Process for producing degradable films and articles made therefrom

Abstract

Articles are formed from biodegradable polymers that have improved elongation properties and toughness. The articles can comprise films and can contain one or more polyhydroxyalkanoate polymers. The articles, in accordance with the present disclosure, are heat treated during the process without being substantially drawn or stretched.

Description

[0001]PROCESS FOR PRODUCING DEGRADABLE FILMS AND ARTICLES MADE THEREFROM CROSS-REFERENCE TO RELATED APPLICATION The present application is related and has right of priority to U.S. Provisional Patent Application No.63 / 688,961 filed on August 30, 2024, which is incorporated by reference in its entireties for all purposes. BACKGROUND Various attempts have been made to form fibers, nonwoven webs, and films from biodegradable polymers. Various problems have been encountered, however, in being able to form fibers and films from biodegradable polymers, such as polylactic acid polymers and polyhydroxyalkanoate polymers. For example, many biodegradable polymers experience a very slow crystallization rate. The crystallization rate of these polymers, for instance, can be much slower than conventional fossil-based polymers, such as polypropylene. The slow crystallization rate can lead to the formation of articles with low strength and a “sticky” surface feature. In addition, articles, such as fibers and films, made from biodegradable polymers typically exhibit low elongations that are not acceptable in certain applications. In view of the above problems, in the past, biodegradable polymers have been combined with other components, such as other polymers including plasticizers, in order to not only make it easier to process the polymers but also to produce articles with better mechanical properties. For instance, U.S. Patent No.8,598,404, U.S. Patent No.8,936,740, U.S. Patent No.9,056,967, U.S. Patent No. 10,718,069, and U.S. Patent No.11,236,443, which are all incorporated herein by reference, disclose combining a biodegradable polymer with other components in forming various articles including fibers and films. Although the above polymer compositions and related processes for forming articles has made great advances in the art, further improvements are needed. In particular, improvements are needed in developing techniques and processes for forming films from biodegradable polymers. A need also exists for films made from biodegradable polymers with improved mechanical properties. SUMMARY In general, the present disclosure is directed to an extruded article, such as a film, made from biodegradable polymers. The film, for instance, can be made primarily from one or more polyhydroxyalkanoate polymers. In accordance with the present disclosure, the articles, such as films, are formed in a manner that prevents the articles from becoming brittle and splitty. Instead, the articles are formed in a manner that produces unexpectedly enhanced stretch characteristics, especially in the cross-direction. In one embodiment, for instance, the present disclosure is directed to a process for producing a film. The process includes extruding a molten thermoplastic polymer through a die to form the film. The polymer composition comprises at least one polyhydroxyalkanoate polymer. In accordance with the present disclosure, the film is heated without substantially stretching the film. For instance, the film can be heated to a temperature of greater than about 80°F, such a greater than about 100°F, such a greater than about 110°F, such as greater than about 120°F, such as greater than about 125°F, such as greater than about 135°F, such as greater than about 145°F, such as greater than about 155°F, and less than about 300°F, such as less than about 180°F, such as less than about 170°F, such as less than about 160°F, such as less than about 150°F, such as less than about 140°F. Heating the film causes the cross-direction break stretch of the film to unexpectedly increase. For instance, the cross-direction break stretch of the film increases by greater than about 50%, such as by greater than about 80%, such as by greater than about 100%, such as by greater than about 125%, such as by greater than about 150%, and generally less than about 2,000%. For instance, in one embodiment, the resulting film can display a cross-directional break stretch of greater than about 200%, such as greater than about 250%, such as greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%, and less than about 1,000%. In one embodiment, the film comprises a cast film. The film can have a basis weight, for instance, of from about 15 gsm to about 70 gsm, such as from about 25 gsm to about 40 gsm. The polymer composition used to form the film can contain one or more polyhydroxyalkanoate polymers in an amount greater than about 40% by weight, such as in an amount greater than about 50% by weight, such as in an amount greater than about 60% by weight, such as in an amount greater than about 70% by weight, such as in an amount greater than about 80% by weight, and, in one embodiment, in an amount greater than about 90% by weight. Optionally, the film can contain a filler, such as calcium carbonate particles. The film can optionally contain a second polymer in addition to one or more polyhydroxyalkanoate polymers. The second polymer can comprise a polycaprolactone, a polyesteramide, a polylactic acid, a polyglycolic acid, a polyalkylene carbonate, a second polyhydroxyalkanoate polymer such as a poly-3-hydroxyvalerate, a polybutylene succinate, a polybutylene succinate adipate, a polyethylene succinate, a polybutylene adipate terephthalate, a polyethylene adipate terephthalate, a polyethylene adipate isophthalate, a polybutylene adipate isophthalate, or mixtures thereof. In one embodiment, the second polymer can comprise a polybutylene adipate terephthalate polymer. The polyhydroxyalkanoate polymer contained in the polymer composition can have a melting point of less than about 190°C, such as less than about 170°C, such as less than about 160°C, such as less than about 155°C, and greater than about 120°C, such as greater than about 130°C. The polyhydroxyalkanoate polymer can display a melt flow rate of less than about 100 g / 10 min, such as less than about 60 g / 10 min, such as less than about 50 g / 10 min, and greater than about 1 g / 10 min, such as greater than about 2 g / 10 min, such as greater than about 5 g / 10 min, such as greater than about 25 g / 10 min, when tested according to ASTM Test D1238-E at a load of 2.16 kg and at a temperature of 190°C, unless otherwise specified. (the melt flow rate can also be measured at 2.16 kg and at a temperature of 175°C). The polyhydroxyalkanoate polymer can display a relative viscosity when tested according to ASTM Test D4603 (0.5% by weight in solvent) of from about 1.5 to about 3.5, such as from about 2 to about 3. The present disclosure is also directed to a film formed from a polymer composition as described above that contains at least one polyhydroxyalkanoate polymer in an amount greater than about 50% by weight. The film can have a basis weight of from about 10 gsm to about 75 gsm , such as from about 12 gsm to about 45 gsm. In accordance with the present disclosure, the film can have a cross-direction break stretch of greater than about 250% and a machine direction break stretch of also greater than about 250%. For instance, the film can have a cross-direction break stretch of greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%. The film of the present disclosure can be incorporated into all different types of products. For instance, in one embodiment, the film can be incorporated into an absorbent article, such as a feminine hygiene product. For example, in one embodiment, the film can be used as a baffle in a feminine pad. The film can also be used to produce a pouch for packaging or can comprise a backsheet of other absorbent articles, such as a diaper. Other features and aspects of the present disclosure are discussed in greater detail below. BRIEF DESCRIPTION OF THE DRAWINGS A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: Figure 1 is a systematic diagram showing one embodiment of a process for producing an article, such as a film, in accordance with the present disclosure; and Figure 2 is a top view of an absorbent article that may be formed in accordance with the present disclosure. Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. DEFINITIONS The term “biodegradable” generally refers to a material that degrades from the action of naturally occurring microorganisms, such as bacteria, fungi, and algae; environmental heat; moisture; or other environmental factors, such as determined according to ASTM Test Method 5338.92. The biodegradable polyesters employed in the present disclosure can have a relatively low glass transition temperature (“Tg”) to reduce stiffness of the film and improve the processability of the polymers. For example, the Tgmay be about 25°C or less, in some embodiments about 0°C or less, and in some embodiments, about −10°C or less. Likewise, the melting point of the biodegradable polyesters is also relatively low to improve the rate of biodegradation. For example, the melting point is typically from about 50°C to about 180°C, in some embodiments from about 80°C to about 160°C, and in some embodiments, from about 100°C to about 140°C. The melting temperature and glass transition temperature may be determined using differential scanning calorimetry (“DSC”) in accordance with ASTM D-3417 as is well known in the art. Such tests may be employed using a DSC Q100 Differential Scanning Calorimeter (outfitted with a liquid nitrogen cooling accessory) and with a THERMAL ADVANTAGE (release 4.6.6) analysis software program, which are available from T.A. Instruments Inc. of New Castle, Del. As used herein, the term “fibers” refer to elongated extrudates formed by passing a polymer through a forming orifice such as a die. Unless noted otherwise, the term “fibers” includes both discontinuous fibers having a definite length and substantially continuous filaments. Substantially filaments may, for instance, have a length much greater than their diameter, such as a length to diameter ratio (“aspect ratio”) greater than about 15,000 to 1, and in some cases, greater than about 50,000 to 1. As used herein, the term “nonwoven web” refers to a web having a structure of individual fibers that are randomly interlaid, not in an identifiable manner as in a knitted fabric. Nonwoven webs include, for example, meltblown webs, spunbond webs, carded webs, wet-laid webs, airlaid webs, coform webs, hydraulically entangled webs, etc. The basis weight of the nonwoven web may generally vary, but is typically from about 5 grams per square meter (“gsm”) to 200 gsm, in some embodiments from about 10 gsm to about 150 gsm, and in some embodiments, from about 15 gsm to about 100 gsm. The term “machine direction” or “MD” as used herein with respect to a film means the direction parallel to the predominant direction of movement of the article through its manufacturing line and can also refer to the length direction. The term “cross machine direction” or “CD” when used herein with respect to a film means the direction perpendicular to the predominant direction of movement of the articles through its manufacturing line and can also be referred to as the width direction. As used herein, an “absorbent article” refers to an article that is capable of absorbing water or other fluids. Examples of some absorbent articles include, but are not limited to, personal care absorbent articles, such as diapers, training pants, absorbent underpants, incontinence articles, feminine hygiene products (e.g., sanitary napkins), swimwear, baby wipes, mitt wipes, and the like; medical absorbent articles, such as garments, fenestration materials, underpads, bed pads, bandages, absorbent drapes, and medical wipes; food service wipers; clothing articles; pouches, and so forth. As used herein “melting point” is determined by differential scanning calorimetry (DSC). For purposes herein, the maximum of the highest temperature peak is considered to be the melting point of the polymer. A “peak” in this context is defined as a change in the general slope of the DSC curve (heat flow versus temperature) from positive to negative, forming a maximum without a shift in the baseline where the DSC curve is plotted so that an endothermic reaction would be shown with a positive peak. A heating rate of 10° C. / minute is used. Tensile properties are measured using sample sizes of 177.8 mm (～7 inch) by 76mm (～3 inch width). A constant speed extension type tensile testing machine is used, such as an MTS SYNERGY 200 tensile testing machine, that is available from MTS Systems company (Minn. Edne Prairie).This tensile testing machine is equipped with TESTWORKS4.08B software of MTS company. Samples are fixed between the gripping apparatus at the front and the back side. The gauge length is 76 mm. The gripping apparatus face is rubbery, and the long limit of this gripping apparatus is perpendicular to draw direction. The gripping apparatus pressure is 40 pounds / square inch pressure with pneumatic mode. The test rate is 305mm / min. A 40% break sensitivity is carried out. Ten samples are tested in the machine direction and ten samples are tested in the cross direction. Results are averaged. Peak load, peak stretch, break load and bread stretch can be measured in each direction. DETAILED DESCRIPTION It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure. In general, the present disclosure is directed to a process for producing articles, such as films, from biodegradable polymers. For example, in one aspect, the films can be made from one or more polyhydroxyalkanoate polymers. The polyhydroxyalkanoate polymers can be used alone or can be combined with various other components, such as other biodegradable polymers, fillers or the like. In one aspect, however, the film can be made solely from one or more biodegradable polymers without having to add a plasticizer. Biodegradable polymers, such as polyester biopolymers, can be processed into various different articles and then degrade over time in the presence of microorganisms. Many biodegradable polymers, such as polyhydroxyalkanoate polymers, however, form elongated articles, such as films, that do not have mechanical properties comparable with fossil-based polymers. For instance, the films tend to be very brittle and splitty. The present disclosure, however, is directed to producing films from biodegradable polymers that are not brittle, have increased toughness, and can bend and flex without cracking or splitting. In accordance with the present disclosure, one or more polyhydroxyalkanoate polymers are used to formulate a polymer composition and form a film. During formation of the film, the film is subjected to an elevated temperature without substantially stretching or drawing the film. Although unknown, it was discovered that the heat treatment of the film during processing can dramatically and unexpectedly improve the physical properties of the film. In particular, it was discovered that the heat treatment can dramatically improve the cross-directional elongation properties of the film, thus increasing toughness and processability. Thermoplastic Composition The thermoplastic polymer composition used to form articles in accordance with the present disclosure generally contains one or more biodegradable polymers. In one aspect, the biodegradable polymer comprises a polyhydroxyalkanoate polymer. Polyhydroxyalkanoate polymers are generally semi-crystalline, thermoplastic polyester polymers that can either be produced by synthetic methods or by a variety of microorganisms, such as bacteria or algae. The latter typically produce optically pure materials. Some of the key characteristics of polyhydroxyalkanoate polymers is that the polymers are biodegradable meaning that they can be broken down by natural biological processes. Thus, the polymers are environmentally friendly and sustainable. In addition, polyhydroxyalkanoate polymers are biocompatible. In particular, polyhydroxyalkanoate polymers are compatible with living tissues making them suitable for medical applications and for producing absorbent articles and other products intended to contact a wearer or patient. Polyhydroxyalkanoate polymers come in various different forms. For instance, there are short chain length polyhydroxyalkanoate polymers that are formed from monomers with three to five carbon atoms such as polyhydroxybutyrate. There are also medium chain length polyhydroxyalkanoate polymers formed from monomers with from about six to about 14 carbon atoms, such as polyhydroxyhexanoate. Polyhydroxyalkanoates include various different homopolymers and copolymers which can all be used in the process of the present disclosure. In addition, the polymer composition of the present disclosure used to produce various articles, such as films, can be produced from a single polyhydroxyalkanoate polymer or from a blend of polyhydroxyalkanoate polymers. Various different polyhydroxyalkanoate homopolymers exist. The most common PHA homopolymers include poly(3-hydroxybutyrate) (PHB) (made up of 3-hydroxybutyrate monomers); poly(4-hydroxybutyrate) (P4HB) (composed of 4-hydroxybutyrate monomers); poly(3-hydroxyvalerate) (PHV) (composed of 3-hydroxyvalerate monomers); and poly(3-hydroxyhexanoate) (PHHx) (made of 3-hydroxyhexanoate monomers). PHA copolymers can be made up of two or more different types of monomers. These copolymers can exhibit a range of properties by varying the ratio and type of monomers used. PHA copolymers include poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (made of 3-hydroxybutyrate and 3-hydroxyvalerate monomers); poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) (composed of 3-hydroxybutyrate and 3-hydroxyhexanoate monomers); poly(3-hydroxybutyrate-co-4- hydroxybutyrate) (P3HB4HB) (contains 3-hydroxybutyrate and 4-hydroxybutyrate monomers); poly(3- hydroxybutyrate-co-3-hydroxydecanoate) (PHBHD) (composed of 3-hydroxybutyrate and 3- hydroxydecanoate monomers); poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (PHBO) (composed of 3-hydroxybutyrate and 3-hydroxyoctanoate monomers); poly(3-hydroxybutyrate-co-3- hydroxyheptanoate) (PHBH) (made of 3-hydroxybutyrate and 3-hydroxyheptanoate monomers); poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) (PHBV4HB) (comprised of 3- hydroxybutyrate, 3-hydroxyvalerate, and 4-hydroxybutyrate monomers); and poly(3-hydroxybutyrate- co-3-hydroxyhexanoate-co-3-hydroxydecanoate) (PHBHHxHD) (made of 3-hydroxybutyrate, 3- hydroxyhexanoate, and 3-hydroxydecanoate monomers). In one aspect, the polyhydroxyalkanoate polymer or polymers contained in the polymer composition of the present disclosure have controlled crystalline or amorphous properties. For instance, the polyhydroxyalkanoate polymer for use in the present disclosure can be substantially amorphous (greater than 50% by weight), substantially crystalline (greater than 50% by weight), or can comprise a mixture of both. Various techniques can be used to produce polyhydroxyalkanoate polymers that are substantially amorphous. Producing amorphous polyhydroxyalkanoate polymers can be done through controlling the process of producing the polymers. For instance, the amorphous portion of the polymer can be increased through using particular types of microorganisms to produce the polymer, through extraction, and through various post-processing techniques. For instance, producing polyhydroxyalkanoate polymers from microorganisms such as Cupriavidus nectaor or Ralstonia eutropha can be used to produce polymers with more amorphous content. In addition, various techniques can be used during fermentation to increase the amorphous content of the polymer. For instance, the selected microorganisms can be grown in a nutrient-rich medium. In addition, the polymer can be grown while limiting specific nutrients in the environment including nitrogen, phosphorus, or oxygen. In addition, an excess of a carbon source can assist in increasing the amorphous content of the polymer. When collecting and purifying the polymer, various other steps can be used to control the amorphous and / or crystalline content of the polymer. For instance, rapidly cooling the extracted polyhydroxyalkanoate polymer can avoid crystallization. In one aspect, for instance, the polymer can be quenched in liquid nitrogen or using a cooling bath. Amorphous and crystalline polyhydroxyalkanoate polymers may be used to produce the polymer composition of the present disclosure. In one aspect, however, a polymer is used having a greater amorphous content which facilitates initial formation of the article. The polyhydroxyalkanoate polymer of the present disclosure generally has a melting point of from about 120°C to about 190°C. In one aspect, the melting point can be relatively low. For instance, the melting point can be less than about 170°C, such as less than about 160°C, such as less than about 155°C, and greater than about 125°C, such as greater than about 130°C. The polyhydroxyalkanoate polymer can also have a relatively high melt flow rate or a relatively low melt flow rate. The melt flow rate, for instance, can be greater than about 1 g / 10 min, such as greater than about 2 g / 10 min, such as greater than about 5 g / 10 min, such as greater than about 15 g / 10 min, such as greater than about 20 g / 10 min, such as greater than about 25 g / 10 min. The melt flow rate is generally less than about 100 g / 10 min, such as less than about 60 g / 10 min, such as less than about 50 g / 10 min, such as less than about 40 g / 10 min, such as less than about 35 g / 10 min, such as less than about 30 g / 10 min. In one aspect, the melt flow rate is from about 1 g / 10 min to about 10 g / 10 min. In another aspect, the melt flow rate is from about 10 g / 10 min to about 35 g / 10 min. In one aspect, a mixture of polymers with different melt flow rates can be used. When tested in a 0.5% by weight solvent, the polyhydroxyalkanoate polymer can display a relative viscosity of from about 1.5 to about 3.5, such as from about 2 to about 3. Relative viscosity can be measured according to ASTM Test D4603. The polymer composition can contain one or more polyhydroxyalkanoate polymers generally in an amount greater than about 40% by weight, such as in an amount greater than about 50% by weight, such as in an amount greater than about 60% by weight, such as in an amount greater than about 70% by weight, such as in an amount greater than about 80% by weight. In one aspect, the polymer composition may only contain polyhydroxyalkanoate polymers and they can be present in the composition in an amount greater than about 85% by weight, such as in an amount greater than about 90% by weight, such as in an amount greater than about 95% by weight. The polymer composition can contain various other components and additives. For instance, the polymer composition can contain a thermoplastic starch as disclosed in U.S. Patent No. 11,236,443, which is incorporated herein by reference. Other additives and components that can be added include plasticizers and other polymers. Plasticizers that may be used include polyethylene glycol or a polycaprolactone. When present, plasticizers are typically included in an amount less than about 10% by weight, such as from about 0.1% by weight to about 5% by weight. Of course, other ingredients may be utilized for a variety of different reasons. For instance, materials that may be used include, without limitation, catalysts, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, solid solvents, compatibilizers, nucleating agents (e.g., titanium dioxide, calcium carbonate, etc.), particulates, and other materials added to enhance the processability of the thermoplastic composition. When utilized, it is normally desired that the amounts of these additional ingredients are minimized to ensure optimum compatibility and cost-effectiveness. Thus, for example, it is normally desired that such ingredients constitute less than about 10 wt. %, in some embodiments less than about 8 wt. %, and in some embodiments, less than about 5 wt. % of the thermoplastic composition. It should also be understood that other components may be included in the thermoplastic composition. One such component that may be employed is an additional biodegradable polymer or polyester, including aliphatic polyesters, such as polycaprolactone, polyesteramides, modified polyethylene terephthalate, polylactic acid (PLA) and its copolymers, terpolymers based on polylactic acid, polyglycolic acid, polyalkylene carbonates (e.g., polyethylene carbonate), poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV), poly-3-hydroxybutyrate-co-4-hydroybutyrate, poly-3- hydroxybutyrate-co-3-hydroxyvalerate copolymers (PHBV), poly-3-hydroxybutyrate-co-3- hydroxyhexanoate, poly-3-hydroxybutyrate-co-3-hydroxyoctanoate, poly-3-hydroxybutyrate-co-3- hydroxydecanoate, poly-3-hydroxybutyrate-co-3-hydroxyoctadecanoate, and succinate-based aliphatic polymers (e.g., polybutylene succinate, polybutylene succinate adipate, polyethylene succinate, etc.); aliphatic-aromatic copolyesters (e.g., polybutylene adipate terephthalate, polyethylene adipate terephthalate, polyethylene adipate isophthalate, polybutylene adipate isophthalate, etc.), and so forth. In one particular embodiment, a polyhydroxyalkanoate polymer is combined with a polybutylene adipate terephthalate polymer in producing articles in accordance with the present disclosure. When another or second biodegradable polymer is present in the polymer composition in addition to a polyhydroxyalkanoate polymer, the second biodegradable polymer can be present generally in an amount less than about 40% by weight, such as in an amount less than about 30% by weight, such as in an amount less than about 20% by weight, such as in an amount less than about 10% by weight, and in an amount greater than about 1% by weight, such as in an amount greater than about 3% by weight, such as in an amount greater than about 5% by weight, such as in an amount greater than about 8% by weight, such as in an amount greater than about 10% by weight, such as in an amount greater than about 15% by weight. Another component that can be present in the polymer composition is a filler. Fillers are particulates or other forms of material that may be added to the polymer composition that will not chemically interfere with the polymer and which may be uniformly dispersed throughout the polymer matrix. The filler can be used to enhance one or more properties. For instance, fillers can be used to increase the porosity of the film, change the color of the extruded article, change the opacity of the extruded article, or can influence one or more other physical properties. Suitable fillers that can be added to the polymer composition include calcium carbonate, magnesium oxide, a clay such as kaolin clay, mica, or the like. In one embodiment, the filler can have an average particle size of less than about 20 microns, such as less than about 15 microns, such as less than about 10 microns, such as less than about 8 microns, such as less than about 5 microns, such as less than about 2 microns, such as less than about 1 micron, and generally greater than about 0.01 microns. When present, a filler can be contained in the polymer composition in an amount greater than about 1% by weight, such as in an amount greater than about 2% by weight, such as in an amount greater than about 5% by weight, such as in an amount greater than about 8% by weight, such as in an amount greater than about 10% by weight, such as in an amount greater than about 15% by weight, and in an amount less than about 30% by weight, such as in an amount less than about 25% by weight, such as in an amount less than about 20% by weight, such as in an amount less than about 18% by weight, such as in an amount less than about 15% by weight. Optionally, the polymer composition can contain a nucleating agent. The nucleating agent can comprise a compound having a melting point higher than the polyhydroxyalkanoate polymer. Examples of nucleating agents include inorganic substances such as boron nitride, titanium oxide, talc, layered silicate, calcium carbonate, and the like. Sugar alcohol compounds, polyvinyl alcohol, chitin, polyethylene oxide, and the like can also be used as nucleating agents. In still another embodiment, the nucleating agent can comprise a sorbitol or sorbitol-based derivative. Nucleating agents are generally present in minor amounts, such as in amounts less than about 3% by weight, such as in an amount less than about 2% by weight, such as in an amount less than about 1% by weight, and in an amount greater than about 0.1% by weight. Film Construction The film of the present invention may be mono- or multi-layered. Multilayer films may be prepared by co-extrusion of the layers, extrusion coating, or by any conventional layering process. Such multilayer films normally contain at least one base layer and at least one skin layer, but may contain any number of layers desired. For example, the multilayer film may be formed from a base layer and one or more skin layers, wherein the base layer is formed from a polymer composition formulated in accordance with the present disclosure that contains one or more polyhydroxyalkanoate polymers. As described above, in one embodiment, the polyhydroxyalkanoate polymer can initially have a substantial amorphous content. Any known technique may be used to form a film from the polymer composition, including blowing, casting, flat die extruding, etc. In one particular embodiment, the film may be formed by a blown process in which a gas (e.g., air) is used to expand a bubble of the extruded polymer blend through an annular die. The bubble is then collapsed and collected in flat film form. Processes for producing blown films are described, for instance, in U.S. Pat. No.3,354,506 to Raley; U.S. Pat. No. 3,650,649 to Schippers; and U.S. Pat. No.3,801,429 to Schrenk et al., as well as U.S. Patent Application Publication Nos.2005 / 0245162 to McCormack, et al. and 2003 / 0068951 to Boggs, et al., all of which are incorporated herein in their entirety by reference thereto for all purposes. In yet another embodiment, however, the film is formed using a casting technique. Referring to FIG.1, for instance, one embodiment of a method for forming a cast film in accordance with the present disclosure is shown. The polymer composition formulated in accordance with the present disclosure containing one or more polyhydroxyalkanoate polymers can be supplied to a melt blending device for forming a feed material to the process. For example, an extruder may be employed that receives all of the components of the polymer composition, blends them together under high shear / pressure and heat to form pellets which can then be supplied to the extrusion apparatus 80 and cast onto a casting roll 90 to form a film 10a as shown in FIG.1. If a multilayered film is to be produced, the multiple layers are co-extruded together onto the casting roll 90. The casting roll 90 may optionally be provided with embossing elements to impart a pattern to the film. The casting roll 90 can be kept at a temperature sufficient to solidify the sheet 10a as it is formed, such as from about 20°C to 150°C. If desired, a vacuum box may be positioned adjacent to the casting roll 90 to help keep the precursor film 10a close to the surface of the roll 90. Additionally, air knives or electrostatic pinners may help force the precursor film 10a against the surface of the casting roll 90 as it moves around a spinning roll. An air knife is a device known in the art that focuses a stream of air at a very high flow rate to pin the edges of the film. Once cast, in accordance with the present disclosure, the film 10a is heated without substantially stretching the film. For instance, as shown in FIG.1, the film can be fed to a plurality of guide rolls 92. The film 10a can be heated using various different techniques and methods. For example, in one embodiment, the guide rolls 92 can be heated for heating the film without substantially stretching the film. Alternatively, the film can be fed through a heating device 94. The heating device 94 can comprise any suitable heating device capable of heating the film traveling therethrough. The heating device 94, for instance, can use gas or electrical heating elements for producing a heated environment through which the film passes. As described above, the film is heated to a temperature of at least about 100°F, such as at least about 110°F, such as at least about 120°F, and at a temperature of less than about 300°F, such as less than about 250°F. The film is heated for a period of time of greater than about 1 second, such as greater than about 3 seconds, such as greater than about 5 seconds, such as greater than about 8 seconds, such as greater than about 10 seconds, such as greater than about 15 seconds, such as greater than about 20 seconds, such as greater than about 25 seconds, such as greater than about 30 seconds, and less than about 5 minutes, such as less than about 3 minutes, such as less than about 2 minutes, such as less than about 1 minute, such as less than about 40 seconds, such as less than about 30 seconds. Although unknown, heating the film as shown in FIG.1 has been found to dramatically and unexpectedly improve the toughness of the film. In particular, especially the elongation of the film in the cross-direction is dramatically improved. As described above, the film 10a is heated in the process as shown in FIG.1 without substantially stretching or drawing the film. For instance, the film is stretched an amount less than about 50%, such as in an amount less than about 40%, such as in an amount less than about 30%, such as in an amount less than about 20%, such as in an amount less than about 10%, such as in an amount less than about 5%, such as in an amount less than about 2% in the machine direction or length direction. Once the film 10a exits the heating zone, the film can optionally be oriented in one or more directions. Orientation may also form micropores in a film containing a filler, thus providing breathability to the film. For example, the film may remain at a temperature below the melting point of one or more polymers in the film, but high enough to enable the composition to be drawn or stretched. In the case of sequential orientation, the “softened” film is drawn by rolls rotating at different speeds of rotation such that the sheet is stretched to the desired draw ratio in the longitudinal direction (machine direction). This “uniaxially” oriented film may then be laminated to a fibrous web. In addition, the uniaxially oriented film may also be oriented in the cross-machine direction to form a “biaxially oriented” film. For example, the film may be clamped at its lateral edges by chain clips and conveyed into a tenter oven. In the tenter oven, the film may be reheated and drawn in the cross-machine direction to the desired draw ratio by chain clips diverged in their forward travel. Referring again to FIG.1, for instance, one method for forming a uniaxially oriented film is shown. As illustrated, the precursor film 10a is directed to a film-orientation unit 100 or machine direction orienter (“MDO”), such as commercially available from Marshall and Willams, Co. of Providence, R.I. The MDO has a plurality of stretching rolls (such as from 5 to 8) which progressively stretch and thin the film in the machine direction, which is the direction of travel of the film through the process as shown in FIG.1. While the MDO 100 is illustrated with eight rolls, it should be understood that the number of rolls may be higher or lower, depending on the level of stretch that is desired and the degrees of stretching between each roll. The film may be stretched in either single or multiple discrete stretching operations. It should be noted that some of the rolls in an MDO apparatus may not be operating at progressively higher speeds. If desired, some of the rolls of the MDO 100 may act as preheat rolls. If present, these first few rolls heat the film 10a above room temperature (e.g., to 125°F). The progressively faster speeds of adjacent rolls in the MDO act to stretch the film 10a. The rate at which the stretch rolls rotate determines the amount of stretch in the film and final film weight. The resulting film 10b may then be wound and stored on a take-up roll 60. While not shown here, various additional potential processing and / or finishing steps known in the art, such as slitting, treating, aperturing, printing graphics, or lamination of the film with other layers (e.g., nonwoven web materials), may be performed without departing from the spirit and scope of the invention. The thickness or basis weight of the formed film 10b can vary depending upon the particular application and the desired result. In one aspect, the film can be relatively thin and can have a thickness of less than about 100 microns, such as less than about 80 microns, such as less than about 50 microns, such as less than about 40 microns, and greater than about 1 micron, such as greater than about 5 microns, such as greater than about 10 microns. The basis weight of the film can be less than about 100 gsm, such as less than about 70 gsm, such as less than about 60 gsm, such as less than about 50 gsm, such as less than about 40 gsm, such as less than about 35 gsm, such as less than about 30 gsm. The basis weight of the film can be greater than about 5 gsm, such as greater than about 10 gsm, such a greater than about 20 gsm, such as greater than about 25 gsm. As stated above, the process of the present disclosure expectedly and dramatically improves the toughness of the film formed. For instance, the elongation characteristics of the film can be dramatically improved in the cross-direction. The cross-direction break stretch of the film, for instance, can be increased by greater than about 50%, such as greater than about 80%, such as greater than about 100%, such as greater than about 125%, such as greater than about 150%, and less than about 2,000% in comparison to the same film that is not heat treated as described above. For instance, the film can display a cross-direction break stretch of greater than about 200%, such as greater than about 250%, such as greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%, and less than about 1,000%. The break stretch of the film in the machine direction can also be greater than about 250%, and, in one aspect, can be within about 40%, such as within about 30%, such as within about 20% of the break stretch of the film in the cross-direction. The break stretch of the film in the machine direction can be greater than about 275%, such as greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%, and generally less than about 1,500%. Films made according to the present disclosure can display a machine direction peak load of greater than about 2,000 gf, such as greater than about 2,400 gf, such as greater than about 2,800 gf, such as greater than about 3,200 gf, such as greater than about 3,600 gf, such as greater than about 4,000 gf, such as greater than about 4,400 gf, and less than about 10,000 gf. The film can display a cross-direction peak load of greater than about 1,500 gf, such as greater than about 1,800 gf, such as greater than about 2,000 gf, such as greater than about 2,200 gf, such as greater than about 2,400 gf, and less than about 10,000 gf. The above mechanical strength properties, for instance, are achievable for films having a basis weight of from about 20 gsm to about 40 gsm, such as from about 25 gsm to about 35 gsm. The biodegradable film of the present invention may be used in a wide variety of applications. For example, as indicated above, the film may be used in an absorbent article. An “absorbent article” generally refers to any article capable of absorbing water or other fluids. Examples of some absorbent articles include, but are not limited to, personal care absorbent articles, such as diapers, training pants, absorbent underpants, incontinence articles, feminine hygiene products (e.g., sanitary napkins, pantiliners, etc.), swim wear, baby wipes, and so forth; medical absorbent articles, such as garments, fenestration materials, underpads, bedpads, bandages, absorbent drapes, and medical wipes; food service wipers; clothing articles; and so forth. Several examples of such absorbent articles are described in U.S. Pat. No.5,649,916 to DiPalma, et al.; U.S. Pat. No.6,110,158 to Kielpikowski; U.S. Pat. No.6,663,611 to Blaney, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Still other suitable articles are described in U.S. Patent Application Publication No. 2004 / 0060112 A1 to Fell et al., as well as U.S. Pat. No.4,886,512 to Damico et al.; U.S. Pat. No. 5,558,659 to Sherrod et al.; U.S. Pat. No.6,888,044 to Fell et al.; and U.S. Pat. No.6,511,465 to Freiburger et al., all of which are incorporated herein in their entirety by reference thereto for all purposes. Materials and processes suitable for forming such absorbent articles are well known to those skilled in the art. In one embodiment, the biodegradable film of the present disclosure containing one or more polyhydroxyalkanoate polymers can be used to produce a film that is incorporated into a feminine hygiene pad as shown in FIG.2. The film, for instance, can be used to construct a release liner for covering adhesive on the flaps, can be used to construct the topsheet, can be used to construct the backsheet, can be used to construct a transfer delay member, or the like. For purposes of illustration only, an absorbent article 20 is shown in FIG.2 such as a sanitary napkin for feminine hygiene. In the illustrated embodiment, the absorbent article 20 includes a main body portion 22 containing a topsheet 40, an outer cover or backsheet 42, an absorbent core 44 positioned between the backsheet 42 and the topsheet 40, and a pair of flaps 24 extending from each longitudinal side 22a of the main body portion 22. The topsheet 40 defines a bodyfacing surface of the absorbent article 20. The absorbent core 44 is positioned inward from the outer periphery of the absorbent article 20 and includes a body-facing side positioned adjacent the topsheet 40 and a garment-facing surface positioned adjacent the backsheet 42. The topsheet 40 is generally designed to contact the body of the user and is liquid-permeable. The topsheet 40 may surround the absorbent core 44 so that it completely encases the absorbent article 20. Alternatively, the topsheet 40 and the backsheet 42 may extend beyond the absorbent core 44 and be peripherally joined together, either entirely or partially, using known techniques. Typically, the topsheet 40 and the backsheet 42 are joined by adhesive bonding, ultrasonic bonding, or any other suitable joining method known in the art. The topsheet 40 is sanitary, clean in appearance, and somewhat opaque to hide bodily discharges collected in and absorbed by the absorbent core 44. The topsheet 40 further exhibits good strike-through and rewet characteristics permitting bodily discharges to rapidly penetrate through the topsheet 40 to the absorbent core 44, but not allow the body fluid to flow back through the topsheet 40 to the skin of the wearer. The topsheet 40 may also contain a plurality of apertures (not shown) formed therethrough to permit body fluid to pass more readily into the absorbent core 44. The apertures may be randomly or uniformly arranged throughout the topsheet 40, or they may be located only in the narrow longitudinal band or strip arranged along the longitudinal axis X-X of the absorbent article 20. The apertures permit rapid penetration of body fluid down into the absorbent core 44. The size, shape, diameter and number of apertures may be varied to suit one's particular needs. As stated above, the absorbent article also includes a backsheet 42. The backsheet 42 is generally liquid-impermeable and designed to face the inner surface, i.e., the crotch portion of an undergarment (not shown). The backsheet 42 may permit a passage of air or vapor out of the absorbent article 20, while still blocking the passage of liquids. The absorbent article 20 also contains an absorbent core 44 positioned between the topsheet 40 and the backsheet 42. The absorbent core 44 may be formed from a single absorbent member or a composite containing separate and distinct absorbent members. It should be understood, however, that any number of absorbent members may be utilized in the present invention. For example, in one embodiment, the absorbent core 44 may contain an intake member (not shown) positioned between the topsheet 40 and a transfer delay member (not shown). The intake member may be made of a material that is capable of rapidly transferring, in the z-direction, body fluid that is delivered to the topsheet 40. The intake member may generally have any shape and / or size desired. In one embodiment, the intake member has a rectangular shape, with a length equal to or less than the overall length of the absorbent article 20, and a width less than the width of the absorbent article 20. For example, a length of between about 150 mm to about 300 mm and a width of between about 10 mm to about 60 mm may be utilized. Any of a variety of different materials may be used for the intake member to accomplish the above-mentioned functions. The material may be synthetic, cellulosic, or a combination of synthetic and cellulosic materials. For example, airlaid cellulosic tissues may be suitable for use in the intake member. The airlaid cellulosic tissue may have a basis weight ranging from about 10 grams per square meter (gsm) to about 300 gsm, and in some embodiments, between about 100 gsm to about 250 gsm. In one embodiment, the airlaid cellulosic tissue has a basis weight of about 200 gsm. The airlaid tissue may be formed from hardwood and / or softwood fibers. The airlaid tissue has a fine pore structure and provides an excellent wicking capacity, especially for menses. If desired, a transfer delay member (not shown) may be positioned vertically below the intake member. The transfer delay member may contain a material that is less hydrophilic than the other absorbent members, and may generally be characterized as being substantially hydrophobic. The transfer delay member may generally have any size, such as a length of about 150 mm to about 300 mm. Typically, the length of the transfer delay member is approximately equal to the length of the absorbent article 20. The transfer delay member may also be equal in width to the intake member, but is typically wider. For example, the width of the transfer delay member may be from between about 50 mm to about 75 mm, and particularly about 48 mm. Besides the above-mentioned members, the absorbent core 44 may also include a composite absorbent member (not shown). In this instance, fluids may be wicked from the transfer delay member into the composite absorbent member. The composite absorbent member may be formed separately from the intake member and / or transfer delay member, or may be formed simultaneously therewith. The absorbent article 20 typically contains an adhesive for securing to an undergarment. An adhesive may be provided at any location of the absorbent article 20, such as on the lower surface of the backsheet 42. In this particular embodiment, the backsheet 42 carries a longitudinally central strip of garment adhesive 54 covered before use by a peelable release liner 58, which may be formed in accordance with the present invention. Each of the flaps 24 may also contain an adhesive 56 positioned adjacent to the distal edge 34 of the flap 24. A peelable release liner 57, which may also be formed in accordance with the present invention, may cover the adhesive 56 before use. Thus, when a user of the sanitary absorbent article 20 wishes to expose the adhesives 54 and 56 and secure the absorbent article 20 to the underside of an undergarment, the user simply peels away the liners 57 and 58 and disposed them in a water-based disposal system (e.g., in a toilet). As described above, the film of the present disclosure can be incorporated into the absorbent article 20 in multiple locations. For example, the film can be used to construct the release liner for covering the adhesive on the flaps, can be used to construct the topsheet, can be used to construct the backsheet, can be used to construct the transfer delay member (e.g. baffle), or the like. The present disclosure may be better understood with reference to the following example. Example Various films were made generally in accordance with the process shown in FIG.1. The films, however, were not drawn during the process. When making some of the films, no heat treatment was applied. In other process runs, however, the films were heat treated as described above with respect to FIG.1. Three different types of films were produced. Sample Nos.1 and 2 were made exclusively from a polyhydroxyalkanoate polymer. Sample Nos.3 and 4, on the other hand, were made from a polymer composition containing the polyhydroxyalkanoate polymer used to produce Sample Nos.1 and 2 in combination with 18% by weight of a polybutylene adipate terephthalate polymer and 12% by weight calcium carbonate particles. For purposes of comparison, Sample Nos.5 and 6 were formed from a polyethylene polymer (Grade 2047 obtained from Dow Chemical) in combination with 20% by weight calcium carbonate particles. The films were formed and tested for various mechanical properties. The following results were obtained:eg k)a arer%(1eB hc8.742.0 2 69 783.60.5 6 170vADt.8er31336395 664 .Ct4S 666 ev Da 13590 4117AMoL 3 2735490324esgsaen)0 0 0rm159 304 544977ev k5cim(0. 0. 0. 0. 0.00.AhT 0 0 0 0 0ega )70346 6 9 4reW mvB s .3.53.43.25.97.Ag( 3 2 3 3 292gniteraeutraTre A / F0 A / F30 A / F30tapmN 1 N 1 N31eHeTe e e elp. lmo pm1. lopm2. l3el4el5el6o pm.pm.pm.pm.o o o oNa a a a a a aN N N N N N S S S S S S S 65123283US01 As shown above, Sample Nos.2, 4, and 6 were heat treated while Sample Nos.1, 3, and 5 were not. The films containing the polyhydroxyalkanoate polymer that were heat treated showed a dramatic and unexpected increase in cross-direction elongation properties. In addition, the biodegradable films were comparable in properties to the polyethylene films. These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.

Claims

65123283US01 What Is Claimed:

1. A process for producing a film comprising: extruding a molten thermoplastic polymer composition through a die to form a film, the thermoplastic polymer composition comprising a polyhydroxyalkanoate polymer; heating the film without substantially stretching the film, the film being heated to a temperature of greater than about 80°F causing the cross-directional break stretch of the film to increase by at least about 50%.

2. A process as defined in claim 1, wherein heating the film without substantially stretching the film causes the cross-directional break stretch to increase by greater than about 80%, such as greater than about 100%, such as greater than about 125%, such as greater than about 150%, and less than about 2,000%.

3. A process as defined in claim 1, wherein the polyhydroxyalkanoate polymer displays a melting point of less than about 190°C, such as less than about 170°C, such as less than about 160°C, such as less than about 155°C, and greater than about 120°C, such as greater than about 130°C.

4. A process as defined in claim 1, wherein the polyhydroxyalkanoate polymer displays a melt flow rate of less than about 100 g / 10 min, such as less than about 50 g / 10 min, and greater than about 1 g / 10 min, such as greater than about 2 g / 10 min, when tested according to ASTM Test D1238- E at a load of 2.16 kg and at a temperature of 190°C.

5. A process as defined in claim 1, wherein the polyhydroxyalkanoate polymer displays a relative viscosity of from about 1.5 to about 3.5, such as from about 2 to about 3, when tested according to ASTM Test D4603 in a 0.5% by weight solution.

6. A process as defined in claim 1, wherein the thermoplastic composition further contains polybutylene adipate terephthalate.

7. A process as defined in claim 1, wherein the thermoplastic composition contains a second polymer, the second polymer comprising a polycaprolactone, a polyesteramide, a polylactic acid, a polyglycolic acid, a polyalkylene carbonate, a poly-3-hydroxyvalerate, a polybutylene succinate, a polybutylene succinate adipate, a polyethylene succinate, a polybutylene adipate terephthalate, a polyethylene adipate terephthalate, a polyethylene adipate isophthalate, a polybutylene adipate isophthalate, or mixtures thereof.

8. A process as defined in claim 6, wherein the thermoplastic composition contains polybutylene adipate terephthalate in an amount of from about 5% by weight to about 40% by weight.

9. A process as defined in claim 1, wherein the polyhydroxyalkanoate polymer is present65123283US01 in the polymer composition in an amount of at least about 50% by weight, such as at least about 60% by weight, such as at least about 70% by weight.

10. A process as defined in claim 1, wherein the polymer composition contains a filler, such as calcium carbonate particles.

11. A process as defined in claim 1, wherein the film displays a cross-directional break stretch of greater than about 200%, such as greater than about 250%, such as greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%, and less than about 1,000%.

12. A process as defined in claim 1, wherein the film comprises a cast film.

13. A process as defined in claim 1, wherein the film has a basis weight of from about 5 gsm to about 70 gsm, such as from about 10 gsm to about 40 gsm.

14. A film formed from a polymer composition, the polymer composition comprising at least about 50% by weight of a polyhydroxyalkanoate polymer, the film having a basis weight of from about 10 gsm to about 70 gsm, the film having a cross-direction break stretch of greater than about 250% and a machine direction break stretch of greater than about 250%.

15. A film as defined in claim 14, wherein the film displays a cross-direction break stretch of greater than about 300%, such as greater than about 350%, such as greater than about 400%, such as greater than about 450%, such as greater than about 500%.

16. A film as defined in claim 14, wherein the film displays a machine direction break stretch that is within about 30% of the cross-direction break stretch.

17. A film as defined in claim 14, wherein the film comprises a cast film.

18. A film as defined in claim 14, wherein the polyhydroxyalkanoate polymer displays a melting point of less than about 190°C, such as less than about 170°C, such as less than about 160°C, such as less than about 155°C, and greater than about 120°C, such as greater than about 130°C.

19. A film as defined in claim 14, wherein the polyhydroxyalkanoate polymer displays a melt flow rate of less than about 100 g / 10 min, such as less than about 50 g / 10 min, and greater than about 1 g / 10 min, such as greater than about 2 g / 10 min, when tested according to ASTM Test D1238- E at a load of 2.16 kg and at a temperature of 190°C.

20. A film as defined in claim 14, wherein the polyhydroxyalkanoate polymer displays a relative viscosity of from about 1.5 to about 3.5, such as from about 2 to about 3, when tested according to ASTM Test D4603 in a 0.5% by weight solution.65123283US01 21. A film as defined in claim 14, wherein the thermoplastic composition further contains polybutylene adipate terephthalate.

22. A film as defined in claim 14, wherein the thermoplastic composition contains a second polymer, the second polymer comprising a polycaprolactone, a polyesteramide, a polylactic acid, a polyglycolic acid, a polyalkylene carbonate, a poly-3-hydroxyvalerate, a polybutylene succinate, a polybutylene succinate adipate, a polyethylene succinate, a polybutylene adipate terephthalate, a polyethylene adipate terephthalate, a polyethylene adipate isophthalate, a polybutylene adipate isophthalate, or mixtures thereof.

23. An absorbent article incorporating the film as defined in claim 14.

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