Use of water-soluble lignin for emulsion stabilization

Abstract

The invention relates to the use of water-soluble lignin for the formulation of oil-in-water emulsions. Water-soluble lignin exhibits properties of interest for various industrial applications, particularly as a durable, biodegradable, and environmentally friendly emulsifying and / or stabilizing agent. This water-soluble lignin can be obtained enzymatically without the use of an organic solvent.

Description

Title of the invention: Use of water-soluble lignin for the stabilization of emulsions Technical field

[0001] The invention relates to the use of lignin soluble in aqueous medium for the formulation of oil / water emulsions.

[0002] Water-soluble lignin has interesting properties for various industrial applications, including as a sustainable, biodegradable and environmentally friendly emulsifying and stabilizing agent.

[0003] Said water-soluble lignin can be obtained enzymatically in the absence of organic solvent.

[0004] Water-soluble lignin-based emulsions can be used in many industrial sectors such as, for example, in the cosmetic, pharmaceutical or food industry. State of the art

[0005] To date, 44% of surfactants and emulsifiers used worldwide are of petro-sourced origin, and 52% are partly derived from biomass and mainly from oleochemical products which are only partially renewable, biodegradable and bio-sourced. Only 4% of surfactants are entirely derived from biomass using chemical production methods. Surfactants, and more generally formulation agents, are used in a wide variety of applications ranging from cosmetic emulsions to detergent products, including ink stabilization, pigment dispersion and cement plasticization.

[0006] Thus, we see that bio-sourced surfactants currently represent only a small share of the surfactant market. Nevertheless, this market is growing strongly due to consumer demand for products that are more respectful of humans and nature, as well as new environmental standards.

[0007] Lignin is a natural polymer (or biopolymer) that is one of the main components of wood along with cellulose and hemicelluloses. It is available in large quantities, particularly as a by-product of the paper industry.

[0008] The use of chemically modified lignin in the field of emulsions has been described. In particular, the use of lignosulfonates, obtained by chemical treatment and functionalization, to stabilize emulsions has been studied (1).

[0009] However, lignosulfonates contain a significant amount of sulfur, which can pose health risks according to international chemical safety data sheets. These risks make lignosulfonates unsuitable for industrial uses. trielles.

[0010] Other chemical derivatives of lignin have been studied, such as derivatives oxidized with ozone to form carboxyl groups in lignin (2), or even amine derivatives of lignin used as cationic emulsifiers (3).

[0011] However, chemical modifications of lignin can be expensive, have an impact on the environment and result in a loss of its natural properties.

[0012] The use of lignin as an additive in the presence of other bio-sourced components, such as hemicellulose with which it interacts to stabilize emulsions in different industrial applications has also been described (4).

[0013] However, these different uses do not solve the problem of the concomitant use of other emulsifying or stabilizing agents which may not be bio-sourced. Furthermore, some of these derivatives, due to their functionalization, can only be used in specific pH ranges.

[0014] The limitation of the use of lignin in industries is mainly due to its insolubility in water. In particular, the formulation of an emulsion is generally obtained by dissolving a soluble emulsifier in the continuous phase. Thus, the effective stabilization of an oil / water emulsion requires a water-soluble emulsifying agent.

[0015] So far, the only lignin soluble in water at neutral pH is lignosulfonate, which contains, as indicated above, sulfonate, and therefore has a high level of toxicity. Lignosulfonate is obtained by chemical functionalization and results in the presence of significant quantities of sulfur impurities. Lignin is also soluble in water at high pH, ​​above 10, but these very basic solutions are limited for many applications.

[0016] There is therefore a need for bio-sourced emulsifying and / or emulsion-stabilizing agents that are soluble in water and can be used alone, or possibly in combination with other emulsifying and / or stabilizing agents to form oil / water emulsions, under pH conditions compatible with the desired applications. Statement of the invention

[0017] The invention relates to the use of water-soluble lignin as an emulsifying and / or stabilizing agent for oil / water emulsions, said water-soluble lignin being obtained enzymatically. The invention also relates to oil / water emulsions formulated from said water-soluble lignin, as well as their applications. Brief description of the figures

[0018] [Fig.l] represents the variation of the dynamic viscosity (Pa.s) as a function of the shear rate (1 / s) for different concentrations of enzymatically treated lignin.

[0019] [Fig.2a] and [Fig.2b] represent the variation of interfacial tension in 3 environments (air, mineral oil and peanut oil) a) for pure water, b) for a 10% lignin solution.

[0020] [Fig.3a] and [Fig.3b] represent the distribution of droplet sizes of oil / water emulsions based on water-soluble lignin as a percentage of the same sample: a) on the day of preparation, b) after a period of 3 months. Detailed description

[0021] It has now been found that lignin obtained by enzymatic treatment, making it water-soluble, can be used as a sustainable, biodegradable and environmentally friendly stabilizing and / or emulsifying agent for the creation of direct emulsions (oil / water) while giving these emulsions very good stability properties, allowing their use in many industrial fields.

[0022] Indeed, it has now been found that aqueous solutions of lignin can stabilize oil droplets in water and can be used for the creation of direct emulsions. Without wishing to link the invention to a theory, it can be hypothesized that the lignin adsorbed at the interface of the oil droplets prevents the coalescence of the latter.

[0023] The subject of the invention is therefore the use of lignin as a stabilizing and / or emulsifying agent in an oil / water emulsion, said lignin being obtained enzymatically and soluble in water at a pH greater than or equal to 4.

[0024] By "emulsifying agent" is meant an agent which promotes the fragmentation of a liquid phase in the form of droplets in another liquid phase, thus promoting the formation of the emulsion. By "stabilizing agent" we mean an agent which limits the coalescence of the droplets formed. Preferably, said lignin being obtained enzymatically is soluble in water at a pH greater than or equal to 5, preferably greater than or equal to 6, preferably greater than or equal to 7, and at a pH less than or equal to 13, preferably less than or equal to 12, preferably less than or equal to 11, preferably less than or equal to 10. In particular, said lignin obtained enzymatically is soluble in water at a pH between 4 and 12, in particular between 5 and 9, and more particularly between 6 and 8.

[0025] The lignin that can be used for the purposes of the invention can be obtained enzymatically as described, in particular, in application WO2019 / 076893. The enzymatic treatment is carried out using at least one bilirubin oxidase (BOD) enzyme. Briefly, the enzymatic production process comprises bringing a lignin into contact, in water, optionally in the presence of a buffering agent, with at least one enzyme, for example of the bilirubin oxidase type, optionally in the presence of a redox mediator, and recovering the lignin solution.

[0026] Advantageously, the soluble lignin thus obtained has a sulfur content 70% lower than known soluble lignins.

[0027] According to one embodiment, the lignin is of the kraft type (or alkaline lignin). Kraft lignin is used when it is obtained by a kraft process (also known as "kraft pulping" or sulfate process) which is a process for converting wood into paper pulp. The kraft process involves treating wood chips with a hot mixture of water, sodium hydroxide, and sodium sulfide, breaking the wood fibers and separating the lignin and hemicellulose from the cellulose. This technique includes mechanical and chemical steps, in particular those called impregnation and cooking. According to one embodiment, the lignin is of the organosolv type.

[0028] The enzyme used may be a bilirubin oxidase (BOD) of fungal origin, for example a BOD described in international application WO 2012 / 160517 (BOD EC 1.3.3.5. of Magnaporthe oryzae origin).

[0029] According to another variant, the BOD is of bacterial origin, in particular a BOD described in international application WO 2011 / 117839 (BOD EC 1.3.3.5. of Bacillus pumilus origin).

[0030] According to one embodiment, the lignin obtained after enzymatic treatment can be subjected to an ultrasound treatment so as to optimize and accelerate its dissolution, and to denature the enzyme at the end of incubation.

[0031] The lignin obtained after enzymatic treatment in aqueous solvent is separated from the salts, for example by dialysis or centrifugation. After centrifugation, the supernatant containing the soluble lignin can be used as is or subjected to lyophilization in powder form for later use.

[0032] Soluble lignin is soluble in water at a concentration of up to 90% by mass relative to the mass of the solution.

[0033] The oils used can be chosen from any type of oil, such as for example vegetable oils, mineral oils such as vaseline oil; synthetic oils such as hydrogenated polyisobutene, esters of fatty acids and fatty alcohols (C6-C30), fatty alcohol ethers (C4 to C30 saturated and / or branched); silicone oils, in particular volatile silicone oils such as cyclomethicones (cyclotetradimethylsiloxane or cyclotetramethicone, cyclopentadimethylsiloxane or cyclopentamethicone, cyclohexadimethylsiloxane or cyclohexamethicone); fluorinated oils and mixtures thereof.

[0034] The vegetable oils may be chosen, for example, from argan oil, avocado oil, linseed oil, sunflower oil, palm oil, saw palmetto oil, coconut oil, grape seed oil, black mustard oil, poppy seed oil, shea butter oil, sweet almond oil, soybean oil, peanut oil, cottonseed oil, sesame oil, olive oil, corn oil, cocoa oil, castor oil, Moringa oil (or Ben oil), rapeseed oil, annatto oil, wheat germ oil, safflower oil, walnut oil, hazelnut oil, rapeseed oil or mixtures thereof.

[0035] Vegetable oil may also be produced synthetically, for example by preparing oils having a similar chemical composition, for example by preparing oils comprising glycerides.

[0036] Emulsions using said soluble lignin can be prepared in the usual manner in the field of oil / water emulsions.

[0037] Said oil / water emulsions may, for example, be obtained according to conventional preparation methods classically used in cosmetics, by gradually incorporating the oily phase into the aqueous phase and homogenizing the whole with stirring. For example, a high-shear mixer may be used for this stirring.

[0038] The aqueous phase (containing the water-soluble lignin) like the oily phase, may optionally also contain additives, depending on their hydrophilic or lipophilic nature, prior to mixing the two phases.

[0039] Advantageously, the mass fraction of said lignin in water is from 0.05 to 20%, preferably from 0.5% to 20%, in particular from 0.5% to 15% and more particularly from 1 to 10%, and the mass fraction of oil is from 0.1% to 80%, in particular from 1% to 50%, in particular from 1% to 30%, and more particularly from 5% to 20%, expressed relative to the total weight of the emulsion.

[0040] Stability can be assessed, for example, by observing good dispersion of the oily phase in the aqueous phase and the absence of clusters of oily drops. The behavior of the emulsion can, for example, be analyzed by diluting the emulsion with water, followed by observing it under a microscope. The emulsion is considered unstable if it exhibits heterogeneity created by the presence of large oil drops. Otherwise, good dispersion of the oil drops and good stability of the emulsion, which is homogeneous, are observed. The size of the drops can be measured, for example, under a microscope.

[0041] Advantageously, in the emulsions prepared using the water-soluble lignin according to the invention, stabilization and the notable absence of coalescence were observed over several months.

[0042] According to one embodiment of the invention, said soluble lignin obtained by enzymatic is used as the sole stabilizing and / or emulsifying agent of the emulsion.

[0043] According to another embodiment, said water-soluble lignin obtained enzymatically is used with at least one other stabilizing and / or emulsifying agent for the emulsion.

[0044] The invention also relates to oil / water emulsions containing said water-soluble lignin, obtained enzymatically and soluble in water at pH greater than or equal to 4 as a stabilizing and / or emulsifying agent, as well as the use of said emulsions in usual industrial applications, such as, for example and without being exhaustive, in the preparation of cosmetic products (creams, lotions, emulsions, etc.), pharmaceutical products (formulations for topical application, formulations for oral administration, etc.), or agri-food products (sauces, seasoning products, dairy products, etc.).

[0045] In a known manner, the emulsions may also contain usual additives depending on the field of application considered, such as solvents, active ingredients, preservatives, antioxidants, complexing agents, perfumes, fillers, bactericides, odor absorbers, coloring matters, etc. Examples

[0046] Example 1: Study of enzymatically treated water-soluble lignin

[0047] 1) Preparation of the lignin solution

[0048] On the first day, 3 g of Kraft sigma lignin are introduced into a three-necked flask equipped with a magnetic stirrer. 100 mL of 50 mmol borate at pH 10 are then added to the lignin. The solution is heated and stirred at 250 rpm using a magnetic bar at 60°C in the presence of oxygen. The enzyme bilirubin oxidase (BOD) of bacterial origin, from Bacillus pumilus in liquid form, is integrated into the solution at 60°C, at a rate of 10 mg of enzyme per 3 g of lignin for 18 hours. Then a dialysis step is initiated by preparing a large 5L beaker containing distilled water. The solution is transferred into this container and dialysis continues for one day, using Spectra / Por 7 Pretreated Regenerated Cellulose (RC) Tubing dialysis bags with a molecular weight cut-off (MWCO) of 10kD, with two water changes performed after 4 hours and 18 hours.Finally, after the last dialysis, the solution is centrifuged at 4297 g for 15 minutes at room temperature and placed in the freezer (-80°C) for 3 hours, before being lyophilized.

[0049] 2) Rheology

[0050] Rheology experiments were carried out on treated aqueous lignin solutions, using an AR2000 rheometer equipped with a cone-plate system of diameter 4 cm and with an angle of 2 degrees. A series of dilutions was subjected to these measurements, with volume percentages varying between 20 and 1%. All these measurements were carried out after preparing the samples overnight, keeping them under agitation with a magnetic stirrer during this period.

[0051] The variation of the dynamic viscosity (Pa.s) as a function of the shear rate (1 / s) was measured for aqueous solutions at different concentrations of lignin obtained by enzymatic treatment, ranging from 20% to 1% (in water), with intermediate concentrations of 16, 13, 10, 8, 5, 3%.

[0052] The results shown in [Fig.l] show that for high concentrations, the lignin solution exhibits thixotropic characteristics, as well as a high viscosity for the most concentrated samples. This increase in viscosity, due to the increase in molecular weight of the lignin treated by BOD, compared to its initial molecular weight, is an advantage for the production of emulsions.

[0053] 3) Interfacial tension

[0054] In order to measure the interfacial tension, analyses of the shape of the drops were carried out using the Teclis Tracker device. These analyses were carried out in 3 different media: air, mineral oil (paraffin oil CAS 8020-83-5) and peanut oil, using lignin volume fractions ranging from 0 to 10%. The drop volume was set between 10 and 15 pL, with a measurement duration of 4 hours.

[0055] The results are shown in Figures 2 a) and 2b). [Fig.2a] shows the variation of interfacial tension in the three media, and [Fig.2b] represents the variation of interfacial tension for 10% lignin solutions. The results show that the presence of lignin leads to a decrease in interfacial tension of approximately 15 mN / m in all three environments.

[0056] Example 2: Creation and analysis of emulsions

[0057] The emulsions are made with a mixer (Silverson L4RT). The constant speed of the mixer was set between 7500 and 7700 rpm. Three types of oil were used: peanut oil, olive oil and mineral oil (paraffin oil CAS 8020-83-5).

[0058] The total volume of oil added is 10% relative to the total volume of emulsion produced, equivalent to 100 pL. The addition of oil is gradual, with incorporation in 25 pL increments. At each addition, an emulsion is created by mixing for 1 minute. This methodology was repeated with 5 concentrations of 1 mL lignin solutions in 4 mL pillboxes, namely 1%, 3%, 5%, 8% and 10%.

[0059] Analysis method:

[0060] All samples were examined on the same day as their preparation, under an optical microscope (Leica DM2500P) with a 10x objective. Dimensional analyses of the emulsions were carried out using Image J software, and a curve illustrating the size distribution was generated using OriginPro software. The analyses are carried out on optical microscopy images. The observations show the formation of emulsion drops with varied sizes.

[0061] Size distributions are performed by measuring approximately 10,000 drops. The stability of the samples was examined in the same way after 3 months, after storage at room temperature, according to the method explained previously. Figures 3a and 3b illustrate the droplet size distribution of an emulsion based on a 5% mass fraction lignin solution in water and mineral oil (paraffin oil CAS 8020-83-5) at the date of their creation and after 3 months. The results show that the size distribution remains constant, with emulsion droplet diameters between 0 and 40 pm. Significantly, the majority of the drops are between 5 and 10 pm, representing the highest percentage. References

[0062] (1) Ruwoldt, J. Emulsion Stabilization with Lignosulfonates. In Lignin; Sand, A., Tuteja, J., Eds.; IntechOpen: Rijeka, 2022 https: / / doi.org / 10.5772 / intechopen.107336.)

[0063] (2) Shi, C.; Zhang, S.; Wang, W.; Linhardt, R. J.; Ragauskas, A. J. Préparation of Highly Reactive Lignin by Ozone Oxidation: Application as Surfactants with An-tioxidant and Anti-UV Properties. ACS Sustain. Chem. Eng. 2020, 8 (1), 22-28, https: / / doi.org / 10.1021 / acssuschemeng.9b05498)

[0064] (3) Yuliestyan, A.; Partal, P.; Navarro, F. J.; Martm-Sampedro, R.; Ibarra, D.; Eugenio, M. E. Emulsion Stabilization by Cationic Lignin Surfactants Derived from Bioethanol Production and Kraft Pulping Processes. Polymers 2022,14 (14). https: / / doi.org / 10.3390 / polyml4142879)

[0065] (4) Mikkonen, K. S. Strategies for Structuring Diverse Emulsion Systems by Using Wood Lignocellulose-Derived Stabilizers. Green Chem 2020, 22 (4), 1019-1037. https: / / doi.org / 10.1039 / C9GC04457D)

Claims

Claims

1. Use of enzymatically obtained lignin as a stabilizing and / or emulsifying agent in an oil / water emulsion, said lignin being soluble in water at a pH greater than or equal to 4.

2. Use according to claim 1, wherein said lignin is soluble in water at pH greater than or equal to 5, preferably greater than or equal to 6, preferably greater than or equal to 7, and pH less than or equal to 13, preferably less than or equal to 12, preferably less than or equal to 11, preferably less than or equal to 10.

3. Use according to claim 1, wherein said lignin is soluble in water at a pH between 4 and 12, in particular between 5 and 9, and more particularly between 6 and 8.

4. Use according to one of claims 1 to 3, in which the enzymatic treatment is carried out using at least one bilirubin oxidase type enzyme.

5. Use according to one of claims 1 to 4, wherein said lignin is obtained by a process comprising bringing a lignin, in water, in the presence or absence of a buffering agent, into contact with at least one bilirubin oxidase type enzyme, in the presence or absence of a redox mediator, and recovering the lignin solution.

6. Use according to one of claims 1 to 5, wherein the mass fraction of said lignin in water is from 0.05 to 20%, preferably from 0.5% to 20%, in particular from 0.5% to 15% and more particularly from 1 to 10%, and the mass fraction of oil is from 0.1% to 80%, in particular from 1% to 50%, in particular from 1% to 30%, and more particularly from 5% to 20%, expressed relative to the total weight of the emulsion.

7. Use according to any one of claims 1 to 6, wherein said oil is selected from vegetable oils, mineral oils and silicone type oils.

8. Use according to any one of claims 1 to 7, wherein said soluble lignin obtained enzymatically is used as the sole stabilizing and / or emulsifying agent of the emulsion.

9. Use according to any one of claims 1 to 8, wherein said enzymatically obtained water-soluble lignin is used with at least one other stabilizing and / or emulsifying agent.

10. the emulsion. Use according to any one of claims 1 to 9 for stabilizing emulsions in the preparation of cosmetic, pharmaceutical or agri-food products.

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