Effect of high-temperature fiberization on the chemical structure of softwood

Softwoods fiberized at high temperatures (above 170 degreesC) were subjecte d to bulk and surface chemical analyses. It was found that the frequency of lignin beta -O-4 linkages declined while that of phenolic hydroxyl groups increased with an increase in fiberization temperature. The amount of water extractable aromatic compounds increased with increasing temperature of fi berization, which was associated with cleavage of lignin ether linkages. Th e water extractable material generated was enriched in hemicelluloses and c ontained aromatic compounds rich in phenolic hydroxyl groups and low in bet a -O-4 linkages. The amount and hemicellulose content of the water extracts increased with increasing fiberization temperature. Lipophilic extractives covered most of the fiber surfaces while the surface lignin content of ext ractives-free fibers roughly doubled their bulk lignin content.