Comparison of Techniques for Drying Cellulose Nanocrystal Pickering Emulsions into Oil Powders

Abstract

A recent push for surfactant-free products driven by environmental awareness has propelled the use of bio-based materials in place of petroleum-derived components. However, both the formulation and processing need to be considered for scale-up feasibility and environmental sustainability. This work investigated the drying of corn oil-in-water emulsions stabilized by cellulose nanocrystals (CNCs), methyl cellulose (MC), and tannic acid via freeze drying, spray freeze drying, and spray drying. All three techniques produced oil powders with low moisture content and high encapsulated oil content (>90%). The oil powders could be redispersed in water by hand shaking to reform the original emulsion and could be stored dry for weeks without oil leakage (in the fridge). The release of oil from the powders on hydrophobic substrates (at room temperature) was controlled by changing the CNC and MC stabilizer content; the spray freeze dried samples were the most tunable. The three drying techniques imparted different surface morphologies that were linked to powder redispersibility and oil release properties. The lack of freezing (and associated ice crystal growth) in spray drying minimized oil droplet agglomeration, and it was the fastest, most scalable, and least energy-intensive drying technique of the three, but it was also the most sensitive to emulsion concentration and susceptible to instabilities associated with high temperature and shear stress. It was demonstrated that essential oils with a range of interfacial tensions and volatilities (e.g., jojoba, lavender, tea tree oil) could also be encapsulated in spray dried oil powders. This general encapsulation strategy can be tailored based on the drying technique selected, uses plant-based industrially-produced feedstocks, works with commercially relevant oils, and will hopefully contribute to the development of sustainable emulsions and oil powders for food, pharmaceutical, agricultural, and cosmetic applications.