Nanocellulose production from low-cost agricultural residues: process development, economic assessment, and process robustness

Abstract

The 21st century has been marked by the transition from a petroleum-based economy to a more renewable and sustainable era. Nanocellulose is a plant-based material and an excellent alternative for petroleum-based materials and chemicals in various applications due to its abundance, sustainability, and exceptional properties. Yet, major barriers such as high production costs hinder nanocellulose from achieving its full application potential. Thus, this research project presented a unique interdisciplinary approach that combined efforts in process engineering, computational modeling, and materials science to develop a sustainable and scalable process to produce nanocellulose from low-cost, unconventional waste feedstocks. First, the conversion process developed in this work effectively produced lignocellulosic nanomaterials from a wide range of low-cost feedstocks (wheat straw, corn stover, reed canary grass, and industrial hemp), as demonstrated through laboratory experimentation. All feedstocks generated two product fractions comprising lignocellulosic nanofibrils (LCNF) and microfibrils (LCMF). LCNFs had similar morphology and behavior in aqueous media as nanofibrils produced via conventional TEMPO oxidation (~2 nm wide and ~1 μm long - characteristic of elementary fibrils) while undergoing a milder and more environmentally friendly process. LCMFs, on the other hand, comprised extremely long fibrils ~16 nm wide that formed a web-like network. Second, a large-scale facility using 100-tonne wheat straw feedstock per day was modeled with process simulation software with an 18,400 tonnes/year of lignocellulosic nanomaterials production capacity. The economic analysis revealed an outstanding minimum product selling price (MPSP) of US$4.60/kg at a 15% discount rate as a result of low-cost feedstock and conversion process simplicity. Finally, the nanomaterials were applied as reinforcing agents in polyvinyl alcohol (PVA) plastic composite films, with a remarkable case of simultaneous strengthening and toughening of the polymer nanocomposite with high specific tensile strength (up to 59.5 MPa g-1 cm3), elastic modulus (up to 2.6 GPa g-1 cm3), and fracture strain (up to 138%), while maintaining excellent optical transmittance in the visible region (up to 92%). The excellent improvements in the composites' mechanical properties demonstrate the application potential of these nanomaterials in plastics and packaging. This research project has shown the effectiveness and robustness of a novel conversion process to produce lignocellulosic nanomaterials using various low-cost feedstocks. The process comprises mild reaction conditions and employs green chemistry principles, resulting in lower cost and environmental impact than conventional nanocellulose production methods. This commercially viable process could produce nanomaterials at a large scale with commodity product economics, enabling their use as petroleum-based materials substitute in high-volume applications.