A reinforced and toughened polylactic acid composite prepared from a bio-based modified calcium carbonate powder and a preparation method thereof

Abstract

The application discloses a kind of bio-based modified calcium carbonate powder preparation's reinforced toughening polylactic acid composite material and preparation method thereof, using bio-based aliphatic diacid to modify calcium carbonate powder, then bio-based epoxy compound is grafted on the surface of the carboxylated calcium carbonate powder, and bio-based modified calcium carbonate crosslinking agent is prepared.Subsequently, carboxylated calcium carbonate powder and bio-based modified calcium carbonate crosslinking agent are added to polylactic acid and middle, and high-strength high-toughness degradable polylactic acid composite material is prepared by blending melt extrusion.The prepared polylactic acid composite material system component is simple, effectively reduces compatibility conflict, realizes high-strength high-toughness and rapid degradation simultaneously, greatly reduces production cost, and can be applied to agricultural film, food, packaging and medical field.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid composite material preparation, and in particular to a reinforced and toughened polylactic acid composite material prepared from bio-based modified calcium carbonate powder and its preparation method. Background Technology

[0002] Polylactic acid (PLA), as a typical biodegradable material, has shown broad application prospects in packaging and medical fields due to its excellent mechanical properties, biodegradability, and superior biocompatibility. However, PLA materials still face many challenges in practical applications, such as insufficient toughness, poor thermal stability, high production costs, and harsh degradation conditions. These factors limit its large-scale commercial application. To improve the performance of PLA materials, researchers generally use melt blending technology to combine it with... PBAT is used for composite modification. PBAT is a biodegradable copolyester. Its unique molecular structure not only exhibits high elongation at break and impact strength, but also good thermal stability and processing performance, which can effectively improve the toughness defects of PLA. However, the following problems often exist in the use of PLA / PBAT biodegradable composite materials: First, PLA, as a crystalline polymer, has poor compatibility with PBAT. Simple blending processes can easily lead to interfacial bonding defects, which in turn cause interfacial separation during the stretching process, seriously affecting the toughening effect; Second, although the introduction of PBAT can enhance the toughness of PLA, it often leads to a significant decrease in the overall mechanical strength and modulus of the material; Third, the high price of PLA and PBAT greatly limits large-scale market application.

[0003] In response, some studies have proposed introducing compatibilizers into PLA / PBAT blends to improve the interfacial bonding between PLA and PBAT. Simultaneously, adding calcium carbonate powder to the polymer effectively reduces the cost of PLA / PBAT composites and enhances the strength and modulus of PLA composites. In the development of PLA / PBAT / calcium carbonate composites, although several patented solutions attempt to improve performance through composite modification, they all have significant limitations. For example, Chinese invention patent CN119529487A uses zinc stearate to surface-modify calcium carbonate, then melt-granulates it with PBAT, and subsequently melt-blends it with PLA modified with an epoxy chain extender. While this improves the dispersibility of calcium carbonate, the epoxy chain extender itself is non-degradable, leading to reduced environmental friendliness of the material. Furthermore, the bonding force between calcium carbonate and the polymer matrix is ​​only achieved through physical coating, lacking chemical bonding and resulting in insufficient interfacial stability. Similarly, CN120888167A improved the toughness and barrier properties of the film by optimizing the ratio of PBAT, PLA, PBS, polycaprolactone, and glycidyl methacrylate grafted polylactic acid copolymer. However, the epoxy groups introduced by the glycidyl methacrylate graft are also non-degradable, and the multi-component blending exacerbates the system complexity, with differences in compatibility between components potentially leading to performance fluctuations. While CN120842818A uses chitosan grafted polyglycidyl methacrylate nanoparticles as a compatibilizer, achieving a balance between high strength and degradability, this system still relies on multiple modified fillers and compatibilizers. Adding too many types may weaken interfacial bonding; for example, the synergistic effect between calcium carbonate and fiber fillers is not fully optimized, leading to easy degradation of mechanical properties under complex stress. In summary, existing solutions generally suffer from defects such as non-degradable compatibilizers, unclear filler bonding forces, and performance instability caused by system complexity, which restrict their large-scale application. Future research should focus on developing biodegradable compatibilizers, strengthening filler-matrix chemical bonding, and simplifying components to improve interfacial compatibility. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a simple PLA / PBAT / calcium carbonate composite material system that exhibits advantages such as high tensile strength, high toughness, high biodegradability, and low cost, and can be applied in agricultural films, food, packaging, and medical fields.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a reinforced and toughened polylactic acid composite material made from bio-based modified calcium carbonate powder comprises the following steps: by mass, 100 parts PLA, 30-50 parts PBAT, 5-20 parts carboxylated calcium carbonate powder, 5-20 parts bio-based modified calcium carbonate crosslinking agent and 0.1-0.3 parts antioxidant are mixed and then added to a screw extruder for melt granulation to obtain the reinforced and toughened polylactic acid composite material made from bio-based modified calcium carbonate powder;

[0007] The preparation method of the bio-based modified calcium carbonate crosslinking agent includes:

[0008] S1. Preparation of carboxylated calcium carbonate powder: First, the calcium carbonate powder is dried in an environment of 120~150℃ to remove moisture. Then, by mass, 10 parts of calcium carbonate powder are ultrasonically dispersed in 40~100 parts of ethanol solution, with an ethanol mass fraction of 40%~60%. The mixture is transferred to a reaction vessel and stirred. When the system temperature rises to 50~70℃, 0.4~0.8 parts of bio-based fatty acid are added. The reaction is maintained at this temperature for 1~4 hours. Finally, the sample after reaction is repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain carboxylated calcium carbonate powder.

[0009] S2. Preparation of bio-based modified calcium carbonate crosslinking agent: 10 parts of carboxylated calcium carbonate powder obtained in step S1 were ultrasonically dispersed in 40-100 parts of ethanol solution, and then 0.8-1.6 parts of bio-based epoxy compound were added. The mixture was stirred at 50-70℃ for 5-10 min. 0.02-0.05 parts of 1,8-diazabicyclo[5.4.0]undec-7-ene were pre-diluted with a small amount of ethanol and then slowly added dropwise to the system. The mixture was stirred for another 5-15 min, heated to 80-100℃, and stirred for 4-6 h. The sample after reaction was repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain the bio-based modified calcium carbonate crosslinking agent. PLA is polylactic acid, PBAT is... .

[0010] Preferably, the bio-based fatty acid in step S1 is one of sebacic acid, azelaic acid, adipic acid, and glutaric acid; the bio-based epoxy compound in step S2 is one of epoxidized soybean oil, epoxidized linseed oil, and castor oil glycidyl ether.

[0011] Preferably, the density of the PLA is 1.24~1.28. The melt flow index is 3~6 g / 10 min; the density of the PBAT is... The melt flow index is 2.5~4.5 g / 10 min; the antioxidant is one of antioxidants 1026, 626, 1010, 300 or 168.

[0012] Preferably, the mass ratio of the carboxylated calcium carbonate powder to the bio-based modified calcium carbonate crosslinking agent is 0.8 to 1.2.

[0013] Preferably, the mass ratio of the carboxylated calcium carbonate powder to the bio-based modified calcium carbonate crosslinking agent is 0.8 to 1.2.

[0014] Preferably, the ethanol solution contains 40%-60% ethanol by mass.

[0015] Preferably, the calcium carbonate powder has a mesh size of 20,000 to 30,000 mesh.

[0016] A bio-based modified calcium carbonate powder-reinforced and toughened polylactic acid composite material is prepared using any one of the above-mentioned methods for preparing bio-based modified calcium carbonate powder-reinforced and toughened polylactic acid composite materials.

[0017] The principle of this invention is as follows:

[0018] This invention utilizes a bio-based fatty diacid to introduce carboxyl groups onto the surface of calcium carbonate via a dehydration condensation reaction, forming a stable carboxylated structure. Subsequently, a bio-based epoxy compound undergoes a ring-opening reaction with the carboxyl groups on the carboxylated calcium carbonate surface through epoxy groups, forming stable ester bonds. The long-chain alkyl structure of the fatty diacid introduced into the carboxylated calcium carbonate effectively reduces interfacial tension and improves the compatibility of calcium carbonate with PLA and PBAT. Furthermore, the bio-based modified calcium carbonate crosslinking agent effectively bridges PLA and PBAT, significantly improving interfacial shear strength. The combination of carboxylated calcium carbonate and bio-based modified calcium carbonate constructs a chemical bond bridging network, improving the self-dispersibility of calcium carbonate and inhibiting filler agglomeration, efficiently transferring dispersed stress, and providing a foundation for higher rigidity and strength in the composite material. Moreover, the introduction of bio-based raw materials ensures the biodegradability of the material throughout its entire life cycle, aligning with environmental protection trends.

[0019] The epoxy groups of the bio-based modified calcium carbonate crosslinking agent can form chemical bonds with the carboxyl groups of calcium carbonate powder, PLA, and PBAT to construct a multi-level crosslinking network, achieving effective stress transfer. The flexible segments of PBAT endow the material with excellent ductility and impact absorption capacity, dispersing external stress by inducing crazing or shear band deformation. The incorporation of calcium carbonate powder can effectively compensate for the strength reduction caused by the introduction of PBAT segments, and its addition can significantly reduce costs. The multi-level crosslinking network between the polymer and powder enhances the overall stability of the material, effectively inhibiting crack propagation and achieving a balance between high strength and high toughness. Through the synergistic design of interface modification, chemical crosslinking, PBAT toughening, and calcium carbonate reinforcement, the system enables polylactic acid composites to possess high tensile strength, high impact strength, high elongation at break, and excellent processing flowability. Furthermore, this system maintains the biodegradable properties of polylactic acid, meeting the requirements of environmentally friendly packaging and high-end applications.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention introduces bio-based fatty acid-modified calcium carbonate, which significantly reduces the interfacial tension with PLA and PBAT through long-chain alkyl groups. At the same time, the bio-based epoxy-grafted calcium carbonate forms chemical bonds with the polymer carboxyl groups to strengthen the interfacial bonding. This modification transforms calcium carbonate from a traditional filler into a functional compatibilizer, which not only improves the rigidity of the material but also ensures its biodegradability throughout its entire life cycle, providing a stable interface for the subsequent construction of crosslinked networks.

[0022] (2) This invention uses a bio-based modified calcium carbonate crosslinking agent as the core to construct a multi-level crosslinking network between powders and between the matrix and powders. This network organically bridges calcium carbonate, PLA, and PBAT through chemical bonding, enhancing the compatibility between components, significantly improving interfacial shear strength, and achieving effective stress transfer while inhibiting crack propagation. Therefore, calcium carbonate, PLA, and PBAT work synergistically to achieve high strength and high toughness in polylactic acid composite materials.

[0023] (3) This invention uses bio-based fatty acid diacid and epoxy compounds to replace petroleum-based compatibilizers, ensuring the biodegradability of the material throughout the entire process from raw materials to waste, which is in line with environmental protection trends. At the same time, the simplified system composition avoids the conflicts of traditional compatibilizers, improves processing fluidity, and makes the composite material easy to melt extrusion molding. Attached Figure Description

[0024] Figure 1 Infrared spectra of original calcium carbonate, carboxylated calcium carbonate powder prepared in Example 1, and bio-based modified calcium carbonate crosslinking agent. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention uses bio-based compounds to modify calcium carbonate powder, coating its surface with carboxyl and epoxy groups. This modified calcium carbonate is then incorporated into a PLA matrix along with PBAT. The flexible segments of PBAT effectively toughen the material, while calcium carbonate compensates for the rigidity of polylactic acid composites, significantly reducing costs. A bio-based modified calcium carbonate crosslinking agent chemically bonds PLA, PBAT, and carboxylated calcium carbonate powder, enhancing the compatibility between polymers and between the polymer and the filler, effectively improving the mechanical properties of the composite material. The final steps of this technical solution utilize melt blending, extrusion, and granulation processes, which are common and well-known technologies in the field and are not described in detail here.

[0027] Example 1

[0028] Carboxylated calcium carbonate powder was prepared by the following method: First, the calcium carbonate powder was dried at 150°C to remove moisture. Then, 10 parts by mass of the calcium carbonate powder were ultrasonically dispersed in 100 parts by mass of an ethanol solution (ethanol mass ratio 60%). The mixture was then placed in a reaction vessel and stirred. When the system temperature reached 50°C, 0.4 parts by mass of sebacic acid were added, and the reaction was maintained at this temperature for 2 hours. Finally, the reacted sample was repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain the carboxylated calcium carbonate powder.

[0029] The bio-based modified calcium carbonate crosslinking agent was prepared by the following method: 10 parts of the carboxylated calcium carbonate powder obtained above were ultrasonically dispersed in 100 parts of ethanol, and then 0.8 parts of epoxidized soybean oil were added. The mixture was stirred at 60°C for 10 min. Subsequently, 0.02 parts of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, and the mixture was stirred for another 10 min. The temperature was then raised to 100°C, and the reaction was stirred for 4 h. Finally, the sample after the reaction was repeatedly washed with ethanol solution and then transferred to an oven to dry thoroughly, thus obtaining the bio-based modified calcium carbonate crosslinking agent.

[0030] The reinforced and toughened polylactic acid (PLA) composite material prepared from bio-based modified calcium carbonate powder was obtained by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 40 parts by weight of PBAT, and 0.2 parts by weight of antioxidant 1010 were mixed and added through the main feed port of a twin-screw extruder. 15 parts by weight of carboxylated calcium carbonate powder and 15 parts by weight of bio-based modified calcium carbonate crosslinking agent were mixed and added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the reinforced and toughened PLA composite material prepared from bio-based modified calcium carbonate powder. The screw extruder speed was 200 rpm, and the extrusion temperature was 160–190°C.

[0031] Figure 1Infrared spectra of pristine calcium carbonate, carboxylated calcium carbonate powder prepared in Example 1, and bio-based modified calcium carbonate crosslinking agent. Compared with pristine calcium carbonate, the modified carboxylated calcium carbonate powder exhibits higher bulk carbonate concentrations at 1400, 860, and... The characteristic absorption peaks at 2980 and 100°C remained stable, indicating that sebacic acid modification did not destroy the calcium carbonate crystal structure. Carboxylated calcium carbonate showed stable absorption peaks at 2980 and 100°C. The characteristic absorption peak of the methylene group appears at this location. The presence of a carbonyl peak indicating a carboxyl group at the powder surface confirms that sebacic acid was successfully grafted onto the powder surface via salt formation bonding with calcium ions on the calcium carbonate surface, thus successfully preparing carboxylated calcium carbonate. The significantly enhanced methylene and ester carbonyl peaks of the bio-based modified calcium carbonate crosslinking agent further confirm that epoxidized soybean oil under DBU catalysis underwent a ring-opening grafting reaction with the carboxyl groups on the surface of carboxylated calcium carbonate, successfully preparing bio-based modified calcium carbonate.

[0032] Example 2

[0033] The preparation methods for carboxylated calcium carbonate powder and bio-based modified calcium carbonate crosslinking agent are the same as in Example 1.

[0034] The reinforced and toughened polylactic acid (PLA) composite material prepared from bio-based modified calcium carbonate powder was obtained by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 30 parts by weight of PBAT, and 0.1 parts by weight of antioxidant 1010 were mixed and added through the main feed port of a twin-screw extruder. 5 parts by weight of carboxylated calcium carbonate powder and 6 parts by weight of bio-based modified calcium carbonate crosslinking agent were mixed and added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the reinforced and toughened PLA composite material prepared from bio-based modified calcium carbonate powder. The screw extruder speed and temperature in each zone were the same as in Example 1.

[0035] Example 3

[0036] Carboxylated calcium carbonate powder was prepared by the following method: First, the calcium carbonate powder was dried at 120°C to remove moisture. Then, 10 parts by mass of the calcium carbonate powder were ultrasonically dispersed in 40 parts by mass of an ethanol solution (ethanol mass fraction 40%). The mixture was then placed in a reaction vessel and stirred. When the system temperature reached 70°C, 0.8 parts by mass of azelaic acid were added, and the reaction was maintained at this temperature for 1 hour. Finally, the sample was repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain the carboxylated calcium carbonate powder.

[0037] The bio-based modified calcium carbonate crosslinking agent was prepared by the following method: 10 parts of the carboxylated calcium carbonate powder obtained above were ultrasonically dispersed in 40 parts of ethanol, and then 1.6 parts of epoxidized linseed oil were added. The mixture was stirred at 70°C for 5 min. Subsequently, 0.05 parts of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, and the mixture was stirred for another 5 min. The temperature was then raised to 80°C, and the reaction was stirred for 6 h. Finally, the sample after the reaction was repeatedly washed with ethanol and water, and then transferred to an oven to dry thoroughly, thus obtaining the bio-based modified calcium carbonate crosslinking agent.

[0038] The reinforced and toughened polylactic acid (PLA) composite material prepared from bio-based modified calcium carbonate powder was obtained by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 50 parts by weight of PBAT, and 0.3 parts by weight of antioxidant 1026 were mixed and added through the main feed port of a twin-screw extruder. 20 parts by weight of carboxylated calcium carbonate powder and 16 parts by weight of bio-based modified calcium carbonate crosslinking agent were mixed and added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the reinforced and toughened PLA composite material prepared from bio-based modified calcium carbonate powder. The screw extruder speed and temperature in each zone were the same as in Example 1.

[0039] Example 4

[0040] The preparation methods for carboxylated calcium carbonate powder and bio-based modified calcium carbonate crosslinking agent are the same as in Example 3.

[0041] The reinforced and toughened polylactic acid (PLA) composite material prepared from bio-based modified calcium carbonate powder was obtained by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 40 parts by weight of PBAT, and 0.2 parts by weight of antioxidant 1026 were mixed and added through the main feed port of a twin-screw extruder. 10 parts by weight of carboxylated calcium carbonate powder and 10 parts by weight of bio-based modified calcium carbonate crosslinking agent were mixed and added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the reinforced and toughened PLA composite material prepared from bio-based modified calcium carbonate powder. The screw extruder speed and temperature in each zone were the same as in Example 1.

[0042] Comparative Example 1

[0043] Polylactic acid (PLA) composite material was prepared by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 40 parts by weight of PBAT, and 0.2 parts by weight of antioxidant 1010 were mixed and added through the main feed port of a twin-screw extruder. 30 parts by weight of calcium carbonate powder were added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the PLA composite material. The screw extruder speed and temperature of each zone were the same as in Example 1.

[0044] Comparative Example 2

[0045] The preparation method of carboxylated calcium carbonate powder is the same as in Example 1.

[0046] The polylactic acid (PLA) composite material was prepared by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 40 parts by weight of PBAT, and 0.2 parts by weight of antioxidant 1010 were mixed and added through the main feed port of a twin-screw extruder. 30 parts by weight of carboxylated calcium carbonate powder were added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the PLA composite material. The screw extruder speed and temperature in each zone were the same as in Example 1.

[0047] Comparative Example 3

[0048] The preparation method of the bio-based modified calcium carbonate crosslinking agent is the same as in Example 1.

[0049] The polylactic acid (PLA) composite material was prepared by the following method: First, PLA and PBAT were dried. Then, 100 parts by weight of PLA, 40 parts by weight of PBAT, and 0.2 parts by weight of antioxidant 1010 were mixed and added through the main feed port of a twin-screw extruder. 30 parts by weight of bio-based modified calcium carbonate crosslinking agent were added through the side feed port. The mixture was then melt-blended, extruded, and granulated to obtain the PLA composite material. The screw extruder speed and temperature in each zone were the same as in Example 1.

[0050] The polylactic acid composite materials prepared in the above embodiments and comparative examples were subjected to the following performance tests, and the experimental results are shown in Table 1.

[0051] Tensile strength and elongation at break: by Standard test, tensile rate 20 mm / min;

[0052] Bending strength: according to Standard test, test speed is 2.0 mm / min;

[0053] Notched impact strength: based on According to standard testing, the pendulum energy is 4.0J;

[0054] Degradation rate: Take an appropriate amount of outdoor soil, place the polylactic acid composite material sample dried to constant weight in the soil, add an appropriate amount of tap water regularly to maintain humidity, take out the sample after 180 days, wash it clean, dry it thoroughly and weigh it, and calculate the degradation rate.

[0055]

[0056] As shown in Table 1, the mechanical properties of polylactic acid (PLA) composites are closely related to the content of PBAT and modified calcium carbonate powder. The PLA composites prepared in Examples 1-4 maintain good overall mechanical properties. This is because the bio-based modified calcium carbonate crosslinking agent connects PLA, PBAT, and carboxylated calcium carbonate powder through chemical bonds to construct a multi-layer crosslinking network. This effectively enhances the dispersibility of calcium carbonate powder and PBAT in the PLA matrix and improves the compatibility and bonding force between the interfaces of each component. In this system, PBAT can significantly improve the toughness, elongation at break, and notched impact strength of PLA composites, while modified calcium carbonate powder increases the tensile strength and flexural strength of PLA composites and reduces costs. By using bio-based fatty acid diacid and epoxy compounds to replace petroleum-based compatibilizers, the degradation rate of the prepared PLA composites reaches 100% after 180 days, effectively avoiding environmental pollution.

[0057] The comparison results of the examples and comparative examples show that:

[0058] Comparative Example 1 differs from Example 1 in that it uses unmodified calcium carbonate powder as a reinforcing filler. The resulting polylactic acid composite material has a tensile strength of 30.7 MPa and a notched impact strength of 26.2 kJ / m. 2 The flexural strength was 92.8 MPa, and the elongation at break was 4.8%. The interfacial bonding between the unmodified calcium carbonate and the PLA matrix and the PBAT toughening agent was poor, with a large number of interfacial defects, which had a very adverse effect on the mechanical properties.

[0059] Comparative Example 2 differs from Example 1 in that it directly combines PLA, PBAT, and carboxylated calcium carbonate powders through melt granulation. The resulting polylactic acid composite material exhibits a tensile strength of 42.2 MPa and a notched impact strength of 31.4 kJ / m². 2 The flexural strength was 110.1 MPa, and the elongation at break was 5.8%. It can be seen that the rigidity and toughness of the polylactic acid composite material deteriorated significantly. Although the long-chain alkyl groups introduced by the carboxylated calcium carbonate powder can improve the compatibility between the filler and the polymer to some extent, the lack of a bio-based modified calcium carbonate crosslinking agent leads to weak interfacial bonding between the polymer and the filler, as well as between polymers, resulting in reduced stress transfer efficiency and limited crack propagation inhibition. Therefore, the tensile strength, impact strength, and elongation at break all decreased significantly.

[0060] Comparative Example 3 differs from Example 1 in that it directly combines PLA, PBAT, and a bio-based modified calcium carbonate crosslinking agent through melt granulation. The resulting polylactic acid composite material exhibits a tensile strength of 60.2 MPa and a notched impact strength of 44.9 kJ / m². 2The composite material exhibits a flexural strength of 123.6 MPa and an elongation at break of 7.3%. However, its mechanical strength is slightly reduced, and its toughness is significantly decreased. Although PLA, PBAT, and the bio-based modified calcium carbonate crosslinking agent can form a multi-linked structure, the bio-based modified calcium carbonate crosslinking agent is rich in epoxy groups, making it difficult for it to react with a sufficient number of carboxyl groups from PLA and PBAT, resulting in insufficient crosslinking within the filler. Therefore, some bio-based modified calcium carbonate is merely uniformly dispersed in the polymer matrix without participating in the reaction to form a crosslinked network. Upon impact, this may become a defect point, initiating crack propagation and leading to a decrease in the impact strength and elongation at break of the polylactic acid composite material.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and variations without departing from the concept of the present invention, and these modifications all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder, characterized in that, The product is prepared by the following steps: 100 parts PLA, 30-50 parts PBAT, 5-20 parts carboxylated calcium carbonate powder, 5-20 parts bio-based modified calcium carbonate crosslinking agent and 0.1-0.3 parts antioxidant are mixed by mass and then added to a screw extruder for melt granulation to obtain a reinforced and toughened polylactic acid composite material prepared by bio-based modified calcium carbonate powder. The preparation method of the bio-based modified calcium carbonate crosslinking agent includes: S1. Preparation of carboxylated calcium carbonate powder: First, the calcium carbonate powder is dried in an environment of 120~150℃ to remove moisture. Then, by mass, 10 parts of calcium carbonate powder are ultrasonically dispersed in 40~100 parts of ethanol solution, with an ethanol mass fraction of 40%~60%. The mixture is transferred to a reaction vessel and stirred. When the system temperature rises to 50~70℃, 0.4~0.8 parts of bio-based fatty acid are added. The reaction is maintained at this temperature for 1~4 hours. Finally, the sample after reaction is repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain carboxylated calcium carbonate powder. S2. Preparation of bio-based modified calcium carbonate crosslinking agent: 10 parts of carboxylated calcium carbonate powder obtained in step S1 are ultrasonically dispersed in 40-100 parts of ethanol solution, and then 0.8-1.6 parts of bio-based epoxy compound are added. The mixture is stirred at 50-70℃ for 5-10 min. 0.02-0.05 parts of 1,8-diazabicyclo[5.4.0]undec-7-ene are pre-diluted with a small amount of ethanol and then slowly added dropwise to the system. The mixture is stirred for 5-15 min, heated to 80-100℃, and stirred for 4-6 h. The sample after reaction is repeatedly washed with ethanol solution and then transferred to an oven for thorough drying to obtain the bio-based modified calcium carbonate crosslinking agent.

2. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The bio-based fatty acid mentioned in step S1 is one of sebacic acid, azelaic acid, adipic acid, and glutaric acid; the bio-based epoxy compound mentioned in step S2 is one of epoxidized soybean oil, epoxidized linseed oil, and castor oil glycidyl ether.

3. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The density of the PLA is 1.24~1.28 g / L. The melt flow index is 3~6 g / 10min; the density of the PBAT is 1.20~1.24 g / min. The melt flow index is 2.5~4.5 g / 10 min; the antioxidant is one of antioxidants 1026, 626, 1010, 300 or 168.

4. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The mass ratio of the carboxylated calcium carbonate powder to the bio-based modified calcium carbonate crosslinking agent is 0.8~1.

2.

5. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The mass ratio of the carboxylated calcium carbonate powder to the bio-based modified calcium carbonate crosslinking agent is 0.8~1.

2.

6. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The ethanol solution contains 40%-60% ethanol by mass.

7. The method for preparing a reinforced and toughened polylactic acid composite material from bio-based modified calcium carbonate powder according to claim 1, characterized in that, The calcium carbonate powder has a mesh size of 20,000 to 30,000 mesh.

8. A reinforced and toughened polylactic acid composite material prepared from bio-based modified calcium carbonate powder, characterized in that: The reinforced and toughened polylactic acid composite material was prepared using the method for preparing bio-based modified calcium carbonate powder according to any one of claims 1 to 7.

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