Janus-type spherical cellulose nanoparticles

Abstract

The present invention relates to Janus-type spherical cellulose nanoparticles and a method for preparing the same. The Janus-type spherical cellulose nanoparticles of the present invention are chemically modified on only one side to produce particles with a hydrophilic face and an opposite lipophilic face. Such particles exhibit excellent surfactant properties and can be used to prepare Pickering emulsions.

Description

[Technical field]

[0001] The present invention relates to Janus-type spherical cellulose nanoparticles, a process for preparing said nanoparticles, and Pickering emulsions comprising said nanoparticles. [Background technology]

[0002] Surfactants are chemical additives used in products such as paints, pesticides, detergents, and cosmetics. Traditional surfactants are molecules with one water-soluble end and one oil-soluble end. This amphiphilic structure allows incompatible liquids such as oils (or oil-soluble compounds) to mix uniformly with water. Surfactants make this mixing possible by sitting at the oil-water interface and stabilizing microscopic bubbles of oil (the dispersed phase) within the water (the continuous phase), producing a homogeneous mixture known as an emulsion. In this context, these surfactants function as emulsifiers.

[0003] The properties of synthetic surfactants can be modified by the length (and chain number) of the lipophilic portion and the size and charge of the hydrophilic portion. An important measure of a surfactant's physical properties is its hydrophilic-lipophilic balance (HLB), which is used to determine the application for which the surfactant is best suited. Depending on the HLB, surfactants can be used as detergents, emulsifiers, wetting agents, foaming agents, dispersants, and defoamers.

[0004] For example, surfactants with HLB values ​​of 13-15 are typically used as detergents, surfactants with HLB values ​​of 8-16 are typically used as oil-in-water emulsifiers, surfactants with HLB values ​​of 3-6 are typically used as water-in-oil emulsifiers, and surfactants with HLB values ​​of 2-3 are typically used as antifoam agents.

[0005] Surfactants currently used cannot be recovered and are discharged into waterways. This issue is facing increased scrutiny from regulatory agencies. They are therefore considered environmental pollutants. Some surfactants have also been found to be endocrine disruptors, such as alkylphenols, a class of surfactants restricted in the European Union due to their impact on human health and the environment (Regulation No 648 / 2004). In addition, the majority of surfactants currently used originate from the petrochemical industry, which is partly or totally unsustainable. Increasing environmental regulations and a strong public demand for green and sustainable technologies have created a need for new surfactants that are sustainably sourced and fully biodegradable.

[0006] Also, emulsions formed from oil and water are not made with molecular surfactants, but with particles. They can be stabilized by adding particulate surfactants. Small molecules do not always provide high emulsion stability over time, as they tend to rapidly adsorb and desorb at the oil-water interface. Particles, due to their large size, are known to have a much higher affinity for the water / oil interface than molecules, stabilizing emulsions more efficiently due to their ability to separate the two immiscible layers. Thus, they act as more efficient emulsifiers. Emulsions formed with particulate surfactants are called Pickering emulsions.

[0007] Pickering emulsions consist of a shell of particles located at the interface between the dispersed phase droplets and the continuous phase. Pickering emulsions are typically created by combining oil, water, and solid particles (usually less than 100 μm in diameter) and vigorously mixing, for example in a blender. Depending on the relative amounts of water and oil, and the size and nature of the solid particles (usually the phase that preferentially wets the particles becomes the continuous phase), either water-in-oil or oil-in-water Pickering emulsions are formed, with the presence of the solid particles preventing the dispersed phase droplets from coalescing and stabilizing the emulsion.

[0008] Well-known particulate surfactants (also called Pickering particles) include hydroxyapatite nanoparticles, silica and clay materials, iron oxide nanoparticles, carbon nanotubes, chitosan nanoparticles, etc. However, cellulose particles are increasingly finding application as particulate surfactants.

[0009] Cellulose, a carbohydrate polymer, is the most abundant renewable polymer in nature, comprising approximately 50% of the Earth's natural biomass. Cellulose ((C6H10O5)n where n = 10,000-15,000) is a tough, fibrous, water-insoluble substance defined as long polymeric chains of 1,4-anhydro-D-glucopyranose units with a flat, ribbon-like structure.

[0010] Native cellulose is fibrous and crystalline. Cellulose does not exist as a single polymer molecule, but rather multiple cellulose polymers (30-100) packed together via van der Waals forces and hydrogen bonding to form material fibrils, the basic units of cellulose fibers, which exist on the nanoscale in diameter and microscale in length. These material fibrils are further assembled by intermolecular and intramolecular hydrogen bonding into microfibrils that exhibit cross dimensions between 2 and 20 nm. Their aspect ratios vary from about 40 (e.g., about 200 nm in length and 5 nm in width for cotton) to about 66 (e.g., about 1 μm in length and 15 nm in width for tunisin).

[0011] Common sources of cellulose include cotton, hemp, flax, hardwood, and bacterial cellulose. Using acid hydrolysis and enzymatic digestion, crystalline regions can be extracted from cellulose microfibers. The crystalline rods formed are known as cellulose nanocrystals, which are approximately 160-200 nm in length and 7-25 nm in cross section.

[0012] While cellulose nanocrystals show promise for a wide range of applications, their high mechanical strength and surface area offer great potential as particulate surfactants, and they are also biodegradable and biocompatible, making them potentially preferable over petrochemically derived molecular surfactants.

[0013] The monomeric glucose units within the cellulose chains have several hydroxyl groups that provide a reactive platform for chemical modification, and therefore the physical properties of cellulose nanocrystals can be easily altered.

[0014] Cellulose is inherently hydrophilic due to the presence of hydroxyl (-OH) groups on its surface that can form hydrogen bonds with water. However, the surface functionality of cellulose nanocrystals can be modified using a number of methods, including but not limited to TEMPO-mediated oxidation, periodate oxidation (to increase hydrophilicity), esterification and long alkyl chain grafting (to decrease hydrophilicity), etc. Many modified cellulose nanocrystals, including spherical cellulose nanoparticles, have been shown to be excellent at stabilizing Pickering emulsions (Dong, Ding, Jiang, Li, & Han, 2021). Another way to improve the surfactant properties of particles is to introduce heterogeneity on the surface of the particle. Janus particles are particles that have two different physical properties on their surface, for example a lipophilic surface opposite a hydrophilic surface. This type of Janus particle combines the amphiphilicity of molecular surfactants with the high interfacial affinity of particulate surfactants, making them excellent emulsifiers.

[0015] C. Casagrande and M. Veyssie reported in 1989 the first Janus "beads" that offered amphiphilicity within a single solid particle in the range of 50-90 μm in diameter (Casagrande, Fabre, Raphael, & Veyssie, 1989). These Janus "beads" were prepared from glass spheres that had a cellulose (hydrophilic) varnish on one side and octadecyltrichlorosilane (oleophilic) on the other. These Janus "beads", when dispersed at an oil-water interface, were found to always be symmetrically positioned at the interface, with the oleophilic half immersed in the oil side and the hydrophilic half immersed in the water.

[0016] Janus particles can be generated by masking one side of a particle (which can be achieved by vapor deposition or by suspending the particle at a two-phase interface) and then chemically modifying the unmasked side. However, methods to generate Janus particles on the nanometer scale are severely limited by the ability of the particles to rotate in solution, resulting in poor control over the modification of a single surface.

[0017] Thus, despite the growing interest in cellulose nanocrystals, Janus cellulose nanocrystals are rare.

[0018] In 2020, Li et al. described the creation of Janus-type cellulose nanocrystals in the production of palladium / cellulose nanoparticle interfacial Pickering catalysts (Li, Jiang, & Cai, 2020). Li et al. formed a Pickering emulsion from cellulose nanocrystals in a wax / water solution at 75 °C in the presence of cetyltrimethylammonium bromide (CTAB). Once the cellulose nanocrystals were located at the emulsion interface, the solution was rapidly cooled, leaving the nanocrystals anchored to the surface of the now solid wax droplets. A lipophilic modifier (1-bromohexadecane) reacted with the exposed surfaces of the cellulose nanocrystals.

[0019] The cellulose nanocrystals used were rod-shaped particles with lengths of about 0.5–3 μm and diameters of 50–150 nm. After modification, the average length of the cetyl-modified cellulose nanocrystals was about 0.5–5 μm.

[0020] The modified cellulose nanocrystals described above are rather large and have a high aspect ratio, making them a suboptimal particulate surfactant. The particles stabilize Pickering emulsions by adsorbing at the high-energy oil-water interface, reducing the surface area where the oil and water phases are in direct contact. Smaller particles are more efficient in this role, as the gaps between the particles are smaller and the oil and water phases can be packed more efficiently where they meet. Spherical particles allow for more efficient packing than elongated rods or fibers, which tend to form bundles or become entangled rather than packing evenly at the interface.

[0021] Unfortunately, researchers have not yet found a way to combine the excellent surfactant properties resulting from surface differentiation with the excellent interfacial stabilization of spherical cellulose nanoparticles, and therefore currently available cellulose-based surfactants are not as effective as products that are not environmentally harmful.

[0022] The present invention therefore aims to provide Janus-type spherical cellulose nanoparticles that at least in some way alleviate some of the shortcomings of prior art surfactants and / or at least provide the public with a useful option.

[0023] Where references are made herein to patents or other external documents or other sources, this is generally for the purpose of providing a context for discussing features of the present invention. Unless expressly stated, the reference to such external documents should not be construed as an admission that such documents or such sources are prior art or form part of the common general knowledge in the art in any jurisdiction. Summary of the Invention

[0024] The present invention generally relates to a process for increasing the lipophilicity of one face of spherical cellulose nanoparticles to improve their surfactant properties.

[0025] The present invention, in one aspect, comprises: (a) preparing an alkaline suspension of spherical cellulose nanoparticles in water; (b) forming an emulsion comprising the spherical cellulose nanoparticles, water, and a water-immiscible lipophilic solvent, (i) the water constitutes a continuous phase; (ii) the lipophilic solvent constitutes the dispersed phase and contains a lipophilic modifier; (iii) the spherical cellulose nanoparticles are localized at the interface between the continuous phase and the dispersed phase; (c) reacting the portion of the spherical cellulose nanoparticles exposed to the lipophilic modifier at the interface between the continuous phase and the dispersed phase with the lipophilic modifier to produce Janus-type spherical cellulose nanoparticles; (d) isolating the Janus-type spherical cellulose nanoparticles from the emulsion.

[0026] In another aspect, the present invention provides Janus-type spherical cellulose nanoparticles. In one embodiment, Janus-type spherical cellulose nanoparticles are prepared according to the process of the present invention. [Brief description of the drawings]

[0027] The present invention will now be described, by way of example only, with reference to the following drawings. [Figure 1] FIG. 1 illustrates the modification process of spherical cellulose nanoparticles with lipophilic modifiers to produce Janus-type spherical cellulose nanoparticles. [Diagram 2] 1 is a pair of micrographs of spherical cellulose nanoparticles prepared according to Example 1. [Diagram 3] 1 is a pair of micrographs of Janus cellulose nanoparticles prepared according to Example 2: a) modified with 1-bromohexadecane for 2 hours; b) modified with 1-bromohexadecane for 12 hours. [Figure 4] FIG. 1 is a pair of photographs of a 1:1 vol. % toluene-in-water emulsion stabilized with Janus-type spherical cellulose nanoparticles at days 0 and 60, as described in Example 3. [Diagram 5] 1 is a set of photographs of 1:1 volume percent toluene-in-water emulsions stabilized with either sodium dodecylbenzenesulfonate or polyoxyethylene (10) oleyl ether, as described in Example 3: A) sodium dodecylbenzenesulfonate, day 0; b) sodium dodecylbenzenesulfonate, day 60; c) polyoxyethylene (10) oleyl ether, day 0; and d) polyoxyethylene (10) oleyl ether, day 60. [Figure 6] A pair of photographs of a 1:9 vol.% toluene-in-water emulsion stabilized with Janus-type spherical cellulose nanoparticles a) at day 0 and b) at day 30 as described in Example 4. [Figure 7] 1 is a set of photographs of 1:9 vol.% toluene-in-water emulsions stabilized with a) polyoxyethylene (10) oleyl ether, day 0, b) polyoxyethylene (10) oleyl ether, day 30, c) sodium dodecylbenzenesulfonate, day 0, and d) sodium dodecylbenzenesulfonate, day 30, as described in Example 4. [Figure 8] FIG. 13 is a graph showing the reduction in surface tension of water by the Janus-type spherical nanoparticles of the present invention prepared without stirring and for different reaction times using chloroform as a water-immiscible lipophilic solvent as described in Example 5. [Figure 9] FIG. 13 is a graph showing the reduction in surface tension of water by the Janus-type spherical nanoparticles of the present invention prepared using chloroform as a water-immiscible lipophilic solvent with stirring for different reaction times as described in Example 5. [Figure 10] FIG. 13 is a graph showing the reduction in surface tension of water by the Janus-type spherical nanoparticles of the present invention prepared without stirring and for different reaction times using toluene as a water-immiscible lipophilic solvent as described in Example 5. [Figure 11] FIG. 1 is a graph showing the reduction in surface tension of water by the Janus-type spherical nanoparticles of the present invention prepared using chloroform as a water-immiscible lipophilic solvent with stirring for different reaction times as described in Example 5. [Figure 12] 1 is a SEM micrograph of emulsion droplets stabilized with Janus-type spherical nanoparticles prepared according to Example 2. [Figure 13] FIG. 1 is a micrograph of an emulsion stabilized with Janus-type spherical nanoparticles prepared according to Example 2 (scale bar: 100 μm). [Figure 14] FIG. 14 is a set of photographs comparing the emulsifying ability of a) commercially available cellulose microparticles, b) cellulose nanocrystals, c) spherical cellulose particles, and d) the Janus-type spherical cellulose nanoparticles of the present invention. [Figure 15A] 1 is a pair of photographs showing the 1:9 toluene-in-water Pickering emulsion after 5 minutes of Example 6. From left to right are Janus spherical particles modified with 1-bromohexadecane for 2 hours, 6 hours, 12 hours, and 24 hours, spherical cellulose particles, and Brij O10. [Figure 15B] 1 is a pair of photographs showing the 1:9 toluene-in-water Pickering emulsion after 7 days of Example 6. From left to right are Janus spherical particles modified with 1-bromohexadecane for 2, 6, 12, and 24 hours, spherical cellulose particles, and Brij O10. [Figure 16A] 1 is a pair of photographs showing the 1:1 toluene-in-water Pickering emulsion after 5 minutes of Example 6. From left to right, Janus spherical particles, spherical cellulose particles, and Brij O10 modified with 1-bromohexadecane for 2, 6, 12, and 24 hours. [Figure 16B] 1 is a pair of photographs showing the 1:1 toluene-in-water Pickering emulsions after 7 days of Example 6. From left to right, Janus spherical particles, spherical cellulose particles, and Brij O10 modified with 1-bromohexadecane for 2, 6, 12, and 24 hours. [Figure 17A] FIG. 13 is a graph showing the creaming index over time for 1:9v 12hr and Brij O10 Pickering emulsions of Example 6. [Figure 17B]Photographs showing the creaming index over time for 1:9v 12h and Brij O10 Pickering emulsions of Example 6 at day 0 (top) and day 14 (bottom). [Figure 18A] FIG. 13 is a graph showing the creaming index over time for 1:1v12h and Brij O10 Pickering emulsions of Example 6. [Figure 18B] Photographs showing the creaming index over time for 1:1v12h and Brij O10 Pickering emulsions of Example 6 at day 0 (top) and day 14 (bottom). [Figure 19A] 1 is a pair of graphs showing the UV absorbance at 550 nm of the Pickering emulsion, a 1:9v emulsion, prepared in Example 6. [Figure 19B] 1 is a pair of graphs showing the UV absorbance at 550 nm of the Pickering emulsion, a 1:1v emulsion, prepared in Example 6. [Figure 20] Photographs of a series of solutions showing the amount of foam generated when a surfactant-containing solution is introduced from a reservoir at a specific height into a column containing the same solution according to the Ross-Miles method (ASTM D1173). A = unmodified spherical cellulose nanoparticles, B = Janus-type spherical cellulose particles modified with 1-bromohexadecane for 12 hours, C = C12-C15 pareth-7, D = lauryl glucoside, E = sodium lauryl sulfate. Each emulsion contained 0.1 wt.% surfactant in 250 mL of deionized water at 21 °C and was measured after 1 min. [Figure 21] 1 is a graph showing the reduction in surface tension of water in the presence of spherical cellulose nanoparticles uniformly modified with the lipophilic modifier bromohexadecane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 5.1 Definitions and Abbreviations As used herein, the term "comprise" means "comprise at least partially." When interpreting each statement in this specification that includes the term "comprise," there may be other features present, or features preceded by that term. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0029] The term "about" as used herein refers to a reasonable amount of deviation of the term modified so as not to significantly change the final result. For example, when applied to a value, the term should be interpreted as including a deviation of + / - 10% of that value.

[0030] The term "emulsion" as used herein refers to a combination of at least two liquids, one of which exists in the form of droplets in the other liquid. IUPAC, Unabridged Dictionary of Chemical Terminology: IUPAC Recommended Second Edition, edited by A.D. McNaught and A. Wilkinson, Oxford, Blackwell (1997).

[0031] The term "surfactant" as used herein refers to a molecule or particle that contains two moieties of different polarity, one generally lipophilic (soluble or dispersible in an oil phase) and the other hydrophilic (soluble or dispersible in water). Surfactants are characterized by their HLB (hydrophilic-lipophilic balance) value. The term "HLB" is well known in the art and is described, for example, in "The HLB System": A Time-Saving Guide to Emulsifier Selection (ICI Americas Inc., 1984). The term "wettability" is commonly used to describe the hydrophilic / lipophilic nature of particles used to stabilize Pickering emulsions. To maintain consistency, the term "HLB" is used herein to describe the surfactant properties of both molecules and particles.

[0032] As used herein, the term "volume particle diameter" refers to the diameter of a sphere having the same volume as the particle being measured. The "volume average particle size" of a particulate material is the average value of the volume particle sizes of the particles being measured.

[0033] The term "sphericity" as used herein is a measure of how closely a particle resembles the shape of a sphere. The sphericity of a particle refers to the ratio of the surface area of ​​the particle to the surface area of ​​a sphere with the same volume as the particle. A perfect sphere has a sphericity of 1. The sphericity of a particle can be evaluated by observing the projected area of ​​the particle in an electron microscope photograph and comparing the ratio of the perimeter of a circle with the same area as the projected area to the perimeter of the particle actually seen in the electron microscope photograph. In this method, each particle is observed only in a plane, but the variation in the observation direction can be taken into account by using the average value of a large number of particles.

[0034] As used herein, the term "spherical" refers to particles with a sphericity of 0.5 to 1.0.

[0035] The term "lipophilic" as used herein refers to the ability of a substance to dissolve in other lipophilic substances, such as fats, oils and non-polar compounds such as hexane.

[0036] As used herein, the term "cellulose nanocrystals" refers to crystalline regions of cellulose microfibers having lengths of about 160-200 nm and cross sections of about 7-25 nm.

[0037] As used herein, the term "cellulose nanoparticles" refers to nanoparticles produced from a cellulose source, such as microcellulose. Cellulose nanoparticles contain at least a cellulose core, although they may be surface modified with other agents.

[0038] Reference to a numerical range disclosed herein (e.g., 1-10) includes all rational numbers within this range (e.g., 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10) and any rational range within this range (e.g., 2-8, 1.5-5.5, and 3.1-4.7), such that all subranges of every range explicitly disclosed herein are expressly disclosed herein. These are merely examples of specific intent, and all possible combinations of numerical values ​​between the lowest and highest values ​​recited should be considered as being expressly set forth herein in a similar manner.

[0039] Whenever a range is given herein, e.g., a temperature range, a time range, or a component range, all intermediate ranges and subranges, as well as all single values ​​contained within the given range, are intended to be included in the disclosure. In the present disclosure and claims, "and / or" denotes additional or alternative. Also, the use of a term in the singular form includes the plural.

[0040] 5.1 Janus-type spherical cellulose nanoparticles of the present invention The present invention generally relates to a process for increasing the lipophilicity of one face of spherical cellulose nanoparticles to improve their surfactant properties.

[0041] This process exploits the affinity of cellulose nanoparticles for the oil / water interface to generate novel Janus-type spherical cellulose nanoparticles. A diagram of one embodiment of the process is shown in Figure 1.

[0042] In one aspect, the present invention provides a process for the preparation of Janus-type spherical cellulose nanoparticles, comprising the steps of: (a) preparing an alkaline suspension of spherical cellulose nanoparticles in water; (b) forming an emulsion comprising the spherical cellulose nanoparticles, water, and a water-immiscible lipophilic solvent, (i) the water constitutes a continuous phase; (ii) the lipophilic solvent constitutes the dispersed phase and contains a lipophilic modifier; (iii) the spherical cellulose nanoparticles are localized at the interface between the continuous phase and the dispersed phase; (c) reacting the portion of the spherical cellulose nanoparticles exposed to the lipophilic modifier at the interface between the continuous phase and the dispersed phase with the lipophilic modifier to produce Janus-type spherical cellulose nanoparticles; (d) isolating the Janus-type spherical cellulose nanoparticles from the emulsion.

[0043] The process of the present invention modifies spherical cellulose nanoparticles to improve their surfactant properties. Conventional cellulose nanoparticles are nanocrystals that have a high aspect ratio and are formed as rods or fibrils. Cellulose nanocrystals are generally prepared from microcellulose (microcrystalline cellulose).

[0044] Spherical cellulose nanoparticles (or nanospheres) have a large surface area and improved surface activity, but are difficult to produce. This is because the microcellulose fibrils are highly crystalline and difficult to break down into nanoscale spherical cellulose. However, numerous preparation processes have been published. Examples include U.S. Pat. No. 8,629,187 and references therein.

[0045] Microcellulose is a commercially available free-flowing powder that contains refined wood pulp. Typically, microcellulose particles have a volume-average particle size of about 18-22 μm.

[0046] Methods to convert microcellulose into spherical cellulose particles often use strong bases such as NaOH or strong acids such as HCl or H2SO4, sometimes combined with sonication to disrupt the fibrils and reduce crystallinity (see, for example, (Meyabadi, Dadashian, Sadeghi, & Asl, 2014) (Li, et al., 2020)). Alternative methods include enzymatic degradation using cellulases and xylanases to break down the polymer (Chen, Deng, Shen, & Jia, 2018).

[0047] The process of the present invention can use spherical cellulose nanoparticles prepared by any known process. As shown in Example 1, the inventors used a modification of the method described in (Zhang, Elder, Pu, & Ragauskas, 2007) to prepare spherical cellulose nanoparticles for modification. Figure 2 shows a micrograph of the prepared nanoparticles.

[0048] In one embodiment, spherical cellulose nanoparticles are prepared from microcellulose derived from kraft pulp by the same procedure as in Example 1, but with the NaOH hydrolysis and acid hydrolysis times optimized.

[0049] In one embodiment, the spherical cellulose nanoparticles have a volume average particle size of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, and more preferably about 20 to about 200 nm.

[0050] In one embodiment, the average sphericity of the spherical cellulose nanoparticles is greater than about 50, 60, 70, 80, 90, 95% or 98%, preferably greater than about 75%, more preferably greater than about 90%.

[0051] In step (a) of the process of the present invention, an alkaline suspension of spherical cellulose nanoparticles in water is formed.

[0052] In one embodiment, an alkaline suspension of spherical cellulose nanoparticles is prepared by adding a strong base to spherical cellulose nanoparticles suspended in water, in one embodiment, the water is deionized, distilled or Milli-Q water.

[0053] In one embodiment, the alkaline suspension comprises from about 0.01 to about 10% by weight of spherical cellulose nanoparticles.

[0054] In one embodiment, the strong base is selected from the group consisting of NaOH, KOH and LiOH, preferably NaOH. In one embodiment, the concentration of the strong base is at least about 2M, preferably about 2-5M.

[0055] In one embodiment, the strong base is added to the suspension of spherical cellulose nanoparticles in a weight ratio of strong base:spherical cellulose nanoparticles of about 1:1 to about 2:1.

[0056] In one embodiment, a salt is added to the alkaline suspension to increase its ionic strength. Any salt that does not interfere with the reaction of step (c) may be used. Typically, the amount of salt added will result in a solution of 0-100 mM salt.

[0057] In one embodiment, the salt is selected from the group consisting of NaCl, KCl, MgCl2, NaNO3, etc. In one embodiment, the salt is NaCl.

[0058] In one embodiment, the salt is added to the alkaline suspension about 5 to about 60 minutes, preferably about 10 to 15 minutes, after addition of the strong base.

[0059] In one embodiment, the alkaline suspension is mixed until the particles are uniformly dispersed.In one embodiment, the alkaline suspension of spherical cellulose nanoparticles is homogenized by ultrasonication.

[0060] In step (b), the alkaline suspension is mixed with a water-immiscible lipophilic solvent to form an emulsion in which water constitutes the continuous phase and the lipophilic solvent constitutes the dispersed phase.

[0061] The water immiscible lipophilic solvent may be a solvent or mixture of solvents having high lipophilicity with water, including but not limited to toluene, chloroform, hexane, pentane, benzene, carbon tetrachloride, heptane dichloromethane, ethyl acetate, etc. In one embodiment, the water immiscible solvent comprises toluene.

[0062] In one embodiment, the resulting emulsion comprises about 0.1-10% by volume of the water-immiscible lipophilic solvent relative to the water.

[0063] The water-immiscible lipophilic solvent comprises a lipophilic modifier, which is a reagent suitable for modifying the lipophilicity of the exposed surface of the spherical cellulose nanoparticles, i.e., the part of the surface that is in contact with the dispersed phase. Such lipophilic modifiers react with the hydroxyl groups present on the surface of the spherical cellulose nanoparticles, converting them into more lipophilic groups, such as ester or ether groups.

[0064] In one embodiment, the lipophilic modifier comprises an organic compound comprising at least one (C1-C20) alkyl group and a leaving group.

[0065] In one embodiment, the lipophilic modifier comprises an ester of at least one (C1-C20) carboxylic acid and an alcohol (eg, glycerin).

[0066] In one embodiment, the lipophilic modifier reacts with hydroxyl groups on the surface of spherical cellulose nanoparticles to generate (C1-C20) ether groups. In one embodiment, the lipophilic modifier reacts with hydroxyl groups on the surface of spherical cellulose nanoparticles to generate (C1-C20) ester groups.

[0067] The lipophilic modifier may be added to the water-immiscible lipophilic solvent prior to emulsification or may itself constitute the water-immiscible lipophilic solvent where this is economical and / or practical.

[0068] Thus, in one embodiment, the water-immiscible lipophilic solvent is also a lipophilicity modifier.

[0069] For example, in one embodiment, the water-immiscible lipophilic solvent and lipophilic modifier are fatty acid-containing lipids or similar reagents, such as triacylglycerides, which contain ester functional groups. The triacylglycerides react with the hydroxyl groups on the surface of the spherical cellulose nanoparticles to produce ester groups, a process known as transesterification.

[0070] In one embodiment, the water-immiscible lipophilic solvent is a vegetable oil. The vegetable oil contains a high concentration of triacylglycerides. When using vegetable oil as the lipophilic solvent, the triacylglycerides contain a lipophilic modifier.

[0071] In one embodiment, the vegetable oil is selected from the group consisting of coconut oil, hemp oil, rapeseed oil, sunflower oil, palm oil.

[0072] In one embodiment, a lipophilic modifier is added to a water-immiscible lipophilic solvent prior to emulsification. Lipophilic modifiers are typically added to another water-immiscible lipophilic solvent when it is too expensive or impractical to also use it as a solvent.

[0073] In one embodiment, the lipophilicity modifier comprises an alkyl halide or pseudohalide, including, but not limited to, alkyl bromides, alkyl chlorides, alkyl iodides, alkyl mesylates, and alkyl tosylates.

[0074] Preferably, it comprises (C1-C20)-bromoalkanes, (C12-C16)-bromoalkanes. In one embodiment, the lipophilic modifier is selected from 1-bromooctane, 1-bromododecane, and 1-bromohexadecane.

[0075] In one embodiment, the lipophilic modifier is a (C1-C20)-carboxylic acid, preferably a (C12-C16)-carboxylic acid.

[0076] In one embodiment, the lipophilic modifier is a (C1-C20)-acid chloride, preferably a (C12-C16)-acid chloride.

[0077] In one embodiment, the lipophilic modifier is a (C1-C20)-ester (e.g., a triglyceride), preferably a (C12-C16-ester.

[0078] In one embodiment, the lipophilic modifier is added to the water-immiscible lipophilic solvent in an amount equivalent to about 0.5 to about 10 moles per glucose unit present in the spherical cellulose nanoparticles. The number of glucose units present can be calculated by dividing the mass of the material by the molecular weight of monomeric glucose. The amount of lipophilic modifier added depends on the degree of modification required and the number of lipophilic groups present on each lipophilic modifier molecule.

[0079] In one embodiment, the molar ratio of lipophilic modifier to water-immiscible lipophilic solvent is from about 1:20 to about 1:1, preferably from about 1:10 to about 1:2, and more preferably from about 1:4 to about 1:5.

[0080] When the lipophilic modifier also constitutes a water-immiscible lipophilic solvent, such as a triacylglyceride, the lipophilic groups are present in excess relative to the spherical cellulose nanoparticles. Similarly, when the water-immiscible lipophilic solvent is a vegetable oil, the triacylglyceride lipophilic modifier is also in excess.

[0081] In many cases, lipophilic modifiers readily react with the hydroxyl groups of cellulose, but the reaction may be accelerated by the use of a reaction promoter.

[0082] In one embodiment, the water immiscible oleophilic solvent comprises a reaction promoter such as an acid (HCl, H2SO4, phosphoric acid), a base (NaOH, KOH, carbonates, alkoxides), a heterogeneous catalyst (alkaline earth metal oxides such as MgO, CaO, SrO), a modified zeolite, anionic clay, an ion exchange resin, a solid catalyst combination (Li / CaO, KF / Al2O3), or a metal catalyst (platinum oxide, nickel oxide).

[0083] Emulsions can be formed by any means known in the art, including sonication, high speed mechanical stirring, use of high pressure, forcing air into the solution, and the like.

[0084] In one embodiment, the emulsion comprises a water-immiscible lipophilic solvent:alkaline suspension of spherical cellulose nanoparticles in a weight ratio of about 1:50 to about 1:2, preferably about 1:20 to about 1:5, more preferably about 1:15 to about 1:8.

[0085] In one embodiment, spherical cellulose nanoparticles, water, and a water-immiscible lipophilic solvent are sonicated to form an emulsion.

[0086] After emulsification, the spherical cellulose nanoparticles are localized at the interface between the continuous (water) and dispersed (water-immiscible lipophilic solvent) phases of the emulsion. As will be understood by those skilled in the art, localization at the interface means that the nanoparticles are found primarily at the interface, with relatively few nanoparticles present in either the continuous or dispersed phase.

[0087] Localization at the water-oil interface can be observed by adding a fluorescent dye such as calcofluor white, a dye that specifically binds to cellulose. Irradiation at the absorption maximum induces the emission of fluorescence that is observed at the water-oil interface. After emulsification, fluorescence emission is observed only at the water-oil interface, indicating that the cellulose particles are mainly (or exclusively) located at the water-oil interface.

[0088] In step (c), the portion of each spherical cellulose nanoparticle exposed to the lipophilic modifier at the interface between the continuous phase and the dispersed phase reacts with the lipophilic modifier to produce Janus-type spherical cellulose nanoparticles. In other words, the hydroxyl groups of the spherical cellulose nanoparticles in contact with the water-immiscible lipophilic solvent react with the lipophilic modifier present in the solvent to selectively modify one side of the nanoparticle.

[0089] In one embodiment, the emulsion is heated to initiate the reaction, hi one embodiment, the emulsion is heated to a temperature of about 30 to about 70°C.

[0090] Those skilled in the art will appreciate that the longer the reaction time, the greater the portion of each spherical cellulose nanoparticle that is modified to be more lipophilic. As the reaction time increases, the lipophilicity of the modified surface relative to the unmodified surface increases, lowering the HLB of the particles.

[0091] In one embodiment, the emulsion is heated until the functionalized moieties comprise on average about 30 to about 70%, preferably about 40 to about 60%, more preferably about 45 to about 55%, and most preferably about 50% of the surface area of ​​the nanoparticles. The functionalized area of ​​spherical nanoparticles can be assessed by measuring the surface tension of water containing such particles.

[0092] Spherical cellulose particles that do not have two faces with different properties do not change the surface tension of water containing such particles. The observation of a decrease in the surface tension of water containing the Janus-type spherical cellulose particles of the present invention confirmed their amphiphilicity, that is, the presence of one lipophilic face and one hydrophilic face (Figures 8 to 11).

[0093] Cellulose spherical particles that do not have two distinct faces do not have this property: for example, a spherical particle that is uniformly modified with a lipophilic modifier over its entire surface does not create two faces and does not significantly reduce the surface tension of water.

[0094] Unmodified spherical cellulose nanoparticles with a uniform hydrophilic surface do not reduce the surface tension of water when the nanoparticles are added to water. The surface tension of water remains at 72 mN / m in the presence of unmodified spherical cellulose nanoparticles, but can be reduced to 58 mN / m in the presence of Janus-type spherical cellulose particles modified with 1-bromohexadecane (Figure 9).

[0095] In one embodiment, the emulsion is heated at about 50° C. for about 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 20, 25, or 30 to about 36 hours. In one embodiment, the emulsion is heated at about 50° C. for about 2 to about 12 hours. In one embodiment, the emulsion is heated at about 50° C. for about 12 to about 36 hours.

[0096] In one embodiment, the lipophilic modifying agent is an alkyl bromide or a triacylglyceride and the emulsion is heated at 50° C. for about 12 hours.

[0097] After reaction, the resulting Janus-type spherical cellulose nanoparticles are separated from the emulsion, which can be accomplished using standard techniques, including but not limited to centrifugation, ultrafiltration, and electrostatic precipitation.

[0098] In one embodiment, the Janus-type spherical cellulose nanoparticles are separated from the emulsion by centrifugation.

[0099] The Janus spherical cellulose nanoparticles are then optionally washed to remove salts, in one embodiment, the Janus spherical cellulose nanoparticles are washed with water followed by ethanol.

[0100] The washed Janus-type spherical cellulose nanoparticles may optionally be resuspended in water and treated with acid to lower the pH of the suspension before being isolated again.

[0101] In one embodiment, the Janus-type spherical cellulose nanoparticles are dried to obtain a powder. Drying can be achieved by any known technique, including but not limited to evaporation at room temperature, drying under reduced pressure, or freeze-drying. In one aspect, the present invention provides Janus-type spherical cellulose nanoparticles.

[0102] In another aspect, the present invention provides Janus-type spherical cellulose nanoparticles. In one embodiment, the Janus-type spherical cellulose nanoparticles are prepared according to the process of the present invention.

[0103] In Example 2, a method for preparing Janus-type spherical cellulose nanoparticles by reacting a lipophilic modifier 1-bromohexadecane in a toluene-in-water emulsion is described. FIG. 3 shows a micrograph of the Janus-type spherical cellulose nanoparticles formed in Example 2.

[0104] The Janus-type spherical cellulose nanoparticles of the present invention are functionalized such that one surface of each sphere is more lipophilic than the remaining surface of the sphere.

[0105] In one embodiment, the surface of the Janus-type spherical cellulose nanoparticles is partially functionalized with (C1-C20) ether groups. In one embodiment, the surface of the Janus-type spherical cellulose nanoparticles is partially functionalized with (C1-C20) ester groups.

[0106] In one embodiment, the functionalized moieties comprise on average about 30 to about 70%, preferably about 40 to about 60%, more preferably about 45 to about 55%, and most preferably about 50% of the surface area of ​​the spherical cellulose nanoparticles.

[0107] In one embodiment, the Janus type spherical cellulose nanoparticles have a volume average particle size of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, and more preferably about 20 to about 200 nm.

[0108] The Janus-type spherical cellulose nanoparticles of the present invention are surfactants that can be used in many applications, including but not limited to emulsifiers for food and beverages, coatings, plastics, cosmetics and pharmaceuticals; foaming and defoaming agents for manufacturing, mining and mineral processing; household, personal and industrial cleaning agents; and wetting agents for agricultural and industrial applications.In another embodiment, the present invention provides a surfactant composition containing the Janus-type spherical cellulose nanoparticles.In one embodiment, the surfactant composition is a Pickering emulsion.

[0109] In one embodiment, the present invention provides a Pickering emulsion comprising Janus-type spherical cellulose nanoparticles.

[0110] To prepare an oil-in-water Pickering emulsion, Janus-type spherical cellulose nanoparticles are dispersed in water by mechanical stirring in the dispersion medium until a homogeneous cellulose nanoparticle / water dispersion is seen. Then, a certain amount of oil (up to 50 vol.% ol) is added to the Janus-type spherical cellulose water dispersion and vigorously shaken or stirred in the dispersion medium to obtain an oil-in-water emulsion.

[0111] In one embodiment, the Pickering emulsion comprises about 0.01-10% by weight, preferably 0.05-5% by weight, more preferably 0.1-2% by weight of Janus-type spherical cellulose nanoparticles.

[0112] In one embodiment, the Pickering emulsion is an oil-in-water emulsion containing about 1 to about 50% by volume of oil, preferably up to about 20% by volume of oil. In one embodiment, the Pickering emulsion does not contain any emulsifiers other than the Janus-type spherical cellulose nanoparticles.

[0113] Example 3 describes the preparation of oil-in-water Pickering emulsions containing Janus-type spherical cellulose nanoparticles in 1:1 toluene / water. The Janus-type spherical cellulose nanoparticles of the present invention show superior emulsification properties to comparable surfactants sodium dodecylbenzenesulfonate and polyoxyethylene (10) oleyl ether (see Figures 5 and 6).

[0114] Similar oil-in-water Pickering emulsions prepared using several water-immiscible liquids were found to be stable for over six months without the need for additives to improve emulsification. Thus, the described Janus-type spherical cellulose nanoparticles of the present invention are excellent oil-in-water emulsifiers.

[0115] The HLB of the Janus-type spherical cellulose nanoparticles of the present invention can be controlled by changing the reaction conditions.

[0116] As explained in Example 5, adding long carbon chains to the surface of cellulose nanoparticles increases the lipophilicity of the surface more than adding short carbon chains (see Figures 8 to 11).

[0117] As also explained in Examples 5 and 6, a longer reaction time promotes the substitution of a proportion of hydroxyl groups with lipophilic chains, increasing the affinity of the spherical cellulose nanoparticles for lipophilic fluids. On the other hand, a shorter reaction time modifies the surface area of ​​the nanoparticles to less than 50%. These spherical cellulose nanoparticles retain more hydrophilicity and can better interact with hydrophilic fluids (see Figures 8-11).

[0118] Longer reaction times and longer carbon chain modifications are conditions that lower the HLB and favor the production of spherical cellulose nanoparticles with the ability to stabilize oil-in-water emulsions with oil concentrations above 20% by volume. Shorter reaction times and shorter carbon chain substitutions maintain most of the hydrophilicity of the particles and favor the production of cellulose nanoparticles with the ability to stabilize oil-in-water emulsions with oil concentrations below 20% by volume.

[0119] The Janus-type spherical cellulose nanoparticles of the present invention having a low HLB value can be used to stabilize water-in-oil emulsions.

[0120] In one embodiment, the Pickering emulsion is a water-in-oil emulsion containing 1-50% water by volume.

[0121] The Janus-type spherical cellulose nanoparticles of the present invention also have the advantage of stabilizing emulsions without producing foam. This is a highly desirable property, as foaming is a problem in many surfactant applications. Foaming artificially increases batch size and can lead to product loss, damage to equipment such as pumps, factory downtime, and environmental pollution. For example, in cosmetic formulations, surfactants are added to act as emulsifiers to ensure that oil-based ingredients mix with water. Foam generated during mixing can clog pipes and valves as well as reduce container capacity and complicate the transfer of materials from one container to another. Foam can also remain in the finished product, causing haze and voids, compromising the integrity of the product.

[0122] In another example, emulsifiers, dispersants, and wetting agents are typically added to paint and coating formulations to ensure that all ingredients in the paint are uniformly mixed. The addition of surfactants can create foam during preparation, packaging, or application of the paint system. Foaming during preparation and packaging can clog equipment and complicate container transfer. Foaming during application can leave defects on the surface, resulting in poor appearance and reducing the protective function of the paint or coating. EXAMPLES

[0123] Example 1: General method for producing highly spherical cellulose particles Microcellulose powder containing particles with an average diameter of 20 μm was first dispersed in a 5 M NaOH solution by mechanical stirring (10 mL NaOH per gram of cellulose). After the particles were dispersed, they were heated at 70° C. and stirred for 5 hours. The cellulose was isolated by cooling to room temperature and filtering through a paper filter. The cellulose was washed with deionized water and dried under reduced pressure at room temperature.

[0124] The dried cellulose was suspended in dimethyl sulfoxide (10 mL dimethyl sulfoxide per 1 g cellulose) and sonicated for 2 min. The suspension was heated to 60°C and allowed to stand for 4 h. The dimethyl sulfoxide was removed by filtration through filter paper. After washing with deionized water, the cellulose was dried under reduced pressure.

[0125] Using acid hydrolysis, microcellulose (~20μm) was converted to nanocellulose (<1μm). To achieve this, dry cellulose was suspended in a 1:2 36N sulfuric acid / water solution with magnetic stirring. The cellulose was acid hydrolyzed at 70°C for 1 hour with stirring. Aliquots of the suspension were taken every hour and analyzed by dynamic light scattering to monitor the size of the particles. The reaction was stopped when an average particle size of 1um was reached. A similar cellulose suspension was further subjected to acid hydrolysis at 60°C, sonication, mechanical stirring and 4 hours. An aliquot was taken to check the size of the cellulose particles.

[0126] Once the desired size was reached, the hydrolysis was stopped by cooling the suspension to room temperature. The particles were separated by centrifugation at 12000 rpm for 10 min. The solid was collected and washed with deionized water. A 5 M NaOH solution was added to the suspension until the pH was about 7. It was washed three more times with deionized water to remove the salts formed during neutralization. The water was removed by freeze-drying. At the end of this stage, spherical cellulose particles with a volume average diameter of 20-1000 nm were produced (depending on when the hydrolysis was stopped).

[0127] After 2 hours of acid hydrolysis, the volume average particle size of the spherical particles was about 500-1000 nm. After 4 hours of acid hydrolysis, the volume average particle size of the spherical particles was about 50-200 nm.

[0128] The spherical cellulose nanoparticles prepared in Example 1 are shown in FIG. Example 2: Preparation of Janus-type spherical nanoparticles of the present invention

[0129] Spherical cellulose nanoparticles (average diameter 50-200 nm) prepared according to Example 1 were modified by etherification reaction with 1-bromohexadecane. To a 1 wt% suspension of spherical cellulose nanoparticles, sodium hydroxide solution (5 M) was added while stirring with a magnetic stirrer. After 30 min, sodium chloride (1 M) was added and the mixture was homogenized and dispersed by sonication. 1-Bromohexadecane (3 equivalents per glucose unit mole) and toluene (volume >99%) were mixed in a ratio of 1:4. To the stable alkaline cellulose suspension, a bromoalkene-toluene mixture was added in a ratio of 1:9 by volume of cellulose suspension to mixture with sonication. After 10 min of sonication, a 1-bromohexadecane-toluene in water emulsion was formed. The emulsion was then heated to 50 °C for 12 h under slow magnetic stirring. The reaction was quenched with cold water. The resulting Janus-type spherical cellulose nanoparticles were separated from the emulsion droplets by high-speed centrifugation (15000 rpm) for 30 min. The cellulose nanoparticles were washed three times with water and three times with ethanol. They were redispersed in water using ultrasonication, and the pH of the suspension was lowered to pH 7 by adding 1 M hydrochloric acid. The suspension was washed three times with water and the particles collected by centrifugation. The Janus-type spherical cellulose nanoparticles were vacuum dried overnight.

[0130] The Janus-type spherical cellulose nanoparticles prepared in Example 2 are shown in FIG. Example 3: Pickering emulsion containing Janus-type spherical nanoparticles of the present invention

[0131] Janus-type spherical cellulose nanoparticles prepared in Example 2 were redispersed in water by mechanical stirring in a sonication bath. An oil-in-water emulsion was prepared using 50% water by volume, 50% toluene by volume, and 0.1% by weight of modified cellulose particles. The mixture was stirred until an emulsion was formed. The emulsion was sonicated to obtain a stable emulsion. Photographs of the emulsion were taken on days 0 and 60, as shown in Figure 4.

[0132] As shown in Figure 4, the emulsions on day 0 are very stable and homogeneous. Even on day 60, the emulsions were still visible in the vials. To compare the stabilizing ability of 1:1 toluene in water emulsions with the spherical cellulose nanoparticles of the present invention, emulsions were prepared using similar conditions with sodium dodecylbenzenesulfonate and polyoxyethylene (10) oleyl ether. Photographs of these emulsions were taken on days 0 and 60, as shown in Figure 5.

[0133] As can be seen from Figures 4 and 5, the Janus-type spherical cellulose nanoparticles of the present invention show better emulsification than the surfactants sodium dodecylbenzenesulfonate and polyoxyethylene (10) oleyl ether. The toluene-in-water emulsion with sodium dodecylbenzenesulfonate (immediately after formation) is not homogenous, with two phases (oil and water) still present and a significant amount of foam formed on top of the liquid. After 60 days there is no evidence of emulsion and the two phases have completely separated. In the second example, the toluene in water emulsion with polyoxyethylene (10) oleyl ether shows similar emulsification properties to the Janus-type spherical cellulose nanoparticles of the present invention on day 0. However, the stability after 60 days shows that the emulsion using polyoxyethylene (10) oleyl ether is not stable because there is evidence of creaming and phase separation. Example 4: Further Pickering emulsions containing Janus-type spherical cellulose nanoparticles of the invention

[0134] Janus-type spherical nanoparticles of the present invention were prepared according to Example 2, except that 1-bromohexadecane was replaced with short-chain 1-bromododecane. The short-chain modified Janus-type spherical cellulose nanoparticles were redispersed in water by mechanical stirring. An oil-in-water emulsion was prepared with a concentration of 90% by volume of Janus-type spherical cellulose nanoparticle suspension (containing 0.1% by weight of dry Janus-type spherical cellulose nanoparticles) and 10% by volume of toluene. The mixture was stirred until an emulsion was visibly formed. The emulsion was sonicated to form a stable emulsion. Photographs of the emulsion were taken on days 0 and 30, as shown in FIG. 6.

[0135] As can be seen in Figure 6, the emulsion stability and homogeneity were high on day 0. Even after 30 days, the emulsion was still visible in the vial. To compare the performance of the Janus-type spherical cellulose nanoparticles of the present invention in stabilizing a 1:9 toluene-in-water emulsion, emulsions were prepared under similar conditions with sodium dodecylbenzenesulfonate and polyoxyethylene (10) oleyl ether. Photographs of the emulsion were taken on days 0 and 30, as shown in Figure 7.

[0136] As can be seen from FIG. 7, the emulsion formed with sodium dodecylbenzenesulfonate is not very stable, since some creaming is observed immediately after emulsification. In contrast, the emulsion obtained with polyoxyethylene (10) oleyl ether is homogeneous and stable. Therefore, it can be said that the emulsion prepared in this example using polyoxyethylene (10) oleyl ether and Janus-type spherical cellulose nanoparticles is similarly stable and homogeneous after emulsification. However, on top of the emulsion stabilized with both polyoxyethylene (10) oleyl ether and sodium dodecylbenzenesulfonate, there is a natural phenomenon where the emulsion becomes unstable and phase separation is prone to occur. On the other hand, the oil emulsion droplets obtained with Janus-type spherical cellulose nanoparticles were still dispersed throughout the aqueous phase, and little creaming was observed. This suggests that the Janus-type spherical nanoparticles modified with 1-bromododecane have better performance than polyoxyethylene (10) and sodium dodecylbenzenesulfonate in stabilizing toluene-in-water emulsions with an oil concentration of 10 vol.%. Example 5: Amphiphilicity of the Janus-type spherical nanoparticles of the present invention

[0137] To investigate how the amphiphilicity of the surface of Janus-type spherical cellulose nanoparticles is controlled by the reaction time or the length of the introduced hydrophobic chains, nanoparticles were prepared according to the process of Example 2. Three sets of Janus-type spherical cellulose nanoparticles were prepared by etherification modification with 1-bromohexadecane, 1-bromododecane, and 1-bromooctane, respectively. The reduction in the surface tension of water is one of the parameters used to estimate the amphiphilicity of a molecule. Figures 8 to 11 show an overview of the reduction in surface tension over time measured by the pendant drop method and using a suspension of 1 wt% Janus-type spherical cellulose nanoparticles in water. They were prepared with the following variations:

[0138] -Chloroform in water emulsion -Chloroform in water emulsion with magnetic stirring -Toluene-water emulsion without stirring -Toluene in water emulsion with magnetic stirring compared to unmodified spherical cellulose nanoparticles. The results in Figures 8 to 11 show that as the reaction time increases, the surface tension decreases until it reaches a plateau. After this point, the surface tension tends to stabilize or increase (see Figure 8). This phenomenon can be explained by the fact that with the modification of the spherical cellulose nanoparticles, a point is reached where the particles become more lipophilic, losing some of their amphiphilicity and increasing the surface tension. When using a toluene-in-water emulsion with magnetic stirring, the highest surface tension reduction observed at a reaction time of 12 hours is 58 mN / m. This value is not as low as the values ​​below 40 mN / m obtained with other surfactants.

[0139] In addition, the water-immiscible solvent used for emulsification prior to the surface modification step was determined to slightly increase or decrease the reaction rate, as determined by the different surface tension values ​​obtained when using chloroform or toluene as the water-immiscible lipophilic solvent. Example 6: Effect of reaction time on Pickering emulsions containing Janus-type spherical nanoparticles of the present invention

[0140] Janus-type spherical nanoparticles of the present invention were prepared according to the process described in Example 2, with different reaction times (2, 6, 12 and 24 hours). The resulting particles were used to prepare a Janus-type spherical cellulose nanoparticle suspension (containing 0.5% by weight of dry Janus-type spherical cellulose nanoparticles) at a concentration of 90% by volume and an oil-in-water Pickering emulsion of 10% by volume of toluene (1:9v). The process used is described in Example 3.

[0141] Similar 1:9v emulsions were prepared using 0.5 wt % of a control surfactant (Brij O10-polyoxyethylene (10) oleyl ether-9004-98-2) and unmodified spherical cellulose nanoparticles (SCN).

[0142] The Pickering emulsions were photographed 5 minutes and 7 days after formation, and the results are shown in Table 15.

[0143] A second set of Pickering emulsions was prepared containing 50% volume of Janus-type spherical cellulose nanoparticle suspension (containing 0.5% weight of dry Janus-type spherical cellulose nanoparticles) and 50% volume of toluene (1:1v). Similar 1:1v emulsions were prepared using 0.5 wt% of a control surfactant (Brij O10-polyoxyethylene (10) oleyl ether-9004-98-2) and unmodified spherical cellulose nanoparticles (SCN).

[0144] The Pickering emulsions were photographed 5 minutes and 7 days after formation, and the results are shown in Figure 16.

[0145] The stability of selected emulsions (1:9v 12h vs Brij O10, and 1:1v 12h vs Brij O10) was determined by measuring the creaming index, which involves determining the ratio of the cream layer height to the total emulsion layer height. The creaming index is a physical assessment of the stability of an emulsion, with values ​​closer to zero indicating greater stability.

[0146] The results are shown in Figures 17 and 18. In both cases, Pickering emulsions containing Janus-type spherical cellulose nanoparticles had lower creaming indexes than the control surfactant (Brij O10).

[0147] The stability of all Pickering emulsions was also evaluated by measuring turbidity as measured by UV absorbance (550 nm). The results are shown in Figure 19 and show that Pickering emulsions containing Janus-type spherical cellulose nanoparticles retain turbidity much longer than Pickering emulsions prepared using unmodified spherical cellulose nanoparticles (SCN). Pickering emulsions containing Janus-type spherical cellulose nanoparticles reacted for 12 and 24 hours have turbidity comparable to that of the surfactant control, Brij O10. Example 7: Foaming properties of Janus-type spherical cellulose nanoparticles in stabilizing Pickering emulsions

[0148] The foaming properties of Janus-type spherical cellulose nanoparticles (prepared according to Example 2) were measured by introducing a surfactant-containing solution in a reservoir from a specific height into a column containing the same solution according to the Ross-Miles method ASTM D1173-07 (reapproved in 2015). A comparison of the standard test method for the foaming properties of surfactants and some commercially available surfactants is shown in Table 1. (J. Ross, 1941)

[0149] [Table 1]

[0150] Janus cellulose particles were shown to not stabilize the shape at all, exhibiting a foam height of 0 cm, whereas surfactants such as C12-C15 Pareth-7, lauryl glucoside and sodium lauryl sulfate exhibited foam heights of 8-11 cm (see Figure 20I). Example 8: Cleaning action of Janus-type spherical cellulose nanoparticles of the present invention

[0151] Pre-stained swatches (obtained from Lubrizol Life Science) were mixed with surfactant (0.083%), placed in an 8-pot James Heal Gyrowash, and mixed using stainless steel ball bearings (to simulate mechanical mixing) for 40 minutes at 30° C. The reflectance of the stains before and after washing was measured with a Datacolor500 spectrophotometer.

[0152] As shown in Table 2, the Janus-type spherical cellulose nanoparticles of the present invention were shown to be able to clearly remove makeup stains, equivalent to commercially available detergents C12-C15 pareth 7, lauryl glucoside, and sodium coco sulfate.

[0153] [Table 2] Example 9: Comparison of surface activity

[0154] To characterize the Janus-type spherical cellulose particles of the present invention, the surface activity was directly compared with homogeneously modified particles. First, unmodified spherical cellulose nanoparticles were homogeneously (without creating two faces) modified by initial treatment with 7 wt% NaOH solution at 60 ° C for 1 h. The samples were then separated, washed, and dried. These activated spherical cellulose particles were dispersed in DMF and sonicated. The lipophilic modifier bromohexadecane was then added dropwise with stirring at 60 ° C for set times (1, 4, 6, 12 h), washed, and separated. The surface activity of these homogeneously modified cellulose particles was measured by the pendant drop method to determine their ability to reduce the surface tension of water. The homogeneously modified particles were not able to significantly reduce the surface tension of water (surface tensions were measured at 70.9-72 mN / m) (Figure 21). On the other hand, the Janus-type spherical cellulose particles of the present invention show higher surface activity, which is consistent with theoretical predictions of the behavior of Janus particles at interfaces (Fletcher, 2001) (Miguel Angel Fernandez-Rodriguez, 2016). 7.Reference materials

[0155] Casagrande, C., Fabre, P., Raphael, E., & Veyssie, M. (1989). “Janus Beads”: Recognition and Behavior at the Water / Oil Interface. EPL Europhys Lett., 9(3), 251. Chen, X.-Q., Deng, X.-Y., Shen, W.-H., & Jia, M.-Y. (2018). Preparation and characterization of spherical nanosized cellulose by enzymatic hydrolysis of pulp fibers. Carbohydrate Polymers, 181, 879. Dong, H., Ding, Q., Jiang, Y., Li, X., & Han, W. (2021). Pickering emulsions stabilized by spherical cellulose nanocrystals. Carbohydrate Polymers, 265, 118101. doi:https: / / doi.org / 10.1016 / j.carbpol.2021.118101 Fletcher, BP (2001). Particles adsorbed at the oil-water interface: A theoretical comparison of uniformly wettable spheres and "Janus" particles. Langmuir, 17, 4708-4710. J. Ross, G.D. (1941). Apparatus for comparing the foaming properties of soaps, detergents, oils and soaps.18, 99-102. Li, D.-d., Jiang, J.-z., & Cai, C. (2020). Palladium nanoparticles anchored on amphiphilic Janus-type cellulose nanocrystals for Pickering interfacial catalysis. Chem. Commun., 56, 9396-9399. Li, T., Liu, B., Wang, W., Sagis, LM, Yuan, Q., Lei, X., ... Li, Y. (2020). Corncob cellulose nanospheres as environmentally friendly detergents. Nature Sustainability, 3, 448. Meyabadi, TF, Dadashian, F., Sadeghi, GM, & Asl, HE (2014). Preparation of spherical cellulose nanoparticles from waste cotton using an eco-friendly method. Powder Technology, 261, 232-240. Miguel Angel Fernandez-Rodriguez, MA-V.-V.-A. (2016). Surface activity of Janus particles adsorbed at fluid-fluid interfaces: Theoretical and experimental aspects. Advances in Colloid and Interface Science, 233, 240-254. Zhang, J., Elder, TJ, Pu, Y., & Ragauskas, AJ (2007). Facile synthesis of spherical cellulose nanoparticles. Carbohydrate Polymers, 69, 607-611.

Claims

1. A process for preparing Janus-type spherical cellulose nanoparticles, comprising: (a) preparing an alkaline suspension of spherical cellulose nanoparticles in water; (b) forming an emulsion comprising the spherical cellulose nanoparticles, water, and a water-immiscible lipophilic solvent, (i) the water constitutes the continuous phase; (ii) the lipophilic solvent constitutes the dispersed phase and comprises a lipophilicity modifier; (iii) the spherical cellulose nanoparticles are localized at the interface between the continuous phase and the dispersed phase; (c) reacting the portion of the spherical cellulose nanoparticles exposed to the lipophilic modifier at the interface between the continuous phase and the dispersed phase with the lipophilic modifier to produce Janus-type spherical cellulose nanoparticles; (d) separating the Janus-type spherical cellulose nanoparticles from the emulsion.

2. 2. The process of claim 1, wherein the alkaline suspension comprises a weight ratio of base to spherical cellulose nanoparticles of about 1:1 to about 2:1, and the base is selected from the group consisting of NaOH, KOH, and LiOH, preferably NaOH.

3. 2. The process of claim 1, wherein the alkaline suspension of spherical cellulose nanoparticles is mixed with the water and the water-immiscible lipophilic solvent to form an emulsion in which the water constitutes the continuous phase and the lipophilic solvent constitutes the dispersed phase.

4. 2. The process of claim 1, wherein the water-immiscible lipophilic solvent is selected from the group consisting of toluene, chloroform, hexane, pentane, benzene, carbon tetrachloride, heptane, dichloromethane, and ethyl acetate.

5. 10. The process of claim 1, wherein the water-immiscible lipophilic solvent consists of or consists primarily of a lipophilic modifier.

6. 6. The process of claim 5, wherein the water-immiscible lipophilic solvent and the lipophilic modifier comprise, consist of, or consist essentially of triacylglycerides.

7. The process of any one of claims 1 to 4, wherein the lipophilic modifying agent is added to the water-immiscible lipophilic solvent before emulsification.

8. 5. The process of any one of claims 1 to 4, wherein the lipophilicity modifier comprises an alkyl halide or alkyl pseudohalide, preferably an alkyl bromide, alkyl chloride, alkyl iodide, alkyl mesylate, alkyl tosylate, more preferably a (C1-C20)-bromoalkane, most preferably a (C12-C16)-bromoalkane.

9. The process of any one of claims 1 to 4, wherein the lipophilic modifying agent comprises an acid chloride, preferably a (C1-C20)-acid chloride, more preferably a (C12-C16)-acid chloride.

10. 5. The process of any one of claims 1 to 4, wherein the lipophilic modifying agent comprises a (C1-C20)-carboxylic acid (preferably a (C12-C16)-carboxylic acid) or a (C1-C20)-ester (preferably a (C12-C16)-ester).

11. 5. The process according to any one of claims 1 to 4, wherein the lipophilic modifying agent is added to the water-immiscible lipophilic solvent in an amount equivalent to about 0.5 to about 10 moles per glucose unit present in the spherical cellulose nanoparticles.

12. 5. The process of any one of claims 1 to 4, wherein the molar ratio of said lipophilic modifier to said water-immiscible lipophilic solvent is from about 1:20 to about 1:1, preferably from about 1:10 to about 1:2, more preferably from about 1:4 to about 1:

5.

13. 5. The process of any one of claims 1 to 4, wherein the emulsion comprises a water-immiscible lipophilic solvent:an alkaline suspension of spherical cellulose nanoparticles in a weight ratio of about 1:50 to about 1:2, preferably about 1:20 to about 1:5, more preferably about 1:15 to about 1:

8.

14. The process of any one of claims 1 to 4, wherein the emulsion is heated to about 30 to about 70°C, preferably to about 50°C.

15. 5. The process of any one of claims 1 to 4, wherein the emulsion is heated until functionalized moieties comprise on average about 30 to about 70%, preferably about 40 to about 60%, more preferably about 45 to about 55%, and most preferably about 50% of the surface area of ​​the spherical nanoparticles.

16. Janus-type spherical cellulose nanoparticles having a volume average particle size of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, more preferably about 20 to 200 nm, wherein one surface of each nanoparticle sphere is functionalized to be more lipophilic than the remaining surface of the sphere.

17. The Janus-type spherical cellulose nanoparticles according to claim 16, which are partially functionalized with (C1-C20) ether groups or (C1-C20) ester groups.

18. Janus-type spherical cellulose nanoparticles according to claim 16 or 17, wherein the functionalized moieties comprise on average about 30 to about 70%, preferably about 40 to about 60%, more preferably about 45 to about 55%, and most preferably about 50% of the surface area of ​​the nanoparticles.

19. A surfactant composition containing the Janus-type spherical cellulose nanoparticles according to claim 16.

20. 20. The surfactant composition according to claim 19, which is a Pickering emulsion comprising about 0.01 to 1 wt. %, preferably 0.05 to 0.5, more preferably about 0.1 wt. % of Janus-type spherical cellulose nanoparticles.

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