CN116020384A

CN116020384A - Device and method for continuously preparing polylactic acid-glycollic acid foaming material

Info

Publication number: CN116020384A
Application number: CN202211542014.7A
Authority: CN
Inventors: 王赛博; 张雄伟; 何忠胜; 孙朝阳; 李闯洋
Original assignee: Pujing Chemical Industry Co Ltd
Current assignee: Pujing Chemical Industry Co Ltd
Priority date: 2022-12-02
Filing date: 2022-12-02
Publication date: 2023-04-28

Abstract

The invention discloses a device and a method for continuously preparing a polylactic acid-glycollic acid foaming material. The device comprises a first reaction kettle, a second reaction kettle, a first film scraping device, a second film scraping device, a static mixer and foaming equipment; the discharge port of the first reaction kettle is connected with the feed port of the first film scraping device through a material conveying pipeline, and the discharge port of the second reaction kettle is connected with the feed port of the second film scraping device through a material conveying pipeline; the discharge port of the first film scraping device and the discharge port of the second film scraping device are respectively connected with the feed port of the static mixer through a material conveying pipeline; the discharge port of the static mixer is connected with the feed port of the foaming equipment through a material conveying pipeline.

Description

Device and method for continuously preparing polylactic acid-glycollic acid foaming material

Technical Field

The invention relates to the field of chemical industry, in particular to a device and a method for continuously preparing polylactic acid-glycollic acid foam materials.

Background

The foaming material is a material with light weight, low density and multiple pores as structural characteristics, has excellent properties of buffering, heat preservation and insulation, flame retardance and the like, and is widely applied to the fields of electronic industry, household appliance packaging, automobiles, sports goods and the like. With the rapid development of industries such as express, logistics, electronics, toys, home decoration, packaging and the like, the demand for polyurethane foam materials is also increasing. However, the traditional polyurethane foaming material is not easy to degrade the waste foaming material in nature, so that the problem of serious white pollution is often caused, and the currently adopted incineration or landfill treatment mode also causes the problems of serious environmental pollution and resource waste, which does not meet the requirements of green environmental protection and sustainable development. Therefore, development and utilization of biodegradable foam materials for foam products is one of the effective means for solving the "white pollution". In this context, biodegradable foam materials have gained increasing attention.

Polylactic acid-glycolic acid (PLGA) is a biodegradable polymer material, can be completely biodegradable after being used and abandoned, and the final decomposition products are carbon dioxide and water, so that the environment is not polluted, and the polylactic acid-glycolic acid (PLGA) is a widely focused green environment-friendly material, and is expected to replace the traditional petroleum-based plastic to be widely applied to various fields. However, there are few reports on the technology for preparing PLGA foam materials, especially on the technology for industrially and continuously producing PLGA foam materials. However, the process for preparing polylactic acid (PLA) or polyglycolic acid (PGA) foaming materials disclosed in the prior art is generally a batch foaming process, which is not suitable for mass production and is difficult to be popularized and applied in large-scale industrialization. In addition, the current method for preparing PLGA based on the ring-opening polymerization process generally comprises the steps of directly carrying out melt mixing on glycolide and lactide in a reaction kettle, and then carrying out ring-opening polymerization under the conditions of high temperature and high vacuum, so that the prepared PLGA belongs to a random copolymer, and the combination of glycolide fragments and lactide fragments in a molecular chain segment is disordered, so that the quality of the obtained copolymer product is unstable. Therefore, the prepared foaming material often has the defects of serious yellowing, poor chromaticity quality, poor uniformity of cell size, low cell density, low foaming multiplying power and the like, and directly causes poor product quality and insufficient competitiveness.

Accordingly, there is a strong need in the art to provide foamed materials and continuous production thereof that have good chromaticity quality, uniform cell size, and high cell density.

Disclosure of Invention

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

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 vessel, a second reaction vessel, 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 with the feed port of the first film scraping device through a material conveying pipeline, and the discharge port of the second reaction kettle is connected with the feed port of the second film scraping device through a material conveying pipeline; the discharge port of the first film scraping device and the discharge port of the second film scraping device are respectively connected with the feed port of the static mixer through a material conveying pipeline; the discharge port of the static mixer is connected with the feed port of the foaming equipment through a material conveying pipeline.

In another embodiment, the first and second film scrapers each comprise a housing; a rotating shaft, a plurality of scraping plates radially connected with the rotating shaft and a film distributor communicated with a feed inlet are arranged in the shell; the film distributor is located above the scraper nearest to the top of the housing.

In another embodiment, the distance between the outer side surface of the scraper and the inner wall of the shell is no more than 5 mm; preferably not greater than 2 mm.

In another embodiment, the first and second scrapers each further comprise a heating element, preferably an electrical heating jacket, arranged outside the housing.

In another embodiment, the top of the shell is provided with an air outlet, and the level of the air outlet is higher than that of the feed inlet;

the device also comprises a first raw material collecting unit and a second raw material collecting unit, wherein the first raw material collecting unit is connected with the air outlet of the first film scraping device through a material conveying pipeline, and the second raw material collecting unit is connected with the air outlet of the second film scraping device through a material conveying pipeline.

In another embodiment, the first raw material collecting unit and the second raw material collecting unit each sequentially comprise a gas-liquid separator, a condenser and a recovery tank in the material feeding direction.

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

In a further embodiment of the present invention,

a melt pump is arranged on a material conveying pipeline connecting a discharge port of the first reaction kettle and a feed port of the first film scraping device;

And/or a melt pump is arranged on a material conveying pipeline connecting the discharge port of the second reaction kettle and the feed port of the second film scraping device;

and/or a melt pump is arranged on a material conveying pipeline connecting the discharge port of the first film scraping device and the feed port of the static mixer;

and/or a melt pump is arranged on a material conveying pipeline connecting the discharge port of the second film scraping device and the feed port of the static mixer;

and/or the discharge port of the static mixer is connected with the feed port of the foaming equipment through a material conveying pipeline, and a melt pump is arranged on the material conveying pipeline.

In another embodiment, the foaming apparatus comprises a foaming machine and supercritical CO ₂ A fluid storage tank; the supercritical CO ₂ The fluid storage tank is connected with an injection port of the foaming machine through a diversion pipeline.

In another embodiment, a metering pump is arranged on the flow guide pipe.

In a second aspect of the present invention, there is provided a method for continuously producing a polylactic acid-glycolic acid foamed material, said method comprising the steps of:

(1) Respectively carrying out polymerization reaction on glycolide and lactide in a first reaction kettle and a second reaction kettle to respectively obtain a glycolide prepolymer and a lactide prepolymer;

(2) Enabling the obtained glycolide prepolymer to enter a first film scraping device for pre-devolatilization treatment, and enabling the obtained lactide prepolymer to enter a second film scraping device for pre-devolatilization treatment;

(3) Materials which are respectively subjected to pre-devolatilization treatment in a first film scraping device and a second film scraping device enter a static mixer for copolymerization reaction to obtain polylactic acid-glycollic acid melt; and

(4) And (3) foaming the polylactic acid-glycollic acid melt in foaming equipment to obtain the polylactic acid-glycollic acid foaming material.

In another embodiment, the polymerization reaction temperature of the glycolide polymerization to obtain the glycolide prepolymer in step (1) is 130-190 ℃; and/or the polymerization reaction temperature of lactide prepolymer obtained by lactide polymerization is 120-180 ℃.

In another embodiment, step (1) results in glycolide prepolymers having a relative molecular weight of 1.2 to 4.0 ten thousand; and/or to obtain lactide prepolymers having a relative molecular weight of 1.2-4.0 ten thousand.

In another embodiment, at least 2 stages of gradient heating modes are adopted in the step (3), wherein the temperature of the first stage is 160-200 ℃, and the temperature of the last stage is 180-220 ℃.

In another embodiment, step (4) comprises reacting the product of step (3)Polylactic acid-glycolic acid melt and supercritical CO ₂ The fluids are mixed in a foaming machine.

In another embodiment, from 3 to 20 weight percent supercritical CO based on the total weight of the polylactic acid-glycolic acid melt is used ₂ A fluid.

In another embodiment, the internal temperature of the foaming machine is controlled to be in the range of 180-220 ℃; and/or controlling the internal pressure of the foaming machine to be between 10 and 25 MPa; and/or the treatment time is between 10 and 60 minutes.

Accordingly, the invention provides a method and a device for continuously producing the foaming material with good chromaticity quality, uniform cell size and high cell density.

Drawings

FIG. 1 is a schematic diagram of a PLGA preparation apparatus I in example 1 of the apparatus.

Detailed Description

The inventor has conducted extensive and intensive studies and has found that it is possible to prepare Glycolide (GA) prepolymer and Lactide (LA) prepolymer, respectively, then to subject the prepolymers to respective pre-devolatilization treatments, and then to employ a static mixer and a stage-wise temperature-raising operation to obtain PLGA melt, and to subject the PLGA foam to a foaming treatment. On this basis, the present invention has been completed.

As used herein, "feed direction" refers to the direction in which the reactant or material to be treated travels forward.

As used herein, the term "film distributor" refers to a film distributor which is advantageous in that liquid materials are uniformly distributed on the inner wall of each heating tube array of a heat exchange tube (a heater) or uniformly distributed on the inner wall of a reaction vessel to uniformly descend in a film shape.

PLGA foaming material preparation facilities

The invention provides a device for continuously preparing a PLGA foaming material, which comprises a first reaction kettle for preparing a GA prepolymer, a second reaction kettle for preparing a LA prepolymer, a first film scraping device connected with the first reaction kettle and used for pre-devolatilizing the GA prepolymer from the first reaction kettle, a second film scraping device connected with the second reaction kettle and used for pre-devolatilizing the LA prepolymer from the second reaction kettle, a static mixer respectively connected with the first film scraping device and the second film scraping device and used for copolymerizing the GA prepolymer and the LA prepolymer, and foaming equipment used for foaming the PLGA copolymer from the static mixer.

The material conveying pipeline between the first reaction kettle and the first film scraping device, the material conveying pipeline between the second reaction kettle and the second film scraping device, the material conveying pipeline between the first film scraping device and the static mixer, the material conveying pipeline between the second film scraping device and the static mixer and the material conveying pipeline between the static mixer and the foaming equipment are all provided with conventional heat tracing, so that the materials conveyed in the heat tracing pipeline are in a melt flow state. In addition, the melt pump with proper model/power can be selected according to the reaction time of raw material monomers in the reaction kettle, the volume of a material conveying pipeline and the time of materials passing through the static mixer, so that the smooth running of continuous production is ensured.

In one embodiment of the invention, the static mixer is a static mixer; such as, but not limited to, SK type static mixers, SX type static mixers, SV type static mixers, and the like.

The reaction kettle used in the invention comprises a shell, a stirring paddle inserted in the shell and a heating element for supplying heat to the shell.

As conventionally used, the stirring paddle inserted in the housing may be suspended so as not to contact both the inner wall and the bottom of the housing; in one embodiment of the invention, the stirring paddle is driven by a driving motor to realize a stirring function.

The heating element is preferably a heat exchanger which is arranged on the inner wall of the housing in the axial direction of the housing.

The upper part of the shell is provided with a feed inlet, the bottom is provided with a discharge outlet, and in one embodiment of the invention, the discharge outlet can be provided with an electromagnetic valve.

In one embodiment of the invention, the bottom of the housing is circular arc shaped.

The film scraping device used in the invention comprises a shell, a rotating shaft axially inserted in the inner cavity of the shell along the shell, a plurality of scraping plates axially and mutually arranged on the rotating shaft at intervals along the shell, and a heating element (such as but not limited to an electric heating sleeve) arranged outside the shell, wherein the scraping plate closest to the top of the shell is also provided with a film distributing device, and the film distributing device is a film distributing device which is used for a film scraping evaporator or a film scraping reactor and is conventional in the market, and special structural modification is not needed. The rotary shaft is typically driven by a drive motor drivingly connected thereto.

The rotating shaft can be provided with a scraping plate in the radial direction, and also can be provided with a scraping plate at each of the two radial ends. The number of the scrapers is generally determined according to the space in the cavity of the shell; in one embodiment of the invention, a gap of not more than 5mm, preferably not more than 2mm, is left between the outer side of the scraper and the inner wall of the housing, depending on the size of the cross section of the housing. The blade thickness may be that used in conventional wiped film evaporators or reactors.

The top of the shell is respectively provided with a feed inlet and an air outlet, the feed inlet is communicated with the film distributor, and the air outlet is communicated with the inner cavity of the shell. Preferably, the air outlet is located at a higher level than the feed inlet.

The bottom of the shell is provided with a discharge hole, and an electromagnetic valve can be arranged at the discharge hole.

The film scraping device used in the invention is also connected with a raw material collecting unit; the raw material collecting unit comprises a gas-liquid separator, a condenser and a raw material recovery tank which are sequentially connected with the film scraping device.

A vacuum pump can be arranged between the gas-liquid separator and the condenser for vacuumizing the film scraping device so that unreacted lactide monomer separated from the serosa is timely pumped out and collected.

The exhaust port of the gas-liquid separator is connected with the material inlet of the condenser through a pipeline, and the material outlet of the condenser is connected to the raw material collecting tank through a pipeline (provided with a conveying pump).

The gas-liquid separator adopts side feeding, and the upper part of the inner side of the gas-liquid separator is provided with a liquid foam preventing device. Preferably, the liquid foam preventing device is a silk screen or a cyclone plate.

Under the working state, materials from the reaction kettle enter the inner part of the film scraping device shell through the feed inlet, the materials are distributed on the inner wall of the film scraping device shell through the film distributing device, and the rotating scraping plate continuously and uniformly scrapes the materials into thick and thin films on the inner wall of the film scraping device shell and pushes the films downwards in a spiral shape; in the process, the rotating scraping plate ensures that continuous and uniform serosity produces high-speed turbulence and prevents the serosity from coking and scaling on the inner wall of the shell of the film scraper, and the lactide monomer which is remained in the serosity and does not participate in reaction breaks away from the serosity in a gas phase form and moves upwards, and is discharged from the gas outlet and recycled by the raw material collecting unit; after purification, the polymer can be used as a reaction raw material to be continuously put into production to prepare the PLGA copolymer.

The foaming equipment used in the invention comprises a foaming machine and supercritical CO ₂ A fluid reservoir. In one embodiment of the present invention, an extrusion foaming machine is employed, such as, but not limited to, a twin screw extruder.

In one embodiment of the invention, the twin-screw extruder is provided with a device for introducing supercritical CO ₂ A fluid injection port communicated with the screw at the machine head and communicated with the external supercritical CO through a diversion pipeline ₂ The fluid storage tanks are connected. More preferably, a metering pump is arranged on the flow guide pipe.

Preparation method of PLGA foaming material

The invention provides a continuous preparation method of PLGA foaming material, which is carried out by the preparation device and comprises the following steps:

firstly, enabling glycolide and lactide to react in a first reaction kettle and a second reaction kettle which are added with catalysts respectively to obtain glycolide prepolymer and lactide prepolymer respectively;

step two, enabling the glycolide prepolymer obtained in the first reaction kettle to enter a first film scraping device for pre-devolatilization treatment, and enabling the lactide prepolymer obtained in the second reaction kettle to enter a second film scraping device for pre-devolatilization treatment;

thirdly, enabling the materials subjected to the pre-devolatilization treatment from the first film scraping device and the second film scraping device to enter a static mixer for copolymerization reaction to obtain PLGA copolymer (or PLGA melt);

Fourthly, foaming the polylactic acid-glycollic acid copolymer in foaming equipment to obtain the PLGA foaming material.

The glycolide and the lactide which are used as raw materials in the first step only need to enter different reaction kettles, and the obtained prepolymer enters corresponding film scraping devices connected with the reaction kettles in the second step.

For convenience in description, the description mode of the first reaction kettle and the second reaction kettle is adopted, and the film scrapers connected with the first reaction kettle and the second reaction kettle are described as the first film scrapers and the second film scrapers.

In one embodiment of the present invention, the first step is to polymerize glycolide in the presence of a catalyst in a first reactor at 130-190 ℃ to produce a glycolide prepolymer having a relative molecular weight of 1.2-4.0 ten thousand.

In one embodiment of the present invention, the first step is to polymerize lactide at 120-180℃in the presence of a catalyst in a second reactor to produce a lactide prepolymer having a relative molecular weight of 1.2-4.0 ten thousand.

The reaction of the first step is carried out under normal pressure.

The catalyst used in the first step may be at least one selected from tin compounds, antimony compounds or zinc compounds, for example, but not limited to, one or more of the following: stannous octoate, stannous chloride, tin lactate, antimony trioxide, diethyl zinc and zinc acetate dihydrate.

In one embodiment of the present invention, in the first step, the catalyst is used in an amount of between 0.001 and 0.3wt% based on the total weight of the raw materials in the reaction vessel.

In one embodiment of the present invention, the molar ratio of glycolide to lactide fed into the first reaction vessel and the second reaction vessel in the first step is 10-90:90-10.

In the second step, the glycolide prepolymer and the lactide prepolymer enter corresponding film scrapers at a feeding speed of 0.2-2.0 kg/h; in one embodiment of the invention, the rate of entry of the glycolide prepolymer and the lactide prepolymer into each respective doctor blade is substantially the same.

In the second step, the absolute pressure in the film scraper is generally about 10-100kPa, the temperature of the inner wall is generally about 150-220 ℃, and the rotating speed of the scraper is about 50-150 rpm.

In the second step, the materials entering the film scraping device are distributed on the inner wall of the film scraping device through the film distributing device, and the scraping plate continuously and uniformly scrapes the materials into a liquid film with uniform thickness on the inner wall of the film scraping device and pushes the liquid film downwards in a spiral shape; in the process, the rotating scraping plate ensures that continuous and uniform serosity produces high-speed turbulence and prevents the serosity from coking and scaling on the inner wall of the shell of the film scraper, and the lactide monomer which is remained in the serosity and does not participate in reaction breaks away from the serosity in a gas phase form and moves upwards, and is discharged from the gas outlet and recycled by the raw material collecting unit; after purification, the polymer can be used as a reaction raw material to be continuously put into production to prepare the PLGA copolymer.

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

And in the third step, the materials led out by the first film scraping device and the second film scraping device are simultaneously conveyed to a static mixer.

In one embodiment of the invention, the temperature of the static mixer is increased in a gradient way in at least two sections, the temperature range of the first section can be 160-200 ℃, and the temperature range of the last section can be 180-220 ℃; the time of passage of the material through the segments also increases in gradient, for example, but not limited to, 5-40 minutes through the first segment and 40-70 minutes through the last segment.

The internal pressure of the static mixer used in the third step was normal pressure.

The fourth step comprises mixing the polylactic acid-glycolic acid copolymer obtained in the third step with supercritical CO ₂ The fluids are mixed in a foaming machine.

In one embodiment of the present invention, in the fourth step, the PLGA melt obtained in the third step is fed into an extrusion foaming machine, and supercritical CO is introduced into the extrusion foaming machine through an injection port ₂ Fluid, under the action of screw, supercritical CO ₂ Mixing the fluid with PLGA melt, foaming, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

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

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

In one embodiment of the invention, the internal temperature of the extrusion foaming machine is controlled to be in the range of 150-250 ℃.

In one embodiment of the invention, the internal pressure of the extrusion foaming machine is controlled to be in the range of 5-30 MPa.

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

In one embodiment of the invention, the pressure inside the extrusion foaming machine is relieved to normal pressure at a speed of 1-8 MPa/min after the foaming treatment.

In a preferred embodiment of the present invention, the process conditions of the foaming treatment are: the internal temperature of the extrusion foaming machine is controlled to be 180-220 ℃, the pressure is controlled to be 10-25MPa, the treatment is carried out for 10-60min, and then the pressure is relieved to normal pressure at the rate of 2-6 MPa/min.

So that those skilled in the art can appreciate the features and effects of the present invention, a general description and definition of the terms and expressions set forth in the specification and claims follows. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and in the event of a conflict, the present specification shall control.

The theory or mechanism described and disclosed herein, whether right or wrong, is not meant to limit the scope of the invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.

In this document, all features, such as values, amounts, and concentrations, are for brevity and convenience only, as defined in the numerical or percent range. Accordingly, the description of a numerical range or percentage range should be considered to cover and specifically disclose all possible sub-ranges and individual values (including integers and fractions) within the range.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain standard deviations found in their respective testing measurements. As used herein, "about" generally means that the actual value is within plus or minus 10%, 5%, 1% or 0.5% of a particular value or range. Alternatively, the term "about" means that the actual value falls within an acceptable standard error of the average value, as determined by one of ordinary skill in the art. Except in the experimental examples, or where otherwise explicitly indicated, all ranges, amounts, values, and percentages used herein (e.g., to describe amounts of materials, lengths of time, temperatures, operating conditions, ratios of amounts, and the like) are to be understood to be modified by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present specification and attached claims are approximations that may vary depending upon the desired properties. At least these numerical parameters should be construed as the number of significant digits and by applying ordinary rounding techniques.

The above-mentioned features of the invention, or of the embodiments, may be combined in any desired manner. All of the features disclosed in this specification may be used in combination with any combination of features, provided that the combination of features is not inconsistent and all such combinations are contemplated as falling within the scope of the present specification. The various features disclosed in the specification may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless expressly stated otherwise, the disclosed features are merely general examples of equivalent or similar features.

The main advantages of the invention are that

1. The PLGA foaming material prepared by the invention effectively solves the problem of serious yellowing of the PLGA foaming material prepared by the existing preparation process.

2. The PLGA foaming material prepared by the invention has obviously improved foaming ratio and cell density, more uniform cell size and more compact cells.

3. The invention realizes continuous production of high-quality PLGA foaming material, can effectively reduce the loss of reaction materials, has no environmental pollution in the production process, is safe in production method, has simple preparation process and is suitable for mass production.

The invention will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. The experimental procedures, which do not address the specific conditions in the examples below, are generally carried out under conventional conditions or under conditions recommended by the manufacturer. All percentages, ratios, proportions, or parts are by weight unless otherwise indicated. The units in weight volume percent are well known to those skilled in the art and refer, for example, to the weight of solute in 100 milliliters of solution (grams). Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred methods and materials described herein are presented for illustrative purposes only.

Device embodiment

A PLGA preparation apparatus as shown in FIG. 1 was provided.

The PLGA preparation device I comprises a first reaction kettle 1000A, a second reaction kettle 1000B, a first film scraping device 2000A, a second film scraping device 2000B, a static mixer 3000 and foaming equipment 4000; the discharge port 1400 at the bottom of the first reaction kettle 1000A shell 1600 is connected with the feed port 2030 at the top of the first film scraping device 2000A shell 2080 through a material conveying pipeline, and the discharge port 1400 at the bottom of the second reaction kettle 1000B shell 1600 is connected with the feed port 2030 at the top of the second film scraping device 2000B shell 2080 through a material conveying pipeline; the discharge ports 2040 at the bottoms of the shells 2080 of the first film scraper 2000A and the second film scraper 2000B are respectively connected with 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 with the feed port 4400 of the foaming equipment 4000 through material conveying pipelines.

Both the first reaction kettle 1000A and the second reaction kettle 1000B comprise a shell 1600, a feed inlet 1300 arranged at the top of the shell 1600, a discharge outlet 1400 arranged at the bottom of the shell 1600, a stirring paddle 1100 suspended in the shell, and a heat exchanger 1200 arranged inside the shell 1600; the paddle 1100 may be coupled to a drive motor 1500.

The first and

second film scrapers

2000A and 2000B are respectively connected to a raw material collecting unit 2100. The raw material collecting unit 2100 includes a gas-liquid separator 2110, a condenser 2120, and a recovery tank 2130; the first film scraping device 2000A and the second film scraping device 2000B are respectively connected with a gas-liquid separator 2110 in the raw material collecting unit 2100 through a material conveying pipeline through a gas outlet 2050 arranged at the top of a shell 2080, the top of the gas-liquid separator 2110 is connected with an inlet of a condenser 2120 through a material conveying pipeline, and an outlet of the condenser 2120 is connected with a recovery tank 2130 through a material conveying pipeline; a vacuum pump 200 is provided on a material transfer line connecting the gas-liquid separator 2110 and the condenser 2120.

The first film scraper 2000A and the second film scraper 2000B each comprise a housing 2080, a rotating shaft 2060, a scraper 2010 radially connected with the rotating shaft and having an outer side surface parallel to the rotating shaft, a feed port 2030 and an air outlet 2050 respectively arranged at the top of the housing 2080, a discharge port 2040 arranged at the bottom of the housing 2080, and an electric heating jacket 2070 arranged at the outer side of the housing 2080; the inside of the housing 2080 is provided with a film distributor 2020 higher than the scraper 2010. The distance of the outer side of the wiper 2010 from the inner wall of the housing 2080 is about 0-5 mm, preferably no more than 2 mm; the rotating shaft 2060 may be connected to a drive motor 1500.

A melt pump 100 is arranged on a material conveying pipeline which is connected with a discharge hole 1400 at the bottom of a first reaction kettle 1000A shell 1600 and a feed hole 2030 at the top of a first film scraping device 2000A shell 2080; a melt pump 100 is arranged on a material conveying pipeline which is connected with a discharge hole 1400 at the bottom of a shell 1600 of the second reaction kettle 1000B and a feed hole 2030 at the top of a shell 2080 of the second film scraper 2000A; melt pumps 100 are respectively arranged on material conveying pipelines respectively connected with a discharge hole 2040 at the bottom of a shell 2080 of a first film scraper 2000A and a second film scraper 2000B and a feed hole 3100 of a static mixer 3000; a melt pump 100 is arranged on a material conveying pipeline connecting a discharge port 3200 of the static mixer 3000 and a feed port 4400 of the foaming equipment 4000.

The extrusion foaming machine 4100 in the foaming apparatus 4000 is a twin screw extruder provided with a device for introducing supercritical CO ₂ An injection port 4300 for fluid, the injection port 4300 being in communication with a screw at the handpiece, and the injection port 4300 being in communication with the external supercritical CO through a diversion line 4500 ₂ Fluid reservoir 4200 is connected; a metering pump 300 is arranged on the diversion pipeline 4500.

Preparation example

Example 1

Introducing inert GAs (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide serving as raw materials (the molar ratio of glycolide and lactide is 70:30) into the first reaction kettle and the second reaction kettle, respectively adding catalysts (stannous octoate which is 0.002% of the mass of raw materials monomer in the corresponding reactor) into the first reaction kettle and the second reaction kettle, controlling the temperature of the first reaction kettle and the second reaction kettle to be 140 ℃ and 120 ℃ respectively, reacting for a period of time under normal pressure until the relative molecular weight of GA prepolymer generated in the first reaction kettle is about 1.5 ten thousand, the relative molecular weight of LA prepolymer generated in the second reaction kettle is about 1.2 ten thousand, respectively introducing materials in the first reaction kettle and the second reaction kettle into a first film scraper and a second film scraper according to a feeding rate of 1 kg/hour, performing pre-volatilizing treatment [ wherein the pressure in the first film scraper and the second film scraper is 60kPa, the temperature of the first film scraper and the second film scraper is about 180 ℃ respectively, and the material is scraped into a film on the film scraper with a uniform thickness of the film after the film is scraped into the film, and the film is scraped into the film scraper with the uniform thickness of the film scraper after the film is continuously rotating for 90 minutes A uniform liquid film (average film thickness of the first film scraper is about 650 μm, average film thickness of the second film scraper is about 520 μm), and is pushed downward in a spiral shape]Then the materials led out from the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (commercial SK type static mixer) for copolymerization reaction (wherein the static mixer is divided into three sections, the temperature of the first section is 170 ℃, the temperature of the second section is 190 ℃, the temperature of the third section is 200 ℃, the time for the materials to pass through the first section is about 10min, the time for the materials to pass through the second section is about 30min, the time for the materials to pass through the third section is about 60min, the inside of the static mixer is normal pressure), thus obtaining PLGA melt, then the PLGA melt is conveyed into an extrusion foaming machine, and supercritical CO is led into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 8% of the mass of PLGA melt, the rotating speed of the screw is controlled to be 100r/min, and supercritical CO is generated under the action of the screw ₂ Uniformly mixing the fluid and PLGA melt, controlling the internal temperature of an extrusion foaming machine to 205 ℃, controlling the pressure to 20MPa, treating for 25min, releasing pressure to normal pressure at a rate of 5MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 2

This example is substantially identical to example 1, except that in this example the static mixer is divided into two sections, the temperature in the first section being 190℃and the temperature in the second section being 200℃and the time for the passage of the material through the first section being about 40 minutes and the time for the passage through the second section being about 60 minutes.

Example 3

Introducing inert gas (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide (the molar ratio of the glycolide to the lactide is 70:30) serving as raw materials into the first reaction kettle and the second reaction kettle, respectively adding a catalyst (stannous octoate with the addition amount of 0.008 percent of the mass of raw material monomer corresponding to the reactor) into the first reaction kettle and the second reaction kettle, controlling the temperature of the first reaction kettle and the second reaction kettle to be 156 ℃ and 142 ℃ respectively, and reacting for a period of time under normal pressure until G generated in the first reaction kettleThe relative molecular weight of the prepolymer A is about 2.2 ten thousand, the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 2.0 ten thousand, then the materials in the first reaction kettle and the second reaction kettle are respectively introduced into a first film scraper and a second film scraper for pre-devolatilization treatment according to the feeding rate of 0.8 kg/hour, wherein the absolute pressure in the first film scraper and the absolute pressure in the second film scraper are both 40kPa, the temperature of the inner wall of the film scraper is 195 ℃, the rotating speed of the scraping plate is about 80 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through the film distributor, the scraping plate continuously and uniformly scrapes the materials into a liquid film with uniform thickness on the inner wall of the film scraper (the average film forming thickness of the first film scraper is about 620 mu m, the average film forming thickness of the second film scraper is about 450 mu m), and the materials entering the film scraper are pushed downwards in a spiral shape ]Then the materials led out by the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (commercial SK type static mixer) for copolymerization reaction (wherein the static mixer is divided into three sections, the temperature of the first section is 160 ℃, the temperature of the second section is 185 ℃, the temperature of the third section is 200 ℃, the time for the materials to pass through the first section is about 5min, the time for the materials to pass through the second section is about 30min, the time for the materials to pass through the third section is about 65min, the inside of the static mixer is normal pressure), thus obtaining PLGA melt, then the PLGA melt is conveyed into an extrusion foaming machine, and supercritical CO is led into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The fluid introduction amount is 12% of the PLGA melt mass, the rotating speed of the screw is controlled to be 100r/min, and the supercritical CO is realized under the action of the screw ₂ Uniformly mixing the fluid and PLGA melt, controlling the internal temperature of an extrusion foaming machine to 210 ℃, controlling the pressure to 24MPa, treating for 30min, releasing pressure to normal pressure at the rate of 2MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 4

Introducing inert gas (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide (the molar ratio of glycolide to lactide is 70:30) serving as raw materials into the first reaction kettle and the second reaction kettle, and respectively adding catalysts (octanoic acid) into the first reaction kettle and the second reaction kettle Stannous, the addition amount of which is 0.01% of the mass of raw material monomers in a corresponding reactor, then controlling the temperature of a first reaction kettle and a second reaction kettle to be 165 ℃ and 170 ℃ respectively, and reacting for a period of time under normal pressure until the relative molecular weight of GA prepolymer generated in the first reaction kettle is about 2.7 ten thousand, the relative molecular weight of LA prepolymer generated in the second reaction kettle is about 2.6 ten thousand, then respectively introducing the materials in the first reaction kettle and the second reaction kettle into a first film scraper and a second film scraper for pre-devolatilization treatment at a feeding rate of 1.2 kg/h, wherein the absolute pressure in the first film scraper and the second film scraper is 80kPa, the temperature of the inner wall of the film scraper is 190 ℃, the rotation speed of the scraping plate is about 100 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through the film distributor, the scraping plate continuously and uniformly scrapes the materials into a thin uniform liquid film (the average film thickness of the first film scraper is about 720 mu m, the average thickness of the second film scraper is about 640 mu m, and the average thickness of the film is pushed down to a spiral shape]Then the materials led out from the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (commercial SK type static mixer) for copolymerization reaction (wherein the static mixer is divided into three sections, the temperature of the first section is 165 ℃, the temperature of the second section is 190 ℃, the temperature of the third section is 205 ℃, the time for the materials to pass through the first section is about 5min, the time for the materials to pass through the second section is about 35min, the time for the materials to pass through the third section is about 60min, the inside of the static mixer is normal pressure), thus obtaining PLGA prepolymer melt, then the PLGA prepolymer melt is conveyed into an extrusion foaming machine, and supercritical CO is led into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 10% of the mass of PLGA prepolymer melt, the rotating speed of the screw is controlled to be 100r/min, and the supercritical CO is caused under the action of the screw ₂ Uniformly mixing the fluid and PLGA prepolymer melt, controlling the internal temperature of an extrusion foaming machine to 215 ℃, controlling the pressure to 25MPa, treating for 10min, releasing pressure to normal pressure at the rate of 6MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 5

To the first reaction kettle and the second reaction kettleIntroducing inert GAs (such as nitrogen) into the reaction kettle to exhaust air in the reaction kettle, respectively adding glycolide and lactide (the molar ratio of glycolide to lactide is 70:30) serving as raw materials into the first reaction kettle and the second reaction kettle, respectively adding catalysts (stannous octoate which is 0.03% of the mass of raw material monomer in the corresponding reactor) into the first reaction kettle and the second reaction kettle, controlling the temperature of the first reaction kettle and the second reaction kettle to be 180 ℃ and 175 ℃ respectively, reacting for a period of time under normal pressure until the relative molecular weight of GA prepolymer generated in the first reaction kettle is about 3.5 ten thousand and the relative molecular weight of LA prepolymer generated in the second reaction kettle is about 3.5 ten thousand, then the materials in the first reaction kettle and the second reaction kettle are respectively led into a first film scraper and a second film scraper for pre-devolatilization treatment according to the feeding rate of 1.5 kg/hour, wherein the absolute pressure in the first film scraper and the second film scraper is 40kPa, the temperature of the inner wall of the film scraper is 200 ℃, the rotating speed of a scraping plate is about 120 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through a film distributor, the scraping plate continuously and uniformly scrapes the materials into a liquid film with uniform thickness on the inner wall of the film scraper (the average film forming thickness of the first film scraper is about 800 mu m, the average film forming thickness of the second film scraper is about 760 mu m), and the materials are pushed downwards in a spiral manner ]Then the materials led out from the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (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 ℃, the temperature of the second section is 195 ℃, the temperature of the third section is 210 ℃, the time for the materials to pass through the first section is about 10min, the time for the second section is about 30min, the time for the third section is about 60min, and the inside of the static mixer is normal pressure), thus obtaining PLGA prepolymer melt, then the PLGA prepolymer melt is conveyed into an extrusion foaming machine, and supercritical CO is led into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 20% of the mass of PLGA prepolymer melt, the rotating speed of the screw is controlled to be 100r/min, and supercritical CO is generated under the action of the screw ₂ Uniformly mixing the fluid and PLGA prepolymer melt, controlling the internal temperature of an extrusion foaming machine to 215 ℃ and controlling the pressureTreating for 60min at 16MPa, releasing pressure to normal pressure at a rate of 4MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 6

Introducing inert GAs (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide (the molar ratio of the glycolide to the lactide is 50:50) serving as raw materials into the first reaction kettle and the second reaction kettle, respectively adding a catalyst (antimony trioxide with the addition of 0.06 percent of the mass of the raw material monomer in the corresponding reactor) into the first reaction kettle and the second reaction kettle, controlling the temperature of the first reaction kettle and the second reaction kettle to be 170 ℃ and reacting for a period of time under normal pressure until the relative molecular weight of GA prepolymer generated in the first reaction kettle is about 2.6 ten thousand and the relative molecular weight of LA prepolymer generated in the second reaction kettle is about 2.9 ten thousand, then the materials in the first reaction kettle and the second reaction kettle are respectively led into a first film scraper and a second film scraper according to the feeding rate of 0.6 kg/hour for pre-devolatilization treatment, wherein the absolute pressure in the first film scraper and the second film scraper is 65kPa, the temperature of the inner wall of the film scraper is 190 ℃, the rotating speed of a scraping plate is about 100 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through a film distributor, the scraping plate continuously and uniformly scrapes the materials into a liquid film with uniform thickness on the inner wall of the film scraper (the average film forming thickness of the first film scraper is about 440 mu m, the average film forming thickness of the second film scraper is about 470 mu m), and the materials are pushed downwards in a spiral manner ]The materials led out from the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (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 ℃, the temperature of the second section is 185 ℃, the temperature of the third section is 192 ℃, the temperature of the fourth section is 205 ℃, the time for the materials to pass through the first section is about 5min, the time for the second section is about 25min, the time for the third section is about 35min, the time for the fourth section is about 55min and the internal part of the static mixer is normal pressure), thus obtaining PLGA prepolymer melt, and then the PLGA prepolymer melt is conveyed into an extrusion foaming machine and extruded and sent into an extrusion foaming machine through a pouring openingIntroducing supercritical CO into bubble machine ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 3% of the mass of PLGA prepolymer melt, the rotating speed of the screw is controlled to be 120r/min, and supercritical CO is generated under the action of the screw ₂ Uniformly mixing the fluid and PLGA prepolymer melt, controlling the internal temperature of an extrusion foaming machine to 196 ℃, controlling the pressure to 12MPa, treating for 50min, releasing pressure to normal pressure at a rate of 4MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 7

Introducing inert GAs (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide (the molar ratio of the glycolide to the lactide is 85:15) serving as raw materials into the first reaction kettle and the second reaction kettle, respectively adding catalysts (namely antimony trioxide and tin lactate with the addition of 0.05 percent and 0.08 percent of the mass of the raw material monomer in the corresponding reactors) into the first reaction kettle and the second reaction kettle, respectively controlling the temperature of the first reaction kettle and the second reaction kettle to be 130 ℃ and 158 ℃ and reacting for a period of time under normal pressure until the relative molecular weight of GA prepolymer generated in the first reaction kettle is about 2.6 ten thousand and the relative molecular weight of LA prepolymer generated in the second reaction kettle is about 3.4 ten thousand, then the materials in the first reaction kettle and the second reaction kettle are respectively led into a first film scraper and a second film scraper for pre-devolatilization treatment according to the feeding rate of 0.5 kg/hour, wherein the absolute pressure in the first film scraper and the absolute pressure in the second film scraper are 70kPa, the temperature of the inner wall of the film scraper is 180 ℃, the rotating speed of a scraping plate is about 90 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through a film distributor, the scraping plate continuously and uniformly scrapes the materials into a liquid film with uniform thickness on the inner wall of the film scraper (the average film forming thickness of the first film scraper is about 380 mu m, the average film forming thickness of the second film scraper is about 430 mu m), and the materials are pushed downwards in a spiral manner ]The materials led out by the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (commercial SK type static mixer) for copolymerization reaction (wherein the static mixer is divided into five sections, the temperature of the first section is 160 ℃, the temperature of the second section is 176 ℃,the third stage has a temperature of 190 ℃, the fourth stage has a temperature of 200 ℃, the fifth stage has a temperature of 210 ℃, the material passes through the first stage for about 5min, the second stage for about 10min, the third stage for about 25min, the fourth stage for about 40min, the fifth stage for about 40min, and the static mixer is at normal pressure), so as to obtain PLGA prepolymer melt, and the PLGA prepolymer melt is conveyed into an extrusion foaming machine and introduced into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 20% of the mass of PLGA prepolymer melt, the rotating speed of the screw is controlled to be 150r/min, and supercritical CO is caused under the action of the screw ₂ And uniformly mixing the fluid and PLGA prepolymer melt, controlling the internal temperature of an extrusion foaming machine to 220 ℃, controlling the pressure to 22MPa, treating for 20min, releasing pressure to normal pressure at a rate of 2MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Example 8

Introducing inert GAs (such as nitrogen) into the first reaction kettle and the second reaction kettle to exhaust air in the kettles, respectively adding glycolide and lactide serving as raw materials (the molar ratio of the glycolide to the lactide is 40:60) into the first reaction kettle and the second reaction kettle, respectively adding catalysts (namely stannous octoate and diethyl zinc) into the first reaction kettle and the second reaction kettle, wherein the addition amounts of the stannous octoate and the diethyl zinc are respectively 0.1 percent and 0.05 percent of the mass of the raw material monomer in the corresponding reactors, then controlling the temperature of the first reaction kettle and the second reaction kettle to be 172 ℃ and 165 ℃ respectively, reacting for a period of time under normal pressure, until the relative molecular weight of the GA prepolymer generated in the first reaction kettle is about 4.0 ten thousand and the relative molecular weight of the LA prepolymer generated in the second reaction kettle is about 3.7 ten thousand, respectively introducing the materials in the first reaction kettle and the second reaction kettle into a first film scraper and a second film scraper according to the feeding rate of 1.0 kg/hour for pre-devolatilization treatment, wherein the absolute pressure in the first film scraper and the second film scraper is 35kPa, the temperature of the inner wall of the film scraper is 195 ℃, the rotating speed of the scraping plate is about 100 revolutions per minute, the materials entering the film scraper are distributed on the inner wall of the film scraper through the film distributor, and the scraping plate continuously and uniformly heats the materials Uniformly scraping the film on the inner wall of the film scraping device to form a liquid film with uniform thickness (the average film forming thickness of the first film scraping device is about 690 mu m, the average film forming thickness of the second film scraping device is about 610 mu m), and pushing the film downwards in a spiral shape]Then the materials led out from the first film scraping device and the second film scraping device are simultaneously conveyed into a static mixer (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 ℃, the temperature of the second section is 195 ℃, the temperature of the third section is 205 ℃, the time for the materials to pass through the first section is about 20min, the time for the second section is about 30min, the time for the third section is about 40min, and the inside of the static mixer is normal pressure), thus obtaining PLGA prepolymer melt, then the PLGA prepolymer melt is conveyed into an extrusion foaming machine, and supercritical CO is led into the extrusion foaming machine through an injection port ₂ Fluid, supercritical CO ₂ The introduction amount of the fluid is 16% of the mass of PLGA prepolymer melt, the rotating speed of the screw is controlled to be 80r/min, and supercritical CO is caused under the action of the screw ₂ Uniformly mixing the fluid and PLGA prepolymer melt, controlling the internal temperature of an extrusion foaming machine to be 180 ℃, controlling the pressure to be 10MPa, treating for 30min, releasing pressure to normal pressure at the rate of 2MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Comparative example 1

Introducing inert gas (such as nitrogen) into a reaction kettle to exhaust air in the kettle, adding glycolide and lactide (the molar ratio of glycolide to lactide is 70:30) into the reaction kettle together, adding a catalyst (namely stannous octoate, the addition of which is 0.01% of the mass of the raw material monomer) into the reaction kettle, reacting for about 2 hours at normal pressure and 180 ℃ before the reaction is carried out for 2 hours at the absolute pressure of 10kPa and 210 ℃, then reacting for 4 hours at the absolute pressure of 2kPa and 220 ℃, then continuously reacting for 4 hours at the absolute pressure of 600Pa and 230 ℃, and finally devolatilizing for 1 hour at the absolute pressure of 200Pa and 240 ℃ to obtain PLGA melt (in the comparative example, coking slag blocks appear at the bottom of the reaction kettle and adhere to the kettle wall, so that the removal is very difficult), conveying the PLGA melt into an extrusion foaming machine, and introducing supercritical CO into the extrusion foaming machine through a pouring port ₂ Fluid, supercritical CO ₂ The fluid introduction amount is 12% of the PLGA melt mass, the rotating speed of the screw is controlled to be 100r/min, and the supercritical CO is realized under the action of the screw ₂ Uniformly mixing the fluid and PLGA melt, controlling the internal temperature of an extrusion foaming machine to 210 ℃, controlling the pressure to 24MPa, treating for 30min, releasing pressure to normal pressure at the rate of 2MPa/min, extruding and foaming through a die, and cooling and shaping to obtain the PLGA foaming material.

Comparative example 2

This example is substantially the same as example 3, except that in this example, the materials in the first and second reaction kettles were directly transferred to a static mixer (commercially available SK type static mixer) simultaneously for copolymerization, and the steps of pre-devolatilizing the glycolide prepolymer and pre-devolatilizing the lactide prepolymer were omitted.

Comparative example 3

The present example was substantially the same as example 3, except that the materials discharged from the first and second film scrapers were simultaneously transferred to the third reaction vessel for copolymerization (nitrogen purging was already employed) under normal pressure at 200℃for 100 minutes.

Correlation test characterization method in the examples:

the term "yellowness index" as used herein refers to a number calculated from spectrophotometric data that describes the change in color of a test sample from clear or white to yellow. The test method may be ASTM E313.

Yellowness index YI test: copolymers were chosen that had smooth surfaces and no significant protrusion. The Yellowness Index (YI) of the product was measured using a 3nh NS series colorimeter. Three measurements were made under 10 degree observation angle, D65 observation light source and reflected light measurement according to ASTM E313, and the average was calculated to determine the Yellowness Index (YI) of the copolymer.

Weight average molecular weight and distribution thereof: the sample was dissolved in 5mmol/L sodium trifluoroacetate in hexafluoroisopropanol to give a 0.05-0.3wt% solution. The solution was then filtered through a polytetrafluoroethylene filter having a pore size of 0.4. Mu.m. 20. Mu.L of the filtered solution was added to a Gel Permeation Chromatography (GPC) sample injector to determine the molecular weight of the sample. Five standard molecular weights of methyl methacrylate having different molecular weights were used for molecular weight correction.

Foaming ratio: the apparent densities of the foamed material and the unfoamed material were respectively tested according to the GB/T6343-2009 standard, the drainage method was used for the foamed sample, and then the foaming ratio of the final microcellular foamed material was calculated. Foaming ratio (Φ) =ρ _polymer /ρ _foam Wherein ρ is _polymer Density of unfoamed material ρ _foam Is the density of the foaming material.

Cell density and cell diameter: and quenching the microporous foaming material by liquid nitrogen, spraying metal on the section, and observing the cell structure inside the foaming material by adopting a Scanning Electron Microscope (SEM). Cell size was measured using Image J software and cell density was calculated. Wherein the cell density N (unit: units/cm ³ )＝(n/A) ^3/2 X.phi.n is the number of cells on the selected scanning electron microscope photograph, A is the actual area of the scanning photograph (unit: cm ² ) Phi is the foaming ratio.

The yellowness index and the weight average molecular weight and the distribution of the PLGA foaming materials prepared in each preparation example and comparative example are specifically shown in Table 1.

TABLE 1

Project	Yellowness Index (YI)	Weight average relative molecular mass	Molecular weight distribution index
				Example 1	11	13.4 ten thousand	1.52
Example 2	13	12.7 ten thousand	1.53
				Example 3	10	15.4 ten thousand	1.48
Example 4	14	16.3 ten thousand	1.47
				Example 5	16	18.1 ten thousand	1.43
Example 6	12	19.5 ten thousand	1.37
				Example 7	11	22.7 ten thousand	1.25
Example 8	17	17.2 ten thousand	1.69
				Comparative example 1	35	14.2 ten thousand	1.94
Comparative example 2	26	14.8 thousands	1.77
				Comparative example 3	15	12.1 ten thousand	1.62

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

TABLE 2

The yellowness index of example 3 was only 10 compared to example 3, which was reduced by about 71.4% compared to comparative example 1. Accordingly, the molecular weight distribution index of PLGA obtained in example 3 was 1.48, which is significantly lower than that of comparative example 1, 1.94. In addition, the PLGA foam obtained in comparative example 1 in Table 2 had a significantly smaller expansion ratio and cell density than those of example 3, and the cell diameter of example 3 based on the present technique was 25. Mu.m, which was much smaller than that of comparative example 1 by 450. Mu.m. It is presumed that since comparative example 1 had a large amount of lactide monomer or oligomer remained in the PLGA melt during the preparation of the PLGA melt, some of these substances may undergo oxidative deterioration due to the effect of high temperature and could not be bonded to the PLGA molecular chain, but remained in the final PLGA foam material, so that the yellowing of the product was serious and the chromaticity quality was poor. In addition, the PLGA melt obtained in comparative example 1 has poor homogeneity, a part of the area has high viscosity, and the other part has low viscosity, so that the uniformity of the melt strength is poor, therefore, in the subsequent foaming treatment, the formed cells have poor uniformity in size, the material is easy to shrink after foaming, the formed cells are easy to collapse, so that the density of the finally formed cells is greatly reduced, and the foaming multiplying power is low.

In the comparative example 2, the step of the pre-devolatilization treatment, that is, the pre-devolatilization treatment was not performed on the obtained GA prepolymer melt and LA prepolymer melt using a doctor blade, was omitted as compared with the example 3. From the test results in table 1, it is understood that the yellowness index of comparative example 2 is significantly higher than that of comparative example 1, although it is smaller than that of example 3, probably because more unreacted lactide monomer or oligomer of lactide monomer remains in the produced GA prepolymer, LA prepolymer, and a part of these substances may undergo oxidative deterioration due to the effect of high temperature during the reaction of the subsequent gradient temperature rise of the static mixer, and cannot be bonded to PLGA molecular chains, but remains in the final PLGA foam, so that the yellowness index is still significantly higher than that of example 3, and also causes an increase in the molecular weight distribution index, and accordingly the foaming ratio and cell density are smaller than those of example 3.

In comparison with example 3, the third reaction vessel was used instead of the static mixer, i.e., the materials led out from the first and second film scrapers were simultaneously fed into the third reaction vessel for copolymerization (reaction at normal pressure and 200 ℃ C., reaction time was the same as the total reaction time of each stage of the static mixer in example 3). From the test results shown in Table 1, the yellowness index of comparative example 3 was significantly lower than that of comparative examples 1 and 2, probably because the pre-devolatilization treatment of the resulting GA prepolymer melt, LA prepolymer melt by a film scraper was conducted to promptly remove the unreacted lactide monomer or oligomer of the lactide monomer remaining therein, i.e., to be separated out in the form of GAs phase and/or GAs phase carrying, and recovered by a raw material collecting unit after being discharged from a GAs outlet at the top of the film scraper. The content of unreacted lactide monomer or oligomer of the lactide monomer remained in the GA prepolymer melt and the LA prepolymer melt after the pre-devolatilization treatment can be greatly reduced, which is beneficial to the improvement of the chromaticity quality of the final PLGA foaming material; however, since the third reaction kettle is used subsequently, compared with the static mixer, the heat transfer and stirring effects are limited, and the PLGA melt generated at the end of the reaction is easy to generate uneven local heating due to rapid increase of viscosity, the accumulated heat can not be timely transferred out, and the molecular chain ends of the corresponding part of PLGA copolymer can generate undesirable thermal oxidation, which still affects the chromaticity quality of the final PLGA foam material, so that the yellowness index of the PLGA foam material of comparative example 3 can be larger than that of example 3; in addition, it is difficult for the prepolymer fed into the third reaction vessel to produce a PLGA melt having a high molecular weight and a relatively narrow molecular weight distribution in a relatively short period of time (for example, 100 min) at a relatively low reaction temperature (for example, 200 ℃ C., compared to the case where glycolide is ring-opening polymerized at 220 to 230 ℃ C.) and thus, the PLGA obtained in comparative example 3 has a weight-average molecular weight of only about 12.1 ten thousand, which is significantly smaller than that of example 3; moreover, the homogeneity of the PLGA melt produced by the third reactor in comparative example 3 was still poor, and the difference in viscosity of the partial region of the melt was still significant, which also affected the homogeneity of the melt strength, so that it was difficult to obtain cells of uniform size in the subsequent foaming treatment, and the strength of the obtained cells was insufficient, or collapse easily occurred, so that the density and expansion ratio of the finally formed cells were smaller than those of examples 1 to 3, but significantly better than those of comparative example 1.

Therefore, the invention not only can obviously improve the chromaticity quality of the final PLGA foaming material, and effectively solve the problem of serious yellowing of the PLGA foaming material obtained by the existing preparation process, but also obviously improve the foaming ratio and the cell density, and the size of the cells is more uniform and the cells are more compact. This is because in the process of preparing PLGA melt, the GA prepolymer melt and the LA prepolymer melt are respectively pre-devolatilized by a film scraper to make residual lactide monomer or oligomer in the GA prepolymer melt and the LA prepolymer melt as much as possibleCan be removed, the residual quantity of lactide monomer or oligomer in PLGA melt obtained by copolymerization reaction can be very small, which is favorable for improving chromaticity quality of final foaming material, in addition, the invention can make GA prepolymer melt and LA prepolymer melt implement cross flow mixing by utilizing self-structural characteristics of static mixer, compared with the existing conventional stirring mode in kettle, it can effectively intensify mixing effect of GA prepolymer melt and LA prepolymer melt, at the same time, the stepped gradient heating treatment mode of static mixer can stepwisely raise reaction degree of GA prepolymer molecular chain and LA prepolymer molecular chain, not only is favorable for controllable relatively mild copolymerization reaction of GA prepolymer molecular chain and LA prepolymer molecular chain, but also is favorable for inhibiting abrupt change of viscosity of reaction system, so that it can prevent occurrence of coking slag formation phenomenon due to excessive accumulation of heat quantity resulted from abrupt change of local viscosity of reaction system, so that uniformity of obtained PLGA melt is better, uniformity of melt strength is good, and supercritical CO is adopted in the following steps ₂ In the foaming treatment process of the fluid, foam holes with uniform sizes are formed, shrinkage of the foamed material can be restrained to a great extent, collapse of the foam holes is not easy to occur, and then the PLGA foamed material with high foam hole density and high foaming multiplying power can be obtained.

The invention can realize continuous production of high-quality PLGA foaming material, can effectively reduce the loss of reaction materials, has no environmental pollution in the production process, is safe in production method, has simple preparation process and is suitable for mass production.

The foregoing description is only illustrative of the preferred embodiments of the present invention and is not intended to limit the scope of the invention, which is defined broadly in the appended claims, and any person skilled in the art to which the invention pertains will readily appreciate that many modifications, including those that fall within the metes and bounds of the claims, or equivalence of such metes and bounds thereof.

Claims

1. An apparatus for continuously preparing polylactic acid-glycollic acid foaming material, which is characterized in that the apparatus comprises a first reaction kettle, a second reaction kettle, a first film scraping device, a second film scraping device, a static mixer and foaming equipment; the discharge port of the first reaction kettle is connected with the feed port of the first film scraping device through a material conveying pipeline, and the discharge port of the second reaction kettle is connected with the feed port of the second film scraping device through a material conveying pipeline; the discharge port of the first film scraping device and the discharge port of the second film scraping device are respectively connected with the feed port of the static mixer through a material conveying pipeline; the discharge port of the static mixer is connected with the feed port of the foaming equipment through a material conveying pipeline.

2. The apparatus of claim 1, wherein the first and second film scrapers each comprise a housing; a rotating shaft, a plurality of scraping plates radially connected with the rotating shaft and a film distributor communicated with a feed inlet are arranged in the shell; the film distributor is located above the scraper nearest to the top of the housing.

3. The apparatus of claim 2, wherein the distance of the outer side of the scraper from the inner wall of the housing is no more than 5 millimeters; preferably not greater than 2 mm.

4. The device according to claim 2, wherein the first and second film scrapers each further comprise a heating element, preferably an electric heating jacket, arranged outside the housing.

5. The device according to claim 2, wherein the top of the shell is provided with an air outlet, and the air outlet is higher than the feed inlet in level;

6. The apparatus of claim 5, wherein the first raw material collecting unit and the second raw material collecting unit each comprise a gas-liquid separator, a condenser, and a recovery tank in this order in a material feed direction.

7. The apparatus of claim 6, wherein a vacuum pump is disposed between the gas-liquid separator and the condenser.

8. The apparatus of any one of claims 1-7,

9. The apparatus of any one of claims 1-7, wherein the foaming device comprises a foaming machine and supercritical CO ₂ A fluid storage tank; the supercritical CO ₂ The fluid storage tank is connected with an injection port of the foaming machine through a diversion pipeline.

10. The apparatus of claim 9, wherein a metering pump is disposed on the delivery conduit.

11. A process for continuously preparing a polylactic acid-glycolic acid foamed material, characterized in that the process comprises the steps of:

(3) Materials which are respectively subjected to pre-devolatilization treatment in a first film scraping device and a second film scraping device enter a static mixer for copolymerization reaction to obtain polylactic acid-glycollic acid melt;

12. The method of claim 11, wherein the polymerization temperature of the glycolide polymerized to form the glycolide prepolymer in step (1) is 130 ℃ to 190 ℃; and/or the polymerization reaction temperature of lactide prepolymer obtained by lactide polymerization is 120-180 ℃.

13. The method of claim 12, wherein step (1) provides glycolide prepolymer having a relative molecular weight of 1.2 to 4.0 tens of thousands; and/or to obtain lactide prepolymers having a relative molecular weight of 1.2-4.0 ten thousand.

14. The method of claim 11, wherein in step (3) at least 2 stages of gradient heating is adopted, the first stage of temperature ranges from 160 ℃ to 200 ℃ and the last stage of temperature ranges from 180 ℃ to 220 ℃.

15. The process according to any one of claims 11 to 14, wherein step (4) comprises reacting the polylactic acid-glycolic acid melt obtained in step (3) with supercritical CO ₂ The fluids are mixed in a foaming machine.

16. The method of claim 15Characterized in that 3-20wt% of supercritical CO is used based on the total weight of the polylactic acid-glycolic acid melt ₂ A fluid.

17. The method of claim 16, wherein the internal temperature of the foaming machine is controlled to be in the range of 180-220 ℃; and/or controlling the internal pressure of the foaming machine to be between 10 and 25 MPa; and/or the treatment time is between 10 and 60 minutes.