WO2006074521A1 - Compositions for scavenging oxygen - Google Patents

Abstract

The present invention provides a method of scavenging oxygen (particularly ground state oxygen) in an atmosphere or liquid comprising the steps of: (i) providing a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub structure wherein the hydrogenated anthraquinone derivative is selected from compounds represented by the formula (I) defined herein and substituted derivatives thereof: wherein at least two of the carbon atoms at positions 1 to 8 are hydrogenated and each remaining non hydrogenated carbon atom at positions 1 to 8 is included in an unsaturated bond to an adjacent non hydrogenated carbon atom at positions 1 to 8; and (ii) exposing the atmosphere or liquid to the composition; such that at least a portion of the oxygen in the atmosphere or liquid is removed by reaction with the composition. Methods of preventing transmission of oxygen across a film or packaging material using the polymeric composition of the invention are also provided. Further provided is a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub structure.

Description

COMPOSITIONS FOR SCAVENGING OXYGEN

FIELD OF THE INVENTION

This invention relates to a method of scavenging oxygen using polymeric compositions comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure, for use in, for example, food and beverage packaging to scavenge unwanted oxygen, which either remains within the package following the packaging of the food or beverage or otherwise enters the package by permeating through the packaging material. The hydrogenated anthraquinone derivative comprising a quinonoid sub-structure may also be incorporated into packaging materials, to prevent oxygen from permeating through the packaging material to enter the inside of a package.

BACKGROUND OF THE INVENTION

A wide variety of foods, beverages, pharmaceuticals and other materials are susceptible to loss in quality if they are exposed to significant amounts of oxygen during storage. The damage can arise from, for example, chemical oxidation of the product and/or microbial growth. In the field of packaging, such damage has been traditionally addressed by generating relatively low-oxygen atmospheres by vacuum packing and/or inert gas flushing. However, these methods are not generally applicable for various reasons. For example, the fast filling speeds commonly used in the food and beverage industries often prevent effective evacuation of, or thorough inert gas flushing of, food and beverage packages, and neither evacuation or inert gas flushing provides any residual capacity for removal of oxygen which may have desorbed from the package contents or entered the package by leakage or permeation. As a consequence, there has been much interest in the identification and development of chemical techniques for generating low-oxygen atmospheres.

In Australian Patent No. 672661 (the entire disclosure of which is incorporated herein by reference), the present applicant describes novel oxygen scavenging compositions comprising a source of labile hydrogen or electrons and a reducible organic compound, which may be readily activated or "triggered" (ie brought to its oxygen scavenging form) as required by exposure to, for example, ultraviolet (UV) light. The oxygen scavenging compositions, once activated, are capable of scavenging oxygen from an oxygenated atmosphere or liquid in substantial darkness for periods ranging from up to a few minutes or hours to over 100 days.

Most of the exemplified oxygen scavenging compositions described in Australian Patent No. 672661, are based on substituted anthraquinones as the reducible organic compound. Further examples of substituted anthraquinones suitable for use as the reducible organic compound in such oxygen scavenging compositions are disclosed in International Patent Application No. PCT/AU02/00341 (WO 02/076916) (the entire disclosure of which is hereby incorporated by reference).

There is a general need for alternative compounds and compositions useful for scavenging oxygen and, in particular, there is a need for compounds and compositions which do not necessarily require activation subsequent to formation into packaging materials in order to scavenge oxygen.

In addition, the substituted anthraquinones of the prior art discussed above tend to be coloured particularly in the reduced states. Compositions and packaging which contain such anthraquinones also tend to be coloured. For instance, films made using anthraquinone-based compositions can turn a deep yellow colour when the anthraquinone is reduced to activate the oxygen scavenging capacity. The coloured nature of the anthraquinone-based compositions is undesirable in many forms of packaging, particularly the packaging of foodstuffs. It is therefore desirable, although not essential, that any alternative compounds and compositions for scavenging oxygen have, in general, substantially less colour than the prior art substituted anthraquinones.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a method of scavenging oxygen (particularly ground state oxygen) in an atmosphere or liquid comprising the steps of:

(i) providing a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure; and

(ii) exposing the atmosphere or liquid to the composition; such that at least a portion of the oxygen in the atmosphere or liquid is removed by reaction with the composition.

In a second aspect, the present invention provides a method of preventing transmission of oxygen (particularly ground state oxygen) across a film or packaging material, the method comprising forming at least a part of the film or packaging material from a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure.

In a further aspect, the present invention provides polymeric compositions suitable for use in the methods of the first and second aspects.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a graph of oxygen transmission vs time of three polymeric compositions comprising 1,2,3,4-THAQ in MXD6 and of three control compositions of MXD6.

Figure 2 shows a graph of oxygen scavenging vs time of polymeric compositions comprising 1,2,3,4-THAQ in MXD6.

Figure 3 shows (a) the absorption spectrum of a polymeric film according to the present invention comprising 2%w/w 1,2,3,4-THAQ in MXD6; and (b) a comparative absorption spectrum of a polymeric film comprising 2%w/w AQSO₃Na in MXD6 following reduction of the AQSO₃Na by exposure to UV radiation.

DETAILED DESCRIPTION OF THE INVENTION

1,2,3,4-Tetrahydroanthraquinone (1,2,3,4-THAQ) is a hydrogenated anthraquinone derivative comprising a quinonoid sub-structure. The present applicant has surprisingly found that an MXD6 film formed by melt compression of a blend of MXD6 and 1,2,3,4-THAQ absorbs oxygen thereby providing an MXD6 film having a substantially enhanced oxygen barrier as disclosed in Examples 1 and 2. MXD6 is a nylon polymer or polyamide formed from the monomers hexanedioic acid and 1,3-benzenedimethanamine. The film does not require activation (eg through exposure to ultraviolet (UV) light) to scavenge oxygen. Moreover, the composition is virtually colourless which is beneficial in many packaging applications. Without being bound by theory, the present applicant posits that there are at least two possible mechanisms for the observed oxygen scavenging by the composition - these are, that hydrogenated anthraquinones comprising a quinonoid sub-structure may be oxidised at the hydrogenated carbon positions by oxygen or that hydrogenated anthraquinones comprising a quinonoid sub-structure may activate the MXD6 or other oxidisable polymer so that it is oxidised by oxygen. A combination of the two mechanisms is also possible.

Accordingly, in a first aspect, the present invention provides a method of scavenging oxygen (particularly ground state oxygen) from an atmosphere or liquid comprising the steps of:

(i) providing a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure; and

(ii) exposing the atmosphere or liquid to the composition;

such that at least a portion of the oxygen in the atmosphere or liquid is removed by reaction with the composition.

As would be understood by a person skilled in the art, the polymeric compositions used in the method of the first aspect would also be useful as barriers to oxygen in, for example, packaging applications.

Accordingly, in a second aspect, the present invention provides a method of preventing transmission of oxygen (particularly ground state oxygen) across a film or packaging material, the method comprising forming at least a part of the film or packaging material from a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure.

The hydrogenated anthraquinone derivative comprising a quinonoid sub-structure of the first and second aspects is selected from the group of compounds represented by the following formula and substituted derivatives thereof:

wherein at least two of the carbon atoms at positions 1 to 8 are hydrogenated and each remaining non-hydrogenated carbon atom at positions 1 to 8 is included in an unsaturated bond to an adjacent non-hydrogenated carbon atom at positions 1 to 8.

Preferred hydrogenated anthraquinone derivatives with a quinonoid sub-structure include compounds represented by the following formulae and substituted derivatives thereof:

1,2,3,4-Tetrahydroanthraquinone 1,4-Dihydroanthraquinone

1,2,3,4,5,6,7,8-Octahydroanthraquinone 1,4,5,8-Tetrahydroanthraquinone

A particularly preferred hydrogenated anthraquinone derivative is 1,2,3,4-Tetrahydroanthraquinone (1,2,3,4-THAQ) and substituted derivatives thereof. Preferred substituents are selected from alkyl, alkenyl, ether, halo, carboxylic acid, ester, anhydride, epoxy, hydroxy, and amine substituents. When a substituent comprises an alkyl group, the group may be branched or unbranched, substituted or unsubstituted, and is preferably Q-C^alkyl, more preferably Q-Qoalkyl, even more preferably Q-Cβalkyl and yet more preferably C;ι-C₃alkyl. When a substituent includes an alkenyl group, the group may be branched or unbranched, substituted or unsubstituted, mono- or poly-unsaturated, and is preferably C₂-C₂oalkenyl, more preferably C₂-C₁oalkenyl, even more preferably C₂-C₆alkenyl and yet more preferably C₂-C₃alkenyl.

Preferably, the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is substantially colourless or shows less colour relative to reduced anthraquinones

(particularly the sodium salt of anthraquinone-2-sulphonic acid (AQSO₃Na)). Preferably, the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is selected such that it has a maximum absorbance in the visible region (400nm-700nm) that is no more than half that of the reduced form of AQSO₃Na in MXD6 under the same conditions.

The polymeric compositions of the present invention are able to scavenge oxygen independently of the presence of a transition metal catalyst. Accordingly, in a preferred embodiment, the polymeric compositions do not comprise a transition metal catalyst.

Polymeric compositions used in the methods of the first to fourth aspects of the present invention may be in a solid, semi-solid (eg a gel) or liquid (eg a polymeric liquid such as an ink) form. They may therefore be applied as, or incorporated in, for example, bottle closure liners, inks, coatings, adhesives (eg polyurethanes), films, sheets or layers in containers such as trays, bottles or blister packaging either alone or as laminations or co-extrusions. When used in films or layers, they may be blended with typical polymers or copolymers used for construction of films or layers such as those approved for food or pharmaceutical contact. Such films or layers may be produced by extrusion at temperatures between 50 ⁰C and 350 ⁰C depending upon chemical composition and molecular weight distribution.

The hydrogenated anthraquinone derivative may be blended into the polymeric composition. The polymeric composition of the first and second aspects may be formed from any suitable polymer or blend of polymers including nylons, polyesters, polyolefins and ethylene- vinyl alcohol copolymers. Preferably, the polymer is nylon and more preferably MXD6.

Alternatively, or additionally, the hydrogenated anthraquinone derivative itself may be in a polymerised form either as a homopolymer or as a copolymer. Oligomer forms may also be suitable. Hydrogenated anthraquinone derivative-based monomers can be made, for example, by covalently bonding an ethylenically unsaturated group to a phenyl ring of the hydrogenated anthraquinone derivative. Alternatively, a polymerised form of the hydrogenated anthraquinone derivative may also be prepared by using an hydrogenated anthraquinone derivative carrying groups, such as carboxylic acid, ester, anhydride, epoxy, hydroxy, and amine groups, that enable the derivative to react with polymerisable molecules and preformed polymers.

In a further aspect, the present invention provides polymeric compositions suitable for use in the methods of the present invention comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure.

In order that the nature of the present invention may be more clearly understood, preferred forms thereof will now be described with reference to the following non-limiting examples.

EXAMPLES

Example 1 Oxygen barrier performance of a composition comprising 1,2,3,4-THAQ in MXD6

Amorphous MXD6 films containing 2% w/w 1,2,3,4-THAQ having film thicknesses in the range 71-74 μm were prepared by melt-mixing, followed by melt-compression at 250⁰C. Amorphous MXD6 films without 1,2,3,4-THAQ, and having film thicknesses of approximately 45 μm were prepared by melt-compression at 25O⁰C and used as controls. The oxygen transmission measurements were conducted using a technique (R.V. Holland, M. L. Rooney, R. A. Santangelo; Die Angewandte Makromoleculare Chemie; 88, 209-221, 1980) involving sandwiching an oxygen-sensitive film containing rubrene between two test films (both test films are either MXD6-THAQ, or MXD6) and sealing the three layers in a test cell. The test cell is then placed in an illuminated controlled temperature/humidity cabinet. The tests in this work were performed in air at 23⁰C and 57% RH. The colour of the rubrene film decreases in the presence of oxygen and light, and this change is used to determine the permeation rate of oxygen through the test films. The light in the storage cabinet was filtered to prevent any absorption of light by the THAQ during the course of experiments. The results for three MXD6-THAQ and three control MXD6 film samples are shown in Figure 1. The amount of oxygen transmitted by the MXD6 films containing 2%w/w 1,2,3,4-THAQ is at least 2 orders of magnitude lower than for the films of MXD6 alone. The MXD6 films containing 2%w/w 1,2,3,4-THAQ were substantially colourless and remained that way after exposure to oxygen.

Example 2 Oxygen scavenging performance of a composition comprising 1,2,3,4-THAQ in MXD6

Two amorphous MXD6 films containing 2% w/w 1,2,3,4-THAQ, and having a thickness of approximately 50 μm were used for oxygen scavenging experiments. The MXD6-THAQ films were vacuum-sealed in foil-laminate pouches and then injected with 10ml of air. The pouches were then placed in a 12O⁰C oven to simulate the temperature of retort processing. The oxygen concentration of the headspace was measured by Gas Chromatography after 30 minutes, and then again after 60 minutes in the oven. The results of oxygen scavenging measurements for the MXD6-THAQ films are shown in Figure 2. The scavenging efficiency is the ratio of the actual volume of oxygen scavenged by the film to the theoretical volume of oxygen that could be removed by the film if each molecule of the 1,2,3,4-THAQ was capable of scavenging a molecule of oxygen. The films were substantially colourless and remained that way after exposure to oxygen.

Example 3 Comparison of the absorption spectra of a polymeric composition comprising 1,2,3,4-THAQ in MXD6 with a polymeric composition comprising the reduced form of AQSOsNa in MXD6

Absorption spectra in this Example were measured using a Cary UV- Visible Spectrophotometer Model 3E. A composition was prepared by blending 1,2,3,4-THAQ at a level of 2%w/w into MXD6. This composition was then melt-compressed to form a film, and the absorption spectrum of this film is shown in Figure 3(a). Another film of comparable thickness was prepared by blending AQSO₃Na at a level of 2%w/w into MXD6 and then melt-compressed. The absorption spectrum of this film after exposure to light from a commercial UV-curing lamp (Fusion Systems Corp., Maryland, USA; model F-300 fitted with a 'D' bulb) is shown in Figure 3(b). As can be seen from Figure 3, the film comprising 1,2,3,4-THAQ displayed substantially less colour than the film comprising reduced AQSO₃Na. In fact, the film comprising 1,2,3,4-THAQ was substantially colourless and remained that way after exposure to oxygen.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed anywhere before the priority date of each claim of this application.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A method of scavenging oxygen from an atmosphere or liquid comprising the steps of:

(i) providing a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure wherein the hydrogenated anthraquinone derivative is selected from compounds represented by the following formula and substituted derivatives thereof:

wherein at least two of the carbon atoms at positions 1 to 8 are hydrogenated and each remaining non-hydrogenated carbon atom at positions 1 to 8 is included in an unsaturated bond to an adjacent non-hydrogenated carbon atom at positions 1 to 8; and

(ii) exposing the atmosphere or liquid to the composition;

such that at least a portion of the oxygen in the atmosphere or liquid is removed by reaction with the composition

2. A method of preventing transmission of oxygen across a film or packaging material, the method comprising forming at least a part of the film or packaging material from a polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure wherein the hydrogenated anthraquinone derivative is selected from compounds represented by the following formula and substituted derivatives thereof:

wherein at least two of the carbon atoms at positions 1 to 8 are hydrogenated and each remaining non-hydrogenated carbon atom at positions 1 to 8 is included in an unsaturated bond to an adjacent non-hydrogenated carbon atom at positions 1 to 8.

3. A method according to claim 1 or 2, wherein the polymeric composition comprises a polymer or blend of polymers selected from nylons, polyesters, poly olefins and ethylene- vinyl alcohol copolymers.

4. A method according to claim 3, wherein the polymeric composition comprises a nylon polymer.

5. A method according to claim 4, wherein the nylon polymer is MXD6.

6. A method according to any one of claims 1 to 5, wherein the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is selected from the following formulae and substituted derivatives thereof:

1,2,3,4-Tetrahydroanthraquinone 1 ,4-Dihydroanthraquinone

1,2,3,4,5,6,7,8-Octahydroanthraquinone 1,4,5,8-Tetrahydroanthraquinone

7. A method according to claim 6, wherein the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is 1,2,3,4-Tetrahydroanthraquinone (1,2,3,4-THAQ) and substituted derivatives thereof.

8. A method according to any one of claims 1 to 7, wherein the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is blended into the polymeric composition.

9. A method according to any one of claims 1 to 8, wherein the hydrogenated anthraquinone derivative comprising a quinonoid sub-structure is in a polymerised or oligomerised form.

10. A polymeric composition comprising an hydrogenated anthraquinone derivative comprising a quinonoid sub-structure wherein the hydrogenated anthraquinone derivative is selected from compounds represented by the following formula and substituted derivatives thereof:

wherein at least two of the carbon atoms at positions 1 to 8 are hydrogenated and each remaining non-hydrogenated carbon atom at positions 1 to 8 is included in an unsaturated bond to an adjacent non-hydrogenated carbon atom at positions 1 to 8.