Improved method of removing charged groups from cellulose nanocrystal surface

What is it about?

This article uses a design space to identify the key factors which contribute to the removal of charged sulfate groups from the surface of cellulose nanocrystals (CNCs). CNCs are a biorenewable resource that is environmentally-friendly, and possess unique physical properties such as high crystallinity, aspect ratio, and large surface area among others. These physical properties are dependent upon the preparatory method, which imparts chemical changes to the CNC surface, including excessive surface charge. In some instances, high surface charge is desirable, however, it is often the case, that surface charged groups must be removed prior to further functionalization for specific purposes. There are multiple methods available to remove surface functional groups, each with their specific benefits and drawbacks. The two most common are hydrolysis with excess acid or base. This changes the surface chemistry of the CNC and in some instances, changes their bulk properties to undesirable effect, moreover, obtaining specific desired surface charge is elusive. In this work, the removal of surface charged groups using base hydrolysis methods was investigated. A Design of Experiments (DOE) was used to determine optimal conditions that minimizes the use of excess base to achieve a tailored response and retain desirable properties.

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Why is it important?

The typical methods used to remove surface sulfate groups are rather harsh and use high concentrations of base and are energy intensive. In this report we show there are multiple factors which contribute to surface desulfation and that by selecting for a specific outcome, the concentration of reagents, reaction time, and energy input (temperature) can be minimized to achieve a desired result.