Solvent selection enables sustainable and affordable lignin biocomposite for cement-free construction

Cement-free construction materials are essential to reduce global carbon emissions, yet scalable alternatives remain limited. We report the development of a lignin-based biopolymer-bound soil composite (BSC), a novel cement-free material with mechanical properties comparable to lightweight concrete. To advance its scalability and environmental performance, we also used a systematic framework for solvent selection in lignin biocomposite fabrication. Applying this approach, we identified an acetic acid–water solvent system that speeds up manufacturing and enhances material quality. BSCs fabricated with this system exhibit increased strength (5.4 MPa vs. 3.7 MPa), attributed to acetylation of lignin. In addition, the acetic acid–water system dramatically reduces drying time compared with the alternative solvent, dimethyl sulfoxide (2 days vs. 14 days), enabling more efficient production. Life cycle assessment reveals additional CO2 sequestration and a 70 % reduction in material cost (US$122–237/m3 vs. US$409–933/m3) relative to lignin biocomposite made using DMSO as the solvent. These improvements stem from solvent-induced modifications in lignin chemistry that enhance composite performance. This work demonstrates how both material design and rational solvent selection can pave the way for adoption of lignin-based composites as scalable, affordable, and low-carbon alternatives for the built environment.