Adsorption and interfacial structure of nanocelluloses at fluid interfaces

Ball milling-induced disassembly of cellulose in coconut endosperm pomace: Structural mechanism for enhanced Pickering emulsification

Coconut endosperm pomace, a major by-product of the coconut milk industry, is rich in cellulose but remains underutilized, primarily as low-value animal feed or a minor ingredient in baked goods. To enhance its functionality, this study investigated the structural modification of coconut endosperm pomace cellulose via wet ball milling for Pickering emulsion stabilization, focusing on its structural evolution, physicochemical properties, and emulsifying performance, as well as its dynamic interactions with oil droplets. As milling time increased from 0 h to 12 h, the cellulose particle size decreased from 15.2 μm to 378 nm, while both crystalline and amorphous regions were progressively disrupted, leading to improved aqueous dispersibility. Among all samples, cellulose subjected to 12 h of wet ball milling exhibited the best emulsifying properties, which was attributed to enhanced molecular flexibility, increased surface roughness, and nanoscale structural alterations induced by mechanical processing. Mechanistic analysis revealed that the primary stabilization mechanism involved the formation of a hydration cage structure between ball-milled cellulose particles and oil droplets, effectively preventing coalescence. These findings establish a structure-function relationship for modified coconut endosperm pomace cellulose and provide a scientific basis for the high-value utilization of coconut processing by-products in emulsion-based formulations.

Food-grade emulsion gels and oleogels prepared by all-natural dual nanofibril system from citrus fiber and glycyrrhizic acid

The natural dual nanofibril system consisting of the rigid semicrystalline nanofibrils disintegrated from citrus fiber (CF) and soft semiflexible nanofibrils self-assembled from glycyrrhizic acid (GA) has been recently shown to be effective structural building blocks for fabrication of emulsion gels. In this work, the effect of the CF nanofibrils prepared by different mechanical disintegration approaches (i.e., high-pressure microfluidization and hydrodynamic cavitation) on the interfibrillar CF-GA interactions and the subsequent formation and properties of emulsion gels were investigated, with the aim of evaluating the potential of the dual nanofibril-stabilized emulsion gels as templates for synthesizing all-natural edible oleogels. The obtained results demonstrate that compared to the cavitation, the high-pressure microfluidization is more capable of generating CF nanofibrils with a higher degree of nanofibrillation and individualization, thus forming a denser CF-GA gel network with higher viscoelasticity and structural stability due to the stronger multiple intrafibrillar and interfibrillar interactions. The emulsion gels stabilized by the dual nanofibril system are demonstrated to be an efficient template to fabricate solid-like oleogels, and the structural properties of the oleogels can be well tuned by the mechanical disintegration of CF and the GA nanofibril concentration. The prepared oleogels possess high oil loading capacity, dense network microstructure, superior rheological and large deformation compression performances, and satisfactory thermal stability, which is attributed to the compact and ordered CF-GA dual nanofibrillar network via multiple hydrogen-bonding interactions in the continuous phase as well as at the droplet surface. This study highlights the unique use of all-natural dual nanofibrils to develop oil structured soft materials for sustainable applications.

Interfacial jamming of surface-alkylated synthetic nanocelluloses for structuring liquids

Nanocelluloses derived from natural cellulose sources are promising sustainable nanomaterials. Previous studies have reported that nanocelluloses are strongly adsorbed onto liquid-liquid interfaces with the concurrent use of ligands and allow for the structuring of liquids, that is, the kinetic trapping of nonequilibrium shapes of liquids. However, the structuring of liquids using nanocelluloses alone has yet to be demonstrated, despite its great potential in the development of sustainable liquid-based materials that are biocompatible and environmentally friendly. Herein, we demonstrated the structuring of liquids using rectangular sheet-shaped synthetic nanocelluloses with surface alkyl groups. Synthetic nanocelluloses with ethyl, butyl, and hexyl groups on their surfaces were readily prepared following our previous reports via the self-assembly of enzymatically synthesized cello-oligosaccharides having the corresponding alkyl groups. Among the alkylated synthetic nanocelluloses, the hexylated nanocellulose was adsorbed and jammed at water-n-undecane interfaces to form interfacial assemblies, which acted substantially as an integrated film for structuring liquids. These phenomena were attributed to the unique structural characteristics of the surface-hexylated synthetic nanocelluloses; their sheet shape offered a large area for adsorption onto interfaces, and their controlled surface hydrophilicity/hydrophobicity enhanced the affinity for both liquid phases. Our findings promote the development of all-liquid devices using nanocelluloses.

Surface Functionalization of Sugarcane-Bagasse-Derived Cellulose Nanocrystal for Pickering Emulsion Gel: Microstructural Properties and Stability Efficiency

An environmentally friendly Pickering stabilizer was developed by upcycling sugarcane bagasse (SCB) into a cellulose nanocrystal (CNC), which was subjected to surface modification by using quaternary ammonium compound to enhance its amphiphilic characteristics. The changes in microstructural properties of modified cellulose nanocrystal (m-CNC), such as surface functional group, thermal stability, surface morphology, elemental composition, and particle size distribution were investigated. Results indicated the success of quaternary ammonium compound grafting with the presence of a trimethyl-alkyl chain on the cellulose structure, while the m-CNC preserves the needle-like nanoparticles in length of ~534 nm and width of ~20 nm. The colloidal profile of m-CNC-stabilized oil-water emulsion gels with different concentrations of m-CNC (1-5 wt%), and oil:water (O:W) ratios (3:7, 5:5, 7:3) were examined. The emulsion gel stability study indicated that the optimal concentration of m-CNC (3 wt%) was able to stabilize all the emulsion gels at different O:W ratios with an emulsion index of >80% for 3 months. It is the minimum concentration of m-CNC to form a robust colloidal network around the small oil droplets, leading to the formation of stable emulsion gels. The emulsion gel with O:W ratio (3:7) with 3 wt% of m-CNC rendered the best m-CNC-oil-droplets dispersion. The m-CNC effectively retained the size of oil droplets (<10 μm for 3 months storage) against coalescence and creaming by creating a steric barrier between the two immiscible phases. Furthermore, the emulsion gel exhibited the highest viscosity and storage modulus which was able to prevent creaming or sedimentation of the emulsion gels.

The Colloidal Properties of Nanocellulose

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

A Mathematical Simulation of Copper and Nickel Ions Separation Using Prepared Nanocellulose Material

Environmental risks can arise from the existence of heavy metals in wastewater and their land disposal. To address this concern, a mathematical technique is introduced in this article that enables the anticipation of breakthrough curves and the imitation of copper and nickel ion separation onto nanocellulose in a fixed-bed system. The mathematical model is based on mass balances for copper and nickel and partial differential equations for pore diffusion in a fixed bed. The study evaluates the impact of experimental parameters such as bed height and initial concentration on the shape of the breakthrough curves. At 20 °C, the maximum adsorption capacities for copper and nickel ions on nanocellulose were 5.7 mg/g and 5 mg/g, respectively. The breakthrough point decreased with increasing solution concentration at higher bed heights, while at an initial concentration of 20 mg/L, the breakthrough point increased with bed height. The fixed-bed pore diffusion model showed excellent agreement with the experimental data. The use of this mathematical approach can help alleviate the environmental hazards that arise from the presence of heavy metals in wastewater. The study highlights the potential of nanocellulose as a material for membrane technology, which can effectively address these risks.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Amyloid fibril-nanocellulose interactions and self-assembly

Amyloid fibrils from inexpensive food proteins and nanocellulose are renewable and biodegradable materials with broad ranging applications, such as water purification, bioplastics and biomaterials. To improve the mechanical properties of hybrid amyloid-nanocellulose materials, their colloidal interactions need to be understood and tuned. A combination of turbidity and zeta potential measurements, rheology and atomic force microscopy point to the importance of electrostatic interactions. These interactions lead to entropy-driven polyelectrolyte complexation for positively charged hen egg white lysozyme (HEWL) amyloids with negatively charged nanocellulose. The complexation increased the elasticity of the amyloid network by cross-linking individual fibrils. Scaling laws suggest different contributions to elasticity depending on nanocellulose morphology: cellulose nanocrystals induce amyloid bundling and network formation, while cellulose nanofibrils contribute to a second network. The contribution of the amyloids to the elasticity of the entire network structure is independent of nanocellulose morphology and agrees with theoretical scaling laws. Finally, strong and almost transparent hybrid amyloid-nanocellulose gels were prepared in a slow self-assembly started from repulsive co-dispersions above the isoelectric point of the amyloids, followed by dialysis to decrease the pH and induce amyloid-nanocellulose attraction and cross-linking. In summary, the gained knowledge on colloidal interactions provides an important basis for the design of functional biohybrid materials based on these two biopolymers.

Formulation and stabilization of high internal phase emulsions: Stabilization by cellulose nanocrystals and gelatinized soluble starch

In this work, high internal phase emulsions (HIPEs) stabilized by naturally derived cellulose nanocrystals (CNC) and gelatinized soluble starch (GSS) were fabricated to stabilize oregano essential oil (OEO) in the absence of surfactant. The physical properties, microstructures, rheological properties, and storage stability of HIPEs were investigated by adjusting CNC contents (0.2, 0.3, 0.4 and 0.5 wt%) and starch concentration (4.5 wt%). The results revealed that CNC-GSS stabilized HIPEs exhibited good storage stability within one month and the smallest droplets size at a CNC concentration of 0.4 wt%. The emulsion volume fractions of 0.2, 0.3, 0.4 and 0.5 wt% CNC-GSS stabilized HIPEs after centrifugation reached 77.58, 82.05, 94.22, and 91.41 %, respectively. The effect of native CNC and GSS were analyzed to understand the stability mechanisms of HIPEs. The results revealed that CNC could be used as an effective stabilizer and emulsifier to fabricate the stable and gel-like HIPEs with tunable microstructure and rheological properties.

Utilization of different wood-based microfibril cellulose for the preparation of reinforced hydrophobic polymer composite films via Pickering emulsion: A comparative study

Pickering emulsion is a promising strategy for the preparation of hydrophobic polymer composite using hydrophilic nanocellulose. Herein, two types of microfibril cellulose, pure mechanical pretreated microfibril cellulose (P-MFC) and Deep eutectic solvents pretreated microfibril cellulose (DES-MFC), were used to fabricate reinforced hydrophobic polystyrene (PS) composites (MFC/PS) with the aid of Pickering emulsion. The results showed that both oil/water ratio and the content as well as surface hydrophilicity of MFC were playing an important role in emulsifying capacity. 8 % MFC/PS emulsion showed the smallest and most uniform emulsion droplets which is similar to nanofibril cellulose (NFC)/PS at the oil/water ratio of 3:1. The mechanical performance of MFC/PS composites verified that the reinforcement effect was closely related to the emulsifying capacity of MFC. Specially, when the content of P-MFC was 8 wt%, the composite exhibited the best mechanical properties with the tensile strength of 44.7 ± 4.4 MPa and toughness of 1162 ± 52.8 kJ/m³ and Young's modulus of 13.5 ± 0.8 GPa, which was comparable to NFC/PS composite. Moreover, the effective enhancement role of P-MFC in hydrophobic polymethyl methacrylate and polycarbonate composites were also realized via Pickering emulsion strategy. Overall, this work constituted a proof of concept of the potential application of P-MFC in nano-reinforced hydrophobic composite.

The Influence of the Surface Chemistry of Cellulose Nanocrystals on Ethyl Lauroyl Arginate Foam Stability

Guanidine-based surfactant ethyl lauroyl arginate (LAE) and cellulose nanocrystals (CNCs) form complexes of enhanced surface activity when compared to pure surfactants. The LAE-CNC mixtures show enhanced foaming properties. The dynamic thin-film balance technique (DTFB) was used to study the morphology, drainage and rupture of LAE-CNC thin liquid films under constant driving pressure. A total of three concentrations of surfactant and the corresponding mixtures of LAE with sulfated (sCNC) and carboxylated (cCNC) cellulose nanocrystals were studied. The sCNC and cCNC suspension with LAE formed thin films, with stability increasing with surfactant concentration and with complex rheological properties. In the presence of LAE, the aggregation of CNC was observed. While the sCNC aggregates were preferentially present in the film volume with a small fraction at the surface, the cCNC aggregates, due to their higher hydrophobicity, were preferentially located at film interfaces, forming compact layers. The presence of both types of aggregates decreased the stability of the thin liquid film compared to the one for the LAE solution with the same concentration. The addition of CNC to LAE was critical for foam formation, and foam stability was in qualitative agreement with the thin films' lifetimes. The foam volume increased with the LAE concentration. However, there was an optimum surfactant concentration to achieve stable foam. In particular, the very resistant foam was obtained with cCNC suspensions that formed the interfaces with a complex structure and rheology. On the other hand, at high LAE concentrations, the aggregates of CNC may exhibit antifoaming properties.

Green and Sustainable Hot Melt Adhesive (HMA) Based on Polyhydroxyalkanoate (PHA) and Silanized Cellulose Nanofibers (SCNFs)

Polyhydroxyalkanoate (PHA), with a long chain length and high poly(4-hydroxybutyric acid) (P4HB) ratio, can be used as a base polymer for eco-friendly and biodegradable adhesives owing to its high elasticity, elongation at break, flexibility, and processability; however, its molecular structures must be adjusted for adhesive applications. In this study, surface-modified cellulose nanofibers (CNFs) were used as a hydrophobic additive for the PHA-based adhesive. For the surface modification of CNFs, double silanization using tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS) was performed, and the thermal and structural properties were evaluated. The hydrophobicity of the TEOS- and MTMS-treated CNFs (TMCNFs) was confirmed by FT-IR and water contact angle analysis, with hydrophobic CNFs well dispersed in the PHA. The PHA-CNFs composite was prepared with TMCNFs, and its morphological analysis verified the good dispersion of TMCNFs in the PHA. The tensile strength of the composite was enhanced when 10% TMCNFs were added; however, the viscosity decreased as the TMCNFs acted as a thixotropic agent. Adding TMCNFs to PHA enhanced the flowability and infiltration ability of the PHA-TMCNFs-based adhesive, and an increase in the loss tangent (Tan δ) and adjustment of viscosity without reducing the adhesive strength was also observed. These changes in properties can improve the flowability and dispersibility of the PHA-TMCNFs adhesive on a rough adhesive surface at low stress. Thus, it is expected that double-silanized CNFs effectively improve their interfacial adhesion in PHA and the adhesive properties of the PHA-CNFs composites, which can be utilized for more suitable adhesive applications.

Protein Adsorption Performance of a Novel Functionalized Cellulose-Based Polymer

Dicarboxymethyl cellulose (DCMC) was synthesized and tested for protein adsorption. The prepared polymer was characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and solid state nuclear magnetic resonance (ssNMR) to confirm the functionalization of cellulose. This work shows that protein adsorption onto DCMC is charge dependent. The polymer adsorbs positively charged proteins, cytochrome C and lysozyme, with adsorption capacities of 851 and 571 mg g^-1, respectively. In both experiments, the adsorption process follows the Langmuir adsorption isotherm. The adsorption kinetics by DCMC is well described by the pseudo second-order model, and adsorption equilibrium was reached within 90 min. Moreover, DCMC was successfully reused for five consecutive adsorption-desorption cycles, without compromising the removal efficiency (98-99%).

A Critical Review on Modification Methods of Cement Composites with Nanocellulose and Reaction Conditions during Nanocellulose Production

Nanocellulose (NC) is a natural polymer that has driven significant progress in recent years in the study of the mechanical properties of composites, including cement composites. Impressive mechanical properties, ability to compact the cement matrix, low density, biodegradability, and hydrophilicity of the surface of nanocellulose particles (which improves cement hydration) are some of the many benefits of using NCs in composite materials. The authors briefly presented a description of the types of NCs (including the latest, little-known shapes), showing the latest developments in their manufacture and modification. Moreover, NC challenges and opportunities are discussed to reveal its hidden potential, as well as the use of spherical and square/rectangular nanocellulose to modify cement composites. Intending to emphasize the beneficial use of NC in cementitious composites, this article discusses NC as an eco-friendly, low-cost, and efficient material, particularly for recycling readily available cellulosic waste. In view of the constantly growing interest in using renewable and waste materials in a wide range of applications, the authors hope to provide progress in using nanocellulose (NC) as a modifier for cement composites. Furthermore, this review highlights a gap in research regarding the preparation of new types of NCs, their application, and their impact on the properties of cementitious composites. Finally, the authors summarize and critically evaluate the type, dosage, and application method of NC, as well as the effects of these variables on the final properties of NC-derived cement composites. Nevertheless, this review article stresses up-to-date challenges for NC-based materials as well as future remarks in light of dwindling natural resources (including building materials), and the principles of a circular economy.

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.

Naturally Derived Janus Cellulose Nanomaterials: Anisotropic Cellulose Nanomaterial Building Blocks and Their Assembly into Asymmetric Structures

Naturally derived cellulose nanomaterials (CNMs) with desirable physicochemical properties have drawn tremendous attention for their versatile applications in a broad range of fields. More recently, Janus amphiphilic cellulose nanomaterial particles with asymmetric structures (i.e., reducing and nonreducing ends and crystalline and amorphous domains) have been in the spotlight, offering a rich and sophisticated toolbox for Janus nanomaterials. With careful surface and interfacial engineering, Janus CNM particles have demonstrated great potential as surface modifiers, emulsifiers, stabilizers, compatibilizers, and dispersants in emulsions, nanocomposites, and suspensions. Naturally derived Janus CNM particles offer a fascinating opportunity for scaling up the production of self-standing Janus CNM membranes. Nevertheless, most Janus CNM membranes to date are constructed by asymmetric fabrication or asymmetric modification without considering the Janus traits of CNM particles. More future research should focus on the self-assembly of Janus CNM particles into bulk self-standing Janus CNM membranes to enable more straightforward and sustainable approaches for Janus membranes. This review explores the fabrication, structure-property relationship, and Janus configuration mechanisms of Janus CNM particles and membranes. Janus CNM membranes are highlighted for their versatile applications in liquid, thermal, and light management. This review also highlights the significant advances and future perspectives in the construction and application of sustainable Janus CNM particles and membranes.

Lipid emulsion interfacial design modulates human in vivo digestion and satiation hormone response

Lipid emulsions (LEs) with tailored digestibility have the potential to modulate satiation or act as delivery systems for lipophilic nutrients and drugs. The digestion of LEs is governed by their interfacial emulsifier layer which determines their gastric structuring and accessibility for lipases. A plethora of LEs that potentially modulate digestion have been proposed in recent years, however, in vivo validations of altered LE digestion remain scarce. Here, we report on the in vivo digestion and satiation of three novel LEs stabilized by whey protein isolate (WPI), thermo-gelling methylcellulose (MC), or cellulose nanocrystals (CNCs) in comparison to an extensively studied surfactant-stabilized LE. LE digestion and satiation were determined in terms of gastric emptying, postprandial plasma hormone and metabolite levels characteristic for lipid digestion, perceived hunger/fullness sensations, and postprandial food intake. No major variations in gastric fat emptying were observed despite distinct gastric structuring of the LEs. The plasma satiation hormone and metabolite response was fastest and highest for WPI-stabilized LEs, indicating a limited capability of proteins to prevent lipolysis due to fast hydrolysis under gastric conditions and displacement by lipases. MC-stabilized LEs show a similar gastric structuring as surfactant-stabilized LEs but slightly reduced hormone and metabolite responses, suggesting that thermo-gelling MC prevents lipase adsorption more effectively. Ultimately, CNC-stabilized LEs showed a drastic reduction (>70%) in plasma hormone and metabolite responses. This confirms the efficiency of particle (Pickering) stabilized LEs to prevent lipolysis proposed in literature based on in vitro experiments. Subjects reported more hunger and less fullness after consumption of LEs stabilized with MC and CNCs which were able to limit satiation responses. We do not find evidence for the widely postulated ileal brake, i.e. that delivery of undigested nutrients to the ileum triggers increased satiation. On the contrary, we find decreased satiation for LEs that are able to delay lipolysis. No differences in food intake were observed 5 h after LE consumption. In conclusion, LE interfacial design modulates in vivo digestion and satiation response in humans. In particular, Pickering LEs show extraordinary capability to prevent lipolysis and qualify as oral delivery systems for lipophilic nutrients and drugs.

Chemical Stabilization behind Cardamom Pickering Emulsion Using Nanocellulose

Cardamom essential oil (EO) is a rare oil of high scientific and economic interest due to its biofunctionality. This work aims to stabilize the EO by Pickering emulsions with nanocellulose, in the form of nanocrystals (CNC) or nanofibers (CNF), and to investigate the stability and chemical and physical interactions involved in the process. The emulsions were characterized by droplet size, morphology, stability, surface charges, Fourier transform infrared spectroscopy, FT-Raman, nuclear magnetic resonance, and scanning electron microscopy. Stable emulsions were prepared with cellulose morphologies and CNCs resulted in a 34% creaming index, while CNFs do not show instability. Emulsions indicate a possible interaction between nanocellulose, α-terpinyl acetate, and 1,8-cineole active essential oil compounds, where α-terpinyl acetate would be inside the drop and 1,8-cineole is more available to interact with cellulose. The interaction intensity depended on the morphology, which might be due to the nanocellulose’s self-assembly around oil droplets and influence on oil availability and future application. This work provides a systematic picture of cardamomum derived essential oil Pickering emulsion containing nanocellulose stabilizers’ formation and stability, which can further be extended to other value-added oils and can be an alternative for the delivery of cardamom essential oil for biomedical, food, cosmetics, and other industries.

Fundamental aspects of nanocellulose stabilized Pickering emulsions and foams

Nanocelluloses in recent years have garnered a lot of attention for their use as stabilizers of liquid-liquid and gas-liquid interfaces. Both cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) have been used extensively in multiple studies to prepare emulsions and foams. However, there is limited literature available that systematically discusses the mechanisms that affect the ability of nanocelluloses (modified and unmodified) to stabilize different types of interfaces. This review briefly discusses key factors that affect the stability of Pickering emulsions and foams and provides a detailed and systematic analysis of the current state knowledge on factors affecting the stabilization of liquid-liquid and gas-liquid interfaces by nanocelluloses. The review also discusses the effect of nanocellulose surface modifications on mechanisms driving the Pickering stabilization of these interfaces.

N2O–Assisted Siphon Foaming of Modified Galactoglucomannans With Cellulose Nanofibers

Foaming of most bio-based polymers is challenged by low pore formation and foam stability. At the same time, the developing utilization of bio-based materials for the circular economy is placing new demands for easily processable, low-density materials from renewable raw materials. In this work, we investigate cellulose nanofiber (CNF) foams in which foaming is facilitated with wood-based hemicelluloses, galactoglucomannans (GGMs). Interfacial activity of the GGM is modulated via modification of the molecule’s amphiphilicity, where the surface tension is decreased from approximately 70 to 30 mN m−1 for unmodified and modified GGM, respectively. The chemical modification of GGMs by substitution with butyl glycidyl ether increased the molecule’s hydrophobicity and interaction with the nanocellulose component. The highest specific foam volume using 1 wt% CNF was achieved when modified GGM was added (3.1 ml g−1), compared to unmodified GGM with CNF (2.1 ml g−1). An amount of 96 and 98% of the GGM and GGM-BGE foams were lost after 15 min of foaming while the GGM and GGM-BGE with cellulose nanofibers lost only 33 and 28% of the foam respectively. In the case of GGM-BGE, the foam stability increased with increasing nanofiber concentration. This suggests that the altered hydrophobicity facilitated increased foam formation when the additive was incorporated in the CNF suspension and foamed with nitrous oxide (N2O). Thus, the hydrophobic character of the modified GGM was a necessity for foam formation and stability while the CNFs were needed for generating a self-standing foam structure.

"Bottom-Up" Assembly of Nanocellulose Microgels as Stabilizer for Pickering Foam Forming

Microgels assembled from bio-based nanomaterials are a promising soft stabilizer for a Pickering system. In this study, nanocellulose microgels with foaming properties were constructed by electrostatic assembly between nisin and 2,2,6,6-tetramethyl piperidine-1-oxyl-oxidized cellulose nanocrystals (TOCNC). Pickering wet foam was prepared by using the microgels as a foaming stabilizer. Nanocellulose microgels exhibited better foaming ability and foam stability than TOCNCs. Quartz crystal microbalance with dissipation and transmission electron microscopy analyses confirmed that the nanocellulose microgels prepared under different nisin concentrations demonstrated significant differences in morphology, conformation, and structural strength. Microgel particles prepared at 0.03 and 0.06 wt % nisin concentrations had a unique dendritic microstructure. Microgels containing 0.06 wt % nisin displayed better foaming ability and foam stability. It was possible that the soft dendritic structure of the microgels could endow bubbles with sufficient thickness and strength to prevent coalescence. This novelty nanocellulose microgel is expected to be used for expanding the application of nanocellulose in the functional interfacial design of Pickering foams.

Physiological fluid interfaces: Functional microenvironments, drug delivery targets, and first line of defense

Fluid interfaces, i.e. the boundary layer of two liquids or a liquid and a gas, play a vital role in physiological processes as diverse as visual perception, oral health and taste, lipid metabolism, and pulmonary breathing. These fluid interfaces exhibit a complex composition, structure, and rheology tailored to their individual physiological functions. Advances in interfacial thin film techniques have facilitated the analysis of such complex interfaces under physiologically relevant conditions. This allowed new insights on the origin of their physiological functionality, how deviations may cause disease, and has revealed new therapy strategies. Furthermore, the interactions of physiological fluid interfaces with exogenous substances is crucial for understanding certain disorders and exploiting drug delivery routes to or across fluid interfaces. Here, we provide an overview on fluid interfaces with physiological relevance, namely tear films, interfacial aspects of saliva, lipid droplet digestion and storage in the cell, and the functioning of lung surfactant. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe therapies and drug delivery approaches targeted at fluid interfaces. STATEMENT OF SIGNIFICANCE: Fluid interfaces are inherent to all living organisms and play a vital role in various physiological processes. Examples are the eye tear film, saliva, lipid digestion & storage in cells, and pulmonary breathing. These fluid interfaces exhibit complex interfacial compositions and structures to meet their specific physiological function. We provide an overview on physiological fluid interfaces with a focus on interfacial phenomena. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe novel therapies and drug delivery approaches targeted at fluid interfaces. This sets the scene for ocular, oral, or pulmonary surface engineering and drug delivery approaches.

Changes in Mechanical Properties of Polyhydroxyalkanoate with Double Silanized Cellulose Nanocrystals Using Different Organosiloxanes

Polyhydroxyalkanoate (PHA) is a biodegradable plastic with great potential for tackling plastic waste and marine pollution issues, but its commercial applications have been limited due to its poor processability. In this study, surface-modified cellulose nanocrystals were used to improve the mechanical properties of PHA composites produced via a melt-extrusion process. Double silanization was conducted to obtain hydrophobically treated CNC-based fillers, using tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS). The morphology, particle size distributions, and surface characteristics of the silanized CNCs and their compatibility with a PHA polymer matrix differed by the organosiloxane treatment and drying method. It was confirmed that the double silanized CNCs had hydrophobic surface characteristics and narrow particle size distributions, and thereby showed excellent dispersibility in a PHA matrix. Adding hydrophobically treated CNCs to form a PHA composite, the elongation at break of the PHA composites was improved up to 301%, with little reduction of Young's modulus, compared to pure PHA. Seemingly, the double silanized CNCs added played a similar role to a nucleation agent in the PHA composite. It is expected that such high ductility can improve the mechanical properties of PHA composites, making them more suitable for commercial applications.

Interfacial and Emulsion Characteristics of Oil-Water Systems in the Presence of Polymeric Lignin Surfactant

It is hypothesized that polymeric lignin surfactants have different affinities for stabilizing oil-water emulsions and that the emulsifying performance of these surfactants is highly affected by their adsorption performance at the oil-water interface. To validate this hypothesis, the adsorption performance of sulfethylated lignin (SEKL) surfactant at different oil-water interfaces was examined by assessing the contact angle, dynamic interfacial tension, and surface loading (Γ). Moreover, the interfacial adsorption kinetics of SEKL was comprehensively assessed in different oil-water systems to reveal the mechanisms of the SEKL adsorption at the interface. Also, the impacts of SEKL concentration and ionic strength on the performance of SEKL as an effective emulsifier for the emulsions were assessed. Furthermore, the droplet size and instability index of the emulsions were systematically correlated with the adsorption performance of SEKL at the interface of oil and water. For the first time, by implementing a modified Ward Toradai diffusion model, two distinct early stages of the adsorption of SEKL at the oil interface were identified. Interestingly, the second stage was the determining stage of adsorption with the diffusion-controlled mechanism when polymers reconfigured at the oil-water interface. Salt screening facilitated the clustering of SEKL upon charge repulsion elimination, which removed the energy barrier in the first stage of adsorption (ΔE_p→0 = 0), but it introduced a steric barrier upon the reconfiguration of polymers at the oil interfaces in the second stage of adsorption. In addition to the kinetics of adsorption, satisfactory correlations were observed between surface pressure (Δγ = γ_∞ - γ₀), surface loading (Γ) of polymers, and contact angle at oil interfaces on one hand and the oil droplet size and emulsion stability on the other hand.

Nanocellulose: From Fundamentals to Advanced Applications

Over the past few years, nanocellulose (NC), cellulose in the form of nanostructures, has been proved to be one of the most prominent green materials of modern times. NC materials have gained growing interests owing to their attractive and excellent characteristics such as abundance, high aspect ratio, better mechanical properties, renewability, and biocompatibility. The abundant hydroxyl functional groups allow a wide range of functionalizations via chemical reactions, leading to developing various materials with tunable features. In this review, recent advances in the preparation, modification, and emerging application of nanocellulose, especially cellulose nanocrystals (CNCs), are described and discussed based on the analysis of the latest investigations (particularly for the reports of the past 3 years). We start with a concise background of cellulose, its structural organization as well as the nomenclature of cellulose nanomaterials for beginners in this field. Then, different experimental procedures for the production of nanocelluloses, their properties, and functionalization approaches were elaborated. Furthermore, a number of recent and emerging uses of nanocellulose in nanocomposites, Pickering emulsifiers, wood adhesives, wastewater treatment, as well as in new evolving biomedical applications are presented. Finally, the challenges and opportunities of NC-based emerging materials are discussed.