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 ¹H magic angle spinning NMR showed altered moisture balance after chemical and thermal modifications because of changed hydrophobicity. The ¹³C 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, T₁H and T₁C, increased with chemical modifications although T₁C decreased with the curing of both resins. In contrast, ¹H spin–lattice relaxation in the rotation frame, T_1ρH, 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 ¹³C 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 ¹³C CP-MAS NMR and T₁H change due to the curing.