CA2168976A1 - Oxygen scavenging thermoplastics - Google Patents

Abstract

Rubber modified styrenic oxygen scavenging compositions, films and articles are set forth. They comprise a solid continuous phase comprising a styrenic phase which has been graft polymerized onto a disperse elastomeric phase to provide a weight ratio of disperse to continuous phase of less than about 30:70. A transition metal catalyst is dispersed in the composition.

Description

wo 95,04776 ~ ~ ~ 8 ~ 7 6 PCT~S94/08535 OXYGEN SCAVENGING THERMOP~ASTICS

i Technical Field The present invention relates to compositions, layers and articles for scavenging oxygen so that oxygen-sensitive products such as foods and beverages are protected from oxidation. More particularly, the invention relates to high impact polymeric oxygen scavenging compositions, layers and articles for such uses.
Backqround Of The Invention ~ imitation of the exposure of oxygen-sensitive products to oxygen maintains the ~uality of such products and increases their shelf life. A
number of different approaches have been utilized to limit the oxygen expo~ure of products such as foods and beverages. Reduced oxygen environments can be employed in the packaging and/or the packaging may serve as an oxygen barrier, for example by scavenging oxygen from the product and by scavenging oxygen which might otherwise pass through the packaging and come into contact with the product.
Oxygen scavengers incorporated into oxygen scavenging walls are set forth in European Applications No. 301,719; 380,319 and 507,207 as well as in U.S. Patents 5,021,515 and 5,211,875. The oxygen scavenging walls utilize a transition metal catalyst and an oxidizable polymer which may be in the nature of a polyamide, polyisoprene, polybutadiene, or copolymers thereof, specifically block copolymers thereof, such as styrene-butadiene.

W095/04776 PCT~S94/08535 ~8~76 Such polymers, when made into walls or layers and/or into articles exhibit a number of drawbacks. First, as portions of the polymer backbone are oxidized by oxygen under the catalytic influence of the transition metal the strength and integrity of the article is reduced as the polymer is broken down.
Second, any toxic or otherwise undesirable products of the oxidation can be released into the package and thereby come in contact with its contents. Third, the gloss of the surface of the article can be reduced as pitting and molecular decomposition takes place near or at the surface.
Rubber modified styrenic thermoplastics such as high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS) and alkyl methacrylate butadiene styrene (MBS) terpolymers are characterized by a continuous phase which has within it a disperse phase of polybutadiene particles. The surface of the disperse phase particles are grafted to the continuous phase. Such rubber modified styrenic thermoplastics by themselves do not exhibit oxygen scavenging ability.

Disclosure Of Invention The present invention is directed to overcoming one or more of the problems as set forth above.
In accordance with an embodiment of the present invention a rubber modified styrenic oxygen scavenging composition is set forth. It comprises a solid styrenic continuous phase which is graft polymerized onto a disperse elastomeric phase. The weight ratio of the disperse phase to the continuous phase is less than about 30:70. The transition metal catalyst is dispersed in the composition.

W095/04776 PCT~S94/08535 In accordance with another embodiment of the present invention a styrenic layer having comprised of a rubber modified styrenic polymer and being suitable for oxygen scavenging includes a composition set forth above.
In still another embodiment of the present invention a styrenic article for packaging oxygen-sensitive products is set forth. The article includes a styrenic layer as set forth above.
Surprisingly, even though the polybutadiene content of the high impact thermoplastic compositions is surrounded by a continuous phase which is not itself oxygen scavenging the resulting rubber modified styrenic composition, layer and article have very significant oxygen scavenging capabilities. And, such compositions, layer and articles can be readily formulated by a simple extrusion process wherein a premade HIPS, A~3S or MBS graft copolymer can simply be fed into a standard extruder along with a salt of the transition metal so as to produce the composition, layer and/or article of the present invention. There are a number of advantages to the composition, layer and article of the present invention as compared to the prior art block copolymers such as those of butadiene and styrene. Since the butadiene in the graft copolymers of the present invention is present as the disperse phase and is surrounded by a continuous phase, deterioration of the butadiene as oxygen is scavenged is not as likely to lead to deterioration of the layer or article since the continuous phase is not affected. Thus, the overall strength of the layer or article is not affected.
This is in contrast to the situation with block copolymers, which contain, for example, butadiene and W095/04776 PCT~S94/08535 21~7~ ~

styrene in a single continuous phase, wherein deterioration of the butadiene portion of the polymer can lead to degradation of the entire polymer and a very significant loss in strength of a layer or article which is formulated of such a polymer.
Further, since the disperse phase is the minor portion of the composition, in a multilayer article the interlayer adhesion is less likely to be degraded.
Still further, since the oxidative decomposition takes place only within the disperse phase any undesirable byproducts of the decomposition would tend to be retained to a greater extent within the composition.
Furthermore, it is surprising that oxygen will diffuse through the surrounding continuous phase in such a manner that sufficient of the oxygen will contact the particles of the disperse phase so that high oxygen scavenging capability results.

Detailed Description Of The Invention In one embodiment, the compositions of the present invention are effective to scavenge oxygen.
The term "scavenge" means to absorb, deplete, or react with oxygen so that a substantial amount of oxygen does not return to the environment from which it was absorbed, depleted, or reacted. A material which absorbs at least 0.5 cc of oxygen per gram of composition per day is considered to be oxygen-scavenging.
In accordance with the present invention certain graft styrenic copolymers, namely graft copolymers which have a continuous styrenic phase graft polymerized onto a dispersed elastomeric phase, have been shown to have oxygen scavenging and other desirable properties when a transition metal catalyst, WO95/04776 ~ 6 8 ~ ~ ~ PCT~S94/~8535 preferably a cobalt catalyst, is dispersed within the composition .
The styrenic continuous phase may be substantially pure polystyrene, poly(4-methylstyrene), poly(~-methylstyrene) or the like or may be polystyrene, poly(4-methylstyrene), poly(~-methylstyrene) or the like which are copolymerized with one another and/or along with acrylonitrile and/or a Cl-Cg alkyl methacrylate. The preferred alkyl methacrylate is methyl methacrylate.
The disperse elastomeric phase will generally comprise polybutadiene, polyisoprene, a butadiene copolymer, an isoprene copolymer or a mixture of two or more thereof. Rubbers made from ethylene propylene diene monomer (referred to in the trade as EDPM rubbers) and copolymers thereof may likewise comprise the elastomeric phase.
Polybutadiene and butadiene copolymers are the preferred elastomeric phase.
The weight ratio of the disperse phase to the continuous phase is generally less than about 30:70. Indeed, the ratio is not normally as high as 30:70 unless the continuous phase is a copolymer of styrene with acrylonitrile or with the aforementioned alkyl methacrylate. When the continuous phase compri es a styrene homopolymer the weight ratio of the disperse phase to the continuous phase will generally fall within a range from about 2:98 to about 19:81.
A transition-metal salt, as the term is used herein, comprises an element chosen from the first, second and third transition series of the periodic table of the elements. This transition-metal salt is in a form which facilitates or imparts scavenging of oxygen by the composition of this invention. It is W095/04776 PCT~S94/08535 ~
~ ~8~ 6 -generally believed that the transition-metal salt is in an ionic state such that the transition element can readily inter-convert between at least two oxidation states. Suitable transition-metal elements include, but are not limited to, manganese II or III, iron II
or III, cobalt II or III, nickel II or III, copper I
or II, rhodium II, III or IV, and ruthenium. The oxidation state of the transition-metal element when introduced into the composition is not necessarily that of the active form. It is only necessary to have the transition-metal element in its active form at or shortly before the time that the composition is required to scavenge oxygen. The transition-metal element is preferably iron, nickel or copper, more preferably manganese and most preferably cobalt.
Suitable counter-ions for the transition element are organic or inorganic anions. These include, but are not limited to, chloride, acetate, stearate, palmitate, 2-ethylhPx~noate, citrate, glycolate, benzoate, neodecanoate or naphthenate.
Particularly preferable salts include cobalt (II) benzoate, cobalt (II) 2-ethylhexanoate and cobalt (II) neodecanoate. The transition-metal element may also be introduced as an ionomer, in which case a polymeric counter-ion is employed. Such ionomers are well known in the art. See U.S. Pat. No. 3,264,272, which is incorporated by reference in its entirety.
The composition of the present invention contains a sufficient quantity of the transition-metal salt to promote oxygen scavenging in the polymer.
Generally, this requires 200 to 2000 ppm by weight, preferably 500 to 1000 ppm, of transition-metal element. The preferred amount of transition-metal element will typically vary with which transition-metal salt is used.

W095/04776 ~ 7 ~ PCT~S94/08535 Additives may also be included in the composition to impart properties desired for a particular use. Such additives include, but are not necessarily limited to, fillers, pigments, dyestuffs, antioxidants, stabilizers, processing aids, plasticizers, fire retardants, anti-fog agents, etc.
The amount of these additives vary by use and typically comprise less than 10~, and preferably less than 5~, of the total weight of the composition.
The composition of the present invention can be made by blending the metal salt with the required solid continuous phase having the required disperse elastomeric phase dispersed therein. Typically the transition metal catalyst might be in the nature of an organic salt, for example the neodecanoate salt, dissolved in a hydrocarbon liquid such as hexane.
Pellets of the solid continuous phase can be contacted with the solution of the transition metal catalyst, the solvent then stripped away and the resulting coated particles of the solid phase can be extruded at an appropriate temperature, for example in the range from about 100C to about 300C and most suitably in the range from about 200C to about 250C, utilizing a conventional extruder. Alternatively, particularly for commercial production, the cobalt solution can be mixed with the molten polymer in a suitable vented extruder whereby the solvent is stripped off in the vent while operating under vacuum. Typically one can simply buy commercially available pelletized HIPS, ABS
or MBS and then treat it as just described.
Commercial HIPS generally has from about 2~ to about 8~, by weight, of disperse elastomeric phase and from about 98~ to about 92~ of the continuous phase. The amount of the disperse phase can, however, go up to 19~ or even higher. Generally, however, commercial WOg5/04776 ~1 6 8 ~ 7 ~ PCT~S94/08535 HIPS will have from 2~ to 15~ of the disperse phase and from 98~ to 85~ of the continuous phase.
Commercial ABS generally has from 12~ to 30~, by weight, of disperse elastomeric phase and commercial MBS terpolymers generally have from 4~ to 12~, by weight, of styrene-butadiene block copolymers.
The compositions of the present invention are useful in many ways. They can be processed into the form of high surface-area fibers for removing oxygen which contacts the fibers. The compositions can be dispersed as small particles for absorbing oxygen or can be coated onto materials such as metallic foil, polymer film, metalized film or cardboard to provide, in some embodiments and/or scavenging properties. The compositions are al~o useful in making articles such as single or multi-layer rigid-walled plastic containers or in making single or multi-layer flexible films. Some of the compositions of the present invention are easily formed into films using well-known means. These films can be used alone or in combination with other films or materials.
The compositions of the present invention may be further combined with one or more polymeric diluents, such as thprmoplastic polymers which are typically used to form film layers in plastic packaging articles. In the manufacture of certain packaging articles, well-known thermosets can also be used as the polymeric diluent.
Selecting combinations of diluent and the composition of the present invention depends on the properties desired. Polymers which can be used as the diluent include, but are not limited to, polyethylene, low or very low density polyethylene, ultra-low density polyethylene, linear low density polyethylene, ~ W095/04776 ~ 8~7 ~ PCT~S94/08535 g polypropylene, polyvinyl chloride, and ethylene copolymers such as ethylene-vinyl acetate, ethylene-alkyl acrylates or methacrylates, ethylene-acrylic acid or methacrylic acid, and ethylene-acrylic or methacrylic acid ionomers. In rigid packaging applications, polystyrene is used, and in rigid articles such as beverage containers, polyethylene terephthalate (PET), is often usèd. See European 10Application 301,719. Blends of different diluents may also be used. However, as indicated above, the selection of the polymeric diluent largely depends on the article to be manufactured and the end use. Such selection factors are well known in the art.
15If a diluent polymer such as a thermoplastic is employed, it should further be selected according to its compatibility with the composition of the present invention. In some instances, the clarity, cleanliness, effectiveness as an oxygen ~cavenger, barrier properties, mechanical properties and/or texture of the article can be adversely affected by a blend cont~;n;ng a polymer which is incompatible with the composition of the present invention.
The composition in accordance with the present invention, if blended with one or more other polymers so as to provide a layer or article having particularly desired properties, will suitably be pre~ent in an amount of about 1~ to about 99~ and preferably from about 10~ to about 99~ by weight o~
the composition, layer or article. The additional polymer which may be blended with the composition of the present invention to form a layer or article will then comprise from about 99~ to about 1~, more preferably from about 90~ to about 1~ of the overall composition, layer or article.

W095/04776~ PCT~S94/08535 ~

A blend of a composition of the present invention with a compatible polymer can be made by dry blending or by melt-blending the polymers together at 5 a temperature in the range of 100C to 300C, more suitably from 150C to 250C. Alternative methods of blending include the use of a solvent followed by evaporation. When making film layers or articles from oxygen-scavenging compositions, extrusion or coextrusion, solvent casting, injection molding, stretch blow molding, orientation, thermoforming, extrusion coating, coating and curing, lamination or combinations thereof would typically follow the blending.
The amounts of transition-metal salt, grafted copolymer and optional polymeric diluents and additives vary depending on the article to be manufactured and its end use. These amounts also depend on the desired scavenging capacity, the desired scavenging rate, the induction period of the oxygen scavenger, and the particular materials selected.
The transition metal catalyst is present in an appropriate amount to provide the desired rate of consumption of oxygen. Typically the amount of transition metal will fall within a range from about 0.02~ to about 0.2~ of the total weight of the composition, layer or article. The weight ~ refers to the weight of the transition metal portion of any salt in which the transition metal might be incorporated.
Additional additives may be utilized but such will normally not comprise more than 10~ of the composition, layer or article and will more usually be less than 5~ by weight thereof.
The compositions of the present invention have various induction periods before the compositions become effective oxygen scavengers. For example, to ~ W095/04776 2 i ~ 8 ~ ~ ~ PCT~S94/08535 scavenge oxygen using such a composition, the induction period must lapse. However, a composition in accordance with the invention will generally have a very short induction period without exposure to actinic radiation, so that the composition is effective to scavenge oxygen almost immediately.
Thus, the particular composition chosen for a given use will depend in part on the length of time that the composition is to be stored prior to scavenging oxygen.
The composition of the present invention may be used to make either rigid or flexible articles which may comprise a single layer or multiple layers.
Such layers may be films and may be heat shrinkable or oriented. Such films may ultimately be processed into bags, boxes or whatever form is desired. Layers may also be simply sheets which may be placed in a packaging cavity. When the articles are cups, cont~'ners, trays or the like, the layer may be within the cont~; ner' S walls or may indeed itself form the walls of the cont~; ner. Alternatively, the layer may be formed into a liner and placed in a lid or cap of a container. Coating or lamination of the layers onto the articles is also a use therefor.
The additional layers may also include one or more layers which are perme~hle to oxygen. In one preferred embodiment, especially for flexible packaging for food, the layers include, in order starting from the outside of the package to the innermost layer of the package, (i) a structural layer to provide mechanical strength and to act as a moisture barrier (e.g. high-density polyethylene), - (ii) an oxygen barrier layer, (iii) a layer comprising the composition of the present invention, and optionally, (iv) an oxygen perme~hle layer, such as W095/04776 - PCT~S94/0853 ~ ~g~ 12 -ethylene vinyl acetate copolymer. Control of the oxygen barrier property of (ii) allows a means to regulate the scavenging life of the package by limiting the rate of oxygen entry to the scavenging component (iii), and thus limiting the rate of consumption of scavenging capacity. Control of the oxygen p~rme~hility of layer (iv), the "functional layer," allows a means to set an upper limit on the rate of oxygen scavenging for the overall structure independent of the composition of the scavenging component (iii). This can serve the purpose of extending the handling lifetime of the films in the presence of air prior to sealing of the package.
Furthermore, the functional layer can provide a barrier to migration of the components within the composition of the present invention, other additives, or by-products of scavenging into the package interior. Even further, the functional layer may also improve the heat-sealability, clarity and/or resistance to blocking of the multi-layer film.
If the layer is used in a multilayered article other layers may be included which have a limited oxygen tr~n~mission rate. For example, the oxygen transmission rate through an exterior layer to the layer of the present invention may be such that oxygen transmission is kept below a desired amount, for example, below 100 cubic centimeters-mil (one mil in thickness) per square meter per day per atmosphere, at room temperature. Such additional external oxygen barriers might comprise polyacrylonitrile, polyethylene terephthalate, poly(ethylene vinyl alcohol), poly(vinylidene dichloride), polyamides and/or silica. Copolymers of such materials and metal foil layers may also be used.

W095/04776 ~ 7 ~ PCT~S94/08535 It is also possible to utilize the layers of the present invention in conjunction with oxygen pPrm~hle layers. Such layers may serve many purposes including improving heat sealability, clarity, or the like.
Multilayered articles can be prepared in conventional manners by utilizing such techniques as coating, lamination and coextrusion. Other layers such as adhesive layers may be located between such layers, if desired. Adhesive layers might be any of those known in the art such as, for example, maleic anhydride functionalized polyolefins.
To determine the oxygen scavenging capabilities of the invention, the rate of oxygen scavenging can be calculated by measuring the time elapsed before the article depletes a certain amount of oxygen from a sealed container. For instance, a film comprising the scavenging component can be placed in an air-tight, sealed cont~'n~r of a certain oxygen cont~;n;ng atmosphere, e.g., air which typically contains 20.9~ oxygen by volume. Then, over a period of time, samples of the atmosphere inside the container are removed to determine the percentage of oxygen rPm~;n;ng.
When an active oxygen barrier is prepared, the scavenging rate can be as low as 0.1 cc oxygen (2) per gram of the composition of the present invention in the scavenging component per day in air at 25C and at 1 atmosphere pressure. However, the composition of this invention has the capability of rates equal to or greater than 1 cc oxygen per gram per day, thus making it suitable for scavenging oxygen from within a - package, as well as suitable for active oxygen barrier applications. The composition is even capable of more W095/04776 PCT~S94/08535 X ~ 6 - 14 -preferable rates equal to or greater than 5.0 cc 2 per gram per day.
Generally, film layers suitable for use as an active oxygen barrier can have a scavenging rate as low as 1 cc oxygen per square meter per mil of thickness per day when measured in air at 25C and 1 atmosphere pressure. However, a layer of this invention is capable of a scavenging rate greater than 10 cc oxygen per square meter per mil per day, and preferably has an oxygen scavenging rate equal to or greater than about 25 cc oxygen per square meter per mil per day under the same conditions, thus making it suitable for scavenging oxygen from within a package, as well as suitable for active oxygen barrier applications. The scavenging rates of the composition and layers of the present invention will change with changing temperature and atmospheric conditions. The rates at room temperature, ambient humidity, and one atmosphere pressure were measured because they best represent the conditions to which the material of the invention will be exposed in many instances.
In an active oxygen barrier application, it is preferable that the combination of oxygen barriers and any oxygen scavenging activity create an overall oxygen transmission rate of less than about 1.0 cubic centimeter-mil per square meter per day per atmosphere at 25C. It is also preferable that the oxygen scavenging capacity is such that this transmission rate is not exceeded for at least two days. See European Application 301,719. Another definition of acceptable oxygen scavenging is derived from testing actual packages. In actual use, the scavenging rate requirement will largely depend on the internal atmosphere of the package, the contents of the package and the temperature at which it is stored. In actual Og5/04776 ~ 9~ ~ PCT~S94/08535 use, it has been found that the scavenging rate of the oxygen scavenging article or package should be sufficient to establish an internal oxygen level of less than 0.1~ in less than about four weeks.
In a packaging article made according to this invention, the scavenging rate will depend primarily on the amount and nature of the composition of the present invention in the article, and secondarily on the amount and nature of other additives (e.g., diluent polymer, antioxidant, etc.) which are present in the scavenging component, as well as the overall m~nner in which the package is fabricated, e.g., surface area/volume ratio.
The oxygen scavenging capacity of an article comprising the invention can be measured by det~rm;n'ng the amount of oxygen consumed until the article becomes ineffective as a scavenger. The scavenging capacity of the package will depend primarily on the amount and nature of the scavenging moieties present in the article, as discussed above.
In actual use, the oxygen scavenging capacity requirement of the article will largely depend on three parameters of each application:
1. the quantity of oxygen initially present in the package, 2. the rate of oxygen entry into the package in the absence of the scavenging property, and 3. the intended shelf life for the package.

- The scavenging capacity of the composition can be as low as 1 cc oxygen per gram, but is preferably at - least 25 cc oxygen per gram. When such compositions are in a layer, the layer will preferably have an oxygen capacity of at least 250 cc oxygen per square W095/04776 PCT~S94/08535 ~
~ 9 ~ 6 16 -meter per mil thickness and more preferably at least 500 cc oxygen per square meter per mil thickness.
Other factors may also affect oxygen scavenging and should be considered when selecting compositions. These factors include but are not limited to temperature, relative humidity, and the atmospheric environment in the package.
As illustrated in the Examples, some embodiments of the invention go through an "induction period" before they exhibit oxygen scavenging. The induction period i9 the period of time before the scavenging composition exhibits useful scavenging properties.
While the exact manner in which oxygen scavenging is initiated is not known, it is believed, without being held to any specific theory, that one or more of the following occurs during the induction period:
a. substantial depletion of any antioxidant(s), if present, thus allowing oxidation to proceed;

b. activation of the transition metal catalyst through a change in the metal's oxidation state and/or its configuration of ligands, thus increasing its effect on scavenging; or c. a substantial increase in free radical and/or peroxide species present in the system, despite the inhibiting effect of any antioxidant(s) if present or r~m~;n;ng.

WO95/04776 ~ 9~ ~ PCT~S94/08535 In order to use the method of this invention in the most efficient manner, it is preferable to select the oxygen scavenging capabilities, e.g., rate, induction period, and capacity, of the oxygen scavenger to most closely match the requirements of the particular application. The rate of oxygen scavenging can be determined by the method described above.
The invention will be better understood by reference to the following illustrative examples:

Example 1 Preparation of Polymer Films The polymer films which were tested were prepared from pelletized commercially available high impact polymers in the manner described in following.
An organocobalt salt, specifically cobalt neodecanoate, in an amount sufficient to provide 1000 ppm by weight of cobalt in the final composition and film was dissolved in hexane in an amount such that the cobalt neodecanoate concentration in the h~X~ne was approximately 20~ by weight. The solution was dispersed over pellets of the commercially available high impact thermoplastic at room temperature. The solvent was then stripped by use of a vacuum rotary evaporator. The resulting pellets were thereby coated with cobalt neodecanoate and were ready for extrusion into films.
Example 2 - Preparation of Films Monolayer polymer films containing the - cobalt salt were made utilizing a Randcastle Micro-truder. Extrusion conditions are set forth in the following table.

WO 95/04776 T~CT~US94/08535 ~
~I6~76 - 18 Resin Die Temp, F~ Ex~ Exbruder C Temp, C Temp, C ~UPM

Norgl 240 240 235 30 * Noryl is a blend of polyphenylene oxide and HIPS
marketed by General Electric The films thickness was controlled by the feeding rate as well as the RPM of the chill roll.
The materials fed into the extruder were those made as set forth in Example 1. The resulting films were kept under a nitrogen atmosphere until tested for oxygen scavenging activity.

2 0 Example 3 Testing Procedure Films produced in accordance with Examples 1 and 2 were cut into 12 inch lengths at a weight of 4 . 5 i 0.2 grams. The pieces were about 4 inches wide by about .005 inches thick. The specimens were cut into strips about 1 to 2 inches wide, weighed to within 0.1 gram and rolled up and placed in a 2 0 mIJ vial in which they filled about 2 0~ of the space. A Teflon backed septum was placed over the mouth of the vial sealing it off. Two of the vials were held at room temperature, two at 55C and two at 5C.
The headspaces in the vials were sampled periodically, usually at 4 hours, 2 4 hours, 4 8 hours, 3 days, 6 days, 10 days, 14 days and 2 1 days. The sampling was carried out with a 250 microliter gas tight syringe. The syringe was first purged with wo 95,04776 ~ g ~ 6 PCT~S94/08535 . .

helium. With 50 microliters of helium being retained in the syringe, the syringe needle was placed through the septum about one-half inch into a vial. The helium was injected into the vial. The syringe was purged twice with the contents of the vial. A 50 microliters sample was then withdrawn into the syringe barrel. This was immediately injected into a gas chromatograph which was calibrated to automatically measure the oxygen content of the sample. All tests were run in duplicate.

Example 4 Preparation of Antioxidant-free HIPS
Commercial grades of HIPS contain varying amounts of antioxidants to enhance resin stability.
The antioxidants were found to inhibit the oxygen scavenging reaction which involves oxidation reactions. The antioxidants in some of the HIPS
samples were removed by dissolving the HIPS resin in chloroform and re-precipitating by addition of methanol.
As an example, Chevron EC2100 HIPS resin (50 gms) was dissolved in 50 mL of chloroform. The resin was precipitated by the addition of 2000 mL of methanol with constant stirring. The re-precipitated polymer was collected and dried overnight in a vacuum oven at about 50C. Cobalt was dispersed in the recovered resin as described in Example 1.
A similar procedure was carried out with a - Noryl sample which initially contained antioxidant(s).

W095/04776 PCT~S94/08535 ~
~aP~7~

Example 5 Test Results Table 1 reports the results obtained in measuring the percent oxygen in the sample vials as a function of time. The initial oxygen content was 20.9 w~.~ in each instance and the cobalt content was 1000 ppm.

W095/04776 PCT~S94/08535 Table 1 C~;~.. ~;;dl C.. ,~ % O~ygen After Time indicated Name D~ ,liu--4 Hrs lD 2D 5D 7D
Dow Magnum 9010 ABS' 1.5 1.8*2.8*
BASF TerbL~c KR2804 Clear ABS' 2.8 2.1 2.4 Che~ron' HIPS (with EC2100 ' ~` 20.8 20.420.4 20.4 pligh impact) Che~ron' }IIPS (after EC2100 remonng (bigh impact) ' '` 173 1.5 Che~ron' HIPS (no remo~al EC6600 of ' ` 14S 8.8 C.63.6 (medium impact) Che~ron' ~.L~S (no remo~al 2 0 EA6765 of ~ ' 20.2 203 13.45.9 (medium impact) Che~ron' HIPS (no remo~al EA9400 of ' 20.620.5 20.7-20.1 ~low impact) 2 5 GE Noryl 50 50 PPO', ~IIPS, 20.6 18.115S 2.0 no Che~ron Clear P~
EA3000 20.9 20.820.1 20.720.7 (not rubber modified) * Values higher than earlier samples indicate leaks in samples. Only marginally higher values can be within experimental error. All samples at time zero showed 20 . 9~ oxygen. All samples contained 1000 ppm cobalt.
a) This product has 12 to 30 weight percent polybutadiene 40 b) This product has 12 to 30 weight percent polybutadiene plus methyl methacrylate c) These products have generally decreasing amounts of antioxidants and o~ rubber as one goes down Table 1.
d) Polyphenylene oxide.

W095/04776 PCT~S94/0853~
9 7 '~ --The above Examples demonstrate oxygen scavenging capability of compositions in accordance with the present invention and of films made with such compositions. Included in the table is a control run with clear (referred to as "crystal" in the industry) polystyrene (not rubber modified) which showed no oxygen scavenging. Comparison of the two Chevron BC2100 tests ~mon~trates the effect of antioxidants in delaying oxygen scavenging initiation. Comparison of the antioxidant free EC2100 test with the EC6600 and EA6765 tests ~mon~trates the effect of rubber content on oxygen scavenging.

Industrial Applicability The present invention provides oxygen scavenging compositions, films and articles.
Advantageously such compositions, films and articles retain structural integrity even as their oxygen scavenging capability is exhausted. Furthermore, because of the specific nature of the compositions, namely that of a continuous phase which surrounds a sacrificial elastomeric phase, any degradation products which may be formed due to oxidation of the elastomeric phase, for example, aldehydes, alcohols, carboxylic acids, etc., which might impart off flavors or otherwise be unacceptable, tend to be retained within the intact continuous phase.
While the invention has been described in connection with specific e-mbodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary W095/04776 ~ 8~9 ~ ~ PCT~S94/08535 practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.
-

Claims (36)

Claims That which is claimed is:

1. A rubber modified styrenic oxygen scavenging composition, comprising:
a solid continuous styrenic phase lacking oxygen scavenging potential graft polymerized onto a disperse elastomeric phase having oxygen scavenging potential, the weight ratio of disperse phase to continuous phase being less than about 30:70; and a transition metal catalyst comprising a transition metal and a counter-ion, the transition metal being selected from the group consisting of cobalt, nickel, iron and manganese dispersed therein ,the transition metal being present in an amount from about 200 to about 2000 ppm of the composition, said amount being sufficient to provide an oxygen scavenging capability of at least 0.1 cc oxygen per gram of composition per day at 25°C and one atmosphere pressure.

2. A composition as set forth in claim 1, wherein the elastomeric phase comprises polybutadiene, polyisoprene, a butadiene copolymer, an isoprene complymer or a mixture of two or more thereof.

3. A composition as set forth in claim 2, wherein the continuous phase comprises a polymer of styrene, 4-methylstyrene, .alpha.-methylstyrene or a copolymer or mixture of two or more thereof.

4. A composition as set forth in claim 2, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

5. A composition as set forth in claim 4, wherein the alkyl methacrylate comprises methyl methacrylate.

6. A composition as set forth in claim 2, wherein the continuous phase comprises polystyrene and wherein the weight ratio of disperse phase to continuous phase falls within a range from about 2:98 to about 19:81.

7. A composition as set forth in claim 1, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

8. A composition as set forth in claim 7, wherein the alkyl methacrylate comprises methyl methacrylate.

9. A composition as set forth in claim 1, wherein the transition metal catalyst comprises a cobalt salt.

10. A composition as set forth in claim 9, wherein n the elastomeric phase comprises polybutadiene, polysoprene, a butadiene copolymer, an isoprene complymer or a mixture of two or more thereof.

11. A composition as set forth in claim 10, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

12. A composition as set forth in claim 11, wherein the alkyl methacrylate comprises methyl methacrylate.

13. A composition as set forth in claim 10, wherein the continuous phase comprises polystyrene and wherein the weight ratio of disperse phase to continuous phase falls within a range from about 2:98 to about 19:81.

14. A composition as set forth in claim 9, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

15. A composition as set forth in claim 14, wherein the alkyl methacrylate comprises methyl methacrylate.

16. A styrenic layer suitable for oxygen scavenging, comprising:
a solid continuous styrenic phase lacking oxygen scavenging potential graft polymerized onto a disperse elastomeric phase having oxygen scavenging potential, the weight ratio of disperse phase to continuous phase being less than about 30:70; and a transition metal catalyst comprising a transition metal and a counter-ion, the transition metal being selected from the group consisting of cobalt, nickel, iron and manganese dispersed therein ,the transition metal being present in an amount from about 200 to about 2000 ppm of the composition, said amount being sufficient to provide an oxygen scavenging capability of at least 0.1 cc oxygen per gram of composition per day at 25°C and one atmosphere pressure.

17. A layer as set forth in claim 16, wherein the elastomeric phase comprises polybutadiene, polyisoprene, a butadiene copolymer, an isoprene copolymer or a mixture of two or more thereof.

18. A layer as set forth in claim 17, wherein the continuous phase comprises a polymer of styrene, 4-methylstyrene, .alpha.-methylstyrene or a copolymer or mixture of two or more thereof.

19. A layer as set forth in claim 18, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

20. A layer as set forth in claim 19, wherein the alkyl methacrylate comprises methyl methacrylate.

21. A layer as set forth in claim 18, wherein the continuous phase comprises polystyrene and wherein the weight ratio of disperse phase to continuous phase falls within a range from about 2:98 to about 19:81.

22. A layer as set forth in claim 17, wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

23. A layer as set forth in claim 22, wherein the alkyl methacrylate comprises methyl methacrylate.

24. A layer as set forth in claim 17, wherein the transition metal catalyst comprises a cobalt salt.

25. A layer as set forth in claim 24, wherein the elastomeric phase comprises polybutadiene, polyisoprene, a butadiene copolymer, an isoprene copolymer or a mixture of two or more thereof.

26. A layer as set forth in claim 25 wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

27. A layer as set forth in claim 26, wherein the alkyl methacrylate comprises methyl methacrylate.

28. A layer as set forth in claim 25, wherein the continuous phase comprises polystyrene and wherein the weight ratio of disperse phase to continuous phase falls within a range from about 2:98 to about 19:81.

29. A layer as set forth in claim 24 wherein the continuous phase comprises a copolymer of styrene with acrylonitrile or a C1-C8 alkyl methacrylate.

30. A layer as set forth in claim 29, wherein the alkyl methacrylate comprises methyl methacrylate.

31. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 16.

32. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 17.

33. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 21.

34. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 24.

35. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 25.

36. An article for packaging oxygen-sensitive products, the article comprising a layer as set forth in claim 28.