Hydrogen Bond Reconfiguration in Wood Polysaccharides Towards Functional Materials

Naturally abundant polysaccharides, particularly cellulose and xylan, constitute a major fraction of the carbohydrate resources in nature and are promising feedstocks for sustainable materials. Their mechanical robustness, biodegradability, structural versatility, and chemical tunability enable broad applications in areas such as biomedicine, food science, and environmental engineering. However, the dense packing and high crystallinity of cellulose, stabilized by extensive intra- and intermolecular hydrogen bonding together with inter-sheet van der Waals/hydrophobic interactions, severely limit heterogeneous chemical reactions by reducing cellulose accessibility. Achieving nanocellulose with exceptional performance therefore requires a balance between preserving desirable crystalline features and enhancing chemical accessibility during processing.

Herein, a LiBr·3H₂O (LBTH) non-dissolving pretreatment at room temperature is introduced to selectively disrupt the hydrogen bond network and partially deconstruct the crystalline structure of cellulose without destroying polymeric integrity. The resulting cellulose exhibits enhanced accessibility, enabling more efficient oxidation and esterification with reduced chemical consumption and increased introduction of functional groups such as aldehyde and formyl moieties. Cellulose formate with elevated formyl content can be homogeneously dissolved in formic acid and reassembled into mechanically robust regenerated cellulose-based materials, including filaments, films, hydrogels, and aerogels.

In parallel, a “hemicellulose-first” biorefining concept is applied to isolate structurally preserved xylan via pressurized hot-water extraction under oxygen-starved conditions, thereby minimizing degradation and deacetylation. The obtained native xylan is an amorphous, acetylated, and branched biopolymer that can be fractionated by membrane ultrafiltration to control molecular weight and dispersity. Subsequent alkaline debranching, together with stabilization of reducing ends, restores stronger intra-/interchain interactions and enables bottom-up formation of crystalline nanoxylan. Leveraging the increased conformational flexibility of debranched xylan, hydrophobic substitution is further employed to rebalance hydrogen bonding and hydrophobic interactions, inducing thermoresponsive self-assembly.

Overall, this thesis demonstrates an interaction-engineering strategy for wood polysaccharides: selectively weakening overly robust interactions in cellulose to unlock accessibility, while strengthening and reconfiguring intermolecular interactions in xylan to drive crystallization and programmable assembly. These findings provide new insights into hydrogen bond reconfiguration in polysaccharides and advance the development of high-performance, recyclable, and functional bio-based materials.