Controllable synthesis of xylan nanoparticles and modifications for versatile applications

Xylan, an emerging candidate for the fabrication of biobased nanoparticles, has garnered considerable attention due to its biodegradability, biocompatibility, sustainability, and natural abundance. However, uncertainties in the shape and size of xylan nanoparticles have limited their further development as functional materials. In this thesis, we present size-controlled fabrication methods for xylan nanoparticles through self-assembly from a supersaturated aqueous solution. By optimizing the physical conditions during preparation, the preparation of xylan particles ranging from the micrometer to nanometer scale was achieved. The processes eliminated the need for additional surfactants or chemicals, thus enabling an environmentally friendly and simple synthesis. Building upon the chemical structure of xylan and the abundance of hydroxyl groups on the surface of xylan nanoparticles, we modified the surface chemistry of the xylan nanoparticles by introducing functional groups via chemical oxidation. The introduction of aldehyde groups was first achieved through periodate oxidation, providing abundant reactive sites for further chemical reactions. Dialdehyde xylan nanoparticles (DAXNPs) with a core-shell structure were successfully obtained by optimizing reaction conditions. Subsequently, the introduction of carboxyl groups into the carboxylated xylan nanoparticles (CXNPs) was achieved by the secondary oxidation of DAXNPs. These CXNPs exhibited high adsorption capability for positively charged pollutants, demonstrating potential as biomass-based adsorbents. In another application, a novel oil-in-water high internal phase Pickering emulsion (HIPPE) system was developed using polyethyleneimine-modified dialdehyde xylan nanoparticles (PEI-DAXNPs) as a stabilizer. The HIPPEs were stabilized with as little as 0.1 wt% PEI-DAXNPs and maintained long-term stability after 180 days of storage. Moreover, these HIPPEs exhibited shear-thinning behavior and promising viscoelastic properties, indicating good processability for fabricating soft materials and porous scaffolds. Overall, this thesis investigated the optimization of xylan nanoparticle preparation methods and their functionalization through chemical modification, enabling their application as advanced materials. The introduction of different functional groups endowed the particles with new surface chemistry, providing insights into the development of functional materials based on xylan nanoparticles. These findings offer a pathway for improved hemicellulose utilization in advanced applications where the heterogeneity of xylan is mitigated through controlled assembly into uniform xylan particles.