PHOTODELIGNIFICATION OF EUCALYPTUS-GRANDIS ORGANOSOLV CHEMICAL PULP

Efficient delignification of Eucalyptus grandis organosolv pulp was ac hieved. The process, which was chlorine and sulphur free, removed 88% of the lignin (kappa number (KN) 65 to 8) with moderate viscosity loss (eta = 19 cP to 12 cP). The best sequence involved three photochemica l stages in alkaline medium (NaOH) at 85 degrees C. The first stage in volved oxygen treatment; this was followed by the action of excited si nglet oxygen produced by methylene blue (4.5 X 10(-5) mol l(1-)). The last stage, using hydrogen peroxide (6% relative to the weight of oven dried pulp (odp)), was the most efficient, the structure of the ligni n having been prepared by the first two stages. The mechanism of the o verall process remains unknown.