Patent Publication Number: US-2013231389-A1

Title: Delivery Of Preservatives By Food Packaging

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/686,869 filed Apr. 12, 2012. This application is also a Continuation-In-Part Application to U.S. Ser. No. 12/658,200 filed Feb. 4, 2010, which is a Continuation of Application U.S. Ser. No. 12/589,155 filed Oct. 19, 2009, now abandoned. This application is also a Continuation-In-Part Application to U.S. Ser. No. 13/065,972. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed towards plastic packaging comprising diffusible preservatives. 
     BACKGROUND OF THE INVENTION 
     Food quality and safety (longevity) are major concerns in the food industry. Contamination of foods with bacteria normally occurs at the surface due to post processing handling. For decontamination, antimicrobial sprays or dips are often applied. A drawback of external sprays and dips is that the active preservatives can be neutralized on contact or diffuse rapidly from the surface into the food mass. On the other hand a gradual diffusion of the preservative from packaging materials allow the preservatives continuously to come into contact with the food for an extended period of time to kill bacteria, before being absorbed by the food or deactivated by materials released by the foods. The diffusion method extends the time during which the food is in contact with preservatives, and maintains an effective level of the preservative around the food. The shelf life of the food is thereby maximized. 
     Incorporating preservatives into thermoplastics is an emerging technology that could have a significant impact on shelf life extension and food safety. 
     According to  The Wiley Encyclopedia of Packaging Technology,  the packaging materials may act as a carrier for antimicrobial agents to perform their active role to control microorganisms. Some of the antimicrobial agents may be coated or directly incorporated into the packaging materials and subsequently migrate to the food system. The antimicrobial action is achieved by release of the antimicrobial agents from the packaging material. The released antimicrobial agents can control the growth of microorganisms by many different mechanisms, for example, such as by altering cell membrane properties or by inhibiting essential metabolic pathways of the microorganisms. 
     Most spoilage incidents occur primarily at the food surface by the contamination of microorganisms. A concentration of antimicrobial agent above its minimum inhibitory concentration (“MIC”) is required to inhibit microbial growth and above its minimum bactericidal concentration (“MBC”) to kill the microbes. Without the antimicrobial packaging concept, an excess amount of preservatives such as benzoates and sorbates should be included in foods to control the spoilage microorganisms. Thus, releasing antimicrobial additives to the food surface conveniently increases the additives concentration in the food surface above the MBC or MIC while maintaining a preservative concentration inside the food at sufficiently low level. Considering that the use of preservatives for shelf-life extension has been strictly controlled by food safety authorities, antimicrobial packaging is advantageous in reducing potential risks of consuming excess amount of food preservatives. 
     An additional advantage of antimicrobial packaging is its sustainable antimicrobial activity. The antimicrobial agents initially included in food ingredients might be inactivated by interacting with other food components. For example, bacteriocins and enzymatic antimicrobial agents applied to foods or onto the food surfaces may interact with proteolytic enzymes in food and may cause the loss of antimicrobial activities. Alternatively, antimicriobial agents can be adsorbed onto food surfaces and thereby lose their activity in the moisture surrounding the foods. On the contrary, incorporation of the above substances in packaging films prevents loss of antimicrobial activity while they remain in the packaging film allowing continuing antimicrobial activity due to their continuous controlled release from the packaging film. Hence antimicrobial activity is maintained over longer periods. 
     Another advantage of antimicrobial packaging is the maintenance of sterility of the packaging material in the event that it is inadvertently contaminated with pathogenic bacteria prior to use. 
     In most cases the incorporated antimicrobials dissolve in the moisture surrounding the food. They then migrate to the food surface in dissolved form. The migrating solutes are nonvolatile materials such as organic acids and their salts, enzymes, bacteriocins, fungicides and some natural extracts. The antimicrobials act on bacteria that may be dispersed in the moisture around the packaged foods and on the bacteria, which are on the surface of the food. The surface of the food includes the crevices and cracks within the bulk of the food where bacteria can migrate and grow. 
     Diffusion is the mechanism by which nonvolatile solute is transferred through the film matrix and it also controls the release rate from the film. The migration kinetics of nonvolatile solute follows Fick&#39;s second law of diffusion, where the diffusion coefficient depends on the type of film materials, microstructural voids in film matrix, and environmental temperature. The migration of the antimicrobial agents from the film to the food surface can be by direct contact with the food surface, through a very thin layer of moisture surrounding the food or through copious liquids, which are generally aqueous, in which the food is immersed. Contact between the film matrix, the food surface, the surface moisture or bulk liquid surrounding the food throughout the shelf-life of the food is needed for antimicrobial migration and, consequently, for effective preservative action. For this, the food should be a continuous matrix without any factors that interfere with the diffusional migration. This food matrix can be a liquid solution, a semisolid paste, or a smooth solid matrix without significant pores, holes, heterogeneous particles or a porous solid with pores, holes or crevices. The antimicrobial agents on the food surface will move through the food in solution by diffusion. Diffusion can be through bulk liquids in which the food is immersed or through the thin layer of surface moisture on the outside or within the food. For example, raw meat, not suspended in an aqueous solution, has an outer exposed surface surrounding the meat. This surface will have a layer of surface moisture, which might be very thin, e.g. 5 water molecules thick, or it might be quite thick e.g. 10 microns thick. Within the meat there are numerous pathways, for example between the meat fibers, which are covered with surface moisture. Diffusion will thus be both on the outer surface of the meat or on the surfaces of the fibers within the meat. The solubility and diffusion coefficients of the agent in the food are very important factors that govern the rate of agent removal in the food surface. The antimicrobial concentration on the food surfaces needs to be maintained above the MIC and preferably above the MBC for effectiveness in controlling the microbial growth. 
     By having functional preservative ingredients either in the bulk or on the surface of the packaging film, the microbial population can be controlled. Many classes of preservatives have been evaluated in film structures both synthetic and natural. Also, various kinds of packaging materials such as polyolefins and edible polymers have been tested. Currently, polyethylene is the most cost effective packaging film. In particular LDPE (low density polyethylene) and LLDPE (linear low density polyethylene) are preferred packaging materials. While natural or modified natural polymers like chitosan or water swellable polymers are also mentioned in the literature to be useful, they are not practical from a cost-effective point of view. 
     When preservatives are incorporated into or on the surface of packaging, they can diffuse through the packaging film and migrate into the liquid surrounding the food and onto the food surface. If the packaging is the sole source of preservative, a good contact between the preservative film and food surface is essential. A number of both synthetic and natural antimicrobials have been investigated as a choice of preservatives with limited success, because none have been shown to be effective against a broad range of pathogens likely encountered in packaged foods. Examples of known preservatives are nisin, grapefruit seed extract, and triclosan. Triclosan is undesirable as a food additive since its safety is unknown. Also, triclosan could be deactivated by fatty acids found in meats, perhaps due to micelle formation or absorption into the fat. 
     Further, preservative films are not commonly employed, because logistics involved in the manufacture of preservative films also affect the release of the preservatives and the performance of the films. When a preservative is added to bulk plastic, it must not deteriorate during film fabrication, distribution, and storage. The preservative is preferably heat stable during extrusion at temperatures that may exceed 200° C., and stable to the shear forces and pressure involved in the process conditions. Also, the preservatives used must not adversely affect or discolor the package polymeric materials. 
     When delivering preservatives from package films, an important factor is the ability of the preservative to diffuse through the packaging material to the film surface. In many cases it is desirable for the preservative to dissolve in the liquid surrounding the food substances. Compounds such as hydrochloride salts of N α -lauroyl arginine ethyl ester (“LAE”) and N α -cocoyl arginine ethyl ester (“CAE”) are safe and effective as preservatives for foods and food products. These salts are easily metabolized in the human body, and they rapidly hydrolyze into their constituent amino acid, fatty acid and alcohol components, all of which are benign and are further broken down eventually into carbon dioxide, water and ammonium salts. 
     U.S. 2010/0056628 to Stockel, et al. teaches a controlled-release composition comprising N α —(C 1 -C 22 ) acyl di-basic amino acid (C 1 -C 22 ) alkyl ester cationic molecules, and polymeric or monomeric anion. 
     U.S. Ser. No. 13/065,972 to Stockel, et al. teaches a method of preserving food using LAE and an anionic counterion in a food product packaging. None of these references addresses the issue that LAE is only slowly soluble in water, or recognizes that LAE might have difficulties in diffusing through plastic films or diffuse therefrom. 
     REFERENCES  
     
         
         Buonocore, G. G., Sinigaglia, M., Corbo, M. R., Bevilacqua, A., La Notte, E., Del Nobile, M. A. J. Food Prot., 67, (2004), pp 1190-1194 
         Cagri et al., J. Food Science 66, (2001), pp 865-870 
         Cagri et al., J., Food Science 67, Number 4, (2004), pp 833-848(16) 
         Chen et al., J. Food Preservation 20, (1996), pp 379-3890 
         Perez et al., Advances in Agricultural and Food Biotechnology (2006), p. 193-216 
       
    
     SUMMARY OF THE INVENTION 
     A composition comprising a polymeric material and a preservative combination comprising 1) a preservative component selected from the salts of N α —(C 1 -C 18 ) acyl di-basic amino acid (C 1 -C 18 ) alkyl ester; 2) a second component selected from a food-safe solvent, food-safe nonionic surfactant and mixtures thereof; and optionally 3) a third component consisting of an acyl mono-glyceride, wherein the preservative is diffusible from the polymeric material. The present invention is further directed towards an article comprising the polymeric material and the preservative combination, wherein the article is in the form of food packaging. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description read in conjunction with the accompanying drawings. 
         FIG. 1  illustrates ATR spectrums of two polymeric films, each respectively contains 4% poly alpha olefin (“PAO”), with or without 1% LAE. A full spectrum of 100% LAE (“Neat LAE”) is also shown. An arrow indicates spectrum peaks specific for LAE. 
         FIG. 2  illustrates ATR spectrums of two polymeric films, each respectively contains 4% mineral oil, with or without 1% LAE. An arrow indicates spectrum peaks specific for LAE. 
         FIG. 3  illustrates ATR spectrums of two polymeric films, each respectively contains 2% glycerol, with or without 1% LAE. An arrow indicates spectrum peaks specific for LAE. 
         FIG. 4  illustrates an ATR spectrum of a polymeric film that contains 2% 1,3-propanediol and 1% LAE, and an ATR spectrum of a polymeric film that contains 2% glycerol and 1% LAE. An arrow indicates spectrum peaks specific for LAE. 
         FIG. 5  illustrates ATR spectrums of four polymeric films, each contains a different amount of 1,3-propanediol, with or without 1% LAE. An arrow indicates spectrum peaks specific for LAE. 
         FIG. 6  illustrates ATR spectrums of four polymeric films, each respectively contains 1% LAE with an enhancement additive. An arrow indicates spectrum peaks specific for LAE. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a composition comprising a polymeric material and a preservative combination comprising 1) a preservative component selected from the salts of N α —(C 1 -C 18 ) acyl di-basic amino acid (C 1 -C 18 ) alkyl ester; 2) a second component selected from a food-safe solvent, food-safe nonionic surfactant and mixtures thereof; and optionally 3) a third component consisting of an acyl mono-glyceride, wherein the preservative is diffusible from the plastic film. The invention is also directed towards an article produced from the polymeric material and the preservative combination, wherein the article is in the form of packaging products. 
     The Preservative Component 
     The preservative component of this invention comprises a salt of N α —(C 1 -C 18 ) acyl di-basic amino acid (C 1 -C 18 ) alkyl ester. The dibasic amino acid portion of the salt is selected from the group consisting of arginine, lysine, histidine, ornithine and tryptophan. The formation of a mono-acyl amide combined with esterification of the carboxylic acid from the dibasic amino acid results in a compound with one active cationic center. The preferred dibasic amino acids are arginine, ornithine and lysine with arginine being the most preferred. 
     While the chain length of the acyl group can be between 1 and 18 carbons in length, it is preferred that the acyl chain length be between 8 and 18. While the chain length of the alkyl group can be between 1 and 18 carbons in length, it is preferred that chain length be between 1 and 8 carbons. In any event, the total number of carbons in the acyl and alkyl chains on the salt of N α —(C 1 -C 18 ) acyl di-basic amino acid alkyl (C 1 -C 18 ) ester should be between about 8 and 20. Examples of preferred preservative components are salts of N α -lauroyl arginine ethyl ester and salts of N α -cocoyl arginine ethyl ester. The anionic portion of the salt is not critical to the preservative performance of the salt as long as the aqueous solubility of the preservative salt is above the MIC and preferably above the MBC of the spoilage bacteria. Preferably the aqueous solubility of the first component should be at least 100 ppm and preferably more than 500 ppm of the total composition at room temperature. Examples of the anionic portion of the first component preservative salt include, but are not limited to, an inorganic ion such as chloride, bromide and iodide, or an organic carboxylate ion, such as acetate, glycolate, lactate, propionate, gluconate, octanoate, decanoate, or ascorbate and its water soluble derivates thereof. 
     A useful amount of the preservative component is in a range of about 0.1% to 80 wt. % of the preservative combination. When the preservative component is being incorporated into an article such as food packaging or products for human use, an amount of 0.1 to 8 wt. % of the article is useful. 
     Second Component 
     The second component of this invention comprises either a solvent or surfactant delivery enhancing agent or a mixture thereof. A critical property of the solvent, if used as the sole delivery-enhancing agent, is its Hildebrand Solubility Parameter (“HSB”). To be effective it needs to be significantly greater than the Hildebrand Solubility Parameter of the plastic used for the packaging. The Hildebrand Solubility Parameter is a numerical value, which that indicates the cohesive forces between the individual molecules of substances. The molecules in a substance with a low Hildebrand Solubility Parameter have limited cohesive forces holding them together generally being limited to weak Van Der Waal forces while the molecules in a compound with a high Hildebrand Solubility Parameter have much stronger cohesive forces which might include, for example, intermolecular hydrogen bonding. In relative terms, two substances with a similar Hildebrand Solubility Parameter will dissolve in one another, whereas two substances with very different Hildebrand Solubility Parameters will tend not to mix. Therefore, Hildebrand Solubility Parameters are most useful in determining the relative solvency behavior or solubility of a solute in a specific solvent. Hildebrand Solubility Parameters are derived from the heat of vaporization. The Hildebrand Solubility Parameter, δ, is equal to the square root of the cohesive energy and can be calculated from the following equation: 
       δ=√c=[(ΔH− R T)]/V m ] 1/2  
 
     where c=cohesive energy density, ΔH=heat of vaporization, R=gas constant, T=temperature, V m =molar volume. 
     Polymeric materials such as polyethylene, polypropylene and polystyrene have relatively low Hildebrand Solubility numbers, because these plastics consist of hydrogen and carbon atoms only. Plastics like nylon have higher Hildebrand Solubility Parameters due to the additional presence of oxygen atoms in the molecule, which allow for hydrogen bonding. 
     It is well known in the literature that if the hydrophobicity of any salt is increased, the diffusion (“diffusibility”) of the salt through any polymer is decreased. This is particularly true for a very hydrophobic polymer such as PE, polypropylene, or copolymers thereof. This is because of the solubility of the hydrophobic salt in a hydrophobic polymer and that more potential energy is required for the hydrophobic salt to diffuse through the polymer layer. 
     For polyethylene, polypropylene and polystyrene plastic films and packages, we have found that a preferable range for the Hildebrand Solubility Parameter of the surfactant or solvent delivery-enhancing agent is equal to or above 11 more preferably above 15. When the Hildebrand Solubility Parameter of the surfactant or solvent delivery-enhancing agent is lower than about 11, the primary preservative component tends to be highly “compatible” with the plastic film and hence does not migrate readily to the plastic film surface. Furthermore the solvent does not promote diffusion of the primary preservative component into or through the aqueous moisture surrounding the food. When the Hildebrand Solubility Parameter of the solvent or surfactant is above 11 it causes the preservative component to diffuse through polyethylene, polypropylene and polystyrene films, which have Hildebrand Solubility Parameters below 9.0, during manufacture, so that much of the preservative component is at or close to the surface of the plastic film. With polycarbonate and nylon films, the minimum Hildebrand Solubility Parameter needs preferably to be higher, for example, from about 13 or higher to help diffusion through the plastic film and for much of the preservative component to migrate to the surface of the plastic film during manufacture. Examples of suitable solvents or surfactants include but are not limited to, glycerol or glycerin, 1,2-propanediol, and 1,3-propanediol. It must be noted that hydrocarbon-based compounds, such as poly alpha olefin and mineral oil, are not desirable because they have very low Hildebrand Solubility Parameter. Indeed these liquids may encase the preservative in the polymeric material and assure minimal diffusion of the preservative through the plastic film. 
     Another advantage of using a solvent with a high Hildebrand Solubility Parameter is that it helps the preservative dissolve in the aqueous layer surrounding the food and helps it migrate to where it is needed for its preservative benefits. In this regard a Hildebrand Solubility Parameter of between 20 and 35 is ideal. 
     A critical property of the surfactant, if used as part of or all of delivery enhancing agent is its Hydrophilic-Lipophilic Balance (“HLB”), which should be between about 4.0 and 25. A preferred range for HLB is between about 10.0 and 20.0. The HLB of a surfactant is its balance between hydrophilic and hydrophobic properties, which defines how water-soluble or water miscible it is and how oil soluble or oil miscible it is. Surfactants with relatively low HLBs tend to mix easily with oils and are effective in producing water in oil emulsions whereas surfactants with relatively high HLBs tend to mix easily with water and are effective at producing oil in water emulsions. The presence of surfactants with the right HLB tend to help to rapidly disperse the preservative component into the aqueous medium surrounding the food being preserved. Furthermore surfactants or the right HLB help the moisture surrounding the food to more effectively wet all surfaces and hence to enhance coverage of the preservative component. 
     Examples of suitable surfactants include, but are not limited to, to sorbitan mono-carboxylates such as sorbitan mono-caprate, sorbitan mono-caprylate, sorbitan mono-laurate, sorbitan mono-myristate, sorbitan mono-palmitate, sorbitan monostearate and sorbitan mono-oleate, some of which are manufactured under the trade name “Span”. Also suitable are the ethoxylated sorbitan mono carboxylates such as ethoxylated sorbitan mono-laurate (polysorbate 20), ethoxylated sorbitan mono-caprate, ethoxylated sorbitan mono-caprylate, ethoxylated sorbitan mono-myristate (polysorbate 40), ethoxylated sorbitan mono-palmitate (polysorbate 60), ethoxylated sorbitan monostearate (polysorbate 80) and ethoxylated sorbitan mono-oleate, some of which are manufactured under the trade name of “Tween”. 
     When incorporating the solvent or surfactant into the bulk polymeric material such as plastic film, another critical property of the solvent or surfactant is their ability to withstand degradation due to heat. Specifically, the solvent and surfactant have to be stable at the melt temperature of the polymer substrate, e.g. LDPE, LLDPE, or VLDPE melt between about 140° C. to about 200° C. Also, the melt process can be conducted under an inert atmosphere, e.g. N 2 , etc. Therefore, to be practical, the second component solvent or surfactant must be stable to temperatures above about 200° C. Thus many solvents or surfactants with an appropriate δ value of greater than about 11.0 cannot be used due to their heat sensitivity. For example, ethanol, with δ=12.92, cannot be used because it is volatile and boils at 78° C. 
     Another factor is the safety of the solvent or surfactant. To be useful in foods, the solvent or surfactant needs to be completely food safe, i.e. it needs to be considered GRAS. Therefore, although solvents such as ethylene glycol (δ=16.3), have useful solubility parameters, many are known to be toxic to humans and not useful for the present invention. 
     A useful amount of the second component is in the range of 0.1 to 80 wt. % of the preservative combination. When the component is being incorporated into an article such as food packaging or products for human use, an amount of 0.01 to 8 wt. % is useful. 
     Third Component 
     The optional third component, acyl monoglyceride, is an agent, which we have found to be synergistic with the first preservative component. To be effective the acyl monoglyceride should have 8 to 16 carbons in the acyl group. The preferred acyl monoglyceride is glycerol monolaurate. Glycerol monolaurate is a GRAS food additive, which is found naturally in breast milk. Glycerol monolaurate has been shown to synergistically enhance the effectiveness of lauroyl arginine ethyl ester hydrochloride as a food preservative. A useful amount of acyl monoglyceride is in a range of about 0.1 to about 50 wt. % of the preservative combination. An amount of 0.1 to 5 wt. % of acyl monoglyceride is also useful. 
     Polymeric Material 
     Examples of suitable polymeric material include, but are not limited to linear or branched very low density, low density, linear low density, medium density and high density polyethylene, polypropylene, polystyrene, ethylene vinyl acetate, polyethylene terephthalate (PET, PETE), modified polyethylene and ethylene copolymers, and polycarbonate. Other suitable polymeric materials include polyolefins and copolymers thereof, polyesters, polyvinyl chloride, polyacrylate, polyamide, etc., that are suitable for packaging food products. More suitable polymeric materials include metallocene-type polyethylene, polylactic acid, bioplastics based on starch, cellulose and polyester, polyethylene, polypropylene, poly(ethylene-vinyl acetate), polystyrene, polyvinylidene chloride, ethylene copolymers and ethylene carboxylic acid copolymers, ethylene alkyl ester copolymers, ethylene cyclic olefin copolymers, polyethylene terephthalates, polyvinyl acetate, polycarbonate, polyamides, polyvinyl alcohols, cellulose and modified cellulose including chitosan, polyethylene copolymers, polypropylene copolymers, poly(ethylene-vinyl acetate) copolymers, polystyrene copolymers, polyvinyl chloride copolymers, polyvinylidene chloride copolymers, ionomers, polyethylene terephthalate copolymers, polyvinyl acetate copolymers, polycarbonate copolymers, polyamide copolymers, polyvinyl alcohol copolymers, and cellulose and modified cellulose copolymers including chitosan. In particular, modified polyethylene and ethylene copolymers such as ethylene/hexene plastomer sold under the trade name EXACT® by ExxonMobil are useful. 
     The polymeric material is in the form of a film or a coating. The polymeric film can be made of any type of plastic, which can be used to package or store foods or other products for human use. 
     Furthermore, the invention is also directed towards an article such as a preservative package for foods or other products for human use comprising about 90 to 99.9 wt. % of a polymeric material, by weight of the packaging material, and a preservative combination comprising 1) about 0.01 to about 8%, by weight of the packaging material, of a preservative component selected from salts of N α —(C 1 -C 18 ) acyl di-basic amino acid (C 1 -C 18 ) alkyl ester, (2) a second component in an amount of from about 0.01% to about 10.0%, by weight of the packaging material, either of a food-safe (GRAS, or “Generally Recognized As Safe”) solvent with a Hildebrand Solubility Parameter of 11 and above and a thermal stability above 200° C., a nonionic surfactant with an HLB between 4.0 and 25 and a thermal stability above 200° C., or mixtures thereof; and optionally (3) from about 0.01 to about 5.0%, by weight of the packaging material, of a third component consisting of an acyl mono-glyceride, which may be synergistic with the first preservative component. 
     For articles such as preservative packages, the polymeric material is preferably in the form of a film layer. The package itself can be either mono-layered or multi-layered, such that the preservative combination is present in the layer that is in a direct contact with the contained food or product for human use, while any extra layer within the package provides protection and other properties 
     Additionally, this invention is also directed towards a method of preserving food or products for human use by the application or incorporation of from 0.01 to about 10% by weight of the packaging material of a preservative combination onto or into packaging material containing the food or products for human use, the preservative combination comprising (1) about 0.1% to about 80%, by weight of the combination, of a preservative component selected from salts of N α —(C 1 -C 18 ) acyl di-basic amino acid alkyl (C 1 -C 18 ) ester, and (2) from about 0.1% to about 80%, by weight of the combination, of a second component consisting either of a food-safe solvent with a Hildebrand Solubility Parameter of at least 11 and a thermal stability above 200° C., from about 0.1% to 80%, by weight of the combination of a nonionic surfactant with an HLB between 4.0 and 25 and a thermal stability above 200° C., or mixtures thereof and, optionally, (3) from about 0.01% to 5% by weight of the combination of a third component consisting of an acyl mono-glyceride, which may be synergistic with the preservative component. 
     EXAMPLE 1  
     Preparation of Multi-Layered Film Comprising Enhancement Additives with or without LAE 
     Firstly, pellets of polymers with enhancement additives were produced. Secondly, those pellets were coated with or without LAE-HCl, melted, mixed and re-formed into pellets. Thirdly, the pellets from the second step were melted and extruded to form a surface layer of a multilayer film. 
     Step 1. Preparation of Polymer/Additive Masterbatch Pellets 
     EXACT® 3040 ethylene/hexene plastomer (ExxonMobil Chemical Company, Houston, Tex.) was loaded into a hopper and fed into the main feed port of a 50 mm co-rotating twin screw extruder. 
     The feed zone of the twin screw extruder was heated to 95° C. and the remainder of the extruder and die was heated to 150° C. The plastomer was fed into the extruder screws, and was extruded at 250 RPM. Upon establishing a stable extrudate, an additive selected from polyalpha olefin fluid, mineral oil, glycerolol or glycerine and 1,3-propanediol was delivered into the molten plastomer with a gear pump via an injection port. Each additive was added to a separate but equal amount of extrudate. 
     Upon exiting the mixing section, the polymer/additive blend moved through the extruder&#39;s pressurization section and a four-hole die to form continuous strands. The strands were immediately chilled in a water bath. Upon exiting the water bath, an air knife removed the remnant surface moisture on the strands. Lastly, the strands where cut into pellets by a rotating knife. 
     Step 2. Preparation of Polymer/Synergist/LAE.HCl Blend Pellets 
     0.1 Kg of the LAE-HCl powder was blended with the previously made plastomer-additive pellets, and sufficient plain plastomer pellets were balanced to produce a final batch of 10 kg. The amount of plastomer-additive pellets varied according to the different additives. This mixture was fed into a 50 mm twin screw extruder at about 45 kg/hr. The twin screw extruder homogenized the mixture at 150 RPM in heated condition. 
     Once mixed, the blend moved through a pressurization section and a four-hole die to form continuous strands. The strands were immediately chilled in a water bath. Upon exiting the water bath, an air knife removed the remnant surface moisture on the strands. Lastly, a rotating knife cut the strands into pellets. A set of pellets without LAE-HCl was also produced. In the samples without LAE-HCl, 0.1 kg of plain pellets were used as replacement. By mass balance, the pellets comprised each additive in final amounts that ranged from 2 to 6 wt. % as listed in Table 1, with or without 1.0% LAE-HCl with the remainder being plastomer. 
     Step 3. Preparation of Polymer/Synergist/LAE.HCl Blend Films 
     A three-extruder cast film line equipped with a die was configured to produce cast film comprising three discrete layers. 
     The first surface layer of the film comprised a blend of 75% by weight of EXACT® 3040 ethylene/hexene plastomer and 25% BYNEL® 41E710 maleic anhydride-grafted polyethylene (E. I. du Pont de Nemours and Company, Wilmington, Del.). The center layer comprised Nippon Gohsei SOARNOL ET3803, a hydrolyzed copolymer of ethylene and vinyl acetate (Noltex, LLC, LaPorte, Tex.). A second surface layer comprised pellets of the processed blend from step 2. 
     The extruder used to process the blend from step 2 had four zones and each operated under different heated conditions. The speed of the extruder was set to 80 RPM. The back pressure, motor load and melt temperature depended on the specific composition being processed. Upon exiting the die at about 200 mm wide, the film was immediately chilled on a cold, rotating roll maintained at a temperature of 15° C. The chilled film was wound into a roll. 
     The multi-layer film samples were subjected to ATR measurement. ATR, or Attenuated Total Reflectance, is an FTIR-based means of characterizing the infrared spectrum of the surface penetrating 0.5-5.0 microns of a tested object. ATR measurement of the film indicated the relative abundances of LAE on the surfaces of the plastic films. An ATR measurement was also conducted on the LAE compound alone (“NEAT LAE”) to detect peaks that identify the presence of LAE. 
     As shown in  FIG. 1 , the ATR spectrum of “NEAT LAE” shows peaks between 1800 cm-1 and 1640 cm-1. During the subsequent analyses, the signals between 1640 cm-1 and 1800 cm-1 baseline are arbitrarily defined as a measurement of the relative abundance of LAE on the surface of the film. 
     Also, in  FIG. 1 , it can be shown that the film that contains 4% PAO with or without LAE shows little or no presence of LAE on the surface of the film. 
     EXAMPLE 2  
     Two film samples were produced according to the method described in Example 1. One film sample contained 4% mineral oil and 1% LAE, the other film contained 4% mineral oil and no LAE. An ATR measurement was conducted on the samples. The ATR results as shown in  FIG. 2  indicate that same as in the previous example, there were little or no peaks of LAE on the surface of the tested films. Thus, there was little or no diffusion of LAE using mineral oil as the enhancement additive. 
     EXAMPLE 3 
     Two film samples were produced according to the method as described in Example 1. One film sample contained 2% glycerol and 1% LAE, and the other film sample contained 2% glycerol and no LAE. An ATR measurement was conducted on the samples. The ATR results as shown in  FIG. 3  indicate that contrary to Examples 2 and 3, there is one sharp peak around 1640 cm-1, indicating a significant presence of LAE, and therefore indicating that LAE had diffused to the surface of the film sample. 
     EXAMPLE 4  
     Two film samples were produced according to the method as described in Example 1. The first film sample contained 2% glycerol and 1% LAE, and the second film sample contained 2% 1,3-propandiol and 1% LAE. An ATR measurement was conducted on the samples. The ATR results as shown in  FIG. 4  indicate that although there was some diffusion of LAE to the surface in the second sample, a greater presence of LAE had diffused to the surface in the first sample. 
     EXAMPLE 5  
     Four film samples were produced according to the method as described in Example 1. The first sample contained 2% 1,3-propandiol. The second sample contained 4% 1,3-propandiol and the third sample contained 6% 1,3-propandiol. All of these samples also contained 1% LAE. The fourth sample contained 2% 1,3-propandiol, without LAE. ATR measurements were conducted on the samples. The ATR results, as shown in  FIG. 5 , indicate that heightened amounts of the 1,3-propandiol increased the presence of LAE on the surface of the film. Baseline and peak values were determined from  FIG. 5 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 1640 cm −1 / 
               
               
                 Additive 
                 Concentration 
                 1800 cm −1   
                 1640 cm −1   
                 1800 cm −1   
               
               
                   
               
             
            
               
                 1,3-propanediol 
                 2% 
                 0.0256 
                 0.029 
                 1.14 
               
               
                 glycerol 
                 2% 
                 0.0248 
                 0.036 
                 1.44 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 6  
     Four film samples were prepared according to the method as described in Example 1. The first film sample contained 2% glycerol and 1% LAE, the second film sample contained 4% 1,3-propandiol and 1% LAE, the third film sample contained 4% mineral oil and 1% LAE, and the fourth sample contained 4% PAO and 1% LAE. 
     ATR measurements were conducted on all four samples. The ATR results as shown in  FIG. 6  indicate that that the first and second samples have a higher surface presence of LAE than the third and fourth samples. This result again demonstrates that solvents of Hildebrand Solubility Parameter of at least 11 facilitate diffusion of LAE to the surface of the film, while solvents with lower Hildebrand Solubility Parameter, such as hydrocarbon compounds retain the LAE within plastic and thereby hinder diffusion. Baseline and peak values were determined from  FIG. 6 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 1640 cm −1 / 
               
               
                 Additive 
                 Concentration 
                 1800 cm −1   
                 1640 cm −1   
                 1800 cm −1   
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 mineral oil 
                 4% 
                 0.0195 
                 0.027 
                 1.36 
               
               
                 PAO fluid 
                 4% 
                 0.0195 
                 0.027 
                 1.36 
               
               
                 1,3-propanediol 
                 4% 
                 0.0195 
                 0.043 
                 2.21 
               
               
                 Glycerol 
                 2% 
                 0.0195 
                 0.037 
                 1.90