PICKERING EMULSIONS

Abstract

The present invention refers to Pickering emulsion comprising (i) water; (ii) 10 to 50 wt.-% oil, based on the total weight of the Pickering emulsion and (iii) 1 to 10 wt.-% of Pickering pigments, based on the total weight of the Pickering emulsion, wherein the Pickering pigments are calcium carbonate particles selected from surface-reacted calcium carbonate (SRCC) or mixtures of ground calcium carbonate (GCC) and surface-reacted calcium carbonate (SRCC) and wherein the calcium carbonate particles have a volume median particle size d.sub.50 value from 0.2 .Math.m to 10 .Math.m. Furthermore, the present invention refers to a composition comprising said Pickering emulsions and a method of preparing such Pickering emulsions. The present invention also refers to the use of calcium carbonate particles as Pickering pigments for stabilizing Pickering emulsions comprising water and 10 to 50 wt.-% oil, based on the total weight of the Pickering emulsion, wherein the calcium carbonate particles are selected from surface-reacted calcium carbonate (SRCC) or mixtures of ground calcium carbonate (GCC) and surface-reacted calcium carbonate (SRCC) and have a volume median particle size d.sub.50 value from 0.2 .Math.m to 10 .Math.m.

Claims

1. Pickering emulsion comprising (i) water; (ii) 10 to 50 wt.-% oil, based on the total weight of the Pickering emulsion and (iii) 1 to 10 wt.-% of Pickering pigments, based on the total weight of the Pickering emulsion, wherein the Pickering pigments are calcium carbonate particles selected from surface-reacted calcium carbonate (SRCC) or mixtures of ground calcium carbonate (GCC) and surface-reacted calcium carbonate (SRCC) and wherein the calcium carbonate particles have a volume median particle size d.sub.50 value from 0.2 .Math.m to 10 .Math.m.

2. The Pickering emulsion according to claim 1, wherein the ground calcium carbonate is selected from the group consisting of marble, limestone, and/or chalk and preferably is marble and/or the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source.

3. The Pickering emulsion according to claim 1, wherein the ground calcium carbonate has a) a volume median particle size d.sub.50 value from 0.3 .Math.m to 5.0 .Math.m, preferably from 0.6 .Math.m to 3 .Math.m and most preferably from above 1.0 .Math.m to 1.7 .Math.m, and/or b) a top cut (d.sub.98(vol)) of ≤20 .Math.m, preferably ≤ 15 .Math.m, more preferably ≤ 10 .Math.m and most preferably ≤ 7 .Math.m, and/or c) a specific surface area (BET) of from 0.5 to 50 m.sup.2/g, preferably from 0.5 to 35 m.sup.2/g, more preferably from 0.5 to 25 m.sup.2/g, and most preferably from 0.6 to 17 m.sup.2/g, as measured by the BET nitrogen method.

4. The Pickering emulsion according to claim 1, wherein the surface-reacted calcium carbonate has a) a volume median particle size d.sub.50 value from 1.5 .Math.m to 9.0 .Math.m, preferably from 2.5 .Math.m to 7.5 .Math.m and most preferably from 3.3 .Math.m to 6.6 .Math.m, and/or b) a top cut (d.sub.98(vol)) of ≤ 20 .Math.m, preferably ≤ 15 .Math.m, more preferably ≤ 10 .Math.m and most preferably ≤ 7 .Math.m, and/or c) a specific surface area (BET) of from 10 to 200 m.sup.2/g, preferably from 20 to 180 m.sup.2/g, more preferably from 25 to 140 m.sup.2/g, and most preferably from 48 to 110 m.sup.2/g, as measured by the BET nitrogen method and/or d) an intra-particle intruded specific pore volume in the range from 0.1 to 2.3 cm.sup.3/g, more preferably from 0.2 to 2.0 cm.sup.3/g, especially preferably from 0.4 to 1.5 cm.sup.3/g, and most preferably from 0.6 to 1.1 cm.sup.3/g, calculated from mercury porosimetry measurement.

5. The Pickering emulsions according to claim 1, wherein the emulsions comprise 10 to 40 wt.-% oil, based on the total weight of the Pickering emulsion, preferably 10 to 30 wt.-% oil and most preferably 10 to 20 wt.-% oil.

6. The Pickering emulsions according to claim 1, wherein the oil is selected from the group consisting of mineral oils, vegetable oils, animal fats, essential oils and mixtures thereof, preferably selected from the group consisting of essential oils, sunflower oil, olive oil, palm oil, coconut oil, peanut oil, palm kernel oil, corn oil, hazelnut oil, sesame oil and mixtures thereof, preferably is selected from sunflower oil, olive oil, palm oil and/or coconut oil and most preferably is sunflower oil and/or is a refined oil having an acid value below 0.6, preferably below 0.5 and most preferably below 0.3 or an unrefined oil having an acid value below 4.0, preferably below 3.0 and most preferably below 2.0.

7. The Pickering emulsions according to claim 1, wherein the emulsions comprise 2 to 10 wt.-% Pickering pigments, based on the total weight of the Pickering emulsion, preferably 4 to 10 wt.-% Pickering pigments and most preferably 6 to 10 wt.-% Pickering pigments.

8. The Pickering emulsions according to claim 1, wherein the emulsions comprise further active ingredients, preferably selected from cosmetic active compounds, pharmaceutical active compounds, nutritional additives, flavoring agents and mixtures thereof.

9. The Pickering emulsions according to claim 1, wherein the emulsions are stable against coalescence for at least 15 days, more preferably for at least 20 days and most preferably for at least 30 days.

10. The Pickering emulsions according to claim 1, wherein the emulsion does not comprise an additional emulsifier for stabilizing the droplets in the Pickering emulsions apart from the Pickering pigments.

11. Composition comprising the Pickering emulsion of claim 1, wherein the composition is a food composition, a cosmetic composition, a pharmaceutical composition or a nutritional formula.

12. Method of preparing a Pickering emulsion, the method comprising the steps of: A) providing water, B) providing oil, C) providing Pickering pigments, wherein the Pickering pigments are calcium carbonate particles selected from surface-reacted calcium carbonate (SRCC) or mixtures of ground calcium carbonate (GCC) and surface-reacted calcium carbonate (SRCC) and wherein the calcium carbonate particles have a volume median particle size d.sub.50 value from above 0.1 .Math.m to 10 .Math.m D) combining the water of step A), the oil of step B) and the Pickering pigments of step C) in any order to obtain a mixture comprising 10 to 50 wt.-% oil, based on the total weight of the mixture and 1 to 10 wt.-% of Pickering pigments, based on the total weight of the mixture and E) mixing the mixture obtained in step D) to prepare a Pickering emulsion.

13. Method according to claim 12, wherein the surface of the Pickering pigments provided in step C) and preferably of the surface-reacted calcium carbonate particles is not coated with a surface treatment agent.

14. A method for stabilizing a Pickering emulsion, comprising adding water, 10 to 50 wt.-% oil based on the total weight of the Pickering emulsion, and calcium carbonate particles as Pickering pigments, wherein the calcium carbonate particles are selected from surface-reacted calcium carbonate (SRCC) or mixtures of ground calcium carbonate (GCC) and surface-reacted calcium carbonate (SRCC) and have a volume median particle size d.sub.50 value from 0.2 .Math.m to 10 .Math.m.

Description

[0229] The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the present invention and are non-limitative.

FIGURES

[0230] FIG. 1: Microscope image of Pickering emulsion 2

[0231] FIG. 2: Microscope image of Pickering emulsion 3

[0232] FIG. 3: Droplet size dependent on storage time of Pickering emulsion 1

EXPERIMENTS

1. Measurement Methods

[0233] In the following, measurement methods implemented in the examples are described.

BET Specific Surface Area (SSA) of a Material

[0234] The BET specific surface area was measured via the BET process according to ISO 9277:2010 using nitrogen, following conditioning of the sample by heating at 250° C. for a period of 30 minutes. Prior to such measurements, the sample was filtered, rinsed and dried at 110° C. in an oven for at least 12 hours.

Particle Size Distribution (% Particles With a Diameter < X), D.SUB.50 Value (Median Grain Diameter) and d.SUB.98 Value of a Particulate Material

[0235] Volume median grain diameter d.sub.50(vol) was evaluated using a Malvern Mastersizer 2000 Laser Diffraction System or a Malvern Mastersizer 3000 Laser Diffraction System. The d.sub.50(vol) or d.sub.98(vol) value, measured using a Malvern Mastersizer 2000 Laser Diffraction System or Malvern Mastersizer 3000 Laser Diffraction System, indicates a diameter value such that 50 % or 98 % by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005.

[0236] The processes and instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments.

[0237] The weight determined or based median grain diameter d.sub.50(wt) was measured by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph™ 5120 of Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments. The measurement was carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonicated.

Porosity / Pore Volume

[0238] The porosity or pore volume is measured using a Micromeritics Autopore IV 9500 mercury porosimeter having a maximum applied pressure of mercury 414 MPa (60 000 psi), equivalent to a Laplace throat diameter of 0.004 .Math.m (~ nm). The equilibration time used at each pressure step is 20 seconds. The sample material is sealed in a 5 ml chamber powder penetrometer for analysis. The data are corrected for mercury compression, penetrometer expansion and sample material compression using the software Pore-Comp (Gane, P.A.C., Kettle, J.P., Matthews, G.P. and Ridgway, C.J., “Void Space Structure of Compressible Polymer Spheres and Consolidated Calcium Carbonate Paper-Coating Formulations”, Industrial and Engineering Chemistry Research, 35(5), 1996, pp 1753-1764.).

Type of Pickering Emulsion

[0239] The drop method was used to determine the type of emulsion. One drop of the emulsion was placed in water and one in oil. In the medium of the continuous phase, the emulsions are dispersible, in the medium of the disperse phase the drops settle on the vessel wall. This means O/W emulsions can be dispersed in water but not in oil and W/O emulsions can only be dispersed in oil.

Droplet Size (Optical and Light Scattering)

[0240] The droplet size is determined by microscopic analysis. Under the microscope (Olympus BX51, Olympus Europa SE& Co KG, Germany), images are taken at two different points on each sample (Olympus SC50, Olympus Europa SE& Co KG, Germany) and ten droplets are measured using cellSens software. From these 20 measured values, the mean value and the standard deviation are determined.

[0241] In addition to the optical evaluation, the droplet size was also determined by light scattering (Mastersizer 3000, Malvern Panalytical GmbH, Germany). For this purpose 2 mL of the emulsion was diluted with water and added to the wet dispersion module for measurement. The evaluation was carried out using Mie theory for round particles and a refractive index of 1.53, which lies between the value for sunflower oil and that for calcium carbonate. Thus the multiple refraction at a Pickering drop (particle-drop particle) is taken into account.

[0242] The measured values determined by light scattering do not differ from the optical evaluation.

2. Material and Equipment

Materials

[0243] Water: Demineralized water [0244] Oil: Sunflower oil, available from M-classic [0245] Pickering pigment: surface-reacted calcium carbonate (SRCC) (d.sub.50(vol) = 6.6 .Math.m, d.sub.98(vol) = 13.7 .Math.m, SSA = 59.9 m.sup.2/g). The intra-particle intruded specific pore volume is 0.939 cm.sup.3/g (for the pore diameter range of 0.004 to 0.51 .Math.m).

[0246] SRCC was obtained by preparing 350 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground limestone calcium carbonate from Omya SAS, Orgon having a weight based median grain diameter d.sub.50(wt) of 1.3 .Math.m, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, is obtained.

[0247] Whilst mixing the slurry at a speed of 6.2 m/s, 11.2 kg phosphoric acid was added in form of an aqueous solution containing 30 wt.-% phosphoric acid to said suspension over a period of 20 minutes at a temperature of 70° C. After the addition of the acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying using a jet-dryer. [0248] Ground calcium carbonate I (GCC I) (d.sub.50(vol) = 1.0 .Math.m, SSA = 3.7 m.sup.2/g). [0249] Ground calcium carbonate II (GCC II) (d.sub.50(vol) = 8.1 .Math.m, SSA = 2.1 m.sup.2/g). [0250] Precipitated calcium carbonate (PCC) (d.sub.50(vol) = 7.65 .Math.m, SSA = 3.3 m.sup.2/g).

Preparation of the Pickering Emulsions 1 to 3

[0251] The oil is added to a glass beaker. Afterwards the Pickering pigment (surface reacted calcium carbonate as mentioned above) is added to the oil and dispersed with a high shear mixer (Polytron PT3100D, Kinematica AG, Switzerland) for 1 minute at 5000 rpm. Subsequently water is added slowly to the slurry over 1 minute and the mixture is homogenized for 4 minutes at 15000 rpm with a high shear mixer (Polytron PT3100D, Kinematica AG, Switzerland).

[0252] The used amounts are given in table 1 below

TABLE-US-00001 Oil content [g] Pigment content [g] Water content [g] Pickering emulsion 1 75 12 63 Pickering emulsion 2 15 1.5 133.5 Pickering emulsion 3 45 4.5 100.5

Preparation of the Emulsions 4 and 5

[0253] The emulsions 4 and 5 were prepared by the method according to the Pickering emulsions 1 to 3. As pigment ground calcium carbonate I (GCC I) has been used.

TABLE-US-00002 Oil content [g] Pigment content [g] Water content [g] Emulsion 4 75 10.5 64.5 Emulsion 5 75 15 60

Preparation of the Pickering Emulsions/Emulsions 6 to 17

[0254] The oil is added to a glass beaker. Afterwards the Pickering pigment (SRCC) (emulsions 10, 11, 16, 17) or the ground calcium carbonate II (GCC II) (emulsions 8, 9, 14, 15) or the precipitated calcium carbonate (emulsions 6, 7, 12, 13) is added to the oil and dispersed with a high shear mixer (Ultra Turrax T25, IKA®-Werke GmbH & CO. KG, Germany) for 30 seconds at 6500 rpm. Subsequently water is added slowly to the slurry over 30 seconds and the mixture is homogenized for 2 minutes at 17500 rpm with a high shear mixer (Ultra Turrax T25, IKA®-Werke GmbH & CO. KG, Germany).

TABLE-US-00003 Oil content [g] Pigment content [g] Water content [g] Emulsion 6 22.5 3.75 48.75 Emulsion 7 22.5 7.5 45 Emulsion 8 22.5 3.75 48.75 Emulsion 9 22.5 7.5 45 Pickering emulsion 10 22.5 3.75 48.75 Pickering emulsion 11 22.5 7.5 45 Emulsion 12 37.5 3.75 33.75 Emulsion 13 37.5 7.5 30 Emulsion 14 37.5 3.75 33.75 Emulsion 15 37.5 7.5 30 Pickering emulsion 16 37.5 3.75 33.75 Pickering emulsion 17 37.5 7.5 30

[0255] In emulsions 6, 8, 9, 12, 13, 14 and 15 the oil and water phase do not form an emulsion but rather each phase is present separately in the mixture.

3. Example Data

[0256] The droplet size of Pickering emulsion 1 has been measured by light scattering on the day of the preparation and after storing for 21 days at room temperature. As can be seen from FIG. 3 the droplet size merely changes from 17 .Math.m to 18 .Math.m and, therefore, is stable against coalescence.

[0257] The droplet size of Pickering emulsions 2 and 3 has been determined by microscopic analysis on the day of the preparation at room temperature. As can be seen from FIGS. 1 and 2 the droplet size is very homogeneous and varies from about 100 .Math.m to 150 .Math.m in Pickering emulsion 2 and from about 30 to 70 .Math.m in Pickering emulsion 3.

[0258] The droplet size of emulsions 4 and 5 has been determined by microscopic analysis on the day of the preparation at room temperature. The droplet size is not very homogeneous and varies from about 30 .Math.m to 150 .Math.m in Emulsion 4 and from about 20 to 80 .Math.m in Emulsion 5.

[0259] Both emulsions prepared merely with GCC (emulsions 4 and 5) were instable after 14 days with a separated oil phase. Therefore no droplet size measurement was possible after that storage time.

[0260] The droplet size of Pickering emulsions/emulsions 6 to 17 has been measured by light scattering after storing for 21 days at room temperature (if an emulsion has been formed). Emulsions 6, 8, 9, 12, 13, 14 and 15 do not form an emulsion but rather each phase (the oil phase and water phase) is present separately in the mixture. The droplet size of emulsion 7 is 305 .Math.m, of emulsion 10 63 .Math.m, of emulsion 11 25 .Math.m, of emulsion 16 145 .Math.m and of emulsion 17 54 .Math.m.

[0261] The above experiments show that it is possible to prepare stable Pickering emulsions with Pickering pigments that have a volume median particle size d.sub.50 value from 0.2 .Math.m to 10 .Math.m and, therefore, do not comprise nanoparticles that have mainly primary diameters below 150 nm. Furthermore, as can be seen from the above experiments, these Pickering emulsion do not need an additional emulsifier or surfactants, co-stabilizers or surface coatings on the surface of the Pickering pigments, for stabilizing the droplets in the Pickering emulsions apart from the Pickering pigments. Additionally, the inventive Pickering emulsions have a white colour. However, it is not possible to prepare such Pickering emulsions merely with ground calcium carbonate (GCC) or merely with precipitated calcium carbonate (PCC). Only with the inventive Pickering pigments it is possible to prepare stable Pickering emulsions that comprise water; 10 to 50 wt.-% oil, based on the total weight of the Pickering emulsion and 1 to 10 wt.-% of Pickering pigments, based on the total weight of the Pickering emulsion and are stable within the claimed range.