Process for making janus-type spherical cellulose nanoparticles

Abstract

The invention relates to a method of improving the surfactant properties of lipophilic spherical cellulose nanoparticles by selective cleavage of lipophilic groups on a single face of the nanoparticles. The resulting nanoparticles can be used as surfactants in many applications, forming stable Pickering emulsions.

Description

[0001] PROCESS FOR MAKING JANUS-TYPE SPHERICAL CELLULOSE NANOPARTICLES

[0002] 1. FIELD OF THE INVENTION

[0003] The present invention relates to Janus-type spherical cellulose nanoparticles, processes for preparing said nanoparticles and Pickering emulsions comprising said Janus-type spherical cellulose nanoparticles.

[0004] 2. BACKGROUND TO THE INVENTION

[0005] Surfactants are chemical additives used in products such as paints, pesticides, cleaning products and cosmetics. Conventional surfactants are molecules with one water-soluble end and one oil-soluble end. This amphiphilic structure allows incompatible liquids, such as oil (or oil-soluble compounds) to mix homogeneously with water. Surfactants facilitate this mixing by sitting at the interface between oil and water, stabilising the microscopic bubbles of oil (the dispersed phase) within the water (the continuous phase) and creating a homogeneous mixture known as an emulsion. In this context, these surfactants act as emulsifiers.

[0006] The properties of a synthetic surfactant can be modified by the length (and number of chains) of the lipophilic portion of the molecule and the size and charge of the hydrophilic portion. A key measure of the physical characteristics of a surfactant is its hydrophilic-lipophilic balance (HLB), a number that is used to determine the application to which it is best suited. Depending on their HLB, surfactants can be used as detergents, emulsifiers, wetting agents, foaming agents, dispersants and defoamers.

[0007] For example, generally surfactants with HLB values of 13-15 are used as detergents; surfactants with HLB values of 8-16 are used as oil-in-water emulsifiers; surfactants with HLB values of 3-6 are used as water-in-oil emulsifiers; and surfactants with HLB values of 2-3 are used as antifoaming agents.

[0008] The surfactants in use today cannot be recovered and are discharged into waterways; an issue facing increasing scrutiny from regulatory organisations. They are thus considered environmental pollutants. Some surfactants have also been found to be endocrine disruptors, such as the alkylphenols - a class of surfactants restricted in the European Union due to its effects on human health and the environment (Regulation No 648 / 2004). In addition, the majority of surfactants in use today are partially or wholly derived from an unsustainable petrochemical industry. The tightening of environmental regulation and strong public demand for green and sustainable technologies has created a need for new surfactants that are sustainably sourced and fully biodegradable.

[0009] Emulsions formed from oil and water can be stabilised by the addition of particles as well as traditional molecule-based surfactants. Small molecules tend to rapidly adsorb and desorb from the oil-water interface and therefore do not always provide high emulsion stability over time. Particles are known to possess a much higher affinity for the water / oil interface than molecules due to their larger size. They stabilise emulsions more efficiently due to their ability to keep the two immiscible layers apart. Thus, they act as more efficient emulsifiers. Emulsions formed using a particulate surfactant are known as Pickering emulsions.

[0010] A Pickering emulsion comprises a shell of particles located at the interfaces between the dispersed phase droplets and the continuous phase. Pickering emulsions are typically made by combining an oil, water and solid particles (typically less than 100 pm in diameter) and then vigorously mixing, for example in a blender. Depending on the relative amounts of the water and oil, the size and nature of the solid particles (generally the phase that preferentially wets the particle will be the continuous phase), a water-in- oil or oil-in-water Pickering emulsion is formed, where the presence of the solid particles stabilises the emulsion by preventing the dispersed phase droplets from coalescing.

[0011] Well-known particulate surfactants (also called Pickering particles) include hydroxyapatite nanoparticles, silica and clay materials, iron oxide nanoparticles, carbon nanotubes and chitosan nanoparticles. However, cellulose particles are increasingly finding application as particulate surfactants.

[0012] Cellulose (a carbohydrate polymer) is the most abundant renewable polymer in nature, representing about 50% of the Earth's natural biomass. Cellulose ((C6HioOs)n where n = 10000 to 15000) is a tough, fibrous, water-insoluble substance defined as a long polymer chain of 1,4-anhydro-D-glucopyranose units, with a flat, ribbon-like conformation.

[0013] Native cellulose is fibrillar and crystalline. Cellulose does not exist as a single polymer molecule. Multiple cellulose polymers (30 to 100) packed together via van der Waals forces and hydrogen bonds form the basic units of cellulose fibres - the elementary fibril, which exists at the nanoscale in diameter and micro-scale in length. These elementary fibrils are further gathered by intermolecular and intramolecular hydrogen bonding into microfibrils that display cross dimensions ranging from 2 to 20 nm. Their aspect ratios can vary from around 40 (e.g., ~200 nm long and 5 nm wide for cotton) to around 66 (e.g., ~1 pm long and 15 nm wide for tunicin).

[0014] Common sources of cellulose include cotton, hemp, flax, hardwood and various bacterial strains. Acid hydrolysis and enzymatic digestion can be used to extract the crystalline regions from the cellulose microfibres. The crystalline rods formed are known as cellulose nanocrystals. These have lengths of about 160-200 nm and cross sections of about 7-25 nm. While showing promise in a vast range of applications, cellulose nanocrystals are of great potential as particulate surfactants because of their high mechanical strength and surface area. They are also biodegradable and biocompatible and so may be preferred to petrochemical-derived molecular surfactants.

[0015] The monomeric glucose units within the cellulose chain possess several hydroxyl groups, which provide reactive platforms for chemical modifications. Accordingly, the physical properties of cellulose nanocrystals can be readily modified.

[0016] Cellulose has an inherently hydrophilic nature due to the presence of hydroxyl (-OH) groups on its surface, which can form hydrogen bonds with water. However, the surface functionality of cellulose nanocrystals can be changed using a number of methods, including but not limited to, TEMPO-mediated oxidation, periodate oxidation (increasing hydrophilicity) and esterification and long alkyl chain grafting (decreasing hydrophilicity). Many modified cellulose nanocrystals have been shown to be good at stabilising Pickering emulsions, including spherical cellulose nanoparticles (Dong, Ding, Jiang, Li, & Han, 2021).

[0017] Another way of improving the surfactant properties of a particle is to introduce heterogeneity into the faces of the particle. Janus particles are particles whose surfaces have two distinct physical properties; for example, a lipophilic face opposite a hydrophilic face. Janus particles make excellent emulsifiers because they combine the amphiphilic properties of molecular surfactants with the higher interface affinity of a particulate surfactant.

[0018] C. Casagrande and M. Veyssie in 1989 reported the first Janus "beads" that offered amphiphilicity within a single solid particle of diameter in the range of 50-90 pm (Casagrande, Fabre, Raphael, & Veyssie, 1989). These Janus "beads" were prepared from glass spheres with one side having a cellulose (hydrophilic) varnish and the other side treated with octadecyltrichlorosilane (lipophilic). It was found that when dispersed at oil-water interfaces, these Janus "beads" were always symmetrically positioned at the interface with the lipophilic half immersed in the oil side and the hydrophilic half in the water.

[0019] Janus particles can be produced by masking one side of the particle (which can be achieved by evaporation deposition or suspending the particles at the interface of two phases) and then chemically altering the unmasked side. However, methods for producing Janus particles at the nanometre scale are severely limited, due to the ability of particles to rotate in solution, causing poor control of modification on a single face. Therefore, despite the growing interest in cellulose nanocrystals, Janus-type cellulose nanocrystals are rare.

[0020] In 2020, Li et al described making Janus-type cellulose nanocrystals in the manufacture 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 had located to the emulsion interface, the solution was rapidly cooled, leaving the nanocrystals locked on the surface of the now solid wax droplets. A lipophilic modifier (1-bromohexadecane) was reacted with the exposed faces of the cellulose nanocrystals.

[0021] The cellulose nanocrystals used were rod-like particles with dimensions of about 0.5-3 pm in length and 50-150 nm in diameter. After modification, the cetyl-modified cellulose nanocrystals had average lengths of about 0.5-5 pm.

[0022] The modified cellulose nanocrystals described above are fairly large and have a high aspect ratio, which is not optimal in a particulate surfactant. Particles stabilise Pickering emulsions by adsorbing at the high-energy oil-water interface, which decreases the area of the surface at which the oil and water phases come directly in contact with each other. Smaller particles are more efficient in this role, as they can be more efficiently packed leaving smaller gaps between particles where the water and oil phases would otherwise be in contact. Spherical particles also allow for more efficient packing than elongated rods or fibres, which tend to form bundles and tangle rather than packing uniformly at the interface.

[0023] Unfortunately, researchers have not yet found a way to combine the superior surfactant properties resulting from facial distinction, with the superior interfacial stabilisation of spherical cellulose nanoparticles. Therefore, presently available cellulose-based surfactants are not as effective as less environmentally detrimental products.

[0024] Accordingly, it is an object of the invention to provide Janus-type spherical cellulose nanoparticles that go at least some way in alleviating some of the deficiencies of the prior art surfactants and / or that will at least provide the public with a useful choice.

[0025] In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. 3. SUMMARY OF THE INVENTION

[0026] The invention relates generally to improving the surfactant properties of lipophilic spherical cellulose nanoparticles (LSCNs) by selective cleavage of lipophilic groups on a single face of the LSCNs.

[0027] Accordingly, in one aspect the invention provides a process for preparing Janus-type spherical cellulose nanoparticles comprising:

[0028] (a) suspending LSCNs in an organic solvent in which the LSCNs are not soluble, to form a 0.1 to 10 wt% suspension;

[0029] (b) optionally adding an oil-soluble surfactant to the suspension to give a concentration of about 0.1 to about 2 wt% surfactant;

[0030] (c) adding an aqueous solution of base or acid to the suspension and forming a Pickering emulsion comprising (i) an aqueous phase containing the acid or base and (ii) an organic phase, wherein the lipophilic spherical cellulose nanoparticles are suspended at the interface of the aqueous and organic phases;

[0031] (d) cleaving the lipophilic groups of the lipophilic spherical cellulose nanoparticles that are exposed to the base or acid in the aqueous phase of the Pickering emulsion;

[0032] (e) optionally neutralising the aqueous phase; and

[0033] (f) recovering the Janus-type spherical cellulose nanoparticles.

[0034] The invention also relates to Janus-type spherical cellulose nanoparticles prepared in accordance with the process of the invention and Pickering emulsions comprising said Janus-type spherical cellulose nanoparticles.

[0035] 4. BRIEF DESCRIPTION OF THE FIGURES

[0036] The invention will now be described by way of example only and with reference to the drawings in which:

[0037] Figure 1 is the infrared (IR) spectrum of palmitic esterified (C16) LSCN as prepared in Example 1.

[0038] Figure 2 is a scanning electron micrograph (SEM) of palmitic esterified (C16) LSCN as prepared in Example 1.

[0039] Figure 3 is a graph showing the average particle size distribution of palmitic esterified LSCN as prepared in Example 1. Figure 4 is an SEM of esterified (C12) LSCN as prepared in Example 2.

[0040] Figure 5 is an SEM of esterified (C8) LSCN as prepared in Example 4.

[0041] Figure 6 is the IR spectrum of LSCN esterified with canola oil. Fig. 6 shows the IR spectrum of the LSCN as prepared in Example 6.

[0042] Figure 7 is the IR spectrum of Janus-type cellulose nanoparticles partially covered with palmitoyl groups as prepared in Example 7.

[0043] Figure 8 is the IR spectrum of Janus-type cellulose nanoparticles partially covered with stearoyl groups as prepared in Example 9. Fig. 8A shows the IR spectrum of the particles after cleavage for 15 min. Fig. 8B shows the IR spectrum of the particles after cleavage for 60 min.

[0044] Figure 9 is the IR spectrum of Janus-type cellulose nanoparticles partially covered with canola oil as prepared in Example 10. Sample MNO216 refers to the Janus-type cellulose nanoparticles prepared in Example 10A (using NaOH at 0.10 M) and sample MNO217 refers to the Janus-type cellulose nanoparticles prepared in Example 10B (using NaOH at 0.05 M).

[0045] Figure 10 is a table summarising the reaction and HLB data for the LSCNs prepared by Example 6 (sample MN0200B2) and for the Janus-type cellulose nanoparticles prepared in Example 10A (sample MNO216) and Example 10B (MNO217). The NaOH concentration provided is the final concentration in the aqueous phase of the suspension.

[0046] Figure 11 is the IR spectrum of Janus-type cellulose nanoparticles partially covered with canola oil as prepared in Example 11. Sample MNO228 refers to the Janus-type cellulose nanoparticles prepared in Example 11 using saturated K2CO3 to partially cleave the lipophilic modifier, which is compared to the data for the LSCNs prepared by Example 6 (sample MN0200B2).

[0047] Figure 12 is the IR spectrum of Janus-type cellulose nanoparticles partially covered with canola oil as prepared in Example 12. Sample MNO229 refers to the Janus-type cellulose nanoparticles prepared in Example 12 using HCI to partially cleave the lipophilic modifier, which is compared to the data for the LSCNs prepared by Example 6 (sample MN0200B2).

[0048] Figure 13 is a graph showing UV absorbance over time of a set of Pickering emulsions prepared using Janus-type cellulose nanoparticles as set out in Example 13.

[0049] Figure 14 is a series of photographs of a set of Pickering emulsions prepared as set out in Example 14. Figure 15 is a set of micrographs showing the Pickering emulsions prepared using Janus-type cellulose nanoparticles as set out in Example 15.

[0050] 5. DETAILED DESCRIPTION OF THE INVENTION

[0051] 5.1 Definitions and abbreviations

[0052] As used herein the term "comprising" means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0053] The term "about" as used herein means a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, when applied to a value, the term should be construed as including a deviation of + / - 10% of the value.

[0054] The term "nanoparticle" as used herein means a particle of size between about 1 and 999 nm. It is acknowledged that the term "nanoparticle" as used herein, may differ from the interpretation used by various industry regulators and may encompass particles that are larger than would be considered to be nanoparticles in some contexts.

[0055] The term "cellulose nanoparticle" as used herein, refers to a nanoparticle produced from a source of cellulose, for example microcellulose. Cellulose nanoparticles may be surface modified with other agents but comprise at least a cellulose core.

[0056] The terms "lipophilic spherical cellulose nanoparticle" and "LSCN" as used herein means a spherical cellulose nanoparticle that has been reacted with a lipophilicity modifier such that at least one third of the hydroxy groups on the surface of the spherical cellulose nanoparticle have been converted to ester groups. In other words, a LSCN has at least 1 ester group present per anhydroglucose unit (AGU) that is present on the surface of the LSCN.

[0057] The term "emulsion" as used herein refers to a combination of at least two liquids, where one of the liquids is present in the form of droplets in the other liquid. IUPAC, Compendium of Chemical Terminology: IUPAC Recommendations, 2nded., compiled by A. D. McNaught and A. Wilkinson, Blackwell, Oxford (1997).

[0058] The term "surfactant" as used herein refers to a molecule or particle comprising two parts of different polarity, one generally being lipophilic (soluble or dispersible in an oily phase) and one being hydrophilic (soluble or dispersible in water). Surfactants reduce the surface tension of a liquid in which they are dissolved. Surfactants are characterised 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" (published by ICI Americas Inc., 1984). The term "wettability" is commonly used to describe the hydrophilicity / lipophilicity of particles used to stabilise Pickering emulsions. To maintain consistency, the term "HLB" is used herein to describe the surfactant properties of both molecules and particles.

[0059] The term "volume particle diameter" as used herein, means the diameter of a sphere that has the same volume as the particle being measured. The "volume average particle diameter" of a particulate substance is the average value of the volume particle diameter of the particles being measured.

[0060] The term "sphericity" as used herein, is a measure of the degree to which a particle approximates the shape of a sphere. The sphericity of a particle is the ratio of the surface area of a sphere with the same volume as the given particle to the surface area of the particle. A perfect sphere has a sphericity of 1. The sphericity of a particle can be assessed by viewing the projected area of a particle appearing in an electron micrographic image and comparing the ratio of the circumferential length of a circle having the same area as the projected area and the actual circumferential length of the particle appearing in the electron micrographic image. In this method, each particle is observed only at a plane, but the variation in the observation direction can be accounted for by using an average value for many particles.

[0061] The term "spherical" as used herein, refers to a particle of sphericity from 0.5 to 1.0.

[0062] The term "lipophilicity" 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.

[0063] The term "cellulosic material" as used herein, includes but is not limited to, wood pulp from which the lignin, pentosan, resins and similar constituents have been removed; material derived from bamboo, reeds, jute, straw, grasses, peanut hulls, bark, and waste plant materials like grape marc, coconut fibre and the like. As would be understood by a person skilled in the art, the cellulosic material for use in the methods of the invention must be very high in cellulose and not contain other constituents that could interfere with processing. The term "cellulose nanocrystals" as used herein, refers to the crystalline regions of cellulose microfibres, that have lengths of about 160-200 nm and cross-sections of about 7-25 nm.

[0064] The terms "acid" and "base" as used herein refer to compounds that can donate or accept a proton respectively. The terms "weak acid" and "weak base" refer to compounds that only partially dissociate into ions when dissolved into water. It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0065] Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. In the disclosure and the claims, "and / or" means additionally or alternatively. Moreover, any use of a term in the singular also encompasses plural forms.

[0066] 5.2 The process of the invention

[0067] The invention provides a process for creating Janus-type spherical cellulose nanoparticles by decreasing the lipophilicity of one face of a LSCN to improve its surfactant properties. This process uses the affinity of LSCNs for an oil / water interface to prepare Janus-type spherical cellulose nanoparticles.

[0068] Accordingly, in one aspect the invention provides a process for preparing Janus-type spherical cellulose nanoparticles comprising:

[0069] (a) suspending LSCNs in an organic solvent in which the LSCNs are not soluble, to form a 0.1 to 10 wt% suspension;

[0070] (b) optionally adding an oil-soluble surfactant to the suspension to give a concentration of about 0.1 to about 2 wt% surfactant;

[0071] (c) adding an aqueous solution of base or acid to the suspension and forming a Pickering emulsion comprising (i) an aqueous phase containing the acid or base and (ii) an organic phase, wherein the lipophilic spherical cellulose nanoparticles are suspended at the interface of the aqueous and organic phases;

[0072] (d) cleaving the lipophilic groups of the lipophilic spherical cellulose nanoparticles that are exposed to the base or acid in the aqueous phase of the Pickering emulsion;

[0073] (e) optionally neutralising the aqueous phase; and

[0074] (f) recovering the Janus-type spherical cellulose nanoparticles. The process modifies LSCNs. LSCNs are spherical cellulose nanoparticles that have been reacted with a lipophilicity modifier that replaces their surface hydroxy groups with lipophilic groups, specifically ester groups.

[0075] Cellulose structures contain three free hydroxyl groups for every anhydroglucose unit (AGU) in the structure. A "lipophilicity modifier" is an agent that reacts with the hydroxy groups on the surface of the cellulosic material to produce ester groups, usually (C1-C20) ester groups.

[0076] A lipophilicity modifier may comprise an organic compound that includes at least one (C1-C20) alkyl group and a leaving group, for example, an acyl chloride such as octanoyl chloride, decanoyl chloride, lauroyl chloride, myristoyl chloride, palmitoyl chloride and stearoyl chloride. Acid anhydrides may also be lipophilicity modifiers, for example octanoyl anhydride, decanoyl anhydride, lauroyl anhydride, myristoyl anhydride, palmitoyl anhydride and stearoyl anhydride.

[0077] Another type of lipophilicity modifier comprises an ester that is formed from at least one (C1-C20) carboxylic acid and an alcohol (e.g. glycerol), for example, a fatty acidcontaining lipid such as a triacylglyceride or similar reagent containing ester functional groups. The triacylglyceride reacts with hydroxyl groups on the surface of the cellulosic material to produce ester groups in a transesterification reaction. Such triacylglycerides are commonly sourced from plants and other renewable sources.

[0078] Processes for producing LSCNs are well known in the art. In some cases, the spherical nanoparticle structure is formed from cellulose polymers that have been modified with a lipophilicity modifier; see for example (Geissler, Biesalski, Heinze, & Zhang, 2014), (Tiban Anrango, 2024) and (Cordt, 2020)

[0079] In other cases, a SCN is made first, before reaction with the lipophilicity modifier (Yan, Yu, & Yao, 2015) and (Ram, 2018)

[0080] Examples 1-6 outline methods used by the inventors to make LSCNs for use in the process of the invention. These methods include direct synthesis of the LSCNs, as well as modification of SCNs. They demonstrate that a person skilled in the art would be able to readily obtain LSCNs with the desired lipophilic substitution pattern.

[0081] In one embodiment the degree of substitution (proportion of available hydroxyl groups esterified) on the surface of the LSCN used in the process of the invention is at least about 1 / 3. Preferably, the degree of substitution is at least about 1 / 2, more preferably at least about 2 / 3. In one embodiment, the degree of substitution is about 100%. The degree of substitution can be can roughly estimated using infrared (IR) spectroscopy, and can be determined using nuclear magnetic resonance (NMR) spectroscopy as would be understood by a person skilled in the art.

[0082] In one embodiment the LSCNs have a volume average particle diameter of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, more preferably about 20 to about 200 nm.

[0083] In one embodiment, the LSCNs have an average sphericity of greater than about 50, 60, 70, 80, 90, 95% or 98%, preferably greater than about 75%, more preferably greater than about 90% or higher.

[0084] In one embodiment, the LSCNs for use in the process of the invention are SCNs esterified with a C8 to C16 fatty acid, preferably a C8, C12, C14 or C16 fatty acid.

[0085] In one embodiment, the LSCNs for use in the process of the invention are SCNs esterified with a vegetable oil, preferably canola oil. Vegetable oils such as canola oil contain a mixture of triglycerides. LSCNs esterified with vegetable oil undergo transesterification with the cellulose surface, resulting in modification of the surface with a mixture of long chain fatty acids.

[0086] In step (a) of the process of the invention, LSCNs are suspended in a solvent to form a suspension comprising about 0.1 to about 10 wt% LSCN.

[0087] The solvent must be one in which the LSCNs are not soluble. The solubility of the LSCNs will depend to some extent on the type of lipophilic groups coating the surface and the degree of modification. Generally, the LSCNs will not be soluble in C6 or longer alkanes (ie, longer than hexane) or triglycerides.

[0088] In one embodiment the solvent in step (a) is selected from the group comprising hexane, heptane, octane and mixtures thereof, preferably hexane. In one embodiment the solvent in step (a) is selected from the group comprising canola oil, olive oil, sunflower oil and mixtures thereof, preferably canola oil.

[0089] Formation of a suspension is by any standard means, such as sonication, but not limited thereto.

[0090] In one embodiment the suspension made in step (a) comprises about 0.3 to about 5 wt% LSCNs, preferably about 0.5 to about 2 wt% LSCNs. In one embodiment, the suspension made in step (a) comprises about 1 wt% LSCNs

[0091] In step (b) an oil-soluble surfactant is optionally added to the suspension to aid the formation of a water-in-oil emulsion. The surfactant helps stabilise the nanoparticles at the liquid-liquid interface of the emulsion to be formed in step (c). In one embodiment the oil-soluble surfactant has an HLB of about 3 to 6. A person skilled in the art would understand when addition of an oil-soluble surfactant would be useful. An oil-soluble surfactant may be usefully added to the suspension when the LSCN is very lipophilic (has a high degree of substitution), as the high lipophilicity prevents wetting by water, and thus requires high volumes of a lipophilic solvent to form a stable Pickering emulsion in the next step. Addition of an oil-soluble surfactant may reduce the volume of lipophilic solvent needed.

[0092] Another reason for the addition of an oil-soluble surfactant is that the surfactant will modify the wettability of the LSCN and therefore affect how it sits at the oil / water interface (how high or low it sits at the interface, according to how much the particle wants to be in contact with oil or water phase). Controlling how much of the particle is wetted by water can be used to control what proportion of the lipophilic groups are cleaved later in the process, thereby changing the Janus character of the final particles.

[0093] Suitable oil-soluble surfactants include lactylated monoglycerides, mono- and diglycerides, succinylated monoglycerides, sucrose monostearate, sorbitan oleate and sorbitan stearate. In one embodiment the oil-soluble surfactant in step (b) is an alcohol ethoxylate. In one embodiment the resulting suspension comprises about 0.1 to about 2 wt% surfactant.

[0094] In step (c) an aqueous solution of base or acid is added to the suspension and then a Pickering emulsion is formed. The base or acid used can be strong or weak, with strong bases and acids preferred, in particular, strong bases.

[0095] In one embodiment adding the aqueous solution comprises adding to the suspension, the base or acid dissolved in or mixed with water. Further water can be added to the suspension to change the concentration of the base or acid.

[0096] In another embodiment, adding the aqueous solution comprises adding a solid base or solid acid to the suspension preceding or following the addition of water.

[0097] In one embodiment, an aqueous solution of strong base is added in step (c). In one embodiment the strong base is selected from the group comprising sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, barium hydroxide and caesium hydroxide.

[0098] In one embodiment, a strong acid is added in step (c). In one embodiment the strong acid is selected from the group comprising hydrochloric acid, sulfuric acid, nitric acid, trifluoroacetic acid, p-toluenesulfonic acid and methanesulfonic acid.

[0099] In one embodiment the aqueous solution of strong base or strong acid is added as the strong base or strong acid dissolved in or mixed with water. In one embodiment, an aqueous solution of weak base is added in step (c). In one embodiment the weak base is selected from the group comprising potassium carbonate, sodium carbonate, and caesium carbonate. In one embodiment the weak base is caesium carbonate or sodium carbonate.

[0100] In one embodiment, an aqueous solution weak acid is added in step (c). In one embodiment the weak acid is selected from the group comprising phosphoric acid, acetic acid, formic acid, benzoic acid, boric acid. In one embodiment the weak acid is phosphoric acid or boric acid.

[0101] In one embodiment the aqueous solution of base or acid is added as the base or acid dissolved in or mixed with water. In one embodiment the aqueous solution of base or acid is added by adding a solid base or solid acid to the suspension after addition of water.

[0102] In one embodiment the aqueous solution of base or acid added in step (c) has a final concentration of about 0.001 to about 3 M, preferably about 0.025 to about 0.5 M. The final concentration is the concentration of base or acid in the aqueous phase of the Pickering emulsion. For example, if 3.75 ml of 1 M NaOH is added to the suspension in step (c) along with 71.25 ml water, the final concentration of strong base is 0.05 M.

[0103] The proportion of organic solvent used in step (a) and the aqueous solution containing acid or base in step (c) needs to be chosen so that a stable Pickering emulsion can be formed. A more lipophilic LSCN with a greater degree of ester substitution will require a greater proportion of organic solvent, up to 9: 1 vol organic solvent / aqueous solution.

[0104] The Pickering emulsion may be formed by any means known in the art including sonication, high speed mechanical stirring, homogenisation, use of high-pressure and pumping air through the solution, but is not limited thereto. As would be appreciated by a person skilled in the art, the best means used to form the Pickering emulsion will depend on the scale of manufacture.

[0105] In one embodiment the aqueous solution of acid or base is injected into the suspension slowly under sonication.

[0106] Following emulsification, the LSCNs are localised at the interface of the continuous (nonpolar solvent) and dispersed (water) phases of the emulsion. Because the emulsion is stabilised by solid particles ((LSCNs) it constitutes a Pickering emulsion. As would be recognised by a person skilled in the art, localisation at the interface means that relatively few LSCNs are present in either the continuous or dispersed phases.

[0107] Localisation at the water-oil interface can be observed by addition of a fluorescent dye such as Calcofluor-white, a dye that binds specifically to the lipophilic groups on the cellulose. Irradiation at the absorption maximum will induce the emission of fluorescence, which is observed at the water-oil interface. Following emulsification, fluorescent emission is observed strongly at the water-oil interface, indicating that the LSCNs are located predominantly (or exclusively) at the water-oil interface.

[0108] In step (d) the lipophilic groups present on the LSCNs that are exposed to the base or acid in the aqueous phase of the Pickering emulsion are cleaved off.

[0109] During cleavage, the acid or base present in the aqueous solution catalyses hydrolysis of the ester groups, leaving hydroxyl groups on the surface.

[0110] The lipophilic ester groups present on the opposite face of the spherical cellulose nanoparticles are solubilised in the organic phase, and so will not be cleaved by the basic or acidic solution. Accordingly, one face of the spherical cellulose nanoparticles remains lipophilic while the opposite face is hydrophilic, as shown in Scheme 1.

[0111] Scheme 1: Cleavage of lipophilic groups exposed to the aqueous phase

[0112] In one embodiment the Pickering emulsion in step (d) is heated for about 5-90 minutes at about 40°C, without stirring. As would be understood by a person skilled in the art, the optimum heating time will depend on the lipophilic groups present and the degree of cleavage desired.

[0113] In one embodiment the Pickering emulsion is heated in step (d) for at least 15 minutes at about 40°C, without stirring. The cleavage of the lipophilic groups can also be performed at room temperature but will require a longer reaction time to obtain the same amphiphilicity.

[0114] Reaction for different lengths of time results in different degrees of cleavage of the lipophilic groups, with longer reaction times resulting in a higher degree of cleavage. The degree of cleavage can be followed using infrared spectroscopy, where longer reaction times result in a greater reduction in the signals due to the presence of the lipophilic group (C-H stretch at 2900 cm-1, and carbonyl stretch at 1750 cm-1), and a greater increase in the O-H stretch at 3300 cm-1, which indicates free hydroxyl groups, liberated following cleavage of the lipophilic chains. The reaction is terminated when the desired extent of cleavage is achieved.

[0115] In one embodiment, the Pickering emulsion in step (d) is heated until the lipophilic portion comprises about 30% to about 70% of the surface area of the spherical cellulose nanoparticles on average, 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 on average.

[0116] The functionalised area of the spherical nanoparticles can also be assessed by measuring the surface tension of water containing such particles.

[0117] Spherical cellulose nanoparticles that do not possess two faces with different properties have a uniformly hydrophobic surface, and do not reduce the surface tension of water when added to it. The observation of a decrease in the surface tension of water containing Janus-type spherical cellulose particles described herein confirms the amphiphilicity of these particles, with one lipophilic face and one hydrophilic face.

[0118] In step (e) the aqueous phase is optionally neutralised to stop the reaction and the Janus-type spherical cellulose nanoparticles recovered in step (f).

[0119] In one embodiment the aqueous phase is basic and is neutralised in step (e) by rapid addition of IM HCI. Recovery can be achieved using any standard techniques including but not limited to centrifugation, ultrafiltration and electrostatic precipitation. In one embodiment the Janus-type spherical cellulose nanoparticles in step (f) are recovered by centrifugation.

[0120] In one embodiment the Janus-type spherical cellulose nanoparticles recovered in step (f) are partially dried to provide a slurry or fully dried to provide a powder. Drying can be achieved by any known technique including but not limited to room temperature evaporation, drying under reduced pressure or freeze drying.

[0121] In another aspect, the invention provides Janus-type spherical cellulose nanoparticles prepared by a process of the invention.

[0122] In one embodiment the surface of the Janus-type spherical cellulose nanoparticles is partially functionalised with (C1-C20) ester groups. In one embodiment, the Janus-type spherical cellulose nanoparticles have a volume average particle diameter of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, more preferably about 20 to about 200 nm.

[0123] In the Janus-type spherical cellulose nanoparticles of the invention, the surface of one face of each sphere is more lipophilic than the other face of the sphere.

[0124] In one embodiment the lipophilic portion comprises about 30% to about 70% of the surface area of the spherical cellulose nanoparticles on average, 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 on average.

[0125] The process of the invention provides a useful way of making Janus-type spherical cellulose nanoparticles starting from a wide range of LSCNs. It is technically easier to remove ester groups from one face of a LSCN to form a Janus-type spherical cellulose nanoparticle, than it is to selectively add ester groups to one face, as described in PCT / IB2022 / 060708 (WO2023 / 084383), particularly where the LSCNs are made using natural and renewable lipophilic modifiers such as plant-based triacylglycerides. Because the step of adding plant-based lipid groups to the spherical cellulose nanoparticle is a transesterification, the reaction is reversible and so requires more driving conditions which may not always be compatible with the formation of a Pickering emulsion.

[0126] In addition, the process of the invention provides easy access to Janus-type particles wherein the lipophilic portion is greater than the water-wettable portion, ie Janus-type particles with low HLB values. This is because the process of the invention begins with lipophilic particles (LSCNs), which predominantly sit in the oil-phase, and only the portion in contact with the aqueous phase will be cleaved to reveal the water-wettable part of the Janus-type particles.

[0127] 5.3 Pickering emulsions of the invention

[0128] The Janus-type spherical cellulose nanoparticles described herein are surfactants that can be used in many applications, including but not limited to: emulsifiers for foods and beverages, coatings, plastics, cosmetics and pharmaceuticals; foamers and defoamers for manufacturing, mining and mineral processing; cleaning agents for household, personal and industrial uses; and wetting agents for agricultural and industrial uses.

[0129] In one aspect the invention provides a surfactant composition comprising Janus-type spherical cellulose nanoparticles produced by a process of the invention. In one embodiment the surfactant composition is a Pickering emulsion. In one embodiment the invention provides a Pickering emulsion comprising Janus-type spherical cellulose nanoparticles produced by a process of the invention.

[0130] To prepare an oil-in-water Pickering emulsion, Janus-type spherical cellulose nanoparticles are dispersed in water by mechanical stirring in a dispersing medium until a homogenous cellulose nanoparticle / water dispersion is visible. A volume of oil (up to 50 %vol) is then added to the Janus-type spherical cellulose water dispersion and vigorously shaken or stirred in a dispersing medium to get oil-in-water emulsions.

[0131] In one embodiment the Pickering emulsion comprises about 0.01 to 10 wt% Janus-type spherical cellulose nanoparticles, preferably 0.05 to 5, more preferably 0.1 to 2 wt%.

[0132] In one embodiment, the Pickering emulsion is an oil-in-water emulsion comprising about 1 to about 50% oil by volume, preferably up to about 20% oil by volume. In one embodiment the Pickering emulsion includes no emulsifiers other than the Janus-type spherical cellulose nanoparticles.

[0133] The HLB of the Janus-type spherical cellulose nanoparticles of the invention may be controlled by modification of the reaction conditions.

[0134] Longer reaction times for the cleavage of the lipophilic groups are conditions that increase the HLB, favouring the production of Janus-type spherical cellulose nanoparticles with the ability to stabilise oil-in-water emulsions with oil concentrations lower than 20% by volume. Shorter reaction times for the cleavage of the lipophilic groups preserve most of the lipophilic groups on the surface of the nanoparticles, favouring the production of Janus-type spherical cellulose nanoparticles with the ability to stabilise oil-in-water emulsions with oil concentrations higher than 20% by volume.

[0135] Janus-type spherical cellulose nanoparticles of the invention with low HLB values can be used to stabilise water-in-oil emulsions.

[0136] In one embodiment, the Pickering emulsion is a water-in-oil emulsion comprising 1-50% water by volume.

[0137] The Janus-type spherical cellulose nanoparticles of the invention also have the advantage that they stabilise emulsions without generating foams. This is a highly desirable property because foaming is a problem in many surfactant applications. Foaming can artificially raise batch volumes and cause product loss, damage to equipment such as pumps, factory downtime and environmental pollution. For example, in the formulation of cosmetics, surfactants are added to act as emulsifiers so that the oily components can mix with water. Foam produced during mixing can clog pipes and valves as well as reducing the capacity of containers and complicating the transfer material from one container to another. Foam can also remain in the finished product causing clouding and voids which compromise the integrity of the product.

[0138] In another example, emulsifiers, dispersants and wetting agents are commonly added to paints and coatings formulations to allow all the components in paint to mix homogeneously. Added traditional surfactants can produce foam during the manufacturing, packaging or application of the paint systems. Foaming during manufacturing and packaging clogs equipment and complicates container transfer. Foaming during application leaves surface defects, gives a poor visual appearance and reduces the protective function of the paint or coating.

[0139] In contrast, the Janus-type spherical cellulose nanoparticles described herein can be used as surfactants in the coating systems as described above without the disadvantage of excessive foam formation.

[0140] In addition, the Janus-type spherical nanoparticles of the invention are able to stabilise emulsions containing a significant proportion of droplets that are above 5 pm in size (see Example 15).

[0141] In one embodiment at least about 5, 10, 15, 20 or 25% of the droplets in the Pickering emulsion are greater than about 5 pm in diameter.

[0142] Various aspects of the invention will now be illustrated in non-limiting ways by reference to the following examples.

[0143] 6. EXAMPLES

[0144] Example 1: Lipophilic spherical cellulose nanoparticles (esterified with C16)

[0145] As an illustrative example, microcrystalline cellulose (MCC) with an average size of 51 pm was modified to obtain hydrophobic esterified cellulose. MCC (100 mg) was placed in an oven at 80 °C for 15 minutes and further dried under high vacuum for 30 min. Then, 10 mL of dried dimethylformamide (solvent) was added and the cellulose was dispersed by means of sonication for 5 min and dried pyridine (150 pL, 3 equiv.) were added to the suspension. The lipophilic modifier used for this reaction was palmitoyl chloride (600 pL, 3.2 equiv.). The acyl chloride was added dropwise and the reaction mixture was heated to 100 °C under stirring. After 6 h, the reaction was quenched with 5 mL of ethanol and the mixture dissolved in 50 mL of dichloromethane. The palmitic esterified cellulose was precipitated by pouring the solution into 100 mL of ethanol and recovered by filtration. Finally, the obtained solid was washed several times with methanol and ethanol and dried by high vacuum. The chemical characterisation was carried out with IR (Figure 1). To prepare the lipophilic spherical cellulose nanoparticles (LSCN), a solution of the esterified cellulose (1% w / v, 10 mL) was dissolved in dichloromethane. Then, the solution was slowly added (1 mL / min) into 100 mL of ethanol under vigorous stirring and sonication. The suspension was further sonicated for 10 min. The LSCN were recovered by means of centrifugation (16 k RCF, 30 min, 25 °C) and dried by high vacuum.

[0146] The morphology of the LSCN was confirmed by scanning electron microscopy (Figure 2) and the size of the LSCN was confirmed using dynamic light scattering (Figure 3).

[0147] Example 2: Lipophilic spherical cellulose nanoparticles (esterified with C12)

[0148] In another example, MCC (100 mg) was esterified with lauroyl chloride (300 pL, 2.8 equiv). In this case, the solvent / base used was pyridine (2 mL, 40 equiv.). Similar to the modification with palmitoyl chloride, the lipophilic modifier was added dropwise and the reaction time was 5 hours. At the end of the reaction, a solid paste was obtained, which was dissolved in 25 mL of chloroform. The esterified cellulose was precipitated by pouring the solution into 50 mL of a mixture ethanol-water 9: 1 v / v. The solid was filtrated and washed several times with methanol.

[0149] A solution of the esterified particles in dichloromethane was prepared (1 w / v, 1 mL), which was poured slowly (1 mL / min) into 10 mL of ethanol under vigorous stirring and sonication. The LSCN were separated by centrifugation (16k RCF, 30 min, 25 °C) and imaged by SEM (Figure 4).

[0150] Example 3: Lipophilic spherical cellulose nanoparticles (esterified with C14)

[0151] In another example, 200 mg of MCC (20 pm) was esterified with myristoyl chloride (tetradeca noyl chloride) using toluene as the solvent. For this purpose, the MCC was dispersed in 10 mL of dried toluene and vigorously stirred. Then, pyridine was added to the suspension (500 pL, 5 equiv.) under stirring. After obtaining a homogenous mixture, the myristoyl chloride (1.2 mL, 3.5 equiv) was added dropwise and the mixture was heated up to 100 °C for 12 h under stirring. Ethanol (0.5 mL) was added to quench the reaction. The product was filtered, and the filtrate was recovered, which was washed with deionised (DI) water to remove impurities and remaining reagents. The toluene phase was dried with anhydrous sodium sulfate, evaporated, and further dried by high vacuum.

[0152] A solution of the esterified particles in toluene was prepared (1% w / v, 1 mL), which was poured slowly (1 mL / min) into 10 mL of a mixture ethanol-isopropanol (1 : 1 v / v) under vigorous stirring and sonication. The LSCN were separated by centrifugation (16k RCF, 30 min, 25 °C) and air-dried. Example 4: Lipophilic spherical cellulose nanoparticles (esterified with C8)

[0153] In another example, the esterification was carried out without pyridine as the catalyst. For instance, 1 g of microcrystalline cellulose (MCC, 20 pm) was suspended in 15 mL of dried dimethylformamide under sonication until the MCC was evenly dispersed. Then, octanoyl chloride (3.2 mL, 3 equiv.) was added to the suspension at room temperature under stirring. The esterification was carried out for 16 h at 110 °C. After this process, 5 mL of ethanol were added to react with any remaining acyl chloride. A viscous paste was obtained that was dissolved in dichloromethane (30 mL) and further reprecipitated by the addition of ethanol (30 mL). The obtained solid paste was once again dissolved in dichloromethane and any by-products or remaining reagents were extracted with water. The organic phase was dried with anhydrous sodium sulfate. Finally, the dichloromethane was removed by evaporation and the solid dried under high vacuum.

[0154] The hydrophobic cellulose (2 g) was dissolved in 50 mL of dichloromethane and reprecipitated in 400 mL of a mixture of ethanol-water (1 : 1 v / v) under sonication and stirring. The rate of the injection was 2 mL per min. The LSCN were then separated by high-speed centrifugation (16k RCF, 30 min, 25 °C) and washed several times with methanol. The LSCN were imaged by SEM (Figure 5).

[0155] Example 5: Lipophilic spherical cellulose nanoparticles (from kraft pulp)

[0156] In another example, cellulose from kraft pulp (500 mg) was crushed into powder and suspended in dried dimethylformamide (5 mL). Next, pyridine (750 pL, 3 equiv.) was slowly added to the suspension under stirring. At room temperature, 3.8 mL (4 equiv.) of stearoyl chloride was added dropwise to the cellulose suspension. The reaction mixture was then heated at 110 °C for 12 h with vigorous stirring. The reaction was quenched by adding methanol (2 mL). After the mixture was cooled down, a brown solid was obtained which was dissolved in dichloromethane (20 mL) under sonication. The material that was not dissolved was separated. Next, the esterified cellulose was reprecipitated by the addition of methanol (50 mL). The solid was recovered and washed several times with methanol.

[0157] The esterified cellulose (1 g) was dissolved in of chloroform (25 mL) and reprecipitated in 200 mL of a mixture of methanol-ethanol (1: 1 v / v) under sonication and stirring. The rate of the addition was 2 mL per min. The particles were then recovered by high-speed centrifugation (16k RCF, 30 min, 25 °C) and washed several times with ethanol.

[0158] Example 6: Lipophilic spherical cellulose nanoparticles (using vegetable oil)

[0159] A different approach was developed to modify cellulose with vegetable oils. SCNs were used as the starting material for this modification. 100 mg of SNCs were suspended in 10 mL of 1 M NaOH under sonication. The suspension was then heated to 60 °C and stirred for 2 h. After this alkali activation, the particles were solvent exchanged with ethanol by centrifugation. The particles were resuspended in ethanol (5 mL) and then canola oil (5 mL) was added and the mixture stirred until a homogenous suspension was formed. The ethanol was removed by vacuum evaporation at room temperature. The suspension of SNCs in canola oil was heated to 110 °C under vigorous stirring for 72 h. The LSCNs were separated by centrifugation (16k RCF, 20 min, 25 °C), washed several times with ethanol and hexane, and air-dried. The IR spectrum confirmed the success of the transesterification reaction (Figure 6).

[0160] Other LSCNs where made from vegetable oils where the degree of lipid substitution on the LSCNs was changed by changing the ratio of canola oil to ethanol.

[0161] Example 7: Janus-type spherical cellulose nanoparticles (palmitoyl-modified)

[0162] The partial cleaving of the esterified cellulose particles was carried out with the palmitoyl-modified LSCNs prepared in Example 1. Firstly, the particles were homogenously dispersed in DCM (1% wt., 10 mL) by means of sonication for 10 min. Then, 0.1 mL of Brij® 030 (an alkyl ethoxylate) surfactant was added to the suspension, which was sonicated for 5 min. An aqueous sodium hydroxide solution (5 M, 1 mL) was injected slowly under sonication and shaking until a homogenous water in oil emulsion was formed. The emulsion was heated to 40 °C and stirred slowly (100 rpm) for 1 h. The emulsion was mixed with ethanol and the Janus-type spherical cellulose nanoparticles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with methanol and hexane was carried out to purify the modified nanoparticles. Finally, the solid product was dried by high-vacuum, and an infrared spectrum taken to determine the success of the cleavage (see Figure 7).

[0163] Example 8: Janus-type spherical cellulose nanoparticles (myristoyl-modified)

[0164] The partial cleaving of the esterified spherical cellulose particles was carried out with the myristoyl-modified LSCNs prepared in Example 3. To form the Janus-type spherical particles, 100 mg of the LSCNs from Example 3 were suspended in 10 mL of hexane (1 % w / v) by sonication for 15 min. Then, 10 mg of an alkyl ethoxylate was added to the suspension. An aqueous solution of potassium carbonate (1 mL, 5 M) was injected into the suspension under sonication and agitation until a water-in-oil emulsion was formed. The reaction was carried out in 3 batches, with heating for 15 min, 30 min and 60 h at 50 °C without stirring. The emulsion was dissolved in methanol and the Janus-type spherical cellulose nanoparticles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with methanol and hexane was carried out to purify the modified nanoparticles. Finally, the solid product was air-dried in 3 batches, each differing in the time of base-promoted cleavage at 50 °C (15 min, 30 min or 60 min). Example 9: Janus-type spherical cellulose nanoparticles (stearoyl-modified)

[0165] The partial cleaving of the esterified cellulose particles was carried out with the stearoyl- modified LSCNs prepared in Example 5. To form the Janus-type spherical particles, 200 mg of the particles from Example 5 were suspended in 20 mL of hexane (1% w / v) by sonicating for 15 min. In this example, the Pickering emulsion was formed without the use of a co-surfactant. Then, an aqueous solution of sodium hydroxide (2 mL, 3 M) was injected into the suspension under sonication and agitation. The reaction was carried out in 3 batches, with heating for 15 min, 30 min and 60 h at 50 °C without stirring. The emulsion is dissolved in methanol and the Janus-type spherical cellulose nanoparticles are separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with methanol and hexane is carried out to purify the modified nanoparticles. Finally, the solid product was air-dried in 3 batches, each differing in the time of base-promoted cleavage at 50 °C (15 min, 30 min or 60 min) and infrared spectra were taken to determine the success of the cleaving procedure (Figure 8).

[0166] Example 1OA: Janus-type spherical cellulose nanoparticles (canola oil modified)

[0167] The partial cleaving of the lipophilic groups was carried out with the canola oil-modified LSCNs prepared in Example 6. Firstly, the LSCNs (500 mg) were homogeneously dispersed in octanol (25 mL) by means of sonication or stirring for 24 h. An emulsion was formed using water (22.5 mL) using a homogenizer and then aqueous sodium hydroxide solution (1 M, 2.5 mL) was injected slowly under homogenization. The emulsion was stirred slowly for 30 min. The emulsion was mixed with chilled ethanol and the Janus-type spherical cellulose nanoparticles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with ethanol and hexane was carried out to purify the modified nanoparticles. Finally, the solid product was air-dried, and an infrared spectrum taken to determine the success of the cleavage (see Figure 9, sample MNO216).

[0168] Example 1OB: Janus-type spherical cellulose nanoparticles (from canola oil modified lipophilic spherical cellulose nanoparticles)

[0169] The partial cleaving of the lipophilic groups was carried out with the canola oil-modified LSCNs prepared in Example 6. Firstly, the LSCNs (500 mg) were homogeneously dispersed in octanol (25 mL) by means of sonication or stirring for 24 h. An emulsion was formed using water (71.25 mL) using a homogenizer and then aqueous sodium hydroxide solution (1 M, 3.75 mL) was injected slowly under homogenization. The emulsion was stirred slowly for 30 min. The emulsion was mixed with chilled ethanol and the Janus-type spherical cellulose nanoparticles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with ethanol and hexane was carried out to purify the modified nanoparticles. Finally, the solid product was air-dried, and an infrared spectrum taken to determine the success of the cleavage (see Figure 9, sample MNO217). Example IOC: HLB Determination of Janus-type spherical cellulose nanoparticles

[0170] The HLB of each type of Janus-type spherical cellulose nanoparticle prepared in Examples 10A-B was determined using a method by Campos and Domingo. httDs: / / books.aooale.co.nz / books / about / A Guide to the Surfactants World.html?id=O nPzOqAACAAJ&redir esc=v. Chapter 7.

[0171] The method involves comparing a series of emulsions prepared using the test surfactant at various ratios, against an analogous series of emulsions prepared using a surfactant standard.

[0172] To allow for positive values for HLBT, two reference surfactants were used for testing: TWEEN 80 for HLB 1-9 and glyceryl mono-oleate (GMO) for HLB 10-20.

[0173] Example 11: Janus-type spherical cellulose nanoparticles formed by cleavage using a weak base

[0174] The partial cleaving of the esterified cellulose particles was carried out with the canola oil-modified cellulose prepared in Example 6. Firstly, the particles (100 mg) were homogenously dispersed in octanol (2 mL) by means of stirring for 24 h. An emulsion was formed by the addition of saturated K2CO3 (8 mL) which was injected slowly under sonication. The emulsion was stirred slowly for 30 min. The emulsion was mixed with chilled ethanol and the particles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with ethanol and water was carried out to purify the modified nanoparticles. Finally, the solid product was air-dried, and an infrared spectrum taken to determine the success of the cleavage (see Figure 11).

[0175] Example 12: Janus-type spherical cellulose nanoparticles formed by cleavage using a strong acid

[0176] The partial cleaving of the esterified cellulose particles was carried out with the canola oil-modified LSCNs prepared in Example 6. Firstly, the LSCNs (100 mg) were homogeneously dispersed in octanol (2 mL) by means of sonication or stirring for 24 h. An emulsion was formed by the addition of water (7.2 mL) under sonication and then aqueous H2SO4 solution (10 M, 0.8 mL) was injected slowly under sonication. The emulsion was stirred slowly for 30 min. The emulsion was mixed with chilled ethanol and the Janus-type spherical cellulose nanoparticles separated by centrifugation (16k RCF, 30 min, 25 °C). Further washing with ethanol and hexane was carried out to purify the modified nanoparticles. Finally, the solid product was air-dried, and an infrared spectrum taken to determine the success of the cleavage (see Figure 12). Example 13: Pickering emulsions comprising Janus-type spherical nanoparticles of the invention

[0177] The Janus-type spherical cellulose nanoparticles prepared in Example 8 were dispersed in water by mechanical stirring in a sonication bath. These particles were prepared by partial cleavage of myristoyl-modified spherical cellulose nanoparticles, as set out in Example 3.

[0178] Oil-in-water emulsions were prepared using 50 vol% of water, 50 vol% of canola oil and 0.1 wt% of the Janus-type spherical cellulose nanoparticles. The mixture was stirred until an emulsion was formed. The emulsions were treated with ultrasonication to obtain stable emulsions. The stability of the emulsions was determined by measuring the turbidity of the water layer using UV spectroscopy. A high absorbance indicates the presence of oil droplets within the water layer which results in the scattering of light.

[0179] Figure 13 shows that completely lipophilic non-Janus myristoyl-modified particles are not able to effectively stabilise emulsions, with a steady decrease in the absorbance of the water layer of the emulsion from t = 0 to t = 600 min.

[0180] Janus-type spherical cellulose nanoparticles produced from cleavage of the myristoyl- modified particles have different abilities to stabilise the emulsion depending on the length of time the particles were subjected to the transesterification reaction (cleavage of the lipophilic chains). The Janus particles formed following 15 min of cleavage are not efficient at stabilising emulsions, while the particles formed following 30 min of cleavage are able to stabilise emulsions, as seen by the small decrease in absorbance over time. The Janus particles formed following 1 hour of cleavage are the best emulsifiers for these particles and no decrease in absorbance is observed after 600 min.

[0181] Example 14: Additional Pickering emulsions comprising Janus-type spherical nanoparticles of the invention

[0182] The Janus-type spherical cellulose nanoparticles prepared in Example 9 were dispersed in water by mechanical stirring in a sonication bath. These particles were prepared by partial cleavage of stearoyl-modified spherical cellulose nanoparticles, as set out in Example 5. Oil-in-water emulsions were prepared using 50 vol% of water, 50 vol% of hexane and 0.1 wt% of the Janus-type spherical cellulose particles. The mixture was stirred until an emulsion was formed. The emulsions were treated with ultrasonication to obtain emulsions that were analysed for their stability. Pictures of the emulsion were taken at day 0, day 1 day 3 and day 7 as seen in Figure 14.

[0183] Figure 14 shows that completely lipophilic non-Janus stearoyl-modified particles are not able to effectively stabilise emulsions, with formation of two separate layers evident even at day 0 (far right vial in the images). The image taken at day 1 shows that oil droplets are being stabilised within the water, given an opaque lower layer. However, these droplets separate steadily from the water layer, and by day 3, a clear water layer is observed.

[0184] The Janus-type spherical cellulose nanoparticles produced from cleavage of the stearoyl- modified particles have different abilities to stabilise the emulsion depending on the length of time the particles were subjected to the transesterification reaction (cleavage of the lipophilic chains). The Janus-type spherical cellulose particles formed after 15 min of transesterification are not able to effectively stabilise emulsions, and by day 3, a clear bottom water layer is observed (1st vial from left). The Janus-type particles formed after 30 min of transesterification are more effective at stabilising emulsions as evidence by the larger bottom water layer after day 1, but by day 3, the bottom water layer can be seen to be relatively clear (2nd vial from left). The Janus-type spherical cellulose particles formed after 1 hour of transesterification are the most effective at stabilising emulsion, as evidenced by the fully opaque bottom layer, which is still visible after 7 days (3rd vial from left).

[0185] Example 15: Additional Pickering emulsions comprising Janus-type spherical nanoparticles of the invention

[0186] The Janus-type spherical cellulose nanoparticles prepared in Examples 10A and 10B were dispersed in water by mechanical stirring. These particles were prepared by partial cleavage of canola oil-modified LSCNs, prepared as set out in Example 6.

[0187] Oil-in-water emulsions were prepared using a 1 : 1 ratio of hexadecane and water, 0.5 wt% of the Janus-type spherical cellulose nanoparticles (MNO216 from Example 10A or MNO217 from Example 10B) and 0.05 wt% of potassium oleate. Dispersed particles in water and potassium oleate were introduced to high shear forces with a homogeniser followed by slow addition of the oil phase.

[0188] The emulsions formed in the presence of MNO216 or MNO217 were both visualised under a microscope (Figure 15). These micrographs show that the Janus-type spherical nanoparticles of the invention are able to stabilise emulsions containing a significant proportion of droplets that are above 5 pm in size. These emulsions are stable for over 24 hours, during which they maintain an emulsion index of 100%. The ability to stabilise emulsions containing such large droplets is surprising, as smaller droplets are generally known to be more stable against sedimentation. Traditional molecule-based surfactants generally form stable emulsions with significantly smaller droplet sizes. (Frelichowska, 2010) 7. REFERENCES

[0189] (n.d.). Retrieved from https: / / books.google.co.nz / books / about / A_Guide_to_the_Surfactants_World.html ?id=0nPz0gAACAAJ8credir_esc=y

[0190] (n.d.). Retrieved from https: / / books.google.co.nz / books / about / A_Guide_to_the_Surfactants_World.html ?id=0nPz0gAACAAJ8credir_esc=y

[0191] Casagrande, C., Fabre, P., Raphael, E., & Veyssie, M. (1989). "Janus Beads": realization and behaviour at water / oil interfaces. EPL Europhys Lett., 9(3), 251.

[0192] Chen, X.-Q., Deng, X.-Y., Shen, W.-H., 8c. Jia, M.-Y. (2018). Preparation and characterization of the spherical nanosized cellulose by the enzymatic hydrolysis of pulp fibers. Carbohydrate Polymers, 181, 879.

[0193] Cordt, C. M. (2020). Entrapment of hydrophobic biocides into cellulose acetate nanoparticles by nanoprecipitation. Nanomaterials, 10, 2447.

[0194] Dong, H., Ding, Q., Jiang, Y., Li, X., 8c Han, W. (2021). Pickering emulsions stabilized by spherical cellulose nanocrystals. Carbohydrate Polymers, 265, 118101. doi: https: / / doi.Org / 10.1016 / j.carbpol.2021.118101

[0195] Fletcher, B. P. (2001). Particles Adsorbed at the Oil-Water Interface: A Theoretical Comparison between Spheres of Uniform Wettability and "Janus" Particles. Langmuir, 17, 4708-4710.

[0196] Frelichowska, J. B.-A. (2010). Effects of solid particle content on properties of o / w Pickering emulsions. J Colloid Interface Sci, 351, 348. doi:doi: 10.1016 / j.jcis.2010.08.019

[0197] Geissler, A., Biesalski, M., Heinze, T., 8 Zhang, K. (2014). Formation of nanostructured cellulose stearoyl esters via nanoprecipitation. J. Mater. Chem., 2, 1107-1116. doi: https: / / doi.org / 10.1039 / C3TA13937A

[0198] J. Ross, G. D. (1941). An Apparatus for Comparison of Foaming Properties of Soaps and Detergents, Oil 8c Soap. 18, 99-102.

[0199] Li, D.-d., Jiang, J.-z., 8c Cai, C. (2020). Palladium nanoparticles anchored on amphiphilic Janus-type cellulose nanocrystals for Pickering interfacial catalysis. Chem. Common., 56, 9396-9399. Li, T., Liu, B., Wang, W., Sagis, L. M., Yuan, Q., Lei, X., . . . Li, Y. (2020). Corncob cellulose nanosphere as an eco-friendly detergent. Nature Sustainability, 3, 448.

[0200] Meyabadi, T. F., Dadashian, F., Sadeghi, G. M., 8<. Asl, H. E. (2014). Spherical cellulose nanoparticles preparation from waste cotton using a green method. Powder Technology, 261, 232-240.

[0201] Miguel Angel Fernandez-Rodriguez, M. A.-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.

[0202] Ram, B. C. (2018). New spherical nanocellulose and thiol-based adsorbent for rapid and selective removal of mercuric ions. Chemical Engineering Journal, 331, 587.

[0203] Tiban Anrango, B. A.-Y. (2024). Nanoprecipitation to produce hydrophobic cellulose nanospheres for water-in-oil Pickering emulsions. Cellulose, 31, 6225.

[0204] Yan, C., Yu, H., & Yao, J. (2015). One-step extraction and functionalization of cellulose nanospheres from lyocell fibers with cellulose II crystal structure. Cellulose, 22, 3773-3788. doi:https: / / doi.org / 10.1007 / sl0570-015-0761-5

[0205] Zhang, J., Elder, T. J., Pu, Y., & Ragauskas, A. J. (2007). Facile synthesis of spherical cellulose nanoparticles. Carbohydrate Polymers, 69, 607-611.

Claims

Claims:

1. A process for preparing Janus-type spherical cellulose nanoparticles comprising:(a) suspending LSCNs in an organic solvent in which the LSCNs are not soluble, to form a 0.1 to 10 wt% suspension;(b) optionally adding an oil-soluble surfactant to the suspension to give a concentration of about 0.1 to about 2 wt% surfactant;(c) adding an aqueous solution of base or acid to the suspension and forming a Pickering emulsion comprising an aqueous phase containing the acid or base and an organic phase, wherein the lipophilic spherical cellulose nanoparticles are suspended at the interface of the aqueous and organic phases;(d) cleaving the lipophilic groups of the lipophilic spherical cellulose nanoparticles that are exposed to the base or acid in the aqueous phase of the Pickering emulsion;(e) optionally neutralising the aqueous phase; and(f) recovering the Janus-type spherical cellulose nanoparticles.

2. A process of claim 1 wherein the LSCNs are SCNs esterified with C8 to C16 fatty acids or vegetable oil, preferably canola oil.

3. A process of claim 1 or claim 2 wherein the degree of substitution on the surface of the LSCN is at least about 1 / 3, preferably at least about 1 / 2, more preferably at least about 2 / 3, even more preferably about 100%.

4. A process of any one of claims 1-3 wherein the LSCNs have a volume average particle diameter of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, more preferably about 20 to about 200 nm, even more preferably about 100 to about 200 nm.

5. A process of any one of claims 1-4 wherein the LSCNs have an average sphericity of greater than about 50, 60, 70, 80, 90, 95% or 98%, preferably greater than about 75%, more preferably greater than about 90% or higher.

6. A process of any one of claims 1-5 wherein the solvent in step (a) is selected from the group comprising hexane, heptane, octane and mixtures thereof, preferably hexane.

7. A process of any one of claims 1-6 wherein the suspension made in step (a) comprises about 0.3 to about 5 wt% LSCNs, preferably about 0.5 to about 2 wt% LSCNs, more preferably about 1 wt% LSCNs.

8. A process of any one of claims 1-7 wherein an oil-soluble surfactant is optionally added to the suspension to aid the formation of a water-in-oil emulsion.

9. A process of claim 8 wherein the oil-soluble surfactant has an HLB of about 3 to 6 and / or comprises lactylated monoglyceride, mono- and diglyceride, succinylated monoglyceride, sucrose monostearate, sorbitan oleate and / or sorbitan stearate.

10. A process of claim 8 wherein the oil-soluble surfactant is an alcohol ethoxylate.

11. A process of any one of claims 8-10 wherein the resulting suspension comprises about 0.1 to about 2 wt% surfactant.

12. A process of any one of claims 1-11 wherein the aqueous solution of base or acid added in step (c) has a final concentration of about 0.001 to about 3 M, preferably about 0.025 to about 0.5 M.

13. A process of any one of claims 1-12 wherein an aqueous solution of strong base is added in step (c), preferably selected from the group comprising sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, barium hydroxide and caesium hydroxide.

14. The process of any one of claims 1-12 wherein an aqueous solution of strong acid is added in step (c), preferably selected from the group comprising hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, p-toluenesulfonic acid and methanesulfonic acid.

15. The process of any one of claims 1-12 wherein an aqueous solution of weak base or weak acid is added in step (c), preferably selected from the group comprising potassium carbonate, sodium carbonate, caesium carbonate, phosphoric acid, acetic acid, formic acid, benzoic acid and boric acid.

16. The process of any one of claims 1-15 wherein the Pickering emulsion in step (d) is heated for about 5-90 minutes at about 40°C, without stirring, preferably at least 15 minutes.

17. The process of any one of claims 1-16 wherein the Pickering emulsion in step (d) is heated until the lipophilic portion comprises about 30% to about 70% of the surface area of the spherical cellulose nanoparticles on average, 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 on average.

18. The process of any one of claims 1-17 wherein the aqueous phase is neutralised in step (e) to stop the reaction.

19. A Janus-type spherical cellulose nanoparticle prepared by a process of any one of claims 1-18, preferably wherein the surface of the Janus-type spherical cellulose nanoparticles is partially functionalised with (C1-C20) ester groups.

20. A Janus-type spherical cellulose nanoparticle of claim 19 which has a volume average particle diameter of about 10 nm to about 1000 nm, preferably about 20 nm to about 600 nm, more preferably about 20 to about 200 nm, even more preferably about 100 to about 200 nm.

21. A Janus-type spherical cellulose nanoparticles of claim 19 or claim 20 wherein the lipophilic portion comprises about 30% to about 70% of the surface area of the spherical cellulose nanoparticle on average, 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 nanoparticle on average.

22. A surfactant composition comprising about 0.01 to 10 wt%, preferably 0.05 to 5, more preferably 0.1 to 2 wt% Janus-type spherical cellulose nanoparticles as claimed in any one of claims 19-21.

23. A Pickering emulsion comprising Janus-type spherical cellulose nanoparticles of any one of claims 19-21.

24. A Pickering emulsion of claim 23 comprising about 0.01 to 10 wt% Janus-type spherical cellulose nanoparticles, preferably 0.05 to 5, more preferably 0.1 to 2 wt%.

5. A Pickering emulsion of claim 24 which is an oil-in-water emulsion comprising about 1 to about 50% oil by volume, preferably up to about 20% oil by volume, preferably wherein at least about 5, 10, 15, 20 or 25% of the droplets in the Pickering emulsion are greater than about 5 pm in diameter.

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