Alcoholysis-induced changes in cell wall surfaces: Structural insights for the effective delignification of lignocellulosic biomass

Abstract

Alcoholysis (organosolv delignification)-induced changes in cell wall surfaces were investigated to verify whether structural assessments are required for effective delignification. Softwood blocks of Cryptomeria japonica were subjected to alcoholysis at 100–150 °C, which gradually decreased their lignin content. Scanning electron microscopy revealed the emergence of amorphous mesh structures on the intercellular side and their transformation into spherical particles with increasing temperature. In addition, warty layers changed from uneven structures into spherical particles on the lumen side of tracheids. These particles produced in cell walls under harsh alcoholysis conditions, damaging the cell wall layers on both sides. Confocal laser scanning microscopy identified that they were mainly lignin eluted by alcoholysis. Alcoholysis at 130 °C providing the largest specific surface area showed intermediate stages of growth into spherical particles but allowed complete delignification when combined with NaClO2 bleaching. Therefore, the role of the spherical particles, which has so far been debatable, was clarified as causing damage rather than a bleaching accelerant. Focusing only on compositional changes while ignoring structural ones leads to the incorrect identification of optimal conditions that remove lignin but damage the cell walls. Our findings demonstrate that structural considerations are required for effective and noninvasive delignification.