Simultaneously Tailoring Surface Energies and Thermal Stabilities of Cellulose Nanocrystals Using Ion Exchange: Effects on Polymer Composite Properties for Transportation, Infrastructure, and Renewable Energy Applications

Abstract

Cellulose nanocrystals (CNCs) have great potential as sustainable reinforcing materials for polymers, but there are a number of obstacles to commercialization that must first be overcome. High levels of water absorption, low thermal stabilities, poor miscibility with nonpolar polymers, and irreversible aggregation of the dried CNCs are among the greatest challenges to producing cellulose nanocrystal-polymer nanocomposites. A simple, scalable technique to modify sulfated cellulose nanocrystals (Na-CNCs) has been developed to address all of these issues. By using an ion exchange process to replace Na with imidazolium or phosphonium cations, the surface energy is altered, the thermal stability is increased, and the miscibility of dried CNCs with a nonpolar polymer (epoxy and polystyrene) is enhanced. Characterization of the resulting ion exchanged CNCs (IE-CNCs) using potentiometry, inverse gas chromatography, dynamic vapor sorption, and laser scanning confocal microscopy reveals that the IE-CNCs have lower surface energies, adsorb less water, and have thermal stabilities of up to 100 °C higher than those of prepared protonated cellulose nanocrystals (H-CNCs) and 40 °C higher than that of neutralized Na-CNC. Methyl(triphenyl)phosphonium exchanged cellulose nanocrystals (MePhP-CNC) adsorbed 30% less water than Na-CNC, retained less water during desorption, and were used to prepare well-dispersed epoxy composites without the aid of a solvent and well-dispersed polystyrene nanocomposites using a melt blending technique at 195 °C. Predictions of dispersion quality and glass transition temperatures from molecular modeling experiments match experimental observations. These fiber-reinforced polymers can be used as lightweight composites in transportation, infrastructure, and renewable energy applications.

Covalent functionalization of solid cellulose by divergent synthesis of chemically active dendrons

“…These attractive properties, especially when coupled with chemical and/or physical modifications that influence function, provide a platform for the development of advanced materials based on cellulose. In fact, during the past several decades, studies have shown that surface modifications of cellulose produce functional surfaces that can be used for high‐value‐added applications in areas as diverse as composite materials, flexible organic electronics, biomedical applications, microfluidic devices, self‐cleaning surfaces, and oil–water separation systems …”

Epoxy Composites Using Wood Pulp Components as Fillers

“…Epoxide content (275 g/equiv) was determined by titration with 0.1 N HBr in acetic acid using a crystal violet endpoint. Cellulose nanocrystals were exchanged using the process described previously [41]. The epoxy composites were prepared by in the following manner.…”

“…A method has recently been developed to modify the surface of sulfated cellulose nanocrystals using a simply, scalable ion exchange process [41]. In this approach, rather than adding a surfactant, the sodium cation is exchanged with a surfactant cation.…”

“…Although dispersion was improved, there was a loss in tensile strength and elongation by adding the surfactant. We have recently developed a simple, scalable, ionexchange method to alter the surface energy of cellulose nanocrystals while retaining much of the cellulose surface intact [41].…”

Impact resistance of nanocellulose films with bioinspired Bouligand microstructures

“…45 MD simulations have been successfully used to study CNC-based materials, which not only corroborate experimental ndings, 46,47 but have also revealed important structural and interfacial mechanisms that contribute to their superior mechanical performance, offering guidance for experimental material design. [48][49][50] Recently, we established an atomistically informed coarse-grained modeling approach to extend analyses of CNCs to larger length and time scales, which has been instrumental in explaining the inuence of overlap length and interfacial interactions on the mechanical properties of neat CNC nanopapers up to micrometer sizes. 51 With the advent of small-scale ballistic experiments, such as laser-induced projectile impact tests (LIPIT), 52,53 MD simulations have successfully been used to explain the failure mechanisms of nanomaterials subjected to ballistic impacts.…”