Polylactic acid composite material capable of realizing rapid secondary crystallization and preparation method thereof

Abstract

The invention discloses a polylactic acid composite material capable of realizing rapid secondary crystallization and a preparation method thereof. The polylactic acid composite material is prepared from the following raw materials in parts by mass: 60-80 parts of polylactic acid, 10-30 parts of poly (adipic acid) / butylene terephthalate, 20-30 parts of boron nitride powder, 0-15 parts of mineral filler, 0.1-0.5 part of a dispersing agent, 0.1-0.5 part of a heat stabilizer, 0.3-1.0 part of a chain extender and 0.1-0.8 part of a lubricating agent. According to the invention, boron nitride is introduced into the system, and the excellent heat-conducting property of boron nitride is utilized, so that the time for reducing the supercooling degree of a sample can be greatly reduced, and boron nitride can be used as a nucleating agent for heterogeneous nucleation to reduce the nucleation time of polylactic acid, so that the overall secondary crystallization time is greatly reduced.

Description

Technical Field

[0001] The invention relates to a thermoplastic degradable composite material, in particular to a polylactic acid composite material capable of rapid secondary crystallization and used for degradable injection molding products and a preparation method thereof. Background Art

[0002] As an important organic synthetic polymer material, plastic is widely used and is an indispensable item in people's daily life. Traditional disposable injection products such as tableware and clothing accessories generally use plastic products such as polyethylene, polypropylene, and melamine. Because they are not degradable, discarded plastic products are very likely to become "white garbage", causing serious pollution to the living environment and ecological environment.

[0003] With the continuous advancement of science and technology, degradable composite materials are gradually appearing in people's lives and production. Degradable composite materials are synthetic materials that are added with a certain amount of additives (such as starch, modified starch or other cellulose, photosensitizer, biodegradation agent, etc.) during the production process to reduce their stability and then degrade more easily in the natural environment. Injection molded products made of degradable materials can be naturally degraded quickly in a variety of ways after being discarded, which meets today's environmental protection requirements. As a degradable material, polylactic acid has good strength and processing properties, making it the main material for disposable injection molding products.

[0004] However, polylactic acid has a slow crystallization rate and poor heat resistance, which limits the application scenarios of this material. The heat resistance of polylactic acid can be improved by adding heat-resistant components such as PBS, or through secondary crystallization. The addition of PBS can improve its heat resistance, but higher components need to be added to have a significant effect, which will greatly increase the material cost. The secondary crystallization method can effectively improve the heat resistance of finished tableware without adding other components, which has a higher economic effect, but the slower crystallization rate of polylactic acid will cause a long secondary crystallization time, resulting in low production efficiency.

[0005] Patent document CN112341766A discloses a fully degradable bio-based composite material product and its preparation method, including: 25-80 parts of biomass, 10-25 parts of dioxanone polymer, 30-50 parts of polylactic acid, 50-100 parts of PBTA resin, 1-10 parts of composite compatibilizer, 0.5-3 parts of lubricant, 0.8-1.5 parts of plasticizer; the composite compatibilizer is composed of coupling agent, mineral oil, and surfactant; the lubricant is a mixture of polyethylene wax, silicone oil, and boron nitride; the plasticizer is a mixture of triacetin, polyethylene glycol, polypropylene glycol, and mannitol monoacetate. However, the composite material of this patent is mainly used to prepare printable plastic packaging bags, which has high cost and is difficult to market in the field of injection molding.

[0006] Patent document CN106366588A discloses a method for producing a gas-barrier fully biodegradable beverage bottle, the steps of which are: adding plastic additives to fully biodegradable materials, mixing and granulating in a certain proportion, mixing the raw materials evenly and processing them into plastic masterbatch, extruding and blowing bottles and injection molding, and surface treatment; the plastic additives are at least one of chain extenders, plasticizers, and plastic expanded microspheres, and the fully biodegradable materials include at least four of polycaprolactone PLA, polybutylene succinate PBS, polycaprolactone PCL, polyhydroxyalkanoate PHA, polybutylene succinate / adipate PBSA, polybutylene adipate / terephthalate PBAT, and starch; the light-proof material includes at least one of carbon black, aluminum powder, mica powder, titanium dioxide, calcium carbonate, talc, boron nitride, hollow glass microspheres, montmorillonite, and organic optical shielding agents. However, this document is mainly used for product processing in the blow molding field, and is not suitable for injection molding applications under high fluidity requirements, and there is no discussion on the speed of secondary crystallization. Summary of the invention

[0007] The purpose of the present invention is to provide a polylactic acid composite material that can be rapidly secondary crystallized and a preparation method thereof. The polylactic acid composite material is a fully degradable material for injection molding tableware to solve the problem of slow secondary crystallization of existing degradable tableware materials and improve their production efficiency.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The invention discloses a polylactic acid composite material capable of rapid secondary crystallization, which is prepared from the following raw materials in parts by weight: polylactic acid: 60-80 parts, polybutylene adipate / terephthalate (PBAT): 10-30 parts, boron nitride powder: 20-30 parts, mineral filler: 0-15 parts, dispersant: 0.1-0.5 parts, heat stabilizer: 0.1-0.5 parts, chain extender: 0.3-1.0 parts, lubricant: 0.1-0.8 parts; wherein the total parts of polylactic acid, PBAT, boron nitride powder and mineral filler is 100 parts;

[0010] The number average molecular weight of the polylactic acid is 50,000 to 100,000; preferably, the number average molecular weight of the polylactic acid is 60,000 to 80,000, the melting point is 165 to 175° C., the melt flow index is 30 to 40 g / 10 min, the glass transition temperature is 55 to 60° C., and the tensile strength is >55 MPa;

[0011] The polybutylene adipate / terephthalate (PBAT) has a number average molecular weight of 40,000 to 100,000, and a melt flow index of 3 to 10 g / 10 min; preferably, the number average molecular weight is 60,000 to 90,000, and the melt flow index is 5 to 7 g / 10 min;

[0012] The particle size of the boron nitride powder is 1250-5000 mesh (preferably 2000-3500 mesh); boron nitride has high rigidity and presents a flaky structure with talc powder, which improves the mechanical properties of the product such as anti-bending. At the same time, the fine boron nitride powder can play a nucleation role in the cooling process of the polylactic acid melt, which is beneficial to improve the crystallinity of PLA, thereby facilitating the application of the product in a high temperature environment;

[0013] The mineral filler is at least one of calcium carbonate, talc, barium sulfate, wollastonite, montmorillonite, silicon dioxide, mica, clay, and ceramic powder; the particle size of the mineral filler is 1250-4000 meshes; if the mesh size of the mineral filler exceeds 4000 meshes, its bulk density is too small and too fluffy, which causes the powder to slide into the screw in advance along the particle gap during the feeding process, resulting in uneven particle density; if the mesh size is too small, agglomeration will occur during the blending process, affecting the mechanical properties of the product;

[0014] The dispersant is ethylene bisstearamide or / and ethylene bis-1,2-hydroxystearamide;

[0015] The heat stabilizer is at least one of phosphites, phenolic antioxidants, and oleic acid amides;

[0016] The chain extender is a copolymer chain extender containing epoxy functional groups, preferably BASF ADR4468;

[0017] The lubricant is erucamide and / or pentaerythritol stearate.

[0018] The polylactic acid composite material capable of rapid secondary crystallization of the present invention has a melting index of 4 to 11 g / 10 min, a tensile strength of 35 to 45 MPa, and an elongation at break of 5 to 30%.

[0019] The method for preparing a polylactic acid composite material capable of rapid secondary crystallization of the present invention comprises the following steps:

[0020] S1, stirring and mixing the polylactic acid and poly(butylene adipate / terephthalate) particles uniformly and drying to obtain a first mixture;

[0021] S2, adding the boron nitride powder, mineral filler, dispersant, heat stabilizer, chain extender and lubricant to the first mixture, stirring at 300-500 r / min for 5-30 min to fully mix; obtaining the second mixture;

[0022] S3, fully mixing the second mixture, and then melting and extruding it through a twin-screw extruder, water-cooling and pelletizing it, and drying it to prepare blended particles, namely the polylactic acid composite material.

[0023] Preferably, in step S1, the method for drying the polylactic acid and poly(butylene adipate) / terephthalate particles is as follows: placing the polylactic acid and poly(butylene adipate) / terephthalate particles in a dehumidifying dryer and drying them for 5 to 10 hours, the drying temperature is set to 70 to 80° C., and the water content of the two plastic particles is controlled below 30 ppm.

[0024] Preferably, the stirring in step S1 is carried out at 100 to 500 r / min for 5 to 20 min; and the stirring in step S2 is carried out at 300 to 700 r / min for 5 to 20 min.

[0025] Preferably, in step S3, the melt temperature of the twin-screw extruder is 160-190° C., and the screw speed is 300-450 r / min.

[0026] The polylactic acid composite material capable of rapid secondary crystallization of the present invention is used for injection molding, the melting temperature of the injection molding is 180-220° C. (preferably 180-200° C.), the injection time is 10-20 seconds, and the holding time is 10-20 seconds.

[0027] The products made from the above particles can have their heat deformation temperature increased from 55°C to 80-100°C after a short annealing treatment.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] In the method of the present invention, the main raw material is polylactic acid particles. As a linear degradable polyester, polylactic acid has the advantages of good processing performance and mechanical properties, and the discarded polylactic acid products can be rapidly degraded in the natural environment by various means, and finally decomposed into carbon dioxide and water. However, due to the presence of side methyl groups in the molecular chain segments, polylactic acid hinders the flexibility of the molecular chain, making its crystallization speed slow, resulting in the heat deformation temperature of the injection molded sample being below 60°C under the injection molding process with a generally short holding time, which greatly limits the application of polylactic acid materials in tableware. Generally, its heat resistance can be improved by the secondary crystallization method, but a longer secondary crystallization process is required to fully crystallize the polylactic acid products. In the secondary crystallization process of polylactic acid, it will experience the process of "reducing supercooling-nucleation-crystallization". By introducing boron nitride into the system and utilizing its excellent thermal conductivity, the time for the sample to reduce supercooling can be greatly reduced. At the same time, it can be used as a nucleating agent for heterogeneous nucleation to reduce the nucleation time of polylactic acid, thereby greatly reducing the overall secondary crystallization time.

[0030] Moreover, polylactic acid has poor toughness, and its injection molded products are easily broken at the sample gate when the mold is opened. Adding poly(butylene adipate / terephthalate) to the first mixture as a toughening agent to improve the toughness of the material can reduce the shrinkage and warping of the composite material during the secondary crystallization process. DETAILED DESCRIPTION

[0031] Those skilled in the art should realize that the present embodiment is only used to illustrate the present invention, but not to limit the present invention.

[0032] The raw materials used in the present invention are all commercially available products.

[0033] Polylactic acid: Fengyuan Bio FY201, number average molecular weight 60,000-80,000, melting point 167-175°C, melt flow index 30-40g / 10min, glass transition temperature 65°C, tensile strength >55MPa.

[0034] Polybutylene adipate / terephthalate (PBAT): T16 produced by Wanhua Chemical Company, with a number average molecular weight of 80,000 to 90,000 and a melt flow index of 3 to 10 g / 10 min.

[0035] Boron nitride powder: Anhui Kerun Nanotechnology Co., Ltd., 2500 mesh.

[0036] Example 1

[0037] The fully degradable material capable of rapid secondary crystallization of Example 1 is prepared by the following steps:

[0038] S1, placing the polylactic acid particles and the PBAT particles in a vacuum drum drying device at 80° C. and drying for 4 hours, wherein the water content of the two particles is controlled to be below 30 ppm; stirring at 300 r / min for 10 minutes to mix them evenly, to obtain a first mixture;

[0039] S2, adding the boron nitride powder (2500 mesh), dispersant EBS, lubricant (erucic acid amide), chain extender (BASF ADR4468) and thermal stabilizer (BASF 1010,168) to the first mixture, stirring at 400 r / min for 10 min to mix evenly, to obtain a second mixture;

[0040] S3, adding the second mixture into a twin-screw extruder for melt extrusion granulation, the extrusion temperature is 160-190° C., and the rotation speed is 450 r / min; drying to form blended particles;

[0041] S4, injection molding the blended particles, the mold is kept at room temperature by a water cooling device, the injection temperature is 190° C., the injection time is 15 s, and the holding time is 10 s, to obtain a polylactic acid composite material.

[0042] Table 1 Formulas of Examples 1 to 5 and Comparative Examples 1 to 3, parts by mass

[0043]

[0044]

[0045] Example 2

[0046] The fully degradable material capable of rapid secondary crystallization of Example 2 is prepared by the following steps:

[0047] S1, placing the polylactic acid particles and the PBAT particles in a vacuum drum drying device at 80° C. and drying for 4 hours, wherein the water content of the two particles is controlled to be below 30 ppm; stirring at 300 r / min for 10 minutes to mix them evenly, to obtain a first mixture;

[0048] S2, adding boron nitride powder (2500 mesh), mineral filler (talc, 3000 mesh), dispersant (EBS), heat stabilizer (BASF antioxidant 1010 and antioxidant 168 = 1:1), chain extender (BASF ADR4468) and lubricant (erucic acid amide) to the first mixture, stirring at 400 r / min for 10 min to mix evenly, to obtain a second mixture;

[0049] S3, adding the second mixture into a twin-screw extruder for melt extrusion granulation, the extrusion temperature is 160-190° C., and the rotation speed is 450 r / min; drying to form blended particles;

[0050] S4, injection molding the blended particles, the mold is kept at room temperature by a water cooling device, the injection temperature is 190° C., the injection time is 15 s, and the holding time is 10 s, to obtain a polylactic acid composite material.

[0051] Example 3

[0052] The fully degradable material capable of rapid secondary crystallization of Example 3 is prepared by the following steps:

[0053] S1, placing the polylactic acid particles and the PBAT particles in a vacuum drum drying device at 70° C. and drying for 8 hours, wherein the water content of the two particles is controlled to be below 30 ppm; stirring at 350 r / min for 7 minutes to mix them evenly, to obtain a first mixture;

[0054] S2, adding boron nitride powder (3500 mesh), EBS dispersant, heat stabilizer (BASF antioxidant 1010 and antioxidant 168 = 1:1), chain extender (BASF ADR4468) and lubricant (erucic acid amide) to the first mixture, stirring at 500 r / min for 6 min to mix evenly, to obtain a second mixture;

[0055] S3, adding the second mixture into a twin-screw extruder for melt extrusion granulation, the extrusion temperature is 160-190° C., and the rotation speed is 400 r / min; drying to form blended particles;

[0056] S4, injection molding the blended particles, the mold is kept at room temperature by a water cooling device, the injection temperature is 200°C, the injection time is 10s, and the holding time is 10s, and the polylactic acid composite material can be obtained.

[0057] Example 4

[0058] The fully degradable material capable of rapid secondary crystallization of Example 4 is prepared by the following steps:

[0059] S1, placing the polylactic acid particles and the PBAT particles in a vacuum drum drying device at 75° C. and drying for 7 hours, wherein the water content of the two particles is controlled to be below 30 ppm; stirring at 250 r / min for 10 minutes to mix them evenly, to obtain a first mixture;

[0060] S2, adding boron nitride powder (4000 mesh), mineral filler (calcium carbonate, 3000 mesh), dispersant (EBS), heat stabilizer (BASF antioxidant 1010 and antioxidant 168 = 1:1), chain extender (BASF ADR4468) and lubricant (erucic acid amide) to the first mixture, stirring at 450 r / min for 8 min to mix evenly, to obtain a second mixture;

[0061] S3, adding the second mixture into a twin-screw extruder for melt extrusion granulation, the extrusion temperature is 160-190° C., and the rotation speed is 450 r / min; drying to form blended particles;

[0062] S4, injection molding the blended particles, the mold is kept at room temperature by a water cooling device, the injection temperature is 190° C., the injection time is 15 s, and the holding time is 10 s, to obtain the polylactic acid composite material.

[0063] Comparative Example 1

[0064] Comparative Example 1 is a comparative example of Example 1, except that: 100 parts of polylactic acid are used and no PBAT is added; the remaining raw materials and process parameters are the same as those of Example 1.

[0065] Comparative Example 2

[0066] Comparative Example 2 is a comparative example of Example 1, except that: 60 parts of polylactic acid, 10 parts of PBAT, 30 parts of talc, and the remaining raw materials and process parameters are the same as those of Example 1.

[0067] Comparative Example 3

[0068] S1, placing the polylactic acid particles and the PBAT particles in a vacuum drum drying device at 80° C. and drying for 4 hours, wherein the water content of the two particles is controlled to be below 30 ppm; stirring at 300 r / min for 10 minutes to mix them evenly, to obtain a first mixture;

[0069] S2, adding polybutylene succinate (Fengyuan, melt flow index 3-20 g / 10 min), mineral filler (talc, 3000 mesh), dispersant (EBS), heat stabilizer (BASF antioxidant 1010 and antioxidant 168 = 1:1), chain extender (BASF ADR4468) and lubricant (erucic acid amide) to the first mixture, stirring at 400 r / min for 10 min to mix evenly, to obtain a second mixture;

[0070] S3, adding the second mixture into a twin-screw extruder for melt extrusion granulation, the extrusion temperature is 160-190° C., and the rotation speed is 450 r / min; drying to form blended particles;

[0071] S4, injection molding the blended particles, the mold is kept at room temperature by a water cooling device, the injection temperature is 190° C., the injection time is 15 s, and the holding time is 10 s to obtain a polylactic acid composite material.

[0072] Detection experiment example

[0073] The polylactic acid composite materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were injection molded, and the secondary crystallization performance of the injection molded strips was tested. The results are shown in Table 1. The secondary crystallization strips had dimensions of 80 mm in length, 10 mm in width, and 4 mm in thickness, and the secondary crystallization temperature was 80°C.

[0074] Table 1 Test results of Examples 1 to 4 and Comparative Examples 1 to 3

[0075]

[0076]

[0077] From the results in Table 1, it can be seen that Examples 1 to 4 begin to crystallize within 0 to 3 minutes of annealing at 80°C, and their heat deformation temperatures have begun to increase. This is because the boron nitride with more components in Examples 1 to 4 constructs a heat conduction path in the material, and during the annealing process, heat is transferred to the interior of the material more quickly and evenly, prompting the polymer molecular chains to be arranged in order into crystals, thereby achieving the purpose of achieving high heat resistance in a shorter secondary crystallization.

[0078] The heat resistance of pure PLA in comparative example 1 is poor, and the secondary crystallization takes a long time. After adding talcum powder or PBS to comparative examples 2 to 3, the overall heat resistance of the material can be slightly improved, but a long annealing time is still required to achieve the effect of secondary crystallization. The greater the content of boron nitride, the shorter the time required for secondary crystallization.

Claims

1. A polylactic acid composite material capable of rapid secondary crystallization, characterized in that: The invention is prepared from the following raw materials in parts by weight: 60 to 80 parts of polylactic acid, 10 to 30 parts of polybutylene adipate / terephthalate, 20 to 30 parts of boron nitride powder, 0 to 15 parts of mineral filler, 0.1 to 0.5 parts of dispersant, 0.1 to 0.5 parts of thermal stabilizer, 0.3 to 1.0 parts of chain extender and 0.1 to 0.8 parts of lubricant; wherein the total parts of polylactic acid, polybutylene adipate / terephthalate, boron nitride powder and mineral filler are 100 parts.

2. The polylactic acid composite material capable of rapid secondary crystallization according to claim 1, characterized in that: The number average molecular weight of the polylactic acid is 50,000 to 100,000; the number average molecular weight of the polybutylene adipate / terephthalate is 40,000 to 100,000, and the melt flow index is 3 to 10 g / 10 min; and the particle size of the boron nitride powder is 1,250 to 5,000 meshes.

3. The polylactic acid composite material capable of rapid secondary crystallization according to claim 1, characterized in that: The number average molecular weight of the polylactic acid is 60,000 to 80,000, the melting point is 165 to 175°C, the melt flow index is 30 to 40 g / 10 min, the glass transition temperature is 55 to 60°C, and the tensile strength is greater than 55 MPa; the number average molecular weight of the polybutylene adipate / terephthalate is 60,000 to 90,000, and the melt flow index is 5 to 7 g / 10 min; the particle size of the boron nitride powder is 2,000 to 3,500 meshes.

4. The polylactic acid composite material capable of rapid secondary crystallization according to claim 1, characterized in that: The mineral filler is at least one of calcium carbonate, talc, barium sulfate, wollastonite, montmorillonite, silicon dioxide, mica, clay, and ceramic powder; and the particle size of the mineral filler is 1250-4000 meshes.

5. The polylactic acid composite material capable of rapid secondary crystallization according to claim 1, characterized in that: The dispersant is ethylene bisstearamide and / or ethylene bis-1,2-hydroxystearamide; the heat stabilizer is at least one of phosphites, phenolic antioxidants, and oleic acid amides; the chain extender is a copolymer chain extender containing epoxy functional groups; and the lubricant is erucamide and / or pentaerythritol stearate.

6. The polylactic acid composite material capable of rapid secondary crystallization according to any one of claims 1 to 5, characterized in that: The melt index is 4 to 11 g / 10 min; the tensile strength of the material is 35 to 45 MPa, and the elongation at break is 5% to 30%.

7. The method for preparing the polylactic acid composite material according to claim 6, characterized in that: The following steps are involved: S1, stirring and mixing the polylactic acid and poly(butylene adipate / terephthalate) particles uniformly and drying to obtain a first mixture; S2, adding the boron nitride powder, mineral filler, dispersant, heat stabilizer, chain extender and lubricant to the first mixture, stirring at 300-500 r / min for 5-30 min to fully mix; obtaining the second mixture; S3, fully mixing the second mixture, and then melting and extruding it through a twin-screw extruder, water-cooling and pelletizing it, and drying it to prepare blended particles, which are the polylactic acid composite material.

8. The method for preparing the polylactic acid composite material according to claim 7, characterized in that: In step S1, the polylactic acid and poly(butylene adipate / terephthalate) particles are dried by placing the polylactic acid and poly(butylene adipate / terephthalate) particles in a dehumidifying dryer for 5 to 10 hours, with the drying temperature set to 70 to 80° C., and the water content of the two plastic particles controlled below 30 ppm.

9. The method for preparing the polylactic acid composite material according to claim 7, characterized in that: The stirring in step S1 is carried out at 100 to 500 r / min for 5 to 20 min; the stirring in step S2 is carried out at 300 to 700 r / min for 5 to 20 min; in step S3, the melt temperature of the twin-screw extruder is 160 to 190° C., and the screw speed is 300 to 450 r / min.

10. Use of the polylactic acid composite material according to claim 6 for injection molding; the melt temperature of injection molding is 180-220°C, the injection time is 10-20s, and the holding time is 10-20s.

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