Sonication-Driven Liberation of Lignin-Rich Fragments Enabled by Surface-Active Additives

Wood delignification is typically achieved by chemical pulping and bleaching, but lignin removal can also be viewed as a dispersion challenge in which lignin-rich fragments are stabilized in the liquid phase. Here, we present a proof-of-concept for additive-assisted lignin liberation from disc-refined spruce fibers using controlled-energy sonication. Sodium dodecyl sulfate (SDS) and carboxymethyl cellulose (CMC) were used as representative surfactant and polyelectrolyte additives. Lignin release was quantified from filtrates by UV absorbance at 280 nm. Sonication alone caused negligible additional lignin release at 23 °C, whereas increasing pH or temperature increased release. Both SDS and CMC increased the filtrate lignin concentration by ∼12%–50%, relative to additive-free references (condition-dependent), although the overall detached fraction remained low (≤4.5% of total lignin), highlighting dispersion stabilization as a lever for lignin release under shear. Low ionic strength appeared beneficial for lignin liberation via dispersion formation.