The crystallinity of cellulose substrates is a key factor in their processability, as well as an indication of their susceptibility to undergo sensitive reactions (such as enzymatic saccharification) with high yields. FT-IR and X-ray diffraction spectroscopy are useful, reliable, and easy-to-reach solid-state characterization methods for assessing the crystallinity of different cellulose substrates including wood and wood-based materials. Due to their specific methodology, they can be used to analyze not only starting materials and their final products but also intermediates. Data obtained by these methods substantiated the structural changes in cellulose substrates, as well as the alterations that occurred in their supramolecular architectures. The conversion of crystalline cellulose I into amorphous cellulose II during enzymatic saccharification, with or without pre-treatment (solubilization in ILs), was evidenced beyond any reasonable doubt by FT-IR and XRD experimental results. Enzyme hydrolysis rates of the ILs-treated cellulose substrates can be significantly increased, as evidenced by reducing sugar yields. Crystallinity index values for cellulose of different origins (initial, pre-treated with ILs, and hydrolyzed with enzyme, as well as cellulose submitted to one-pot procedure with ILs and enzyme) can be determined using FTIR and X-ray diffraction data and discussed for comparison purposes. The same solid-state characterization methods can be also successfully employed for investigation of surface changes, expressed as cellulose crystallinity, in wood samples before and after impregnation with natural-based products, as well as under biodegradation conditions in soil burial tests.

Global resources have to be used in responsible ways to ensure the world’s future need for advanced materials. Ecologically friendly functional materials based on biopolymers can be successfully obtained from renewable resources, and the most prominent example is cellulose, the well-known most abundant polysaccharide which is usually isolated from highly available biomass (wood and wooden waste, annual plants, cotton, etc.). Many other polysaccharides originating from various natural resources (plants, insects, algae, bacteria) proved to be valuable and versatile starting biopolymers for a wide array of materials with tunable properties, able to respond to different societal demands. Polysaccharides properties vary depending on various factors (origin, harvesting, storage and transportation, strategy of further modification), but they can be processed into materials with high added value, as in the case of gels. Modern approaches have been employed to prepare (e.g., the use of ionic liquids as “green solvents”) and characterize (NMR and FTIR spectroscopy, X ray diffraction spectrometry, DSC, electronic and atomic force microscopy, optical rotation, circular dichroism, rheological investigations, computer modelling and optimization) polysaccharide gels. In the present paper, some of the most widely used polysaccharide gels will be briefly reviewed with emphasis on their structural peculiarities under various conditions.