Softwoods fiberized at high temperatures (above 170°C) were subjected to bulk and surface chemical analyses. It was found that the frequency of lignin β-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 fiberization, which was associated with cleavage of lignin ether linkages. The water extractable material generated was enriched in hemicelluloses and contained aromatic compounds rich in phenolic hydroxyl groups and low in β-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 extractives-free fibers roughly doubled their bulk lignin content.
Widsten, P., Laine, J. E., Qvintus-Leino, P., & Tuominen, S. (2001). Effect of high-temperature fiberization on the chemical structure of softwood. Journal of Wood Chemistry and Technology, 21(3), 227-245. https://doi.org/10.1081/WCT-100105374