Patent Application
20250171585
This invention relates to highly branched poly(meso-lactide) compositions.
Polylactide resins are thermoplastics that are melt-processed into a variety of end-use products. The adoption of polylactide resins into certain applications has been held back due to difficulties in melt-processing the material. Polylactide resins tend to have narrow processing windows and low melt strengths, which makes them difficult to use at industrial scale in some applications.
Melt strength can be increased by branching the polylactide resin. Various branching methods have been described before. These include, for example, copolymerizing lactide with an epoxidized fat or oil as described in U.S. Pat. No. 5,359,206, or with a bicyclic lactone comonomer, as described in WO 2002/100921A. Polyfunctional initiators have been used in lactide polymerization processes as described in U.S. Pat. Nos. 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.
Polylactide resins have been treated with linear peroxides, as described in U.S. Pat. Nos. 5,594,095 and 5,798,435. This branching reaction is difficult to control and produces a substantial quantity of crosslinked gels. These gels create various problems when the polylactide is melt-processed. Branching with a combination of triallyl isocyanurate (TAIC) and dicumyl peroxide, as described by Yang et al. in “Thermal and Mechanical Properties of Chemical Crosslinked Polylactide (PLA)”, Polymer Testing 27 (2008) 957-963, also leads to very high gel fractions. Cyclic peroxides have been described as branching agents for polylactide resins in U.S. Pat. No. 8,334,348. These are very inefficient with only small increases in weight average molecular weight (Mw) being obtained.
WO 2019/152264 describes hyperbranched polylactide resins formed by treating a linear polylactide with a combination of a polyene compound such as TAIC with certain cyclic peroxides. This combination of branching agents overcomes the poor performance of cyclic peroxides by themselves, and also produces hyperbranched products that exhibit fewer gels than the combination of TAIC and dicumyl peroxide. However, gel contents frequently are still too high for the hyperbranched polymer to be useful in some film, sheet, and fiber applications, which can be quite sensitive to the presence of gels.
The invention is in one aspect a method for making a branched polylactide composition, comprising the steps of
The branching reaction has been found to be unexpectedly facile; the poly(meso-lactide) branches rapidly and easily. The branched product exhibits exceptional melt strength (as indicated by tan δ values as measured using the procedure described hereinbelow), comparable or even better than highly branched semi-crystalline polylactide grades. By a “semi-crystalline grade”, it is meant the PLA contains greater than 5 J/g of crystallites, and more preferably at least 15 J/g of crystallites, after being heated at 110° C. in air for one hour. This melt strength is accompanied by a surprisingly low viscosity, which is significantly lower than that of a branched semi-crystalline polylactide grade that has similar melt strength characteristics. Gelling is sharply reduced compared to that seen in branched semi-crystalline grades of polylactide that exhibit similar melt strengths. The combination of melt strength, viscosity, and low gel content render the branched poly(meso-lactide) of the invention useful in a wide range of melt-processing applications, notably film, sheet, and fiber manufacturing operations in which low gel content is required. This combination of low melt viscosity and high melt strength allows for wider processing windows.
Accordingly, the invention is also a branched poly(meso-lactide), the poly(meso-lactide) being a copolymer of 80% to 100% (by weight) meso-lactide and 0% to 20% of L-lactide and/or D-lactide, the branched poly(meso-lactide) having an absolute Mw of at least 350,000 g/mol, a polydispersity of at least 4, a branching number (Bn) of 5 to 8, an absolute Mz of at least 2,000,000 g/mol, and a gel number of less than 20,000 as measured in a 309.7 cm2 (48 in2), 0.2 mm (8 mil) thick sheet of the branched poly(meso-lactide).
The branched polylactide composition may be used by itself in a melt-processing operation. However, it is often convenient to dilute the branched polylactide by melt-blending it with another polymer, in particular another linear polylactide resin, to form a let-down composition that is melt-processed. The let-down compositions exhibit the desired attributes of low melt viscosity and increased melt strength.
Thus, in yet another aspect, the invention is a polylactide composition comprising a) a branched poly(meso-lactide) of the invention and b) at least one linear polylactide.
Component i) is a linear poly(meso-lactide). For the purposes of this invention, the term a “poly(meso-lactide)” is a homopolymer of meso-lactide or a copolymer of a lactide mixture that includes at least 80 weight-%, preferably at least 85%, or at least 90% meso-lactide and, correspondingly, up to 20%, preferably up to 15%, or up to 10% of L- 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 molecule of lactide produces two adjacent lactic units in the polymer chain. Lactic units contain a chiral carbon atom and therefore exist in two enantiomeric forms, the “L” (or “S”) enantiomer and the “D” (or “R”) enantiomer. The ratio of L-lactic repeating units to D-lactic repeating units in the poly(meso-lactide) may be 60:40 to 40:60, 57.5:42.5 to 42.5:57.5, or 55:45 to 45:55. The linear poly(meso-lactide) may be heterotactic, syndiotactic, or partially heterotactic and partially syndiotactic. The average length of blocks of L-lactic units and D-lactic units is generally less than 2.0 and may be less than 1.75 or less than 1.5, to as low as 1.0. The distribution of L- and D-lactic units can be ascertained using proton NMR methods. The linear poly(meso-lactide) is an amorphous grade, which forms fewer than 5 J/g of crystallites after being heated at 110° C. in air for one hour.
By “linear” it is meant that the poly(meso-lactide) contains no branches that have 6 or more carbon atoms. Side-chains or pendant groups having fewer than 6 carbon atoms (including pendant methyl groups on each lactic unit of the poly(meso-lactide) are not considered as “branches” for purposes of this invention and are not counted toward the branching number Bn of the starting or branched poly(meso-lactide).
The poly(meso-lactide) may contain minor amounts, such as up to 10%, preferably up to 5%, and more preferably up to 2% by weight, based on total polymer weight, of residues of an initiator compound and/or repeating units derived from other monomers that are copolymerizable with lactide. Suitable such initiators include compounds such as water, lactic acid, other monoalcohols, glycol ethers, and other polyhydroxy compounds of various types (such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and the like). Examples of copolymerizable monomers include glycolic acid; 2-hydroxybutyric acid and other α-hydroxyacids which can condense with lactic acid and generate cyclic diesters therewith; alkylene oxides (including ethylene oxide, propylene oxide, butylene oxide, tetramethylene oxide, and the like); cyclic lactones; and cyclic carbonates. The poly(meso-lactide) most preferably is essentially devoid of such repeating units derived from other monomers.
The poly(meso-lactide) can be prepared by polymerizing meso-lactide or a mixture of meso-lactide and L- and/or D-lactide as described above in the presence of a polymerization catalyst as described in, for example, U.S. Pat. Nos. 5,247,059, 5,258,488 and 5,274,073. This 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).
The poly(meso-lactide) may include virgin materials and/or recycled post-industrial or post-consumer resin(s). The starting linear poly(meso-lactide) or mixture of poly(meso-lactide)s 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 is up to 3.0. Relative viscosity is the ratio of the viscosity of a 1% wt/vol solution of the poly(meso-lactide) in chloroform to that of a chloroform standard, as measured using a capillary viscometer at 30° C.
The linear poly(meso-lactide) has an absolute weight average molecular weight (Mw) of at least 100,000 g/mol. 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. The linear (meso-lactide) also has an absolute Z-average molecular weight (Mz) of at least 150,000 g/mol, preferably at least 200,000 g/mol, and at most 400,000 g/mol. Absolute molecular weights are determined by gel permeation chromatography/size exclusion chromatography using triple detection (light scattering, differential viscometer, and refractive index detection).
The linear poly(meso-lactide) may have hydroxyl end groups, carboxyl end groups, or both hydroxyl and carboxyl end groups.
The polyene compound(s) contain(s) 2 to 6 vinyl group per molecule. A “vinyl” group for purposes of this invention is a —CHR═CHR group, where each R is independently hydrogen or linear, branched or cyclic alkyl having up to 6 carbon atoms, or phenyl. The vinyl groups preferably are allylic, i.e., part of a larger group having the form —CH2—CHR═CHR, and/or are enones i.e., part of a larger group having the form —C(O)—CHR═CHR. R is preferably hydrogen in each case.
In some embodiments, the polyene compound(s) each (if more than one) contains 2 to 4 vinyl groups per molecule and in particular embodiments contains 2 or 3 vinyl groups per molecule.
Each polyene compound may have an equivalent weight per vinyl group of up to 500. This 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 gram/equivalent.
Examples of suitable polyene compounds include, for example, various compounds corresponding to esters of acrylic acid and a polyol. These 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, cyclohexane dimethanol diacrylate, alkoxylated hexanediol diacrylate, propoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, glycerine triacrylate, ethyloxylated and/or propoxylated glycerine triacrylate, pentaerythritol di-, tri-, or tetraacrylate, erythritol di-, tri-, or tetraacrylate, acrylated polyester oligomer, bisphenol A diacrylate, acrylated bisphenol A diglycidyl ether, ethyoxylated bisphenol A diacrylate, and the like. Other suitable acrylate compounds include tris(2-hydroxyethyl)isocyanurate triacrylate and acrylated urethane oligomers.
Other suitable polyene compounds are compounds having two or more allylic groups. Examples of these include polyallyl ethers of a polyol and polyallyl esters of a polycarboxylic acid.
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, cyclohexane dimethanol diallyl ether, alkoxylated hexanediol diallyl ether, propoxylated neopentyl glycol diallyl ether, trimethylolpropane di- or triallyl ether, ethoxylated trimethylolpropane di- or triallyl ether, propoxylated trimethylolpropane di- or triallyl ether, glycerine di- or triallyl ether, ethyloxylated and/or propoxylated glycerine di- or triallyl ether, pentaerythritol di-, tri-, or tetraallyl ether, erythritol di-, tri-, or tetraallyl ether, acrylated polyester oligomer, bisphenol A diacrylate, acrylated bisphenol A diglycidylether, ethyoxylated bisphenol A diallyl ether, and the like.
Examples of suitable polyallyl esters include diallyl maleate, diallyl fumarate, diallyl phthalate, diallyl terephthalate, diallyl succinate, di- or triallyl citrate, and the like.
Other useful polyene compounds include triallyl cyanurate and triallyl isocyanurate (TAIC).
The free radical initiator is one or more compounds that thermally react 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 at most 5 minutes, preferably at most 120 seconds, at 210° C. The cyclic peroxide may a half-life of 5 to 120 seconds or 10 to 60 seconds at 210° C.
Useful free radical initiators include, for example, 1) acyl peroxides such as acetyl or benzoyl peroxides, 2) alkyl peroxides such as cumyl, dicumyl, lauroyl, or t-butyl peroxides, 3) hydroperoxides such as t-butyl or cumyl hydroperoxides, 4) peresters such t-butyl perbenzoate, 5) other organic peroxides including acyl alkylsulfonyl peroxides, dialkyl peroxydicarbonates, diperoxyketals, or ketone peroxides, 6) cyclic ketones and 1,2,4-trioxepanes as described, for example, in U.S. Pat. No. 8,334,348, 7) azide compounds, 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.
The preferred cyclic peroxides are characterized as having at least one cyclic structure in which one or more peroxide (—O—O—) linkages form part of a ring. Among the suitable cyclic peroxides (component iii) are cyclic ketones and 1,2,4-trioxepanes as described, for example, in U.S. Pat. No. 8,334,348.
Among the useful cyclic ketones are those having any of the structures I-III:
wherein each of R1-R6 are independently selected from the group consisting of hydrogen, C1-20 alkyl, C3-20 cycloalkyl, C6-20 aryl, C7-20 aralkyl, and C7-20 alkaryl, any of which may optionally be substituted with one or more groups selected from hydroxyl, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido. The cyclic ketone peroxides preferably contain only carbon, hydrogen and oxygen atoms.
Suitable 1,2,4-trioxepanes (1,2,4-cycloheptanes) include those having the structure:
Wherein R7, R8, and R9 are independently hydrogen or hydrocarbyl that may be substituted with one or more groups selected from hydroxyl, alkoxy, linear, or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido and provided that any two of R7, R8, and R9 may together form a divalent moiety that forms a ring structure with the intervening atoms of the trioxepane ring.
In some embodiments, R7 and R9 each independently may be C1-6 alkyl with methyl and ethyl being preferred. R8 in some embodiments may be hydrogen, methyl, ethyl, isopropyl, isobutyl, t-butyl, amyl, iso-amyl, cyclohexyl, phenyl, CH3C(O)CH2—, C2H5OC(O)CH2—, HOC(CH3)2CH2—, or
In other embodiments R7 and R8 together with the carbon atom to which they are bonded form a cyclohexane ring.
Specific cyclic peroxides include 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxononane, which is available as Trigonox® 301 from Akzo Nobel; 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, which is available as Trigonox® 311 from Akzo Nobel; and 3-ethyl-3,5,7,7-tetramethyl-1,2,4-trioxepane, which is available as MEK-TP from Akzo Nobel.
A branched poly(meso-lactide) composition is made 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).
The molten mixture contains heat-softened linear poly(meso-lactide) and melted (if not a liquid at room temperature) polyene compound. The free radical initiator preferably is dissolved in one or more of the other components of the molten mixture (i.e., into one or both of components i) and ii) and/or is dissolved in a solvent that is also a solvent for with the poly(meso-lactide).
The order of mixing components i), ii), and iii) is not especially critical except that they should be mixed before or at the same time the cyclic peroxide compound is brought to a temperature at which it has a half-life of 5 minutes or less. Thus, for example, all three of components i), ii), and iii) can be mixed simultaneously, preferably while component i) is in the solid state. For example, a dry blend of components i), ii), and iii) can be formed, which dry blend is then heated to melt the poly(meso-lactide) and (if necessary) the polyene compound and perform the reaction.
Components i) and ii) instead can be mixed and optionally melted together before adding component iii). Alternatively, component iii) and all or a portion of component i) can be mixed first, with or without first melting the starting poly(meso-lactide), and then combined with component ii) and any remaining amount of component i) and brought to the reaction temperature. For example, component iii) can be absorbed onto solid poly(meso-lactide) particles to form a concentrate (as described in U.S. Pat. No. 9,527,967) which is then added to component ii) and more component i) to form the molten mixture. It is also possible to first combine components ii) and iii) and then to blend the resulting combination with component i).
The amount of component ii) provided to the molten mixture is 0.025 to 0.5 weight percent, based on the weight of the starting linear poly(meso-lactide). A preferred lower amount is 0.05 or 0.075 weight percent on the same basis, and a preferred upper amount is 0.3 or 0.25 weight percent, again on the same basis.
The amount of component iii) provided to the molten mixture is 0.001 to 0.2 weight percent, based on the weight of the starting linear poly(meso-lactide). A preferred lower amount is 0.01 or 0.02 weight percent on the same basis, and a preferred upper amount is 0.15, 0.1, or 0.075 weight percent, again on the same basis.
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). A suitable reaction temperature is at least 150° C., preferably at least 170° C., at least 190° C., or at least 200°. 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 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.
The time required to perform the reaction (i.e., the period of time during which the molten mixture is subjected to the reaction temperature) may be, for example, 0.25 to 60 minutes. In general, the reaction time is at least equal to the half-life of the cyclic peroxide at the reaction temperature and may be at least 2 times or at least 3 times that half-life at the reaction temperature. A preferred reaction time is 0.25 to 10 minutes, and a more preferred reaction time is 15 to 60 seconds.
A convenient way of performing 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 separate ports, and heated together in the extruder to form the molten mixture. The molten mixture is then brought to the reaction temperature, and maintained at the reaction temperature for the requisite time before being cooled by passing it through one or more cooling zones and/or removing it from the outlet end of the extruder.
A lubricant or other extrusion processing aid may be present during the branching reaction, particularly if performed in a kneader or extruder. An inhibitor and/or retarder for the free radical initiator may be present during the branching reaction. Examples of such inhibitors and/or retarders include quinones, quinone derivatives, sterically hindered phenols such as t-butyl catechol, butylated hydroxytoluene, and 4-methoxyphenol, and nitro- and/or nitroso derivatives of aromatic compounds.
When an extrusion process is used, the extrudate may be chilled such as by immersing it in cool water or other liquid and then chopped to form pellets that are useful in a subsequent melt-processing operation. In an integrated branching/melt processing operation, the extruder may directly or indirectly feed downstream melt-processing apparatus, in some cases without solidifying the extruded material.
The branched poly(meso-lactide) has an absolute Mz of at least 2,000,000 g/mol. The Mz may be at least 2,250,000 or at least 2,500,000 g/mol, and in some embodiments is up to 5,000,000 g/mol, up to 4,000,000 g/mol, or up to 3,000,000 g/mol. Mz is calculated as:
where Mi is the molecular weight of a polymer chain and Ni is the number of chains of that molecular weight, the summations being across all chain molecular weights.
The branched poly(meso-lactide) may in addition have an absolute weight average molecular weight at least 200%, preferably 250% to 500%, especially 300% to 500%, of that 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 up to, for example, 1,000,000 g/mol, up to 750,000 g/mol, or up to 650,000 g/mol.
The branched poly(meso-lactide) may have a polydispersity (absolute Mw/absolute Mn) of at least 2.5. The polydispersity may 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.
The branched poly(meso-lactide) typically has an intrinsic viscosity between 0.8 and 1.35 times that of the starting linear poly(meso-lactide). The intrinsic viscosity may be between 0.9 and 1.15 times that of the starting linear poly(meso-lactide). In absolute terms, the intrinsic viscosity of the branched poly(meso-lactide) may 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. Intrinsic viscosity (11) may be measured by using size exclusion chromatography (SEC) coupled to a viscometer. SEC is operated using tetrahydrofuran (THF) as the mobile phase and is calibrated to known polystyrene standards. Polymer concentration is calculated using a dη/dc value of 0.046 for PLA in THF.
The branched poly(meso-lactide) may have a branching number (Bn) of at least 3, at least 3.5, at least 4, at least 5, at least 6, or at least 7 and may be, for example, up to 12, up to 10, or up to 8. Branching number is measured using the method described in the examples of WO 2019/152264.
The branched poly(meso-lactide) is characterized by a gel number of less than 25,000, preferably less than 20,000, even more preferably less than 17,000. Gel number is measured on sheets made from the neat, branched poly(meso-lactide) or from a blend of the branched poly(meso-lactide) and a linear PLA resin that has been filtered to remove gels. In the former case, 0.2 mm (8 mil) sheets are made from the neat, branched poly(meso-lactide) using a Leistritz 3-roll-stack sheet line or equivalent apparatus. Film specimens 20.32 cm (8 inches)×(15.24 cm (6 in) (309.7 cm2) are tested for the size and number distribution of gels (across a gel size of 20 to 1000 μm) using a film quality analyzer (FQA) setup from Schenk Vision (Woodbury, MN). The gel number is total number of gels in the film specimen within the size range of 20 to 1000 μm, as determined by the film quality analyzer.
When gel number is measured on sheets made from a blend of the branched poly(meso-lactide) and a linear PLA resin that has been filtered to remove gels, the branched poly(meso-lactide) and linear PLA resin are melt-blended in a twin screw extruder at a known ratio R, defined as the ratio of branched poly(meso-lactide) to the combined weight of branched poly(meso-lactide) and linear PLA. A sheet is produced from the blend as described before, and the gels measured. A control film is made of the same linear PLA resin used to let down the branched meso-lactide, and the number of gels of that film is measured. The gel number of the branched poly(meso-lactide) is determined using the relationship:
The gel number in each instance is the number of gels of 20 to 1000 m in size in a (309.7 cm2 (48 in2) specimen of an 0.2 mm (8-mil)-thick film.
The branched poly(meso-lactide) exhibits an increased melt strength compared to the unbranched starting linear poly(meso-lactide). Increased melt strength, for purposes of this invention, is indicated by a decreased tan δ value at a shear rate of 1/sec, measured as described in the following examples and/or an increased haul-off force, as determined at a haul-off speed of 5 meters/minute using a capillary rheometer, as described in the examples of WO 2019/152264. The branched polylactide may, for example, exhibit a tan δ value at 210° C. of up to 3, up to 2.5, or up to 2 at a shear rate of 0.8/sec. The branched poly(meso-lactide) may exhibit a haul-off force of at least 5, at least 10, at least 15, or at least 20 cN.
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 1.0 radian/second, at most 2,000 Pa·s at an angular frequency of 10 radians/second, and/or at most 700 Pa·s at an angular frequency of 100 radians/second, measured at a temperature of 210° C. according the method described in the examples below. An advantage of this invention is that complex viscosities are generally significantly lower than those of branched poly(L-lactide) resins that contain at most 5% D-lactic units and exhibit similar tan δ values. The lower complex viscosities allow the branched poly(meso-lactide) to be melt-processed more easily.
The branched poly(meso-lactide) can be used directly (i.e., without being combined with one or more other resins) in a variety of 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 manufacture; and the like. The compositions are particularly beneficial in applications in which high melt strength and/or high drawability are needed. These include melt coating, film and sheet extrusion, extrusion foaming, and deep draw thermoforming.
The branched poly(meso-lactide) by itself in many cases exhibit very high melt strengths, which may be in excess of what is needed for specific melt-processing operations. In addition, very highly branched compositions of the invention, such as those exhibiting Bn values of 4 or greater, may exhibit somewhat reduced extensibility. This can limit their ability to be drawn at higher ratios during certain melt processing operations.
Accordingly, in some embodiments, the branched poly(meso-lactide) is let down with one or more additional polymers to form a blend that has properties which are particularly beneficial for specific melt-processing operations. The branched polylactide composition may be let down by blending it, for example, with 0.25 to 199 parts by weight of additional resin per part by weight of branched polylactide composition. This ratio in some embodiments is 1 to 199, 3 to 99, 3 to 49, 3 to 24, 3 to 9, or 4 to 9 parts by weight of additional resin(s) per part by weight of branched polylactide composition.
The additional resin may be, for example, a linear polylactide resin (which may be an amorphous or a semi-crystalline grade), another polyester, an acrylate or methacrylate polymer or copolymer, a polyolefin, a polyether, a polyamide, or other organic polymer. A particularly preferred additional resin is a linear thermoplastic polylactide having a polydispersity (Mw/Mn) of less than 2.5 and a branching number of less 3.0, preferably less than 2.2. The linear thermoplastic polylactide preferably is a copolymer of at least 75% by weight L-lactide and up to 25% by weight of D- and/or meso-lactide.
The branched poly(meso-lactide) preferably is melt-blended with the additional resin. The melting 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 particles of the branched poly(meso-lactide) and particles of the additional resin can be formed and fed into melt-processing apparatus to produce the melt blend.
The ability to form a very highly branched composition and let it down is a significant advantage. This allows smaller volumes of material to be processed under reaction conditions, thereby reducing production and allows for better control of temperature and residence time.
The branched poly(meso-lactide) generally does not engage in further cross-linking or branching reactions when melt-processed or let down (unless additional measures 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 let-down. Therefore, it is not necessary for secondary fabricators to employ special process conditions or tight process controls as are needed in reactive extrusion processes in which branching takes place during the secondary fabrication. This leads to wider processing windows, easier processing generally, and a more consistent end product.
Still another advantage is that the let-down step can be performed under less stringent conditions, in particular at lower shear, and thus can be performed using a wider variety of types of equipment, such as a single-screw extruder. The dilution step can be incorporated into a melt-processing operation for forming the branched polylactide composition into a downstream product.
The following examples are provided to illustrate the invention, but not to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.
PMLA1 is a random copolymer of 90% meso-lactide and 10% L-lactide. It has an absolute Mn of about 84,000 g/mol, an absolute Mw of about 175,000 g/mol, an absolute Mz of about 254,000 g/mol, and a Bn of 2 (indicative of a linear polymer). Its relative viscosity is 2.88.
PMLA2 is a random copolymer of 90% meso-lactide and 10% L-lactide. It has an absolute Mn of about 62,000 g/mol, an absolute Mw of about 106,000 g/mol, an absolute Mz of about 157,000 g/mol, and a Bn of 2. Its relative viscosity is 2.06.
crPLLA1 is a random copolymer of about 2.8% meso-lactide and 97.2% L-lactide that is partially crystallized when introduced into the branching process. It has an absolute Mn of about 63,000 g/mol, an absolute Mw of about 118,000 g/mol, an absolute Mz of about 178,000 g/mol, and a Bn of 2. Its relative viscosity is 3.94.
amPLLA1 is the same copolymer as crPLLA. This copolymer is a semi-crystalline grade capable of being crystallized, but in this case has not been crystallized and so is almost entirely amorphous when introduced into the branching process.
PLLA2 is a random copolymer of about 1.4% meso-lactide and 98.6% L-lactide that is partially crystallized when introduced into the branching process. It has an absolute Mn of about 38,000 g/mol, an absolute Mw of about 60,000 g/mol, an absolute Mz of about 87,000 g/mol, and a Bn of 2. Its relative viscosity is 2.55.
PMLA1, PMLA2, crPLLA1, amPLLA1, and PLLA2 are separately branched by reaction with 0.14 parts of TAIC and 0.1 part of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxononane as follows. A commercial masterbatch (Trigonox 301-40 PLA from Nouryon) in pellet form is used containing 60% of a polylactide, 24% of a solvent (Isopar M), and 16% of the peroxide. Separately, a second masterbatch is produced containing 97% of a linear PLA resin and 3% of a 70/30 mixture of TAIC and silica. The masterbatches are let down into the starting resin using a 30-mm (44.33 L/D), 10-zone co-rotating twin screw extruder with a first feed zone set at 100° C., zones 2-5 set at 170° C., and zones 6-10 set at 210° C. Screw speed is 300 rpm; throughput is 40 pounds (18.18 kg) per hour; residence time is 40 seconds. The resulting branched products (designated BrPMLA1, BrPMLA2, crBrPLLA1, amBrPLLA1 and BrPLLA2, respectively) have the following characteristics:
The gel number of each of BrPMLA1, crBrPLLA, amBrPLLA, and BrPLLA2 are determined by separately melt-blending them with a linear PLA base resin at a 20:80 weight ratio. Sheets are produced and the number of gels determined according to the method described before, the value of R being 0.2 in each case. The base PLA resin into which the branched products are let down has a gel number of 871. Results are as follows:
PMLA has a much lower relative viscosity than PLLA, at similar molecular weights. Equivalently, PMLA has a much higher molecular weight than PLLA at equivalent relative viscosity.
PLLA1, whether used in the crystalline or amorphous form, is branched to produce a material that has a tan δ value (and therefore melt strength) equivalent to that of the branched PMLA1. However, the viscosity of the branched PLLA1 is about 10 to almost 60% higher than that of BrPMLA1, and the number of gels is 70 to over 300% higher. It is noted that crystallinity of the PLLA at the start of the branching process affects both the viscosity and gel number. PMLA is entirely amorphous and cannot be crystallized.
PLLA2, despite its much higher relative viscosity when compared to PMLA2, branches to produce a material that has a tan S three times higher (and melt strength three times lower) than that of BrPMLA2.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2023/065086 | 3/29/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63325206 | Mar 2022 | US |
