Variable-temperature solid-state NMR analysis of woody materials in the presence of small hydroxyl molecules

Abstract

Interactions between the hierarchical structure of Japanese cypress and small hydroxylic solvents with high polarity were studied using variable-temperature ¹³C cross-polarization and magic-angle spinning nuclear magnetic resonance (CP/MAS) NMR spectroscopy, including low-temperature measurements. ¹³C CP/MAS NMR spectra were enhanced by dipolar interactions closely related to ¹H–¹³C magnetization transfer, providing information about the interaction between woody materials and small hydroxyl molecules. The change in interaction was particularly near the melting point of the hydroxylic solvent, where a decrease in the intensity of the cypress carbohydrate signal and the appearance of the signal of solvent molecules were observed. The trend of signal intensity in the variable-temperature ¹³C CP/MAS NMR spectra of cypress and cellulose fibers in the presence of hydroxylic solvents indicated that the decrease in the carbohydrate signal intensity due to the transfer of magnetization near the melting point of the hydroxyl molecule is greater when the size of the hydroxyl molecule is smaller. Furthermore, molecular association in the nanopores of the hierarchical structure allowed the hydroxyl molecular signals of the impregnated cypress to appear above the melting point.

Keywords:

• Impregnation
• cross-polarization
• interaction
• nanopore
• molecular association

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

Part of this work was financed by Grants-in-Aid (KAKENHI) for the Promotion of Joint International Research (Fostering Joint International Research (A) 18KK0417 to TM) from the Japan Society for the Promotion of Science (JSPS).