Hyperbranched poly (meso-lactide) resin composition

Abstract

Poly (meso-lactide) is branched by reaction with a mixture of a polyene compound and a radical initiator. Such a branching process produces products with very high polydispersity, high branching number (Bn) and excellent melt strength, as well as especially low amounts of gelling materials. The branched poly (meso-lactide) may be used in many melt processing operations, particularly sheet and film extrusion, extrusion foaming, extrusion coating, and fiber processing. It is characterized by easy processing and allows for broadening the processing window.

Description

Technical Field

[0001] The present invention relates to highly branched poly(meso-lactide) compositions. Background Art

[0002] Polylactide resins are thermoplastics that are melt processed into a variety of end-use products. The adoption of polylactide resins in certain applications has been hampered by the difficulty of melt processing the material. Polylactide resins tend to have a narrow processing window and low melt strength, which makes them difficult to use on an industrial scale in some applications.

[0003] Melt strength can be increased by branching the polylactide resin. Various branching methods have been described before. These methods include, for example, copolymerizing lactide with epoxidized fats or oils (as described in U.S. Patent number 5,359,206) or with bicyclic lactone comonomers (as described in WO 2002 / 100921 A). Multifunctional initiators have been used in lactide polymerization processes, as described in U.S. Patent numbers 5,210,108 and 5,225,521, GB 2277324 and EP 632 081. Epoxy-functional acrylate polymers have been used to branch polylactide resins, as described in WO 2006 / 002372.

[0004] Polylactide resins have been treated with linear peroxides, as described in U.S. Patent Nos. 5,594,095 and 5,798,435. This branching reaction is difficult to control and produces a large amount of crosslinked gels. When polylactide is melt processed, these gels produce various problems. Branching with a combination of triallyl isocyanurate (TAIC) and dicumyl peroxide also results in very high gel fractions, as described by Yang et al. in "Thermal and Mechanical Properties of Chemical Crosslinked Polylactide (PLA)", Polymer Testing 27 (2008) 957-963. In U.S. Patent No. 8,334,348, cyclic peroxides have been described as branching agents for polylactide resins. These methods are very inefficient, and only a weight average molecular weight (M) of 1.5-1.0 is obtained. w ) a small increase.

[0005] WO 2019 / 152264 describes a hyperbranched polylactide resin formed by treating a linear polylactide with a combination of polyene compounds such as TAIC and certain cyclic peroxides. This combination of branching agents overcomes the poor performance of cyclic peroxides themselves, and also produces a hyperbranched product that exhibits less gel than the combination of TAIC and dicumyl peroxide. However, for hyperbranched polymers, the gel content is generally still too high to be used in some films, sheets and fiber applications, which are very sensitive to the presence of gel. Summary of the invention

[0006] In one aspect, the present invention is a method for preparing a branched polylactide composition, the method comprising the steps of:

[0007] I. Forming a molten mixture of:

[0008] i) at least one starting linear poly(meso-lactide), the poly(meso-lactide) being a polymer containing at least 90 wt. % lactide units, wherein from 80% to 100% of the lactide units are polymerized meso-lactide and from 0% to 20% are polymerized L-lactide and / or D-lactide; the at least one starting linear poly(meso-lactide) having a relative viscosity of at least 2.0, an absolute weight average molecular weight (M) of at least 100,000 g / mol, and a molecular weight of at least 100,000 g / mol. w ) and an absolute Z average molecular weight (M) of at least 150,000 g / mol and at most 400,000 g / mol z );and

[0009] ii) 0.025 to 0.5 wt. %, based on the weight of component i), of at least one polyene compound having from 2 to 6 vinyl groups and an equivalent weight per vinyl group of up to 500; and

[0010] iii) 0.001 to 0.2 wt. %, based on the weight of component i), of at least one free radical initiator; and

[0011] II. reacting the molten mixture at a temperature sufficient to decompose component iii) and branch at least a portion of the linear poly(meso-lactide) resin to produce a branched poly(meso-lactide) having an absolute Z-average molecular weight of at least 2,000,000 g / mol and a gel number of less than 25,000, the gel number being as measured at 309.7 cm 2 (48 square inches (in 2 )), measured in a 0.2 mm (8 mil) thick sheet of branched poly(meso-lactide).

[0012] It has been found that the branching reaction is unexpectedly easy; poly(meso-lactide) branches quickly and easily. The branched product exhibits excellent melt strength (as represented by tan delta values ​​measured using the procedure described below), comparable to or even better than highly branched semi-crystalline polylactide grades. "Semi-crystalline grades" means that after heating at 110°C in air for 1 hour, the PLA contains greater than 5 J / g of crystallites, and more preferably at least 15 J / g of crystallites. This melt strength is accompanied by an unexpectedly low viscosity, which is significantly lower than the viscosity of branched semi-crystalline polylactide grades with similar melt strength characteristics. The gelation is dramatically reduced compared to the gelation seen in branched semi-crystalline grades of polylactide exhibiting similar melt strength. The combination of melt strength, viscosity and low gel content makes the branched poly(meso-lactide) of the present invention useful for a wide range of melt processing applications, notably film, sheet and fiber manufacturing operations requiring low gel content. This combination of low melt viscosity and high melt strength allows for a wider processing window.

[0013] Thus, the present invention is also a branched poly(meso-lactide) which is a copolymer of 80% to 100% (by weight) meso-lactide and 0% to 20% L-lactide and / or D-lactide, the branched poly(meso-lactide) having an absolute M of at least 350,000 g / mol. w , a polydispersity of at least 4, a branching number (B n ), an absolute M of at least 2,000,000 g / mol z and a gel number of less than 20,000, the gel number being as at 309.7 cm 2 (48in 2 ), 0.2 mm (8 mil) thick sheets of branched poly(meso-lactide).

[0014] The branched polylactide composition can be used by itself in melt processing operations. However, it is often convenient to dilute the branched polylactide by melt blending it with another polymer, particularly another linear polylactide resin, to form a melt-processed let-down composition. These let-down compositions exhibit the desirable attributes of low melt viscosity and increased melt strength.

[0015] Thus, in yet another aspect, the present invention is a polylactide composition comprising a) a branched poly(meso-lactide) of the present invention and b) at least one linear polylactide.

[0016] Component i) is a linear poly(meso-lactide). For the purposes of the present invention, the term "poly(meso-lactide)" is a homopolymer of meso-lactide or a copolymer of a lactide mixture, the copolymer comprising at least 80% by weight, preferably at least 85% or at least 90% of meso-lactide and, correspondingly, up to 20%, preferably up to 15% or up to 10% of L-lactide and / or D-lactide. The polymerized lactide constitutes at least 90%, preferably at least 95% or at least 98% of the total weight of the linear poly(meso-lactide). Each lactide molecule produces two adjacent lactic acid units in the polymer chain. The lactic acid units contain chiral carbon atoms and therefore exist in two enantiomeric forms, namely the "L" (or "S") enantiomer and the "D" (or "R") enantiomer. The ratio of L-lactic acid repeating units to D-lactic acid repeating units in poly(meso-lactide) can be from 60:40 to 40:60, from 57.5:42.5 to 42.5:57.5, or from 55:45 to 45:55. Linear poly(meso-lactide) can be heterotactic, syndiotactic, or partially heterotactic and partially syndiotactic. The average length of the blocks of L-lactic acid units and D-lactic acid units is generally less than 2.0, and can be less than 1.75 or less than 1.5, as low as 1.0. The distribution of L-lactic acid units and D-lactic acid units can be determined using proton NMR methods. Linear poly(meso-lactide) is an amorphous grade that forms crystallites of less than 5 J / g after heating at 110° C. in air for 1 hour.

[0017] By "linear" is meant that the poly(meso-lactide) contains no branches having 6 or more carbon atoms. Side chains or pendant groups having fewer than 6 carbon atoms (including pendant methyl groups on each lactic acid unit of the poly(meso-lactide)) are not considered "branches" for the purposes of this invention and are not counted in the branching number B of the starting or branched poly(meso-lactide). n .

[0018] The poly(meso-lactide) may contain small amounts, such as up to 10%, preferably up to 5%, and more preferably up to 2% by weight, based on the total weight of the polymer, of initiator compounds and / or residues of repeating units derived from other monomers copolymerizable with lactide. Suitable such initiators include compounds such as water, lactic acid, other monools, glycol ethers, and other various types of polyols (e.g., ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and the like). Examples of copolymerizable monomers include glycolic acid; 2-hydroxybutyric acid and other α-hydroxy acids, which can condense with lactic acid and form cyclic diesters therewith; alkylene oxides (including ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, and the like); cyclic lactones; and cyclic carbonates. The poly(meso-lactide) is most preferably substantially free of such repeating units derived from other monomers.

[0019] Poly(meso-lactide) can be prepared by polymerizing meso-lactide or a mixture of meso-lactide and L-lactide and / or D-lactide as described above in the presence of a polymerization catalyst, as described, for example, in U.S. Pat. Nos. 5,247,059, 5,258,488, and 5,274,073. The preferred polymerization process typically includes a devolatilization step during which the free lactide content of the polymer is reduced, preferably to less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, and especially less than 0.2% by weight. The polymerization catalyst is preferably deactivated or removed from the poly(meso-lactide).

[0020] The poly(meso-lactide) may comprise virgin material and / or one or more recycled post-industrial or post-consumer resins. The starting linear poly(meso-lactide) or mixture of poly(meso-lactide) has a relative viscosity of at least 2.0. The relative viscosity may be at least 2.25, at least 2.5, or at least 2.75, and in some embodiments up to 3.0. The relative viscosity is the ratio of the viscosity of a 1% wt / vol solution of poly(meso-lactide) in chloroform to the viscosity of a chloroform standard, as measured using a capillary viscometer at 30°C.

[0021] The linear poly(meso-lactide) has an absolute weight average molecular weight (M) of at least 100,000 g / mol. w The absolute Mw may be at least 125,000 g / mol or at least 150,000 g / mol, and may be up to, for example, 200,000 g / mol. Linear (meso-lactide) also has an absolute Z average molecular weight (Mw) of at least 150,000 g / mol, preferably at least 200,000 g / mol and up to 400,000 g / mol. z ). Absolute molecular weights were determined by gel permeation chromatography / size exclusion chromatography using triple detection (light scattering, differential viscometer, and refractive index detection).

[0022] The linear poly(meso-lactide) can have hydroxyl end groups, carboxyl end groups, or both hydroxyl and carboxyl end groups.

[0023] The one or more polyene compounds contain from 2 to 6 vinyl groups per molecule. A "vinyl" group for the purposes of the present invention is a -CHR=CHR group, wherein each R is independently hydrogen or a linear, branched or cyclic alkyl group having up to 6 carbon atoms, or a phenyl group. The vinyl group is preferably an allyl group, i.e. part of a larger group of the form -CH2-CHR=CHR, and / or an enone group, i.e. part of a larger group of the form -C(O)-CHR=CHR. R is preferably hydrogen in each case.

[0024] In some embodiments, the one or more polyene compounds each (if more than one) contain from 2 to 4 vinyl groups per molecule, and in particular embodiments contain 2 or 3 vinyl groups per molecule.

[0025] Each polyene compound may have an equivalent weight per vinyl group of up to 500. The equivalent weight may be at least 50, at least 70, or at least 90 and up to 400, up to 300, or up to 250 grams per equivalent.

[0026] Examples of suitable polyene compounds include, for example, various compounds corresponding to esters of acrylic acid and polyols. These compounds include, for example, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexanedimethanol diacrylate, alkoxylated hexanediol diacrylate, propoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, ethoxylated Suitable acrylate compounds include tris(2-hydroxyethyl)isocyanurate triacrylate, propoxylated trimethylolpropane triacrylate, glycerol triacrylate, ethoxylated and / or propoxylated glycerol triacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate or pentaerythritol tetraacrylate, erythritol diacrylate, erythritol triacrylate or erythritol tetraacrylate, acrylated polyester oligomers, bisphenol A diacrylate, acrylated bisphenol A diglycidyl ether, ethoxylated bisphenol A diacrylate, etc. Other suitable acrylate compounds include tris(2-hydroxyethyl)isocyanurate triacrylate and acrylated urethane oligomers.

[0027] Other suitable polyene compounds are compounds having two or more allyl groups. Examples of these compounds include polyallyl ethers of polyols and polyallyl esters of polycarboxylic acids.

[0028] Suitable polyallyl ethers include, for example, 1,4-butanediol diallyl ether, 1,5-pentanediol diallyl ether, 1,6-hexanediol diallyl ether, neopentyl glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, dipropylene glycol diallyl ether, tripropylene glycol diallyl ether, cyclohexanedimethanol diallyl ether, alkoxylated hexanediol diallyl ether, propoxylated neopentyl glycol diallyl ether, trimethylolpropane diallyl ether or trimethylolpropane triallyl ether, ethoxylated trimethylolpropane diallyl ether or ethoxylated trimethylolpropane diallyl ether. ethylated trimethylolpropane triallyl ether, propoxylated trimethylolpropane diallyl ether or propoxylated trimethylolpropane triallyl ether, glycerol diallyl ether or glycerol triallyl ether, ethoxylated and / or propoxylated glycerol diallyl ether or glycerol triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether or pentaerythritol tetraallyl ether, erythritol diallyl ether, erythritol triallyl ether or erythritol tetraallyl ether, acrylated polyester oligomer, bisphenol A diacrylate, acrylated bisphenol A diglycidyl ether, ethoxylated bisphenol A diallyl ether, and the like.

[0029] Examples of suitable polyallyl esters include diallyl maleate, diallyl fumarate, diallyl phthalate, diallyl terephthalate, diallyl succinate, diallyl citrate, triallyl citrate, and the like.

[0030] Other useful polyene compounds include triallyl cyanurate and triallyl isocyanurate (TAIC).

[0031] The free radical initiator is one or more compounds that react thermally and / or decompose under the conditions of step b) of the process to produce free radicals. The free radical initiator may have a half-life of up to 5 minutes, preferably up to 120 seconds at 210°C. The cyclic peroxide may have a half-life of 5 to 120 seconds or 10 to 60 seconds at 210°C.

[0032] Useful free radical initiators include, for example, 1) acyl peroxides such as acetyl peroxide or benzoyl peroxide, 2) alkyl peroxides such as cumyl peroxide, dicumyl peroxide, lauroyl peroxide or t-butyl peroxide, 3) hydroperoxides such as t-butyl hydroperoxide or cumyl hydroperoxide, 4) peresters such as t-butyl perbenzoate, 5) other organic peroxides including acyl alkylsulfonyl peroxides, dialkyl peroxydicarbonates, diperoxyketals or ketone peroxides, 6) cyclic ketones and 1,2,4-trioxepane, as described, for example, in U.S. Pat. No. 8,334,348, 7) azides, 8) various tetrazines, 9) various azo compounds, 10) various persulfate compounds such as potassium persulfate, and 11) cyclic peroxides. Cyclic peroxides are a preferred type.

[0033] Preferred cyclic peroxides are characterized by having at least one cyclic structure in which one or more peroxide (-OO-) bonds form part of the ring. Suitable cyclic peroxides (component iii) are, among others, cyclic ketones and 1,2,4-trioxepane as described, for example, in U.S. Pat. No. 8,334,348.

[0034] Among the useful cyclic ketones are those having any of structures I-III:

[0035]

[0036]

[0037] Where R 1 -R 6 Each of which is independently selected from the group consisting of: hydrogen, C 1-20 Alkyl, C 3-20 Cycloalkyl, C 6-20 Aryl, C 7-20 Aralkyl and C 7-20 Alkaryl groups, any of which may be optionally substituted by one or more groups selected from hydroxyl, alkoxy, linear or branched alkyl, aryloxy, ester, carboxyl, nitrile and amide groups. The cyclic ketone peroxide preferably contains only carbon atoms, hydrogen atoms and oxygen atoms.

[0038] Suitable 1,2,4-trioxepane (1,2,4-cycloheptane) include those having the following structure:

[0039]

[0040] Where R 7 , R 8 and R 9are independently hydrogen or a hydrocarbon group which may be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxyl, nitrile and amide, and provided that R 7 , R 8 and R 9 Any two of the may be taken together to form a divalent moiety which forms a ring structure with the middle atom of the trioxepane ring.

[0041] In some embodiments, R 7 and R 9 Each independently can be C 1-6 Alkyl, of which methyl and ethyl are preferred. In some embodiments, R 8 It can be hydrogen, methyl, ethyl, isopropyl, isobutyl, tert-butyl, pentyl, isopentyl, cyclohexyl, phenyl, CH3C(O)CH2-, C2H5OC(O)CH2-, HOC(CH3)2CH2- or

[0042]

[0043] In other embodiments, R 7 and R 8 Together with the carbon atoms to which they are bonded they form a cyclohexane ring.

[0044] Specific cyclic peroxides include 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane, which is available from Akzo Nobel as 301 available; 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, which is obtained from Akzo Nobel as 311 available; and 3-ethyl-3,5,7,7-tetramethyl-1,2,4-trioxepane, which is available from Akzo Nobel as MEK-TP.

[0045] The branched poly(meso-lactide) composition is prepared by forming a molten mixture of components i), ii), and iii) and reacting the molten mixture at a temperature sufficient to decompose component iii) and branch at least a portion of the linear poly(meso-lactide).

[0046] The molten mixture contains heat-softened linear poly(meso-lactide) and molten (if not liquid at room temperature) polyene compound. The free radical initiator is preferably dissolved in one or more of the other components of the molten mixture (i.e., in one or both of components i) and ii) and / or in a solvent that is also a solvent for the poly(meso-lactide).

[0047] The order in which components i), ii) and iii) are mixed is not particularly critical except that they should be mixed before or at the same time as the cyclic peroxide compound reaches a temperature at which it has a half-life of 5 minutes or less. Thus, for example, all three components i), ii) and iii) can be mixed simultaneously, preferably when component i) is in the solid state. For example, a dry blend of components i), ii) and iii) can be formed and then heated to melt and react the poly(meso-lactide) and, if necessary, the polyene compound.

[0048] On the contrary, before adding component iii), components i) and ii) can be mixed and optionally melted together. Alternatively, with or without first melting the starting poly (meso-lactide), component iii) can be first mixed with all or part of component i), and then combined with component ii) and any remaining amount of component i), and the reaction temperature is reached. For example, component iii) can be absorbed onto solid poly (meso-lactide) particles to form a concentrate (as described in U.S. Patent No. 9,527,967), which is then added to component ii) and more component i) to form a molten mixture. Components ii) and iii) can also be first combined and then the resulting combination is blended with component i).

[0049] The amount of component ii) provided to the molten mixture is 0.025 to 0.5 wt % based on the weight of the starting linear poly(meso-lactide). On the same basis, the preferred lower limit is 0.05 or 0.075 wt %, and also on the same basis, the preferred upper limit is 0.3 or 0.25 wt %.

[0050] The amount of component iii) provided to the molten mixture is 0.001 to 0.2 wt % based on the weight of the starting linear poly(meso-lactide). On the same basis, the preferred lower limit is 0.01 or 0.02 wt %, and also on the same basis, the preferred upper limit is 0.15, 0.1 or 0.075 wt %.

[0051] The molten mixture is reacted at a temperature sufficient to decompose component iii) and branch at least a portion of the linear poly(meso-lactide). Suitable reaction temperatures are at least 150°C, preferably at least 170°C, at least 190°C or at least 200°C. The reaction temperature may be, for example, up to 260°C, but is preferably lower to reduce thermal degradation of the poly(meso-lactide). An upper temperature limit of 235°C or up to 225°C is preferred. The reaction temperature may be a temperature at which the cyclic peroxide has a half-life of 5 to 120 seconds, preferably 10 to 60 seconds.

[0052] The time required for the reaction (i.e. the time period during which the molten mixture is subjected to the reaction temperature) can be, for example, 0.25 to 60 minutes. Typically, the reaction time is at least equal to the half-life of the cyclic peroxide at the reaction temperature, and can be at least 2 times or at least 3 times the half-life at the reaction temperature. The preferred reaction time is 0.25 to 10 minutes and the more preferred reaction time is 15 to 60 seconds.

[0053] A convenient way to carry out the branching reaction is to process the ingredients through a kneader or an extruder. For example, the ingredients can be added together at the main inlet port and / or in different ports and heated together in an extruder to form a molten mixture. The molten mixture is then brought to the reaction temperature and maintained at the reaction temperature for the necessary time and then cooled by passing it through one or more cooling zones and / or removing it from the outlet end of the extruder.

[0054] During the branching reaction, particularly if carried out in a kneader or extruder, a lubricant or other extrusion processing aid may be present. Inhibitors and / or retarders for free radical initiators may be present during the branching reaction. Examples of such inhibitors and / or retarders include quinones, quinone derivatives, sterically hindered phenols such as tert-butylcatechol, butylated hydroxytoluene and 4-methoxyphenol, and nitro and / or nitroso derivatives of aromatic compounds.

[0055] When an extrusion process is used, the extrudate can be cooled, such as by immersing it in cold water or other liquid, and then chopped to form pellets that can be used in subsequent melt processing operations. In an integrated branching / melt processing operation, the extruder can feed directly or indirectly to downstream melt processing equipment, in some cases without solidifying the extruded material.

[0056] The branched poly(meso-lactide) has an absolute M of at least 2,000,000 g / mol. z . M z It may be at least 2,250,000 or at least 2,500,000 g / mol, and in some embodiments up to 5,000,000 g / mol, up to 4,000,000 g / mol, or up to 3,000,000 g / mol. z is calculated as:

[0057]

[0058] Among them, M i is the molecular weight of the polymer chain, and N i is the number of chains of this molecular weight, summed across all chain molecular weights.

[0059] Furthermore, the branched poly(meso-lactide) may have an absolute weight average molecular weight of at least 200%, preferably 250% to 500%, especially 300% to 500% of the starting linear poly(meso-lactide). The absolute weight average molecular weight of the branched poly(meso-lactide) may be, for example, at least 280,000 g / mol, at least 400,000 g / mol, or at least 500,000 g / mol, and may be, for example, up to 1,000,000 g / mol, up to 750,000 g / mol, or up to 650,000 g / mol.

[0060] The branched poly(meso-lactide) may have a polydispersity (absolute M) of at least 2.5. w / Absolute M n ). The polydispersity can be at least 2.7, at least 3.0, at least 3.3, at least 3.5, at least 3.8, or at least 4.0. In some embodiments, the polydispersity is up to 6 or up to 5.

[0061] The intrinsic viscosity that branched poly (meso-lactide) typically has is 0.8 to 1.35 times of the intrinsic viscosity of the starting linear poly (meso-lactide). The intrinsic viscosity can be 0.9 to 1.15 times of the intrinsic viscosity of the starting linear poly (meso-lactide). In terms of absolute value, the intrinsic viscosity of branched poly (meso-lactide) can be, for example, 1.1 to 1.35 dL / g, 1.1 to 1.30 dL / g or 1.1 to 1.20 dL / g. The intrinsic viscosity (η) can be measured by using a size exclusion chromatography (SEC) coupled to a viscometer. SEC is operated using tetrahydrofuran (THF) as a mobile phase, and is calibrated according to known polystyrene standards. The dη / dc value of 0.046 of PLA in THF is used to calculate polymer concentration.

[0062] The branched poly(meso-lactide) can have a branching number (B) of at least 3, at least 3.5, at least 4, at least 5, at least 6, or at least 7. n ), and can be, for example, up to 12, up to 10, or up to 8. The branching number is measured using the method described in the Examples of WO 2019 / 152264.

[0063] The branched poly(meso-lactide) is characterized by a gel number of less than 25,000, preferably less than 20,000, and even more preferably less than 17,000. The gel number is measured on sheets made from pure branched poly(meso-lactide) or from a blend of branched poly(meso-lactide) and a linear PLA resin that has been filtered to remove the gels. In the former case, 0.2 mm (8 mil) sheets are made from pure branched poly(meso-lactide) using a Leistritz three-roll stack sheet line or equivalent. A 20.32 cm (8 in) x (15.24 cm (6 in) (309.7 cm 2 ) of a membrane sample having a gel size of 20 to 1000 μm. The gel number is the total number of gels in the membrane sample in the size range of 20 to 1000 μm as determined by a membrane mass analyzer.

[0064] When measuring the number of gels on a sheet made from a blend of branched poly(meso-lactide) and a linear PLA resin (which has been filtered to remove gels), the branched poly(meso-lactide) and the linear PLA resin are melt blended in a twin screw extruder at a known ratio R, which is defined as the ratio of the branched poly(meso-lactide) to the combined weight of the branched poly(meso-lactide) and the linear PLA. Sheets are produced from the blend as described above, and the gels are measured. A control film is prepared from the same linear PLA resin used to thin the branched meso-lactide, and the number of gels for the film is measured. The number of gels for branched poly(meso-lactide) is determined using the following relationship:

[0065] Gel quantity = (Gel quantity 测试样品 - Gel quantity 对照 ) / R

[0066] In each case the amount of gel was measured on a 0.2 mm (8 mil) thick film (309.7 cm 2 (48in 2 ) The number of gels with a size range of 20 to 1000 μm in the sample.

[0067] Compared with the unbranched starting linear poly (meso-lactide), the branched poly (meso-lactide) exhibits increased melt strength. For the purposes of the present invention, the increased melt strength is represented by a tan δ value (measured as described in the following examples) and / or an increased haul-off force (measured using a capillary rheometer at a haul-off speed of 5 m / min) at a shear rate of 1 / sec, as described in the examples of WO 2019 / 152264. Branched polylactide can, for example, exhibit a tan δ value of up to 3, up to 2.5, or up to 2 at 210°C at a shear rate of 0.8 / sec. Branched poly (meso-lactide) can exhibit a haulage of at least 5, at least 10, at least 15, or at least 20 cN.

[0068] The branched poly(meso-lactide) may exhibit a complex viscosity of at most 5,000 Pa·s at an angular frequency of 0.1 radian / second, at most 3,500 Pa·s at an angular frequency of 1.0 radian / second, at most 2,000 Pa·s at an angular frequency of 10 radian / second, and / or at most 700 Pa·s at an angular frequency of 100 radian / second, the complex viscosity being measured at a temperature of 210° C. according to the method described in the Examples below. An advantage of the present invention is that the complex viscosity is substantially lower than the complex viscosity of a branched poly(L-lactide) resin containing at most 5% D-lactic units and exhibiting similar tan δ values. The lower complex viscosity allows the branched poly(meso-lactide) to be more easily melt processed.

[0069] The branched poly(meso-lactide) can be used directly (i.e., not combined with one or more other resins) in various melt processing operations. These melt processing operations include, for example, extrusion foaming; melt coating; melt fiber spinning; injection molding; blow molding, injection stretch blow molding; sheet extrusion and thermoforming; film coextrusion; blown film manufacturing; etc. These compositions are particularly beneficial in applications where high melt strength and / or high drawability are required. These include melt coating, film and sheet extrusion, extrusion foaming, and deep draw thermoforming.

[0070] Branched poly(meso-lactide) itself in many cases exhibits very high melt strengths, which may exceed the melt strength required for a particular melt processing operation. In addition, very highly branched compositions of the present invention, such as those exhibiting a B of 4 or greater n Those with values ​​of 0.1% to 0.2% may exhibit slightly reduced extensibility. This may limit their ability to be stretched at higher ratios during certain melt processing operations.

[0071] Thus, in some embodiments, the branched poly(meso-lactide) is diluted with one or more additional polymers to form a blend having properties that are particularly beneficial for a particular melt processing operation. The branched polylactide composition can be diluted by blending it, for example, at 0.25 to 199 parts by weight of the additional resin per part by weight of the branched polylactide composition. In some embodiments, the ratio is 1 to 199, 3 to 99, 3 to 49, 3 to 24, 3 to 9, or 4 to 9 parts by weight of the one or more additional resins per part by weight of the branched polylactide composition.

[0072] The additional resin may be, for example, a linear polylactide resin (which may be an amorphous or semi-crystalline grade), another polyester, an acrylate or methacrylate polymer or copolymer, a polyolefin, a polyether, a polyamide or other organic polymer. Particularly preferred additional resins are those having a polydispersity (M) of less than 2.5. w / M n ) and a linear thermoplastic polylactide having a branching number of less than 3.0, preferably less than 2.2. The linear thermoplastic polylactide is preferably a copolymer of at least 75% by weight of L-lactide and up to 25% by weight of D-lactide and / or meso-lactide.

[0073] The branched poly(meso-lactide) is preferably melt blended with the additional resin. The melt blending can be performed as part of a melt processing operation and / or as a separate manufacturing step to produce, for example, flakes or pellets of the melt blended material. If desired, a dry blend of the branched poly(meso-lactide) particles and the additional resin particles can be formed and fed into a melt processing device to produce a melt blend.

[0074] The ability to form very highly branched compositions and dilute them is a significant advantage. This allows smaller volumes of material to be processed under reaction conditions, thereby reducing throughput, and allows for better control of temperature and residence time.

[0075] When melt processed or letdown, the branched poly(meso-lactide) generally does not participate in additional crosslinking or branching reactions (unless additional steps are taken to produce more branching). The amount of branching is set when the poly(meso-lactide) is produced, rather than during subsequent melt processing or letdown. Therefore, it is not necessary for the secondary manufacturer to employ specific process conditions or tight process controls as are required in reactive extrusion processes (where branching occurs during secondary manufacturing). This generally results in a wider processing window, simpler processing, and a more consistent final product.

[0076] Yet another advantage is that the thinning step can be performed under less stringent conditions, particularly at lower shear, and can therefore be performed using a wider variety of equipment such as single screw extruders. The thinning step can be incorporated into the melt processing operation to form the branched polylactide composition into a downstream product. DETAILED DESCRIPTION

[0077] The following examples are provided to illustrate the present invention without limiting its scope. Unless otherwise indicated, all parts and percentages are by weight.

[0078] PMLA1 is a random copolymer of 90% meso-lactide and 10% L-lactide. It has an absolute M of about 84,000 g / mol. n , absolute M of about 175,000 g / mol w , absolute M of about 254,000 g / mol z and 2 (representing a linear polymer) n . Its relative viscosity is 2.88.

[0079] PMLA2 is a random copolymer of 90% meso-lactide and 10% L-lactide. It has an absolute M of about 62,000 g / mol. n , absolute M of about 106,000 g / mol w , absolute M of about 157,000 g / mol z and 2 B n . Its relative viscosity is 2.06.

[0080] crPLLA1 is a random copolymer of about 2.8% meso-lactide and 97.2% L-lactide, which partially crystallizes when introduced into the branching process. It has an absolute M of about 63,000 g / mol. n , absolute M of about 118,000 g / mol w , absolute M of about 178,000 g / mol z and 2 B n . Its relative viscosity is 3.94.

[0081] amPLLA1 is the same copolymer as crPLLA. This copolymer is a semi-crystalline grade that is capable of crystallization, but in this case has not yet crystallized and is therefore almost completely amorphous when introduced into the branching process.

[0082] PLLA2 is a random copolymer of about 1.4% meso-lactide and 98.6% L-lactide, which partially crystallizes when introduced into the branching process. It has an absolute M of about 38,000 g / mol. n , absolute M of about 60,000 g / molw , absolute M of about 87,000 g / mol z and 2 B n . Its relative viscosity is 2.55.

[0083] As described below, PMLA1, PMLA2, crPLLA1, amPLLA1 and PLLA2 were branched by reaction with 0.14 parts of TAIC and 0.1 parts of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxanonane, respectively. A commercial masterbatch in pellet form (Trigonox 301-40PLA from Nouryon) containing 60% polylactide, 24% solvent (Isopar M) and 16% peroxide was used. Separately, a second masterbatch was produced containing 97% linear PLA resin and 3% of a 70 / 30 mixture of TAIC and silica. The masterbatch was diluted in the starting resin using a 30-mm (44.33 L / D), 10-zone co-rotating twin-screw extruder, with the first feed zone set at 100°C, zones 2-5 set at 170°C, and zones 6-10 set at 210°C. The screw speed was 300 rpm; the throughput was 40 pounds (18.18 kg) / hour; and the residence time was 40 seconds. The resulting branched products (named BrPMLA1, BrPMLA2, crBrPLLA1, amBrPLLA1, and BrPLLA2, respectively) had the following characteristics:

[0084]

[0085] *Complex viscosity and tan delta measurements were performed on samples dried overnight at 48 °C under vacuum. Use with ARES G2 Rheometer with 25-mm parallel plate fixture and 2-mm gap for dry samples Taking measurements At 210°C, 0.1 arc The viscosity was measured at a shear rate of 0.5 rad / s (complex viscosity) and 0.8 rad / s (tan δ).

[0086] The gel number of each of BrPMLA1, crBrPLLA, amBrPLLA and BrPLLA2 was determined by melt blending them with a linear PLA base resin in a weight ratio of 20:80. Sheets were produced and the gel number was determined according to the aforementioned method, with a value of R of 0.2 in each case. The base PLA resin in which the branched product was diluted had a gel number of 871. The results are as follows:

[0087]

[0088] *Every 48in 2 (307.23cm 2 ) of an 8 mil thick (0.2 mm) film.

[0089] At similar molecular weights, PMLA has a much lower relative viscosity than PLLA. Equivalently, at equivalent relative viscosities, PMLA has a much higher molecular weight than PLLA.

[0090] PLLA1, whether used in crystalline or amorphous form, is branched to produce a material having a tan delta value (and therefore melt strength) equivalent to that of branched PMLA1. However, the viscosity of branched PLLA1 is about 10% to nearly 60% higher than that of BrPMLA1, and the number of gels is 70% to over 300% higher. It should be noted that at the beginning of the branching process, the crystallinity of PLLA affects both viscosity and the number of gels. PMLA is completely amorphous and cannot crystallize.

[0091] Although PLLA2 has a much higher relative viscosity when compared to PMLA2, it is branched to produce a material with three times higher tan delta (and three times lower melt strength) than BrPMLA2.

Claims

1. A method for preparing a branched polylactide composition, the method comprising the following steps: I. Forming a molten mixture of: i) at least one starting linear poly(meso-lactide), the at least one poly(meso-lactide) being a polymer containing at least 90 wt. % lactide units, wherein from 80% to 100% of the lactide units are polymerized meso-lactide and from 0 to 20% are polymerized L-lactide and / or D-lactide units, the at least one starting linear poly(meso-lactide) having a relative viscosity of at least 2.0, an absolute weight average molecular weight (M) of at least 100,000 g / mol, and a molecular weight of at least 100,000 g / mol. w ) and an absolute Z average molecular weight (M) of at least 150,000 g / mol and at most 400,000 g / mol z );and ii) 0.025 to 0.5 wt. %, based on the weight of component i), of at least one polyene compound having from 2 to 6 vinyl groups and an equivalent weight per vinyl group of up to 500; as well as iii) 0.001 to 0.2 wt. %, based on the weight of component i), of at least one free radical initiator; as well as II. reacting the molten mixture at a temperature sufficient to decompose component iii) and branch at least a portion of the linear poly(meso-lactide) to produce a branched poly(meso-lactide) having an absolute Z-average molecular weight of at least 2,000,000 g / mol and a gel number of less than 25,000, the gel number being as measured at 48 in. 2 (309.7cm 2 ), 8 mil (0.2 mm) thick sheets of the branched poly(meso-lactide).

2. The method of claim 1, wherein: The at least one poly(meso-lactide) has a relative viscosity of at least 2.5, an absolute weight average molecular weight (M) of at least 140,000 g / mol, w ) and an absolute Z average molecular weight (M) of at least 200,000 g / mol and at most 400,000 g / mol z ).

3. The method according to claim 1 or 2, wherein: The polyene compound is one or more of the following: 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexanedimethanol diacrylate, alkoxylated hexanediol diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate esters, glycerol triacrylate, ethoxylated and / or propoxylated glycerol triacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate or pentaerythritol tetraacrylate, erythritol diacrylate, erythritol triacrylate or erythritol tetraacrylate, acrylated polyester oligomers, bisphenol A diacrylate, acrylated bisphenol A diglycidyl ether, ethoxylated bisphenol A diacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, acrylated urethane oligomers, 1,4-butanediol diallyl ether, 1,5-pentanediol diallyl ether, 1,6-hexanediol diallyl ether, neopentyl glycol Diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, dipropylene glycol diallyl ether, tripropylene glycol diallyl ether, cyclohexanedimethanol diallyl ether, alkoxylated hexanediol diallyl ether, neopentyl glycol diallyl ether, propoxylated neopentyl glycol diallyl ether, trimethylolpropane diallyl ether or trimethylolpropane triallyl ether, ethoxylated trimethylolpropane diallyl ether or ethoxylated trimethylolpropane triallyl ether, propoxylated trimethylolpropane diallyl ether or propoxylated trimethylolpropane triallyl ether, glycerol diallyl ether or glycerol triallyl ether ethers, ethoxylated and / or propoxylated glyceryl diallyl ether or glyceryl triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether or pentaerythritol tetraallyl ether, erythritol diallyl ether, erythritol triallyl ether or erythritol tetraallyl ether, acrylated polyester oligomers, bisphenol A diacrylate, acrylated bisphenol A diglycidyl ether, ethoxylated bisphenol A diallyl ether, including diallyl maleate, diallyl fumarate, diallyl phthalate, diallyl terephthalate, diallyl succinate, diallyl citrate or triallyl citrate, triallyl cyanurate and triallyl isocyanurate.

4. The method according to any one of claims 1 to 3, wherein: The free radical initiator includes at least one cyclic peroxide.

5. A method as claimed in any preceding claim, wherein: The amount of component ii) in the molten mixture is 0.075 to 0.25 weight percent, based on the weight of the at least one starting linear poly(meso-lactide), and the amount of component iii) in the molten mixture is 0.02 to 0.075 weight percent, based on the weight of the starting linear poly(meso-lactide).

6. A method as claimed in any preceding claim, wherein: Step II is performed at a temperature of 150° C. to 235° C. for a period of 15 to 60 seconds.

7. A branched poly(meso-lactide) which is a copolymer of 80% to 100% meso-lactide and 0 to 20% L-lactide and / or D-lactide, the branched poly(meso-lactide) having an absolute M of at least 300,000 g / mol w , a polydispersity of at least 3.5, a branching number (B n ), an absolute M of at least 1,500,000 g / mol z and a gel number of less than 20,000, which is as in 48in 2 (309.7cm 2 ), 8 mil (0.2 mm) thick sheets of the branched poly(meso-lactide).

8. The branched poly(meso-lactide) of claim 7 having an absolute M of at least 350,000 g / mol. w , a polydispersity of at least 4, a branching number (B n ), an absolute M of at least 2,000,000 g / mol z and a gel number of less than 20,000, which is as in 48in 2 (309.7cm 2 ), 8 mil (0.2 mm) thick sheets of the branched poly(meso-lactide).

9. The branched poly(meso-lactide) of claim 7 having an absolute M of at least 500,000 g / mol. w , a polydispersity of at least 4, a branching number (B n ), an absolute M of at least 2,500,000 g / mol z and a gel number of less than 20,000, which is as in 48in 2 (309.7cm 2 ), 8 mil (0.2 mm) thick sheets of the branched poly(meso-lactide).

10. A polylactide composition comprising a) the branched poly(meso-lactide) of any one of claims 7 to 9 and b) at least one linear polylactide.

11. The polylactide composition of claim 10, comprising: 5 to 50% by weight of a) based on the combined weight of a) and b) and 50 to 95% by weight of b) based on the combined weight of a) and b).

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