The nanoscale structure of lignocellulosic biomass plays a crucial role in an extensive variety of its applications, ranging from physico-chemical or enzymatic modification of biomass to the use of wood as construction material. Also from a biological point of view, the nanoscale morphology of cellulose microfibrils, their hierarchical assembly into bundles and larger fibrillar structures, as well as the complicated interplay of enzymes and physical restrictions in the biosynthesis of cellulose offer many unresolved yet highly relevant research questions. Understanding the nanoscale structure of the plant cell wall requires the combined use of various experimental methods, where the lacks of each of them are complemented by the benefits of the others.<br/><br/>One of the highly potential but currently underused methods for characterizing the plant cell wall structure in its native state is small-angle scattering. Small-angle scattering of x-rays and neutrons, SAXS and SANS, are particularly sensitive to the morphology and aggregation of cellulose microfibrils, which are directly linked for instance to the accessibility of cellulose to enzymes or the moisture behavior of wood. Until recently, a major challenge for an efficient implementation of these techniques has been the complicated analysis of the scattering data. For this purpose, we developed a versatile and easy-to-use model based on hexagonally assembled cylinders, that can be fitted to the equatorial SAXS or SANS data of wood. The method works reasonably well for both softwoods and hardwoods and allows the determination of the microfibril diameter (2.1-2.5 nm) and their packing distance in both wet (3-4 nm) and dry states (3 nm). Moreover, the model allows real-time monitoring of these parameters during moisture changes of wood, which was demonstrated by SAXS measurements at different moisture contents obtained at controlled humidity conditions. The latest results indicate that the water adsorption ability of cellulose microfibrils was not fully recovered after a drying cycle from a never-dried state to a rewetted state.<br/><br/>This contribution presents applications of a relatively new methodology for understanding the nanoscale structure of cellulosic biomass and particularly the implications of moisture changes on it. The current results obtained with wood samples may reflect the general behavior of cellulosic biomass and are important for various applications of this naturally abundant, renewable raw material.

Investigating the nanostructure of cellulosic materials with small-angle scattering

2019 Spring National Meeting

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