WO1989003412A1

WO1989003412A1 - Vinylidene chloride interpolymer

Info

Publication number: WO1989003412A1
Application number: PCT/US1988/003516
Authority: WO
Inventors: Mark J. Hall; Kun S. Hyun; Steven R. Jenkins; Paul T. Louks; Stephen R. Betso; Duane F. Foye
Original assignee: The Dow Chemical Company
Priority date: 1987-10-09
Filing date: 1988-10-11
Publication date: 1989-04-20
Also published as: EP0382792A4; AU2921489A; AU629195B2; CA1329288C; KR970006904B1; JPH03501866A; KR890701681A; EP0382792A1

Abstract

The present invention is a composition and process for making a vinylidene chloride interpolymer with improved extrudability, wherein the vinylidene chloride interpolymer is blended and a unique combination of additives which comprises an extrusion aid selected from the group consisting of oxidized polyethylene; oxidized polypropylene; or mixtures thereof, in an amount of from about 0.01 to about 0.5 weight percent; a paraffin wax present in an amount of from about 0.005 to about 1 weight percent; ethylene-vinyl acetate is present in an amount of from about 0.5 to about 2 weight percent, and an epoxidized oil or resin present in an amount of from about 0.8 to about 3 weight percent, all percentages being based on the total weight of the mixture. In a preferred embodiment the present invention further comprises blending the above-described mixture with an inorganic base present in an amount of from about 0.01 to about 5 weight percent, based upon the weight percent of the mixture. Exemplary inorganic bases include magnesium hydroxide, tetrasodium pyrophosphate, magnesium oxide, and calcium hydroxy phosphate.

Description

VINYLIDENE CHLORIDE INTERPOLYMER

The present invention relates to a vinylidene chloride interpolymer possessing an improved combination of properties. Specifically, this invention relates to an improved barrier resin comprising a mixture of a vinylidene chloride interpolymer and a unique combination of additives, which resin has improved barrier to atmospheric gases and has, after being subject to a heat history during processing, a reduced level of carbon contamination and good extrudability e:g., color.

Vinylidene chloride interpolymers are well-known in the prior art. In the past, vinylidene chloride interpolymers have been produced by an emulsion or suspension polymerization process. Both the emulsion and suspension polymerization processes produce an aqueous dispersion of polymer particles having a relatively small particle diameter. The polymer particles are recovered from the aqueous dispersion by drying or other means for removing a majority of the aqueous phase. In the past, the practice has been to extrude the vinylidene chloride interpolymer directly from the form in which it is recovered.

In an effort to improve the extrudability of compounds comprising vinylidene chloride interpolymers, such compounds are fabricated mainly from vinylidene chloride interpolymers and an adequate amount of modifiers such as stabilizers, plasticizers, etc. When using no modifiers with the resin, the melt viscosity of the resin is sufficiently high that the load on the extruder screw is too large and the extruded compound is subject to thermal decomposition and discoloration due to the close proximation of the compound's thermal decomposition point and melting point. Moreover, the decomposed interpolymer may generate an undesirable level of carbon contamination in the extrudate, which could have an effect upon the gas barrier of the extrudate.

In order to industrially extrude and process the compound of vinylidene chloride resin by using a conventional screw-type extruder without thermal decomposition and discoloration of the product, a relatively large amount of a stabilizer and plasticizer would inevitably have to be incorporated in the resin. The larger amount of stabilizer and plasticizer. would lower the melting point of the vinylidene chloride resin, with an accompanied reduction of melt viscosity and improvement of thermal stability of the compound, but with a decrease in barrier to atmospheric gases.

In some instances, it is desirable to form the vinylidene chloride interpolymer into pellets prior to final extrusion. With the increased demand for pellets, the processing conditions in which pellets are exposed has become more demanding. Although satisfactorily extrudable for a period, it has been found that attempts to extrude vinylidene chloride interpolymer pellets over long periods on certain extrusion equipment have also proven unsatisfactory due to an undesirable level of carbon contamination in the extrudate, and discoloration of the extrudate.

It is desirable to produce a vinylidene chloride interpolymer which interpolymer, in either powder or pellet form, is capable of being extruded without having an unacceptable level of carbon contamination, as well as having good color. It is to this goal that the present invention is directed.

In the case of packing perishable foods such as processed meats and cooked foods which are highly sensitive to permeated oxygen through the packing material, better barrier resins is demanded. It is to this goal that another aspect of the present invention is directed.

It would also be desirable to produce an article from a vinylidene chloride interpolymer which exhibits a decreased permeability to atmospheric gases.

The present invention concerns a process for improving the extrudability of a thermally sensitive resin comprising the step of blending into a generally homogeneous mixture a vinylidene chloride interpolymer and a unique combination of additives which comprises an extrusion aid selected from the group consisting of oxidized polyethylene; oxidized polypropylene; or mixtures thereof, in an amount of from about 0.01 to about 0.5 weight percent; an ethylene-vinyl acetate copolymer present in an amount of from about 0.5 to about 2 weight percent; a paraffin wax present in an amount of from about 0.005 to about 1 weight percent; and an epoxidized oil or resin present in an amount of from about 0.1 to about 3 weight percent, all weight percentages being based on the total weight of the mixture.

Additionally, the present invention concerns a composition comprising a generally homogeneous mixture of a vinylidene chloride interpolymer and a unique combination of additives which comprises an extrusion aid selected from the group consisting of oxidized polyethylene; oxidized polypropylene; or mixtures thereof, in an amount of from about 0.01 to about 0.5 weight percent; an ethylene-vinyl acetate copolymer present in an amount of from about 0.5 to about 2 weight percent; a paraffin wax present in an amount of from about 0.005 to about 1 weight percent; and an epoxidized oil or resin present in an amount of from about 0.1 to about 3 weight percent, all weight percentages being based on the total weight of the mixture.

Vinylidene chloride Interpolymers suitable for use in the present invention are those vinylidene chloride interpolymers formed from vinylidene chloride and an amount of one or more monoethylenically unsaturated monomers copolymerizable with vinylidene chloride.

The vinylidene chloride interpolymers have selectively polymerized therein vinylidene chloride in an amount of from about 40 to about 98 weight percent, beneficially from about 50 to about 96 weight percent, and desirably from about 60 to about 94 weight percent, based on total weight of the vinylidene chloride interpolymer.

The vinylidene chloride interpolymer is selected to comprise one or more monoethylenically unsaturated monomers copolymerizable with vinylidene chloride. The amount of monoethylenically unsaturated monomer is suitably from about 60 to about 2 weight percent, beneficially from about 50 to about 4 weight percent, and desirably from about 40 to about 6 weight percent, based on total weight of the vinylidene chloride interpolymer.

Monoethylenically unsaturated monomers suitable for use in the present invention include vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and methacrylonitrile. The ethylenically unsaturated monomers are desirably selected from the group consisting of vinyl chloride, alkyl acrylates, and alkyl methacrylates, the alkyl acrylates and alkyl methacrylates having from about 1 to about 8 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates preferably have from about 1 to about 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates are most preferably selected from the group consisting of methylacrylates, ethylacrylates, and methyl methacrylates.

Methods of forming the vinylidene chloride interpolymers suitable for use in the present invention are well-known in the prior art. The vinylidene chloride interpolymer is generally formed through an emulsion or suspension polymerization process. Exemplary of such processes are U.S. Patents 2,558,728; 3,007,903; 3,642,743; and 3,879,359; .and the methods described by R. A. Wessling, in Polyvinylidene Chloride, Gordon and Breach Science Publishers, New York, 1977, Chapter 3; all of which are incorporated herein by reference. Typically, the monomeric materials are emulsified or suspended in an aqueous phase. The aqueous phase contains a polymerization initiator and a surface active agent capable of emulsifying or suspending the monomeric materials in the aqueous phase. The polymerization of the monomeric materials is usually carried out with heating and agitation.

After polymerization is complete, the resulting suspension or emulsion of vinylidene chloride interpolymer has a majority of an aqueous phase. The resultant polymeric material is vacuum stripped. Thereafter, the slurry is cooled down, unloaded and dewatered, and the resin Is collected and further dried.

The inventors have found that a particular combination of additives yields a resin, in either powder or pellet form, which when extruded provides an article having good color characteristics, low carbon contamination, and low permeability to oxygen.

The preferred vinylidene chloride interpolymer formulation comprises the following additives. An extrusion aid of oxidized polyethylene; oxidized polypropylene; or mixtures thereof is employed. Oxidized polyethylene and oxidized polypropylene are well-known in the prior art. Oxidized polyethylene and oxidized polypropylene are generally prepared by forming the ethylene or propylene polymer through methods well-known in the art, and subsequently exposing said polymer to oxygen at an elevated temperature and for a time sufficient to achieve the desired degree of oxidation. Preferably, oxidized polyethylene is employed as an extrusion aid. Suitably, Allied 629A oxidized polyethylene, commercially available from Allied Corp., is the oxidized polyethylene. The oxidized polyethylene is incorporated into the vinylidene chloride interpolymer in the useful range of from about 0.01 to about 0.5 weight percent, preferably in the range of from about 0.02 to about 0.08 weight percent, most preferably in the range of from about 0.03 to about 0.04 weight percent.

An ethylene-vinyl acetate copolymer is employed as an additional extrusion aid; suitably, EVA 3180 ethylene-vinyl acetate copolymer which contains about 28 percent vinyl acetate and is commercially available from E. I. DuPont de Nemours Co. The EVA 3180 or an equivalent ethylene-vinyl acetate copolymer is incorporated into the vinylidene chloride interpolymer in the range of from about 0.5 to about 2 weight percent.

A paraffin wax is employed as an extrusion aid. For example, a paraffin, commercially available from Bohler Industries under the trade designation Bohler 1421, may be incorporated into the vinylidene chloride interpolymer. The paraffin wax is present in an amount in the range of from about 0.005 to about 1 weight percent, most preferably in the range of from about 0.1 to about 0.2 weight percent. Epoxidized oils and resins are suitably employed as plasticizers, stabilizers and lubricants; for example, Vikoflex 7177 epoxidized soybean oil which contains oxirane groups is commercially available from Viking Chemical Co. The Vikoflex 7177 epoxidized soybean oil or an equivalent epoxidized soybean oil is incorporated into the vinylidene chloride interpolymer in the range of from about 0.1 to about 3 weight percent, preferably, from about 0.5 to about 2 weight percent, and most preferably, from about 0.8 to about 1.2 weight percent.

In a preferred embodiment of the present Invention, the additive package comprises an additive comprising at least one inorganic base. Preferred inorganic bases are magnesium hydroxide, tetrasodium pyrophosphate, magnesium oxide, and calcium hydroxy phosphate (commonly referred to tricalcium phosphate), with magnesium hydroxide being most preferred. An exemplary magnesium hydroxide is Kisuma 5B, commercially available from the Kyowa Chemical Co.

When the inorganic base is included in the additive package, it is suitably present in. an amount of from about 0.01 to about 5 weight percent of the total mixture weight. Preferably, the inorganic base is present in an amount of from about 0.1 to about 4 weight percent of the total mixture weight. Most preferably, the inorganic base is present in an amount of from about 0.5 to about 2 weight percent of the total mixture weight.

The inventors have found that a specific combination of additives provides particularly beneficial results. The combination comprises the following: an oxidized polyethylene, such as Allied 629A, in an amount of about 0.03 weight percent; an ethylene-vinyl acetate copolymer, such as EVA 3180, in an amount of about 0.65 weight percent; a paraffin wax, such as Bohler 1421, present in an amount of about 0.12 weight percent; an epoxidized oil, such as Vikoflex 7177, in an amount of about 1.0 weight percent; and magnesium hydroxide, such as Kisuma 5B, in an amount of about 0.65 weight percent.

The exact quantities of the compounds of the additives blended with the vinylidene chloride interpolymer should be selected to provide a resin having an oxygen permeability according to the Dow permeability index of no more than about 0.09 units, the Dow index being calculated as follows: units are in (cc«mil)/(100 in²·day·atm), wherein cc is the cubic centimeters of oxygen, mil is the sample thickness, in² is the surface area of the sample, day represents a 24 hour time period, and atm is atmospheric pressure in atmospheres. Beneficially the oxygen permeability of mixtures according to the present invention will be less than about 0.08 Dow unit. The selection of suitable proportions to satisfy the above criteria is known by skilled artisans.

The additive package may contain additional additives well-known to those skilled in the art. Exemplary of additives which may be incorporated in the package are light stabilizers such as hindered phenol derivatives; pigments such as titanium dioxide and the like. Each of these additives is known and several types of each are commercially available. Blending of the vinylidene chloride and the additive package can be accomplished by using conventional melt processing, as well as dry blending techniques.

For melt blending, two conditions must be met.

First, melt processing must be accomplished at a temperature below that at which decomposition of the vinylidene chloride interpolymer becomes significant. Second, sufficient shear must be generated during melt processing to provide a generally homogenous extrudate within a reasonable mixing time. Conventional melt processing equipment which may be used includes heated two-roll compounding mills, Brabender mixers, Banbury mixers, single screw extruders, twin screw extruders, and the like. Desirable results are obtained when an extruder, either single screw or twin screw, is used for melt blending the vinylidene chloride interpolymer and the additives.

When dry blending, the components should form a visually uniform admixture. Suitable dry blending equipment Includes Hobart mixers, Welex mixers, Henschel High Intensity mixers, and the like.

After being blended into a mixture, the vinylidene chloride interpolymer and additive package is then extruded. In one embodiment, the mixture is physically blended and then melt processed into any suitable final product.

In a preferred embodiment of the present invention, the mixture of vinylidene chloride interpolymer and additive package is pelletized.

Methods of forming the mixture into pellets are well- known to those skilled in the art. Any method capable of forming the mixture into pellets is suitable for use in the present invention. For the purposes of this application, the terms "pellet" or "pellets" refer to particles having a minimum cross-sectional dimension of at least 1/32 inch, beneficially of at least 1/16 inch, and preferably of at least 1/8 inch, said pellets suitably have a maximum cross-sectional dimension of at least 1/2 inch, beneficially of at least 3/8 inch, and preferably of at least 1/4 inch. Exemplary of a method suitable for use in forming the pellets of the mixture are extrusion through a strand die and pelletization by chopping the extruded strand into pellets.

Applicants have discovered that the process and composition according to the present invention improves the extrudability of the vinylidene chloride interpolymer and allows for the satisfactory extrusion of vinylidene chloride interpolymer pellets formed therefrom. The pellets are considered to possess improved extrudability when the mixture of vinylidene chloride interpolymer and additives can be formed into an article which possesses less carbon contamination and less discoloration than from pellets formed from the vinylidene chloride interpolymer alone.

The process of the present invention can be used to form a variety of films or other articles. As is well known in the art, the films and articles are fabricated with conventional coextrusion, e.g, feedblock coextrusion, multimanifold die coextrusion, or combinations of the two; injection molding; extrusion molding; and lamination techniques. Articles formed therefrom include blown and cast, mono and multilayer, films; rigid and foam sheet; tubes; pipes; rods; fibers; and various profiles. Lamination techniques are particularly suited to produce multi-ply sheets. As is known in the art, specific laminatng techniques Include fusion, i.e., whereby self-sustaining lamina are bonded together by applications of heat and pressure; wet combining, i.e., whereby two or more plies are laminated using a tie coat adhesive, which is applied wet, the liquid driven off, and combining by subsequent pressure laminating in one continuous process; or by heat reactivation, i.e., combining a precoated film with another film by heating and reactivating the precoat adhesive so that it becomes receptive to bonding after subsequent pressure laminating.

Exemplary articles include rigid containers used for the preservation of food, drink, medicine and other perishables. Such containers should have good mechanical properties, as well as low gas permeabilities to, for example, oxygen, carbon dioxide, water vapor, odor bodies or flavor bodies, hydrocarbons or agricultural chemicals. Most organic polymers such as the polyolefins, styrene polymers and the like, by themselves, do not possess sufficent resistance to transmission of atmospheric gases and vapors. Consequently, multilayer sheet structures employed in packaging materials have organic polymer skin layers laminated on each side of a vinylidene chloride interpolymer barrier layer, generally with glue layers used to promote adhesion between the barrier layer and dissimilar material layers.

Articles formed from the preferred formulation exhibit decreased oxygen permeabilty. The present invention is illustrated in further detail by the following examples. The examples are for the purposes of illustration only, and are not to be construed as limiting the scope of the present invention. All parts and percentages are by weight unless otherwise specifically noted.

Examples 1-6

Blends of vinylidene chloride are prepared with various additives as set forth in Table 1.

A vinylidene chloride interpolymer is formed through a suspension polymerization process. The vinylidene chloride interpolymer is formed from a monomer mixture comprising about 94 weight percent vinylidene chloride and about 6 weight percent methyl acrylate, based on total monomer mixture weight, the copolymer has a weight average molecular weight of 100,000.

The interpolymer produced as described above is melt blended into a generally homogeneous mixture with the various quantities of the following additives: (a) Vikoflex 7177 epoxidized soybean oil commercially available from Viking Chemical Co; (b) ethylene-vinyl acetate copolymer commercially available from E. I. DuPont de Nemours under the trade designation EVA 3180; (c) a paraffin wax commercially available from Bohler Industries under the trade designation Bohler 1421; and an oxidized polyethylene commercially available under the trade designation as Allied 629A from Allied Corp.

The mixtures described immediately above are, in some examples, melt blended with one of the following inorganic bases: (a) magnesium hydroxide, commercially available from the Kyowa Chemical Co., under the trade designation Kisuma 5B; (b) tetrasodium pyrophospahate commercially available from Monsanto Chemical Co.; magnesium oxide, commercially available from Merck & Co., under the trade designation Maglite S 3331; and (d) calcium hydroxy phpsphate commercially available from Monsanto, under the trade designation polymer grade tricalcium phosphate.

The mixture of vinylidene chloride interpolymer and additives is pelletized. Pelletizing is accomplished using a commercially available strand die and cutter. The pellets have an average length of about 0.130 inch and an average diameter of about 0.145 inch.

The pellets are extruded through a 2 1 /2" extruder having a length to diameter ratio of 21/1. The extruder has the following set temperatures: (a) first zone temperature = 174°C; (b) second zone temperatures 168°C; (b) third zone temperature = 163°C; and (c) die temperatures 165°C.

The molten blend is extruded through a single tape die to form a tape which is tested.

Extrudability Testing

As the resin decomposes, it discolors i.e., becomes brownish. The extrudate tape is also visually inspected to determine its color. Color is qualitatively rated on a scale of 1 to 5 over a continous range of discoloration, wherein 1 represents a creamy color and 5 a rather dark brown. Carbon Contamination Testing

The decomposition of the extruded resin into carbon is determined on the root of the extruder screw heel, on the extruder die, and in the extrudate tape. When evaluating the root of the extruder screw heel and the extruder die, pellets are extruded in a continuous process for a period of about 2 hours. The extent of carbon formation is qualitatively rated on a scale of 1 to 5 over a continous range of carbon buildup, wherein 1 represents generally no visible carbon on the surface and 5 represents a layer of carbon generally completely covering the surface.

Carbon contamination in the extrudate tape is determined by counting specks of carbon over a one minute period every during the two hour extrusion trial. The extent of carbon formation is qualitatively rated on a scale of 1 to 5 over a continous range of carbon buildup, wherein 1 represents less than 20 carbon speck counts per minutes and 5 represents greater than 100 carbon specks counts per minute.

Oxygen Permeability Testing

The samples in examples are measured for oxygen permeability. The oxygen permeability of blends according to the present invention is measured according to a Dow permeability index, the Dow index being calculated as follows: units are in (cc·mil) /(100 in²·day·atm), wherein cc is the cubic centimeters of oxygen, mil is the sample thickness, in² is the surface area of the sample, day represents a 24 hour time period, and atm is atmospheric pressure in atmospheres. Oxygen permeability of the extrudate tapes is measured using an instrument commercially available from Modern Controls, Incorporated , under the trade designation Oxtran 1050. Oxygen permeability measurements are made at 23° Centigrade.

* = not an example of the present invention. ** = not measured.

1 VdMA = All examples are carried out with a vinylidene chloride copolymer of 94 weight percent vinylidene chloride and 6 weight percent methyl acrylate, having a weight average molecular weight of 100,000.

2 OP = oxidized polyethylene, commercially available from Allied Corp., under the trade designation Allied 629A. Weight percent is based upon the total mixture weight. 3 Wax = paraffin wax, commercially available from Bohler Industries, under the trade designation Bohler 1421. Weight percent is based upon the total mixture weight.

4 ESO = epoxidized soybean oil, commercially available from Viking Chemical Company, under the trade designation Vikoflex 7177. Weight percent is based upon the total mixture weight.

5 EVA = ethylene-vinyl acetate, commercially available from E.I. DuPont de Nemours Co., under the trade designation EVA 3180. Weight percent is based upon the total mixture weight. 6 Inorganic Bases: (a) Mg(OH)₂ = magnesium hydroxide, commercially available from the Kyowa Chemical Co., under the trade designation Kisuma 5B; (b) TSPP = tetrasodium pyrophospahate commercially available from Monsanto Chemical Co.; (c) TCP = commercially available from Monsanto, under the trade designation polymer grade tricalcium phosphate. Weight percent is based upon the total mixture weight.

7 Color = according to visual inspection.

8 Carbon contamination = according to visual inspection of (a) the extruder screw, (b) the extruder die, and (3) the extrudate. Carbon formation on the screw and die is rated on a scale of 1 to 5 over a continous range of carbon buildup, wherein 1 represents generally no visible carbon on the surface and 5 a represents a layer of carbon generally completely covering the surface. Carbon contamination in the extrudate tape is qualitatively rated on a scale of 1 to 5 over a continous range of carbon buildup, wherein 1 represents less than 20 carbon speck counts per minutes and 5 represents greater than 100 carbon specks counts per minute.

O₂ perm. = oxygen permeabilty measured in cubic centimeters of oxygen times mils of thickness divided by the product of (a) 100, (b) area in square inches, (c) 24 hours and (d) the atmospheric pressure in atmospheres.

As can be seen from the above table, the compositions of the present invention possess good color characteristics, low carbon contamination, and low permeability to oxygen.

Although the invention has been described in considerable detail, with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

Claims

CLAIMS :

1. A process for improving the extrudability of a thermally sensitive resin which comprises the step of blending into a generally homogeneous mixture a vinylidene chloride interpolymer and a combination of additives which comprises an extrusion aid selected from the group consisting of oxidized polyethylene; oxidized polypropylene; or mixtures thereof, in an amount of from about 0.01 to about 0.5 weight percent; an ethylene-vinyl acetate copolymer present in an amount of from about 0.5 to about 2 weight percent; a paraffin wax present in an amount of from about 0.005 to about 1 weight percent; and an epoxidized oil or resin present in an amount of from about 0.1 to about 3 weight percent, all weight percentages being based on the total weight of the mixture.

2. The process of Claim 1 wherein the vinylidene chloride interpolymer is formed from a monomer mixture comprising vinylidene chloride in an amount of from about 40 to about 98 percent, based on total weight of monomer mixture, and at least one monoethylenically unsaturated monomer copolymerizable therewith in an amount of from about 60 to about 2 percent based on the total weight of the monomer mixture.

3. The process of Claim 2 wherein the vinylidene chloride interpolymer is formed from a monomer mixture comprising vinylidene chloride in an amount of from about 50 to about 96 percent, based on total weight of monomer mixture, and at least one monoethylenically unsaturated monomer copolymerizable therewith in an amount of from about 50 to about 4 percent based on the total weight of the monomer mixture.

4. The process of Claim 3 wherein the vinylidene chloride interpolymer is formed from a monomer mixture comprising vinylidene chloride in an amount of from about 60 to about 94 percent, based on total weight of monomer mixture, and at least one monoethylenically unsaturated monomer copolymerizable therewith in an amount of from about 40 to about 6 percent based on the total weight of the monomer mixture.

5. The process of Claim 1 wherein the monomer or monomers copolymerizable with the vinylidene chloride are selected from the group consisting of vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and methacrylonitrile.

6. The process of Claim 5 wherein the monoethylenically unsaturated monomer copolymerizable with the vinylidene chloride is an alkyl acrylate, the alkyl acrylate having from about 1 to about 8 carbon atoms per alkyl group.

7. The process of Claim 6 wherein the alkyl acrylate is selected from the group consisting of methyl acrylate and ethylacrylate.

8. The process of Claim 1 wherein the monomer copolymerizable with the vinylidene chloride is vinyl chloride.

9. The process of Claim 1 wherein the extrusion aid is oxidized polyethylene.

10. The process of Claim 9, wherein the oxidized polyethylene is present in an amount of from about 0.02 to about 0.08 weight percent.

11. The process of Claim 10, wherein the oxidized polyethylene is present in an amount of from about 0.03 to about 0.04 weight percent.

12. The process of Claim 1, wherein the EVA is present in an amount of from about 0.01 to about 2 weight percent, based on the total weight of the mixture.

13. The process of Claim 12, wherein the EVA is present in an amount of from about 0.5 to about 1 weight percent, based on the total weight of the mixture.

14. The process of Claim 1, wherein the paraffin wax is present in an amount of from about 0.1 to about 0.2 weight percent.

15. The process of Claim 1, wherein the epoxidized oils or resins are present in an amount of from about 0.5 to about 2 weight percent, based on the total weight of the mixture.

16. The process of Claim 15, wherein the epoxidized oils and resins are present in an amount of from about 0.8 to about 1.2 weight percent, based on the total weight of the mixture.

17. The process of Claim 1, further comprising blending into the resin an inorganic base present in an amount of from about 0.01 to about 5 weight percent, based on the total weight of the mixture.

18. The process of Claim 17, wherein the inorganic base is present in an amount of from about 0.1 to about 4 weight percent, based on the total weight of the mixture.

19. The process of Claim 18, wherein the inorganic base is present in an amount of from about 0.5 to about 2 weight percent, based on the total weight of the mixture.

20. The process of Claim 17, wherein the inorganic base is selected from the group consisting of magnesium hydroxide, tetrasodium pyrophosphate, magnesium oxide, and calcium hydroxy phosphate.

21. The process of Claim 20, wherein the inorganic base is magnesium hydroxide.

22. A process for improving the extrudability of a thermally sensitive resin which comprises the step of blending into a generally homogeneous mixture a vinylidene chloride interpolymer and a combination of additives which comprises an oxidized polyethylene in an amount of about 0.03 weight percent; an ethylenevinyl acetate copolymer in an amount of about 0.65 weight percent; a paraffin wax present in an amount of about 0.12 weight percent; an epoxidized oil in an amount of about 1.0 weight percent; and magnesium hydroxide in an amount of about 0.65 weight percent.

23. A composition comprising a generally homogenuous mixture of a vinylidene chloride interpolymer and a combination of additives which comprises an extrusion aid selected from the group consisting of oxidized polyethylene; oxidized polypropylene; or mixtures thereof, in an amount of from about 0.01 to about 0.5 weight percent; an ethylene-vinyl acetate copolymer present in an amount of from about 0.5 to about 2 weight percent; a paraffin wax present in an amount of from about 0.005 to about 1 weight percent; and an epoxidized oil or resin present in an amount of from about 0.1 to about 3 weight percent, all weight percentages being based on the total weight of the mixture.

24. A composition comprising a generally homogenuous mixture of a vinylidene chloride interpolymer and a combination of additives which comprises an oxidized polyethylene in an amount of about 0.03 weight percent; an ethylene-vinyl acetate copolymer in an amount of about 0.65 weight percent; a paraffin wax present in an amount of about 0.12 weight percent; an epoxidized oil in an amount of about 1.0 weight percent; and magnesium hydroxide in an amount of about 0.65 weight percent.

25. A pellet formed from the composition of Claim 23.

26. An article for the storage of foods which are sensitive to atmospheric gases, said article being formed from the composition of Claim 23.