Characterizing Molecular Structure of Water Adsorbed by Cellulose Nanofiber Film Using in situ Micro-FTIR Spectroscopy

Abstract

In situ micro-Fourier transform infrared (FTIR) spectra of a typical cellulose nanofiber (CNF) film (i.e., CNF with cellulose I structure) were collected within the full relative humidity (RH) range from 0% to 90%. Red shifts of two peaks at 1036 and 1204 cm⁻¹ and the variation of different spectra indicated the chemical adsorption sites for adsorbed water. From component band analysis of the spectral range of 2900–3700 cm⁻¹, three component peaks at 3293, 3397, and 3543 cm⁻¹ were due to strongly, moderately, and weakly hydrogen-bonded water. The signatures of these three types of hydrogen-bonded water were then observed to rise with an increase in RH. Based on growth regularities of these three types of hydrogen-bonded water, the water adsorption process of CNF film was divided into three stages; most of the water absorbed in these three stages was demonstrated to be CNF⋅⋅⋅HOH⋅⋅⋅CNF, WATER⋅⋅⋅⋅HOH⋅⋅⋅⋅WATER, and five-molecule tetrahedral structure, respectively.

KEYWORDS:

• Cellulose nanofiber film
• relative humidity
• hydrogen-bonded water
• molecular structure
• water adsorption

FUNDING

The work was financed by the Natural Science Foundations of China (Grant No. 31530009 and 31500475), China Postdoctoral Science Foundation (Grant No. 2014M562146 and 2016T90768), Research Foundation of Education Bureau of Hunan Province (Grant No. 15B256), Hunan Province Science and Technology Project (Grant No. 2015RS4046) and Hunan Provincial Technical Innovation Platform and Talent Program in Science and Technology (Grant No. 2016RS2010 and 2016TP1013). The authors were grateful to Qinglin Wu at Louisiana State University AgCenter for skilled preparation of cellulose nanofiber film.