Sorghum as a novel biomass for the sustainable production of cellulose nanofibers

Abstract

Agricultural residues are emerging as a viable biomass resource for various industries and applications due to their abundant growth, relatively low starting value, and suitability for integration into a biorefinery system, alongside their fast regeneration time. Further, their favourable biochemical composition with a relatively high hemicellulose and low lignin content enables sustainable processing into cellulose nanofibres (CNF). Sorghum (Sorghum bicolor L. Moench) is a highly adapted and widely bred agricultural crop with drought resistance, lodging tolerance, high biomass production, and excellent nitrogen usage efficiency. To introduce sorghum agricultural residues as a sustainable biomass resource for CNF production, four phenotypically diverse sorghum varieties (Sugargraze, Yemen, GreenleafBMR, Graingrass) were selected, grown, harvested, and separated into 4 different plant sections (leaf, sheath, stem(<1 m), stem(>1 m)). Each sample within this biomass library underwent a mild NaOH treatment (2%, 80 °C, 2 h), followed by high pressure homogenisation at 3 subsequent energy levels (Low, Medium, High). Tracking the evolution of nanopaper material properties over this mechanical processing series, we found the average tensile strength of sorghum-derived CNF nanopaper ranged from 51 to 115 Nm/g. GreenleafBMR and Graingrass stem produced the strongest nanopaper, Yemen consistently produced tough nanopaper, and sheath sections were highly amenable to nanofibrillation at relatively low energy input. Transmission electron microscopy (TEM) analysis of sorghum-derived CNF quantified the fibre width across all samples to range from ∼6 nm – 5.4 μm. Sorghum-derived cellulose nanofibres present outstanding material performance under low chemical and energy input processing, launching sorghum as a compelling biomass resource for sustainable nanomaterial production.