A device and process for preparing PGLA by ring-opening copolymerization of glycolide and lactide

Abstract

The present application relates to the technical field of polymer chemistry engineering, and particularly relates to a device and process for preparing PGLA by ring-opening copolymerization of glycolide and lactide. The process comprises: (1) pre-polymerization of glycolide to provide PGA oligomer; (2) pre-polymerization of lactide to provide PLA oligomer; (3) transesterification of the PGA oligomer and the PLA oligomer under the action of a transesterification catalyst to provide a low-molecular-weight PGLA polymer melt; and (4) chain extension, devolatilization and granulation of the low-molecular-weight PGLA polymer melt to obtain PGLA polymer. The present application shortens the reaction time by pre-polymerization of glycolide and lactide, respectively, and then transesterification of the obtained PLA oligomer and PGA oligomer, so that the composition and randomness of the formed PGLA copolymer are relatively uniform, and after chain extension, the PGLA copolymer with high molecular weight, narrow molecular weight distribution and low yellowness index is formed.

Description

Technical Field

[0001] This invention relates to the field of polymer chemical engineering technology, specifically to an apparatus and process for preparing PGLA by ring-opening copolymerization of glycolide and lactide. Background Technology

[0002] With increasing emphasis on energy consumption and environmental protection, biodegradable plastics are receiving growing attention. Polyglycolic acid (PGA), also known as polylactic acid, is a biodegradable aliphatic polymer that can be hydrolyzed in microorganisms or organisms under the catalysis of enzymes or acids and alkalis, ultimately forming carbon dioxide and water. It is a biodegradable material with great development potential. However, PGA's melting point of approximately 220°C is close to its decomposition temperature of 250°C, limiting its applications. By polymerizing lactide segments to lower its melting point and introducing lactic acid segments, PGLA combines the advantages of both polyglycolic acid and polylactic acid, greatly expanding its application range.

[0003] Typically, high molecular weight PLA and PGA are prepared using ring-opening polymerization. In conventional polymerization, glycolide and lactide are added together to the same polymerization reactor. Due to the presence of side methyl groups in lactide, its polymerization reactivity ratio is much lower than that of glycolide. Forming the random copolymer PGLA requires the initial generation of PGA and PLA, followed by transesterification of PGA and PLA to generate PGLA. In this process, lactide polymerization is slow and the reaction time is long; the overall polymerization rate is determined by the number of lactide polymerization steps. PGA has a high melting point and high reaction temperature, and is unstable and easily decomposes at high temperatures, making prolonged high-temperature residence time unsuitable. PGA has a higher density than lactide and is only soluble in the sole solvent hexafluoroisopropanol. The generated PGA tends to deposit at the bottom of the lactide layer, reducing mass transfer efficiency and requiring a longer copolymerization time, making it impossible to form a PGLA copolymer with uniform composition and randomness. Furthermore, the generated PGA deposits in dead corners or corners, easily causing reactor blockage and coking.

[0004] CN101445595B discloses a method for preparing poly(glycolic acid) and its applications. The method involves heating glycolide and lactide to melt, followed by copolymerization under reduced pressure and in the presence of a catalytically applied catalyst in an inert atmosphere. The reaction temperature is 100–160°C, the reaction time is 8–15 hours, and the polymerization reactor is a reaction vessel. This copolymerization method has a long reaction time, and due to the different reactivity rates of glycolide and lactide, the randomness and compositional reproducibility of the PGLA copolymer are difficult to strictly control. This is especially true for copolymerization processes with high glycolide content, where the reactivity rate of glycolide is much higher than that of lactide, resulting in the formation of a small amount of poorly soluble PGA, making it difficult to generate a homogeneous PGLA random copolymer with a high glycolic acid content. Therefore, traditional PLA and PGA reactors cannot meet the requirements for continuous and process-oriented production of PGLA. CN106928437B discloses an apparatus and process for preparing high molecular weight polyesters via ring-opening polymerization of cyclic esters. A monomer and catalyst mixture is atomized by an atomizer at the top of a reactive fluidized bed and injected into the bed, which has already been supplied with high-temperature inert gas at the bottom. The resulting polymer powder is then conveyed into a solid-phase thickening fluidized bed for solid-phase thickening. Although PGLA copolymers are prepared, the composition and randomness of the product are not described. Furthermore, since the products are all powders, the energy consumption for conveying them during industrial production is high, and the pipelines are prone to clogging, resulting in poor continuity of the production process. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an apparatus and process for preparing PGLA by ring-opening copolymerization of glycolide and lactide. The process involves parallel polymerization, i.e., glycolide and lactide are polymerized separately, and finally transesterification reaction is carried out in the same reactor to generate PGLA copolymer, thereby solving the problems in the prior art.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a process for preparing PGLA by ring-opening copolymerization of glycolide and lactide, the process comprising at least the following steps:

[0008] (1) Prepolymerize glycolide to provide PGA oligomers;

[0009] (2) Prepolymerize lactide to provide PLA oligomers;

[0010] (3) The PGA oligomers provided in step (1) and the PLA oligomers provided in step (2) are subjected to transesterification reaction under the action of transesterification catalyst to provide a low molecular weight PGLA polymer melt.

[0011] (4) The low molecular weight PGLA polymer melt provided in step (3) is then subjected to chain extension, devolatilization and pelletizing to obtain PGLA polymer.

[0012] Another aspect of the present invention provides an apparatus for preparing PGLA by ring-opening copolymerization of glycolide and lactide in the process described in the present invention, comprising: a third tubular reactor, a chain extender extruder, a devolatilizer extruder and a pelletizer arranged sequentially in the flow direction; further comprising a first tubular reactor and a circulating tubular reactor, wherein the first tubular reactor and the circulating tubular reactor are respectively connected to the third tubular reactor in the flow direction.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] This process involves the separate prepolymerization of glycolide and lactide. Under the action of a transesterification catalyst, PLA oligomers and PGA oligomers undergo transesterification, thus shortening the reaction time. The resulting PGLA copolymer has a relatively uniform composition and randomness. After chain extension, it can form a PGLA copolymer with high molecular weight, narrow molecular weight distribution, and low yellowness index. A stirred tubular reactor is used in the prepolymerization stage to enhance mass and heat transfer. A circulation system is incorporated into the tubular reactor during the PLA prepolymerization stage, which helps to shorten the reaction time. In the final polymerization stage, due to the high viscosity of the polymer melt, the stirred tubular reactor is prone to "rod climbing," affecting mass and heat transfer. Therefore, a static mixing reactor is used. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0016] Figure 2 This is a schematic diagram of the tubular reactor used in this invention.

[0017] Figure 3 This is a schematic diagram of the device of the present invention.

[0018] Component labels in the diagram:

[0019] 1 First melting vessel

[0020] 2 First batching vessel

[0021] 3 Second melting vessel

[0022] 4 Second batching vessel

[0023] 5. First tubular reactor

[0024] 6. Circulating tubular reactor

[0025] 61 Second Tubular Reactor

[0026] 62 Circulating Melt Pump

[0027] 7. Third Tubular Reactor

[0028] 8. Chain extender extruder

[0029] 9. Deviation extruder

[0030] 10 Pelletizer Detailed Implementation

[0031] The following details the implementation of the apparatus and process for preparing PGLA based on the ring-opening copolymerization of glycolide and lactide.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the process includes steps (1) and (2), indicating that the process may include steps (1) and (2) performed sequentially, or it may include steps (2) and (1) performed sequentially. For example, the mention that the process may also include step (3) indicates that step (3) may be added to the process in any order. For example, the process may include steps (1), (2) and (3), or it may include steps (1), (3) and (2), or it may include steps (3), (2) and (1), etc.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] This invention provides a process for preparing PGLA by ring-opening copolymerization of glycolide and lactide, the process comprising at least the following steps:

[0039] (1) Prepolymerize glycolide to provide PGA oligomers;

[0040] (2) Prepolymerize lactide to provide PLA oligomers;

[0041] (3) The PGA oligomers provided in step (1) and the PLA oligomers provided in step (2) are subjected to transesterification reaction under the action of transesterification catalyst to provide a low molecular weight PGLA polymer melt.

[0042] (4) The low molecular weight PGLA polymer melt provided in step (3) is then subjected to chain extension, devolatilization and pelletizing to obtain PGLA polymer.

[0043] In this context, PGA stands for polyglycolic acid, PLA for polylactide, and PGLA for polyglycolic acid.

[0044] In the process for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by this invention, the raw materials include glycolide and lactide. The glycolide and lactide raw materials need to be thoroughly dried. In some embodiments, the drying conditions may be, for example, vacuum drying; the drying conditions may be, for example, vacuum drying, with an absolute pressure of 1-20 kPa, 1-5 kPa, 5-10 kPa, 10-15 kPa, or 15-20 kPa, etc. Preferably, it is 5-10 kPa. The drying temperature conditions may be, for example, 30-60°C, 30-40°C, 40-50°C, or 50-60°C, etc. Preferably, it is 40-50°C; the drying time may be, for example, 2-6 h, 2-4 h, or 4-6 h, etc. Preferably, it is 4-6 h.

[0045] In the process of preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, step (1) is to prepolymerize glycolide to provide PGA oligomers with a certain degree of polymerization.

[0046] In step (1) of this invention, the prepolymerization reaction of the glycolide further includes a first catalyst and a first initiator. In some embodiments, the first catalyst is selected from one or more combinations of stannous chloride, stannous octoate, stannous tetrachloride, stannous oxide, stannous acetate, zinc oxide, and bismuth acetate. The first initiator is selected from one or more combinations of lauryl alcohol, 1,4-butanediol, polyethylene glycol, glycerol, and pentaerythritol.

[0047] In step (1) of this invention, the amounts of the first catalyst and the first initiator typically need to meet certain requirements. In some specific embodiments, the mass of the first catalyst can be 0.01–2.0 wt%, 0.01–1.0 wt%, 1.0–2.0 wt%, 0.01–0.05 wt%, 0.05–0.1 wt%, 0.1–0.5 wt%, 0.5–1.0 wt%, 1.0–1.5 wt%, or 1.5–2.0 wt%, etc., of the mass of glycolide. In some specific embodiments, the mass of the first initiator is 0-2.0 wt%, 0.01-2.0 wt%, 0.01-1.0 wt%, 1.0-2.0 wt%, 0.01-0.05 wt%, 0.05-0.1 wt%, 0.1-0.5 wt%, 0.5-1.0 wt%, 1.0-1.5 wt%, or 1.5-2.0 wt%, etc., of the mass of glycolide.

[0048] In step (1) of this invention, the prepolymerization reaction of glycolide typically needs to be carried out at a specific temperature, such as 100–245°C, 100–150°C, 150–200°C, or 200–245°C. The reaction can be carried out, for example, in a tubular reactor with a stirrer, and the residence time can be, for example, 0.5–200 min, 0.5–10 min, 10–50 min, 50–100 min, 100–150 min, or 150–200 min. After the reaction, PGA oligomers with a certain degree of polymerization are formed. The molecular weights of PGA oligomers can be 5,000–150,000, 5,000–10,000, 10,000–50,000, 50,000–100,000, 100,000–150,000, 5,000–8,000, 8,000–10,000, 10,000–30,000, 30,000–50,000, 50,000–80,000, 80,000–100,000, 100,000–120,000, or 120,000–150,000, etc.

[0049] In the process for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, step (2) involves prepolymerizing lactide to provide PLA oligomers with a certain degree of polymerization. There is no specific order between steps (1) and (2), for example, they can be carried out simultaneously in different tubular reactors.

[0050] In step (2) of this invention, the prepolymerization reaction of the lactide further includes a second catalyst and a second initiator. In some examples, the second catalyst is selected from one or more combinations of stannous chloride, stannous octoate, stannous tetrachloride, stannous oxide, stannous acetate, zinc oxide, bismuth acetate, etc. The second initiator is selected from one or more combinations of lauryl alcohol, 1,4-butanediol, polyethylene glycol, glycerol, pentaerythritol, etc.

[0051] In step (2) of this invention, the amounts of the second catalyst and the second initiator typically need to meet certain requirements. The mass of the second catalyst can be, for example, 0.01–2.0 wt%, 0.01–1.0 wt%, 1.0–2.0 wt%, 0.01–0.05 wt%, 0.05–0.1 wt%, 0.1–0.5 wt%, 0.5–1.0 wt%, 1.0–1.5 wt%, or 1.5–2.0 wt% of the mass of lactide. The mass of the second initiator can be, for example, 0–2.0 wt%, 0.01–2.0 wt%, 0.01–1.0 wt%, 1.0–2.0 wt%, 0.01–0.05 wt%, 0.05–0.1 wt%, 0.1–0.5 wt%, 0.5–1.0 wt%, 1.0–1.5 wt%, or 1.5–2.0 wt% of the mass of lactide.

[0052] In step (2) of this invention, the prepolymerization reaction of lactide typically needs to be carried out at a specific temperature, such as 100–245°C, 100–150°C, 150–200°C, or 200–245°C. The reaction can be carried out, for example, in a circulating tubular reactor with a stirrer, and the residence time can be, for example, 0.5–200 min, 0.5–10 min, 10–50 min, 50–100 min, 100–150 min, or 150–200 min. After the reaction, PGA oligomers with a certain degree of polymerization are formed. PLA oligomers can have molecular weights of 5,000–150,000, 5,000–10,000, 10,000–50,000, 50,000–100,000, 100,000–150,000, 5,000–8,000, 8,000–10,000, 10,000–30,000, 30,000–50,000, 50,000–80,000, 80,000–100,000, 100,000–120,000, or 120,000–150,000, etc.

[0053] In the process of preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, step (3) is to carry out transesterification reaction of the PGA oligomer provided in step (1) and the PLA oligomer provided in step (2) under the action of transesterification catalyst to provide a low molecular weight PGLA polymer melt.

[0054] In step (3) of this invention, the transesterification reaction needs to be carried out under the catalysis of a transesterification catalyst. The transesterification catalyst is selected from one or more combinations of aluminum chloride, zinc chloride, zinc acetate, tin tetrachloride, stannous octoate, titanium tetrachloride, butyl titanate, dibutyltin oxide, etc.

[0055] In step (3) of this invention, the amount of transesterification catalyst used usually needs to meet certain requirements. The mass of the transesterification catalyst can be, for example, 0.01–2.0 wt%, 0.01–1.0 wt%, 1.0–2.0 wt%, 0.01–0.05 wt%, 0.05–0.1 wt%, 0.1–0.5 wt%, 0.5–1.0 wt%, 1.0–1.5 wt%, or 1.5–2.0 wt%, etc., which is the sum of the masses of glycolide and lactide.

[0056] In step (3) of this invention, the transesterification reaction typically needs to be carried out at a certain temperature, such as 100–245°C, 100–150°C, 150–200°C, or 200–245°C. The PGA prepolymer and PLA prepolymer can be mixed in a tubular reactor, which is a static mixing reactor. Its mixing internal components include one or more combinations of SX, SK, SL, SH, corrugated plate, or Chinese knot type mixing internal components. The reaction residence time of the mixture of PGA and PLA prepolymer is 0.5–200 min, 0.5–10 min, 10–50 min, 50–100 min, 100–150 min, or 150–200 min, etc.

[0057] In step (3) of the present invention, the molecular weight of the low molecular weight PGLA polymer melt obtained by the reaction can be 50,000-300,000, 50,000-100,000, 100,000-200,000, 200,000-300,000, 50,000-80,000, 80,000-100,000, 100,000-150,000, 150,000-200,000, 200,000-250,000, or 250,000-300,000, etc.

[0058] In the process of preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, step (4) involves further processing the low molecular weight PGLA polymer melt provided in step (3) through chain extension, devolatilization, and pelletizing to obtain the PGLA polymer.

[0059] In step (4) of this invention, the chain extension process needs to be carried out under certain temperature conditions. The temperature during the chain extension process can be 100-245℃, 100-150℃, 150-200℃, or 200-245℃, etc. The reaction can be carried out, for example, on a chain-extending extruder, which is one or more combinations of a single-screw, twin-screw, or twin-rotor extruder, and the reaction residence time can be, for example, 0.5-50 min, 0.5-10 min, 10-20 min, 20-30 min, 30-40 min, or 40-50 min, etc.

[0060] In step (4) of this invention, the chain extension process includes a chain extender. The chain extender is selected from one or more of carbodiimide, epoxy polymers, and polyhydroxy polymers.

[0061] In step (4) of this invention, the amount of chain extender usually needs to meet certain requirements. The mass of the chain extender is 0.1-10 wt%, 0.1-1 wt%, 1-2 wt%, 2-3 wt%, 3-4 wt%, 4-5 wt%, 5-6 wt%, 6-7 wt%, 7-8 wt%, 8-9 wt%, or 9-10 wt%, etc., which is the sum of the masses of glycolide and lactide.

[0062] In step (4) of this invention, the devolatilization process needs to be carried out under certain temperature conditions. The temperature of the devolatilization process is 120-245℃, 100-150℃, 150-200℃, or 200-245℃, etc. The devolatilization process can be carried out, for example, on a devolatilization extruder, and the residence time can be, for example, 0.5-50 min, 0.5-10 min, 10-20 min, 20-30 min, 30-40 min, or 40-50 min, etc.

[0063] In step (4) of the present invention, pelletizing can be performed by a pelletizer, and the pelletizing method is selected from one of underwater strip pelletizing, strip air-cooled pelletizing, or die surface hot cutting.

[0064] In step (4) of the present invention, the molecular weight of the PGLA polymer finally obtained can be 150,000-500,000, 150,000-200,000, 200,000-250,000, 250,000-300,000, 300,000-350,000, 350,000-400,000, 400,000-450,000, 450,000-500,000, 150,000-250,000, 250,000-350,000, 350,000-450,000, or 550,000-500,000, etc. Yellowness index can be, for example, 2-30, 2-10, 10-20, 20-30, 2-5, 5-10, 10-15, 15-20, 20-25, or 25-30, etc.

[0065] In one specific embodiment of the process for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the glycolide and lactide need to be thoroughly dried. a) Most of the dried glycolide is preheated to a temperature of 83–170°C, preferably 90–140°C. The remaining small portion of glycolide is mixed and melted with additives such as a first catalyst and a first initiator. This small portion of glycolide is used to dissolve the first catalyst and the first initiator. In some embodiments, the small portion of glycolide may be, for example, 5–20 wt% glycolide. The two liquid phases are then added to a first tubular reactor for reaction. The reaction operating temperature is 100–245°C, preferably 140–230°C; the residence time is 0.5–200 min, preferably 10–150 min. The reaction yields PGA oligomers. b. Preheat most of the dried lactide to a temperature of 93–170°C, preferably 105–140°C. Mix and melt a small portion of the lactide with a certain mass ratio of a second catalyst, a second initiator, and other additives. The small portion of lactide is used to dissolve the second catalyst and the second initiator. In some embodiments, the small portion of lactide may be, for example, 5–20 wt% lactide. Add the two liquid phases separately to a circulating reactor, adjusting the circulation ratio and residence time. The operating temperature is 100–245°C, preferably 100–200°C; the residence time is 0.5–200 min, preferably 100–150 min. The reaction yields PLA oligomers. c. Then, mix the PGA oligomers and PLA oligomers for transesterification. The operating temperature is 100–245°C, preferably 150–230°C; the residence time is 0.5–200 min, preferably 5–100 min. The reaction yields a low molecular weight PGLA polymer melt. d. Low molecular weight PGLA undergoes a chain extension process at an operating temperature of 100–245°C, preferably 150–230°C, with a residence time of 0.5–50 min, preferably 2–20 min. It then undergoes a devolatilization process at an operating temperature of 120–245°C, preferably 150–230°C, with a residence time of 0.5–50 min, preferably 2–20 min. Finally, it is pelletized to obtain the finished PGLA polymer product.

[0066] In another aspect, the present invention provides an apparatus for the ring-opening copolymerization of glycolide and lactide to prepare PGLA using the process described in the first aspect of the present invention. For example... Figure 3 As shown, the device includes: a third tubular reactor 7, a chain extender extruder 8, a devolatilizer extruder 9, and a pelletizer 10 arranged sequentially along the material flow direction; it also includes a first tubular reactor 5 and a circulating tubular reactor 6, which are respectively connected to the third tubular reactor 7 along the material flow direction.

[0067] The apparatus for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention further includes a first melting vessel 1 and a first batching vessel 2; a first tubular reactor 5 is connected to both the first melting vessel 1 and the first batching vessel 2. More specifically, the outlet of the first melting vessel 1 is connected to the inlet of the first tubular reactor 5, and the outlet of the first batching vessel 2 is connected to the inlet of the first tubular reactor 5. A stirrer is installed inside the first tubular reactor 5. In practical applications, typically, most of the dried glycolide is added to the first melting vessel 1 for preheating. A small portion of the glycolide is mixed and melted with a first catalyst and a first initiator in the first batching vessel 2. Then, the two liquid phases are each added to the first tubular reactor 5 for reaction.

[0068] The apparatus for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by this invention further includes a second melting vessel 3 and a second batching vessel 4; the circulating tubular reactor 6 is connected to both the second melting vessel 3 and the second batching vessel 4. More specifically, the outlet of the second melting vessel 3 is connected to the inlet of the circulating tubular reactor 6, and the outlet of the second batching vessel 4 is connected to the inlet of the circulating tubular reactor 6. A stirrer is installed inside the circulating tubular reactor 6. In practical applications, typically, most of the dried lactide is added to the second melting vessel 3 for preheating. A small portion of the lactide is mixed and melted with the second catalyst and the second initiator in the second batching vessel 4. Then, the two liquid phases are each added to the circulating tubular reactor 6 for reaction.

[0069] In the apparatus for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the circulating tubular reactor 6 includes a second tubular reactor 61 and a circulating melt pump 62 for driving the circulation of the second tubular reactor 61; the second tubular reactor 61 is connected to the third tubular reactor 7. A stirrer is provided inside the second tubular reactor 61; the third tubular reactor 7 is a static mixing reactor. More specifically, the outlet of the second tubular reactor 61 is connected to the inlet of the third tubular reactor 7, the outlet of the second melting vessel 3 is connected to the inlet of the second tubular reactor 61, and the outlet of the second batching vessel 4 is connected to the inlet of the second tubular reactor 61.

[0070] In the apparatus for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the first tubular reactor 5 has an average of n-1 layers of guide plates and n layers of flat paddles arranged sequentially inside, where n is 5-100, 5-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 70-80, 80-90, or 90-100, etc.

[0071] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, n - 1 layers of flow guiding plates and n layers of flat paddles are arranged in sequence inside the circulating tubular reactor 6 on average, where n is 5 - 100, 5 - 10, 10 - 20, 20 - 30, 30 - 40, 40 - 50, 50 - 60, 60 - 70, 70 - 80, 80 - 90, or 90 - 100, etc., and its circulation ratio is 0 - 50, 1 - 50, 1 - 10, 10 - 20, 10 - 30, 30 - 40, or 40 - 50, etc. By regulating the circulation ratio of the circulating tubular reactor 6 with stirring, in an industrial-scale device, the segment ratio of lactic acid and glycolic acid in poly (lactic-co-glycolic acid) (PGLA) can be flexibly adjusted to meet the continuous production requirements and improve production efficiency.

[0072] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the third tubular reactor 7 is selected from a static mixing reactor, and the mixing internal components of the static mixing reactor include one or a combination of multiple types of mixing internal components such as SX type, SK type, SL type, SH type, corrugated plate type or Chinese knot type.

[0073] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the chain extender extruder 8 is selected from one or a combination of multiple types such as single-screw, double-screw or double-rotor extruders.

[0074] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, the devolatilization extruder 9 is selected from one or a combination of multiple types such as single-screw, double-screw or double-rotor extruders.

[0075] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, a vacuum pump is further provided on the devolatilization extruder 9. More specifically, the devolatilization extruder 9 is configured with a single-stage or multi-stage combined vacuum pump.

[0076] In the device for preparing PGLA by ring-opening copolymerization of glycolide and lactide provided by the present invention, a vacuum unit supporting the devolatilization extruder 9 and a melt pump for inter-stage transportation, etc. are also provided.

[0077] In one specific embodiment, the raw materials glycolide and lactide need to be thoroughly dried. The drying conditions are: vacuum drying; absolute pressure 1-20 kPa, preferably 5-10 kPa; temperature 30-60°C, preferably 40-50°C; time 2-6 h, preferably 4-6 h. Most of the dried glycolide is preheated in a first melting vessel 1 at a preheating temperature of 83-170°C, preferably 90-140°C. A small portion of the glycolide is mixed and melted with a certain mass ratio of a first catalyst, a first initiator, and other additives in a first batching vessel 2. The two liquid phases are then separately added to a first tubular reactor 5 equipped with a stirrer. The operating temperature is 100-245°C, preferably 140-230°C; the residence time is 0.5-200 min, preferably 10-150 min. Most of the dried lactide is preheated in a second melting vessel 3 at a preheating temperature of 93-170°C, preferably 105-140°C. A small portion of lactide is mixed and melted with a certain mass ratio of a second catalyst, a second initiator, and other additives in a second batching vessel 4. The two liquid phases are then separately added to a stirred circulating tubular reactor 6. The circulation ratio is adjusted, and the residence time is varied. The operating temperature is 100–245°C, preferably 100–200°C; the residence time is 0.5–200 min, preferably 100–150 min. Subsequently, the PGA oligomers from the outlet of the stirred first tubular reactor 5 and the PLA oligomers from the outlet of the stirred circulating tubular reactor 6 are continuously fed into a third tubular reactor 7 for transesterification. The operating temperature of the third tubular reactor 7 is 100–245°C, preferably 150–230°C, and the residence time is 0.5–200 min, preferably 5–100 min. The low molecular weight PGLA from the outlet of the third tubular reactor 7 is fed into a chain extender extruder 8. The operating temperature of the chain extender extruder 8 is 100–245°C, preferably 150–230°C, and the residence time is 0.5–50 min, preferably 2–20 min. The low molecular weight PGLA from the outlet of the chain extender extruder 8 is fed into a devolatilization extruder 9. The operating temperature of the devolatilization extruder 9 is 120–245°C, preferably 150–230°C, and the residence time is 0.5–50 min, preferably 2–20 min. The devolatilized PGLA is pelleted to obtain the finished PGLA product.

[0078] The beneficial effects of this invention are:

[0079] (1) The process of the present invention involves the separate prepolymerization reaction of glycolide and lactide. Under the action of the transesterification catalyst, PLA oligomers and PGA oligomers undergo transesterification reaction, thereby shortening the reaction time. The resulting PGLA copolymer has a relatively uniform composition and randomness. After chain extension, it can form a PGLA copolymer with high molecular weight, narrow molecular weight distribution and low yellowness index.

[0080] (2) The present invention uses a tubular reactor with stirring, which enhances the mass and heat transfer in the prepolymerization process;

[0081] (3) The present invention shortens the reaction time and controls the degree of polymerization of PLA oligomers by adjusting the circulation ratio of the circulating tubular reactor with stirring.

[0082] (4) This invention shortens the reaction time of conventional copolymerization process by transesterification reaction of PGA oligomers and PLA oligomers, and solves the problems of small amount of PGA deposited in the corner of the reactor, which is easy to clog and easy to coke and carbon deposit.

[0083] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0084] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0085] Furthermore, it should be understood that the existence of other process steps before or after the combined steps, or the insertion of other process steps between these explicitly mentioned steps, does not preclude the existence of other process steps before or after the combined steps, or the insertion of other process steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each process step is merely a convenient tool for identifying each process step, and not intended to limit the order of the process steps or limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0086] Unless otherwise specified, all reagents, materials and instruments used in the following embodiments are commercially available.

[0087] Example 1

[0088] (1) Melt 90 parts (wt%) of glycolide at 120°C, and continuously add it to the first tubular reactor with stirring, along with 0.18 parts (wt%) of stannous octoate and 0.9 parts (wt%) of 1,4-butanediol. The operating temperature is 140°C and the residence time is 30 min.

[0089] (2) Melt 10 parts (wt%) of lactide at 120°C, and continuously add it to a second tubular reactor with stirring, along with 0.02 parts (wt%) of stannous octoate and 0.1 parts (wt%) of 1,4-butanediol. The operating temperature is 140°C and the residence time is 120 min.

[0090] (3) The products from the first tubular reactor and the second tubular reactor are continuously fed into the third tubular reactor at an operating temperature of 230°C and a residence time of 10 min. Then, they are fed into a chain extender extruder for chain extension reaction at an operating temperature of 230°C and a residence time of 10 min. The chain extender is 0.5 parts (wt%) of ADR chain extender. Finally, they are fed into a devolatilization extruder for devolatilization at an operating temperature of 230°C and a residence time of 10 min. The product is collected after pelleting.

[0091] The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 272,000, the molecular weight distribution was 2.3, the melt index was 20 g / 10 min, and the yellowness index (YI) was 21.2.

[0092] The testing method is as follows:

[0093] (1) Weight-average molecular weight and molecular weight distribution

[0094] Weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined using gel permeation chromatography (GPC), with PMMA as the GPC standard.

[0095] (2) Melt indexer

[0096] The test conditions were a test temperature of 230℃ and a nominal load of 2.16kg.

[0097] (3) Yellowness Index

[0098] The YI value was measured using a yellowness index meter.

[0099] Example 2

[0100] The difference between this embodiment and Example 1 is that in step (1), the amount of glycolide is 80 parts (wt%), stannous octoate is 0.16 parts (wt%), and 1,4-butanediol is 0.8 parts (wt%); in step (2), the amount of lactide is 20 parts (wt%), stannous octoate is 0.04 parts (wt%), and 1,4-butanediol is 0.2 parts (wt%). The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 243,000, the molecular weight distribution was 2.3, the melt index was 23 g / 10 min, and the yellowness index (YI) was 15.8. The testing method was the same as in Example 1.

[0101] Example 3

[0102] The difference between this embodiment and Example 1 is that in step (1), the amount of glycolide is 70 parts (wt%), stannous octoate is 0.14 parts (wt%), and 1,4-butanediol is 0.7 parts (wt%); in step (2), the amount of lactide is 30 parts (wt%), stannous octoate is 0.06 parts (wt%), and 1,4-butanediol is 0.3 parts (wt%). The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 223,000, the molecular weight distribution was 2.0, the melt index was 27 g / 10 min, and the yellowness index (YI) was 14.6. The testing method was the same as in Example 1.

[0103] Example 4

[0104] The difference between this embodiment and Example 1 is that in step (1), the amount of glycolide is 50 parts (wt%), stannous octoate is 0.1 parts (wt%), and 1,4-butanediol is 0.5 parts (wt%); in step (2), the amount of lactide is 50 parts (wt%), stannous octoate is 0.1 parts (wt%), and 1,4-butanediol is 0.5 parts (wt%). The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 205,000, the molecular weight distribution was 1.8, the melt index was 30 g / 10 min, and the yellowness index (YI) was 12.5.

[0105] Example 5

[0106] The difference between this embodiment and Example 1 is that lauryl alcohol was used as the initiator. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 225,000, the molecular weight distribution was 2.3, the melt index was 25 g / 10 min, and the yellowness index (YI) was 14.9. The testing methods were the same as in Example 1.

[0107] Example 6

[0108] The difference between this embodiment and Example 2 is that lauryl alcohol was used as the initiator. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 191,000, the molecular weight distribution was 2.3, the melt index was 30 g / 10 min, and the yellowness index (YI) was 10.2. The testing method was the same as in Example 1.

[0109] Example 7

[0110] The difference between this embodiment and Example 3 is that lauryl alcohol was used as the initiator. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 188,000, the molecular weight distribution was 2.0, the melt index was 34 g / 10 min, and the yellowness index (YI) was 9.9. The testing method was the same as in Example 1.

[0111] Example 8

[0112] The difference between this embodiment and Example 4 is that lauryl alcohol was used as the initiator. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 159,000, the molecular weight distribution was 1.8, the melt index was 39 g / 10 min, and the yellowness index (YI) was 6.3. The testing method was the same as in Example 1.

[0113] Example 9

[0114] The difference between this embodiment and Example 1 is that the initiator is polyethylene glycol. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 284,000, the molecular weight distribution was 2.5, the melt index was 18 g / 10 min, and the yellowness index (YI) was 21.4.

[0115] Example 10

[0116] The difference between this embodiment and Example 2 is that the initiator is polyethylene glycol. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 255,000, the molecular weight distribution was 2.5, the melt index was 20 g / 10 min, and the yellowness index (YI) was 17.9. The testing method was the same as in Example 1.

[0117] Example 11

[0118] The difference between this embodiment and Example 3 is that the initiator is polyethylene glycol. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 234,000, the molecular weight distribution was 2.3, the melt index was 24 g / 10 min, and the yellowness index (YI) was 15.5. The testing method was the same as in Example 1.

[0119] Example 12

[0120] The difference between this embodiment and Example 4 is that the initiator is polyethylene glycol. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 216,000, the molecular weight distribution was 2.1, the melt index was 27 g / 10 min, and the yellowness index (YI) was 14.0. The testing method was the same as in Example 1.

[0121] Example 13

[0122] The difference between this embodiment and Example 9 is that the chain extender is 0.3 parts (wt%) of ADR chain extender. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 266,000, the molecular weight distribution was 2.4, the melt index was 21 g / 10 min, and the yellowness index (YI) was 19.7. The testing method was the same as in Example 1.

[0123] Example 14

[0124] The difference between this embodiment and Example 9 is that the chain extender is 0.7 parts (wt%) of ADR chain extender. The weight-average molecular weight (Mw) of the obtained PGLA resin was measured to be 303,000, the molecular weight distribution was 2.5, the melt index was 15 g / 10 min, and the yellowness index (YI) was 23.5. The testing method was the same as in Example 1.

[0125] Example 15

[0126] 100 parts (wt%) of glycolide were melted at 120°C and continuously added to a first tubular reactor equipped with a stirrer, along with 0.2 parts (wt%) of stannous octoate and 1.0 parts (wt%) of 1,4-butanediol. The operating temperature was 140°C and the residence time was 30 min. The mixture was then transferred to a third tubular reactor, where the operating temperature was 230°C and the residence time was 10 min. Next, it was fed into a chain extender extruder for chain extension reaction, where the operating temperature was 230°C and the residence time was 10 min. The chain extender used was 0.5 parts (wt%) of ADR chain extender. Finally, it was fed into a devolatilization extruder for devolatilization, where the operating temperature was 230°C and the residence time was 10 min. The product was then pelletized and collected. The obtained PGA resin had a weight-average molecular weight (Mw) of 313,000, a molecular weight distribution of 2.5, a melt index of 15 g / 10 min, and a yellowness index (YI) of 23.9. The testing methods were the same as in Example 1.

[0127] Example 16

[0128] 100 parts (wt%) of lactide were melted at 120°C and continuously added to a second tubular reactor with stirring, along with 0.2 parts (wt%) of stannous octoate and 1.0 parts (wt%) of 1,4-butanediol. The operating temperature was 140°C and the residence time was 120 min. The mixture was then transferred to a third tubular reactor at 230°C for 10 min. Next, it was fed into a chain extender extruder for chain extension at 230°C for 10 min, using 0.5 parts (wt%) of ADR chain extender. Finally, it was fed into a devolatilization extruder for devolatilization at 230°C for 10 min. The product was then pelletized and collected. The obtained PLA resin had a weight-average molecular weight (Mw) of 145,000, a molecular weight distribution of 1.6, a melt index of 35 g / 10 min, and a yellowness index (YI) of 5.3. The testing methods were the same as in Example 1.

[0129] The apparatus and process for preparing PGLA by ring-opening copolymerization of glycolide and lactide proposed in this invention have been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the apparatus and process described herein without departing from the content, spirit, and scope of this invention to achieve the technical requirements of this invention. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A process for preparing PGLA by ring-opening copolymerization of glycolide and lactide, the process comprising at least the following steps: (1) pre-polymerizing glycolide to provide PGA oligomer; wherein the pre-polymerization of the glycolide further comprises a first catalyst and a first initiator; the first catalyst is selected from a combination of one or more of stannous chloride, stannous octoate, tin tetrachloride, tin oxide, stannous acetate, zinc oxide, bismuth acetate; the first initiator is selected from a combination of one or more of lauryl alcohol, 1, 4-butanediol, polyethylene glycol, glycerol, pentaerythritol; the pre-polymerization of the glycolide is at a temperature of 100-245℃ and a residence time of 0.5-200 min; the PGA oligomer has a molecular weight of 5000-150000; (2) pre-polymerizing lactide to provide PLA oligomer; wherein the pre-polymerization of the lactide further comprises a second catalyst and a second initiator; the second catalyst is selected from a combination of one or more of stannous chloride, stannous octoate, tin tetrachloride, tin oxide, stannous acetate, zinc oxide, bismuth acetate; the second initiator is selected from a combination of one or more of lauryl alcohol, 1, 4-butanediol, polyethylene glycol, glycerol, pentaerythritol; the pre-polymerization of the lactide is at a temperature of 100-245℃ and a residence time of 0.5-200 min; the PLA oligomer has a molecular weight of 5000-150000; (3) transesterifying the PGA oligomer provided in step (1) and the PLA oligomer provided in step (2) in the presence of a transesterification catalyst to provide a low molecular weight PGLA polymer melt; wherein the transesterification is at a temperature of 100-245℃; the mixture of the PGA oligomer and the PLA oligomer has a residence time of 0.5-200 min; (4) further chain extending, devolatilizing and pelletizing the low molecular weight PGLA polymer melt provided in step (3) to obtain PGLA polymer; wherein the chain extending is at a temperature of 100-245℃ and a residence time of 0.5-50 min; the chain extending comprises a chain extender; the chain extender is selected from one or more of carbodiimide, epoxy polymer, polyhydroxy polymer; the devolatilizing is at a temperature of 120-245℃ and a residence time of 0.5-50 min. In step (1), the mass of the first catalyst is 0.01-2.0 wt% of the mass of the glycolide; the mass of the first initiator is 0.01-2.0 wt% of the mass of the glycolide. In step (2), the mass of the second catalyst is 0.01-2.0 wt% of the mass of the lactide; the mass of the second initiator is 0.01-2.0 wt% of the mass of the lactide. ​ ​ ​ ​ 2. The process for the preparation of PGLA by ring opening copolymerization of glycolide, lactide according to claim 1, characterized in that, ​ 3. The process for the preparation of PGLA by ring opening copolymerization of glycolide, lactide according to claim 1, characterized in that, ​ 4. The process for the preparation of PGLA by ring opening copolymerization of glycolide, lactide according to claim 1, characterized in that, In step (3), the transesterification catalyst is selected from a combination of one or more of aluminum chloride, zinc chloride, zinc acetate, tin tetrachloride, stannous octoate, titanium tetrachloride, butyl titanate; the mass of the transesterification catalyst is 0.01-2.0wt% of the sum of the masses of glycolide and lactide.

5. The process for the preparation of PGLA by ring opening copolymerization of glycolide, lactide according to claim 1, characterized in that, In step (3), the low-molecular-weight PGLA polymer melt has a molecular weight of 50,000-300,000.

6. The process for the preparation of PGLA by ring opening copolymerization of glycolide, lactide according to claim 1, characterized in that, In step (4), any one or more of the following features are included: D1) the mass of the chain extender is 0.1-10wt% of the sum of the masses of glycolide and lactide; D2) the manner of pelletization is selected from one of underwater strand pelletization, strand air cooling pelletization, or die face hot cutting; D3) the PGLA polymer has a molecular weight of 150,000-500,000; D4) the PGLA polymer has a yellowness index of 2-30.

7. A device for the preparation of PGLA by ring opening copolymerization of glycolide and lactide for use in the process according to any one of claims 1 to 6, characterized in that, A third tubular reactor (7), a chain extension extruder (8), a devolatilization extruder (9), and a pelletizer (10) are sequentially connected in the direction of material flow; a first tubular reactor (5) and a circulating tubular reactor (6) are also included, which are respectively connected to the third tubular reactor (7) in the direction of material flow.

8. The device for the ring opening copolymerization of glycolide and lactide to produce PGLA according to claim 7, characterized in that, Any one or more of the following conditions are also included: E1) the device further includes a first melting kettle (1) and a first batching kettle (2); the first tubular reactor (5) is respectively connected to the first melting kettle (1) and the first batching kettle (2); E2) the device further includes a second melting kettle (3) and a second batching kettle (4); the circulating tubular reactor (6) is respectively connected to the second melting kettle (3) and the second batching kettle (4); E3) the circulating tubular reactor (6) includes a second tubular reactor (61) and a circulating melt pump (62) for driving the second tubular reactor (61) to circulate; the second tubular reactor (61) is connected to the third tubular reactor (7); E4) the first tubular reactor (5) has an average of n-1 layers of flow guides and n layers of flat paddles arranged in sequence inside; n is 5-100; E5) the circulating tubular reactor (6) has an average of n-1 layers of flow guides and n layers of flat paddles arranged in sequence inside; n is 5-100, and the circulation ratio is 0-50; E6) the third tubular reactor (7) is selected from a static mixing reactor, and the mixing internal components of the static mixing reactor include a combination of one or more of SX-type, SK-type, SL-type, SH-type, corrugated plate-type, or Chinese knot-type mixing internal components; E7) the chain extension extruder (8) is selected from a combination of one or more of a single-screw, double-screw, or double-rotor extruder; E8) the devolatilization extruder (9) is selected from a combination of one or more of a single-screw, double-screw, or double-rotor extruder; E9) a vacuum pump is further provided on the devolatilization extruder (9).

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