Summary
The present paper aims at elucidating the effect of high-temperature defibration at different temperatures
on the bulk and surface chemical properties of defibrated birch, aspen and eucalypt. The results indicate
that defibration of these hardwoods results in partial depolymerization of fiber lignin via (homolytic)
cleavage of interunit alkyl-aryl (β-O-4) ether bonds. This increases the phenolic hydroxyl content and
produces relatively stable (phenoxy) radicals. Syringyl-type lignin is more extensively depolymerized
than guaiacyl-type lignin. Defibration generates water-extractable material, which is enriched in hemicellulose-derived carbohydrates and has a substantial content of aromatic compounds rich in phenolic
hydroxyl groups. The amount of water-extract and the extent of lignin interunit ether bond cleavage
increase with an increase in defibration temperature. The differences between various hardwood species
in this respect are small. The surface chemical composition of the fibers differs considerably from their
bulk composition, but is not significantly influenced by variations in defibration temperature. Lipophilic
extractives cover a large portion of the fiber surface, while the lignin content of lipophilic extractives-free
fiber surfaces is 2–3 times as high as the bulk lignin content of the fibers.
The Flexible Surface: Molecular Studies Explain the Extraordinary Diversity of Surface Chemical Properties
