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

Pinus radiata chips were pulped on a laboratory scale to yields betwee n 47% and 96%. A ''delayed contact'' pulse sequence was used to separa te 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 prefe rential loss of disordered cellulose in the early stages of pulping. C ellulose 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. N MR estimates of residual lignin contents were in good agreement with K lason lignin values.