Integrated analysis of modified Japanese cypress using solid-state NMR spectra and nuclear magnetic relaxation times

Acetylation and resin impregnation of Japanese cypress and subsequent heating of these modified cypresses were examined using an integrated analysis of solid-state NMR spectra and relaxation times. The 1 H magic angle spinning NMR showed altered moisture balance after chemical and thermal modifications because of changed hydrophobicity. The 13 C cross-polarization/magic angle spinning (CP-MAS) NMR spectra showed that acetylation predominately occurred for carbohydrates while phenol formaldehyde (PF) and melamine formaldehyde (MF) resins permeated all biomass constituents in cypress samples. Spin–lattice relaxation times in the laboratory frame, T 1 H and T 1 C, increased with chemical modifications although T 1 C decreased with the curing of both resins. In contrast, 1 H spin–lattice relaxation in the rotation frame, T 1ρ H, increased with the curing as well as acetylation. The tendencies of relaxation times with curing suggested that faster molecular motions were suppressed in the MHz frequency range, and slower molecular motions were enhanced in the kHz frequency range, which generally matched with the signal changes in the 13 C pulse saturation transfer/magic angle spinning NMR spectra. Scanning electron microscope observation showed different adhesion distribution between PF and MF resins, affecting the cellulose signals of 13 C CP-MAS NMR and T 1 H change due to the curing. Graphical abstract