Section: Methodology and research methods. Models and forecasts
Polylactide is one of the most environmentally friendly polymers to replace fossil-based materials. In this work we
quantitatively evaluated the effectiveness of new photostabilizers in preventing the photodegradation of polylactide under UVC radiation by using the spectrometric criteria calculated from FTIR spectra. We have proposed a method including a treatment of the samples of polylactide mixed with the photostabilizers by the UV radiation with a wavelength of 254 nm for 4 hours followed by the calculation of the effectiveness of the photostabilizer based on the FTIR spectrometric data. The number of terminal hydroxyl groups increased during photodegradation due to the cleavage of ester bonds in the polymer, this caused the increase of the absorption at 3600–3100 cm -1 in the FTIR spectra. Several photostabilizers of the terpenophenol class were studied, namely 4-methyl-2,6-diisobornylphenol, 2-isobornylphenol, 2-isobornyl-4-methylphenol
and 2-isobornyl-6-methylphenol, as well as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate – the well-known hindered
amine light stabilizer. The mass concentrations of these photostabilizers varied from 0.05 to 1.00%.
The best protection effect from the UVC radiation in regard to polylactide was shown by 4-methyl-2,6-diisobornylphenol at the concentration of 0.05% by weight. Its photoprotective activity was almost 2 times higher
than that of bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate of the same concentration. The high photoprotecting
activity of 4-methyl-2,6-diisobornylphenol was due to the increased stability of the phenoxy radical provided by
bulky isobornyl substituents in the aromatic ring. In the opposite, the strong photosensitizing effect accelerating the photodegradation of polylactide was manifested by 1% concentrations of 2-isobornyl-4-methylphenol and
2-isobornyl-6-methylphenol. In this case, the delocalization of the unpaired electron in the conjugation chain with the formation of many resonance forms contributed to the transfer of the radical to polylactide macromolecules. The protection of polylactide from UVC radiation opens up prospects for expanding the areas of application of polylactide, a polymer synthesized from renewable raw materials.
Keywords: renewable raw materials, polylactide, photoprotectors, infrared spectrometry
Article published in number 3 for 2022 DOI: 10.25750/1995-4301-2022-3-026-033
ISSN 1995-4301
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