ADHESIVE COMPOSITION FOR FLEXIBLE CONTAINERS

Abstract

A water-based adhesive composition for a multilayer system comprising a flexible packaging which includes selenium nanoparticles in a range of 10 to 2500 ppm. The nanoparticles that confer antioxidant properties to the flexible packaging, allow for better preservation of the biological material. Said adhesive composition has the technical advantage of being highly effective, namely, has the dual capacity of being an adhesive and an antioxidant, such that there is no migration of selenium particles from the packaging to the biological material contained in said packaging, as said adhesive composition is located between layers and not in direct contact with the biological material.

Claims

1. A water based adhesive composition for bonding a plurality of layers in a film-film multilayer system containing elemental selenium nanoparticles in suspension, characterised in that the concentration of selenium nanoparticles is comprised in a range of 10 to 2500 ppm.

2. (canceled)

3. Adhesive composition according to claim 1 wherein the adhesive composition comprises the following components in the following proportions by weight, such that the sum thereof does not exceed 100% of the composition: TABLE-US-00004 Component % by weight Aqueous plastic dispersion 60-95% Nanoparticle suspension 10-2500 ppm 0.5-20%  Wetting agent 0-5% Water 0-5% Defoamer 0-5%

4. Film-film multilayer system formed of a plurality of layers comprising the adhesive composition of claim 1 between at least two of the layers of the multilayer system.

5. Film-film multilayer system according to claim 3 wherein the layers of the system are joined by a laminating process.

6. Film-film multilayer system according to claim 3 wherein the film-film multilayer system has between 2 and 10 layers.

7. A flexible packaging with antioxidant properties characterised by comprising the adhesive composition of claim 1.

8. A method, said method comprises using the adhesive composition according to claim 1 for the manufacture of a suitable antioxidant system for manufacturing flexible packaging that protects and preserves biological material of plant or animal origin.

9. A method, said method comprises using the flexible packaging according to claim 7 for packaging and protecting a biological material environment of both plant and animal origin.

10. The method according to claim 8 wherein the biological material is a food.

11. The method according to claim 8 wherein the biological material is cellular.

12. The method for obtaining the adhesive composition according to claim 1, wherein the adhesive composition comprises the following steps: a.-) taking a suspension of elemental selenium nanoparticles at a concentration between 10 and 2500 ppm and keep the suspension of elemental selenium nanoparticles stabilized at ambient temperature, b.-) charging a reactor with a plastic dispersion and beginning to agitate, c.-) adding step b.-) to the reactor, mechanically mixing, by means of a continuous mixer, the suspension of nanoparticles from step a.-), a wetting agent, an antifoam agent and water at a constant speed between 500 and 2000 rpm in a period between 30 minutes and 3 hours at ambient temperature, obtaining an optimal mixture of the adhesive composition, and d.-) discharging the mixture from step c.-) of the reactor by passing the mixture through two consecutive filters; the first having a 25 micron pore size and the second a 5 micron pore size, obtaining the final adhesive composition.

13. A process for obtaining the adhesive composition according to claim 1, wherein the suspension of selenium nanoparticles of step a.) is obtained by adding an amount between 0.01 and 0.1 M of ascorbic acid as reducing agent to a solution of sodium selenite stabilized with a mixture of sodium sulfosuccinate and ethoxylated sodium as a stabilizing agent.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0061] As a complement of the description being made and for a better understanding of the characteristics of the invention, according to an example of a practical preferred embodiment thereof, attached as an integral part of the aforementioned description are the following figures where, for purposes of illustration and in a non-limiting manner, the following is shown:

[0062] FIG. 1.—FIG. 1 shows an example of the results obtained with an antioxidant acrylic adhesive. As can be seen, what is measured is the percent inhibition of the free radical, which means the radical scavenging capacity of the sample studied. This ability to scavenge free radicals increases with the concentration of the nanoparticles, both if selenium nanoparticle suspension is added and if the adhesive containing said nanoparticles of Se is added. The results show great efficiency of free radical scavenging.

[0063] FIG. 2.—FIG. 2 measures the performance of the polyurethane and acrylic adhesives with different amounts of Se nanoparticles compared to time (min) measured by the DPPH test. This figure shows another example of the sequestering capacity using different concentrations of the selenium nanoparticles in a polyurethane adhesive. As observed, again the sequestration capacity of free radicals, and therefore the antioxidant capacity, increases with the concentration of the nanoparticles.

[0064] FIG. 3.—FIG. 3 shows the results obtained when various stabilizers were used. As seen, the adhesive shows increased capacity to sequester free radicals with the increased concentration of adhesive and a clear correlation between the concentration and antioxidant capacity (CAOX). This test demonstrates that the adhesive containing nanoparticles of Se significantly increases the antioxidant capacity of the adhesive.

[0065] FIG. 4.—FIG. 4 shows the free radical scavenging capacity of the multilayer system produced from the antioxidant adhesive containing the selenium (Se) nanoparticles, object of the present invention. FIG. 4 shows the antioxidant scavenging capacity of several free radicals multilayer systems containing different concentrations of SENPs used in a plastic bag against a blank (without SENPs multilayer system). As seen in FIG. 4, there is an absolute evidence that the multilayer system comprising the SeNPs is more effective as a free radical scavenger when compared to a multilayer system without adhesive or compared to a multilayer system with adhesive but without SeNPs.

DETAILED DESCRIPTION OF THE INVENTION

[0066] It can be said that the traditional function of the package is changing from being simply the material that contains the food and protects it from the external environment to become a functional material, which allows both the producer and the consumer to verify the product they are selling/buying and with proper nutritional and microbial quality.

[0067] The trend is once again to imitate nature, protecting food with functional packaging such as, for example, packaging for fruit such as bananas or oranges, including others, which in addition to protecting the contents of the environment indicate how ripe they are.

[0068] One of the main purposes of packaging containing nanomaterials is to achieve a longer preservation time by improving the barrier functions of the material used for packaging food, in order to reduce the exchange of gases and moisture and exposure to ultraviolet rays.

[0069] The packaging materials that release chemical substances make it possible for food packaging to interact with its contents. The exchange can occur in both directions. The packaging can release antimicrobial agents, antioxidants, flavours, fragrances or nanoscopic nutraceuticals to the food and beverages they contain, in order to prolong their shelf life or improve their organoleptic properties. Nanomaterials for packaging are also being developed which can absorb unwanted tastes.

[0070] In many cases, the packaging materials release chemical substances that also incorporate control elements, namely, elements that determine that the nano chemicals should be released only in response to specific conditions that have been triggered.

[0071] There are other packaging materials and materials in contact with food that, unlike the packaging materials that release chemicals based on certain triggering circumstances (e.g. biocides that are released in response to the growth of the microbial population, moisture or other changing conditions) have antimicrobial nanomaterials incorporated such that the packaging itself acts as an antimicrobial agent as a result of being in direct contact with the packaged product. These products generally use silver nanoparticles, although some use zinc oxide nanoparticles or chlorine dioxide.

[0072] However, and as shown in the section of the state of the art, there is no publication which discloses the subject matter of the present invention that relates primarily to an adhesive composition for a multilayer system comprising a flexible packaging which includes selenium nanoparticles that confer antioxidant properties to the flexible packaging, allowing better preservation of the biological material.

[0073] Said adhesive composition, object of the invention herein, has the technical advantage that is highly effective, namely, has the dual capacity of being an adhesive and an antioxidant, meaning certain layers can be dispensed with in the final packaging (as additional layers of adhesive and/or antioxidant material are not required) and more importantly, that said composition does not cause migration of selenium particles from the packaging to the biological material contained in said packaging as said adhesive composition is located between layers of polymer that make up the packaging.

[0074] The need for prevention or elimination of migration of materials used in adhesives to packaged food products, was recently revealed in The First Industry Meeting of the Spanish Institute of Packaging, held on 29th May 2014 referred to the importance of migration of adhesives for packaging intended for food use. The importance of migration studies were explained in respect of the possible components of adhesives transferring into the food, including the possibilities and limitations thereof. After reviewing the legal framework currently in force, the EU Regulation 1934/2004 on materials and objects intended to come into contact with food and RD 847/2011, which establishes the positive list of permitted substances for the manufacture of polymeric materials intended for coming into contact with food.

[0075] Accordingly, the researchers of the present invention, painstakingly researched how to provide adhesive manufacturers of adhesives with the methods to ensure the safety thereof when in contact with food products taking into account that: there are a lot of toxic compounds; that there are no similar adhesives and that migration largely depends on substances and functional barriers (e.g. a large amount of substances can pass through polyethylene).

[0076] In addition, this is more relevant in the case of water-based adhesives as they are most commonly used in the flexible packaging industry, where it is necessary to obtain water-based adhesives that exhibit the advantages of being perfect for contact with foods, they can be cut immediately, they do not need to be left standing or cure time and costs are reduced.

[0077] Therefore, the researchers of the present invention have developed an adhesive composition that has all the aforementioned advantages thereby being extremely versatile for use in multilayer systems used for manufacturing flexible packaging for storage of biological material, in particular for food.

[0078] On the other hand, researchers of the present invention have been mainly focused on incorporating selenium nanoparticles (SeNPs) as a functional antioxidant component of the adhesive composition. The reason is because the SeNPs have high antioxidant capacity due to sequestration of free radicals that capture said nanoparticles in the environment.

[0079] Free radicals are atoms or groups of atoms having one unpaired or free electron, therefore, they are very reactive, as they tend to capture an electron from stable molecules in order to achieve electrochemical stability. Once the free radical has managed to extract the electron it needs, the stable molecule that releases it, in turn, becomes a free radical as it remains with an unpaired electron, starting a real chain reaction that destroys our cells. The average biological life of the free radical is microseconds, but has the capacity to react to everything around it causing great damage to molecules, cell membranes and tissues through oxidation reactions.

[0080] The processes of oxidation are free radical chemical reactions, namely, that they are initiated by free radicals and pass through radical transfer. They are chain reactions, such that once started they spontaneously spread and only end when the radicals disappear. The antioxidant performance of the new adhesive that has been developed, and object of the present invention is based on the ability to scavenge free radicals. This antioxidant concept is based on the principle of oxidation processes, where the organic substrate, oxygen and free radicals are the three main actors of the reaction and therefore play a very important role. The removal of one of these agents prevents the process of oxidation. In general, the oxygen is removed, but a more appealing option is to remove the free radicals. As the oxidation process is a reaction involving radicals, if free radicals are present in the oxidation reaction environment, the process is not carried out.

[0081] Accordingly, the new approach of the present invention is to use a scavenging agent of said free radicals which is selenium, in particular in the form of selenium nanoparticulates.

[0082] Selenium has been extensively studied for its antioxidant properties. Selenium in the form of selenocysteine is necessary for the antioxidant activity of enzymes such as peroxidases or reductases. It also coordinates with metal ions in active sites forming dehydrogenases and [NiFeSe] hydrogenases. In addition to the selenoproteins, small molecule selenium (Se) metabolites are essential for the antioxidant biological activity of this element.

[0083] The protective effects of selenium are due primarily to its presence as a cofactor, in the form of the 21st amino acid SeCyst, in enzymes such as glutathione peroxidase (GPx) and thioredoxin reductase (TRx), which act as protective agents for the cellular components against oxidative damage. Glutathione peroxidase detoxifies a wide variety of oxidizing substances such as H.sub.2O.sub.2, fatty acid hydroperoxides, phospholipid hydroperoxides and other reactive oxygen species (ROS).

[0084] Studies performed both in vitro and in vivo have demonstrated the protective effect of various forms of selenium against oxidative stress. The diet is the main source of supply of this trace element to organisms. The bioavailability of selenium in foods is highly variable and depends primarily on its chemical form. γ-Selenium in foods can be found in different chemical forms, Se (IV), Se (VI) and in the form of seleno-amino acids (selenomethionine, selenocysteine, seleno-methyl-selenocysteine, γ-glutamyl selenomethyl selenocysteine, seleno-methyl-methionine) incorporated or not to the proteins.

[0085] It also coordinates with metal ions in active sites forming dehydrogenases and [NiFeSe] hydrogenases. In addition to the selenoproteins, small molecule selenium metabolites are essential for the antioxidant biological activity of this element.

[0086] Furthermore, it has been shown that selenium nanoparticles have an antioxidant capacity by means of capturing free radicals and protect DNA from oxidation. The smaller the size of the nanoparticles, the greater the antioxidant capacity. Both their chemical and biological properties have not been studied in depth but some trials have shown that their antioxidant properties are much better than those that the aforementioned selenium compounds confer.

[0087] It has been proven in tests carried out in vitro that the toxicity of selenium nanoparticles appears at much higher concentrations than those of other species for this element. There is evidence to show that selenium nanoparticles have a double effect, which is essential for the purpose of this invention: [0088] 1.—Low impaired growth of healthy cells, and [0089] 2.—High inhibition of cell growth in cancer cells.

[0090] The present invention also relates to an antioxidant multilayer system for manufacturing flexible packaging comprising the adhesive composition according to the present invention, and the final packaging comprising the multilayer system with highly safe antioxidant capacity for material of biological origin which is packaged as there is no migration of selenium particles to the product.

[0091] With the exception of glass, most of the materials used in flexible packaging, in particular food packaging, are formed by more than one material. In fact, to improve the characteristics of the packaging, the latter is manufactured by combining several basic materials. The most common are: [0092] Metals: the most common is aluminum. [0093] Metallic films: usually PP-aluminum and PET-aluminum. [0094] Polymers: PE, PP, polystyrene, PVC, PET, polyamides. [0095] Paper or cardboard.

[0096] In addition, film-film multilayer materials consist of multiple layers, on occasion more than ten, depending on the application. The philosophy of a film-film multilayer material consists of using a layer of plastic to solve each of the problems that the packaging of a product exhibits. Therefore, different layers will be used depending on whether films with barrier properties to gases, aromas, resistance to high or low temperatures, anti-fog, anti-static, high chemical resistance, abrasion resistance, mechanical strength, biodegradable and recycled etc. are required

[0097] There are many applications for multilayer and multimaterial materials in the food industry, from dry packaged goods, frozen foods, meat, fish, prepared foods, sauces and cheeses, etc.

[0098] One or more adhesives can be used to bond these layers in order to firmly attach the layers without affecting the properties of the materials joined. This process is called lamination and allows a variety of multilayers to be created by combining different materials with complete freedom in respect of thickness. Furthermore, lamination means non-plastic materials such as aluminum and paper can be used in the multilayers.

[0099] As described herein, adhesives are required for the formation of multilayers. In view of the foregoing, creating an antioxidant container by adding nanoparticles in the adhesive involves the advantage of not having to add an additional layer to the multilayer, but rather that the layer of adhesive is used which must be present in the packaging anyway. Reduced financial and environmental costs is thereby achieved than is the case of adding an additional layer of another material. In this manner, the packaged product will be protected against oxidation without the need to use a high barrier material that prevents oxygen from entering, as the antioxidant effect is achieved by removing (sequestering) the free radicals, not the molecular oxygen.

[0100] For the purpose of the present invention the term “film-film multilayer system,” “multilayer system”, “multilayer material” or “film-film multilayer materials” are defined interchangeably as the material obtained by the affixed joint of a plurality of layers of different types (plastic, metal, polymer, cellulose, paper, cardboard, etc.) in the form of sheets, generally by means of a process known as lamination which is well known in the state of the art.

[0101] The present invention further relates to the method for obtaining the adhesive composition and the suspension of selenium nanoparticles (SeNPs), and the use of the adhesive composition according to the present invention for producing an antioxidant multilayer system suitable for making flexible packaging that protect and preserve the biological material of plant or animal origin, such as food, cell cultures, organs, sperm, etc.

[0102] The method for manufacturing the adhesive or adhesive composition is a mechanical mixture inside a batch reactor. The reactor is equipped with a stirrer and is loaded with commercial products following established methods, known in the state of the art and the mixture is stirred at a given speed in a range between 500 and 2000 rpm and a period ranging from 30 minutes and 3 hours (depending on the type of adhesive) at ambient temperature.

[0103] These new adhesives have the particular characteristic that a suspension of selenium nanoparticles are added thereto. Firstly, the plastic dispersion (that which confers adherence) is charged in the reactor and then, and during stirring, the nanoparticle suspension and the remaining components are added.

[0104] A general formulation of the following invention is the following, which comprises the following components in the following proportions by weight, such that the sum thereof does not exceed 100% of the composition:

TABLE-US-00001 Component % by weight Aqueous plastic dispersion 60-95% Nanoparticle suspension 10-2500 ppm 0.5-20%  Wetting agent 0-5% Water 0-5% Defoamer 0-5%

[0105] Wherein the aqueous plastic dispersion are commercial products comprising 35%-65% of active material content based on acrylic polymers (pure acrylic, acrylic-vinyl, acrylic-styrene, etc.), vinyl (for example, copolymers of ethylene vinyl acetate, vinyl acrylate acetate, for example, butyl acrylate, 2-ethyl-hexyl acrylate, etc.), polyurethanes. Some trade names are Acronal® and Epotal® by BASF, Mowilith® by Celanese, Carbobond® by Lubrizol.”

[0106] The suspension of nanoparticles 10-2500 mg/Kg (ppm) is prepared by adding a reducing agent to a solution of sodium selenite stabilised with a surfactant. The humectant is an anionic or non-ionic surfactant and the defoamer is oil-based (vegetable oils or mineral oils), silicone-based or EO/PO based (polyethylene glycol and polypropylene copolymers).

[0107] The plastic dispersion is the main raw material of a white glue type adhesive, is a whitish fluid having different levels of viscosity depending on the type. Various additives to modify the characteristics of the dispersion (viscosity, surface tension, adhesion, solids content, pH, etc.) is usually added to the plastic dispersion. Some of the most common additives are thickeners, surfactants, humectants, defoamers, plasticizers, antioxidants, fillers, pigments, preservatives or crosslinkers.

[0108] Industrially, the dispersion mixture with the different additives is carried out in closed reactors (with a volume of 1 m.sup.3 to 10 m.sup.3) equipped with a Cowles type toothed agitator rotating at a speed in a range between 500 and 2000 rpm (preferably 1,500 rpm). Raw materials are supplied in tanks, containers, drums or bottles, depending on the provider and the required volume. The raw materials are introduced into the reactor and agitated for a period of time ranging from 30 minutes to 3 hours (depending on the product type) at ambient temperature. Once the period of production has elapsed, the product is discharged through two filters (25 micron and 5 micron).

[0109] Selenium nanoparticles were prepared by adding an appropriate reducing agent to a solution of sodium selenite in the presence of a surfactant such as a stabilizer. Neither the reducing agent nor the stabilizing agents should have toxic effects and they should be compatible with the adhesive.

[0110] A method for measuring the quantitative efficiency of obtaining selenium nanoparticles (hereafter SeNPs) is ultrafiltration and dialysis. For the present invention, it was possible to demonstrate the absence of inorganic ionic selenium in the adhesive medium, thereby avoiding adhesive the undesirable effect of selenium ionic migration to the medium, and ensuring that the nanoparticles have a high degree of selenium encapsulation and security in adhesive samples, as they do not migrate towards the products of biological origin, such as foodstuffs might be.

[0111] To manufacture the SeNPs, a concentration of an amount between 0.01 and 0.1 moles of ascorbic acid was added to the medium which assures the correct reduction of selenite to elemental selenium in order to form selenium nanoparticles (SeNPs). These SeNPs are stable and spherical and have an average diameter between 30 nm and 60 nm without forming agglomerates and fully compatible with the adhesive.

[0112] The right morphology and growth of the SeNPs is obtained by using the stabilizing agent or surfactant, which is preferably a mixed type of ethoxylated sodium sulfosuccinate (the Surfynol® type) resulting in SeNPs with an average particle size diameter of 50 nm. The initial concentration of the selenite solution that has been tested in the present invention ranges between 10 to 2500 mg/kg (ppm) in selenium. The preferred concentration of selenite is 10 to 2500 ppm, although increasing concentrations were tested up to 10,000 ppm, at which the precipitation and agglomeration of the nanoparticles occurs.

[0113] A water-based adhesive composition for bonding a plurality of layers in a film-film multilayer system which comprises elemental selenium nanoparticles in suspension is therefore an object of the present invention. Preferably, the selenium nanoparticles comprise elemental selenium in a range of 10 to 2500 ppm.

[0114] One aspect of the present invention is an adhesive composition which comprises the following components in the following proportions by weight, such that the sum thereof does not exceed 100% of the composition:

TABLE-US-00002 Component % by weight Aqueous plastic dispersion 60-95% Nanoparticle suspension 10-2500 ppm 0.5-20%  Wetting agent 0-5% Water 0-5% Defoamer 0-5%

[0115] One aspect of the present invention is a film-film multilayer formed of a plurality of layers comprising the adhesive composition of claims 1 to 4 between at least two of the layers of the system. Importantly, the layers are joined by means of a laminating process and has between 2 and 10 layers.

[0116] Another aspect of the present invention is a flexible container with antioxidant properties that is manufactured from the aforementioned multilayer system and because it comprises the adhesive composition according to the present invention.

[0117] Another aspect of the present invention is the use of the adhesive composition according to the invention herein for the manufacture of a suitable antioxidant system for manufacturing flexible packaging that protects and preserves biological material of plant or animal origin.

[0118] Another aspect of the present invention is the use of the aforementioned flexible package to package and protect biological material environment of both plant and animal origin. The biological material is preferably a foodstuff or cellular.

[0119] Another important aspect of the present invention is a method for obtaining the adhesive composition according to the present invention, comprising the following steps:

[0120] a.-) taking a suspension of elemental selenium nanoparticles at a concentration between 10 and 2500 ppm and keep it stabilized at ambient temperature,

[0121] b.-) charging a reactor with plastic dispersion and beginning to agitate,

[0122] c.-) adding step b.-) to the reactor, mechanically mixing, by means of a continuous mixer, the suspension of nanoparticles from step a.-), a wetting agent, an antifoam agent and water at a constant speed between 500 and 2000 rpm in a period between 30 minutes and 3 hours at ambient temperature, obtaining an optimal mixture of the adhesive composition, and

[0123] d.-) discharging the mixture from step c.-) of the reactor by passing it through two consecutive filters; the first having a 25 micron pore size and the second a 5 micron pore size, obtaining the final adhesive composition.

[0124] Importantly, the selenium nanoparticle suspension in step a.-) of the process described above is obtained by adding an amount between 0.01 and 0.1 M of ascorbic acid as a reducing agent to a solution of sodium selenite stabilized with a mixture of ethoxylated sodium with sodium sulfosuccinate as the surfactant or stabilizer (for example, Surfynol®).

EXAMPLES OF EMBODIMENTS

[0125] The following specific examples provided here illustrate the nature of the present invention. These examples are included for illustrative purposes only and are not to be construed as limitations to the invention claimed herein.

Example 1. Preparation of Selenium Nanoparticles (SeNPs)

[0126] Selenium nanoparticles were prepared by adding an appropriate reducing agent, in this case ascorbic acid 0.054M to a solution of sodium selenite to an initial concentration in the range of 10 to 2500 ppm of selenium in the presence of a mixture of ethoxylated sodium with sodium sulfosuccinate as a stabilizing agent. Neither the reducing agent nor the stabilizing agents should have toxic effects and they should all be compatible with the adhesive.

[0127] Quantitative efficiency for obtaining selenium nanoparticles (SeNPs) was tested by means of ultrafiltration techniques, dialysis and ICP-MS (Inductively coupled plasma mass spectrometry) which is capable of identifying and quantifying the performance of encapsulation of the Se nanoparticles.

[0128] Migration studies were conducted to verify the absence of inorganic ionic selenium in the adhesive medium, avoiding the effect of selenium ionic migration and ensuring that the nanoparticles have a high degree of selenium encapsulation and security in the adhesive samples.

Example 2: Production of Antioxidant Adhesive Containing SeNPs

[0129] Two different adhesives were manufactured: An acrylic adhesive and a new formulation of advanced technology polyurethane adhesive.

[0130] The performance and compatibility with the nanoparticle solution, the stability based on time and the functionality of the adhesive was evaluated. Various parameters such as strength of adhesion, viscosity, stability and thermal behaviour in the presence and absence of Se nanoparticles were evaluated. Several developer trays (two sheets glued together) of multilayer material (with different types of plastic sheets) were prepared in order to carry out these tests using an application of adhesive between 1-5 g/m.sup.2 of dry adhesive applied. The adhesion strength is measured by means of a T-peel test in a vertical dynamometer at 100 mm/min feed rate and a resistance value expressed in N/15 mm. The same test is repeated after storage at temperatures of 50-100° C. after a sterilization test lasting 45 mins. at 120° C., after immersion in edible liquids (ketchup, mayonnaise, soup, etc.) for 7 days at 50° C. The viscosity is typically measured in a No. 4 Ford Viscosity Cup at 23° C. and stability is measured after subjecting the adhesive to accelerated aging of 7, 15 and 30 days at 50° C., checking visually that there is no physical separation in the product (sedimentation or separation of phases) and their adhesive ability remains intact.

[0131] Once the adhesive properties were evaluated, the antioxidant capacity was measured. The antioxidant capacity of the adhesive and subsequently the multilayer material containing selenium nanoparticles was evaluated by three different procedures which are described below, and provided very good results. The three methods used to measure the antioxidant capacity (CaOx) has been extensively compared, scientifically recognised at international level and endorsed by numerous scientific publications.

[0132] A general formulation of the following invention prepared in this example is as follows:

TABLE-US-00003 Component % by weight Aqueous plastic dispersion 60-95% Nanoparticle suspension 10-2500 ppm 0.5-20%  Wetting agent 0-5% Water 0-5% Defoamer 0-5%

[0133] It is formed by a series of components in the weight ratios as indicated, such that the sum thereof does not exceed 100% of the composition:

[0134] The plastic dispersion was prepared first as it is the main raw material of a white glue-type adhesive.

[0135] Various additives to modify the characteristics of the dispersion (viscosity, surface tension, adhesion, solids content, pH, etc.) is usually added to the plastic dispersion. Some of the most common additives are thickeners, surfactants, humectants, defoamers, plasticizers, antioxidants, fillers, pigments, preservatives or crosslinkers.

[0136] Industrially, the dispersion mixture with the different additives is carried out in closed reactors (with a volume of 1 m.sup.3 to 10 m.sup.3) equipped with a Cowles type toothed agitator rotating at a speed in a range between 500 and 2000 rpm (preferably 1,500 rpm). Raw materials are supplied in tanks, containers, drums or bottles, depending on the provider and the required volume. The raw materials are introduced into the reactor and agitated for a period of time ranging from 30 minutes to 2-3 hours (depending on the product type) at ambient temperature. Once the period of production has elapsed, the product is discharged through two filters (25 micron and 5 micron).

[0137] Next, a suspension of nanoparticles was prepared in a range from 10 to 2500 ppm by adding ascorbic acid as a reducing agent to a solution of sodium selenite stabilized with a mixture of ethoxylated sodium+sodium sulfosuccinate as a surfactant.

[0138] The humectant is an anionic or non-ionic surfactant and the defoamer is oil-based (vegetable oils or mineral oils), silicone-based or EO/PO based (polyethylene glycol and polypropylene copolymers).

[0139] Then, the wetting agent and antifoaming agent is added to the plastic dispersion in the same reactor, and it is agitated at 500-2000 rpm for a period of time ranging from 30-180 minutes. Finally, the suspension of selenium nanoparticles is added and allowed to stabilize for 30 minutes/hour to obtain the final adhesive product.

Example 3: Calculation of Antioxidant Properties of the Adhesive and the SeNPs

[0140] In the following example, the antioxidant properties of both the selenium nanoparticles and the final adhesive containing the nanoparticles were studied by two different methods: [0141] 1-. ORAC (Oxygen Radical Absorbance Capacity Test) [0142] 2-. DPPH (measuring the capacity for the elimination of the 1.1-diphenyl-2-picrylhidrazyl radical).

[0143] Results are expressed as μgTrolox/g of nanoparticle solution or per gram of adhesive or in the ORAC method and as a percent inhibition of DPPH radicals by means of the DPPH method after different reaction times. Trolox is a well known antioxidant that is used as a reference standard in this method.

[0144] Two different adhesives, each intended to be used for different materials and purposes were tested. Both the compatibility of the nanoparticles and the adhesive formula were studied and tested.

[0145] FIG. 1 shows an example of the results obtained with an antioxidant acrylic adhesive. As can be seen, what is measured is the percent inhibition of the radical, which means the radical scavenging capacity of the sample, which increases with the concentration of the nanoparticles. Said antioxidant capacity is observed whether the selenium nanoparticle solution is added or if the adhesive containing said Se nanoparticles is added. The results show great efficiency of free radical scavenging.

[0146] FIG. 2 measures the performance of the polyurethane and acrylic adhesives with different amounts of Se nanoparticles compared to time (min) measured by the DPPH test. This figure shows another example of the sequestering capacity using different concentrations of the selenium nanoparticles in a polyurethane adhesive based on time. This effect, as seen, increases with the concentration of the nanoparticles and with time.

[0147] A major theme of the new active adhesive is stability over time. Various stabilizers were tested and optimized. FIG. 3 shows the results obtained when various stabilizers were used. As seen, the adhesive shows increased capacity to sequester free radicals with the increased concentration of adhesive and a clear correlation between the concentration and antioxidant capacity (CAOX). This test demonstrates that the adhesive containing the Se nanoparticles has a much greater antioxidant capacity than the adhesive without nanoparticles.

[0148] The antioxidants adhesives according to the present invention were used to make several multilayer materials, by combining multiple layers of plastic, such as PET and PE, PP and paper and other materials. Each adhesive formula was optimized depending on the application it was intended for.

Example 4: Calculation of Antioxidant Properties of Packages Comprising the Adhesive with the SeNPs

[0149] Several bags made from plastic multilayers produced from antioxidants adhesives were evaluated following the Pezo et al method (2008) (Pezo, D; Salafranca, J; Nerín, C. Determination of the antioxidant capacity of active food packagings by in situ gas-phase hydroxyl radical generation and high performance liquid chromatography-fluorescence detection. J. of Chromatography A, 178, Issues 1-2, 18, 126-133, 2008).

[0150] This method involves exposing a sample to an atmosphere rich in free radicals and observing the effect of the antioxidant material trapping the free radicals. The method by Pezo et al., developed in 2008 is based on an experimental system at laboratory level to determine the antioxidant capacity directly in a layer of plastic used as a packaging material. The experimental device designed by Pezo et al. was used for all tests conducted in the present example. An atmosphere enriched in free radicals, generated by the irradiation of UV light in an aqueous solution of H.sub.2O.sub.2 (0.29 mol L.sup.−1) is passed through the plastic bag that is the object of the invention. After reacting in situ with eight polymer samples in parallel (the eight parallel samples correspond to eight replicas of each polymer), the remaining free radicals (which were not trapped by the antioxidant polymer) is reacted with a solution of salicylic acid at a pH of 4.5, yielding 2.3-DHB and 25-DHB. Antioxidant capacity was indirectly assessed by HPLC-fluorescence determination of the highly sensitive 2.5-dihydroxybenzoic (2.5-DHB) acid formed. Chromatographic analysis of the 2.5-dihydroxybenzoic acid and residual salicylic acid is performed in an Alliance 2695 Separations Module (Waters, Milford, Mass., USA) coupled to a 474 Scanning Fluorescence Detector (Waters, Milford, Mass., USA). The chromatographic separation was performed on a reversed phase water column (100 mm long, 4.6 mm i.d., 3 μm) Atlantis® dC18. The isocratic mobile phase was an aqueous mixture of acetate buffer solution (35 mmol L-1, pH 5.8, 1.0 mL min-1) and methanol, 90:10 (v/v). The injection volume was 20 μl. The wavelengths of excitation and emission were set at 324 and 448 nm, respectively.

[0151] The results obtained (see FIG. 4) confirmed the free radical scavenging capacity of the multilayer system produced from the antioxidant adhesive containing the selenium nanoparticles, object of the present invention. FIG. 4 shows the antioxidant scavenging capacity of several free radicals multilayer systems used in a plastic bag that contains different concentrations of SeNPs. As shown in FIG. 4 there is absolute evidence that the multilayer system comprising the SeNPs is absolutely more effective as free radical scavenger and, therefore, as an antioxidant.