阅读说明：本技术 一种高耐热和耐水解3d打印立构聚乳酸产品及其制备方法 (High-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product and preparation method thereof ) 是由 李蔚 杨静 杨一奇 徐荷澜 侯秀良 于 2021-09-17 设计创作，主要内容包括：本申请公开了一种高耐热和耐水解3D打印立构聚乳酸产品及其制备方法,属于3D打印高分子材料改性领域。本发明解决了聚乳酸立构复合技术难以直接应用于3D打印制造高质量产品的瓶颈问题,将L/D聚乳酸线材通过3D打印机打印出产品并进行后续热处理,得到高耐热和耐水解3D打印立构聚乳酸产品。本发明提出的一种简单、环保的多级热处理方法,突破技术壁垒,无需使用溶剂作为反应介质,也无需使用其它非聚乳酸物质作为改性剂。该方法使得高性能产品的3D打印制作效率提高,可控实现>99%的全立构复合晶体结构,从而得到的立构聚乳酸3D打印产品具有高耐热性和耐水解性能,整个反应高效清洁,绿色环保。(The application discloses a high-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product and a preparation method thereof, and belongs to the field of modification of 3D printing high polymer materials. The invention solves the bottleneck problem that the polylactic acid stereocomplex technology is difficult to be directly applied to 3D printing to manufacture high-quality products, and the L/D polylactic acid wire is printed out by a 3D printer and then is subjected to subsequent heat treatment to obtain the high-heat-resistance and hydrolysis-resistance 3D printing stereopolylactic acid product. The simple and environment-friendly multistage heat treatment method provided by the invention breaks through the technical barrier, does not need to use a solvent as a reaction medium, and does not need to use other non-polylactic acid substances as a modifier. The method improves the 3D printing manufacturing efficiency of high-performance products, and can controllably realize the all-dimensional composite crystal structure of more than 99%, so that the obtained 3D printing product of the stereopolylactic acid has high heat resistance and hydrolysis resistance, the whole reaction is efficient and clean, and the method is green and environment-friendly.)

1. A preparation method of a 3D printing stereo polylactic acid product with high heat resistance and hydrolysis resistance is characterized by comprising the following steps:

the first step is as follows: fully drying the initial wire by using a vacuum drying oven at the drying temperature of 40-70 ℃ for 12-24h, and printing the fully dried initial L/D polylactic acid 3D printing wire into an initial L/D polylactic acid 3D printing part by using a fused deposition molding 3D printer;

the second step is that: and fully drying the initial L/D3D printed part by using a vacuum drying oven at the drying temperature of 40-70 ℃ for 12-24h, and placing the fully dried initial L/D polylactic acid 3D printed part in a blast oven for subsequent heat treatment to obtain the high-heat-resistance and hydrolysis-resistance 3D printed stereopolylactic acid product.

2. The method for preparing a highly heat and hydrolysis resistant 3D printed stereogenic polylactic acid product according to claim 1, wherein said initial L/D polylactic acid 3D printed wire is prepared by the steps of:

the first step is as follows: according to the following steps: 1, respectively weighing 1 part of levorotatory polylactic acid PLLA powder and 1 part of dextrorotatory polylactic acid PDLA powder, and preliminarily stirring and mixing for 20 minutes at 200rpm under the stirring action of a ball mill to obtain an L/D polylactic acid powder mixture;

the second step is that: putting the L/D powder mixture into a vacuum drying oven for full drying, wherein the temperature of the vacuum drying oven is 40-70 ℃, and the drying time is 12-24 hours; taking out, adding the mixture into a co-rotating/counter-rotating double-screw extruder, heating to 225-235 ℃, and fully mixing for 1-5 minutes at 50-100rpm until the mixture is uniform to obtain an L/D polylactic acid molten mixture;

the third step: placing the L/D polylactic acid molten mixture into a vacuum drying oven for fully drying, wherein the temperature of the vacuum drying oven is 40-70 ℃, and the drying time is 12-24 hours; taking out, adding the mixture into a wire extruder, and performing melt extrusion and wire drawing molding, wherein the wire extruder is a single-screw extruder, a co-rotating/counter-rotating double-screw extruder or a multi-screw wire extruder, the temperature in a cavity is 225-235 ℃, and the rotating speed of screws is 10-35 rpm; cooling, shaping and drawing to obtain an initial L/D polylactic acid 3D printing wire; the cooling shaping is air cooling, and the air temperature is controlled to be 0-100 ℃.

3. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 1, is characterized in that: the fused deposition modeling 3D printer adopts an FDM fused deposition modeling 3D printer which is provided with a nozzle, a heater, a cooling fan, a printing platform, namely a hot bed, and a temperature control system capable of controlling the temperature of the nozzle, the hot bed and a cabin body, and the model of the fused deposition modeling 3D printer is a Creatbot/Correit F430 type 3D printer; the temperature of the printing platform reaches 110 ℃; the temperature control system with the controllable nozzle, the hot bed and the cabin body adopts electric heating, the controller commands the heating rod to gradually heat the temperature in the cabin body from room temperature to a set temperature, and the temperature in the cabin is kept constant by feeding back the temperature sensor to the controller in the printing process.

4. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 1, is characterized in that: the specific printing process of the first step is as follows:

step 1, after the printing operation of the fused deposition modeling 3D printer is started, the 3D printer automatically loads a printing head according to a received command;

step 2, the printing head moves on the printing platform in parallel to the plane of the hot bed; meanwhile, the L/D polylactic acid wire is brought into a high-temperature spray head by a gear and a roller under the action of a stepping motor, heated to a molten state and then extruded from a nozzle; the temperature range of a spray head is selected from 235-265 ℃ when the fused deposition modeling 3D printer is used for printing; the temperature of the hot bed is always consistent with the temperature in the printer cabin, and the temperature range is selected to be 60-105 ℃;

and 3, when the filament from the nozzle reaches the surface of the hot bed, the filament is rapidly solidified, after extrusion printing of one layer is completed, the moving mechanism drives the lifting device to descend to a preset height along the Z direction, the molten filament is attached to the previous layer, and the next layer is deposited until the initial L/D polylactic acid 3D printing part is completed.

5. The preparation method of the high heat-resistant and hydrolysis-resistant 3D printing stereogenic polylactic acid product according to claim 4, which is characterized in that: the temperature of the spray head when the fused deposition modeling 3D printer prints is 250 ℃, and the temperature of the hot bed and the temperature in the printer cabin are 90 ℃.

6. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 1, is characterized in that: after the printing of the initial L/D polylactic acid 3D printing part is finished, preheating treatment is carried out on a hot bed at 90 ℃ for 30min, then natural cooling is carried out to room temperature, then the heating treatment is carried out in a vacuum drying oven at 50 ℃, a sample is taken out from the vacuum drying oven after 24h and immediately placed in a common blast drying oven heated to 160-220 ℃, heat treatment is carried out for 60min, and then the sample is placed in a constant temperature and humidity chamber at 21 ℃ and the humidity of 65% for natural cooling.

7. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 6, which is characterized in that: the temperature of the common air-blast oven is 200 ℃, and the temperature is higher than the melting point of the conventional polylactic acid homogeneous phase crystal but lower than the melting point of the L/D polylactic acid stereo composite crystal.

8. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 2, is characterized in that: the dextro-polylactic acid is synthesized by the following synthesis steps:

the first step is as follows: taking 10000 parts of dextro-lactide, 5 parts of stannous octoate serving as a catalyst and 15.5 parts of dodecanol serving as an initiator according to the mass part ratio, putting the materials into a reactor together, vacuumizing, then filling nitrogen, repeating for 5-6 times to achieve high vacuum degree, and removing water for 1-3 hours at 40 ℃;

the second step is that: then heating to 150 ℃, keeping the vacuum degree at-0.08 to-0.085 MPa, and continuing to react for 2 to 4 hours;

the third step: then heating to 180 ℃, keeping the vacuum degree at high vacuum, and continuing to react for 3-4 hours to obtain the catalyst.

9. The preparation method of the 3D printing stereogenic polylactic acid product with high heat resistance and hydrolysis resistance according to claim 2, is characterized in that: the temperature in the cavity of the co-rotating/counter-rotating twin-screw extruder is 230 ℃, the mesh number of the levorotatory polylactic acid PLLA powder and the dextrorotatory polylactic acid PDLA powder is 200-300, 1: 1, the polylactic acid with a stereo composite structure is obtained to the maximum extent in the subsequent treatment; the molecular weight of the levorotatory polylactic acid powder is 10-20 ten thousand, the molecular weight of the dextrorotatory polylactic acid powder is 15-25 ten thousand, and the melting points are 155-180 ℃.

10. The utility model provides a high heat-resisting and hydrolysis-resistant 3D prints stereogenic polylactic acid product which characterized in that: the high-heat-resistance and hydrolysis-resistance 3D printing stereogenic polylactic acid product is prepared by the preparation method, and the high-heat-resistance and hydrolysis-resistance 3D printing stereogenic polylactic acid product is a pure polylactic acid fused deposition molding 3D printing product.

Technical Field

The invention belongs to the technical field of 3D printing polymer material modification, and particularly relates to a 3D printing stereo polylactic acid product with high heat resistance and hydrolysis resistance and a preparation method thereof.

Background

In recent years, 3D printing has become one of the research hotspots of material molding technology. The rapid prototyping technology is a rapid prototyping technology which is based on digital simulation, adopts powder metal or plastic and other bondable materials, and constructs an object in a layer-by-layer printing mode. The 3D printing technology originated from the massachusetts institute of technology, is a technology for generating a three-dimensional entity by adding materials layer by layer through the superposition of continuous physical layers based on the principle of discrete/stack molding, and breaks through the traditional processing mode, which is called as a representative technology of the third industrial revolution. Compared with traditional material processing, 3D printing has unique advantages: high efficiency, material savings, unlimited design space for designers, etc.

Fused Deposition Modeling (FDM) is a 3D printing technique that heats and fuses thermoplastic filamentary materials to form shapes. The principle of the method is that filamentous materials are extruded into a spray head and heated to a temperature higher than a melting point, and the materials are stacked layer by layer into a solid body with the same shape as a model under the driving of a control system according to a set layering and forming path. The FDM technology has the advantages of simple mechanical structure, relatively low manufacturing cost, maintenance cost and material cost, and is widely applied to aspects of personalized product customization, product trial production, teaching aids and the like.

The conventional commercial polylactic acid is mainly L-polylactic acid (PLLA). The polylactic acid material has excellent biodegradability and biocompatibility, and the final degradation products are carbon dioxide and water, so that the environment is not polluted; meanwhile, the printing ink has good processing flowability and can be printed and molded through 3D. By using polylactic acid as a raw material and adopting a 3D printing and forming mode to prepare a product, the problem of white pollution can be solved, and the purpose of rapid forming can be achieved. However, polylactic acid has inherent defects of thermolabile property (low softening temperature) and easy hydrolysis, and is difficult to adapt to various processing and use environments, so that the application of polylactic acid products is limited, and the worldwide production value in 2019 is only 40 hundred million dollars, which is less than one fifth of that of polypropylene. Therefore, the manufacturing method for forming the polylactic acid 3D printing product with high heat resistance and hydrolysis resistance is particularly critical.

Chinese patent application CN 106046726A discloses a composite polylactic acid material for 3D printing and a preparation method thereof, and the composite polylactic acid material is a high heat-resistant stereo composite polylactic acid composition material which is prepared by melt blending 58-85wt% of a mixture of levorotatory polylactic acid (PLLA) and dextrorotatory polylactic acid (PDLA), 0.2-2wt% of uracil derivative nucleating agent, 5-10wt% of polyethylene glycol and 10-30wt% of hydroxyalkanoate copolymer and is suitable for 3D printing. The method improves the crystallinity and the heat-resistant temperature of the polylactic acid to a certain extent, but the modified substances of uracil derivatives nucleating agent, polyethylene glycol and hydroxyalkanoate copolymer adopted by the polylactic acid composite material are non-renewable resources and can not be effectively biodegraded, thus destroying the precious degradability of the polylactic acid material.

Research on forming a structural composite structure by blending PLLA and PDLA while improving the water stability and heat resistance of polylactic acid is receiving increasing attention. After PLLA and PDLA are blended and processed, the L and D optical isomers realize crystallization, and a stereo composite PLA can be formed. Compared with PLLA or PDLA, the crystal structure of the stereocomplex polylactic acid is more closely arranged, intermolecular force is larger, and the material has high melting point, high strength and high tolerance of organic solvents. Therefore, the two core problems of thermolabile property and easy hydrolysis of the polylactic acid can be effectively solved.

However, how to apply the stereocomplex technology to 3D printing manufacturing is a bottleneck problem currently faced. The polylactic acid stereocrystals are very easy to form in the process of preparing the printing wire, and the high melting point of the polylactic acid stereocrystals ensures that the materials are fully melted by adopting high temperature during 3D printing; however, the low thermal decomposition temperature of polylactic acid itself limits the choice of higher printing temperatures in actual printing. The technology does not need to add other materials except polylactic acid, can develop 3D printing stereo composite polylactic acid products with different performances and structures, and has important theoretical guiding significance for realizing wide application of high-quality polylactic acid.

Disclosure of Invention

The technical problem to be solved is as follows: this application mainly provides one kind and carries out the new technology of regulation and control in order to polylactic acid crystal structure through the thermal induction at three in-process of printing wire rod preparation, 3D printing, printing aftertreatment to obtain high heat-resisting and hydrolysis resistance 3D and print stereogenic polylactic acid product, solve the technical problem that the softening point temperature that exists is low among the prior art, the melting point is low, the hydrolysis resistance is poor, with high costs.

The technical scheme is as follows:

a preparation method of a 3D printing stereo polylactic acid product with high heat resistance and hydrolysis resistance specifically comprises the following steps:

the first step is as follows: fully drying the initial wire by using a vacuum drying oven at the drying temperature of 40-70 ℃ for 12-24h, and printing the fully dried initial L/D polylactic acid 3D printing wire into an initial L/D polylactic acid 3D printing part by using a fused deposition molding 3D printer;

the second step is that: and fully drying the initial L/D3D printed part by using a vacuum drying oven at the drying temperature of 40-70 ℃ for 12-24h, and placing the fully dried initial L/D polylactic acid 3D printed part in a blast oven for subsequent heat treatment to obtain the high-heat-resistance and hydrolysis-resistance 3D printed stereopolylactic acid product.

As a preferred technical scheme of the invention: the initial L/D polylactic acid 3D printing wire is prepared by the following steps:

the first step is as follows: according to the following steps: 1, respectively weighing 1 part of levorotatory polylactic acid PLLA powder and 1 part of dextrorotatory polylactic acid PDLA powder, and preliminarily stirring and mixing for 20 minutes at 200rpm under the stirring action of a ball mill to obtain an L/D polylactic acid powder mixture;

the second step is that: putting the L/D powder mixture into a vacuum drying oven for full drying, wherein the temperature of the vacuum drying oven is 40-70 ℃, and the drying time is 12-24 hours; taking out, adding the mixture into a co-rotating/counter-rotating double-screw extruder, heating to 225-235 ℃, and fully mixing for 1-5 minutes at 50-100rpm until the mixture is uniform to obtain an L/D polylactic acid molten mixture;

the third step: placing the L/D polylactic acid molten mixture into a vacuum drying oven for fully drying, wherein the temperature of the vacuum drying oven is 40-70 ℃, and the drying time is 12-24 hours; taking out, adding the mixture into a wire extruder, and performing melt extrusion and wire drawing molding, wherein the wire extruder is a single-screw extruder, a co-rotating/counter-rotating double-screw extruder or a multi-screw wire extruder, the temperature in a cavity is 225-235 ℃, and the rotating speed of screws is 10-35 rpm; cooling, shaping and drawing to obtain an initial L/D polylactic acid 3D printing wire; the cooling shaping is air cooling, and the air temperature is controlled to be 0-100 ℃.

As a preferred technical scheme of the invention: the fused deposition modeling 3D printer adopts an FDM fused deposition modeling 3D printer which is provided with a nozzle, a heater, a cooling fan, a printing platform, namely a hot bed, and a temperature control system capable of controlling the temperature of the nozzle, the hot bed and a cabin body, and the model of the fused deposition modeling 3D printer is a Creatbot/Correit F430 type 3D printer; the temperature of the printing platform reaches 110 ℃; the temperature control system with the controllable nozzle, the hot bed and the cabin body adopts electric heating, the controller commands the heating rod to gradually heat the temperature in the cabin body from room temperature to a set temperature, and the temperature in the cabin is kept constant by feeding back the temperature sensor to the controller in the printing process.

As a preferred technical scheme of the invention: the specific printing process of the first step is as follows:

step 1, after the printing operation of the fused deposition modeling 3D printer is started, the 3D printer automatically loads a printing head according to a received command;

step 2, the printing head moves on the printing platform in parallel to the plane of the hot bed; meanwhile, the L/D polylactic acid wire is brought into a high-temperature spray head by a gear and a roller under the action of a stepping motor, heated to a molten state and then extruded from a nozzle; the temperature range of a spray head is selected from 235-265 ℃ when the fused deposition modeling 3D printer is used for printing; the temperature of the hot bed is always consistent with the temperature in the printer cabin, and the temperature range is selected to be 60-105 ℃;

and 3, when the filament from the nozzle reaches the surface of the hot bed, the filament is rapidly solidified, after extrusion printing of one layer is completed, the moving mechanism drives the lifting device to descend to a preset height along the Z direction, the molten filament is attached to the previous layer, and the next layer is deposited until the initial L/D polylactic acid 3D printing part is completed.

As a preferred technical scheme of the invention: the temperature of the spray head when the fused deposition modeling 3D printer prints is 250 ℃, and the temperature of the hot bed and the temperature in the printer cabin are 90 ℃.

As a preferred technical scheme of the invention: after the printing of the initial L/D polylactic acid 3D printing part is finished, preheating treatment is carried out on a hot bed at 90 ℃ for 30min, then natural cooling is carried out to room temperature, then the heating treatment is carried out in a vacuum drying oven at 50 ℃, a sample is taken out from the vacuum drying oven after 24h and immediately placed in a common blast drying oven heated to 160-220 ℃, heat treatment is carried out for 60min, and then the sample is placed in a constant temperature and humidity chamber at 21 ℃ and the humidity of 65% for natural cooling.

As a preferred technical scheme of the invention: the temperature of the common air-blast oven is 200 ℃, and the temperature is higher than the melting point of the conventional polylactic acid homogeneous phase crystal but lower than the melting point of the L/D polylactic acid stereo composite crystal.

As a preferred technical scheme of the invention: the dextro-polylactic acid is synthesized by the following synthesis steps:

the first step is as follows: taking 10000 parts of dextro-lactide, 5 parts of stannous octoate serving as a catalyst and 15.5 parts of dodecanol serving as an initiator according to the mass part ratio, putting the materials into a reactor together, vacuumizing, then filling nitrogen, repeating for 5-6 times to achieve high vacuum degree, and removing water for 1-3 hours at 40 ℃;

the second step is that: then heating to 150 ℃, keeping the vacuum degree at-0.08 to-0.085 MPa, and continuing to react for 2 to 4 hours;

the third step: then heating to 180 ℃, keeping the vacuum degree at high vacuum, and continuing to react for 3-4 hours to obtain the catalyst.

As a preferred technical scheme of the invention: the temperature in the cavity of the co-rotating/counter-rotating twin-screw extruder is 230 ℃, the mesh number of the levorotatory polylactic acid PLLA powder and the dextrorotatory polylactic acid PDLA powder is 200-300, 1: 1, the polylactic acid with a stereo composite structure is obtained to the maximum extent in the subsequent treatment; the molecular weight of the levorotatory polylactic acid powder is 10-20 ten thousand, the molecular weight of the dextrorotatory polylactic acid powder is 15-25 ten thousand, and the melting points are 155-180 ℃.

In addition, the invention also discloses a high-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product prepared by the preparation method, and the high-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product is a pure polylactic acid fused deposition molding 3D printing product.

Has the advantages that: compared with the prior art, the high-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product and the preparation method thereof adopt the technical scheme, and have the following technical effects:

1. the bottleneck problem that the polylactic acid stereocomplex technology is difficult to be directly applied to 3D printing to manufacture high-quality products is solved, the technical barrier is broken through, the method is simple and easy to implement, and a reference is provided for further improving the performance of the polylactic acid 3D printing products in subsequent research;

2. according to the invention, the stereopolylactic acid 3D printing product obtained by the multistage heat treatment method can controllably realize an all-stereo composite crystal structure of more than 99%, and the molecular regularity is greatly superior to that of common polylactic acid, so that the aims of high heat resistance and hydrolysis resistance are fulfilled;

3. the obtained stereopolylactic acid 3D printing product not only keeps the biodegradability, biocompatibility and renewable property of polylactic acid, but also improves the heat resistance and hydrolysis resistance of the product at the same time to a great extent, and has potential application in the aspects of food packaging, outdoor shed building, crop cultivation, automobile and airplane parts and the like;

4. at present, the known methods for improving the heat resistance of polylactic acid 3D printing products are to add some non-environment-friendly non-degradable substances, and even to use a large amount of solvent, but the modification method used in the invention does not need solvent, has less pollution, less consumables, low cost and is more environment-friendly;

5. the softening point temperature of the high-heat-resistant and hydrolysis-resistant 3D printed stereo polylactic acid product is 116-138 ℃, the melting point is 225 ℃, the softening point temperature of the product is 50-60 ℃ higher than that of a product printed by common polylactic acid 3D, and the melting point is 50 ℃ higher, so that the high-heat-resistant and hydrolysis-resistant 3D printed stereo polylactic acid product can adapt to variable processing and using conditions;

6. the high heat-resisting hydrolysis resistance that prints stereo polylactic acid product with hydrolysis resistance of this application improves by a wide margin, and the concrete expression does: on one hand, under the same hydrolysis condition, after a common polylactic acid 3D printed product is hydrolyzed, the product is hydrolyzed to be incapable of being molded, and the tensile property of the product can not be measured, but the retention rate of the mechanical property of the stereo polylactic acid 3D printed product prepared by the method is up to more than 90%; on the other hand, under the same hydrolysis condition, after the common polylactic acid 3D printing product is hydrolyzed, the viscosity average molecular weight of the material is reduced by 67.0 percent, while the viscosity average molecular weight of the stereopolylactic acid 3D printing product obtained by the invention is reduced by only 5.5 percent;

drawings

FIG. 1 shows the results of the tensile properties of L/D prints at different nozzle temperatures according to the invention.

FIG. 2 shows a graph of the rate of change of the tensile properties of an L/D print before and after subsequent heat treatment at different ambient temperatures (temperature in the heat bed and printer cabin) according to the invention.

FIG. 3 shows DSC plots of L/D prints of the invention at different ambient temperatures (temperature in the heat bed and printer cabinet) without subsequent heat treatment.

FIG. 4 shows DSC plots of unhydrolyzed L/D prints at various post heat treatment temperatures of the present invention.

FIG. 5 shows WAXD spectra of L/D prints of the invention before and after hydrolysis at different post-heat treatment temperatures.

FIG. 6 shows graphs of retention of tensile properties of L/D prints before and after hydrolysis at different subsequent heat treatment temperatures according to the invention.

FIG. 7 is a graph showing the change in molecular weight of L/D prints before and after hydrolysis at different subsequent heat treatment temperatures according to the present invention.

FIG. 8 shows a graph of the softening temperatures of unhydrolyzed L/D prints for different subsequent heat treatment temperatures according to the present invention.

Detailed Description

The present invention will be better understood from the following examples. However, those skilled in the art will readily appreciate that the specific material ratios, process conditions and results thereof described in the examples are illustrative only and should not be taken as limiting the invention as detailed in the claims.

Example 1

A preparation method of a 3D printing stereo polylactic acid product with high heat resistance and hydrolysis resistance specifically comprises the following steps:

the first step is as follows: taking 10000 parts of dextro-lactide, 5 parts of stannous octoate serving as a catalyst and 15.5 parts of dodecanol serving as an initiator according to the mass part ratio, putting the materials into a reactor together, vacuumizing, then filling nitrogen, repeating for 5-6 times to achieve high vacuum degree, and removing water for 1-3 hours at 40 ℃;

the second step is that: then heating to 150 ℃, keeping the vacuum degree at-0.08 to-0.085 MPa, and continuing to react for 2 to 4 hours;

the third step: heating to 180 deg.C, maintaining the vacuum degree at high vacuum, and reacting for 3-4 hr to obtain poly (D-lactic acid) (PDLA).

The fourth step: according to the following steps: 1, weighing 1 part of levorotatory polylactic acid (PLLA) powder and 1 part of dextrorotatory polylactic acid (PDLA) powder respectively, wherein the mesh number is 200-300. The proportion can obtain the polylactic acid with a stereo composite structure to the maximum extent in subsequent treatment. Primarily stirring and mixing for 20 minutes at 200rpm under the stirring action of a ball mill machine to obtain an L/D polylactic acid powder mixture;

the fifth step: putting the L/D powder mixture into a vacuum drying oven for fully drying; the temperature of the vacuum drying oven is 40-70 ℃, the drying time is 12-24 hours, after being taken out, the mixture is added into a co-rotating/counter-rotating double-screw extruder to be heated to 230 ℃, and the mixture is fully mixed for 5 minutes to be uniform at 50-100rpm, so that an L/D molten mixture is obtained; the temperature in the cavity of the co-rotating/counter-rotating double-screw extruder is 225-235 ℃, and the rotating speed of the screws is 50-100 rpm;

and a sixth step: fully drying the L/D molten mixture in a vacuum drying oven at the temperature of 40-70 ℃ for 12-24 hours; taking out, adding the obtained product into a wire extruder, carrying out melt extrusion and wire drawing forming, and carrying out cooling shaping and traction to obtain an initial L/D polylactic acid 3D printing wire; the wire extruder is a single-screw extruder, a co-rotating/counter-rotating double-screw extruder or a multi-screw wire extruder, the temperature in the cavity is 225-235 ℃, and the rotating speed of the screws is 10-35 rpm; the cooling and shaping is air cooling, and the air temperature is controlled to be 0-100 ℃;

the seventh step: fully drying the initial wire by using a vacuum drying oven, wherein the drying temperature is 40-70 ℃, the drying time is 12-24h, and after the printing operation of the fused deposition modeling 3D printer is started, the 3D printer automatically loads a printing head according to a received command;

eighth step: the printing head moves on the printing platform in parallel to the plane of the hot bed; meanwhile, the L/D polylactic acid wire is brought into a high-temperature spray head by a gear and a roller under the action of a stepping motor, heated to a molten state and then extruded from a nozzle;

the ninth step: when the filament coming out of the nozzle reaches the surface of the hot bed, the filament is rapidly solidified, after extrusion printing of one layer is completed, the moving mechanism drives the lifting device to descend to a preset height along the Z direction, the molten filament is attached to the previous layer, the next layer is deposited until the initial L/D polylactic acid 3D printing part is completed, and the temperature range of a spray head during printing is selected to be 235-265 ℃; the temperature of the hot bed is always consistent with the temperature in the printer cabin, and the temperature range is selected to be 60-105 ℃;

the tenth step: fully drying the initial L/D3D printing part by using a vacuum drying oven at the drying temperature of 40-70 ℃ for 12-24h, placing the fully dried initial L/D3D printing part in a blast oven, after the initial printing part is printed by fused deposition molding, preheating on a heating bed at the temperature of 90 ℃ for 30min, naturally cooling to the room temperature, then placing the part in a vacuum drying oven at the temperature of 50 ℃ for drying, taking out a sample from the vacuum oven after 24h, immediately placing the sample in a common blast oven heated to the temperature of 160-220 ℃, carrying out heat treatment at the set temperature for 60min, then placing the sample in a constant temperature and humidity chamber at the temperature of 21 ℃ and the humidity of 65%, and naturally cooling to obtain the high-heat-resistance and hydrolysis-resistance 3D printing stereo polylactic acid product.

The fused deposition modeling 3D printer adopts a fused deposition modeling 3D printer (Creatbot/Critide F430 type 3D printer) which is provided with a nozzle, a heater, a cooling fan, a printing platform, namely a hot bed, and a temperature control system capable of controlling the temperature of the nozzle, the hot bed and a cabin body, wherein the printing platform can move in three dimensions; the temperature of the printing platform reaches 110 ℃; the temperature control system with the controllable nozzle, the hot bed and the cabin body adopts electric heating, the controller commands the heating rod to gradually heat the temperature in the cabin body from room temperature to a set temperature, and the temperature in the cabin is kept constant by feeding back the temperature sensor to the controller in the printing process.

The molecular weight of the levorotatory polylactic acid powder is 10-20 ten thousand, the molecular weight of the dextrorotatory polylactic acid powder is 15-25 ten thousand, and the melting points are 155-180 ℃.

The nozzle temperature of the fused deposition modeling 3D printer is 250 ℃, the temperature in the hot bed and printer cabin is 90 ℃, and the temperature time of the subsequent heat treatment of the air-blast oven is 200 ℃ and 60 min. The crystallinity of the obtained part was 54.3%, and the tacticity was 99.1%; the tensile strength is 58.78MPa, the elongation at break is 1.59 percent, and the tensile modulus is 3.13 Gpa; the softening point temperature is 138 ℃; before and after hydrolysis, the retention of tensile strength was 90.4%, the retention of elongation at break was 88.1%, the retention of tensile modulus was 93.7%, and the retention of molecular weight was 94.5%.

Example 2

Printing the initial L/D polylactic acid 3D printing wire material into an initial L/D polylactic acid 3D printing part through a fused deposition molding 3D printer; and then carrying out subsequent heat treatment on the initial L/D polylactic acid 3D printed part through a blast oven to obtain the final stereostructural polylactic acid 3D printed part. The nozzle temperature of the fused deposition modeling 3D printer was 250 ℃, the temperature in the hot bed and printer cabin was 90 ℃, and no subsequent heat treatment was performed. The crystallinity of the obtained part was 41.0%, and the tacticity was 8.9%; the tensile strength was 61.85MPa, the elongation at break was 1.69%, and the tensile modulus was 3.18 GPa.

Example 3

Printing the initial L/D polylactic acid 3D printing wire material into an initial L/D polylactic acid 3D printing part through a fused deposition molding 3D printer; and then carrying out subsequent heat treatment on the initial L/D polylactic acid 3D printed part through a blast oven to obtain the final stereostructural polylactic acid 3D printed part. The nozzle temperature of the fused deposition modeling 3D printer is 250 ℃, the temperature in the hot bed and the printer cabin is 60 ℃, and the temperature time of the subsequent heat treatment of the air-blast oven is 200 ℃ and 60 min. The crystallinity of the obtained part was 41.9%, and the tacticity was 99.0%; the tensile strength was 22.18MPa, the elongation at break was 1.81%, and the tensile modulus was 2.20 GPa.

Example 4

Printing the initial L/D polylactic acid 3D printing wire material into an initial L/D polylactic acid 3D printing part through a fused deposition molding 3D printer; and then carrying out subsequent heat treatment on the initial L/D polylactic acid 3D printed part through a blast oven to obtain the final stereostructural polylactic acid 3D printed part. The nozzle temperature of the fused deposition modeling 3D printer was 250 ℃ and the temperature in the hot bed and printer cabin was 60 ℃ without subsequent heat treatment. The tensile strength of the obtained part was 45.84MPa, the elongation at break was 2.19%, and the tensile modulus was 2.53 GPa.

Example 5

Printing the initial L/D polylactic acid 3D printing wire material into an initial L/D polylactic acid 3D printing part through a fused deposition molding 3D printer; and then carrying out subsequent heat treatment on the initial L/D polylactic acid 3D printed part through a blast oven to obtain the final stereostructural polylactic acid 3D printed part. The nozzle temperature of the fused deposition modeling 3D printer was 235 deg.C, the temperature in the hot bed and printer cabin was 60 deg.C, and no subsequent heat treatment was performed. The tensile strength of the obtained part was 36.60MPa, and the elongation at break was 2.41%.

Example 6

Printing the initial L/D polylactic acid 3D printing wire material into an initial L/D polylactic acid 3D printing part through a fused deposition molding 3D printer; and then carrying out subsequent heat treatment on the initial L/D polylactic acid 3D printed part through a blast oven to obtain the final stereostructural polylactic acid 3D printed part. The nozzle temperature of the fused deposition modeling 3D printer is 250 ℃, the temperature in the hot bed and printer cabin is 90 ℃, and the temperature time of the subsequent heat treatment of the air-blast oven is 160 ℃ and 60 min. The crystallinity of the obtained part was 55.9%, and the tacticity was 31.9%; the tensile strength is 49.18MPa, the elongation at break is 2.14 percent, and the tensile modulus is 2.0 Gpa; the softening point temperature is 120 ℃; before and after hydrolysis, the retention of tensile strength was 43.3%, the retention of elongation at break was 38.3%, the retention of tensile modulus was 41.8%, and the retention of molecular weight was 59.3%.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.