Integrated analysis of solid-state NMR spectra and nuclear magnetic relaxation times for the phenol formaldehyde (PF) resin impregnation process into soft wood

Abstract

The effects of phenol formaldehyde (PF) resin impregnation into Japanese cedar plates were studied by the integrated analysis of solid-state NMR spectra and relaxation times. ¹³C cross-polarization/magic angle spinning (CP-MAS) NMR spectra showed that PF resin permeated near carbohydrate polymers as well as lignin regions, providing hydrophobicity in a woody material. Additionally, ¹³C pulse saturation transfer/magic angle spinning (PST-MAS) NMR spectra revealed that the molecular mobility of cellulose endocyclic groups was suppressed by the PF resin impregnation. Spin-lattice relaxation times in the laboratory frame, T₁H and T₁C, for both untreated and impregnated woods decreased in humid conditions while they were increased by the PF resin impregnation. Meanwhile, spin-lattice relaxation in the rotation frame, T_1ρH, decreased in humid conditions as well as being a result of the PF resin impregnation. According to the tendencies of the T₁H, T₁C, and T_1ρH values associated with the PF resin impregnation, although faster molecular motions of lignin OCH₃ group were increased in the MHz frequency range, slower molecular motions of the cellulose ring were suppressed in the kHz frequency range, which confirmed the result from the ¹³C PST-MAS NMR spectra.