Cellulose nanocrystal surface functionalization for the controlled sorption of water and organic vapours

Abstract

The surface grafting of cellulose nanocrystals (CNC) is a valuable tool to increase opportunities for their application. This work had several goals designed to improve CNC: reduction of hornification, increased re-dispersibility after CNC drying, and tuning of the surface graft to enhance the adsorption of particular molecules. To achieve this, the CNC surfaces were modified chemically with aromatic surface grafts using widely employed methods: the creation of urethane linkages, silylation and esterification. Even a low degree of grafting sufficed to increase water contact angles to as much as 96°. The analysis of water sorption isotherms showed that at high water activities, capillary condensation could be suppressed and hysteresis was decreased. This indicates that hornification was significantly suppressed. However, although the contact angles increased, the water sorption isotherms were changed only slightly because of reduced hysteresis. The grafts were not able to shield the surface from water vapour sorption. A comparison of the sorption isotherms of anisole and cyclohexane, sorbates with a similar surface area, showed that the sorption of anisole was three times higher than that of cyclohexane. The specific sorption of aromatic molecules was achieved and the most efficient methodology was the esterification of CNC with carboxylic acids containing a flexible linker between the aromatic moiety and ester bond.

Changes in the hygroscopic behavior of cellulose due to variations in relative humidity

“…This is supported by observation that there were no expected changes in isotherm shape or adsorption heat at RH values where water monolayer should have been completed (Greyson and Levi 1963). Nevertheless, even recently researchers have been using water as a probe molecule in specific surface area analysis which has shown high surface areas in comparison to typical nitrogen adsorption data (Espino-Pérez et al 2016;Häggkvist et al 1998;Ioelovich and Leykin 2011;Klemm et al 1998;Rowen and Blaine 1947;Zografi et al 1984). Some of the authors have even used this as a proof for their conclusions on sample properties.…”

“…GAB was chosen, since water sorption on cellulose is specific at low RH and there is no well-defined cellulose surface when water is used as the probe molecule, which means that the BET method is ineffective for such H 2 O sorption studies (Greyson and Levi 1963). Nevertheless, both methods are still being used and therefore they need further examination (Häggkvist et al 1998;Ioelovich and Leykin 2011;Espino-Pérez et al 2016).…”

TransPoly: A theoretical model to quantify the dynamics of water transfer through nanostructured polymer films

“…6). Espino-Pérez et al [28] studied the water vapour isotherms at 25 ˝C of CNC and grafted CNC powders. They observed that the equilibrium moisture content (X eq ) of CNC powders was of 98.5% (at 82% HR).…”

Applications of cellulose nanomaterials in pharmaceutical science and pharmacology

“…Owing to the susceptibility of the amorphous regions in the cellulose chains to acidity, acid treatment of cellulose or CNFs removes the amorphous sections, and therefore, the cellulose chains are cleaved transversely with only the highly crystalline regions retained, namely, CNCs. Commonly used source for CNCs include P. oceanica leaves (POL) and balls [43], Posidonia oceanic [44], curauá [3], kenaf bast [45], capim dourado [46], MCC [47]. In rare case, spherical CNCs were obtained via hydrolysis of a combination of sulfuric and hydrochloric acids under ultrasonication [48,49].…”