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Keywords = alkoxyl free radical decay

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16 pages, 3712 KiB  
Article
On the Mechanism of Electron Beam Radiation-Induced Modification of Poly(lactic acid) for Applications in Biodegradable Food Packaging
by Eleanor C. Grosvenor, Justin C. Hughes, Cade W. Stanfield, Robert L. Blanchard, Andrea C. Fox, Olivia L. Mihok, Kristen Lee, Jonathan R. Brodsky, Ann Hoy, Ananya Uniyal, Sydney M. Whitaker, Chris Acha, Kalina Gibson, Lilly Ding, Catherine A. Lewis, Lorelis González López, Charlotte M. Wentz, Lawrence R. Sita and Mohamad Al-Sheikhly
Appl. Sci. 2022, 12(4), 1819; https://doi.org/10.3390/app12041819 - 10 Feb 2022
Cited by 13 | Viewed by 4872
Abstract
Poly(lactic acid) (PLA) is a biodegradable polymer used for food packaging. The effects of electron beam radiation on the chemical and physical properties of amorphous PLA were studied. In this study, amorphous, racemic PLA was irradiated at doses of 5, 10, 15, and [...] Read more.
Poly(lactic acid) (PLA) is a biodegradable polymer used for food packaging. The effects of electron beam radiation on the chemical and physical properties of amorphous PLA were studied. In this study, amorphous, racemic PLA was irradiated at doses of 5, 10, 15, and 20 kGy in the absence of oxygen. Utilizing electron paramagnetic resonance spectrometry, it was found that alkoxyl radicals are initially formed as a result of C-O-C bond scissions on the backbone of the PLA. The dominant radiation mechanism was determined to be H-abstraction by alkoxyl radicals to form C-centered radicals. The C-centered radicals undergo a subsequent peroxidation reaction with oxygen. The gel permeation chromatography (GPC) results indicate reduction in polymer molecular mass. The differential scanning calorimetry and X-ray diffraction results showed a subtle increase in crystallinity of the irradiated PLA. Water vapor transmission rates were unaffected by irradiation. In conclusion, these results support that irradiated PLA is a suitable material for applications in irradiation of food packaging, including food sterilization and biodegradation. Full article
(This article belongs to the Special Issue Applied Radiation Chemistry: Theory, Methods and Applications)
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21 pages, 6038 KiB  
Article
On the Mechanisms of the Effects of Ionizing Radiation on Diblock and Random Copolymers of Poly(Lactic Acid) and Poly(Trimethylene Carbonate)
by Agnieszka Adamus-Wlodarczyk, Radoslaw A. Wach, Piotr Ulanski, Janusz M. Rosiak, Marta Socka, Zois Tsinas and Mohamad Al-Sheikhly
Polymers 2018, 10(6), 672; https://doi.org/10.3390/polym10060672 - 16 Jun 2018
Cited by 21 | Viewed by 5971
Abstract
This article demonstrates that ionizing radiation induces simultaneous crosslinking and scission in poly(trimethylene carbonate-co-d-lactide) diblock and random copolymers. Copolymer films were electron-beam (EB) irradiated up to 300 kGy under anaerobic conditions and subsequently examined by evaluation of their structure [...] Read more.
This article demonstrates that ionizing radiation induces simultaneous crosslinking and scission in poly(trimethylene carbonate-co-d-lactide) diblock and random copolymers. Copolymer films were electron-beam (EB) irradiated up to 300 kGy under anaerobic conditions and subsequently examined by evaluation of their structure (FT-IR, NMR), molecular weight, intrinsic viscosities, and thermal properties. Radiation chemistry of the copolymers is strongly influenced by the content of ester linkages of the lactide component. At low lactide content, crosslinking reaction is the dominant one; however, as the lactide ratio increases, the ester linkages scission becomes more competent and exceeds the crosslinking. Electron paramagnetic resonance (EPR) measurements indicate that higher content of amorphous carbonate units in copolymers leads to a reduction in free radical yield and faster radical decay as compared to lactide-rich compositions. The domination of scission of ester bonds was confirmed by identifying the radiolytically produced alkoxyl and acetyl radicals, the latter being more stable due to its conjugated structure. Full article
(This article belongs to the Special Issue Radiation Effects in Polymers)
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