Influence of solvent quality on the mechanical strength of ethylcellulose oleogels

Ethylcellulose (EC) is the only known food-grade polymer able to structure edible oils. The gelation process and gel properties are similar to those of polymer hydrogels, the main difference being the nature of the solvent. The present study examines the influence of solvent quality on the large deformation mechanical behavior of EC oleogels. Two alternative strategies for manipulating the mechanical response of these gels were evaluated; manipulating the bulk solvent polarity and the addition of surface active small molecules. Gel strength was positively correlated to solvent polarity when blending soybean oil with either mineral oil or castor oil. This behavior was attributed to the ability of the polar entities present in the oil phase to interact with the EC gel network. The addition of the small molecules oleic acid and oleyl alcohol resulted in a substantial enhancement in gel strength up to 10wt% addition, followed by a gradual decrease with increasing proportions. Binding interactions between EC and these molecules were successfully modeled using a Langmuir adsorption isotherm below 10wt% addition. Furthermore, the thermal behavior of stearic acid and stearyl alcohol also indicated a direct interaction between these molecules and the EC network. Differences in the mechanical behavior of gels prepared using refined, bleached, and deodorized canola or soybean oils, and those made with cold-pressed flaxseed oil could be attributed to both oil polarity, and the presence of minor components (free fatty acids). Shorter pulsed NMR T2 relaxation times were observed for stronger gels due to the more restricted mobility of the solvent when interacting with the polymer. This work has demonstrated the strong influence of the solvent composition on the mechanical properties of EC oleogels, which will allow for the tailoring of mechanical properties for various applications.