Study on thermal behavior of regenerated micro-crystalline cellulose containing slight amount of water induced by hydrogen-bonds transformation

Abstract Cellulose exhibit an excellent ability to adsorb water because of its strong hydrophilicity. The effect of water present in natural cellulose on the structure and thermal property has been paid attention. However, the influence is not clear on the cellulose after regeneration, in the process of which a large amount of water is usually used. In the present study, two important thermal behavior of water-loss and oxidation respectively in the temperature range of 20–165 °C and 165–300 °C was identified in the heating process of the regenerated microcrystalline cellulose (MCC) with the water content of 2.4 wt%. By using perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy combined with generalized 2D correlation spectroscopy (2DCOS), the successive changes in the physical loss of water, the initial inter- and intrachain H-bonds weakening, and the formation of the weak/free H-bonds are illustrated during the first process. While continuous development of the weak/free H-bonds network and the transition from the OH groups within H-bonds to the C =O group are closely linked in the subsequent oxidation process. Furthermore, it is found that a higher crystallinity and a lower water-content can be obtained in the sample after high-temperature annealing. Thus prepared MCC go through the same two stages but with high-temperature shift of ca. 10 °C. The structural changes in H-bonds correlated to the thermal behavior mentioned above exhibit a high-temperature shift correspondingly. Temperature-dependent WAXD spectra reveals that the higher thermal stability of the sample is contributed from the structural regularity and the high crystallinity of the regenerated cellulose II improved by decreased water content. Our results indicate that water existence should be considered in the process of the preparation and industrialization of cellulose.