Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity
Highly crystallized polylactic acid (PLA) is suitable for industrial applications due to its stiffness, heat resistance, and dimensional stability. However, crystal lamellae in PLA products might delay PLA decomposition in the environment. This study clarifies how the initial crystal structure influ...
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-12-01
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| Series: | Polymers |
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| Online Access: | https://www.mdpi.com/2073-4360/13/24/4324 |
| _version_ | 1797501243622424576 |
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| author | Yutaka Kobayashi Tsubasa Ueda Akira Ishigami Hiroshi Ito |
| author_facet | Yutaka Kobayashi Tsubasa Ueda Akira Ishigami Hiroshi Ito |
| author_sort | Yutaka Kobayashi |
| collection | DOAJ |
| description | Highly crystallized polylactic acid (PLA) is suitable for industrial applications due to its stiffness, heat resistance, and dimensional stability. However, crystal lamellae in PLA products might delay PLA decomposition in the environment. This study clarifies how the initial crystal structure influences the hydrolytic degradation of PLA under accelerated conditions. Crystallized PLA was prepared by annealing amorphous PLA at a specific temperature under reduced pressure. Specimens with varied crystal structure were kept at 70 °C and in a relative humidity (RH) of 95% for a specific time. Changes in crystal structure were analyzed using differential calorimetry and wide-angle X-lay diffraction. The molecular weight (MW) was measured with gel permeation chromatography. The crystallinity of the amorphous PLA became the same as that of the initially annealed PLA within one hour at 70 °C and 95% RH. The MW of the amorphous PLA decreased faster even though the crystallinity was similar during the accelerated degradation. The low MW chains of the amorphous PLA tended to decrease faster, although changes in the MW distribution suggested random scission of the molecular chains for initially crystallized PLA. The concentrations of chain ends and impurities, which catalyze hydrolysis, in the amorphous region were considered to be different in the initial crystallization. The crystallinity alone does not determine the speed of hydrolysis. |
| first_indexed | 2024-03-10T03:15:35Z |
| format | Article |
| id | doaj.art-72230488972f43a285fe30a22b3f761f |
| institution | Directory Open Access Journal |
| issn | 2073-4360 |
| language | English |
| last_indexed | 2024-03-10T03:15:35Z |
| publishDate | 2021-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Polymers |
| spelling | doaj.art-72230488972f43a285fe30a22b3f761f2023-11-23T10:14:43ZengMDPI AGPolymers2073-43602021-12-011324432410.3390/polym13244324Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High HumidityYutaka Kobayashi0Tsubasa Ueda1Akira Ishigami2Hiroshi Ito3Research Center for GREEN Materials and Advanced Processing (GMAP), 4-3-16 Jonan, Yonezawa 992-8510, JapanGraduate School of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, JapanResearch Center for GREEN Materials and Advanced Processing (GMAP), 4-3-16 Jonan, Yonezawa 992-8510, JapanResearch Center for GREEN Materials and Advanced Processing (GMAP), 4-3-16 Jonan, Yonezawa 992-8510, JapanHighly crystallized polylactic acid (PLA) is suitable for industrial applications due to its stiffness, heat resistance, and dimensional stability. However, crystal lamellae in PLA products might delay PLA decomposition in the environment. This study clarifies how the initial crystal structure influences the hydrolytic degradation of PLA under accelerated conditions. Crystallized PLA was prepared by annealing amorphous PLA at a specific temperature under reduced pressure. Specimens with varied crystal structure were kept at 70 °C and in a relative humidity (RH) of 95% for a specific time. Changes in crystal structure were analyzed using differential calorimetry and wide-angle X-lay diffraction. The molecular weight (MW) was measured with gel permeation chromatography. The crystallinity of the amorphous PLA became the same as that of the initially annealed PLA within one hour at 70 °C and 95% RH. The MW of the amorphous PLA decreased faster even though the crystallinity was similar during the accelerated degradation. The low MW chains of the amorphous PLA tended to decrease faster, although changes in the MW distribution suggested random scission of the molecular chains for initially crystallized PLA. The concentrations of chain ends and impurities, which catalyze hydrolysis, in the amorphous region were considered to be different in the initial crystallization. The crystallinity alone does not determine the speed of hydrolysis.https://www.mdpi.com/2073-4360/13/24/4324biopolymershydrolytic degradationcrystal structure |
| spellingShingle | Yutaka Kobayashi Tsubasa Ueda Akira Ishigami Hiroshi Ito Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity Polymers biopolymers hydrolytic degradation crystal structure |
| title | Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity |
| title_full | Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity |
| title_fullStr | Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity |
| title_full_unstemmed | Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity |
| title_short | Changes in Crystal Structure and Accelerated Hydrolytic Degradation of Polylactic Acid in High Humidity |
| title_sort | changes in crystal structure and accelerated hydrolytic degradation of polylactic acid in high humidity |
| topic | biopolymers hydrolytic degradation crystal structure |
| url | https://www.mdpi.com/2073-4360/13/24/4324 |
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