Recycling of bioplastics in polymerization

Abstract

This invention relates to a method for reusing a biodegradable polymer composition comprising a polyester mixture in polymerization. The method comprises the following steps: 1) reacting the polymer composition with water at a temperature above the melting temperature of at least one of the polyesters to obtain a depolymerization product comprising a mixture of monomers and / or oligomers of the polyester; 2) separating portions containing impurities and / or fillers from the depolymerization product; and 3) polymerizing the monomers and / or oligomers in an amount from 1% to 100% by weight relative to the polymerized mixture to obtain a biodegradable polymer composition. A further object of the invention is a polymer obtained by the aforementioned reuse method, a biodegradable polymer composition comprising the polymer, and biodegradable articles obtained from the composition.

Description

[0001] The present invention relates to a method for polymerizing monomers and / or oligomers generated from the depolymerization of bioplastics, particularly biodegradable compositions comprising biopolymers such as polyhydroxyalkyl esters and diacid-diol polyesters.

[0002] The term biopolymer generally refers to biodegradable and / or bio-based polymers. Biodegradable polymers are those that, after reaching the end of their initial use, can be organically degraded and recycled by feeding microorganisms without creating waste accumulation in the environment. Bio-based polymers are defined as polymers obtained from natural or renewable resources, that is, from sources that are renewable on a timescale of human life by their very nature.

[0003] Given the widespread use of bioplastics as an alternative to conventional plastics, sustainability can be further enhanced by increasing the possibility of reusing their monomers. This creates a true circular economy by minimizing land use and renewable CO2 production through the net carbon sink effect of converting waste into fertile humus, without the risk of any persistent substances accumulating in the environment.

[0004] Furthermore, some of the most commonly used bio-based polymers, such as polylactic acid (PLA), while biodegradable under industrial or household composting conditions, may slowly degrade under normal conditions if processed in bulk. Therefore, the extensive processing of these polymers and the waste of valuable raw materials can also have environmental impacts.

[0005] For this reason, in addition to conventional plastic recycling, new methods for recycling / reusing biopolymers are also being considered.

[0006] While non-biodegradable bio-based polymers can be recycled in recycling plants that have already been used for their fossil-based counterparts, biodegradable polymers require alternatives and specific solutions depending on the properties of the polymer itself.

[0007] Currently, the main recycling technologies for biopolymers include sorting, mechanical recycling, chemical recycling, and enzymatic depolymerization, which can be applied to post-industrial or post-consumer waste.

[0008] For example, methods for mechanically recovering biopolymers, particularly those from post-industrial waste, through shredding, grinding, and melting operations are known, in which the material is reused as is. However, biopolymers such as PLA and polyhydroxyalkyl esters are generally particularly sensitive to the presence of temperature and moisture, which can be caused by the presence of other components. This can lead to degradation and stickiness problems during processing.

[0009] Such problems are also encountered in chemical recycling processes (e.g., via hydrolysis, alcoholysis, or pyrolysis). For example, the method described in EP 2 022 818 B1 involves hydrolyzing solid PLA articles by exposing them to water-saturated vapor at a temperature below the melting point of PLA and the corresponding saturated vapor pressure. This method requires careful control of temperature and pressure to avoid bringing the material into a molten state.

[0010] Furthermore, biodegradable articles, such as packaging films, bags, and printed or thermoformed articles used in the food service industry, can consist of one or more different biodegradable compositions, arranged, for example, in single or multiple layers, containing, in addition to polyhydroxyalkyl esters such as PLA, other classes of biodegradable polymers such as diacid-diol polyesters (aliphatic and / or aliphatic-aromatic) and polymers of natural origin, as well as fillers and / or other additives. This heterogeneity further complicates the recycling of biodegradable compositions, as processing conditions must be adjusted to take into account the chemical and physical properties of each component and any degradation phenomena that may occur.

[0011] For these reasons, methods have been developed, for example, for recovering PLA from waste mixtures, in which PLA is dissolved in a suitable solvent and separated from other solid polymers and undissolved components (e.g., by filtration or precipitation). This separation allows for subsequent chemical recovery of PLA (typically via hydrolysis, alcoholysis, or pyrolysis) with or without a catalyst.

[0012] For example, patents EP 2 419 396 B1 and US 8,431,686 respectively relate to methods in which PLA is extracted in a solvent and subsequently subjected to hydrolysis or alcoholysis to produce lactic acid or lactate esters.

[0013] However, these methods only allow the recovery of lactic acid and its derivatives, i.e., only one type of monomer, and require the use of organic solvents.

[0014] Therefore, there is a need for a method that may have a low environmental impact, allowing the recovery of heterogeneous biodegradable compositions by reusing the different components generated from the depolymerization of the heterogeneous biodegradable composition during polymerization.

[0015] To meet this requirement, the applicant has developed a method that combines the depolymerization of biodegradable polyester blends with their reuse in the polymerization of monomers and / or oligomers obtained therefrom.

[0016] In fact, it has been unexpectedly observed that by depolymerizing the polyester mixture with water at a temperature above the melting point of at least one of the polyesters, for example 120°C or higher, preferably 250°C or lower, a mixture of monomers and / or oligomers is obtained. After properly separating any impurities or fillers present and adjusting the content of any hydroxy acids and / or their oligomers that may be present, the mixture of monomers and / or oligomers can be effectively subjected to subsequent repolymerization to obtain new biodegradable polymer compositions.

[0017] The resulting mixture of monomers and / or oligomers can be advantageously used in the production of biodegradable polyesters in an amount of 1% to 100% by weight, preferably 2% to 50% by weight, and more preferably 5% to 30% by weight, relative to the weight of the mixture being polymerized.

[0018] Therefore, one object of the present invention is to provide a method for reusing a biodegradable polymer composition comprising a polyester blend in polymerization, the method comprising the following steps:

[0019] 1) The polymer composition is reacted with water at a temperature above the melting point of at least one of the polyesters, preferably 120°C or higher, and preferably at a pressure above atmospheric pressure, to produce a mixture of depolymerization products comprising monomers and / or oligomers of the polyester.

[0020] 2) Separate the portion containing impurities and / or fillers from the depolymerization product.

[0021] 3) The monomers and / or oligomers are subjected to polymerization in an amount of 1% to 100% by weight, preferably 2% to 50% by weight and more preferably 5% to 30% by weight relative to the mixture in which polymerization is carried out, thereby producing a biodegradable polymer composition.

[0022] According to a preferred aspect of the invention, the biodegradable polymer composition comprises one or more polyhydroxyalkyl esters, and the reaction in step 1) is carried out at a temperature above the melting point of the polyhydroxyalkyl ester. According to this aspect, polymerization step 3) is preferably carried out while maintaining the amount of hydroxy acid or its oligomers at 0% to 25% by weight, preferably 2% to 15% by weight, relative to the total weight of the polymerization mixture. By maintaining the content of the hydroxy acid and / or its oligomers within these ranges, the amount of lactide produced during polymerization and the content of lactate units in the polymer are more easily controlled. The method is described in more detail below.

[0023] The biodegradable polymer composition subjected to the method according to the invention comprises a mixture of two or more different polyesters selected from polyhydroxyalkyl esters and diacid-diol polyesters. The latter is selected from aliphatic polyesters, aromatic polyesters, aliphatic / aromatic polyesters, or mixtures thereof.

[0024] Such polyesters have an advantageous melting point of 250°C or lower, preferably 200°C or lower.

[0025] According to a preferred aspect, the polyester blend comprises at least one polyhydroxyalkyl ester (A) and at least one diacid-diol polyester (B) in any proportion; preferably, it is a blend having 10% to 90% by weight of polyhydroxyalkyl ester (A) and 90% to 10% by weight of diacid-diol polyester (B) of the total weight of the blend, and particularly preferably, it is a blend having 20% ​​to 80% by weight of polyhydroxyalkyl ester (A) and 80% to 20% by weight of diacid-diol polyester (B).

[0026] The polyhydroxyalkyl ester (A) is preferably selected from lactic acid polyester, poly-ε-caprolactone, polyhydroxybutyl ester (PHB), polyhydroxybutyl valerate (PHBV), polyhydroxybutyl propionate, polyhydroxybutyl hexanoate (PHBH), polyhydroxybutyl decanoate, polyhydroxybutyl dodecanoate, polyhydroxybutyl hexadecanoate, polyhydroxybutyl octadecanoate, poly-3-hydroxybutyl ester-4-hydroxybutyl ester, or mixtures thereof.

[0027] Preferably, the polyhydroxyalkyl ester comprises at least 70% by weight of one or more lactic acid polyesters.

[0028] In a preferred embodiment, the lactic acid polyester is selected from poly-L-lactic acid, poly-D-lactic acid, poly-DL-lactic acid stereocomplexes, copolymers containing more than 50% of the lactic acid polyester on a molar basis, or mixtures thereof.

[0029] Particularly preferred are lactic acid polyesters comprising at least 95% by weight repeating units derived from L-lactic acid or D-lactic acid or combinations thereof.

[0030] In a particularly preferred embodiment of the invention, the lactic acid polyester comprises at least 95% by weight of units derived from L-lactic acid, ≤5% by weight of repeating units derived from D-lactic acid, and has a melting point in the range of 135°C to 175°C.

[0031] The diacid-diol polyester (B) is selected from aliphatic polyesters, aromatic polyesters, aliphatic / aromatic polyesters or mixtures thereof; preferably, it is an aliphatic / aromatic polyester (B1) and / or an aliphatic polyester (B2).

[0032] In the case of aliphatic / aromatic polyester B1, the diacid-diol polyester (B) preferably contains...

[0033] (a) a dicarboxylic acid component, the dicarboxylic acid component comprising

[0034] (a1) Units derived from at least one aromatic dicarboxylic acid and

[0035] (a2) A unit derived from at least one saturated or unsaturated (preferably saturated) aliphatic dicarboxylic acid.

[0036] (b) A diol component comprising a unit derived from at least one saturated or unsaturated (preferably saturated) aliphatic diol.

[0037] The aromatic dicarboxylic acid of component a1) is preferably selected from: phthalic acid-type aromatic dicarboxylic acids, preferably terephthalic acid or isophthalic acid, more preferably terephthalic acid; and aromatic dicarboxylic acid heterocyclic compounds, preferably 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 2,3-furandicarboxylic acid, 3,4-furandicarboxylic acid, more preferably 2,5-furandicarboxylic acid; its esters, salts and mixtures.

[0038] In a preferred embodiment, these aromatic dicarboxylic acids comprise:

[0039] - 1% to 99%, preferably 5% to 95%, and more preferably 10% to 80% of terephthalic acid, its esters or salts, on a molar basis;

[0040] - 99% to 1%, preferably 95% to 5%, and more preferably 90% to 20% of 2,5-furan dicarboxylic acid, its ester or salt, on a molar basis.

[0041] The aliphatic dicarboxylic acid of component a2) is preferably selected from: saturated C2-C 24 C4-C is preferred. 13 C4-C is preferred. 11 Dicarboxylic acid; its C1-C 24 Preferably, C1-C4 alkyl esters; their salts; and mixtures thereof. Preferably, the saturated aliphatic dicarboxylic acid is selected from: succinic acid, 2-ethylsuccinic acid, glutaric acid, 2-methylglutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, brassic acid, and their C1-C4 alkyl esters. 24 Alkyl esters. In a preferred embodiment of the invention, saturated aliphatic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, and mixtures thereof.

[0042] The possible unsaturated aliphatic dicarboxylic acids of component a2) are preferably selected from: itaconic acid, fumaric acid, maleic acid, 4-methylene-heptanediol, 3,4-bis(methylene)azelaic acid, 5-methylene-azelaic acid, whose C1-C 24Preferably, C1-C4 alkyl esters, their salts, and mixtures thereof. In a preferred embodiment of the invention, the unsaturated aliphatic dicarboxylic acid consists of itaconic acid, or contains itaconic acid comprising at least 50% (molar), preferably greater than 60% (molar), more preferably greater than 65% (molar), of C1-C4 alkyl esters, their salts, and mixtures thereof. 24 A mixture of C1-C4 esters is preferred.

[0043] Regarding the saturated aliphatic diol of component b), it is preferably selected from 1,2-ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tetanediol, 1,4-cyclohexanediol, neopentyl glycol, 2-methyl-1,3-propanediol, sorbitol dihydrate, mannitol dihydrate, idioyl alcohol dihydrate, cyclohexanediol, cyclohexanemethyldiol, dialenyl glycol, and polyalkylene glycols (e.g., polyethylene glycol, polypropylene glycol), and mixtures thereof. Preferably, the diol component comprises at least 50% by molar amount of one or more diols selected from 1,2-ethylene glycol, 1,3-propanediol, and 1,4-butanediol. More preferably, the diol component comprises or is composed of 1,4-butanediol.

[0044] Regarding any unsaturated aliphatic diol in component b), it is preferably selected from cis-2-buten-1,4-diol, trans-2-buten-1,4-diol, 2-butyn-1,4-diol, cis-2-penten-1,5-diol, trans-2-penten-1,5-diol, 2-pentyn-1,5-diol, cis-2-hexen-1,6-diol, trans-2-hexen-1,6-diol, 2-hexyn-1,6-diol, cis-3-hexen-1,6-diol, trans-3-hexen-1,6-diol, and 3-hexyn-1,6-diol.

[0045] In the case of aliphatic polyester (B2), the diacid-diol polyester (B) preferably comprises:

[0046] (c) A dicarboxylic acid component, said dicarboxylic acid component comprising units derived from self-saturated or unsaturated aliphatic dicarboxylic acids.

[0047] (d) Diol component, said diol component comprising units derived from saturated or unsaturated aliphatic diols.

[0048] Relative to the total dicarboxylic acid component, the saturated aliphatic dicarboxylic acid of component c) is preferably present in an amount of 95% to 100% on a molar basis; it is preferably selected from: saturated C2-C 24 C4-C is preferred. 13 C4-C is preferred.11 Dicarboxylic acid; its C1-C 24 Preferably, C1-C4 alkyl esters; their salts; and mixtures thereof. Preferably, the saturated aliphatic dicarboxylic acid is selected from succinic acid, 2-ethylsuccinic acid, glutaric acid, 2-methylglutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, brassic acid, hexadecanoic acid, octadecanoic acid, and their C1-C4 alkyl esters. 24 Alkyl ester. Preferably, the dicarboxylic acid component comprises or is composed of units derived from succinic acid.

[0049] Relative to the total dicarboxylic acid component, the possible unsaturated aliphatic dicarboxylic acid of component c) is preferably present in an amount of 0% to 5% on a molar basis; it is preferably selected from itaconic acid, fumaric acid, maleic acid, 4-methyl-heptanediol, 3,4-bis(methylene)azelaic acid, 5-methylene-azelaic acid, whose C1-C 24 Preferably, C1-C4 alkyl esters, their salts, and mixtures thereof. In a preferred embodiment of the invention, the unsaturated aliphatic dicarboxylic acid comprises itaconic acid, or comprises itaconic acid containing at least 50% (molar), preferably greater than 60% (molar), more preferably greater than 65% (molar), and its C1-C4 alkyl esters. 24 A mixture of C1-C4 esters is preferred.

[0050] Regarding the saturated aliphatic diols in component d), they are preferably present in an amount of 95% to 100% molar relative to the total diol composition; they are preferably selected from 1,2-ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11... -Undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,4-cycloalkylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, bis(sorbitol), bis(mannitol), bis(idylol), cyclohexanediol, cyclohexanemethyldiol, dienyl glycol, and polyalkylene glycols (e.g., polyethylene glycol, polypropylene glycol) with a molecular weight of 100 to 4000, and mixtures thereof. Preferably, the glycol component comprises at least 50% by molar amount of one or more glycols selected from 1,2-ethylene glycol, 1,3-propanediol, and 1,4-butanediol. More preferably, the glycol component comprises or consists of 1,4-butanediol.

[0051] Regarding the unsaturated aliphatic diol of component d2), it is preferably present in an amount of 0% to 5% molar relative to the total diol component; it is preferably selected from cis-2-buten-1,4-diol, trans-2-buten-1,4-diol, 2-butyn-1,4-diol, cis-2-penten-1,5-diol, trans-2-penten-1,5-diol, 2-pentyn-1,5-diol, cis-2-hexen-1,6-diol, trans-2-hexen-1,6-diol, 2-hexyn-1,6-diol, cis-3-hexen-1,6-diol, trans-3-hexen-1,6-diol, and 3-hexyn-1,6-diol.

[0052] In a particularly preferred embodiment, the biodegradable composition fed to the method according to the invention comprises one or more diacid-diol (B) polyesters selected from: poly(1,4-butanediol succinate), poly(1,4-butanediol succinate-copoly-1,4-butanediol adipate), poly(1,4-butanediol succinate-copoly-1,4-butanediol azelaic acid), poly(1,4-butanediol adipate), and poly(1,4-butanediol azelaic acid). Poly(1,4-butanediol terephthalate), poly(1,4-butanediol succinate-copolymer-1,4-butanediol terephthalate), poly(1,4-butanediol azelaic acid-copolymer-1,4-butanediol terephthalate), poly(1,4-butanediol brassic acid-copolymer-1,4-butanediol terephthalate), poly(1,4-butanediol sebacic acid-copolymer-1,4-butanediol terephthalate) ester), poly(1,4-butanediol adipate-copolymer-1,4-butanediol sebacate-copolymer-1,4-butanediol terephthalate), poly(1,4-butanediol azelaate-copolymer-1,4-butanediol sebacate-copolymer-1,4-butanediol terephthalate), poly(1,4-butanediol adipate-copolymer-1,4-butanediol azelaate-copolymer-1,4-butanediol terephthalate), poly (1,4-Butanediol succinate-copolymer-1,4-Butanediol sebacate-copolymer-1,4-Butanediol terephthalate), poly(1,4-Butanediol adipate-copolymer-1,4-Butanediol succinate-copolymer-1,4-Butanediol terephthalate), poly(1,4-Butanediol azelaate-copolymer-1,4-Butanediol succinate-copolymer-1,4-Butanediol terephthalate), and mixtures thereof.

[0053] Relative to the total molar amount of the dicarboxylic acid component, the aliphatic polyester and / or aliphatic / aromatic polyester (referred to as diacid-diol polyester (B)) in the biodegradable composition subjected to the method according to the invention may also contain, for example, 0% to 49% molar, preferably 0% to 30%, repeating units derived from at least one hydroxy acid. Examples of suitable hydroxy acids are glycolic acid, hydroxybutyric acid, hydroxyhexanoic acid, hydroxyvalerate, 7-hydroxyheptanoic acid, 8-hydroxyhexanoic acid, 9-hydroxynonanoic acid, lactic acid, or lactide.

[0054] Long molecules containing two functional groups (which need not be terminal functional groups) can also typically exist in an amount not exceeding 10% of the total molar amount of the dicarboxylic acid component. Examples include dimer acids, ricinoleic acid, acids with epoxy functional groups, and polyoxyethylene with a molecular weight of 200 to 10,000.

[0055] Diamines, amino acids, and amino alcohols may also be present at a maximum of 30% of the total molar percentage of the dicarboxylic acid component.

[0056] In addition, one or more polyfunctional molecules may typically be present in amounts ranging from 0.01% to 3% molar relative to the total molar amount of the dicarboxylic acid component. Examples of such molecules include glycerol, pentaerythritol, trimethylolpropane, citric acid, dipentaerythritol, monosorbitol, monomannitol, triglycerides, polyglycerol, etc.

[0057] The biodegradable polymer composition subjected to the method according to the invention also optionally contains one or more polymers of natural origin.

[0058] These naturally derived polymers are advantageously selected from starch, chitin, chitosan, alginate, proteins (e.g., gluten, corn protein, casein, collagen), gelatin, natural gums, cellulose (also in the form of nanofibrils), and pectin.

[0059] As used herein, starch refers to all types of starch, namely flour, natural starch, hydrolyzed starch, destructured starch, gelatinized starch, plasticized starch, thermoplastic starch, compound starch containing bio-fillers, or mixtures thereof. Starches commonly found in biodegradable compositions include those such as potato starch, corn starch, cassava starch, and pea starch. Included in the definition are starches that are readily deformable and have a high initial molecular weight, such as potato starch or corn starch.

[0060] Starch can exist as is or in chemically modified forms, such as starch esters with a degree of substitution of 0.2 to 2.5, hydroxypropylated starch, or starch modified with fatty chains.

[0061] With regard to allosteric starch, with reference to the teachings included in patents EP-0 118240 and EP-0 327 505, starch is understood to be starch processed in such a way that it substantially does not show the so-called "maltese cross" in polarized light under an optical microscope and substantially does not show the so-called "ghost" in phase-contrast light under an optical microscope.

[0062] In cases where the biodegradable composition contains allosteric starch, the biodegradable composition typically also contains 1% to 40% by weight of a plasticizer selected from water and polyols having 2 to 22 carbon atoms, relative to the weight of the starch. The water may also be water naturally present in the starch. Preferred polyols are those having 1 to 20 hydroxyl groups and / or containing 2 to 6 carbon atoms, their ethers, thioethers, and organic and inorganic esters. Examples of polyols include glycerol, diglycerol, polyglycerol, pentaerythritol, ethoxylated polyglycerol, ethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, sorbitol, sorbitol monoacetate, sorbitol diacetate, sorbitol monoethoxylate, sorbitol diethoxylate, and mixtures thereof. Examples of mixtures contain 2% to 90% by weight of glycerol.

[0063] The biodegradable polymer compositions processed according to the present invention may optionally contain one or more fillers or fillers.

[0064] The filler or filler is preferably selected from kaolin, wollastonite, barite, clay, talc, calcium carbonate and magnesium carbonate, iron carbonate and lead carbonate, aluminum hydroxide, diatomite, aluminum sulfate, barium sulfate, silicon dioxide, mica, and titanium dioxide.

[0065] Such fillers, such as talc, calcium carbonate, or mixtures thereof, are typically in the form of particles with an arithmetic mean diameter greater than 1 micrometer when measured along the long axis of the particle.

[0066] In addition to the polyhydroxyalkyl esters (A), diacid-diol polyesters (B), and polymers of natural origin listed above, the biodegradable polymer compositions subjected to the methods according to the invention may optionally contain one or more other polymers.

[0067] The other polymers are selected, for example, from vinyl polymers, diacid-diol polyesters other than polyester (B), polyamides, polyurethanes, polyethers, polyureas, polycarbonates, and mixtures thereof.

[0068] Examples of vinyl polymers include: polyethylene, polypropylene and their copolymers, polyvinyl alcohol and its copolymers such as butene glycol / vinyl alcohol copolymer, polyvinyl acetate, polyethylvinyl acetate and polyvinyl alcohol, polystyrene, chlorinated vinyl polymers, and polyacrylates.

[0069] In addition to polyvinyl chloride, vinyl chloride polymers are to be understood herein to include polyvinylidene chloride, poly(vinyl chloride-vinyl acetate), poly(vinyl chloride-ethylene), poly(vinyl chloride-propylene), poly(vinyl chloride-styrene), poly(vinyl chloride-isobutylene), and copolymers wherein polyvinyl chloride comprises more than 50% by molar weight. The copolymers may be random copolymers, block copolymers, or alternating copolymers.

[0070] Regarding polyamides that may be present in biodegradable compositions subjected to the method according to the invention, they are selected, for example, from polyamides 6 and 6,6, polyamides 9 and 9,9, polyamides 10 and 10,10, polyamides 11 and 11,11, polyamides 12 and 12,12, and combinations thereof of the 6 / 9, 6 / 10, 6 / 11, 6 / 12 types, mixtures thereof, and copolymers (both random and block).

[0071] The polycarbonate that may be present is selected, for example, from polyalkylene carbonate, preferably polyethylene carbonate, polypropylene carbonate, polybutylene carbonate, mixtures thereof, and both random copolymers and block copolymers.

[0072] Examples of polyethers include those selected from polyethylene glycol, polypropylene glycol, polybutane glycol, copolymers thereof, and mixtures thereof.

[0073] Regarding diacid-diol polyesters other than polyester (B), they include, for example:

[0074] (e) a dicarboxylic acid component, which, relative to the total dicarboxylic acid component, comprises:

[0075] (e1) 20% to 100% by molar amount of units derived from at least one aromatic dicarboxylic acid,

[0076] (e2) 0% to 80% by molar amount of units derived from at least one saturated or unsaturated aliphatic dicarboxylic acid.

[0077] (f) a diol component comprising a unit derived from at least one saturated or unsaturated aliphatic diol.

[0078] Preferably, the aromatic dicarboxylic acid (e1), aliphatic dicarboxylic acid (e2), and aliphatic diol (f) used in the polyester are selected from those described above for the polyester (B) of the composition according to the invention.

[0079] Other examples of diacid glycol polyesters besides polyester (B) are chemically modified and / or low-melting-point aliphatic and / or aliphatic-aromatic polyesters. Chemically modified polyesters include, for example, polyesters modified by grafting with α,β-unsaturated monocarboxylic acids, α,β-unsaturated dicarboxylic acids and / or anhydrides or combinations thereof.

[0080] In addition to the components described above, the biodegradable composition according to the invention optionally also contains one or more additives selected from the following: plasticizers, UV stabilizers, lubricants, nucleating agents, surfactants, antistatic agents, pigments, flame retardants, compatibilizers, lignin, organic acids, antioxidants, mildew inhibitors, waxes, and processing aids.

[0081] Regarding plasticizers, in addition to the plasticizers preferably used in the preparation of allosteric starch and described above, one or more plasticizers selected from the following may be present: phthalates such as diisononyl phthalate, trimellitic esters such as those with C4-C 20 Triterpenoid esters of monools (preferably selected from n-octanol and n-decanol), and aliphatic esters of monocarboxylic acids and dicarboxylic acids with linear or branched C2-C8 olefins (e.g., neopentyl glycol). When present, the selected plasticizer is preferably present in up to 10% by weight relative to the total weight of the composition.

[0082] The lubricant is, for example, zinc stearate, calcium stearate, aluminum stearate, and acetyl stearate. Preferably, the composition contains up to 1% by weight of lubricant relative to the total weight of the composition according to the invention, more preferably up to 0.5% by weight.

[0083] Examples of nucleating agents include sodium saccharin, calcium silicate, sodium benzoate, calcium titanate, boron nitride, isotactic polypropylene, and low molecular weight PLA.

[0084] Processing aids include, for example, lubricants. Lubricants include, for example, biodegradable fatty acid amides such as oleamide, erucamide, ethylene-bis-stearamide, fatty acid esters such as glyceryl oleate or glyceryl stearate, and saponified fatty acids such as stearates.

[0085] Pigments may also be present, such as titanium dioxide, clay, copper phthalocyanine, silicates / esters, iron oxides and iron hydroxides, carbon black and magnesium oxide.

[0086] Examples of compatibilizers include those containing isocyanate groups, peroxide groups, carbodiimide groups, and isocyanurate groups. Bifunctional and / or polyfunctional compounds of azoline, epoxide, anhydride, divinyl ether, and mixtures thereof.

[0087] These additives are preferably present in an amount of up to 10% by weight, more preferably up to 6% by weight, and even more preferably up to 2% by weight, relative to the total weight of the composition.

[0088] Within the meaning of this invention, a biodegradable composition means a polymer composition that is biodegradable according to standard EN 13432.

[0089] The biodegradable composition subjected to step 1) of the method according to the invention is preferably derived from post-industrial and / or post-consumer waste, such as biodegradable articles derived from industrial waste or at the end of their lifespan, such as packaging films, bags, and printed or thermoformed food service products.

[0090] Optionally, the waste may be subjected to one or more preliminary operations to remove organic or inorganic debris and residues, thereby obtaining a homogeneous composition and increasing the surface area to facilitate subsequent hydrolysis reactions in step 1) of the method.

[0091] These preliminary operations are advantageously selected from: washing, screening, separation, crushing, and conditioning.

[0092] Separation can be performed, for example, manually, by density, by an optical system, or by dissolution.

[0093] Crushing operations include, for example, crushing, grinding, and granulation.

[0094] According to a first embodiment of the invention, a biodegradable composition wherein the polymer component comprises or mainly comprises one or more polyhydroxyalkyl esters (A) and one or more aliphatic-aromatic diacid glycol polyesters (B1) is fed into step 1 of the method.

[0095] According to a second embodiment of the invention, a biodegradable composition comprising or primarily comprising one or more polyhydroxyalkyl esters (A), one or more aliphatic-aromatic diacid glycol polyesters (B1), and one or more fillers is fed to step 1 of the method.

[0096] According to a third embodiment of the invention, a biodegradable composition comprising or primarily comprising one or more polyhydroxyalkyl esters (A) and one or more aliphatic diacid glycol polyesters (B2) is fed to step 1 of the method.

[0097] According to a fourth embodiment of the invention, a biodegradable composition comprising or primarily comprising one or more polyhydroxyalkyl esters (A), one or more aliphatic diacid glycol polyesters (B2), and one or more fillers is fed to step 1 of the method.

[0098] According to the fifth embodiment, a biodegradable composition comprising or primarily comprising one or more polyhydroxyalkyl esters (A), one or more aliphatic diacid glycol polyesters (B2), one or more fillers, and one or more additional polymers including one or more vinyl polymers and one or more diacid glycol polyesters other than (B) is fed to step 1 of the method.

[0099] If the biodegradable starting composition contains one or more polymers of natural origin, the method according to the invention advantageously includes a preliminary pretreatment step prior to step 1), during which the polymers of natural origin are optionally partially or completely removed along with one or more possible fillers (organic and / or inorganic) and / or additives.

[0100] The preliminary pretreatment step is advantageously carried out by dissolution or by hydrolysis (e.g., chemical hydrolysis, enzymatic hydrolysis) that can completely or partially destroy the polymer chains of the natural polymer (e.g., polysaccharide chains in the case of starch).

[0101] This preliminary step is carried out at lower temperature and pressure conditions than those used in step 1) of the method, preferably in the presence of water and advantageously in the presence of a catalyst (e.g., an acidic catalyst, a basic catalyst, or an enzyme catalyst).

[0102] In addition to polymers of natural origin, this pretreatment also removes other components of polymeric or non-polymeric nature that are soluble under the conditions employed, such as certain plasticizers, from the biodegradable composition.

[0103] The soluble components are then removed after the liquid phase is separated from the solid biodegradable composition.

[0104] It is preferable to completely or substantially completely remove hydrolytic residues that may cause degradation under process conditions. Therefore, pretreatment advantageously includes one or more washing and / or filtering operations.

[0105] In step 1) of the method according to the invention, the biopolymer present in the biodegradable polymer starting composition undergoes a hydrolysis reaction, i.e., the ester bond of the polymer chain is broken, until a mixture of oligomers and / or monomers is formed.

[0106] Hydrolysis requires the presence of water and suitable temperature, pH, and pressure conditions. Depending on the reaction conditions and the amount of water used, hydrolysis will cause polymer chains to break down to obtain monomer units such as hydroxy acids, dicarboxylic acids, and diols (complete hydrolysis), or partially break down into oligomers or a mixture of monomers and oligomers (partial hydrolysis).

[0107] The hydrolysis reaction in step 1) is carried out with water at a temperature above the melting point of at least one of the polyesters and preferably at a pressure above atmospheric pressure.

[0108] Therefore, the reaction in step 1) is preferably carried out in an apparatus suitable for processing fluids (including fluids with high viscosity). For example, a reactor, such as an autoclave (preferably equipped with a stirring system) or an extruder, that allows for effective mixing, sufficient heat exchange surface, and high pressure will be preferred. A reactor capable of ensuring sufficient contact surface between the polymer melt and the gas phase will also be preferred.

[0109] One or more reactors, which may be the same or different from each other, can be used in series.

[0110] The starting biodegradable polymer composition is mixed with water to achieve a water-to-polymer composition weight ratio that is advantageously 3:1 to 1:2, preferably 2.5:1 to 1:1.5, and even more preferably 2:1 to 1:1.

[0111] The water and polymer composition are advantageously brought into contact at room temperature or at least at a temperature below the reaction temperature. Therefore, heating to the reaction temperature is preferably carried out in the presence of water.

[0112] The temperature during the hydrolysis reaction is maintained above 120°C, preferably at 150°C or above, more preferably at 170°C or above, even more preferably at 200°C or above, and advantageously at 250°C or below, preferably at 240°C or below, more preferably at 230°C or below. These conditions are particularly advantageous because they allow the reaction to work even in the absence of a catalyst.

[0113] According to the invention, a biodegradable composition comprising a mixture of aromatic aliphatic (B1) type diacid glycol polyesters and / or aliphatic (B2) type diacid glycol polyesters (e.g., polybutylene succinate and / or copolymers thereof) containing units derived from succinic acid is fed to one aspect of hydrolysis step 1), with the temperature advantageously maintained at 120°C to 200°C. At higher temperatures, loss of 1,4-butanediol can be observed due to an increase in its cyclization products (e.g., tetrahydrofuran).

[0114] The hydrolysis reaction is carried out at a pressure preferably equal to the liquid vapor pressure. Therefore, during step 1 of the method, the pressure is maintained at ambient pressure (about 1 bar), or at 2 bar (0.2 MPa) or more, 5 bar (0.5 MPa) or more, 10 bar (1 MPa) or more, or preferably 15 bar (1.5 MPa) or more, and advantageously 50 bar (5 MPa) or less, preferably 40 bar (4 MPa) or less, or more preferably 30 bar (3 MPa) or less.

[0115] Compositions primarily comprising diacid-diol polyesters prepared from aliphatic dicarboxylic acids typically require lower pressure and temperature conditions than diacid-diol polyesters prepared from aliphatic and aromatic dicarboxylic acids. Therefore, those skilled in the art will be able to adjust the reaction conditions within the above ranges depending on the biodegradable composition fed to the method.

[0116] According to one embodiment of the method, during step 1), the hydrolysis reaction is carried out in two or more consecutive steps, at the end of each step separating the aqueous phase containing the soluble monomers and / or oligomers obtained by hydrolysis, and feeding fresh water / vapor into the next step. These steps can be carried out under the same pressure and temperature conditions, or, according to a preferred aspect, each step is carried out under higher pressure and / or temperature conditions than the previous step.

[0117] The duration of the hydrolysis reaction varies primarily depending on the temperature and pressure conditions used and the manner of contact between water and the composition to be hydrolyzed, ranging from a few minutes under harsh conditions to 10 hours under milder conditions, preferably 30 minutes to 4 hours, and more preferably 60 minutes to 3 hours. According to a preferred aspect of the invention, for example, the reaction achieves 95% conversion within 2 hours.

[0118] The hydrolysis reaction in step 1) can be promoted in the presence of an acidic catalyst, a basic catalyst, or a metal salt. Examples of suitable catalysts are inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; bases such as alkali metal and alkaline earth metal oxides and hydroxides; and salts such as zinc acetate and magnesium acetate.

[0119] Alkaline catalysts have the advantage that they allow acid monomers (such as furan dicarboxylic acid and terephthalic acid) that are otherwise insoluble in water to enter the aqueous solution in a dissociated form, thereby simplifying the recovery process.

[0120] The catalyst is preferably used in an amount of 0 ppm to 1000 ppm relative to the biodegradable composition.

[0121] One advantage of this method is that it can be carried out efficiently in the absence of organic solvents. However, the hydrolysis reaction in step 1) can be promoted by the presence of a small amount of water-miscible organic solvent (e.g., ethanol, propanol, isopropanol, butanol). In practice, it is advantageous to remove such solvents prior to polymerization step 3).

[0122] The depolymerization product obtained at the end of the hydrolysis reaction comprises a mixture of monomers of the polyester present in the initial biodegradable composition (e.g., hydroxy acids, dicarboxylic acids, and diols selected from those mentioned above as components of the initial biodegradable composition) and / or oligomers thereof.

[0123] The monomers are advantageously selected from azelaic acid, azelaic acid, sebacic acid, succinic acid, terephthalic acid, furan dicarboxylic acid, lactic acid, 3-hydroxybutyric acid, 3-hydroxyvalerate and 3-hydroxyhexanoic acid, 1,2-ethylene glycol, 1,3-propanediol, and 1,4-butanediol.

[0124] In the context of this invention, the term "oligomer" refers to groups of repeating units (i.e., hydroxy acid units or diacid-diol units) in a water-soluble polymer chain, such as groups of two, three, or four repeating units. The molecular weight of the oligomers according to the invention is typically less than 2000.

[0125] The oligomer may be present in an amount of 1% to 100% by weight, preferably 10% to 50% by weight, of the total weight of the monomers and oligomers in the depolymerization product.

[0126] In step 2) of the method, the portion containing impurities and / or fillers is separated from the depolymerization product. This separation is carried out according to known techniques and preferably includes a solid / liquid separation operation. Such separation makes it possible to remove additives that are no longer reactive, such as insoluble branching agents and slip agents, thus making the method according to the invention particularly advantageous compared to mechanical recovery techniques in which such additives would accumulate during the polymerization stage. According to a preferred aspect, in step 2), the monomers are selectively separated by adjusting the separation conditions based on their solubility.

[0127] According to one aspect of the method, the depolymerization product comprises water-soluble monomers and / or oligomers, such as glycols, hydroxy acids, and aliphatic dicarboxylic acids, and possibly dicarboxylate salts. On the other hand, insoluble monomers and / or oligomers, such as phthalic acid-type aromatic dicarboxylic acids in undissociated form, remain in a heterogeneous phase and, after cooling the mixture below its melting point, are in a solid state along with any insoluble fillers and / or impurities.

[0128] According to this aspect of the method, the separation in step 2) is carried out after the depolymerization product is cooled to a temperature below the melting point; thus, the soluble monomer and / or oligomer is advantageously present in solution in an aqueous phase together with any soluble additives such as plasticizers, branching agents or other soluble polymers.

[0129] Therefore, in addition to any insoluble fillers and / or impurities, step 2) of the method according to the invention may also separate a portion from the depolymerization product that also contains insoluble monomers and / or oligomers and / or residues from the unhydrolyzed starting mixture. According to another aspect of the method, for example, if a limited amount of water is present or in the case of partial hydrolysis, the depolymerization product at the end of the hydrolysis step exists essentially as a fluid substance containing fillers and / or impurities that are solid at the hydrolysis temperature. These fillers and / or impurities are then separated from the fluid substance as a solid portion.

[0130] In this case, in particular, the depolymerization products containing monomers and / or oligomers are advantageously returned to the hydrolysis step or subsequent further purification operation (e.g., washing) prior to the polymerization step to remove any water-soluble molecules, such as branching agents, that may interfere with subsequent polymerization steps, for example, those present as additives in the biodegradable starting composition.

[0131] However, one advantage of this method is that the additives from the starting polyester mixture can be fed together with monomers and / or oligomers into polymerization step 3 in an amount of up to 5% by weight, preferably 1% to 2% by weight, relative to the mixture undergoing polymerization. In fact, not only can the depolymerized purified monomers from the starting mixture be reused in the polymerization, but also the partially hydrolyzed products and / or partially purified hydrolyzed products can be reused.

[0132] The separation operation in step 2) is selected from, for example, filtration, centrifugation, and sedimentation. Filtration includes, for example, microfiltration and ultrafiltration. According to one aspect of the invention, one or more liquid / liquid separations are performed during step 2).

[0133] The solid fraction separated in step 2) comprises one or more components selected from fillers, unhydrolyzed or non-hydrolyzed polymers, insoluble oligomers and monomers, insoluble impurities such as additives or degradation products.

[0134] For example, at the end of step 2), the depolymerization product containing monomers and / or oligomers is sent to polymerization step 3) as is, or after one or more optional further separation operations to completely or partially separate the monomers and / or oligomers from each other and / or completely or partially separate them from impurities (e.g., heavy metals) before being sent to polymerization step 3).

[0135] The optional further separation operations are advantageously selected, for example, from crystallization, distillation, microfiltration, nanofiltration, ultrafiltration, and dialysis.

[0136] Crystallization allows for the separation of any aliphatic acid from components that have high solubility in water, such as glycols and hydroxy acids. For example, succinic acid can be advantageously separated from lactic acid and butanediol by crystallization.

[0137] Distillation allows monomers to be fractionated based on different boiling points, but favorable conditions must be selected that do not promote esterification side reactions between acids and hydroxyl groups in the mixture.

[0138] If an acidic or basic catalyst is used during hydrolysis step 1), a portion of the depolymerized product separated in step 2) is also advantageously fed to a neutral pH before being fed to polymerization step 3).

[0139] In step 3) of the method, the monomers and / or oligomers obtained downstream of filler and / or impurity separation are polymerized in an amount of 1% to 100% by weight, preferably 2% to 50% by weight and more preferably 5% to 30% by weight relative to the polymerized mixture, thereby obtaining a biodegradable polymer composition.

[0140] According to the present invention, the weight of the polymerized mixture is calculated without taking into account any solvents present (e.g., water).

[0141] The amount of hydroxy acid or its oligomer in the polymer mixture is advantageously from 0% to 25% by weight, preferably from 2% to 15% by weight, relative to the total weight of the polymer mixture.

[0142] According to one aspect, by one of the above separation operations, such as by distillation of the hydroxy acid or its oligomers, the amount of the hydroxy acid or its oligomers that may be present in the polymer mixture is maintained within the range shown.

[0143] In another aspect, the amounts of monomers and / or oligomers are kept within the indicated range by adding additional new monomers or recycled monomers to the polymerization mixture.

[0144] Polymerization according to the method of the invention is carried out according to any method known in the art. In particular, it can be advantageously carried out by polycondensation. Examples of synthetic methods that can be advantageously used to prepare polyesters are described in International Patent Application WO 2016 / 050963.

[0145] The polymerization reaction according to the present invention preferably comprises:

[0146] (i) The oligomer product is prepared by esterification and / or transesterification of a mixture comprising:

[0147] a) a dicarboxylic acid component, said dicarboxylic acid component comprising:

[0148] a1) 0% to 80% (by molar weight) of units derived from at least one aromatic dicarboxylic acid and / or its esters, salts or derivatives relative to the total dicarboxylic acid composition, and

[0149] a2) Units derived from at least one aliphatic dicarboxylic acid and / or its esters, salts or derivatives, comprising 20% ​​to 100% of the total dicarboxylic acid composition on a molar basis, and

[0150] b) Diol component,

[0151] c) A hydroxy acid component, wherein the amount of the hydroxy acid component is from 0% to 25% by weight of the total weight of the mixture, preferably from 2% to 15% by weight.

[0152] (ii) Polycondense the oligomer product obtained from step (i), and

[0153] (iii) Granulate the polyester obtained from step (ii).

[0154] Aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and diols are preferably selected from those mentioned above as components of the biodegradable starting composition.

[0155] The synthesis process can be advantageously carried out in the presence of a suitable catalyst. Suitable catalysts include organotin compounds such as stannate derivatives, titanium compounds such as tetrabutyl titanate, aluminum compounds such as triisopropylaluminum, antimony compounds, zinc compounds, and zirconium compounds, and mixtures thereof.

[0156] It is advantageous to completely remove water from the polymerization mixture prior to such polymerization to avoid interfering with the esterification step.

[0157] During polymerization, branching agents, compatibilizers, or stabilizers, such as those described above, are advantageously added as components of the biodegradable starting composition.

[0158] The obtained polymer product is a biodegradable polyester, which can then be subjected to reactive extrusion to prepare a biodegradable polymer composition.

[0159] Therefore, the present invention also covers polymers obtained by the above methods.

[0160] According to one different aspect, the present invention relates to biodegradable polymer compositions comprising the polymer as well as optionally other biodegradable polymers and additives known in the art, such as those selected above for biodegradable compositions undergoing depolymerization processes.

[0161] The biodegradable polymer composition obtained according to the present invention can be advantageously used in processes such as blown film forming, cast extrusion, thermoforming or injection molding to obtain biodegradable articles having applications in, for example, the packaging, food service or agricultural textile fields.

[0162] According to another aspect, the present invention therefore relates to biodegradable articles comprising the said biodegradable polymer composition.

[0163] Examples of products comprising the composition according to the present invention are as follows:

[0164] - Both single-oriented and double-oriented films, as well as multilayer films with other polymer materials;

[0165] - A film used as a covering sheet in agriculture;

[0166] - Fabrics used in the agricultural sector as agricultural textiles;

[0167] - Films used in the hygiene field (e.g., for linings of diapers, tampons, etc.);

[0168] - Stretch film used for food, agricultural bundling, and waste wrapping, as well as cling film;

[0169] - Bags and linings used for organic collection, such as collecting food waste and grass clippings;

[0170] - Fruit and vegetable bags, as well as shopping bags;

[0171] - Coatings obtained using extrusion coating technology;

[0172] - A multilayer composite material consisting of paper, plastic, aluminum, and metal film layers;

[0173] - Expandable or expandable particles used for producing molded parts by sintering;

[0174] - Expanded and semi-expanded products, including expanded blocks made from pre-expanded granules;

[0175] - Expanded sheets, thermoformed expanded sheets, and containers made from them for food packaging;

[0176] - Composite materials containing gelatinized starch, allosteric starch and / or compound starch, natural starch, flour, or other fillers of natural, plant or inorganic origin as fillers;

[0177] - Items produced by thermoforming, such as containers, trays, plates, beverage dispensing capsules, and printed circuit boards for electronic devices.

[0178] - Fibers, microfibers, composite fibers, textiles and nonwovens used in health, hygiene, agriculture and clothing. Example

[0179] Example 1

[0180] 102.5 g of a formulation mainly composed of 78% by weight PBAT (i.e., poly(1,4-butanediol adipate-copolymer-1,4-butanediol terephthalate)), 19.5% by weight PLA and 2.5% by weight talc was placed in a pressure reactor along with 200 g of water and heated to 200°C. This temperature was maintained for 2 hours (step 1).

[0181] After 2 hours, the reactor was cooled and the product was collected. It was then heated to 60°C to ensure that the released adipic acid was completely dissolved. The product was then filtered under vacuum using Buchner paper to separate the insoluble fraction (which mainly contains terephthalic acid and talc) (Step 2).

[0182] The total 270g of liquid phase mainly contains 1,4-butanediol, lactic acid, adipic acid, trace amounts of dimers and linear trimers containing lactate units, 1,4-butanediol terephthalate and / or 1,4-butanediol adipic acid.

[0183] HPLC-MS analysis was performed as follows: A Phenomenex Luna Omega C18 PS 100 mm × 2.1 mm × 1.6 μm column was used. Gradient elution was performed with acetonitrile (A) and 0.1% formic acid in water (B), increasing the concentration of A from 5% to 95%. Mass spectrometry was used to acquire signals under positive ESI ionization (for oligomers) and negative ESI ionization (for acids and hydroxy acids), showing the presence of lactic acid, adipic acid, butanediol, and dimers and trimers containing lactic esters, 1,4-butanediol adipic acid ester, and / or 1,4-butanediol terephthalate ester units. The analysis did not show any polymer chains with a molecular weight greater than 2,000, therefore depolymerization was considered quantitative, and 25 g of lactic acid, 29.6 g of adipic acid, and 34.4 g of 1,4-butanediol were present in the liquid phase as free acids or oligomers.

[0184] 372.6 g (2.2445 mol) of terephthalic acid, 299.4 g (2.0507 mol) of adipic acid, 645 g (7.1633 mol) of 1,4-butanediol, 0.66 g (0.007163 mol) of glycerol, 0.25 g of Tyzor TE, and 270 g of a solution obtained by filtering the depolymerization product, containing approximately 89 g of the depolymerization product (equivalent to 6.3 wt% of the total weight of the polymerization mixture), were placed in a 2-liter glass reactor equipped with a mechanical stirring system, a nitrogen inlet, and a distillation line with a Vigreux column, cooling water, and a collection flask. Therefore, the lactic acid reused in the mixture constituted 5.8% of the total acids and hydroxy acids used, equivalent to 1.8 wt% of the total weight of the polymerization mixture.

[0185] The reactor was immersed in an oil bath, and the oil temperature was gradually increased to approximately 250°C over 2 hours, reaching a melt temperature of approximately 235°C. Esterification was carried out for 4 hours, and the melt was clear at the end of the esterification reaction. The esterification product was found to be a white, waxy solid similar to that obtained from a similar mixture without the introduction of depolymerization products.

[0186] 170 g of the esterification product was placed in a 1000 ml glass conical reactor equipped with mechanical stirring, a nitrogen inlet, and a vacuum line with a boilover suppression system connected to a mechanical vacuum pump. The reactor was immersed in an oil bath, and the esterification product (oligomer) was melted under a nitrogen flow. The oil temperature was raised to 240 °C, and then 0.18 g of a catalyst mixture (30% by weight tetrabutyl titanate and 70% by weight tetrabutyl zirconate) was added, and the vacuum was increased to less than 3 mbar over 30 minutes. The reaction was carried out at 240°C and a residual pressure of less than 3 mbar for 6 hours to produce a polyester with an MFR (190°C / 2.16 kg) of 5.0 g / 10 min, a viscosity in solution of 1.04 dl / g (2 g / l, chloroform, 25°C), and color L* = 67.9, color a* = 8.1 and color b* = 12.9 as measured on the particles according to ASTM D6290.

Claims

1. A method for reusing a biodegradable polymer composition comprising a polyester blend in polymerization, the method comprising the following steps: 1) The polymer composition is reacted with water at a temperature above the melting point of at least one of the polyesters to produce a mixture of monomers and / or oligomers of the polyester as a depolymerization product. 2) Separate the portion containing impurities and / or fillers from the depolymerization product. 3) The monomers and / or oligomers are polymerized in an amount from 1% to 100% by weight relative to the polymerized mixture to produce a biodegradable polymer composition. In step 1), the polymer composition comprises at least one polyhydroxyalkyl ester and at least one polyester from a diacid-diol, and the reaction is carried out at a temperature above the melting temperature of the polyhydroxyalkyl ester, and wherein an additive from the starting polyester mixture is fed together with monomers and / or oligomers to polymerization step 3 in an amount of up to 5% by weight relative to the mixture undergoing polymerization.

2. The method according to claim 1, wherein step 1) is performed at a pressure higher than atmospheric pressure.

3. The method of claim 1, wherein in step 3), the monomer and / or the oligomer are polymerized in an amount of 2% to 50% by weight relative to the polymerized mixture.

4. The method of claim 1, wherein in step 3), the monomer and / or the oligomer are polymerized in an amount of 5% to 30% by weight relative to the polymerized mixture.

5. The method according to claim 1, wherein the polymerization in step 3) is carried out by maintaining the amount of hydroxy acid or its oligomer at 0% to 25% by weight of the total weight of the polymerization mixture.

6. The method according to any one of claims 1 to 5, wherein the polyester mixture comprises at least one aliphatic-aromatic diacid glycol polyester.

7. The method according to any one of claims 1 to 5, wherein the polyester mixture comprises at least one aliphatic diacid glycol polyester.

8. The method according to any one of claims 1 to 5, wherein the biodegradable composition comprises one or more polyhydroxyalkyl esters, one or more aliphatic diacid glycol polyesters, one or more aliphatic-aromatic diacid glycol polyesters, and one or more additional polymers comprising one or more vinyl polymers.

9. The method according to any one of claims 1 to 5, wherein the biodegradable composition comprises one or more fillers.

10. The method according to any one of claims 1 to 5, wherein the biodegradable polymer composition further comprises a polymer of natural origin.

11. The method of claim 10, comprising a pretreatment step prior to step 1 to remove the naturally derived polymer from the biodegradable polymer composition comprising the polyester mixture.

12. A polymer obtained by the recycling method according to claim 1.

13. A biodegradable polymer composition comprising the polymer according to claim 12.

14. A biodegradable article comprising the polymer of claim 12 or the biodegradable polymer composition of claim 13.