard- and soft- segment ratios on pyrolysis behavior of polyurethane elastomers
( Yuya Nishiyama ),( Shogo Kumagai ),( Tomohito Kameda ),( Yuko Saito ),( Atsushi Watanabe ),( Suguru Motokucho ),( Hisayuki Nakatani ),( Toshiaki Yoshioka ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1
Introduction Polyurethane elastomers (PUEs) are typical block copolymers which are composed of alternative hard segment (HS) and soft segment (SS), with the physical and chemical properties of them can be varied by changing HS and SS ratios. Pyrolysis is a promising method for polymeric wastes recycling because it can convert various polymers into chemical feedstock only by heat1). In this study, seven kinds of PUEs with different HS and SS ratios were synthesized (Fig. 1), then influences of hard- and soft-segment ratios on pyrolysis behavior were investigated. Methods, Results and discussion 1. Identification of pyrolysis products: Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to characterize the pyrolysis products under elevated temperature shown in Fig. 2. All the PUEs produced MDI, MAI and MDA (Fig. 3) from HS through pyrolysis, which were formed by pyrolytic urethane bond cleavage via 4-membered and 6-membered transition states shown in Scheme1. 2. In-situ monitoring of ticpyrolysis products: In-situ monitoring of pyrolysis products, called evolved gas analysis-MS (EGA-MS), was performed under the same pyrolysis conditions as the previous section. EGA chromatogram and representative products are shown in Fig. 4. Pyrolysis of various PUEs with different HS and SS clearly showed presence of three pyrolysis zones. In the zone 1, HS decomposition products such as CO<sub>2</sub>, butanediol (BD) and MDI are generated from five PUEs having HS. This suggested that formation of isocyanate end shown in Scheme1-I was dominant at this temperature. In the zone 2, SS-derived products and CO<sub>2</sub> were mainly formed from the five PUEs with low HS ratios. MDI was not produced in this zone, while MAI and MDA were produced. These results revealed that the high temperature promoted formation of the amine end shown in Scheme1-Ⅱ. In addition, a part of the SS-derived product could be generated by decomposition of MDI between HS and SS. In the zone 3, SS-derived products were produced from all PUEs, and the SS decomposition was continued. Thus, the temperature-dependent pyrolysis behavior was proposed (Scheme2) based on the findings in this work. Conclusion Temperature-dependent pyrolysis behavior of PUEs with different hard- and soft-segment ratios was investigated through pyrolysis tests employing Py-GC/MS and EGA-MS techniques. The findings in this work will be helpful to control product selectivity and feedstock recovery through pyrolytic approach.
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