Polylactic acid (PLA) with improved barrier properties, related articles, and related methods

Abstract

The disclosure relates to biodegradable and / or compostable polyester single- or multilayer films having improved barrier properties, in particular moisture or water barrier properties. In some cases, the films can be formed from stereocomplex polylactic acid (sc- PLA), which has favorable water barrier properties, can be conveniently formed via cast-film extrusion, and is biodegradable and compostable. In some cases, the films can be multilayer films including an sc-PLA or polyhydroxyalkanoate (PHA) layer to provide water barrier properties, a hydrophilic polymer / filler layer to provide oxygen barrier properties, and biodegradable polyester layer to sealing or other mechanical properties. The films can be used to package a variety of articles to improve their storage life, in particular for articles that are sensitive to water and / or oxygen, for example including food items, while still providing environmentally friendly end-of-life disposal options via composting.

Description

POLYLACTIC ACID (PLA) WITH IMPROVED BARRIER PROPERTIES, RELATED ARTICLES, AND RELATED METHODSCROSS REFERENCE TO RELATED APPLICATION

[0001] Priority is claimed to U.S. Provisional Application No. 63 / 619,989 filed on January 11 , 2024, and U.S. Provisional Application No. 63 / 671 ,886 filed on July 16, 2024, each of which is incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT INTEREST

[0002] None.BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0003] The disclosure relates to biodegradable and / or compostable polyester single- or multilayer films having improved water barrier properties that are useful for packaging items. The films can include stereocomplex polylactic acid (SC-PLA), which has favorable water barrier properties, can be conveniently formed via cast-film extrusion, and is biodegradable and compostable. Multilayer films can include an sc-PLA or polyhydroxyalkanoate (PHA) layer to provide water barrier properties in combination with two or more other layers to provide oxygen barrier properties, sealing properties, and / or mechanical properties.Background

[0004] The global flexible packaging industry is expected to grow from approximately $129 billion (USD) in 2020 to roughly $178 billion (USD) by 2027. The growth is attributed to the increased demand in the food, beverage, cosmetics, personal care, and pharmaceutical industries. By 2030, the demand is expected to reach an estimated $272 billion (USD). Along with the growth of plastic usage comes the issue of disposal. According to the U.S. EPA, in 2018, 35.7 million tons of plastic waste were generated only in the U.S., representing 12.2% of the total municipal solid waste (MSW). Of the 35.7 million tons, only 8% were recycled, 16% were incinerated, and 76% were sent to landfills.

[0005] Poly (lactic acid) (PLA) is a candidate for replacing fossil-fuel-based polymers since it has the most significant commercial production capacity with increasing market growth. It is used in several industrial applications, including biodegradable thermoplastics and food and agricultural packaging. However, there are a few issues with its widespread usage and potentially increased commercialization, including low heat distortion temperature, brittleness, poor thermal and hydrolytic stability, and only moderate barrier properties.

[0006] Among the plastic packaging applications, the global market for flexible packaging laminations is projected to surge from 6.3 million USD in 2024 to 9.7 M million USD in 2034. Laminations enhance flexible packaging by merging the properties of individual layers, boosting physical durability, aesthetic appeal, and barrier effectiveness beyond what single layers can achieve. However, this innovation has a significant environmental drawback: the fused layers in these flexible single-use plastic (FSUP) films complicate recycling processes, rendering the films inseparable and frequently consigned to landfills, exacerbating the MSW crisis.

[0007] A trait for recyclable multilayer structures is consistency in material composition across all layers, with only a minimal presence of ancillary components. Achieving the necessary barrier properties using uniform materials remains a formidable challenge. For instance, while polyethylene (PE) offers excellent moisture resistance, it falls short of providing an adequate oxygen barrier. An alternative approach involves engineering multilayer structures where every layer is biodegradable, thus enabling the entire structure to break down naturally and avoid contributing to landfill accumulation. While several alternatives exist for compostable FSUP multilayer films, transparency and nonmetallization remain rare.SUMMARY

[0008] In an aspect, the disclosure relates to a multilayer barrier article comprising: a first layer (e.g., water or moisture barrier layer) comprising a first polyester selected from the group consisting of a stereocomplex polylactic acid (SC-PLA), a polyhydroxyalkanoate (PHA), and combinations thereof; a second layer (e.g., oxygen barrier layer) adjacent to the first layer, the second layer comprising a hydrophilic polymer and a filler distributed throughout the hydrophilic polymer; and a third layer (e.g., base / sealant layer or substrate) adjacent to the second layer at a position further from the first layer than the second layer, the third layer comprising a second polyester (e.g., PLLA).

[0009] In a refinement of the multilayer barrier article, the first layer comprises the sc-PLA as the first polyester. In a further refinement, the first layer comprises (or contains) 25 wt.% to 90 wt.% of poly(L-lactic acid) (PLLA) relative to total sc-PLA in the first layer; the first layer comprises (or contains) 10 wt.% to 75 wt.% of poly(D-lactic acid) (PDLA) relative to total SC- PLA in the first layer; and a stereocomplex-crystalline (SC-crystalline) content in the first layer is in a range of 10 wt.% to 70 wt.% relative to a total crystalline content in the sc-PLA (e.g., SC-crystalline content plus a-crystalline content for WAXD measurement or SC- crystalline content plus HC-crystalline content for DSC measurement). In a yet furtherrefinement, the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa. In a yet further refinement, the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 1 g / ( 10 min) or 3 g / ( 10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

[0010] In a refinement of the multilayer barrier article, the first layer comprises poly-3- hydroxybutyrate-co-valerate (PHBV) as the first polyester.

[0011] In a refinement of the multilayer barrier article, the third layer comprises poly(L- lactic acid) (PLLA) as the second polyester.

[0012] In a refinement of the multilayer barrier article, monomer units of the first polyester and the second polyester are independently selected from Formula I: -O-R-C(=O)- (I), in which R is a hydrocarbon group having 1 to 9 carbon atoms.

[0013] In a refinement of the multilayer barrier article, the hydrophilic polymer comprises polyvinyl alcohol (PVOH); and the filler comprises a nanoclay. In a further refinement, the hydrophilic polymer is present in an amount of 30 wt.% to 98 wt.% relative to the second layer; the filler is present in an amount of 2 wt.% to 70 wt.% relative to the second layer; and optionally, a weight ratio of hydrophilic polymer: filler in the second layer is in a range of 6:1 to 1 :3.

[0014] In a refinement of the multilayer barrier article, the multilayer barrier article has a thickness in a range of 40 pm to 500 pm.

[0015] In a refinement of the multilayer barrier article, the first layer has a first thickness in a range of 15% to 90% relative to a total thickness of the multilayer barrier article; the second layer has a second thickness in a range of 5% to 80% relative to a total thickness of the multilayer barrier article; the third layer has a third thickness in a range of 3% to 30% relative to a total thickness of the multilayer barrier article; and optionally, a ratio of the first thickness:second thickness is in a range of 12:1 to 1 :6.

[0016] In a refinement , the multilayer barrier article has a moisture vapor transmission rate (MVTR) in a range of 0.1 to 100 g / (m2»d) at 38°C / 90% RH; and / or the multilayer barrier article has an oxygen transmission rate (OTR) in a range of 0.1 to 1000 cc / (m2»d) at23°C / 50% RH. In a further refinement, the MVTR is in a range of 5 to 50 g / (m2»d) at 38°C / 90% RH; and / or the OTR is in a range of 5 to 100 cc / (m2»d) at 23°C / 50% RH. In a further refinement, the multilayer barrier article has a thickness in a range of 120 pm to 200 pm.

[0017] In a refinement, the multilayer barrier article has an optical transmission at 600 nm (T6OO) in a range of 20% to 80%.

[0018] In a refinement, the multilayer barrier article further comprises at least one of: a first adhesive layer positioned between the first layer and the second layer; and a second adhesive layer positioned between the second layer and the third layer.

[0019] In a refinement of the multilayer barrier article, each of the first layer, the second layer, and the third layer is independently selected to be biodegradable, compostable, or both biodegradable and compostable.

[0020] In a refinement, the multilayer barrier article contains not more than 10 wt.% of components other than the first layer, the second layer, and the third layer, relative to the multilayer barrier article. For example, the multilayer barrier article can contain not more than 0.001 , 0.01 , 0.1 , 0.2, 0.5, 1 , 2, 3, 5, 7, or 10 wt.% of components other than the first layer, the second layer, and the third layer.

[0021] In a refinement, the multilayer barrier article is free or substantially free from metalcontaining components and / or polyvinylidene chloride (PVDC). For example, the multilayer barrier article can contain not more than 0.001 , 0.01 , 0.1 , 0.2, 0.5, or 1 wt.% of metalcontaining components and / or PVDC.

[0022] In a refinement of the multilayer barrier article, the first layer comprises at least one of the sc-PLA and poly-3-hydroxybutyrate-co-valerate (PHBV) as the first polyester; the hydrophilic polymer comprises polyvinyl alcohol (PVOH) present in an amount of 30 wt.% to 90 wt.% relative to the second layer; the filler comprises a nanoclay present in an amount of 10 wt.% to 70 wt.% relative to the second layer; a weight ratio of hydrophilic polymer :f iller in the second layer is in a range of 6:1 to 1 :3; the third layer comprises poly(L-lactic acid) (PLLA) as the second polyester; the first layer has a first thickness in a range of 15% to 90% relative to a total thickness of the multilayer barrier article; the second layer has a second thickness in a range of 5% to 80% relative to a total thickness of the multilayer barrier article; the third layer has a third thickness in a range of 3% to 30% relative to a total thickness of the multilayer barrier article; a ratio of the first thickness:second thickness is in a range of12:1 to 1 :6; the multilayer barrier article has a thickness in a range of 120 pm to 200 pm; and the multilayer barrier article is free from metal-containing components.

[0023] In another aspect, the disclosure relates to a packaged article comprising: an item to be packaged (e.g., food or medical item); and the multilayer barrier article according to the disclosure at least partially enclosing (or fully enclosing) the item. For example, the third layer can be an inner surface in contact with the packaged item and the first layer can be an outer surface in contact with ambient air or other external environment.

[0024] In another aspect, the disclosure relates to a method for forming a multilayer barrier article according to the disclosure, the method comprising: cast-film extruding a feed comprising the first polyester or components thereof, thereby forming a film (e.g., comprising the SC-PLA); (optionally) thermally annealing the film, thereby forming the first layer (e.g., increasing the crystallinity of the first polyester); applying the second layer (e.g., as a coating or via lamination) on a surface of the first layer; and applying the third layer (e.g., as a coating or via lamination) on a surface the second layer. In a refinement, the feed can comprise a feed mixture comprising PLLA and PDLA to form a corresponding film and first layer comprising the sc-PLA. In a refinement or alternative aspect, the method can comprise stretching or biaxially stretching the film (e.g., before, during, after, or instead of thermal annealing, for example to (further) increase crystallinity and improve water barrier properties).

[0025] In a refinement of the method, the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 1 g / (10 min) or 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

[0026] In a refinement, the method comprises: combining the PLLA and the PDLA as separate materials when forming the feed mixture (e.g., pre-mixed separate PLLA and PDLA materials or separately fed PLLA and PDLA materials to an extruder, but without masterbatch formation or other pre-compounding / melt-mixing of the PLLA and the PDLA); cast-film extruding the feed mixture at a temperature in a range of 225 °C to 250 °C; and thermally annealing the first film at a temperature in a range of 140 °C to 170 °C.

[0027] In another aspect, the disclosure relates to a stereocomplex polylactic acid (SC- PLA) film comprising: poly(L-lactic acid) (PLLA) present in an amount of 25 wt.% to 90 wt.% relative to total poly(lactic acid) in the film; and poly(D-lactic acid) (PDLA) present in an amount of 10 wt.% to 75 wt.% relative to total poly(lactic acid) in the film; wherein the filmhas at least one of properties (A), (B), (C), and (D): (A) the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min); (B) the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa; (C) the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa; and (D) the film has a stereocomplex-crystalline (SC- crystalline) content in a range of 10 wt.% to 70 wt.% relative to a total crystalline content in the film.

[0028] In a refinement, the sc-PLA film has all properties (A), (B), (C), and (D).

[0029] In a refinement of the sc-PLA film, the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 1 g / (10 min) or 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

[0030] In a refinement of the sc-PLA film, the film has an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and a- crystalline content in the film, as determined by wide angle X-ray diffraction (WAXD).

[0031] In a refinement of the sc-PLA film, the film has an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and HC- crystalline content in the film, as determined by differential scanning calorimetry (DSC).

[0032] In a refinement of the sc-PLA film, the film has a total crystalline content in a range of 10 wt.% to 60 wt.% relative to a combined amount of crystalline content and amorphous content in the film.

[0033] In a refinement of the sc-PLA film, the film has a moisture vapor transmission rate (MVTR) in a range of 0.1 to 100 g / (m2»d) at 38°C / 90% RH.

[0034] In a refinement of the sc-PLA film, the film has a moisture vapor permeability coefficient (MVPC) in a range of 0.01 to 2 (kg»m) / (m2»s*Pa) x 10-14at 38 °C / 90% RH.

[0035] In a refinement of the sc-PLA film, the film has a thickness in a range of 20 pm to 300 pm.

[0036] In a refinement of the sc-PLA film, the film has a thickness in a range of 40 pm to 150 pm.

[0037] In a refinement of the sc-PLA film, the film is in the form of a continuous film (e.g., in a roll) having a length dimension, a width dimension, and thickness dimension (e.g., allmutually orthogonal dimensions, such as with rectangular faces) such that a ratio of the length dimensiomwidth dimension (or aspect ratio) is at least 50:1 . For example, the continuous film (or roll) can have an aspect ratio that is at least and / or up to 50, 100, 200, 500, 1000, 2000, 5000, or 10000 and ranges therebetween. Alternatively, or additionally, the continuous film can have a width dimension in a range of 5 cm to 500 cm or 20 cm to 100 cm, for example at least and / or up to 5, 10, 20, 50, 100, 200, or 500 cm and ranges therebetween.

[0038] In a refinement of the sc-PLA film, the film has an optical transmission at 600 nm (Teoo) of at least 50%.

[0039] In another aspect, the disclosure relates to a method for forming a stereocomplex polylactic acid (SC-PLA) film, the method comprising: cast-film extruding a feed mixture comprising poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA), thereby forming a film; (optionally) thermally annealing the film, thereby forming the sc-PLA film; wherein the PLLA and the PDLA have at least one of properties (A), (B), and (C): (A) the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min); (B) the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa; and (C) the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa. In a refinement or alternative aspect, the method can comprise stretching or biaxially stretching the film (e.g., before, during, after, or instead of thermal annealing, for example to (further) increase crystallinity and improve water barrier properties).

[0040] In a refinement of the method, the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 1 g / (10 min) or 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

[0041] In a refinement, the method comprises: combining the PLLA and the PDLA as separate materials when forming the feed mixture (e.g., pre-mixed separate PLLA and PDLA materials or separately fed PLLA and PDLA materials to an extruder, but without masterbatch formation or other pre-compounding / melt-mixing of the PLLA and the PDLA); cast-film extruding the feed mixture at a temperature in a range of 225 °C to 250 °C; and thermally annealing the film at a temperature in a range of 140 °C to 170 °C.

[0042] In a refinement, the method comprises: forming the film as a continuous film (e.g., in a roll) having a length dimension, a width dimension, and thickness dimension (e.g., allmutually orthogonal dimensions) such that a ratio of the length dimensiomwidth dimension (or aspect ratio) is at least 50:1 (e.g., and / or up to 10000:1 , depending film sheet width, which could be in a range of 5 cm to 500 cm as described above).

[0043] In a refinement of the method, the resulting sc-PLA film formed by the method can have any of the variously disclosed properties, features, characteristics described herein for the sc-PLA film as a standalone film or as a component of the multilayer barrier article.

[0044] While the disclosed methods, compositions, and articles are susceptible of embodiments in various forms, specific embodiments of the disclosure are illustrated (and will hereafter be described) with the understanding that the disclosure is intended to be illustrative and is not intended to limit the claims to the specific embodiments described and illustrated herein.BRIEF DESCRIPTION OF THE FIGURES

[0045] Figure 1 is a side cross-sectional view illustrating multilayer barrier articles according to the disclosure, including (A) an article with a first water or moisture barrier layer, a second oxygen barrier layer, and a third sealant layer; and (B) an article further including adhesive layers between the first, second, and third layers.

[0046] Figure 2 illustrates a cast-film extrusion method for forming a stereocomplex polylactic acid (sc-PLA) film according to the disclosure.

[0047] Figure 3 is a graph showing wide angle X-ray diffraction (WAXD) patterns for castfilm extruded mixtures of PLLA / PDLA (70 / 30 w / w) at varying thermal annealing times after extrusion.

[0048] Figure 4 is a graph showing MVTR values of four multilayer laminated structures at 37.8 °C / 90% RH, 23.0 °C / 85% RH, and 11 .0 °C / 85% RH. The four multilayer structures include: (1) PLLA / PDLA 50-50-A30 / PVOH-Nc / Adh / PLLA, (2) PLLA / PDLA 85-15-A3 / PVOH- Nc / Adh / PLLA, (3) PLLA / PDLA 50-50-A3 / PVOH-Nc / Adh / PLLA, and (4) PHBV / PVOH- Nc / Adh / PLLA.

[0049] Figure 5 is a graph showing OTR values at 23.0 ‘0 / 50% RH of the same four laminated structures as in Figure 4.

[0050] Figure 6 is a side cross-sectional view illustrating representative multilayer barrier articles according to the disclosure, including (A) a multilayer structure prioritizing MVTR barrier properties, and (B) a multilayer structure prioritizing OTR barrier properties.DETAILED DESCRIPTION

[0051] Given the lack of recycling and recyclability of current plastic packaging materials, it would be desirable to provide industrial compostable polymers that can potentially replace non-biodegradable and fossil-based plastics since they can be disposed of with organic waste when contaminated.

[0052] One potential solution to overcome some of the issues related to the use of PLA as a biodegradable plastic is to combine the two enantiomeric forms of PLA, namely L-PLA (PLLA) and D-PLA (PDLA), to produce stereocomplex PLA (sc-PLA). For a well-blended PLLA and PDLA mixture, multi-center hydrogen bonding leads to a potential alternative arrangement of helical chains between L-lactyl and D-lactyl portions with opposing chiral confirmation for PLA stereocomplex formation. The stereocomplex formed from the PLLA / PDLA enantiomers allows for improved intermolecular interactions via dipole-dipole interaction and hydrogen bonding. A more tightly packed chain conformation results side- by-side within the stereocomplex crystal structure, allowing for improved thermal stability and mechanical properties. sc-PLA has a melting temperature (Tm) of approximately 225 °C, while homocrystallite PLA (HC-PLA) melts around 180 °C, exhibiting about a 50 °C variance between them. Tensile strength, Young’s modulus, and elongation at break of sc-PLA are improved over HC-PLA. Annealed films, after extrusion, increase crystallinity, and annealing is a common technique in processing polymers to alter their physical and chemical properties. Producing sc-PLA within the PLA matrix and increasing its crystallinity through annealing can improve barrier properties. The moisture vapor transmission rate (MVTR) of solvent-cast sc-PLA films is about 14-23% better than that of HC-PLA, allowing uses such as in packaging. The higher the crystallinity of SC-PLA, the better the water barrier properties may be if the rigid amorphous fraction (RAF) - the phase between the crystalline fraction (CF) and the mobile amorphous fraction (MAF) - is fully controlled.

[0053] sc-PLA can be made by different methods known in the art, for example, including injection molding, such as by solvent casting a masterbatch for injection molding or by twin- screw extrusion of pellets for injection molding. In an aspect, the disclosure relates to an improved method for forming sc-PLA sheets and films, namely via cast-film extrusion. In various embodiments and as illustrated in the examples herein, sc-PLA films can be produced via cast film extrusion using a single screw extruder without first making a masterbatch. Unlike other methods for forming sc-PLA, cast film extrusion provides a means for producing commercial-scale sc-PLA films and sheets (e.g., in one long, continuous roll of film suitable for packaging many individual items at a subsequent time).

[0054] In an aspect, the disclosure relates to a production method for improving barrier properties of polylactic acid (PLA) and stereocomplex PLA (sc-PLA) via cast film extrusion and annealing. Cast film extrusion and annealing of L-PLA(PLLA), D-PLA (PDLA), and SC- PLA in varying ratios to improve the moisture vapor transmission rate (MVTR). Example formulations have sc-PLA ratios including 85% PLLA / 15 % PDLA, 70 % PLLA / 30 % PDLA, 50 % PLLA / 50 % and PDLA, 30 % PLLA / 70 % PDLA (e.g., 25-90, 30-85, or 40-70 wt.% PLLA and 10-75, 15-70, or 30-60 wt.% PDLA, such as with not more than 0.1 , 1 , 2, 3, 5, 7, or 10 wt.% other components).

[0055] In an aspect, the disclosure relates to multilayer structure and a related production method for improving barrier properties of a biodegradable structure incorporating stereocomplex PLA (sc-PLA) and / or poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) via cast film extrusion and annealing in a laminate structure with other polymers and fillers. For example, a high oxygen and moisture barrier structure can be produced by incorporating SC-PLA or PHBV via cast extrusion and annealing as the base layer, coated with a combination of polyvinyl alcohol (PVOH) and nanoclay, then laminated to PLLA. The PLA and sc-PLA can be L-PLA(PLLA), D-PLA (PDLA), and sc-PLA in varying ratios to improve the moisture vapor transmission rate (MVTR). sc-PLA can be produced with variable ratios of PLLA and PDLA, for example including 85% PLLA / 15 % PDLA, 70 % PLLA / 30 % PDLA, 50 % PLLA / 50 % and PDLA, 30 % PLLA / 70 % PDLA (e.g., 25-90, 30-85, or 40-70 wt.% PLLA and 10-75, 15-70, or 30-60 wt.% PDLA, such as with not more than 0.1 , 1 , 2, 3, 5, 7, or 10 wt.% other components). The coating of PVOH / nanoclay adds the oxygen barrier.Multilayer Barrier Article

[0056] Figure 1 illustrates a multilayer barrier article 100 according to the disclosure. The article 100 includes a first layer 110 selected primarily as a barrier layer limiting water or moisture transport through the article 100, a second layer 120 selected primarily as a barrier layer limiting oxygen transport through the article 100, and a third layer 130 selected primarily as a base substrate, sealant layer or food contact layer. The second layer 120 is adjacent to both of the first layer 110 and the third layer 130, generally at opposing surfaces of the second layer 120. Whereas the second layer 120 is an interior or internal layer of the article, the first layer 110 and the third layer 130 are generally outer layers of the article 100 that are exposed to the external environment, for example, ambient air (e.g., for the first layer 110) or a packaged item (e.g., for the third layer 130 in contact with a food item or other packaged item). In some embodiments and as illustrated in panel (A) of Figure 1 , the second layer 120 can be in direct contact with the first layer 110 and the third layer 130, forexample as a result of directly coating one layer with another layer. In some embodiments and as illustrated in panel (B) of Figure 1 , the article 100 can include one or more adhesives to assist with inter-layer bonding, for example, a first adhesive layer 142 positioned between the first layer 110 and the second layer 120, and / or a second adhesive layer 144 positioned between the second layer 120 and the third layer 130.

[0057] As illustrated in Figure 1 , the article 100 can be characterized as having an overall thickness T, which is in a direction generally perpendicular to the outer surfaces of the article 100 and generally aligned with the direction of bulk water or oxygen transport through the article 100. As further illustrated, each of the layers can be characterized as individually having a first thickness Ti for the first layer 110, a second thickness T2for the second layer 120, and a third thickness T2for the third layer 130.

[0058] As described in more detail below, the first layer 110 and the third layer 130 can include polyester materials, which generally include biodegradable and / or compostable (co)polyesters formed from one or more hydroxyalkanoic acid monomer units such as poly(lactic acid) or polyhydroxyalkanoates (PHA), but not exclusively. In embodiments, the first layer 110 can be formed from or otherwise include stereocomplex polylactic acid (SC- PLA) or poly-3-hydroxybutyrate-co-valerate (PHBV). Such polyester materials can have relatively good water barrier properties, thus contributing to relatively low overall MVTR values for the article 100 as a whole. In embodiments, the third layer 130 can be formed from or otherwise include a poly(lactic acid) (PLA) such as poly(L-lactic acid) (PLLA). Such polyester materials need not have relatively good barrier properties, but they can contribute to sealing or other mechanical / physical properties of the article 100 as a whole. The second layer 120 can include a hydrophilic polymer 122 as a bulk or other continuous matrix material and a filler 124 distributed throughout the hydrophilic polymer 122, for example as discrete particles (e.g., nano-sized particles). The components of the second layer 120 are generally biodegradable and / or compostable. In embodiments, the second layer 120 can include polyvinyl alcohol (PVOH) as the hydrophilic polymer 122 and a nanoclay as the filler 124. Such materials can have relatively good oxygen barrier properties, thus contributing to relatively low overall OTR values for the article 100 as a whole. When present, the adhesives 142, 144 can be any suitable adhesive known in the art, for example, a polyurethane adhesive (e.g., one- or two-component adhesive, with or without a solvent or carrier). Such adhesives are commercially available and can be selected to be biodegradable and / or compostable, as are the other layers of the article 100.

[0059] The polyesters that are suitable for one or both of the first layer 110 and the third layer 130 can generally include poly(lactic acid) (PLA) and / or polyhydroxyalkanoates (PHAs). In embodiments, the first layer 110 and / or the third layer 130 can include only their polyester component(s) or otherwise be substantially free from components other than their polyester component(s) (e.g., containing not more than 0.001 , 0.01 , 0.1 , 1 , 2, or 5 wt.% of non-polyester components).

[0060] PLA exists in two enantiomeric forms, poly(L-lactic acid) (PLLA or L-PLA) and poly(D-lactic acid) (PDLA or D-PLA), as well as a racemic form, poly(DL-lactic acid) (PDLLA or DL-PLA). When combined, PLLA and PDLA can form stereocomplex PLA (sc-PLA), which has some enhanced properties over PLA, for example, thermal stability and mechanical properties, as well as water barrier properties (e.g., in particular after annealing). SC-PLA is particularly suitable as the first layer 110 to provide a water transmission barrier to the article 100. Other forms of PLA, such as PLLA, PDLA, and / or PDLLA, are particularly suitable as the third layer 130 to provide a sealant layer to the article 100.

[0061] PHAs are generally homo- or copolyesters with one or more hydroxyalkanoic acids as monomer units. Various PHAs can be synthesized directly via fermentation of a carbon substrate inside a bacterium or other microorganism. Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) is a biodegradable thermoplastic produced naturally by bacteria. It exhibits a reasonable moisture barrier similar to non-biodegradable films, such as polyethylene terephthalate (PET) and polyvinyl chloride (PVC). PHBV, part of the polyhydroxyalkanoates (PHA) family, has better moisture barrier properties than most biodegradable plastics; however, its oxygen barrier properties are not as reasonable. Other representative PHAs include poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-4- hydroxybutyrate (P(3-HB-co-4-HB)), poly-hydroxyvalerate (PHV), and polyhydroxybutyrate- co-hydroxyhexanoate (PHBH). PHAs are particularly suitable as the first layer 110 to provide a water transmission barrier to the article 100.

[0062] More generally, polyesters that are suitable for one or both of the first layer 110 and the third layer 130 can include homopolyesters or copolyesters of one or more monomer units selected from Formula I:-O-R-C(=O)- (I).In Formula I, R can be a hydrocarbon group having 1 to 9 carbon atoms, for example 1 , 2, 3, 4, 5, 6, 7, 8, or 9 carbon atoms. A hydroxyacid monomer corresponding to the monomer unit of Formula I can be represented by HO-R-C(=O)OH. The R group can be a linear or branched alkyl group (e.g., containing only C and H atoms and / or otherwise free fromheteroatoms). The oxygen atom and the carbonyl group can be at opposing or terminal ends of the R group, or the oxygen atom and the carbonyl group can be at intermediate positions along the length of the R group. For example, PLA can be represented by Formula I when R is a 2-carbon group with the oxygen atom in the first position relative to the carbonyl group (e.g., CH3CH(O-)C(=O)- as monomer unit or CH3CH(OH)C(=O)OH as hydroxyacid monomer). Similarly, a 3-hydroxybutyrate monomer can be represented by R as a 3-carbon group (e.g., CH3CH(O-)CH2C(=O)- as monomer unit or CH3CH(OH)CH2C(=O)OH as hydroxyacid monomer) and a 3-hydroxyvalerate monomer can be represented by R as a 4-carbon group (CH3CH2CH(O-)CH2C(=O)- as monomer unit or CH3CH2CH(OH)CH2C(=O)OH as hydroxyacid monomer) in a corresponding PBHV copolyester PHA.

[0063] The hydrophilic polymers 122 that are suitable for the second layer 120 can include hydroxy-functional and / or water-soluble materials such as polyvinyl alcohol (PVOH). PVOH is a biodegradable polymer that has both oxygen barrier and biodegradable properties. The hydrogen bonding between the polymer chains and its crystalline structure makes it an ideal oxygen barrier. However, due to its hydrophilic nature, the hydrogen bonding also makes PVOH susceptible to water, so it is protected as an internal layer within the article 100 to prevent water from affecting the absorption and diffusion of other gases and degrading the polymer. Other hydrophilic polymers can include alginates (e.g., sodium alginate), starches, proteins (e.g., water-soluble proteins), etc.

[0064] The fillers 124 that are suitable for the second layer 120 can include various nanoclays (Nc). Incorporating nanoclay (Nc) is an excellent way to improve the oxygen barrier of the second layer 120 and the article 100. Clay is impermeable, and its large (plate-like) aspect ratio increases the tortuosity of a gas molecule through the second layer 120, thereby increasing the oxygen barrier. Nanoclay is typically composed of phyllosilicates compounds based on oxygen, silicon, and other components. It includes groups of minerals, including talc, mica, montmorillonite (MMT), and kaolin. In some embodiments, the nanoclay or other filler can be organomodified for improved compatibility with the hydrophilic polymer 122, such as an organomodified montmorillonite (OMMT) (e.g., containing MMT and a surfactant). Other fillers can include graphene oxide, graphene, graphene sheets, silicon dioxide (silica), aluminum oxide, cellulose nanocrystals, carbon nanotubes, titanium dioxide (titania), layered double hydroxides (LDH), laponite, diatomaceous earth, etc.

[0065] The hydrophilic polymer 122 and the filler 124 can be incorporated into the second layer 120 in any desired amounts and / or relative proportions. In embodiments, thehydrophilic polymer 122 can be present in an amount of 30 wt.% to 98 wt.% relative to the second layer 120, for example at least 30, 40, 50, 60, to 70 wt.% and / or up to 50, 60, 70, 80, 90, 95, or 98 wt.%. In embodiments, the filler 124 can be present in an amount of 2 wt.% to 70 wt.% relative to the second layer 120, for example at least 2, 5, 10, 20, 30, 40, to 50 wt.% and / or up to 30, 40, 50, 60, to 70 wt.%. In embodiments, a weight ratio of hydrophilic polymer:filler in the second layer 120 can be in a range of 6:1 to 1 :3, for example at least and / or up to 6:1 , 5:1 , 4:1 , 3:1 , 2.5:1 , 2:1 , 1 .5:1 , 1 :1 , 1 :1 .5, 1 :2, 1 :2.5, or 1 :3, and ranges there between.

[0066] The overall thickness T and the different layer thicknesses Ti, T2, and T3are not particularly limited and can be independently selected based on desired barrier properties and mechanical properties of the article 100. In embodiments, the article 100 can have a thickness T in a range of 40 pm to 500 pm or 120 pm to 200 pm, for example at least 40, 50, 70, 100, 120, 140, 160, 180, or 200 pm and / or up to 140, 160, 180, 200, 220, 250, 300, 400, or 500 pm. In embodiments, the first layer 110 can have a first thickness Ti in a range of 15% to 90% relative to the total thickness T of the article 100, for example at least and / or up to 15, 20, 25, 30, 35, 45, 55, 65, 75, 85, or 90% and ranges therebetween. In embodiments, the second layer 120 can have a second thickness T2in a range of 5% to 80% relative to the total thickness T of the article 100, for example at least and / or up to 5, 10, 15, 25, 35, 45, 55, 65, 75, or 80% and ranges therebetween. In embodiments, the third layer 130 can have a third thickness T3in a range of 3% to 30% relative to the total thickness T of the article 100, for example at least and / or up to 3, 6, 9, 12, 15, 18, 21 , 25, or 30% and ranges therebetween. In embodiments, a ratio of the first thickness:second thickness can be in a range of 12:1 to 1 :6, for example at least and / or up to 12:1 , 10:1 , 8:1 , 6:1 , 5:1 , 4:1 , 3:1 , 2.5:1 , 2:1 , 1 .5:1 , 1 :1 , 1 :1 .5, 1 :2, 1 :2.5, 1 :3, 1 :4, 1 :5, or 1 :6, and ranges therebetween. In embodiments, a combined thickness of the first, second, and third layers (e.g., Tn-T2+T3) can be at least 90% of the overall thickness of the article 100, example at least and / or up to 90, 95, 98, 99, 99.5, 99.8, 99.9, or 100%, and ranges therebetween.

[0067] In embodiments, the article 100 can include no adhesives, only the first adhesive 142, only the second adhesive 144, or both first and second adhesives 142, 144. As illustrated in Example 2, for instance, the second layer 120 can be applied to the first layer 110 as a coating without an adhesive, and then the second adhesive 144 can be used to laminate the second layer 120 to the third layer 130 when forming the final article 100. As a further illustration, the first adhesive 142, for example a primer or adhesion promotor, can be applied to the first layer 110 before coating the second layer 120 thereon, and then the second adhesive 144 can be used to laminate the second layer 120 to the third layer 130when forming the final article 100. As a yet further illustration, the second layer 120 can be applied to the first layer 110 as a coating without an adhesive, and then the second layer 120 can be sealed or laminated to the third layer 130 without an adhesive (e.g. using heat, a solvent, and / or pressure) when forming the final article 100. As an alternative illustration, the second layer 120 can be applied to the third layer 130 as a coating without an adhesive, and then the first adhesive 142 can be used to laminate the second layer 120 to the first layer 110 when forming the final article 100. The adhesives 142, 144, when present, can generally include any adhesive, primer, adhesion promoter, etc. known in the art to enhance interlayer adhesion between (different) polymeric layer surfaces. Examples of suitable adhesives include polyurethane adhesives (e.g., one- or two-component adhesive, with or without a solvent or carrier), soy polyol adhesives, etc. Such adhesives, primers, adhesion promoters, etc. are commercially available and can be selected to be biodegradable and / or compostable. When incorporated, the adhesives 142, 144 are typically very thin layers relative to the article 100, for example each independently being not more than 0.01 , 0.1 , 0.2, 0.5, 1 , or 2% of the overall thickness or weight of the article 100.

[0068] The article 100 provides a combination of barrier properties, limiting the transmission of water or moisture and oxygen through the article. The specific barrier properties can be independently tailored based on selection of one or more of first layer components, first layer thickness, second layer components, second layer thickness, and overall article thickness. In embodiments, the article 100 can have a moisture vapor transmission rate (MVTR) in a range of 0. 1 to 100 g / (m2»d) or 5 to 50 g / (m2»d), for example measured at 38°C / 90% RH. More generally, the MVTR can be at least and / or up to 0.1 , 0.2, 0.5, 1 , 2, 3, 5, 7, 10, 15, 20, 30, 50, 100, 200, 500, or 1000 g / (m2*d) and ranges therebetween. The foregoing MVTR values are typically expressed at 38°C / 90% RH, but alternative ranges and selections can be expressed at 23°C / 85% RH or 11 °C / 85% RH. In embodiments, the article 100 can have an oxygen transmission rate (OTR) in a range of 0.1 to 1000 cc / (m2»d) or 5 to 100 cc / (m2»d), for example measured at 23°C / 50% RH. More generally, the OTR values can be at least and / or up to 0.1 , 0.2, 0.5, 1 , 1.5, 2, 5, 10, 20, 40, 50, 100, 200, 500, 1000, 10000, 100000, or 1000000 cc / (m2*d) at 23°C / 50% RH and ranges therebetween. The MVTR and OTR values can be determined using suitable water- and oxygen-transmission detection apparatus and methods generally known in the art, such as described in the examples below.

[0069] Specific MVTR and / or OTR values for a given article 100 can be selected based on particular items or other contents to be packaged using the article 100. For example, when items to be packaged include food items, the MVTR and OTR values can be selectedbased on a particular item’s sensitivity to spoilage or other deterioration when contacted with water or oxygen, respectively. Table 1 below provides representative ranges suitable for particular food items to be packaged, and a given article 100 can have MVTR and OTR values that correspond to, overlap, lie within, or are entirely below the various ranges.Table 1. Representative Barrier Properties for Packaged Food Items

[0070] The article 100 is a generally transparent structure, and its % transmission value at 600 nm light wavelength can be used to characterize its transparency. In embodiments, the article 100 can have an optical transmission at 600 nm (T6oo) in a range of 20% to 80%, for example at least and / or up to 20, 30, 40, 50, 60, 70, or 80% and ranges therebetween.

[0071] The article 100 and / or its individual components (e.g., sc-PLA film individually, first layer, second layer, third layer and / or adhesives) are suitably biodegradable, compostable, or both biodegradable and compostable. In embodiments, the article or components thereof can have a percent biodegradation (%B) upon composting (e.g., according to the methods described below or in Example 3) of at least 50% at 90 days, at least 90% at 120 days, or at least 95% at 180 days, for example at least and / or up to 50, 60, 70, 80, 85, 90, 95, 97, 98, 99, or 100% at 90, 120, or 180 days, and ranges therebetween. Compostable material is any product specifically manufactured to break down in a compost system at the end of its useful life. Another similar definition is a product that can break down into natural elements in a compost environment. They must be able to be broken down completely by microorganisms within a specific time frame, under specific conditions, and not leave behind any toxic residue or chemicals. Compostable products require microorganisms, heat, and humidity to undergo the composting process.

[0072] Suitable methods for characterizing the article 100 and / or its individual components as compostable include ASTM D6400-21 and ASTM D6868-21 . The basic requirements for both D6400-21 and D6868-21 include the following: a. disintegration during composting; b. biodegradation; and c. no adverse impacts on the ability of compost tosupport plant growth. For ASTM D6400-21 , a plastic product must demonstrate a satisfactory rate of biodegradation by achieving the following ratio of conversion to carbon dioxide within 180 days using Test Method ASTM D5338-15, ISO14855-1 or ISO 14855-2: 90% of the organic carbon in the whole item or for each organic constituent, which is present in the material at a concentration of more than 1% (by dry mass), shall be converted to carbon dioxide by the end of the test period when compared to the positive control or in the absolute. For ASTM D6868-21 , the plastic coating or polymeric additives must meet the requirements of ASTM D6400-21 . The substrates of the end item are to individually demonstrate that 90% of the organic carbon is converted to carbon dioxide using Test Method ASTM D5338 within 180 days at 58 °C (+ / -2 °C) when compared to the positive control.

[0073] The multilayer barrier article 100 can be fabricated from its individual layer components using any suitable film formation, coating, and / or laminating methods generally known in the art. For example, the first layer 110 can be formed using a cast-film extrusion method as generally described below for sc-PLA film formation, but also for other polyester film formation (e.g., PHBV or other PHA, PLLA, etc.). The second layer 120 can be applied as coating on the first layer 110 using any suitable coating technology, such as using wire wound coating rods or Mayer rods, gravure coating, etc. The third layer 130 can be applied to second layer 120 using any suitable lamination technology and adhesive (e.g., the second adhesive 144 as illustrated), such using a carrier-based adhesive (e.g., with a solvent or water as a carrier) or a solventless adhesive (e.g., 100% solids).

[0074] The disclosure also relates to a packaged article incorporating the multilayer barrier article 100 according to any of the various disclosed embodiments. For example, the packaged article can include an item to be packaged (e.g., food item) that is fully or at least partially enclosed by the article 100. Typically, the third layer 130 of the article 100 represents an inner surface in contact with the item being packaged, and the first layer 110 of the article 100 represents an outer surface in contact with ambient air or other external environment.Stereocomplex Polylactic Acid (SC-PLA)

[0075] Figure 2 illustrates a method for forming a stereocomplex polylactic acid (SC-PLA) film according to the disclosure. The sc-PLA film is illustrated as element 110 Figure 2, because the film (or a portion thereof) can be used subsequently as the first layer 110 in the multilayer barrier article 100 described above. As shown, a cast film extrusion apparatus 10 can include an extrusion apparatus 20 and a film processing apparatus 30 that are used incombination to form the sc-PLA film 110. The sc-PLA film 110 can be biodegradable and / or compostable as described above for the article 100 (e.g., meeting thresholds or ranges for %B at different compost periods / times).

[0076] As illustrated, a feed mixture 22 including poly(L-lactic acid) (PLLA) 114 and poly(D-lactic acid) (PDLA) 116 is fed to an extruder 24. The PLLA 114 and the PDLA 116 suitably are combined as separate materials when forming the feed mixture 24. “Separate materials” can represent pellets, particles, or other solid fragments that are essentially either only PLLA or only PDLA. For example, separate feeds of PLLA 114 and PDLA 116 can be fed to the extruder 24 such the feed mixture 22 is formed in the extruder 24 (e.g., in the hopper thereof). Alternatively, separate PLLA 114 and PDLA 116 materials can be combined to form a (heterogeneous) mixture, which is then fed to the extruder 24 as the feed mixture 22. More generally, the method according to the disclosure suitably does not utilize masterbatch formation or other pre-compounding / melt-mixing of the PLLA and the PDLA before being fed to the extruder 24.

[0077] The feed mixture 22 suitably can contain 25 wt.% to 90 wt.% PLLA relative to total PLLA and PDLA combined. In embodiments, the feed mixture 22 can contain at least and / or up to 25, 30, 40, 50, 60, 70, 80, or 90 wt.% PLLA and ranges therebetween. The feed mixture 22 suitably can contain 10 wt.% to 75 wt.% PDLA relative to total PLLA and PDLA combined. In embodiments, the feed mixture 22 can contain at least and / or up to 10, 15, 25, 35, 45, 55, 65, or 75 wt.% PDLA and ranges therebetween. The foregoing ranges can similarly apply to the relative proportions of PLLA and PDLA in the sc-PLA film 110.

[0078] The feed mixture 22 travels into the extruder 24 barrel, where it contacts the screw(s) (not shown). Typically, multiple heating zones within the barrel are controlled to gradually increase the temperature of the melt from the beginning to the end of the barrel. At the end of the barrel, molten feed mixture 22 fed into a slit die 26 as it exits the extruder 24. The slit die 26 feeds the exiting material in the form of a melt 118 to chill rolls 32 of the film processing apparatus 30. The melt 118 is guided onto the surface of the chill roll 32 via an air knife 28 or vacuum system near the roll 32. This allows the melt 118 to be rapidly quenched and thereby form the corresponding film 110, which improves the physical properties and clarity. The film 110 is then transported through a set of chill rolls 32 and nip rolls 34, which dictate the final film thickness before it is trimmed via edge trimmers 36 and wound onto a rewinder 38 to form a continuous roll 112 of the film 110. Prior to being used as a moisture barrier material, the film 110 is thermally annealed at sufficient temperature and / or pressure (e.g., between two opposing plates in a hydraulic press or online in atentering line) to increase crystallinity of the film 110 and its corresponding moisture barrier properties. The film 110 can also be biaxially oriented or stretched to improve properties such as toughness and barrier (e.g., to increase crystallinity and / or improve water barrier properties).

[0079] The processing temperatures for the extrusion and annealing steps can be selected in view of the melting temperatures (Tm) of sc-PLA and homocrystalite PLA (HC- PLA), both of which are generally present in different proportions in the sc-PLA film. The extrusion temperature (e.g., final or highest temperature in the extruder 24) is generally selected to be above the Tmof SC-PLA, which is about 225°C. In embodiments, the extrusion temperature can be in a range of 225 °C to 250 °C, such as at least 225 or 230 °C and / or up to 240qC, 250qC, or 275°C. Alternatively, or additionally, the extrusion temperature can be expressed relative to the Tmof SC-PLA, for example 1 °C to 20 °C, 2qC to 10°C, or 3°C to 5°C above the Tmof sc-PLA. The annealing temperature is generally selected to be below the Tmof HC-PLA, which is about 180 °C. In embodiments, the annealing temperature can be in a range of 140 °C to 170 °C, such as at least 120, 130, 140, or 150 °C and / or up to 160 °C, 170 °C, or 175 °C. Alternatively, or additionally, the annealing temperature can be expressed relative to the Tmof HC-PLA, for example, 1 °C to 20 °C, 2 °C to 10°C, or 3 °C to 5 °C below the Tmof HC-PLA. Suitable annealing times can be 2-60 min or 5-30 min, for example at least and / or up to 1 , 2, 3, 5, 7, 10, 15, 20, 25, 30, 40, 50, or 60 min and ranges therebetween.

[0080] To form a film 110 containing substantial proportions of sc-PLA (e.g., as a fraction of the film as a whole and / or as a fraction of total crystalline content), the PLLA 114 and the PDLA 1 16 are selected so that they have relatively similar melting characteristics, which can be represented by the PLLA 114 and the PDLA 116 materials having one or more of (A) relatively close melt flow rate (MFR) values, (B) relatively close weight-average molecular weight (Mw) values, and (C) relatively close number-average molecular weight (Mn) values. When the melting characteristics of the two PLA materials are too dissimilar, the result can be an inability to form a film via cast extrusion, for example due to film crystallization in the die 26 of the extruder 24.

[0081] In embodiments, the PLLA 1 14 and the PDLA 116 can have a difference in melt flow rate (MFR) that is not more than 1 g / ( 10 min), 3 g / ( 10 min), or 5 g / ( 10 min), for example, an MFR difference that is at least and / or up to 0.1 , 0.2, 0.5, 1 , 2, 3, 4, or 5 g / ( 10 min) and ranges therebetween. The MFR difference can reflect an absolute value of the difference between the two values, or it can reflect a selection in which one MFR value is selected tobe higher than the other value. Absolute MFR values for the PLLA 114 and the PDLA 1 16 can independently be in a range of 1 -40, 2-30, 3-20, or 5-15 g / (10 min). MFR can be determined using ASTM D1238-20, for example, as described in the examples below.

[0082] In embodiments, the PLLA 1 14 and the PDLA 116 can have a difference in weightaverage molecular weight (Mw) that is not more than 20 kDa or 100 kDa, for example, an Mwdifference that is at least and / or up to 1 , 2, 5, 10, 15, 20, 30, 40, 50, 60, 80, or 100 kDa and ranges therebetween. The Mwdifference can reflect an absolute value of the difference between the two values, or it can reflect a selection in which one Mwvalue is selected to be higher than the other value. Absolute Mwvalues for the PLLA 114 and the PDLA 1 16 can independently be in a range of 20-500, 30-300, 40-200, or 60-150 kDa. Mwcan be determined using size exclusion chromatography (SEC), for example as described in the examples below.

[0083] In embodiments, the PLLA 1 14 and the PDLA 1 16 can have a difference in number-average molecular weight (Mn) that is not more than 12 kDa or 50 kDa, for example an Mndifference that is at least and / or up to 1 , 2, 5, 10, 12, 15, 20, 30, 40, or 50 kDa and ranges therebetween. The Mndifference can reflect an absolute value of the difference between the two values, or it can reflect a selection in which one Mnvalue is selected to be higher than the other value. Absolute Mnvalues for the PLLA 114 and the PDLA 1 16 can independently be in a range of 10-250, 15-150, 20-100, or 30-80 kDa. Mncan be determined using size exclusion chromatography (SEC), for example as described in the examples below.

[0084] The sc-PLA film 1 10 has a significant crystalline PLA content, for example a stereocomplex-crystalline (SC-crystalline) content, which in turn improvise the moisture barrier properties of the film 1 10. The various crystalline contents can be expressed relative to the film 110 as a whole (e.g., crystalline and amorphous film content) and / or relative to total crystalline content of the film 110 (e.g., SC-crystalline content relative to total crystalline content). Crystalline contents can be determined by one or both of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) as described in the examples. In embodiments, the film 110 can have an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a total crystalline content in the film, for example at least and / or up to 10, 20, 30, 40, 50, 60, or 70% and ranges therebetween. In more specific embodiments, the film 110 can have an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and a-crystalline content in the film, as determined by WAXD, for example at least and / or up to 10, 20, 30, 40, 50, 60, or70% and ranges therebetween. In more specific embodiments, the film 110 can have an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and HC-crystalline content in the film, as determined by DSC, for example at least and / or up to 10, 20, 30, 40, 50, 60, or 70% and ranges therebetween. In embodiments, the film 110 can have a total crystalline content in a range of 10 wt.% to 60 wt.% relative to a combined amount of crystalline content and amorphous content in the film (or total film weight), for example at least and / or up to 10, 20, 30, 40, 50, or 60% and ranges therebetween. The total crystalline content can reflect SC-crystalline content and a- crystalline content combined (WAXD) or SC-crystalline content and HC-crystalline content combined (DSC).

[0085] The thickness of the film 110 is not particularly limited and can be selected based on desired barrier properties and mechanical properties of the film 110. In embodiments, the film 110 can have a thickness in a range of 20 pm to 300 pm or 40 pm to 150 pm, for example at least 20, 30, 40, 50, 60, 80, 100, or 120 pm and / or up to 40, 60, 80, 100, 120, 150, 200, or 300 pm.

[0086] The sc-PLA film 110 provides improved water barrier properties, limiting the transmission of water or moisture through the film 110. In embodiments, the film 110 can have a moisture vapor transmission rate (MVTR) in a range of 0.1 to 100 g / (m2»d) or 5 to 50 g / (m2»d), for example measured at 38°C / 90% RH. More generally, the MVTR can be at least and / or up to 0.1 , 0.2, 0.5, 1 , 2, 3, 5, 7, 10, 15, 20, 30, 50, 100, 200, 500, or 1000 g / (m2»d) and ranges therebetween. The foregoing MVTR values are typically expressed at 38°C / 90% RH, but alternative ranges and selections can be expressed at 23 °C / 85% RH or 11 °C / 85% RH. Alternatively, or additionally, the film 110 can be characterized based on its moisture vapor permeability coefficient (MVPC). MVPC and MVTR are related as MVPC=MVTRxl / AP, where I is film thickness and AP is the difference in water vapor pressure across the film. In embodiments, the MVPC can be in a range of 0.01 to 2 (kg»m) / (m2»s*Pa) x 10-14at 38°C / 90% RH, for example at least and / or up to 0.01 , 0.02, 0.05, 0.1 , 0.2, 0.5, 0.7, 1 , 1 .2, 1 .5 or 2 (kg*m) / (m2*s*Pa) x 1014at 38°C / 90% RH, and ranges therebetween.

[0087] The MVTR and MVPC values can be determined using suitable water-transmission detection apparatus and methods generally known in the art, such as described in the examples below.

[0088] The sc-PLA film 110 is a generally transparent film, and its % transmission value at 600 nm light wavelength can be used to characterize its transparency. In embodiments,the film 110 can have an optical transmission at 600 nm (T6oo) of at least 50%, for example at least and / or up to 50, 60, 70, 80, 90, 95, 98, 99, or 100% and ranges therebetween.Examples

[0089] The following examples illustrate the disclosed compositions and methods but are not intended to limit the scope of any claims thereto.Example 1 : Synthesis of sc-PLA by Cast Film Extrusion

[0090] In this example, sc-PLA films were formed on a single screw extruder without first making a masterbatch. Blends of 85 / 15, 70 / 30, 50 / 50, and 30 / 70 PLLA / PDLA, along with PLLA and PDLA for comparison, were produced. Larger relative amounts of PLLA can be desirable, given PLLA’s widespread commercial availability, while relatively lower amounts of PDLA can be desirable based on PDLA’s lower commercial availability, with PDLA providing nucleation of PLLA and production of sc-PLA. The role of sc-PLA content on the properties of these blends, such as thermal, mechanical, and moisture barrier measurements, was measured.

[0091] Materials: PLLA (LUMINY L175, 3;99%(L-isomer)99%(L-isomer)), PDLA (LUMINY D070, 3s99%(D-isomer)99%(D-isomer)) were supplied by TotalEnergies Corbion (Gorinchem, Netherlands). All homopolymers were crystalline white pellets in appearance, with a reported weight average molecular weight (Mw) of 175 kDa for L175, 130 kDa for L130, 70 kDa for D070, and 120 kDa for D120. The resins were used as received. Tetrahydrofuran (THF), HPLC grade and stabilized with butylated hydroxytoluene, was procured from Pharmco (Brookfield, CT).

[0092] Film processing: The PLLA and PDLA resins were dried in a vacuum oven (VWR International, USA) overnight (minimum 12 h) at 60 °C and 24 in-Hg before processing to prevent hydrolytic degradation during processing. Dried PLLA and PDLA resins were processed separately to produce respective cast films. Then, the two isomers in a weight ratio of 85 / 15, 70 / 30, 50 / 50, and 30 / 70 PLLA / PDLA were weighed and thoroughly mixed in a plastic bag before being introduced into the extruder. Each mix was extruded with a microextruder (Randcastle Extrusion Systems, Cedar Grove, NJ, USA) and made into a cast film as a monolayer film. The extruder has a 1 .5875 cm diameter screw, 34 cm3 volume, and a 24 / 1 L / D ratio. The processing temperature and the extrusion conditions are provided in Table 2 below. The machine was allowed to stabilize at a chill roll speed of 10 RPM, and the first film sample was collected. The nip roller speed was increased to 15 RPM and then 20 RPM to obtain samples with the desired film thickness.Table 2. Cast film extrusion parameters used for PLLA and PDLA processingProcessing Location Temperature (°C)Zone 1 210Zone 2 220Zone 3 230Transfer tube 230Adapter 230Feedblock 220Die 215Chill Roll 22Extrusion Settings Speed (RPM)Screw 25Chill roll speed 10 to 20

[0093] Thermal annealing: Each film sample of approximately 25.4 x 16.5 cm was annealed in a QL438-C hydraulic press (PHI, USA) at 160 °C. Samples were placed between 25.4 x 25.4 cm plates lined with non-stick aluminum foil. The annealing was conducted below the Tmof the HC-PLA, and 160 °C was determined to be the optimal temperature for maximum crystallization without destroying the film’s integrity. All the samples were annealed for 5, 15, and 30 min; after annealing in the press, the samples were allowed to cool at ambient temperatures. The annealed samples were stored in a freezer at -20 °C until further analysis.

[0094] Size exclusion chromatography (SEC): The Mwand the number average molecular number (Mn) of the PLLA and PDLA resins were measured using an SEC system from Waters (Milford, MA, USA) equipped with an isocratic pump, an autosampler, a refractive index detector, and a series of STYRAGEL columns (STYRAGEL HR-4, HR-3, HR-2), with a controlled temperature of 35 °C and flow rate of 1 mL min-1. Approximately 20 mg of each resin was dispersed in 10 mL of THF and stored overnight to dissolve. Each sample was filtered, transferred to a 2 mL glass vial, and capped. The Mw, Mn, and the polydispersity index, D, were analyzed using the WATERS BREEZE2 software. Six replicates of each resin were measured.

[0095] Melt flow rate (MFR): The MFR of each resin was measured using a Ray Ran (New Castle, DE, USA) Melt Flow Indexer MK II Digital Model 2A. MFR was evaluated at 190 °C with a 2.16 kg weight as per procedure A of the ASTM D1238-20 test standard. Atleast 8 specimens, each of PLLA and PDLA, were evaluated to obtain a low dispersion on the results.

[0096] Thermogravimetric analysis (TGA): PLLA and PDLA resin samples were characterized using a Q50 thermogravimetric analyzer (TA Instruments, USA) from 100 to 600 °C at 10 °C min-1, under 50 mL min-1nitrogen gas flow. Three samples (5-10 mg) of each resin were evaluated.

[0097] Differential scanning calorimetry (DSC): Thermal analysis was conducted using a Q100 differential scanning calorimeter (TA Instruments) with a refrigerated cooling system under a 70 mL min-1nitrogen flow. Resin and film samples, each weighing between 5 and 10 mg, were packed and sealed in a standard aluminum pan and lid. The samples were equilibrated to 20 °C, ramped to 0 °C at 10 °C min-1, ramped to 260 °C at 10 °C min-1, held isothermal for 1 min, ramped to 0 °C at 10 °C min-1, and then to 260 °C at 10 °C min-1for a total of two cycles. The heat of fusion (AH) of 100% HC-PLA used for the Xc calculation was 139 J g-1. The AH of 100% sc-PLA used for the analysis was 142 J g-1. Three replicates of each resin and film were tested.

[0098] Wide angle X-ray diffraction (WAXD): The wide-angle X-ray diffraction was analyzed on an AXS D8 Advance X-ray diffractometer (Broker Co., USA) equipped with a global mirror filter Cu Ka radiation source at 40 kV 100 mA. The diffraction pattern was recorded between a 20 range from 10° and 40° at a rate of 0.24° min-1and an increment of 0.01 °. The instrument worked in combination with DIFFRAC. MEASUREMENT CENTER version 7.5.0 software (Broker Co.) to collect the data. One replicate each of PLLA, PDLA, and produced blend compositions, with each annealing time was studied.

[0099] Thickness: Caliper measurements of each film (n = 3) were recorded with a TMI digital micrometer (model 49-70-01-0001 ; USA).

[0100] Barrier properties: Moisture vapor transmission rate (MVTR) was evaluated for PLLA, PDLA, and the produced blended films on a PERMATRAN-W 3 / 34 instrument (MOCON, USA) at 38 °C and 90% RH according to ASTM F1249-20. Six or more replicates were evaluated for each film.

[0101] Tensile strength: Tensile testing was conducted on a Universal Testing System Model #5565 (Instron, USA) and measured according to ASTM D882-18. The samples were evaluated in the machine direction (MD) and cross direction (CD). The initial strain rate was 0.1 mm mm-1min-1. The grip separation was 12.7 cm for the MD samples and 7.62 cm for the CD samples. The annealed samples were not wide enough in the CD to achieve a 12.7cm grip separation, as recommended by the standard. All non-annealed samples and the 85 / 15 and 70 / 30 PLLA / PDLA samples annealed at 5 and 15 minutes were also tested for comparison. All samples were conditioned at 23 °C and 50% RH for over 40 h before testing. The BLUEHILL version 4.25 software (Instron) is integrated with the Universal Testing System to record and calculate the data. Eight replicates of each variable were evaluated.

[0102] Results: In a first trial to form a blended PLA film via cast extrusion, high MwPLLA and PDLA were used, PLLA (L175) and PDLA (D070), and several trials were conducted to produce sc-PLA films. Due to the markedly different MFRs of PLLA (L175) and PDLA (D070), master-batches were attempted in a twin extruder such that the resulting masterbatches could be used to produce sc-PLA. However, due to sc-PLA formation during masterbatch production, the films could not be cast in a single extruder from the masterbatches since the films crystallized in the die, even at multiple temperature settings.

[0103] Another attempt was to vigorously mix PLLA (L175) and PDLA (D070) in a plastic bag and then cast them in a single extruder. The Tmmeasured was 176.5 ± 1 .3 °C and 177.4 ± 0.5 °C for PLLA and PDLA, respectively, and reported as 175 °C for both resins according to the manufacturer. However, due to the different MFRs of PLLA (L175) and PDLA (D070), 3.5 ± 0.3 and 10.0 ± 0.9 g per 10 min (190 °C per 2.16 kg), respectively, a good mixing was not achieved, and the films could not be cast. Extrusion was attempted at a lower temperature closer to the Tmof the two resins and then at a higher temperature closer to the Tmof sc-PLA. Still, the difference in MFR prevented sc-PLA formation, regardless of the extrusion temperature.

[0104] Two alternative resins were then tested, PLLA (L130) and PDLA (D120), which had similar measured MFRs of 12.1 ± 1.5 and 12.2 ± 1.8 g per 10 min (190 °C per 2.16 kg), respectively, potentially facilitating the extrusion mixing. The data sheet reported the MFR as 10 g per 10 min for both resins (190 °C per 2.16 kg). The Tmmeasured was 176.2 ± 0.5 °C and 179.4 ± 1 .2 °C for PLLA and PDLA, respectively, and reported as 175 °C for both resins according to the manufacturer. Table 3 below summarizes the thermal and physical properties of all four resins used.Table 3. Physical properties of PLLA and PDLA resins usedThermal Properties PLLA (L175)nPDLA (D070) nTd,1%, °C 318 ± 5 3 314 ± 1 3Tg, °C 78 ± 1 3 75 ± 0 3Tm, °C 177 ± 1 3 177 ± 1 3Xc, % 37 + 8 3 56 ± 19 3Melt Flow Rate, g / 10 min 3.5 ± 0.3 8 10.0 ± 0.9 8Physical PropertiesDensity, g / cm31 .25 ± 0.0 9 1 .24 ± 0.0 9Mw, kDa 157 ± 6 6 38 ± 3 6Mn, kDa 87 ± 7 6 22 ± 2 60 1 .7 ± 0 6 1 .8 ± 0.1 6Thermal Properties PLLA (L130) n PDLA (D120) nTd,1%, °C 303 + 5 3 319 ± 5 3Tg, °C 74 ± 1 3 72 ± 7 3Tm, °C 176 ± 1 3 179 ± 1 3Xc, % 30 ± 1 3 30 ± 5 3Melt Flow Rate, g / 10 min 12.1 ± 1 .5 13 12.1 ± 1 .8 13Physical PropertiesDensity, g / cm31 .25 ± 0 19 1 .25 ± 0 12Mw, kDa 120 ± 0 6 101 ± 0 6Mn, kDa 70 ± 1 6 59 ± 1 60 1 .7 ± 0.0 6 1 .7 ± 0.0 6Note: n indicates the number of samples

[0105] The PLLA (L130) and PDLA (D120) resins with comparable MFR at a similar Tmpermitted the formation of a homogeneous mixture and optimized the temperature profile for SC-PLA to be formed during the extrusion process while extruding and casting it into a film in one process. Suitable temperature profiles were tested: At too low of a temperature, only HC-PLA was achieved, while at high temperatures, the mixture flowed too rapidly and did not form a film.

[0106] Cast film production of PLLA / PDLA blend ratios: Several blends of PLLA / PDLA resins with similar MFR, Tm, and similar Mnwere combined and directly extruded in a single-screw extruder without the assistance of a master batch. The film combinations included 85 / 15, 70 / 30, 50 / 50, and 30 / 70 PLLA / PDLA and homopolymer PLLA and PDLA films for comparison purposes. Visual observation of the final films produced and the accompanying LIV transmission values at 600 nm demonstrated the transparency of the formed films. Percent transmission at 600 nm (T6oo) values were 76.0% (PLLA), 84.8% (85 / 15 PLLA / PDLA), 84.1% (70 / 30 PLLA / PDLA), 81 .4% (50 / 50 PLLA / PDLA), 69.3% (30 / 70 PLLA / PDLA), and 83.2% (PDLA). The films were tested for their mechanical properties, and the films were analyzed via DSC and WAXD. The PLLA and PDLA thermograms (not shown) do not show melting peaks at about 220 °C since they are only HC-PLA. All the PLLA / PDLA blends have the characteristic sc-PLA peak, with the 50 / 50 PLLA / PDLA blend having the most significant enthalpy depression due to the equimolar composition of L and D-PLA, maximizing the sc-PLA formation. The other four PLLA / PDLA blends have an excess of either PLLA or PDLA and can only form the stereo-complex until one of them is fully consumed.

[0107] Annealing the cast film: After the films were successfully produced, the effect of annealing was evaluated. The optimal annealing temperature was determined by running trials at 100, 140, 160, and 180 °C (data not shown). Annealing at temperatures higher than 160 °C made the film unusable since the HC-portion of the material melted. After reviewing the Xc data from the trials, it was established to use 160 °C as the annealing temperature. WAXD analysis of the annealed films showed that at 15 min, crystallization started in the PLLA and PDLA films, but full crystallization was not obtained until 30 minutes. In contrast, all PLLA / PDLA blends exhibited almost full crystallization at 5 min and complete saturation in crystal growth was observed at 15 min. Figure 3 is an illustrative WAXD pattern of PLLA- PDLA (70 / 30)-A-0,5, 15,30 min (i.e., annealed for 0,5,15, or 30 min), and they show distinct peaks corresponding to a-crystals (20 at 14.9°, 16.8°, and 19.2 “ associated with the 010, 110 / 220, and 203 crystal planes) and SC-crystals (20 at 12.0°, 20.8°, and 24.1 “ associated with the 110, 300 / 030 and 200 crystal planes) not present in the non-annealed samples.

[0108] Table 4 below summarizes the tensile stress and strain results for the two blends and shows that all the annealed samples had significantly lower tensile stress and tensile strain than the non-annealed samples; most annealed samples were not significantly different (P > 0.05). The samples in this example were all annealed at 160 °C to maximize crystallization and nucleation of SC. The process of annealing the samples had a beneficial effect on inducing crystallinity but had a detrimental impact on the film’s overall strength. However, samples with 5 min of annealing time provide sufficient crystallization to tailorother properties, including barrier properties such as moisture vapor transmission rate, described below.Table 4. Tensile stress and stain for PLLA / PDLA annealed filmsTensile stress at Maximum load Tensile strain at tensile strengthMD CD MD CDMaterial MPa MPa % %PLLA / PDLA(70 / 30)-0 minutes 35.49 ± 2.66a30.19 ± 3.93d2.34 ± 0.14* 1.82 ± 0.16hPLLA / PDLA(70 / 30) A160-5 minutes 5.15 ± 1.25b5.49 ± 2.23e0.74 ± 0.149 0.86 ± 0.14iPLLA / PDLA(70 / 30) A160-15 minutes 5.37 ± 1 ,36b8.21 ± 2.38e0.6 ± 0.069 0.93 ± 0.10'PLLA / PDLA(85 / 15)-0 minutes 43.97 ± 4.94c28.77 ± 1 .15d2.42 ± 0.22f1.33 ± 0.10'PLLA / PDLA(85 / 15) A160-5 minutes 8.80 ± 3.54b5.63 ± 1.82e0.73 ± 0.109 0.63 ± 0.11kPLLA / PDLA(85 / 15) A160-15 minutes 5.70 ± 2.91b8.10 ± 1.22e0.73 ± 0.199 0.86 ± 0.22'

[0109] Moisture vapor barrier characteristics: Annealed and non-annealed samples were evaluated for moisture vapor transmission to confirm the benefit of the increased crystallinity. The moisture vapor permeability coefficient (MVPC) for PLLA, PDLA, and all the blends annealed at 30 min was compared. The annealed samples had significantly better (lower) MVPCs than the non-annealed samples; however, there was no difference among any of the annealed samples. Increasing crystallinity generally reduces a polymer’s solubility, diffusion, and permeability. In this case, the increase of crystallinity directly affected the reduction in MVPC. In addition, the intermediate blends of PLLA / PDLA (85 / 15, 70 / 30, 50 / 50, and 30 / 70) also resulted in significantly improved barriers.

[0110] Table 5 summarizes the MVPC for each treatment and includes the Xc obtained by DSC and WAXD for each annealing time. There was a direct correlation between the improved barrier and the overall percentage of crystallinity. The same trend discussed earlier concerning crystallinity at the various annealing times also appears valid for the MVPC. The blended non-annealed samples significantly differ from the annealed blend composition for all annealing times i.e. 5, 15, and 30 min. The PLLA samples do not vary considerably from the non-annealed sample until 15 min of annealing time. The 15 min and 30 min annealed PDLA samples show a significant difference from the non-annealed sample; however, the 5 min PDLA sample does not differ significantly from the other PDLA samples. This example demonstrates that the intermediate blends of PLLA / PDLA (85 / 15, 70 / 30, and 30 / 70) also resulted in significantly improved barriers, in addition to the equimolar (50 / 50) blend. Thismeans that improvement is obtained with as low as 15% PDLA, which is beneficial since PLLA is more economical and commercially available than PDLA at present.Table 5. MVPC, DSC, and WAXD results for PDLA, PLLA, and blends thereofPLLA-A160-30 min 12 0.853 ± 0.324e-* 41 — 41 — 31 — 31 —PLLA-A160-15 min 12 0.892 ± 0.233e-* 42 — 42 — 26 — 26 —PLLA-A160-5 min 9 1 .62 ± 0.320a’c’d27 — 27 — 16 — 16 —PLLA-A160-0 min 14 2.15 ± 0.720a’b0 — 0 — 0 — 0 —PLLA / PDLA(85 / 15)-A160-30 min 10 0.508 ± 0.269* 31 14 44 31 34 8 42 19PLLA / PDLA(85 / 15)-A160-15 min 12 0.744 ± 0.3260e’* 26 15 41 38 29 13 42 30PLLA / PDLA(85 / 15)-A160-5 min 14 1 .130 ± 0.590d’e’* 29 12 41 28 23 5 28 18PLLA / PDLA(85 / 15)-A160-0 min 8 1 .960 ± 0.240a-b-c-d0 0 0 — 0 0 0 —PLLA / PDLA(70 / 30)-A160-30 min 23 0.798 ± 0.617e-* 28 15 42 35 24 12 36 34PLLA / PDLA(70 / 30)-A160-15 min 7 0.981 ± 0.312e-* 22 17 39 44 20 13 33 40PLLA / PDLA(70 / 30)-A160-5 min 10 1 .140 ± 0.230d-e-* 30 19 49 39 29 5 34 14PLLA / PDLA(70 / 30)-A160-0 min 8 2.520 ± 0.590b0 0 0 — 0 0 0 —PLLA / PDLA(50 / 50)-A160-30 min 21 0.953 ± 0.341e-* 19 24 42 56 15 22 37 59PLLA / PDLA(50 / 50)-A160-15 min 8 0.918 ± 0.113e-* 21 25 47 54 40 7 47 15PLLA / PDLA(50 / 50)-A160-5 min 10 0.998 ± 0.179e’* 26 22 48 47 38 7 45 16PLLA / PDLA(50 / 50) A160-0 min 9 2.36 ± 0.230a’b0 0 0 — 0 0 0 —PLLA / PDLA(30 / 70)-A160-30 min 8 0.433 ± 0.310* 29 17 46 37 25 7 32 21PLLA / PDLA(30 / 70)-A160-15 min 8 0.856 ± 0.450e’* 26 17 43 40 22 13 35 37PLLA / PDLA(30 / 70)-A160-5 min 10 0.741 ± 0.287e-* 18 16 34 47 11 12 23 51PLLA / PDLA(30 / 70)-A160-0 min 15 2.61 ± 0.370b0 0 0 — 0 0 0 —PDLA-A160-30 min 8 0.732 ± 0.293e’* 43 — 43 — 37 — 37 —PDLA-A160-15 min 6 1 .270 ± 1 ,530d’e’* 48 — 48 — 21 — 21 —PDLA-A160-5 min 6 1 .290 ± 0.820c-d-e-* 34 — 34 — 22 — 22 —PDLA-A160-0 min 7 2.250 ± 0.600a’b’c0 — 0 — 0 — 0 —

[0111] The WAXD crystallinity was decoupled between the a-crystal and the SC-crystal by looking at the various peaks. The peaks at 20 = 14.9°, 16.8°, and 19.2 “correspond to the a -crystal. The peaks at 20 = 12.0°, 20.8°, and 24.1 “correspond to the SC-crystal. The a - crystal dominates in all the blends except the 50 / 50 PLLA / PDLA blend. In the PLLA / PDLA 50 / 50 scenario, equal amounts of PLLA and PDLA can maximize the interactivity between the two enantiomeric materials, increasing the amount of sc-PLA formed. Hence, the 50 / 50 blend has the highest sc-PLA amount of all the samples. In all other combinations, PLLA or PDLA is present at different levels, limiting the reaction between the two and leaving an abundance of unreacted PLLA or PDLA, depending on the blend ratio. This does not stop the remaining PLLA or PDLA from forming a-crystal at the annealing temperature / time combination. The overall WAXD Xc,tfor all the annealed materials ranges from 16% to 47%, depending on the annealing time. The MVPC is also about the same for all the annealed samples since there is no significant difference between the annealed blended samples or the HC-PLA annealed samples at 15 min of annealing or more. The overall Xc improves the barrier more than the individual XHC or XSc formed.Example 2: Multilayer Barrier Films

[0112] In this example, PHBV and sc-PLA base films produced through cast extrusion were enhanced with a PVOH-nanoclay (Nc) coating to improve the oxygen barrier. Subsequently, these coated films were laminated to PLLA with a compostable adhesive to form a sealant layer. All components of the multilayer film are biodegradable, and there are no metal or polyvinylidene chloride (PVDC) components or layers. The moisture barrier properties were examined under conditions of 37.8 °C / 90% RH, 23 °C / 85% RH, and 11 °C / 85% RH, enabling the calculation of barrier activation energy. Additionally, the oxygen barrier properties were assessed at 23 °C / 50% RH, illustrating the robustness of this structure.

[0113] Materials. The PLA resins were supplied by TotalEnergies Corbion (Netherlands), PLLA (LUMINY L130) (^99% (L-isomer)) and PDLA (LUMINY D120) (^99% (D-isomer)). The PHBV resin was purchased from TianAn Biopolymer (China), grade Y1000P. Kuraray (Japan) provided the PVOH, EXCEVAL HR3010, a white powder with a degree of hydrolysis of 99.2 mol %. The adhesive, FLEXTRA SF-1000CP / XR-2000XP, is a two-part polyurethane, 100% solids compostable adhesive supplied by H.B. Fuller (USA).Organomodified montmorillonite (OMMT), NANOMER 1.34 TCN was obtained from Nanocor (USA), consisting of 80% montmorillonite (MMT) and 20% surfactant. Dimethyl sulfoxide (DMSO), a spectrophotometric grade of 99.9+%, was purchased from Alfa Aesar (USA).

[0114] Film Processing. PLLA and PDLA were dried in a vacuum oven (VWR International, USA) at 80 °C and 24 in-Hg for at least 12 h before processing to minimize hydrolytic degradation due to moisture during processing. PLLA and PDLA films were produced. Then, the two resins were mixed, by weight, in ratios of 50-50 and 85-15 for PLLA / PDLA before being introduced to the extruder. Each film was extruded on a pilot-scale microextruder (Randcastle Extrusion Systems, USA) as described above in Example 1. PHBV was run in the same microextruder to produce cast films, and the processing conditions are summarized Table 6 below.Table 6. Cast film extrusion parameters used for PHBV processing.Processing Location Temperature (°C)Zone 1 166Zone 2 166Zone 3 166Transfer tube 166Adapter 168Feedblock 168Die 166Chill Roll 70Extrusion Settings Speed (RPM)Screw 35Chill roll speed 20

[0115] Thermal Annealing. The PHBV and the 50-50 and 85-15 PLLA / PDLA film samples were annealed in a hydraulic press (model number QL438-C, PHI, USA) heated to 160 °C, to induce crystallinity. The Xcimproves the water vapor permeability. Each sample was approximately 25.4 x 16.5 cm2. Two 25.4 x 25.4 cm2plates lined with nonstick aluminum foil were used, and the samples were placed between the two plates of the press. The samples were annealed for 3, 5, or 30 min and then cooled at room temperature. After cooling, the samples were stored at -20 °C to reduce polymeric chain mobility and any possible morphological changes associated with it so they could be analyzed later.

[0116] Plasma Treatment. A PE-25 Series Plasma system (Plasma-Etch, USA) treated the films to increase the surface tension above 44 dyn / cm before applying the coating. Treating the film increases surface tension, allowing the coating to wet out effectively on the film’s surface. Before treating the film, the surface tension was less than 34 dyn / cm, which was too low for the coating to wet out on the substrate. The coated barrier and sealant layers were treated before coating or laminating. The plasma treatment time was set to 8 s.

[0117] Coating Preparation. The coating was prepared stepwise. PVOH and OMMT Nc were added to DMSO at 5 and 2.5%, respectively, while stirring at room temperature. The solution was heated to 95 °C, stirred for 2 h, and then slowly cooled to room temperature. It was used at room temperature to coat the films, and it was continually stirred between coating applications.

[0118] Coating and Laminating. A K303 Multicoater (RK Printing Instruments, UK), with various size Mayer rods, was used for coating the film substrates with a coating or adhesive, depending on the step in the process. The speed setting was 1 m / min. A #3 Mayer rod was used for the coating process. The coating was applied onto the barrier film, either sc-PLA or PHBV film, in multiple layers, allowing each layer to dry for a minimum of 6 h before applying the next layer; four layers of the coating were used for each substrate. In a commercial application, the layers would be dried in an oven at typical line speeds, but since this was performed in a lab setting, extra time was required to dry each layer between applications. The coated substrates were dried in a PT-1 Peltier effect temperature-controlled portable cabinet with a PELT-5 Temperature Controller (Sable Systems, USA) set to 45 °C.

[0119] The coating combination was PVOH and OMMT dispersed in DMSO for lab testing simplicity, but other greener solvents, such as deionized water, could be used. DMSO offers a low surface tension of 43.5 dyn / cm, improving the coating application. After the coating was applied and subsequently dried, the adhesive was applied, and the layer of PLLA was placed on top. The structure was then placed into the compression molder at 55 °C for 5 min to simulate a heated nip roller. A #2 Mayer rod was used for the adhesive application. The samples were then stored under pressure for 3 days to cure. The recommended curing time for the adhesive to reach maximum bond strength and chemical resistance is a minimum of 24-48 h, and 72 h was selected to ensure the structures were fully cured.

[0120] UV / Vis Measurement. A UV / vis spectrophotometer (model 1800, Shimadzu, Japan) measured film transparency (% T) from 200 to 800 nm. Three samples of each film, including the base and laminated samples, were tested.

[0121] Barrier Properties. The barrier properties of each structure were measured with a PERMATRAN-W 3 / 34 (Mocon, USA), determined at 37.8 °C / 90% RH, 23 °C / 85% RH, 11 °C / 85% RH, and an OX-TRAN 2 / 20 at 23 °C / 50% RH according to ASTM F1249- 2047 and ASTM D3985-1748 for the moisture vapor transmission rate (MVTR) and the oxygen transmission rate (OTR), respectively. A foil mask was used, with a sample size of 3.14 in2(20.3 cm2) exposed to the sensor. Six or more replicates were evaluated for each film sample.

[0122] Differential Scanning Calorimetry. Thermal analysis was conducted on the base films chosen as the likely candidates to determine the Xc and the split between the homocomplex (HC) and SC crystalline portions for the sc-PLA samples. The HC crystals are formed from PLLA or PDLA, while the SC crystals are a polymorph between PLLA and PLDA chains that interact through dipolar and intermolecular hydrogen bonding. During the extrusion process, full stereocomplexation is not achieved, so there is a mixture of HC and SC crystals present. The differential scanning calorimetry (DSC) thermogram procedure of Example 1 was used. Three replicates were tested for each film produced. For the Xc calculation of the sc-PLA samples, 139 and 142 J / g were used for the heat of fusion (AH) of 100% HC-PLA and SC-PLA, respectively. For the Xccalculation of PHBV samples, 143 J / g was used for the AH of 100% crystalline HPBV.

[0123] Results: PLLA was selected as an outer sealant layer for all multilayer structures. PLLA also protects an interior PVOH / Nc layer from direct exposure to the ambient environment, since it is so hydrophilic. The outer barrier layers (PLLA / PDLA or PBHV) were plasma treated, and the PVOH / Nc coating was applied via Mayer rod to the film in multiple stages. After coating, the bi-barrier layer combination was laminated to the PLLA sealant layer using an intermediate adhesive (Adh). The final structures assembled were: (1) 55 pm PLLA / PDLA-50-50-A30 min / 29 pm PVOH-Nc / Adh / 49 pm PLLA; (2) 67 pm PLLA / PDLA- 50-50-A3 min / 24 pm PVOH-Nc / Adh / 63 pm PLLA; (3) 81 pm PLLA / PDLA-85-15-A3 min / 25 pm PVOH-Nc / Adh / 63 pm PLLA; and (4) 48 pm PHBV / 20 pm PVOH-Nc / Adh / 63 pm PLLA

[0124] After 3 days of curing, the four main structures were tested for UV / vis transmission and oxygen and moisture barrier levels. The films were generally transparent structures, and their % transmission values at 600 nm were measured to characterize their transparency. Percent transmission at 600 nm (T6oo) values were (1) 54%, (2) 53%, (3) 45%, and (4) 22%. Film 4 was hazier than the other three structures, indicated by the lowest transmission value (22%). The base films had slightly higher transmission values at 600 nm than the laminated structures.

[0125] Figures 4 and 5 show the MVTR and OTR values obtained for the four laminated structures at three testing conditions. All MVTR values were similar, but there was a statistical difference at 37.8 °C / 90% RH between the structure with PLLA / PDLA 85-15 and those with PHBV and PLLA / PDLA 50-50. This aligns with the fact that the PLLA / PDLA 85-15 base layer was the thickest of the four materials, at 81 pm, and most of the moisturebarrier comes from the base film layer. Comparing the MVTR of the base layers of the four materials shows no significant difference between any of the four materials, which reinforces the fact that the moisture barrier is all related to the base layer (i.e., PLLA / PDLA 85-15, PLLA / PDLA 50-50, and PHBV). The OTR of the four structures were not statistically different, which is unsurprising since the coating layer is similar in all of them, and the oxygen barrier is mainly provided by the PVOH-Nc layer. A statistical difference between the OTR of the base films and the final structures reinforces that the coating layer adds the oxygen barrier to the structures.

[0126] The contribution to the barrier layers can be estimated using Equation 1 for multilayer structures, and individual barrier contributions can be calculated (e.g., as the sum of individual barrier contributionswhere ltis the total thickness of the material; h, l2, and h are the thicknesses of layers 1 , 2, and 3, respectively; Ptis the permeability coefficient of the overall structure; and Pi, P2, and P3 are the permeability coefficients of layers 1 , 2, and 3, respectively. Using Equation 1 and the determined permeability coefficients of the various layers, representative multilayer structures were designed that would preferentially prioritize either MVTR or OTR. Figure 6 shows the designed structures and the relative layer thickness values for (A) the prioritized MVTR structure and (B) the prioritized OTR structure, both of which had a general layer structure of PHBV / PVOH-Nc / Adh / PLLA. Computed MVTR values (at 38°C / 90% RH) and OTR values (at 23°C / 50% RH) for the designed structures are (A) MVTR = 10.23 g / (m2»d) and OTR = 59.87 cc / (m2*d) for the optimized MVTR structure and (B) MVTR = 24.28 g / (m2»d) and OTR = 14.61 cc / (m2»d) for the optimized OTR structure.Example 3: Compostability and Biodegradability of sc-PLA

[0127] In this example, SC-PLA, PDLA, and PLLA films were formed via cast-film extrusion as described above in Example 1 . One sc-PLA film was annealed (160 °C for 30 min as described above), and the remaining films were not annealed. The films, along with a cellulose control, were then tested for their biodegradation under controlled composting conditions.

[0128] Biodegradation Test in Compost: The films and cellulose control were prepared for composting analysis by first grinding frozen film samples and sieving with a 20-mesh screen (841 pm) to provide a 20-mesh-pass powder sample of 24 g (or more). Manure compost for the analysis was sifted with a 10-mm screen and conditioned to 58 ± 2 °C and50 ± 5 % RH. The powder samples were evaluated under aerobic conditions using a direct measurement respirometric (DMR) system, which includes a non-dispersive infrared gas analyzer (LI-COR, USA) to measure the carbon dioxide (CO2) that evolved throughout the experiment in a contained bioreactor. The bioreactor chamber's temperature and relative humidity (RH) were maintained at 58 ± 2 °C and 50 ± 5 % RH. The airflow rate was regulated at 40 ± 2 cm3 / min. Samples were tested in triplicate by adding 400 g of compost and 8 g powder sample to a given bioreactor chamber. A blank (only 400 g compost) and positive control (400 g of compost and 8 g cellulose) were included in the test.

[0129] During the test, deionized water was injected into the bioreactors weekly to maintain the moisture content at the controlled level. Air without CO2was introduced to each bioreactor, and the amount of CO2 liberated was measured over a finite period. The system was purged after each measurement to eliminate any CO2 left over from the previous measurement and to maintain a clean baseline. The percent biodegradation (%B), which is the amount of carbon transformed to CO2, was calculated from Equation 2:(CMOtAX- Ct(X "where (C02)t is the average total CO2 evolved from the bioreactor containing the sample; (CO2)bis the average total CO2 evolved from the blank; Mtis the total mass of the sample in the bioreactor; Ctis the total carbon content of the sample as measured by carbon- hydrogen-nitrogen (CHN) analysis (e.g., using a suitable elemental analyzer such as an ELEMENTAL ANALYZER, 2400 Series II, Perkin Elmer, Waltham, MA, USA); 44 is the molecular weight of CO2, and 12 is the atomic weight of carbon.

[0130] Results: CO2 evolution over a 120-day test period was measured and converted to percent biodegradation as described above. Table 7 below summarizes the biodegradation results as a function of time. By 120 days, the percent biodegradation of the annealed SC-PLA-50-50 was greatest, at 97%, followed closely by that of SC-PLA-50-50 at 86%, while PDLA biodegraded the least, at only 40%. The biodegradation values for annealed SC-PLA-50-50 and (non-annealed) SC-PLA-50-50 had overlapping error bars at the 120-day mark. Even though the presence of crystalline content can impede biodegradation, the biodegradation performance of the annealed sample, in comparison to amorphous sc- PLA and HC-PLA, does not show a detrimental effect on the overall biodegradation process, highlighting the potential of sc-PLA for packaging applications that provide improved moisture barrier properties during its useful life as compared to HC-PLA, while still providing a highly compostable material for its end-of-life disposal.Table 7. Biodegradation in compostNote: For sc-PLA samples, the numbers are [wt.% PLLA]-[wt.% PDLA]

[0131] Because other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the disclosure is not considered limited to the example chosen for purposes of illustration and covers all changes and modifications that do not constitute departures from the true spirit and scope of this disclosure.

[0132] Accordingly, the foregoing description is given for clarity of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the disclosure may be apparent to those having ordinary skill in the art.

[0133] All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In case of conflict, the present description, including definitions, will control.

[0134] Throughout the specification, where the compositions, processes, kits, or apparatus are described as including components, steps, or materials, it is contemplated that the compositions, processes, or apparatus can also comprise, consist essentially of, or consist of, any combination of the recited components or materials, unless described otherwise. Component concentrations can be expressed in terms of weight concentrations, unless specifically indicated otherwise. Combinations of components are contemplated to include homogeneous and / or heterogeneous mixtures, as would be understood by a person of ordinary skill in the art in view of the foregoing disclosure.List of Figure Elements10 cast film extrusion apparatus20 extrusion apparatus22 feed mixture24 extruder26 die27 air knife30 film processing apparatus32 chill rolls34 nip rolls36 edge trimmers38 rewinder / winding roll100 multilayer barrier structure / film110 first layer or sc-PLA film (e.g., water or moisture barrier layer such as sc-PLA or PHBV)112 (continuous) roll of first layer material (e.g., sc-PLA)114 L-PLA (PLLA) feed116 D-PLA (PDLA) feed118 melt120 second layer (e.g., oxygen barrier layer)122 second layer matrix material (e.g., PVOH)124 second layer particulate / filler material (e.g., nanoclay)130 third layer (e.g., base / sealant layer or substrate)142 first adhesive layer144 second adhesive layer

Claims

What is claimed is:

1. A multilayer barrier article comprising: a first layer comprising a first polyester selected from the group consisting of a stereocomplex polylactic acid (SC-PLA), a polyhydroxyalkanoate (PHA), and combinations thereof; a second layer adjacent to the first layer, the second layer comprising a hydrophilic polymer and a filler distributed throughout the hydrophilic polymer; and a third layer adjacent to the second layer at a position further from the first layer than the second layer, the third layer comprising a second polyester.

2. The article of claim 1 , wherein the first layer comprises the sc-PLA as the first polyester.

3. The article of claim 2, wherein: the first layer comprises 25 wt.% to 90 wt.% of poly(L-lactic acid) (PLLA) relative to total sc-PLA in the first layer; the first layer comprises 10 wt.% to 75 wt.% of poly(D-lactic acid) (PDLA) relative to total sc-PLA in the first layer; and a stereocomplex-crystalline (SC-crystalline) content in the first layer is in a range of 10 wt.% to 70 wt.% relative to a total crystalline content in the sc-PLA.

4. The article of claim 3, wherein: the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa.

5. The article of claim 3, wherein: the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

6. The article of claim 1 , wherein the first layer comprises poly-3-hydroxybutyrate- co-valerate (PHBV) as the first polyester.

7. The article of claim 1 , wherein the third layer comprises poly(L-lactic acid) (PLLA) as the second polyester.

8. The article of claim 1 , wherein monomer units of the first polyester and the second polyester are independently selected from Formula I:-O-R-C(=O)- (I), in which R is a hydrocarbon group having 1 to 9 carbon atoms.

9. The article of claim 1 , wherein: the hydrophilic polymer comprises polyvinyl alcohol (PVOH); and the filler comprises a nanoclay.

10. The article of claim 1 , wherein: the hydrophilic polymer is present in an amount of 30 wt.% to 98 wt.% relative to the second layer; the filler is present in an amount of 2 wt.% to 70 wt.% relative to the second layer; and optionally, a weight ratio of hydrophilic polymer: filler in the second layer is in a range of 6:1 to 1 :3.

11. The article of claim 1 , wherein the multilayer barrier article has a thickness in a range of 40 pm to 500 pm.

12. The article of claim 1 , wherein: the first layer has a first thickness in a range of 15% to 90% relative to a total thickness of the multilayer barrier article; the second layer has a second thickness in a range of 5% to 80% relative to a total thickness of the multilayer barrier article; the third layer has a third thickness in a range of 3% to 30% relative to a total thickness of the multilayer barrier article; and optionally, a ratio of the first thickness:second thickness is in a range of 12:1 to 1 :6.

13. The article of claim 1 , wherein: the multilayer barrier article has a moisture vapor transmission rate (MVTR) in a range of 0.1 to 100 g / (m2»d) at 38°C / 90% RH; andthe multilayer barrier article has an oxygen transmission rate (OTR) in a range of 0.1 to 1000 cc / (m2*d) at 23°C / 50% RH.

14. The article of claim 13, wherein : the MVTR is in a range of 5 to 50 g / (m2»d) at 38°C / 90% RH; and the OTR is in a range of 5 to 100 cc / (m2»d) at 23°C / 50% RH.

15. The article of claim 14, wherein the multilayer barrier article has a thickness in a range of 120 pm to 200 pm.

16. The article of claim 1 , wherein the multilayer barrier article has an optical transmission at 600 nm (T6oo) in a range of 20% to 80%.

17. The article of claim 1 , further comprising at least one of: a first adhesive layer positioned between the first layer and the second layer; and a second adhesive layer positioned between the second layer and the third layer.

18. The article of claim 1 , wherein each of the first layer, the second layer, and the third layer is independently selected to be biodegradable, compostable, or both biodegradable and compostable.

19. The article of claim 1 , wherein the multilayer barrier article contains not more than 10 wt.% of components other than the first layer, the second layer, and the third layer, relative to the multilayer barrier article.

20. The article of claim 1 , wherein the multilayer barrier article is substantially free from metal-containing components and polyvinylidene chloride (PVDC).

21. The article of claim 1 , wherein: the first layer comprises at least one of the sc-PLA and poly-3-hydroxybutyrate-co- valerate (PHBV) as the first polyester; the hydrophilic polymer comprises polyvinyl alcohol (PVOH) present in an amount of 30 wt.% to 90 wt.% relative to the second layer; the filler comprises a nanoclay present in an amount of 10 wt.% to 70 wt.% relative to the second layer; a weight ratio of hydrophilic polymer:filler in the second layer is in a range of 6:1 to1 :3; the third layer comprises poly(L-lactic acid) (PLLA) as the second polyester; the first layer has a first thickness in a range of 15% to 90% relative to a totalthickness of the multilayer barrier article; the second layer has a second thickness in a range of 5% to 80% relative to a total thickness of the multilayer barrier article; the third layer has a third thickness in a range of 3% to 30% relative to a total thickness of the multilayer barrier article; a ratio of the first thickness:second thickness is in a range of 12:1 to 1 :6; the multilayer barrier article has a thickness in a range of 120 pm to 200 pm; and the multilayer barrier article is free from metal-containing components.

22. A packaged article comprising: an item to be packaged; and the multilayer barrier article of claim 1 at least partially enclosing the item.

23. A method for forming the multilayer barrier article of claim 4, the method comprising: cast-film extruding a feed mixture comprising the PLLA and the PDLA, thereby forming a film; thermally annealing the film, thereby forming the first layer comprising the sc-PLA; applying the second layer on a surface of the first layer; and applying the third layer on a surface the second layer.

24. The method of claim 23, further comprising: biaxially stretching the film.

25. The method of claim 23, wherein: the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

26. The method of claim 23, comprising: combining the PLLA and the PDLA as separate materials when forming the feed mixture; cast-film extruding the feed mixture at a temperature in a range of 225°C to 250 °C;thermally annealing the first film at a temperature in a range of 140 °C to 170 °C.

27. A stereocomplex polylactic acid (SC-PLA) film comprising: poly(L-lactic acid) (PLLA) present in an amount of 25 wt.% to 90 wt.% relative to total poly(lactic acid) in the film; and poly(D-lactic acid) (PDLA) present in an amount of 10 wt.% to 75 wt.% relative to total poly(lactic acid) in the film; wherein the film has at least one of properties (A), (B), (C), and (D):(A) the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min);(B) the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa;(C) the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa; and(D) the film has a stereocomplex-crystalline (SC-crystalline) content in a range of 10 wt.% to 70 wt.% relative to a total crystalline content in the film.

28. The sc-PLA film of claim 27, wherein the film has all properties (A), (B), (C), and (D).

29. The sc-PLA film of claim 27, wherein: the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 3 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

30. The sc-PLA film of claim 27, wherein the film has an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and a- crystalline content in the film, as determined by wide angle X-ray diffraction (WAXD).

31. The sc-PLA film of claim 27, wherein the film has an SC-crystalline content in a range of 10 wt.% to 70 wt.% relative to a combined amount of SC-crystalline content and HC-crystalline content in the film, as determined by differential scanning calorimetry (DSC).

32. The sc-PLA film of claim 27, wherein the film has a total crystalline content in a range of 10 wt.% to 60 wt.% relative to a combined amount of crystalline content and amorphous content in the film.

33. The sc-PLA film of claim 27, wherein the film has a moisture vapor transmission rate (MVTR) in a range of 0.1 to 100 g / (m2»d) at 38°C / 90% RH.

34. The sc-PLA film of claim 27, wherein the film has a moisture vapor permeability coefficient (MVPC) in a range of 0.01 to 2 (kg»m) / (m2»s*Pa) x 10-14at 38°C / 90% RH.

35. The sc-PLA film of claim 27, wherein the film has a thickness in a range of 20 pm to 300 pm.

36. The sc-PLA film of claim 27, wherein the film has a thickness in a range of 40 pm to 150 pm.

37. The sc-PLA film of claim 27, wherein the film is in the form of a continuous film having a length dimension, a width dimension, and thickness dimension such that a ratio of the length dimensiomwidth dimension is at least 50:1 .

38. The sc-PLA film of claim 27, wherein the film has an optical transmission at 600 nm (T6oo) of at least 50%.

39. A method for forming a stereocomplex polylactic acid (SC-PLA) film, the method comprising: cast-film extruding a feed mixture comprising poly(L-lactic acid) (PLLA) and poly(D- lactic acid) (PDLA), thereby forming a film; thermally annealing the film, thereby forming the sc-PLA film; wherein the PLLA and the PDLA have at least one of properties (A), (B), and (C):(A) the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 5 g / (10 min);(B) the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 100 kDa; and(C) the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 50 kDa.

40. The method of claim 39, further comprising: biaxially stretching the film.

41. The method of claim 39, wherein: the PLLA and the PDLA have a difference in melt flow rate (MFR) that is not more than 1 g / (10 min); the PLLA and the PDLA have a difference in weight-average molecular weight (Mw) that is not more than 20 kDa; and the PLLA and the PDLA have a difference in number-average molecular weight (Mn) that is not more than 12 kDa.

42. The method of claim 39, comprising: combining the PLLA and the PDLA as separate materials when forming the feed mixture; cast-film extruding the feed mixture at a temperature in a range of 225°C to 250 °C; and thermally annealing the film at a temperature in a range of 140 °C to 170 °C.

43. The method of claim 39, comprising forming the film as a continuous film having a length dimension, a width dimension, and thickness dimension such that a ratio of the length dimensiomwidth dimension is at least 50:1 .

44. The method of claim 39, wherein the sc-PLA film is the sc-PLA film according to any one of claims 27 to 38.

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