Crystallinity Changes in Modified Cellulose Substrates Evidenced by Spectral and X-Ray Diffraction Data

Abstract

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.