Microparticulate composite material based on zinc oxide grafted to diatomaceous earth, method for preparing same and uses thereof as an Anti-uv active agent

Abstract

The invention relates to a method for preparing a composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth particles, comprising a step of milling in the presence of an agent for stabilizing the electron charges created during the milling, and also to a composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth particles, and to the use thereof as an active agent for protection against UV radiation.

Description

Description Title: Microparticulate composite material based on zinc oxide grafted onto diatomaceous earth, its preparation process and its applications as an anti-UV active ingredient. Technical field

[0001] The present invention relates to the field of microparticulate composite materials, in particular based on zinc oxide. Prior art

[0002] It is well known that ultraviolet (UV) radiation, emitted naturally by the sun or by artificial sources, is beneficial in small quantities for the human body and essential for the synthesis of vitamin D, which is itself essential for the fixation of calcium on bones and the prevention of osteoporosis. However, overexposure to UV is responsible for an alteration of the cutaneous (accelerated aging, cancers, etc.), ocular and immune systems.

[0003] A sunscreen is a cream or lotion used to reduce the skin's exposure to the sun's ultraviolet radiation. As such, it constitutes a means of passive external photoprotection, functioning as an ultraviolet filter. Such a sunscreen product is composed of ultraviolet filters in a base that can be an oil or more frequently an emulsion (cream or lotion). Effective protection must block both UVA and UVB rays: UVB (and to a lesser extent UVA) can cause sunburn, UVA causes premature aging of the skin, UVA and especially UVB cause skin cancer.

[0004] An ultraviolet filter, or UV filter, is a chemical compound that blocks or absorbs ultraviolet radiation. All sunscreens contain ultraviolet sunscreens, which are divided into two families of molecules: chemical (or organic) filters and mineral (or inorganic) filters.

[0005] Organic filters are easier to use but they pollute the water, are difficult to eliminate, even by treatment plants, can be allergenic and are toxic to both humans and the environment, particularly aquatic biotopes.

[0006] An alternative to organic filters is the use of mineral filters. In cosmetics, only two mineral filters are authorized: titanium dioxide and zinc oxide. These two filters provide immediate protection against UV rays, unlike chemical filters, which take up to 25 minutes to provide the claimed protection.

[0007] The mineral filters in so-called "organic" creams are hypoallergenic and photostable (making them the recommended sunscreen for allergy sufferers and children). For a long time, they were less popular with consumers because they were more difficult to spread and gave users an unattractive whitish tint. To solve this problem and improve the cosmetic appearance, laboratories have reduced these mineral filters to the form of nanoparticles to formulate sunscreens. However, numerous studies have been conducted on nanoparticles and have demonstrated their harmful effects on the environment, particularly on phytoplankton, and their potential effects on health, as these particles penetrate the skin. In particular, TiO2 nanoparticles have become the main oxidizing agent entering coastal waters, with direct ecological consequences for the ecosystem.Titanium dioxide nanoparticles disperse in water and are found in filter-feeding organisms (particularly oysters and mussels) or the cells of other marine animals.

[0008] Zinc oxide remains a preferred choice due to its many qualities as an effective filtering agent for UVB and UVA radiation, photostable, and non-allergenic. However, it presents a risk to the environment and potentially to human health in its native nanoparticle form (particles smaller than 100 nm) due to this size and its oxidizing properties under the action of UV radiation.

[0009] Given this observation regarding the limits and dangers of using organic filters in sunscreens and to take into account the risk of using nanoparticle mineral filters, it is therefore necessary to find an alternative that can combine protection that is both effective for humans and safe for the environment. General description

[0010] It is to the Applicant's credit that this problem was resolved by developing a process for obtaining a composite material comprising zinc oxide nanoparticles grafted onto natural mineral microparticles of diatomaceous earth, said composite material having a particle size ranging from 30 to 200 nm.

[0011] Patent EP 2 375 575 describes a cosmetic composition comprising a composite material based on diatomaceous earth and zinc. This composite material is prepared on the basis of unmodified diatomaceous earth and therefore has an average size of 10 microns which leads to poor dispersion of the material in a composition cosmetic. Furthermore, the Applicant was able to note that under the zinc chloride concentration conditions described in this patent, the proposed zinc oxide concentration leads to very partial coverage of the diatomaceous earth particles by the zinc crystals and that the zinc oxide concentration of the final product is 10 times lower than that indicated. As it stands, the proposed preparation method cannot lead to the production of a material capable of claiming the alleged anti-UV properties.

[0012] On the contrary, within the composite material according to the invention, the modification of the diatomaceous earth in the form of microparticles allows a very significant increase in the specific surface area of ​​the material leading to a very significant increase in the crystallization surfaces of the zinc oxide. This makes it possible to increase for the same quantity of material the surface properties and in particular the surface area exposed to light radiation including UV rays and the possibility of diffraction and refraction of these rays. This technique allows the development of large surfaces of zinc nanocrystals while very significantly limiting the diffusion of the material into the environment since the zinc oxide nanoparticles are fixed to this non-nanometric support and are therefore not passively diffusible into cells or living organisms.

[0013] A first object of the invention is thus a process for preparing a composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth particles, comprising the following steps: 1) preparation of diatomaceous earth microparticles by grinding diatomaceous earth; 2) grafting zinc salt crystals onto the surface of diatomaceous earth microparticles; 3) transformation of said zinc salt crystals grafted onto the surface of the diatomaceous earth microparticles into zinc oxide crystals grafted onto the surface of the diatomaceous earth microparticles; 4) grinding of the microparticles obtained in step 3) to an individual particle size ranging from 10 to 300 nm, this grinding being carried out in the presence of a stabilizing agent for electronic charges created during grinding.

[0014] A second subject of the invention is a composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth particles, said grafted diatomaceous earth particles having an individual particle size ranging from 10 to 300 nm. This composite material is advantageously prepared according to the method of the invention. The invention also relates to the use of the composite material according to the invention or prepared according to the process according to the invention as an active ingredient for protection against UV radiation, in particular in cosmetic compositions.

[0015] Another subject of the invention is a cosmetic composition comprising the composite material according to the invention or prepared according to the process according to the invention. Detailed description

[0016] A first subject of the invention is a method for preparing a composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth particles, comprising the following steps: 1) preparation of diatomaceous earth microparticles by grinding diatomaceous earth in an aqueous medium; 2) grafting zinc salt crystals onto the surface of diatomaceous earth microparticles; 3) transformation of said zinc salt crystals grafted onto the surface of the diatomaceous earth microparticles into zinc oxide crystals grafted onto the surface of the diatomaceous earth microparticles; 4) grinding of the microparticles obtained in step 3) in aqueous media to an individual particle size ranging from 10 to 300 nm, this grinding being carried out in the presence of a stabilizing agent for electronic charges created during grinding.

[0017] Diatomaceous earth (also called kieselguhr or diatomite) is a microscopic, single-celled fossilized algae found in large geological deposits located in ancient marine sedimentary basins. This sedimentary rock appears as a protective silica-based envelope, called a frustule, of predominantly silicic composition and whose shape and size vary according to the age and origin of the sediment. Frustules have a remarkable structure, composed of a large network of macroscopic canals that can represent up to more than 80% of the total volume of the structure.

[0018] In step 1) of the process according to the invention, the diatomaceous earth is advantageously ground to an individual particle size ranging from 50 nm to 2 pm, preferably from 100 nm to 1 pm and more preferably from 150 nm to 500 nm. By "an individual particle size" is meant that each particle of the material has a particle size falling within the indicated range of values. The particle size is determined by scanning electron microscopy (SEM).

[0019] Advantageously, the grinding of the 1 ère step is carried out in such a way as to preserve the silanol groups on the surface of the diatomaceous earth. The Applicant has in fact noticed that too great an increase in the temperature of the material induces a phenomenon of amorphization of the silicic structure with disappearance of the surface silanol groups by dehydroxylation of these groups.

[0020] The preservation of a maximum of surface silanol groups can be achieved by a sequential aqueous grinding technique which limits the temperature rise during grinding below a threshold of 200°C.

[0021] Thus, step 1) of grinding of the process according to the invention is advantageously carried out in aqueous media using a planetary type grinder.

[0022] This type of mill operates according to the following principle: The grinding bowl is arranged eccentrically on the sun gear of the planetary ball mill. The sun gear rotates in the opposite direction to the rotation of the grinding bowl. The grinding balls located in the bowl are deflected as a result of superimposed rotational movements, which is responsible for the so-called Coriolis force. The Coriolis force is a force that deflects the trajectory of a moving object on the surface of a rotating object. It applies in particular to moving air and water masses. The speed differences between the balls and the grinding bowl lead to an interaction between impact and friction forces, releasing significant dynamic energies. The combination of these forces results in the high and highly efficient grinding degree of planetary ball mills.

[0023] This grinding step can be carried out by varying one or more of the following parameters: - the volume of grinding charge, namely the volume occupied by the grinding balls in relation to the volume of the grinding bowl; - the granulometry of the grinding load (the size of the grinding bodies determines the fineness of the output granulometry: the smaller the grinding balls, the finer the final granulometry can be); - the feed charge of product to be ground, and the proportional water charge; - the rotation speed of the crusher, - the number of grinding cycles; - the temperature of the mixture during the .

[0024] The skilled person knows how to adapt his parameters in order to obtain the desired particle size. Generally, he will use a grinding charge volume of approximately 15% to 25%. The grinding balls are advantageously balls of less than 1 mm, preferably 0.5 mm. The number of grinding cycles is generally from 1 to 20, preferably from 5 to 15 and more preferably from 8 to 12. As indicated previously, the temperature during grinding is advantageously kept below 200°C, preferably it is below 150°C. As for the rotation speed of the grinder, this is advantageously of the order of 300 to 800 rpm, for example 550 rpm.

[0025] Step 2) of the process according to the invention may comprise the following steps: a) placing diatomaceous earth particles obtained during step 1 in aqueous suspension with calcium carbonate; b) placing the mixture obtained at the end of step a) in contact with an aqueous suspension of zinc chloride; c) stirring the mixture obtained at the end of step b) at a temperature ranging from 5°C to 40°C, preferably 15°C to 25°C, for a period ranging from 24 to 72 hours, preferably 48 hours; d) recovering the composite material obtained at the end of step c), in particular by sedimentation or centrifugation; e) drying the composite material at a temperature ranging from 50°C to 90°C, preferably 70°C, for a period ranging from 12 to 48 hours, preferably 24 hours.

[0026] This second step of the process allows the zinc salts to react with the silanol groups on the surface of the diatomaceous earth particles. In particular, this step allows the calcium carbonate present in the diatomaceous earth to solubilize by releasing hydroxyl and carbonate species into the medium, leading to the crystallization of hydrated zinc carbonate hydroxide phases of chemical formula Zn4(CO3)(OH)6-H2O on the surface of the diatomaceous earth particles at the surface silanol groups.

[0027] In particular, the diatomaceous earth particles obtained in step 1 may be suspended in water at a rate of 0.1 to 100 grams of powder per liter of water, preferably 10 grams of powder per liter of water.

[0028] Similarly, calcium carbonate can be suspended in water at a rate of 0.1 to 100 grams of calcium carbonate per liter of water, preferably 10 grams of calcium carbonate per liter of water.

[0029] The aqueous suspension of zinc chloride used in step b) has a concentration of 5.10-3 to 5 mole.L-1, preferably 2 to 3 mole.L-1, in particular approximately 1 mole.L-1.

[0030] Advantageously, the hydration of the suspension obtained at the end of step a) and of the zinc chloride suspension can be carried out separately for 15 to 60 minutes, preferably 30 minutes before bringing these two suspensions together in step b).

[0031] Step c) of stirring the mixture can be carried out using a paddle mixer at a rotation speed of approximately 100 revolutions / minute.

[0032] Step e) of drying the composite material can be carried out in an oven or furnace.

[0033] Step 3) of the process according to the invention can be carried out by heat treatment at a temperature ranging from 500°C to 900°C, preferably 700°C, for a duration ranging from 1 hour to 4 hours, preferably 2 hours.

[0034] This third step allows the transformation of the zinc salt crystals formed in step 2) into zinc oxide crystals distributed on the surface of the diatomaceous earth particles. The zinc oxide is advantageously covalently bonded to the surface of the diatomaceous earth particles.

[0035] The heat treatment implemented in step 3) can be carried out in a furnace, in particular with a temperature rise of 190°C / hour up to 700°C then a plateau at 700°C for 2 hours before a decrease to room temperature by stopping the furnace. A more gradual temperature rise and a longer plateau could also be planned without altering the result.

[0036] Step 4) of grinding the microparticles obtained in step 3) to an individual particle size ranging from 10 to 300 nm is carried out in aqueous media in the presence of an agent for stabilizing electronic charges created during grinding. The inventors have in fact found that grinding these microparticles in an aqueous medium without any addition gives rise to reagglomeration or recrystallization of the microparticles obtained during and at the end of grinding and therefore does not make it possible to obtain the desired particle size. Quite surprisingly, the inventors have found, after extensive research, that grinding in the presence of an agent for stabilizing electronic charges created during grinding, such as an aqueous solution of alkali metal silicate, makes it possible to prevent or at least limit this phenomenon of reagglomeration or recrystallization and thus obtain an individual particle size ranging from 10 to 300 nm.Without wishing to be bound by any theory, the inventors believe that during the grinding of zinc crystals an imbalance of electronic charges is created and that the phenomenon of reagglomeration or recrystallization is due to the attraction of the opposite charges created during grinding. According to the inventors' findings, the use of an agent for stabilizing electronic charges created during grinding, such as an aqueous solution of alkali metal silicate, makes it possible to stabilize the new electronic environment created during grinding by compensating for the charges that appear. Indeed, in the case of an alkali metal silicate, the alkali metal cations would come. compensate for the negative charges and the anions resulting from the dissolution of the alkali metal silicate would compensate for the positive charges.

[0037] The alkali metal silicate may be selected from sodium silicate, lithium silicate and potassium silicate. Preferably, the alkali metal silicate is sodium silicate.

[0038] The alkali metal silicate is used in the form of an aqueous solution. The alkali metal silicate is used in a suitable amount to stabilize the imbalance of electronic charges during grinding. In the case of sodium silicate, it is advantageously used in an amount of 3% to 20%, preferably 5% to 15%, in particular 10% to 15%, the percentages being expressed by weight relative to the weight of the microparticles obtained in step 3) of the process according to the invention.

[0039] The grinding of step 4) can be carried out in a similar manner to that of step 1) using in particular the same type of equipment, more particularly a planetary ball mill. The person skilled in the art knows how to adapt the grinding conditions in order to obtain the desired particle size.

[0040] The microparticles obtained in step 3) are ground in step 4) to an individual particle size ranging from 10 to 300 nm. Preferably, they are ground to an individual particle size ranging from 15 nm to 250 nm. Such particle sizes were, to the inventors' knowledge, not previously available for zinc oxide particles grafted to the surface of diatomaceous earth particles.

[0041] Thus, a second subject matter of the invention is a composite material comprising zinc oxide particles grafted onto the surface of diatomaceous earth particles, the grafted diatomaceous earth particles having an individual particle size ranging from 10 to 300 nm, preferably from 15 to 250 pm. As previously indicated, by "an individual particle size" is meant that each particle of the material has a particle size falling within the indicated range of values. The particle size is determined by scanning electron microscopy (SEM).

[0042] Advantageously, the composite material according to the invention comprises zinc oxide present on the surface of the diatomaceous earth particles at a concentration of 50% to 90% by weight, preferably 50% to 80% by weight, preferably 65% ​​to 75% by weight, more preferably approximately 70% by weight relative to the weight of the composite material.

[0043] The invention also relates to the use of the composite material according to the invention or prepared according to the process according to the invention as an active agent for protection against UV radiation, in particular in cosmetic compositions.

[0044] With regard to cosmetic compositions, the composite material according to the invention has both a high anti-UV efficacy, and numerous advantages due to its size: a very strong limitation of the diffusion of this material in the environment compared to zinc oxide nanoparticles alone, combined with a very homogeneous diffusion in the excipients and a limitation of the effect of reflection of visible light by the particles, which reduces the major disadvantage of whitish surface effects on the skin, compared to a larger size material, such as unground diatomaceous earth.

[0045] Another subject of the invention is a cosmetic composition comprising the composite material according to the invention or prepared according to the process according to the invention. The cosmetic compositions according to the invention include, but are not limited to, formulations for topical application, such as creams, oils, milks, suspensions, sprays, lotions, balms and serums.

[0046] The invention will be better understood with the aid of the following figures and examples. Figures

[0047] [Fig. 1] is a scanning electron microscopy image of crushed diatomaceous earth particles.

[0048] [Fig. 2] is a scanning electron microscopy image of a composite material according to the invention according to an embodiment using 5% by weight of sodium silicate.

[0049] [Fig. 3] is a scanning electron microscopy image of a composite material according to the invention according to an embodiment using 10% by weight of sodium silicate.

[0050] [Fig. 4] is a scanning electron microscopy image of a composite material obtained by grinding in the absence of an electronic charge stabilizing agent.

[0051] [Fig. 5] shows the in vivo anti-UV effect of a composite material according to an embodiment using 10% by weight of sodium silicate 24 hours after exposure of the volunteer to the sun. Examples

[0052] Example 1: Preparation of the composite material comprising zinc oxide crystals grafted to the surface of diatomaceous earth microparticles (steps 1) to 3) of the process according to the invention) 40 grams of diatomaceous earth were ground in a planetary type mill (Retsch PM100) equipped with a 50 mL bowl with the following parameters: - Volume of the grinding load: 60% of the capacity of the grinding bowl; - Grinding charge particle size. Grinding balls with a diameter of 0.5mm; - Product feed load: 16% of the bowl volume; - Water load: 24% of the bowl volume; - Rotation speed: 550 rpm; - Number of grinding cycles. 8 cycles of 10 minutes with 10-minute breaks between each grinding phase.

[0053] Several batches of 40 grams of diatomaceous earth were ground in this way to recover 1000 grams of diatomaceous earth powder. This powder presents, according to scanning electron microscopy analyses, a fairly homogeneous grinding of diatomaceous earth particles below 500 nm (see Fig. 1). The recovered powder was suspended in tap water at a mass concentration of 10g of powder per liter of water, then 1000 grams of calcium carbonate were added at a mass concentration of 10g per liter of water.

[0054] In parallel, 13,600 grams of ZnCl2 were dissolved in tap water to prepare a solution with a concentration of 1 mole / liter. The hydration of the two suspensions was carried out separately for 30 minutes before mixing. The two aqueous phases thus obtained were then mixed in a suitable tank. The agitation of the aqueous mixture thus obtained was carried out using a paddle mixer at a rotation speed of approximately 100 rpm and at a temperature between 15°C and 25°C, for a period of 48 hours.

[0055] The composite obtained after mixing the two aqueous phases was then recovered by a first step of gravity draining the mixing tank into a recovery tank with a plastic bag. Several decantation phases were carried out to remove surface water, then the material thus recovered in the form of cream was then dried by placing the cream in tanks which were then dried in an oven at 90°C for 24 hours.

[0056] The powder resulting from this drying was then transferred into calcination gazettes which were finally placed in the oven for calcination with a temperature increase program of 190°C / hour up to 700°C then a plateau at 700°C for 2 hours before lowering to room temperature by stopping the oven. At the end of this stage, approximately 10 kg of the composite material according to the invention were recovered.

[0057] Example 2: Grinding of the composite material obtained in Example 1 in the presence of sodium silicate

[0058] 10 g of composite material obtained according to Example 1 was subjected to grinding in the presence of tap water and an aqueous solution of sodium silicate (40% Sodium Silicate from Arcane Industries, CAS No. 1344-09-8) in a planetary mill equipped with a 50 ml bowl and 0.5 mm grinding balls at a rate of 1 / 10 ème of the available quantity, i.e. approximately 100g. The grinding parameters were as follows: - Total cycle time: 8 hours - Settings: 32 cycles of 10 minutes of grinding separated by 5-minute breaks (i.e. 5 hours 20 minutes of effective grinding) - Rotation speed: # 500 rpm - Wait for the cycle to end and the bowl to cool down - Rinse with new Retsch 250pm sieve with water and a brush to recover the beads. Weigh the water additions - Recovery and conservation of the different creams obtained: approximately 10 g of dry equivalent recovered per test.

[0059] Two tests with different concentrations of sodium silicate were carried out: - Test 2-1: 5% by weight of sodium silicate relative to the weight of the composite material, i.e. 1250 mg of 40% sodium silicate solution per 10 g of composite material used; - Test 2-2: 10% by weight of sodium silicate relative to the weight of the composite material, i.e. 2500 mg of 40% sodium silicate solution per 10 g of composite material used.

[0060] For both tests, the individual particle size is in the range of 10 to 300 nm, as shown in Figures 1 and 2.

[0061] Example 3: Grinding of the composite material obtained in Example 1 without adding sodium silicate

[0062] 10 g of composite material obtained according to Example 1 was subjected to grinding in the presence of 20 g of tap water in a planetary mill equipped with a 50 mL bowl and 0.5 mm grinding balls at a rate of 1 / 10 ème of the available quantity, i.e. approximately 100g. The grinding parameters were as follows: - Total cycle time: 8 hours - Settings: 32 cycles of 10 minutes of grinding separated by 5-minute breaks (i.e. 5 hours 20 minutes of effective grinding) - Rotation speed: # 500 rpm - Wait for the cycle to end and the bowl to cool down - Rinse with new Retsch 250pm sieve with water and a brush to recover the beads. Weigh the water additions - Recovery and conservation of the cream obtained: approximately 10g of dry equivalent recovered. Example 4: Evaluation of the in vivo anti-UV effect of the material of Example 2 prepared with 10% sodium silicate

[0063] The material of Example 2 prepared with 10% sodium silicate was tested to evaluate its ability to protect human skin against UV radiation (anti-UV effect). The test was carried out on a healthy human volunteer without photosensitivity problems having type I skin, i.e. skin that always reddens and never tans.

[0064] Approximately 1 g of the cream recovered from Example 2 using 10% sodium silicate was applied in a V shape to the volunteer's torso and the volunteer was then exposed to the sun from 1 p.m. to 3 p.m. at the end of May in Brittany (France).

[0065] After exposure, the unprotected skin had become very red, while the V-shaped area protected by the material according to the invention remained unchanged. After 24 hours, the unprotected skin was still very red and the protected area unchanged, as can be seen in Figure 4.

Claims

Demands

1. A method for preparing a composite material comprising zinc oxide crystals grafted onto the surface of diatomaceous earth particles, comprising the following steps: 1) preparation of diatomaceous earth microparticles by grinding diatomaceous earth in an aqueous medium; 2) grafting of zinc salt crystals onto the surface of diatomaceous earth microparticles; 3) transformation of said zinc salt crystals grafted onto the surface of diatomaceous earth microparticles into zinc oxide crystals grafted onto the surface of diatomaceous earth microparticles; 4) grinding of the microparticles obtained in step 3) in aqueous media to an individual particle size ranging from 10 to 300 nm, this grinding being carried out in the presence of a stabilizing agent for electronic charges created during grinding.

2. A method according to claim 1, wherein step 1 of grinding is carried out using a planetary type mill.

3. A process according to claim 1 or 2, wherein step 2 comprises the following steps: a) aqueous suspension of diatomaceous earth particles obtained in step 1) with calcium carbonate; b) mixing the mixture obtained at the end of step a) with an aqueous suspension of zinc chloride; c) stirring the mixture obtained at the end of step b) at a temperature of 5°C to 40°C, preferably 15°C to 25°C, for a period of 24 to 72 hours, preferably 48 hours; d) recovery of the composite material obtained at the end of step c), in particular by sedimentation or centrifugation; e) drying of the composite material at a temperature of 50°C to 90°C, preferably 70°C, for a period of 12 to 48 hours, preferably 24 hours.

4. A method according to any one of claims 1 to 3, wherein step 3 is carried out by heat treatment at a temperature of 500°C to 900°C, preferably 700°C, for a period of 1 to 4 hours, preferably 2 hours.

5. A method according to any one of claims 1 to 4, wherein the agent stabilizing electronic charges created during grinding is an aqueous solution of alkali metal silicate.

6. A method according to claim 5, wherein the alkali metal silicate solution is a sodium silicate solution.

7. Composite material comprising zinc oxide crystals grafted onto the surface of diatomaceous earth particles, said grafted diatomaceous earth particles having an individual particle size ranging from 10 to 300 nm.

8. A composite material according to claim 7, wherein zinc oxide is present on the surface of diatomaceous earth particles at a concentration of 50% to 80% by weight, preferably 65% ​​to 75% by weight, and preferably about 70% by weight relative to the weight of the composite material.

9. Use of the composite material as defined in claim 7 or 8 or prepared according to any one of claims 1 to 6 as an active ingredient for protection against UV radiation, particularly in cosmetic compositions.

10. Cosmetic composition comprising the composite material as defined according to claim 7 or 8 or prepared according to any one of claims 1 to 6.

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