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Conference papers

Radiation-induced degradation of polysaccharides: quantification of the protective effect by aromatic additives on pullulan

Abstract : The behavior of polysaccharides submitted to ionizing radiation is roughly described by their general trend towards chain scission with a degree depending primarily on the structure of the polymer, its pre-irradiation chemical treatment, and the degree of hydration. Though certain applications aim at decreasing the polysaccharides molecular weight by radiation-induced chain scission, for biomass deconstruction, or to produce various types oligomers, the degradative behavior is often a limitation in developing new applications based on radiation-induced modification such as grafting.1,2 To overcome the radiation-induced degradation of polysaccharides, processing methods with corrective actions involve either blending them with monomers that polymerize and form crosslinks under ionizing radiation or converting reactive side-groups with appropriate functionalities, e.g. as acetates or acrylates, try to balance chain scission by simultaneous cross-linking. In the frame of our program on radiation-induced modification of starch, a promising bio-based substitute to plastics, we have reported on original methods to mitigate the water sensitivity and to reduce retrogradation of amorphized starch by blending it with lignin or with allyl urea followed by electron beam (EB) processing.3-6 Further studies on starch and maltodextrin including low MW aromatic additives such as cinnamyl alcohol (CA) revealed a strong dependence of the radiation-induced degree of modification on the (i) chemical composition of the blend, and (ii) inter-molecular associations between the blends constituents.7,8. The changes in number-average (M̅n) and weight-average molecular weights (M̅w,) were monitored by size exclusion chromatography with differential refractive index and UV detection, starting from a fractionated pullulan sample exhibiting a most probable MW distribution (dispersity Ð ~ 2). The radiation chemical yields G(S)corr and G(X)corr can be calculated from these measurements by taking into account the fraction in weight (fw) of pullulan within the hydro-alcoholic blends. The G values (in mmol J-1) for pullulan submitted to electron beam radiation in the dry state (G(S) = 0.59, G(X) < 0.02) complement the available data on polysaccharide radiolysis. The variations measured in presence of CA bring new insight into the complex effects of irradiation on pullulan in such blends. The introduction of small quantities of CA in the hydro-alcoholic blends of pullulan leads to a significant decrease in both, G(S) and G(X) providing protection against radiation-induced effects, likely due to energy and electron transfer mechanisms from the primary excited species to the aromatic additive. A significant influence of CA was observed at concentrations as low as 5 mmol kg-1 in the blend. In presence of larger amounts of CA, irradiation at higher dose levels induces an increase in molecular mass, with concomitant grafting of the aromatic additive when present in higher concentration. Furthermore, these results emphasize the influence of hydro-alcoholic media on paste-like pullulan blends, showing that indirect effects of water radiolysis are overcome by alcohol that scavenge HO● radicals, resulting in a decrease of G(S). The influence of other natural aromatic compounds such a ferulic acid is under investigation. References 1. K. Furtak et al., Radiat. Phys. Chem. 2018, 94-99. 2. G. Tataru et al., Radiat. Phys. Chem. 2020, doi.org/10.1016/j.radphyschem.2019.108663. 3. A. Olivier et al., Biomacromolecules 2001, 282-289. 4. A. Olivier et al. Biomacromolecules 2001, 1260-1266. 5. S. Lepifre et al., Ind. Crop Prod. 2004, 219-230. 6. S. Lepifre et al., Biomacromolecules 2004, 1678-1686. 7. D. Khandal et al., Radiat. Phys. Chem. 2012, 986-990. 8. D. Khandal et al., Carbohydr. Polym. 2015, 150–159.
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Contributor : Xavier Coqueret Connect in order to contact the contributor
Submitted on : Tuesday, February 1, 2022 - 5:44:46 PM
Last modification on : Friday, February 25, 2022 - 10:55:22 AM

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Xavier Coqueret, Dhriti Khandal. Radiation-induced degradation of polysaccharides: quantification of the protective effect by aromatic additives on pullulan. 8th Asian Pacific Symposium on Photopolymer Science, Japanese Society of Radiation Chemistry, Apr 2020, Takasaki, Japan. ⟨hal-03551672⟩

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