C-13 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF KRAFT PULPING

Pinus radiata chips were pulped on a laboratory scale to yields between 47% and 96%. A ''delayed contact'' pulse sequence was used to separate C-13 CP/MAS NMR spectra into subspectra of pulp components. Results showed a smooth increase in the degree of crystallinity of the intact cellulose fibrils from 0.53 for the high-yield pulps to a plateau at about 0.60 for low-yield pulps. This was interpreted in terms of preferential loss of disordered cellulose in the early stages of pulping. Cellulose damage was observed for pulp yields below 57%. with a maximum of 16% of total cellulose being physically damaged at 47% pulp yield. A combination of chemical analysis and NMR spectra provided evidence for molecular ordering in about half of the residual hemicelluloses. NMR estimates of residual lignin contents were in good agreement with Klason lignin values.