High-flow polyhydroxyalkanoate composition, and polyhydroxyalkanoate molded body and preparation method therefor

Abstract

The present invention relates to the technical field of polyhydroxyalkanoate materials. Specifically disclosed are a high-flow polyhydroxyalkanoate composition, and a polyhydroxyalkanoate molded body and a preparation method therefor. The polyhydroxyalkanoate composition comprises polyhydroxyalkanoate and a melt flow rate adjustment aid, wherein the melt flow rate adjustment aid is at least one alkali metal compound. The melt flow rate adjustment aid can promote ester bond breakage of polyhydroxyalkanoate, thereby reducing the weight-average molecular weight of the polyhydroxyalkanoate, and improving the melt flow rate of the polyhydroxyalkanoate. In addition, the melt flow rate adjustment aid provided by the present invention has the advantages of being safe, environmentally friendly, food-contactable, etc., and has wide usage scenarios.

Description

A high-fluidity polyhydroxyalkanoate composition, molded body and preparation method thereof Technical Field

[0001] The present invention relates to the technical field of polyhydroxyalkanoate materials, and in particular to a high-fluidity polyhydroxyalkanoate composition, a formed body and a preparation method thereof. Background Art

[0002] Polyhydroxyalkanoates (PHAs or PHAs) are intracellular polyesters synthesized by many microorganisms and are natural high-molecular-weight biomaterials. Most of the monomers of polyhydroxyalkanoates are 3-hydroxy fatty acids with a chain length of 3 to 14 carbon atoms. Their side chains are highly variable saturated or unsaturated, linear or branched, aliphatic or aromatic groups. The diversity of their compositional structures leads to diverse performance, giving them obvious advantages in applications. At the same time, polyhydroxyalkanoates are a bio-based polymer that is biodegradable in the marine environment. They can solve the environmental problems caused by discarded plastics and have excellent biocompatibility and mechanical properties. Therefore, they can be processed into various molded bodies, such as films, straws, tableware, medical stents, daily necessities, etc.

[0003] In the field of polymer materials, different applications require the use of raw materials with different melt flow rates (also known as melt index, MFR) for processing. For example, straw extrusion and thin-wall injection molding require completely different melt flow rates. Because polyhydroxyalkanoates are natural polymer biomaterials synthesized by microorganisms, their melt flow rate cannot be adjusted through polymerization processes like chemically polymerized polymers. Therefore, a certain method is needed to achieve controllable adjustment of the melt flow rate to adapt to more application scenarios.

[0004] Some existing technologies use methods such as chemical depolymerization to reduce the weight-average molecular weight of polymer materials and increase their MFR. However, these methods not only require specialized reactors, adding additional processing costs, but also introduce depolymerization catalysts or initiators, such as organotin compounds, that may be incompatible with the biocompatibility of the polymer composition. With the increasing global focus on safe and environmentally friendly chemicals, there is a desire to reduce the use of organotin catalysts, and some regulatory organizations have even restricted the scope and concentration of their use.

[0005] Furthermore, although there are studies in the prior art on the melt index of polymer materials such as polyethylene, polylactic acid, polybutylene adipate, polycaprolactone, and polybutylene terephthalate-adipate, these polymer materials differ from polyhydroxyalkanoates in monomers, and in terms of intermolecular configuration and intermolecular interactions, resulting in significant differences in physical properties. This, in turn, makes it difficult to mutually transfer and apply the melt index adjustment methods and the regulators used for these polymer materials. Therefore, it is urgent to develop a melt index regulator specifically for polyhydroxyalkanoates.

[0006] Summary of the Invention

[0007] One of the objects of the present invention is to provide a polyhydroxyalkanoate composition.

[0008] A second object of the present invention is to provide a polyhydroxyalkanoate shaped body prepared from the polyhydroxyalkanoate composition.

[0009] A third object of the present invention is to provide a method for preparing the above-mentioned polyhydroxyalkanoate molded body.

[0010] A fourth object of the present invention is to provide an application of an alkali metal compound in regulating the melt index of polyhydroxyalkanoate.

[0011] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0012] In a first aspect, the present invention provides a polyhydroxyalkanoate composition comprising:

[0013] polyhydroxyalkanoates, and

[0014] A melt flow rate regulating aid, wherein the melt flow rate regulating aid is at least one alkali metal compound.

[0015] Exemplary components included in the polyhydroxyalkanoate composition will be described in detail below.

[0016] Polyhydroxyalkanoates:

[0017] The polyhydroxyalkanoate may be a single polymer or a combination of two or more polymers, wherein each polymer may contain one or more monomers (ie, the structural units in the polymer may be one or more).

[0018] Specifically, any polymer contains a structural unit represented by the following general formula I: [OCHR1(CH2) x CO] General Formula I

[0019] Where R1 is C p H 2p+1The alkyl group represented by the formula (a) is an integer from 1 to 15, preferably an integer from 1 to 10, and more preferably an integer from 1 to 8; R1 includes, for example, a linear or branched alkyl group such as a methyl group, an ethyl group, a propyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, and a hexyl group;

[0020] x is 1, 2, or 3.

[0021] When x = 1, Formula I represents a 3-hydroxyalkanoate structural unit; when x = 2, Formula I represents a 4-hydroxyalkanoate structural unit; and when x = 3, Formula I represents a 5-hydroxyalkanoate structural unit. Among these, 3-hydroxyalkanoate structural units and 4-hydroxyalkanoate structural units are more common, such as the 3-hydroxybutyrate structural unit (sometimes referred to as 3HB) and the 4-hydroxybutyrate structural unit (sometimes referred to as 4HB).

[0022] Preferably, the polyhydroxyalkanoate includes at least one poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as PHB).

[0023] Furthermore, the poly(3-hydroxyalkanoate) is a poly(3-hydroxybutyrate) homopolymer containing only 3-hydroxybutyrate structural units, or a poly(3-hydroxybutyrate) copolymer containing 3-hydroxybutyrate structural units and other hydroxyalkanoate structural units.

[0024] The method for producing the polyhydroxyalkanoate of the present invention is not particularly limited, and may be a method of producing by chemical synthesis or a method of producing by microorganisms.

[0025] The polyhydroxyalkanoate of the present invention is particularly preferably a polyhydroxyalkanoate produced by a microorganism. In the polyhydroxyalkanoate produced by the microorganism, all 3-hydroxyalkanoate structural units are contained in the form of (R) 3-hydroxyalkanoate structural units. In one embodiment of the present invention, microbial cells containing a polyhydroxyalkanoate resin can be obtained by culturing a microorganism capable of producing polyhydroxyalkanoate.

[0026] Furthermore, polyhydroxyalkanoate is a general term for poly(3-hydroxyalkanoate) polymerized with 3-hydroxybutyric acid as a monomer. Poly(3-hydroxyalkanoate) (PHB) can be a homopolymer of 3-hydroxybutyric acid, poly(3-hydroxybutyric acid), or a copolymer of 3-hydroxybutyric acid and other hydroxyalkanoic acids. As other hydroxyalkanoic acids, 3-hydroxyalkanoic acid, 4-hydroxyalkanoic acid, 5-hydroxyalkanoic acid, etc. can be used. Among them, 3-hydroxyalkanoic acid, for example, can be selected from 3-hydroxyhexanoic acid (hereinafter also referred to as 3HH), 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxypentadecanoic acid and 3-hydroxyhexadecanoic acid. One or more monomers can be used.

[0027] Among them, in the poly (3-hydroxyalkanoate), the average content ratio of the 3-hydroxybutyrate structural unit to other 3-hydroxyalkanoate structural units is 50 / 50 to 99 / 1 (mol% / mol%); when the polyhydroxyalkanoate raw material is a mixture of two or more polyhydroxyalkanoate monomers, the average content ratio refers to the molar ratio of each monomer contained in the entire mixture.

[0028] In short, specific examples of poly(3-hydroxyalkanoate) include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviated as P3HB3HV, hereinafter referred to as PHBV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (hereinafter referred to as P3HB3HV3HH), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviated as P3 HB3HH, hereinafter referred to as PHBH), poly (3-hydroxybutyrate-co-3-hydroxyheptanoate), poly (3-hydroxybutyrate-co-3-hydroxyoctanoate) (hereinafter referred to as PHBO), poly (3-hydroxybutyrate-co-3-hydroxynonanoate), poly (3-hydroxybutyrate-co-3-hydroxydecanoate), poly (3-hydroxybutyrate-co-3-hydroxyundecanoate), poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as: P3HB4HB, hereinafter referred to as P34HB), etc.

[0029] Furthermore, as poly(3-hydroxyalkanoate), from the perspective of ease of industrial production, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), etc. are preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred. The composition ratio of the monomer units constituting the copolymer PHBH of the two components 3HB and 3HH is not particularly limited. When the total of all monomer units is set to 100 mol%, the 3HH unit can be 1 mol% to 50 mol%, 1 mol% to 25 mol%, or 1 mol% to 15 mol%.

[0030] In one embodiment of the present invention, the microorganism having the ability to produce polyhydroxyalkanoates is not particularly limited, and microorganisms isolated from nature, microorganisms preserved in a strain collection institution (e.g., IFO, ATCC, etc.), or mutants and transformants prepared from these microorganisms can be used. For example, the genus Cupriavidus, the genus Alcaligenes, the genus Ralstonia, the genus Pseudomonas, the genus Bacillus, the genus Azotobacter, the genus Nocardia, the genus Aeromonas, etc. are particularly preferred strains such as Alcaligenes lipolytica (A.lipolytica), A.latus, A.caviae, A.hydrophila, and C.necator. In addition, when the microorganism does not originally have the ability to produce polyhydroxyalkanoates, or when the production volume is low, a transformant obtained by introducing a synthase gene of the target polyhydroxyalkanoate and / or its mutant into the microorganism can also be used. The synthase gene of the polyhydroxyalkanoate used in the production of such a transformant is not particularly limited, but is preferably a gene for the polyhydroxyalkanoate synthase from Aeromonas caviae.

[0031] Furthermore, the polyhydroxyalkanoate has a weight-average molecular weight of 100,000 to 1,000,000, preferably 200,000 to 900,000, and even more preferably 300,000 to 800,000. A weight-average molecular weight of less than 100,000 tends to reduce the mechanical properties of the resulting polyhydroxyalkanoate resin molded article. On the other hand, a weight-average molecular weight exceeding 1,000,000 tends to increase the load on machinery during melt processing, resulting in reduced productivity.

[0032] Studies have shown that the melt flow rate regulating agent of the present invention can adjust the weight average molecular weight and melt flow rate of a molded body prepared from polyhydroxyalkanoates with different structural monomers, or adjust the weight average molecular weight and melt flow rate of a molded body prepared from a mixture of multiple polyhydroxyalkanoates.

[0033] Melt flow rate regulating additives:

[0034] The melt flow rate regulating agent is one or more alkali metal compounds. Alkali metal compounds refer to compounds with alkali metals as cations and other anions, wherein the anions can be hydroxides, organic acid radicals, or inorganic acid radicals. In other words, the alkali metal compounds include one or more alkali metal hydroxides, alkali metal organic acid salts, and alkali metal inorganic acid salts.

[0035] Among them, alkali metals refer to the six metal elements in Group IA of the periodic table except hydrogen (H), namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The outermost layer of the atoms of alkali metal elements has one electron, which is easy to lose (forming M + , valence is +1), making the sub-outer layer become the outermost layer and reaching a stable structure of 8 or 2 electrons (that is, reaching a stable state of electron saturation). Therefore, alkali metal elements have strong metallic properties, their elements are very active, have strong reducing properties, and their hydroxides (MOH) are all strong bases.

[0036] In some embodiments, the melt flow rate regulating aid is selected from one or more of alkali metal hydroxides, alkali metal organic acid salts, alkali metal inorganic acid salts, and the like.

[0037] In some embodiments, the melt flow rate regulating aid is an alkali metal hydroxide, such as one or more selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, and the like.

[0038] In some embodiments, the melt flow rate regulating aid is an alkali metal organic acid salt, such as potassium acetate, sodium acetate, lithium acetate, cesium acetate, rubidium acetate, sodium stearate, potassium stearate, lithium stearate, cesium pivalate, L-sodium lactate, L-lithium lactate, L-potassium lactate, D-sodium lactate, D-lithium lactate, D-potassium lactate, DL-sodium lactate, DL-lithium lactate, DL-potassium lactate, lithium bis(oxaloyl)borate, potassium sorbate, sodium 3-hydroxybutyrate, sodium 2-hydroxybutyrate, etc. One or more.

[0039] In some embodiments, the melt flow rate regulating agent is an alkali metal inorganic acid salt, such as one or more of lithium zirconate, lithium tungstate, lithium aluminate, lithium titanate, lithium arsenate, sodium zirconate, potassium fluorozirconate, potassium chloropalladate and potassium zirconium carbonate.

[0040] The present invention has found that when alkali metal compounds are added as additives to polyhydroxyalkanoates, the weight average molecular weight can be lower than that of polyhydroxyalkanoates without any additives during thermoplastic processing to prepare various molded bodies, and the melt flow rate (MFR) of the particle molded body can be higher, making the molded body adaptable to more processing methods.

[0041] In some embodiments, the amount of the melt flow rate regulating agent added is 0.0001%-10% of the mass of the polyhydroxyalkanoate; preferably 0.001%-5%.

[0042] Degradation reactions are also known as reactions that cause a decrease in the molecular weight of a polymer. There are many reasons for degradation, the most common of which are thermal degradation, chemical degradation, and mechanical degradation. Examples of chemical degradation include: the molecular chains of polyether, polyester, and polyesteramine polymers break and the degree of polymerization decreases under the catalysis of acids or bases. Most chemical degradation is the reverse reaction of polycondensation. For example, starch or cellulose decomposes under the catalysis of acids, bases, or enzymes to produce oligosaccharides. For example, surgical sutures made from polylactic acid do not need to be removed after the wound heals. This is because polylactic acid is hydrolyzed into lactic acid in the body, which is then absorbed by the organism. Another example is the degradation of polyester at a certain temperature and pressure using ethylene glycol using dibutyltin dilaurate as a catalyst, resulting in a reactive polymer precursor with active terminal functional groups.

[0043] Unlike existing polymer catalytic degradation technologies, this study found that polyhydroxyalkanoates (PHA) have strong thermal motion in the molten state, and alkali metal compounds can act on the ester bonds in the main chain of the PHA, breaking them, reducing the weight-average molecular weight, and increasing the melt flow rate. This study found that using alkali metal compounds to adjust the weight-average molecular weight of the PHA can effectively adjust the melt flow rate of the polyester, and the adjustment can maintain a uniform molecular weight distribution. Unlike the alcoholysis of polyesters in the presence of small molecule alcohols, the direct action of alkali metal compounds can induce chain scission reactions in PHA, and the entire process is independent of the presence or amount of small molecule alcohols.

[0044] Therefore, the amount of alkali metal compound added is related to the number of ester bonds that can act. Adding too much will result in the excess melt flow rate regulating additive having no substantial effect. At the same time, in order to ensure that the material still has certain performance, the melt flow rate cannot be too high, that is, the weight average molecular weight cannot drop too low. Therefore, it is further preferred that the amount of the alkali metal compound added is 0.001%-2% of the mass of the polyhydroxyalkanoate. Studies have shown that by controlling the addition ratio of the alkali metal compound within this preferred range, the processability and mechanical properties of the molded body can be balanced. Typically, but not restrictively, the amount of the alkali metal compound added can be, for example, 0.001%, 0.01%, 0.1%, 0.5%, 1%, 1.5%, or 2%.

[0045] Other components:

[0046] In addition, other additives (or adjuvants) may be added to the composition according to the production requirements of the molded article without inhibiting the effects of the present invention. These may include, but are not limited to, nucleating agents, plasticizers, toughening agents, reinforcing agents, crosslinking agents, chain extenders, lubricants, fillers, and other organic or inorganic materials. These may be used alone or in combination of two or more. Furthermore, the amount of additives added may be adjusted according to production requirements, and the present invention does not particularly limit this.

[0047] Preferably, in some embodiments, the polyhydroxyalkanoate composition further comprises a nucleating agent. Adding a nucleating agent can reduce the time required for the polyhydroxyalkanoate to stop sticking, thereby improving processing efficiency.

[0048] More preferably, the amount of the nucleating agent added to the polyhydroxyalkanoate composition is 0.1-10% by weight, for example 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 8%. Too much nucleating agent will reduce the mechanical properties of the polyhydroxyalkanoate.

[0049] In some embodiments, the nucleating agent can be one or more selected from calcium carbonate, talc, titanium dioxide, uracil, galactitol, zirconium hydrogen phosphate, amide compounds, and boron nitride; wherein the amide compound is selected from N,N'-hexyl-1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide, tetramethylthiuram disulfide; tetramethylthioperoxydicarbonamide, N,N'-1,6-hexanediylbis[N-(2,2,6,6-tetramethylthiuram disulfide, One or more of: [methyl-4-piperidinyl)]-formamide, N,N'-1,2-ethanediylbisoctadecylamide, (Z,Z)-N,N'-1,2-ethanediylidenebis-9-octadecylamide, behenamide (behenic acid amide), octadecylamide, erucamide, behenamide, oleamide, stearyl erucamide, N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-benzenedicarboxamide, and N,N-bis(hydroxyethyl)cocamide.

[0050] In addition, the nucleating agent in the present invention can also be one or more selected from fatty acids, fatty alcohols, aliphatic hydroxy acids, aliphatic carboxylates, lactic acid or chain ester derivatives thereof.

[0051] Specifically, the fatty acid can be a fatty acid with 5-30 carbon atoms, such as pentanoic acid, dodecanoic acid (decanoic acid / decanoic acid); preferably, it is a higher fatty acid with 10 or more carbon atoms; further preferably, it is a long-chain high-carbon fatty acid with an even number of carbon atoms, specifically but not limited to, for example, one or more of lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), stearic acid (octadecanoic acid), arachidic acid (eicosanoic acid), behenic acid (docosanoic acid), lignoic acid (tetracosanoic acid), cerotic acid (hexacosanoic acid), montanic acid (octacosanoic acid) or melissic acid (triacontanoic acid); more preferably, it is behenic acid.

[0052] Specifically, the fatty alcohol can be a fatty alcohol with 5-30 carbon atoms, such as amyl alcohol, octyl alcohol, etc.; preferably, a higher fatty alcohol with 10 or more carbon atoms; further preferably, a long-chain high-carbon fatty alcohol with an even number of carbon atoms, specifically but not limited to, for example, one or more of 1,16-hexadecanediol, stearyl glycol (1,2-octadecanediol), 1,22-docosanediol, lauryl alcohol (dodecyl alcohol), myristyl alcohol (tetradecyl alcohol), palmityl alcohol (cetyl alcohol), arachidyl alcohol (eicosyl alcohol), behenyl alcohol (behenyl alcohol), wax alcohol (hexacosanol), policosanol (octacosanol), myristyl alcohol (triacontanol), and ceryl alcohol (triacontanol); more preferably, behenyl alcohol.

[0053] Specifically, the aliphatic hydroxy acid can be an aliphatic hydroxy acid having 5 to 30 carbon atoms, preferably an aliphatic hydroxy acid having 10 or more carbon atoms, specifically but not limited to, one or more of 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 8-hydroxytetradecanoic acid, 15-hydroxypentadecanoic acid, 2-hydroxyhexadecanoic acid, 3-hydroxyhexadecanoic acid, 16-hydroxyhexadecanoic acid, 9,10,16-trihydroxyhexadecanoic acid, 3-hydroxyheptadecanoic acid, 17-hydroxyheptadecanoic acid, 2-hydroxyoctadecanoic acid, 3-hydroxyoctadecanoic acid, 12-hydroxyoctadecanoic acid, 20-hydroxyeicosanoic acid, 2-hydroxydocosanoic acid, and 22-hydroxydocosanoic acid.

[0054] Specifically, the aliphatic carboxylic acid ester can be an aliphatic carboxylic acid ester having 5 to 30 carbon atoms, preferably an aliphatic carboxylic acid ester having 10 or more carbon atoms, and specifically, but not limiting, can be one or more of ethyl hexadecanoate, 2-ethylhexyl hexadecanoate, hexadecanoate, methyl nonadecanoate, methyl eicosanoate, ethyl eicosanoate, methyl docosanoate, ethyl docosanoate, methyl tetracosanoate, ethyl tetracosanoate, and methyl triacontadecanoate.

[0055] Specifically, the lactic acid or its chain ester derivatives are one or more of L-lactic acid, D-lactic acid, DL-lactic acid, lactide, methyl lactate, ethyl lactate, and butyl lactate.

[0056] In some embodiments, the plasticizer can be: a high boiling point ester of a polyacid, such as diisodecyl phthalate, diisooctyl phthalate, diisoheptyl phthalate, diheptyl phthalate, heneicosyl phthalate, diisononyl phthalate, diisononyl phthalate, diisodecyl phthalate or diisobutyl phthalate or tricosyl phthalate; a citric acid ester, such as triethyl citrate, trimethyl citrate, tri-n-hexyl citrate, tri-n-butyl citrate; esters; adipates such as di-2-ethylhexyl adipate, diisodecyl adipate, diisononyl adipate, dioctyl adipate, etc.; sebacates such as dioctyl sebacate, behenyl sebacate, dibutoxyethyl sebacate or di-n-butyl sebacate; azelaic acid esters such as di-n-butyl azelate and diisooctyl azelate; high molecular weight glycols such as triethylene glycol diacetate, triethylene glycol octanoate; polyglycols such as polyethylene glycol, poly(propylene glycol); glycerol derivatives such as tricaprylic acid glycerol, triglycerol triacetate ... butyrates; pentaerythritol and its derivatives; sulfonic acid derivatives such as toluenesulfonamide; epoxy derivatives, for example, epoxidized esters of fatty acids, epoxidized soybean oil, epoxidized linseed oil, epoxidized octyl esters, epoxidized ethanol oleate; substituted fatty acids, for example, palmitic acid esters, stearic acid esters, oleic acid esters, ricinoleic acid esters and lauric acid esters, for example, sorbitan monolaurate, sorbitan monooleate, poly(oxyethylene)sorbitan monolaurate, poly(oxyethylene) lauryl ethyl ether, butyl acetyricinoleate; phosphoric acid derivatives Bio-(phosphate esters), such as phosphate esters, triisopropyl phosphate; phosphonic acid derivatives and phosphites; chlorinated paraffins; polymeric esters, such as glutaric acid polyesters (polyester glutarates) with a molecular weight of 2000 to 20,000, adipic acid polyesters (polyester adipates) with a molecular weight of 200 to 20,000, succinic acid polyesters, sebacic acid polyesters (polyester sebacates) with a molecular weight of 4,000-10,000, preferably 8,000, mixed esters of adipic acid, glutaric acid and succinic acid with isodecyl alcohol, polycaprolactone triol, etc.

[0057] Generally preferred plasticizers should be biodegradable. Preferred plasticizers are polymeric esters, high molecular weight glycols, polyglycols, poly(oxyethylene) sorbitan monolaurate, poly(oxyethylene) lauryl ether, glycerol derivatives, epoxidized soybean oils that are optionally substituted and optionally terminally esterified, adipates, sebacates, phosphates, phthalates, citrates, ricinoleate, chlorinated paraffins, and toluenesulfonamides. Particularly preferred plasticizers are epoxidized soybean oils, phthalates, polyester adipates, phosphoric acid derivatives, polymeric esters, polypropylene glycol adipates, substituted polyethylene glycols, polyester glutarates, and epoxidized soybean oil.

[0058] In some embodiments, the toughening agent may be a rubber, a thermoplastic elastomer, or the like, for example, an acrylic or olefin polymer.

[0059] In some embodiments, the reinforcing agent may be a fiber reinforcing agent, such as carbon fiber, an organic or inorganic reinforcing agent, or a composite reinforcing agent.

[0060] In some embodiments, the cross-linking agent is also called a bridging agent, such as an organic peroxide.

[0061] In some embodiments, the chain extender, also known as a chain extender, is a substance that reacts with functional groups on linear polymer chains to extend the molecular chain and increase the molecular weight. Examples of amine chain extenders include MOCA and liquid MOCA modified with formaldehyde, ethylenediamine (DA), N,N-dihydroxy(diisopropyl)aniline (HPA), and the like. In some embodiments, the chain extender comprises a reactive monomer and a vinyl monomer. For example, the chain extender comprises at least one epoxy-functional (meth)acrylic monomer as the reactive monomer and at least one styrene monomer and / or (meth)acrylic monomer as the vinyl monomer. The chain extender may also be an isocyanate chain extender, specifically, diisocyanates, diepoxides, anhydrides, bisoxazolines, and the like. Diisocyanates include 2,4-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, phenylenediisocyanate, hydrogenated phenylenediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like. Bisoxazolines include 2,2'-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, 1,4-bis(2-oxazolinyl)butane, 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene, and 1,3-bis(2-oxazolinyl)benzene.

[0062] In some embodiments, the lubricant can be behenamide, stearamide, erucamide, oleamide, or a combination of two or more thereof. Combinations of lubricants other than behenamide, stearamide, erucamide, and oleamide (hereinafter referred to as "other lubricants") can also be used. Other lubricants include, for example, alkylene fatty acid amides such as alkylene bisstearamide and ethylene bisstearamide; polyethylene wax, oxidized polyester wax; glyceryl monostearate, such as glyceryl monostearate, glyceryl monobehenate, and glyceryl monolaurate; fatty acid esters; organic acid monoglycerides, such as succinic acid saturated fatty acid monoglyceride; sorbitan fatty acid esters such as sorbitan behenate, sorbitan stearate, and sorbitan laurate; stearic acid diglyceride, lauric acid diglyceride, stearic acid tetraglyceride, and lauric acid tetraglyceride; polyglycerol fatty acid esters such as lactic acid ester, stearic acid decaglyceride, and lauric acid decaglyceride; aliphatic higher alcohol esters, such as stearyl stearate, but are not limited thereto. These and other lubricants can be used alone or in combination of two or more.

[0063] In some embodiments, the filler may be an inorganic filler or an organic filler, or a combination of the two.

[0064] Specifically, the type of organic filler is not particularly limited, as long as it is an organic filler that can be added to the resin material. Examples of organic fillers include (a) wood materials, such as wood chips, wood flour, sawdust, etc.; (b) organic fibers, such as natural fibers and synthetic fibers made from organic substances; and (c) polyester, polyacrylic acid, polyamide, nylon, polyethylene, polyolefin, polyvinyl alcohol, polyvinyl chloride, polyurethane, polyacetal, aramid, PBO (polymerized resin material such as p-phenylene benzobisoxazole), polyphenylene sulfide, acetyl cellulose, polybenzoxazole, polyarylate, polyvinyl acetate, and synthetic rubber.

[0065] Specifically, the kind of inorganic filler is not particularly limited, as long as it is an inorganic filler that can be added to the resin material. As the inorganic filler, for example, quartz, fumed silica, anhydrous silicon, fused silica, crystalline silica, amorphous silica, fillers obtained by condensation of alkoxysilane, ultrafine amorphous silica, silica-based inorganic fillers, aluminum oxide, zircon, iron oxide, zinc oxide, titanium oxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, glass, silicone rubber, silicone resin, titanium oxide, carbon fiber, mica, graphite, carbon black, ferrite, graphite, diatomaceous earth, white clay, clay, talc, calcium carbonate, manganese carbonate, magnesium carbonate, barium sulfate, silver powder, etc. can be enumerated. These fillers can be used alone or in combination of two or more.

[0066] The polyhydroxyalkanoate composition of the present invention can be prepared using conventional techniques and equipment known in the art, and can be directly added to the processing equipment using a liquid feeding device and blended at room temperature.

[0067] In a second aspect, the present invention further provides a polyhydroxyalkanoate shaped body prepared from the polyhydroxyalkanoate composition according to the present invention.

[0068] The polyhydroxyalkanoate molded article provided herein has a melt flow rate greater than 7.0 g / 10 min at 165° C. and 5 kg. Specifically, the melt flow rate of the polyhydroxyalkanoate molded article at 165° C. and 5 kg is greater than 7.15 g / 10 min, and more preferably greater than 11.45 g / 10 min.

[0069] The polyhydroxyalkanoate molded body obtained by the present invention has the advantages of good processing stability and balanced processing performance and mechanical properties, and thus has a wider range of application scenarios.

[0070] The polyhydroxyalkanoate molded body of the present invention may include various forms, such as injection molded parts, films, fibers, straws, plates, sheets, pellets, etc.

[0071] In a third aspect, the present invention further provides a method for preparing a polyhydroxyalkanoate shaped body according to the present invention, comprising:

[0072] The polyhydroxyalkanoate composition is heated at a first temperature and then melted (the first stage); and cooled at a second temperature and formed (the second stage).

[0073] The present invention has found that the temperature in the first stage affects the extent of the decrease in weight-average molecular weight and the increase in melt flow rate. Under the same melt flow rate regulating agent dosage and the same processing technology, the decrease in weight-average molecular weight and the increase in melt flow rate are smaller at lower temperatures, while the decrease in weight-average molecular weight and the increase in melt flow rate are larger at higher processing temperatures. However, the longer it takes for the molded article to remain free of blocking in the second stage, the longer the temperature is. Taking all factors into consideration, the system temperature in the first stage should be controlled to be 10°C to 60°C above the melting point of the polyhydroxyalkanoate.

[0074] At the same time, the present invention also found that the temperature of the second stage affects the length of time required for the polyhydroxyalkanoate molded body to reach a non-adhesive state; through a large number of experiments, it was verified that in the second stage, the system temperature is controlled between the glass transition temperature and the melting point temperature of the obtained molded body, preferably at least 30°C higher than the glass transition temperature of the obtained molded body and less than 20°C lower than the melting point temperature of the obtained molded body.

[0075] The molding methods of the present invention are divided into thermoplastic molding methods and non-thermoplastic molding methods. The thermoplastic molding methods include extrusion molding, injection molding, calendaring molding, tape casting, blow molding, biaxial stretch molding, etc.; the non-thermoplastic molding methods include solution casting, etc. The thermoplastic molding method is preferred.

[0076] In a fourth aspect, the present invention provides a use of an alkali metal compound for regulating the melt index of a polyhydroxyalkanoate, wherein the alkali metal compound is as described above. Specifically, the alkali metal compound described above can increase the melt index of the polyhydroxyalkanoate.

[0077] The alkali metal compound is used as a melt flow rate regulating agent, and after being mixed with polyhydroxyalkanoate to form a polyhydroxyalkanoate composition, the weight average molecular weight of the polyhydroxyalkanoate is reduced and the melt flow rate is increased.

[0078] The polyhydroxyalkanoate composition comprises the following components: polyhydroxyalkanoate, a melt flow rate regulating agent, wherein the melt flow rate regulating agent is at least one alkali metal compound, and optionally other additives, wherein the other additives are selected from nucleating agents, plasticizers, toughening agents, reinforcing agents, and fillers. Beneficial effects

[0079] 1. The melt flow rate modifier provided by the present invention, when applied to polyhydroxyalkanoates, effectively cleaves the ester bonds of the polyhydroxyalkanoates, reduces the weight-average molecular weight, and increases the melt flow rate. Furthermore, the melt flow rate modifier provided by the present invention offers advantages such as safety, environmental friendliness, and food contact compatibility, thus having a wide range of applications.

[0080] 2. The molecular weight distribution of the high-flow polyhydroxyalkanoate molded body provided by the present invention does not increase significantly, indicating that its weight-average molecular weight is adjusted relatively evenly, and mechanical properties such as tensile strength do not change significantly, which does not affect the performance of the molded body; the obtained polyhydroxyalkanoate molded body has a melt index greater than 7 g / 10 min, a weight-average molecular weight less than 300,000, and a PDI value less than 4.

[0081] 3. The melt flow rate regulating agent for polyhydroxyalkanoate molded bodies provided by the present invention is easy to use and can be blended and compounded with the composition as an additive without requiring any extra preparation methods and steps, thereby reducing production costs.

[0082] 4. The high-flowability polyhydroxyalkanoate molded body and preparation method thereof provided by the present invention can be carried out using traditional plastic processing equipment without the need for synthesis equipment such as high-pressure reactors, and thus has great convenience in processing technology.

[0083] The present invention has been described in detail above, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the above prior art or invention summary or the following examples.

[0084] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. DETAILED DESCRIPTION

[0085] The present invention will be further described below with reference to the examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed in the present invention.

[0086] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0087] Unless otherwise specified, all raw materials used in the following examples and comparative examples were commercially available.

[0088] raw material:

[0089] Poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), Beijing Lanjing Microbiology Technology Co., Ltd., 3HB (3-hydroxybutyrate unit) content 94% (hereinafter referred to as PHBH-1).

[0090] Poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), Beijing Lanjing Microbiology Technology Co., Ltd., 3HB (3-hydroxybutyrate unit) content 89% (hereinafter referred to as PHBH-2).

[0091] Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), Beijing Lanjing Microbiology Technology Co., Ltd.

[0092] Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) was purchased from Beijing Lanjing Microbiology Technology Co., Ltd.

[0093] Poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (PHBO) was purchased from Beijing Lanjing Microbiology Technology Co., Ltd.

[0094] Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH) was purchased from Beijing Lanjing Microbiology Technology Co., Ltd.

[0095] Various melt flow rate regulating additives, Shanghai Aladdin Biochemical Technology Co., Ltd., AR grade.

[0096] equipment:

[0097] The mixing equipment used in the examples is an SHR-50L high-speed mixer produced by Zhangjiagang Zhengde Machinery Factory.

[0098] The extrusion granulation equipment used in the examples is a HK36 twin-screw extruder unit manufactured by Nanjing Keya.

[0099] The injection molding equipment used in the embodiment is a UN120A5S precision machine hinged servo pump horizontal injection molding machine produced by Guangdong Yizumi.

[0100] Preparation of particle moldings in Examples 1 to 32 and Comparative Examples 1 to 4

[0101] The compositions provided in Examples 1-32 and Comparative Examples 1-4 in Tables 1-4 were respectively used to prepare particle moldings, and the specific steps were as follows:

[0102] Step 1: Mixing: Place polyhydroxyalkanoate powder and various additives in a high-speed mixer and mix at room temperature at a mixing speed of 200 r / min for 5 minutes; after mixing, place the mixture in the lower hopper of a twin-screw extruder;

[0103] Step 2: Extrusion: Set the screw speed of the extrusion granulation equipment to 100-500 r / min, and perform melt extrusion at a melt temperature of about 165°C;

[0104] Step 3: Granulation: Granulation is carried out by water bath strand granulation, with the water bath heating temperature being 50°C to allow the strands to crystallize and solidify; the strands are then cut into particles of uniform size by a pelletizer;

[0105] Step 4, drying: drying the particles prepared in step 3 in a vacuum oven at a temperature of 40-80° C. for 4-8 hours to complete the preparation of the polyhydroxyalkanoate particle molding.

[0106] Preparation of injection molded parts

[0107] The particle molded body prepared in the above embodiment was selected and an injection molded body was prepared using a horizontal injection molding machine. The temperature of each heating section of the injection molding machine barrel was set at 120-160°C (first temperature). The injection mold was selected to be a tensile test piece for subsequent performance evaluation. The mold temperature was adjusted to 40-60°C (second temperature) using a mold temperature controller to allow the injection molded part to crystallize and solidify. This completed the preparation of the polyhydroxyalkanoate injection molded body.

[0108] In the above-mentioned polyhydroxyalkanoate injection-molded body, the tensile performance test piece meets the ISO 527-2:2012, 1A type test standard.

[0109] Performance evaluation

[0110] The weight average molecular weight, melt flow rate (MFR), and dispersion index (PDI) were tested using the pelletized bodies, and other properties were tested using injection molded bodies further prepared from the pelletized bodies.

[0111] Weight average molecular weight (Mw):

[0112] The measurement was performed using a gel permeation chromatograph (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution and in terms of polystyrene. As the column for the gel permeation chromatograph, any column suitable for measuring the weight average molecular weight may be used.

[0113] Polymer Dispersibility Index (PDI):

[0114] The above-mentioned gel permeation chromatography (GPC) technique is also used to measure and obtain a molecular weight distribution curve, thereby calculating the PDI (Mw / Mn) molecular weight.

[0115] Note: A smaller PDI value indicates a narrower distribution of weight-average molecular weights (Mw) in the polymer, meaning the smaller the differences between the individual Mws in the polymer. Conversely, a larger PDI value indicates a wider distribution of weight-average molecular weights (Mw), meaning the differences between the individual Mws in the polymer are greater. Generally speaking, PDI values ​​range from 1 to 10, with lower values ​​generally being better, such as below 4. For example, the PDI of better polymer materials is generally between 1 and 3, or even between 1 and 2.

[0116] Melt flow rate (MFR):

[0117] The test standard is ISO1133-1:2011, and the test equipment is a melt flow rate tester. The melt flow rate is measured using the above-mentioned polyhydroxyalkanoate particle molding under the conditions of 165°C and 5 kg; the unit of melt flow rate is g / 10min.

[0118] Tensile Strength:

[0119] The test standard is ISO527-2:2012, and the test equipment is a universal material testing machine. The tensile performance test piece in the above-mentioned polyhydroxyalkanoate injection molding is used to measure the tensile strength at a test speed of 50 mm / min. The unit of tensile strength is MPa.

[0120] The compositions (unit: parts by weight) and performance test results of the examples are provided in Tables 1 to 4 below.

[0121] Table 1

[0122] In Table 1, Comparative Example 1 and Examples 1-5 use PHBH-1 as the raw material, and the melt flow rate regulating agent is sodium L-lactate. Examples 1-5 add different amounts of sodium L-lactate. Compared with the blank control comparative example 1, Examples 1-5 can all reduce the weight average molecular weight Mw, and within the above range, the degree of reduction of the weight average molecular weight Mw increases with the increase of the addition amount. Comparative Example 2 and Examples 6-8 use PHBH-2 as the raw material, and Examples 6-8 add different amounts of sodium L-lactate. Compared with the blank control comparative example 2, Examples 6-8 can all reduce the weight average molecular weight Mw, and within the above range, the degree of reduction of the weight average molecular weight Mw increases with the increase of the addition amount. In addition, the same amount of sodium L-lactate has a more obvious effect on PHBH-1 and a greater degree of reduction in the weight average molecular weight Mw. The obtained molded body has a low weight-average molecular weight (less than 300,000), a high melt index (greater than 7 g / 10 min, even greater than 17 g / 10 min), and the PDI does not increase significantly (the PDI values ​​of Examples 1-8 are basically between 2.50 and 3.00, all lower than 4), indicating that the effect of the regulator is stable.

[0123] Table 2

[0124] In Table 2, Examples 9-18, using PHBH-2 as the raw material and employing different types of alkali metal compounds, all effectively reduce the weight-average molecular weight (Mw) and adjust the melt index. The resulting molded bodies have low weight-average molecular weights (less than 300,000), high melt indexes (significantly greater than 7 g / 10 min, even greater than 400 g / 10 min), and no significant increase in PDI (PDI values ​​for Examples 9-18 are generally between 2.00 and 2.50, all below 4), demonstrating the stable effect of the modifier.

[0125] Table 3

[0126] Comparative Example 3, Comparative Example 4, and Examples 19-24 in Table 3 are embodiments of the combination of a melt flow rate regulating agent and a nucleating agent. From the results of the above table combined with Comparative Examples 1-2, it can be seen that when only a nucleating agent is introduced, the molecular weight of the material will increase relatively and the tensile strength will also increase relatively; when only a melt flow rate regulating agent is added, although the melt index will increase and the molecular weight will decrease more, the relative tensile strength will also decrease slightly. Therefore, when preparing a molded body, it is necessary to comprehensively consider the melt index and tensile strength, and then choose to compound the melt flow rate regulating agent with the nucleating agent, so that not only a higher melt index can be obtained, but also a certain tensile strength can be maintained; the molded body has a weight average molecular weight of less than 300,000, a melt index greater than 7g / 10min, a PDI less than 3, a stable regulating agent effect, and a tensile strength of more than 20MPa.

[0127] To further verify whether the melt flow rate regulating agent can also play a role in regulating the melt index of different PHAs, the following Examples 25-32 use blends of different PHAs as raw materials and adopt a combination of a melt flow rate regulating agent and a nucleating agent:

[0128] Table 4

[0129] The results in Table 4 show that after the blends of different PHAs are compounded with a melt flow rate regulator and a nucleating agent, the resulting molded bodies can obtain low molecular weight and certain tensile strength. The weight-average molecular weight of the molded bodies is less than 300,000, the melt index is greater than 11 g / 10 min, the PDI is below 3, the regulator has a stable effect, and the tensile strength remains above 18 MPa.

[0130] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced with equivalents, without departing from the spirit and substance of the present invention; and such modifications or replacements remain within the scope of the present invention.

Claims

1. A polyhydroxyalkanoate composition, characterized in that: include: Polyhydroxyalkanoates, and A melt flow rate regulating aid, wherein the melt flow rate regulating aid is at least one alkali metal compound.

2. The polyhydroxyalkanoate composition according to claim 1, characterized in that The added amount of the melt flow rate regulating auxiliary agent is 0.0001%-10% of the mass of the polyhydroxyalkanoate.

3. The polyhydroxyalkanoate composition according to claim 1, characterized in that The amount of the melt flow rate regulating agent added is 0.001%-2% of the mass of the polyhydroxyalkanoate.

4. The polyhydroxyalkanoate composition according to claim 1, characterized in that The alkali metal compound includes one or more of an alkali metal hydroxide, an alkali metal organic acid salt and an alkali metal inorganic acid salt.

5. The polyhydroxyalkanoate composition according to claim 1, characterized in that The melt flow rate regulating auxiliary agent is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, potassium acetate, sodium acetate, lithium acetate, cesium acetate, rubidium acetate, sodium stearate, potassium stearate, lithium stearate, cesium pivalate, L-sodium lactate, L-lithium lactate, L-potassium lactate, D-sodium lactate, D-lithium lactate, D-potassium lactate, DL-sodium lactate, DL-lithium lactate, DL-potassium lactate, lithium bis(oxalate borate), potassium sorbate, sodium 3-hydroxybutyrate, sodium 2-hydroxybutyrate, lithium zirconate, lithium tungstate, lithium aluminate, lithium titanate, lithium arsenate, sodium zirconate, potassium fluorozirconate, potassium chloropalladate and potassium zirconium carbonate.

6. The polyhydroxyalkanoate composition according to claim 1, characterized in that The polyhydroxyalkanoate composition also includes a nucleating agent; the nucleating agent is one or more selected from calcium carbonate, talc, titanium dioxide, uracil, galactitol, zirconium hydrogen phosphate, amide compounds, boron nitride, fatty acids, fatty alcohols, aliphatic hydroxy acids, aliphatic carboxylates, lactic acid or its chain ester derivatives.

7. The polyhydroxyalkanoate composition according to any one of claims 1 to 6, characterized in that The polyhydroxyalkanoate contains the structural unit represented by the following general formula I: [OCHR1(CH2) x CO] General Formula I Where R1 is C p H 2p+1 The alkyl group shown, p is an integer from 1 to 15; x is 1, 2, or 3.

8. The polyhydroxyalkanoate composition according to claim 7, characterized in that The poly(3-hydroxyalkanoate) is a poly(3-hydroxybutyrate) homopolymer containing only 3-hydroxybutyrate structural units, or a poly(3-hydroxybutyrate) copolymer containing 3-hydroxybutyrate structural units and other hydroxyalkanoate structural units.

9. A polyhydroxyalkanoate molded body, characterized in that: The polyhydroxyalkanoate composition is prepared from any one of claims 1 to 8.

10. The polyhydroxyalkanoate molded article according to claim 9, characterized in that: At 165° C. and 5 kg, the melt flow rate of the polyhydroxyalkanoate molded body is greater than 7.0 g / 10 min.

11. A method for preparing the polyhydroxyalkanoate molded body according to claim 9 or 10, comprising heating the polyhydroxyalkanoate composition according to any one of claims 1 to 8 at a first temperature and then melting it; and cooling it at a second temperature to form it.

12. The method according to claim 11, characterized in that The first temperature is 10° C. to 60° C. higher than the melting point of the polyhydroxyalkanoate, and the second temperature is 30° C. or higher than the glass transition temperature of the obtained molded body and 20° C. or lower than the melting point of the obtained molded body.

13. The preparation method according to claim 11, characterized in that: The polyhydroxyalkanoate composition comprises: polyhydroxyalkanoate, a melt flow rate regulating agent, wherein the melt flow rate regulating agent is at least one alkali metal compound, and optionally other additives, wherein the other additives are selected from nucleating agents, plasticizers, toughening agents, reinforcing agents, and fillers; Wherein, the addition amount of the melt flow rate regulating agent is 0.001%-5% of the mass of the polyhydroxyalkanoate; The alkali metal compound is one or more selected from alkali metal hydroxides, alkali metal organic acid salts and alkali metal inorganic acid salts selected from lithium zirconate, lithium tungstate, lithium aluminate, lithium titanate, lithium arsenate, sodium zirconate, potassium fluorozirconate, potassium chloropalladate and potassium zirconium carbonate; The polyhydroxyalkanoate is a single polymer or a combination of two or more polymers; the polymer contains a structural unit represented by the following general formula I: [OCHR1(CH2) x CO] General Formula I Where R1 is C p H 2p+1 The alkyl group shown in FIG. 1 is an integer of 1 to 15; and x is 1, 2 or 3.

14. Use of an alkali metal compound in improving the melt index of a polyhydroxyalkanoate, wherein: The alkali metal compound is used as a melt flow rate regulating auxiliary agent, and after being mixed and compounded with polyhydroxyalkanoate to form a polyhydroxyalkanoate composition, the weight average molecular weight of the polyhydroxyalkanoate is reduced and the melt flow rate is increased.

15. The use according to claim 14, characterized in that: The amount of the melt flow rate regulating agent added is 0.001%-5% of the mass of the polyhydroxyalkanoate; The alkali metal compound is one or more selected from alkali metal hydroxides, alkali metal organic acid salts and alkali metal inorganic acid salts selected from lithium zirconate, lithium tungstate, lithium aluminate, lithium titanate, lithium arsenate, sodium zirconate, potassium fluorozirconate, potassium chloropalladate and potassium zirconium carbonate; The polyhydroxyalkanoate composition comprises: polyhydroxyalkanoate, a melt flow rate regulating agent, wherein the melt flow rate regulating agent is at least one alkali metal compound, and optionally other additives, wherein the other additives are selected from nucleating agents, plasticizers, toughening agents, reinforcing agents, and fillers; The polyhydroxyalkanoate is a single polymer or a combination of two or more polymers; the polymer contains the following The structural unit represented by formula I is: [OCHR1(CH2) x CO] General Formula I Where R1 is C p H 2p+1 The alkyl group shown in FIG. 1 is an integer of 1 to 15; and x is 1, 2 or 3.

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