WO2022006644A1 - Nanofibrillated cellulose emulsion, emulsification process, use of cationic nanofibrillated cellulose and use of emulsion - Google Patents

Nanofibrillated cellulose emulsion, emulsification process, use of cationic nanofibrillated cellulose and use of emulsion Download PDF

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WO2022006644A1
WO2022006644A1 PCT/BR2020/050249 BR2020050249W WO2022006644A1 WO 2022006644 A1 WO2022006644 A1 WO 2022006644A1 BR 2020050249 W BR2020050249 W BR 2020050249W WO 2022006644 A1 WO2022006644 A1 WO 2022006644A1
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cationic
nanofibrillated cellulose
cellulose
pulp
emulsions
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French (fr)
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Juliana BERNARDES
Caroline DA SILVA
Watson LOH
Kam Chiu Tam
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Cnpem - Centro Nacional De Pesquisa Em Energia E Materiais
Unicamp - Universidade Estadual De Campinas
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Priority to PCT/BR2020/050249 priority Critical patent/WO2022006644A1/en
Priority to BR112023000267A priority patent/BR112023000267A2/en
Publication of WO2022006644A1 publication Critical patent/WO2022006644A1/en

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
    • D21H11/18—Highly hydrated, swollen or fibrillatable fibres
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L29/00—Foods or foodstuffs containing additives; Preparation or treatment thereof
    • A23L29/20—Foods or foodstuffs containing additives; Preparation or treatment thereof containing gelling or thickening agents
    • A23L29/206—Foods or foodstuffs containing additives; Preparation or treatment thereof containing gelling or thickening agents of vegetable origin
    • A23L29/262—Cellulose; Derivatives thereof, e.g. ethers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
    • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
    • C08B15/04—Carboxycellulose, e.g. prepared by oxidation with nitrogen dioxide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B3/00—Preparation of cellulose esters of organic acids
    • C08B3/14—Preparation of cellulose esters of organic acids in which the organic acid residue contains substituents, e.g. NH2, Cl
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
    • C08H8/00—Macromolecular compounds derived from lignocellulosic materials
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
    • C08L1/02—Cellulose; Modified cellulose
    • C08L1/04—Oxycellulose; Hydrocellulose, e.g. microcrystalline cellulose
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
    • C08L1/08—Cellulose derivatives
    • C08L1/10—Esters of organic acids, i.e. acylates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L91/00—Compositions of oils, fats or waxes; Compositions of derivatives thereof
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
    • D21H11/20—Chemically or biochemically modified fibres

Definitions

  • the present invention provides cationic nanofibrillated cellulose (cNFC), which can be used as stabilizer for emulsions, and provides processes to obtain those cNFCs and emulsions.
  • cNFC cationic nanofibrillated cellulose
  • Those emulsions can be used in many applications, e.g. for preparing cosmetics and pharmaceutical formulations.
  • the present invention is within the field of Physical-Chemistry, Nanotechnology, Cosmetology and Pharmacy.
  • Pickering emulsions are emulsions (O/W, W/O, or multiple) stabilized by solid particles instead of surfactants.
  • This surfactant-free character makes this type of emulsion attractive to be used in cosmetics and pharmaceutical applications, in which some surfactants can cause adverse effects (irritancy, hemolytic behavior, etc.).
  • the preferable type of emulsion can be predicted by the contact angle value: O/W when 0 ⁇ 90° and W/O when 0 > 90° (Binks, 2002).
  • the document CN110563964A discloses nanofibrillated cellulose oxidized with TEMPO.
  • the present invention uses a different NFC, different emulsion proportion as well a different preparation method of the NFCs.
  • the document KR20190127150A discloses emulsions stabilized by cellulose nanocrystal for the production of microcapsules.
  • the document CN110343260A discloses aminosilicone nanofibrillated cellulose.
  • the document CN107254002A discloses nanofibrillated cellulose functionalized with cinnamyl groups.
  • the present invention has the object to solve the problems present in the state of the art by providing cationic nanofibrillated cellulose as stabilizers for emulsions.
  • the present application provides a emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
  • the present invention provides a method for producing cationic nanofibrillated cellulose aqueous suspension, wherein it comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
  • the present application provides use of cationic nanofibrillated cellulose as stabilizers for emulsions, wherein the cationic nanofibrillated cellulose is present in an amount of 0.1% to 5% by weight of the final mixture.
  • the present application provides a method for preparing compositions for cosmetics, pharmaceutical and food products, wherein the method comprises an emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
  • FIG. 1 Topography images acquired by AFM of cationic nanofibrillated celluloses prepared with GTMAC: glucose molar ratios (a) 2:1 and (b) 10:1. Scale bars of 1 pm.
  • Figure 2 Instability indexes obtained after 19h of centrifugation at 5590 g for O/W Pickering stabilized by cNFCs 2:1 and 10:1 and oNFC, with concentrations of 0.5 wt. % and 1.0 wt. %.
  • FIG. 1 Photographs of NFCs- Pickering emulsions after centrifugation. Solid content of 0.5 wt. % for cNFC 2:1 (a), cNFC10:1 (c) and oNFC (e), and 1.0 wt. % for cNFC 2:1 (b), cNFC10:1 (d) and oNFC (f).
  • Figure 4 Optical micrographs and droplet size for freshly prepared and diluted cNFC-Pickering emulsions. Solid content of: 0.5 wt. % for (a) cNFC 2:1 and (c) cNFC10:1 , and 1.0 wt. % for (b) cNFC 2:1 and (d) cNFC10:1.
  • FIG. 1 Cryo-TEM images of the top creaming layer diluted of O/W (cNFC 10:1 0.5 wt. %) showing: regions when the oil is attached to the cNFCs (a) and (b). Scale bars of 200 nm.
  • cationic NFCs with different degrees of substitution were applied to stabilize oil-in-water dispersions.
  • the results presented herein show that by using positively charged cellulose nanoparticles, high aspect ratio, and flexibility, O/W emulsions with excellent colloidal stability can be produced.
  • NFCs adsorb onto the interface and form a network in the continuous aqueous phase, increasing the viscosity and, consequently, reducing the oil droplets coalescence without the need of adding other nanoparticles or additives.
  • the O/W Pickering emulsions obtained with the cationic NFCs were stable for up to 6 months without phase separation. Comparing with other emulsion prepared with anionic NFCs, CNCs, cationic chitin and silica, the present emulsion can display lesser toxicity, and better colloidal stability, mainly by two stabilization mechanisms: (i) increasing the viscosity/elasticity of the continuous phase and (ii) attractive electrostatic interaction between oil (negatively charged) and cNFCs. The entanglement of the cNFCs fibers are correspondent to the rheological properties of the continuous aqueous phase of the emulsion.
  • the present invention provides stable O/W Pickering emulsions, prepared by a facile and simple method, using renewable nanomaterials without acids and other co-stabilizers, such as salts, polymers and/or surfactants.
  • the present application provides a emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Flomogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
  • the cationic nanofibrillated cellulose aqueous suspension is prepared by a method comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
  • the cationic nanofibrillated cellulose has dimensions from 200 nm to 2000 nm in length and from 2 nm to 10 nm in width, when functionalized by a cationic agent.
  • the oil phase is selected from the group consisting of mineral oils and organic oils from animals or vegetable origin and mixtures thereof. In one embodiment, the oil phase is selected from: organic oils (plant or animal origin) and minerals oils (petroleum derivatives).
  • nanofibers can also stabilize emulsions with additives dissolved in the oil phase, such as lipophilic vitamins, drugs, dyes or other additives for food, biomedical, cosmetic or industrial purposes.
  • the present invention provides a method for producing cationic nanofibrillated cellulose aqueous suspension, wherein it comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
  • the cationization step comprises at least one cationic reagent selected from the group consisting of glycidyl trimethylammonium chloride GTMAC, chloro-2-hydroxypropyl- trimethylammonium chloride (CHPTAC), chlorocholine chloride, or (2- hydrazinyl-2-oxoethyl)-trimethylazanium chloride.
  • the cation is glycidyl trimethylammonium chloride GTMAC.
  • the cationic reagent is GTMAC at GTMAC anhydroglucose ratios from 2:1 to 10:1.
  • the cationic nanofibrillated cellulose has a degree of substitution from 0.07 to 1.5 mmol/g. In one embodiment, the cationic nanofibrillated cellulose has a degree of substitution from 0.14 to 0.51 mmol/g. [0040] In one embodiment, the cationization step is maintained at 60-65°C for 4h.
  • the present application provides use of cationic nanofibrillated cellulose as stabilizers for emulsions, wherein the cationic nanofibrillated cellulose is present in an amount of 0.1% to 5% by weight of the final mixture.
  • the present application provides a method for preparing compositions for cosmetics, pharmaceutical and food products, wherein the method comprises an emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
  • the emulsion possesses antimicrobial property promoted by cationized nanocelluloses
  • CNCs are obtained via acid hydrolysis of cellulose fibers, displaying an average diameter of 5-70 nm and an average length of 100-250 nm. Therefore, CNCs have a rigid, rod-like morphology.
  • NFCs are produced through the delamination of cellulosic pulp by mechanical processes before or after chemical or enzymatic treatments. NFCs have typical diameters ranging from 3 from 60 nm and lengths from 400 nm to 1 pm.
  • NFCs have a high aspect ratio than CNCs, presenting a fibrillar-like morphology and remarkable flexibility, that is important for its adsorption onto the oil droplets and entanglement in solution to provide high viscosity to the medium (Klemm et al., 2011 ).
  • NFCs with their larger aspect ratio can provide this property in lower concentrations than CNC.
  • Cationic nanofibrillated Cellulose was prepared by a method comprising the steps: i) Processing sugarcane bagasse fibers with organosolv and bleaching processes [4, 5]; ii) Cationization process [6], wherein the cationization was performed with never-dried cellulose pulp (1 Og) that was mixed with sodium hydroxide solution (25 mL, 1 mol L 1 ) in a polyethylene bag, followed by the addition of a cationic reagent GTMAC at GTMAC anhydroglucose ratios of: 2:1 and 10:1.
  • the reaction was performed in a Cole-Parmer ultrasonic bath (110W) at 60-65°C for 4h; iii) Washing of the cationic pulp with ethanol and 0.02 mol L 1 hydrochloric acid; iv) Separation of the pulp by centrifugation and dialyzed against Milli-Q water for 15 days using an INLAB membrane with a MWCO of 22 kDa; v) Fibrillation of cellulose pulp by microfluidization of 1 wt. % suspension was conducted in a Microfluidizer® M-110P (Microfluidics Corp.), using three passes at a pressure of 600 bar. The degree of cationization was determined by conductimetric titration. Typically, 9 mg of cationic nanocellulose in 90 mL Milli- Q water was titrated with a silver nitrate solution (0.0010 mol L 1 ) and monitored by an AJMICRONAL AJX-515 conductometer.
  • TEMPO-oxidized nanofibrillated Cellulose was prepared by a method comprising the steps: i) Processing sugarcane bagasse fibers with organosolv and bleaching processes [4, 5]; ii) Oxidation process [7], wherein the oxidation was performed with never-dried cellulose pulp (5g) was hydrated in Milli-Q water (500 ml_) for 24 h and then TEMPO (0.08 g) and sodium bromide (0.5 g) were added to the suspension. The oxidation started by the addition of (15.6 ml_) of a 12 (w/v) % NaCIO solution, and the fibers were stirred at room temperature until no more NaOH consumption was detected.
  • Cationic nanofibrillated cellulose were dispersed in a NaCI solution (0.05 wt. %, NaCI 10 mmol L 1 ), and the electrophoretic mobility was determined using a ZetaSizer Nano ZS (Malvern Panalytical Ltd., Malvern, UK) at 25 °C, where the Smoluchowski model was used to extract the zeta potential. Three measurements were performed for each sample.
  • the elemental surface composition of cNFC was measured by X-ray photoelectron spectroscopy (XPS) analyses using a Thermo K-Alpha (Thermo Scientific, Inc.) equipment, with a monochromatic Al Ka X-ray (1486.7 eV) source. Survey spectra were obtained with a pass energy of 200 eV.
  • XPS X-ray photoelectron spectroscopy
  • NFC The morphology of NFC was observed by atomic force microscopy (AFM, Park NX10) using the tapping mode and a Nanoworld cantilever with a stiffness of 42 N m 1 and resonance frequency between 260-320 kFIz.
  • AFM atomic force microscopy
  • a droplet of diluted cNFC suspension (10 mL, 5 mg/L) was deposited onto a silicon substrate (TED PELLA, Wafer in 5x5 mm chips) and dried overnight at room temperature.
  • the length and width of cNFC were measured via Gwyddion software by counting 30-100 independent nanofibers.
  • Apparent zeta potential values of cNFCs are positive, confirming the grafting.
  • DS degree of substitution
  • Table 1 The degree of substitution (DS) of cNFC was investigated by conductimetric titration, yielding gravimetrically normalized values of 0.14 (2:1 cNFC) and 0.51 mmol/g (10:1 cNFC), Table 1. DS values ranging from 0.04 to 2.31 mmol/g were previously reported for derivatized cNFCs isolated from Eucalyptus [8], “fiber sludge” [9], softwood pulp [10, 11], bamboo Kraft pulp [12] and oat [13], also modified with GTMAC. For comparison purposes, oxidized nanofibrillated cellulose (oNFC), also extracted from sugarcane bagasse, was used throughout this work. This oNFC has a degree of substitution of 0.40 mmol/g (amount of COO- groups) and an apparent zeta potential value of -36 mV (Table 1).
  • cNFCs prepared with a higher degree of cationization are mostly disaggregated, without junction points, differently from cNFC 2:1 that presents partially disassembled fibers, as indicated by the red arrows.
  • the O/W Pickering emulsions were prepared by a method comprising: i) Preparing an aqueous phase suspension comprising 0.5 wt. % or 1 .0 wt. % of NFCs (cNFC 2:1 and 10:1 and oNFC); ii) Adding 1 .5 ml_ of almond oil to 3.5 ml_ of the aqueous phase prepared in step iii) Emulsification using a high-speed blender (Ultra Turrax T10 basic IKA with an S10N-5G disperser) for 5 min at 20000 rpm in neutral pH.
  • a high-speed blender Ultra Turrax T10 basic IKA with an S10N-5G disperser
  • the interfacial tension was measured in an optical tensiometer (Attension Biolin Scientific ®) by injecting a water or cNFC aqueous dispersion (0.01 , 0.05, 0.1 , 0.5 and 1%) droplet via a hookle needle inside a glass cuvette containing almond oil. Droplets were equilibrated for at least 30 min inside the cuvette. The equipment recorded at least 100 droplet profiles and the interfacial tension was determined from the analysis of the droplet shape.
  • AFM was used to investigate the nanofibers after preparing the Pickering emulsions.
  • An aliquot of the aqueous phase was obtained after these liquid-liquid extractions was diluted in water (1:1) again and deposited (10 pL) onto a mica substrate.
  • Stability The colloidal stability of all the emulsions was analyzed using a Dispersion Analyser LUMiSizer ® (LUM GmbH, Berlin, Germany). 200 mI_ of each sample was placed in a polycarbonate cell and submitted to 134 g rotor speed at 25 °C for 19 hours. A total of 1000 profiles were recorded at different time intervals during the whole experiment. Instability indexes were calculated by the SEPView® software supplied with this equipment.
  • Phase separation To determine the phase separation profile, the Pickering emulsions were centrifuged for 10 minutes at 5590 g in an Eppendorf MiniSpin centrifuge.
  • Emulsion morphology O/W Pickering emulsions were slightly diluted in water and placed directly onto a glass slide, being imaged in a Zeiss Axiocam ICc5 optical microscope with a magnification of 200x. Images were processed using the AxioVision SE64 Rel. 4.9.1 Software.
  • % of cNFC 2:1 and 10:1 diluted in water 10x were prepared for cryogenic transmission electron microscopy (cryo-TEM) in a controlled environment vitrification system (Vitrobot Mark IV, Thermo Fischer Scientific- formerly FEI, USA). Before the application of the sample, the grids were subjected to a glow discharge treatment using a Pelco easiGlow discharge system (Ted Pella, USA) with 15 mA current, for 25 s in an air atmosphere.
  • a 3 pL sample droplet was deposited on a 300-mesh lacey carbon-coated copper grid (Ted Pella, USA) and prepared with a 3s blot time, 0 blot force, 0 drain time and 10s of waiting time before blotting.
  • the samples were analyzed in low dose condition, using a JEOL JEM 2100 LaB6 TEM with a single-tilt holder operating at 120 kV.
  • % of free oleic acid (pKa 5.0) in the almond oil which is deprotonated at the pH used to prepare the Pickering emulsions, providing negative charges to the oil droplets, thus favoring cNFCs adsorption at the oil-water interface due to electrostatic attraction.
  • NFCs are flexible due to the presence of amorphous regions. Therefore, when the fibers adsorb on the droplet surface, they may adopt configurations that minimize the repulsion between the cationic groups.
  • Droplet size was monitored by measuring the diameter of the cNFCs emulsions by optical microscopy, as seen in Figure 4. By increasing the degree of cationization and the concentration, the oil droplet size was slightly reduced, considering the standard deviation. The emulsions were imaged again after three months, and no significant change in the size and morphology of the drops was detected.
  • Suspensions of chemically pretreated NFCs typically form stronger networks compared to suspensions of enzymatically hydrolyzed or just mechanically fibrillated NFCs [25, 26]
  • Surface modified NFCs display higher specific surface area and hence, more entanglements, despite a strong electrostatic repulsion along the nanofibrils [17].
  • Diluted O/W emulsions were imaged by cryo-TEM to elucidate how the nanofibers were dispersed in the system and their relationship with dispersion stability.

Abstract

The present application provides cationic nanofibrillated cellulose (cNFC), which can be used as stabilizer for emulsions, and provides processes to obtain those cNFCs and emulsions. Those emulsions can be used in many applications, e.g. for preparing cosmetics and pharmaceutical formulations. The present application is within the field of Physical-Chemistry, Nanotechnology, Cosmetology and Pharmacy.

Description

Descriptive Report of Invention Patent
NANOFIBRILLATED CELLULOSE EMULSION, EMULSIFICATION PROCESS, USE OF CATIONIC NANOFIBRILLATED CELLULOSE AND USE OF
EMULSION
Field of the Invention
[0001] The present invention provides cationic nanofibrillated cellulose (cNFC), which can be used as stabilizer for emulsions, and provides processes to obtain those cNFCs and emulsions. Those emulsions can be used in many applications, e.g. for preparing cosmetics and pharmaceutical formulations. The present invention is within the field of Physical-Chemistry, Nanotechnology, Cosmetology and Pharmacy.
Background of the Invention
[0002] Pickering emulsions are emulsions (O/W, W/O, or multiple) stabilized by solid particles instead of surfactants. This surfactant-free character makes this type of emulsion attractive to be used in cosmetics and pharmaceutical applications, in which some surfactants can cause adverse effects (irritancy, hemolytic behavior, etc.).
[0003] Similar to emulsions containing surfactants, these emulsions droplets are stabilized via adsorption of solid particles at their surface. However, the adsorption mechanism is different, not involving molecules amphiphilicity or the HLB concept. Partial wetting, measured by the contact angle (Q) between the particle and the interface, is the key property behind the stabilization of Pickering emulsions. The energy of attachment of a particle to a liquid-liquid interface is also related to the interfacial tension between the liquid 1 and liquid 2 (y12), as shown in Equation 1 :
Figure imgf000003_0001
[0004] where AFads represents the free energy required to remove the particle from the interface and r is the radius of the spherical particle (Chevalier and Bolzinger, 2013). The sign inside the bracket is negative for removal into the water phase (0 < 90°, more hydrophobic particles) and positive for removal into an oil phase (0 > 90°, more hydrophilic particles). Analyzing the Equation 1 , it is possible to deduce that the adsorption is strongest when the 0 = 90°, that is a situation in which the particle has a partial wetting in the two liquids (Binks, 2002). The free energy of adsorption of these particles is very high when compared to the thermal energy, kT, which makes this adsorption irreversible. This is a big contrast to surfactant molecules that adsorb and desorb on a fast timescale (Binks, 2002).
[0005] The preferable type of emulsion can be predicted by the contact angle value: O/W when 0 < 90° and W/O when 0 > 90° (Binks, 2002).
[0006] An infinite number of types of particles, organic or inorganic, can fulfill approximately the partial wetting condition. Surface modification of particles is an additional strategy to improve their wetting and enlarges the possibilities. In the present case, the electrostatic attraction between the positively charged nanocellulose and the negatively charged oil droplet is an additional factor towards the emulsion stability.
[0007] Based on their characteristics previously cited, Pickering emulsions can replace the classical ones stabilized by surfactants, offering high resistance to coalescence and make them suitable for countless applications.
[0008] In the search for the state of the art in scientific and patent literature, the following documents dealing with the topic were found:
[1] D. Saidane, E. Perrin, F. Cherhal, F. Guellec, I. Capron, Some modification of cellulose nanocrystals for functional Pickering emulsions, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 374 (2016) 20150139. https://doi.org/10.1098/rsta.2015.0139.
[2] H. Zhang, Y. Qian, S. Chen, Y. Zhao, Physicochemical characteristics and emulsification properties of cellulose nanocrystals stabilized O/W pickering emulsions with high -0S03- groups, Food Hydrocolloids. 96 (2019) 267-277. https://doi.Org/10.1016/j.foodhyd.2019.05.023.
[3] L. Bai, S. Huan, W. Xiang, L. Liu, Y. Yang, R.W.N. Nugroho, Y. Fan, O.J. Rojas, Self-Assembled Networks of Short and Long Chitin Nanoparticles for Oil/Water Interfacial Superstabilization, ACS Sustainable Chem. Eng. 7 (2019) 6497-6511. https://doi.org/10.1021/acssuschemeng.8b04023.
[4] F.B. de Oliveira, J. Bras, M.T.B. Pimenta, A.A. da S. Curvelo, M.N.
Belgacem, Production of cellulose nanocrystals from sugarcane bagasse fibers and pith, Industrial Crops and Products. 93 (2016) 48-57. https://doi.Org/10.1016/j.indcrop.2016.04.064.
[5] E. de M. Teixeira, T.J. Bondancia, K.B.R. Teodoro, A.C. Correa, J.M.
Marconcini, L.H.C. Mattoso, Sugarcane bagasse whiskers: Extraction and characterizations, Industrial Crops and Products. 33 (2011) 63-66. https://doi.Org/10.1016/j.indcrop.2010.08.009.
[6] M. Zaman, H. Xiao, F. Chibante, Y. Ni, Synthesis and characterization of cationically modified nanocrystalline cellulose, Carbohydrate Polymers. 89 (2012) 163-170. https://doi.Org/10.1016/j.carbpol.2012.02.066.
[7] A. Isogai, T. Saito, H. Fukuzumi, TEMPO-oxidized cellulose nanofibers, Nanoscale. 3 (2011) 71-85. https://doi.org/10.1039/C0NR00583E.
[8] A. Chaker, S. Boufi, Cationic nanofibrillar cellulose with high antibacterial properties, Carbohydrate Polymers. 131 (2015) 224-232. https://doi.Org/10.1016/j.carbpol.2015.06.003.
[9] H. Sehaqui, A. Mautner, U. Perez de Larraya, N. Pfenninger, P. Tingaut, T. Zimmermann, Cationic cellulose nanofibers from waste pulp residues and their nitrate, fluoride, sulphate and phosphate adsorption properties, Carbohydrate Polymers. 135 (2016) 334-340. https://doi.Org/10.1016/j.carbpol.2015.08.091.
[10] N. Odabas, H. Amer, M. Bacher, U. Henniges, A. Potthast, T. Rosenau,
Properties of Cellulosic Material after Cationization in Different Solvents, ACS Sustainable Chem. Eng. 4 (2016) 2295-2301. https://doi.Org/10.1021 /acssuschemeng.5b01752. [11] A. Pei, N. Butchosa, L.A. Berglund, Q. Zhou, Surface quaternized cellulose nanofibrils with high water absorbency and adsorption capacity for anionic dyes, Soft Matter. 9 (2013) 2047-2055. https://doi.org/10.1039/C2SM27344F.
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[25] O. Nechyporchuk, M.N. Belgacem, F. Pignon, Concentration effect of TEMPO-oxidized nanofibrillated cellulose aqueous suspensions on the flow instabilities and small-angle X-ray scattering structural characterization, Cellulose. 22 (2015) 2197-2210. https://doi.org/10.1007/s10570-015-0640-0.
[26] D. Tatsumi, S. Ishioka, T. Matsumoto, Effect of Fiber Concentration and Axial Ratio on the Rheological Properties of Cellulose Fiber Suspensions, Nihon Reoroji Gakkaishi. 30 (2002) 27-32. https://doi.org/10.1678/rheology.30.27. [0009] The document WO201468196A2 discloses a method for producing oxidized nanofibrillated cellulose (oNFCs) of low viscosity. In addition, the document discloses a composition with those oNFCs in combination with surfactants.
[0010] The document CN110563964A discloses nanofibrillated cellulose oxidized with TEMPO. The present invention uses a different NFC, different emulsion proportion as well a different preparation method of the NFCs.
[0011] The document KR20190127150A discloses emulsions stabilized by cellulose nanocrystal for the production of microcapsules.
[0012] The document CN110343260A discloses aminosilicone nanofibrillated cellulose.
[0013] The document CN107254002A discloses nanofibrillated cellulose functionalized with cinnamyl groups.
[0014] The document Bertsch and Fischer, 2019, discloses the use of nanocelulose: (i) not modified; (ii) modified with functional nonionic and highly hydrophobic groups; and (iii) in combination with surfactants in the stabilization of liquid-liquid and liquid-air interfaces.
[0015] Thus, from what can be inferred from literature, there are no documents suggesting or anticipating the teachings of the present invention, so that the solution proposed here has novelty and inventive activity outside the state of the art.
[0016] The solution proposed herein provides alternative green stabilizers for emulsions, without the further need of combination with surfactants or other compounds.
Summary of the Invention
[0017] Therefore, the present invention has the object to solve the problems present in the state of the art by providing cationic nanofibrillated cellulose as stabilizers for emulsions.
[0018] In a first aspect, the present application provides a emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
[0019] In a second aspect, the present invention provides a method for producing cationic nanofibrillated cellulose aqueous suspension, wherein it comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
[0020] In a third aspect, the present application provides use of cationic nanofibrillated cellulose as stabilizers for emulsions, wherein the cationic nanofibrillated cellulose is present in an amount of 0.1% to 5% by weight of the final mixture.
[0021] In a fourth aspect, the present application provides a method for preparing compositions for cosmetics, pharmaceutical and food products, wherein the method comprises an emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
[0022] These and other objects of the invention will be immediately appreciated by the well versed in the art, and for companies with interests in the product segment and will be described in sufficient detail to be reproduced in the following description.
Description of the Drawings [0023] Figure 1. Topography images acquired by AFM of cationic nanofibrillated celluloses prepared with GTMAC: glucose molar ratios (a) 2:1 and (b) 10:1. Scale bars of 1 pm.
[0024] Figure 2. Instability indexes obtained after 19h of centrifugation at 5590 g for O/W Pickering stabilized by cNFCs 2:1 and 10:1 and oNFC, with concentrations of 0.5 wt. % and 1.0 wt. %.
[0025] Figure 3. Photographs of NFCs- Pickering emulsions after centrifugation. Solid content of 0.5 wt. % for cNFC 2:1 (a), cNFC10:1 (c) and oNFC (e), and 1.0 wt. % for cNFC 2:1 (b), cNFC10:1 (d) and oNFC (f).
[0026] Figure 4. Optical micrographs and droplet size for freshly prepared and diluted cNFC-Pickering emulsions. Solid content of: 0.5 wt. % for (a) cNFC 2:1 and (c) cNFC10:1 , and 1.0 wt. % for (b) cNFC 2:1 and (d) cNFC10:1.
[0027] Figure 5. Cryo-TEM images of the top creaming layer diluted of O/W (cNFC 10:1 0.5 wt. %) showing: regions when the oil is attached to the cNFCs (a) and (b). Scale bars of 200 nm.
[0028] Figure 6. Double stabilization mechanism proposed for O/W Pickering emulsions stabilized by cationic nanofibrillated cellulose.
Detailed Description of the Invention
[0029] The use of cationic nanoparticles is an interesting approach for Pickering emulsion systems. The electrostatic attraction between particles and oil droplets, which possess a negative charge on the surface when dispersed in water, can favor stabilization, as observed for nanochitin [3]
[0030] In the present invention, cationic NFCs with different degrees of substitution were applied to stabilize oil-in-water dispersions. The results presented herein show that by using positively charged cellulose nanoparticles, high aspect ratio, and flexibility, O/W emulsions with excellent colloidal stability can be produced. NFCs adsorb onto the interface and form a network in the continuous aqueous phase, increasing the viscosity and, consequently, reducing the oil droplets coalescence without the need of adding other nanoparticles or additives.
[0031] The O/W Pickering emulsions obtained with the cationic NFCs were stable for up to 6 months without phase separation. Comparing with other emulsion prepared with anionic NFCs, CNCs, cationic chitin and silica, the present emulsion can display lesser toxicity, and better colloidal stability, mainly by two stabilization mechanisms: (i) increasing the viscosity/elasticity of the continuous phase and (ii) attractive electrostatic interaction between oil (negatively charged) and cNFCs. The entanglement of the cNFCs fibers are correspondent to the rheological properties of the continuous aqueous phase of the emulsion.
[0032] Thus, the present invention provides stable O/W Pickering emulsions, prepared by a facile and simple method, using renewable nanomaterials without acids and other co-stabilizers, such as salts, polymers and/or surfactants.
[0033] In a first aspect, the present application provides a emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Flomogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
[0034] In one embodiment, the cationic nanofibrillated cellulose aqueous suspension is prepared by a method comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
[0035] In one embodiment, the cationic nanofibrillated cellulose has dimensions from 200 nm to 2000 nm in length and from 2 nm to 10 nm in width, when functionalized by a cationic agent. [0036] In one embodiment, the oil phase is selected from the group consisting of mineral oils and organic oils from animals or vegetable origin and mixtures thereof. In one embodiment, the oil phase is selected from: organic oils (plant or animal origin) and minerals oils (petroleum derivatives). In addition, nanofibers can also stabilize emulsions with additives dissolved in the oil phase, such as lipophilic vitamins, drugs, dyes or other additives for food, biomedical, cosmetic or industrial purposes.
[0037] In a second aspect, the present invention provides a method for producing cationic nanofibrillated cellulose aqueous suspension, wherein it comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
[0038] In one embodiment, the cationization step comprises at least one cationic reagent selected from the group consisting of glycidyl trimethylammonium chloride GTMAC, chloro-2-hydroxypropyl- trimethylammonium chloride (CHPTAC), chlorocholine chloride, or (2- hydrazinyl-2-oxoethyl)-trimethylazanium chloride. In one embodiment the cation is glycidyl trimethylammonium chloride GTMAC. In one embodiment, the cationic reagent is GTMAC at GTMAC anhydroglucose ratios from 2:1 to 10:1. [0039] In one embodiment, the cationic nanofibrillated cellulose has a degree of substitution from 0.07 to 1.5 mmol/g. In one embodiment, the cationic nanofibrillated cellulose has a degree of substitution from 0.14 to 0.51 mmol/g. [0040] In one embodiment, the cationization step is maintained at 60-65°C for 4h.
[0041] In a third aspect, the present application provides use of cationic nanofibrillated cellulose as stabilizers for emulsions, wherein the cationic nanofibrillated cellulose is present in an amount of 0.1% to 5% by weight of the final mixture.
[0042] In a fourth aspect, the present application provides a method for preparing compositions for cosmetics, pharmaceutical and food products, wherein the method comprises an emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
[0043] In one embodiment, the emulsion possesses antimicrobial property promoted by cationized nanocelluloses;
[0044] The two main differences between cellulose nanocrystalline (CNC) and nanofibrillated cellulose (NFC) are related to the nanoparticle isolation process and the aspect ratio of these nanoparticles. CNCs are obtained via acid hydrolysis of cellulose fibers, displaying an average diameter of 5-70 nm and an average length of 100-250 nm. Therefore, CNCs have a rigid, rod-like morphology. On the other hand, NFCs are produced through the delamination of cellulosic pulp by mechanical processes before or after chemical or enzymatic treatments. NFCs have typical diameters ranging from 3 from 60 nm and lengths from 400 nm to 1 pm. NFCs have a high aspect ratio than CNCs, presenting a fibrillar-like morphology and remarkable flexibility, that is important for its adsorption onto the oil droplets and entanglement in solution to provide high viscosity to the medium (Klemm et al., 2011 ).
[0045] As one of the stabilization mechanisms of the present emulsion involves viscosity increase in the continuous phase, NFCs with their larger aspect ratio can provide this property in lower concentrations than CNC.
Examples
[0046] The examples shown here are intended to only illustrate one of several ways to implement this invention, however, without limiting the scope thereof. Materials
[0047] Sugarcane bagasse used throughout this work was obtained from the LNBR (Brazilian Biorenewables National Laboratory), Campinas, Brazil. Hydrogen peroxide, sodium hydroxide, and ethanol were purchased from Synth. Glycidyltrimethylammonium chloride (GTMAC), almond oil, silver nitrate, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium borohydride were purchased from Sigma Aldrich, and sodium hypochlorite (12% w/v) from Star Flash.
Cellulose Fiber Preparation
[0048] Cationic nanofibrillated Cellulose (cNFC) was prepared by a method comprising the steps: i) Processing sugarcane bagasse fibers with organosolv and bleaching processes [4, 5]; ii) Cationization process [6], wherein the cationization was performed with never-dried cellulose pulp (1 Og) that was mixed with sodium hydroxide solution (25 mL, 1 mol L 1) in a polyethylene bag, followed by the addition of a cationic reagent GTMAC at GTMAC anhydroglucose ratios of: 2:1 and 10:1. The reaction was performed in a Cole-Parmer ultrasonic bath (110W) at 60-65°C for 4h; iii) Washing of the cationic pulp with ethanol and 0.02 mol L 1 hydrochloric acid; iv) Separation of the pulp by centrifugation and dialyzed against Milli-Q water for 15 days using an INLAB membrane with a MWCO of 22 kDa; v) Fibrillation of cellulose pulp by microfluidization of 1 wt. % suspension was conducted in a Microfluidizer® M-110P (Microfluidics Corp.), using three passes at a pressure of 600 bar. The degree of cationization was determined by conductimetric titration. Typically, 9 mg of cationic nanocellulose in 90 mL Milli- Q water was titrated with a silver nitrate solution (0.0010 mol L 1) and monitored by an AJMICRONAL AJX-515 conductometer.
[0049] TEMPO-oxidized nanofibrillated Cellulose (oNFC) was prepared by a method comprising the steps: i) Processing sugarcane bagasse fibers with organosolv and bleaching processes [4, 5]; ii) Oxidation process [7], wherein the oxidation was performed with never-dried cellulose pulp (5g) was hydrated in Milli-Q water (500 ml_) for 24 h and then TEMPO (0.08 g) and sodium bromide (0.5 g) were added to the suspension. The oxidation started by the addition of (15.6 ml_) of a 12 (w/v) % NaCIO solution, and the fibers were stirred at room temperature until no more NaOH consumption was detected. iii) Washing of the oxidized pulp thoroughly with Milli-Q water by centrifugation until constant conductivity was reached; iv) Fibrillation of cellulose pulp by using a 130 W ultrasonic processor (Vibra- Cell VCX130, SONICS) with power level set at 40 % of strength for 30 min, inside a beaker immersed in an ice-water bath to avoid overheating.
Cellulose Fiber Characterization
[0050] Cationic nanofibrillated cellulose were dispersed in a NaCI solution (0.05 wt. %, NaCI 10 mmol L 1), and the electrophoretic mobility was determined using a ZetaSizer Nano ZS (Malvern Panalytical Ltd., Malvern, UK) at 25 °C, where the Smoluchowski model was used to extract the zeta potential. Three measurements were performed for each sample.
[0051] The elemental surface composition of cNFC was measured by X-ray photoelectron spectroscopy (XPS) analyses using a Thermo K-Alpha (Thermo Scientific, Inc.) equipment, with a monochromatic Al Ka X-ray (1486.7 eV) source. Survey spectra were obtained with a pass energy of 200 eV.
[0052] The morphology of NFC was observed by atomic force microscopy (AFM, Park NX10) using the tapping mode and a Nanoworld cantilever with a stiffness of 42 N m 1 and resonance frequency between 260-320 kFIz. Before AFM analyses, a droplet of diluted cNFC suspension (10 mL, 5 mg/L) was deposited onto a silicon substrate (TED PELLA, Wafer in 5x5 mm chips) and dried overnight at room temperature. The length and width of cNFC were measured via Gwyddion software by counting 30-100 independent nanofibers. [0053] Apparent zeta potential values of cNFCs are positive, confirming the grafting. As expected, z increased from +24 to + 37 mV when the molar ratio between GTMAC and glucose was increased from 2:1 to 10:1 , as shown in Table 1. The presence of cationic groups was also confirmed by the elemental surface composition derived from XPS analyses; the atomic percentage of nitrogen was 0.7% for 2:1 cNFC and 1.3% for 10:1 cNFC.
[0054] The degree of substitution (DS) of cNFC was investigated by conductimetric titration, yielding gravimetrically normalized values of 0.14 (2:1 cNFC) and 0.51 mmol/g (10:1 cNFC), Table 1. DS values ranging from 0.04 to 2.31 mmol/g were previously reported for derivatized cNFCs isolated from Eucalyptus [8], “fiber sludge” [9], softwood pulp [10, 11], bamboo Kraft pulp [12] and oat [13], also modified with GTMAC. For comparison purposes, oxidized nanofibrillated cellulose (oNFC), also extracted from sugarcane bagasse, was used throughout this work. This oNFC has a degree of substitution of 0.40 mmol/g (amount of COO- groups) and an apparent zeta potential value of -36 mV (Table 1).
Table 1. Degree of substitution (DS), nitrogen content (N), average width (w) and length (I) and apparent zeta potential (z), values for cationic, and oxidized nanofibrillated celluloses used in this study.
Figure imgf000016_0001
*oNFC used in this work was previously characterized by Pinto et al. [0055] The cellulose nanoparticle morphology was evaluated by atomic force microscopy, and the topography images are depicted in Figure 1 . cNFCs possess characteristic features of nanofibers, presenting kinks and a relatively constant width (around 3 nm), which may correspond to elementary fibril dimensions [14]. By increasing the degree of substitution, the aspect ratio (L/d) varied from -200 to -170, revealing that the cationization, besides aiding the lateral disassembling due to electrostatic repulsion, also promoted cleavage of the cellulosic fibers. Besides, cNFCs prepared with a higher degree of cationization (cNFC 10:1 ) are mostly disaggregated, without junction points, differently from cNFC 2:1 that presents partially disassembled fibers, as indicated by the red arrows.
Preparation of O/W Emulsions
[0056] The O/W Pickering emulsions were prepared by a method comprising: i) Preparing an aqueous phase suspension comprising 0.5 wt. % or 1 .0 wt. % of NFCs (cNFC 2:1 and 10:1 and oNFC); ii) Adding 1 .5 ml_ of almond oil to 3.5 ml_ of the aqueous phase prepared in step iii) Emulsification using a high-speed blender (Ultra Turrax T10 basic IKA with an S10N-5G disperser) for 5 min at 20000 rpm in neutral pH.
O/W Emulsions Characterization cNFC at oil-in-water interface
[0057] To evaluate the adsorption of cNFC at oil-in-water interface, the interfacial tension was measured in an optical tensiometer (Attension Biolin Scientific ®) by injecting a water or cNFC aqueous dispersion (0.01 , 0.05, 0.1 , 0.5 and 1%) droplet via a hookle needle inside a glass cuvette containing almond oil. Droplets were equilibrated for at least 30 min inside the cuvette. The equipment recorded at least 100 droplet profiles and the interfacial tension was determined from the analysis of the droplet shape.
[0058] AFM was used to investigate the nanofibers after preparing the Pickering emulsions. About 0.2g of creaming, produced by centrifuging the O/W emulsions with 1 wt. % of cNFC (2:1 and 10:1), were extensively diluted in water (around 1500x) and then subjected to four liquid-liquid extractions using hexane (1 :1 volume ratio) in order to remove the almond oil. An aliquot of the aqueous phase was obtained after these liquid-liquid extractions was diluted in water (1:1) again and deposited (10 pL) onto a mica substrate. The samples were dried at room temperature and imaged using the tapping mode in a MultiMode VIII NanoScope V (Bruker) using a ScanAsyst-Air (Bruker) cantilever with stiffness of a 0.4 N m 1 and resonance frequency of 70 kHz. All the recorded AFM images were processed and analyzed using the Gwyddion Software (Version 2.5). cNFC Pickering emulsions characterization
[0059] Stability: The colloidal stability of all the emulsions was analyzed using a Dispersion Analyser LUMiSizer ® (LUM GmbH, Berlin, Germany). 200 mI_ of each sample was placed in a polycarbonate cell and submitted to 134 g rotor speed at 25 °C for 19 hours. A total of 1000 profiles were recorded at different time intervals during the whole experiment. Instability indexes were calculated by the SEPView® software supplied with this equipment.
[0060] Phase separation: To determine the phase separation profile, the Pickering emulsions were centrifuged for 10 minutes at 5590 g in an Eppendorf MiniSpin centrifuge.
[0061] Emulsion morphology: O/W Pickering emulsions were slightly diluted in water and placed directly onto a glass slide, being imaged in a Zeiss Axiocam ICc5 optical microscope with a magnification of 200x. Images were processed using the AxioVision SE64 Rel. 4.9.1 Software.
[0062] Rheological behavior: Viscous and viscoelastic behaviors of cNFC aqueous dispersions (2:1 and 10:1 in a concentration of 0.5 and 1.0 wt. %) and their O/W Pickering emulsions were evaluated in a Thermo Scientific HAAKE Mars III rheometer equipped with a plate-plate sensor (35 mm of diameter and 1 mm of gap). Flow curves (105 - 500 s 1) and stress sweep curves (0.1 - 20 Pa / f = 1 Hz) were acquired at 25 °C. [0063] cNFC distribution throughout the emulsion: Samples (emulsions stabilized by 1 wt. % of cNFC 2:1 and 10:1 diluted in water 10x) were prepared for cryogenic transmission electron microscopy (cryo-TEM) in a controlled environment vitrification system (Vitrobot Mark IV, Thermo Fischer Scientific- formerly FEI, USA). Before the application of the sample, the grids were subjected to a glow discharge treatment using a Pelco easiGlow discharge system (Ted Pella, USA) with 15 mA current, for 25 s in an air atmosphere. A 3 pL sample droplet was deposited on a 300-mesh lacey carbon-coated copper grid (Ted Pella, USA) and prepared with a 3s blot time, 0 blot force, 0 drain time and 10s of waiting time before blotting. The samples were analyzed in low dose condition, using a JEOL JEM 2100 LaB6 TEM with a single-tilt holder operating at 120 kV.
[0064] To investigate the adsorption behavior of cNFCs, water-almond oil interfacial tension (y) measurements were performed with and without cNFCs. From 0 wt. % up to 0.1 wt. % of NFCs, the y values were ca. 22-24 mN/m. By increasing the nanofiber content to 0.5 wt. %, the water droplets were completed deformed, and y could not be calculated. The increase in the oil surface area indicates a better interaction between the liquid phases and, thus, a reduction of the interfacial tension.
[0065] Besides the interfacial tension reduction, another feature that may indicate strong interaction of the cNFCs with the oil is that a complete removal of almond oil from diluted cNFC Pickering emulsion was not observed even after four washing steps with hexane. AFM images of cNFCs after this extraction revealed the presence of oil droplets attached to cationic nanofibers, especially in the upper phase, as can be seen in Figure 1. A plausible explanation is the presence of 0.03 wt. % of free oleic acid (pKa 5.0) in the almond oil, which is deprotonated at the pH used to prepare the Pickering emulsions, providing negative charges to the oil droplets, thus favoring cNFCs adsorption at the oil-water interface due to electrostatic attraction.
[0066] Moreover, when 20 mI_ of a sodium sulfate aqueous solution (50 mmol/L) were added to 2 mL of each O/W Pickering, flocculation was instantaneously observed, indicating that the presence of charges at the oil-water interface that played a key role in the colloidal stability.
Stability and morphology of O/W Pickering emulsions
[0067] The Pickering emulsions using cNFC dispersions (0.5 and 1 wt. %) were prepared with oil/water volume ratio 30/70 and they exhibited remarkable stability against creaming and oiling off even after six months. In the case of oNFC emulsions, prepared using identical conditions, phase separation was observed after 24h of storage.
[0068] Besides, in contrast to emulsions prepared with rigid cellulose nanocrystals, where the addition of salt or surfactant [1 , 2] was required to improve the stability, no such additives were needed for cNFCs. NFCs are flexible due to the presence of amorphous regions. Therefore, when the fibers adsorb on the droplet surface, they may adopt configurations that minimize the repulsion between the cationic groups.
[0069] For a comparative study on the colloidal stability, cNFC emulsions were analyzed at accelerated gravitation due to their excellent stability observed under gravity. Photocentrifuge LUMiSizer® is the equipment used for these experiments, and its software calculates an instability index based on transmittance profiles acquired during centrifugation at accelerated gravitation (134 g in this work). For the Pickering emulsions prepared with the cationic NFCs, the instability index increased slightly during the experiment (Figure 2), revealing good colloidal stability associated to the small changes in the transmittance over time. Moreover, NFC content (increasing from 0.5 to 1 wt. %) had a more pronounced effect on the stability than the degree of cationization (2:1 or 10:1).
[0070] The samples prepared with oxidized NFC (COO- groups on the surface) presented higher instability indexes, under the same experimental conditions, confirming that the cationic groups contributed to the emulsion stability, due to the electrostatic attraction at the oil-water interface, as previously discussed. The use of electrostatic complexation at oil: water interface was recently reported by Calabrese et al. [15]. Negatively charged NFCs adsorb at oihwater interface at high pH due the presence positively charged oleylamine at the oil surface, which improves the colloidal stability.
[0071] Bai et al [3] reported a similar oil/water interfacial super stabilization (up to 2 months) using highly positively charged chitin nanoparticles (z = +105 mV) of varying aspect ratios (from 5 to >60) for O/W Pickering emulsions, again without the need of adding salt or surfactant. These authors explained the stabilization using arguments related to enhanced particle wettability, electrostatic repulsion, and network formation. However, as they used sunflower oil (63.1 wt. % linoleic acid and 25.2 wt. % oleic acid), the electrostatic interaction between the carboxylic groups and cationic nanoparticles could also be considered. In a similar manner, Kedzior et al. [5] observed increased colloidal stability for O/W emulsion prepared with cationic cellulose nanocrystal (apparent diameter of 120 nm and z = +30 mV) compared to its analogous anionic CNC, but it required the addition of surfactants.
[0072] By centrifuging the Pickering emulsions in a conventional centrifuge for 10 minutes at 5590g, two-phase separation profiles were detected: for cationic NFCs emulsions (2:1 and 10:1) a creaming and a bottom aqueous phase were observed, as shown in Figure 3 (a, b, c and d). On the other hand, for the emulsions prepared with oNFCs significant oiling off were noticed (Figure 3e and f), suggesting limited adsorption of the negatively charged oNFCs on the almond oil: water interface due to electrostatic repulsion.
[0073] Droplet size was monitored by measuring the diameter of the cNFCs emulsions by optical microscopy, as seen in Figure 4. By increasing the degree of cationization and the concentration, the oil droplet size was slightly reduced, considering the standard deviation. The emulsions were imaged again after three months, and no significant change in the size and morphology of the drops was detected.
[0074] Rotational and oscillatory rheological experiments were performed on the cNFC aqueous suspensions. The h0 values obtained for cNFCs samples were remarkably high, for the concentration of 1 .0 wt. %, h0 reached values in the order of 103 Pa s. The high viscosity values of cNFCs suspensions can be explained by the mechanical disintegration used to produce the nanofibers. It reduces the interfibrillar interactions and generates high viscous suspensions at low solid content [16, 17]. The hygroscopic character of cNFCs and their high aspect ratio and specific surface area are the key factors for the strong networks [17]. Another possible reason for such high viscosity could be the presence of macromolecules liberated during the mechanical treatment of these fibers. Flowever, this was ruled out by the absence of extra peaks in the GPC curves of the filtrate.
[0075] Flow curves of cNFC suspensions (0.5 wt. % and 1.0 wt. %) show a typical shear thinning behavior, which is a result of the progressive breakdown of hydrogen-bonded nanofibrils network under the action of shear force. The nanofibrils aligned along the shear direction, leading to a gradual decrease in the viscosity [12]. For all samples, increasing the concentration, the zero-shear viscosity (ho) sharply increases, due to the larger number of entanglement points.
[0076] By increasing the degree of substitution, h0 values decreased slightly. This behavior can be explained by the morphological changes promoted by increasing the degree of cationization, as discussed before and observed herein. The cNFC length and molar weight were reduced for the more highly substituted nanofiber (10:1), see Table 1. Besbes et al. [18] and Ru et al. [12] reported the same DS effect using TEMPO-oxidized NFC and cationized NFCs and attributed this reduction in viscosity to the electrostatic repulsion that hindered the interaction between the nanofibers.
[0077] Strain sweeps curves of cNFCs suspensions exhibited gel-like behavior throughout the frequency range (G’ > G”). The interconnected network was formed at 0.125 wt. %, this concentration being known as the gelation point [19]. The storage modulus extrapolated to zero stress (Go) increased with the concentration because a stronger network was formed, agreeing with previous reports [16, 20-24] Besides, Go had lower values for the less charged cNFC 10:1 , likely due to the same reasons reported for the rotational experiments. [0078] Suspensions of chemically pretreated NFCs typically form stronger networks compared to suspensions of enzymatically hydrolyzed or just mechanically fibrillated NFCs [25, 26] Surface modified NFCs display higher specific surface area and hence, more entanglements, despite a strong electrostatic repulsion along the nanofibrils [17].
[0079] Rheological results for the Pickering emulsions prepared with cNFCs are very similar to the results obtained with their respective aqueous suspensions, which is indicative that the viscosity and elasticity enhancement are controlled by the continuous phase. This high viscous character is, therefore, another factor that contributes to the high stability of these emulsions (Table 2).
Table 2. Zero-shear viscosity h0 (Pa s) and zero-strain elastic modulus G0' (Pa) values of cNFC based-Pickering emulsions and cNFC aqueous suspensions calculated from the flow and oscillatory strain curves.
Figure imgf000023_0001
cNFC distribution throughout the emulsion
[0080] Diluted O/W emulsions were imaged by cryo-TEM to elucidate how the nanofibers were dispersed in the system and their relationship with dispersion stability.
[0081] The blue arrows in images shown in Figures 5a and 5b confirmed that cNFCs were adsorbed at the liquid-liquid interface, even after the dilution performed to prepare the specimen for cryo-TEM, which reinforced the strong electrostatic interaction between the cNFCs and negatively charged oil droplets. [0082] Moreover, images acquired in the vicinity of oil drops and throughout the aqueous phase revealed that cNFCs created a network, which restricted the oil droplets collision resulting in the high viscosity (as confirmed by measurements discussed above).
[0083] Flexible cationic NFCs wrap themselves and adsorb onto the oil droplets favored by strong electrostatic interaction with the negative oil interface. The cNFCs remaining in the aqueous phase display strong entanglements, forming networks that give rise to high viscosity of the continuous medium and, as a consequence, contribute to the stability of the dispersion. The high aspect ratio, flexibility and high content of positive charges of these cNFCs represent the key and unique features that enable these nanofibers to produce high stability O/W emulsions, without the need for extra additives. These dual stabilization mechanism accounts for the high stability of the emulsions, without the need of other nanoparticles or additives (Figure 6).
[0084] Those well versed in the art will value the knowledge here, and may reproduce the invention in the manner provided and other variants, covered within the scope of appended claims.

Claims

Claims
1. Emulsification process comprising the steps: a) Adding from 1% to 50% v/v of oil phase to a cationic nanofibrillated cellulose aqueous suspension; b) Homogenization of the mixture obtained in step a, wherein the cationic nanofibrillated cellulose is present in 0.1% to 5% by weight of the final mixture.
2. Emulsification process according to claim 1 , wherein the cationic nanofibrillated cellulose aqueous suspension is prepared by a method comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
3. Emulsification process according to any of the claims 1 to 2, wherein the cationic nanofibrillated cellulose has dimensions ranging from 200 nm to 2000 nm in length and from 2 nm to 10 nm in width.
4. Emulsification process according to any of the claims 1 to 3, wherein the oil phase is selected from the group consisting of mineral oils and organic oils from animals or vegetable origin and mixtures thereof.
5. A method for producing cationic nanofibrillated cellulose aqueous suspension, wherein it comprising the following steps: a) Cationization of never-dried cellulose pulp with sodium hydroxide solution and cationic reagent; b) Washing of the cationic pulp with ethanol and hydrochloric acid; c) Separation of the pulp by centrifugation and dialyzation against water; d) Fibrillation of cellulose pulp by microfluidization.
6. Method for producing cationic nanofibrillated cellulose aqueous suspension according to claim 5, wherein the cationization step comprises at least one cationic reagent selected from the group consisting of glycidyl trimethylammonium chloride GTMAC, chloro-2-hydroxypropyl- trimethylammonium chloride (CHPTAC), chlorocholine chloride, and (2- hydrazinyl-2-oxoethyl)-trimethylazanium chloride.
7. Method for producing cationic nanofibrillated cellulose aqueous suspension according to claim 6, wherein the cationic reagent is GTMAC at
GTMAC anhydroglucose ratios from 2:1 to 10:1.
8. Method for producing cationic nanofibrillated cellulose aqueous suspension according to any of the claims 5 to 7, wherein the cationic pulp obtained in the cationization step has a degree of substitution from 0.07 to 1.5 mmol/g.
9. Method for producing cationic nanofibrillated cellulose aqueous suspension according to any of the claims 5 to 8, wherein the cationization step is maintained at 60-65°C for 4h.
10. Use of cationic nanofibrillated cellulose as stabilizers for emulsions, wherein the cationic nanofibrillated cellulose is present in an amount of 0.1% to 5% by weight of the final mixture.
11. Use of cationic nanofibrillated cellulose as stabilizers for emulsions, according to claim 10, wherein the cationic nanofibrillated cellulose has dimensions ranging from 200 nm to 2000 nm in length and from 2 nm to 10 nm in width.
12. Use of cationic nanofibrillated cellulose as stabilizers for emulsions, according to any of the claims 10 to 11 , wherein the cationic nanofibrillated cellulose comprises at least one cationic reagent selected from the group consisting of glycidyl trimethylammonium chloride GTMAC, chloro-2- hydroxypropyl-trimethylammonium chloride (CHPTAC), chlorocholine chloride, and (2-hydrazinyl-2-oxoethyl)-trimethylazanium chloride.
13. Use of cationic nanofibrillated cellulose as stabilizers for emulsions, according to any of the claims 10 to 12, wherein the cationic nanofibrillated cellulose has a degree of substitution from 0.07 to 1.5 mmol/g.
14. Use of emulsification process as defined in any of the claims 1 to 9 for preparing compositions for cosmetics, pharmaceutical and food products.
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