Patent Description:
The present disclosure is directed to a Pickering emulsion comprising cellulose filaments.

A Pickering emulsion essentially consists of a two-phase emulsion that is stabilized by solid particles. When oil and water are mixed, in order to avoid collapse of the formed droplets of oil, solid particles are needed. The solid particles bind to the interface between the oil and water and stabilize the droplets. The emulsion can also contain water droplets stabilized in oil.

Cellulosic materials are known to be used as solid particles to stabilize Pickering emulsions. The effect of the morphology of cellulosic materials on the formation of Pickering emulsions has been studied for cellulose nanocrystals (CNC) or nanofibrils (CNF). <NPL>) prepared oil-in-water (o/w) emulsions using cellulose nanocrystals derived from different sources with aspect ratios ranging from <NUM> to <NUM>, and explored the stabilizing effects of unsulfated CNC. The electrostatic repulsion between the negatively charged sulfate groups on the surfaces of CNC has been shown to affect the stability of emulsions, and the ionic strength of the aqueous phase typically controls these interactions.

<NPL>) used surface modified CNF to prepare water-in-oil (w/o) emulsions and investigated the effect of the structure of CNF at the water/oil interface. It was found that large entangled networks and small CNF aggregates did not stabilize the emulsion.

<NPL>) prepared microfibrillated cellulose (MFC) stabilized o/w emulsions and investigated the effect of MFC morphology and MFC concentration on the properties of the emulsions. It was concluded that the oil droplets were stabilized by the MFC fibrils adsorbed at the oil/water interface as well as the inter-droplet network and MFC network formed in the water phase. The same stabilization mechanism was also observed in bacterial cellulose stabilized emulsions owing to a similar entangled network structure within bacterial cellulose.

All of the known work, and research to-date involving cellulosic materials stabilized emulsions only examined low-internal phase systems, where the dispersed phase is <NUM> % or lower (by volume) in the emulsion.

High-internal phase emulsions (HIPEs) are emulsion systems containing an internal, or dispersed, phase volume fraction greater than <NUM>%, which is the maximum volume ratio of monodispersed non-deformable spheres when packed at the most efficient manner. The emulsions with an internal phase of <NUM>-<NUM>% are normally called medium-internal phase emulsions (MIPEs).

There is still a need to be provided with alternative methods for producing Pickering emulsions, particularly MIPEs and/or HIPEs Pickering emulsions.

In accordance to an embodiment, it is provided an emulsion according to claim <NUM>.

It is also provided a method of producing an emulsion according to claim <NUM>.

In an embodiment, the emulsion described herein comprises <NUM>% or more in volume of the internal phase.

In another embodiment, the emulsion comprises between <NUM>%-<NUM>% in volume or more of the internal phase.

In an additional embodiment, the emulsion comprises between <NUM>%- <NUM>% in volume of the internal phase.

In the claimed invention, the internal phase is hydrophobic and the external phase is hydrophilic.

In the claimed invention, the internal phase comprises oil and the external phase comprises water.

In a further unclaimed embodiment, the internal phase is hydrophilic and the external phase is hydrophobic.

In an additional unclaimed embodiment, the internal phase comprises water and the external phase comprises oil.

In another embodiment, the cellulose filaments concentration is below <NUM> wt%.

In the claimed invention, the cellulose filaments concentration is between <NUM> -<NUM> wt%.

In an additional embodiment, the cellulose filaments concentration is between <NUM>-<NUM> wt%.

In the claimed invention, the cellulose filaments are from bleached or unbleached cellulose pulp fibers.

In an additional embodiment, the cellulose pulp fibers are from softwood, hardwood, perennial fibers, recycled fibres, or a combination thereof.

In an additional embodiment, the perennial fibers are from bagasse, flax, kenaf, hemp or a combination thereof.

In a further embodiment, the cellulose pulp fibers are from northern bleached softwood, hardwood kraft fibers, bleached chemi-thermo-mechanical pulps, thermo-mechanical pulps, or unbleached pulps.

In another embodiment, the cellulose filaments are inhomogeneous in mass and dimension.

In a further embodiment, the surface properties of the cellulose filaments are adjusted by changing the pH of suspension.

In a supplemental embodiment, the surface properties of cellulose filaments are partially modified by grafting/adsorbing hydrophobic molecules or introducing other functional groups via chemical reactions.

In an embodiment, the cellulose filaments are chemically modified to be hydrophobic before being incorporated in the external phase comprising hydrophobic liquid.

In a further embodiment, the cellulose filaments dispersed in water comprising a salt prior to be incorporated to the internal phase.

In a further embodiment, the salt is monovalent, divalent, or trivalent.

In an embodiment, the cellulose filaments derived from unbleached pulps possess more hydrophobic surfaces compared to those from bleached pulps.

In a further embodiment, the unbleached cellulose filaments disperse in water.

In an additional embodiment, the unbleached cellulose filaments stabilize hydrophobic internal phase in water.

In an embodiment, the surface properties of the unbleached cellulose filaments can be adjusted by changing the pH of the aqueous phase, in which the cellulose filaments are dispersed.

In a further embodiment, the pH of the aqueous phase is <NUM> or higher.

In an additional embodiment, the pH of the aqueous phase is <NUM> or higher.

In an additional embodiment, the unbleached cellulose filaments distribute more homogeneous at the interface of oil and water at higher pH.

In an embodiment, the emulsions stabilized with unbleached cellulose filaments at high pH are highly stable.

In an additional embodiment, the cellulose filaments are incorporated to the internal phase by homogenization at a mixing speed of <NUM> to <NUM><NUM> rpm.

Reference will now be made to the accompanying drawings.

In accordance with the present disclosure, there is provided a Pickering emulsion comprising cellulose filaments. The emulsion described herein comprises an internal phase dispersed in a continuous external phase and cellulose filaments located at the interface of the internal phase and the external phase, wherein the emulsion comprises <NUM>% in volume or more of the internal phase.

Disclosed herein are a method and system for preparing medium- and high-internal phase oil-in-water Pickering emulsions stabilized by a thin layer of controllably distributed cellulose filaments and whole or partial fibrous fragments of significantly larger dimensions. The fine fibrils surround the oil droplets without a high level of entanglement, and the emulsions exhibit viscous gel-like appearance. The total cellulose filament concentration encompassed herein is below <NUM> wt. %, otherwise the level of entanglement increases and the emulsions are de-stabilized. The inhomogeneity of the cellulose filament material is critical and beneficial to the formation of emulsions. The removal of large fragments to produce a homogeneous distribution of fibrillar mass or uniform physical dimensions, as in cellulose microfibrils or nanofibrils, leads to a higher level of entanglement and the lowering of the maximum oil content in the emulsion. This causes de-stabilization of the emulsion over time, and fails to produce high-internal phase Pickering emulsions.

The distribution of the fibrillar component and the whole, or partial, fibre fragments within the cellulose filament material are controlled by the magnitude of the mechanical energy applied to produce cellulose filaments. If the cellulose filaments are suitably rendered hydrophobic, they can be used to stabilize water-in-oil Pickering emulsions.

Contrary to <CIT>) which uses cellulose nanocrystals, which have a uniform distribution of size and charge, and are structurally and morphologically different from cellulose filaments as encompassed herein, it is provided the use of cellulose filamentous materials of controllably heterogeneous distribution of fibrillar material and fibrous segments, whole or partial, to stabilize medium- and high-internal phase Pickering emulsions. In particular, the cellulose filamentous materials, which are hydrophilic, can be used as-is in oil-in-water emulsions, or suitably modified by chemical means, for instance, to render them hydrophobic, and hence suitable for water-in-oil emulsions.

Cellulose filaments are typically obtained by applying mechanical forces (a combination of shearing, tensile and radial compressive forces) to native cellulose pulp fibres. The starting raw material can essentially be pure or a combination of lignocellulosic biomass, e.g., bleached or unbleached chemical, mechanical or chemi-mechanical wood pulp fibres. The native fibres can be softwood, hardwood, or perennial fibres, like bagasse, flax and kenaf. Perennial fibres, like bagasse, kenaf, flax or hemp can also be used as raw materials to produce CF. In certain cases, chemical or biochemical processing can additionally be applied to reduce the mechanical energy input and impart desirable attributes related to controlling fibrillation. It may thus be necessary to use selective chemical or enzymatic treatment to both, control the energy input and produce controllable distributions of heterogeneous physical components. The cellulose filaments thus produced necessarily possess a controlled combination of fine fibrils and some larger fibrous fragments. The quantity of large fragments is primarily related to the mechanical operating conditions. The ratio of the highly fibrillated component to fibrous fragments essentially influences the oil/water ratio and the total CF consistency in the water phase. Together, these factors can controllably tune the formation of medium- or high-internal phase emulsions.

Since CF is produced mainly by mechanical means, the chemical composition of the starting raw materials will be retained and can influence the properties of the final CF. For example, the CF produced from unbleached kraft pulp contains lignin and the presence of lignin can affect the surface properties of CF fibrils, thereby changing the level of entanglement by interfering with the formation of hydrogen bonding among the fibrils. When applied to an emulsion, this type of CF would be easier to distribute at the oil/water interface leading to more stable emulsions. When the surface property of this type of CF is further changed by adjusting the pH of CF suspension, i.e., increase the pH to a level where the lignin becomes soluble in water, CF fibrils can be further disentangled to form a much more uniform network at the oil/water interface. As a results, the formed emulsions have smaller oil droplet size, more uniform size distribution, and high stability in centrifuge test. Besides the composition of the raw materials, the surface properties of CF fibrils can also be modified chemically by attaching hydrophobic molecules, e.g., paper sizing agents, or physically by adsorptionof hydrophobic molecules, e.g., surfactants. In this case, the change of surface property should be controlled to a level where the CF still disperse in water, yet the CF fibrils should be disentangled. The other ways to modify CF include introduction of new functional groups on fibril surfaces, e.g., carboxymethylation, esterification.

The physical dimensions of the cellulose filamentous materials cover a spectrum for the fibrillar material, which can have micron to nanometer widths, and varying lengths in the range of microns to millimetres. The fibre segments can typically be in the micron to submicron range. It is critical that both, fibrillar materials or elements are present, as well as whole or partial fibrous segments to function as efficient and effective stabilizers to these emulsions. Solely fibrillar or fibrous segments of uniform size will fail to stabilize the emulsions.

CF can be produced using various levels of refining energy ranging from several hundred to several thousand kWh/T. The level of refining energy imparts a specific level of fibrillation and generation of fibre fragments through either fibre cutting, fibre splitting or defibrillation. The raw material when subjected to refining mechanical action undergoes a combination of shear and tensile forces, as well as radial compressive forces. Selective chemical, enzymatic or combinations of both can be applied to lower the mechanical energy input, on the one hand, but also to guide the level and manner of fibre development, i.e., the extent to which fibrillation can occur and fibre fragments generated.

The starting raw material for producing CF can be, for example, but not limited to, northern bleached softwood kraft (NBSK) pulp fibres. Subsequently, for the preparation of emulsions, CF can be used dry or in a slurry of any practical consistency (<NUM>-<NUM> wt. When preparing the Pickering emulsions, the CF aqueous suspensions should ideally be at a specific concentration, such as for example <NUM> wt. %, following a simple disintegration and/or homogenization protocol.

To disperse CF in water, wet CF (containing, for instance, <NUM> of dry weight) is mixed with <NUM> of <NUM> hot deionized water (DI) water in a standard pulp disintegrator and beaten for <NUM>,<NUM> revolutions or <NUM>. The resulting viscous CF slurry will have a consistency of <NUM> wt. To get CF slurries with higher consistency, this <NUM> % CF slurry can further be concentrated using, for example, Whatman # <NUM> filter paper on a Buchner funnel with the assistance of low pressure from a water aspirator. The resulting concentrated CF slurry can then be homogenized using a standard mixing assembly on a homogenizer (Silverson L4RT-A) equipped with a general purpose disintegrating screen and an axial flow head for <NUM> sec at <NUM>,<NUM> rpm. The consistency of CF in the final slurry can be determined gravimetrically.

The range of suitable CF concentrations for preparing medium- or high-internal phase Pickering emulsions is limited to <NUM> to <NUM> wt. % in order to maximize stability of the resulting emulsion. <FIG> depicts the physical state of higher-solid contents CF, and the ideal low-solids content CF to be used for preparing emulsions. The consistency of the CF in the final slurry can be determined gravimetrically, and to avoid any potential surface charge interference, a small amount of monovalent salt, say <NUM> of NaCl, can be added to the CF slurry.

<FIG> illustrates the typical morphology of the mechanically produced CF, the subject of the present disclosure, in relation to CNF, a type of cellulose fibrils processed using a combination of mechanical as well as chemical and/or enzymatic treatments leading to a highly homogeneous material relative to CF. CF is also compared to two distinctly different cellulose-based materials, wood pulp fibres (the starting raw material) and chemically-produced microcrystalline cellulose (MCC) particles.

To create the most efficient and effective system, it is disclosed the preparation of CF-stabilized Pickering emulsions via a two-step homogenization process using, for instance, a <NUM>" tubular mixing assembly equipped with a general purpose disintegrating head on a homogenizer (Silverson L4RT-A). In the first step, a low amount of homogenization energy, between <NUM> and <NUM> rpm, is applied for a short interval, ≤ <NUM>. At this stage, the mixing head is lowered to the bottom of the vessel, or beaker, and only a portion of the oil phase is allowed to mix with the CF aqueous suspension. The second step entails rapidly increasing the mixing speed to <NUM>,<NUM> rpm (or higher, if necessary, but likely not to exceed <NUM>,<NUM> rpm). During the second step, this level of energy input is ideally maintained for an additional one minute, but not longer than <NUM>. Variations on this approach are, however, possible and will lead to similar results.

Following the second homogenization step, the mixture instantaneously forms a gel-like emulsion (<FIG>). The morphology of a typical CF-stabilized high-internal phase Pickering emulsion prepared according to the method and systems disclosed herein is illustrated in <FIG>. The optical micrograph clearly shows each of the individual oil droplets being surrounded by a thin layer of cellulose filaments, thus preventing the oil droplets from coalescing. The oil droplets, depending on the specific requirements for producing a desired emulsion, can have a size distribution over a wide range from tens of microns to hundreds of microns. The oil droplets, in all cases, possess a compact structure with preferential polygonal shapes. Both the fibrils and large fragments of CF are clearly visible in the image shown in <FIG>, thereby confirming the underlying mechanism of the disclosed approach that both fibrillar and fibre fragments are needed to ensure stability of the emulsion, i.e., a controlled distribution of the fibrillated material at the micron or sub-micron scale and fibre fragments at the millimeter scale.

The cellulose filaments (CF) encompassed herein are heterogeneous systems consisting of fine fibrils and large fragments (<FIG>). The presence of large fragments can prevent the entanglement of fine fibrils in two particular ways. The fibre fragments can controllably and selectively infiltrate the fibrillar network, and thus prevent the fibrillar network from being entangled. In addition, the fibre fragments can effectively reduce the quantity of fine fibrils at the same mass consistency, thereby controllably creating a heterogeneous distribution of fibrillar mass and fibre fragments. Since the entanglement level of CF fibrils plays an important role in influencing the formation, and subsequent stability, of the emulsions, it was of relevance to investigate a system without the large fragments, i.e., a more homogeneous distribution of fibrillar mass, unlike the CF material being described in this disclosure. For this purpose, a cellulose nanofibrils (CNF) sample produced from bleached softwood kraft pulp, a similar raw material as CF's, is used to compare with CF. At similar concentration of cellulose materials and oil content, the emulsion containing CNF shows different appearance and is unstable. This discrepancy is clearly revealed by <FIG>. It is apparent from <FIG> that the highly entangled CNF fibrils cannot disentangle and distribute at the oil/water interface. Rather, the majority of the CNFs exist in the system as entangled blobs (the white clouds in <FIG>), and the dimensions of oil droplets in the CNF-stabilized emulsion become very large due to lack of stabilizing materials.

Accordingly, it is not the chemical composition per se, but the geometry and morphology that are key factors to stabilizing Pickering emulsions. For instance, CF-stabilized Pickering emulsions can be contrasted with those prepared using northern bleached softwood kraft (NBSK) fibres or microcrystalline cellulose (MCC), both commonly used in a variety of emulsion systems. NBSK pulp fibres, a typical raw material for producing CF, consist of discrete fibres whose widths fall in the range <NUM>-<NUM> and lengths <NUM>-<NUM> (<FIG>). MCC, on the other hand, is composed of discrete particulates with irregular shapes whose average size is approximately <NUM> (<FIG>).

The entanglement of fine fibrils de-stabilizes emulsions and prevents increasing the oil content to reach the level of high-internal phase Pickering emulsions. The unique mechanism responsible for stabilizing both medium- and high-internal phase Pickering emulsions using CF, where there is a heterogeneous distribution of fibrillar mass and fibre fragments, is explained in <FIG>. In this mechanism, the properties of the emulsions are primarily influenced by the level of entanglement of CF fibrils and infiltration of fibrous fragments, which is directly related to CF consistency in the aqueous phase. The homogenization processing used for preparing the Pickering emulsions is incapable of de-entangling the fibrillar networks. Hence, the oil droplets in the emulsion system can only stay in the free space or voids within the entangled network. These oil droplets will thus take the shape permitted by the specific geometry imparted by the specific distribution of fibrillar network, and may undergo some deformation. This is clearly evidenced by the wide range of size distribution and hexagonal geometry of the oil droplets within the high-internal phase Pickering emulsion presented in <FIG>.

As an illustrative example, oil-in-water emulsions with <NUM> vol. % oil and <NUM> % NBSK or MCC were prepared and their properties compared with those of the high-internal phase Pickering emulsions stabilized with <NUM> % CF. Unlike the gel-like appearance of the CF-stabilized Pickering emulsion, both NBSK- and MCC-stabilized emulsions exhibit low viscosity and appear free to flow (see <FIG>). Furthermore, the oil droplets in the NBSK or MCC emulsions are very large and directly visible in the photographs owing to the large dimension of the NBSK pulp fibres or MCC particles (<FIG>), and the NBSK pulp or MCC particles appear precipitated at the bottom with a layer of water clearly separated in both cases. On the other hand, the CF-stabilized emulsion is unperturbed over a <NUM>-day storage period. Indeed, it remains stable over storage, at ambient conditions, for over <NUM> months (and counting).

In another example, oil-in-water emulsions were prepared using CF produced from unbleached kraft pulp. At <NUM> wt. % CF concentration and <NUM> vol. % oil content, the emulsions demonstrated totally different stability in the centrifugation test when the CF suspension was at neutral and high pH. As shown in <FIG>, owing to the high oil content, most of the neutral pH emulsion phase-separate after centrifuging at <NUM>,<NUM> rpm for <NUM>. However, drastic change occurred by merely increasing the pH to <NUM>, where most of the emulsion phase was retained after centrifugation at the same conditions. The optical microscopy images in <FIG> reveal the difference of oil droplets in these two emulsions. At neutral pH, the oil droplets are large polygonal shaped with a wide size distribution, which is similar to the emulsion stabilized with CF produced from NBSK pulp (see <FIG>). At high pH, however, the oil droplets become much smaller and more uniform.

Claim 1:
An emulsion comprising an internal phase dispersed in a continuous external phase and cellulose filaments located at the interface of the internal phase and the external phase, wherein the emulsion comprises <NUM>% in volume or more of the internal phase, wherein the cellulose filaments concentration is between <NUM>-<NUM> wt%, and wherein the cellulose filaments are inhomogeneous in mass and dimension, wherein the inhomogeneous cellulose filaments comprises fibrils that are smaller than fibrous fragments, the inhomogeneous cellulose filaments being from bleached or unbleached cellulose pulp fibers on which mechanical forces characterized by a combination of shearing, tensile and radial compressive forces are applied to obtain the cellulose filaments, wherein the internal phase comprises oil and the external phase comprises water.