Abstract
Thin film coating of charged nanoparticles with oppositely charged polymers is an efficient and straightforward way for surface modification, but synthetic polyelectrolytes should be replaced by abundant biopolymers. In this study a thin film of chitosan was adsorbed onto colloidal lignin particles (CLPs) that were then systematically studied for olive oil stabilization with an objective to develop shape-retaining microcapsules that comprised of only renewable biomaterials. Full surface coverage was achieved with merely 5 wt% of chitosan relative to the dry weight of CLPs, reversing their surface charge from negative to positive. Such modification rendered the chitosan-coated particles excellent stabilizers for forming Pickering emulsions with olive oil. The emulsion droplets could be further stabilized by sodium triphosphate that provided ionic intra- and inter-particle cross-linking of the chitosan corona on the CLPs. Following the optimum conditions, the non-cross-linked microcapsules exhibited a strong stability against coalescence and the electrostatically stabilized ones additionally retained their shape upon drying and rewetting. Non-cross-linked microcapsules were used to demonstrate encapsulation and rapid release of ciprofloxacin as a model lipophilic drug in aqueous media. Overall, the combination of antimicrobial chitosan and antioxidative lignin nanoparticles hold unprecedented opportunities as biocompatible and biodegradable materials for controlled drug delivery.
Highlights
Lignin is the second most abundant natural biopolymer and the most abundant aromatic polymer in nature (Ragauskas et al, 2014)
The overarching objective of this work was to establish a reliable approach for chitosan-coated colloidal lignin particles (CLPs), and application of the modified particles in stabilization of olive oil-in-water Pickering emulsion capsules
The obtained CLPs were modified with thin film coating of chitosan by physical adsorption and systematically studied for the stabilization of Pickering emulsions
Summary
Lignin is the second most abundant natural biopolymer and the most abundant aromatic polymer in nature (Ragauskas et al, 2014). Over 70 million tons of industrial lignin is produced as a by-product in the pulp/paper industry. Only 5% of industrial lignin is commercialized as value-added products, such as additives, dispersants, adhesives, or surfactants (Laurichesse and Avérous, 2014). The rest 95% is used as low value energy source or treated as waste. The low extent of commercialization of lignin is mainly due to its complex and inhomogeneous structure resulting from different sources and extraction processes (Li et al, 2015). Recent studies have shown that fabricating spherical micro- or nanoparticles from lignin enables the large scale utilization of lignin (Ago et al, 2016; Leskinen et al, 2017a; Ashok et al, 2018; Lintinen et al, 2018), and improves properties such as surface activity, antioxidative, UV shielding, and antimicrobial activity for potential high-value applications (Beisl et al, 2017)
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