OXYGEN-ABSORBENT COMPOSITION COMPRISING A SILICA MATRIX THAT ENCAPSULATES FATTY ACIDS, UNSATURATED ESTERS OR COMPOUNDS CONTAINING SAME, AND METHOD FOR PRODUCING SAID COMPOSITION

Abstract

The production of an oxygen-absorbent composition is provided, having: (a) a porous silica encapsulation matrix; and (b) a composition containing an oxygen-absorbent compound selected from fatty acids, unsaturated esters or compounds containing same, and, optionally, a catalyst based on an inorganic salt of a transition metal, wherein the composition (b) is encapsulated in the porous silica matrix (a). The composition can form part of the structure of the packaging for oxidation sensitive products or be placed in the surrounding atmosphere to reduce the concentration of oxygen. A method for encapsulating the active compound or the active compound together with a catalyst, and subsequently incorporating same into polymer matrices is also provided.

Claims

1. An oxygen-absorbent composition that protects packed products that are susceptible to oxidation comprising: (a) an encapsulating porous silica matrix; (b) a composition that contains an oxygen-absorbent compound selected from fatty acids, unsaturated esters or compounds containing them and optionally a catalyst based on an inorganic salt of a transition metal; and in which composition (b) is encapsulated in the porous silica matrix (a).

2. The oxygen-absorbent composition according to claim 1, wherein the oxygen-absorbent compound is selected from the group consisting of linseed oil, methyl oleate, methyl linoleate and soybean lecithin.

3. The oxygen-absorbent composition according to claim 1, wherein the inorganic salt of a transition metal is selected from the group consisting of copper (I) chloride, ferrous sulfate, ferrous fumarate and a combination thereof.

4. The oxygen-absorbent composition according to claim 1, wherein the inorganic salt of a transition metal is in a ratio between 0.01 and 5 grams per gram of the oxygen-absorbent substance.

5. The oxygen-absorbent composition according to claim 1, wherein the porous silica matrix is a hydrated silica gel of molecular formula SiO.sub.2xH.sub.2O.

6. A method for preparing the oxygen-absorbent composition according to claim 1, comprising: (a) forming an aqueous suspension of oxygen-absorbent compound or of a mixture of oxygen-absorbent compound and catalyst based on an inorganic salt of a transition metal; (b) while stirring continuously, adding an amount of silicate precursor to a solution of acid until a maximum pH of 2 is reached; (c) adding the aqueous suspension obtained in step (a) to the solution obtained in step (b); (d) adding additional silicate precursor to the solution obtained in step (c), obtaining a gel with a pH between 6 and 9; (e) leaving the gel obtained in step (d) to stand for 1 to 48 hours; (f) washing the gel with water, removing the salts that result from the neutralization reaction; and (g) drying the gel obtained.

7. The method according to claim 6, wherein the absorbent composition is incorporated in a polymer matrix, further comprising the following steps after step (g): (a) submitting the dry gel to operations of size reduction and homogenization and selecting the particles of absorbent composition with a size less than 45 micrometers; and (b) incorporating the particles of the oxygen-absorbent composition, with a size less than 45 micrometers, in a polymer matrix in a proportion from 1 to 10 wt %, relative to the polymer, using a mixer with variable angular velocity.

8. The oxygen-absorbent composition according to claim 4, wherein the inorganic salt of a transition metal is in a ratio between 0.39 grams and 2 grams per gram of the oxygen-absorbent substance.

Description

4. BRIEF DESCRIPTION OF THE FIGURES

[0034] FIG. 1 shows the method for encapsulating the oxygen-absorbent compound and the catalyst based on an inorganic salt of a transition metal.

[0035] FIG. 2 shows the results of measurement of the molar percentage of oxygen (mole fraction of oxygen) as a function of time for the absorbent compound prepared. It shows the capacity for oxygen capture in a container with 38 ml of headspace that contains 1 gram of linseed oil encapsulated in silica gel and the capacity for oxygen capture in a container with 38 ml of headspace that contains 1 g of linseed oil and ferrous sulfate encapsulated in silica gel, activated by moisture of 99% relative humidity for 1 hour without grinding.

[0036] FIG. 3 shows the results of measurement of the molar percentage of oxygen (mole fraction of oxygen) as a function of time for the absorbent active compound prepared. It shows the capacity for oxygen capture in a 38 ml flask that contains 1 gram of linseed oil and ferrous sulfate encapsulated in silica gel, activated by moisture (99% relative humidity) for 1 hour, dried and ground to a particle size between 25 and 45 micrometers.

[0037] FIG. 4 shows the results for oxygen capture of the films made from linseed oil-ferrous sulfate encapsulated in silica gel with polypropylene. It shows the results for: an encapsulated linseed oil composition, ground for 180 minutes until a particle size less than 25 micrometers is reached; an encapsulated linseed oil composition with a catalyst; an encapsulated linseed oil composition; and an encapsulated linseed oil composition ground for 90 minutes until a particle size less than 25 micrometers is reached.

[0038] FIG. 5 compares the efficiency of oxygen absorption capacity of two films obtained by different methods.

[0039] FIG. 6 shows the results for oxidation in an air atmosphere in a study of the oxidation capacity of methyl linolenate.

[0040] FIG. 7 shows results in an atmosphere with 99% oxygen content in a study of the oxidation capacity of methyl linolenate.

[0041] FIG. 8 shows the effect of sol-gel encapsulation on the absorption capacity of a mixture of soybean lecithin+copper chloride.

5. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention relates to an oxygen-absorbent composition that comprises: a porous silica matrix prepared by sol-gel reaction that encapsulates an active composition comprising an oxygen-absorbent compound and optionally a catalyst based on an inorganic salt of a transition metal.

4.1. Description of the Oxygen-Absorbent Compound

[0043] The oxygen-absorbent compound may be an unsaturated fatty acid, an unsaturated ester, a phospholipid or a compound containing them. In particular, the oxygen-absorbent compound is selected from the group consisting of (but not limited to) linseed oil, methyl oleate, methyl linoleate, methyl linolenate and/or soybean lecithin.

4.2. Description of the Catalyst Based on an Inorganic Salt of a Transition Metal

[0044] An inorganic salt of a transition metal, which acts as a catalyst of the absorption reaction, may optionally be used in combination with the oxygen-absorbent compound. Said catalyst is an inorganic salt of a transition metal, which may be a copper (I) chloride, a ferrous sulfate, a ferrous fumarate or a combination thereof. For suitable catalytic action, the inorganic salt of a transition metal is present in a ratio between 39% and 200% w/w with respect to the oxygen-absorbent substance.

4.3. Description of the Porous Silica Matrix

[0045] The oxygen-absorbent substance, individually or in combination with the catalyst based on an inorganic salt of a transition metal, is encapsulated in a porous silica matrix. Encapsulation in this matrix offers the following advantages: the possibility of incorporating the oxygen-absorbent compound in a polymer layer that forms part of a packaging structure or in a polymer patch that adheres to the interior thereof, the possibility of being incorporated inside a cell or porous sachet to prevent direct contact with the product being packed, protection of the components of the oxygen-absorbent compound against premature thermal degradation during manufacture of the packaging structure, to control the kinetics of the action of the absorbent compound and retain the products generated during oxidation of the absorbent.

4.4. Description of the Method for Encapsulating the Oxygen-Absorbent Compound Individually or in Combination with the Catalyst Based on a Inorganic Salt of a Transition Metal in a Silica Matrix

[0046] The method for encapsulating the oxygen-absorbent compound individually or in combination with the catalyst based on an inorganic salt of a transition metal includes the steps given in detail hereunder: [0047] (a) At a temperature between 283.15K and 323K, preferably between 283.15K and 298.15K, in the case of an absorbent compound in powder form, mixing it with the catalyst based on an inorganic salt of a transition metal in a ratio between 0.01 and 5 grams, preferably 0.39 grams and 2 grams per gram of absorbent compound, and forming an aqueous suspension of the mixture, with a concentration between 67 kg/m.sup.3 and 133 kg/m.sup.3. When the catalyst is not included, the suspension is prepared with the oxygen absorbent alone. [0048] (b) At a temperature between 283.15K and 323K, preferably between 283.15K and 298.15K, adding, while stirring continuously and monitoring the pH, to a solution of an organic acid such as citric acid or inorganic such as hydrochloric acid with a concentration between 1M and 5M, preferably 1.55M and 3.00M, and with a pH less than 1, an amount of silicate precursor, for example such as sodium silicate or tetraethyl orthosilicate in the range between 22 kg and 56 kg per cubic meter of hydrochloric acid solution and whose concentration is between 40 kg/m.sup.3 and 560 kg/m.sup.3, by stirring at a maximum of 100 Hz (6000 rpm), until a maximum pH of 2 is reached. [0049] (c) Adding the suspension prepared in step (a) or the individual oxygen-absorbent compound, depending on the case, continuing to add the silicate precursor in a ratio from 10 to 40 kilograms of solution of silicate precursor per m.sup.3 of hydrochloric acid solution, until a gel is obtained, at pH between 6 and 9. [0050] (d) The gel obtained is left to rest for a time between 1 hour and 48 hours, at a temperature between 283.15K and 323K. [0051] (e) After the resting time, the gel is washed several times (preferably once or twice) with water, to remove the salts that result from the neutralization reaction, using vacuum between 600 and 6000 Pa, preferably between 600 and 2000 Pa. [0052] (f) After washing, drying the gel at temperatures between 333.15 K. and 363.15 K., at atmospheric pressure or under vacuum.

[0053] An example of the method for encapsulating the oxygen-absorbent compound individually or in combination with the catalyst based on an inorganic salt of a transition metal is shown in FIG. 1.

4.5. Description of the Method for Incorporating the Oxygen-Absorbent Composition in a Polymer Matrix

[0054] The method for incorporating the oxygen-absorbent composition obtained by the aforesaid method in a polymer matrix includes the following steps: [0055] (a) Subjecting the oxygen-absorbent composition to operations of size reduction and homogenization, in a ball mill for 30 to 210 min, and selecting the particles of the absorbent compound with a size less than 45 micrometers; [0056] (b) Incorporating the oxygen-absorbent composition, with a size less than 45 micrometers, in the polymer matrix in a proportion from 1 to 10 wt %, relative to the polymer; a compatibilizer may be included to prevent agglomeration of the oxygen-absorbent composition, in a proportion up to 5%, relative to the polymer, by means of a mixer with variable angular velocity that may operate at between 0 and 1.67 Hz (0 and 100 rpm), with a melt viscosity in the range 10.sup.3-10.sup.6 Pa-s.

[0057] Size reduction of the oxygen-absorbent composition is carried out by means of a grinding system. In addition, uniformity of size is achieved by sieving operations using mesh sizes less than or equal to 180 micrometers.

6. EXAMPLES

[0058] The following examples illustrate the present invention. However, it must be understood that these are not limiting, according to the knowledge of a person of average skill in the art.

Example 1

Specifications of Silicate Precursor: Sodium Silicate

[0059] A sodium silicate with the specifications illustrated in Table 1 is used for producing the oxygen-absorbent composition.

TABLE-US-00001 TABLE 1 Sodium silicate specifications Parameter Value Density, degrees B at 50 1 293.15 K. (20 C.) Specific gravity 1.48 to 1.5 Alkalinity (% Na.sub.2O) 12.5 1 Silica (% SiO.sub.2) 31.20 to 33.15 Ratio (Na.sub.2O:SiO.sub.2) 1:2.10 to 1:2.40 Viscosity 600 to 850 centipoise pH 12 0.5

Example 2

Illustration of the Method of Encapsulation of the Oxygen-Absorbent Active Compound in the Silica MatrixFIG. 1

[0060] The steps carried out for encapsulation of an absorbent compound (double boiled linseed oil), individually, in the silica matrix, are presented below. [0061] 1. Dissolve 38.05 g of concentrated hydrochloric acid (37% w/w) to a volume of 250 ml [0062] 2. Dissolve 170 g of sodium silicate (specifications in Table 1) to a volume of 1000 ml [0063] 3. Put all the dilute acid in a beaker on a stirring plate with monitoring of pH [0064] 4. Put the sodium silicate solution in a washing funnel [0065] 5. Start neutralization of the acid by adding silicate until a pH of 2 is reached [0066] 6. Add 76 g of double boiled linseed oil [0067] 7. Continue adding silicate until a gel is obtained [0068] 8. Leave the gel to age for 24 h [0069] 9. Dry the gel in a stove at 60 C. and atmospheric pressure, until a weight change of less than 10% is obtained [0070] 10. Grind the composition in a ball mill with a ratio between 10:1 (weight of balls:sample to be ground) and 20:1 by weight [0071] 11. Sieve, selecting the sample with size less than 25 m.

Example 3

Illustration of the Absorption Capacity of the Oxygen-Absorbent Active Compound with Addition of Metal CatalystFIG. 2

[0072] The effect of adding catalyst is compared for the active ingredient double boiled linseed oil. The first sample consists of linseed oil without addition of catalyst encapsulated in silica gel by the method described in example 2; the second sample consists of a mixture of linseed oil and ferrous sulfate as metal catalyst (weight ratio of catalyst 0.5% of the weight of linseed oil), encapsulated in silica gel. 1 gram of each sample is put in different vessels, each with a volume of 38 ml, they are put in a chamber with relative humidity of 99%, at 25 C. for one hour, and then the concentration of oxygen was monitored for 10 days in ambient conditions. For this example the catalyst shows a slight acceleration in the rate of oxygen capture.

Example 4

Illustration of the Absorption Capacity of the Oxygen-Absorbent CompositionEffect of GrindingFIG. 3

[0073] A mixture of linseed oil and ferrous sulfate in a weight ratio of 100:0.5 was encapsulated in silica gel, dried, and ground for 90 minutes; another sample with the same characteristics of composition is ground for 180 minutes. Each sample is sieved and the particles with size less than 25 micrometers are selected. 1 gram of each sample was put in different vessels, each with a volume of 38 ml, they are put in a chamber with a relative humidity of 99%, at 25 C. for one hour and then the concentration of oxygen was monitored for 10 days in ambient conditions. The sample that was ground for a longer time showed a considerable loss of capacity for oxygen capture, and the influence of the processing variables on the performance of the oxygen-absorbent composition was noted.

Example 5

Illustration of the Absorption Capacity of the Oxygen-Absorbent Composition in a Polymer Such as PolypropyleneFIG. 4

[0074] The mixture of linseed oil and ferrous sulfate encapsulated in a ratio (100:0.5 correspondingly) was mixed with polypropylene in a twin-screw extruder at a constant temperature of 190 C. in all the extrusion zones and then activated by moisture. FIG. 4 shows the effect on the oxygen capture of the activated film as a function of the rotary speed. The film that is obtained at a higher speed reduces the oxygen concentration more slowly than that processed at 35 rpm, but both have the same average performance.

Example 6

Technical Advantages of the Method Used in the Present ApplicationFIG. 5

[0075] The efficiency of oxygen absorption capacity of two films obtained by different methods is compared in FIG. 5.

[0076] Sample 1 is formed from polypropylene (PP) and encapsulated soybean lecithin and in a ratio 90% PP and 10% of encapsulated lecithin by weight.

[0077] Sample 2 is formed from polypropylene and an encapsulated mixture of linseed oil and ferrous sulfate in a ratio 90% of PP and 10% of encapsulated mixture. Moreover, for sample 2, the following operations described in this patent were carried out: [0078] 1. Grinding, sieving and selection of particles encapsulated in silica gel. [0079] 2. Control of extrusion speed, extrusion equipment and temperature profile.

Example 7

Oxidation Capacity of Methyl Linolenate

[0080] The oxidation capacity of methyl linolenate in an air atmosphere and an oxygen atmosphere was investigated by thermogravimetry. FIG. 6 shows the results for oxidation in an air atmosphere and FIG. 7 shows the results in an atmosphere with 99% oxygen content. The unsaturated ester achieves an increase of 3.5 wt %, attributable to oxygen consumed during thermal oxidation at 80 C.

Example 8

Effect of Copper Chloride Catalyst and Encapsulation in Soybean Lecithin

[0081] FIG. 8 shows the effect of sol-gel encapsulation on the absorption capacity of a soybean lecithin+copper chloride mixture.