Unmodified Cellulose Nanocrystals Research Articles

Multiple noncovalent interactions tailored crystallization and performance reinforcement mechanisms of Biopolyester Composites with functional Cellulose Nanocrystals

The slow crystallization and weak mechanical features of poly (butylene adipate-co-terephthalate) (PBAT) have become a severe industrial problem in food packaging. Inspired by principle of bionic structure, functional cellulose nanocrystals (CNC) modified with hexamethylene diisocyanate (HMDI) and toluene diisocyanate (TDI) can enhance the crystallization ability and mechanical properties of PBAT nanocomposites. Significantly, CNC-T (CNC modified by TDI) showed a stronger reinforced effect on PBAT properties than unmodified CNCs and CNC-H (CNC modified by HMDI) nanofillers due to hydrogen bonds, π-π interaction between PBAT matrix and CNC-T nanofillers with benzene ring structure. Thus, compared with pure PBAT, PBAT/5CNC-T composites displayed an enhancement of 34.5 % on the tensile strength and exhibited the most robust nucleation ability on PBAT crystallization than CNC and CNC-H. Meanwhile, the possible nucleation, crystallization, and performance reinforcement mechanisms of PBAT nanocomposites have been presented, which is very beneficial for designing robust PBAT nanocomposites with functional cellulose nanocrystals for potential green packaging.

A hydrophobic coating on cellulose nanocrystals improves the mechanical properties of polyamide-6 nanocomposites

Recent demands for high-performance lightweight materials have brought researchers’ attention to various nanoparticles to reinforce polymeric materials. As such, sustainable and stiff cellulose nanocrystals (CNC) have become a popular candidate as nano-reinforcements. While CNC can offer great advantages, such as high mechanical properties and low density, it might agglomerate even in hydrophilic polymers because of its strong affinity to itself (intra and intermolecular hydrogen bonds) which prevents its broader use in industrial applications. This study aims to improve the compatibility between CNC and polyamide 6 (PA6) by a chemical modification that produces a surface polarity drastically different from non-modified CNC. The surface of CNC was rendered by the covalent coupling of stearic acid (SA) to the surface hydroxyl groups to produce stearate modified CNC (CNC SA). The effect of the modification was analyzed for CNC SA reinforced PA6 nanocomposites, and the results are compared to that of non-modified CNC reinforced PA6 samples. The addition of unmodified CNC to PA6 provided a modest improvement while the addition of CNC-SA provided substantial improvement on the modulus and tensile strength of the nanocomposite films.

Incorporation of Polymer-Grafted Cellulose Nanocrystals into Latex-Based Pressure-Sensitive Adhesives.

While the improvement of water-based adhesives with renewable additives is important as industry shifts toward more sustainable practices, a complete understanding of how the compatibility between additives and polymers affects adhesive performance is currently lacking. To elucidate these links, cellulose nanocrystals (CNCs) were first functionalized via surface-initiated atom-transfer radical polymerization with the hydrophobic polymers poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) to facilitate their incorporation into latex-based pressure-sensitive adhesives (PSAs). Next, PBA latexes were synthesized using seeded semibatch emulsion polymerization with unmodified or polymer-grafted CNCs added in situ at a loading of 0.5 or 1 phm (parts per hundred parts of monomer). Viscosity and electron microscopy suggested that the polymer-grafted CNCs were incorporated inside or on the latex particles. PSAs containing any CNC type had one or more improved properties (compared to the no-CNC "base case"); CNCs with a low degree of polymerization (DP) grafts exhibited improved tack (up to 2.5-fold higher) and peel strength (up to 6-fold higher) relative to PSAs with unmodified CNCs. The best performing PSA contained the low DP PMMA-grafted CNCs, which is attributed to the higher glass transition temperature and the higher wettability of the PMMA grafts compared to PBA, and the more uniform dispersion of polymer-grafted CNCs throughout the PSA film. In contrast, PSAs containing CNCs with high DP grafts resulted in reduced tack and peel strength (compared to low DP grafts) due to enhanced CNC aggregation. Unfortunately, all PSAs containing polymer-grafted CNCs exhibited inferior shear strength relative to PSAs with unmodified CNCs (and comparable shear strength to the no-CNC "base case"). Collectively, these results provide guidelines for future optimization of more sustainable latex-based PSAs.

Nanocomposites Assembled via Electrostatic Interactions between Cellulose Nanocrystals and a Cationic Polymer.

On account of their high strength and stiffness and their renewable nature, cellulose nanocrystals (CNCs) are widely used as a reinforcing component in polymer nanocomposites. However, CNCs are prone to aggregation and this limits the attainable reinforcement. Here, we show that nanocomposites with a very high CNC content can be prepared by combining the cationic polymer poly[(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) and negatively charged, carboxylated CNCs that are provided as a sodium salt (CNC-COONa). Free-standing films of the composites can be prepared by simple solvent casting from water. The appearance and polarized optical microscopy and electron microscopy images of these films suggest that CNC aggregation is absent, and this is supported by the very pronounced reinforcement observed. The incorporation of 33 wt % CNC-COONa into PMETAC allowed increasing the storage modulus of this already rather stiff, glassy amorphous matrix polymer from 1.5 ± 0.3 to 6.6 ± 0.1 GPa, while the maximum strength increased from 11 to 32 MPa. At this high CNC content, the reinforcement achieved in the PMETAC/CNC-COONa nanocomposite is much more pronounced than that observed for a reference nanocomposite made with unmodified CNCs (CNC-OH).

Bringing Sustainability to Macroporous Polystyrene: Cellulose Nanocrystals as Cosurfactant and Surface Modifier in Deep Eutectic Solvent-Based Emulsion Templating

Macroporous polymers were produced from nonaqueous high internal phase emulsions (HIPEs) containing a deep eutectic solvent (DES) and stabilized by mixtures of unmodified cellulose nanocrystals (CNCs) and a nonionic surfactant. The effect of the CNC/surfactant ratio on HIPEs morphology and rheological properties was thoroughly investigated. Upon free-radical polymerization of styrene/divinylbenzene in the continuous phase, highly interconnected macroporous structures with cellulose-functionalized surfaces and robust mechanical properties were obtained. Additionally, the generation of nanocellulose dispersions from biomass in situ in the acidic DES internal phase of HIPEs and subsequent polymerization was proposed to synthesize interconnected macroporous polymers. Biomass incorporation into macroporous polymers further emphasizes the sustainable character of the DES-based emulsion templating introduced in this work.

Scaled Synthesis of Polyamine-Modified Cellulose Nanocrystals from Bulk Cotton and Their Use for Capturing Volatile Organic Compounds.

We have previously demonstrated that cellulose nanocrystals modified with poly(ethylenimine) (PEI-f-CNC) are capable of capturing volatile organic compounds (VOCs) associated with malodors. In this manuscript, we describe our efforts to develop a scalable synthesis of these materials from bulk cotton. This work culminated in a reliable protocol for the synthesis of unmodified cellulose nanocrystals (CNCs) from bulk cotton on a 0.5 kg scale. Additionally, we developed a protocol for the modification of the CNCs by means of sequential 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidation and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) coupling to modify their surface with poly(ethylenimine) on a 100 g scale. Subsequently, we evaluated the performance of the PEI-f-CNC materials that were prepared in a series of VOC capture experiments. First, we demonstrated their efficacy in capturing volatile fatty acids emitted at a rendering plant when formulated as packed-bed filter cartridges. Secondly, we evaluated the potential to use aqueous PEI-f-CNC suspensions as a spray-based delivery method for VOC remediation. In both cases, the PEI-f-CNC formulations reduced detectable malodor VOCs by greater than 90%. The facile scaled synthesis of these materials and their excellent performance at VOC remediation suggest that they may emerge as a useful strategy for the remediation of VOCs associated with odor.

Cellulose Nanocrystals Influence Polyamide 6 Crystal Structure, Spherulite Uniformity, and Mechanical Performance of Nanocomposite Films

Cellulose nanocrystals (CNCs) are an ideal reinforcing agent for polymer nanocomposites. CNCs can form hydrogen bonds with polyamide 6 (PA6); however, the direct effects of unmodified CNCs on PA6 morphology and crystal structure have not been fully elucidated. This work investigated the influence of CNCs on the mechanical performance and physicochemical properties of spin-coated CNC–PA6 films through quantitative analysis using techniques that probe multiple length scales. CNCs interacted with PA6 to induce the γ (chiral) allomorph over the α allomorph at low CNC loadings (≤1 wt %) and nucleated a high density of small uniform spherulites, leading to stiffer nanocomposites. Higher loadings caused CNC aggregation and crystalline, non-spherulitic features. Overall, we hypothesize that the reinforcement mechanism of CNCs in PA6 is dominated by morphological changes in the matrix, not percolation. Understanding CNC–polymer interactions and morphology (on films prepared without thermal processing or surface modification of CNCs) offers “design rules” for how to incorporate CNCs into nanocomposites for optimized material performance in various applications, for example, membranes, coatings, and packaging.

Lauric acid adsorbed cellulose nanocrystals retained the physical stability of oil-in-water Pickering emulsion during different dilutions, pH, and storage periods

Due to increased environmental and health concerns, there has been an increased demand for sustainable and natural emulsifiers/stabilizers to create a stable O/W emulsion. Due to their unique properties, cellulose nanocrystals (CNC) have been considerably investigated as a stabilizer for producing a stable emulsion. However, the utilization of CNC stabilized emulsion is only limited to viscous or semi-solid foods. Hence this study investigates the modification of CNC by adsorbing lauric acid and its suitability for producing a stable beta-carotene O/W Pickering emulsion for nutraceutical beverages. The efficacy of modified CNC on the physicochemical stability of the emulsion was monitored under different environmental conditions such as dilution factors of 1–10, pH of 1–11, and 30 days of storage period at room temperature. Results depicted that the modified CNC above 1.5% (w/v) significantly (p ≤ 0.05) retained the average droplet size, morphology, and creaming index at different dilutions. However, the droplet size increased by 150–300% for the emulsions stabilized with unmodified CNC with noticeable changes in creaming index and morphology of the droplets. Unexpectedly, higher thiobarbituric acid reactive substances (TBARS) concentrations were recorded for the emulsions stabilized by modified and unmodified CNC compared to the control emulsion, which contained gum arabic as a reference stabilizer. Transition metals in the CNC may have catalyzed lipid oxidation; however, their source and role in oxidation warrant further study.

Effect of Reaction Media on Grafting Hydrophobic Polymers from Cellulose Nanocrystals via Surface-Initiated Atom-Transfer Radical Polymerization.

Hydrophobic polymer-grafted cellulose nanocrystals (CNCs) were produced via surface-initiated atom-transfer radical polymerization (SI-ATRP) in two different solvents to examine the role of reaction media on the extent of surface modification. Poly(butyl acrylate)-grafted CNCs were synthesized in either dimethylformamide (DMF) (D-PBA-g-CNCs) or toluene (T-PBA-g-CNCs) alongside a free polymer from a sacrificial initiator. The colloidal stability of unmodified CNCs, initiator-modified CNCs, and PBA-g-CNCs in water, DMF, and toluene was evaluated by optical transmittance. The enhanced colloidal stability of initiator-modified CNCs in DMF led to improved accessibility to initiator groups during polymer grafting; D-PBA-g-CNCs had 30 times more grafted chains than T-PBA-g-CNCs, determined by thermogravimetric and elemental analysis. D-PBA-g-CNCs dispersed well in toluene and were hydrophobic with a water contact angle of 124° (for polymer grafts > 13 kDa) compared to 25° for T-PBA-g-CNCs. The cellulose crystal structure was preserved, and individual nanoparticles were retained when grafting was carried out in either solvent. This work highlights that optimizing CNC colloidal stability prior to grafting is more crucial than solvent-polymer compatibility to obtain high graft densities and highly hydrophobic CNCs via SI-ATRP.

Cellulose nanocrystals produced using recyclable sulfuric acid as hydrolysis media and their wetting molecular dynamics simulation

Cellulose nanocrystals (CNCs) were successfully produced with good nanoscales and dispersibility, using a recycled sulfuric acid (H2SO4) hydrolysis process. This method, at the cost of an overall 25% increase in the hydrolysis time, could significantly reduce the dosage of H2SO4 by approximately 40% without affecting the per-batch yield and performance of CNCs. The obtained CNCs with an average diameter of 6.0–6.5 nm and an average length of 126–134 nm, were successfully applied in the preparation of oil-in-water (O/W) Pickering emulsions via high-pressure homogenization. The emulsions exhibited good storage stability when the concentration of CNC was 1.0 wt%. Further, understanding the wetting behaviors of surface modified CNCs with solvent is critical for the functional designing of Pickering emulsion. Hence, we gained insights into the wetting of hydrophobic and hydrophilic surfaces of sulfate modified CNCs with water and organic solvent (hexadecane) droplets, using molecular dynamic simulation. The results showed that both surfaces had hydrophilic as well as lipophilic properties. Although the sulfate-grafted surface was more hydrophilic than unmodified CNC, substantial local wetting heterogeneities appeared for both solvents. It provides a deeper understanding of the interfacial interactions between modified CNCs and solvent molecules at the molecular level.

Synthesis of bio-inspired cellulose nanocrystals-soy protein isolate nanoconjugate for stabilization of oil-in-water Pickering emulsions

The development of hybrid polysaccharide-protein complexes as Pickering emulsion stabilizers has attracted increasing research interest in recent years. This work presents an eco-friendly surface modification strategy to functionalize hydrophilic cellulose nanocrystals (CNC) using hydrophobic soy protein isolate (SPI) via mussel adhesive-inspired poly (l-dopa) (PLD) to develop improved nanoconjugates as stabilizers for oil-in-water Pickering emulsion. The physicochemical properties of the CNC-PLD-SPI nanoconjugate were evaluated by solid-state 13C NMR, FT-IR, TGA, XRD, contact angle analysis, and TEM. The modified CNC (conjugation content of 38.22 ± 1.21%) had lowered crystallinity index, higher thermal stability, and more hydrophobic than unmodified CNC, with an average particle size of 309.9 ± 8.0 nm. Use of amphiphilic CNC-PLD-SPI nanoconjugate with greater conformational flexibility as Pickering stabilizer produced oil-in-water emulsions with greater physical stability.

Poly (ethyl methacrylate) composites reinforced with modified and unmodified cellulose nanocrystals and its application as a denture resin

The aim of this study was to characterize cellulose nanocrystals (CNC) used to the preparation of nanocomposites and evaluate the influence of incorporating the CNC on flexural strength of a denture rebase resin. CNC were isolated from wood pulp by acid hydrolysis. In addition, maleic anhydride was used to superficially modify the CNCs. The modified (CNCmod) and unmodified nanocrystals (CNC) were suitably characterized and used separately as a reinforcement element in situ in a denture rebase resin consisting of poly ethyl methacrylate, at 0% (control group), 0.25%, 0.5%, 0.75% and 1%. The flexural strength of the groups was measured using a 3-point bending test with EMIC DL 2000 machine. AFM images showed that CNC and CNCmod samples presented nanoparticles with typical acicular shape and similar dimensions. A significant improvement of the flexural strength was obtained, even at low load levels, especially considering the nanoparticles with chemically modified surface. The incorporation of both modified and unmodified CNCs represents an alternative that can maximize the mechanical properties of acrylic resins and their respective dental applications.

Water-assisted extrusion and injection moulding of composites with surface-grafted cellulose nanocrystals – An upscaling study

The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples.

Acrylic Functionalization of Cellulose Nanocrystals with 2-Isocyanatoethyl Methacrylate and Formation of Composites with Poly(methyl methacrylate).

Cellulose nanocrystals (CNCs) derived from renewable plant-based materials exhibit strong potential for improving properties of polymers by their dispersal in the polymer matrix as a composite phase. However, the hydrophilicity and low thermal stability of CNCs lead to compromised particle dispersibility in common polymers and limit the processing conditions of polymer–CNC composites, respectively. One route that has been explored is the modification of CNCs to alter surface chemistry. Acrylic materials are used in a broad class of polymers and copolymers with wide commercial applications. Yet, the available methods for adding groups that react with acrylics to enhance dispersion are quite limited. In this work, a versatile chemical modification route is described that introduces acryloyl functional groups on CNCs that can in turn be polymerized in subsequent steps to create acrylic–CNC composites. The hydroxyl group on CNC surfaces was reacted with the isocyanate moiety on 2-isocyanatoethyl methacrylate (IEM), a bifunctional molecule possessing both the isocyanate group and acryloyl group. The resulting modified CNCs (mCNCs) showed enhanced hydrophobicity and dispersibility in organic solvent relative to unmodified CNCs. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis verified the surface modification and allowed an estimation of the degree of modification as high as 0.4 (26.7% surface hydroxyl substitution CNC). The modified CNCs were copolymerized with methyl methacrylate, and the composites had improved dispersion relative to composites with unmodified CNCs and enhanced (104%) tensile strength at 2 wt % CNC when compared to the neat poly(methyl methacrylate) (PMMA), indicating a benefit of the reactive acryloyl groups added to the CNC surface. Overall, the modification strategy was successful in functionalizing CNCs, opening possibilities for their use in organic media and matrices.

Kinetics Study of Cellulose Nanocrystals Modification Using Rarasaponins by Elovich Equation

The modification of cellulose nanocrystals (CNCs) using rarasaponins (RSs) was carried out to enhancing the hydrophobicity of the CNCs. The RSs are a natural surfactant that has hydrophilic and hydrophobic sides. The linked RSs on the CNCs surface can be used to bond the hydrophobic drugs so that the modified CNCs can be applied as the hydrophobic drugs carrier in the medical field. The kinetics study was successfully carried out using the Elovich equation as the modeling equation. The Elovich equation fits the modification results well based on two parameters, i.e., the RSs/CNCs ratios and the times. The dispersion characteristics analysis was carried out to figure the enhancement of the hydrophobicity on the modified CNCs compared to the unmodified CNCs. According to the kinetics study and the dispersion characteristics analysis, the modification of CNCs using RSs could enhance CNCs utilization in the hydrophobic drug delivery system

Preparation and Mechanical, Thermal and Oil-resistance Properties of Acrylic Rubber Nanocomposites Reinforced with Cellulose Nanocrystals

Acrylic rubber (ACM) nanocomposites reinforced with cellulose nanocrystals (CNCs) were prepared and the properties were characterized. CNCs were produced by hydrochloric acid hydrolysis of microcrystalline cellulose powder and used without further chemical modification of the surfaces. The CNCs were already aggregated in aqueous suspension. However, their aggregated sizes and uniform distribution in the ACM did not change with increase in the concentration of CNC. This result suggested good compatibility of the CNC with ACM. Fourier-transform infrared/attenuated total reflection spectroscopy revealed that the good compatibility could be attributed to attractive interactions between CNC and ACM. The good compatibility led to an increase in breaking stress of the ACM/CNC nanocomposites, up to about 10 MPa at a high concentration of 24 phr of CNC. Thermal decomposition of the nanocomposites occurred due to first the CNC followed by the ACM. More weight residues of the nanocomposites were found above 400 °C with increase in the concentration of CNC. The char produced by the decomposition of CNC is suggested the act as a flame retardant for ACM. In addition, the swelling ratio of the ACM/CNC nanocomposites against hydrophobic solvents decreased with increase in the concentration of CNC. The hydrophilic properties of the unmodified CNC from the surface hydroxyl groups increased the oil-resistant properties of the ACM.

Thermomechanical, antioxidant and moisture behaviour of PVA films in presence of citric acid esterified cellulose nanocrystals

In the present work, poly(vinyl alcohol) (PVA) active packaging films containing different amounts (1, 3, 5, 10 and 15% wt.) of unmodified cellulose nanocrystals (CNC) and citric acid modified cellulose nanocrystals (mCNC) were prepared by solvent casting and their effect on thermal, mechanical and wettability behaviour of the resulted films was investigated. Results showed that both CNC and mCNC improved the thermal stability of the neat PVA matrix, but different mechanical properties and water wettability were found. Thermal stability of the materials was enhanced, by measuring shift of onset and peak temperatures that moved, respectively, from 251.5 to 298.1 °C and from 283.4 to 374.2 °C, in the case of PVA/15CNC and PVA/15mCNC films. The presence of mCNC contribute to increase the crystallinity up to 52% for PVA/10mCNC film, while it was limited to 39% for PVA/10CNC. Interestingly, PVA/mCNC composite films showed a clear UV shielding effect, while no UV resistance behaviour was detected for PVA/CNC films. Overall migration tests revealed that the migration value was well below the legislative limits (60 mg kg−1) for food contact materials, PVA/mCNC composite films have higher radical scavenging activity than PVA/CNC films and moisture content of PVA films containing mCNC was reduced at high RH. In conclusion, PVA/mCNC films could be considered as high-performance active food packaging materials.

Silane modified cellulose nanocrystals and nanocomposites with LLDPE prepared by melt processing

Cellulose nanocrystals (CNCs) were surface modified with 3-isocyanatopropyl triethoxysilane (ICPTS) in tetrahydrofuran at 62–63 °C using triethylamine as a catalyst. ICPTS modified CNCs were further studied as a nanofiller in nanocomposites with linear low-density poly(ethylene) (LLDPE) prepared by melt processing. The modification of CNCs was confirmed by FTIR, solid state NMR, and thermogravimetric analysis. Compared to unmodified CNCs, the ICPTS modified CNCs show enhanced compatibility with LLDPE as shown by SEM. Nanocomposites processed at 70 °C reveal slightly enhanced mechanical properties and this effect was further intensified by increasing the molding temperature up to 120 °C. Under such conditions, a 20% increase in Young’s modulus and 30% increase in tensile strength are achieved compared to neat LLDPE. Differential scanning calorimetry confirms the degree of LLDPE crystallinity, beside the CNC reinforcing network formation, as an important decisive factor in defining the final mechanical properties of LLDPE/CNC nanocomposites. The maximal enhancement of mechanical properties was observed at rather low amount of added ICPTS modified CNC (1–2 wt.%), which is important for practical application as CNCs are still rather expensive nanofiller. By modification of CNC with ICPTS the CNC polarity is reduced, which result in their improved compatibility with LLDPE, while on the other hand they function as a plasticizer and thus reduce the LLDPE crystallization degree, especially at high CNC concentrations.

Polyphosphoester-modified Cellulose Nanocrystals for Stabilizing Pickering Emulsion Polymerization of Styrene

The structure and properties of functional nanoparticles are important for stabilizing Pickering emulsion polymerization. Recently, cellulose nanocrystals (CNCs) are increasingly favored as a bio-based stabilizer for Pickering emulsions. In this study, we reported a novel functionalized polyphosphoester-grafted CNCs for the stabilization of oil-in-water Pickering emulsions and the emulsion polymerization of styrene. First, polyphosphoester containing an amino group at one end of the chain, abbreviated as PBYP-NH2, was prepared by ring-opening polymerization (ROP) and hydrolysis reaction, wherein PBYP represents poly[2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane]. Subsequently, CNC-COOH was obtained via 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation of CNCs. The functionalized nanocrystals CNC-PBYP-COOH with carboxyl groups and polyphosphoester on the surface were obtained by the amidation reaction of PBYP-NH2 with CNC-COOH. Finally, we used CNC-PBYP-COOH as sole particle emulsifiers to stabilize styrene-in-water Pickering emulsions and studied its effects on the emulsions in details by using dynamic light scattering (DLS). The results indicated that the properties of these emulsions depended on the concentration of hydrophobically modified CNCs, volume ratios of oil to water, and pH values. The modified CNCs had higher ability to stabilize the styrene-in-water emulsions relative to the unmodified CNCs, and a stable oil-in-water (o/w) Pickering emulsion with diameter of hundreds of nanometers could be obtained. The resulting emulsions could be polymerized to yield nanosized latexes. The polyphosphoester-modified CNCs as green particle emulsifiers can efficiently stabilize nanoemulsions and latexes, which would promote the development of novel environmentally friendly materials.

Tuning the stability and microstructure of fine Pickering emulsions stabilized by cellulose nanocrystals

Cellulose nanocrystals (CNCs) as Pickering emulsion stabilizers have attracted fast increasing interests in the food, pharmaceutical and cosmetic fields, due to their sustainability and biocompatibility. However, it still remains a debate for unmodified CNCs to act as a kind of effective Pickering stabilizers, due to their high hydrophilic nature. This work for the first time reported that CNCs were compatible with using microfluidization as the emulsification process to produce a kind of fine Pickering emulsions, with surface-average droplet sizes as low as 0.22 μm. As compared with other emulsification processes, the Pickering emulsions by the microfluidization were more stable against coalescence but readily prone to droplet flocculation and creaming. The droplet flocculation in these emulsions was mainly associated with the formation of bridging droplets with two different droplets sharing a same monolayer. The droplet size, microstructure and stability (against creaming and coalescence) of these emulsions by the microfluidization could be well tuned by varying the particle concentration (c; 0.3–1.2 wt%) and/or oil fraction (ø; 0.1-0.4). In general, the finer Pickering emulsions with more serious bridging flocculation were formed at lower ø and/or higher c values, while the emulsions at lower ø and c values were more prone to creaming. The Pickering emulsions with smaller droplet sizes exhibited a much better coalescence stability. Interestingly, the amount of adsorbed CNCs at the interface was relatively high, and the percentage of surface coverage at interface was low (ranging from 11.3 to 50.0%). The results confirmed that using the microfluidization as the emulsification technique, CNCs exhibit a good ability to stabilize the Pickering emulsions, with the microstructure and stability well-modulated by varying the c and/or ø. The findings would be of great relevance for the development of nanoscale CNC Pickering emulsions suitable for food and pharmaceutical formulations.