EP3009558A2

EP3009558A2 - Self-cleaning composite material, respective method of obtention and uses thereof

Info

Publication number: EP3009558A2
Application number: EP15186576.3A
Authority: EP
Inventors: Carla Joana Dos Santos Marinho Da Silva; Andreia Sofia De Sousa Monteiro; Domingos Alberto Oliveira Tavares Moreira; Antonio Rafael Ferreira Vieira; Filipe Cerqueira Da Silva
Original assignee: CENTI CT DE NANOTECNOLOGIA E MATERIAIS TECNICOS FUNCIONAIS E INTELIGENTES; Centitvc Centro de Nanotecnologia e Materiais Tecnicos Funcionais e Inteligentes
Current assignee: Centitvc - Centro De Nanotecnologia E Materiais Te
Priority date: 2014-09-23
Filing date: 2015-09-23
Publication date: 2016-04-20
Also published as: EP3009558A3

Abstract

The present disclosure relates to a self-cleaning composite material capable of removing contaminants, in particular stains or spots, of solid structures after activation. Thus, the present invention describes self-cleaning structures, particularly rigid, flexible or mixed structures, and processes for producing such self-cleaning structures, especially indicated for clothing and textile articles.

The referred self-cleaning composite material, by activation, comprises a substrate, a plurality of nanocomposites; wherein each nanocomposite comprises in its core SiO₂ particles coated with TiO₂ particles, wherein the nanocomposite is covalently linked to the substrate, in particular by the linkage of a silane group to a hydroxyl group.

Description

Technical Field

The present disclosure relates to a self-cleaning composite material capable of removing contaminants, in particular stains or spots, of solid structures after activation. Thus, the present disclosure describes self-cleaning structures, particularly rigid, flexible or mixed structures, and processes for producing such self-cleaning structures.

Background

The presence of contaminants, such as stains or spots, occurs or may occur anywhere and in any situation. The presence of contaminants is therefore responsible for letting a solid substance or structure or material stained. Frequently, a stain or spot is the result of a chemical reaction between a colouring agent and the surface of a substance or structure or solid material and is responsible for its deterioration.
There are documents in the state of art that describe structures that have a cleaning capability for some stains, however, such structures with cleaning capability have several drawbacks, namely characterized by the degradation of the base substrate, yellowing and resistance decrease of such structures and lack of fastness due to washing, friction, abrasion and general use.
The documents EP2479226 A2 , WO2009136186 A1 , US2012276617 A1 disclose self-cleaning structures obtained by means of a suitable functionalisation with enzymes or SiO₂/TiO₂ nanocomposites, capable of promoting a deep cleaning by removing contaminants from the surface by means of external stimuli such as UV radiation or sunlight. However, these solutions do not have fastness to washing and they change the colour/touch of the fabrics.
These documents illustrate the technical problem to be solved by the present solution.

General Description

The present disclosure relates to the removal of contaminants, in particular stains or spots, of solid structures. Thus, the present disclosure describes self-cleaning structures, particularly rigid, flexible or mixed structures and processes for producing such self-cleaning structures.
By self-cleaning structure is meant any rigid, flexible or mixed material, capable of promoting the degradation or removal of contaminants present on its surface by means of an external factor such as UV light, sunlight, moisture and combinations thereof. The contaminants may relate to an organic or inorganic matter; they might be originated from external residues such as common stains, particularly stains of coffee, chocolate, ketchup, several sauces or others; they might also be the result of the growth of microorganisms or other contaminants that are not part of the ab initio structure.
By rigid structure is meant any material that is usually processed industrially in sheet-to-sheet processes, such as, but not limited to, wood, cork, ceramic, glass, plastics, and combinations thereof, among others.
By flexible structure is meant any material that is usually processed industrially in roll-to-roll processes or finishing coatings of rigid or flexible structures, such as, but not limited to, textiles, paper, nonwoven fabrics, polymers, paints, lacquers, and combinations thereof, among others.
In the particular case of textiles structures it shall be considered structures comprising in its composition textile fibres, natural or synthetic. Hence, it is part of the present disclosure fabrics, knitted fabrics, fibres or yarns or other rigid structure comprising fabrics, knitted fabrics, fibres or yarns in its composition. These textile structures applied to several sectors such as clothing, decoration, home textiles, upholstery and automobile.
The composite materials described in the present disclosure are obtained by means of a process that involves the synthesis of functional nanoparticles/nanocomposites and its incorporation in the substrate, in order to ensure that the substrate do not undergo any kind of visual or qualitative change, maintaining unchanged its macroscopic properties such as visual appearance, colour, touch and feel.
An aspect of the present invention concerns to a self-cleaning composite material by activation comprising:

a substrate selected from the following list: textile, paper, polymer material, and combinations thereof;
a plurality of nanocomposites;
wherein each nanocomposite comprises in its core particles of SiO₂ coated with TiO₂ particles wherein the size of the TiO₂ particles is inferiorto the size of the SiO₂ particles, wherein the ratio of TiO₂ particles/SiO₂ particles ranges between 2:1-10:1, preferably the ratio of TiO₂ nanoparticles and SiO₂ nanoparticles is 5:1-8:1;
wherein the nanocomposite is covalently linked to the substrate by the linkage of a silane group to a hydroxyl group.

The nanocomposite features combined with the covalent bond of the nanocomposite to the substrate surprisingly allows to keep the self-cleaning properties of the substrate even after several washing cycles and also not change the colour/touch of the substrate, especially in textile substrates.
In one embodiment, for best results the ratio of TiO₂ particles/SiO₂ particles can be 40:5, 5:1.
The ratio of TiO₂ particles/SiO₂ particles on the surface may be determined by several conventional methods namely SEM-EDS, enabling to assess the amount of each atomic element on the substrate's surface, particularly on textile substrates.
In one embodiment, the self-cleaning material of the present invention eliminates efficiently stains of coffee, tea, milk, chocolate, juices, soft drinks, sauces, blood, wine, and combinations thereof, does not change the colour and touch of the substrates in particular fabrics and can withstand numerous washing cycles.
In one embodiment, for best results the size of SiO₂/TiO₂ nanocomposite of the self-cleaning material of the present invention can vary between 30 and 120 nm, preferably between 50 and 100 nm. The dimensions of the nanocomposites can be calculated by several methods, namely electron microscopy - scanning electron microscope (SEM) or dynamic light scattering (DLS).
In one embodiment, the self-cleaning material the nanocomposites are activated by ultraviolet light, visible light, sunlight, moisture and combinations thereof.
In one embodiment, for best results the amount of nanocomposite on the substrate's surface, particularly a textile, can vary between 1 and 50 g/m²; preferably between 2 and 20 g/m²; more preferably between 5 and 10 g/m².
Another aspect of the present disclosure relates to an article comprising a composite material described in the present invention wherein the article is a piece of clothing, garment, piece of laundry, fabric for shirt, curtain, sofa upholstery, motor vehicle upholstery.
Another aspect of the present disclosure relates to a method for preparing the SiO₂/TiO₂ nanocomposite that comprises the following steps:

preparing a first mixture of distilled water, acetic acid and nitric acid, in a ratio of 100:10:1, respectively, under vigorous stirring;
adding 1-10 parts of titanium isopropoxide;
heating the mixture;
preparing a second mixture of distilled water, ethanol, hexadecyltrimethylammonium chloride (HTAC), tetraethylorthosilicate (TEOS) in a ratio of 64:10:10:4, under vigorous stirring;
dispersing the mixtures in an ultrasonic bath.

In one embodiment, the stirring steps the preparation method of the SiO₂/TiO₂ nanocomposite are performed for 0.5 - 3 hours, particularly for 1 - 2 hours.
In one embodiment, the said stirring steps are performed between 20 - 80 °C, particularly at 40 - 60 °C.
In one embodiment, the step of dispersing the mixtures in the ultrasonic bath is performed for 1- 24 hours.
In one embodiment, the method herein described can further comprise an alkaline washing step.
The present disclosure also relates to a method of fixing the nanocomposites to the material comprising the following steps:

Impregnate the material with the SiO₂/TiO₂ nanocomposite;
Pressing the impregnated material with a pressure between 1 and 4 bar and at 0.5 - 5.0 m/s;
Drying the impregnated material at a temperature between 20 and 180 °C for 1- 60 minutes;
Curing the impregnated material at a temperature between 20 and 180 °C for 1- 60 minutes.

The nanocomposites described in this disclosure are mixtures of silica nanoparticles and titanium nanoparticles, particularly nanoparticles of silicon dioxide (SiO₂) and nanoparticles of titanium dioxide (TiO₂).
It is a further object of this disclosure that the functionalization process of the structures described herein allows for a significant saving of chemicals and others auxiliaries by means of a deposition technology by ultrasound technology and that is resistance to washings.
Another object of the disclosure presented herein is the effectiveness and the durability of the functionalization given to the structures, enabling them to withstand external aggressions such as washes, abrasion, friction, weathering exposure, among others.
Throughout the description and claims the word "comprise" and variations of the word does not intend to exclude other technical characteristics, such as other components, or steps. Additional objects, advantages and features of the invention will become clear for experts in the technique upon examination of the description or may be learned by practicing the invention. The following examples and figures are provided as a way to illustrate, and do not intend to limit the present invention. Furthermore, the present disclosure covers all the possible combinations of particular or preferred embodiments described herein.

Brief Description of the Drawings

For an easier understanding of the present invention figures are enclosed, which represent preferred embodiments that, however, are not intended to limit the scope of the present disclosure.

Figure 1 : Schematic representation of the transversal section of a self-cleaning structure in the first layer wherein:
1. 1 represents the self-cleaning layer;
2. 2 represents a support structure.
Figure 2 : Schematic representation of the transversal section of a self-cleaning structure in the second layer.
Figure 3 : Schematic representation of the acting system of the self-cleaning structures via photocatalysis wherein:
- 3 represents dirtiness;
- 4 represents the UV radiation application;
- 5 represents carbon dioxide;
- 6 represents water.
Figure 4 : Schematic representation of the core-shell type-nanocomposite, obtained from agro-industrials residues wherein:
- 7 represents TiO₂;
- 8 represents SiO₂.
Figure 5 : Visualization of the hot coffee stains after 0h and 8h of UV radiation exposure, as well as visualization of the SiO₂/ TiO₂ nanocomposite, by scanning electron microscope (SEM) after testing abrasion resistance.

Detailed Description

The present disclosure describes a process for producing rigid, flexible or mixed self-cleaning composite materials, namely structures and article. Through the object of this disclosure it is possible to obtain self-cleaning structures, by an external stimulus such as ultraviolet light, visible light, sunlight, moisture, or combinations of these parameters.
The present disclosure further relates to a self-cleaning composite material capable of removing contaminants, in particular stains or spots, of solid structures after activation. Thus, the present disclosure describes self-cleaning structures, particularly rigid, flexible or mixed structures and processes for producing such self-cleaning structures, especially indicated for clothing and textile articles.
It is further object of this disclosure the development of structures with self-cleaning capability using a nanocomposite comprising SiO₂ nanoparticles/TiO₂ nanoparticles, particularly in the anatase and rutile phases. The nanoparticles of TiO₂ and the nanoparticles of SiO₂ are synthesised by low-temperature sol-gel processes. The resulting silica nanoparticles, particularly silicon dioxide, are added to the TiO₂ nanoparticles and thereafter the mixture (SiO₂ nanoparticles and TiO₂ nanoparticles) is dispersed in an ultrasonic bath, particularly for 15 minutes. The reaction mixture is maintained, particularly for 12 hours to form the SiO₂/TiO₂ nanocomposite with a core-shell type structure.
In one embodiment, the percentage ratio of TiO₂ nanoparticles in relation to SiO₂ nanoparticles is, particularly, of 40:5, more preferably of 20:2, and further preferably of 10:1. The conditions for the SiO₂/TiO₂ nanocomposites formation process are such that it is carried out so that the crystallization and formation process of SiO₂/TiO₂ nanocomposites leads to a final dimension of thereof, particularly in the range of 100 nm, more preferable in the range of 50 nm.
One embodiment comprises the use of agro-industrial residues as a source of silica, particularly, lignocellulosic crop residues such as, but not limited to, rice hulls have been used for the synthesis of SiO₂ nanoparticles.
Hence, the present disclosure also relates to an ecological, effective and economic process of synthesis of SiO₂/TiO₂ nanocomposites, favouring the already ecological application of the self-cleaning structures, since they require a significantly lower number of washing operations and consequently lower consumptions of water, surfactants and energy.
In one embodiment, the SiO₂/TiO₂ nanocomposite was incorporated in the structures by several processes, such as impregnation and/or spraying.
In one embodiment, several flexible structures such as fabrics for shirts and other clothing articles were impregnated for a defined period of time, particularly for 60 seconds, with the obtained SiO₂/TiO₂ nanocomposite, being subsequently subjected to a pressure, particularly 2 bar and a rotational speed, particularly of 2.0m/s in the foulard roles, being this process repeated up to six times. Thereafter, the structures were dried, particularly at 80 °C for 2 minutes, followed by curing, particularly at 100 °C for 1 minute. This process was performed in natural-based flexible textiles structures such as cotton, synthetic such as polyesters, or mixtures thereof.
In one embodiment and to guarantee the permanence of the functionalization, the obtained SiO₂/TiO₂ nanocomposites were subjected to a preliminary step of derivatization, thereby ensuring a suitable functionalization of the substrates in question. Hence, the obtained substrates have a high self-cleaning capability, with permanence of their visual aspect, touch and colour. Additionally, the substrates thus obtained ensure its high self-cleaning performance, even after several standard washing cycles at 40 °C.
In one embodiment, the functionalization of flexible structures for application in the automotive sector, such as curtains and upholstery for public transportation. These structures, due to their application are mainly used during the day, therefore are subjected to a high solar incidence, which makes them as the excellence application objects for the self-cleaning structures. In these substrates, it is intended that the self-cleaning functionalization is at two levels: an outer level, being more exposed to strong solar radiation, and one inner level working in a second layer that could be combined with a functionalization for easy cleaning in the superficial layer, thus enabling repellency of contaminants in a higher percentage and total elimination of those that are able to penetrate into the second layer.
In one embodiment, the development of a cleaning system by means of ultraviolet radiation to place inside the automotive vehicles, more preferably for public transportation is also disclosed. These vehicles are generally at rest at night-time, so they may have self-cleaning structures activated by ultraviolet light placed in the centre console, which will be activated during this specific period, thus enhancing the action of the solar daylight.
In one embodiment, several rigid structures were submitted to functionalization with synthesized SiO₂/TiO₂ nanocomposites, by an ultrasonic spraying process. The nanocomposite dispersions were atomized using, for instance, a spraying system by ultrasound, particularly at 20 kHz for the structures surface. Thereafter, suitable derivatization and curing processes were used to ensure the permanence of the effect to several external factors. This functionalization process ensures a high saving in the consumptions of water, energy and SiO₂/TiO₂ nanocomposite, further allowing that the nanocomposite be directly on the structures' surface and thus potentiate its photocatalytic action.
The present disclosure describes a method for functionalization of substrates for obtaining self-cleaning properties, involving the synthesis of SiO₂/TiO₂ nanocomposites, its anchoring via chemical bond to the substrates and its performance test, through visualization of actual stains' degradation.
The materials/substrates comprising the SiO₂/TiO₂ nanocomposites can be fabrics, fibres, yarns, films or structures of natural or synthetic origin, such as, but not limited to: cotton, flax, silk, wool, hemp, cork, lyocell, polyamide, polyester, polypropylene, polyurethane, acrylic, acetate, elastane, viscose, among others.
The materials/substrates obtained through the functionalization process described in this disclosure are harmless to the user's health and do not present any damage to the substrate such as change in the initial touch or colour, since the described process enables to obtain a self-cleaning substrate but without promoting degradation of the base substrate.
On the other hand, the functionality imparted to the material/substrate has a high degree of fastness to wash and friction, which until now was not possible to achieve with the current solutions, giving to the final product suitable characteristics to a wide variety of applications, ranging from clothing, footwear and upholstery, among others.
Surprisingly, the functionalization process described herein occurs at low temperature conditions and using conventional equipment previously existing in the companies and without damaging the base material/substrate, being highlighted also its high resistance to the usage conditions, such as washing and abrasion, which makes this a more effective and cost-effective process from the economic and ecological point of view.
The following examples are given only to provide a further understanding of the subject disclosed herein, and should not be considered as limiting in the scope of the present invention and may be combined with each other.
Example 1. In one embodiment, the preparation method of the SiO₂/TiO₂ nanocomposite can comprise the following steps:

Mix in a reactor 100 parts of distilled water, 1 part of nitric acid and 10 parts of acetic acid, under vigorous stirring, during XXX time;
Add 5 parts of titanium isoproxide;
Heating the mixture, particularly at 60 °C for 16 hours;
Prepare separately another mixture, particularly with 64 parts of distilled water, 10 parts of ethanol, 10 parts of hexadecyltrimethylammonium chloride (HTAC) and 4 parts of tetraethylorthosilicate (TEOS), under vigorous stirring for 2 hours at 60 °C;
Disperse the mixtures in an ultrasonic bath, particularly for 12 hours.

The nanocomposites are attached to the material/substrate by means of an impregnation and/or spraying technique.
By scanning electron microscopy it was found that the addition of the silanes surprisingly promoted the covalent bond of the SiO₂/TiO₂ nanocomposite to the textile material/substrate, having occurred by the linkage to the cotton hydroxyl groups given the high reactivity of silica.
In one embodiment, a 100% cotton taffeta fabric was impregnated with the SiO₂/TiO₂ nanocomposite resulting from the previously described process, particularly for 5 minutes, followed by a pressing step, particularly with a pressure of 2 bar and at 2.0m/s. Thereafter the fabric was subjected to a drying step, particularly at 80 °C for 10 minutes, followed by a curing step, particularly at 100 °C for 5 minutes.
After the functionalization step described above, the mechanical proprieties of the fabric and the white degree, according to Berger Whiteness, was determined, in order to verify whether there was any damage in the material/substrate.
Surprisingly it was confirmed that the material/substrate showed no damage or had changed its colour to a yellowish shade, a feature of the functionalized substrates by the currently existing methods.
For comparison purposes between the present disclosure and other current solutions, a cotton fabric was functionalized using for this purpose a commercially available product of TiO₂ for obtaining the photocatalytic effect.

The following table gives the comparative results obtained for the present disclosure and another current solution, being clear the yellowing and the lower tensile strength of the fabric functionalized with the commercial product. On the other hand, the obtained values highlight the high degree of whiteness and the high tensile strength of the functionalized fabric by the process disclosed, being indicative of the absence of damage in the same.

Table 1 -Values obtained for tensile strength and Berger Whiteness, for 100% cotton fabric with and without self-cleaning effect.

Sample	Tensile Strength (N)	Berger Whiteness, W_B
Control fabric	560 ± 12 (100 %)	145 (100 %)
Self-cleaning fabric subjected to the functionalization process disclosed herein	565 ± 9 (101 %)	125 (86 %)
Fabric subjected to the functionalization process with a commercial TiO₂	450 ± 15 (80%)	28 (19%)

The fabric functionalized by the method now disclosed was also subjected to efficacy tests, where common stains were used, such as coffee, chocolate, juices, among others.
In one embodiment, the efficacy test enabled the evaluation of the self-cleaning effect through the stain removal capability after exposure to a lamp emitting ultraviolet (UV) light, with a wavelength between 250 - 380 nm, particularly 365 nm.
In one embodiment, the efficacy test was performed in the following conditions: a soluble coffee solution with a concentration of 2g/100 mL of boiling water was prepared. When the temperature of the coffee solution reached values between 60-65 °C, 30 µl of the solution was applied onto the control fabric and the SiO₂/TiO₂ nanocomposite functionalized fabric in order to obtain a coffee stain in the corresponding fabrics. The fabrics, control and functionalized with SiO₂/TiO₂ nanocomposite, were then subjected to the action of ultraviolet light with emission in a wavelength of 365 nm.
In one embodiment, the coffee stain was chosen to perform the efficacy since it is common knowledge that the coffee stain, particularly hot coffee stains are difficult to remove.
In one embodiment, the efficacy test was repeated after several washes and the results are shown in figure 5.
The analysis of figure 5 shows that the self-cleaning substrate obtained by the present disclosure has the capability of removing completely the hot coffee stain, after 8 hours of exposure to an ultraviolet light. This efficacy in removing the coffee stain is maintained, even after the fabric is subjected to several washing cycles, particularly 30 washing cycles, performed according to the ISO standard 6330:2010. The analysis of figure 5 also reveals that the removal of coffee stain has not occurred in the control fabric (non-functionalized fabric).
In one embodiment, after several washing cycles, particularly 50 washing cycles, it is found that the coffee stain was not completely removed from the control fabric and was partially removed from the functionalized fabric by the method now disclosed. Nevertheless, after exposure to ultraviolet radiation, particularly for a period of 24 hours, the complete removal of coffee stain was surprisingly obtained for the functionalized fabric.
This observation highlights that although a partial removal of the SiO₂/TiO₂ nanocomposite may occur at the material/substrate surface, perhaps due to removal of some fabric microfibrils that naturally occur in the washing cycles, the SiO₂/TiO₂ nanocomposite remains predominantly bonded to the surface of the material/substrate, particularly by covalent bonds, and therefore it is still able to remove completely a stain, only requiring a higher exposure time.
In one embodiment, the self-cleaning material/substrate of the present disclosure was further analysed in a certified reference laboratory regarding abrasion resistance, according to the ASTM standard D4966 (Standard Test Method for Abrasion Resistance of Textile Fabrics (Martindale Abrasion Tester Method)), and it has been found by scanning electron microscopy the presence of SiO₂/TiO₂ nanocomposite on the substrate surface, even after 10,000 cycles of abrasion, for all tested samples of the functionalized fabrics by the method of the present disclosure. The exception to this observation was naturally the control fabric.
Example 2. In one embodiment, the preparation method of the SiO₂/TiO₂ nanocomposite can comprise the same steps described in the preparation method of the SiO₂/TiO₂ nanocomposite of example 1, with the following variations: the percentages of hexadecyltrimethylammonium chloride (HTAC) and tetraethylorthosilicate (TEOS) were added to 4 parts of silica obtained from rice husks, after a calcination process at 600 °C and a further alkaline washing step, in order to provide a nanocomposite reactivity suitable to polyester substrates.
In one embodiment, the 100% polyester material/substrate/fabric was introduced in an atmospheric pressure plasma reactor, in order to increase its reactivity, and subjected to a plasma discharge, particularly under the following conditions: fabric passage speed 10m/min, 3% oxygen reactive gas in a stream of argon and plasma discharge power of 9 kW.
In one embodiment, the referred 100% polyester material/substrate/fabric was functionalized with an ultrasonic spraying deposition of the SiO₂/TiO₂ nanocomposite, particularly under the following conditions: speed of 2 m/min and compressed air pressure in the nozzles of 3 bar.
By scanning electron microscope it was found that the addition of silanes promoted the covalent bond of the SiO₂/TiO₂ nanocomposite to the textile substrate. Thereafter the fabric was subjected to a drying and curing process, particularly under the following conditions 100 °C for 4 minutes.
In one embodiment, a mixture fabric containing 67% cotton and 33% polyester was additionally tested, using the same procedure described in example 2.
In one embodiment, after the functionalization process, the mechanical properties of the fabric, the white degree (Berger whiteness) and the efficacy in removing hot coffee stain was determined, being found that no damage occurred in the substrate and that the functionalized fabric was capable of eliminating the coffee stain after 24 hours of solar radiation exposure and spraying with distilled water to maintain the moisture level, particularly at 10 % on the substrate surface.
In one embodiment, the stain removal, particularly coffee, by exposure to solar radiation and moisture was complete, even after 30 washing cycles and 10,000 abrasion cycles (Martindale).
In one embodiment, the functionalized fabrics by the method disclosed herein were subjected to evaluation tests of antibacterial activity according to the ASTM 2149-10 method and using a Staphylococcus aureus strain, particularly the Staphyloccoccus aureus ATCC 6538 strain.

In one embodiment, the functionalised fabrics with SiO₂/TiO₂ nanocomposites and corresponding controls (non-functionalised fabrics) were evaluated without and with 1 hour of UV radiation exposure. In table 2 the obtained results, for the antimicrobial activity, are found.

Table 2 - Obtained values for % reduction in Staphylococcus aureus ATCC 6538 strain, according to the ASTM 2149-10 method.

Sample	Time of UV light exposure	Determination of antimicrobial activity /% of microorganism reduction
100% PES control	0h	7
100% PES control	1h	0
100% PES functionalised	0h	78
100% PES functionalised	1h	62
67% cotton /33% PES control	0h	10
67% cotton /33% PES control	1h	13
67% cotton /33% PES functionalised	0h	44
67% cotton /33% PES functionalised	1h	65

The analysis of the table indicates that the percentage of growth inhibition of a Staphylococcus aureus strain, particularly the Staphyloccoccus aureus ATCC 6538 strain, is superior in relation to its control. No significant differences are found in the reduction of antimicrobial activity for this strain, regarding the time of UV radiation exposure, therefore it can be concluded that the functionalised substrates by the method of the invention disclosed herein have surprisingly the additional advantage of having antimicrobial properties.
It was also assessed the skin irritant potential of the functionalized samples by means of corneometry probes for evaluation of the skin properties in vivo, namely the transepidermal water loss (TEWL) and erythema. The obtained results show that despite the significant variability of the skin behaviour to the samples application, from individual to individual, the statistical analysis of the results (ANOVA analysis) did not detect significance associated to the samples or to the brands as a variation source of both analysed parameters, for a 95% confidence level, therefore it is concluded that none of the samples originated changes in the barrier function of the skin stratrum corneum or the redness, thus not showing skin irritant potential. It should be highlighted that all the volunteers involved in the test had basal transepidermal water loss values between 2 and 12 g.h^-1m², which indicates a healthy or very healthy skin condition.
The processing and subsequent achievement of the structures with the characteristics specified are achieved by means of technologies, equipment and technical knowledge whose innovation enabled to achieve the result described in this patent. It should be highlighted the need to process the different materials in different equipment and stages, according to suitable procedural conditions to each specific material. After the correct and suitable functionalization for obtaining the self-cleaning structures, comparative studies of the performance against non-functionalized controls were carried out, ensuring a high efficiency of the self-cleaning effect, as well as its durability.
Although the present disclosure has only represented and described particular embodiments of the solution, a skilled person in the area will know how to make changes and replace some technical characteristics by other equivalents, depending on the requirements of each situation, without exceeding the scope of protection defined by the enclosed claims.
The embodiments presented herein are suitable of combination with each other. The following claims further define preferred embodiments.

Claims

Self-cleaning composite material by activation comprising
a substrate selected from the following list: textile, paper, polymer material, and combinations thereof;

a plurality of nanocomposites;

wherein each nanocomposite comprises in its core particles of SiO₂ coated with TiO₂ particles wherein the size of the TiO₂ particles is inferiorto the size of the SiO₂ particles, wherein the ratio of TiO₂ particles/SiO₂ particles ranges between - 2:1 - 10:1,

wherein the nanocomposite is covalently linked to the substrate, particularly by the linkage of a silane group to a hydroxyl group.
Composite material according to the previous claims wherein the relation of TiO₂ nanoparticles and SiO₂ nanoparticles is 5:1 - 8:1.
Composite material according to the previous claims wherein the dimension of SiO₂/TiO₂ nanocomposite is between 30 - 120 nm, preferably between 50 - 100 nm.
Composite material according to the previous claims wherein the amount of nanocomposite at the substrate surface ranges between 1- 50 g/m², preferably 2 - 10 g/m².
Composite material according to the previous claims wherein the textile substrate is a fabric, nonwoven fabric, or knitted fabric, or a technical textile, or combinations thereof.
Composite material according to the previous claims wherein the nanocomposites are activated by ultraviolet light, visible light, sunlight, moisture and combinations thereof.
Article comprising the composite material described in any of the previous claims.
Article according to the previous claims wherein the article is a garment, piece of clothing, fabric for shirt, curtain, sofa upholstery, motor vehicle upholstery.
Method of preparation of the SiO₂/TiO₂ nanocomposite comprising the following steps:
preparing a first mixture of distilled water, acetic acid and nitric acid, in a ratio of 100:10:1, respectively, under vigorous stirring;

adding 1-10 parts of titanium isopropoxide;

heating the mixture,

preparing a second mixture of distilled water, ethanol, hexadecyltrimethylammonium chloride, tetraethylorthosilicate in a ratio of 64:10:10:4, under vigorous stirring;

dispersing the mixtures in an ultrasonic bath.
Method according to claim 9 wherein the stirring steps are performed for 0.5 - 3 hours, particularly for 1- 2 hours.
Method according to claims 9-10 wherein the stirring steps are performed between 20 - 80 °C, particularly at 40 - 60 °C.
Method according to claims 9-11 wherein the step of dispersing the mixtures in the ultrasonic bath is performed for 1- 24 hours.
Method according to claims 9-12 further comprising an alkaline washing step.