the invention is a closure comprised of a composition that is capable of preventing oxygen from entering a container once the closure is attached thereto . preferably , the closure is a rigid , unitary structure that does not require additional , separate layers in order to block oxygen . in the food and beverage industry , because of their ease of use and low cost , it is often desirable to use plastic closures or caps to close a container . however , typical plastic closures allow oxygen to migrate through them and enter the closed container . additionally , oxygen leakage can occur at the interface between the closure and the container . this oxygen can then react with the food or beverage and result in a product of lesser quality . to resolve this problem , some have added additional layers of material called liners into the cap top to prevent the oxygen from passing into the closed container . however , these additional layers can add substantial cost . the current invention relates to a closure having a top and depending sidewalls . preferably , the inner portion of the side walls has threads or other features which allow it to connect with and close off the container . the closure may have a flange or other suitable feature that is disposed on the closure such that it interfaces with a rim of the container to close off the container more resolutely . the top and side walls can have a thickness that is between 0 . 020 and 0 . 075 inches . most preferably , the thickness of the top is between 0 . 040 and 0 . 060 inches while the thickness of the sidewalls is between 0 . 040 and 0 . 060 inches . the closure preferably is made out of polypropylene (“ pp ”) or high - density polyethylene (“ hdpe ”) which is combined with an oxygen scavenger that is capable of reacting with oxygen and deactivating it by conversion to an inactive form of oxygen . more preferably , the closure further contains a catalyst that increases the reaction rate of the oxygen scavenger with oxygen . the production of closures made of only pp and hdpe are well known in the art . relevant to the current invention are the high temperatures that are associated with production of such closures . in a typical closure extrusion , temperatures between 325 and 500 degrees fahrenheit can be utilized . therefore , for the current invention , it is necessary to use an oxygen scavenger that is thermally stable up to that temperature . scavengers could include ascorbates or isoascorbates , ascorbic acid , sodium sulfite , polyalkylamines , or ferrous oxide . in a preferred embodiment , the closure is composed of pp ( or hdpe ) and an effective amount of sodium sulfite ( na 2 so 3 ). the sodium sulfite reacts with oxygen to form sodium sulfate . when manufactured , a substantially anhydrous composition of sodium sulfite is preferably employed . further , it is preferable to maintain the closure in a dry environment prior to placing it on the closure . most preferably , the sodium sulfite is relatively uniformly disbursed throughout the closure so that all portions of the closure are effective barriers to ambient oxygen . it may be desirable to increase the reaction rate of an oxygen scavenger with oxygen that occurs in a typical packaging or storage environment . to effect such an increase , the present invention provides for the use of one or more catalysts for that reaction . as mentioned earlier , the closure may be subjected to substantial temperatures . therefore , the catalyst , like the oxygen scavenger , must be stable up to a temperature of 500 degrees fahrenheit . further , it is preferable to have the catalyst evenly distributed throughout the closure in an effective amount . the catalyst can be a transition metal that can be supplied from a salt or an amine . examples include iron and copper salts . most preferably , the catalyst is slightly acidic . in one embodiment , two or more co - catalysts may be employed . in one embodiment , the acidifying component can be calcined sodium acid pyrophosphate , which is added in an amount to obtain a desired ph . the invention disclosed herein thus allows for a pp or hdpe closure with an oxygen scavenger and at least one catalyst integral with the closure . the closure is thus an integral composition that can act as an oxygen scavenger in and of itself , without the need for additional layers to provide that functionality . preferably , the closure is a homogeneous composition with effective amounts of the oxygen scavenger and catalyst disbursed relatively uniformly throughout the closure . the ratio of oxygen scavenger / catalyst / pp or hdpe , expressed in weight , is preferably about 1 - 140 parts scavenger and about 0 . 01 to 5 parts catalyst to about 100 parts polymer . more preferably , the closure is composed of about 5 - 70 parts scavenger and about 0 . 5 to 3 parts catalyst to about 100 parts polymer . most preferably , the closure is composed of about 20 - 40 parts scavenger and about 1 - 2 parts catalyst to about 100 parts polymer . to construct the closure of the invention described herein , it is preferable to use a powdered form of the oxygen scavenger and catalyst . particle sizes of 100 mesh or smaller are preferred . more preferably , the oxygen scavenger and catalyst are processed into pellets for addition into the machinery used to injection mold the closure . most preferably , the oxygen scavenger and catalyst are processed into individual pellets which are combined with the pp or hdpe just before the injection molding process . this helps to preserve the capability of the oxygen scavenger to react with oxygen once it is integrated into the closure . such a composition can be purchased from alpha - gary corporation of leicestershire , england under the tradename alpha seal , agppoxmb , which is an acronym for alpha gary polypropylene oxygen scavenger master batch . in the present disclosure , the words “ a ” or “ an ” are to be taken to include both the singular and the plural . conversely , any reference to plural items shall , where appropriate , include the singular . from the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention . it is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred . the disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims .