WO2008009216A1 - Preparation of composite nano/microcapsules comprising nanoparticles - Google Patents

Abstract

A process is disclosed for making nano composite microcapsules. In the process, a first matrix, a first auxiliary material and nanoparticles are combined to form a mixture. An emulsion comprising a discontinuous phase dispersed in a continuous phase is then prepared, in which the discontinuous phase comprises the mixture and the continuous phase comprises a second matrix. A polymerisable preparation is added to the emulsion, and the polymerisable preparation is polymerised so as to form a shell around a core, said core being formed from the discontinuous phase.

Description

Preparation of Composite Nano/Microcapsules Comprising

Nanoparticles

Technical Field

The present invention relates to a process for making composite nano and microcapsules comprising nanoparticles distributed therein and/or thereon.

Background of the Invention

Microencapsulation is an effective way to protect functional core material by shell-core structure. Microcapsules are tiny containers which comprise a core material surrounded by a film material (skin, shell etc). Microencapsulation technology has been widely applied in food, chemicals, printing, the oil industry, and pharmaceuticals as well as in textile industries etc. Such microencapsulating technologies, used for protection or controlling release for core material to outside, are well known.

Prior art microencapsulation patents disclose methods relating to encapsulation of functional core material for controlled release, for protection of the core material from environmental influences, to decrease the chemical activity and/or toxity of the core material, to provide protection for pressure or temperature sensitive materials used in specialised industrial fields, to provide a liquid component in a powder delivery vehicle, to allow for delivery of the core material to a specified target location, for compatiblising a core material with a matrix etc.

Commonly, the prior art disclosures describe processes for forming microcapsules with specified functions and with particular structures. The processes provide different chemical polymerization processes and different procedures for producing microcapsules as well as different mechanisms for use of the microcapsules. In order to vary the structure of the particle, therefore, it is necessary using the prior art processes to use a completely different process. There is a need for a process which is capable of providing microcapsules comprising nanoparticles which is sufficiently versatile to enable production of microcapsules with different structures using essentially the same process.

The microcapsules disclosed in the prior art may be described as having a shell- core structure, in which a core material is surrounded by a shell material, with a continuous or multi-nucleus core structure. Capsule shells may be either single or multilayer, each of which are obtained by specific techniques and chemical reactions. The core materials may operate by changing environmental factors, for example to achieve controlled release of a core material into the surrounding environment. Core materials commonly act as the main functional component in a core/shell structure and the shell materials provide insulation from the environment and a means to protect the core from the environment.

In recent years, there has been a great deal of interest in designing and assembling polymer materials with novel morphologies having special properties and functions in various application fields. Core-shell microcapsules exhibit significant promise for providing new "smart" functionality for applications related to the general field of intelligent microstructures and microsystems.

Various materials which possess special structures and morphologies have gained wide attention in recent years, and there has been increasing interest in composite functional materials, such as hollow sphere particles and composite shell structures, which are developed from core/shell structured materials. These materials often show unique optical, thermal, electronic, magnetic and/or catalytic properties by virtue of controlled structure, size and composition of the particles of the material. These materials commonly have high surface area and special particle structures in order to achieve these properties.

"Ideal" capsules with high mechanical stability and other unique properties are attractive for applications requiring enhanced performance and have a wide range of applications, such as those requiring constrained environments for the preparation of nanostructured materials, the encapsulation of guest molecules, drug delivery, catalysis, and host containers for nucleic acid.

Certain microcapsules have been reported in which the shells of the capsules are porous, in order to allow capture and/or release of core materials or nano particles. However, such structures are not desirable when the core contents are not to be released for example in applications such as phase change materials that are used for temperature regulating purposes.

Object of the Invention

It is an object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages, or at least to provide the public with a useful choice.

Summary of the Invention

In a first aspect of the invention there is provided a process for making microcapsules, each of said microcapsules comprising nanoparticles, said process comprising:

- combining a first matrix, a first auxiliary material and the nanoparticles to form a mixture; - preparing an emulsion comprising a discontinuous phase dispersed in a continuous phase, whereby the discontinuous phase comprises the mixture and the continuous phase comprises a second matrix and optionally a second auxiliary material;

- adding a polymerisable preparation to the emulsion; and

- polymerising the polymerisable preparation so as to form a shell around a core, said core being formed from the discontinuous phase.

The microcapsules may be nanocomposite capsules. They may be composite microcapsules. They may be nanoscale and/or microscale capsules. The first mixture may comprise a liquid. The first mixture may be liquid during the step of preparing the emulsion. The mixture may comprise a suspension and/or an emulsion.

The process may comprise selecting the first and second auxiliary materials so that the nanoparticles are located in a desired location in the microcapsules. The first and second auxiliary materials may be selected such that at least one interfacial tension selected from the group consisting of the first matrix-nanoparticle, the polymerisable preparation-nanoparticle, the first matrix-polymerisable preparation, the nanoparticle- second matrix and the polymerisable preparation-second matrix interfacial tension is such that the nanoparticles are located in the desired location. The desired location may be within the shell, within the core, on the surface of the shell or between the core and the shell, or it may be some combination of any two or more of these.

The emulsion may be an oil-in-water (O/W) emulsion. .

The first matrix may be a liquid matrix. The first matrix may comprise a substance which is solid at room temperature or at a temperature of between about 10 and about 5O⁰C. which may be liquid at the temperature at which the mixture, or the emulsion, is formed. The first matrix may comprise a solidifiable, e.g. polymerisable, compound or mixture and/or a carrier, and the polymerisable compound or mixture (if present) may be dissolved in the carrier (if present). The carrier may be hydrophobic, and may comprise a hydrocarbon or a mixture of hydrocarbons. The first matrix may also comprise a functional additive. The functional additive may be releasable from the particles or may be non-releasable. The functional additive may be for example a phase change material, or a therapeutic material or some other functional additive. The first matrix may comprise a non-releasable phase change material. The second matrix may be a liquid matrix. It may be liquid at the temperature at which the emulsion is formed, and may be liquid at room temperature. It may be liquid at a temperature (but not necessarily at all temperatures) at which the dispersed phase of the emulsion is a solid. The second matrix may comprise a protective colloid. Suitable protective colloids include copolymers of styrene with a second monomer. The protective colloid may also comprise a second polymer, e.g. polyacrylic acid or some other ionisable polymer. The second monomer may be maleic acid, maleic anhydride, methyl methacrylate, methyl acrylate or some other suitable monomer or a mixture of any two or more of these. The copolymers may be random, block or alternating copolymers, or may have some other structure. The first matrix may also comprise a carrier. The carrier may be hydrophobic, and may comprise a hydrocarbon or a mixture of hydrocarbons. The carrier may comprise a phase change material e.g. an optionally halogenated (e.g. chlorinated or brominated) hydrocarbon having a melting point between about 10 and 5O⁰C. The step of preparing the emulsion may be conducted at a temperature at which the first matrix is a liquid. If the first matrix comprises a phase change material, the step of preparing the emulsion may be conducted at a temperature above the melting point of the phase change material. The step of preparing the emulsion may comprise heating one or more components to a temperature above the temperature of the phase change material.

The polymerisable preparation may be a precondensate or a prepolymer, or may be monomeric. It may be soluble, miscible, dispersible or compatible in the second matrix. It may be a precondensate of an amine, e.g. melamine, with an aldehyde, e.g. formaldehyde. Thus the precondensate may be for example a melamine formaldehyde precondensate.

The first auxiliary material may be capable of altering the surface tension, or the interfacial tension with a particular liquid (e.g. water, the first matrix, the carrier, the polymerisable preparation etc.) of the nanoparticles. It may be capable of treating the nanoparticles so as to alter the surface tension or interfacial tension thereof. It may be capable of adjusting the relationships of surface tensions and the balance of hydrophobicity/hydrophilicity between the first matrix and the nanoparticles. It may be capable of coupling with the nanoparticles. It may for example be a silane coupling agent. The step of combining the first matrix, the first auxiliary material and the nanoparticles to form a mixture may be under conditions suitable for treating or reacting the nanoparticles with the first auxiliary material. The second auxiliary material may be capable of altering the interfacial tension between the shell and the continuous phase. It may be a surfactant or a polymer. The polymer may be compatible with (e.g. soluble in or dispersible in) the continuous phase. The second auxiliary may be capable of controlling, altering or affecting the interfacial tension between the shell material and the continuous phase.

The second matrix may be hydrophilic. It may be aqueous. It may comprise water. The second auxiliary material may be dissolved or dispersed in the second matrix. The nanoparticles may be any desired nanoparticles. They may be solid nanoparticles. They may be releasable or not releasable from the microcapsules. They may be functional. They may comprise nanomaterials. They may for example comprise inorganic metal oxide nanoparticles, inorganic nanopowders or mixtures thereof, metal nanopowders, Chinese traditional fine medicine powders, etc. Suitable inorganic metal oxide nanoparticles include TiO₂, ZnO, Al₂O₃, Fe₂O₃, MgO, SiO₂, B₂O₃, CeO₂, CoO, NiO, Sb₂O₃, or mixtures thereof. Other inorganic nanopowders and mixtures may also be used, for example infusorial earth, kaoline, montmorillonite, bentonite, talcum powder, mica, pearl powder etc. These may be applied in the invention as functional additives, in forming a stable emulsion, and to strengthen the performances of the microcapsules, for example by increasing thermal stability, reinforcing shell materials and improving mechanical properties of core/shell structure, shielding from electromagnetic radiation etc. They may be added during shell formation. They may be added as a component of the composition used in making the shell. Nano particles may be added with the first matrix. It may also be added with polymerisable preparation (e.g., M-F prepolymer), or with the mixture and polymerisable preparation. As well as functional nanopowders, carbon black, nanowire and nanofibers and/or carbon nanotubes may be used as functional additives in fabricating microcapsules with special functionality. Metal nanopowders such as Al, Ag, Au, Cu, Fe, or other metal nanopowders or mixtures thereof which have unique properties and chemical stability may also be used. Other materials, such as Chinese traditional fine medicine powders, e.g. pearl nanopowders, grape seed extract powder, herbal abstracts and the like, which are wildly applied in health care and beauty culture applications, may also be used as components in the process in order to fabricate microcapsules with health keeping and beauty culture properties.

The process of the present invention may encapsulate a core component together with nanofunctional materials to form the microcapsules.

In an embodiment the process comprises the steps of:

- dissolving a polymerisable compound or mixture in a carrier to form a first matrix, said first matrix being a liquid;

- mixing nanoparticles (e.g. nanowires or some other type of nanoparticle) with a first auxiliary material, for example using an ultrasound mixer;

- combining the first matrix with the nanoparticles mixed with the first auxiliary material to form a mixture, e.g. a suspension;

- combining melamine and formaldehyde, e.g. in a molar ratio between about 2:3 and 3:2 (e.g. about 1:1) on a functional group basis, for sufficient time and at a sufficient temperature (e.g. at about 70⁰C for about 30 minutes) to form a precondensate, said precondensate being at least partially liquid;

- combining (e.g. mixing or blending) a protective colloid with a second auxiliary material and water to form an aqueous solution;

- dispersing the mixture (e.g. the suspension) in the aqueous solution, e.g. using homogenizer. to form an emulsion, wherein the dispersed phase of the emulsion comprises cores which comprise the nanoparticles and the continuous phase of the emulsion comprises the aqueous solution;

- combining the precondensate and the emulsion;

- initiating polymerisation of the polymerisable compound or mixture, e.g. by decreasing the pH of the emulsion (for example to about pH 6, 5.5, 5, 4.5, 4, 3.5, 3 or less than 3) and/or by heating the emulsion (for example to at least about 60, 70 or 8O⁰C);

- maintaining the emulsion under acidic conditions for sufficient time and at a sufficient temperature (e.g. at about 7O⁰C for about 3 hours) to at least partially form aminoplastic shells from the precondensate, said shells at least partially surrounding the cores.

The carrier may comprise natural mineral oils, animal oils, vegetable oil and synthetic oils, phase change materials, agriculture medicine (herb extracts), or a mixture of any two or more of these. Suitable mineral oils include petroleum, kerosene, gasoline, naphtha and paraffin compounds or other mineral compounds or mixtures of any two or more of these. Suitable animal oils include lanolin, fish oil and lard oil, cod liver oil, and the like or other animal oil of mixtures of any two or more of these. Suitable vegetable oils include peanut oil, linseed oil, soybean oil, corn oil, myrcia oil, tea tree oil, eucalyptus oil, ginger oil, olive oil, lavender oil, mentha arvensis oil, onion oil, propolis, rose oil, garlic oil, and other vegetable oils, or a mixture of any two or more of these. Suitable synthetic oils include include biphenyl oil, phosphoric compounds, etc. Other oils that may be used include Vitamin E. Suitable phase change material include paraffin hydrocarbons with low melting point, such as bromooctadecane, tetradecane, pentadecane, hexadecane, nonadecane, eicosane, heneicosane, docosane, tricosane, etc.

The carrier may comprise diols and/or glycerol with an appropriate molar weight, which are compatible with core materials, such as polyethylene glycol (Mw=2,000), polypropylene glycol (Mw=2,000 or more), etc. The diols and/or glycerol may react with an isocyanate added to the mixture used to form the discontinuous phase of the emulsion, to form polyurethane during the encapsulation process. This may occur when the temperature of the mixture reaches a particular value. The polyurethane, together with an aminoplastic shell formed from the polymerisable preparation, may at least partially encapsulate the core in the microcapsule. Thus the diols and/or glycerol are converted during the process of making the microcapsules into materials which are not compatible with the continuous phase. The molecular weight of the diol may be chosen according to its compatibility with core materials, since with an increase in molecular weight the compatibility of the diol with the first matrix (commonly a hydrophobic liquid) will generally increase. Thus the microparticles produced by the process of the present invention may comprise an inner shell comprising polyurethane and an outer shell comprising aminoplast polymer (e.g. melamine-formaldehyde polymer). Alternatively the shell of the microparticles may comprise both polyurethane and aminoplast polymer. Commonly the aminoplast polymer is present in greater amount than the polyurethane (e.g. 2, 3, 4, 5, 6, 7, 8, 9, 10 or more than 10 fold greater amount on a weight, volume or mole basis) in the shell structure of the microparticles. The inventors hypothesise that the presence of the polyurethane may facilitate formation of the aminoplast polymer on the cores rather than as separate shells. Thus it is thought that the main function of polyurethane is to encourage the precondensate to deposit onto the surface of core droplets, rather than to remain in the discontinuous (core) phase of the emulsion, as polymerisation of the precondensate progresses and its molecule weight increases until it is not compatible with aqueous phase. This hypothesis is supported by the observation that in the absence of polyurethane formation, a considerable amount of aminoplast particles were observed among the microcapsules by SEM.

The polymerisable compound or mixture may comprise isocyanates (e.g. di-, tri- or poly-isocyanates), such as HDI (hexamethylene diisocyanate), TDI (toluene diisocyanate), MDI (methylene diphenyl diisocyanate).

The first matrix and/or the nanoparticles, may comprise health keeping materials, such as agriculture medicine (herbal extracts), medicines, and perfumes, for example, ginseng root (American), Ginkgo bilora, green tea extract, gynostemma, honegsukle flower, kidney bean, lotus leafe extract, pine bark, Ganodenna, feverfew, pear powders, etc. These materials may be present in the core. They may dissolve in the first matrix, or may not dissolve in the first matrix. They may be present in the core in solution or as particles, e.g. nanoparticles.

The first auxiliary material may serve to modify the surface tension of the nanoparticles. It may comprise a silane coupling agent or a mixture of two or more silane coupling agents. Suitable silane coupling agents include sulfur-functional silanes, such as mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, etc., amino-functional silanes, such as aminopropyltriethoxy silane, 3 -aminopropyltriethoxysilane, aminopropyltrimethoxysilane, aminopropylmethyldiethoxysilane, aminoethylaminopropylmethyldimethoxysilane, phenylaminomethyltriethoxysilane, diethylaminomethyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, aminoethylaminopropyltriethoxysilane and the like, acrylic functional silanes such as methacryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropylmethyldimethoxysilane, etc. epoxy-functional silanes such as glycidoxypropyltrimethoxysilane, glycidoxypropylmethyldimethoxysilane, glycidoxypropylmethyldietlioxysilane, etc. These silane coupling agents may function as surface modifiers in order to provide improved bonding between inorganic substrate and organic polymers. After been treated by first auxiliary material, the surface property of the nanoparticles may be different to the surface properties of the untreated nanoparticles.

The second auxiliary material may modify the interfacial tension between the shell of the capsules and the continuous phase. It may comprise a surfactant, for example sodium lauryl sulfate, sodium dodecanesulfonate, span-20, span-40, span-60, tween-20, tween-40, tween-80, Gum Arab or mixtures of any two or more of these. It may additionally or alternatively comprise high polymers, for example PVA (polyvinyl alcohol), PEO (polyethylene oxide) of molecule weight (e.g. about 20,000 to 60,000), and polyacrylic acid (molecule weight about 2000 to about 5000), PVP (poly vinylpyrrolidone), CMC (carboxymethyl cellulose), etc.

The protective colloid may comprise a copolymer of styrene and maleic acid (or anhydride), sodium salt of poly (styrene-alt-maleic acid), poly (styrene-co-maleic anhydride), poly (styrene-co-methyl methacrylate), polymer SMA (styrene maleic acid) etc. or may comprise some other styrene copolymer. The protective colloid may provide a suitable environment for microcapsule formation. It may facilitate the formation of the emulsion. It may comprise a surface active colloid. It may comprise a polymeric surfactant.

The surface tensions of the nanoparticles emulsions may be controlled so as to form a nanocomposite structure in which the nanoparticles are distributed within the shell of the microcapsules, or within the core of the microcapsules, or on the surface of the shell of the microcapsules or at the interface between the core and the shell of the microcapsules. The surface tensions may be controlled by selection of the first and second auxiliary materials. Brief Description of the Drawings

Preferred embodiments of the present invention will now be explained by way of examples and with reference to the accompany drawings in which:

Figure 1 is a flow chart showing a process for preparing microcapsules according to the present invention;

Figure 2 shows schematic diagrams of different types of structures of microcapsules according to the invention;

Figure 2a illustrates the contact angle between nanoparticles, oily phase and continuous phase; _;

Figure 3 shows an SEM (scanning electron micrograph) of microcapsules of structure type (a) of Figure 2;

Figure 4 shows an SEM of microcapsules of structure type (b) of Figure 2;

Figure 5 shows an SEM of microcapsules of structure type (c) of Figure 2;

Figure 6 shows an SEM of microcapsules of structure type (d) of Figure 2;

Figure 7 shows an SEM of microcapsules comprising carbon nanotubes and having structure type (b) of Figure 2;

Figure 8 shows an SEM of microcapsules comprising pearl nanopowders and having structure type (b) of Figure 2;

Figure 9 shows schematic diagrams of reactors designed to prepare the microcapsules of the present invention;

Figure 10 shows a graph illustrating the temperature regulating effect of fabrics treated with the microcapsules comprising phase change materials;

Figure 11 shows a graph illustrating the UV blocking effect of fabrics treated with the microcapsules comprising phase change materials;

Figure 12 shows a graph illustrating the antibacterial effect of fabric treated with microcapsules comprising nanocomposite phase change materials on Staphylococcus aureus; and

Figure 13 shows a graph illustrating the antibacterial effects of fabrics treated with microcapsules comprising NCJPCMM on Escherichia coli.

Detailed Description of the Preferred Embodiments

The present invention provides a process for making nanocomposite microcapsules (microcapsules) with multiple functions. In the nanocomposite microcapsules, nanoparticles comprising nanomaterials, are incorporated within the structure of microcapsules in different distributions and locations, in order to achieve different functional characteristics for various applications. The different distributions and locations may be selected by adjusting parameters and/or components of the process. The nanoparticles may be any desired shape, for example speherical, irregular, acicular, polyhedral, and may be for example, nanofibres and/or carbon nanotubes, or some other type of nanoparticle.

In the present specification the term "nanomaterials" may refer to nanoparticles, nanowires and/or nanotubes such as nanocarbon (NCT). The nanomaterials may be in any particulate forms. The nanomaterials may be fabricated in the core and/or on the surface of the microcapsules of the invention. They may be observed by SEM (scanning electron microscopy) and/or TEM (transmission electron microscopy). To determine the location of the nanomaterials in the microcapsules, SEM and TEM may used, optionally together with other techniques, such as EDX (Energy Dispersive X-ray fluorescence (EDX) to determine the surface elemental composition.

An example of the process for preparing the microcapsules is outlined in Figure 1, and the steps are described below. Step 1: Preparation of a first matrix-nanoparticle mixture

A polymerisable mixture (comprising monomers) is dissolved in the core material (a carrier) to form a first matrix, which is maintained in a liquid state. Nanoparticles (nanofunctional materials) that have been mixed with the first auxiliary material using an ultrasonic mixer in order to adjust the relationship of surface tensions between the core material and the nanoparticles are then added to the first matrix to form the first matrix-nanoparticle mixture.

Step 2: Preparation of a polymerisable preparation (precondensate) Melamine and formaldehyde are mixed in a molar ratio (based on functional groups) of about 1:2 at about 70°C for about 30 minutes to form a precondensate. This step may be conducted in solution, for example in aqueous solution. Step 3: Preparation of the continuous phase (an aqueous solution) A protective colloid is mixed with the second auxiliary material and water to form the continuous phase. The second auxiliary material controls the interfacial tension between the shell materials and the continuous phase;

Step 4: Preparation of an emulsion and start of polymerization of the polymerisable mixture

The first matrix-nanoparticle is dispersed in the continuous phase to form an emulsion by means of a homogenizer.

Step 5: Shell formation through in-situ polymerization

The precondensate (optionally in solution) is added to the emulsion produced in step 4 under acidic conditions, and the dispersion (emulsion) is heated to about 70⁰C in order to start polymerization of the monomers. It is maintained at that temperature for about 3 hours to form amino-plastic shells around a core comprising the nanoparticles.

During the process outlined above, different types of structures of nano composite microcapsules may be fabricated, as illustrated in Figure 2. Microcapsules with different structural features may be prepared by selecting appropriate auxiliary materials in order to control interfacial tensions of nanoparticles and core materials. The location of the nanoparticles in the microcapsules may be influenced by the surface characteristics of the nanoparticles. For example the interfacial tension between the nanoparticles and other components used in making the microcapsules may influence the location and/or distribution of the nanopartilces in the microcapsules. The surface characteristics of the nanoparticles (e.g. the interfacial tension as described) may be modified by the first auxiliary material.

The distribution and location of nanoparticles in the microcapsules may be determined by their interfacial tensions with core materials, precondensate and continuous phase. At the stage of the process when the distribution and location of the nanoparticles is determined, the precondensate has not converted into solid aminoplast polymer. The relationships between the surface tensions for core material, continuous phase and nanoparticles may be expressed as:

COSθ where, γ_nc is the interfacial tension between the core material (the first matrix) and the nanoparticles; γ_ns is the interfacial tension between the continuous phase and the nanoparticles; γ_cs is the interfacial tension between the core material and the continuous phase; and θ is the contact angle between the core materials, continuous phase and nanoparticles. Contact angle θ is illustrated in Fig. 2a. Several different conditions may be envisaged:

Condition (I): If γ_ns >γ_nc, cosθ > 0, θ < 90°, nanoparticles may be easily wetted by the continuous phase. Thus, they have strong tendency to be distributed in the continuous phase and not in the core or shell of the microcapsules.

Condition (II): If γ_ns < γ_no, cosθ < 0, θ > 90°, nanoparticles may be easily wetted by the core material and will be distributed in the core materials to form structure (d) of Fig 2. Condition (III): If γ_πc ⁼ Y_ns> cosθ = 0, θ = 90°, nanoparticles may be equally wetted by both shell and core materials, and hence will be distributed in the interface between the shell and core to form structure (a) and (c) of Fig 2.

Additionally, the relationships between the interfacial tensions for core, shell material and nanoparticles need to be considered. This relationship may be expressed as:

γ_n0 is the interfacial tension between the core materia (oil phase)l (the first matrix) and the nanoparticles; γ_ns is the interfacial tension between the shell material and the nanoparticles; γ_os is the interfacial tension between the shell material and the core material (oil phase); and θ' is the contact angle between the core materials, shell material and nanoparticles. In this case, Fig. 2a illustrates the surface tension between the three phase system of nanomaterial (as the solid phase), shell (continuous) material, and oil phase (core) in the initiating stage (in which the angle shown as θ in Fig. 2a is θ'). During this stage, the precondensate has not polymerised to form a solid shell. Although it is largely present in the aqueous phase, the precondensate (shell material) present different surface tension between nano particles and core material in the complex system Accordingly, the relationships between the interfacial tensions for core, shell materia 1 (precondensate) and nanoparticles should be considered, in this stage.

Once again, different conditions may be envisaged:

Condition (A): If γ_no > γ_ns, cosθ' > 0, θ' < 90°, nanoparticles may be easily wetted by shell material and shall be distributed within the shell.

Condition (B): If γ_no < γ_ns, cosθ' < 0, θ' > 90°, nanoparticles may be easily wetted by the core material, and will be distributed within core.

Condition (C): If γ_ns = γ_no, cosθ' = 0, θ' = 90°, nanoparticles may be easily wetted by both shell material and the core, and hence will be distributed in the interface between the core and the shell material.

To ensure that all the nanoparticles are encapsulated in the microcapsules, Condition A, B, and C should be satisfied. At the same time, the surface tension between the nanoparticles and shell (γ_ns) needs to be controlled such that γ_ns ≥ γ_no, so that the nanoparticles will be controlled to form a desired structure of that into core and within the shell, not escape into the continuous phase during the preparation process. The combination of Condition (A) and Condition (B)should produce structure (b) of Fig. 2.

Therefore, the critical issues in fabricating microcapsules according to the present invention are to control the interfacial tensions of the core materials, nanoparticles, and the continuous phase by correct selection of the first and second auxiliary materials. Using the principles outlined above, it is possible design and fabricate microcapsules with different structural features, i.e. nanoparticles may be located in different parts of the microcapsule structure, for example within the core, on the shell surface, or within the shell structure.

The nanocomposite microcapsules comprising nanoparticles, as made by the process of the present invention, may have a range of different functions, such as thermal regulation, UV blocking and antimicrobial effects, depending on the encapsulated core materials and nanoparticles used. The microcapsules may be used as functional materials for fabricating smart thermal regulating textiles with multiple functions of UV blocking and anti-bacterial for apparel products, filters, medical textiles and other industrial textiles.

The present invention provides a preparation technique for microcapsules comprising nanoparticles and formation of nanostructures on the surface of capsule shell or within capsule. The sizes (e.g. the mean diameter) of the microcapsules made by the process of the invention may be in the range between lOOnm and 20 microns, or between about lOOnm and 1 micron, 100 and 500nm, 100 and 200nm, 200nm and 20 microns, 500nm and 20 microns, 1 and 20 microns, 5 and 20 microns, 10 and 20 microns, 500nm and 10 microns, 1 and 10 microns or 500nm and 5 microns, and may be about 100, 200, 300, 400, 500, 600, 700, 800 or 900nm or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 microns. The microcapsules may have nanostructures on the surface or within the microcapsule. Nanopowders, nano-fibers and carbon nanotubes may provide valuable properties for polymer nanocomposites. Applications include electrically conducting products, nanocomposites having enhanced strength, high-power electrochemical capacitors, high surface-area electrodes, products for shielding of electromagnetic radiation, multi-functions involving thermal regulating, anti-bacterial, ultra-violet radiation blockers. The application will depend on the selection of core materials and nanoparticles. The structure of the microcapsules may also influence their final properties and consequently the applications for which they are suited.

Examples of core materials (i.e. the first matrix or carrier or functional additive) for use in the present invention include natural mineral oils, animal oils, vegetable oils, synthetic oils, phase change materials, agriculture medicine (herbal extracts), etc. Herbal extracts may comprise part of the core material and may be distributed in core. Herbal extracts may be in forms of particles or may be in a liquid state. The herbal extracts may be compatible with (soluble in or dispersible in) core and may remain in the core. They may not migrate to the continuous phase.

Suitable mineral oils include petroleum, kerosene, gasoline, naphtha and paraffin compounds. Suitable animal oils include lanolin, fish oil, lard oil, cod liver oil, etc. Suitable vegetable oils include peanut oil, linseed oil, soybean oil, corn oil, myrcia oil, tea tree oil, eucalyptus oil, ginger oil, olive oil, lavender oil, mentha arvensis oil, onion oil, propolis, rose oil, garlic oil, etc. Other suitable oils include biphenyl oil, phosphoric compounds, Vitamin E, etc. Phase change materials which may be used include paraffin hydrocarbons with low melting point, such as bromooctadecane, tetradecane, pentadecane, hexadecane, nonadecane, eicosane, heneicosane, docosane, tricosane, etc. or may be a mixture or two or more such materials. The phase change materials may be used as the carrier in the core. They may comprise the major portion of nanocomposite microcapsule. They may occupy up to about 80% by weight of the microcapsule, or up to about 70, 60 or 50% or the microcapsule. They may in some embodiments comprise less than 50% of the microcapsule, e.g. up to about 40, 30, 20 or 10% of the microcapsule. The phase change material may comprise for example about 10, 20, 30, 40, 50, 60, 70 or 80% by weight of the microcapsule. The microcapsule in some embodiments may comprise no phase change material. Phase change materials may be used for regulating temperature. Thus they may be substances having a suitable melting temperature, so that when the microcapsules are heated to that temperature, additional heat energy is used to melt the phase change material rather than heat the microcapsules. Similarly when the microcapsules are at a temperature above the melting point of the phase change material, at which the phase change material is a liquid, if the microcapsules are cooled to the freezing point of the phase change material, energy may be released from the phase change material as it freezes, thus maintaining the temperature of the microcapsules. In this fashion the phase change materials provide a thermal buffering effect. The phase change materials may have a melting point between about 0 and about 100⁰C, or between about 0 and 80, 0 and 50, 0 and 30, 0 and 20, 10 and 100, 10 and 80, 10 and 50, 20 and 100, 50 and 100, 10 and 30, 10 and 20, 20 and 50 or 30 and 5O⁰C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100⁰C. The phase change material may be selected to have the appropriate melting point or melting point range.

The core (i.e. the first matrix) may also comprise one or more monomers (polymerisable compounds), or a polymerisable mixture. Suitable components of a polymerisable mixture include polyols and isocyanates. Suitable polyols include diols, glycerol polyethylene glycol (Mw=2,000), polypropylene glycol (Mw=2,000 or more) etc. The polymers or polymerisable mixture should be compatible with the first matrix or the carrier (e.g. soluble or dispersible therein). A preferred choice of polyol is polypropylene glycol (PPG2000, having molecule weight of 2000).

Suitable isocyanates include as HDI (hexamethylene diisocyanate), TDI (toluene diisocyanate), MDI (methylene diphenyl diisocyanate). These additives may condense within the core, and may serve to strengthen the shell formation process, especially during the early stages when polymerisable preparation is deposited onto interphase of core droplet and continuous phase. In order to strengthen the health keeping property of of the microcapsules, it is also possible to add agriculture medicine (herb extracts), medicines, and/or perfumes as core materials or core material additives (i.e. as components of the first matrix), to fabricate functional products. Suitable such materials include such as ginseng root (American), Ginkgo bilora, green tea extract, gynostemma, honegsukle flower, kidney bean, lotus leafe extract, pine bark, Ganodenna, feverfew, pear powders, tea tree oil etc, depending on the purpose of final products and the desired microcapsule structure.

Many functional nanoparticles may be used in the present invention. For example inorganic metal oxide nanoparticles such as TiO₂, ZnO, Al₂O₃, Fe₂O₃, MgO, SiO₂, B₂O₃, CeO₂, CoO, NiO, Sb₂O₃ may be used. TiO₂, SiO₂ and ZnO may be used as UV blocking substances, catalysts and/or catalyst supports. SiO₂ and Al₂O₃ may be use for absorption/reflection of infrared radiation, ZnO and Ag nanopowders show antibacterial effects. Other powders, such as anatase TiO₂ and Fe₂O₃, as well as MgO, have unique performance in the field of catalyst due to their photocatalysis properties. Sb₂O₃ may be used as a flame retardant additive, or may be combined with other flame resistant materials in some special areas.

Other inorganic nanopowders and mixtures, such as infusorial earth, kaoline, montmorillonite, bentonite, talcum powder, mica and etc, may be applied in the invention as functional additives in forming of stable emulsions, and to enhance the performances of the microcapsules, for example by increasing thermal stability, reinforcement of shell materials and/or improving mechanical properties of the core/shell structure, shielding of electromagnetic radiation etc. With the assistance of these nanoparticles, the overall properties of microcapsules may also be improved. Additional functions may be added, so that the microcapsules may be fabricated into multifunctional products. This may provide broader application in various industrial fields.

Functional nanopowders, carbon black, nanowires and nanofibers, such as carbon nanotubes, may be used as functional additives in fabricating the microcapsules. Suitable nanotubes may have a diameter of about 10+3 nm. For example, carbon black located on the surface of a microcapsule may provide static charge blocking for microcapsules used in a coating layer on fabric. Such a fabric may be for example used as protection shelter for delicate electrical apparatus. Carbon nanotubes may be incorporated in a microcapsule structure in order to provide electromagnetic shielding performance for a treated substrate. Metal nanopowders which may be used include Al, Ag, Au, Cu, Fe, or other metal nano powders which have unique properties and chemical stability. For example, Ag metal powder incorporated into microcapsules may be used as high thermal conductivity material and infrared ray absorbent as well as microbicide. Al nanopowders incorporated into microcapsules may also be used as an electrically or thermally conductive material. Moreover, such materials may also be used as electromagnetic wave shielding material for functional clothing applications etc.

Other materials, such as many Chinese traditional fine medicine powders, like pearl nano powders, grape seed extract powder, herb abstracts and similar substances, which are wildly applied for health care and beauty culture functions, may also be used to fabricate microcapsules with health keeping and beauty culture properties.

Microcapsules according to the present invention may be high value added products, which have multifunctional properties present in a single product due to the presence of functional nanoparticles incorporated within in the microcapsule or distributed on the shell surface, as shown in Figures 3 to 8.

For example, phase change materials (e.g. paraffin hydrocarbons with low melting point, such as bromooctadecane, tetradecane, pentadecane, hexadecane, nonadecane, eicosane, heneicosane, docosane, tricosane, etc.) together ZnO and anatase TiO₂ nanoparticles were incorporated into microcapsules to produce a microcapsule having the dual functions of thermal regulation and anti-bacterial properties, as well as ultraviolet rays blocking properties. As well as these functions, the mechanical properties of the composite microcapsules are also improved, in that the thermal stability has been greatly improved.

These microcapsules are capable of withstanding high temperatures without damage. Such a product may be used in many applications, such as multi-functional air conditioning filters and thermal regulating felting product used in apparel and ornament textiles products. Images of these microcapsules are shown in Figures 3 and 4.

In other examples, microcapsules comprising both phase change materials and Al and Ag metal nanopowders display better thermal conductivity and show improved thermal regulating performance, and may be applied various fabrics, yarns and fibers. In addition to the above applications, microcapsules comprising phase change materials may also be used as functional additives in clothing for specialised applications, such as fire fighter clothing, diving suits, military uniforms and the like, which provide improved protections under extreme circumstances.

The process for making the microcapsules is based on in situ polymerization, in which monomer or reactants for polymerization are supplied either from inside or from outside of the core, or both, and form a coating membrane on the surface of the core by the polymerization reaction. Monomers which may be applied in the invention include urea, melamine, and formaldehyde. Monomers may be partially polymerized to form a precondensate (N-methylol resin). Polymerisation may be continued, allowing the resulting polymer to condense to form a shell around the core as the molar weight increases to a certain value. This process may be facilitated by decreasing the pH of the continuous phase, thereby triggering the condensation polymerization in order to form an animoplast shell material.

Nanoparticles may be pretreated by the first auxiliary material in order to control the surface tension (surface energy) of the nanoparticles. It will be understood that the terms "surface tension" and "interfacial tension" may be used interchangably, in that surface tension is the interfacial tension between a surface and a matrix adjoining that surface. The surface tension of the nanoparticles is important in the formation of the microcapsules. Moreover it is crucial in determining the distribution of the nanoparticles in the microcapsules.

The amount of nanoparticles is about 0.5 to about 20 % on a w/w, w/v or v/v basis, based on the amount of core material. The amount of nanoparticles may be between about 1 and 20, 5 and 20, 10 and 20, 0.5 and io; 0.5 and 5, 0.5 and 2, 1 and 10, 1 and 5, 5 and 10 or 1 and 3%, and may be about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20%. Commonly the amount is about 2%. Different nanoparticles have different surface characteristics, so pretreatment for these materials is an important step in preparing nano-composite microcapsules with a predetermined structure. Adjusting surface tension to ensure that the nanoparticles have predetermined hydrophilic or hydrophobic properties is important in determining whether the nanoparticles will be distributed on the interface between discontinuous phase and continuous phase or within the discontinuous phase (core material).

The first auxiliary material may be a silane coupling agent. These materials have the ability to couple inorganic materials, such as glass, mineral solids, metals and metal oxides to organic resins.

Sulfur-containing functional silanes, such as mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane etc. may be used to adjust the surface tension, surface energy or interfacial tension of the nanoparticles. Other silane coupling agents which may be used include amino functional silanes, such as aminopropyltriethoxysilane, 3 -aminopropyltriethoxy silane, aminopropyltrimethoxysilane, aminopropylmethyldiethoxysilane, aminoethylaminopropylmethyldimethoxysilane, phenylaminomethyltriethoxysilane, diethylaminomethyltriethoxysilane and the like, may also be used to modify the surface tension of the nanoparticles. Epoxy functional silanes which may also be used include: glycidoxypropyltrimethoxysilane, glycidoxypropylmethyldimthoxysilane, glycidoxypropylmethyldiethoxysilane etc. Methacryl functional silanes which may be used include: methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropylmethyldimethoxysilane, etc. It will be understood that other silanes than those specified above may also be used.

These silane coupling agents may serve as surface modifiers to provide superior bonds between inorganic substrate and organic polymers. After been treated by a silane coupling agent, the surface properties of some inorganic nanoparticles may be altered relative to their original values.

The amount of the first auxiliary material (e.g. silane coupling agent) may be between about 0.1 and 2% based on the weight of nanoparticles. It may be between about 0.1 and 1, 0.1 and 0.5, 0.1 and 0.2, 0.2 and 2, 0.5 and 2, 1 and 2, 1.5 and 2, 0.2 and 1.5, 0.15 and 1, 0.15 and 0.5, 0.5 and 1 or 0.5 and 1.5%, for example about 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, nl, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2%.

The second auxiliary material may be a surfactant. Examples of suitable surfactants include sodium lauryl sulfate, sodium dodecanesulfonate, span-20, span-40, span-60, tween-20, tween-40, tween-80 and Arab gum. These materials may function as surface tension adjusters. The amount of the second auxiliary material may be in the range of about 0.1 to about 5% based on the weight of nano inorganic material, or in the range of about 0.1 to 2.5, 0.1 to 1, 0.1 to 0.5, 0.5 to 5, 1 to 5, 2.5 to 5, 0.5 to 2 or 0.8 to 1.2%, and may be about 0.1, 0.2, 0.3, 04, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1, 2.5, 3, 3.5, 4, 4.5 or 5%.

Protective colloids (or system modifiers) may also be used in the present invention. These materials are long chain polymer electrolytes in which the main chain in the polymer is hydrophobic and along the main chain are distributed hydrophilic groups which may orient at the interface of oil phase and water phase. The hydrophilic groups prefer to reside in the water phase (continuous phase), while the hydrophobic chain retains the molecule close to the oil phase (discontinuous phase). As the protective colloid and the hydrophobic core material are mixed and homogenized, the molecules of protective colloid tend to orient at the interface. Thus the protective colloids may function as polymeric surfactants.

The role of protective colloid in the microencapsulation system may be described as as emulsifying and stabilization. The inventors hypothesise that the oriented chemical chain and groups of the protective colloid on the interface of oil and water phase may form high intensity negative electric fields, which may attract materials with a positive charge, such as the polymerisable preparation (precondensate) and the nanoparticles. The polymerisable preparation, together with charged nanoparticles may be attracted to the surroundings of hydrophobic droplets, thereby forming a region of relatively higher concentration in the system. This may promote formation of the shell material around the hydrophobic droplets. This phenomenon may be observed in Figure 3, which shows nanoparticles encapsulated by shell material. Another effect of the protective colloid is preventing coacervation of adjacent hydrophobic droplets due to the steric obstacle effect, suitable protective colloids include copolymers of styrene and maleic acid (or anhydride), sodium salts of poly(styrene-alt-maleic acid), poly(styrene-co-maleic anhydride), poly(styrene-co-methyl methacrylate), polymer SMA (styrene maleic acid) etc.

The second auxiliary material may be a high polymers, such as PVA (polyvinyl alcohol), PEO (polyethylene oxide) with molecule weight 20,000 -60,000, and polyacrylic acid (molecular weight about 2000 to 5000), PVP (polyvinylpyrrolidone), CMC (carboxymethyl cellulose). These materials may serve to adjust the system viscosity and/or electric charge equilibrium.

The amount of protective colloid may be between about 0.5% and about 5.0%, or between about 1 and 5, 2 and 5, 0.5 and 2, 0.5 and 1, 1 and 4 or 2 and 4, and may be about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5%, based on the total weight of the core material.

The protective colloid may be same as the second auxiliary material, or may be different. In some embodiments other auxiliaries may also be added, such as PEO (polyethylene oxide, Mw=60000) or gum arabic. Besides acting as an emulsifier in the system, the protective colloid may facilitate the formation of the shell during the microencapsulating process. It may be a thickener or a rheology modifier. In some cases, the second auxiliary material is not necessary. Commonly in order to fabricate composite microcapsules with hydrophobic nanoparticles such as carbon nanotubes, PEO (polyethylene oxide) (e.g. of molecule weight of more than about 20,000) should be used as the second auxiliary material. In such cases, the emulsion would not readily form in the absence of the second auxiliary due to the hydrophobic character of the nanoparticles.

Whether the nanoparticles are dispersed in the continuous phase, on the droplet surface of the dispersed phase or in the dipsersed phase, depends on the interfacial tensions between the core, the nanoparticles and the continuous phase), and balance of hydrophobic/hydrophilic properties, as well as electrical charge of the nanoparticles.

In the case in which the nanoparticles are located in the shell of the micropariticles, in order to avoid coacervation or aggregation between nanoparticles, the nanoparticles should be distributed evenly in the shell to ensure they retain their nanometer size, so that their functions can be folly utilized. In order to achieve this it is important to control the pH of the system. The inventors have shown that the control of pH is an effective means to manipulate the deposition rate of the polymerisable preparation and nanoparticles onto the hydrophobic droplets due to the fact that pH may influence the charge properties of the nanoparticles within the core material.

When the polymerisable preparation is deposited onto the surface of the core, the nanoparticles are also attracted to that location and fixed to the polymeric shell during forming and solidifying. pH of the system may be monitored by pH meter during the encapsulation process. Stepwise addition of acetic acid may be used to ensure that the chemical reaction equilibrium proceeds to formation of aminoplast microcapsule shell.

Beside acetic acid other acids may be used as catalyst, for example formic acid, citric acid and acrylic acid. As the system approaches chemical equilibrium, the pH value increases, and acid is used to decrease pH in order to disturb the equilibrium. Formation of animoplast shell material is therefore promoted. This process may be conducted several times (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 times). The process of forming the shell may take at least about 30 minutes until the pH value stabilizes. Control of pH values may be facilitated by using a portable pH meter.

Figure 9 shows a schematic diagram of a reactor designed to prepare microcapsules according to the present invention. In Fig. 9, reactor 10 is used for forming a polymerisable preparation, e.g. a precondensate of melamine and formaldehyde. Containers 20 hold the raw materials for the process, and reactor 30 is used for formation of the microcapsules of the invention. Thus in operation, the first matrix, the first auxiliary material and the nanoparticles are added to reactor 30 from the respective containers 20 through pipe 25 to form a mixture. These are then mixed within reactor 30 to form an emulsion. The polymerisable preparation is then added from reactor 10 to the emulsion in reactor 30; and, optionally heated in order to initiate polymerisation of the polymerisable preparation. The polymerisable preparation is polymerised so as to form a shell around a core, said core being formed from the discontinuous phase of the emulsion.

A process according to the present invention is described in detail below. Step 1: Preparation of suspension of nanoparticles in a first matrix.

The nanoparticles are added at about 1 to 10% (for example 1 to 5, 1 to 2, 2 to 10, 5 to 10, 2 to 5 or 1.5 to 2.5%, e.g. 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10%), based on the weight of the first matrix. The nanoparticles are first dispersed and pulverized together with the first auxiliary material (e.g. a silane such as aminopropyltriethoxysilane or some other suitable silane coupling agent, hydrolysable silane, trialkoxysilane etc.). The amount of the first auxiliary added is about 0.1 to about 1% based on the weight of nanoparticles (for example about 0.1 to 0.5, 0.1 to 0.2, 0.2 to 1, 0.5 to 1, 0.2 to 0.8, 0.3 to 0.7 or 0.4 to 0.6, e.g. 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1%). The nanoparticles are then dried, for example by heating at temperature of about 80°C (or 40, 50, 60, 70, 80, 90 and 100⁰C) for at least 60 minutes (or at least about 90, 120, 150 or 180 minutes, e.g. for about 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 minutes or more than 150 minutes) to remove residual water. This process may also serve to react the first auxiliary material with the nanoparticles. The nanoparticles may again be pulverised, e.g. by grinding and/or ultrasonication. The particle size (e.g. diameter) of the resulting nanoparticles may be in the range of about 10 to about lOOnm or about 10 to about lOOnm, or about 10 to 50, 10 to 20, 20 to 10O₃ 50 to 100, 20 to 50, 30 to 50, 20 to 80, 30 to 70 or 40 to 60nm. The mean particle size, for example, may be about 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or lOOnm. The nanoparticles are then added to the carrier (e.g. tetradecane, or some other suitable alkane with for example between 5 and 20 carbon atoms, linear, branched and/or cyclic, aromatic or aliphatic or arlylalkyl). The temperature at this stage may be maintained between about 20 and 8O⁰C, or between about 30 to 50, 20 to 50, 30 to 80, 50 to 80 or 30 to 60° C, for example about 20, 30, 40, 50, 60, 70 or 8O⁰C. A polymerisable mixture is then added, or the components of the polymerisable mixture may be added separately. Suitable components of the polymerisable mixture are an isocyanate (e.g. hexamethylene diisocyanate - HDI) and polypropyl glycol 2000 (PPG). The amount of HDI and PPG may be between about 0.1 and about 5%, for example between about 0.15 and 1.5, 0.1 and 2, 0.1 and 1, 0.1 and 0.5, 0.5 and 5, 1 and 5, 2 and 5, 0.2 and 2 or 0.2 and 1%, for example 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5%, based on the weight of carrier. The functional additive, e.g. vitamin E is then added. The amount of functional additive may be in the range of about 5 to about 30% of the total amount of core materials (carrier, nanoparticles, first auxiliary and functional additive), or about 10 to 20, 5 to 20, 5 to 10, 10 to 30, 20 to 30 or 25 to 25, for example about 5, 10, 15, 20, 25 or 30%. The core materials are then mixed, for example using a homogenizer. An ultrasonic device may then be used to disperse the nanoparticles to ensure they do not agglomerate. Step 2: Preparation of a protective colloid

A copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid may be used as a protective colloid. It may be added in water. The pH of the water may be controlled in the range from about 4.0 to about 9.0, for example between about 4 and 7, 7 and 9, 6 and 8, 5 and 7, 7 and 8, 8 and 9 (e.g. about 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5 or 9), preferably about 7.5. For the copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid, the addition should be limited to about 1.0% to about 5.0%, for example between about 1 and 3, 3 and 5 or 2 and 5% (e.g. about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5%), preferably 3%, based on the total weight of the core material. For example when adding PVA (polyvinylalcohol 87% hydrolyzed as the second auxiliary material), the addition should be limited to about 3% to about 8%, for example between about 3 and 6, 3 and 4, 4 and 8, 6 and 8, 4 and 7, 4 and 6 or 5 and 7% (e.g. about 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 or 7%) by weight, based on the total weight of core material. The ratio of protective colloid to water may be between about 5 and about 10% w/w, or between about 5 and 9, 5 and 7, 6 and 9 or 7 and 8%, e.g. about 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9, 9.5 or 10% w/w. The protective colloid may be dispersed or dissolved in the water by stirring, shaking, swirling, sonicating or some other method, or a combination of such methods may be used. Step 3: Preparation of precondensate (polymerisable preparation)

Melamine, formaldehyde and pure water are mixed at about 40 to about 9O⁰C, or about 50 to 80, 40 to 70, 70 to 90, 50 to 80, 60 to 80, 65 to 75 or 50 to 75⁰C (e.g. about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 or 9O⁰C), preferably about 70⁰C to form a transparent precondensate solution. The preferred molar ratio of formaldehyde and melamine is about 1.5 to about 2.5, or about 1.8-2.5, 2-2.5, 1.5-2, 1.8-2.3 or 1.8-2.1, e.g. about 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4 or 2.5. The preferred precondensate to core weight ratio is in the range from about 1:5 to about 1:20, for example between about 1:6 and 1:10, 1:5 and 1:15, 1:5 and 1:10, 1 :10 and 1:20, 1:6 and 1:15, 1:6 and 1:9, 1 :7 and 1:8 or 1:7 and 1:9, e.g. about 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, preferably 1:8. Similarly, urea-formaldehyde precondensate may also be prepared in the same way. The polymerisable preparation may be cooled, for example to ambient temperature or some other convenient temperature (for example about 10, 15, 20, 25 or 3O⁰C) and may be stored prior to use. Step 4: Preparation of Emulsion

The temperature of the discontinuous phase (comprising the second matrix, e.g. water) and second auxiliary material) is held at about 25 to about 45°C, for example about 25 to 35, 35 to 45, 30 to 40, 30 to 38, 30 to 35, 35 to 4O⁰C (e.g. about 15, 27, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 42 or 45⁰C). The mixture of first matrix, first auxiliary material and nanoparticles (the discontinuous phase) is then added, and an emulsion is formed by means of stirring for at least 10 to 25 minutes, for example using a stirrer, a blender, an emulsifier a sonicator or some other suitable agitation device. For example, if a stirrer is used, it may have a stirring speed of between about 1,000 and about 20,000 rpm (or between about 2000 and 10000, 1000 and 10000, 1000 and 5000, 2000 and 5000, 5000 and 10000, 10000 and 20000, or 5000 and 15000, for example about 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000, 12000, 1300O₅ 14000, 15000, 16000, 17000, 18000, 19000 or 20000rpm). The resulting emulsion may have a droplet size with average diameter of about 0.5 to 10 micrometers (microns), or between about 1 and 5, 1 and 2, 2 and 5, 0.5 and 5, 0.5 and 2, 0.5 and 1, 5 and 10, 2 and 10, 20 and 5 or 1 and 3 microns, for example about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 microns, or more than 10 microns. Step S: Encapsulation process

The precondensate solution may be added to the emulsion gradually, for example over at least 30 minutes, or at least I₅ 1.5, 2, 2.5 or 3 hours or more The emulsion may be stirred, swirled or otherwise agitated during the addition. The pH of the resulting emulsion may be adjusted to between about 5 and 6, or between about 5.5 and 5.7, 5 and 5.5, 5.5 and 6, 5.3 and 5.8 or 5.4 and 5.8, for example about 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.. The pH is adjusted by adding acetic acid or some other suitable acid slowly, e.g. dropwise. Other acids that may be used include mineral acids and organic acids, such as sulfuric, nitric, hydrochloric or phosphoric acid, or propionic, butanoic acid etc. The acid may be added in solution, e.g. in aqueous solution The temperature is then raised to a temperature of at least about 6O⁰C, or at least about 65, 70, 75, 80, 85 or 90⁰C (for example about 60, 65, 70, 75, 80, 85 or 9O⁰C) to promote the condensation reaction. The reaction may be continued for a period of time ranging from about 0.5 to about 10 hours, or 1 to 4, 0.5 to 5, 1 to 10, 1 to 5, 5 to 10, 1 to 3 or 2 to 4 hours, e.g. 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 hours. In the later stage, a formaldehyde scavenger such as ethylene urea or urea may be added to ensure that the amount free formaldehyde in the emulsion is minimised. After the required period of time, the bath pH may be adjusted to a basic pH, for example by addition of an alkali such as sodium hydroxide or potassium hydroxide (optionally in aqueous solution) or some other base. The pH may be adjusted to greater than pH 7, 7.2, 7.5 or 7.8, for example to pH 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9 or 8.

The resulting microcapsules may be washed, e.g. using warm water or other suitable solvent (e.g. at about 30, 35, 40, 45, 50, 55, 60 or 65⁰C) and dried at elevated temperature, e.g. at 4, 50, 60, 70, 80 or 90°C for at least about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 hours (e.g. for about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 hours) to obtain a free flowing white powder. The powders may be then applied to textiles to manufacture multifunctional fabric for skincare or for some other suitable application. Figure 8 shows the composite microcapsules with nano pearl powder distributed on the shell surface prepared.

Example 1

Microcapsules with the structure type (b), as shown in Fig. 2b, nanoparticles were fabricated using pearl nanopowders, Vitamin E and bromo-tetradecane as first matrix. This type of microcapsule may be used in skincare products. The preparation process is presented below: Step 1 : Preparation of core-nano materials suspension

Pearl nanopowders have strong affinity (low surface tension) for an oil phase. As targeting to skincare application, it is desirable to distribute the pearl powder on the capsule surface. The amount of pearl nanopowders added was about 2% based on the weight of core material. The pearl powder was dispersed and pulverized together with aminopropyltriethoxysilane (as the first auxiliary material). The amount of silane added was about 10% based on the weight of pear powder. Then the powder plus silane was dried at about 60°C for about 60 minutes to ensure no water remained. The pearl powder was again pulverised by grinding to ensure that the size of the pear powder was in the range of about 40nm.

The pearl nanopowder was added into the core material (tetradecane), keeping temperature at 30^c _* The core additives: isocyanate (hexamethylene diisocyanate: HDI) and polypropyl glycol 2000 (PPG) were then added. The amounts of HDI and PPG were each 0.3% based on the weight of core material. Vitamin E was added as a core functional material, at about 10% of the weight of core materials. The core materials (nanoparticles, tetradecane and core additives) were mixed evenly using a homogenizer and then using an ultrasonic device to disperse the nanoparticles in order to prevent coacervation. Step 2: Preparation Protective colloid

A copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid was used as protective colloid. The bath pH for the protective colloid was controlled at 7.5. The addition rate of the copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid was limited to 3%, based on the total weight of the core material. If PVA (poly vinyl alcohol 87% hydrolysed is used as the second auxiliary material), the addition should be limited to 3% ,based on the total weight of core material. Step 3: Preparation of Emulsion The temperature of the aqueous solution was maintained at 33^°C while adding the core-nano materials suspension (the discontinuous phase). The resulting mixture was emulsified by stirring for lOminutes using a stirrer with stirring speed of lOOOOrpm. This resulted in production of oil droplets with average diameters of 1 to 5 micrometers. Step 4: Preparation of precondensate

Melamine, formaldehyde and pure water were mixed at 70° to form a transparent precondensate solution. The molar ratio of formaldehyde and melamine was around 2.3:1. The precondensate to core weight ratio was about 1:7. Similarly, urea- formaldehyde precondensate can also been prepared in the same way. The system was then cooled to ambient temperature and stored for use. Step S: Encapsulation process

The precondensate solution was added to the emulsified system gradually and the pH of the system to was adjusted to 5.5 by adding acetic acid dropwise. The bath temperature was then raised to 7O⁰C to initiate the condensation reaction and was maintained at that temperature for 4 hours to continue the reaction. In the later stages of the reaction, formaldehyde scavengers such as ethylene urea or urea were added to ensure that the free formaldehyde remaining was minimised. Once the reaction was complete, 10%(w/w) sodium hydroxide was added to adjust the bath pH to 7.5.

The resulting microcapsules were filtered off washed with warm water and dried at 60⁰C for about 2 hours to obtain a free flow white powder. The resulting microcapsule powders are suitable for application to textiles to manufacture multifunctional fabric for skincare. Figure 8 shows the composite microcapsules with pearl nanopowder distributed on the shell surface. Example 2

To make composite microcapsules with structure type (a) as shown in Fig 2a, composite microcapsules were fabricated using novel photocatalyst, anatase TiO₂, as a component in the shell structure for enhancing UV blocking effects. Phase change material, bromo-octadecane was used as core material. This material can undergo phase change by release or absorption of large amount of heat as the temperature changes. Thus this type of microcapsule has both temperature regulating and UV blocking functions. Stepl: Preparation of nano-core suspension

The surface of anatase TiO₂ powders is hydrophilic. It was therefore important to reduce the surface tension of anatase TiO₂ nanopowders with the core material (i.e. make the powder more hydrophobic) prior to incorporating them in the capsule shell in order to prevent them from entering the water phase. Span-20 (sorbitan monolaurate, Aldrich chemicals) and glycidoxypropyltrimethoxysilane (Acros product) were used as the first auxiliary material to modify the surface tension of the TiO₂ powder. The amount of span-20 was 6% based on the weight of anatase TiO₂ πanopowder. Coupling agent (glycidoxypropyltrimethoxysilane) was added at a ratio of 20% of the weight of the nanopowder. Dispersing and mixing the powder and the coupling agent was accomplished using an ultrasonic mixer. The amount of TiO₂ was 1.5% of the core material.

The anatase TiO₂ nanoparticle were added to the core material (bromo-octadecane) and the temperature maintained at 33 ° C. The core additives, isocyanate, toluene diisocyanate (TDI) and polypropyl glycol 2000 (PPG), were then added with the amount of TDI and PPG each being 0.3% by weight of the weight of core material. The core materials (nanoparticles and core additives) were mixed evenly using a homogenizer and then using an ultrasonic device to disperse the nanoparticles to prevent coacervation. Step 2: Protective colloid and aqueous solution preparation

Styrene maleic acid (SMA, SHANGHAI, JICHEN fine Chemical Ltd) high polymer with molecule weight of about 110,000 was selected as protective colloid. The protective colloid was dissolved in water in the concentration of 5.5% (w/w). The bath pH for the protective colloid was controlled at 7.5 by acetate acid. The addition of protective colloid was at a ratio of about 5.0% of the weight of the core material. A nonionic high polymer-polyethylene oxide (PEO with Mw=60,000) was used as a second auxiliary to adjust the surface tension between nanoparticles and the continuous phase in microcapsule formation process. The amount of PEO was 1% based on core material.

The remaining steps were as described above in Example 1. Figure 3 shows the composite microcapsules with TiO₂ nanoparticles distributed on the shell surface prepared. Figure 11 shows the UV blocking effects of cotton fabrics coated with these nanocomposite PCM microcapsules in comparison with similar fabric coated with pure PCM microcapsules, which shows that the UV transmission rate can be significantly reduced using the nanocomposite PCM microcapsules as described herein. Example 3

To make microcapsules with structure type (b), as shown in Fig. 2b, nanocomposite microcapsules were fabricated using carbon nanotubes and silver nanoparticles. Step 1 : Preparation of nano-core suspension The surface of carbon nanotubes is hydrophobic. As carbon nanotubes exhibit excellent electric conductivity, thermal conductivity and strengths, they can be used to enhance the electromagnetic shielding effect, electric conductivity, thermal conductivity and strengths of the microcapsules. Further, silver nanoparticles can be added to further strengthen the electronic conductivity and thermal conductivity with additional antibacterial effects. To achieve such effects, it is desirable to distribute these nanoparticles at the surface of the shell surface. Thus, it is necessary to increase the interfacial tension between these nanoparticles and the core materials and shell materials, i.e. to make the surface of the particles hydrophilic.

Coupling agent glycidoxypropyltrimethoxysilane (Acros product) was used as the first auxiliary to modify the surface tension of the carbon nanotubes. The amount of glycidoxypropyltrimethoxysilane was about 10% of the weight of carbon nanotubes. The silane and the nanotues were mixed well and then added to the core material, bromo-octadecane, maintaining the temperature at 33 ° C. Then the core additives, diisocyanate -MDI (methylene diphenyl diisocyanate) and polypropyl glycol 2000 (PPG), were added. The silver nanopowder was then added. The amounts of MDI and PPG were each 0.3% of the weight of core material and addition of silver nanopowder was about 3% of the total weight of core material. The core materials (carbon nanotubes and core additives) were mixed evenly and then ultrasonicated for at least 20 minutes.

The remaining steps were the same as described above in Example 1. Figure 7 shows the composite microcapsules with carbon nanotubes and silver nanopowders distributed on the shell surface, as prepared by the above method. Example 4

To make microcapsules with structure type b, as shown in Fig. 2b, nanocomposite microcapsules were fabricated using zinc oxide (ZnO) nanoparticles. Bromoctadecane with (melting point of 27~28°C) was used as a core material. As zinc oxide (ZnO) nanoparticles have demonstrated excellent antibacterial effects and UV blocking function, it is essential to distribute them on the shell surfaces. Stepl: Preparation of nano-core suspension

Zinc oxide (ZnO) nanopowders have strong affinity for a water phase, which has a higher surface energy than the oil phase. There it is necessary to modify their surface energy to ensure that they stay at the interface between the water phase and oil phase during the encapsulation process. The amount of nanopowder was about 2% of the weight of core material, Silane coupling agent, methacryloxypropylmethyldimethoxysilane, was added into the ZnO nanopowder. The amount of silane coupling agent was about 0.5% of the weight of the nanopowder. The resulting mixture was dried at 90°C for 100 minutes to ensure no water remained. It was then ground to ensure that the size of the nanopowder was in the range of 40~60nm.

The remaining steps are as described above in Example 1. Figure 4 shows the composite microcapsules with ZnO nanoparticles distributed on the shell surface, as prepared by the above method. Figures 12 and 13 show the antibacterial effects of polyester fabrics coated with these nanocomposite PCM microcapsules in comparison with the uncoated control fabrics. These figures illustrate that the ZnO nanocomposite PCM microcapsules significantly reduced the population of Staphylococcus aureus and Escherichia coli after 1 hour of contact. Example 5

To make microcapsules with structure type d, as shown in Fig. 2d, microcapsules were fabricated using of Al₂O₃ (aluminium oxide) nanoparticles. Then nanoparticles were distributed within the core material. Bromohexadecane (melting point 17~18°C) was used as a core materials. Al₂O₃ (aluminium oxide) nanoparticles have the ability to absorb far infrared rays and increase the thermal conductivity. These microcapsules can be used as functional materials in garment products used in ski wear and other applications for warmth and comfort. Stepl: Preparation of nano-core suspension

Aluminium oxide nanopowders have lower contact angle with the water phase than that with the oil phase. To increase the thermal conductivity and IR absorption of the nanocomposite PCM microcapsules, Al₂O₃ nanopowders may be distributed within the core. The amount of nanopowder was about 5% of the core material. Silane coupling agent, diethylaminornethyltriethoxysilane, was added into the nanopowder at 10% of the weight of the nanopowder. The resulting mixture was dried at 100^°C for 120 minutes to ensure no water remained. The powder was then grind to ensure that the size of nanopowder was in the range of 40~60nm.

The remaining steps were as described above in Example 1. Figure 6 shows the resulting composite microcapsules with Al₂O₃ nanoparticles distributed in the core material with smooth shell surfaces. Figure 10 shows the temperature regulating effects of polyester fabrics coated with such nanocomposite PCM microcapsules in comparison with different levels of nanopowder. (the different levels of nanoparticle uptake are 1%, 5% and 8% ) This figure illustrates that the temperature regulating effect increases with the amount of A12O3 nanocomposite PCM microcapsules coated on the fabric. Example 6

To make microcapsules with structure type (c), as shown in Fig. 2c, nanocomposite microcapsules were fabricated using magnetic nanoparticles such as iron. Magnetic iron nanoparticles exhibit excellent electromagnetic properties, which can vibrate and generate heat under the electromagnetic fields. Thus, Magnetic iron nanoparticles are preferably located at the interface between the core and shell materials in microcapsules. The core materials may contain drugs or other materials, which require protection by the shell. The microcapsules may be used to deliver the core materials and release them at the targeted location. Microcapsules containing the magnetic nanoparticles may be injected into fluid, which could be attracted (should be responded) to the stronger magnetic field. When the microcapsules reach the targeted location, an external dynamic magnetic field can be applied, causing the nano magnetic particles to vibrate and be heated up, so that the microcapsules break and release the core materials. Stepl: Preparation of nano-core suspension

The surface of magnetic iron nanoparticles is hydrophobic. Thus, it is necessary to modify the surface tension of these nanoparticles to match the core materials and shell materials, i.e. to ensure the particles be distributed at the interface between the two.

Coupling agent glycidoxypropyltrimethoxysilane (Acros product) was used as first auxiliary material to modify the surface tension of the agnetic iron nanoparticles. The amount of glycidoxypropyltrimethoxysilane was 3% of the weight of nanoparticles. The silane and the nanoparticles were mixed well, and the pretreated nanoparticles were added into the core material, Vitamin E oil, and the temperature maintained at 40° C. Then core additives, diisocyanate MDI (methylene diphenyl diisocyanate) and polypropyl glycol 2000 (PPG) were added. The amount of MDI and PPG was each 0.3% of the weight of core material. The core materials were mixed evenly and an ultrasonic device used for 20 minutes to disperse the nanoparticles thoroughly.

The remaining steps were as described above in Example 1. Figure 5 shows the resulting composite microcapsules with magnetic iron nanoparticles distributed at the interface between the shell and core materials, with a relative smooth shell surface.

Claims

Claims:

1. A process for making nano composite microcapsules, said process comprising:

- combining a first matrix, a first auxiliary material and the nanoparticles to form a mixture;

- preparing an emulsion comprising a discontinuous phase dispersed in a continuous phase, whereby the discontinuous phase comprises the mixture and the continuous phase comprises a second matrix;

- adding a polymerisable preparation to the emulsion; and

- polymerising the polymerisable preparation so as to form a shell around a core, said core being formed from the discontinuous phase.

2. The process of claim 1 wherein the continuous phase comprises a second auxiliary material.

3. The process of claim 1 comprising the step of selecting the first auxiliary material and, if present, the second auxiliary material so that the nanoparticles are located in a desired location in the microcapsules.

4. The process of claim 2 wherein the first auxiliary material and, if present, the second auxiliary material, is selected such that at least one interfacial tension selected from the group consisting of the first matrix-nanoparticle, the polymerisable preparation-nanoparticle, the first matrix-polymerisable preparation, the nanoparticle- second matrix and the polymerisable preparation-second matrix interface is such that the nanoparticles are located in the desired location.

5. The process of claim 3 wherein the desired location is selected from the group consisting of within the shell, within the core, on the surface of the shell and between the core and the shell.

6. The process of claim 1 wherein the emulsion is an oil-in- water emulsion.

7. The process of claim 1 wherein the first matrix comprises a polymerisable compound or mixture.

8. The process of claim 1 wherein the first matrix comprises a carrier.

9. The process of claim 8 wherein carrier has a polymerisable compound or mixture dissolved therein.

10. The process of claim 1 wherein the first matrix comprises a functional additive.

11. The process of claim 10 wherein the functional additive comprises a phase change material.

12. The process of claim 1 wherein the second matrix comprises a protective colloid.

13. The process of claim 12 wherein the protective colloid comprises a copolymer of styrene with a second monomer.

14. The process of claim 1 wherein the polymerisable preparation is a precondensate.

15. The process of claim 14 wherein the precondensate is melamine formaldehyde precondensate.

16. The process of claim 1 wherein the first auxiliary material is a silane coupling agent.

17. The process of claim 2 wherein the second auxiliary material is selected from the group consisting of a surfactant and a hydrophilic polymer.

18. The process of claim 1 wherein the nanoparticle is selected from the group consisting of metal oxide nanoparticles, metal nanoparticles, nanopowdered therapeutic materials, nanopowdered Chinese medicines and carbon nanoparticles.

19. A process for making microcapsules substantially as hereinbefore described with reference to any one of the examples.

20. A microparticulate substance comprising microcapsules made by the process of any one of claims 1 to 19.

21. A microparticulate substance substantially as hereinbefore described with reference to any one of the examples.