Packaging

The present invention provides a wall for a package comprising: (a) an outer set of one or more layers (1-4) and (b) an inner set of one or more layers (5-6) which layer or the outermost of which layers (5) comprises a composition comprising a polymer and having oxygen-scavenging properties, wherein (i) the outer set of layers would have, if separate from the inner set and in the absence of any oxygen-scavenging properties in any of the layers or the layer constituting the set, a permeance, for oxygen, of not more than 1.5 cm.sup.3 /(m.sup.2 atm day); (ii) the inner set of layers would have, if separate from the outer set and in the absence of oxygen-scavenging properties in any of the layers or the layer constituting the set, a permeance, for oxygen, of at least 2.0 cm.sup.3 /(m.sup.2 atm day); and (iii) the inner set of layers would have, if separate from the outer set, a permeance, for oxygen, less than the permeance specified in (ii) by at least 1.0 cm.sup.3 /(m.sup.2 atm day) by virtue of oxygen-scavenging in at least the layer specified in (b). In a preferred combination one of the outer layers (3) is of metal and the composition in the outermost of the inner layers (5) scavenges oxygen through the metal-catalyzed oxidation of an oxidizable organic component thereof. The wall is suitable for packaging uses, with the inner set of layers disposed towards the product, where headspace scavenging is especially desired.

FIELD OF INVENTION 
The present invention relates to packaging of oxygen-sensitive foods and 
beverages. 
BACKGROUND OF INVENTION 
Among substances that are oxygen-sensitive we would particularly mention 
beers (especially lager beers), wines (especially white ones), fruit 
juices, some carbonated soft drinks, fruits, nuts, vegetables, meat 
products, baby foods, coffee, sauces, and dairy products. Almost all foods 
and beverages are sensitive to some degree. 
One approach to oxygen-sensitive products has been the inclusion in the 
pack of a sachet containing a compound such as iron or a lower iron oxide 
or hydroxide. This material reacts with ("scavenges") oxygen packed with 
the product or transmitted through the wall of the package. 
Another approach has been the inclusion of scavenger in the walls of the 
package. Where the walls comprise a polymer and are appreciably 
oxygen-permeable this has the advantage of scavenging at least a part of 
the oxygen before it reaches the package contents at all. 
Some discussion of the conventional measurements and units of oxygen 
permeation is appropriate at this point. The measurement is made by 
exposing a package wall of area A to a partial pressure p of oxygen on the 
one side and to an essentially zero partial pressure of oxygen on the 
other. The quantity of oxygen emerging on the latter side is measured and 
expressed as a volume rate dV/dt, the volume being converted to some 
standard conditions of temperature and pressure. After a certain time of 
exposure (usually a few days) dV/dt is generally found to stabilise, and a 
P.sub.W value is calculated from the equation (1). 
EQU dV/dt=P.sub.W Ap (1) 
P.sub.W in the present specification and claims is called the permeance of 
the wall. (Analogy with magnetic permeance and electrical conductance 
would suggest that P.sub.W should be described as "permeance per unit 
area", but we are following the nomenclature in Encyclopaedia of Polymer 
Science and Technology, Vol. 2, Wiley Interscience, 1985, page 178.) The 
standard conditions for expressing dV/dt used generally and in this 
specification are 0.degree. C. and 1 atm (1 atm=101 325 N m.sup.-2). If 
the thickness of the area of wall is substantially constant over the area 
A with value T and the wall is uniform through the thickness (i.e. the 
wall is not a laminated or coated one) then the permeability of the 
material in the direction normal to the wall is calculated from the 
equation (2). 
EQU dV/dt=P.sub.M Ap/T (2) 
For non-scavenging materials, P.sub.W and P.sub.M are to a reasonable 
approximation independent of t, p, and T although they are often 
appreciably dependent on other conditions of the measurement such as the 
humidity of the atmosphere on the oxygen-rich side and the temperature of 
the measurement. 
For oxygen-scavenging walls, P.sub.W and P.sub.M are functions of t because 
the concentrations and activity of scavenger vary with time (particularly 
as the scavenger is consumed). This has not prevented us usually from 
measuring P.sub.W and P.sub.M reasonably accurately as a function of time 
(the changes in dV/dt being relatively gradual once the normal initial 
equilibration period of a few days is over). However, it should be 
recognised that, whereas after a few days' exposure to the measurement 
conditions a non-scavenging wall achieves a steady state in which dV/dt is 
equal to the rate of oxygen ingress to the wall, a scavenging wall 
achieves an (almost) steady state in which dV/dt is considerably less than 
the rate of oxygen ingress to the wall. This being the case, it is likely 
that P.sub.W calculated from (1) is a function of p as well as of t and 
that P.sub.M in (2) is a function of p and T as well as of t. P.sub.W and 
P.sub.M for scavenging walls are, strictly speaking, not true permeances 
and permeabilities at all (since permeation and scavenging are occurring 
simultaneously) but, rather, apparent ones. However, we have chosen to 
retain the conventional terms "permeance" and "permeability". So long as 
the conditions of the measurement are sufficiently specified they are 
suitable for characterising the walls in a manner relevant to the 
packaging user (i.e. in terms of the oxygen emerging from the wall). 
All values of P.sub.W and P.sub.M hereinafter in this specification (except 
where stated otherwise) are to be understood to refer to conditions in 
which p=0.21 atm, the relative humidity on the oxygen-rich side of the 
wall is 50% and the temperature is 23.degree. C. Conditions close to these 
are conventional in the packaging industry. 
It is possible for P.sub.W and P.sub.M to be affected by the illumination 
of the wall under test. All P.sub.W and P.sub.M values hereinafter, and 
indeed all references to oxidation, oxidisability, and oxygen-scavenging 
properties, refer to the dark or else to conditions of irradiation not 
appreciably contributing to oxygen-scavenging. 
In our copending UK patent application 88 15699.7, we have described and 
claimed a wall for a package, which wall comprises, or includes a layer 
comprising, a composition comprising a polymer and having 
oxygen-scavenging properties, characterised in that the composition 
scavenges oxygen through the metal-catalysed oxidation of an oxidisable 
organic component thereof. 
In a second aspect, the invention of the aforesaid UK patent application 
provides a composition for packaging use which comprises a polymer, an 
oxidisable organic component, and a metal catalyst for the oxidation of 
the oxidisable organic component. 
The composition provided by the aforesaid invention has three major uses, 
namely as the material for a wall or a layer of a wall, as a masterbatch 
for blending with another polymer for such use, and as a head-space 
scavenger. 
In a third aspect the aforesaid invention provides a package, whether 
rigid, semi-rigid, collapsible, lidded or flexible or a combination of 
these, a wall of which is a wall as provided by the invention in its first 
aspect or comprises entirely, as a layer, or as a blend the composition 
provided by the invention in its second aspect. 
The UK patent application corresponds to EPC patent application 88 306175.6 
and PCT patent application GB/8800532. The UK patent application has been 
published under number GB 2207439A and the EPC under number EP 301719 A1. 
The entire disclosure of the aforesaid patent applications is incorporated 
herein by this reference. However, it is convenient here to note the 
following points relating to our earlier invention: 
(1) The oxidisable organic component may be an oxidisable polymer. The use 
of an oxidisable polymer as the oxidisable organic component has the 
advantage, broadly speaking, over the use of an oxidisable non-polymeric 
component that it is less likely to affect adversely the properties of a 
non-oxidisable polymer with which is is blended. It is possible for an 
oxidisable polymer to be used as the sole polymer in the composition, 
serving a dual function as polymer and oxidisable organic component. 
(2) It is of course possible for two or more polymers, two or more 
oxidisable organic components, or two or more catalysts to be used. It is 
possible also for a metal catalyst to be used in combination with a 
non-metal catalyst. 
(3) The word "catalyst" is used in a general way readily understood by the 
man skilled in the art, not necessarily to imply that it is not consumed 
at all in the oxidation. It is indeed possible that the catalyst may be 
converted cyclically from one state to another and back again as 
successive quantities of oxidisable component are consumed by successive 
quantities of oxygen. However, it may be that some is lost in side 
reactions, possibly contributing directly to oxygen-scavenging in small 
measure, or indeed that the "catalyst" is more properly described in an 
initiator (e.g. generating free radicals which through branching chain 
reactions lead to the scavenging of oxygen out of proportion to the 
quantity of "catalyst"). 
(4) Polyesters and polyolefins are especially suitable as non-oxidisable 
polymeric components, especially ethylene terephthalate or ethylene 
naphthalate polyesters. Oxidisable organic components include amides, 
especially polyamides and most especially MXD6, which is a condensation 
polymer of m-xylylenediamine and adipic acid. Metal catalysts include 
cobalt, copper, and rhodium compounds. 
The aforesaid patent applications describe most particularly walls which 
would have a permeance in the range from 1.5, preferably 3.0 to 30, 
preferably 18.0 cm.sup.3 /(m.sup.2 atm day), in the absence of scavenging. 
Various multi-layer structures for walls are also described. 
SUMMARY OF INVENTION 
The present invention provides a wall comprising 
(a) an outer set of one or more layers; and 
(b) an inner set of one or more layers, which layer or the outermost of 
which layers comprises a composition comprising a polymer and having 
oxygen-scavenging properties, 
wherein 
(i) the outer set of layers would have, if separate from the inner set, a 
permeance, for oxygen, of not more than 1.5 cm.sup.3 /(m.sup.2 atm day); 
(ii) the inner set of layers would have, if separate from the outer set and 
in the absence of oxygen-scavenging properties, a permeance, for oxygen, 
of at least 2.0 cm.sup.3 /(m.sup.2 atm day); and 
(iii) the inner set of layers would have, if separate from the outer set, a 
permeance, for oxygen, less than the permeance specified in (ii) by at 
least 1.0 cm.sup.3 /(m.sup.2 atm day). 
If, as may be the case for instance if a reclaim layer is present, there 
may be some oxygen scavenging in the outer set of layers, the permeance 
(i) is in the absence of such scavenging. 
In (iii), of course, oxygen-scavenging in the inner set of layers is to be 
deemed unaffected by the separation from the outer set of layers. If the 
inner set of layers consists of two or more layers, and one of these (for 
instance a reclaim layer) is scavenging in addition to the outermost one, 
then this will of course contribute to the difference specified in (iii). 
By "wall for a package" in the present specification and claims is included 
(except where the context indicates otherwise) not only a wall when 
incorporated into a package structure but also packaging materials capable 
of forming walls, such as package bases, packaging sheet, and so on. 
In the above "inner", "outer", and "outermost" are understood purely as 
conventional reference terms (albeit referring to the eventual use of the 
wall), not referring necessarily to any observable feature of the wall 
prior to its use. As will be apparent from the usage of these terms 
hereinafter, the progression from the inside of the wall to the outside is 
in a constant sense from the one face of the wall to the other (not from 
the central portion of the wall to the faces in two opposed senses). 
Accordingly, where the inner set comprises two or more layers, the 
outermost of these is immediately adjacent to a single layer comprising 
the outer set (or to the innermost of the layers of the outer set where 
the outer set comprises two or more layers). 
Preferably, the permeance referred to in (i) is less than 1.0 cm.sup.3 
/(m.sup.2 atm day), more preferably less than 0.5 cm.sup.3 /(m.sup.2 atm 
day), and above all less than 0.1 cm.sup.3 /(m.sup.2 atm day). 
Advantageously, the permeances referred to in (ii) and (iii) are such that 
the difference specified in (iii) is at least 2.0 cm.sup.3 /(m.sup.2 atm 
day), preferably at least 3.0 cm.sup.3 /(m.sup.2 atm day), more preferably 
at least 10.0 cm.sup.3 /(m.sup.2 atm day), especially at least 30 cm.sup.3 
/(m.sup.2 atm day), and above all at least 100 cm.sup.3 /(m.sup.2 atm 
day). The latter four figures are also advantageous, preferred, etc. for 
the permeance specified in (ii). 
The time period for which the difference specified in (iii) is maintainable 
should be greater the longer is the exposure time prior to filling of the 
package, the larger is the volume of oxygen likely to be enclosed on 
filling, and the higher is the permeance specified in (i). In general, 
however, it would be of interest for this difference to be maintainable 
(under standard conditions of p=0.21 atm, 23.degree. C., and 50% relative 
humidity) for at least two, preferably at least ten, and especially at 
least twenty days, and above all at least one hundred days. 
An important aspect of the wall provided by the present invention is that; 
if used for the packaging of an oxygen-sensitive product with the 
aforesaid inner set of walls disposed towards the product and the outer 
set towards the atmosphere, it will serve to a very significant degree to 
scavenge the oxygen packed with the product. Especially if the permeance 
specified in (i) is less than 0.1 cm.sup.3 /(m.sup.2 atm day), such 
scavenging is very likely to preponderate in the short run at least over 
scavenging of oxygen inwardly transmitted. The relatively high 
permeability in the absence of scavenging of the materials constituting 
the inner layers ((ii) above) facilitates the entry of head space oxygen 
into the inner layers where it is scavenged. The difference (iii) above is 
a measure of the scavenging power of the inner set of walls. The wall may 
be rigid, a flexible sheet, or a clinging film. 
Before proceeding to discuss the present invention in more detail, it is 
appropriate to consider how it is possible to determine permeances, 
especially those referred to in (ii), which are permeances in hypothetical 
conditions where there is no scavenging to sufficient accuracy to know 
whether or not a particular limit is observed. 
In this respect, it is useful to note that the inner layers if separate 
will have a permeance to oxygen that will increase with time as the 
scavenging component of the composition is consumed. The time dependence 
of permeance of the layers, we believe, will in general be essentially as 
shown by the bold line in FIG. 1, in which the wall is formed at time t=0. 
In the scavenging systems described in our copending applications we have 
sometimes observed that there may be a time delay between the formation of 
a wall and the full appearance of the scavenging effect. In these cases 
FIG. 1 for low times is modified essentially as shown by the dashed curve 
marked X in the figure. 
The difference referred to in (iii) at any time t.sup.1 is shown by D.sup.1 
in FIG. 1, where P.sub.W (t=.infin.) is the value P.sub.W would have in 
the absence of scavenging. 
The standard storage conditions in between P.sub.W measurements at 
different times for the purposes of determining D.sup.1 are storage in air 
(p=0.21 atm) at 23.degree. C. and 50% relative humidity, both surfaces of 
the wall being exposed. Storage is in the dark or conditions of 
illumination not appreciably contributing to oxygen-scavenging. 
P.sub.W (t=.infin.) may be determined in any one of several ways, or at 
least a lower limit put upon P.sub.W (t=.infin.), as follows: 
(I) The full form of the curve in FIG. 1 is determined experimentally. This 
is of course very time consuming if the oxygen-scavenging capacity of the 
wall is very high. 
(II) A wall is prepared in which the scavenging is absent but which is 
otherwise very similar and its P.sub.W is measured. For instance, in 
catalysed scavenging systems it is often very reasonable to omit the 
catalyst and take P.sub.W measured in the absence of catalyst as P.sub.W 
(t=.infin.) for the wall containing the catalyst. 
(III) If scavenging appears fully only after a time delay, early 
measurements of P.sub.W put a lower limit on P.sub.W (t=.infin.). 
(IV) Oxygen-scavenging may be suppressed by cooling the wall and P.sub.W 
measured and adjusted to allow for the effect of changed temperature. 
(V) Measurements of P.sub.W are made with an inert gas such as carbon 
dioxide, making due allowance for the difference between P.sub.W for that 
gas and for oxygen as observed in walls made of broadly similar 
non-scavenging materials. 
In its simplest form the wall provided by the present invention comprises 
just two layers, i.e. a single layer on the outside and a single layer 
comprising the aforesaid composition on the inside. Other forms can be 
considered as modifications of the above. For instance, there may be a tie 
layer between the two layers just described (this tie layer then being the 
innermost layer of the outer set) and/or an additional layer on the inside 
of the layer comprising the composition. This additional layer (if 
necessary attached to the layer comprising the composition by a tie layer) 
may serve one or both of the following functions: it may separate the 
layer comprising the composition from the contents of the package (e.g. to 
avoid possible food contact problems); and it may serve as a heat sealing 
layer. 
If the wall is rigid, as in the wall of a bottle, scavenging properties 
will decay during prolonged storage in air prior to filling, and such 
prolonged storage should preferably be avoided. 
If the wall is flexible sheet or film, it is possible to roll it up so as 
to largely to prevent access to air and to unroll immediately prior to 
use. An analogous technique is applicable in principle to flat or 
otherwise stackable rigid walls. 
Layers or the layer in the outer set referred to under (a) above 
advantageously comprise one or more suitably high-barrier polymers, 
metals, inorganic oxides such as silica or alumina, or carbon in graphitic 
or diamond form. High barrier polymers may be readily selected by the man 
skilled in the art from their reported permeabilities. Among numerous such 
polymers we may mention MXD6 (already referred to in another context as an 
oxidisable organic component), poly(vinylidene chloride), vinylidene 
chloride-vinyl chloride copolymers, and copolymers of ethylene and vinyl 
alcohol. 
The composition referred to under (b) above is advantageously a composition 
as provided by UK patent application 88 15699.7 in its second aspect. 
Especially in order to achieve high differences as specified in (iii) 
above, a non-oxidisable polymer having a P.sub.M of at least 3.0, most 
especially at least 10, and above all at least 50 cm.sup.3 mm/(m.sup.2 atm 
day) is suitable. Polyolefins are especially suitable, most particularly 
polyethylene (especially low-density polyethylene) and polypropylene. 
Oxidisable organic components and metal catalysts preferred are those 
described in GB 88 306175.6.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 2, 1 represents a layer of oriented polyethylene terephthalate 25 
micrometer in thickness, 2 represents a layer of polyurethane adhesive 5 
micrometer in thickness, 3 represents a layer of aluminium metal 15 
micrometer in thickness, and 4 represents a layer of polyurethane adhesive 
5 micrometer in thickness. 1 to 4 together constitute the outer set of 
layers of the wall. 
5 represents a layer of thickness 100 micrometer of a composition 
consisting of MXD6 in a weight fraction of 10%, cobalt Siccatol in a 
weight fraction of 200 ppm expressed as metal, the balance being 
polypropylene. 6 represents a layer of polypropylene of thickness 20 
micrometer. This serves as a heat seal layer, and also avoids direct 
contact of layer 5 with the package contents. 5 and 6 together constitute 
the inner set of layers of the wall, of which 5 is the outermost. 
In a modification of the structure shown in FIG. 2, layer 3 of aluminium is 
40 micrometer in thickness instead of 15 micrometer. While a thickness of 
15 micrometer is indeed satisfactory if the layer is well made, use of a 
nominal thickness of 40 micrometer reduces the risk that pinholes will be 
present. 
The permeance of the outer set of layers 1-4, for oxygen, is below the 
limit of detection on an OXTRAN machine (about 0.05 cm.sup.3 /(m.sup.2 atm 
day)) essentially because of the aluminium layer 3. 
In Example 10 of our copending patent application 88 15699.7 the permeance 
of a 1.5 mm wall containing 10% by weight of MXD6 and 90% by weight of 
polypropylene (without added cobalt) is given as 26 cm.sup.3 /(m.sup.2 atm 
day). The literature value for pure polypropylene's permeability is 70 
cm.sup.3 /(m.sup.2 atm day). Accordingly, the permeance in the absence of 
scavenging of layer 5 can be calculated to be 
##EQU1## 
and of layer 6 
##EQU2## 
It follows that the permeance in the absence of scavenging of the inner 
set of layers 5 and 6 is 
##EQU3## 
The scavenging in layer 5 reduces this permeance by more than 1 cm.sup.3 
/(m.sup.2 atm day) for more than 2 days. 
The structure shown in FIG. 2 may be conveniently fabricated by the steps 
of 
(i) coextruding layers 5 and 6 together, and 
(ii) adhesive lamination of the 5/6 coextrusion with layers 1 and 3 by use 
of the polyurethane adhesive. 
The preparation of the composition used in layer 5 is described in Example 
10 of our copending patent application 88 15699.7. 
In FIG. 3, layer 7 is of polypropylene and of thickness 50 micrometer, 
layer 8 is a reclaim layer of thickness 600 micrometer, layer 9 is a tie 
layer of maleic anhydride--modified polypropylene of thickness 40 
micrometer, layer 10 is a layer of a vinylidene chloride/vinyl chloride 
copolymer of thickness 150 micrometer, and layer 11 is a tie layer of 
maleic anhydride-modified polymer of thickness 40 micrometer. Layers 7 to 
11 constitute the outer set of layers. 
Layer 12 is 600 micrometer thick, has the same composition as layer 5 in 
FIG. 2, and is oxygen-scavenging Layer 13 is a polypropylene layer 50 
micrometer thick. This serves the same heat seal and separation function 
as layer 6 in FIG. 2. Layers 12 and 13 together constitute the inner set 
of layers, of which layer 12 is the outermost. 
The composition of the reclaim layer is, of course, a weighted average of 
that of the other layers. 
The permeance of the outer set of layers 7 to 11 (ignoring any scavenging 
in the reclaim layer 8) can be calculated from permeabilities in the 
literature. By virtue of layer 10 alone, the material of which has a 
permeability of 0.06 cm.sup.3 mm/(atm m.sup.2 day), this permeance is less 
than 0.4 cm.sup.3 /(m.sup.2 atm day). 
The permeance in the absence of scavenging of inner layers 12 and 13 
separately and taken together can be computed as was done above with 
reference to FIG. 2. For layer 12 it is 
##EQU4## 
For layer 13 it is 
##EQU5## 
For the outer layers 12 and 13 together it is 
##EQU6## 
Scavenging in layer 12 reduces this permeance by more than 1 cm.sup.3 
/(m.sup.2 atm day) for more than 2 days. 
The structure shown in FIG. 3 can be conveniently fabricated by coextrusion 
as sheet in a single step, followed by thermoforming (with some thickness 
reduction in parts) to afford the desired tray shape, and recycling the 
skeletal material. 
In FIG. 4 is shown, in schematic section, a tray 14 the wall of which has 
the section shown in FIG. 3, bearing a lid 15 heat-sealed thereon. The lid 
has the section shown in FIG. 2. In FIG. 4, the scale does not permit the 
layers within 14 and 15 to be shown; only the positions of the outermost 
and innermost layers are indicated. 
In FIG. 5, 16 represents an aluminium sheath enclosing an injection-moulded 
pot 17. To the top of the pot is clinched an aluminium beverage can end 
shell 18 having a central hole 23 which receives a rubber septum 20. 19 
represents conventional sealing compound. The pot contains water 21 to 
simulate a food or beverage product. Septum 20 permits sampling the head 
space gas 22 at intervals. 
The pot 17 was made as follows. Low-density polyethylene was mixed with 
MXD6 and a solution of cobalt (II) neodecanoate in a hydrocarbon solvent 
of low aromatic content with a boiling range at 760 mmHg of 155.degree. C. 
to 173.degree. C., and dried overnight in a dehumidifying air dryer. The 
mixture was then injection-moulded to form a cylindrical pot with a wall 
thickness of 1.5 mm, an outside diameter of 61 mm, and an external height 
of 70 mm. The weight fractions used were as follows: MXD6, 10 percent 
relative to the total composition; cobalt (expressed as metal), 500 ppm 
relative to the total composition; balance, polyethylene. The amount of 
solvent used was such that the weight fraction of cobalt (expressed as 
metal) was 5 percent relative to the solution. 
The injection moulding machine was a Meiki 200. The materials used were as 
follows: 
Low-density polyethylene 
Dutch State Mines grade Stamylan LD 2308A. 
MXD6 
Grade Remy 6001 from Mitsubishi Gas Chemicals of Japan. This is a polymer 
of meta-xylylenediamine, H.sub.2 NCH.sub.2 -m-C.sub.6 H.sub.4 -CH.sub.2, 
with adipic acid, HO.sub.2 (CH.sub.2).sub.4 CO.sub.2 H. The relative 
viscosity of the polyamide is 2.1, for a solution in 95% aqueous sulphuric 
acid containing 1 g of polymer per 100 cm.sup.3 of solution. 
CobaIt (II) neodecanoate 
Supplied by Shepherd Chemical Company, Cincinnati, Ohio. 
Solvent 
Isopar G supplied by Esso Chemical Ltd of Southampton, England. 
The arrangement shown simulates a package containing a food or beverage 
product in accordance with the invention. 17 comprises the inner set of 
layers (in this case a single layer) and 16 the outer set of layers (in 
this case also a single layer). The permeance of the outer set of layers 
16 is less than 0.05 cm.sup.3 /(m.sup.2 atm day) being of aluminium. The 
permeance of the inner set of layers 17 was measured directly on the 
OXTRAN machine on a similar pot not sheathed with aluminium. Very 
remarkably, it was less than 0.05 cm.sup.3 /(m.sup.2 atm day) both two 
days after fabrication of the pot and fourteen days after fabrication. In 
contrast a comparison pot identical except that no cobalt was present 
(i.e. in the absence of oxygen scavenging) had a permeance of 41 cm.sup.3 
/(m.sup.2 atm day). This value is therefore the value specified in (ii) 
above, and the value specified in (iii) above is practically the same. 
Both a very high accessibility of the scavenger in layer 17 to headspace 
oxygen 22 and high scavenging power of layer 17 are strongly indicated. 
Direct observation confirmed the performance in headspace scavenging 
resulting from these characteristics of layer 17. When the pot was filled 
with enough water to leave a headspace 22 of volume 50 cm.sup.3, the 
oxygen content fell from an initial 21 percent by volume relative to the 
headspace gas (initially air) to 8 percent after 7 days and 4.5 percent 
after 14 days. 
All measurements and storage in the above were under the standard 
conditions referred to previously. The permeance measurements were 
performed on an OXTRAN machine 10/50A made by Mocon Inc. of U.S.A.