Recent advances in the radiation chemistry of destructured starch and other glucans as model compounds
Published:15 Dec 2021
D. Khandal, S. Fatahiyah Mohamad, and X. Coqueret, in Carbohydrate Chemistry: Chemical and Biological Approaches, Volume 45, ed. A. Pilar Rauter, T. K. Lindhorst, and Y. Queneau, The Royal Society of Chemistry, 2021, vol. 45, pp. 609-639.
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This chapter overviews the influence of radiation processing applied to thermoplastic starch and some other glucans in blends prepared with various types of plasticizers and additives. Our studies on the radiation-mediated modification of starch-based materials were primarily motivated by the pressing need for alternative sustainable plastics to reduce the environmental footprint of commodity polymers as structural and/or functional materials, particularly due to their use in packaging applications which represent about 40% of the global plastic production. We have started to explore the potentialities of electron beam irradiation applied to thermoplastic starch blends prepared with various composition in plasticizer and reactive additives, to improve the initial bulk and surface properties of the obtained materials and to limit the changes in structural features and mechanical performances with time. The reactivity of the blends submitted to radiation was studied in terms of kinetics and chemical mechanism to provide sufficient control over the transformations occurring at the molecular and macromolecular levels. The changes in physical and mechanical properties were correlated to the modifications performed by blending with reactive plasticizers and then with lignin and aromatic alcohols followed by irradiation at acceptable radiation dose to define conditions inducing significant improvements on the performances of the resulting thermoplastic material. The context of starch-based bioplastics as an alternative to synthetic polymer materials produced from fossil resources and from biomass is introduced at first. The key aspects of radiation treatments applied to polysaccharides are then summarized in terms of basic chemical reactivity and controlled adjustment of functional properties with respect to representative target applications. Electron beam irradiation of thermoplastic starch blends and of model compounds such as maltodextrin and maltotriose mixed with a selected reactive plasticizer, N-allylurea, was shown to yield blends exhibiting improved thermodynamic stability and reduced the rate of retrogradation upon ageing. Various types of lignin, aromatic alcohols and phenols with some structural features of lignin monomers were blended with starch and its model glucans to induce additional effects due the hydrophobicity of the additives. A strong influence of the aromatic additives and of glycerol on the response of the blends to irradiation was evidenced and quantified by measuring the changes of glucans molecular weight as a function of blends composition and of irradiation dose. The protective effect against radiation provided by the aromatic additives is emphasized and quantified by determining the changes in radiation chemical yields for scission G(S) and for cross-linking G(X) for hydro-alcoholic pullulan blends containing various amounts of cinnamyl alcohol.