Effects of NaOH Addition on Cellulose Nanocrystal Functionalization with 2,4-Dichlorophenoxyacetic Acid

Abstract

This article investigates the necessity of sodium hydroxide (NaOH) addition for the amine functionalization of sulfated cellulose nanocrystals (CNCs) and its effect on nanocrystal reactivity with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The use of CNCs as a nanocarrier of active biomolecules has grown in the past decade. Previously, CNCs were produced by laboratory sulfuric acid hydrolysis protocols that imparted sulfate half-ester groups with hydrogen counterions. Because of this, researchers cited the need to add a deprotonating base such as NaOH before amination, a common precursor reaction for further biomolecule functionalization. However, current commercially produced sulfated CNCs have a sodium counterion instead of hydrogen. This work explores whether the use of commercial sulfated CNCs negates the need for sodium hydroxide addition in amine functionalization. We investigated the effect of 10 wt% sodium hydroxide solution on the amination of 1 wt% and 2 wt% CNC dispersions. Following this step, CNCs were then further modified via EDC/NHS chemistry to attach 2,4-D. Thermogravimetric analysis coupled with infrared spectroscopy was used to qualitatively confirm attachment. Elemental analysis determined that the degree of amine substitution for all dispersions ranged from 5.4–6.7%. 2,4-D attachment to amine groups varied from 3.9–6.5% when NaOH was present to 7.1% when NaOH was not added. These results highlight how the evolution in CNC extraction methods has resulted in NaOH addition no longer being necessary for successful reactions when using commercially sourced sulfated CNCs with a sodium counterion.