Patent Application
20130046262
The present invention relates to a composition for flexible polyolefin-based films that contain thermoplastic starches. In particular, the invention pertains to packaging films that include polyolefins, renewable polymers, and a compatibilizer, and describes a method to overcome their material incompatibility to make packaging films of desirable physical and mechanical properties.
In recent years as petroleum resources have become more scarce or expensive and manufacturers and consumers alike have become more aware of the need for environmental sustainability, interest in biodegradable and renewable films containing renewable and or natural polymers for a variety of uses has grown. Renewable polymers available today, such as polylactic acid (PLA), polyhydroxyalkanoate (PHA), thermoplastic starch (also referred to herein as “TPS”) and the like, however, all have deficiencies in making thin, flexible packaging films such as those that are typically used as packaging films for bath tissues, facial tissue, wet wipes and other consumer tissue products, product bags for personal care products, away-from-home products, and health care products. For instance, PLA thin film exhibits a high stiffness and very low ductility, sometimes costly bi-axial stretching process is used to produce thin PLA films, which results in relatively high “rustling” noise levels when handled and very stiff films, making the material unsuitable for flexible thin film packaging uses. PHA is difficult to make into thin films. Poor film processability (i.e., slow crystallization, “extreme” stickiness prior to solidification) retards fabrication-line speeds and results in relatively expensive production costs. Some PHA such as poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) films have high stiffness and low ductility, making them unsuitable for flexible thin film applications. When used alone as a film, thermoplastic starch has a low tensile strength, low ductility, and also severe moisture sensitivity. Due to its low melt strength and extensibility, thermoplastic starch has been unsuitable for stand-alone packaging film applications unless blended with an expensive biodegradable polymer such as Ecoflex™, an aliphatic-aromatic copolyester by BASF AG.
Typical existing packaging equipment are optimal for converting polyethylene (also referred herein as “PE”)-based films, efforts to replace or upgrade the packaging hardware to run 100% renewable polymers is likely to require high capital expenditures. The poor processability of 100% renewable polymers also increases production cost due to reduced line speed, etc. Therefore, there is a need for thin packaging films containing a renewable polymer to reduce the carbon footprint and improve environmental benefits at an affordable cost. The packaging films must have good performance required for packaging applications in terms of heat seal, tensile properties, and free of any visible defects, and suitability for high speed packaging applications.
The present invention relates to a multiple layer polymeric film comprising at least three layers wherein at least two layers comprise at least one polyolefin and the third layer comprises from about 5% to about 45% of a thermoplastic starch, from about 55% to about 95% of at least one polyolefin, and from about 0.5% to about 10% of a compatibilizer, wherein said compatibilizer is selected from the group consisting of graft copolymers, block copolymers, and random copolymers of non-polar and polar monomers.
The present invention also relates to a flexible multiple layer polymeric film comprising from about 5% to about 55% of a thermoplastic starch masterbatch and from about 40% to about 95% of a polyolefin or mixtures of polyolefins.
Further, the present invention relates to a packaging material or a consumer product comprising a portion made from the multiple layer polymeric film of the present invention. The consumer product may be an absorbent article such as diapers, pantiliners, feminine pads, adult incontinence products, wipes, tissues, and the like.
All percentages, parts and ratios are based upon the total weight of the compositions of the present invention, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the active level and, therefore, do not include solvents or by-products that may be included in commercially available materials, unless otherwise specified. The term “weight percent” may be denoted as “wt. %” herein. Except where specific examples of actual measured values are presented, numerical values referred to herein should be considered to be qualified by the word “about”.
As used herein, “comprising” means that other steps and other ingredients which do not affect the end result can be added. This term encompasses the terms “consisting of” and “consisting essentially of”. The compositions and methods/processes of the present invention can comprise, consist of, and consist essentially of the essential elements and limitations of the invention described herein, as well as any of the additional or optional ingredients, components, steps, or limitations described herein.
While the specification concludes with the claims particularly pointing out and distinctly claiming the invention, it is believed that the present invention will be better understood from the following description.
The term “biodegradable,” as used herein, refers generally to a material that can degrade from the action of naturally occurring microorganisms, such as bacteria, fungi, yeasts, and algae; or environmental heat, moisture, or other environmental factors. If desired, the extent of biodegradability may be determined according to ASTM Test Method 5338.92.
“Energy-to-break” refers to the total area under the stress vs. strength curve.
The term “modified starch” as used herein, refers to starches which have been modified chemically or enzymatically by the typical processes known in the art (e.g., esterification, etherification, oxidation, acidic hydrolysis, enzymatic hydrolysis, crosslinking, carboxymethylation, etc.). Typical modified starches are starch ethers (e.g. methyl starch, ethyl starch, propyl starch, etc.), esters (e.g. starch acetate, starch propionate, starch butyrate, etc.), hydroxyalkyl starches (hydroxymethyl starch hydroxyethyl starch, hydroxypropyl starch, etc.); carboxymethyl starches, etc.
“Modulus” refers to the slope of the initial portion of the stress vs. strength curve.
The term “native starch” as used herein, refers to unmodified starch separated from plants, typical sources includes seeds of cereal grains, such as corn, waxy corn, wheat, sorghum, rice, and waxy rice; tubers, such as potatoes; roots, such as tapioca, (i.e. cassava and manioc), sweet potatoes, and arrowroot; and the pith of the sago palm.
“Peak stress” refers to the value of stress level at peak.
The term “renewable” as used herein refers to a material that can be produced or is derivable from a natural source which is periodically (e.g., annually or perennially) replenished through the actions of plants of terrestrial, aquatic or oceanic ecosystems (e.g., agricultural crops, edible and non-edible grasses, forest products, seaweed, or algae), or microorganisms (e.g., bacteria, fungi, or yeast).
“Strength-at-break” refers to the strength value when the sample breaks.
In general, the invention describes a flexible polymeric film having from about 5% to about 45% of a thermoplastic starch, from about 55% to about 95% of a polyolefin or mixtures of polyolefins, and from about 0.5% to about 10% of a compatibilizer, which is a graft copolymer of a non-polar backbone and a grafted polar monomer, or a block copolymer of both a non-polar block and a polar block, or a random copolymer of a non-polar monomer and a polar monomer. The amounts of said thermoplastic starch and compatibilizer, respectively, can be present in a ratio of between about 2.5:1 to about 95:1. Typically, the ratio of said thermoplastic starch and compatibilizer, respectively, is between about 5:1 and about 55:1. More typically, the ratio of said thermoplastic starch and compatibilizer, respectively, is between about 10:1 and about 30:1.
The invention relates, in part, to a method of forming a polymeric film, the method comprising: preparing a polyolefin mixture, blending said polyolefin mixture with a thermoplastic starch and a compatibilizer, which is a graft copolymer having a non-polar backbone and a grafted polar monomer or a block copolymer of both a non-polar block and a polar block or a random copolymer of a non-polar monomer and a polar monomer, said thermoplastic starch and compatibilizer, respectively, are present in amounts in a ratio of between about 2.5:1 to about 95:1; extruding said film of said blended polyolefin mixture.
In another aspect the present invention pertains to a packaging material or assembly made from the polymeric film composition such as described. The film can be fabricated to be part of a packaging assembly. The packaging assembly can be used to wrap consumer products, such as absorbent articles including diapers, adult incontinence products, pantiliners, feminine hygiene pads, or tissues. In other iterations, the invention relates to a consumer product having a portion made using a flexible polymeric film, such as described. The polymeric film can be incorporated as part of consumer products, e.g., baffle films for adult and feminine care pads and liners, outer cover of diapers or training pants, and the like.
Additional features and advantages of the present invention will be revealed in the following detailed description. Both the foregoing summary and the following detailed description and examples are merely representative of the invention, and are intended to provide an overview for understanding the invention as claimed.
The present invention addresses a need for a flexible polymeric film that is better or improved over conventional polyolefin films in terms of its environmental impact. The use of renewable materials in films containing natural or new carbon, or recently fixed CO2, can slightly reduce global warming effects. The production of the present inventive films can reduce energy input and greenhouse gas emissions. The relative degree of biodegradation somewhat depends on the amount of biodegradable component present in the films, but it is more biodegradable than pure polyolefin thin films.
Additionally, the present invention enables packaging manufacturers to make use of a majority of polyolefins and a minority of renewable materials to achieve good processing characteristics and mechanical properties at low cost. The present invention describes a composition for and method of making thin packaging films for consumer packaged goods and products with suitable performance, renewable polymer content to reduce their environmental footprint, and at an attractive cost. The composition incorporates renewable polymers such as thermoplastic starch as a renewable component. The amount of renewable polymers has to be at a volumetric minority so the polyolefin properties will dominate the blend properties. An appropriate type of compatibilizer at the right amount must be employed to compatibilize the hydrophobic polyolefin(s) phase and hydrophilic thermoplastic starch phase to create an adequate dispersion and good film properties.
It was surprisingly found that a range and ratio of thermoplastic starch, polyolefin and compatibilizer allows the blends to have good physical and mechanical properties. At a particular range and ratio, compositions of the present invention were found to have good mechanical properties, good processability, and to be free from any visible defects. As shown in
In comparison to conventional polyolefin-based films, the inventive polymeric film may be much softer and more breathable to moisture. In some applications, such as absorbent articles, the film of the present invention is able to keep a user's skin drier. When the present films are employed in such articles as a baffle film in a feminine or adult care pad or the outer cover film of a diaper, training pants, or adult incontinence pants, the film will feel more comfortable against the user's skin as a consequence of a more micro-grainy or micro-textured surface, and will not have as slippery or rubbery a feeling as conventional polyethylene-based films.
The thermoplastic starch in the polymeric film comprises either a native starch or a modified starch with a plasticizer. The native starch can be selected from corn, wheat, potato, rice, tapioca, cassava, etc. The modified starch can be a starch ester, starch ether, oxidized starch, hydrolyzed starch, hydroxyalkylated starch, and the like. Genetically modified starch can also be used. Such genetically modified starch may have a different ratio from that of amylose and amylopectin than native starches. Mixtures of two or more different types of native starch or modifications thereof can also be used in this invention.
The thermoplastic starch may include a plasticizer or mixture of two or more plasticizers selected from polyhydric alcohols including glycerol, glycerine, ethylene glycol, polyethylene glycol, sorbitol, citric acid and citrate, aminoethanol, and the like. In certain embodiments, the concentration of starch in thermoplastic starch may be from about 45 wt. % or 50 wt. % to about 85 wt. % or 90 wt. %. One may include proportionate amounts of mixed starches of different origins or types (e.g., starches selected from corn, wheat, potato, rice, tapioca, cassava, etc.). According to certain other embodiments, the amount of thermoplastic starch may include from about 60 wt. % or about 65 wt. % to about 85 wt. % or about 90 wt. % starch, and from about 10 wt. % or about 15 wt. % to about 35 wt. % or about 40 wt. % plasticizers, inclusive of any combination of ranges there between.
Thermoplastic starch based biodegradable plastics of the present invention have a starch content greater than about 60% and are based on vegetable starch. With the use of specific plasticizers, such plastics can produce thermoplastic materials with good performance properties and inherent biodegradability. Starch is typically plasticized, destructured, and/or blended with other materials to form thermoplastic starch with useful mechanical properties. Importantly, such thermoplastic starch compounds can be processed on existing plastics fabrication equipment.
High starch content plastics are highly hydrophilic and may absorb moisture upon extended exposure to high humidity or upon contact with water. This can be overcome through blending with other polymers. Alternatively, as the starch has free hydroxyl groups which readily undergo a number of reactions such as acetylation, esterification and etherification, thermoplastic starch can be made from modified starch (e.g. starch ethers, esters, etc.) to reduce its water sensitivity.
The resulting flexible film includes about 5% to about 45% of a renewable polymer such as thermoplastic starch, from about 55% to about 95% of at least one polyolefin, and from about 0.5% to about 10% of a compatibilizer, wherein the compatibilizer has a graft copolymer having a non-polar backbone and a grafted polar monomer or a block copolymer of both a non-polar block and a polar block or a random copolymer of a non-polar monomer and a polar monomer.
According to alternate embodiments, the flexible polymeric film may incorporate a masterbatch or a concentrate of thermoplastic starch (“TPS masterbatch”). As used herein, “TPS masterbatch” refers to a blend of thermoplastic starch, at least one polyolefin or a mixture of polyolefins, and compatibilizers. The TPS masterbatch of the present invention may comprise from about 40% to about 90% of a thermoplastic starch, from about 10% to about 45% of a polyolefin or a mixture of polyolefins, and from about 1% to about 10% of compatibilizers, wherein said compatibilizers may be a graft copolymer of a non-polar backbone and a grafted polar monomer or a block copolymer of both a non-polar block and a polar block or a random copolymer of a non-polar monomer and a polar monomer. The mixture of polyolefins may comprise low density polyethylene, high density polyethylene, linear low density polyethylene, linear medium density polyethylene, linear ultra-low density polyethylene, polypropylene, ethylene propylene copolymers, and the like.
According to alternate embodiments of the present invention, the flexible polymeric film may incorporate a color concentrate, and a polyolefin or a mixture of polyolefins. The flexible film may comprise from about 1% to about 15% of a color concentrate. The color concentrate can be added to make the otherwise clear film opaque, or white, or other colors. Color concentrates may include, for instance, various dyes, titanium oxide, calcium carbonate, opacifiers such as clays, and the like. Alternatively, the TPS masterbatch may also comprise a color concentrate and may have from about 50% to about 90% by weight a thermoplastic starch, from about 5 to about 40% a polyolefin or a mixture of polyolefins, and from about 0.5% to about 5% a compatibilizer, and from about 1% to about 15% a color concentrate.
Examples of the polyolefins that may be incorporated include low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), metallocene catalyzed polyolefins, very low density polyethylene (VLDPE), ultra-low density polyethylene (ULDPE), single site catalyzed polyethylene, polypropylene (PP), ethylene-propylene copolymers, polyolefin elastomers such as Vistmaxx® from Exxon Mobil, ethylene copolymers, polyolefin elastomers of block copolymers of ethylene and propylene, or ethylene copolymers with vinyl acetate, methacrylate, acrylic acid, methacrylic acid, and the like.
The compatibilizer may include: polyethylene-co-vinyl acetate (EVA), polyethylene-co-vinyl alcohol (EVOH), polyethylene-co-acrylic acid (EAA), polyethylene-co-methacrylic acid (EMAA), polyolefin graft copolymer of non-polar polyolefin backbone grafted with a polar monomer such as a polyethylene grafted with maleic anhydride or polypropylene grafted with maleic anhydride or polyethylene grafted with glycidyl methacrylate. The polar monomer can include maleic anhydride, acrylic acid, vinyl acetate, vinyl alcohol, vinyl amine, acrylamide, or acrylate, glycidyl acrylate, glycidyl methacrylate, and the like. The polar monomer may be present in an amount that ranges from about 0.1%, about 0.3%, about 0.5% or about 1% to about 35%, about 37%, about 40%, about 45% by weight of the composition. Mixed polyolefins or polyethylene/polypropylene blends can also be used in this invention. The composition may also contain from about 0.5% to about 30% of a biodegradable polymer.
The polymeric film can include a mineral filler that is present in an amount from about 5% or about 8% to about 33% or about 35% by weight of the composition. Typically, the mineral filler is present in an amount from about 10% or about 12% to about 25% or about 30% by weight of the composition. The mineral filler may be selected from any one or a combination of the following: talcum powder, calcium carbonate, magnesium carbonate, clay, silica, alumina, boron oxide, titanium oxide, cerium oxide, germanium oxide, diatomaceous earth (DE), and the like.
The polymeric packaging films can have multiple layers, for instance, from 2 to 7 or 20 layers; or in some embodiments, from 2 or 3 to 10 layers. Each layer may have a thickness from about 0.05 mil to about 2.0 mil (1 mil=25.4 micrometers). Typically, each layer has a thickness from about 0.1 mil to about 1 mil or from about 0.2 mil to about 0.5 mil. The combined polymeric film layers can have an overall thickness from about 0.5 mil to about 5.0 mil, typically from about 0.7 mil to about 4 mil or from about 1 mil to about 2 mil. Each layer can have a different composition, but at least one of the layers is formed from the present inventive film composition. At least one layer of the present invention is formed with a TPS masterbatch. The thermoplastic starch content (“TPS content”) of a TPS masterbatch, can range from about 40% to about 90% by weight of the TPS masterbatch. In some embodiments, the TPS content may be from about 50% to about 85% of the masterbatch. The polyolefin in the layer can be low density polyethylene, linear low density polyethylene, linear medium density polyethylene, linear ultra-low density polyethylene, high density polyethylene or ethylene copolymers, polypropylene, or mixtures of polyolefins. At least one layer on the seal side of the film comprises polyolefin. As used herein, “seal side” refers to the layer of the film that is the innermost layer.
In an alternative embodiment, the outside layer of the multi-layer film may comprise at least one polyolefin or a mixture of polyolefins. Such embodiment is ideal when forming a product or a product bag such as that to package or bundle diapers. In yet another embodiment, the printing layer and the seal side layers may comprise at least one polyolefin or a mixture of polyolefins, or a mixture of polyolefins with a TPS masterbatch. As used herein, the “printing layer” refers to the outermost layer of a product or package. The mixture of polyolefins may comprise low density polyethylene, high density polyethylene, linear low density polyethylene, linear medium density polyethylene, polypropylene, and the like. The polyolefin content in these layers ranges from about 10% to about 90%, by weight of the composition and the total thermoplastic starch and compatibilizer constitute from about 10% to about 90%, by weight of the composition. In an embodiment of the present invention comprising more than three layers, at least one inside layer (not including the seal side layer) may comprise at least one polyolefin, a mixture of polyolefins or a mixture of polyolefins with a TPS masterbatch. Additionally, in an embodiment wherein there are more than three layers, at least one outer layer (not including the printing layer) may comprise at least one polyolefin or a mixture of polyolefins, or a mixture of polyolefins with a TPS masterbatch.
In one particular embodiment, the multi-layer film has three layers. Each of the outside layers constitutes from about 5% to about 45% of the total thickness of the three-layer film and the middle layer constitutes from about 5% to about 45% of the total layer film thickness. In one embodiment, a three layer film has a heat seal layer A with a thickness of about 20% of the overall thickness of the three-layer film, a middle layer B, which is about 55% of the total thickness, and an outside printing layer C, which is about 25% of the total film thickness (as shown in
Generally, the flexible polymeric film according to the invention exhibits a modulus from about 50 MPa to about 300 MPa, and a peak stress range from about 15 MPa to about 50 MPa, at a strain-at-break of from about 200% to about 1000% of original dimensions. Typically, the modulus is in a range from about 55 MPa or 60 MPa to about 260 MPa or 275 MPa, and more typically from about 67 MPa or 75 MPa to about 225 MPa or 240 MPa, inclusive of any combination of ranges there between. Typically, the peak stress can range from about 20 MPa or 23 MPa to about 40 MPa or 45 MPa, inclusive of any combination of ranges there between.
The polymeric film will tend to have a micro-textured surface with topographic features, such as ridges or bumps, of between about 0.5 micrometers or 1 micrometers up to about 10 micrometers or 12 micrometers in size. Typically the features will have a dimension of about 2 micrometers or 3 micrometers to about 7 micrometers or 8 micrometers, or on average about 4 micrometers, 5 micrometers, or 6 micrometers. The particular size of the topographic features will tend to depend on the size of the individual thermoplastic starch particles, and/or their agglomerations and also the process conditions used to fabricate the overall film(s).
In contrast to others, which describe rigid injection molding products, the present invention can be used to create thin flexible films based on polyolefins and TPS masterbatch, which are more suited to the specific requirements of packaging films.
In another aspect, the invention describes a method of forming a polymeric film. The method comprising: preparing a polyolefin mixture, blending said polyolefin mixture with a thermoplastic starch and a compatibilizer, which is a graft copolymer of a non-polar backbone and a grafted polar monomer or a block copolymer of both a non-polar block and a polar block or a random copolymer of the non-polar monomer and a polar monomer, said thermoplastic starch and compatibilizer, respectively, are present in amounts in a ratio of between about 2.5:1, 5:1, 7.5:1 10:1, 15:1, 30:1 or about 95:1; extruding said a film of said blended polymer mixture. Desirably, the compatibilizer includes a graft copolymer of polyethylene and maleic anhydride, polyethylene-co-acrylic acid (EAA), polyethylene-co-vinyl alcohol (EVOH), polyethylene-co-vinyl acetate (EVA).
Alternatively, the method of forming a polymeric film may include the steps of preparing a polyolefin mixture; blending the polyolefin mixture with a TPS masterbatch or concentrate; and extruding said mixture to form a film of said blended polymer mixture. The TPS masterbatch or concentrate and polyolefins, respectively, are present in amounts in a ratio of between about 1:1 to about 0.1:1.
In contrast to other methods of preparing thermoplastic starch and synthetic polymer blends, no water-based suspension, evaporation step is needed in the present invention. Also, the present invention does not employ starch-polyester graft copolymers.
The following description and examples will further illustrate the present invention. It is understood that these specific embodiments are representative of the general inventive concept.
For purposes of illustration, TPS samples are prepared with a twin-screw compounding extruder. As an example, cornstarch is incorporated at about 50 or 70 wt. % to about 85 or 90 wt. %, and a plasticizer, such as glycerol or sorbitol, is added up to about 30 or 33 wt. %. A surfactant, such as Excel P-40S, is added to help lubricate the thermoplastic mixture. The mixture is extruded under heat and mechanical shear to form TPS. Blending the TPS with a polyolefin (e.g. LLDPE, LDPE, HDPE, PP, etc.) polymer produces films with un-dispersed aggregates of TPS in the films. The thermoplastic starch and polyolefin are observed to be incompatible with each other. An explanation appears to be found in the molecular structure of each material. The starch is comprised of two components: Amylopectin, which exists as about 70-80% of corn starch's composition, is a highly branched component of starch. Its structure is illustrated in
In contrast, the molecular structure of polyolefin is a simple saturated hydrocarbon polymer. Polyolefin does not contain any polar functional groups such as hydroxyl groups nor are they linked by oxygen atoms. Thus, mixing of the polyolefin and the thermoplastic starch is not fully homogenous because polyolefin does not contain any polar functional groups that are needed to disperse the thermoplastic starch moieties evenly throughout the film material. Films created from thermoplastic starch and polyolefin alone exhibit many undispersed thermoplastic starch aggregates and holes due to their incompatibility.
For example,
To improve the compatibility and dispersion characteristics of thermoplastic starch in polyolefins, several compatibilizers with both polar and non-polar groups are incorporated in the present invention. The compatibilizers may include several different kinds of copolymers including graft copolymers having a non-polar backbone and a grafted polar monomer or a block copolymer of a non-polar block and a polar block, or a random copolymer of a non-polar monomer and a polar monomer, for example, polyethylene-co-vinyl acetate (EVA), polyethylene-co-vinyl alcohol (EVOH), polyethylene-co-acrylic (EAA), and a graft copolymer of a polyolefin (e.g., polyethylene or polypropylene) (e.g., DuPont Fusabond® MB-528D) and maleic anhydride based on molecular structure considerations. EVA, EVOH, EAA, etc. both have a non-polar polyethylene subunit in their backbones. The vinyl acetate subunit contains an ester group, which can hydrogen bond with the hydroxyls of the amylopectin and amylose. EVOH has a vinyl alcohol group, which can hydrogen bond with the hydroxyl groups in starch. The ester group in EVA and the hydroxyl group in EVOH do not chemically react with the hydroxyl groups in starch molecules. Instead, they associate with starch through hydrogen bonding or polar-polar molecular interactions. Using these two physical compatibilizers, blends of TPS and EVA or TPS and EVOH, showed improved compatibility versus the un-compatibilized PE/TPS blends.
As a graft copolymer of polyethylene and maleic anhydride, Fusabond® MB-528D has a structure shown in
The EVA and EVOH worked sufficiently well to disperse the starch particles. In comparison to the graft copolymer of polyethylene and maleic anhydride, however, EVA and EVOH, even at higher percentages of about 10 or about 15%, did not fully disperse the TPS in the film. DuPont Fusabond® MB-528D, however, completely dispersed the TPS in the film when present at a concentration of about 1% to about 5%. Hence, the graft copolymer of polyethylene and maleic anhydride appears to be a more effective compatibilizer.
An example of a film made according to the present invention, shown in
The graft copolymer of polyethylene and maleic anhydride appears to better compatibilize blends when a melt blended resin was made on a ZSK-30 twin screw extruder. In comparison, dry blends with the compatibilizer did not give the same homogenization as the extrusion melt compounded resin. The dry blends are placed directly into the hopper of a HAAKE single screw extruder, but the machine did not exhibit the same shear provided by the twin screws on the ZSK-30 extruder. The twin screw, along with specific mixing capability of the screws, provides a much more effective mixing of all the ingredients. This same mixing cannot be accomplished on the HAAKE extruder.
When the graft copolymer of polyethylene and maleic anhydride, Fusabond® MB-528D, disperses the TPS, it does so partially by chemical reaction. Therefore, a stoichiometric amount of Fusabond® MB-528D will provide ample homogenization to the film. Generally, the more TPS content that is added in the blend, the more Fusabond® MB-528D needs to be added to provide sufficient bonding sites for the hydroxyl groups of the starch molecule. When different Fusabond® MB-528D ratios are tried, two types of undispersed polymer aggregates tend to form: TPS aggregates, which are yellowish accumulations of TPS in the film, and Fusabond® MB-528D aggregates. The second aggregate type forms when too much Fusabond® MB-528D is added to the film; the Fusabond® will not be fully dispersed. A control was prepared to show this effect. LLDPE was mixed with Fusabond® MB-528D at 2.5%. The film produced showed clear polymer aggregates and streaks, which is a sign of unreacted Fusabond®. For each particular ratio of PE to TPS, there is a specific amount of the Fusabond® compatibilizer that will provide successful dispersion for all components of the film.
According to the present invention, the amount of polyolefin and compatibilizer, present in the composition can be expressed as a ratio of between about 5:1 or about 6:1 to about 90:1 or about 95:1, or any combination or permutation of ratio values there between. Alternatively, the ratio may be, for instance, between about 10:1 or about 12:1 to about 60:1 or about 70:1, or preferably between about 15:1 or about 17:1 to about 50:1 or about 55:1, or more preferably between about 20:1 or about 22:1 to about 40:1 or about 45:1 (e.g., 25:1, 27:1, 30:1, 33:1, or 35:1).
The polymeric films are subjected to tensile testing to evaluate their physical properties.
Adding Fusabond® MB-528D as a compatibilizer has effects on the physical properties of the film. It chemically bonds the grafted LLDPE to the TPS. The more bonds that are formed in the film, the more rigid the film will become. The effects of this compatibilizer can be seen from the following tensile data.
The present thermoplastic film materials can be used to make packaging for various kinds of consumer products in general terms. For purpose of illustration, certain package embodiments may be for health care products or consumer products such as absorbent articles (e.g., baby diapers or feminine hygiene articles). The package can have one or more absorbent articles disposed therein. As used herein, the term “absorbent article” refers to devices that absorb and/or contain a substance such as body exudates. A typical absorbent article can be placed against or in proximity to the body of the wearer to absorb and contain various body excretions such as in diapers, incontinence articles, feminine hygiene articles and the like.
Linear low density polyethylene produced by The Dow Chemical Company, Midland, Mich. This resin was used as the main, nonrenewable component of the partially renewable films.
Produced by Cargill, Inc. Hammond, Ind. This was the native cornstarch source used to produce the homemade TPS.
Plasticizer purchased from Sigma-Aldrich, St. Louis, Mo. Sorbitol was used at 30% along with cornstarch while compounding the thermoplastic starch.
Surfactant produced by The Kao Corporation, Tokyo, Japan. Surfactant was added at 2% to lubricate the polymer and reduce torque on the extruder screws.
Compatibilizer produced by DuPont Canada Company, Mississauga, Ontario. Fusabond® MB-528D is >99% maleic anhydride modified polyethylene (LLDPE). Used as a compatibilizer.
Produced by ExxonMobil Chemical Company, Houston, Tex. EVA was tried as a potential compatibilizer. It contained<0.2% vinyl acetate.
Produced by EVAL Company of America, Houston, Tex. This is a copolymer of ethylene and vinyl alcohol via EVA.
Blended resins are made on the ZSK-30 Twin Screw Extruder. TPS was prepared according to U.S. patent application Ser. No. 11/640,109 by Wang et al. TPS was fed by one feeder and a blend of 2244G LLDPE and Fusabond® MB-528D were fed by another. The dry blend of LLDPE and Fusabond® MB-528D was prepared by the addition of compatibilizer such that when fully mixed with TPS, the desired ratio was obtained.
The TPS was often fed by Feeder 2 and the LLDPE/Fusabond® blend was fed by Feeder 3. The ZSK-30 ran at 20 lbs/hr. For 90/10 blends, Feeder 2 was set to 2 lbs/hr and Feeder 3 was set to 18 lbs/hr. The ratios of mass flow rates were adjusted to give the desired ratio of LLDPE and TPS while keeping the overall flow rate of 20 lbs/hr. The temperature profile on the ZSK-30 extruder is shown in Table 1.
The melt temperature of the blend, Tm=197° C., was approximately the same for all blends. The pressure ranged from 350-500 psi and torque from 60-80%. The compounding screw and a 3-hole die were used for every trial. The screw speed was set to 200 rpm. The resin strands produced by the ZSK-30 were cooled on a cooling belt by a series of fans. Once the resin had cooled, it was pelletized and placed in a bag for shipping.
The processing conditions for TPS alone are different than that for the LLDPE/TPS blending. The temperature profile on the ZSK-30 extruder is shown in Table 2.
The screw speed was set to 150 rpm and the pressure ranged from 700-1300 psi. The melt temperature, Tm was 130° C. and the torque ranged from 30-47%. The powder feeder was used and ran at 20 lbs/hr. A nip was used to draw down the stands of the TPS before being pelletized.
All films were cast on the HAAKE Rheomex 252 Single Screw Extruder. A chill roll was used to cool the polymer as it came from the cast film die and to flatten it to form the thin film. The processing conditions for the extruder were the same for all films cast. They were as follows is shown in Table 3.
The screw speed was set to 50-60 rpm. The pressure was kept around 1000 psi and the torque ranged between 3000-4000 m·g. The chill roll settings were adjusted as needed to obtain films with a gauge of 2.0 mil. If the film was too thick, the chill roll was sped up to draw the polymer out of the die faster, making a thinner film. If the film was too thin, the chill roll was slowed down.
The HAAKE extruder has fewer temperature zones than the ZSK-30 extruder. This is because the ZSK-30 has much longer screws than the HAAKE, so more zones are needed to obtain the same accuracy of the temperature distribution.
Each data point on the graph in
All tensile properties were tested on the MTS Sintech 1/D tensile testing apparatus. Samples were prepared for testing by taking a portion of the film, and cutting five dog-bone shaped samples in each direction (i.e., machine direction (MD) and cross-machine direction (CD)). The test length of each dog-bone was 18 mm, the width of the test area was 3 mm, and the thickness varied by about 2 mil. Each dog-bone was tested separately. During the test, samples were stretched at a crosshead speed of 5.0 inches/minute until breakage occurred. The computer program TestWorks 4 collected data points during the testing and generated a stress (MPa) versus strain (%) curve from which a variety of properties were determined: modulus, peak stress, strength-at-break, and energy-to-break.
The following examples further describe and demonstrate embodiments within the scope of the present invention. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention.
A mixture of 60% of a thermoplastic starch masterbatch (BL-F, produced by Cardia, formerly Biograde, Nanjing, China), 32% of a linear low density polyethylene (LLDPE) (melt flow rate of 1 and density of 0.918 g/cc, Grade 118 W, supplied by SABIC), and 8% white master batch (Shanghai Ngai Hing Plastic Materials Co., Ltd.) was fed to a three-layer blown film line. The extruders had a screw diameter of 250 mm, and a Length/Diameter of 30/1. The die gap was 2.2 mm.
The film extrusion conditions are listed in the following table:
Unlike conventional polyethylene-based films, biodegradable polymeric films according to the present invention exhibit a more micro-textured surface.
1. Tensile test results:
The tensile properties of the comparative films were very poor for packaging film applications. The film ripped easily.
A mixture of 17% of a TPS masterbatch (BL-F, produced by Cardia, formerly Biograde, Nanjing, China), 38% of a linear low density polyethylene (LLDPE) (melt flow rate of 1 and density of 0.918 g/cc, Grade 118 W, supplied by SABIC) and 38% low density polyethylene (LDPE) (melt flow rate of 2.8 g/10 min and density: 0.925, Grade: Q281, supplied by SINOPEC Shanghai, Shanghai, China), and 7% white color masterbatch (Shanghai Ngai Hing Plastic Materials Co., Ltd.) was fed to a single screw extruder blown film machine, the screw diameter was 150 mm, the Length/Diameter was 30/1. The die gap was 1.8 mm.
The other process conditions are listed in the following table:
A mixture of 37% of a TPS masterbatch (BL-F, produced by Biograde, Nanjing, China), 28% of a linear low density polyethylene (LLDPE) (melt flow rate of 1 and density of 0.918 g/cc, Grade 118 W, supplied by SABIC) and 28% low density polyethylene (LDPE) (melt flow rate of 2.8 g/10 min and density: 0.925, Grade Q281, supplied by SINOPEC Shanghai, Shanghai, China), and 7% white masterbatch (Shanghai Ngai Hing Plastic Materials Co., Ltd.) was fed to a single screw extruder blown film machine, the screw diameter was 150 mm, the Length/Diameter was 30/1. The die gap was 1.8 mm.
A mixture of 57% of a TPS masterbatch (BL-F, produced by Cardia, formerly Biograde, Nanjing, China), 18% of a linear low density polyethylene (LLDPE) (melt flow rate of 1 and density of 0.918 g/cc, Grade 118 W, supplied by SABIC) and 18% low density polyethylene (LDPE) (melt flow rate of 2.8 g/10 min and density: 0.925, Grade: Q281, supplied by SINOPEC Shanghai, Shanghai, China), and 7% white masterbatch (Shanghai Ngai Hing Plastic Materials Co., Ltd.) was fed to a single screw extruder blown film machine, the screw diameter was 150 mm, the Length/Diameter was 30/1. The die gap was 1.8 mm.
All the films from Examples 1, 2, and 3 were printed with conventional dyes/inks used in packaging. The printing quality of Example 1 appeared to be the best. These films were also converted into product bags for absorbent products, and no physical or visual issues were encountered. The winding tension was reduced from 10.6 kgf to 6.1 kgf to overcome wrinkle issues. Mechanical and other physical testing were performed, the results were listed in the following tables:
Considering the renewable film package will be stored or used in places with high humidity, such as lavatories or bathrooms, a hot water vapor and/or liquid submersion test was conducted to test how well the films may withstand liquid water or water vapor. Since the films according to the present invention contain TPS that is water sensitive, it was expected that the tensile strength of the films would be easier to compromise when exposed to or immersed in water. The results are summarized in the following tables. A finding of interest is that the MD/CD tensile strength and elogation percentage values are even better that those samples that were not subjected to the water vapor or liquid immersion.
Test Condition
Performance Test Result
This example demonstrates a three layer film made on a pilot blown film extrusion line. In this example, the exterior layers A and C are identical and comprise of 45% Dow LLDPE 2085B (density 0.919), 45% Dow LMDPE 2038.68G (density: 0.935), and 10% Dow LDPE 501I. The interior layer contains 32% Dow 2085B, 32% 2038.68G, 10% Dow 501I, and 26% of Biograde BL-F resin. The film had an overall 10% by weight of plant starch-based material.
The co-extrusion was process on a three-layer blown film line, the extruders for Layer A and Layer C were single screw extruders manufactured by Collins which had a diameter of ¾″ and L/D of 26:1 D. The core layer (Layer B) extruder was a single screw extruder with a diameter of 1.5″ and an L/D of 28/1, manufactured by Killion. The processing temperatures for Layer A (heat heal layer) were: 70, 175, 205, 230, 212, 212, and 213° C. respectively for zones 1 to 6 and the melt temperature, the melt pressure was 167 bar. The processing temperatures for Layer B were: 245, 280, 320, 340, 340, 340, and 319° F. respectively for zones 1 to 3, Die 1 to 3, and melt temperature, the melt pressure was 2900 psi. The processing temperatures for Layer C (the printing surface) were: 95, 175, 205, 230, 212, 212, and 217° C. respectively for zones 1 to 6 and the melt temperature, the melt pressure was 84 bar. The die was capable of producing films of 20/60/20 configuration, the upper block temperature, lower block temperature, adaptor, clamp ring temperatures were 335° C., 335° C., 335° C., and 340° C.
This example demonstrates a three layer film made on a pilot blown film extrusion line. In this example, the exterior layers A and C are identical and comprise of 45% Dow LLDPE 2085B (density 0.919), 45% Dow LMDPE 2038.68G (density: 0.935), and 10% Dow LDPE 501I. The interior layer contains 32% Dow 2085B, 32% 2038.68G, 10% Dow 501I, and 26% of Biograde BL-F resin. The 3-layer film had 20% by weight of plant starch based materials based on the total weight of the films.
The co-extrusion was process on a three-layer blown film line, the extruders for Layer A and Layer C were single screw extruders manufactured by Collins which had a diameter of ¾″ and L/D of 26:1 D. The core layer (Layer B) extruder was a single screw extruder with a diameter of 1.5″ and an L/D of 28/1, manufactured by Killion. The processing temperatures for Layer A (heat heal layer) were: 70, 175, 205, 230, 212, 212, and 213° C. respectively for zones 1 to 6 and the melt temperature, the melt pressure was 167 bar. The processing temperatures for Layer B were: 245, 280, 320, 340, 340, 340, and 319° F. respectively for zones 1 to 3, Die 1 to 3 and melt temperature, the melt pressure was 2900 psi. The processing temperatures for Layer C (the printing surface) were: 95, 175, 205, 230, 212, 212, and 217° C. respectively for zones 1 to 6 and the melt temperature, the melt pressure was 84 bar. The die was capable of producing films of 20/60/20 configuration, the upper block temperature, lower block temperature, adaptor, clamp ring temperatures were 335° C., 335° C., 335° C., and 345° C.
As one incorporates more corn resin into the blend the films become more bio-degradable. Even though embodiments of the present film materials that have a heightened level of starch within will tend to have rougher film surfaces (on a micron scale) than other polyolefin-based packaging film materials, any difference in appearance of finely printed designs or pattern details are virtually imperceptible to the naked eye. Mechanical performance of the film is within commercial tolerances. Favored features of certain film embodiments (e.g., Example 1) have a natural matte finish and a “soft” feel to the touch that is preferred by consumers.
The present invention has been described in general and in detail by way of examples. Persons of skill in the art understand that the invention is not limited necessarily to the embodiments specifically disclosed, but that modifications and variations may be made without departing from the scope of the invention as defined by the following claims or their equivalents, including other equivalent components presently known, or to be developed, which may be used within the scope of the present invention. Therefore, unless changes otherwise depart from the scope of the invention, the changes should be construed as being included herein.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
The present application is a continuation-in-part and claims benefit of priority to U.S. patent application Ser. No. 13/211,572, filed on Aug. 17, 2011, the contents of which are incorporated herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13211572 | Aug 2011 | US |
| Child | 13219984 | US |
