Dimensionally stable biodegradable film

Abstract

A method for improving the dimensional stability of a biodegradable film. The method includes providing a poly (hydroxyalkanoate)-based blown polymer film to a roll, feeding the poly (hydroxyalkanoate)-based blown polymer film to an annealing roll, and heating the blown film by contacting with the annealing roll at a temperature range of about 80 DEG C to about 150 DEG C for a predetermined period of time.

Description

[0001] Related Applications

[0002] This application claims priority to provisional application No. 63 / 369,997 filed on August 1, 2022. Technical Field

[0003] The present invention relates to biodegradable films and, more particularly, to methods for improving the dimensional stability of poly(hydroxyalkanoate) based polymer films. Background Art

[0004] Blown polymer film is the primary processing technology used by film manufacturers to transform polymer films for food packaging applications. Blown polymer films are typically used in bag making and heat sealing processes that are widely used in flexible packaging. The stability of blown polymer films is critical to maintaining product quality during storage and preventing deterioration of food quality. Bag making and heat sealing processes are typically performed at elevated temperatures. As semi-crystalline polymer films cool down from elevated temperatures, they tend to shrink. The extent of shrinkage depends largely on the composition of the film material and the processing conditions used to produce the film. Semi-crystalline materials shrink more than amorphous materials. Dimensional instability or shrinkage of the film when cooling from elevated temperatures plays an important role in the overall quality of the finished product. Significant shrinkage after bag making or heat sealing processes can lead to several defects in the finished product, including leaks, risk of pinhole formation, and rupture of the sealed area.

[0005] Biodegradable poly(hydroxyalkanoate)-based polymer films also shrink when cooled from elevated temperatures to room temperature. The shrinkage properties of poly(hydroxyalkanoate)-based films can cause significant problems during coating, metallization, lamination, printing, bagging and sealing processes in which the films are used. Conventional blown film processes produce poly(hydroxyalkanoate)-based polymer films that have been measured to shrink 45% to 50% in the machine direction (MD) at 110°C. The temperature selected for shrinkage measurements is the temperature used by most film post-processing equipment. The shrinkage values ​​for poly(hydroxyalkanoate)-based polymer films are significantly higher than the industry standard of less than 5% for other polymer films. Therefore, there is a need for an improved process for making poly(hydroxyalkanoate)-based polymer films to provide films with significantly lower shrinkage when used in packaging applications. Summary of the invention

[0006] In view of the above, embodiments of the present invention provide a method for improving the dimensional stability of a machine direction oriented (MDO) biodegradable film, the method comprising providing a poly(hydroxyalkanoate)-based blown polymer film to a nip roll, feeding the poly(hydroxyalkanoate)-based blown polymer film to an annealing roll, and heating the blown film by contacting the annealing roll at a temperature ranging from about 80° C. to about 150° C. for a predetermined period of time.

[0007] In one embodiment, the method includes heating the blown film to a temperature in the range of about 100°C to about 120°C by contact with an annealing roll.

[0008] In one embodiment, the blown film has a thickness ranging from about 7 microns to about 260 microns.

[0009] In another embodiment, the predetermined time period according to the method ranges from about 1 second to about 1 minute.

[0010] In another embodiment, a machine direction oriented (MDO) poly(hydroxyalkanoate)-based film is provided, which is prepared by providing a poly(hydroxyalkanoate)-based blown polymer film to a nip roll, feeding the poly(hydroxyalkanoate)-based blown polymer film into an annealing roll, and heating the blown film by contacting the annealing roll for a predetermined period of time at a temperature ranging from about 80°C to about 150°C.

[0011] In another embodiment, a dimensionally stable, biodegradable packaging film is provided, which is prepared by providing a poly(hydroxyalkanoate)-based blown polymer film to a nip roll, feeding the poly(hydroxyalkanoate)-based blown polymer film into an annealing roll, and heating the blown film by contacting the annealing roll for a predetermined period of time at a temperature ranging from about 80°C to about 150°C.

[0012] In another embodiment, a method for improving the dimensional stability of a biodegradable film is provided, comprising providing a poly(hydroxyalkanoate)-based biaxially oriented polymer film having various machine direction orientations (MDOP) and various transverse direction orientations (TDO), feeding the biaxially oriented film into an annealing roll, and heating the biaxially oriented film by contacting the annealing roll for a predetermined period of time at a temperature ranging from about 80° C. to about 150° C.

[0013] In another embodiment, the biodegradable film is stretched in the machine direction by about 0.3 to about 10 times.

[0014] In another embodiment, the biodegradable film is stretched in the transverse direction by about 0.3 to about 10 times.

[0015] As described in more detail below, certain blown film annealing conditions can provide optimal dimensional stability or minimize shrinkage of poly(hydroxyalkanoate)-based films. According to the present invention, a thermal treatment process is used to relieve the inherent stresses generated during the blown film extrusion process. If annealed properly, the diameter of the poly(hydroxyalkanoate)-based film should not change over time or when exposed to high temperatures. Therefore, embodiments of the present invention provide blown film annealing conditions that can provide poly(hydroxyalkanoate)-based films with a shrinkage of 4% or less at high temperatures (100°C). Dimensionally stable poly(hydroxyalkanoate)-based films prepared according to the present invention may be particularly suitable for use in the food packaging industry. DETAILED DESCRIPTION

[0016] In one aspect, the present invention provides polymer film compositions particularly suitable for use in consumer product packaging.

[0017] Preferably, the polymer film composition is biodegradable and / or compostable. More specifically, the polymer film composition is both biodegradable and compostable.

[0018] As used herein, the term "biodegradable" refers to a plastic or polymer material that will biodegrade by living organisms (microorganisms) in anaerobic and aerobic environments (as determined by ASTM D5511), in soil environments (as determined by ASTM5988), in freshwater environments (as determined by ASTMD5271 (EN 29408)), or in marine environments (as determined by ASTM D6691). The biodegradability of biodegradable plastics can also be determined using ASTM D6868 and European EN 13432.

[0019] The polymer film compositions of the present invention are also preferably "compostable" as determined by ASTM D6400 for industrial or home compostability.

[0020] In particular, the biodegradable polymer film composition comprises a poly(hydroxyalkanoate) as the first biodegradable polymer. The composition is typically composed of about 5 weight percent to about 95 weight percent of the poly(hydroxyalkanoate). More preferably, the composition is composed of about 35 weight percent to about 90 weight percent of the poly(hydroxyalkanoate). More preferably, the polymer composition comprises about 40 weight percent to about 70 weight percent of the poly(hydroxyalkanoate).

[0021] In some cases, the poly(hydroxyalkanoate) in the composition preferably consists of a mixture of a first copolymer and a second copolymer. The first copolymer includes about 90 to about 99.9 mole percent of 3-hydroxybutyrate monomer residues and about 0.1 to about 10 mole percent of a second 3-hydroxyalkanoate monomer residue having 5 to 12 carbon atoms. The second copolymer includes at least 70 mole percent of 3-hydroxybutyrate monomer residues and a second 3-hydroxyalkanoate monomer residue having 5 to 12 carbon atoms in an amount at least 6 mole percent less than the amount of the second 3-hydroxyalkanoate in the first polymer.

[0022] It has been found that when the difference in the mole percentage of the second 3-hydroxyalkanoate in the first copolymer and the second copolymer is at least 6 mole percent, the first and second copolymers are no longer miscible with each other, but separate into different poly(hydroxyalkanoates) in the composition. This can be used to advantageously alter the properties of the final composition.

[0023] In this case, the inclusion of a relatively small amount of the second poly(hydroxyalkanoate) copolymer improves the impact resistance or toughness of the composition, providing an article with improved properties.

[0024] The polymer composition further comprises a second biodegradable polymer selected from the group consisting of poly(butylene succinate), poly(butylene succinate-adipate), polylactic acid, cellulose esters (e.g., cellulose acetate), thermoplastic starch, and mixtures thereof. The amount of the second biodegradable polymer is generally about 5 weight percent to about 95 weight percent of the total composition.

[0025] In some embodiments, the second biodegradable polymer may include poly(butylene succinate) in an amount of about 5 weight percent to about 50 weight percent of the polymer composition. More preferably, the polymer composition includes about 10 weight percent to about 30 weight percent of poly(butylene succinate).

[0026] According to some embodiments, the second biodegradable polymer may include poly(butylene succinate)-butylene adipate in an amount of about 5 weight percent to about 50 weight percent of the polymer composition. More preferably, the polymer composition includes about 10 weight percent to about 30 weight percent of poly(butylene succinate)-butylene adipate.

[0027] In some cases, the second biodegradable polymer may include polylactic acid in an amount of about 10 weight percent to about 70 weight percent of the polymer composition. More preferably, the polymer composition includes about 20 weight percent to about 60 weight percent of polylactic acid.

[0028] In certain embodiments, the second biodegradable polymer may include cellulose acetate or another cellulose ester in an amount of about 5 weight percent to about 50 weight percent of the polymer composition. More preferably, the polymer composition includes about 10 weight percent to about 30 weight percent of cellulose acetate or another cellulose ester.

[0029] In each of the various compositions described above, the poly(hydroxyalkanoate) polymer can be a homopolymer consisting of only a single type of monomer residue. Typically, the poly(hydroxyalkanoate) polymer is a copolymer consisting of at least two different types of monomer residues. In some cases, the poly(hydroxyalkanoate) polymer can be a terpolymer consisting of at least three different types of monomer residues.

[0030] For example, in some embodiments, the at least one poly(hydroxyalkanoate) polymer is preferably a copolymer consisting of about 75 to about 99.9 mole percent of monomer residues of 3-hydroxybutyrate and about 0.1 to about 25 mole percent of monomer residues of a second 3-hydroxyalkanoate having 5 to 12 carbon atoms.

[0031] In other embodiments, the at least one poly(hydroxyalkanoate) polymer is preferably a terpolymer composed of about 75 to about 99.9 mole percent monomer residues of 3-hydroxybutyrate and about 0.1 to about 25 mole percent monomer residues of 3-hydroxyhexanoate, and about 0.1 to about 25 mole percent monomer residues of a third 3-hydroxyalkanoate having 5 to 12 carbon atoms.

[0032] Typically, the at least one poly(hydroxyalkanoate) polymer has a weight average molecular weight of about 50,000 Daltons to about 7.5 million Daltons, more preferably about 300,000 Daltons to about 3 million Daltons, as determined by ASTM D6474-20.

[0033] In certain embodiments, the poly(hydroxyalkanoate) and the at least one biodegradable polymer preferably react with each other in an ester exchange reaction. In this case, a small amount of a catalyst (e.g., tin ethylhexanoate) can optionally be added to the composition to promote the ester exchange reaction. The ester exchange reaction of the poly(hydroxyalkanoate) and the at least one biodegradable polymer produces, for example, a branched structure that provides better processing performance with lower energy consumption. The ester exchange reaction can also provide improved physical properties because the ester exchange polymer can act as an interfacial agent and improve the compatibility of other polymer molecules in the composition that may not have fully reacted.

[0034] Most commonly, the transesterification reaction is performed by reacting the poly(hydroxyalkanoate) and the at least one biodegradable polymer with each other in a reactive extrusion process.

[0035] Nucleating agents are also typically present in the polymer composition in an amount of about 0.1 weight percent to about 5 weight percent. In certain embodiments, the core layer nucleating agent is preferably selected from the group consisting of erythritol, pentaerythritol, dipentaerythritol, artificial sweeteners, stearates, polysaccharides, sorbitol, mannitol, inositol, polyester waxes, nanoclays, behenic acid amide, erucic acid amide, stearamide, oleamide, polyhydroxybutyrate, thymine, cyanuric acid, cytosine, adenine, uracil, guanine, boron nitride, and mixtures thereof.

[0036] The polymer composition may also include an optional plasticizer material. Suitable materials for plasticizers are generally selected from the group consisting of sebacate, citrate, fatty esters of adipic acid, succinic acid and glucaric acid, lactates, alkyl diesters, citrates, alkyl methyl esters, diphenylmethyl esters, propylene carbonate, caprolactone diols having a number average molecular weight of 200-10000 g / mol as determined by ASTM D6474-20, polyethylene glycols having a number average molecular weight of 400-10000 g / mol as determined by ASTM D6474-20, vegetable oil esters, long chain alkyl acids, adipic acid esters, glycerol, isosorbide derivatives or mixtures thereof, polymeric plasticizers, poly(hydroxyalkanoate) copolymers comprising at least 18 mole percent of hydroxyalkanoate monomer residues other than hydroxybutyrate, and mixtures thereof.

[0037] The amount of plasticizer in the polymer composition may be up to about 15 weight percent. More preferably, the polymer composition consists of about 5 weight percent to about 15 weight percent of plasticizer.

[0038] Optionally, the polymer composition may also include a filler. Suitable materials for the filler are typically selected from the group consisting of calcium carbonate, talc, nanoclay, nanocellulose, hemp fiber, kaolin, carbon black, wollastonite, glass fiber, carbon fiber, graphite fiber, mica, silicon dioxide, dolomite, barium sulfate, magnetite, halloysite, zinc oxide, titanium dioxide, montmorillonite, feldspar, asbestos, boron, steel, carbon nanotubes, cellulose fiber, flax, cotton, starch, polysaccharides, aluminum hydroxide, magnesium hydroxide, modified starch, chitin and chitosan, alginate, gluten, zein, casein, collagen, gelatin, polysaccharides, guar gum, xanthan gum, succinoglycan, natural rubber, rosin acid, lignin, natural fibers, jute, kenaf, hemp, peanut shells, wood flour, and mixtures thereof.

[0039] The amount of filler in the polymer composition may be up to about 50 weight percent. More preferably, the core layer polymer composition consists of about 5 weight percent to about 40 weight percent filler.

[0040] Further, the polymer composition may also include up to 20 weight percent of an impact modifier. More preferably, the polymer composition includes about 5 weight percent to about 15 weight percent of an impact modifier. Suitable impact modifiers for polymer compositions are preferably selected from the group consisting of acrylic resins and emulsions, isosorbide derivatives, natural rubber, aliphatic polyesters, or mixtures thereof.

[0041] Additionally, in some cases, the polymer composition may include up to 50 weight percent of one or more additives selected from the group consisting of polyvinyl alcohol, polyvinyl acetate, polyvinyl laurate, ethylene-vinyl acetate copolymers, polyglycolic acid, furan dicarboxylic acid-based polyesters, cellulose, nanocellulose, dextran, and mixtures thereof.

[0042] In each of the various polymer compositions described above, the poly(hydroxyalkanoate) polymer can be a homopolymer consisting of only a single type of monomer residue. Typically, the poly(hydroxyalkanoate) polymer is a copolymer consisting of at least two different types of monomer residues. In some cases, the poly(hydroxyalkanoate) polymer can be a terpolymer consisting of at least three different types of monomer residues.

[0043] For example, in some embodiments, the at least one poly(hydroxyalkanoate) polymer is preferably a copolymer consisting of about 75 to about 99.9 mole percent monomer residues of 3-hydroxybutyrate and about 0.1 to about 25 mole percent monomer residues of a second 3-hydroxyalkanoate having 5 to 12 carbon atoms.

[0044] In other embodiments, the at least one poly(hydroxyalkanoate) polymer is preferably a terpolymer composed of about 75 to about 99.9 mole percent monomer residues of 3-hydroxybutyrate and about 0.1 to about 25 mole percent monomer residues of 3-hydroxyhexanoate, and about 0.1 to about 25 mole percent monomer residues of a third 3-hydroxyalkanoate having 5 to 12 carbon atoms.

[0045] Typically, the at least one poly(hydroxyalkanoate) polymer has a weight average molecular weight of about 50,000 Daltons to about 7.5 million Daltons, more preferably about 300,000 Daltons to about 3 million Daltons, as determined by ASTM D6474-20.

[0046] In another aspect, the present invention also provides a product packaging for consumer products, which utilizes the above polymer composition. Specifically, the product packaging includes at least one biodegradable packaging portion, and the packaging portion includes the above polymer composition. The product packaging can be used for packaging of clothing, household items, food, and health and beauty products.

[0047] In certain embodiments, the biodegradable packaging portion may be formed by a process selected from the group consisting of injection molding, compression molding, thermoforming, cast and blown film, extrusion coating, extrusion blow molding, injection stretch blow molding, and extrusion molding.

[0048] Crystallinity

[0049] The volume percent crystallinity (Φc) of a semicrystalline polymer (or copolymer) often determines what type of end-use properties the polymer has. For example, high (greater than 50%) crystalline polyethylene polymers are strong and rigid, suitable for products such as plastic milk containers. On the other hand, low crystalline polyethylene is flexible and strong, suitable for products such as food packaging and trash bags. Crystallinity can be determined in a variety of ways, including X-ray diffraction, differential scanning calorimetry (DSC), density measurement, and infrared absorption. The most appropriate method depends on the material being tested.

[0050] The volume percent crystallinity (Φc) of the poly(hydroxyalkanoate) copolymer can vary depending on the mole percentage of poly(3-hydroxyhexanoate) in the poly(hydroxyalkanoate) copolymer. Adding poly(3-hydroxyhexanoate) effectively reduces the volume percent crystallinity, crystallization rate, and melting temperature of the poly(hydroxyalkanoate) copolymer, while increasing the flexibility and degradability of the copolymer. Nucleating agents as described herein can be used to accelerate the crystallization process of the poly(hydroxyalkanoate) copolymer.

[0051] Generally, the poly(hydroxyalkanoates) of the present invention preferably have a crystallinity of about 0.1% to about 99%, more preferably about 2% to about 80%, more preferably about 20% to about 70%, as measured by X-ray diffraction.

[0052] When the poly(hydroxyalkanoate) of the present invention is processed into a molded article or a film, the crystallinity of such poly(hydroxyalkanoate) as measured by X-ray diffraction is more preferably from about 10% to about 80%, more preferably from about 20% to about 70%, more preferably from about 30% to about 60%.

[0053] Melting temperature

[0054] Preferably, the biodegradable poly(hydroxyalkanoate) of the present invention has a melting temperature (T m), more preferably, about 90°C to about 165°C, more preferably, about 130°C to about 160°C.

[0055] Thin film manufacturing method

[0056] The films of the present invention for use as container labels with improved biodegradability and / or compostability can be processed using conventional procedures for producing monolayer or multilayer films on conventional film manufacturing equipment. The poly(hydroxyalkanoate) particles of the present invention can be dry blended and then melt mixed in a film extruder. Alternatively, if insufficient mixing occurs in the film extruder, the particles can be dry blended and then melt mixed in a pre-mixing extruder and then re-granulated before film extrusion.

[0057] The poly(hydroxyalkanoates) of the present invention can be melt processed into films using cast or blown film extrusion methods, both of which are described in PLASTICS EXTRUSION TECHNOLOGY (2nd edition) by Allan A. Griff (Van Nostrand Reinhold-1976). In the cast film process, the molten polymer mixture is extruded through a linear slot die. Typically, a flat web is cooled on a large moving polished metal roll. The web quickly cools and peels off this first roll, passes through one or more auxiliary cooling rolls, then through a set of rubber-coated traction or "pull-out" rolls, and finally reaches a winder.

[0058] In the blown film extrusion process, the molten polymer formulation is extruded upward through a thin annular die. The blown film process is also known as tubular film extrusion. Air is introduced through the center of the die to inflate the tube causing it to expand. Thus, a moving bubble is formed which is maintained at a constant size by controlling the internal air pressure. The film tube is cooled by air being blown through one or more cooling rings around the tube. The tube is then pulled into a flattened frame by a pair of pulling rollers and into a winder, which collapses the tube. For label applications, the flattened tubular film is then slit, unrolled, and further cut into widths suitable for use as labels.

[0059] Both cast film and blown film processes can be used to produce single-layer or multi-layer film structures. For the production of a single-layer film from a single thermoplastic material or a mixture of thermoplastic components, only a single extruder and a single manifold die are required.

[0060] For the production of multi-layer films, a co-extrusion process is preferably used. This process requires more than one extruder and a co-extrusion feed block or a multi-manifold die system or a combination of the two to achieve a multi-layer film structure.

[0061] It has been quite surprising to discover that the annealing temperature of the annealing rolls can control or minimize the shrinkage of poly(hydroxyalkanoate)-based polymer films during blown film and cast film production processes. An improved annealing process for poly(hydroxyalkanoate)-based polymer films can be achieved by heating the film to a temperature above its glass transition temperature and below its melting temperature for a period of time, and then allowing the film to cool to room temperature so that the material can relax. It is believed that annealing semi-crystalline film materials at relatively higher temperatures can improve the quality of the film in terms of micro- and macrostructural features, such as crystal morphology, density, grain size, etc. Therefore, the improved annealing process can provide film dimensional stability and / or minimize shrinkage by releasing internal stresses within the film material. The improvement in overall shrinkage depends on the annealing temperature and annealing time.

[0062] The following non-limiting examples illustrate processes for controlling shrinkage of poly(hydroxyalkanoate) based polymer films having both machine direction orientation (MDO) for a blown film process and both machine direction orientation (MDO) and transverse direction orientation (TDO) for a biaxial orientation process.

[0063] Example 1

[0064] The formulated poly(hydroxyalkanoate) based polymer material was converted into barrier and printed films by using a conventional blown film process (MDO) stretched three times in the machine direction. Experiments were conducted using different annealing roll temperatures under the same extruder and MDO characteristics. Film samples were prepared using annealing roll temperatures of 60°C, 80°C, 100°C, 110°C and 120°C. The shrinkage of both the machine direction (MD) and the transverse direction (TD) was studied at 45°C, 80°C, 100°C and 110°C using the method described in ASTM D2732. The film annealing temperatures and shrinkage data at 45°C, 80°C, 100°C and 110°C are shown in Table 1. The selection of shrinkage measurement temperature is based on the storage temperature of 45°C for storage and transportation of the finished product, as well as post-processing temperatures, such as coating, metallization and sealing temperatures (80°C, 100°C and 110°C).

[0065] Table 1

[0066] Annealing roller temperature (℃) Shrinkage measurement temperature (℃) Time in oil bath (seconds) MD shrinkage (%) TD shrinkage (%) 60 45 30 4 0 60 80 30 33 -1.3 60 100 30 43 -1.7 60 110 30 49.3 -2 80 45 30 2 0 80 80 30 26.7 -3.7 80 100 30 37.7 -4.2 80 110 30 44.8 -4.5 100 45 30 1.7 0 100 80 30 14.7 -3 100 100 30 25.7 -4.2 100 110 30 32.7 -5 110 45 30 0.8 0 110 80 30 6.7 -1 110 100 30 13 -2.3 110 110 30 18 -2.7 120 45 30 0 0 120 80 30 1.8 -0.2 120 100 30 4 -1 120 110 30 6 -1

[0067] As shown in the table above, the shrinkage values ​​for poly(hydroxyalkanoate) films at the lower annealing temperature (60°C) are very high compared to the industry standard of less than 5%. When the annealing temperature is above 100°C, the shrinkage values ​​decrease significantly, reaching the industry standard value of less than 5% when the annealing temperature is 120°C.

[0068] The following non-limiting example illustrates a method of controlling shrinkage of a poly(hydroxyalkanoate) based polymer film made by a biaxially oriented film process.

[0069] Example 2

[0070] Using the same extruder and MDO features, poly(hydroxyalkanoate) based film samples were prepared using different transverse direction orientation (TDO) annealing temperatures. The transverse direction (TD) annealing temperatures used were 60°C, 93°C and 129°C. The shrinkage measurement temperatures were selected based on the maximum expected temperature of the finished product storage / transportation and post-processing processes (45°C); such as coating, metallization and sealing temperatures (80°C, 100°C and 110°C). The machine direction (MD) and transverse direction (TD) shrinkage were studied by heating the finished film in an oven at 110°C for 10 minutes. ISO 14616 was used to determine the shrinkage values. The results are shown in the table below.

[0071] Table 2

[0072]

[0073]

[0074] The shrinkage values ​​for poly(hydroxyalkanoate) films at lower annealing temperatures (60°C) are very high compared to the industry standard of less than 5%. The shrinkage values ​​decrease significantly with increasing annealing temperature and reach the industry standard value of less than 5% at an annealing temperature of 129°C.

[0075] Poly(hydroxyalkanoate)-based polymer films are prepared by modifying poly(hydroxyalkanoate) using melt strength enhancers, chain extenders and other processing aids. The poly(hydroxyalkanoate)-based films prepared according to the present invention may contain about 50 to 80 weight percent of a poly(hydroxyalkanoate) copolymer and about 20 to about 50 wt.% of a polymer modifier. In some embodiments, the poly(hydroxyalkanoate) copolymer is poly-3-hydroxybutyrate-co-3-hydroxyhexanoate.

[0076] The following table shows exemplary formulations that can be used to prepare biodegradable films according to the present invention.

[0077] Table 3

[0078]

[0079] Poly(hydroxyalkanoate) films have been formulated to run on cast and blown film lines, in both oriented and non-oriented conditions. Poly(hydroxyalkanoate) films provide excellent barrier properties for packaging applications, up to 1 oz levels providing excellent printability for labels. Several formulations have been tested in making poly(hydroxyalkanoate) films, which can be varied and optimized for individual applications and devices.

[0080] For the purpose of illustration and description, the present invention has been given the above description of preferred embodiments. They are not intended to be exhaustive or to limit the present invention to the precise form disclosed. Obvious modifications or changes can be made based on the above teachings. The embodiments are selected and described in order to provide the best description of the principles of the present invention and its practical application, so that those of ordinary skill in the art can utilize the present invention in various embodiments and make various modifications to suit the intended specific use. All these modifications and changes are within the scope of the present invention as determined by the appended claims when interpreted according to the scope to which they are fairly, legally and equitably entitled.

Claims

1. A method for improving the dimensional stability of a biodegradable film, comprising providing a poly(hydroxyalkanoate)-based blown polymer film to a nip roll, feeding the poly(hydroxyalkanoate)-based blown polymer film into an annealing roll, and heating the blown film by contacting the annealing roll at a temperature ranging from about 80°C to about 150°C for a predetermined period of time.

2. The method of claim 1, wherein the blown film is heated to a temperature in the range of about 100°C to about 120°C.

3. The method of claim 1, wherein the blown film has a thickness ranging from about 7 microns to about 250 microns. The method of claim 1 , wherein the predetermined period of time ranges from about 1 second to about 1 minute.

5. The method of claim 1, wherein the poly(hydroxyalkanoate)-based blown polymer film is stretched in the machine direction by a factor of about 0.3 to about 10.

6. The method of claim 1, wherein the poly(hydroxyalkanoate)-based blown polymer film is stretched in the transverse direction by a factor of about 0.3 to about 10.

7. A poly(hydroxyalkanoate)-based film prepared by the method of claim 1.

8. A dimensionally stable, biodegradable packaging film comprising the poly(hydroxyalkanoate)-based film of claim 7.

9. A method for improving the dimensional stability of a biodegradable film, comprising providing a poly(hydroxyalkanoate)-based biaxially oriented polymer film having various machine direction orientations (MDO) and various transverse direction orientations (TDO), feeding the biaxially oriented film to an annealing roll, and heating the biaxially oriented film by contacting the annealing roll for a predetermined period of time at a temperature ranging from about 80°C to about 150°C.

10. The method of claim 9, wherein the biaxially oriented polymer film is heated to a temperature in the range of about 100°C to about 120°C.

11. The method of claim 9, wherein the biaxially oriented polymer film has a thickness ranging from about 7 microns to about 250 microns.

12. The method of claim 7, wherein the predetermined period of time ranges from about 1 second to about 1 minute.

13. A biaxially oriented poly(hydroxyalkanoate)-based film prepared by the method of claim 9.

14. A dimensionally stable, biodegradable packaging film comprising the biaxially oriented poly(hydroxyalkanoate)-based film of claim 13.

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