The color change from pale yellow to vermilion due to the UV-irradiation and the reverse color change due to the heating at about the glass transition temperature (
Tg) were investigated for the poly(lactic acid) (PLA) mixed with 9,10-anthraquinone (AQ) by electronic absorption and IR analysis. The absorption of the broad band around 485 nm assigned to the electron donor acceptor (EDA) between AQ and anthrahydroquinone (AQH
2) was increased by UV-irradiation and was decreased by the heating at about the glass transition temperature. The color change and reversion was possible by repeating the UV irradiation and the heating operations. A decrease of AQ and a formation of AQH
2 by the UV irradiation and a increase of AQ and a small decrease of AQH
2 by the heating were observed from the IR measurements. The formation of the AQ-AQH
2EDA complex which hydrogen bonded with PLA was a cause of coloration and the dissociation of EDA was a cause of fading. At the same time, some of AQH
2 was oxidized to AQ.
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