Optimizing carboxylated nanocellulose preparation: A kinetic and mechanistic study on the enhancement of TEMPO-mediated oxidation via swelling treatment

Int J Biol Macromol. 2024 Aug;274(Pt 1):133342. doi: 10.1016/j.ijbiomac.2024.133342. Epub 2024 Jun 21.

Abstract

This study explored the application of swelling pretreatment as a solution to the high cost and contamination associated with the process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation for nanocellulose preparation. The results demonstrated that swelling significantly expanded the fibers while preserving the degree of polymerization (DP) of cellulose (approximately 95 %). The native crystal structure and hydrogen bonding of cellulose were disrupted after swelling, leading to a reduction in crystallinity and crystallite size, and the decrease of bonding energy and content of intermolecular O6-H⋯O3'. The TEMPO-mediated oxidation processes of cellulose fibers with or without swelling were successfully fitted using a consecutive first-order reaction kinetic model. The fitting results indicated that swelling significantly reduced the activation energy of TEMPO-mediated oxidation and enhanced the reaction rate. Among three swelling systems, the NaOH/thiourea/water system exhibited the optimal promotion effect. Consequently, the swelling treatment enables a significant reduction of 30 % in the catalyst dose for the TEMPO-mediated oxidation while preserving a competitive reaction rate, yield, and product performance. Lower catalyst dosage helps to reduce cost and environmental impact, facilitating the industrial application of the TEMPO-mediated oxidation process.

Keywords: Hybrid Pennisetum; Kinetics; Nanocellulose; Swelling; TEMPO-mediated oxidation.

MeSH terms

  • Catalysis
  • Cellulose* / chemistry
  • Cyclic N-Oxides* / chemistry
  • Hydrogen Bonding
  • Kinetics
  • Nanostructures / chemistry
  • Oxidation-Reduction*
  • Polymerization
  • Thiourea / chemistry
  • Water / chemistry

Substances

  • Cellulose
  • Cyclic N-Oxides
  • TEMPO
  • Water
  • Thiourea