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

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

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 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.