Polylactide resin composition and biaxial stretching method for polylactide resin composition

Abstract

The polylactide resin composition includes a mixture of 40% to 95% by weight of a crystallizable polylactide resin and 5% to 60% by weight of a certain non-crystallizable polylactide resin. The polylactide resin composition is useful in the manufacture of oriented films, particularly biaxially oriented films. These compositions can be stretched on commercially available biaxial stretching equipment since they can be stretched to a higher stretch ratio than sheets made from crystallizable polylactide resins alone.

Description

Technical Field

[0001] The present invention relates to a polylactide resin composition and a method for producing an oriented film from the polylactide resin composition. Background Art

[0002] Oriented polymer films are manufactured in large quantities for use as flexible packaging materials, particularly when properties such as optical clarity, moisture resistance, and high tensile strength are required. Biaxially oriented films are used to package many food, beverage, medical, and personal care products, among many others. These films are manufactured by producing a sheet and then stretching the sheet to produce the final film.

[0003] Polylactide (also known as polylactic acid or PLA) can be used in these applications, but its penetration into these markets is limited because PLA sheets cannot be stretched to high draw ratios, particularly when biaxially stretched. The most common industrial-scale biaxial stretching equipment operates at a draw ratio of 3 to 5 in the machine direction and a draw ratio of 4 to 10 in the transverse direction. PLA sheets cannot be stretched at these ratios without breaking, and therefore, the most commonly used biaxial stretching equipment cannot be used to process PLA into biaxially stretched film without modification. This significantly limits PLA's penetration into this market because oriented film manufacturers have invested in equipment that must operate at these high draw ratios and is not easily adapted to operate at lower draw ratios. There is a need for polylactide compositions that can be stretched at higher draw ratios while maintaining other useful properties, such as the ability to be oriented while producing a film with acceptable mechanical properties, as well as methods for producing PLA biaxially oriented films at higher draw ratios. Summary of the Invention

[0004] The present invention is a polylactide resin composition comprising a melt or solution blend of:

[0005] (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards, and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards, and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20.

[0006] FIG1 is an atomic force micrograph of the polylactide resin composition of the present invention (Example 5).

[0007] FIG2 is an atomic force micrograph of the second polylactide resin composition of the present invention.

[0008] Surprisingly, the polylactide resin compositions of the present invention can be stretched to higher draw ratios than crystallizable polylactide alone. Consequently, the polylactide resin compositions of the present invention can be processed on a wider range of industrial-scale biaxial stretching equipment than conventional polylactide resins. In many cases, such polylactide resin compositions can be processed on existing polypropylene and PET biaxial stretching lines with little or no modification to the equipment.

[0009] In some embodiments, the non-crystallizable polylactide grade is poly(meso-lactide). For purposes of the present invention, poly(meso-lactide) is a polymer or copolymer of meso-lactide, wherein at least 80% of the lactic acid units are formed by polymerization of meso-lactide, the poly(meso-lactide) having blocks of L-lactic acid units and D-lactic acid units having an average length of at least 1.1 and at most 2.0. The polylactide resin compositions of the present invention in which the amorphous polylactide grade is poly(meso-lactide) exhibit a number of unusual and beneficial properties. Surprisingly, it has been found that at these blend ratios, the crystallizable polylactide and poly(meso-lactide) are immiscible with each other. Consequently, melt or solution blends of these polylactides are typically phase separated, with the crystallizable polylactide (i) occupying one phase and the poly(meso-lactide) occupying a different phase in the blend. When the crystallizable polylactide content is high (such as greater than about 50 wt.%), the crystallizable polylactide tends to form a continuous phase, with poly(meso-lactide) present as a discontinuous amorphous phase. At lower crystallizable polylactide content (such as about 50 wt.% or less), the crystallizable polylactide and poly(meso-lactide) tend to form a co-continuous phase, with the poly(meso-lactide) phase also being amorphous. The poly(meso-lactide) phase cannot crystallize and therefore remains amorphous even after the polylactide resin composition is stretched. On the other hand, the crystallizable polylactide phase can be crystallized thermally and / or mechanically (such as by stretching). This allows the blend to develop the desired thermal and physical properties associated with crystals.

[0010] In another aspect, the present invention is a method for producing an oriented polylactide film comprising (a) forming a polylactide resin composition by melt or solution blending, the polylactide resin composition comprising:

[0011] (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20;

[0012] (b) extruding the polylactide resin composition in a machine direction through an extrusion die to produce a polylactide sheet; and

[0013] (c) stretching the sheet at a temperature of 50°C to 120°C to produce an oriented polylactide film.

[0014] In another aspect, the present invention is a method for producing a biaxially oriented polylactide film, comprising (a) forming a polylactide resin composition by melt or solution blending, the polylactide resin composition comprising

[0015] (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20;

[0016] (b) extruding the polylactide blend in a machine direction through an extrusion die to produce a polylactide sheet having a machine direction and an orthogonal transverse direction, the machine direction corresponding to the direction of movement of the polylactide blend through the extrusion die; and

[0017] (c) stretching the sheet in orthogonal directions sequentially or simultaneously at a temperature of 50°C to 120°C to produce a biaxially oriented polylactide film.

[0018] In yet another aspect, the present invention is a method for producing a biaxially oriented polylactide film comprising (a) forming a polylactide resin composition by melt or solution blending, the polylactide resin composition comprising:

[0019] (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20;

[0020] (b) extruding the polylactide resin composition to form a tubular article;

[0021] (iii) quenching and collapsing the tubular article;

[0022] (iv) heating the collapsed tube to a temperature of 50° C. to 120° C. and re-expanding the tube to stretch the tube in the transverse direction while simultaneously pulling the tube in the machine direction to produce a biaxially oriented polylactide film.

[0023] The crystallizable polylactide has a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography (GPC) relative to a polystyrene standard. The number average molecular weight can be, for example, up to 200,000 g / mol. A number average molecular weight of about 30,000 g / mol to 130,000 g / mol is generally preferred. In some embodiments, the crystallizable polylactide is characterized in that it has a relative viscosity of 1.1 to 6, such as 1.25 to 5 or 1.5 to 4.5, measured at 30°C using a 1% wt / vol polylactide resin solution in chloroform relative to a chloroform standard on a capillary viscometer.

[0024] Lactic acid units constitute at least 90% or at least 95% by weight of the crystallizable polylactide. The crystallizable polylactide may also contain repeating units formed from other monomers copolymerizable with lactide, such as alkylene oxides (including ethylene oxide, propylene oxide, butylene oxide, tetramethylene oxide, etc.), cyclic lactones, or carbonates. The repeating units derived from these other monomers may be present in block and / or random arrangements. These other repeating units suitably constitute up to 10% by weight, preferably 0% to 5% by weight, and especially about 0% to 2% by weight of the crystallizable polylactide, and may be absent.

[0025] The crystallizable polylactide (i) may also contain residues of initiator compounds, which are typically used to provide molecular weight control during the polymerization process. Suitable such initiators include, for example, water, alcohols, various types of polyols (such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, other glycol ethers, glycerol, trimethylolpropane, pentaerythritol, polymerization initiators having hydroxyl and / or carboxyl groups, such as polylactic acid oligomers, hydroxyl-terminated butadiene polymers, polyether polyols, and polyesters, etc.), polycarboxyl-containing compounds, and compounds having at least one carboxyl group and one hydroxyl group (such as lactic acid or lactic acid oligomers). The initiator residues preferably constitute no more than 10% by weight of the crystallizable polylactide, especially no more than 5% by weight or no more than 2% by weight, except in the case where the initiator is a residue of lactic acid or a lactic acid oligomer, in which case the residues of lactic acid or lactic acid oligomers may constitute the crystallizable polylactide in any proportion.

[0026] The lactic acid units in the crystallizable polylactide are composed of L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93. This ratio can be, for example, 93:7 to 100:0, 95:5 to 100:00, 7:93 to 0:100, or 5:95 to 0:100. Preferably, the L-lactic acid units and D-lactic acid units are randomly arranged.

[0027] In some embodiments, the crystallizable polylactide is a homopolymer of L-lactide or a random copolymer of L-lactide and one or more of meso-lactide, D-lactide, and racemic-lactide. In the case of such a copolymer, the ratio of the lactides is selected to provide a ratio of L-lactic units to D-lactic units of 93:7 to 99.9:0.1 or 95:5 to 99.9:0.1.

[0028] In alternative embodiments, the crystallizable polylactide is a homopolymer of D-lactide or a random copolymer of D-lactide and one or more of meso-lactide, L-lactide, and racemic-lactide. In this case, the ratio of the lactides is selected to provide a ratio of L-lactic units to D-lactic units of 7:93 to 0.1:99.9 or 5:95 to 0.1:99.9.

[0029] Crystallizable polylactide can crystallize to form a semi-crystalline polymer. "Crystallizable" means that the polylactide contains at least 5 J / g, preferably at least 15 J / g or at least 20 J / g of crystallites after being heated in air at 110°C for 1 hour. For the purposes of the present invention, a polylactide that forms less than 5 J / g of crystallinity under these conditions is "non-crystallizable". The sample is preheated to at least 220°C to melt any crystallites and then quenched by rapidly cooling to room temperature (23 ± 3°C). The quenched sample is then heated at 110°C for 1 hour and quenched again by cooling to room temperature. The degree of crystallinity is then conveniently measured using differential scanning calorimetry (DSC). This amount of crystallinity is expressed herein in J / g, i.e., the melting enthalpy of the polylactic acid crystals in the sample (in joules) divided by the weight of the polylactide in the sample (in grams). A convenient test protocol for DSC measurements is to heat 5-10 mg of sample from 25°C to 225°C at 20°C / min in air on a Mettler Toledo DSC 3+ calorimeter or equivalent running STARE V.16 software.

[0030] In some embodiments, the crystallizable polylactide has a glass transition temperature of 55°C to 65°C and, when crystallized, a crystalline melting temperature of 95°C to 195°C, specifically 120°C to 185°C.

[0031] The crystallizable polylactide (i) may have long-chain branches (having 3 or more carbon atoms). Long-chain branches can be introduced into the polylactide in various ways, such as by reacting carboxyl groups on the polylactide with epoxy groups present on a (meth)acrylate polymer or copolymer to form a polylactic acid. The (meth)acrylate polymer or copolymer is characterized by being solid at 23°C, containing an average of about 2 to about 15 free epoxy groups per molecule (such as about 3 to about 10 or about 4 to about 8 free epoxy groups per molecule), and being the polymerization product of at least one epoxy-functional acrylate or methacrylate monomer, preferably copolymerized with at least one other monomer. The (meth)acrylate polymer or copolymer suitably has a number average molecular weight per epoxy group of about 150 g / mol to about 700 g / mol, such as 200 g / mol to 500 g / mol or 200 g / mol to 400 g / mol. The (meth)acrylic acid polymer or copolymer suitably has a number average molecular weight of 1000 g / mol to 6000 g / mol, such as about 1500 g / mol to 5000 g / mol or about 1800 g / mol to 3000 g / mol. Other methods of introducing long chain branches are described in U.S. Patent Nos. 5359026 and 7015302, WO 06 / 002372A2 and WO 2019 / 152264.

[0032] In a preferred embodiment, the crystallizable polylactide (i) lacks long chain branches.

[0033] Two molecules of lactic acid can condense by eliminating two molecules of water to form 3,6-dimethyl-1,4-dioxane-2,5-dione, referred to herein as "lactide." Lactide can be considered to be composed of two "lactic acid units," each of which has the following structure:

[0034]

[0035] Each lactic acid unit in the lactide molecule contains a chiral center and exists in either the D- or L- form. Lactide can take one of three forms: 3S,6S-3,6-dimethyl-1,4-dioxane-2,5-dione (L-lactide), 3R,6R-3,6-dimethyl-1,4-dioxane-2,5-dione (D-lactide), and 3R,6S-3,6-dimethyl-1,4-dioxane-2,5-dione (meso-lactide). These have the following structures:

[0036]

[0037] L-lactide and D-lactide are a pair of enantiomers, while meso-lactide is a stereoisomer with one L-lactic unit and one D-lactic unit. Furthermore, a mixture of approximately 50% L-lactide and 50% D-lactide forms a high-melting material known as racemic lactide (or "rac-lactide"). Hydrolysis of both meso-lactide and racemic lactide produces a mixture of 50% L-lactic acid and 50% D-lactic acid.

[0038] The crystallizable polylactide (i) is preferably produced by polymerizing L-lactide or D-lactide by itself, or by copolymerizing L-lactide or D-lactide and meso-lactide, preferably in a random manner so as to copolymerize L-lactic acid units:D-lactic acid units in a ratio of ≥93:7 or ≤7:93. The polymerization can be carried out batchwise, semi-continuously, or continuously.

[0039] Suitable polymerization temperatures are preferably above the melting temperature of the monomer or monomer mixture and above the melting temperature of the crystallizable polylactide produced, but below the temperature at which significant polymer degradation occurs. The temperature range may be, for example, as low as 60°C or as high as 225°C.

[0040] Molecular weight and conversion are controlled by polymerization time and temperature, the balance between free lactide and polymer, and by the use of an initiator compound. Generally, increasing the amount of initiator compound on a molar basis tends to reduce the molecular weight of the product polymer. Molecular weight control agents, such as those described in U.S. Patent No. 6,277,951, can also be added to achieve the desired molecular weight.

[0041] Preferably, the polymerization is carried out in the presence of a polymerization catalyst. Examples of such catalysts include various tin compounds such as SnCl2, SnBr2, SnCl4, SnBr4, SnO, tin(II) bis(2-ethylhexanoate), butyltin tris(2-ethyladipate), hydrated monobutyltin oxide, dibutyltin dilaurate, tetraphenyltin, etc.; PbO; zinc alkoxide; zinc stearate; compounds such as aluminum alkoxide; compounds such as antimony triacetate and antimony (2-ethylhexanoate); compounds such as bismuth (2-ethyladipate); calcium stearate; magnesium stearate; Certain yttrium and rare earth compounds, such as those described in U.S. Pat. No. 5,208,667 to McLain et al.; chiral (R)-(SalBinap)-AlOCH3 complexes as described in Macromol.Chem.Phys.1996,197,2627-2637; single-site-β-diimidate zinc catalysts as described in JACS1999,121,11583-11584; lithium tert-butoxide aggregates as described in Macromolecules 1995,28,3937-3939and Polymer 1999,40,5455-5458; aluminum and yttrium-based catalyst complexes as described in JACS2002,124,1316-1326; binuclear indium catalysts as described in Macromolecules 2016,49,909-919, etc. The catalyst is used in a catalytically effective amount which depends somewhat on the particular catalyst but generally ranges from 1 mole of catalyst per 3,000 moles to 50,000 moles of monomer.

[0042] The resulting crystallizable polylactide contains metal catalyst residues, which are preferably deactivated by contacting the crystallizable polylactide with a deactivating agent.

[0043] The residence time under polymerization conditions is selected to produce a polymer of the desired molecular weight and / or the desired monomer conversion.

[0044] Other methods for making crystallizable polylactide include the polycondensation of lactic acid, and solid-state polymerization methods starting from oligomeric polylactic acid.

[0045] The crystallizable polylactide may contain residual lactide. If present, lactide may constitute at most 1%, at most 0.5%, at most 0.3% or at most 0.2% by weight of the polylactide (i).

[0046] The non-crystallizable polylactide (ii) has a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography against a polystyrene standard, and at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20. In some embodiments, the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of 20:80 to 40:60 or 80:20 to 60:40. The non-crystallizable polylactide can be prepared in the same general manner as described for the crystallizable polylactide, except that the lactide is selected to produce the above ratio of L-lactide units to D-lactide units. The non-crystallizable polylactide may be, for example, (a) a copolymer of L-lactide and one or more of D-lactide or meso-lactide; (b) a copolymer of D-lactide and one or more of L-lactide or meso-lactide; (c) a polymer of racemic lactide; (d) a copolymer of racemic lactide and meso-lactide, or (e) a homopolymer of meso-lactide.

[0047] In a preferred embodiment, the non-crystallizable polylactide is poly(meso-lactide). For the purposes of the present invention, poly(meso-lactide) (PMLA) is a homopolymer of meso-lactide or a copolymer of at least 80% meso-lactide and up to 20% of another lactide, preferably a copolymer of at least 88% meso-lactide and up to 12% of another lactide, or a copolymer of at least 90% meso-lactide and up to 10% of another lactide. If it is a copolymer, the copolymer may be a random copolymer and / or a block copolymer. The other lactide may be any other lactide, including L-lactide, D-lactide, or a mixture of any two or more thereof.

[0048] Among these different forms of lactide, meso-lactide is unique in that when meso-lactide is homopolymerized, the number of consecutive L-lactic and D-lactic units produced in the polymer is a minimum of one and a maximum of two. Polymerization of a mixture of L- and D-lactide will introduce segments of an even number of lactic units into the polymer, with the average block length of these segments determined by the ratio of the monomers present in the starting materials. During polymerization, when a meso-lactide molecule is added to the end of a growing polymer chain, it introduces one L-lactic unit and one D-lactic unit at the end of the chain. If meso-lactide is polymerized in a "head-to-tail" manner (i.e., D-lactic units are added to the terminal L-lactic units in the polymer chain, or vice versa), the resulting stereoregular polymer has the following form:

[0049] D-(LDLD) n ,

[0050] where D represents a D-lactic unit and L represents an L-lactic unit. PMLA with this configuration is sometimes referred to as "syndiotactic." In this configuration, the number of consecutive D-lactic and L-lactic units is always 1. In contrast, if meso-lactide is polymerized in a "head-to-head" fashion (i.e., if a D-lactic unit is added to a terminal D-lactic unit), a polymer having the following form is produced instead:

[0051] D-(DLLD) n .

[0052] PMLA with this structure is sometimes called "heterotactic" or "syndiotactic." In this case, the number of consecutive D-lactic and L-lactic units is always 2. When meso-lactide is randomly polymerized, the number of consecutive D-lactic and L-lactic units is sometimes 1, sometimes 2, and on average is between 1 and 2.

[0053] PMLA may be heterotactic, or partially syndiotactic and partially heterotactic. The choice of catalyst and polymerization temperature both affect the stereochemistry of PMLA. Generally, it has been found that selecting a higher polymerization temperature, particularly 120°C or higher, and especially 150°C or higher, results in a decrease in the stereospecificity of PMLA, resulting in an average block length greater than 1 and less than 2. Similarly, tin-based catalysts also tend to favor lower stereospecificity. In some embodiments, PMLA is polymerized using a tin catalyst at a temperature of at least 120°C, preferably at least 150°C and up to 225°C, more preferably up to 190°C.

[0054] The average length of the blocks of L-lactic acid units and D-lactic acid units in PMLA can be, for example, equal to at least 1.1, at least 1.2, at least 1.25, or at least 1.3, and for example at most 2, at most 1.75, at most 1.5, or at most 1.4. The average block length can be determined by proton NMR using the method described by Coates et al. in J. American Chemical Society 2002, 124, 1316. m The method and the following relationship are used to determine:

[0055] Average block length = 1 + (P m / (1+(1-P m )))

[0056] At least 90% by weight or at least 95% by weight of the non-crystallizable polylactide consists of lactic acid units.

[0057] The number average molecular weight of the non-crystallizable polylactide (ii) can be, for example, in the range of 5,000 to 250,000 g / mol as measured by GPC relative to polystyrene standards. The number average molecular weight is preferably about 30,000 to 130,000 g / mol.

[0058] In some embodiments, the non-crystallizable polylactide (ii) is characterized by a relative viscosity of 1.1 to 6, 1.25 to 5, or 1.5 to 3.5 as measured at 30°C using a 1% wt / vol solution of the polylactide resin in chloroform in a capillary viscometer relative to a chloroform standard.

[0059] In some embodiments, the non-crystallizable polylactide has a glass transition temperature of 38°C to 50°C.

[0060] Other characteristics of the non-crystallizable polylactide (ii) and the manner of its production are as described above with respect to the crystallizable polylactide (i).

[0061] The polylactide resin composition comprises a mixture of a crystallizable polylactide (i) and a non-crystallizable polylactide (ii). The polylactide resin is melt- or solution-blended, rather than being a physical mixture of individual particles comprising the polylactide. The crystallizable polylactide (i) may comprise 40 to 95% by weight of the total weight of all polylactides in the polylactide resin composition. In specific embodiments, the crystallizable polylactide comprises at least 50%, at least 60%, or at least 65%, and at most 90%, at most 85%, or at most 80% of the total weight of all polylactides in the polylactide resin composition.

[0062] When used in the method for preparing an oriented film according to the present invention, the non-crystallizable polylactide (ii) may constitute 5 to 60% by weight of the total weight of all polylactides in the polylactide resin composition. In some embodiments, the non-crystallizable polylactide (ii) may constitute at least 10%, at least 15%, at least 20%, at least 25%, and up to 45%, up to 40%, or up to 35% of all polylactides in the polylactide resin composition.

[0063] Other polylactides other than the crystallizable polylactide (i) and the non-crystallizable polylactide (ii) may be present, but if present, such other polylactides preferably constitute no more than 10%, no more than 5%, or no more than 2% of the total weight of the constituent polylactides, and may be absent.

[0064] The polylactide resin composition may contain other materials that are useful for the particular end-use application that the polylactide resin composition is to be used in. These may include, for example, polymers other than polylactide, ie, non-polylactide polymers.

[0065] If present, the non-polylactide polymer can constitute, for example, 0.1% to 50%, 1% to 25%, or 1% to 10% of the combined weight of the non-polylactide polymer and polylactide.

[0066] Other optional materials that may be present in the polylactide resin composition include crystallization nucleating agents, such as finely divided solids; colorants; impact modifiers; internal and / or external lubricants, anti-blocking agents and other extrusion processing aids; additives for controlling the hydrolysis and / or biodegradation properties of PLA, and the like.

[0067] The polylactide resin composition can be formed by forming a solution of both polylactide (i) and polylactide (ii) in a suitable solvent and then removing the solvent. If desired, separate solutions of polylactide (i) and (ii) can be formed and combined to form the polylactide resin composition. Alternatively, polylactide (i) and polylactide (ii) can be dissolved together in a single solvent to form a solution, and the solvent can then be removed from the solution.

[0068] The preferred method for preparing the polylactide resin composition is by melt blending. The crystallizable and non-crystallizable polylactides are conveniently heated to a temperature higher than the crystalline melt temperature of the crystallizable polylactide and mixed at this temperature, preferably under shear, to form a blend. The polylactide can be heated separately, but it is generally preferred to form a mixture of polylactide particles (pellets, powders) and melt them together. The preferred apparatus is a single-screw or twin-screw extruder. The granular polylactide can be fed into an extruder alone or as a mixture, in which the granular polylactide is melted and mixed by operating the screws to form the polylactide resin composition. In a particularly preferred method, the melt blending step is combined with all or part of a subsequent stretching process to form a biaxially oriented film.

[0069] The polylactide resin composition of the present invention has been found to have particular application in the preparation of oriented films. In one method for preparing such films, the polylactide resin composition is extruded to form a sheet. The sheet may have a thickness of, for example, at least 250 μm, at least 500 μm, or at least 750 μm and at most 2000 μm, at most 1500 μm, at most 1250 μm, or at most 1000 μm. The sheet is formed by performing a melt blending step in an extruder and then extruding the resulting blended polylactide through an extrusion die attached to the same extruder. The sheet extrusion step is conveniently, but not necessarily, combined with the melt blending step to form the polylactide resin composition to produce the sheet. However, it is within the scope of the present invention to melt blend the crystallizable polylactide and the non-crystallizable polylactide and to form the sheet in different apparatuses and / or at different times.

[0070] The sheet is formed by heating a polylactide resin composition to above the crystalline melting temperature of the crystallizable polylactide, preferably to a temperature between 190°C and 225°C, to form a melt, and then passing the melt through an annular or slot die to produce the sheet. The direction of movement of the polylactide resin composition through the die is referred to as the "machine" direction of the process and the resulting sheet. The sheet is then cooled to below the glass transition temperature of the crystallizable polylactide. Unless the sheet is to be stretched immediately, it is generally preferred to "quench" the sheet by rapidly cooling it to below the glass transition temperature of the crystallizable polylactide to minimize crystallization.

[0071] The sheet is then stretched in at least one direction to produce an oriented film. With uniaxial orientation, stretching occurs in only one direction, typically the machine direction. Biaxially oriented films are stretched in two orthogonal directions, typically the machine direction and the transverse direction (i.e., the direction in the plane of the sheet, perpendicular to the machine direction). When biaxially oriented, stretching can occur simultaneously or sequentially in both directions. When done sequentially, it is often beneficial to stretch in the machine direction first, followed by the transverse direction.

[0072] Stretching can be performed, for example, by passing the sheet through two successive sets of rollers, with the second set of rollers operating at a faster rate than the first set, thereby stretching and uniaxially orienting the sheet. Stretching can also be performed using, for example, a tenter frame or other device with clamps attached to opposing sides of the sheet. The clamps are operated to pull the opposing sides apart, thereby stretching the sheet.

[0073] By carrying out the stretching step immediately after sheet extrusion, stretching can be integrated with the sheet extrusion step.The temperature of the newly extruded sheet is adjusted to the temperature as described below, then uniaxial (preferably along the machine direction) or biaxial stretching (usually first stretched along the machine direction, then stretched in the transverse direction). After the stretching step is completed, the oriented film is cooled to below the glass transition temperature of crystallizable polylactide. In this method, two groups of continuous rollers as mentioned above can be used to carry out machine direction stretching, to produce uniaxially oriented films. In this method, the first group of rollers may include a chill roller, or a chill roller may be arranged in front, and the sheet is cooled to a stretching temperature as shown below by this chill roller. Subsequent transverse stretching is preferably carried out continuously by attaching a fixture to a side of the uniaxially stretched film and operating the fixture to pull the opposite side apart in the transverse direction. After the first stretching step, a cooling step can be carried out, then heated to the temperature of carrying out the second stretching step as required.

[0074] Alternatively, the sheet can be stretched in both the machine and cross directions simultaneously, for example by attaching clips to all four sides of the sheet and pulling the opposing sides apart, or by a combination of tenter stretching in the cross direction and a roller system stretching in the machine direction.

[0075] In other embodiments, the sheet extrusion and stretching (orientation) steps are not integrated but performed in separate manufacturing steps. In such methods, the extruded sheet is conveniently prepared as described above and, after extrusion, is cooled to below the glass transition temperature of the crystallizable polylactide, preferably rapidly to avoid excessive crystallization of the crystallizable polylactide phase, and stretched in subsequent operations. Apparatus as described above is useful.

[0076] Suitable commercially available equipment for biaxially stretching flat sheets is available from, for example, Parkinson Technologies, Inc. (under the Marshall and Williams Plastics brand), Biax Fiberfilm Corporation ( Stretching equipment), Brueckner USA, Andritz Bias SAS, Japan Steel Works, Ltd., etc.

[0077] The stretching step is carried out at a temperature of 50° C. to 120° C. The preferred lower temperature limit is at least 55° C., at least 60° C. or at least 70° C. The preferred upper temperature limit is at most 100° C.

[0078] In a sequential stretching process in which machine direction stretching is first performed and then transverse direction stretching is performed, the machine direction stretching is preferably performed at a temperature of 50°C to 120°C, preferably 55°C to 100°C, and the subsequent transverse direction stretching is preferably performed at a temperature of 70°C to 120°C, most preferably 70°C to 100°C.

[0079] Simultaneous biaxial stretching is preferably carried out at a temperature of 70°C to 120°C, most preferably 70°C to 100°C.

[0080] Given sufficient time, the crystallizable polylactide phase of the sheet will crystallize when the stretching temperature is reached. If it crystallizes too much, it becomes more difficult to stretch. It is preferred that all stretching steps be performed on a sheet that has been at the stretching temperature for a cumulative time of no more than 2 minutes, preferably no more than 1 minute or no more than 30 seconds, to avoid excessive crystallization of the polylactide (i).

[0081] The stretching rate can be, for example, 10% to 500% of the pre-stretched size (in the stretching direction) of the initial sheet per second, i.e., the sheet can be stretched in the stretching direction by a distance equal to 10% to 500% of its original size per second. A preferred stretching rate is 25% to 200% per second or 25% to 100% per second.

[0082] When stretching a flat sheet, the stretch ratio in each of the machine and transverse directions is typically 3 to 10. Preferred stretch ratios in the machine direction are 3 to 6 or 3 to 5, and preferred stretch ratios in the transverse direction are 3 to 10, 4 to 10, 5 to 9, or 5.5 to 9. Slightly lower stretch ratios are sometimes seen in the machine direction. The area of ​​a uniaxially oriented film can be 3 to 10 times the area of ​​the original sheet, and the thickness of a uniaxially oriented film can be, for example, one-third to one-tenth the thickness of the original sheet. The area of ​​a biaxially oriented film can be, for example, 9 to 100 times the area of ​​the original sheet, preferably 9 to 64 times, 12 to 50 times, or 15 to 36 times. The thickness of a biaxially oriented film can be, for example, one-ninth to one-hundredth the thickness of the original sheet. In the case of uniaxial or biaxial orientation, the oriented film thickness can be, for example, at least 4 μm, at least 8 μm, or at least 12 μm, and at most 200 μm, at most 100 μm, or at most 50 μm.

[0083] The stretch ratio achievable by the method of the present invention depends at least in part on the proportion of non-crystallizable polylactide in the polylactide resin composition. Increasing the proportion of non-crystallizable polylactide generally allows for greater stretch ratios to be achieved.

[0084] Increasing the sheet temperature during stretching also tends to achieve larger stretch ratios.

[0085] Alternatively, biaxially stretched films can be produced using the so-called "double-bubble" process. In this process, a polylactide resin composition is extruded to form a tube. The tube is then quenched and collapsed by cooling it to a temperature near or below the glass transition temperature of the crystallizable polylactide. The collapsed tube is then heated to a temperature between 50°C and 120°C, preferably between 70°C and 120°C, and re-expanded with air or another gas to stretch the tube in the transverse direction while simultaneously stretching it in the machine direction. The double-bubble biaxial film process is described, for example, in WO 2001 / 070483.

[0086] After the stretching step is complete, the resulting biaxially oriented film can be thermally annealed at a temperature of, for example, 70°C to 150°C, preferably 120°C to 140°C or 120°C to 135°C. Annealing at such temperatures can be carried out for a period of, for example, 5 seconds to 5 minutes, especially 5 to 30 seconds. Annealing should be carried out under tension. Annealing in this manner reduces shrinkage of the film upon exposure to high temperatures. DETAILED DESCRIPTION

[0087] The following examples illustrate the present invention but are not intended to limit the present invention in any way. Unless otherwise stated, all parts and percentages are by weight.

[0088] Non-crystallizable PLAA is poly(meso-lactide). It is a linear copolymer made by polymerizing a mixture of approximately 90% meso-lactide and 10% L-lactide at 160°C to 180°C in the presence of a tin catalyst. Lactic acid units constitute over 98% of the total weight of non-crystallizable PLAA. 45% of the lactic acid units are D-lactic acid units, and 55% are L-lactic acid units. Non-crystallizable PLAA has an average block length of L-lactic acid units to D-lactic acid units between 1.1 and 1.75. Its relative viscosity is 2.7.

[0089] Non-crystallizable PLAB is a linear copolymer made by polymerizing a mixture of L-lactide, meso-lactide, and D-lactide. Lactic acid units constitute over 98% of the total weight of non-crystallizable PLAB. 80% of the lactic acid units are L-lactic acid units, and 20% are D-lactic acid units.

[0090] Crystallizable PLAA was purchased from NatureWorks LLC, Plymouth, Minnesota US. 4032D resin is commercially available. Lactic acid units constitute over 98% of the total weight of the crystallizable PLAA. Approximately 1.4% of the lactic acid units are D-lactic acid units, and approximately 98.6% are L-lactic acid units. The relative viscosity of the crystallizable PLAA is 4.0.

[0091] Crystallizable PLA B was purchased from NatureWorks LLC. It is commercially available as 4043D resin. Lactic acid units constitute over 98% of the total weight of crystallizable PLA B. 4.25% of the lactic acid units are D-lactic acid units, and 95.75% are L-lactic acid units. The relative viscosity of crystallizable PLA B is 4.0.

[0092] Crystallizable PLA C was purchased from NatureWorks LLC. It is commercially available as 2500HP resin. Lactic acid units constitute more than 98% of the total weight of the crystallizable PLA C. 0.5% of the lactic acid units are D-lactic acid units, and 99.5% are L-lactic acid units. The relative viscosity of the crystallizable PLA C is 4.0.

[0093] Examples 1-8 and Comparative Samples AB

[0094] Cast sheets with a thickness of 650 to 800 μm were prepared from crystallizable PLA A, crystallizable PLA B, and mixtures of crystallizable PLA A or crystallizable PLA B with non-crystallizable PLA A, as shown in Table 1. Pellets of PLA material were melted in a twin-screw extruder, where they were mixed and extruded, then cast into sheets and quenched.

[0095] Table 1

[0096] name Crystallizable PLA type / wt.-% Non-crystallized PLA A, wt.-% A* A / 100％ 0 1 A / 90％ 10％ 2 A / 80％ 20％ 3 A / 60％ 40％ 4 A / 40％ 60％ B* B / 100％ 0％ 5 B / 90％ 10％ 6 B / 80％ 20％ 7 B / 60％ 40％ 8 B / 40％ 60％

[0097] *Not an embodiment of the present invention.

[0098] The sample of Example 5 was examined by atomic force microscopy in tapping mode at 25°C and 95% RH using a Keysight 5500 instrument equipped with high-speed force curve mapping. Prior to AFM analysis, the sample was microtomed at -120°C to produce a smooth, flat scanning area. Crystallizable PLA B and non-crystallizable PLA A were imaged as separate phases. As shown in Figure 1, crystallizable PLA B formed a continuous phase, and non-crystallizable PLA A formed discrete domains with a size of approximately 5-10 nm dispersed in the continuous phase.

[0099] A 50 / 50 weight mixture of crystallizable PLA B and non-crystallizable PLA A was prepared in the manner described above and then examined by atomic force microscopy as just described. Images of crystallizable PLA B and non-crystallizable PLA A showed a co-continuous phase with domain sizes of approximately several μm, as shown in Figure 2.

[0100] The sheets shown in Table 2 below were sequentially stretched on a Brueckner Karo 5.0 biaxial stretching unit at the various temperatures shown in Table 2, first in the machine direction at a draw ratio of 3.5 and then in the transverse direction until rupture. The transverse draw ratios at rupture are shown in Table 2.

[0101] Table 2

[0102]

[0103] *Not an example of the present invention. a Sample had visible surface defects before stretching.

[0104] The sheets shown in Tables 3 to 11 were then stretched sequentially on a Brueckner Karo 5.0 biaxial stretching unit at different temperatures and different stretch ratios as shown in Tables 3, 6, and 9, i.e., first in the machine direction and then in the transverse direction. In each case, the preheating time was 30 seconds. Immediately after stretching, the stretched samples were annealed at 120° C. under tension for 30 seconds. The total haze % of the stretched sheets was evaluated according to ASTM D1003-21, and the shrinkage was evaluated according to ASTM D2732-14. For some samples, the internal haze was evaluated by immersing the samples in clear corn oil in glass test tubes and then re-measuring the haze according to ASTM D1003-21. The haze of the blank (oil and test tube) was subtracted from the measured sample to determine the internal haze of the sample. The difference between the total haze (original) and the internal haze is attributed to the surface haze. Mechanical properties were measured according to ASTM D882. The results of this test are shown in Table 4, Table 5, Table 7, Table 8, Table 10 and Table 11.

[0105] Table 3 - Stretch ratio, 75°C stretch

[0106]

[0107]

[0108] *Not an example of the present invention. a Sample had visible surface defects before stretching. 1 The product of the machine and transverse direction stretch ratios represents the increase in surface area relative to the unstretched sheet.

[0109] Table 4 - Properties of biaxial films stretched at 75°C

[0110]

[0111] *Not an embodiment of the present invention. 1 The stretched sample has many flow lines.

[0112] Table 5 - Mechanical properties of biaxial films stretched at 75°C

[0113]

[0114] *Not an embodiment of the present invention.

[0115] Table 6 - Stretch ratio, 80°C stretch

[0116]

[0117] *Not an example of the present invention. a Sample had visible surface defects before stretching. 1The product of the machine and transverse direction stretch ratios represents the increase in surface area relative to the unstretched sheet.

[0118] Table 7 - Properties of biaxial films stretched at 80°C

[0119]

[0120] *Not an embodiment of the present invention.

[0121] Table 8 - Mechanical properties of biaxial films stretched at 80°C

[0122]

[0123] *Not an embodiment of the present invention.

[0124] Table 9 - Stretch ratio, 85°C stretch

[0125]

[0126] *Not an example of the present invention. a Sample had visible surface defects before stretching. 1 The product of the machine and transverse direction stretch ratios represents the increase in surface area relative to the unstretched sheet.

[0127] Table 10 - Properties of biaxial films stretched at 85°C

[0128]

[0129] *Not an embodiment of the present invention.

[0130] Table 11 - Mechanical properties of biaxial films stretched at 85°C

[0131]

[0132]

[0133] *Not an embodiment of the present invention.

[0134] As shown in the data in the above table, sheets containing 10% to 60% non-crystallizable polylactide can be stretched significantly more in the transverse direction (in these examples, machine direction stretching was held constant) than crystallizable polylactide sheets alone, resulting in significantly higher overall drawdown ratios. The exceptions are the 90 / 10 blend of crystallizable PLA A10 and non-crystallizable PLA, and the 80 / 20 blend of crystallizable PLA B and non-crystallizable PLA, which are due to defects in the sheets before stretching. Increasing the proportion of non-crystallizable PLA generally allows for more transverse stretching before breaking.

[0135] Mechanical properties and appearance are generally applicable to most embodiments of the present invention. However, a 40 / 60 blend of crystallizable PLA and non-crystallizable PLA tends to exhibit a significant increase in haze (especially surface haze) and a substantial loss in elongation at break. These effects are more pronounced when the crystallizable PLA is very pure from an enantiomerical perspective (i.e., crystallizable PLA A vs. crystallizable PLA B), and therefore crystallizes more quickly under stretching conditions. While not limited to any theory, the observed increase in haze and decrease in elongation in the 40 / 60 sample may be attributed to changes in the microphase structure of the polylactide resin composition due to the increased proportion of non-crystallizable PLA.

[0136] Polylactide resin composition Examples 1-8 were simultaneously stretched on a Brueckner Karo 5.0 biaxial stretching unit at various temperatures as shown in Table 12. The stretch ratios were as shown in Table 12. Under these stretching conditions, the highest stretch ratios could be achieved without tearing the film.

[0137] Table 12 - Simultaneous Biaxial Stretching Ratios

[0138]

[0139]

[0140] Another biaxially stretched film was prepared using the same stretching sequence as described above using Example 2. The stretching temperature and stretch ratio are shown in Table 13.

[0141] Table 13 - Biaxially stretched films using Example 2

[0142]

[0143] 1 The product of the machine and transverse direction stretch ratios represents the increase in surface area relative to the unstretched sheet.

[0144] Examples 9-10 and Comparative Sample C

[0145] Cast sheets with thicknesses ranging from 650 μm to 800 μm were prepared from crystallizable PLA C, and mixtures of crystallizable PLA C and non-crystallizable PLA A, as shown in Table 14. Pellets of PLA material were melted in a twin-screw extruder, blended and extruded in the twin-screw extruder, and then cast into sheets and quenched.

[0146] Table 14

[0147] name Wt.-% crystallizable PLA C Wt.-% Non-crystallizable PLA A C* 100％ 0 9 80％ 20％ 10 60％ 40％

[0148] *Not an embodiment of the present invention.

[0149] The sheets were then sequentially stretched at 85°C in the manner described in the previous examples to produce biaxially oriented films. Comparative Sample C could not be stretched to a draw ratio greater than 2.0 in the transverse direction when the machine direction draw ratio was greater than 2.0. Therefore, Comparative Sample C was stretched only to a draw ratio of 2.0 in the machine direction before attempting transverse stretching. Examples 9 and 10 were stretched to a draw ratio of 3.5 in the machine direction before being stretched in the transverse direction at draw ratios of 6.0 (Ex. 9) and 7.0 (Ex. 10). Film properties were measured as described above, and the results are shown in Table 15. Crystallinity was measured by differential scanning calorimetry.

[0150] Table 15-85℃ stretched biaxial film properties

[0151]

[0152] *Not an example of the present invention. a Samples stretched more than 2X in the machine direction should not be stretched more than 2X in the transverse direction. b Crystallinity divided by the proportion of crystalline PLA C in the sample.

[0153] Examples 9 and 10 demonstrate the beneficial effects of the present invention, even when the crystallizable PLA resin is very enantiomerically pure and crystallizes very quickly when subjected to temperatures above its glass transition temperature (approximately 65°C). Crystallizable PLA C by itself is difficult to stretch and can only be stretched to low draw ratios in the machine direction. Adding 20% ​​to 40% of non-crystallizable PLA A allows the sheet to be stretched to high total draw ratios and produces films with excellent properties.

[0154] Examples 11-13 and Comparative Sample D

[0155] Biaxially stretched films were produced using separate sequential stretching elements on a continuous pilot coextrusion line consisting of three single screw extruders operating at 4.54 kg / hr, 50 kg / hr, and 4.54 kg / hr, respectively. These extruders fed a 12" (30.5 cm) wide extrusion die. The line was designed to produce a transverse direction stretch ratio of 4 to 10. Stretching in the machine direction was performed by passing the extruded film through a slow stretch roll maintained at 57°C to 58°C, then through a fast stretch roll maintained at 54°C to 56°C, and then through an annealing roll maintained at 43°C to 45°C. The stretch ratios in the machine direction are shown in Table 16. The film was then transferred to a transverse direction stretching zone which included preheating to 65°C to 66°C, stretching at 79°C to 80°C, and annealing at 121°C for approximately 30 seconds. The transverse direction stretch ratios are shown in Table 16. The machine direction stretch ratio for Comparative Sample D was limited to 2.8 to allow the film to be stretched in the transverse direction within the operating limits of the equipment (i.e., at least 4X TD stretch ratio) without breaking. The final film thicknesses are shown in Table 16. Shrinkage and crystallinity were measured as previously described and the results are shown in Table 16.

[0156] The resins used in Examples 11-13 and Comparative Sample D are as follows:

[0157]

[0158] Table 16

[0159]

[0160] *Not an embodiment of the present invention. C The degree of crystallinity is divided by the proportion of crystallizable PLA C in the sample. 1 The product of the machine and transverse direction stretch ratios represents the increase in surface area relative to the unstretched sheet.

[0161] The total stretch ratio for each of Examples 11-13 was more than double that of Comp. D, which had a total stretch ratio of 15.8, as great as that achievable under these conditions using crystallizable PLA A alone. Examples 11 and 13 are notable in that the major blend components processed through Extruder 2 were fed as a pelletized mixture; this indicates that pre-melt blending is not required, as blending can be performed in-line on a continuous extrusion / stretching apparatus, and a single screw extruder can provide adequate mixing.

[0162] Examples 14-17

[0163] Biaxially stretched films were prepared according to the sequential stretching method described in Examples 1-8, except that the annealing conditions were varied as shown in Table 17. The stretch ratios were shown in Table 17.

[0164] Example 14 was made from an 80 / 20 blend of crystallizable PLA A and non-crystallizable PLA A.

[0165] Example 15 was made from a 60 / 40 blend of crystallizable PLA A and non-crystallizable PLA A.

[0166] Example 16 was made from an 80 / 20 blend of crystallizable PLA B and non-crystallizable PLA A.

[0167] Example 17 was made from a 60 / 40 blend of crystallizable PLA B and non-crystallizable PLA A.

[0168] Shrinkage in the machine and transverse directions was measured as described above. The results are shown in Table 17. It should be noted that crystallinity is at most slightly affected by annealing under certain conditions. Crystallinity is almost entirely due to the orientation that occurs during the stretching step.

[0169] Table 17

[0170]

[0171] Example 18

[0172] Cast sheets with a thickness of 650 to 800 μm were prepared from a 60 / 40 mixture of crystallizable PLA A and non-crystallizable PLA B in the general manner described above. The sheets were then sequentially stretched at 80° C. and 85° C. in the manner described in the previous examples to produce biaxially oriented films. The film properties were measured as described above and the results are shown in Table 18.

[0173] Table 18 - Example 18 - Biaxial Film Properties

[0174]

Claims

1. A polylactide resin composition comprising a melt or solution blend of: (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to a polystyrene standard and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight of a non-crystallizable polylactide, based on the weight of all polylactides in the composition, wherein the non-crystallizable polylactide has a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to a polystyrene standard and contains at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:

20. 2 . The polylactide resin composition according to claim 1 , which is phase-separated.

3. The polylactide resin composition according to claim 2, wherein The non-crystallizable polylactide exists as a discontinuous amorphous phase dispersed in a continuous phase of the crystallizable polylactide.

4. The polylactide resin composition according to claim 3, comprising 65 to 90 wt% of crystallizable polylactide, based on the weight of all polylactides in the composition, and 10 to 35 wt% of non-crystallizable polylactide, based on the mass of all polylactides in the composition.

5. The polylactide composition according to any one of claims 1 to 4, comprising 65 to 80 wt% of crystallizable polylactide, based on the weight of all polylactide in the composition, and 15 to 35 wt% of non-crystallizable polylactide, based on the weight of all polylactide in the composition.

6. The polylactide resin composition according to claim 2, wherein The non-crystallizable polylactide and the crystallizable polylactide exist as co-continuous phases, and the non-crystallizable phase is amorphous.

7. The polylactide resin composition according to claim 6, comprising 55 to 64 wt% of crystallizable polylactide, based on the weight of all polylactides in the composition, and 45 to 36 wt% of non-crystallizable polylactide, based on the weight of all polylactides in the composition.

8. The polylactide composition of claim 1 , comprising 55 to 64 weight percent of crystallizable polylactide, based on the weight of all polylactide in the composition, and 45 to 36 weight percent of non-crystallizable polylactide, based on the weight of all polylactide in the composition.

9. The polylactide composition according to any one of the preceding claims, wherein The non-crystallizable polylactide is poly(meso-lactide).

10. The polylactide resin composition according to any one of the preceding claims, in the form of a uniaxially or biaxially oriented film.

11. A method for producing an oriented polylactide film, comprising (a) forming a polylactide resin composition by melt or solution blending; extruding the polylactide blend according to any one of claims 1 to 10 through an extrusion die in a machine direction to produce a polylactide sheet; and stretching the sheet at a temperature of 50° C. to 120° C. to produce the oriented polylactide film.

12. A method for producing an oriented polylactide film, comprising (a) forming a polylactide resin composition by melt or solution blending, the polylactide resin composition comprising (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20; (b) extruding the polylactide resin composition in a machine direction through an extrusion die to produce a polylactide sheet; and (c) stretching the sheet at a temperature of 50° C. to 120° C. to produce the oriented polylactide film.

13. A method for producing a biaxially oriented polylactide sheet, comprising: (a) extruding the polylactide resin composition according to any one of claims 1 to 10 in a machine direction through an extrusion die to produce a polylactide sheet, the polylactide sheet having a machine direction and an orthogonal transverse direction, the machine direction corresponding to the direction of movement of the polylactic acid blend through the extrusion die; as well as (b) stretching the sheet in orthogonal directions sequentially or simultaneously at a temperature of 50° C. to 120° C. to produce the biaxially oriented polylactide film.

14. A method for producing a biaxially oriented polylactide film, comprising: (a) forming a polylactide resin composition by melt or solution blending, the polylactide resin composition comprising (i) 40% to 95% by weight, based on the weight of all polylactides in the composition, of a crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 95% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥93:7 or ≤7:93, and (ii) 60% to 5% by weight, based on the weight of all polylactides in the composition, of a non-crystallizable polylactide having a number average molecular weight of at least 5000 g / mol as measured by gel permeation chromatography relative to polystyrene standards and containing at least 90% by weight of lactic acid units, wherein the lactic acid units are L-lactic acid units and D-lactic acid units in a ratio of ≥20:80 or ≤80:20; (b) extruding the polylactide resin composition through an extrusion die in a machine direction to produce a polylactide sheet, the polylactide sheet having a machine direction and an orthogonal transverse direction, the machine direction corresponding to the direction of movement of the polylactic acid blend through the extrusion die; and (c) stretching the sheet in orthogonal directions sequentially or simultaneously at a temperature of 50° C. to 120° C. to produce the biaxially oriented polylactide film.

15. The method according to claim 14, wherein In step (c), the sheet is stretched in the machine direction and in an orthogonal transverse direction, with a stretch ratio of 3 to 5 in the machine direction and a stretch ratio of 4 to 9 in the transverse direction.

16. The method according to claim 14 or 15, wherein: In step (c), the sheet is first stretched in the machine direction at a temperature of 50°C to 100°C and subsequently stretched in the orthogonal transverse direction at a temperature of 70°C to 120°C.

17. The method according to any one of claims 11 to 16, wherein The sheet is stretched at a stretching rate of 25% to 100% per second.

18. A method for producing a biaxially oriented polylactide film, comprising: (a) extruding the polylactide resin composition according to any one of claims 1 to 10 to form a tubular article; (b) quenching and collapsing the tubular article; (c) heating the collapsed tube to a temperature of 50°C to 120°C and re-expanding the tube to stretch the tube in the transverse direction while simultaneously stretching the tube in the machine direction.

19. The method according to claim 18, wherein In step (c), the stretching ratio in the machine direction is 3 to 8, and the stretching ratio in the transverse direction is 3 to 8.

20. The method according to claim 18 or 19, wherein In step (c), the sheet is stretched in the machine direction and the transverse direction at a stretching rate of 25% to 100% per second.

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