Unveiling the heterogeneous structure of native lignin in bamboo cell walls via a novel isolation method for high-value applications

Abstract

Elucidating the inherent structural heterogeneity of native lignin in lignocellulosic biomass is critical for advancing precision biorefining strategies. This study presents a novel homogenized enzymatic lignin (HEL) isolation protocol, designed to resolve the native structural profiles of lignin across distinct bamboo tissues (parenchyma cells and fibers). The HEL methodology was rigorously evaluated against the established benchmarks including milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and double enzymatic lignin (DEL) separation methods. The results show that the HEL method not only maintains the original structural integrity of lignin but also demonstrates significant advantages over traditional lignin separation methods in terms of yield and retention of β-O-4 aromatic ether bonds. In particular, bamboo parenchyma cell lignin (HEL-P) exclusively contained β-O-4 linkages (70.86/100 Ar), whereas bamboo fiber lignin (HEL-F) incorporated mixed linkages (β-O-4, β–β and β-5) with relatively lower β-O-4 abundance (62.74/100 Ar). These structural differences fundamentally dictate their performance in downstream valorization pathways. HEL-P demonstrated exceptional depolymerization efficiency under hydrogen-free catalytic conditions, affording a monomeric yield of 37.81 wt% at 220 °C, attributed to its highly labile ether-rich structural framework. In contrast, HEL-F served as an excellent precursor for hierarchically porous carbon, delivering a specific capacitance of 283 F g⁻¹ and outstanding electrochemical stability (97.63% retention after 10 000 cycles) in supercapacitor assemblies. By linking lignin structural properties to functionality for tailored applications, this study establishes possible application routes for the valorization of bamboo lignin, highlighting strategies for biomass valorization that take advantage of inherent structural heterogeneity to achieve targeted biorefinery outputs.