HK40104084A - A polyhydroxyalkanoate composition, polyhydroxyalkanoate molded article and preparation method thereof - Google Patents

Description

A polyhydroxyalkanoate composition, a polyhydroxyalkanoate molded article and a method for preparing the same.

Technical Field

This invention relates to the field of bio-based polymer materials technology, and in particular to a polyhydroxyalkanoate composition, a polyhydroxyalkanoate molded body, and a method for preparing the same.

Background Technology

Polyhydroxyalkanoates (PHAs) are intracellular polyhydroxyalkanoates synthesized by many microorganisms, and are natural polymeric biomaterials. Most PHA monomers are 3-hydroxy fatty acids with chains ranging from 3 to 14 carbon atoms in length. Their side chains are highly variable, consisting of saturated or unsaturated, straight or branched, aliphatic or aromatic groups. This diversity in composition leads to a variety of properties, giving them significant advantages in applications. Furthermore, PHAs are bio-based polymers that are biodegradable in marine environments, helping to address environmental problems caused by waste plastics. They also possess excellent biocompatibility and mechanical properties, allowing them to be processed into various molded products such as films, straws, and tableware.

Controlling the crystallization rate is a crucial factor in the processing rate of polyhydroxyalkanoates (PHA). Current technologies often employ methods such as adding nucleating agents to increase the crystallization rate of PHA.

Nucleating agents in existing technologies are mainly inorganic substances or metal salts. While they can improve the crystallization rate and crystallinity of molded products prepared from traditional polyhydroxyalkanoates to some extent, the improvement is limited, and they can also cause the molded products to have color, reduce their transparency, and affect their applications. In addition, for polyhydroxyalkanoate materials with a wide melting range, there are often problems such as low processing efficiency, difficulty in achieving a certain degree of curing, and long curing time during the preparation process.

Summary of the Invention

In view of the problems existing in the prior art, one of the objectives of the present invention is to provide a polyhydroxy fatty acid ester composition containing lactic acid and/or organic lactic acid derivatives, which can effectively solve the problems of low crystallization rate and low processing and curing efficiency of polyhydroxy fatty acid esters.

A second objective of this invention is to provide a polyhydroxyalkanoate molded article prepared from the above-mentioned polyhydroxyalkanoate composition.

The third objective of this invention is to provide a method for preparing the above-mentioned polyhydroxyalkanoate molded articles.

To achieve the above objectives, the technical solution adopted by the present invention is as follows:

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

Polyhydroxy fatty acid esters; and at least one of the following general formula I: lactic acid or organic lactic acid derivatives:

R ² CH ₂ -CH(OH)-COYR ¹ I

Wherein, ^R1 is H or a hydrocarbon group, ^R2 is H or a hydrocarbon group, and Y is any one of C, O, N, and S.

In this invention, ^R1 and ^R2 in general formula I are H or short-chain hydrocarbon groups of C1 to C16, respectively, and Y is any one of C, O, N, and S. That is, the composition includes short-chain ketones, esters/acids, sulfur-containing, and nitrogen-containing lactic acid organic derivatives represented by general formula I.

In this invention, Y in general formula I is O, and ^R1 and ^R2 are H, representing lactic acid. Lactic acid can be divided into two categories based on its chiral structure: L-lactic acid and D-lactic acid. In this invention, the lactic acid is selected from L-lactic acid, D-lactic acid, or a combination thereof; wherein, in the combination of L-lactic acid and D-lactic acid, the ratio of L-lactic acid to D-lactic acid is 0.01–99.99:99.99–0.01.

In this invention, the lactic acid derivatives can be further classified into organic ester derivatives and organic acid derivatives of lactic acid.

In general formula I, Y is O, ^{and R1} is a C1-C16 hydrocarbon group, meaning that the lactic acid organic derivative is a lactic ester derivative with the structure ^R2CH2 - _CH (OH) ^-COOR1 , wherein ^R2 is H or a C1-C16 hydrocarbon group; and/or,

In general formula I, Y is O, ^R1 is H, and ^R2 is a C1-C16 hydrocarbon group, that is, the structure of the lactic acid organic derivative is ^R2CH2 _- CH(OH)-COOH lactic acid organic acid derivative.

The organic ester derivatives of lactic acid described in this invention include lactic acid ester derivatives with the structure ^R2CH2 _- CH(OH) ^-COOR1 formed by substitution of lactic acid (including L-lactic acid, D-lactic acid, or any combination thereof, preferably L-lactic acid), wherein ^R1 is a C1-C16 hydrocarbon group, ^R2 is H or a C1-C16 hydrocarbon group, and ^R1 and ^R2 are preferably C1-C10 hydrocarbon groups, C1-C8 hydrocarbon groups, or C1-C4 hydrocarbon groups, such as methyl, ethyl, propyl, butyl, isopentyl, phenyl, benzyl, tetradecyl, and hexadecyl. In some specific embodiments, the organic ester derivatives of lactic acid can be methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isopentyl lactate, benzyl lactate, tetradecyl lactate, hexadecyl lactate, or methyl 3-phenyllactic acid.

In this invention, the organic acid derivatives of lactic acid include organic acid derivatives formed by retaining the lactic acid hydroxyl and carboxyl groups in lactic acid (including L-lactic acid, D-lactic acid or any combination thereof, preferably L-lactic acid), with the structure R ² CH ₂ -CH(OH)-COOH, wherein R ² is a C1-C16 hydrocarbon group, more preferably a C1-C10 hydrocarbon group, a C1-C8 hydrocarbon group, or a C1-C4 hydrocarbon group, and examples include methyl, ethyl, propyl, butyl, and phenyl, specifically 3-phenyllactic acid.

In addition to the lactic acid organic derivatives mentioned above, it can be inferred that when Y in general formula I is C, N, or S (carbon, nitrogen, sulfur), the organic derivatives also have a similar structure to the organic derivatives mentioned above (Y is O), all retaining the α-hydroxyl group of the lactic acid organic derivatives. It can be inferred that they can also obtain similar effects. Therefore, the present invention should not be limited to the specific lactic acid organic derivatives mentioned above.

In a specific embodiment, the composition contains lactic acid.

In specific embodiments, the composition contains L-lactic acid, D-lactic acid, or a mixture thereof in any proportion, for example, the ratio of L-lactic acid to D-lactic acid is 0.01 to 99.99: 99.99 to 0.01, preferably 0.1 to 1: 1 to 0.1, such as 0.1:1, 1:9, 1:8, 1:5, 1:4, 0.5:1, 1:1, 1:0.5, 4:1, 5:1, 8:1, 9:1, 1:0.1.

In a specific embodiment, the composition contains any one selected from L-lactic acid, D-lactic acid, DL-lactic acid, or a combination thereof; wherein, DL-lactic acid is lactic acid in a ratio of L-lactic acid to D-lactic acid of 1:1.

In a specific embodiment, the composition contains L-lactic acid.

In a specific embodiment, lactic acid or lactic acid derivatives act as nucleating agents in the composition.

In specific embodiments, the amount of lactic acid and/or lactic acid derivatives added is 0.01%-20% of the mass of the polyhydroxyalkanoate; preferably 0.1%-10%; more preferably 0.1%-3%, for example 0.1%-2%, 0.1%-1.5%, 0.5%-1.5%; typically, without limitation, the amount of lactic acid and/or lactic acid derivatives added may be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 2%, 2.5%, or 3% of the mass of the polyhydroxyalkanoate.

The polyhydroxyalkanoate described in this invention can be a single polymer or a composition of two or more polymers. Each polymer may contain one or more monomers (i.e., the polymer may contain one or more structural units).

Specifically, any polymer contains a structural unit represented by the following general formula II:

In general formula II, R represents an alkyl group represented by C _{_p} H _{_2p+1} , and p represents an integer from 1 to 15, preferably an integer from 1 to 10, and more preferably an integer from 1 to 8. Examples of R include straight-chain or branched alkyl groups such as methyl, ethyl, propyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl.

m can be 1, 2, or 3; when m = 1, general formula II represents a 3-hydroxyalkanoate structural unit, when m = 2, general formula II represents a 4-hydroxyalkanoate structural unit, and when m = 3, general formula II represents a 5-hydroxyalkanoate structural unit; among them, the 3-hydroxyalkanoate structural unit and the 4-hydroxyalkanoate structural unit are more common, such as the 3-hydroxybutyrate structural unit (hereinafter sometimes referred to as 3HB) and the 4-hydroxybutyrate structural unit (hereinafter sometimes referred to as 4HB).

In a specific embodiment, the polyhydroxy fatty acid ester of the present invention includes at least one poly(3-hydroxyalkanoate).

Furthermore, the poly(3-hydroxyalkanoate) contains only 3-hydroxybutyrate structural units, or contains 3-hydroxybutyrate structural units and other hydroxyalkanoate structural units.

Furthermore, the other hydroxyalkanoate structural units include one or more of the following: 3-hydroxypropionate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynonanoate, 3-hydroxydecanoate, 3-hydroxyundecanoate, or 4-hydroxybutyrate; preferably 3-hydroxyhexanoate.

In other words, specific examples of poly(3-hydroxyalkanoates) include: poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviated as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviated as P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as P3HB4HB), etc. In particular, considering processability and mechanical properties, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred.

In general, lactic acid or its organic derivatives in the compositions of this invention can accelerate crystallization, regardless of the proportion of structural monomers in the polyhydroxyalkanoate (PHA) in the composition. This may be because specific structures in lactic acid or its organic derivatives can better "bind" to the PHA, thus tending to "induce" PHA crystallization. The manufacturing method of the PHA described in this invention is not particularly limited; it can be a chemical synthesis method or a microbial manufacturing method. Microbially produced PHAs are particularly preferred, in which all 3-hydroxyalkanoate structural units are contained in the form of (R)3-hydroxyalkanoate structural units. The poly(3-hydroxyalkanoate) comprises a copolymer of 3-hydroxybutyrate structural units and other structural units, and the average content ratio of the 3-hydroxybutyrate structural units to other structural units in the poly(3-hydroxyalkanoate) is 50/50 to 99/1 (mol%/mol%), preferably 80/20 to 94/6 (mol%/mol%). When the polyhydroxyalkanoate raw material is a mixture of two or more polyhydroxyalkanoates, the average content ratio refers to the molar ratio of each monomer contained in the mixture as a whole.

Furthermore, the weight-average molecular weight of the polyhydroxyalkanoate is 100,000 to 1,000,000 Da; preferably 200,000 to 900,000 Da; more preferably 300,000 to 800,000 Da or 600,000 to 800,000 Da. When the weight-average molecular weight is less than 100,000 Da, there is a tendency for the mechanical properties of the obtained polyhydroxyalkanoate resin molded article to decrease. On the other hand, when the weight-average molecular weight exceeds 1,000,000 Da, there is a tendency for the mechanical load during melt processing to increase and the productivity to decrease.

The polyhydroxy fatty acid ester compositions of the present invention can be prepared using conventional techniques and equipment known in the art, for example, by directly mixing them in a mixing apparatus to obtain powder, or by blending them at room temperature in a high-speed mixer.

To facilitate the processing of the polyhydroxyalkanoate composition of the present invention into molded articles, the polyhydroxyalkanoate composition may also include certain additives to increase the fluidity of the material and facilitate molding.

Furthermore, the additives can be: dispersants, plasticizers, internal lubricants, external lubricants, release agents, and other additives that promote flowability; for example, specific additives can be: amides such as vinyl bis-stearamide (EBS), erucamide, oleamide, linoleamide, palmitamide, stearamide, polyethylene wax, rice bran wax, 8024 (amide wax rheology modifier), silicone oil additives, stearic acid, stearate, epoxidized soybean oil, and one or more other additives with dispersing and lubricating effects.

Furthermore, the amount of the additive is approximately 2%-5% of the mass of the polyhydroxyalkanoate.

Secondly, the present invention provides a polyhydroxyalkanoate molded article prepared from a polyhydroxyalkanoate composition according to the present invention.

The polyhydroxyalkanoate molded body described in this invention may include various forms, such as granules, films, fibers, nonwoven fabrics, straws, sheets, paper-plastic composites, and plates.

The polyhydroxyalkanoate molded articles of the present invention can be prepared by thermal processing molding methods or by non-thermal processing molding methods such as solution casting molding. Therefore, in a third aspect, the present invention also provides a method for preparing the above-mentioned polyhydroxyalkanoate molded articles.

In a specific embodiment, the method for preparing the above-mentioned polyhydroxyalkanoate molded article includes the following steps:

(1) The above-mentioned polyhydroxy fatty acid ester composition, which is mixed evenly, is melted at a temperature higher than the melting point of polyhydroxy fatty acid ester to form a melt;

(2) The melt in step (1) is crystallized at a temperature of 65°C or below.

In a specific implementation, the melt temperature in step (1) of the above preparation method is 140-180°C.

In a specific embodiment, in step (2) of the above preparation method, the melt crystallizes at a temperature of 40°C or below, for example, 20 to 40°C.

In specific embodiments, the polyhydroxyalkanoate molded articles of the present invention can be prepared by various thermoforming methods such as extrusion molding, injection molding, calendering, casting, blow molding, and biaxial stretching.

In a specific embodiment, the polyhydroxyalkanoate molded body of the present invention is prepared into particle molded body by extrusion granulation method, including the following steps:

(1) Melt extrusion: The above-mentioned polyhydroxy fatty acid ester composition, which is mixed evenly, is melt extruded in an extrusion granulation equipment, and the temperature of the extrusion granulation equipment is set to 50-180°C;

(2) Granulation: The melt extruded material is crystallized and granulated at a temperature of 65°C or below.

In the above extrusion granulation method, in step (1), the extrusion granulation equipment can be any conventional granulation equipment in the art, such as parallel co-rotating twin-screw extruders, parallel counter-rotating twin-screw extruders, conical twin-screw extruders, and single-screw extruders with different length-to-diameter ratios. The temperature of the extrusion granulation equipment is set within the range of 50℃ to 180℃, the main engine speed is 50-500 r/min, and the feed rate or production capacity is adjusted according to the actual production status.

In a specific implementation, while maintaining crystallization efficiency and processing effect, a lower energy consumption crystallization temperature can be used. In step (2), the molten extrudate is crystallized and granulated at a temperature of 40°C or below, for example, 20°C to 40°C.

In a specific implementation, step (2) can be carried out by pelletizing methods such as air-cooled strip pelletizing, water bath strip pelletizing, grinding surface hot cutting, water ring cutting and underwater pelletizing.

In a specific implementation, after step (2), there is also a step of drying the prepared particles. Specifically, the prepared particles can be dried using a forced-air drying oven to remove the influence of moisture on the particle performance and to make the particles crystallize completely.

Beneficial effects

(1) The present invention has found that lactic acid or its organic derivatives can be used as nucleating agents to significantly improve the crystallization rate and crystallinity of polyhydroxy fatty acid esters when preparing molded bodies.

(2) Under normal circumstances, the crystallization temperature required to prepare polyhydroxy fatty acid ester molded body is about 40-65℃. In this invention, lactic acid or its organic derivatives can reduce the crystallization temperature of polyhydroxy fatty acid ester with a wide melting range (20-40℃), effectively shorten the curing time of the molded body, and have high nucleation efficiency. At the same time, by using a lower crystallization temperature, a molded body with better crystallization can be obtained without continuous heating, making the processing method simpler and effectively reducing energy consumption.

Detailed Implementation

In the field of thermoplastic processing, the crystallization of polymer materials is, at the microscopic level, a process in which polymer chains partially arrange themselves. During this process, the polymer chains fold up, forming ordered regions called lamellar crystals. These lamellar crystals can stack to form larger spherical structures, called spherulites, thus constituting macroscopically crystalline bodies. In this invention, polyhydroxyalkanoate (PHA), as a polymer raw material with excellent fully biodegradable capabilities, exhibits significant differences in its physical properties, such as glass transition temperature, crystallization temperature, melting point, and melting range, compared to other materials like polyglycolic acid (PGA), polylactic acid (PLA), and polycaprolactone (PCL). In conventional processing, materials like PLA crystallize rapidly, while PHA, due to its lower glass transition temperature (PHA's Tg is approximately 0°C, while PLA's Tg is approximately 60°C), often cannot crystallize rapidly during processing.

Considering the unique characteristics of polymer crystallization, the inventors specifically investigated the effects of nucleating agents commonly used in thermoplastic processing, such as inorganic nucleating agents including nano-calcium carbonate, nano-silica, terephthalic acid, titanium dioxide, hydrotalcite, and boron nitride, organic nucleating agents such as dedicated nucleating agents for polylactic acid (PLA) (e.g., TMC-306, TMC-200), and lactic acid or its derivatives used in this invention, on the crystallization effect of PHA, and found a more suitable solution for promoting PHA crystallization.

The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. The present invention will be described in detail below through embodiments. In the following embodiments, unless otherwise specified, all materials used are commercially available, and unless otherwise specified, the methods used are conventional methods in the art.

The endpoints and any values of the ranges 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 endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

The present invention will be described in more detail through the following embodiments, but these embodiments do not constitute a limitation thereof. Unless otherwise specified, all raw materials used in the following embodiments and comparative examples are commercially available.

Raw materials and their sources:

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), product number: BP350, Beijing Lanjing Microbial Technology Co., Ltd., contains 89% 3HB (3-hydroxybutyrate unit) and has a weight-average molecular weight of approximately 600,000-800,000.

L-Lactic acid ((S)-2-hydroxypropionic acid), product number: L118493, Aladdin, >98.0% (T), refractive index 1.4260-1.4310, specific rotation -10.0-15.0 deg (C=2.5, 1.5mol/L NaOH sol.).

D-Lactic Acid ((R)-2-Hydroxypropionic Acid), Product No.: S161106, Aladdin, >90.0% (T), Refractive Index 1.43, Specific Rotation 13° (C = 2.5, 1.5 mol/L NaOH).

Methyl lactate (methyl DL-lactic acid ester), product number: M158854, Aladdin, >98.0% (GC), refractive index 1.413.

Ethyl lactate (ethyl α-hydroxypropionate), product number: E108230, Aladdin, 98.0% (GC), refractive index 1.4125.

Butyl lactate (α-hydroxypropionate butyl ester), product number: B111190, Aladdin, 98.0% (GC), refractive index 1.421, specific rotation -10.0-13.0 deg (neat).

equipment:

High-speed mixer: Zhangjiagang Zhengde Machinery Factory, Model: SHR-50L.

Twin-screw extruder granulator: Nanjing Keya Chemical Complete Equipment Co., Ltd., Model: HK36.

Preparation methods of polyhydroxyalkanoate particle molded bodies in Experiments 1-35:

Preparation of granulated particles: Twin-screw extrusion granulation was used; the formulations of the polyhydroxyalkanoate compositions used in Examples 1-35 (components in the formulations are by mass) are shown in Tables 1-4. The specific preparation steps are as follows:

(1) Mixing: Place the polyhydroxy fatty acid ester powder and nucleating agent in a high-speed mixer and mix at room temperature. The mixing speed is 200 r/min and the mixing time is 5 min. After mixing, place the mixture in the hopper of a twin-screw extruder.

(2) Melt extrusion: Set the conditions of the extrusion granulation equipment and carry out melt extrusion at a melt temperature of 150°C;

(3) Granulation: Granulation is carried out by underwater cutting system, and the water bath heating temperature is set as shown in Tables 1 to 4.

Performance evaluation methods for polyhydroxyalkanoate particle molded articles in Examples 1-35:

Crystallinity:

Using a differential scanning calorimeter (TA Instruments DSC25 model), 2-10 mg of polyhydroxyalkanoate molded part was measured and heated from -50°C to 180°C in a single step at a heating rate of 10°C/min to obtain DSC curves. Further data on the glass transition temperature, melting temperature, melt peak area, and cold crystallization peak area of the polyhydroxyalkanoate composition DSC curves were obtained.

Crystallinity (%) = 100% × enthalpy of fusion / enthalpy of fusion for 100% crystallization;

The enthalpy of 100% crystallization is the theoretical enthalpy of a 100% crystalline material. Higher crystallinity indicates higher crystallinity of the molded body, which is more conducive to subsequent processing and shaping.

Difficulty of thermoplastic processing of particle molded parts:

○: It can be processed continuously and stably, and the curing time of the molded body is short.

△: Stable extrusion during thermoplastic processing, but the cured body takes a long time to solidify.

×: The extruder is unstable during extrusion, and the molded body has a long curing time.

Weight-average molecular weight:

The weight-average molecular weight was determined using a gel permeation chromatography system (HPLC GPC system manufactured by Shimadzu Corporation) with chloroform solution and by polystyrene conversion. A column suitable for determining weight-average molecular weight was used as the chromatographic column in this gel permeation chromatography system.

The performance evaluation results of the polyhydroxyalkanoate particle molded bodies in Experiments 1 to 35 above are shown in Tables 1 to 4.

Example 1: Effects of lactic acid, organic lactic acid derivatives, and similar substances on nucleation of molded articles

Table 1

As shown in Experiments 1-8, compared with the blank control Experiment 8, the addition of lactic acid (Experiments 1-3) and its organic derivatives (Experiments 4-7) can both improve the crystallization nucleation ability of PHA. Relatively speaking, lactic acid has a superior crystallization nucleation ability, and its crystallization nucleation effect is much greater than that of lactic acid organic ester derivatives. In addition, the study found that lactide, which forms a six-membered ring as a lactic acid dimer, actually reduces the crystallinity of PHA (Experiment 4). It can be seen that adding six-membered ring lactide without retaining α-hydroxyl groups to PHA does not play a role in improving crystallinity. This also verifies that retaining the α-hydroxyl groups of lactic acid organic derivatives can achieve a similar crystallization-promoting effect. Therefore, the present invention should not be limited to the specific lactic acid organic derivatives containing α-hydroxyl groups listed above.

Example 2: Effect of lactic acid and other existing nucleating agents on the molding effect of molded articles

Table 2

Comparing Experiment 1 with Experiments 9-19, it can be seen that lactic acid nucleating agent significantly improves crystallinity and has a higher nucleation efficiency than other existing nucleating agents. Furthermore, compared to other existing nucleating agents, lactic acid is more readily available, has good applicability, and the prepared molded articles exhibit excellent environmental and bio-friendly properties.

Example 3: Effect of adding different weight parts of lactic acid on the nucleation effect and properties of the molded article

Table 3

Experimental Example 20 twenty one twenty two twenty three twenty four 25 26 27 28 29 30 BP350 100 100 100 100 100 100 100 100 100 100 100 L-lactic acid 0.1 0.2 0.3 0.4 0.5 0.7 1.2 1.5 2 2.5 3 total 100.1 100.2 100.3 100.4 100.5 100.7 101.2 101.5 102 102.5 103 Melting temperature (°C) 150 150 150 150 150 150 150 150 150 150 150 Water bath temperature (°C) 50 50 50 50 50 50 50 50 50 50 50 Crystallinity (%) 26.12 26.73 25.93 29.70 29.64 29.80 28.74 29.27 26.67 28.12 25.41

Regarding crystallinity, higher crystallinity results in better nucleation efficiency. As shown in Examples 1 and 20-30, compared to the blank control Example 8, the addition of lactic acid significantly improves the crystallinity of the raw materials. Within the range of 0.1-3 parts added in the above examples, lactic acid promotes crystallization, leading to better crystallization and improved processability of the prepared molded articles. In this example, it was found that the effect is not significant when the added amount of lactic acid is less than 0.01%, while when the added amount is greater than 20%, it often causes resin depolymerization and produces an off-odor. Therefore, the range of lactic acid added can be 0.01% to 20%.

Example 4: Other effects of lactic acid and other additives on the molding process

Table 4

Experimental Example 31 32 33 34 35 BP350 100 100 100 100 100 L-lactic acid 1 behenic acid 1 Boron nitride 1 16-Hydroxyhexadecanoic acid 1 TMC-200 1 total 101 101 101 101 101 Melting temperature (°C) 150 150 150 150 150 Water bath temperature (°C) 38 38 38 38 38 Curing time (s) 10 30 Unable to cure 60 85 Processing difficulty o △ × △ △

The symbols have the following meanings:

○: It can be processed continuously and stably, and the curing time of the molded body is short.

△: Stable extrusion during thermoplastic processing, but the cured body takes a long time to solidify.

×: The extruder is unstable during extrusion, and the molded body has a long curing time.

Comparing the data in Table 4, it was found that when the crystallization temperature was lowered, i.e., the water bath temperature was set to 20℃-40℃ (38℃), compared with the addition of additives such as behenic acid, boron nitride, 16-hydroxyhexadecanoic acid, and TMC-200 (Experiments 32-35), the addition of lactic acid (Experiment 31) could effectively solidify PHA in a short time, improve processing efficiency, and reduce processing difficulty. It can be seen that when lactic acid is added, a lower crystallization temperature can be used, which can not only ensure the crystallization quality of the molded body and reduce the curing time to improve efficiency, but also reduce the energy consumption in actual production.

Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims (10)

1. A polyhydroxyalkanoate composition comprising: Polyhydroxy fatty acid esters; and at least one of the following general formula I: lactic acid or organic lactic acid derivatives: R ² CH ₂ -CH(OH)-COYR ¹ I Wherein, ^R1 is H or a hydrocarbon group, ^R2 is H or a hydrocarbon group, and Y is any one of C, O, N, and S. 2. The polyhydroxyalkanoate composition according to claim 1, characterized in that Y in general formula I is O, and ^R1 and ^R2 are H respectively, that is, the composition includes lactic acid, wherein the lactic acid is selected from L-lactic acid, D-lactic acid or a combination thereof; In the combination of L-lactic acid and D-lactic acid, the ratio of L-lactic acid to D-lactic acid is 0.01 to 99.99 to 99.99 to 0.01. 3. The polyhydroxyalkanoate composition according to claim 1, characterized in that, in general formula I, Y is O, ^R1 is a C1-C16 hydrocarbon group, and ^R2 is H or a C1-C16 hydrocarbon group; or, In general formula I, Y is O, ^R1 is H, ^{and R2} is a C1-C16 hydrocarbon group. 4. The polyhydroxy fatty acid ester composition according to claim 3, wherein the lactic acid organic derivative comprises methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isoamyl lactate, benzyl lactate, tetradecyl lactate, hexadecyl lactate, methyl 3-phenyllactic acid, and 3-phenyllactic acid. 5. The polyhydroxyalkanoate composition according to any one of claims 1-4, characterized in that the amount of lactic acid and/or lactic acid organic derivatives added is 0.01%-20% of the mass of the polyhydroxyalkanoate. 6. The polyhydroxyalkanoate composition according to claim 1, characterized in that the polyhydroxyalkanoate contains a structural unit represented by the following general formula II: Wherein, R represents an alkyl group represented by C _p H _2p+1 , and p represents an integer from 1 to 15, preferably an integer from 1 to 10, and more preferably an integer from 1 to 8; m can be 1, 2, or 3. 7. A polyhydroxyalkanoate molded body, prepared from the polyhydroxyalkanoate composition according to any one of claims 1-6. 8. The method for preparing the polyhydroxyalkanoate molded article according to claim 7, characterized in that it comprises the following steps: (1) The polyhydroxy fatty acid ester composition of any one of claims 1-6 is mixed evenly and melted at a temperature higher than the melting point of the polyhydroxy fatty acid ester to form a melt; (2) The melt in step (1) is crystallized at a temperature of 65°C or below. 9. The method for preparing polyhydroxyalkanoate molded body according to claim 8, characterized in that, in step (2), the melt is crystallized at a temperature of 40°C or below. 10. The preparation method according to claim 8 or 9, characterized in that the polyhydroxyalkanoate molded body is prepared into particle molded body by extrusion granulation, comprising the following steps: (1) Melt extrusion: The polyhydroxy fatty acid ester composition of any one of claims 1-6 is mixed evenly and melt extruded in an extrusion granulation equipment, wherein the temperature of the extrusion granulation equipment is set to 50-180°C; (2) Granulation: The melt extruded material is crystallized and granulated at a temperature of 20-40℃.