Abstract
Carboxylated cellulose nanocrystals (cCNC) are highly dispersible particles useful in many industries. In particular, they can be applied to form Pickering emulsions and foams for “green” applications in the cosmetics, pharmaceutical industry or food processing. We demonstrated that carboxylated cellulose nanocrystals enhance foamability and foam stability when mixed with cationic surfactant ethyl lauroyl arginate (LAE), having superior properties over sulfated cellulose nanocrystals (sCNC) concerning surfactant concentration range and foam volume. Mixtures of LAE and cCNC were characterized for their hydrodynamic diameter, zeta potential, surface tension and surface rheological properties. The influence of electrolytes, namely, sodium chloride, guanidine hydrochloride and sodium salicylate, and the addition of concentrated urea to LAE-cCNC mixtures on foamability and foam stability were investigated. Electrolytes in the concentration of 5 mM showed a moderate effect on foam stability. In contrast, spectacular foam collapse was detected after adding concentrated urea. The preliminary rheological data from the pendant drop oscillations revealed low elastic modulus upon urea addition and the loss modulus that increased with the frequency, which suggested a viscous interfacial layer.
Highlights
Cellulose nanocrystals released by chemical hydrolysis or oxidation were first produced in 1947
The concentration of 5 mM was chosen for electrolytes when preparing different mixtures of 0.3% by weight of cCNC from the same stock of particles 0.6 wt.%, dispersed in water to avoid particle aggregation, which may affect foaming properties and interfacial rheology
The addition of urea caused a faster decrease in the surface tension compared to the pure lauroyl arginate (LAE)-cCNC mixture; after the 2000 s of adsorption, similar surface tension values (c.a. 40 mN/m) could be observed
Summary
Nanocellulose crystals and fibers are twisted [15], which affects the exposure of their more hydrophobic crystallographic planes at the air/water interface Depending on their concentration, cellulose nanocrystals may form liquid crystals in water [16]. Guanidine hydrochloride (GuaHCl), is an even stronger protein denaturant than urea It contains a common cation as a positively charged group of LAE and is well known for its chaotropic properties. We studied the effect of the addition of electrolytes, a common salt—NaCl, hydrotropic sodium salicylate, and chaotropic guanidine hydrochloride or urea on ethyl lauroyl arginate—carboxylated CNC dispersions bulk and interfacial properties. They can provide information about the selection of components that could be used as defoamers
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