Abstract:

Hemicellulose is ubiquitous in plant cell walls, comprising one of the three major components. Currently, the industrial utilization of hemicellulose primarily focuses on its degradation to produce low-molecular-weight xylo-oligosaccharides, xylose, and furfural. Recent studies have shown that crystalline xylan exhibit unique physicochemical properties and can be converted into high-value-added xylan nanocrystals, which has become a research hotspot in the utilization of plant polysaccharides in recent years. Xylan nanocrystals are primarily composed of the five-carbon sugar xylose as the repeating structural unit, and the relatively weak interchain interactions usually require external stabilizers such as water molecules to stabilize the crystalline structure. Xylan nanocrystals exhibit spherical, lamellar, and rod-like morphologies, with sizes typically ranging from tens to hundreds of nanometers, which are determined by the different preparation methods. The unique chemical structure of xylans also leads to their preparation methods being different from those of traditional lignocellulosic-based nanocrystals. Additionally, xylan nanocrystals possess excellent biocompatibility and nanoscale effects, making them have great application potential in various fields. This review summarizes the typical structures of hydrate xylan nanocrystals, acetylated xylan nanocrystals, and xylan co-nanocrystals, and introduces the influence of water molecules and the chemical structure of xylan on their unit cell parameters. The review systematically discusses the top-down and bottom-up approaches for the preparation of xylan nanocrystals, with a focus on analyzing the effects of different preparation methods on the morphology, size, degree of polymerization, yield, and physicochemical properties of the xylan nanocrystals. It also provides an overview of their applications in emulsification, consumer chemicals, and anti-counterfeiting materials, and discusses the current challenges and future development and application prospects of xylan nanocrystals based on the related research achievements.

Key words: crystalline polysaccharides, xylan nanocrystals, self-assemble, top-down, carbon neutrality