Polymer composition for scavenging oxygen

A method of producing a polymer composition adapted to be added to a sealed volume to increase the durability of goods contained in said volume comprising treating a polyamide or copolyamide with a metal compound contained in a volatile solvent composition during refluxing conditions to obtain an active component having capacity to consume oxygen, the metal of said compound being iron, nickel, cobalt, copper or manganese, said active component being a metal complex.

FIELD OF THE INVENTION 
The present invention relates to a polymer composition adapted for 
increasing the durability of goods contained in a sealed package, and to a 
method of producing said composition and to a method of use of said 
composition. 
BACKGROUND 
In filled and sealed packages a head-space is provided which is filled with 
a gas which generally contains oxygen. If the packages are filled with 
products which are susceptible to oxygen, i.e. which consists of or 
contain components able to react with oxygen changing the properties or 
the character of the product, it is important for the contents of the 
packages to be subjected to the oxygen present in said gas filled space to 
the least possible extent. In particular, in the case of packages 
containing dry products susceptible to oxygen, for example, coffee, 
spices, pharmaceutical preparations in the form of powders or tablets, 
etc. the ratio between the volume of said head-space (and consequently the 
amount of oxygen) and the product is often relatively great. Thus, in such 
cases it is especially desirable to provide a means by which the amount of 
oxygen present in said head-space can be reduced or eliminated in a simple 
way which does not interfere with the products contained in the packages. 
Such means will, of course, also react with oxygen entering the head-space 
after the package has been sealed, for example, if the package is opened 
and resealed, or if the package is manufactured of a material which is 
permeable to oxygen, for example, plastic or paper/cardboard. 
An object of the invention is to provide a composition which can be placed 
into operative association with the head-space of a sealed package so that 
the product contained in the package will not be affected by the presence 
of oxygen in the head-space. 
In accordance with the invention the composition is effective to reduce or 
eliminate oxygen present in said head-space. In further accordance with 
the invention, the composition is placed in a permeable cover, such as a 
net, a bag or the like, which is included in the package. Especially, the 
composition is introduced in said gas filled space, i.e. as a rule said 
head space. 
SUMMARY OF THE INVENTION 
The invention is based on the finding that certain metal complexes, 
especially of transition metals, have the capacity to bond with oxygen, 
and in this way eliminate molecular oxygen from said space, and in the 
utilization of this effect in connection with polymers. 
The polymers comprise thermoplastic resins and especially polyamides and 
copolyamides, the latter comprising copolymers of polyamides and other 
polymers. The polyamides can be aromatic and aliphatic, for example 
poly-m-xylylene-adipamide or nylon 6.6. A preferred group of polyamides 
are MX nylons. These are polymers containing at last 70 mol % of 
structural units obtained from m-xylylenediamine alone or a 
xylylenediamine mixture containing m-xylylene-diamine and 
p-xylylenediamine in an amount of less than 30% of the total amount and an 
.alpha...omega.-aliphatic dicarboxylic acid having 6-10 carbon atoms. 
Examples of these polymers include the homopolymers such as poly-m-xylylene 
adipamide, poly-m-xylylene sebacamide and poly-m-xylylene speramide, 
copolymers such as m-xylylene/p-xylylene adipamide copolymer, 
m-xylylene/p-xylylene pyperamide copolymer and m-xylylene/p-xylylene 
azelamide copolymer, and copolymers of these homopolymer or copolymer 
components and aliphatic diamines such as hexamethylenediamine, cyclic 
diamines such as piperazine, aromatic diamines such as 
p-bis(2-aminoethyl)benzene, aromatic dicarboxylic acids such as 
terephthalic acid, lactams such as .epsilon.-caprolactam, 
.omega.-aminocarboxylic acids such as .omega.-amino-heptoic acid and 
aromatic aminocarboxylic acids such as p-aminobenzoic acid. 
In these MX nylons there may be incorporated polymers such as nylon 6, 
nylon 66, nylon 610 and nylon 11. 
The invention will be explained hereafter in connection with polyamides but 
it is not limited thereto. 
The effect of the polymer composition according to the invention, i.e. its 
capacity to consume oxygen, is referred to as the "oxygen scavenger" 
effect or only the "scavenger" effect. It is theorized that a prerequisite 
for attaining this effect is the formation of an active metal complex, 
which is only possible if the polymer contains groups and/or atoms having 
the capacity to coordinate to the metal ion, and the polymer chain or 
chains are able to achieve a conformation in which the groups and/or the 
atoms are present in the correct positions in relation to the metal ion. 
Another prerequisite is that the metal ion which has the capacity to form 
the active metal complex is present at a location in the molecular 
structure where the formation of the complex is possible. The metal 
complex has ligands originating from groups and/or atoms present in the 
polymer or formed therefrom. 
It is believed that the effect of the active metal complex is irreversible 
in that the coordinating oxygen molecule is converted to highly oxidizing 
ions, for example, ions of superoxide or peroxide, which react further in 
the "organic" plastic phase in which they are present. 
As to the theory described above, to which the invention is not bound, and 
which may explain the present invention it may be noted that the theory is 
rather of academic than of technical interest and that the primary feature 
is the capacity of the polymer composition to consume (scavenge) oxygen in 
applications where an environment containing oxygen is detrimental. 
According to a preferred embodiment of the invention, polyamides or 
copolyamides are used together with at least one of the following metal 
ions; cobalt, nickel, iron, the palladium metals, i.e. ruthenium, rodium, 
palladium; the platinum metals, i.e. osmium, iridium, platinum; copper or 
manganese. Among these, iron and cobalt are preferred, and cobalt is most 
preferred. 
Secondary components can be present in the composition of the invention, 
which are conventional and do not substantially interfere with the 
scavenging effect. Examples of such components are drying agents, 
anti-clogging agents, dyes, diluents, fillers etc. 
According to another preferred embodiment of the invention the composition 
is present in the form of particles, such as granules and pellets. Pellets 
normally as spheres or small cylinders are most preferred, mainly due to 
their durability. 
The size of the particles is not critical but for effective results it is 
preferably in the range of 0.001-0.05 cm.sup.3. The amount of particles in 
relation to the volume of the head space is a function of the 
susceptibility of the goods to oxygen degradation and, in general, the 
volume of particles present in the head space should be between 1 and 50 
per cent of the head space volume exclusive of the composition. 
A further object of the invention is to provide a method of producing the 
polymer composition. 
In further accordance with the invention, the method comprises treating the 
polymer, preferably in particulate form, with a metal compound, in 
dissolved or slurry state in a volatile solvent composition. 
In performing the method according to the invention the volatile solvent 
composition can be a single solvent or a mixture of solvents all of which 
need not be volatile. 
According to a preferred embodiment, the solvent is ethanol, preferably 96% 
ethanol. 
The polymer, which preferably is granulated or pelleted, is refluxed with 
the metal compound dissolved or suspended in slurry state in the volatile 
composition for a sufficient time period to form the active oxygen 
consuming (scavenging) component of the composition. The length of the 
time period, during which refluxing takes place, is readily determined by 
one skilled in the art in each case and is not critical according to the 
invention. 
According to still another preferred embodiment of the invention, the metal 
compound comprises a salt, preferably a halide, and particularly a 
chloride, of the above discussed metals, and especially iron, cobalt and 
nickel. These metals, i.e. iron, cobalt and nickel, the palladium metals 
and the platinum metals are designated as transition metals belonging to 
series 1, 2 and 3 in the Periodic Table. The choice of the appropriate 
salt depends on its solubility in the solvent composition in that the time 
that it takes to prepare the active component is proportionately reduced 
in relation to higher solubility of the metal salt. The anion of the metal 
compound can be inorganic, for example, a chloride, or organic, for 
example an acetate or stearate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention will be further described below in detail with reference to 
working examples and experiments conducted to show the oxygen scavenger 
effect of the composition according to the invention. 
EXAMPLE 1 
500 g nylon 6.6 ("Ultramid", BASF) in the form of pellets were refluxed for 
about 24 h with 500 ml of an ethanolic aqueous solution of cobalt chloride 
(CoCl.sub.2.6H.sub.2 O) at a concentration of 0.24 g/ml. After refluxing 
during said time period the pellets were dried and the cobalt was found to 
be present in the amount of 7000 ppm (mean value). 
EXAMPLE 2 
The procedure of Example 1 was repeated but instead of nylon 6.6 
poly-m-xylylene-adipamide was used (a polymer manufactured and sold by 
Mitsubishi Gas Chemical Co., Japan under the designation "MXD6"). The 
cobalt content of the dried pellets obtained amounted to 4500 ppm (mean 
value). By increasing the concentration of cobalt chloride in the solution 
and the proportion between the amount of solution and the amount of 
polyamide, pellets of nylon 6.6 having a cobalt content of 15 000 ppm in 
accordance with example 1 and pellets of poly-m-xylylene-adipamide having 
a cobalt content of 9000 ppm in accordance with example 2 were prepared. 
An examination of the dried pellets according to examples 1 and 2 was made 
which revealed that the polymer was not saturated with metal ions. 
EXAMPLE 3 
The procedure of example 2 was repeated but with the metal compounds iron 
chloride and nickel chloride respectively in solution at a concentration 
of 0.24 g/ml. The polymer was "MXD6". By varying the amount of solution in 
relation to the amount of polyamide, pellets were prepared having various 
metal contents. 
EXAMPLE 4 
The procedure of example 1 was repeated but various salts of metals 
belonging to the palladium group and the platinum group were used, i.e. 
ruthenium, rodium and palladium and osmium, iridium and platinum, 
respectively. 
EXPERIMENTS FOR DETERMINING THE OXYGEN CONTENT IN HERMETICALLY SEALED CANS 
CONTAINING THE COMPOSITION ACCORDING TO THE INVENTION 
Pellets comprising nylon 6.6 containing 7000 ppm cobalt prepared in 
accordance with example 1 and pellets comprising poly-m-xylyleneadipamide 
containing 4500 ppm cobalt prepared in accordance with example 2 were 
packed in metal cans (40 g/68 ml can) which were sealed by means of 
double-seamed metal lids. The size of the pellets was 0.01-0.02 cm.sup.3 
and the volume of the head-space was 33-35 cm.sup.3. Samples were taken 
from the head-space (one sample per can) immediately after the filling, 
after two weeks and after 4 weeks for gas chromatographic determination of 
the oxygen content. The results appear from table I. 
TABLE I 
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Oxygen content % 
metal imm. after after after 
polymer complex filling 2 weeks 4 weeks 
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poly-m- Co 20.4 20.4 10.2 10.2 4.3 2.5 
xylyene- 
adipamide 
nylon 6.6 
Co 19.5 19.6 5.9 3.4 0.3 0.3 
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Corresponding samples taken from cans packed with particulate polymers 
(granulate, pellets) which were conventional and consequently outside the 
scope of the invention, did not show any change as to the oxygen content 
in the head-space. The effect obtained by the invention, which clearly 
appears from Table I can be increased by increasing the metal ion 
concentration in the polymer and by increasing the contact surface between 
the polymer composition and the head-space.