Interaction of Poly(lactic acid) with Water Using FT-IR Spectroscopy under Humidity Conditioning
ORAL
Abstract
Introduction
In recent years, polylactic acid has been one of the materials attracting attention due to its low harmfulness during processing and carbon-neutral properties. Polylactic acid is a polymer with high moisture permeability and very high affinity with water molecules. Absorption of water molecules naturally plays a very important role in the adsorption of water molecules on the cell and film surfaces. However, the surface structure of polylactic acid film is very complex because of its crystalline nature. In order to clarify the interaction between water molecules and the surface of polylactide films heat-treated under various conditions, we used a microbeam infrared spectrometer equipped with a humidity control device and DSC measurements.
Experiments
Poly L-lactic acid (PLLA), poly D-lactic acid (PDLA), and Sc-PLA (a blend of PLLA:PDLA = 50:50) with a weight average molecular weight of approximately 170,000 were used as samples, which were made into films using a heat press machine. Two types of films were prepared for each sample: amorphous film, which was melted above the melting point and quenched, and crystalline film, which was annealed to form spherulites in this film. In the humidity-controlled microbeam infrared spectroscopy measurement, the irradiation position of the crystalline film sample was changed from the center of the spherulite to the edge and then to the amorphous part under humidity control.
Results
We observed that the peak near 3560 cm-1 increased toward the center of the spherulite. The 3560 cm−1 are attributed to absorbed water that is weakly hydrogen-bonded to carbonyl groups of the polymer. This result indicates that more water molecules are adsorbed at the surface of center of the spherulite. On the other hand, no difference was observed between the amorphous and crystalline portions of Sc-PLA. These results might be due the orientation of the lamellae of the spherulites surface.
In recent years, polylactic acid has been one of the materials attracting attention due to its low harmfulness during processing and carbon-neutral properties. Polylactic acid is a polymer with high moisture permeability and very high affinity with water molecules. Absorption of water molecules naturally plays a very important role in the adsorption of water molecules on the cell and film surfaces. However, the surface structure of polylactic acid film is very complex because of its crystalline nature. In order to clarify the interaction between water molecules and the surface of polylactide films heat-treated under various conditions, we used a microbeam infrared spectrometer equipped with a humidity control device and DSC measurements.
Experiments
Poly L-lactic acid (PLLA), poly D-lactic acid (PDLA), and Sc-PLA (a blend of PLLA:PDLA = 50:50) with a weight average molecular weight of approximately 170,000 were used as samples, which were made into films using a heat press machine. Two types of films were prepared for each sample: amorphous film, which was melted above the melting point and quenched, and crystalline film, which was annealed to form spherulites in this film. In the humidity-controlled microbeam infrared spectroscopy measurement, the irradiation position of the crystalline film sample was changed from the center of the spherulite to the edge and then to the amorphous part under humidity control.
Results
We observed that the peak near 3560 cm-1 increased toward the center of the spherulite. The 3560 cm−1 are attributed to absorbed water that is weakly hydrogen-bonded to carbonyl groups of the polymer. This result indicates that more water molecules are adsorbed at the surface of center of the spherulite. On the other hand, no difference was observed between the amorphous and crystalline portions of Sc-PLA. These results might be due the orientation of the lamellae of the spherulites surface.
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Presenters
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Go Matsuba
Yamagata University, Yamagata Univ
Authors
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Go Matsuba
Yamagata University, Yamagata Univ
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Tomoka Kokuzawa
Yamagata University
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Yuka Ikemoto
JASRI/SPring-8