Disassembling of TEMPO-oxidized cellulose fibers: intersheet and interchain interactions in the isolation of nanofibers and unitary chains

TL;DR

This study combines experimental AFM data and first-principles calculations to understand how TEMPO oxidation weakens cellulose fiber interactions, enabling disassembly into nanofibers and individual chains through electrostatic repulsion and bond breaking.

Contribution

It provides an atomistic understanding of cellulose disassembly mechanisms, highlighting the role of electrostatic interactions and hydrogen bonds in the process.

Findings

Oxidation introduces charged carboxylate groups that increase electrostatic repulsion.

Interchain hydrogen bonds are primarily responsible for fiber disassembly.

Weaker intersheet interactions are less involved in the disassembly process.

Abstract

Cellulose disassembly is an important issue in designing nanostructures using cellulose-based materials. In this work, we present a joint of experimental and theoretical study addressing the disassembly of cellulose nanofibrils. Through 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidation processes, combined with atomic force microscopy results, we find the formation of nanofibers with diameters corresponding to a single cellulose polymer chain. The formation of these polymer chains is ruled by repulsive electrostatic interactions between the oxidized chains. Further first-principles calculations have been done in order to provide an atomistic understanding the cellulose disassembling processes, focusing on the balance of the interchain and intersheet interactions upon oxidation. Firstly we analyse these interaction in pristine systems, where we found the intersheet interaction stronger than the interchain one. In the oxidized systems, we have considered the formation of (charged) carboxylate groups along the inner sites of elementary fibrils. We show a net charge concentration on the carboxylate groups, supporting the emergence of repulsive electrostatic interactions between the cellulose nanofibers. Indeed, our total energy results show that the weakening of the binding strength between the fibrils is proportional to the concentration and the net charge density of the carboxylate group. Moreover, by comparing interchain and intersheet binding energies, we found that most of the disassembly processes should take place by breaking the interchain O--H$\cdots$O hydrogen bond interactions, and thus supporting the experimental observation of single and double cellulose polymeric chains.