ALLOYS OF VINYLIDENE CHLORIDE INTERPOLYMERS AND OLEFIN POLYMERS

Abstract: A compatibilized blend of at least three polymers is provided. One polymer is a vinylidene chloride interpolymer, such as a copolymer of vinylidene chloride and vinyl chloride. A second polymer is an olefin polymer, such as polyethylene. A third polymer is a compatibilizing polymer such as an ethylene/alkyl acrylate or an ethylene/alkyl methacrylate copolymer. The compatibilized blend, after melt processing, has mechanical properties which are better than those predicted by a straight line volume fraction relationship of the vinylidene chloride interpolymer and the olefin polymer. Impact energy is one mechanical properties which is greater for the compatibilized blend than for the two-component blend of the vinylidene chloride interpolymer and the olefin polymer.

Description: The present invention relates to compatibilized blends of at least two normally incompatible polymers. More particularly, the present invention relates to compatibilized and melt processible blends of a vinylidene chloride interpolymer and an olefin polymer. Vinylidene chloride interpolymers are well known for their excellent barrier to mass transport of atmospheric gases and moisture vapor. These interpolymers have limited areas of application, however, because of poor melt processing characteristics. In particular, vinylidene chloride interpolymers in a melt plasticized state have poor heat stability and low melt strength. These same interpolymers, when fabricated, tend to be brittle and to have low impact strength. Olefin polymers, such as high density poly­ ethylene, generally have better melt processing charac­ teristics than vinylidene chloride interpolymers. That is, they are melt processible over a wider range of temperatures. The olefin polymers are readily fabricated into articles. They also provide rigidity without brittle­ ness when so fabricated. Notwithstanding such processing advantages, the olefin polymers are excessively permeable to atmospheric gases. Efforts to combine the best features of vinyl­ idene chloride interpolymers and olefin polymers in a polymer-polymer blend have been unsuccessful. Lack of success has been determined by comparing physical proper­ ties of the polymer-polymer blend with those of the blend components in a straight line volume fraction relationship (hereinafter referred to as "the rule of mixtures"). The physical properties of the polymer-polymer blends have generally been poorer than those predicted by following the rule of mixtures. Various explanations have been advanced to explain the aforementioned lack of success. One such explanation was that mixing procedures used to disperse one polymer in a second polymer were inadequate. It is now believed that the lack of success may be attributed to inherent physical incompatibility of vinylidene chloride interpolymers with olefin polymers. The lack of success may also be attributed to inadequate adhesion between vinylidene chloride interpolymers and olefin polymers. The present invention concerns a compatibilized blend of polymers comprising: (a) a vinylidene chloride interpolymer, the interpolymer having polymerized therein vinylidene chloride in an amount of from 40 to 98 percent by weight of interpolymer and at least one monoethylenically unsaturated monomer copolymerizable therewith in an amount of from 60 to 2 percent by weight of interpolymer; (b) an olefin polymer and (c) a compatibilizing amount of a compatibilizing polymer, said compatibilizing polymer being selected from the group consisting of (i) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight per­ cent of at least one oxygen containing species copolymer­ izable therewith; and (ii) olefin polymers having halogen chemically affixed thereto in an amount of from 24 to 44 percent by weight of polymer. Vinylidene chloride interpolymers suitable for use with the present invention are those which have polymerized therein an amount of vinylidene chloride monomer and an amount of monoethylenically unsaturated monomer copolymerizable therewith. The vinylidene chloride interpolymers are desirably melt processible. The amount of polymerized vinylidene chloride monomer is suitably from 40 to 98 percent by weight of interpolymer, beneficially from 50 to 96 percent by weight of interpolymer, and desirably from 60 to 94 percent by weight of interpolymer. The vinylidene chloride interpolymer comprises one or more monoethylenically unsaturated monomers which are copolymerizable with the vinylidene chloride monomer. The amount of monoethylenically unsaturated monomer is suitably from 60 to 2 percent by weight of interpolymer, beneficially from 50 to 4 percent by weight of interpolymer, and desirably from 40 to 6 percent by weight of interpolymer. Monoethylenically unsaturated monomers suitable for copolymerization with vinylidene chloride include vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylo­ nitrile and methacrylonitrile. The unsaturated monomers are desirably selected from the group consisting of vinyl chloride, alkyl acrylates and alkyl methacylates, the alkyl acrylates and alkyl methacrylates having from 1 to 8 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates benefically have from 1 to 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates are preferably selected from the group consisting of methyl acrylate, ethyl acrylate and methyl methacrylate. Olefin polymers suitable for use in the present invention are those olefin homopolymers and interpolymers which can be compatibilized with the vinylidene chloride interpolymers through the use of the compatibilizing polymers of the present invention. Beneficially, the olefin polymers are selected from the group consisting of (1) low density polyethylene, (2) medium density polyethylene, (3) high density polyethy­ lene, (4) polypropylene, (5) poly 1-butene, (6) generally linear interpolymers of ethylene having polymerized therein from 2 to 98 weight percent of ethylene and from 98 to 2 weight percent of at least one 1-alkene, said alkene having from 3 to 18 carbon atoms, (7) copolymers of two or more alpha-olefins, having from 3 to 18 carbon atoms per molecule, (8) rubbery ethylene-propylene-diene monomer interpolymers, and mixtures thereof. Low density polyethylenes which are useful in the present invention have a density of from 0.917 to 0.929 grams per cubic centimeter. The low density poly­ ethylenes also have a melt index of from 0.1 to 20 grams per 10 minutes as measured in accordance with American Society for Testing and Materials (ASTM) Test D-1238. Medium density polyethylenes which are useful in the present invention have a density of from 0.930 to 0.939 grams per cubic centimeter. The medium density polyethylene also have a melt index of from 0.08 to 100 grams per 10 minutes (ASTM Test D-1238). High density polyethylenes which are useful in the present invention have a density of from 0.940 to 0.965 grams per cubic centimeter. The high density polyethylenes also have a melt index of from 0.08 to 100 grams per 10 minutes (ASTM Test D-1238). For purposes of the present invention, useful polypropylenes are the normally solid isotactic poly­ propylenes. The isotactic polypropylenes have an insolu­ bility in hot heptane of greater than 90 percent. These polypropylenes also have a melt flow rate of from 0.3 to 35 grams per 10 minutes at a temperature of 230°C with a load of 2160 grams. The polypropylene beneficially has a melt flow rate of from 0.3 to 12 grams per 10 minutes. Any poly 1-butene is believed to be suitable for use in the percent invention so long as it meets the other requirements for the olefin polymer. For purposes of the present invention, the linear interpolymers of ethylene have polymerized therein an amount of ethylene and an amount of at least one 1-alkene. The amount of ethylene is suitably from 2 to 98 percent, by weight of the interpolymer. The amount of 1-alkene is suitably from 98 to 2 percent, by weight of interpolymer. The 1-alkene is selected from the group of 1-alkenes which have from 3 to 18 carbon atoms per molecule. The 1-alkene is beneficially selected from the group of 1-alkenes which have from 3 to 10 carbon atoms per molecule. The 1-alkenes having from 3 to 10 carbon atoms per molecule include propene, butene, hexene and octene. A beneficial ethylene/1-alkene interpolymer is an ethylene/propylene copolymer. The ethylene/propylene copolymer has polymerized therein ethylene in an amount of up to 50 percent by weight of copolymer and propylene in an amount of up to 98 percent by weight of copolymer. The ethylene/propylene copolymer suitably has a melt index of greater than 0.1 grams per 10 minutes (ASTM D-1238). Desirable results are obtained when the ethylene/­ propylene copolymer has a melt index of from 0.4 to 4.0 grams per 10 minutes (ASTM D-1238). Because polyethylene and polypropylene are both useful materials for purposes of the present invention, it is believed that any ratio of ethylene to propylene in an ethylene/propylene copolymer would also be useful. Linear copolymers of ethylene and another olefin are described in U.S. Patent No. 4,076,698. Alpha-olefin interpolymers suitable for use with the present invention have polymerized therein two or more monomers selected from the group of alpha-olefin monomers having from 3 to 18 carbon atoms per molecule. The alpha-olefin monomers are represented by the general formula R-CH=CH₂wherein R is a alkyl group of 1 to 16 carbon atoms. Examples of suitable alpha-olefin monomers include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1- decene, 4-methyl-1-­ pentene, 4-methyl-1-hexene and 4,4-dimethyl-1-pentene. Rubbery ethylene-propylene-diene monomer inter­ polymers useful for purposes of the present invention have polymerized therein (a) ethylene in an amount of from 20 to 90 percent by weight of interpolymer, (b) propylene in an amount of from 10 to 80 percent by weight of interpolymer and (c) a nonconjugated diene in an amount of from 2 to 25 percent by weight of interpolymer. Processes for preparing these interpolymers are disclosed in U.S. Patent Numbers 3,957,919; 3,657,395; and 4,156,767. Examples of suitable nonconjugated dienes include dicyclopentadiene, methyltetrahydroindene, methylene norbornene, ethylidene norbornene, and 1,4-hexadiene. Beneficial results are obtained when the nonconjugated diene is either ethylidene norbornene or dicyclopentadiene. Desirably, the nonconjugated diene is dicyclopentadiene and has an iodine value of at least 20. The rubbery ethylene-propylene-diene monomer interpolymers hereinabove specified suitably have a Mooney viscosity (ML 1+4 at 125° Centigrade) of from 35 to 75 beneficially from 45 to 65 and a specific gravity of from 0.86 to 0.88. The compatibilizing polymer is selected from the group consisting of (i) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one oxygen containing species copolymerizable therewith; and (ii) olefin polymers having halogen chemically affixed thereto in an amount of from 24 to 44 percent by weight of polymer. The compatibilizing polymer must be capable of compatibilizing a blend of the vinylidene chloride interpolymer and the olefin polymer. For the purposes of this application the blend of vinylidene chloride interpolymer and olefin polymer is considered compat­ ibilized when the blend has mechanical properties which are generally better than those suggested by the rule of mixtures. Specifically, the impact strength of the blend should be better than suggested by the rule of mixtures in order to say the blend is compatibilized. The oxygen permeability of compatibilized blends according to the present invention will be less than 1.76 cubic centimeters of oxygen times centimeters of sample thickness divided by the product of (a) area in square centimeters (b) one second, and (c) barometric pressure in centimeters of mercury. Beneficially the compatibilizing polymer will meet two additional criteria. First, it will be melt processible with the vinylidene chloride interpolymer. Second, it will have a melt index or melt viscosity which is sufficiently close to that of the olefin polymer to allow adequate mixing to occur within a reasonable processing time. In determining whether or not the compatibilizing polymer is melt processible with the vinylidene chloride interpolymer, two factors are of prime importance. The two factors, which are interrelated, are processing time and processing temperature. In melt processing polymers, it is generally recognized that as processing temperatures increase, processing times must decrease in order to avoid undesirable results such as polymer degradation. This is especially true for vinylidene chloride interpolymers. Vinylidene chloride interpolymers may be melt processed at temperatures of up to 200°C provided processing time is less than one minute. Temperatures greater than 200°C may be employed provided the processing time is sufficiently short and provided the vinylidene chloride polymer is not in contact with iron or black plate steel. For example, vinylidene chloride polymers are melt process­ ible at temperatures as high as 230°C at processing times of less than ten seconds when the vinylidene chloride polymer forms an inner layer in a coextruded structure. Melt index or melt viscosity differences affect both ease of mixing and mixing times. If the melt index of the compatibilizing polymer is nearly equal to that of the olefin polymer, mixing is generally easy and is accomplished in a relatively short period of time. All other conditions being equal, as melt index disparity increases, mixing times also increase whereas ease of mixing decreases. The first class of compatibilizing polymer, (i), are ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one oxygen containing species copolymerizable therewith. The ethylene interpolymer is suitably selected from the group consisting of (a) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one ethylenically unsaturated carboxylic acid monomer copolymerizable therewith, the interpolymer being esterified after preparation thereof; (b) copolymers of ethylene and at least one alkyl acrylate; (c) copolymers of ethylene and at least one alkyl methacrylate; (d) copolymers of ethylene and carbon monoxide; (e) interpolymers of ethylene carbon monoxide and 1) an ester of an ethylenically unsaturated carboxylic acid or 2) vinyl acetate; (f) copolymers of ethylene and vinyl acetate; (g) ethyl oxazoline modified copolymers of ethylene and acrylic acid; (h) interpolymers of ethylene, carbon monoxide and acrylic acid; (i) interpolymers of ethylene, carbon monoxide and methacrylic acid; and (j) interpolymers of ethylene, carbon monoxide and vinyl acetate. Beneficially, the ethylene interpolymer is either (a), (b), (c), (d), (e), or (f). Desirable results are obtained when the eth­ ylene interpolymer has polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one ethylenically unsaturated carboxylic acid monomer copolymerizable therewith, the interpolymer being esterified after preparation thereof. Suitable ethylenically unsaturated carboxylic acid monomers copolymerizable with ethylene include acrylic acid, metharylic acid, and the like. Preferably, the unsaturated carboxylic acid monomer is acrylic acid. Desirable results are also obtained when the ethylene interpolymer is selected from the group consisting of ethylene/alkyl acrylate and ethylene/alkyl methacrylate copolymers wherein the alkyl group contains from 1 to 8 preferably, from 1 to 4 carbon atoms; and ethyl oxazoline modified copolymers of ethylene and acrylic acid. Ethylene/acrylic acid copolymers are suitably prepared as outlined in U.S. Patent Numbers 3,520,861 and 4,351,931. Methods of esterifying such copolymers are well-known in the prior art. Preferred ethylene/acrylic acid copolymers, prior to esterification, have polymerized therein acrylic acid in an amount of from 6 to 30 percent by weight of the copolymer. The ethylene/acrylic acid copolymers also have a melt index, measured in accordance with American Society for Testing and Materials (ASTM) Test D-1238 of from 0.01 to 100 decigrams per minute. Copolymers of ethylene with either alkyl acryl­ ates or alkyl methacrylates are readily prepared using conventional technology. One process for preparing such copolymers is disclosed in U.S. Patent Number 2,497,323. Copolymers of ethylene and carbon monoxide are also readily prepared using conventional technology. Processes for preparing ethylene/carbon monoxide copoly­ mers are disclosed in U.S. Patent Numbers 4,024,325; 4,024,326; and 4,143,096. Interpolymers of ethylene, carbon monoxide and (1) an ester of an ethylenically unsaturated car­ boxylic acid or (2) vinyl acetate are prepared using the process suitable for preparation of copolymers of ethylene and carbon monoxide. Ethyl oxazoline modified copolymers of ethylene and acrylic acid are suitably prepared by contacting ethylene/acrylic acid copolymers with an excess of ethyl oxazoline at a temperature of from 110 to 120°C for a period of from 2 to 24 hours. Methods of producing copolymers of ethylene and vinyl acetate; interpolymers of ethylene, carbon monoxide, and acrylic acid; interpolymers of ethylene carbon monoxide and methacrylic acid; and interpolymers of ethylene, carbon monoxide, and vinyl acetate are well-known in the art and need not be detailed here. The second class of compatibilizing polymers are olefin polymers having halogen chemically affixed thereto in an amount of from 24 to 44 percent by weight of polymer. Olefin polymers having halogen chemically affixed thereto suitably have chlorine as the halogen. The term "olefin polymer" is meant to include olefin homopolymers and olefin interpolymers. Suitable olefin polymer are formed from one or more olefin monomers having from 2 to 18 carbon atoms. Beneficial compatibilizing olefin polymers include olefin homopolymers formed from a mono-olefin monomer having from 2 to 4 carbon atoms. Exemplary of such olefin homopolymers are polyethylene, polypropylene and polybutylene. Preferred olefin homopolymers are the polyethylene resins. The olefin homopolymers have halogen chemically affixed thereto. Beneficial compatibilizing olefin polymers also include olefin interpolymers formed from at least one mono-olefin monomer having from 2 to 4 carbon atoms and up to 98 weight percent of at least one 1-alkene monomer having from 4 to 18 carbon atoms. A preferred group of olefin interpolymers contain at least 90 mole percent of ethylene and 10 mole percent of at least one 1-alkene having from 4 to 18 carbon atoms. Exemplary of suitable 1-alkenes are 1-butene, octene, 1,7-octadiene and the like. Another preferred olefin interpolymer comprises two mono-olefin monomers having from 2 to 4 carbon atoms. Exemplary of such interpolymers are interpolymers of ethylene and propylene. The olefin interpolymers have halogen chemically affixed thereto. The compatibilizing olefin polymers having chlorine as the halogen chemically affixed thereto suit­ ably have a chemically combined chlorine content of from 24 to 44 percent by weight of polymer. The resins also have a heat of fusion of from 2 to 13 calories per gram and a melt viscosity of from 8,000 to 20,000 poise. Melt viscosity is determined using a capillary rheometer at a temperature of 190°C, a shear rate of 145 reciprocal seconds and a capillary size of .127 by 5.08 centimeters. The compatibilizing olefin polymers, prior to chlorination, suitably have a weight average molecular weight of less than 1,000,000 grams per mole, beneficially between 20,000 and 300,000 grams per mole. The compatibilizing olefin polymers are suitably prepared under the influence of catalyst systems comprising admixtures of strong reducing agents, such as triethyl aluminum, and compounds of groups IV-B, V-B and VI-b metals of the Periodic System, such as titanium tetra­ -chloride, and the like. Desirable compatibilizing olefin polymers are the chlorinated polyethylenes. Chlorinated polyethylene resins desirable for use with the present invention are prepared by suspension chlorination as disclosed in U.S. Patent No. 3,454,544. The present invention is not restricted to chlorinated polyethylene resins prepared by suspension or slurry chlorination processes. Solution chlorination and bulk, or fluidized bed, chlorination procedures may also be used provided the interpolymers produced thereby meet the aforementioned requirements with regard to chlorine content, heat of fusion and melt viscosity. The compatibilized blends of the present invention are readily prepared by using conventional melt processing techniques provided two conditions are 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 visually homogeneous blend 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 processing the compatibilized blends of the present invention. One factor in determining satisfactory mixing times is the melt index of the components of the compat­ ibilized blend. If component melt indexes are nearly equal, a relatively short mixing time yields satisfactory results. If there is a disparity among component melt indexes, a longer mixing time is necessary. A second factor in determining satisfactory mixing times is mixing shear rate. All other parameters being equal, a relatively low shear rate is needed when the components have a relatively low viscosity or a high melt index. Conversely, a relatively high shear rate is needed when the components have a relatively high viscosity or a low melt index. By way of example, only, a blend comprising a high melt index low density polyethylene requires a much shorter mixing time than a blend comprising a low melt index high density polyethylene. A third factor in determining satisfactory mixing times is temperature. As noted hereinbefore, an upper limit on temperature is the temperature at which decomposition of the vinylidene chloride interpolymer becomes significant. A lower limit on temperature is dictated by the polymer blend component which has the greatest melting point. If the temperature does not exceed the melting point of that polymer blend component, a visually homogeneous melt will be difficult, if not impossible, to obtain. A fourth factor in determining satisfactory mixing times is mixing efficiency of the melt processing equipment. Certain melt processing equipment mixes more efficiently than other melt processing equipment. Selection of melt processing equipment which will produce a visually homogeneous melt within a reasonable processing time is, however, not difficult and can be accomplished without undue experimentation. A fifth factor in determining satisfactory mixing times is polymer feed form. The polymeric components of the compatible blends are generally avail­ able either in finely divided powder form or in pellet form. Either form is suitable for purposes of the present invention. The pellet form, if available, is preferred over the powder form. A variety of additives may be added to the compatibilized blends of the present invention. Additive type and amounts thereof will depend upon several factors. One factor is the intended use of the blends. A second factor is tolerance of the blends for the additives. That is, how much additive can be added before physical properties of the blends are adversely affected to an unacceptable level. Other factors are apparent to those skilled in the art of polymer formulation and compounding. Additives which may be incorporated into the compatibilized blends of the present invention are selected from the group consisting of plasiticizers, heat stabilizers, light stabilizers, pigments, processing aids, lubricants and the like. Each of these additives is known and several types of each are commercially available. The compatibilized blends can be used to form a variety of cast, blown, extruded, molded, injection molded, or calendered articles. Physical properties of the blends depend largely upon two factors. One factor is selection of the polymer components of the compati­ bilized blends. A second factor is the ratio of polymer components to each other within said compatibilized blends. The present invention is illustrated in further detail by the following examples and comparative examples. The examples and comparative examples are for purposes of illustration only and are not to be construed as limiting the scope of the present invention. All parts and percent­ ages are by weight unless otherwise specifically noted. Blend Preparation Three polymeric components (a) a vinylidene chloride interpolymer, (b) an olefin polymer and (c) a compatibilizing polymer, each of which was in pellet form, were dry blended to form a visually uniform admixture. Blending was accomplished by placing the components in a bag and then shaking them. More sophisticated equipment could have been used but was not necessary. The admixture was then fed to an extruder via a rate controlled feeding mechanism. Each of the polymeric components used in the examples and comparative examples is described hereinafter at Table I. Melt blending of the admixture was accomplished in two stages using one of two extruders. One extruder, hereinafter designated as "Extruder A", was a 1.90 centi­ meter single screw Brabender extruder. Extruder A had a length to diameter ratio of 20:1. It had the following set temperatures: (a) hopper temperature = 160°C; (b) melt zone temperature = 165°C; and (c) die temperature = 170°C. A second extruder, hereinafter designated as "Extruder B", was a 5.08 centimeter single screw Hartig extruder. Extruder B had a length to diameter ratio of 12:1. It had the following set temperatures: (a) hopper temperature = 165°C; (b) melt zone temperature = 170°C; and (c) die temperature = 175°C. In a first stage, the admixture was added to the extruder hopper and thereafter converted to a molten blend. The molten blend, or preliminary blend, was extruded through a single strand die, passed through a water bath, and then pelletized. The strand die had an internal diameter of 0.32 centimeter. Pelletizing was accomplished using a Model 304, 15.24 centimeter strand cutter commercially available from Conair Incorporated. In a second stage, which was used to promote complete mixing, a tape die was substituted for the strand die. The pelletized preliminary blend was added to the extruder hopper and thereafter converted to a molten blend. This molten blend was extruded through the tape die to form a tape having a width of 5.08 centimeters and a thickness of 0.42 centimeters. The tape was cut directly from the tape die using a pair of scissors into strips having a length of from 20 to 26 centimeters. The strips were laid on a clean smooth surface to cool. The surface used was chrome plated steel. Other surfaces known to those skilled in the art could also have been used. Compression Molding to Prepare Impact Test Specimens A stainless steel template measuring 16.5 centimeters by 16.5 centimers by 0.16 centimeters was used to prepare a sample sheet from which impact test samples were cut. A "sandwich" was created by (a) placing the template on a sheet of polyester film having a thick­ ness of 0.009 centimeter, (b) placing 65 grams of the strips side-by-side in the template, and (c) covering the template and strips with a second sheet of polyester film. The sandwich was placed into a compression molding press. It was first processed for a period of one minute at a temperature of 175-180°C and at a force of about 909 kilograms. The sandwich was then processed for an additional period of two minutes at the same temperature but at a force of 15,909 kilograms. After the additional period, the sandwich was allowed to cool to a temperature of about 25°C before being removed from the press. The sample sheet was then separated from the sandwich. Instrumented Puncture Impact test specimens were prepared by using a band saw to cut the sample sheet into square pieces measuring 5.08 centimeters on a side. The test specimens were then annealed, conditioned and subjected to impact testing as hereinafter detailed. Test Specimen Annealing The impact test specimens were annealed by being subjected to a set temperature of about 60°C for a period of 16 hours in a convention air oven. The oven was commercially available from Precision Scientific, Incorpor­ ated under the trade designation Model 625. Impact Test Specimen Conditioning After being annealed, the impact test specimens were further conditioned prior to impact testing. Further conditioning was accomplished in a controlled humidity room having a relative humidity of 50±5 percent and a temperature of 23±2°C for a period of 24 hours. Instrumented Puncture Impact Testing Impact testing was done with a High Rate Impact Tester commercially available from Rheometrics, Incorporated under the traqde designation RIT-8000. Specimens were tested at a temperature of 23±2°C with a ram speed of 20,320 centimeters per minute. Compression Molding to Prepare Oxygen Permeability Test Specimens Permeability test specimens having a thickness of from 0.013 to 0.018 centimeters were prepared by using a modification of the procedure set forth hereinabove with respect to preparation of impact test specimens. The procedure was modified by eliminating the stainless steel template so that the strips were placed between the two sheets of polyester film to form the sandwich. After compression molding, permeability test specimens were cut from the sheet using a pair of scissors. The test specimens were annealed using the procedure set forth hereinabove with respect to the impact test specimens. Oxygen Permeability Testing Oxygen permeability of the compression molded samples was measured using an instrument commercially available from Modern Controls, Incorporated, under the trade designation Oxtran 1050. Oxygen permeability measurements were made at 40°C, 50°C and 60°C and then extrapolated to 25°C. Temperature dependence of permeability is known to be represented by an equation of the form P = P o raised to the exponent of (-E a /RT) where P = permeability P o = a constant E a = activation energy of permation R = gas constant T = absolute temperature From the equation, it is apparent that permeability increases rapidly with increasing temperature. Accordingly, an Arrhenius plot at several elevated temperatures (log P vs 1/T, wherein P and T are as identified hereinabove) can be used to extrapolate to permeabilities at lower temperatures. Extrapolation is valid so long as there is no transitions over the range of temperatures selected for taking measurements. Those skilled in the art recognize that oxygen permeability values obtained from compression molded samples may vary from the values obtained by testing samples prepared in a different manner. Compression molded sample data is, however, a valid basis for com­ parison. Polymers used in preparing polymer blends of the examples and comparative examples are set forth hereinafter in Table I. Various combinations of the polymer components set forth in Table I were prepared as hereinbefore specified. Impact test and permeability test specimens were prepared, also as hereinbefore specified, and subjected to physical property testing. Results of the physical property tests, where available, are set forth hereinafter together with identity and amount of polymer components of each of the respective combinations. Examples of the present invention are represented by Arabic numerals. Comparative Examples, which are not representative of the present invention, are represented by alphabetic characters. The data presented in Table IIA discloses several points of interest. First, a simple two-component blend (Comparative Example A) has very low impact energy and poor barrier to oxygen. Second, addition of a compatibilizing amount of a third polymer component to the two-component blend, as in Example 1, produces dramatic improvements in both impact energy and barrier to oxygen. Third, by varying the ratio of olefin polymer to vinylidene chloride interpolymer, as in Example 2, barrier to oxygen can be varied without significant effect upon impact energy of the three component blend. Similar results are obtained with other three-component blends using other vinylidene chloride interpolymer resins and compatibilizing polymer resins, both of which are described hereinabove. Similar results are also obtained with other olefin polymers. Variations in each of the components are shown in Tables IIB through IIK which follow. The data presented in Table IIB shows that results similar to those presented in Table IIA were obtained when the olefin polymer was high density polyethylene rather than low density polyethylene. The data presented in Table IIC shows that results similar to those presented in Table IIA were obtained with a variety of olefin polymers, all of which are described hereinabove. The data presented in Tabel IID shows that a variety of compatibilizing polymers were suitable for use in preparing the compatibilized blends of the present invention. The data presented in Tabel IIE shows that another group of compatibilizing polymers, the ethyloxazoline-modified ethylene/acrylic acid polymers, also produced satisfactory results provided two conditions are met. First, the polymer, prior to modification must have a polymerized acrylic acid content which is greater than 3 percent but less than 20 percent by weight of polymer. Second, a ratio of vinylidene chloride polymer to low density polyethylene of greater than 1:1 is necessary. The data presented in Tabel IIF amply demonstrates that unmodified ethylene/acrylic acid copolymers were not effective compatibilizers (Comparative Examples F and G). By way of contrast, the same copolymers, when modified by ethyloxazoline, were effective compatiblizers (Examples 20 and 21, Table IIE). The data presented in Table II-G demonstrates that ethylene/carbon monoxide copolymers are effective compatibilizers provided the copolymer has polymerized therein a sufficient amount of carbon monoxide. It is clear that a carbon monoxide content of one percent is inadequate and that a carbon monoxide content of ten percent provides satisfactory results. Similar results are obtained with other ethylene/carbon monoxide copolymers having a sufficient polymerized carbon monoxide content. The data presented in Table II-H shows that several interrelated factors must be considered in selecting an ethylene/vinyl acetate copolymer as a compatibilizing polymer. One factor is ratio of vinylidene chloride interpolymer to olefin polymer. A second factor is melt index of the ethylene/vinyl acetate polymer in comparison with that of the olefin polymer. A third factor is the polymerized vinyl acetate content of the ethylene/vinyl acetate polymer. A comparison of Example 24 with Example 25 indicates that as the ratio of vinylidene chloride inter­ polymer to olefin polymer decreases, impact energy of the compatibilized blend increases. In Example 24, the ratio is 1:1 and the impact energy is 23.0 Joules whereas in Example 25, the ratio is 3:1 and the impact energy is 10.8 Joules. A comparison of Comparative Example L with Example 26 indicates that impact energy measurements are higher when the melt index of the ethylene/vinyl acetate polymer is lower than that of the olefin polymer than when it is higher. In Comparative Example L, the melt index was 2.5 grams per 10 minutes. In Example 26, the melt index was 0.65 grams per 10 minutes. That of the olefin polymer was 2.0 grams per 10 minutes. A comparison of Example 25 with Comparative Example K, indicates that impact energy measurements increase with increasing polymerized vinyl acetate content in the ethylene/vinyl acetate polymer. In Example 25, the ethylene vinyl acetate copolymer had a polymerized vinyl acetate content of 18 percent by weight of polymer. In Comparative Example K, the ethylene vinyl acetate copolymer had a polymerized vinyl acetate content of 9.5 percent by weight of polymer. The data presented in Table II-I shows that a hydrolyzed ethylene/vinyl acetate copolymer (Example 27) and an ethylene/vinyl acetate terpolymer (Example 28) were also effective as compatibilizers. The data presented in Table II-J demonstrates that a variety of halogenated olefin polymers were also effective as compatibilizers. The data presented in Table II-K shows that a variety of vinylidene chloride copolymers produced compatible blends of the present invention. The three-­ component blend of Comparative Example M produced unsatisfactory results. It is believed that the blend of Comparative Example M was unsatisfactory because the melt viscosity of the vinylidene chloride copolymer was too low in comparison to that of the ethylene/methyl acrylate copolymer and the low density polyethylene. As noted hereinabove, achieving a visually homogeneous melt becomes more difficult as disparity of melt viscosity increases. A review of the physical property data set forth in Table IIA-IIJ brings out several points. First, a binary blend of an olefin polymer and a vinylidene chloride interpolymer has low impact energy and high permeability to oxygen (Comparative Examples A, B and C). A ternary blend of an olefin polymer, a vinylidene chloride interpolymer and a compatibilizing amount of at least one other polymer selected from the polymers hereinbefore identified has much higher impact energy (Examples 1 and 2). In addition, the ternary blend has, depending upon relative proportions of olefin polymer and vinylidene chloride interpolymer either low permeability to oxygen (Example 1) or high permeability to oxygen (Example 2). Second, a variety of olefin polymers may be used in conjunction with a vinylidene chloride interpolymer and a compatibilizing amount of at least one other polymer. See , Examples 3, 5-7, 9, 11. Third, a variety of polymers are suitable for use as compatibilizing polymers. See , Examples 1, and 12-32. Similar results are obtained with other compatibilized blends prepared as hereinbefore specified using polymer components, also as hereinbefore specified.

Claims: 1. A compatibilized blend of polymers comprising: (a) a vinylidene chloride interpolymer, the interpolymer having polymerized therein vinylidene chloride in an amount of from 40 to 98 percent by weight of interpolymer and at least one monoethylenically unsaturated monomer copolymerizable therewith in an amount of from 60 to 2 percent by weight of interpolymer; (b) an olefin polymer and (c) a compatibilizing amount of a compatibilizing polymer, said compatibilizing polymer being selected from the group consisting of (i) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one oxygen containing species copolymerizable therewith; and (ii) olefin polymers having halogen chemically affixed thereto in an amount of from 24 to 44 percent by weight of polymer. 2. The compatibilized blend of Claim 1 wherein the olefin polymers of (b) are selected from the group consisting of (1) low density polyethylene; (2) medium density polyethylene, (3) high density polyethylene, (4) polypropylene, (5) poly 1-butene, (6) generally linear interpolymers of ethylene having polymerized therein from 2 to 98 weight percent of ethylene and from 98 to 2 weight percent of at least one 1-alkene, said alkene having from 3 to 18 carbon atoms, (7) interpolymers of two or more alpha-olefins having from 3 to 18 carbon atoms per molecule, and (8) rubbery ethylene-propylenediene monomer interpolymers, and mixtures thereof. 3. The compatibilized blend of Claim 1 having a ratio of (a) to (b) of from 9:1 to 1:9. 4. The compatibilized blend of Claim 1 having a ratio of (a) to (b) of from about 1:1 to about 1:9. 5. The compatibilized blend of Claim 1 wherein the monomer copolymerizable with vinylidene chloride is selected from the group consisting of vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile and meth­ acrylonitrile. 6. The compatibilized blend of Claim 1 wherein the vinylidene chloride interpolymer has polymerized therein vinylidene chloride in an amount of from 89 to 95 percent by weight of interpolymer and methyl acrylate in an amount of from 11 to 5 percent by weight of interpolymer. 7. The compatibilized blend of Claim 2 wherein the olefin polymer of (b) is low density polyethylene, the low density polethyelne having a density of from 0.917 to 0.929 grams per cubic centimeter and a melt index, measured in accordance with American Society for Testing and Materials Test D-1238, of from 0.1 to 20 grams per 10 minutes. 8. The compatibilized blend of Claim 2 wherein the olefin polymer of (b) is medium density polyethylene, the medium density polyethylene having a density of from 0.930 to 0.939 grams per cubic centimeter and a melt index, measured in accordance with American Society for Testing and Materials Test D-1238, of from 0.08 to 100 grams per 10 minutes. 9. The compatibilized blend of Claim 2 wherein the olefin polymer of (b) is high density polyethylene, the high density polyethylene having a density of from 0.940 to 0.965 grams per cubic centimeter and a melt index, measured in accordance with American Society for Testing and Materials Test D-1238, of from 0.08 to 100 grams per 10 minutes. 10. The compatibilized blend of Claim 2 wherein the olefin polymer of (b) is a linear copolymer of ethylene and at least one 1-alkene, the copolymer having polymerized therein ethylene in an amount of from 80 to 98 percent by weight of copolymer and one or more 1-alkenes in a total amount of from 20 to 2 percent by weight of copolymer. 11. The compatibilized blend of Claim 2 wherein the olefin polymer of (b) is a copolymer of ethylene and at least one monomer copolymerizable therewith, the monomer being selected from the group consisting of alpha-olefin monomers having from 3 to 18 carbon atoms per molecule. 12. The compatibilized blend of Claim 1 wherein the compatiblizing polymer is selected from the group consisting of (a) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one ethylenically unsaturated carboxylic acid monomer copolymerizable therewith, the interpolymer being esterified after preparation thereof; (b) copolymers of ethylene and at least one alkyl acrylate, the alkyl acrylate having from 1 to 8 carbon atoms per alkyl group; (c) copolymers of ethylene and at least one alkyl methacrylate, the alkyl methacrylate having from 1 to 8 carbon atoms per alkyl group; (d) copolymers of ethylene and carbon monoxide; (e) interpolymers of ethylene, carbon monoxide and (1) an ester of an ethylenically unsaturated carboxylic acid or (2) vinyl acetate; (f) copolymers of ethylene and vinyl acetate; and (g) ethyl oxazoline modified copolymers of ethylene and acrylic acid. 13. The compatibilized blend of Claim 1 wherein the compatibilizing polymer is selected from the group consisting of (a) copolymers of ethylene and at least one alkyl acrylate, the alkyl acrylate having from 1 to 4 carbon atoms per alkyl group; (b) copolymers of ethylene and at least one alkyl methacrylate, the alkyl methacrylate having from 1 to 4 carbon atoms per alkyl groups; and (c) 2-ethyl-2-oxazoline modified copolymers of ethylene and acrylic acid. 14. The compatibilized blend of Claim 1 wherein the compatibilizing polymer is a copolymer of ethylene and methyl acrylate, the copolymer having polymerized therein ethylene in an amount of from 95 to 80 percent by weight of copolymer and methyl acrylate in an amount of from 5 to 20 percent by weight of copolymer. 15. The compatibilized blend of Claim 1 wherein said compatible blend has an impact energy which is greater than the impact energy of a blend of the vinylidene chloride interpolymer and the olefin polymer. 16. The compatiblized blend of Claim 1 wherein the compatibilizing amount is from 2 to 35 parts per hundred parts of (a) plus (b). 17. A compatibilized blend of Claim 1 wherein said olefin polymer is a copolymer of ethylene and at least one alpha-olefin. 18. A compatibilized blend of polymers according to Claim 1 having an oxygen permeability rate less than 1.76 measured as cubic centimeters of oxygen times centi­ meters of sample thickness divided by the product of (a) area in square centimeters (b) one second and (c) baro­ metric pressure in of mercury centimeters. 19. A process for the preparation of a compati­ bilized blend of polymers comprising: (a) a vinylidene chloride interpolymer, the interpolymer having polymerized therein vinylidene chloride in an amount of from 40 to 98 percent by weight of interpolymer and at least one mono­ ethylenically unsaturated monomer copolymerizable therewith in an amount of from 60 to 2 percent by weight of interpolymer; (b) an olefin polymer and (c) a compatibilizing amount of a compatibilizing polymer, said compatibilizing polymer being selected from the group consisting of (i) ethylene interpolymers having polymerized therein from 97 to 60 weight percent of ethylene and from 3 to 40 weight percent of at least one oxygen containing species copolymerizable therewith; characterized in that the admixture of said three polymeric components (a), (b) and (c) is melt blended at the temperature below that at which decomposition of the vinylidene chloride interpolymer becomes significant and under shear sufficient to provide a visually homogeneous blend within reasonable mixing time. 20. A process for the preparation of a compati­ bilized blend of polymers according to Claim 19, character­ ized in that the melt blending of the admixture of said three polymeric components is accomplished in two stages. 21. A process of Claim 20, characterized in that the melt blending is accomplished in an extruder. 22. A process of Claim 21 characterized in that the three zones of the extruder are kept at the following temperatures: (a) hoffer zone at a temperature from 160-165°C, (b) melt zone at a temperature from 165-170°C, and (c) die zone at a temperature from 170-175°C.

Inventors: BURGERT, BILL E., RANCK, DAN E.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1985
Main classification: C08L27
IPC codes: C08L23, C08L21, C08L7, C08L101, C08L27, C08L1, C08L33