MICRO- OR NANOCAPSULES HAVING PHOTOCATALYTIC PROPERTIES FOR CONTROLLED RELEASE OF DIFFUSING AGENTS AND RESPECTIVE METHOD OF PRODUCTION

Abstract

The present disclosure relates to the production of functional coatings for the controlled release of volatile agents. More specifically, the present disclosure relates to capsules, in particular microcapsules or nanocapsules, chemically functionalised with photocatalytic nanomaterials upon the internal or external surface of the wall of the capsule. The capsule, by solar action or artificial light, can have the same spectrum of electromagnetic radiation, and can release an active agent. The capsule can also transport the active agent, which has photocatalytic properties. The capsule has an external diameter of 0.1-500 m and can be formed by a wall and a nucleus to lodge the active agent. The present disclosure further relates to a method of obtainment of the capsules.

Claims

1. A capsule for transporting an active agent having photocatalytic properties, the capsule having an external diameter from 0.05-500 m, and the capsule comprising: a capsule wall; a nucleus containing at least one active agent; wherein the capsule wall comprises a polymeric film selected from the group consisting of parylene, poly(p-xylene), poly(lactic acid), poly(-caprolactone), polyoxyethylenated derivatives, phthalocyanine, melamine-formaldehyde, polyurethane, polysulfone, cellulose acetate, acrylic polymers, collagen, chitosan, and mixtures thereof, wherein the polymeric film comprises, upon its external surface, nanomaterials chemically functionalised with a photocatalytic compound selected from the group consisting of: TiO2, WO3, WS2, Nb2O5, MoO, MoS2, V2O5, MgF2, Cu2O, NaBiO3, NaTaO3, SiO2, RuO2, BiVO4, Bi2WO6, Bi12TiO20. NiOK4NB6O17, SrTiO3, Sr2NbO7, Sr2TaO7, BaTiO3, BaTaTi2O5, ZnO, ZrO2, SnO2, ZnS, CaBi2O4, Fe2O3, Al2O3, Bi2O6, Bi2S3, CdS, CdSe, and mixtures thereof, and wherein the at least one active agent is in a liquid, solid or gaseous state.

2. The capsule of claim 1, wherein the distribution of the photocatalytic nanomaterials upon the surface of the capsule is 0.1-5% w/v of total capsule.

3. The capsule of claim 1, wherein the wall of the capsule is a distribution of the polymeric film and the photocatalytic nanomaterials, and wherein the polymeric film comprises from 55-80% w/v of the total wall and the photocatalytic nanomaterials comprises from 20-45% w/v of the total wall.

4. (canceled)

5. The capsule of claim 1, wherein the polymeric film is selected from the group consisting of: poly(methyl methacrylate), polysulfone, polyurethane, and mixtures thereof.

6. The capsule of claim 1, wherein the polymeric film comprises poly(methyl methacrylate) and the photocatalytic compound is selected from the group consisting of: TiO2, WO3, SrTiO3, ZnO, and mixtures thereof.

7. The capsule of claim 1, wherein the polymeric film comprises polyurethane and the photocatalytic compound is selected from the group consisting of: TiO2, WO3, SrTiO3, ZnO, and mixtures thereof.

8. The capsule of claim 1, wherein the polymeric film comprises polysulfone the photocatalytic compound is selected from the group consisting of: TiO2, WO3, SrTiO3, ZnO, and mixtures thereof.

9. The capsule of claim 1, wherein the external diameter of the capsule ranges from 0.1-500 m.

10. The capsule of claim 1, wherein the nanomaterials are in the form of nanoparticles and have a diameter of between 5 and 50 nm.

11. The capsule of claim 1, wherein the nanomaterials are in the form of nanofibres and have lengths ranging from 10-500 nm.

12. The capsule of claim 1, wherein the nanomaterials are in the form of nanotubes and have diameters of 5-100 nm, and lengths from 20 nm-1 m.

13. The capsule of claim 1, wherein the thickness of the wall of the capsule ranges from 0.05-25 m.

14. The capsule of claim 1, wherein the wall of the capsule is formed of a plurality of layers.

15. The capsule of claim 1, wherein the active agent has a volume that ranges from 10-25-10-5 mL.

16. The capsule of claim 1, wherein the active agent is an insect repellent, an insecticide, a therapeutic agent, a radiotherapy agent, a deodorising agent, a natural essence, a fragrance, a moisturising agent, a component of a varnish or paint, or an agrochemical.

17. The capsule of claim 1, further comprising surfactant, an emulsifier, a binder, or mixtures thereof.

18. The capsule of claim 17, wherein the surfactant is selected from the group consisting of: tetramethylammonium hydroxide, cetrimonium chloride, cetrimonium bromide, and benzalkonium chloride.

19. (canceled)

20. (canceled)

21. A method for obtaining a capsule, comprising: preparing a first organic solution comprising 5-30% (w/v) of a reactive compound selected from the group consisting of: 2,4-toluene diisocyanate, 2,4-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, and 10-20% w/v of a polymer selected from the group consisting of polysulfone, poly(methyl acrylate), cellulose acetate, and polyacrylonitrile; preparing a second organic solution comprising 1) a volatile solvent selected from the group consisting of: dichloromethane, N,N-dimethylformamide, acetone, and chloroform; and 2) 70-95% (w/v) of a hydrophobic active agent; combining the first and second organic solutions to form a combined organic solution; stirring the combined organic solution; preparing an aqueous solution comprising an emulsifier, a colloidal agent, or mixtures thereof, wherein the emulsifier is gum arabic (15-20% w/v), Tween 20 (1-3% v/v) or mixtures thereof and wherein the colloidal agent is poly(vinyl acid) (1-3% w/v); adding an active diffusing agent into the organic or aqueous solution; forming an oil/water emulsion by mixing the combined organic solution with the aqueous solution, and mechanically stirring the resulting mixture at 400-1200 rpm for 3-8 min; for the encapsulation of hydrophobic active agents using the reactive monomers 2,4-toluene diisocyante, 2,4-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, adding to the emulsion a hydrophilic monomer selected from the group consisting of: ethylenediamine, diethylenetriamine, hexamethylenediamine, p-phenylenediamine, 1,4-butanediol, 1,6-hexanediol, ethylene glycol and polyethylene glycol in a range of concentrations comprised between 0.2 and 1 mol/dm3; or for the encapsulation of hydrophilic active agents using polysulphone, poly(methyl methacrylate), cellulose acetate and polyacrylonitrile, adding the emulsion to a precipitation bath and evaporating the solvent; stirring the emulsion; collecting nano- or microcapsules by centrifugation or filtration at ambient temperature; dispersing the collected nano- or microcapsules in an aqueous solution comprising 10-20% v/v of amines, polyols, polyethers, or mixtures thereof; and adding, to a suspension of the obtained nano- or microcapsules, a nanomaterial comprising a photocatalytic material, wherein the nanomaterial is selected from the group consisting of: TiO2, WO3, WS2, Nb2O5, MoO, MoS2, V2O5, MgF2, Cu2O, NaBiO3, NaTaO3, SiO2, RuO2, BiVO4, Bi2WO6, Bi12TiO20. NiOK4NB6O17, SrTiO3, Sr2NbO7, Sr2TaO7, BaTiO3, BaTaTi2O5, ZnO, ZrO2, SnO2, ZnS, CaBi2O4, Fe2O3, Al2O3, Bi2O6, Bi2S3, CdS, CdSe, and mixtures thereof.

22. The method of claim 21, wherein the aqueous solution in which the nano- or microcapsules are dispersed comprises one or more surfactants.

23. (canceled)

24. The method of claim 21, wherein the polyol is selected from the group consisting of: 1,4-butanediol, ethylene glycol, 1,6-butanediol, and mixtures thereof.

25. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0085] For easier understanding of the solution the figures are attached in an annex, representing preferred embodiments of the solution here and divulged which, nevertheless, do not have the intention of limiting the object of the present application.

[0086] FIGS. 1A-1C: Diagrams representing the production of the system for controlled release of hydrophobic diffusing agents by solar activation in samples of microcapsules having a polyurethane film chemically functionalised with photocatalytic nanomaterials, wherein:

[0087] FIG. 1A: EMULSION PREPARATION [0088] 1Organic phase: hydrophobic monomer (e.g. 4,4-diphenyl diisocyanate)+active agent [0089] 2Aqueous phase: aqueous solution with emulsifier (e.g. PVA, Tween 20) [0090] 3Emulsification: 3 to 5 min [0091] 4Droplet of the active agent [0092] 5Formation of the polymeric premembrane

[0093] FIG. 1B: PRECIPITATION OF THE POLYMER AND MICROENCAPSULATION [0094] 6Addition of the hydrophilic monomer (e.g. 1,4-butanediol) to the emulsion [0095] 7Mechanical stirring [0096] 8Condensation reactions between the reactive monomers [0097] 9Polymeric wall [0098] 10Polymeric microcapsule containing the active agent

[0099] FIG. 1C: CONTROLLED RELEASE OF THE ACTIVE AGENT [0100] 11Coating of the microcapsules with nanoparticles of TiO.sub.2 [0101] 12Nanoparticles of TiO.sub.2 [0102] 13UV irradiation [0103] 14Oxidation-reduction reactions on the surface of the wall of the microcapsule functionalised with TiO.sub.2 [0104] 15Rupture of the polymeric wall of the microcapsule [0105] 16Release of the active agent from the interior of the microcapsule

[0106] FIGS. 2A-2D: Diagram representing the production of the system for controlled release of hydrophilic diffusing agents by solar activation in samples of microcapsules having a poly(methyl methacrylate) or polysulfone film chemically functionalised with photocatalytic nanomaterials, wherein:

[0107] FIG. 2A: PREPARATION OF THE PRIMARY EMULSION [0108] 1Aqueous phase: aqueous solution of the hydrophilic active agent [0109] 2Organic phase: polymeric solution (e.g. poly(methyl methacrylate) or polysulfone) containing a volatile solvent [0110] 3Emulsification [0111] 4Primary water-in-oil emulsion [0112] 5Droplet of the hydrophilic active agent

[0113] FIG. 2B: PRECIPITATION OF THE POLYMER BY IMMERSION AND MICROENCAPSULATION [0114] 6Immersion of the primary emulsion in a precipitation bath containing a non-solvent [0115] 7Solution of a non-solvent (e.g. water) [0116] 8Diffusion of the solvent into the bath and of the non-solvent into the polymeric solution [0117] 9Precipitation of the polymer [0118] 10Polymeric wall [0119] 11Polymeric microcapsule containing the active agent

[0120] FIG. 2C: PRECIPITATION OF THE POLYMER BY EVAPORATION OF THE SOLVENT AND MICROENCAPSULATION [0121] 12Dispersion of the primary emulsion in an aqueous solution containing one or more emulsifiers [0122] 13Double water-in-oil-in-water emulsion [0123] 14Evaporation of the solvent [0124] 15Precipitation of the polymer [0125] 16Polymeric matrix

[0126] FIG. 2D: CONTROLLED RELEASE OF THE ACTIVE AGENT [0127] 17Coating of the microcapsules with TiO.sub.2 nanoparticles [0128] 18Nanoparticles of TiO.sub.2 [0129] 19UV irradiation [0130] 20Oxidation-reduction reactions on the wall of the surface of the microcapsule functionalised with TiO.sub.2 [0131] 21Rupture of the polymeric wall of the microcapsule [0132] 22Release of the active agent from the interior of the microcapsule

[0133] FIG. 3: Graph illustrating the evaluation, by gas chromatography coupled with mass spectrometry, of the controlled release from samples of microcapsules loaded with a pine fragrance (for example), with and without TiO.sub.2 nanoparticles chemically functionalised on the exterior wall of the microcapsule. When the microcapsules are functionalised with the photocatalytic nanoparticles the release of molecules of the essence of pine (bornyl acetate/isoborneol) which are absorbed into the PDMS fibre is much greater.

[0134] FIG. 4: Example micrograph of photocatalytic microcapsules of the present invention loaded with a diffusing agent.

PROCESS FOR THE PREPARATION OF THE MICROCAPSULES OR NANOCAPSULES

[0135] In general terms, the process is initiated through polymerization or precipitation reactions leading to the formation of microcapsules or nanocapsules which can be based on polyurethane inter alia other polymers such as parylene, poly(p-xylylene), poly(acid lactic), poly(-caprolactone), polyoxyethylenated derivatives, phthalocyanine, polysulfone, polystyrene, cellulose acetate, acrylic polymers, collagen, or chitosan encapsulating the diffusing agent which it is intended be released, which can be in the liquid, solid or gaseous state. Subsequently, the photocatalytic nanomaterials, that is to say nanoparticles, nanotubes, or nanofibres, based on TiO.sub.2, or another type of nanomaterials having demonstrated photocatalytic activity, such as based on WO.sub.3, WS.sub.2, Nb.sub.2O.sub.5, MoO, MoS.sub.2, V.sub.2O.sub.5, MgF.sub.2, Cu.sub.2O, NaBiO.sub.3, NaTaO.sub.3, SiO.sub.2, RuO.sub.2, BiVO.sub.4, Bi.sub.2WO.sub.6, Bi.sub.12TiO.sub.20. NiOK.sub.4NB.sub.6O.sub.17, SrTiO.sub.3, Sr.sub.2NbO.sub.7, Sr.sub.2TaO.sub.7, BaTiO.sub.3, BaTaTi.sub.2O.sub.5, ZnO, ZrO.sub.2, SnO.sub.2, ZnS, CaBi.sub.2O.sub.4, Fe.sub.2O.sub.3, Al.sub.2O.sub.3, Bi.sub.2O.sub.6, Bi.sub.2S.sub.3, CdS, or CdSe, synthesised by a hydrothermal synthesis process in autoclave, are added to the solution of the microcapsules or nanocapsules, under the effect of mechanical homogenisation. The process having finished, microcapsules or nanocapsules are obtained which, by solar activation, the oxidation/reduction (redox) mechanisms initiated by the photocatalytic nanomaterials lead to the degradation or rupture of the wall of the microcapsule or nanocapsule, promoting the diffusion of the specific agent which was encapsulated.

[0136] More specifically, for the microencapsulation of hydrophobic diffusing agents, the interfacial polymerization technique is used based on the interfacial reaction between different monomers solubilised in different phases. The first stage of the process of microencapsulation is the emulsification, wherein one of the monomers containing the diffusing agent is solubilised in an aqueous disperse phase. In one embodiment, prior to the step of emulsion, an organic solution containing 0.1 to 5 mL of diffusing agent and 0.25 to 8 mL of organic monomer is prepared, under vortex stirring for 1 to 2 min. Various organic monomers are used to promote the formation of the wall of the microcapsule or nanocapsule, depending on the type of desired polymer. In the case of polyurethane, the monomers 2,4-toluene diisocyanate, 2,4-diphenylmethane diisocyanate, and 1,6-hexamethylene diisocyanate are used. The next step of the process is the formation of an oil-in-water (O/W) emulsion for the use of oils as diffusing agents. Under mechanical stirring (400-1200 rpm), the organic solution is dispersed in the aqueous phase containing an emulsifier (15-20% gum arabic and 1-2% Tween 20), or a colloidal agent (1-3% polyvinyl alcohol). To ensure the stability thereof the emulsion is stirred for a period of time of 3 to 8 min. The size of the final microcapsules or nanocapsules is directly related to the size of the droplets of the emulsion resulting from the rupture of the oil phase by the action of surface tension and intermolecular collisions caused by the mechanical agitation.

[0137] In the final stage of the process, an aqueous solution containing the hydrophilic monomer, in a range of concentration between 0.2 and 1 mol/dm.sup.3 is added. For polyurethane coatings, the hydrophilic monomers used are polyols, such as 1,4-butanediol, 1,6-hexanediol, ethylene glycol, or polyethylene glycol. The addition of these monomers to the emulsion initiates the polymerisation reactions between the organic monomer and the hydrophilic monomer resulting in a polymeric film at the interface of the already emulsified oil droplets, giving rise to the wall of the microcapsules or nanocapsules. The suspension of microcapsules or nanocapsules formed is maintained under stirring for a maximum time of 40 minutes for the maturation and stabilization of the polymeric coating around the microcapsule. The speed of stirring during the process ranges from 400 to 800 rpm. The final microcapsules or nanocapsules are furthermore subjected to a washing process with cyclohexane or water for the removal of the excess solvents. In one embodiment, for the incorporation of the nanoparticles, nanotubes or nanofibres, based on TiO.sub.2 upon the surface of the microcapsules or nanocapsules during the process of synthesis, monomers having chemical affinity for such materials, in particular amines, are used. Using an excess concentration of the hydrophilic monomer in relation to the hydrophobic monomer, the OH reactive groups will be chemically available for the reaction of polymerisation with the organic monomer and furthermore for chemical bonding to the titanium dioxide. For this procedure, ratios of concentration of hydrophilic and hydrophobic monomers used are 3:1, 4:1, or 5:1. For the chemical adsorption of the TiO.sub.2 nanoparticles to be effective it is necessary that the pH of the suspension of the microcapsules is alkaline, having values from 9-11.

[0138] In one embodiment, for the microencapsulation of hydrophilic active compounds, the invention employs the phase inversion technique. The precipitation of the microcapsules or microspheres can be induced by a process of immersion or by evaporation of the solvent. For both processes the first stage consists in preparing a primary water-in-oil (W/O) emulsion. An aqueous solution containing the active agent is added to a polymeric solution and emulsified through mechanical stirring for a period of time of between 2 and 8 hours, forming the W/O emulsion (see FIGS. 2A-2D). Prior to the stage of emulsification, the polymeric solution is prepared by dissolving the polymer in a suitable solvent under magnetic stirring for 2-3 h. Different polymers can be used, such as polysulfone, cellulose acetate, poly(methyl acrylate) and polyacrylonitrile. The concentration of the polymer in solution must be 10 to 20% (w/v). The used solvent must be capable of solubilising the polymer, have low solubility in water, high volatility and low toxicity. Among the most common solvents there can be highlighted dichloromethane, N,N-dimethylformamide, acetone and chloroform. The precipitation of the microcapsules can take place through the immersion of the primary emulsion in a bath containing a non-solvent, represented in the diagram of FIG. 2B, or by the technique of solvent evaporation, represented by FIG. 2C. In the first case, the final microcapsules are obtained by dispersing the W/O primary emulsion in the form of microdroplets in a water bath. The polymeric coating of the active agent occurs by a rapid process of gelatinisation (5-10 s), based on processes of diffusion between the solvent and the non-solvent, leading to the separation and the precipitation of the polymer around the active agent.

[0139] In addition to the technique of immersion, the formation of the microcapsules can be induced by evaporation of the solvent of the polymeric solution (see FIG. 2C). As in the foregoing process, the first stage of the microencapsulation consists in the homogeneous dispersion of the active agent in the solution of polymer and of the volatile solvent, yielding a primary water-in-oil (W/O) emulsion. This emulsion is then added to an aqueous solution containing one or more emulsifiers to form a double water-in-oil-in-water (W/O/W) emulsion. Amongst the most used emulsifiers highlighted Tween 20 (1-2%) or poly(vinyl acid) (1-3%) can be selected. The double W/O/W emulsion is generated mechanically in vigorous manner until the evaporation of the volatile solvent is complete, leading to the precipitation of the polymer and formation of the capsules.

[0140] This technique can be used for the microencapsulation of solid active compounds, having as principal difference the time of stirring the solution containing the polymer, the solvent and the active agent. In this case, the mixture must be stirred for between 12 and 24 hours to ensure that the polymeric coating of the solid is homogeneous.

[0141] For both processes the microcapsules can be harvested by centrifugation or filtration and dried at ambient temperature.

[0142] Subsequent to the synthesis and washing of the microcapsules obtained by the different techniques the coating with the nanomaterials based on photocatalytic titanium dioxide is proceeded to. In the case of nanoparticles of TiO.sub.2, these are dispersed in aqueous solution having a pH exceeding 9, using ultrasound for 30 min. following this period of time, the photocatalytic nanoparticles are added to the suspension of microcapsules under mechanical stirring using a shaft of the propeller type at a speed of 400 rpm. The mixture continues to be stirred for 30 min and is then collected. The resulting microcapsules containing nanoparticles of titanium dioxide adsorbed onto the surface thereof remain in aqueous dispersion or are filtered and dried in the oven at 40 C.

[0143] The process of coating the micro- or nanocapsules with nanomaterials based on titanium dioxide, such as the nanoparticles, can also be achieved by using external compounds having affinity for the nanoparticles, in particular compounds having reactive OH groups. Examples of such compounds are polyethylene glycol, polyethylene oxide and polypropylene oxide. Chain extenders such as 1,4-butanediol, ethylene glycol or 1,6-hexanediol can also be used to increase the density of hydrogen bonds on the wall of micro- or nanocapsules. For this type of process, the nanomaterials of titanium dioxide are solubilised in the stated solvents and incorporated into the micro- or nanocapsules subsequent to the production and washing thereof.

DETAILED DESCRIPTION

[0144] An example of photocatalytic nanomaterials are the nanoparticles based on TiO.sub.2. These materials are synthesised using a hydrothermal sol-gel process in an autoclave. A colloidal solution is prepared with water and 2-propanol (10:1). As an example, 125 L of 2-propanol and 1125 L of water are mixed at ambient temperature and under vortex stirring in a homogeniser at a pH of 2.40 (adjusted with a solution of 0.1 M HCl). Optionally, the nanoparticles based on TiO.sub.2 can be prepared with triethylamine for them to be doped with nitrogen for the purpose of increasing the semiconductor band-gap energy and the efficiency of absorption of solar light. Under strong magnetic stirring at 400-600 rpm and at ambient temperature 1000 L of titanium isopropoxide (precursor source of atoms of titanium) are added to a volume of 1250 L of a colloidal solution. In the case of synthesis of doped particles 3000 L of triethylamine are added to the resulting white suspension. The amine is responsible for doping of the TiO.sub.2 with nitrogen. In order for the doping of the particles of TiO.sub.2 with nitrogen to occur, it is necessary to leave the reaction under magnetic stirring for 2 days. Following this period, 10 mL of water and 10 mL of 2-propanol are added to the suspension and the mixture is placed in an autoclave at 200 C. for 2 hours. Following cooling to ambient temperature, the washing of the particles is proceeded to. For this purpose, an organic solvent (2-propanol) is used to permit the precipitation of the particles subsequent to centrifugation. The process of washing is repeated several times in order to ensure that all the unreacted solvents are eliminated. The particles collected are dried in an oven at 80 C. for 8 h. Optionally, in order to reduce the size of the crystallites of nanoparticles to between 5 and 50 nm, the particles are placed in an oven to carry out the heat treatment at 635 C. and ensure the formation of the crystalline allotropic phases of the material, in this case anatase, preferably, and rutile, which demonstrate having catalytic photoactivity. Following all this process, the characterisation of the material is proceeded to: assessment of the photocatalytic activity in a photoreactor in the presence of a pollutant simulator; X-ray diffraction characterization experiment to determine the crystalline phases which have developed (anatase, rutile); dynamic light scattering characterization experiment to assess the size and size distribution of the nanoparticles; evaluation of the morphology of the particles using scanning electron microscopy.

[0145] An example of polymeric microcapsules obtained by interfacial polymerisation are the microcapsules having a polyurethane coating. In a first phase of the process, the organic solution is prepared by mixing 5 mL of active diffusing agent and 5 mL of organic monomer (4,4-diphenylmethane diisocyanate) in an organic solvent (dichloromethane) under vortex stirring with a homogeniser, in particular for 2 min. In a second phase, the organic solution previously prepared is added dropwise to an aqueous solution of 2% PVA (polyvinyl alcohol) under mechanical stirring with a cowles-type rod at a speed of 1000 rpm. This polymer is used as emulsifying agent permitting the dispersion of the oil droplets of the organic solution in the aqueous phase. The formed emulsion is allowed to stir for 3 min.

[0146] Following this stage the stirring speed is reduced to 600 rpm and an aqueous solution of 1,4-butanediol is added, in particular at a concentration 0.32 mol/dm.sup.3 and a rate of 0.6 mL/min. The addition of the hydrophilic monomer initiates the reactions of polymerisation between the organic monomer and the hydrophilic monomer, resulting in a polymeric film of polyurethane at the interface of the already-emulsified droplets of oil, giving rise to the microcapsules wall. The addition being complete, the solution is allowed to be stirred for a further 30 min to ensure that the process of polymerisation is complete in its entirety. This process is described in FIGS. 1A-1C.

[0147] In order to remove excesses of solvents it is necessary to proceed to washing the capsules with water and cyclohexane. The process is carried out by vacuum filtration using a polycarbonate membrane of 2 m porosity. The microcapsules are collected and dispersed again in water.

[0148] An example of polymeric microcapsules obtained by the technique of phase inversion are the microcapsules of polysulfone containing in the interior thereof solid diffusing agents having hydrophilic properties. In a first phase of the process the polymeric solution constituting the wall of the final capsules is prepared by dissolving 1.5 g of polysulfone in 10 mL of N,N-dimethylformamide under magnetic stirring for 2 h. Following the complete dissolution 0.5 g of the solid diffusing agent is added to the polymer solution. The suspension is allowed to be stirred magnetically for a period of time never less than 12 hours to ensure that the polymeric coating of the solid is homogeneous. Using a compressed air pistol, the polymeric suspension containing the diffusing agent is dispersed in the form of microdroplets into a water bath (200 mL) at ambient temperature. The process of precipitation is immediate and the microcapsules formed are collected by centrifugation or filtration and dried at ambient temperature. In order to remove excesses of solvents it is necessary to proceed to the washing of the capsules with water. The process is conducted by vacuum filtration using a porous polycarbonate membrane of 2 m porosity. The size, distribution, morphology of the microcapsules are directly related to parameters such as the quantity of active agent, concentration of the emulsifier, concentration of the polymer, stirring speed, temperature and pressure.

[0149] Subsequent to the synthesis and washing of the microcapsules obtained by the different techniques the chemical functionalisation thereof with the nanomaterials based on photocatalytic titanium dioxide is proceeded to. In the case of nanoparticles of TiO.sub.2, these are dispersed in aqueous solution having a pH exceeding 9, using ultrasound for 30 min. Following this period of time, the photocatalytic nanoparticles are added to a suspension of microcapsules under mechanical stirring, using a shaft of the propeller type at a speed of 400 rpm. The mixture is left to be stirred for 30 min and then collected. The resulting microcapsules containing chemically functionalised nanoparticles of titanium dioxide upon the surface thereof remain in aqueous dispersion or are filtered and dried in the oven at 40 C.

[0150] To evaluate the success of the microencapsulation of the diffusing agent the analytical techniques of thermogravimetry (TGA) and Fourier transform infrared spectroscopy (FTIR) are used.

[0151] The pure diffusing agent, the polymeric wall, and the microcapsules previously dried at 40 C. for 6 h are evaluated in the FTIR analysis. The KBr powder (spectroscopic grade) is mixed in a mortar together with the pure diffusing agent and the dry polymeric wall or dry microcapsules (1%). The resulting powder is placed in a mould of 1 cm diameter and taken to a hydraulic press to form the translucent pellet used for the analysis. To prepare the samples the microcapsules are crushed and washed several times with water and ethanol. The chemical structure of the diffusing agent, polymeric wall and resulting microcapsules is characterised by FTIR in a range of wavelengths ranging from 400 cm.sup.1 to 4000 cm.sup.1. In a first analysis the spectrum obtained to determine the chemical bonds characteristic of the diffusing agent are evaluated. The presence of the characteristic absorption bands in the spectrum indexed to the diffusing agent allows for the conclusion that the diffusing agent is successfully encapsulated within the interior of the microcapsules. As an example, the analysis of the polyurethane wall permits it to be determined whether the process of polymerisation has been completed in its entirety by means of the presence of the absorption bands characteristic of the NH urethane bonds between 3300 and 3200 cm.sup.1, CO bonds between 1730 and 1715 cm.sup.1, and NCO bonds between 1640 and 1600 cm.sup.1. For the thermogravimetric analyses, 10-20 mg of the previously dried microcapsules at 40 C. for 6 h are placed into a Teflon or platinum crucible. The sample is heated at a temperature increasing from 60 to 600 C. under an argon atmosphere and at a rate of heating of 10 C./min. The percentage of diffusing agent encapsulated within the resulting microcapsules is determined by the value of loss of mass associated with the temperature of ebullition or degradation of the diffusing agent; the loss of mass in relation to the degradation of the polymeric wall of the microcapsules occurs at temperatures exceeding 300 C.

[0152] For the thermogravimetric analyses, 10-20 mg of microcapsules previously dried at 40 C. for 6 h are placed into a Teflon or platinum crucible. The sample is heated at a rate of 10 C./min from 60 to 600 C. under an argon atmosphere. The percentage of encapsulated diffusing agent within the resulting microcapsules is determined by the value of loss of mass associated with the temperature of ebullition or degradation of the diffusing agent; in the case of dodecane (example of diffusing agent) from 190-220 C. The loss of mass in relation to the degradation of the polymeric wall of the microcapsules occurs at temperatures exceeding 300 C.

[0153] For a quantitative analysis of the diffusing agent encapsulated within the interior of the microcapsule the technique of gas chromatography coupled with mass spectrometry is used (see FIG. 3). Analyses are performed in a chromatograph with equipped a column provided with an ion trap detector having an ionization energy of 70 eV. The method of solid phase microextraction (SPME), in the headspace mode, is used as extraction technique.

[0154] To quantify the output release of the diffusing agent it is necessary to analyse samples of polymeric microcapsules loaded with a diffusing agent, with or without titanium dioxide nanoparticles functionalized with the microcapsule adsorbed upon the surface of the wall, under UV irradiation (5 mW/cm.sup.2) and in the dark.

[0155] For the preparation of the samples to be analyzed by gas chromatography, the microcapsules are placed within a hermetically sealed vial for 2 h under UV irradiation and in the dark. Following this period of time, a polymeric fibre of PDMS (polydimethylsiloxane) having a length of 10 mm is injected into the interior of the vial without coming into direct contact with the microcapsules sample, but solely with the vapour phase, adsorbing the volatile analytes of the sample. Immediately following the extraction, the fibre is collected and injected into the gas chromatograph. The collected analytes are separated and detected by the equipment. The diffusing agent is identified through the analysis of the chromatograms and mass spectra obtained for each sample. The concentration thereof is determined through a linear regression obtained from the calibration curve relating the calculated peak area from the integration of the peaks from the chromatogram and the mass of the compound. The calibration curve is obtained by the injection of standards containing known masses of the diffusing agent.

[0156] Although in the detailed description of this example solely particular embodiments of the solution have been shown and described, a person skilled in the art will know how to introduce modifications and substitute some technical characteristics for others being equivalent, depending on the requirements of each situation, without diverging from the scope of protection defined by the appended claims.

[0157] The embodiments presented achievements are combinable one with another. The following claims additionally define preferential embodiments.