On the Mechanism of Electron Beam Radiation-Induced Modification of Poly(lactic acid) for Applications in Biodegradable Food Packaging

Featured Application Electron beam radiation induces C-O-C bond scissions on the backbone of the amorphous poly(lactic acid) (PLA) used for food packaging. The radiolytically produced alkoxyl radicals abstract hydrogen atoms from the neighboring PLA molecules, leading to the formation of carbon-centered radicals. Since all PLA samples were exposed to air after irradiation and electron paramagnetic resonance (EPR) measurements, the carbon-centered radicals react with oxygen to form the corresponding peroxyl radicals. The resultant PLA is suitable for food irradiation and is biodegradable after the packaging is discarded. The radiation of sterilization has no detrimental effect on the water vapor diffusion through the PLA membrane. 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.