Partially acetylated cellulose nanofibrils from Agave tequilana bagasse and Pickering stabilization

Preparation and functionalization of cellulose nanofibers using a naturally occurring acid and their application in stabilizing linseed oil/water Pickering emulsions

Finding efficient and environmental-friendly methods to produce and chemically modify cellulose nanofibers (CNFs) remains a challenge. In this study, lactic acid (LA) treatment followed by microfluidization was employed for the isolation and functionalization of CNFs. Small amounts of HCl (0.01, 0.1, and 0.2 M) were used alongside LA to intensify cellulose hydrolysis. FTIR spectroscopy and solid-state 13C NMR confirmed the successful functionalization of CNFs with lactyl groups during isolation, while SEM, AFM, and rheological tests revealed that the addition of HCl governed the fibers' sizes and morphology. Notably, the treatment with LA and 0.2 M HCl resulted in a more efficient defibrillation, yielding smaller nanofibers sizes (62 nm) as compared to the treatment with LA or HCl alone (90 and 108 nm, respectively). The aqueous suspension of CNFs treated with LA and 0.2 M HCl showed the highest viscosity and storage modulus. LA-modified CNFs were tested as stabilizers for linseed oil/water (50/50 v/v) emulsions. Owing to the lactyl groups grafted on their surface and higher aspect ratio, CNFs produced with 0.1 and 0.2 M HCl led to emulsions with increased stability (a creaming index increase of only 3 % and 1 %, respectively, in 30 days) and smaller droplets sizes of 23.4 ± 1.2 and 35.5 ± 0.5 μm, respectively. The results showed that LA-modified CNFs are promising stabilizers for Pickering emulsions.

Review of Functional Aspects of Nanocellulose-Based Pickering Emulsifier for Non-Toxic Application and Its Colloid Stabilization Mechanism

In the past few years, the research on particle-stabilized emulsion (Pickering emulsion) has mainly focused on the usage of inorganic particles with well-defined shapes, narrow size distributions, and chemical tunability of the surfaces such as silica, alumina, and clay. However, the presence of incompatibility of some inorganic particles that are non-safe to humans and the ecosystem and their poor sustainability has led to a shift towards the development of materials of biological origin. For this reason, nano-dimensional cellulose (nanocellulose) derived from natural plants is suitable for use as a Pickering material for liquid interface stabilization for various non-toxic product formulations (e.g., the food and beverage, cosmetic, personal care, hygiene, pharmaceutical, and biomedical fields). However, the current understanding of nanocellulose-stabilized Pickering emulsion still lacks consistency in terms of the structural, self-assembly, and physio-chemical properties of nanocellulose towards the stabilization between liquid and oil interfaces. Thus, this review aims to provide a comprehensive study of the behavior of nanocellulose-based particles and their ability as a Pickering functionality to stabilize emulsion droplets. Extensive discussion on the characteristics of nanocelluloses, morphology, and preparation methods that can potentially be applied as Pickering emulsifiers in a different range of emulsions is provided. Nanocellulose's surface modification for the purpose of altering its characteristics and provoking multifunctional roles for high-grade non-toxic applications is discussed. Subsequently, the water-oil stabilization mechanism and the criteria for effective emulsion stabilization are summarized in this review. Lastly, we discuss the toxicity profile and risk assessment guidelines for the whole life cycle of nanocellulose from the fresh feedstock to the end-life of the product.