Abstract
The continuous fabrication via membrane emulsification of stable microcapsules using renewable, biodegradable biopolymer wall materials keratin and chitosan is reported here for the first time. Microcapsule formation was based on opposite charge interactions between keratin and chitosan, which formed polyelectrolyte complexes when solutions were mixed at pH 5.5. Interfacial complexation was induced by transfer of keratin-stabilized primary emulsion droplets to chitosan solution, where the deposition of chitosan around droplets formed a core–shell structure. Capsule formation was demonstrated both in batch and continuous systems, with the latter showing a productivity up to 4.5 million capsules per minute. Keratin–chitosan microcapsules (in the 30–120 μm range) released less encapsulated nile red than the keratin-only emulsion, whereas microcapsules cross-linked with glutaraldehyde were stable for at least 6 months, and a greater amount of cross-linker was associated with enhanced dye release under the application of force due to increased shell brittleness. In light of recent bans involving microplastics in cosmetics, applications may be found in skin-pH formulas for the protection of oils or oil-soluble compounds, with a possible mechanical rupture release mechanism (e.g., rubbing on skin).
Highlights
Microencapsulated oils have a wide variety of applications across a range of industries, including food, household,[1] cosmetic,[2] and pharmaceutical[3] products
The diameter of microcapsules can range between 1 μm and a few mm,[5] making them small enough to pass through wastewater treatment plants into aquatic environments,[6] contributing to microplastic pollution when synthetic and non-biodegradable wall materials are used
The environment is polluted with 36,000 tons of microplastics each year in the EU alone[9] and concerns over the implications for aquatic life and human health have grown with the emergence of studies confirming the presence of microplastics in the entire human food supply chain.[10]
Summary
Microencapsulated oils have a wide variety of applications across a range of industries, including food, household,[1] cosmetic,[2] and pharmaceutical[3] products. The production of microcapsules from the primary emulsion was obtained by adsorption of chitosan to oppositely charged keratin at the droplet surface and cross-linking with glutaraldehyde (GTA).
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