Device and method for continuously preparing polylactic acid-glycolic acid foamed materials

Abstract

The present invention discloses a device and a method for continuously preparing a polylactic acid-glycolic acid foamed material. The device includes a first reaction kettle, a second reaction kettle, a first film scraper, a second film scraper, a static mixer and a foaming device; the discharge port of the first reaction kettle is connected to the feed port of the first film scraper through a material conveying pipeline, and the discharge port of the second reaction kettle is connected to the feed port of the second film scraper through a material conveying pipeline; the discharge ports of the first film scraper and the second film scraper are respectively connected to the feed port of the static mixer through material conveying pipelines; the discharge port of the static mixer is connected to the feed port of the foaming device through a material conveying pipeline.

Description

Technical Field

[0001] The present invention relates to the chemical industry field, and in particular to an apparatus and a method for continuously preparing polylactic acid-glycolic acid foamed materials. Background Art

[0002] Foamed materials are a class of materials characterized by light weight, low density, and multi-porous structure, and have excellent properties such as cushioning, heat insulation, and flame retardancy. They have now been widely used in the fields of the electronics industry, household appliance packaging, automobiles, sports goods, etc. With the rapid development of industries such as express delivery, logistics, electronics, toys, home improvement, and packaging, the demand for polyurethane foam materials has also been increasing continuously. However, traditional polyurethane foamed materials are not easily degraded in nature, and the discarded foamed materials often cause serious "white pollution" problems. The current treatment methods of incineration or landfill will also cause serious environmental pollution and resource waste problems, which do not meet the requirements of green environmental protection and sustainable development. Therefore, for foam products, developing and utilizing biodegradable foamed materials is one of the effective means to solve the "white pollution" problem. In this context, biodegradable foamed materials have now received more and more attention.

[0003] Polylactic acid-glycolic acid (PLGA) is a biodegradable polymer material. After it is discarded, it can be completely biodegradable, and the final decomposition products are carbon dioxide and water, without causing any pollution to the environment. It is a green environmental protection material that has received extensive attention and is expected to replace traditional petroleum-based plastics and be widely used in various fields. However, at present, there are few reports on the technology for preparing PLGA foamed materials, especially on the industrial continuous production process technology of PLGA foamed materials. The existing publicly reported processes for preparing polylactic acid (PLA) or polyglycolic acid (PGA) foamed materials are usually batch foaming processes, which are not suitable for large-scale production and are difficult to be popularized and applied on a large scale industrially. In addition, the current method for preparing PLGA based on the ring-opening polymerization process usually directly melts and mixes glycolide and lactide in a reaction kettle, and then carries out ring-opening polymerization under high-temperature and high-vacuum conditions. The PLGA thus prepared belongs to a random copolymer, and the combination of glycolide segments and lactide segments in its molecular chain segments is disorderly, resulting in unstable quality of the copolymer product. Therefore, the prepared foamed materials often have defects such as serious yellowing resulting in poor chromaticity quality, poor uniformity of cell size, low cell density, and low foaming ratio, directly leading to poor product quality and insufficient competitiveness.

[0004] Therefore, there is an urgent need in the art to provide foamed materials with good chromaticity quality, uniform cell size, and high cell density and their continuous production methods. Summary of the Invention

[0005] The present invention aims to provide an apparatus and a corresponding method for continuously preparing polylactic acid-glycolic acid foamed materials.

[0006] In a first aspect of the present invention, there is provided an apparatus for continuously preparing a polylactic acid-glycolic acid foamed material, the apparatus comprising a first reaction kettle, a second reaction kettle, a first scraping film device, a second scraping film device, a static mixer and a foaming device; the discharge port of the first reaction kettle is connected to the feed port of the first scraping film device through a material conveying pipeline, and the discharge port of the second reaction kettle is connected to the feed port of the second scraping film device through a material conveying pipeline; the discharge ports of the first scraping film device and the second scraping film device are respectively connected to the feed port of the static mixer through material conveying pipelines; the discharge port of the static mixer is connected to the feed port of the foaming device through a material conveying pipeline.

[0007] In another embodiment, both the first scraping film device and the second scraping film device include a housing; a rotating shaft, a plurality of scraping plates radially connected to the rotating shaft, and a film distributing device communicating with the feed port are provided inside the housing; the film distributing device is located above the scraping plate closest to the top of the housing.

[0008] In another embodiment, the distance between the outer side surface of the scraping plate and the inner wall of the housing is not greater than 5 mm; preferably not greater than 2 mm.

[0009] In another embodiment, both the first scraping film device and the second scraping film device further include a heating element provided outside the housing, preferably an electric heating jacket.

[0010] In another embodiment, an air outlet is provided at the top of the housing, and the horizontal height of the air outlet is higher than the horizontal height of the feed port;

[0011] The apparatus further includes a first raw material collection unit and a second raw material collection unit, the first raw material collection unit is connected to the air outlet of the first scraping film device through a material conveying pipeline, and the second raw material collection unit is connected to the air outlet of the second scraping film device through a material conveying pipeline.

[0012] In another embodiment, both the first raw material collection unit and the second raw material collection unit sequentially include a gas-liquid separator, a condenser and a recovery tank in the direction of material feeding.

[0013] In another embodiment, a vacuum pump is provided between the gas-liquid separator and the condenser.

[0014] In another embodiment,

[0015] A melt pump is provided on the material conveying pipeline connecting the discharge port of the first reaction kettle and the feed port of the first scraping film device;

[0016] and / or, a melt pump is provided on the material conveying pipeline connecting the discharge port of the second reaction kettle and the feed port of the second scraping film device;

[0017] And / or, a melt pump is provided on the material conveying pipeline connecting the discharge port of the first film scraping device and the feed port of the static mixer;

[0018] And / or, a melt pump is provided on the material conveying pipeline connecting the discharge port of the second film scraping device and the feed port of the static mixer;

[0019] And / or, the discharge port of the static mixer and the feed port of the foaming device are connected through a material conveying pipeline, and a melt pump is provided on the material conveying pipeline.

[0020] In another embodiment, the foaming device includes a foaming machine and a supercritical CO 2 fluid storage tank; the supercritical CO 2 fluid storage tank is connected to the injection port of the foaming machine through a diversion pipeline.

[0021] In another embodiment, a metering pump is provided on the diversion pipeline.

[0022] In the second aspect of the present invention, a method for continuously preparing a poly(lactic acid-glycolic acid) foamed material is provided, and the method includes the steps of:

[0023] (1) Subjecting glycolide and lactide to a polymerization reaction in a first reaction kettle and a second reaction kettle respectively to obtain a glycolide prepolymer and a lactide prepolymer respectively;

[0024] (2) Feeding the obtained glycolide prepolymer into a first film scraping device for pre-devolatilization treatment, and feeding the obtained lactide prepolymer into a second film scraping device for pre-devolatilization treatment;

[0025] (3) Feeding the materials that have undergone pre-devolatilization treatment in the first film scraping device and the second film scraping device respectively into a static mixer for a copolymerization reaction to obtain a poly(lactic acid-glycolic acid) melt; and

[0026] (4) Subjecting the poly(lactic acid-glycolic acid) melt to a foaming treatment in a foaming device to obtain a poly(lactic acid-glycolic acid) foamed material.

[0027] In another embodiment, the polymerization reaction temperature for polymerizing glycolide to obtain a glycolide prepolymer in step (1) is 130-190 °C; and / or the polymerization reaction temperature for polymerizing lactide to obtain a lactide prepolymer is 120-180 °C.

[0028] In another embodiment, a glycolide prepolymer with a relative molecular weight of 12,000-40,000 is obtained in step (1); and / or a lactide prepolymer with a relative molecular weight of 12,000-40,000 is obtained.

[0029] In another embodiment, in step (3), at least two-stage gradient heating is adopted, the temperature range of the first stage is between 160°C and 200°C, and the temperature range of the last stage is between 180°C and 220°C.

[0030] In another embodiment, step (4) includes mixing the polylactic acid-glycolic acid melt obtained in step (3) and supercritical CO 2 fluid in a foaming machine.

[0031] In another embodiment, based on the total weight of the polylactic acid-glycolic acid melt, 3-20 wt% of supercritical CO 2 fluid is used.

[0032] In another embodiment, the internal temperature of the foaming machine is controlled within the range of 180°C - 220°C; and / or the internal pressure of the foaming machine is controlled within the range of 10 - 25 MPa; and / or the treatment time is within the range of 10 - 60 minutes.

[0033] Accordingly, the present invention provides a method and device for continuously producing a foamed material with good chromaticity quality, uniform cell size, and high cell density. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of the PLGA preparation device I in Device Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0035] Through extensive and in-depth research, the inventors found that glycolide (GA) prepolymer and lactide (LA) prepolymer can be prepared separately first, then the prepolymers are respectively subjected to pre-devolatilization treatment, and then a static mixer and segmented temperature increase operation are used to obtain a PLGA melt, and a foaming treatment is carried out to obtain a PLGA foamed material. Based on this, the present invention is completed.

[0036] As used in the present invention, the "feeding direction" refers to the direction in which the reaction material or the material to be processed advances forward.

[0037] As used in the present invention, the "film distributor" refers to a film distribution device that is conducive to the uniform distribution of liquid materials on the inner wall of each heating tube of a heat exchange tube (a kind of heater) or on the inner wall of a reaction kettle, and descends in a uniform film shape.

[0038] PLGA Foamed Material Preparation Device

[0039] The present invention provides a device for continuously preparing PLGA foamed materials, including a first reaction kettle for preparing GA prepolymer, a second reaction kettle for preparing LA prepolymer, a first wiped film evaporator connected to the first reaction kettle and used for pre-devolatilization treatment of the GA prepolymer from the first reaction kettle, a second wiped film evaporator connected to the second reaction kettle and used for pre-devolatilization treatment of the LA prepolymer from the second reaction kettle, a static mixer respectively connected to the first wiped film evaporator and the second wiped film evaporator and used for copolymerization reaction of the GA prepolymer and the LA prepolymer, and a foaming device for foaming the PLGA copolymer from the static mixer.

[0040] The material conveying pipelines between the first reaction kettle and the first wiped film evaporator, between the second reaction kettle and the second wiped film evaporator, between the first wiped film evaporator and the static mixer, between the second wiped film evaporator and the static mixer, and between the static mixer and the foaming device are all equipped with conventional heat tracing to keep the materials transported therein in a melt flow state. In addition, a melt pump with a suitable model / power can be selected according to the reaction time of the raw material monomers in the reaction kettle, the volume of the material conveying pipeline, and the time for the material to pass through the static mixer to ensure the smooth progress of continuous production.

[0041] In an embodiment of the present invention, the static mixer is a static mixer; for example but not limited to, SK type static mixer, SX type static mixer, SV type static mixer, etc.

[0042] The reaction kettle used in the present invention includes a shell, a stirring paddle inserted in the shell, and a heating element for heating the shell.

[0043] As commonly used, the stirring paddle inserted in the shell can be suspended and not in contact with the inner wall and bottom of the shell; in an embodiment of the present invention, the stirring paddle is driven by a driving motor to achieve the stirring function.

[0044] The heating element is preferably a heat exchanger arranged along the axial direction of the shell on the inner wall of the shell.

[0045] The upper part of the shell is provided with a feed inlet, and the bottom is provided with a discharge outlet. In an embodiment of the present invention, a solenoid valve may be provided at the discharge outlet.

[0046] In an embodiment of the present invention, the bottom of the shell is arc-shaped.

[0047] The scraping film device used in the present invention includes a housing, a rotating shaft axially inserted into the inner cavity of the housing along the housing axis, a plurality of scraping plates arranged on the rotating shaft along the housing axis and spaced apart from each other, and a heating element (such as, but not limited to, an electric heating jacket) arranged outside the housing. A film distributor is also provided above the scraping plate closest to the top of the housing. Among them, the film distributor can adopt a conventional film distributor on the market for a scraping film evaporator or a reactor, and no special structural modification is required. The rotating shaft is generally driven by a driving motor in transmission connection with it.

[0048] One scraping plate can be arranged in the radial direction of the rotating shaft, or one scraping plate can be arranged at each of the two radial ends. The number of scraping plates usually depends on the inner cavity space of the housing; the radial distance between the outer side surface of the scraping plate and the rotating shaft depends on the size of the cross-section of the housing. In an embodiment of the present invention, a gap not greater than 5 mm, preferably not greater than 2 mm, is left between the outer side surface of the scraping plate and the inner wall of the housing. The thickness of the scraping plate can be that used in a conventional scraping film evaporator or reactor.

[0049] An inlet and an outlet are respectively provided at the top of the housing, and the inlet is communicated with the film distributor, and the outlet is communicated with the inner cavity of the housing. Preferably, the horizontal height where the outlet is located is higher than the horizontal height where the inlet is located.

[0050] An outlet is provided at the bottom of the housing, and a solenoid valve can be provided at the outlet.

[0051] The scraping film device used in the present invention is also connected with a raw material collection unit; the raw material collection unit includes a gas-liquid separator, a condenser and a raw material recovery tank connected to the scraping film device in sequence.

[0052] A vacuum pump can be arranged between the gas-liquid separator and the condenser to evacuate the scraping film device, so that the unreacted lactide monomer separated from the film can be timely extracted and collected.

[0053] The exhaust port of the gas-liquid separator is connected to the material inlet of the condenser through a pipeline, and the material outlet of the condenser is connected to the raw material collection tank through a pipeline (equipped with a delivery pump).

[0054] The gas-liquid separator adopts side-line feeding, and an anti-entrainment device is provided at the upper part inside the gas-liquid separator. Preferably, the anti-entrainment device is a wire mesh or a swirl plate.

[0055] Under working conditions, the materials from the reactor enter the inside of the wiping film evaporator housing through the feed inlet. The materials are distributed onto the inner wall of the wiping film evaporator housing via the film distributor. The rotating scraper continuously and evenly scrapes the materials into a slurry film with uniform thickness on the inner wall of the wiping film evaporator housing and advances downward in a spiral shape. During this process, the rotating scraper ensures that a continuous and uniform slurry film generates high-speed turbulence and prevents the slurry film from coking and scaling on the inner wall of the wiping film evaporator housing. The lactide monomers that remain in the slurry film and do not participate in the reaction are separated from the slurry film in the gas phase and move upward, and are discharged through the gas outlet and recovered by the raw material collection unit. After purification, they can be used as reaction raw materials and put back into production to prepare PLGA copolymers.

[0056] The foaming equipment used in the present invention includes a foaming machine and a supercritical CO 2 fluid storage tank. In one embodiment of the present invention, an extrusion foaming machine is used. For example, but not limited to, the extrusion foaming machine is a twin-screw extruder.

[0057] In one embodiment of the present invention, the twin-screw extruder is provided with an injection port for introducing supercritical CO 2 fluid. The injection port is communicated with the screw at the head, and the injection port is connected to an external supercritical CO 2 fluid storage tank through a diversion pipeline. More preferably, a metering pump is provided on the diversion pipeline.

[0058] PLGA Foaming Material Preparation Method

[0059] The present invention provides a continuous preparation method of a PLGA foaming material. This method is carried out through the above-mentioned preparation device and includes the steps:

[0060] In the first step, glycolide and lactide are respectively reacted in a first reactor and a second reactor with a catalyst added to obtain a glycolide prepolymer and a lactide prepolymer respectively.

[0061] In the second step, the glycolide prepolymer obtained in the first reactor enters the first wiping film evaporator for pre-devolatilization treatment, and the lactide prepolymer obtained in the second reactor enters the second wiping film evaporator for pre-devolatilization treatment.

[0062] In the third step, the materials that have undergone pre-devolatilization treatment from the first wiping film evaporator and the second wiping film evaporator both enter a static mixer for copolymerization reaction to obtain a PLGA copolymer (or called PLGA melt).

[0063] In the fourth step, the poly(lactic acid-glycolic acid) copolymer is subjected to foaming treatment in a foaming device to obtain a PLGA foaming material.

[0064] In the above first step, as long as glycolide and lactide as raw materials enter different reactors, the obtained prepolymers enter the corresponding wiping film evaporators connected to the reactors in the second step.

[0065] For the convenience of description in the present invention, the description methods of the first reaction kettle and the second reaction kettle are adopted, and the wiped film evaporators connected thereto are described as the first wiped film evaporator and the second wiped film evaporator.

[0066] In one embodiment of the present invention, in the first step, in the first reaction kettle, in the presence of a catalyst, glycolide is subjected to a polymerization reaction at 130-190 °C to obtain a glycolide prepolymer with a relative molecular weight of 12,000-40,000.

[0067] In one embodiment of the present invention, in the first step, in the second reaction kettle, in the presence of a catalyst, lactide is subjected to a polymerization reaction at 120-180 °C to obtain a lactide prepolymer with a relative molecular weight of 12,000-40,000.

[0068] The reaction in the first step is carried out under normal pressure.

[0069] The catalyst used in the first step can be selected from at least one of tin compounds, antimony compounds or zinc compounds, such as, but not limited to, one or more of the following: stannous octoate, stannous chloride, stannous lactate, antimony trioxide, diethylzinc and zinc acetate dihydrate.

[0070] In one embodiment of the present invention, in the first step, based on the total weight of the raw materials in the reaction kettle, the dosage of the catalyst is between 0.001-0.3 wt%.

[0071] In one embodiment of the present invention, in the first step, the molar ratio of glycolide and lactide respectively entering the first reaction kettle and the second reaction kettle is 10-90:90-10.

[0072] In the second step, the glycolide prepolymer and the lactide prepolymer enter the corresponding wiped film evaporators at a feeding speed of 0.2-2.0 kg / h; in one embodiment of the present invention, the speeds of the glycolide prepolymer and the lactide prepolymer entering the respective wiped film evaporators are basically the same.

[0073] In the second step, the absolute pressure in the wiped film evaporator is generally about 10-100 kPa, the inner wall temperature is generally about 150-220 °C, and the rotation speed of the scraper is about 50-150 revolutions per minute.

[0074] In the above second step, the material entering the scraper is distributed to the inner wall of the scraper through the film distributor, and the scraper continuously and evenly scrapes the material on the inner wall of the scraper into a liquid film of uniform thickness, and pushes it downward in a spiral shape; in this process, the rotating scraper ensures that the continuous and uniform slurry film produces high-speed turbulence, and prevents the slurry film from coking and scaling on the inner wall of the scraper shell, while the lactide monomers remaining in the slurry film that have not participated in the reaction are separated from the slurry film in the form of gas phase and move upward, and are discharged from the gas outlet and recovered by the raw material collection unit; after purification, it can be used as a reaction raw material to continue to be put into production to prepare PLGA copolymers.

[0075] In one embodiment of the present invention, the average film thickness of the first film scraper is about 200-1000 μm, and the average film thickness of the second film scraper is about 300-900 μm. The average film thickness of the two film scrapers may be the same.

[0076] The third step enables the materials discharged from the first film scraper and the second film scraper to be simultaneously conveyed to the static mixer.

[0077] In one embodiment of the present invention, the static mixer is gradually heated in at least two stages, the temperature range of the first stage can be between 160-200°C, and the temperature range of the last stage can be between 180-220°C; the time taken for the material to pass through each stage also increases gradually, for example but not limited to, the time taken to pass through the first stage is 5-40 minutes, and the time taken to pass through the last stage can be 40-70 minutes.

[0078] The internal pressure of the static mixer used in the above third step is normal pressure.

[0079] The fourth step comprises reacting the polylactic acid-glycolic acid copolymer obtained in the third step with supercritical CO 2 The fluids are mixed in the foaming machine.

[0080] In one embodiment of the present invention, in the fourth step, the PLGA melt obtained in the third step is transported to an extrusion foaming machine, and supercritical CO is introduced into the extrusion foaming machine through the injection port. 2 The screw makes supercritical CO 2 The fluid is mixed with the PLGA melt, and then foamed. The mixture is then extruded through a die to form foam, and then cooled and shaped to obtain a PLGA foam material.

[0081] In one embodiment of the present invention, the speed of the screw in the extrusion foaming machine can be controlled to be 80-150 r / min.

[0082] In one embodiment, based on the total weight of the PLGA melt obtained in the third step, 3-30 wt% of supercritical CO is introduced. 2 Fluids such as, but not limited to, supercritical CO 2The introduction amount of the fluid is 3-20 wt% of the mass of the PLGA melt.

[0083] In one embodiment of the present invention, the internal temperature of the extrusion foaming machine is controlled within the range of 150-250 °C.

[0084] In one embodiment of the present invention, the internal pressure of the extrusion foaming machine is controlled within the range of 5-30 MPa.

[0085] In one embodiment of the present invention, the foaming treatment time is between 10 and 90 minutes.

[0086] In one embodiment of the present invention, after the foaming treatment, the internal pressure of the extrusion foaming machine is depressurized to atmospheric pressure at a rate of 1-8 MPa / minute.

[0087] In a preferred embodiment of the present invention, the process conditions for the foaming treatment are: controlling the internal temperature of the extrusion foaming machine to 180-220 °C, the pressure to 10-25 MPa, treating for 10-60 min, and then depressurizing to atmospheric pressure at a rate of 2-6 MPa / min.

[0088] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art with respect to the present invention. In case of conflicts, the definition in this specification shall prevail.

[0089] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0090] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be considered as having covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0091] Although the numerical ranges and parameters used to define the broader scope of the present invention are approximate values, the relevant numerical values in the specific embodiments have been presented as precisely as possible herein. However, any numerical value inherently and inevitably contains standard deviations resulting from individual testing methods. Herein, "about" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific numerical value or range. Alternatively, the term "about" represents that the actual value falls within the acceptable standard error of the average value, depending on the consideration of those skilled in the art. Except for experimental examples or unless otherwise clearly stated, it is understood that all ranges, amounts, numerical values, and percentages used herein (such as those used to describe material amounts, time lengths, temperatures, operating conditions, quantity ratios, and others similar) are modified by "about". Therefore, unless otherwise stated to the contrary, the numerical parameters disclosed in this specification and the appended claims are approximate values and can be varied as needed. At least these numerical parameters should be understood as the values obtained by indicating the significant digits and applying the general rounding method.

[0092] The above-mentioned features mentioned in the present invention, or the features mentioned in the embodiments, can be combined arbitrarily. All the features disclosed in the specification of this case can be used in combination with any composition form, as long as there is no contradiction in the combination of these features, and all possible combinations should be considered as the scope described in this specification. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specifically stated, the disclosed features are only general examples of equivalent or similar features.

[0093] The main advantages of the present invention are

[0094] 1. The PLGA foamed material prepared by the present invention effectively overcomes the problem that the PLGA foamed material obtained by the existing preparation process is severely yellowed.

[0095] 2. The foaming ratio and cell density of the PLGA foamed material prepared by the present invention have been significantly improved, the cell size is more uniform, and the cells are more dense.

[0096] 3. The present invention realizes the continuous production of high-quality PLGA foamed materials, can effectively reduce the loss of reaction materials, has no environmental pollution during the production process, the production method is safe, the preparation process is simple, and it is suitable for mass production.

[0097] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions, or parts are by weight. The units in the weight / volume percentage in the present invention are well-known to those skilled in the art, for example, it refers to the weight (grams) of the solute in 100 ml of the solution. Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention. The preferred implementation methods and materials described herein are for illustrative purposes only.

[0098] Device Embodiment

[0099] Provide a PLGA preparation device as shown in the appendix Figure 1 as shown.

[0100] The PLGA preparation device I includes a first reaction kettle 1000A, a second reaction kettle 1000B, a first film scraper 2000A, a second film scraper 2000B, a static mixer 3000, and a foaming device 4000; the discharge port 1400 at the bottom of the housing 1600 of the first reaction kettle 1000A is connected to the feed port 2030 at the top of the housing 2080 of the first film scraper 2000A through a material conveying pipeline, and the discharge port 1400 at the bottom of the housing 1600 of the second reaction kettle 1000B is connected to the feed port 2030 at the top of the housing 2080 of the second film scraper 2000B through a material conveying pipeline; the discharge ports 2040 at the bottoms of the housings 2080 of the first film scraper 2000A and the second film scraper 2000B are respectively connected to the feed port 3100 of the static mixer 3000 through material conveying pipelines, and the discharge port 3200 of the static mixer 3000 is connected to the feed port 4400 of the foaming device 4000 through a material conveying pipeline.

[0101] Both the first reaction kettle 1000A and the second reaction kettle 1000B include a housing 1600, a feed port 1300 provided at the top of the housing 1600, a discharge port 1400 provided at the bottom of the housing 1600, a stirring paddle 1100 suspended in the housing, and a heat exchanger 1200 provided inside the housing 1600; the stirring paddle 1100 can be connected to a driving motor 1500.

[0102] The first film scraper 2000A and the second film scraper 2000B are respectively connected to a raw material collection unit 2100. The raw material collection unit 2100 includes a gas-liquid separator 2110, a condenser 2120, and a recovery tank 2130; the first film scraper 2000A and the second film scraper 2000B are respectively connected to the gas-liquid separator 2110 in the raw material collection unit 2100 through the gas outlet 2050 provided at the top of the housing 2080 through a material conveying pipeline. The top of the gas-liquid separator 2110 is connected to the inlet of the condenser 2120 through a material conveying pipeline, and the outlet of the condenser 2120 is connected to the recovery tank 2130 through a material conveying pipeline; a vacuum pump 200 is provided on the material conveying pipeline connecting the gas-liquid separator 2110 and the condenser 2120.

[0103] Both the first film scraper 2000A and the second film scraper 2000B include a housing 2080, a rotating shaft 2060, a scraper 2010 radially connected to the rotating shaft and with its outer side parallel to the rotating shaft, a feed inlet 2030 and a gas outlet 2050 respectively provided at the top of the housing 2080, a discharge outlet 2040 provided at the bottom of the housing 2080, and an electric heating jacket 2070 provided on the outside of the housing 2080; a film distributor 2020 is provided inside the housing 2080 above the scraper 2010. The distance between the outer side of the scraper 2010 and the inner wall of the housing 2080 is about 0 - 5 mm, preferably not more than 2 mm; the rotating shaft 2060 can be connected to a driving motor 1500.

[0104] A melt pump 100 is provided on the material conveying pipeline connecting the discharge outlet 1400 at the bottom of the housing 1600 of the first reaction kettle 1000A and the feed inlet 2030 at the top of the housing 2080 of the first film scraper 2000A; a melt pump 100 is provided on the material conveying pipeline connecting the discharge outlet 1400 at the bottom of the housing 1600 of the second reaction kettle 1000B and the feed inlet 2030 at the top of the housing 2080 of the first film scraper 2000A; melt pumps 100 are respectively provided on the material conveying pipelines connecting the discharge outlets 2040 at the bottoms of the housings 2080 of the first film scraper 2000A and the second film scraper 2000B and the feed inlet 3100 of the static mixer 3000; a melt pump 100 is provided on the material conveying pipeline connecting the discharge outlet 3200 of the static mixer 3000 and the feed inlet 4400 of the foaming device 4000.

[0105] The extruder 4100 in the foaming device 4000 is a twin-screw extruder, which is provided with an injection port 4300 for introducing supercritical CO 2 fluid. The injection port 4300 is communicated with the screw at the head, and the injection port 4300 is connected to an external supercritical CO 2 fluid storage tank 4200 through a diversion pipeline 4500; a metering pump 300 is provided on the diversion pipeline 4500.

[0106] Preparation Example

[0107] Example 1

[0108] An inert gas (e.g., nitrogen) was introduced into the first reactor and the second reactor to exhaust the air in the reactors. The raw material monomers glycolide and lactide (with a molar ratio of 70:30) were respectively added into the first reactor and the second reactor, and a catalyst (stannous octoate, with an addition amount of 0.002% of the mass of the raw material monomers in the corresponding reactor) was added into the first reactor and the second reactor. Then, the temperatures of the first reactor and the second reactor were controlled at 140 °C and 120 °C respectively, and the reaction was carried out at normal pressure for a period of time until the relative molecular weight of the GA prepolymer formed in the first reactor was about 15,000, and the relative molecular weight of the LA prepolymer formed in the second reactor was about 12,000. Then, the materials in the first reactor and the second reactor were respectively introduced into the first wiped film evaporator and the second wiped film evaporator at a feeding rate of 1 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in the first wiped film evaporator and the second wiped film evaporator was 60 kPa, the temperature of the inner wall of the wiped film evaporator was 180 °C, the rotation speed of the scraper was about 90 revolutions per minute, the materials entering the wiped film evaporator were distributed onto the inner wall of the wiped film evaporator via a film distributor, and the scraper continuously and evenly scraped the materials into a liquid film with uniform thickness on the inner wall of the wiped film evaporator (the average film thickness of the first wiped film evaporator was about 650 μm, and the average film thickness of the second wiped film evaporator was about 520 μm), and advanced downward in a spiral shape], and then the materials derived from the first wiped film evaporator and the second wiped film evaporator were simultaneously transported to a static mixer (a commercially available SK type static mixer) for copolymerization reaction (wherein, the static mixer was divided into three sections, the temperature of the first section was 170 °C, the temperature of the second section was 190 °C, the temperature of the third section was 200 °C, the time for the materials to pass through the first section was about 10 min, the time for passing through the second section was about 30 min, the time for passing through the third section was about 60 min, and the inside of the static mixer was at normal pressure), and thus a PLGA melt was obtained. Then, the PLGA melt was transported to an extrusion foaming machine, and supercritical CO 2 fluid was introduced into the extrusion foaming machine through an injection port. The introduction amount of the supercritical CO 2 fluid was 8% of the mass of the PLGA melt. The rotation speed of the screw was controlled at 100 r / min, and the supercritical CO 2 fluid was uniformly mixed with the PLGA melt under the action of the screw. Then, the internal temperature of the extrusion foaming machine was controlled at 205 °C, the pressure was controlled at 20 MPa, and the treatment was carried out for 25 min. Then, the pressure was released to normal pressure at a rate of 5 MPa / min. Subsequently, foaming was carried out through a die, and then cooling and shaping were carried out, and thus a PLGA foamed material was prepared.

[0109] Example 2

[0110] This example is basically the same as Example 1, except that in this example, the static mixer is divided into two sections. The temperature of the first section is 190 °C, the temperature of the second section is 200 °C, the residence time of the material in the first section is about 40 min, and the residence time in the second section is about 60 min.

[0111] Example 3

[0112] An inert gas (e.g., nitrogen) is introduced into the first reactor and the second reactor to exhaust the air in the reactors. The raw material monomers glycolide and lactide (the molar ratio of the two is 70:30) are respectively added into the first reactor and the second reactor, and a catalyst (stannous octoate, and the addition amount is 0.008% of the mass of the raw material monomers in the corresponding reactor) is added into the first reactor and the second reactor. Then, the temperatures of the first reactor and the second reactor are controlled to be 156 °C and 142 °C respectively, and the reaction is carried out at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer formed in the first reactor is about 22,000, and the relative molecular weight of the LA prepolymer formed in the second reactor is about 20,000. Then, the materials in the first reactor and the second reactor are respectively introduced into the first wiped film evaporator and the second wiped film evaporator at a feeding rate of 0.8 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in the first wiped film evaporator and the second wiped film evaporator is 40 kPa, the temperature of the inner wall of the wiped film evaporator is 195 °C, the rotation speed of the scraper is about 80 r / min, the material entering the wiped film evaporator is distributed onto the inner wall of the wiped film evaporator via a film distributor, and the scraper continuously and evenly scrapes the material into a liquid film with uniform thickness on the inner wall of the wiped film evaporator (the average film thickness of the first wiped film evaporator is about 620 μm, and the average film thickness of the second wiped film evaporator is about 450 μm), and advances downward in a spiral shape], and then the materials derived from the first wiped film evaporator and the second wiped film evaporator are simultaneously transported to a static mixer (a commercially available SK type static mixer) for copolymerization reaction (wherein, the static mixer is divided into three sections, the temperature of the first section is 160 °C, the temperature of the second section is 185 °C, the temperature of the third section is 200 °C, the residence time of the material in the first section is about 5 min, the residence time in the second section is about 30 min, the residence time in the third section is about 65 min, and the inside of the static mixer is at atmospheric pressure), that is, a PLGA melt is obtained. Then, the PLGA melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid is introduced into the extrusion foaming machine through an injection port. The introduction amount of the supercritical CO 2 fluid is 12% of the mass of the PLGA melt. The rotation speed of the screw is controlled to be 100 r / min. Under the action of the screw, supercritical CO 2The fluid is mixed evenly with the PLGA melt. Then, the internal temperature of the extrusion foaming machine is controlled at 210 °C, the pressure is controlled at 24 MPa, and it is processed for 30 min. Then, the pressure is released to atmospheric pressure at a rate of 2 MPa / min. Subsequently, it is extruded and foamed through a die, and then cooled and shaped to obtain the PLGA foamed material.

[0113] Example 4

[0114] An inert gas (e.g., nitrogen) is introduced into the first reaction kettle and the second reaction kettle to exhaust the air in the kettles. The raw material monomers glycolide and lactide (the molar ratio of the two is 70:30) are respectively added into the first reaction kettle and the second reaction kettle, and a catalyst (stannous octoate, and its addition amount is 0.01% of the mass of the raw material monomers in the corresponding reactor) is added into the first reaction kettle and the second reaction kettle. Then, the temperatures of the first reaction kettle and the second reaction kettle are controlled at 165 °C and 170 °C respectively, and they are reacted at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer generated in the first reaction kettle is about 27,000, and the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 26,000. Then, the materials in the first reaction kettle and the second reaction kettle are respectively introduced into the first wiped-film evaporator and the second wiped-film evaporator at a feeding rate of 1.2 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in the first wiped-film evaporator and the second wiped-film evaporator is 80 kPa, the temperature of the inner wall of the wiped-film evaporator is 190 °C, the rotation speed of the scraper is about 100 revolutions per minute, the materials entering the wiped-film evaporator are distributed onto the inner wall of the wiped-film evaporator via a film distributor, and the scraper continuously and evenly scrapes the materials into a liquid film with uniform thickness on the inner wall of the wiped-film evaporator (the average film-forming thickness of the first wiped-film evaporator is about 720 μm, and the average film-forming thickness of the second wiped-film evaporator is about 640 μm), and it advances downward in a spiral shape], and then the materials derived from the first wiped-film evaporator and the second wiped-film evaporator are simultaneously transported to a static mixer (a commercially available SK-type static mixer) for copolymerization reaction (wherein, the static mixer is divided into three sections, the temperature of the first section is 165 °C, the temperature of the second section is 190 °C, the temperature of the third section is 205 °C, the time for the materials to pass through the first section is about 5 min, the time for passing through the second section is about 35 min, the time for passing through the third section is about 60 min, and the inside of the static mixer is at atmospheric pressure), and thus the PLGA prepolymer melt is obtained. Then, the PLGA prepolymer melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid, supercritical CO 2 The import amount of the fluid is 10% of the mass of the PLGA prepolymer melt. The rotation speed of the screw is controlled at 100 r / min. Under the action of the screw, supercritical CO 2The fluid is mixed evenly with the PLGA prepolymer melt. Then, the internal temperature of the extrusion foaming machine is controlled at 215 °C, the pressure is controlled at 25 MPa, and it is processed for 10 min. Then, the pressure is released to atmospheric pressure at a rate of 6 MPa / min. Subsequently, it is extruded and foamed through a die, and then cooled and shaped to obtain the PLGA foamed material.

[0115] Example 5

[0116] An inert gas (e.g., nitrogen) is introduced into the first reaction kettle and the second reaction kettle to exhaust the air in the kettles. The raw material monomers glycolide and lactide (the molar ratio of the two is 70:30) are respectively added into the first reaction kettle and the second reaction kettle, and a catalyst (stannous octoate, and its addition amount is 0.03% of the mass of the raw material monomers in the corresponding reactor) is added into the first reaction kettle and the second reaction kettle. Then, the temperatures of the first reaction kettle and the second reaction kettle are controlled at 180 °C and 175 °C respectively, and they are reacted at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer generated in the first reaction kettle is about 35,000, and the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 35,000. Then, the materials in the first reaction kettle and the second reaction kettle are respectively introduced into the first wiped film evaporator and the second wiped film evaporator at a feeding rate of 1.5 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in both the first wiped film evaporator and the second wiped film evaporator is 40 kPa, the temperature of the inner wall of the wiped film evaporator is 200 °C, the rotation speed of the scraper is about 120 revolutions per minute, the materials entering the wiped film evaporator are distributed onto the inner wall of the wiped film evaporator via a film distributor, and the scraper continuously and evenly scrapes the materials into a liquid film with uniform thickness on the inner wall of the wiped film evaporator (the average film-forming thickness of the first wiped film evaporator is about 800 μm, and the average film-forming thickness of the second wiped film evaporator is about 760 μm), and it advances downward in a spiral shape]. Subsequently, the materials derived from the first wiped film evaporator and the second wiped film evaporator are simultaneously transported to a static mixer (a commercially available SK type static mixer) for copolymerization reaction (wherein, the static mixer is divided into three sections, the temperature of the first section is 180 °C, the temperature of the second section is 195 °C, the temperature of the third section is 210 °C, the time for the materials to pass through the first section is about 10 min, the time for passing through the second section is about 30 min, the time for passing through the third section is about 60 min, and the inside of the static mixer is at atmospheric pressure), and thus the PLGA prepolymer melt is obtained. Then, the PLGA prepolymer melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid, supercritical CO 2 The import amount of the fluid is 20% of the mass of the PLGA prepolymer melt. The rotation speed of the screw is controlled at 100 r / min. Under the action of the screw, supercritical CO 2The fluid is mixed evenly with the PLGA prepolymer melt. Then, the internal temperature of the extrusion foaming machine is controlled at 215 °C, the pressure is controlled at 16 MPa, and it is processed for 60 min. Then, the pressure is released to atmospheric pressure at a rate of 4 MPa / min. Subsequently, it is extruded and foamed through a die, and then cooled and shaped to obtain the PLGA foamed material.

[0117] Example 6

[0118] An inert gas (e.g., nitrogen) is introduced into the first reaction kettle and the second reaction kettle to exhaust the air in the kettles. The raw material monomers glycolide and lactide (the molar ratio of the two is 50:50) are respectively added into the first reaction kettle and the second reaction kettle, and a catalyst (antimony trioxide, and its addition amount is 0.06% of the mass of the raw material monomers in the corresponding reactor) is respectively added into the first reaction kettle and the second reaction kettle. Then, the temperatures of the first reaction kettle and the second reaction kettle are both controlled at 170 °C, and the reaction is carried out at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer generated in the first reaction kettle is about 26,000, and the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 29,000. Then, the materials in the first reaction kettle and the second reaction kettle are respectively introduced into the first wiping film evaporator and the second wiping film evaporator at a feeding rate of 0.6 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in the first wiping film evaporator and the second wiping film evaporator is both 65 kPa, the temperature of the inner wall of the wiping film evaporator is both 190 °C, the rotation speed of the scraper is about 100 revolutions per minute, the materials entering the wiping film evaporator are distributed onto the inner wall of the wiping film evaporator via a film distributor, and the scraper continuously and evenly scrapes the materials into a liquid film with uniform thickness on the inner wall of the wiping film evaporator (the average film-forming thickness of the first wiping film evaporator is about 440 μm, and the average film-forming thickness of the second wiping film evaporator is about 470 μm), and it advances downward in a spiral shape], and then the materials exported from the first wiping film evaporator and the second wiping film evaporator are simultaneously transported to a static mixer (a commercially available SK type static mixer) for copolymerization reaction (wherein, the static mixer is divided into four sections, the temperature of the first section is 168 °C, the temperature of the second section is 185 °C, the temperature of the third section is 192 °C, the temperature of the fourth section is 205 °C, the time for the materials to pass through the first section is about 5 min, the time for passing through the second section is about 25 min, the time for passing through the third section is about 35 min, the time for passing through the fourth section is about 55 min, and the inside of the static mixer is at atmospheric pressure), and thus the PLGA prepolymer melt is obtained. Then, the PLGA prepolymer melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid, supercritical CO 2 The import amount of the fluid is 3% of the mass of the PLGA prepolymer melt. The rotation speed of the screw is controlled at 120 r / min. Under the action of the screw, supercritical CO 2The fluid is mixed evenly with the PLGA prepolymer melt. Then, the internal temperature of the extrusion foaming machine is controlled at 196 °C, the pressure is controlled at 12 MPa, and it is treated for 50 min. Then, the pressure is released to atmospheric pressure at a rate of 4 MPa / min. Subsequently, it is extruded and foamed through a die, and then cooled and shaped to obtain the PLGA foamed material.

[0119] Example 7

[0120] An inert gas (e.g., nitrogen) is introduced into the first reactor and the second reactor to exhaust the air in the reactors. The raw material monomers glycolide and lactide (the molar ratio of the two is 85:15) are respectively added to the first reactor and the second reactor, and catalysts (i.e., antimony trioxide and stannous lactate, and the addition amounts of the two are 0.05% and 0.08% of the mass of the raw material monomers in the corresponding reactors respectively) are added to the first reactor and the second reactor. Then, the temperatures of the first reactor and the second reactor are controlled at 130 °C and 158 °C respectively, and they are reacted at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer generated in the first reactor is about 26,000, and the relative molecular weight of the LA prepolymer generated in the second reactor is about 34,000. Then, the materials in the first reactor and the second reactor are respectively introduced into the first wiped film evaporator and the second wiped film evaporator at a feeding rate of 0.5 kg / h for pre-devolatilization treatment [wherein, the absolute pressure in the first wiped film evaporator and the second wiped film evaporator is 70 kPa, the temperature of the inner wall of the wiped film evaporator is 180 °C, the rotation speed of the scraper is about 90 revolutions per minute, the materials entering the wiped film evaporator are distributed onto the inner wall of the wiped film evaporator via a film distributor, and the scraper continuously and evenly scrapes the materials into a liquid film with uniform thickness on the inner wall of the wiped film evaporator (the average film thickness of the first wiped film evaporator is about 380 μm, and the average film thickness of the second wiped film evaporator is about 430 μm), and it is pushed downward in a spiral shape]. Subsequently, the materials exported from the first wiped film evaporator and the second wiped film evaporator are simultaneously transported to a static mixer (a commercially available SK type static mixer) for copolymerization reaction (wherein, the static mixer is divided into five sections, the temperature of the first section is 160 °C, the temperature of the second section is 176 °C, the temperature of the third section is 190 °C, the temperature of the fourth section is 200 °C, the temperature of the fifth section is 210 °C, the time for the materials to pass through the first section is about 5 min, the time for passing through the second section is about 10 min, the time for passing through the third section is about 25 min, the time for passing through the fourth section is about 40 min, the time for passing through the fifth section is about 40 min, and the inside of the static mixer is at atmospheric pressure), and the PLGA prepolymer melt is obtained. Then, the PLGA prepolymer melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid, supercritical CO 2 The import amount of the fluid is 20% of the mass of the PLGA prepolymer melt. The rotation speed of the screw is controlled at 150 r / min. Under the action of the screw, supercritical CO 2The fluid is mixed evenly with the PLGA prepolymer melt. Then, the internal temperature of the extrusion foaming machine is controlled at 220 °C, the pressure is controlled at 22 MPa, and it is processed for 20 min. Then, the pressure is released to atmospheric pressure at a rate of 2 MPa / min. Subsequently, it is extruded and foamed through a die, and then cooled and shaped to obtain the PLGA foamed material.

[0121] Example 8

[0122] An inert gas (e.g., nitrogen) is introduced into the first reaction kettle and the second reaction kettle to exhaust the air in the kettles. The raw material monomers glycolide and lactide (the molar ratio of the two is 40:60) are respectively added into the first reaction kettle and the second reaction kettle, and catalysts (i.e., stannous octoate and diethyl zinc, and the addition amounts of the two are 0.1% and 0.05% of the mass of the raw material monomers in the corresponding reactors respectively) are respectively added into the first reaction kettle and the second reaction kettle. Then, the temperatures of the first reaction kettle and the second reaction kettle are controlled at 172 °C and 165 °C respectively, and they are reacted at atmospheric pressure for a period of time until the relative molecular weight of the GA prepolymer generated in the first reaction kettle is about 40,000, and the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 37,000. Then, the materials in the first reaction kettle and the second reaction kettle are respectively introduced into the first wiped film evaporator and the second wiped film evaporator at a feeding rate of 1.0 kg / h for pre-devolatilization treatment [wherein, the absolute pressures in the first wiped film evaporator and the second wiped film evaporator are both 35 kPa, the temperatures of the inner walls of the wiped film evaporators are both 195 °C, the rotation speed of the scraper is about 100 revolutions per minute, the materials entering the wiped film evaporator are distributed onto the inner wall of the wiped film evaporator via a film distributor, and the scraper continuously and evenly scrapes the materials into a liquid film with uniform thickness on the inner wall of the wiped film evaporator (the average film-forming thickness of the first wiped film evaporator is about 690 μm, and the average film-forming thickness of the second wiped film evaporator is about 610 μm), and it advances downward in a spiral shape], and then the materials derived from the first wiped film evaporator and the second wiped film evaporator are simultaneously transported to a static mixer (a commercially available SK-type static mixer) for copolymerization reaction (wherein, the static mixer is divided into three sections, the temperature of the first section is 185 °C, the temperature of the second section is 195 °C, the temperature of the third section is 205 °C, the time for the material to pass through the first section is about 20 min, the time for passing through the second section is about 30 min, the time for passing through the third section is about 40 min, and the inside of the static mixer is at atmospheric pressure), and thus the PLGA prepolymer melt is obtained. Then, the PLGA prepolymer melt is transported to an extrusion foaming machine, and supercritical CO 2 fluid, supercritical CO 2 The import amount of the fluid is 16% of the mass of the PLGA prepolymer melt. The rotation speed of the screw is controlled at 80 r / min. Under the action of the screw, supercritical CO 2The fluid and the PLGA prepolymer melt are mixed evenly, and then the internal temperature of the extrusion foaming machine is controlled to 180°C, the pressure is controlled to 10MPa, and the process is carried out for 30 minutes. Then, the pressure is released to normal pressure at a rate of 2MPa / min, and then extruded through a die for foaming, and then cooled and shaped to obtain a PLGA foaming material.

[0123] Comparative Example 1

[0124] An inert gas (e.g., nitrogen) is introduced into the reactor to exhaust the air in the reactor, and the raw monomers glycolide and lactide (the molar ratio of the two is 70:30) are added to the reactor together, and a catalyst (i.e., stannous octoate, the amount of which is 0.01% of the mass of the raw monomer) is added to the reactor. The reaction is first carried out at normal pressure and 180° C. for about 2 hours, and then at an absolute pressure of 10 kPa and 210° C. for 2 hours, then at an absolute pressure of 2 kPa and 220° C. for 4 hours, and then at an absolute pressure of 600 Pa and 230° C. for 4 hours, and finally at an absolute pressure of 200 Pa and 240° C. for 1 hour. Devolatilization treatment is carried out to obtain a PLGA melt (in this comparative example, a coke slag block appears at the bottom of the reactor and adheres to the reactor wall, which is very difficult to remove). The PLGA melt is then transported to an extrusion foaming machine, and supercritical CO is introduced into the extrusion foaming machine through the injection port. 2 Fluid, supercritical CO 2 The amount of fluid introduced was 12% of the mass of the PLGA melt, and the speed of the screw was controlled to be 100 r / min. Under the action of the screw, supercritical CO 2 The fluid and the PLGA melt are mixed evenly, and then the internal temperature of the extrusion foaming machine is controlled to 210°C, the pressure is controlled to 24MPa, and the process is carried out for 30min. Then, the pressure is released to normal pressure at a rate of 2MPa / min, and then extruded through a die for foaming, and then cooled and shaped to obtain a PLGA foaming material.

[0125] Comparative Example 2

[0126] This embodiment is basically the same as Embodiment 3, except that, in this embodiment, the materials in the first reaction kettle and the second reaction kettle are directly transported to a static mixer (commercially available SK type static mixer) at the same time for copolymerization reaction, thereby eliminating the steps of pre-devolatilization treatment of glycolide prepolymer and pre-devolatilization treatment of lactide prepolymer.

[0127] Comparative Example 3

[0128] This embodiment is basically the same as Embodiment 3, except that in this embodiment, the materials discharged from the first scraper and the second scraper are simultaneously transported to the third reactor for copolymerization reaction (nitrogen has been used for evacuation), and the reaction conditions are normal pressure and 200°C for 100 minutes.

[0129] Related test characterization methods in the examples:

[0130] The term "yellowness index" used in this article refers to a number calculated from spectrophotometric data that describes the change in the color of the test sample from transparent or white to yellow. The test method can be ASTM E313.

[0131] Yellowness index YI test: Select a copolymer with a smooth surface and no obvious protrusions. Use a NS series colorimeter from 3nh to measure the yellowness index (YI) of the product. According to ASTM E313, three measurements are taken under the conditions of a 10-degree observation angle, a D65 observation light source, and reflection light measurement, and the average value is calculated to determine the yellowness index (YI) of the copolymer.

[0132] Weight-average molecular weight and its distribution: Dissolve the sample in a hexafluoroisopropanol solution of 5 mmol / L sodium trifluoroacetate to prepare a 0.05 - 0.3 wt% solution. Then filter the solution through a polytetrafluoroethylene filter with a pore size of 0.4 μm. Add 20 μL of the filtered solution to a gel permeation chromatography (GPC) injector to measure the molecular weight of the sample. Five standard molecular weights of methyl methacrylate with different molecular weights are used for molecular weight calibration.

[0133] Foaming ratio: According to the GB / T6343-2009 standard, measure the apparent density of the foamed material and the unfoamed material respectively. For the foamed sample, use the drainage method to measure, and then calculate the foaming ratio of the final microcellular foamed material. Foaming ratio (Φ) = ρ polymer / ρ foam where ρ polymer is the density of the unfoamed material, and ρ foam is the density of the foamed material.

[0134] Cell density and cell diameter: Quench the microcellular foamed material with liquid nitrogen, sputter the cross-section with gold, and then use a scanning electron microscope (SEM) to observe the cell structure inside the foamed material. Use Image J software to measure the cell size and calculate the cell density. Among them, the cell density N (unit: number / cm 3 ) = (n / A) 3 / 2 ×Φ, where n is the number of cells in the selected SEM photo, A is the actual area of the scanned photo (unit: cm 2 ), and Φ is the foaming ratio.

[0135] For the yellowness index, weight-average molecular weight and its distribution of the PLGA foamed materials prepared in each preparation example and comparative example, please refer to Table 1 specifically.

[0136] Table 1

[0137] Project Yellowness Index (YI) Weight-average relative molecular mass Molecular weight distribution index Example 1 11 134,000 1.52 Example 2 13 127,000 1.53 Example 3 10 154,000 1.48 Example 4 14 163,000 1.47 Example 5 16 181,000 1.43 Example 6 12 195,000 1.37 Example 7 11 227,000 1.25 Example 8 17 172,000 1.69 Comparative Example 1 35 142,000 1.94 Comparative Example 2 26 148,000 1.77 Comparative Example 3 15 121,000 1.62

[0138] The foaming ratio, cell density and diameter of the PLGA foamed materials prepared in each preparation example and comparative example are specifically shown in Table 2.

[0139] Table 2

[0140]

[0141] Compared with Example 3, the yellowness index of Example 3 is only 10, which is about 71.4% lower than that of Comparative Example 1. Accordingly, the molecular weight distribution index of the PLGA obtained in Example 3 is 1.48, which is significantly lower than 1.94 of Comparative Example 1. In addition, the foaming ratio and cell density of the PLGA foamed material obtained in Comparative Example 1 in Table 2 are significantly smaller than those in Example 3. The cell diameter of Example 3 based on the present technology is 25 μm, which is much smaller than 450 μm of Comparative Example 1. It is speculated that in the process of preparing the PLGA melt in Comparative Example 1, a large amount of lactide monomers or oligomers remain in the PLGA melt, and some of these substances may be oxidized and deteriorated due to high temperature, and cannot be bonded to the PLGA molecular chain, but remain in the final PLGA foamed material, so that the product is severely yellowed and the color quality is poor. In addition, the homogeneity of the PLGA melt obtained in Comparative Example 1 is poor, the viscosity of one area is high, while the viscosity of another area is low, so that the uniformity of the melt strength is poor. Therefore, in the subsequent foaming process, the uniformity of the size of the formed pores is poor, and the material is prone to shrinkage after foaming, and the formed pores are prone to collapse, so that the density of the final pores is greatly reduced and the foaming ratio is low.

[0142] Compared with Example 3, the above Comparative Example 2 omits the step of pre-devolatilization treatment, that is, the scraper is not used to pre-devolatilize the obtained GA prepolymer melt and LA prepolymer melt. From the test results in Table 1, it can be seen that although the yellowness index of Comparative Example 2 is less than that of Comparative Example 1, it is still significantly higher than that of Example 3. This may be due to the fact that there are still more unreacted lactide monomers or oligomers of lactide monomers in the generated GA prepolymer and LA prepolymer, and in the subsequent gradient heating reaction process of the static mixer, some of these substances may be oxidized and deteriorated due to the high temperature, and cannot be bonded to the PLGA molecular chain, but remain in the final PLGA foaming material, so that the yellowness index is still significantly higher than that of Example 3, and it also causes an increase in the molecular weight distribution index, and correspondingly the foaming ratio and the cell density are both less than that of Example 3.

[0143] In Comparative Example 3 compared with Example 3, a third reaction kettle was used to replace the static mixer, that is, the materials derived from the first and second wiped film evaporators were directly transported to the third reaction kettle for copolymerization reaction (reacting at normal pressure and 200 °C, and the reaction time was the same as the total reaction time of each section of the static mixer in Example 3). It can be seen from the test results in Table 1 that the yellowness index of Comparative Example 3 is significantly lower than that of Comparative Examples 1 and 2. This may be because the wiped film evaporator was used to pre-remove volatile components from the generated GA prepolymer melt and LA prepolymer melt, and the residual unreacted lactide monomers or oligomers of lactide monomers could be removed in time, that is, separated in the form of gas phase and / or carried by gas phase, discharged from the gas outlet at the top of the wiped film evaporator and then recycled by the raw material collection unit. After the above pre-removal of volatile components, the content of residual unreacted lactide monomers or oligomers of lactide monomers in the GA prepolymer melt and LA prepolymer melt will be greatly reduced, which is beneficial to improving the chromaticity quality of the final PLGA foamed material; however, since the third reaction kettle is used subsequently, compared with the static mixer, its heat transfer and stirring effects are limited. At the end of the reaction, the viscosity of the generated PLGA melt increases sharply, and local uneven heating is likely to occur, and the heat accumulated here cannot be transferred out in time. As a result, the molecular chain ends of some PLGA copolymers will undergo undesired thermal oxidation, which still affects the chromaticity quality of the final PLGA foamed material, so that the yellowness index of the PLGA foamed material in Comparative Example 3 is greater than that in Example 3; in addition, it is difficult for the prepolymer entering the third reaction kettle to generate a PLGA melt with a high molecular weight and a relatively narrow molecular weight distribution in a short time (for example, 100 min) and at a relatively low reaction temperature (for example, 200 °C, compared with the ring-opening polymerization of glycolide usually carried out at 220-230 °C). Therefore, the weight-average relative molecular mass of the PLGA obtained in Comparative Example 3 is only about 121,000, which is significantly smaller than that in Example 3; moreover, the homogeneity of the PLGA melt prepared in Comparative Example 3 by the third reaction kettle is still poor, and the viscosity difference in some regions of the melt is still obvious, which also affects the uniformity of the melt strength. As a result, in the subsequent foaming treatment, it is difficult to obtain uniformly sized pores, and the strength of the obtained pores is insufficient and still prone to collapse, so that the finally formed pore density and foaming ratio are both smaller than those in Examples 1-3, but significantly better than those in Comparative Example 1.

[0144] It can be seen that the present invention can not only significantly improve the chromaticity quality of the finally obtained PLGA foamed material, effectively overcome the problem of serious yellowing of the PLGA foamed material obtained by the existing preparation process, but also significantly improve the foaming ratio and cell density, with more uniform cell sizes and denser cells. This is because in the process of preparing the PLGA melt, the GA prepolymer melt and the LA prepolymer melt are first subjected to pre-devolatilization treatment by a film scraper to remove as much as possible the residual lactide monomers or oligomers in the GA prepolymer melt and the LA prepolymer melt. As a result, the residual amount of lactide monomers or oligomers in the PLGA melt obtained by copolymerization reaction will be very small, which is beneficial to improving the chromaticity quality of the final foamed material. In addition, by utilizing the structural characteristics of the static mixer, the GA prepolymer melt and the LA prepolymer melt can be cross-flow mixed. Compared with the conventional in-kettle stirring method, it can effectively strengthen the mixing effect of the GA prepolymer melt and the LA prepolymer melt. At the same time, the segmented gradient heating treatment method of the static mixer can stepwise increase the reaction degree of the GA prepolymer molecular chain and the LA prepolymer molecular chain, which is not only beneficial to the controlled and relatively mild copolymerization reaction of the GA prepolymer molecular chain and the LA prepolymer molecular chain, but also conducive to suppressing the sharp change in the viscosity of the reaction system, thereby avoiding the occurrence of excessive heat accumulation and coking and slagging phenomena due to the sharp change in the local viscosity of the reaction system. The obtained PLGA melt has good homogeneity and good uniformity of melt strength. In the subsequent process of foaming treatment with supercritical CO 2 fluid, it is beneficial to form cells with uniform sizes and can largely inhibit the shrinkage of the material after foaming, making it difficult for the cells to collapse, and thus a PLGA foamed material with a high cell density and a high foaming ratio can be obtained.

[0145] The present invention can realize the continuous production of high-quality PLGA foamed materials, effectively reduce the loss of reaction materials, have no environmental pollution during the production process, have a safe production method, a simple preparation process, and is suitable for large-scale production.

[0146] The above are only the preferred embodiments of the present invention, and are not used to limit the scope of the essential technical content of the present invention. The essential technical content of the present invention is broadly defined in the scope of the claims of the application. Any technical entity or method completed by others, if it is exactly the same as that defined in the scope of the claims of the application, or is an equivalent change, will be regarded as covered by the scope of that claim.

Claims

1. An apparatus for continuously preparing polylactic acid-glycolic acid foamed materials, characterized in that, the apparatus comprises a first reaction kettle, a second reaction kettle, a first film scraper, a second film scraper, a static mixer and a foaming device; the discharge port of the first reaction kettle is connected to the feed port of the first film scraper through a material conveying pipeline, and the discharge port of the second reaction kettle is connected to the feed port of the second film scraper through a material conveying pipeline; the discharge ports of the first film scraper and the second film scraper are respectively connected to the feed port of the static mixer through material conveying pipelines; the discharge port of the static mixer is connected to the feed port of the foaming device through a material conveying pipeline.

2. The apparatus according to claim 1, characterized in that, both the first film scraper and the second film scraper contain a housing; a rotating shaft, a plurality of scraping plates radially connected to the rotating shaft, and a film distributor communicated with the feed port are arranged inside the housing; the film distributor is located above the scraping plate closest to the top of the housing.

3. The apparatus according to claim 2, characterized in that, the distance between the outer side surface of the scraping plate and the inner wall of the housing is not more than 5 mm.

4. The apparatus according to claim 3, characterized in that, the distance between the outer side surface of the scraping plate and the inner wall of the housing is not more than 2 mm.

5. The apparatus according to claim 2, characterized in that, both the first film scraper and the second film scraper further comprise heating elements arranged on the outer side of the housing.

6. The apparatus according to claim 5, characterized in that, the heating element arranged on the outer side of the housing is an electric heating sleeve.

7. The apparatus according to claim 2, characterized in that, an air outlet is arranged at the top of the housing, and the horizontal height of the air outlet is higher than the horizontal height of the feed port; the apparatus further comprises a first raw material collection unit and a second raw material collection unit, the first raw material collection unit is connected to the air outlet of the first film scraper through a material conveying pipeline, and the second raw material collection unit is connected to the air outlet of the second film scraper through a material conveying pipeline.

8. The apparatus according to claim 7, characterized in that, both the first raw material collection unit and the second raw material collection unit sequentially contain a gas-liquid separator, a condenser and a recovery tank in the material feeding direction.

9. The apparatus according to claim 8, characterized in that, a vacuum pump is arranged between the gas-liquid separator and the condenser.

10. The apparatus according to any one of claims 1-9, characterized in that, a melt pump is arranged on the material conveying pipeline connecting the discharge port of the first reaction kettle and the feed port of the first film scraper; and / or, a melt pump is arranged on the material conveying pipeline connecting the discharge port of the second reaction kettle and the feed port of the second film scraper; and / or, a melt pump is arranged on the material conveying pipeline connecting the discharge port of the first film scraper and the feed port of the static mixer; and / or, a melt pump is arranged on the material conveying pipeline connecting the discharge port of the second film scraper and the feed port of the static mixer; and / or, the discharge port of the static mixer is connected to the feed port of the foaming device through a material conveying pipeline, and a melt pump is arranged on the material conveying pipeline.

11. The device according to any one of claims 1-9, characterized in that, The foaming device includes a foaming machine and a supercritical CO 2 fluid storage tank; the supercritical CO 2 fluid storage tank is connected to the injection port of the foaming machine through a diversion pipeline.

12. The device according to claim 11, characterized in that, a metering pump is provided on the diversion pipeline.

13. A method for continuously preparing a poly(lactic acid-glycolic acid) foamed material, characterized in that, the method comprises the steps of: (1) respectively carrying out polymerization reactions of glycolide and lactide in a first reaction kettle and a second reaction kettle to respectively obtain a glycolide prepolymer and a lactide prepolymer; (2) feeding the obtained glycolide prepolymer into a first wiped film evaporator for pre-devolatilization treatment, and feeding the obtained lactide prepolymer into a second wiped film evaporator for pre-devolatilization treatment; (3) feeding the materials that have undergone pre-devolatilization treatment in the first wiped film evaporator and the second wiped film evaporator respectively into a static mixer for copolymerization reaction to obtain a poly(lactic acid-glycolic acid) melt; (4) carrying out foaming treatment on the poly(lactic acid-glycolic acid) melt in a foaming device to obtain a poly(lactic acid-glycolic acid) foamed material.

14. The method according to claim 13, characterized in that, in step (1), the polymerization reaction temperature for polymerizing glycolide to obtain a glycolide prepolymer is 130-190 °C; and / or the polymerization reaction temperature for polymerizing lactide to obtain a lactide prepolymer is 120-180 °C.

15. The method according to claim 14, characterized in that, in step (1), a glycolide prepolymer with a relative molecular weight of 12,000-40,000 is obtained; and / or a lactide prepolymer with a relative molecular weight of 12,000-40,000 is obtained.

16. The method according to claim 13, characterized in that, in step (3), at least a two-stage gradient heating mode is adopted, the temperature range of the first stage is between 160-200 °C, and the temperature range of the last stage is between 180-220 °C.

17. The method according to any one of claims 13-16, characterized in that, Step (4) includes mixing the polylactic acid-glycolic acid melt obtained in step (3) with supercritical CO 2 fluid in a foaming machine.

18. The method according to claim 17, characterized in that, Based on the total weight of the polylactic acid-glycolic acid melt, 3-20 wt% of supercritical CO 2 fluid is used.

19. The method according to claim 18, characterized in that, controlling the internal temperature range of the foaming machine to be between 180-220 °C; and / or controlling the internal pressure range of the foaming machine to be between 10-25 MPa; and / or the treatment time to be between 10-60 minutes.

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