Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1999-07-12
2002-02-12
Anthony, Joseph D. (Department: 1714)
Liquid purification or separation
Processes
Chemical treatment
C210S750000, C252S188280, C252S188210, C252S188250, C252S397000, C426S107000, C428S411100
Reexamination Certificate
active
06346200
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions for reducing the oxygen concentration present in an atmosphere or liquid (often referred to as oxygen scavenging). In one particular application, the compositions are used in or in association with food packaging.
BACKGROUND OF THE INVENTION
A wide variety of foods and other materials are susceptible to loss in quality during storage under atmospheric levels of oxygen. The damage can arise from chemical oxidation of the product, from microbial growth, and from attack by vermin—much of which may be avoided by reducing the oxygen availability in the environment of the materials. In the field of packaging, relatively low-oxygen atmospheres have traditionally been generated by vacuum packing and inert gas flushing. Such methods are not, however, generally applicable for various reasons. For example:
soft porous foods such as cakes cannot be subjected to strong vacuum;
fast filling speeds generally preclude substantial evacuation of or thorough inert gas flushing of food packages;
filling some gas-flushed containers, such as beer bottles often results in occlusion of air;
evacuation or flushing offers no residual capacity for removal of oxygen, which may have desorbed from the food or entered the package by leakage or permeation.
As a consequence there has been much interest in chemical techniques for generating low-oxygen atmospheres and deoxygenating liquid or semi-liquid foods. Thus, there are approaches based on the use of oxidisable solids, for example porous sachets containing iron powder. In another technique, oxidisable MXD-6 Nylon is blended with polyester in the walls of blow-moulded containers—the effectiveness of this depends on the presence of a cobalt salt catalyst, moreover the speed of oxygen removal is limited by the oxygen permeability of the polyester. Further methods include sandwiching crystalline oxidisable material between the layers of multilayer containers, and including a catalyst for the reaction of oxygen with hydrogen in a sandwich arrangement as above or as a deposit on the inner surface of the package.
Heterogeneous systems such as described above do not, however, adequately meet the general needs of the packaging industry, largely because they are often oxygen-sensitive prior to use or can be activated only under restricted conditions of, for example, temperature or humidity. U.S. Pat. No. 5,211,875 proposes a composition intended to avoid the problem of oxygen-sensitivity prior to use, involving an oxidizable organic compound (typically 1,2-polybutadiene)and a transition metal catalyst (typically cobalt salt). Oxygen scavenging is initiated by exposing the composition to an electron beam, or ultraviolet or visible light.
However, the inclusion of a transition metal catalyst has a number of disadvantages including added cost, solubility difficulties, and a “gritty” appearance and reduced transparency of films made from such compositions. Some transition metal catalysts are also considered toxic and may not, therefore, be used with food.
The present invention avoids the disadvantages of including a transition metal catalyst. It may be based on plastic or other polymer-based compositions which can be activated as required, to effect reduction of ambient oxygen levels.
SUMMARY OF THE INVENTION
Accordingly, in a first aspect the present invention provides a composition for reducing the concentration of molecular oxygen present in an atmosphere or liquid, comprising at least one reducible organic compound which is reduced under predetermined conditions, the reduced form of the compound being oxidizable by molecular oxygen, wherein the reduction and/or subsequent oxidation of the organic compound occurs independent of the presence of a transition metal catalyst.
Preferably, the reduction and/or subsequent oxidation of the at least one reducible organic component is also independent of the presence of an alkali or acid catalyst.
The reducible organic compound for use in this invention may be reduced under predetermined conditions such as by exposure to light of a certain intensity or wavelength or, alternatively, by the application of heat, &ggr;-irradiation, corona discharge or an electron beam. Possibly, also, the compound may be reduced by incorporating in the composition a reducing agent which in turn can be activated under predetermined conditions, say by heating.
DETAILED DESCRIPTION OF THE INVENTION
Typically the reducible organic compound will be a compound having the capacity to be converted to an excited state such as a triplet form, which then becomes reduced to an essentially stable state by gaining or abstracting an electron or hydrogen atom from other molecules or by redistributing an electron or hydrogen atom within the compound itself. The reduced molecule is reactive towards molecular oxygen to produce activated species such as hydrogen peroxide, hydroperoxy radical or a superoxide ion. Preferably, the reducible organic compound is stable in air at room temperature or is in its fully oxidized state. Examples of suitable compounds include quinones, such as benzoquinone, anthraquinone (preferably, 9,10-anthraquinone) and naphthoquinone (preferably, 1,4-napthoquinone); and photoreducible dyes and carbonyl compounds which have absorbance in the UV spectrum, such as azo, thiazine, indigoid and triarylmethane compounds.
Most preferably, the reducible organic compound is a substituted anthraquinone such as 2-methylanthraquinone and 2-ethylanthraquinone. In some applications, 2-ethylanthraquinone shall be preferred to 2-methylanthraquinone due to its greater solubility.
The reducible organic compound component may comprise 0.1-99.9 wt % of the composition. More preferably, the reducible organic compound comprises 0.1-50 wt % of the composition.
Compositions of this invention which involve the formation of an activated oxygen species (eg, peroxide) may further comprise a scavenging component reactive towards the activated species. This may be embodied in the reducible organic compound itself, for example a quinone having an amine group would be effective, but in any event it should be an agent which is substantially stable in contact with air at room temperature. Suitable examples of the activated oxygen scavenging component include antioxidants such as alkylated phenols and bisphenols, alkylidene bis-, tris- and polyphenols, thio- and bis-, tris- and polyalkylated phenols, phenol condensation products, amines, sulfur-containing esters, organic phosphines, organic phosphites, organic phosphates, hydroquinone and substituted hydroquinones; inorganic compounds such as sulphates, sulfites, phosphites and nitrites of metals, particularly those of groups 1 and 2 of the periodic table and first row transition metals, zinc and tin; sulfur-containing compounds such as thiodipropionic acid and its esters and salts, thio-bis(ethylene glycol &bgr;-aminocrotonate), as well as the amino acids cysteine, cystine and methionine; and nitrogen-containing compounds capable of reacting with activated forms of oxygen include primary, secondary and tertiary amines and their derivatives including polymers.
Preferably, the scavenging component reactive towards the activated oxygen species is selected from the group consisting of triphenylphosphine, triethylphosphite, triisoproppylphosphite, triphenylphosphite, tris(nonylphenyl) phosphite, tris(mixed mono- and bis-nonylphenyl) phosphite, butylated hydroxytoluene, butylated hydroxyanisole, tris(2,4-di-tert-butylphenyl) phosphite, dilaurylthiodiprpionate, 2,2-methylene-bis-(6-t-butyl-p-cresol), tetrakis(2,4-dt-tert-butylphenyl)4,4′-biphenylene diphosphonite, poly(4-vinylpyridine) and mixtures thereof.
The activated oxygen species-scavenging component may be in the form of a polymer or oligomer. Such forms may be prepared by, for example, covalently bonding a compound such as those activated oxygen species-scavenging compounds listed above to a monomer or co-monomer. A limitation on the molecular size of the activated oxygen species-scavenging component will
Anthony Joseph D.
Commonwealth Scientific and Industrial Research Organisation
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