Proton magnetic relaxation study of the thermodynamic characteristics of water adsorbed by cellulose fibers

Qualitatively and quantitatively characterizing water adsorption of a cellulose nanofiber film using micro-FTIR spectroscopy

“…Water adsorption is a key property of cellulose materials, and it has been studied via a number of experimental approaches, such as quartz crystal microgravimetry, 10 dynamic vapor sorption, 11,12 dielectric relaxation spectroscopy, 13 Fourier transform infrared spectroscopy, 14 and nuclear magnetic resonance spectroscopy. 15,16 Of these experimental approaches, dynamic vapor sorption (DVS) is an important quantitative method which has been widely used and has provided vast amounts of water sorption data. [17][18][19] Using this method, sorption isotherm and sorption hysteresis of many cellulose materials including natural bers, 20,21 regenerated cellulose, 22 microcrystalline cellulosic bers, 23 and wood powder, 24 have been analyzed.…”

Cellulose–water system’s state analysis by proton nuclear magnetic resonance and sorption measurements

“…In the framework of the Bloembergen-Purcell-Pound theory (BPP), correlation times describe thermal motions of molecules that have Arrhenius character. This allows associating the activation energies of molecular motions with their correlation times in the first two layers of aqueous adsorbate (Grunin et al 2016). For the first water adsorption layer:…”

“…In the framework of the BPP theory, correlation times in adsorbed water layers are related to their spin-spin relaxation times (under the condition (ωτ) 2 ≫ 1, where ω is the circular NMR frequency, τ is the correlation time) by the formula (Grunin et al 2016): where T (1) 2 and T (2) 2 are the true spin-spin relaxation times of first and second adsorbate layers, respectively. The measured spin-spin relaxation time of the first layer is equivalent to its true value due to the very slow proton exchange of cellulose with adsorbed water.…”

“…Since a part of the heat is released during adsorption, the change in entropy is related to the change in Gibbs free energy and the net heat of adsorption in accordance with the following expression (Grunin et al 2016):…”

“…Time-domain NMR applications do not only cover research and development but also provide the organization of routine on-line and at-line procedures of quality assurance and quality control in production processes (Mitchell et al 2014). The possibility of using 1 H NMR in the analysis of water adsorption on cellulose is shown in researches (Leisen et al 2002;Banas et al 2000;Taylor et al 2008;Grunin et al 2016Grunin et al , 2017Grunin et al , 2018. Leisen et al (2002) measured the entire adsorption/ desorption isotherm at precisely defined levels of relative humidity using NMR data.…”