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Hemicelluloses are regarded as one of the first candidates for the development of value-added materials due to their renewability, abundance, and functionality. However, because most hemicelluloses are brittle, they can only be processed as a solution and cannot be processed using industrial melt-based polymer processing techniques. In this study, arabinoxylan (AX) was hydrophobized by incorporating butyl glycidyl ether (BuGE) into the hydroxyl groups through the opening of the BuGE epoxide ring, yielding alkoxy alcohols with terminal ethers. The formed BuGE derivatives were melt processable and can be manufactured into stretchable thermoplastic films through compression molding, which has never been done before with hemicellulose modified in a single step. The structural and thermomechanical properties of the one-step synthesis approach were compared to those of a two-step synthesis with a pre-activation step to demonstrate its robustness. The strain at break for the one-step synthesized AX thermoplastic with 3 mol of BuGE is ≈200%. These findings suggest that thermoplastic polymers can be composited with hemicelluloses or that thermoplastic polymers made entirely of hemicelluloses can be designed as packaging and stretchable electronics supports.

Developing flexible, stretchable, and thermally processable materials for packaging and stretchable electronic applications from polysaccharide-based polymers contributes to the smooth transition of the fossil-based economy to the circular bioeconomy. We present arabinoxylan (AX)-based thermoplastics obtained by ring-opening oxidation and subsequent reduction (dA-AX) combined with hydrophobization with three different glycidyl ethers [n-butyl (BuGE), isopropyl (iPrGE), and 2-ethyl hexyl (EtHGE) glycidyl ether]. We also investigate the relationship between structural composition, thermal processing, and thermomechanical properties. BuGE- A nd iPrGE-etherified dA-AXs showed glass-transition temperatures (Tg) far below their degradation temperatures and gave thermoplastic materials when compression-molded at 140 °C. The BuGE (3 mol)-etherified dA-AX films at 19 and 31% oxidation levels show 244% (±42) and 267% (±72) elongation, respectively. In contrast, iPrGE-dA-AX samples with shorter and branched terminals in the side chains had a maximum of 60% (±19) elongation. No studies have reported such superior elongation of AX thermoplastic films and its relationship with molar substitution and Tg. These findings have implications on the strategic development of chemical modification routes using commercial polymer processing technologies and on fine-tuning structures and properties when specific polysaccharide-based polymers are used to engineer bio-based products for film, packaging, and substrates for stretchable electronic applications.

International audience; We show here how the structure of polygalacturonate (polyGalA) hydrogels cross-linked by Ca2+ cations via external gelation controls the loading and the release rate of betalactoglobulin (BLG), a globular protein. Hydrogels prepared from a polyGalA/BLG solution are found similar to those obtained from a polyGalA solution in our previous study (Maire du Poset, et al. Biomacromolecules 2019, 20(7), 2864-2872): they exhibit similar transparencies and gradients of mechanical properties and polyGalA concentration. The nominal BLG/polyGalA ratio of the mixtures is almost recovered within the whole mixed hydrogel despite such strong concentration gradients, except in the part of hydrogels with the largest mesh size, where more BLG proteins are present. This gradient enables to tune the amount of protein loaded within the hydrogel. At local scale, the proteins are distributed evenly within the hydrogel network, as shown by small-angle neutron scattering (SANS). The release of proteins from hydrogels is driven by Fickian diffusion and the release rate increases with the mesh size of the network, with a characteristic time of a few hours. The specific structure of these polysaccharide-based hydrogels allows to control both the dosage and the release rate of the loaded protein and make them good candidates for use as oral controlled delivery systems.

Polysaccharide-based hydrogels were prepared by the diffusion of various divalent cations (X2+) into the polygalacturonate (polyGal) solution through a dialysis membrane. The diffusion of various divalent cations (Mg2+, Ca2+, Zn2+ and Ba2+) was investigated. The polyGal gel growth was studied as a function of the initial cation concentration by both viscoelastic and turbidity measurements. We have demonstrated for the first time that the determination of the spatiotemporal variation of turbidity during the gelation process allowed to study the gel front migration. For Ca-polyGal, Zn-polyGal and Ba-polyGal, the gel front migration was characterized by the presence of a peak at the sol/gel interface. This peak was not observed in the case of Mg-polyGal where the gel was not formed. The apparent diffusion coefficient of the gel front (Dapp) which was calculated from the evolution of this peak increased when the initial cation concentration was increased. Moreover, we have suggested a gelation mechanism based on the presence of a threshold molar ratio R* (=[X2+]/[Galacturonic unit]) in which some point-like crosslinks are precursors of the formation of dimers and multimers inducing the contraction of the gel and thus the formation of the gel front.

International audience; The local structure of Fe2+ in Fe2+-polygalacturonic acid (polyGalA) hydrogels has been studied by coupling Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and molecular dynamics (MD) simulation. The EXAFS fitting results reveal an octahedral coordination geometry of Fe2+ both in aqueous solution and in the hydrogel, with similar Fe-O distances (2.09 ± 0.01 Å in the hydrogel and 2.11 ± 0.01 Å in aqueous solution). The MD simulations evidence that standard empirical force fields are unable to accurately reproduce the EXAFS spectra of Fe2+ in both aqueous solution and hydrogel. Based on the EXAFS distance determinations, we then performed restrained MD simulations of hypothetical octahedral coordination modes of Fe2+ with polyGalA chains. The best agreement between experimental and simulated EXAFS spectra was found when Fe2+ is monodentately coordinated to two carboxylate and two hydroxyl oxygens from a pair of polyGalA chains as well as to two water oxygens in an octahedral coordination geometry compatible with the "egg-box model".

International audience; We designed stable and highly reproducible hydrogels by external unidirectional diffusion of Fe2+ ions into aqueous solutions of polygalacturonate (polyGal) chains. The Fe2+ ions act as cross-linkers between the Gal units in such a way that both the molar ratio R ([Fe2+]/[Galunits]=0.25) and the mesh size of the polyGal network at the local scale (zeta=75 +/- 5 angstrom) have constant values within the whole gel, as respectively determined by titration and Small Angle Neutron Scattering. From macroscopic point of view, there is a progressive decrease of polyGal concentration from the part of the gel formed in the early stages of the gelation process, which is homogeneous, transparent and whose Young modulus has a high value of similar to 10(5) Pa, up to the part of the gel formed in the late stages, which is heterogeneous, highly turbid and has a much lower Young modulus of similar to 10(3) Pa. Since the local organization of the polyGal chains remains identical all along the hydrogels, this macroscopic concentration gradient originates from the formation of heterogeneities at a mesoscopic length scale during the gelation process. In addition, X-ray Absorption Spectroscopy measurements remarkably reveal that Fe2+ ions keep their +II oxidation state in the whole gels once they have cross-linked the Gal units. These polyGal hydrogels thus protect iron against oxidation and could be used for iron fortification.