Degradation selectivity for bamboo fiber and parenchyma lignin-carbohydrates complexes (LCC) esters

Abstract

The degradation of lignin-carbohydrate complex (LCC) esters has been proven to be crucial for the selective separation of lignocellulosic components. This study utilized Raman microspectroscopy to image the preferential degradation of lignin and LCC esters from the bamboo wall during successive NaOH (0.2 to 5.0 % w/w), H₂SO₄ (1 to 8 % v/v), and NaClO₂ (5 to 20 min) treatments. Raman imaging showed that lignin and LCC esters were selectively removed from the middle lamella of fibers and the secondary wall of parenchyma during NaOH and NaClO₂ treatments. In contrast, H₂SO₄ primarily caused the simultaneous removal of lignin and LCC esters from the fiber wall under harsh conditions (8 %), while the middle lamella of parenchyma was less affected, both morphologically and topochemically. Raman spectral analysis indicated that the band intensity at 1605 cm^-1 for lignin and at 1173 cm^-1 for LCC esters decreased by >87.0 % in the highly lignified parenchyma secondary wall after a 5.0 % NaOH treatment, while the decrease was <67 % in the fiber wall. Interestingly, a strong linear correlation was observed between LCC esters and carbohydrates in the parenchyma (R² > 0.912). These findings provide important insights into the graded and classified utilization of bamboo resources.

Keywords: Bamboo fiber and parenchyma; Degradation correlation; LCC esters; Pretreatment.