Process-intensified production of TEMPO-oxidized cellulose nanofibrils: Application to several lignocellulosic feedstocks

• Scalability of TEMPO-mediated oxidation enables industrial CNF production with consistent quality. • Five reactor setups compared: kneader and 1 pass TSE the most efficient in production. • Feedstock choice drives CNF differences while process configuration has only minor influence. • TMO conditions remain critical for nanoscale fibrillation and substantially reduce water use. Despite the remarkable properties of cellulose nanofibrils (CNFs), large-scale production remains limited by the lack of efficient, scalable oxidation and fibrillation technologies. Achieving processes that ensure product quality at industrial performance levels is essential for cost reduction and broadening CNF applications. This study addresses the scale-up of TEMPO-mediated oxidation (TMO) to produce oxidized pulps (OPs) from five lignocellulosic materials, and CNFs after mechanical fibrillation. Five oxidation configurations were tested under comparable conditions: laboratory-scale batch oxidation in a stirred reactor, a batch kneader (K100), and a continuous twin-screw extruder (TSE) in three configurations. Results showed that K100 and the single-pass TSE achieved the highest OP production efficiency, reaching 0.57 kg/h. Although additional TSE passes progressively lowered throughput, they yielded greater reductions in degree of polymerization, facilitating microfibril disintegration. Comparative analysis, including PCA, revealed that the raw material is the dominant factor driving differences among the CNFs, while variations in the TMO configuration caused only minor effects. Nonetheless, the oxidation step remains essential to achieve nanoscale fibrillation, with carboxyls in 0.7-1.0 mmol COOH/g depending on feedstock and configuration. These findings validate the technical feasibility of scaling-up the TMO process, providing viable, sustainable routes for industrial CNF manufacturing, demonstrating significant water consumption reduction.