Recycling or repurposing of polyhydroxyalkanoates

Abstract

A method for depolymerizing a poly(hydroxyalkanoate) by reaction with a depolymerase enzyme to produce a mixture of poly(hydroxyalkanoate) degradation products. The present disclosure also provides methods for recycling or repurposing the poly(hydroxyalkanoate) to provide a new poly(hydroxyalkanoate) or to produce a biogas feedstock.

Description

Atty. Doc. No. DASC-113-A-WO PATENTRECYCLING OR REPURPOSING OF POLYHYDROXYALKANOATESCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 63 / 691,634, filed September 6, 2024, the entire disclosure of which is hereby incorporated by reference.TECHNICAL FIELD

[0002] This disclosure relates to biodegradable polymeric compositions. More particularly, this disclosure relates to the recycling or other repurposing of biodegradable polymeric compositions which include polyhydroxy alkanoates.BACKGROUND

[0003] Biodegradable polymers are an area of significant and increasing commercial interest. An important class of biodegradable polymer are polyhydroxyalkanoates or PHAs. PHAs are biodegradable aliphatic and aromatic polyesters typically produced by large-scale bacterial fermentation. There are a wide variety of different polymer structures within the class of PH A polymers, including homopolymer, copolymer, and terpolymers forms.

[0004] Biodegradable polymers such as polyhydroxyalkanoates may advantageously be derived from renewable biomass resources, rather than from fossil fuels. Moreover, polyhydroxyalkanoates are biodegradable and / or compostable, in contrast to conventional petroleum-based polymers which can take centuries to degrade after typical landfill disposal. Consequently, products manufactured from polyhydroxyalkanoates have a significantly reduced carbon footprint as compared to comparable products made from conventional petroleum-based polymers.

[0005] Nonetheless, it would be desirable to reduce the carbon footprint of products manufactured from polyhydroxyalkanoates. For instance, it would be desirable if, at the end of their service life, products manufactured from polyhydroxyalkanoates could be recycled and reused to form a new generation of products or if the products manufactured from polyhydroxyalkanoates could otherwise be repurposed. Such recycling or repurposing of the polyhydroxyalkanoates would further reduce the carbon footprint of thepolyhydroxyalkanoate-based products.

[0006] In certain situations, polyhydroxyalkanoates in general can experience hydrolysis due to environmental conditions such as humidity, pH shifts 9either acidic or alkaline) or as a result of other factors including chemical exposure. This can render it difficult to reuse the polyhydroxyalanoate material.

[0007] Thus, it is an object of the present disclosure to provide a method for enzymatically depolymerizing a polyhydroxyalkanoate or polyhydroxyalkanoates under controlled conditions. It is also an object of the present disclosure to provide repurposes and / or reused material emanating from polyhydroxyalkanoates, particularly biodegradable and / or compostable poly hydroxy alkanoates.

[0008] It is also an object of the present disclosure to provide a method for recycling a polyhydroxyalkanoate in order to form a second polyhydroxyalkanoate from the first poly hydroxy alkanoate.

[0009] It is a further object of the present disclosure to provide a method for using a poly hydroxy alkanoate as a carbon source for a biomass which synthesizes a second polyhydroxyalkanoate.

[0010] It is still another object of the present disclosure to provide a method for using a polyhydroxyalkanoate to produce a biogas feedstock.SUMMARY

[0011] Disclosed herein provides a method for depolymerizing a polyhydroxyalkanoate under controlled conditions and / or for using a polyhydroxyalkanoate that has been hydrolyzed as by processes due to environmental exposure (naturally or chemically). The present disclosure also provides methods for recycling or repurposing the polyhydroxyalkanoate to provide a new polyhydroxyalkanoate or to produce a biogas feedstock.

[0012] In one aspect, the present disclosure provides a method for depolymerizing a polyhydroxyalkanoate. According to one embodiment, the method includes a step of mixing an initial polyhydroxyalkanoate having an initial weight average molecular weight with a depolymerase enzyme. The amount of the depolymerase enzyme in the mixture is from about 0.0005% to about 50% of the amount of the initial poly9hydroxyalkanoate), by weight. The method also includes a step of reacting the initial polyhydroxyalkanoate with the depolymerase enzyme for a time period of at least 96 hours to produce a mixture ofpolyhydroxyalkanoate degradation products. These polyhydroxyalkanoate degradation products in the mixture have a final weight average molecular weight which is at least 10 percent less than the initial weight average molecular weight of the initial polyhydroxyalkanoate. All of the aforementioned weight average molecular weights are determined in accordance with ASTM D5296.

[0013] In certain embodiments, wherein the depolymerase enzyme is preferably a depolymerase enzyme selected from the group consisting of intracellular depolymerase, extracellular depolymerase, oligomer hydrolase, carhoxylesterase, esterase, lipase, phaZ gene products, and mixtures thereof. Also, in accordance with certain embodiments, the amount of the depolymerase enzyme in the mixture is preferably from about 0.05% to about 20% of the amount of the initial poly(hydroxyalkanoate), by weight, wherein all weight average molecular weights are determined in accordance with ASTM D5296.

[0014] In some embodiments, the depolymerase enzyme is preferably mixed and reacted with the initial poly(hydroxyalkanoate) extracellularly.

[0015] In some instances, the polymerase enzyme is preferably reacted with the initial poly(hydroxyalkanoate) at a temperature of less than 60 °C. More preferably, the polymerase enzyme is preferably reacted with the initial poly(hydroxyalkanoate) at a temperature of less than 50 °C.

[0016] According to some embodiments, the poly(hydroxyalkanoate) mixture degradation products preferably have a final weight average molecular weight which is at least 20 percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate), wherein all weight average molecular weights are determined in accordance with ASTM D5296.

[0017] In a second aspect, the present disclosure provides a method for polymerizing a poly(hydroxyalkanoate). According to one embodiment, the method includes an initial step of depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products as discussed above. The method then includes a step of combining the poly(hydroxyalkanoate) degradation products with a polymerase enzyme and a step of repolymerizing the degradation products to produce a second poly(hydroxyalkanoate). This second poly(hydroxyalkanoate) has an average molecular weight of at least 20,000 daltons, as determined in accordance with ASTM D5296.Preferably, the second poly(hydroxyalkanoate) has an average molecular weight of at least 100,000 daltons and more preferably 300,000 daltons, as determined in accordance withASTM D5296.

[0018] According to certain embodiments, the polymerase enzyme is preferably made up of phaC gene products.

[0019] In some embodiments, the amount of the polymerase enzyme is preferably from about 0.0005% to about 50% of the amount of the poly(hydroxyalkanoate) degradation products by weight. More preferably, the amount of the polymerase enzyme is from about 0.05% to about 20% of the amount of the poly (hydroxy alkanoate) degradation products by weight.

[0020] In some instances, the polymerase enzyme is preferably combined with the poly(hydroxyalkanoate) degradation products extracellularly.

[0021] In certain embodiments, the second poly(hydroxyalkanoate) is preferably made up of poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (“P(3HB-co-3HHx)”) component. More preferably, this P(3HB-co-3HHx)component is made up of from about 83 to about 99 mole percent hydroxybutyrate monomer repeat units and from about 1 to about 17 mole percent hydroxyhexanoate monomer repeat units.

[0022] In some embodiments, the second poly(hydroxyalkanoate) is preferably made up of from about 0.05 to about 25 mole percent monomer repeat units selected from the group consisting of hydroxypropionate, hydroxy valerate, hydroxyhexanoate, hydroxyoctanoate, hydroxydecanoate, and mixtures thereof.

[0023] In some instances, the second poly(hydroxyalkanoate) preferably includes a terpolymer that is made up of from about 75 to about 99.8 mole percent monomer repeat units of 3 -hydroxybutyrate, from about 0.1 to about 24.9 mole percent monomer repeat units of 3 -hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomer repeat units of a third 3 -hy doxy alkanoate having from 5 to 12 carbon atoms.

[0024] In a third aspect, the present disclosure provides a method for polymerizing a poly(hydroxyalkanoateO in which an environmentally or chemically hydrolyzed poly(hydroxyalkanoate) is added into a mixture with one or more polymerization enzymes to provide poly(hydroxyalkanoate) degradation products in whole or in part as discussed above. The method then includes a step of combining the poly(hydroxyalkanoate) degradation products with a polymerase enzyme and a step of repolymerizing the degradation products to produce a second poly (hydroxy alkanoate). This second poly(hydroxyalkanoate) has an average molecular weight of at least 20,000 daltons, as determined in accordance with ASTM D5296. Preferably, the secondpoly(hydroxyalkanoate) has an average molecular weight of at least 100,000 daltons and more preferably 300,000 daltons, as determined in accordance with ASTM D5296.

[0025] According to certain embodiments, the polymerase enzyme is preferably made up of phaC gene products.

[0026] In some embodiments, the amount of the polymerase enzyme is preferably from about 0.0005% to about 50% of the amount of the poly(hydroxyalkanoate) degradation products by weight. More preferably, the amount of the polymerase enzyme is from about 0.05% to about 20% of the amount of the poly(hydroxyalkanoate) degradation products by weight.

[0027] In some instances, the polymerase enzyme is preferably combined with the poly(hydroxyalkanoate) degradation products extracellularly.

[0028] In certain embodiments, the second poly(hydroxyalkanoate) is preferably made up of poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (“P(3HB-co-3HHx)”). More preferably, this P(3HB-co-3HHx) is made up of from about 83 to about 99 mole percent hydroxybutyrate monomer repeat units and from about 1 to about 17 mole percent hydroxyhexanoate monomer repeat units.

[0029] In some embodiments, the second poly(hydroxyalkanoate) is preferably made up of from about 0.05 to about 25 mole percent monomer repeat units selected from the group consisting of hydroxypropionate, hydroxy valerate, hydroxyhexanoate, hydroxy octanoate, hydroxydecanoate, and mixtures thereof.

[0030] In some instances, the second poly(hydroxyalkanoate) preferably includes a terpolymer that is made up of from about 75 to about 99.8 mole percent monomer repeat units of 3 -hydroxybutyrate, from about 0.1 to about 24.9 mole percent monomer repeat units of 3 -hydroxyhexanoate, and from about 0. 1 to about 24.9 mole percent monomer repeat units of a third 3 -hydoxy alkanoate having from 5 to 12 carbon atoms.

[0031] In a further aspect, the present disclosure provides an alternative method for polymerizing a poly(hydroxy alkanoate). According to one embodiment, this method includes an initial step of depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products as discussed above. The method then includes a step of mixing the poly(hydroxyalkanoate) degradation products with a biomass made up of microorganisms selected from the group consisting of Cupriavidus sp., Pseudomonas sp., Escherichia sp., Bacillus sp., Rhodococcus sp., thermophilic bacteria, halophilic bacteria, and mixtures thereof. The degradation products and the biomass are maintained at atemperature from about 25 °C to about 35 °C for a period of at least 24 hours so that the microorganisms consume at least a portion of the degradation products and intercellularly synthesize a second poly(hydroxyalkanoate). The second poly(hydroxyalkanoate) is then separated from the biomass.

[0032] In still another aspect, the present disclosure provides a method for producing a biogas. In one embodiment, this method includes an initial step of depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly (hydroxy alkanoate) degradation products as discussed above. The method then includes a step of combining the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms in an anaerobic digester, wherein the microorganisms of the biomass comprise a mixture of acetogens, methanogens, hydrolytic bacteria, and acid-forming bacteria. The degradation products and the biomass are maintained at a temperature from about 20 °C to about 60 °C for a period of at least 24 hours so that the microorganisms of the biomass digest at least a portion of the degradation products and thereby release a biogas comprising methane, hydrogen, and carbon dioxide.

[0033] In some embodiments, this biomass preferably includes at least one microorganism selected from the group consisting of Clostridium sp., Streptococcus sp., Enterobacterium sp., Pseudomonas, Bacillus, Micrococcus, Flavobacterium, Syntrophomonas, Syntrophobacter, Methanobacterium suboxydans, Methanobacterium propionicum, Syntrophospora, Desulfotomaculum thermobenzoicum subsp. Thermosyntrophicum, Desulfovibrio, Methanosarcina barkeri, Methanosarcina sp, Methanoculleus thermophilicus, Methanosarcina thermophila, Methanosphaera stadtmanae, Methanobrevibacterwolinii, Methanosaeta sp., Clostridium ultunense, Syntrophaceticus schinkii, Thermacetogenium phaeum, Thermotoga lettingae, Methanosaeta sp, Geobacter sp., Pseudomonas mendocina, Bacillus halodurans, Clostridium hastiforme, Gracilibacter thermo tolerans, Thermonas haemolytica, and mixtures thereof.

[0034] Moreover, in certain embodiments this method preferably also includes a further step of separating the biogas methane from the biogas hydrogen and carbon dioxide.DETAILED DESCRIPTION

[0035] The present disclosure first provides a method for depolymerizing a poly(hydroxyalkanoate) by mixing an initial poly(hydroxyalkanoate) with a depolymerase enzyme and reacting initial poly(hydroxyalkanoate) with the depolymerase enzyme toproduce a mixture of poly(hydroxyalkanoate) degradation products. In certain embodiments, the biodegradation products can be composed in whole or in part of material produced by the method disclosed herein. It is also considered within the purview of this disclosure to produce a mixture of suitable biodegradation products that include materials derived in whole or in part from additional source(s). One nonlimiting example of such poly(hydroxyalkanoate) material is environmentally or chemically hydrolyzed PHA. Nonlimiting examples of suitable chemically hydrolyzed PHA or suitable environmentally hydrolyzed PHA include material that has been hydrolyzed due to environmental conditions such as humidity pH shifts (either acidic or alkaline or a result of chemical exposure.

[0036] According to the present disclosure, the initial poly(hydroxyalkanoate) which is to be depolymerized is mixed with a depolymerase enzyme. Typically, the initial poly(hydroxyalkanoate) and the depolymerase enzyme are mixed extracellularly in an aqueous solution. Alternatively, the initial poly(hydroxyalkanoate) and the depolymerase enzyme may be mixed in a solution using an alcohol (such as ethanol or isopropanol) as a solvent. In still other embodiments, the depolymerase may be mixed with the initial poly(hydroxyalkanoate) without a solvent.

[0037] The initial poly(hydroxyalkanoate) may comprise poly(hydroxyalkanoate) homopolymers, copolymers, terpolymers, or a mixture thereof.

[0038] The poly(hydroxyalkanoate) has an initial weight average molecular weight, prior to depolymerization, which is typically from about 20,000 to about 2,000,000 daltons. More preferably, the initial poly(hydroxyalkanoate) has an initial weight average molecular weight from about 50,000 to about 1,000,000 daltons.

[0039] Unless otherwise noted, all weight average molecular weights described herein are determined in accordance with ASTM D5296.

[0040] Suitable depolymerase enzymes which may be mixed with the poly(hydroxyalkanoate) include, but are not limited to, depolymerase enzymes selected from the group consisting of intracellular depolymerase, extracellular depolymerase, oligomer hydrolase, carboxylesterase, esterase, lipase, phaZ gene products, and mixtures thereof.

[0041] Once combined, the amount of the depolymerase enzyme in the mixture is from about 0.0005% to about 50% of the amount of the initial poly (hydroxy alkanoate), by weight. More preferably, the amount of the depolymerase enzyme in the mixture is from about 0.05% to about 20% of the amount of the initial poly(hydroxyalkanoate), by weight.

[0042] According to the present disclosure, the poly(hydroxyalkanoate) and depolymerase enzyme are reacted with one another to produce a mixture of poly (hydroxy alkanoate) degradation products.

[0043] Typically, the poly(hydroxyalkanoate) and depolymerase enzyme are reacted with one another for a period of time of at least 96 hours and at a temperature of less than 60 °C. More preferably the reaction temperature is a temperature of less than 50 °C.

[0044] The pH of the reaction mixture may vary depending upon the particular depolymerase enzyme used but is typically from about 5.0 to about 9.0.

[0045] The reaction of the poly(hydroxyalkanoate) and depolymerase enzyme is typically carried out in a stirred tank reactor or in a recirculated tank or in a bubble column.

[0046] The reaction converts the initial poly(hydroxyalkanoate) into a mixture of poly (hydroxy alkanoate) degradation products. These poly (hydroxy alkanoate) degradation products have been observed to have a final weight average molecular weight which is at least 10 percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate). In some instances, the poly(hydroxyalkanoate) degradation products more preferably have a final weight average molecular weight which is at least 20 percent, 30 percent, 40 percent, or 50 percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate).

[0047] The present disclosure also provides a method for polymerizing a poly(hydroxyalkanoate), utilizing poly(hydroxyalkanoate) degradation products such as those described above. According to this method, the aforementioned poly(hydroxyalkanoate) degradation products are combined with a polymerase enzyme, and the degradation products are then repolymerized to produce a second poly(hydroxyalkanoate). In general, the poly(hydroxyalkanoate) degradation products and the polymerase enzyme are combined extracellularly in an aqueous solution.

[0048] Preferred polymerase enzymes which may be mixed with the poly(hydroxyalkanoate) include, but are not limited to, phaC gene products.

[0049] The amount of the polymerase enzyme in the mixture is from about 0.0005% to about 50% of the amount of the initial poly (hydroxy alkanoate), by weight. More preferably, the amount of the depolymerase enzyme in the mixture is from about 0.05% to about 20% of the amount of the initial poly(hydroxyalkanoate), by weight.

[0050] After repolymerization, the resultant second poly(hydroxyalkanoate) generally has a weight average molecular weight of at least 20,000 daltons, as determined inaccordance with ASTM D5296. Preferably, the second poly(hydroxyalkanoate) has an average molecular weight of at least 100,000 daltons and more preferably 300,000 daltons, as determined in accordance with ASTM D5296.

[0051] The second poly(hydroxyalkanoate) produced from the repolymerization reaction may comprise poly(hydroxyalkanoate) homopolymers, copolymers, terpolymers, or a mixture thereof.

[0052] In some embodiments, the second poly(hydroxyalkanoate) may comprise a homopolymer such as poly (hydroxybutyrate).

[0053] In other embodiments, the second poly(hydroxyalkanoate) may comprise a copolymer, such as poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (“P(3HB-co-3HHx)”). More preferably, this P(3HB-co-3HHx) is made up of from about 83 to about 99 mole percent hydroxybutyrate monomer repeat units and from about 1 to about 17 mole percent hydroxyhexanoate monomer repeat units.

[0054] In some embodiments, the second poly(hydroxyalkanoate) is preferably made up of from about 0.5 to about 25 mole percent monomer repeat units selected from the group consisting of hydroxypropionate, hydroxy valerate, hydroxyhexanoate, hydroxy octanoate, hydroxydecanoate, and mixtures thereof.

[0055] In still other embodiments, the second poly(hydroxyalkanoate) may comprise a terpolymer which includes from about 75 to about 99.8 mole percent monomer repeat units of 3-hydroxybutyrate, from about 0. 1 to about 24.9 mole percent monomer repeat units of 3-hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomer repeat units of a third 3 -hy doxy alkanoate having from 5 to 12 carbon atoms, (valerate preferred third monomer)

[0056] Alternatively, in a further aspect of the present disclosure, a new poly(hydroxyalkanoate) may be produced by using the previously described poly(hydroxyalkanoate) degradation products as a carbon source (i.e. food) for a biomass which synthesizes a second poly(hydroxyalkanoate). In accordance with this method, an initial poly(hydroxyalkanoate) is depolymerized as discussed above to provide a mixture of poly(hydroxyalkanoate) degradation products. These poly(hydroxyalkanoate) degradation products are then mixed with a biomass made up of microorganisms selected from the group consisting of Cupriavidus sp., Pseudomonas sp., Escherichia sp., Bacillus sp., halophilic bacteria, thermophilic bacteria, and mixtures thereof. The degradation products and the biomass are maintained at a temperature from about 25 °C to about 35 °C for aperiod of at least 24 hours so that the microorganisms consume at least a portion of the degradation products and intercellularly synthesize a second poly (hydroxy alkanoate). The second poly(hydroxyalkanoate) is then separated from the biomass.

[0057] Examples of suitable halophilic bacterial include bacteria selected from the group consisting of Haloarcula sp., Haloferax sp., Halopiger sp., Haloquadratum sp., Halobacterium sp., Halostagnicola sp., Haloterrigena sp., Halobiforma sp., Halococcus sp., Halorubrum sp., Halalkalicoccus sp., Halogeometricum sp., Halogranum sp., Natrinema sp., Natronobacterium sp., Natronorubrum sp., Natronococcus sp. Halomonas sp., Cobetia sp., Paracoccus sp. and mixtures thereof.

[0058] Examples of suitable thermophilic bacteria include bacteria selected from the group consisting of Chelatococcus thermostellatus, Caldimonas taiwanesis, Aneurinibacillus sp.Hl, Tepidimonas taiwanensis LMG 22826, Moorella thermoacetica, Schlegelella sp., Kyrpidia spormannii, Moorella thermoautotrophica, Thermus thermophilus, Archaeoglobales sp., Ferroglobus placidus, Geoglobus sp., Geobacillus species, and mixtures thereof.

[0059] In still another aspect, the present disclosure provides a method for producing a biogas. In one embodiment, this method includes an initial step of depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products as discussed above. The method then includes a step of the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms in an anaerobic digester, wherein the microorganisms of the biomass comprise a mixture of acetogens, methanogens, hydrolytic bacteria, and acid-forming bacteria. The degradation products and the biomass are maintained at a temperature from about 20 °C to about 60 °C for a period of at least 24 hours so that the microorganisms of the biomass digest at least a portion of the degradation products and thereby release a biogas comprising methane, hydrogen, and carbon dioxide.

[0060] In some embodiments, this biomass preferably includes at least one microorganism selected from the group consisting of Clostridium sp., Streptococcus sp., Enterobacterium sp., Pseudomonas, Bacillus, Micrococcus, Flavobacterium, Syntrophomonas, Syntrophobacter, Methanobacterium suboxydans, Methanobacterium propionicum, Syntrophospora, Desulfotomaculum thermobenzoicum subsp. Thermosyntrophicum, Desulfovibrio, Methanosarcina barkeri, Methanosarcina sp, Methanoculleus thermophilicus, Methanosarcina thermophila, Methanosphaera stadtmanae,Methanobrevibacterwolinii, Methanosaeta sp., Clostridium ultunense, Syntrophaceticus schinkii, Thermacetogenium phaeum, Thermotoga lettingae, Methanosaeta sp, Geobacter sp., Pseudomonas mendocina, Bacillus halodurans, Clostridium hastiforme, Gracilibacter thermo tolerans, Thermonas haemolytica, and mixtures thereof.

[0061] Moreover, in certain embodiments this method preferably also includes a further step of separating the biogas methane from the biogas hydrogen and carbon dioxide.EMODIMENTS

[0062] The present disclosure is also further illustrated by the following embodiments:

[0063] Embodiment 1. A method for depolymerizing a poly(hydroxyalkanoate) comprising the steps of:

[0064] mixing an initial poly(hydroxyalkanoate) having an initial weight average molecular weight with a depolymerase enzyme, wherein the amount of the depolymerase enzyme in the mixture is from about 0.0005% to about 50% of the amount of the initial poly(hydroxyalkanoate), by weight; and

[0065] reacting the initial poly (hydroxy alkanoate) with the depolymerase enzyme for a period of time of at least 96 hours to produce a mixture of poly(hydroxyalkanoate) degradation products, wherein the poly(hydroxyalkanoate) degradation products in the mixture have a final weight average molecular weight which is at least 10 percent less than the initial weight average molecular weight of the initial poly (hydroxy alkanoate), wherein all weight average molecular weights are determined in accordance with ASTM D5296.

[0066] Embodiment 2. The method of Embodiment 1, wherein the depolymerase enzyme is a depolymerase enzyme selected from the group consisting of intracellular depolymerase, extracellular depolymerase, oligomer hydrolase, carboxylesterase, esterase, lipase, phaZ gene products, and mixtures thereof.

[0067] Embodiment 3. The method of any of preceding embodiments, wherein the amount of the depolymerase enzyme in the mixture is from about 0.05% to about 20% of the amount of the initial poly (hydroxy alkanoate), by weight, wherein all weight average molecular weights are determined in accordance with ASTM D5296.

[0068] Embodiment 4. The method of any of preceding embodiments, wherein the depolymerase enzyme is mixed and reacted with the initial poly(hydroxyalkanoate) extracellularly.

[0069] Embodiment 5. The method of any of preceding embodiments, wherein the polymerase enzyme is reacted with the initial poly(hydroxyalkanoate) at a temperature ofless than 60 °C.

[0070] Embodiment 6. The method of any of preceding embodiments, wherein the polymerase enzyme is reacted with the initial poly(hydroxyalkanoate) at a temperature of less than 50 °C.

[0071] Embodiment 7. The method of any of preceding embodiments, wherein the poly(hydroxyalkanoate) mixture degradation products have a final weight average molecular weight which is at least 20 percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate), wherein all weight average molecular weights are determined in accordance with ASTM D5296.

[0072] Embodiment 8. A method for polymerizing a poly(hydroxyalkanoate) comprising the steps of:

[0073] depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with any of Embodiments 1 - 7;

[0074] combining the poly(hydroxyalkanoate) degradation products with a polymerase enzyme; and

[0075] repolymerizing the degradation products to produce a second poly(hydroxyalkanoate) having a weight average molecular weight of at least 20,000 daltons, as determined in accordance with ASTM D5296.

[0076] Embodiment 9. The method of Embodiment 8, wherein the polymerase enzyme comprises phaC gene products.

[0077] Embodiment 10. The method of Embodiments 8 or 9, wherein the amount of the polymerase enzyme is from about 0.0005% to about 50% of the amount of the poly(hydroxyalkanoate) degradation products by weight.

[0078] Embodiment 11. The method of any of Embodiments 8 - 10, wherein the amount of the polymerase enzyme is from about 0.05% to about 20% of the amount of the poly(hydroxyalkanoate) degradation products by weight.

[0079] Embodiment 12. The method of any of Embodiments 8 - 11, wherein the polymerase enzyme is combined with the poly(hydroxyalkanoate) degradation products extracellularly.

[0080] Embodiment 13. The method of any of Embodiments 8 - 12, wherein the second poly(hydroxyalkanoate) has a weight average molecular weight of least 100,000 daltons, as determined in accordance with ASTM D5296.

[0081] Embodiment 14. The method of any of Embodiments 8 - 13, wherein the second poly(hydroxyalkanoate) comprises poly-3-hydroxybutyrate-co-3-hydroxyhexanoate C‘P(3HB-co-3HHx)”).

[0082] Embodiment 15. The method of Embodiment 13, wherein the P(3HB-co-3HHx) comprises from about 83 to about 99 mole percent hydroxybutyrate monomer repeat units and from about 1 to about 17 mole percent hydroxyhexanoate monomer repeat units.

[0083] Embodiment 16. The method of any of Embodiments 8 — 13, wherein the second poly(hydroxyalkanoate) comprises from about 0.05 to about 25 mole percent monomer repeat units selected from the group consisting of hydroxypropionate, hydroxyvalerate, hydroxyhexanoate, hydroxyoctanoate, hydroxydecanoate, and mixtures thereof.

[0084] Embodiment 17. The method of any of Embodiments 8 - 13, wherein the second poly(hydroxyalkanoate) comprises a terpolymer which includes from about 75 to about 99.8 mole percent monomer repeat units of 3 -hydroxy butyrate, from about 0.1 to about 24.9 mole percent monomer repeat units of 3-hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomer repeat units of a third 3-hydoxyalkanoate having from 5 to 12 carbon atoms.

[0085] Embodiment 18. A method for polymerizing a poly(hydroxyalkanoate) comprising the steps of:

[0086] depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with any of Embodiments 1 - 7;

[0087] mixing the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms selected from the group consisting of Cupriavidus sp., Pseudomonas sp., Escherichia sp., Bacillus sp., thermophilic bacteria, halophilic bacteria, and mixtures thereof.

[0088] maintaining the degradation products and the biomass at a temperature from about 25 °C to about 35 °C for a period of at least 24 hours so that the microorganisms consume at least a portion of the degradation products and intercellularly synthesize a second poly(hydroxyalkanoate); and

[0089] separating the second poly(hydroxyalkanoate) from the biomass.

[0090] Embodiment 19. A method for producing a biogas comprising the steps of:

[0091] depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with any of Embodiments 1 -7;

[0092] mixing the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms in an anaerobic digester, wherein the microorganisms of the biomass comprise a mixture of acetogens, methanogens, hydrolytic bacteria, and acidforming bacteria.

[0093] maintaining the degradation products and the biomass at a temperature from about 20 °C to about 60 °C for a period of at least 24 hours so that the microorganisms of the biomass digest at least a portion of the degradation products and thereby release a biogas comprising methane, hydrogen, and carbon dioxide.

[0094] Embodiment 20. The method of Embodiment 19, wherein the biomass comprises at least one microorganism selected from the group consisting of Clostridium sp., Streptococcus sp., Enterobacterium sp., Pseudomonas, Bacillus, Micrococcus, Flavobacterium, Syntrophomonas, Syntrophobacter, Methanobacterium suboxydans, Methanobacterium propionicum, Syntrophospora, Desulfotomaculum thermobenzoicum subsp. Thermos yntrophicum, Desulfovibrio, Methanosarcina barkeri, Methanosarcina sp, Methanoculleus thermophilicus, Methanosarcina thermophila, Methanosphaera stadtmanae, Methanobrevibacterwolinii, Methanosaeta sp., Clostridium ultunense, Syntrophaceticus schinkii, Thermacetogenium phaeum, Thermotoga lettingae, Methanosaeta sp, Geobacter sp., Pseudomonas mendocina, Bacillus halodurans, Clostridium hastiforme, Gracilibacter thermo tolerans, Thermonas haemolytica, and mixtures thereof.

[0095] Embodiment 21. The method of Embodiments 19 or 20 further comprising a step of separating the biogas methane from the biogas hydrogen and carbon dioxide.

[0096] While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

What is claimed is:

1. A method for depolymerizing a poly(hydroxyalkanoate) comprising steps of: mixing an initial poly(hydroxyalkanoate) having an initial weight average molecular weight with an amount of depolymerase enzyme to produce a mixture, wherein the amount of the depolymerase enzyme in the mixture is from about 0.0005% to about 50% of the amount of the initial poly (hydroxy alkanoate), by weight; and reacting the initial poly(hydroxyalkanoate) with the depolymerase enzyme for a period of time of at least 96 hours to produce a mixture of poly(hydroxyalkanoate) degradation products, wherein the mixture of poly(hydroxyalkanoate) degradation products in the mixture have a final weight average molecular weight which is at least 10 percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate), wherein all weight average molecular weights are determined in accordance with ASTM D5296.

2. The method of Claim 1 , wherein the depolymerase enzyme is a depolymerase enzyme selected from the group consisting of intracellular depolymerase, extracellular depolymerase, oligomer hydrolase, carboxylesterase, esterase, lipase, phaZ gene products, and mixtures thereof.

3. The method of Claim 1 or 2, wherein the amount of the depolymerase enzyme in the mixture is from about 0.05% to about 20% of the amount of the initial poly(hydroxyalkanoate), by weight, wherein all weight average molecular weights are determined in accordance with ASTM D5296.

4. The method of Claim 1, 2 or 3, wherein the depolymerase enzyme is mixed and reacted with the initial poly(hydroxyalkanoate) extracellularly.

5. The method of Claim 1, 2, 3, or 4, wherein the depolymerase enzyme is reacted with the initial poly(hydroxyalkanoate) at a temperature of less than 60 °C.

6. The method of Claim 1, 2, 3, 4 or 5, wherein the depolymerase enzyme is reacted with the initial poly(hydroxyalkanoate) at a temperature of less than 50 °C.

7. The method of any preceding claims, wherein the poly (hydroxy alkanoate) mixture degradation products have a final weight average molecular weight which is at least 20percent less than the initial weight average molecular weight of the initial poly(hydroxyalkanoate), wherein all weight average molecular weights are determined in accordance with ASTM D5296.

8. A method for polymerizing a poly(hydroxyalkanoate) comprising the steps of; depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with Claim 1 ; combining the poly(hydroxyalkanoate) degradation products with a polymerase enzyme; and repolymerizing the degradation products to produce a second poly(hydroxyalkanoate) having a weight average molecular weight of at least 20,000 daltons, as determined in accordance with ASTM D5296.

9. The method of Claim 8, wherein the polymerase enzyme comprises phaC gene products.

10. The method of Claim 8 or 9, wherein the amount of the polymerase enzyme is from about 0.0005% to about 50% of the amount of the poly(hydroxyalkanoate) degradation products by weight.

11. The method of Claim 8, 9 or 10, wherein the amount of the polymerase enzyme is from about 0.05% to about 20% of the amount of the poly(hydroxyalkanoate) degradation products by weight.

12. The method of Claim 8, 9, 10 or 11, wherein the polymerase enzyme is combined with the poly (hydroxy alkanoate) degradation products extracellularly.

13. The method of Claim 8, 9, 10, 11, or 12, wherein the second poly(hydroxyalkanoate) has a weight average molecular weight of at least 100,000 daltons, as determined in accordance with ASTM D5296.

14. The method of Claim 8, 9, 10, 11, 12, or 13 wherein the second poly(hydroxyalkanoate) comprises a poly-3 -hydroxybutyrate-co-3-hydroxyhexanoate (“P(3HB-co-3HHx)”).

15. The method of Claim 8.

9.

10.

11.

12. 13 or 14, wherein the P(3HB-co-3HHx)comprises from about 83 to about 99 mole percent hydroxy butyrate monomer repeat units and from about 1 to about 17 mole percent hydroxyhexanoate monomer repeat units.

16. The method of Claim 8, 9, 10 11, 12, 13, 14, or 15, wherein the second poly(hydroxyalkanoate) comprises from about 0.05 to about 25 mole percent monomer repeat units selected from the group consisting of hydroxypropionate, hydroxyvalerate, hydroxyhexanoate, hydroxyoctanoate, hydroxydecanoate, and mixtures thereof.

17. The method of Claim 8, 9, 10, 11, 12, 13, 14, 15 or 16 wherein the second poly(hydroxyalkanoate) comprises a terpolymer which includes from about 75 to about 99.8 mole percent monomer repeat units of 3-hydroxybutyrate, from about 0.1 to about 24.9 mole percent monomer repeat units of 3-hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomer repeat units of a third 3-hydoxyalkanoate having from 5 to 12 carbon atoms.

18. A method for polymerizing a poly(hydroxyalkanoate) comprising the steps of: depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with Claim 1; mixing the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms selected from the group consisting of Cupriavidus sp. , Pseudomonas sp., Escherichia sp., Bacillus sp., thermophilic bacteria, halophilic bacteria, and mixtures thereof; maintaining the degradation products and the biomass at a temperature from about 25 °C to about 35 °C for a period of at least 24 hours so that the microorganisms consume at least a portion of the degradation products and intercellularly synthesize a second poly(hydroxyalkanoate); and separating the second poly(hydroxyalkanoate) from the biomass.

19. A method for producing a biogas comprising the steps of: depolymerizing a poly(hydroxyalkanoate) to produce a mixture of poly(hydroxyalkanoate) degradation products in accordance with Claim 1; mixing the poly(hydroxyalkanoate) degradation products with a biomass comprising microorganisms in an anaerobic digester, wherein the microorganisms of the biomass comprise a mixture of acetogens, methanogens, hydrolytic bacteria, andacid-forming bacteria; maintaining the degradation products and the biomass at a temperature from about 20 °C to about 60 °C for a period of at least 24 hours so that the microorganisms of the biomass digest at least a portion of the degradation products and thereby release a biogas comprising methane, hydrogen, and carbon dioxide.

20. The method of Claim 19, wherein the biomass comprises at least one microorganism selected from the group consisting of Clostridium sp., Streptococcus sp., Enterobacterium sp., Pseudomonas, Bacillus, Micrococcus, Flavobacterium, Syntrophomonas, Syntrophobacter, Methanobacterium suboxydans, Methanobacterium propionicum, Syntrophospora, Desulfotomaculum thermobenzoicum subsp. Thermosyntrophicum, Desulfovibrio, Methanosarcina barkeri, Methanosarcina sp, Methanoculleus thermophilicus, Methanosarcina thermophila, Methanosphaera stadtmanae, Methanobrevibacterwolinii, Methanosaeta sp., Clostridium ultunense, Syntrophaceticus schinkii, Thermacetogenium phaeum, Thermotoga lettingae, Methanosaeta sp, Geobacter sp., Pseudomonas mendocina, Bacillus halodurans, Clostridium hastiforme, Gracilibacter thermotolerans, Thermonas haemolytica, and mixtures thereof.

21. The method of Claim 19 or 20 further comprising a step of separating the biogas methane from the biogas hydrogen and carbon dioxide.