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放射線架橋と高濃度可塑剤添加によるポリ乳酸弾性体の開発

Development of elastic poly(L-lactic acid) material with high content of plasticizer modified by radiation-induced crosslinking

長澤 尚胤; 金澤 進一*; 吉井 文男; 玉田 正男; 田口 光正

Nagasawa, Naotsugu; Kanazawa, Shinichi*; Yoshii, Fumio; Tamada, Masao; Taguchi, Mitsumasa

植物由来のバイオプラスチックであるポリ乳酸は、低環境負荷材料としての利用が注目されている。これまで我々は放射線架橋によるポリ乳酸の耐熱性向上に成功してきた。今回は、可塑剤添加による柔軟性や弾性の改善について検討した。可塑剤(リケマールPL-019)を混練にて20%添加したポリ乳酸を2MeVの電子線照射(20kGy)で架橋することで、引張伸度が数%から30%まで向上し、柔軟性が改善された。さらに、浸漬法による架橋ポリ乳酸の可塑剤添加量の増大に伴い、引張伸度が70%以上まで増大し、添加量を35%以上にすることでゴム弾性が発現することを見出した。この弾性体は、ポリ乳酸のガラス転移温度以上である80$$^{circ}$$Cで一週間加熱しても可塑剤が染み出さず弾性を保持していた。以上のことから、ポリ乳酸の柔軟性の向上と共に弾性体の創製に成功し、架橋ポリ乳酸の応用拡大に繋がる見通しを得た。

Poly(L-lactic acid), [PLLA] one of bioplastics, is the most attractive materials because it is the most promising candidate for replacement of petrochemical plastics from the viewpoint of the global warming protection. The heat resistance property of PLLA has been improved by radiation-induced crosslinking with triallyl isocyanurate (TAIC). The applications of crosslinked PLLA, however, are limited, because the lack of flexibility is nearly un-improved. The plastics are currently soften by adding plasticizers. However, the plasticizer exudes from PLLA because of recrystallization even at room temperature, and PLLA becomes hard consequently with cloudiness. To solve the problem and expand further the applications of PLLA, effect of additive plasticizers on radiation-crosslinking of PLLA with TAIC and retention capacity in crosslinked PLLA were investigated. The crosslinking structures were formed in electron beam-irradiated PLLA with 3 phr (per hundred resin) TAIC and various content of plasticizer (acetylated monoglycerides or adipate ester mixture). The gel content of PLLA increased with the mixing ratio of the plasticizer and absorbed dose. At the dose of 20 kGy and more, the network was formed about 90% in the crosslinked PLLA. The plasticizer didn't exude from the crosslinked PLLA even if heated for a week at 80 $$^{circ}$$C because of non-recrystallization, and so the crosslinked PLLA kept transparency. Improvement of elasticity was succeeded by adding high concentrated plasticizer ($$>$$ 35%) in PLLA. Therefore, the applications of bioplastic will be expanded by the combination method of the radiation-induced crosslinking and adding high content of the plasticizer.

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