PLA composite material and preparation method and application thereof

Abstract

The application discloses a PLA composite material and a preparation method and application thereof, and belongs to the field of high polymer materials. The application adds a specific amount of a specific aromatic polycarbodiimide into polylactic acid, and controls the weight average molecular weight, the polydispersity coefficient and the D-lactic acid structural unit content of the obtained PLA resin within a specific range, so that the PLA resin has good wire drawing performance and low yellowness, is suitable for the high-speed 3D printing wire market, and the obtained wire can be used for 3D printing toys, ornaments, medical human simulation organs, artworks, topographic maps, house models and the like.

Description

Technical Field

[0001] This application relates to the field of polymer materials, specifically to a PLA composite material, its preparation method, and its application. Background Technology

[0002] With the development of 3D printing technology, polylactic acid (PLA) has become a widely used thermoplastic material in the 3D printing field due to its good biocompatibility, biodegradability, and processability. However, as the industry's requirements for filament production efficiency continue to increase, the following technical pain point has gradually become prominent: when the production speed of PLA 3D printing filament is high, filament breakage becomes a key issue restricting print quality. Therefore, researching and solving the filament breakage problem in the high-speed 3D printing filament production process of PLA is of great significance for improving printing efficiency and product quality. Summary of the Invention

[0003] Based on the deficiencies of the existing technology, the purpose of this application is to provide a PLA composite material, its preparation method and application. The obtained PLA composite material has low yellowness and is suitable for the production of high-speed 3D printing filaments.

[0004] To achieve the above objectives, in a first aspect, this application provides a PLA composite material comprising the following components in parts by weight: 100 parts of PLA resin, Aromatic polycarbodiimide 2.4~3.6 parts; The PLA resin has a weight-average molecular weight of 95,000 Da to 230,000 Da, a polydispersity index (PDI) of 1.1 to 1.9, and a molar fraction of D-lactic acid structural units not exceeding 2%. The aromatic polycarbodiimide includes At least one of the following, where n is an integer from 7 to 11.

[0005] Carbodiimide compounds are often used as hydrolysis-resistant agents. However, the inventors discovered during their research that monomeric carbodiimides have no significant cross-linking effect, while polycarbodiimides can act as cross-linking agents to promote the cross-linking of PLA resin, improve its winding degree, and enhance the melt strength of the composite material. Among these, the aromatic polycarbodiimides with the aforementioned specific structure exhibit suitable reactivity and good compatibility with PLA resin, which helps alleviate stringing defects during high-speed 3D printing filament production and avoids gel points. In contrast, aliphatic polycarbodiimides have high reactivity, poor compatibility with PLA resin, and are prone to gel point formation. By adding a specific amount of the aforementioned aromatic polycarbodiimide to PLA resin and controlling the weight-average molecular weight, polydispersity index, and D-lactic acid structural unit content of the PLA resin within the aforementioned specific ranges, the synergistic effect of PLA and aromatic polycarbodiimides ensures that the composite material has high melt strength. When applied to the production of high-speed 3D printing filaments, it is less prone to stringing and gel point formation, and the composite material also exhibits low yellowness.

[0006] The PLA composite material not only has low yellowness, but is also suitable for the production of 3D printing filaments, especially for the production of high-speed 3D printing filaments with printing speeds of 200 mm / min or higher.

[0007] The carbodiimide compound is in the range of 2.4 to 3.6 parts by weight, for example, 2.4 parts by weight, 2.6 parts by weight, 2.8 parts by weight, 3 parts by weight, 3.2 parts by weight, 3.4 parts by weight, 3.6 parts by weight, or any two of the above values ​​forming a range.

[0008] The PLA resin has a weight-average molecular weight of 95,000 Da to 230,000 Da, for example, within the range formed by any two of the following values: 95,000 Da, 100,000 Da, 110,000 Da, 120,000 Da, 130,000 Da, 140,000 Da, 150,000 Da, 160,000 Da, 170,000 Da, 180,000 Da, 190,000 Da, 200,000 Da, 210,000 Da, 220,000 Da, 230,000 Da.

[0009] The polydispersity index of the PLA resin is 1.1 to 1.9, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or any two of the above values ​​forming a range.

[0010] The molar fraction of the D-lactic acid structural unit of the PLA resin does not exceed 2%, for example, 2%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3% or any two values ​​within the range formed by these values.

[0011] Preferably, the PLA resin has a weight-average molecular weight of 150,000 Da to 210,000 Da, a polydispersity index of 1.2 to 1.6, and a molar fraction of D-lactic acid structural units of 1.3% to 1.8%. When the weight-average molecular weight, polydispersity index, and D-lactic acid structural unit content of the PLA resin are within this range, its molecular weight distribution is more suitable. This allows for better utilization of low molecular weight PLA to improve the plasticizing properties of the composite material, and also allows for better utilization of high molecular weight PLA to improve melt flow strength. This, in turn, can better optimize the production of high-speed 3D printing filaments (such as printing speeds above 200 mm / min) and the filament drawing performance.

[0012] The polydispersity index and weight-average molecular weight of the PLA resin were determined by gel permeation chromatography (GPC). For example, a sample solution with a concentration of 1 mg / mL was prepared by dissolving PLA resin in tetrahydrofuran and tested using a Waters GPC instrument at 40°C. A 2414 differential refractive index detector was used, and four columns were connected in series: WAT045835 STYRAGEL HR0.5 ID4.6, WAT045850 STYRAGEL HR1 ID4.6, WAT045880 STYRAGEL HR3 ID4.6, and WAT045895 STYRAGEL HR4 ID4.6. The mobile phase was tetrahydrofuran, and the flow rate was 0.3 mL / min. Polystyrene standard was used as the standard sample, and the results were the average of three measurements.

[0013] The molar fraction of D-lactic acid structural units in the PLA resin was determined as follows: 100 mg of PLA resin sample was added to 10 mL of methanol, and one drop of 1 mol / L NaOH aqueous solution was added. The mixture was then sealed in a 20 mL hydrothermal reactor and heated at 180 °C for 1 hour. After cooling to room temperature, the solution was filtered through a 0.45 μm PTFE membrane, and the filtrate was analyzed by gas chromatography. An Agilent 8860 gas chromatograph with a CP7502 column was used for gas chromatography. The peaks corresponding to D-lactic acid methyl ester and L-lactic acid methyl ester were determined based on their retention times, and their peak areas were recorded. The area ratio of D-lactic acid methyl ester based on the total area of ​​these two lactic acid methyl esters was calculated, which represents the molar fraction of D-lactic acid structural units in the PLA resin.

[0014] The n is an integer from 7 to 11, such as 7, 8, 9, 10 or 11.

[0015] Preferably, it further includes the following components in parts by weight: 0.1 to 0.3 parts of antioxidant. For example, the amount of antioxidant is 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, or any range formed by any two of the above values.

[0016] Preferably, the antioxidant comprises at least one of 3,9-bis[1,1-dimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (i.e., antioxidant OA-80) and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (i.e., antioxidant 1010).

[0017] More preferably, the antioxidant comprises 3,9-bis[1,1-dimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane.

[0018] During their research, the inventors unexpectedly discovered that antioxidant OA-80 can synergistically improve the fiber-drawing problem of composite materials in high-speed 3D printing with aromatic polycarbodiimide compounds.

[0019] The PLA resin can be commercially available or homemade. For example, the preparation method of the PLA resin includes the following steps: Under an inert atmosphere, lactide is melted and then a catalyst and chain transfer agent are added to react. After the reaction is completed, a catalyst passivating agent is added, residual lactide is evaporated to remove it, the mixture is pulled into strands, cooled, and pelletized to obtain PLA resin.

[0020] In some embodiments, the inert atmosphere includes at least one of nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, etc.

[0021] In some embodiments, the melting temperature of lactide is 120~180°C.

[0022] In some embodiments, the mass of the catalyst is 1 to 100 ppm based on the mass of the lactide, and / or the mass of the chain transfer agent is 0 to 50 ppm, and / or the mass of the catalyst passivator is 1 to 200 ppm.

[0023] In some embodiments, the catalyst comprises a tin catalyst. For example, the catalyst comprises at least one of stannous isooctanoate and stannous oxide.

[0024] In some embodiments, the chain transfer agent includes at least one of lauryl alcohol and n-octanol.

[0025] In some embodiments, the catalyst passivator is an acidic catalyst passivator. For example, the catalyst passivator includes at least one of triphenyl phosphate and phosphoric acid.

[0026] In some embodiments, the reaction is carried out by adding a catalyst and a chain transfer agent as follows: adding the catalyst and chain transfer agent, stirring and dispersing, heating to 180°C while stirring (10~20 rpm) and maintaining this temperature for reaction, and continuing to keep the reaction at this temperature for 0~60 min after the torque no longer increases.

[0027] In some embodiments, the process conditions for evaporating and removing residual lactide are as follows: absolute pressure (i.e., absolute pressure) 50 Pa, temperature 210 °C, time 5~20 min.

[0028] The PLA resin can also be prepared according to CN110054762B, CN111499842B, etc.

[0029] In some embodiments, after pelleting, the PLA resin is further dried. The drying temperature is 80°C, and the drying time is 4 hours.

[0030] The PLA material may further comprise the following components by weight: 0-1 parts of additives. The additives may include at least one of light stabilizers and fluorescent whitening agents. For example, the light stabilizer may include at least one of triazine light stabilizers (such as ADKSTAB LA-46) and imidazole light stabilizers (such as ADK STAB LA-31); the fluorescent whitening agent may include at least one of titanium dioxide, pyrazoline, stilbene, and phthalimide.

[0031] Secondly, this application provides a method for preparing the PLA composite material, comprising the following steps: The components are mixed and dispersed, melt-extruded, granulated, and dried to obtain PLA composite material.

[0032] Preferably, the temperature of the melt extrusion is 140~240℃.

[0033] Thirdly, this application provides the application of the PLA composite material in 3D printing. The PLA composite material is suitable for the production of 3D printing filaments, especially high-speed 3D printing filaments, such as those with a printing speed of 200 mm / min or higher. The resulting 3D printing filaments can be used to 3D print toys, ornaments, medical human body simulation organs, art pieces, topographic maps, house models, and other products.

[0034] Fourthly, this application also provides a 3D printing filament, including the PLA composite material.

[0035] Compared with the prior art, the beneficial effects of this application are as follows: By adding a specific amount of a specific aromatic polycarbodiimide to polylactic acid and controlling the weight-average molecular weight, polydispersity index and D-lactic acid structural unit content of PLA resin within a specific range, the resulting composite material not only has low yellowness, but is also suitable for the production of 3D printing filaments, especially for the production of high-speed 3D printing filaments with printing speeds of 200 mm / min or higher. The resulting filaments can be used to 3D print toys, ornaments, medical human body simulation organs, art pieces, topographic maps, house models and other products. Detailed Implementation

[0036] To better illustrate the purpose, technical solutions, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are commonly used reagents and instruments. In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0037] The following examples and comparative examples all provide a PLA composite material. The formulations of these PLA composite materials are shown in Table 1. Their preparation methods include the following steps: after mixing and dispersing the components, they are fed into a twin-screw extruder, granulated underwater, and dried at 80°C for 4 hours to obtain the PLA composite material. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, a screw speed of 250 r / min, and a melt extrusion temperature of 180℃.

[0038] The raw materials used in the above embodiments and comparative examples are shown below. Unless otherwise specified, all raw materials were prepared in-house. Furthermore, the same raw materials were used in all parallel experiments. PLA 1: Weight-average molecular weight is 183,000 Da, PDI is 1.05, and the molar fraction of D-lactic acid structural units is 1.5%; PLA 2: Weight-average molecular weight is 181,000 Da, PDI is 1.13, and the molar fraction of D-lactic acid structural units is 1.3%; PLA 3: Weight-average molecular weight is 182,000 Da, PDI is 1.21, and the molar fraction of D-lactic acid structural units is 1.6%; PLA 4: Weight-average molecular weight is 179,000 Da, PDI is 1.46, and the molar fraction of D-lactic acid structural units is 1.5%; PLA 5: Weight-average molecular weight of 180,000 Da, PDI of 1.58, and molar fraction of D-lactic acid structural units of 1.7%; PLA 6: Weight-average molecular weight is 176,000 Da, PDI is 1.90, and the molar fraction of D-lactic acid structural units is 1.7%; PLA 7: Weight-average molecular weight is 183,000 Da, PDI is 2.03, and the molar fraction of D-lactic acid structural units is 1.5%; PLA 8: Weight-average molecular weight is 72,000 Da, PDI is 1.43, and the molar fraction of D-lactic acid structural units is 1.5%; PLA 9: Weight-average molecular weight of 95,000 Da, PDI of 1.48, and molar fraction of D-lactic acid structural units of 1.6%; PLA 10: Weight-average molecular weight of 152,000 Da, PDI of 1.46, and molar fraction of D-lactic acid structural units of 1.3%; PLA 11: Weight-average molecular weight is 209,000 Da, PDI is 1.41, and the molar fraction of D-lactic acid structural units is 1.7%; PLA 12: Weight-average molecular weight of 227,000 Da, PDI of 1.45, and molar fraction of D-lactic acid structural units of 1.5%; PLA 13: Weight-average molecular weight of 251,000 Da, PDI of 1.44, and molar fraction of D-lactic acid structural units of 1.4%; PLA 14: Weight-average molecular weight of 179,000 Da, PDI of 1.51, and molar fraction of D-lactic acid structural units of 2.0%; PLA 15: Weight-average molecular weight of 184,000 Da, PDI of 1.47, and molar fraction of D-lactic acid structural units of 4.7%; Aromatic polycarbodiimide 1: n=9~11, HyMax213, Langyi; Aromatic polycarbodiimide 2: n=9~11, STABAXOL P-100, LANXESS (Germany). Monomeric carbodiimide: HyMax1010, Langyi; Aliphatic polycarbodiimide compound: HyMax210, Langyi; Antioxidant OA-80: ADEKA, ADK STAB AO-80; Antioxidant 1010: Rianon.

[0039] Table 1 Table 2 The following performance tests were performed on the PLA composite materials of the above embodiments and comparative examples: (1) Fiber drawing performance test: The pellets were prepared into 3D printing filaments with a diameter of 1.75 mm using a filament machine. A self-designed printing model was used, which consisted of 9 pillars printed on a 5cm×5cm platform. The pillars were arranged in a 3×3 square, with a height of 5cm and a horizontal or vertical distance of 2cm between the bottoms of two adjacent pillars. The diameter of the bottom of the pillars was 2mm. The printing speed was 200mm / min. The printing direction was from bottom to top. If obvious gel points appeared, making it impossible to draw into a printing filament, the fiber drawing performance was not evaluated; if it could be drawn into a printing filament, the fiber drawing grade was evaluated according to Table 3. (2) b-value test: Take 27g of PLA composite material granules and use a colorimeter (model WF30) produced by Shenzhen Weifu Optoelectronics Technology Co., Ltd. to test the b-value. The test temperature is 25℃, the measuring diameter is 16mm, and the illumination mode is 8 / d.

[0040] Table 3 The test results are shown in Table 4.

[0041] Table 4 As can be seen from the above data, the PLA materials in the various embodiments of this application have both good drawing performance and low yellowness, such as a drawing grade of 0 to 2 and a b value of less than 6.

[0042] Comparative Example 6 suffered from severe stringing due to insufficient addition of aromatic polycarbodiimide. Comparative Example 5, with excessive addition of aromatic polycarbodiimide, exhibited obvious gel points, making it impossible to draw into printing filaments and resulting in excessive yellowness. In Comparative Example 3, the low weight-average molecular weight of PLA led to low melt strength and severe stringing. In Comparative Example 4, the high weight-average molecular weight of PLA resulted in poor flowability, making it impossible to draw into printing filaments. In Comparative Example 2, the high PDI of PLA resulted in a low proportion of polymer material, low melt strength, and severe stringing. In Comparative Example 1, the low PDI of PLA failed to balance plasticizing properties and melt strength, leading to severe stringing. In Comparative Example 9, the high molar fraction of D-lactic acid structural units in PLA caused severe stringing. Comparative Example 7, using monomeric carbodiimide, lacked significant cross-linking, resulting in low melt strength and severe stringing. Comparative Example 8 used an aliphatic polycarbodiimide compound, which had poor compatibility with the PLA system and was highly reactive and prone to forming gel points, making it impossible to draw into printing filaments and causing 3D printing failure.

[0043] Comparison of Examples 1-9 and 15 shows that when the weight-average molecular weight of PLA resin is 150,000 Da to 210,000 Da, the polydispersity index is 1.2 to 1.6, and the molar fraction of D-lactic acid structural units is 1.3% to 1.8%, better fiber drawing performance can be obtained.

[0044] Compared with Example 1, Examples 12-13 used a combination of aromatic polycarbodiimide and antioxidant AO-80, which improved melt strength by utilizing the synergistic effect of the two and obtained better 3D printing filament drawing performance.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A PLA composite material, characterized in that, The components include the following parts by weight: 100 parts of PLA resin, Aromatic polycarbodiimide 2.4~3.6 parts; The PLA resin has a weight-average molecular weight of 95,000 Da to 230,000 Da, a polydispersity index of 1.1 to 1.9, and a molar fraction of D-lactic acid structural units of no more than 2%. The aromatic polycarbodiimide includes At least one of the following, where n is an integer from 7 to 11.

2. The PLA composite material as described in claim 1, characterized in that, The PLA resin has a weight-average molecular weight of 150,000 Da to 210,000 Da, a polydispersity index of 1.2 to 1.6, and a molar fraction of D-lactic acid structural units of 1.3% to 1.8%.

3. The PLA composite material as described in claim 1, characterized in that, It also includes the following components in parts by weight: antioxidant 0.1 to 0.3 parts.

4. The PLA composite material as described in claim 3, characterized in that, The antioxidant includes at least one of 3,9-bis[1,1-dimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

5. The PLA composite material as described in claim 4, characterized in that, The antioxidant comprises 3,9-bis[1,1-dimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane.

6. The method for preparing PLA composite material as described in claim 1, characterized in that, The process includes the following steps: mixing and dispersing the components, melt extrusion, granulation, and drying to obtain a PLA composite material.

7. The application of the PLA composite material as described in any one of claims 1 to 5 in 3D printing.

8. A 3D printing filament, characterized in that, Including the PLA composite material as described in any one of claims 1 to 5.

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