AKD-Modification of bacterial cellulose aerogels in supercritical CO2

Abstract

Different approaches towards hydrophobic modification of bacterial cellulose aerogels with the alkyl ketene dimer (AKD) reagent are presented. If AKD modification was performed in supercritical CO 2 , an unexpectedly high degree of loading was observed. About 15 % of the AKD was bound covalently to the cellulose matrix, while the other part consisted of re-extractable AKD-carbonate oligomers, which are novel chemical structures described for the first time. These oligomers contain up to six AKD and CO 2 moieties linked by enolcarbonate structures. The humidity uptake from environments with different relative humidity by samples equipped with up to 30 % AKD is strongly reduced, as expected due to the hydrophobization effect. Samples above 30 % AKD, and especially at very high loading between 100 and 250 %, showed the peculiar effect of increased humidity uptake which even exceeded the value of unmodified bacterial cellulose aerogels.

Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer

“…Typically, the procedures reported involved cellulose dissolved in a lithium chloride/1, 3-dimethyl-2-imidazolidinone (LiCl/DMI) system, where subsequently reaction with AKD melt under homogeneous condition took place. Cellulose fibers were modified heterogeneously by AKD vapor redeposition (Hutton and Shen 2005;Zhang et al 2007) or impregnated with subcritical and supercritical carbon dioxide (Hutton and Parker 2009;Russler et al 2012). However, these treatment processes are always laborious or result in uneven AKD distribution, which may limit their suitability for scaling up in industry.…”

Nanocellulose properties and applications in colloids and interfaces

“…Lightweight aerogels (8.25±0.7 mg.cm -3 ) with well-defined porous structure (10 nm) and high surface area (200 m 2 /g) were obtained. Hydrophobization of aerogels prepared from bacterial cellulose was achieved by reaction with alkyl ketene dimer through different methodologies followed by supercritical drying in CO 2 (Russler et al, 2012).…”

Bacterial cellulose films: influence of bacterial strain and drying route on film properties

“…Evacuation of solvents in supercritical conditions is commonly used to produce aerogels which is a term given to open pore materials presenting low density and large specific surface area. The most known aerogels are silica, (Murillo-Cremaes et al 2010;Moner-Girona et al 2003;Martin et al 2008;Budunoglu et al 2011) carbon, (Wu et al 2013;Mecklenburg et al 2012) organic-inorganic aerogels (Hendel et al 2013;Ennajih et al 2012) and more recently thick pieces of BC aerogels have also been reported (Hendel et al 2013;Liebner et al 2010;Cai et al 2008;Russler et al 2012).…”