Applications of 13C CP/MAS NMR to the study of the wood-phenol formaldehyde bondline

The utility of C-13 CP/MAS NMR, in the characterization of wood phenol-formaldehyde (PF) bondlines, is discussed. Relative degrees of neat resin conversion were assessed by monitoring the relative ratios of hydroxylmethyl and methylene carbon signals. Measured glass transition temperatures) and crosslink densities of neat cured resins were found to correlate with the proton spin lattice relaxation in the rotating frame (T-H(1rho)). Relative degrees of resin cure were assessed in wood flake composites via the use of C-13 labeling and monitoring of the hydroxylmethyl and methylene carbon signals. Cure measurements within the wood flake composites via T-H(1rho), were complicated by the effects of spin diffusion. These effects were removed by the use of deuterium labeling. Relaxation measurements revealed that wood induces heterogeneity in cure PF, whereas neat, cured PF is normally homogenous.. Extension of this technique was made to pilot scale waferboard panels. Differences in cure state and cure chemistry were noted between face and core samples. Relaxation measurements were further complicated by the complex role of water during resin cure.