Compatilizer for carbon dioxide-based biodegradable mulching film, preparation method of compatilizer, carbon dioxide-based biodegradable mulching film and preparation method of carbon dioxide-based biodegradable mulching film

Abstract

The invention provides a compatilizer for a carbon dioxide-based biodegradable mulching film, a preparation method of the compatilizer, the carbon dioxide-based biodegradable mulching film and a preparation method of the carbon dioxide-based biodegradable mulching film, and belongs to the technical field of biodegradable plastics. The compatilizer comprises a PPC / PLA block copolymer, the PPC / PLA block copolymer can play a unique'molecular bridge 'role in a blending system, and due to the fact that the structure of the PPC / PLA block copolymer has excellent thermodynamic compatibility with PPC and PLA homopolymers, the interfacial tension between the PPC phase and the PLA phase can be remarkably reduced, the interfacial bonding force is enhanced, and transmission of external field stress between the two components is effectively promoted. Performance tests show that the tensile strength of the biodegradable mulching film can reach 23 MPa or above, and the elongation at break reaches 215% or above and can reach 344%.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable plastics technology, specifically relating to a compatibilizer for carbon dioxide-based biodegradable mulch film and its preparation method, and a carbon dioxide-based biodegradable mulch film and its preparation method. Background Technology

[0002] With the development of modern agriculture, plastic mulch films have been widely used due to their excellent properties in retaining moisture, increasing temperature, and suppressing weeds. However, traditional polyethylene (PE) mulch films are difficult to degrade in the natural environment, posing a long-term threat to soil structure, crop growth, and the ecological environment.

[0003] To address this challenge, biodegradable materials have become a hot topic in research and application. Polypropylene carbonate (PPC) is a carbon dioxide-based biodegradable material with excellent toughness and ductility. PPC not only has good film-forming properties but also excellent gas barrier properties (especially against oxygen and water vapor). This characteristic is crucial for maintaining the microenvironment under mulch film and delaying crop root senescence, making it a potential high-performance mulch film substrate. However, PPC also has drawbacks, mainly its low glass transition temperature, poor thermal stability, and insufficient modulus. This causes pure PPC to easily become sticky, soften, and deform during use, and its strength is insufficient to meet the mechanical requirements of agricultural operations, limiting its application alone.

[0004] To improve the performance of polylactic acid (PPC), engineers often blend it with biodegradable materials possessing complementary properties. Polylactic acid (PLA), a widely available biodegradable material with high strength and modulus, exhibits good performance complementarity with PPC. Therefore, the PPC / PLA blend system is considered a potential system for preparing high-performance biodegradable mulch films. However, simple physical blending faces a core challenge: the poor compatibility between PPC and PLA leads to phase separation in the blended material, resulting in weak interfacial bonding. Macroscopically, this prevents the effective combination of PLA's rigidity and PPC's toughness advantages, potentially leading to a decrease in the material's mechanical properties.

[0005] Meanwhile, the process of making mulch film from PPC / PLA blends using biaxial stretching technology faces technical bottlenecks such as poor compatibility leading to film breakage, uneven thickness, and decreased optical performance during stretching. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a compatibilizer for carbon dioxide-based biodegradable mulch films and a method for preparing the same, as well as a carbon dioxide-based biodegradable mulch film and a method for preparing the same. The compatibilizer plays a unique "molecular bridging" role in the blend system, significantly reducing the interfacial tension between the PPC and PLA phases, enhancing interfacial adhesion, and effectively promoting the transfer of external stress between the two components.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a compatibilizer for carbon dioxide-based biodegradable mulch films, the compatibilizer comprising a PPC / PLA block copolymer.

[0009] Preferably, the molar content of PPC segments in the PPC / PLA block copolymer is 75%~95%, and the molar content of PLA segments is 2%~5%.

[0010] Preferably, the PPC / PLA block copolymer has a number-average molecular weight of 80-170 kg / mol and a molecular weight distribution of 1.5-3.5.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned compatibilizer, comprising the following steps:

[0012] A compatibilizer is prepared by copolymerization of carbon dioxide, propylene oxide, and lactide under the action of a catalyst.

[0013] A preferred preparation method includes the following steps:

[0014] a) Polymerization reaction

[0015] In a high-pressure reactor pretreated with anhydrous and oxygen-free materials, a self-made porphyrin aluminum catalyst (removed by freeze-drying), diethyl carbonate, propylene oxide, and lactide were added sequentially in calculated amounts, followed by the introduction of carbon dioxide. The reactor was heated to 65–75°C, and the pressure inside the reactor rose to 6–7 MPa during the reaction. Once the set temperature was reached, timing was started, and the reaction was maintained at 65–75°C for 10–12 hours.

[0016] The 65~75℃ mentioned above can be 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, etc.

[0017] The aforementioned 6~7 MPa can be 6 MPa, 6.2 MPa, 6.5 MPa, 6.8 MPa, or 7 MPa, etc.

[0018] The aforementioned 10~12 h can be 10 h, 10.5 h, 11 h, 11.5 h or 12 h, etc.

[0019] b) Product separation and post-processing

[0020] After the reaction was complete, the reactor was quickly transferred to an ice-water bath, and coolant was introduced through the internal cooling coil to rapidly cool the system to below 40°C. The pressure inside the reactor was slowly released to atmospheric pressure, and then the reactor was opened to remove the mixed product. The product was placed in a vacuum oven and dried at 35–40°C and -0.1–-0.08 MPa for 10 h to remove unreacted propylene oxide and residual carbon dioxide, ultimately yielding the PPC / PLA block copolymer.

[0021] The above-mentioned 35~40℃ can be 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃, etc.

[0022] The range of -0.1 to -0.08 MPa mentioned above can be -0.1 MPa, -0.09 MPa, or -0.08 MPa, etc.

[0023] Thirdly, the present invention provides a carbon dioxide-based biodegradable mulch film, comprising, by weight: 40-60 parts of PPC, 40-60 parts of PLA, and 0.5-2 parts of compatibilizer; wherein the compatibilizer is the compatibilizer involved in the above technical solution.

[0024] Preferably, the PPC has a number-average molecular weight of 80~220 kg / mol and a molecular weight distribution of 2.1~3.2.

[0025] Preferably, the PLA has a number-average molecular weight of 90-200 kg / mol and a molecular weight distribution of 1.5-2.5.

[0026] Preferably, the carbon dioxide-based biodegradable mulch film further includes functional additives.

[0027] Preferably, the functional additives include, but are not limited to, any one or more of ultraviolet absorbers, antioxidants, or inorganic fillers.

[0028] Preferably, the thickness of the carbon dioxide-based biodegradable mulch film is 6~15 μm.

[0029] Fourthly, the present invention provides a method for preparing the above-mentioned carbon dioxide-based biodegradable mulch film, comprising the following steps:

[0030] S1: Mix PPC, PLA and compatibilizer, and then melt-blend, extrude, cool and granulate the resulting mixture in a twin-screw extruder to obtain the material;

[0031] S2: The material is processed into a film to obtain a carbon dioxide-based biodegradable mulch film.

[0032] Preferably, the processing temperature range of the twin-screw extruder is 120~170℃.

[0033] Preferably, the film-forming process includes, but is not limited to, casting and stretching film formation or blow molding film formation.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] This invention first provides a compatibilizer for carbon dioxide-based biodegradable mulch films, comprising a PPC / PLA block copolymer. The PPC / PLA block copolymer plays a unique "molecular bridging" role in the blend system. Due to its excellent thermodynamic compatibility with both PPC and PLA homopolymers, it can significantly reduce the interfacial tension between the PPC and PLA phases, enhance interfacial adhesion, and effectively promote the transfer of external stress between the two components.

[0036] While existing PPC / PBAT compatibilizers can improve the processability of blends, their molecular structures have limited compatibility with PLA, making it difficult to form a strong "bridge" at the PPC-PLA interface. This invention, however, synthesizes a block copolymer containing both PPC and PLA segments, enabling it to interact strongly with both phases when compatibilizing the PPC / PLA system, significantly improving the compatibility and mechanical properties of the blend. This not only provides a new design approach but also offers a superior and more targeted technical solution for the specific application scenario of PPC / PLA mulch films.

[0037] In this invention, under the action of the aforementioned compatibilizer, the initially coarse dispersed phase morphology in the blend system is significantly refined, the dispersed phase size is reduced, and the distribution is more uniform, thereby forming a stable and homogeneous co-continuous structure. This optimization of the microstructure not only overcomes the problems of phase separation and performance instability caused by poor compatibility in simple blends, but also achieves synergy and complementarity of the properties of the PPC and PLA components: while maintaining the high rigidity and strength of the PLA matrix, the excellent toughness of the PPC component is fully introduced, so that the final mulch film has both high tensile strength and good elongation at break.

[0038] Performance tests show that the biodegradable mulch film prepared by this invention has a tensile strength of over 23 MPa and an elongation at break of over 215%, reaching as high as 344%. Compared with the control sample without compatibilizer, its elongation at break and tensile strength are significantly improved. Attached Figure Description

[0039] Figure 1 The hydrogen nuclear magnetic resonance spectrum of the PPC / PLA block copolymer in Example 1 was obtained.

[0040] Figure 2 SEM images of the carbon dioxide-based biodegradable mulch films prepared in Example 1 and Comparative Example 1;

[0041] in, Figure 2 In this context, 'a' corresponds to Example 1. Figure 2 The ratio of b to the corresponding ratio is 1. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] To address the problem of poor mechanical properties in existing PPC / PLA blended mulch films, this invention first provides a compatibilizer for carbon dioxide-based biodegradable mulch films, wherein the compatibilizer comprises a PPC / PLA block copolymer.

[0044] In this invention, the PPC / PLA block copolymer is prepared by copolymerization of carbon dioxide, propylene oxide, and lactide under the action of a bimetallic cyanide complex catalyst.

[0045] The PPC / PLA block copolymer has a number-average molecular weight of 80-170 kg / mol and a molecular weight distribution of 1.5-3.5. Based on the total molar amount of the copolymer, the molar content of PPC segments is 75%-95%, such as 75%, 78%, 80%, 82%, 85%, 88%, 90%, 93%, or 95%, etc.; the molar content of PLA segments is 2%-5%, such as 2%, 3%, 4%, or 5%, etc. Preferably, the PPC / PLA block copolymer has a number-average molecular weight of 90-160 kg / mol and a molecular weight distribution of 1.9-3.3; more preferably, its number-average molecular weight is 100-150 kg / mol and its molecular weight distribution is 2.0-3.0. Regarding the segment composition, preferably, the molar content of PPC segments is 85%-90%, and the molar content of PLA segments is 3%-4%; more preferably, the molar content of PPC segments is 87%-90%, and the molar content of PLA segments is 3.5%-4%.

[0046] This illustrates that the molecular weight distribution of PPC / PLA block copolymers directly affects the regularity of copolymer arrangement and compatibilization effect at the interface. If the molecular weight distribution is too narrow (<1.5), synthesis is extremely difficult and costly, and the overly regular chain segments may lead to insufficient interfacial toughness. Conversely, if the molecular weight distribution is too wide (>3.5), the low molecular weight fraction has a plasticizing effect, while the high molecular weight fraction is prone to self-aggregation, which can damage the interface. For example, using a PPC / PLA block copolymer with a molecular weight distribution of 5.0 as a compatibilizer, the resulting PPC / PLA mulch film has a tensile strength of approximately 17 MPa and an elongation at break of approximately 110%, showing limited performance improvement compared to the film without a compatibilizer (15 MPa, 96%).

[0047] Meanwhile, the segment ratio of the aforementioned PPC / PLA block copolymer (75%~95% PPC, 2%~5% PLA) is the optimal choice after comprehensive consideration in this invention. In this invention, a higher PLA content is beneficial for improving compatibility, but its application in PPC / PLA mulch films faces practical constraints: the synthesis process of high PLA content copolymers is complex, significantly increasing costs, and offering limited additional improvement to the key mechanical properties of the mulch film (e.g., increasing PLA content to 10% only improves mechanical properties by 5%, while increasing costs by 4 times), resulting in low cost-effectiveness. In contrast, the segment ratio specified in this invention effectively achieves molecular interface anchoring and bridging, significantly improving the mechanical properties of the mulch film to meet agricultural requirements; simultaneously, its synthesis route is simpler and more controllable, with significantly optimized costs, laying a solid foundation for the industrialization and promotion of the technology. Therefore, this segment ratio is a proactive optimization based on technological understanding and market orientation, reflecting the practicality and advancement of this invention.

[0048] Based on the above-mentioned compatibilizer, the present invention also provides a carbon dioxide-based biodegradable mulch film, which, by weight, comprises: 40-60 parts of PPC, 40-60 parts of PLA, and 0.5-2 parts of compatibilizer.

[0049] In this invention, the PPC is 40-60 parts by weight, such as 40, 42, 45, 48, 50, 52, 55, 58, or 60 parts. This invention does not impose any special restrictions on the source of the PPC, which can be obtained from the market. The number-average molecular weight of the PPC is preferably 80-220 kg / mol, more preferably 120-220 kg / mol; the molecular weight distribution is 2.1-3.2, more preferably 2.2-3.0; and the melt index is 0.3-1.5 g / 10min, more preferably 0.5-1.0 g / 10min. The melt index is preferably measured at a temperature of 170°C and a weight mass of 2.16 kg. The carbonate content in the molecular chain of the PPC is 88%-99%; and the catalyst residue of the PPC is 1-100 ppm.

[0050] In this invention, the PLA is 40-60 parts by weight, such as 40, 42, 45, 48, 50, 52, 55, 58, or 60 parts. This invention does not impose any special restrictions on the source of the PLA, which can be obtained from the market. The number-average molecular weight of the PLA is 90-200 kg / mol; the molecular weight distribution of the PLA is 1.5-2.5; preferably, the number-average molecular weight of the PLA is 110-200 kg / mol; and the density of the PLA is 1.10-1.40 g / cm³. 3 The PLA has a melt index of 1~12 g / 10 min (190℃), a melting point of 170~180℃, and a glass transition temperature of 50~60℃; the molecular weight distribution of the PLA is 1.5~2.0, more preferably 1.5~1.9; preferably, the density of the PLA is 1.20~1.30 g / cm3, the melt index is 2~12 g / 10 min, and the melt index is measured at a weight of 2.16 kg (190℃).

[0051] In this invention, the compatibilizer is 0.5 to 2 parts, which can be 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, or 2.0 parts, etc.

[0052] It should be noted that in the carbon dioxide-based biodegradable mulch film provided by this invention, in addition to core components such as PPC, PLA, and compatibilizers, various functional additives can be incorporated to customize the final performance of the mulch film according to actual application requirements. For example, ultraviolet absorbers can be added to slow down the photoaging process during outdoor use; antioxidants can be added to inhibit thermo-oxidative degradation during processing and use; or appropriate amounts of inorganic fillers (such as nano-kaolin and calcium carbonate) can be introduced to further enhance the modulus and dimensional stability of the material while reducing costs.

[0053] The types of UV absorbers and antioxidants mentioned above can be selected as needed. For example, the UV absorber can be one or more of UV-326, UV-329, UV-531, UV-570, and UV-9; the antioxidant can be one or more of 1010, 1076, 168, and DSTDP.

[0054] In this invention, the thickness of the carbon dioxide-based biodegradable mulch film can be 6~15 μm, such as 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0055] The present invention also provides a method for preparing the above-mentioned carbon dioxide-based biodegradable mulch film, comprising the following steps:

[0056] S1: Mix PPC, PLA and compatibilizer, and then melt-blend, extrude, cool and granulate the resulting mixture in a twin-screw extruder to obtain the material;

[0057] S2: The material is processed into a film to obtain a carbon dioxide-based biodegradable mulch film.

[0058] According to the present invention, PPC, PLA and compatibilizer are first mixed in the required proportion in a high-speed mixer. The mixture obtained after uniform mixing is melt-blended, extruded, cooled and granulated in a twin-screw extruder to obtain uniform granular material.

[0059] In the twin-screw melt granulation process, the length-to-diameter ratio of the twin screws is preferably (40~52):1, more preferably (45~50):1, and even more preferably 48:1; the processing temperature range of the twin-screw extruder is preferably 120~170℃. In some embodiments of the present invention, the temperature of the twin screws is set as follows: zone 1 120℃, zone 2 125℃, zone 3 135℃, zone 4 150℃, zone 5 150℃, zone 6 150℃, zone 7 165℃, zone 8 165℃, zone 9 170℃, zone 10 170℃, zone 11 145℃, and the die head 140℃.

[0060] After obtaining the above-mentioned uniform granular material, the material is subjected to film-forming treatment according to the present invention to obtain a carbon dioxide-based biodegradable mulch film.

[0061] It should be noted that the film-forming processes involved in this invention include, but are not limited to, casting and stretching film formation or blow molding film formation.

[0062] In some embodiments of the present invention, casting and stretching are preferably employed to form the film. Specifically, the granular material is added to a casting forming device equipped with a 1000-mesh filter, such as a casting machine, and after being melted and plasticized, it is cast into a sheet through a slit head. Subsequently, the sheet enters a biaxial stretching unit, where it undergoes synchronous or stepwise biaxial stretching at a set temperature. In some embodiments of the present invention, the screw unit temperature of the casting machine is set to 150°C in zone one, 160°C in zone two, and 175°C in zone three, while the head unit temperature is 190°C, ultimately yielding the carbon dioxide-based biodegradable mulch film.

[0063] In this invention, the temperature of the screw conveyor unit in the casting machine is 150~180℃, and the temperature of the slit head unit is 180~200℃. In some embodiments of this invention, the temperature of the screw conveyor unit of the casting machine is set to 150℃ in zone one, 160℃ in zone two, and 175℃ in zone three, the temperature of the slit head unit is 190℃, and the front-end filter screen is 1000 mesh.

[0064] In this invention, the biaxial stretching process helps to form a more regular microstructure, which can, to a certain extent, promote the stability of the mulch film's performance during its service life and achieve more controllable degradation behavior in the later stages. All components of the mulch film provided by this invention are completely biodegradable, meeting environmental protection requirements. Furthermore, this invention anticipates that by adjusting the proportions of each component and the stretching process parameters, the degradation cycle, mechanical properties, and durability of the mulch film can be synergistically controlled within a certain range to meet the usage needs of different agronomic conditions, demonstrating broad application prospects in the field of sustainable agricultural development.

[0065] The method for preparing the above-mentioned carbon dioxide-based biodegradable mulch film provided by the present invention can significantly improve the mechanical properties of the mulch film by adding PPC / PLA block copolymer as a compatibilizer.

[0066] The equipment used in the above preparation methods are all commercially available general-purpose equipment, which are simple and convenient to operate, easy to implement, and conducive to large-scale production.

[0067] The present invention conducted performance tests on the obtained mulch film. The test results show that the tensile strength of the mulch film obtained in the corresponding embodiment is above 23 MPa, and the elongation at break is above 215%. The results indicate that the compatibilizer provided by the present invention effectively enhances the interfacial adhesion between the PPC and PLA phases, enabling the blend to withstand higher loads. Simultaneously, the addition of the compatibilizer greatly improves the toughness of the material, allowing it to undergo greater deformation before fracture, fundamentally overcoming the brittleness of simple blends.

[0068] In summary, the compatibilizer innovatively proposed in this invention, with its excellent thermodynamic compatibility with PPC and PLA homopolymers, acts as a "molecular bridge" to effectively inhibit phase separation, achieving synergistic and complementary properties of the two components. This allows the mulch film to retain the rigidity and strength of PLA while fully absorbing the toughness of PPC. Finally, through a biaxial stretching process, the mulch film is further endowed with both high tensile strength and high elongation at break, resulting in a high-performance carbon dioxide-based biodegradable mulch film.

[0069] To further illustrate the present invention, the following examples provide a detailed description. The PPC used in the following examples was purchased from Huafeng Chemical Co., Ltd.; PLA was purchased from Pulis Biotechnology Co., Ltd.; and the PPC / PLA copolymer compatibilizer was synthesized by our company. In the following examples, the aspect ratio of the twin-screw is 48:1, and the aspect ratio of the inner and outer conveying screws of the casting machine is 48.

[0070] Preparation Example 1

[0071] In this preparation example, the specific preparation process of the PPC / PLA block copolymer is as follows:

[0072] a) Polymerization reaction

[0073] In a 5000 mL high-pressure reactor that had undergone anhydrous and oxygen-free pretreatment, 4 g of a self-made porphyrin aluminum system catalyst (prepared by freeze-drying to remove solvent, see reference: Liehang Yang, et al. Macromolecules, 2024, 57(1), 150–161.), 1500 mL of diethyl carbonate, 1500 mL of propylene oxide, and 30 g of lactide were added sequentially, followed by the introduction of 2100 g of carbon dioxide. The reactor was heated to 70 °C, and the pressure inside the reactor reached a maximum of 7 MPa during the reaction. Once the set temperature was reached, the timer was started, and the reaction was maintained at 70 °C for 12 h.

[0074] b) Product separation and post-processing

[0075] After the reaction was complete, the reactor was quickly transferred to an ice-water bath, and coolant was introduced through the internal cooling coil to rapidly cool the system to below 40°C. The pressure inside the reactor was slowly released to atmospheric pressure, and then the reactor was opened to remove the mixed product. The product was placed in a vacuum oven and dried at 40°C and -0.1 MPa for 10 h to remove unreacted propylene oxide and residual carbon dioxide, ultimately yielding a PPC / PLA block copolymer. Analysis showed that the copolymer contained 88.2% PPC segments, 3.5% PLA segments, had a number-average molecular weight of 130 kg / mol, and a molecular weight distribution of 3.1.

[0076] Preparation Example 2

[0077] a) Polymerization reaction

[0078] In a 5000 mL high-pressure reactor pretreated with anhydrous and oxygen-free materials, 3.7 g of a self-made porphyrin aluminum system catalyst (freeze-dried to remove solvent), 1500 mL of diethyl carbonate, 1500 mL of propylene oxide, and 25 g of lactide were added sequentially, followed by the introduction of 2100 g of carbon dioxide. The reactor was heated to 70 °C, and the pressure inside the reactor reached a maximum of 7 MPa during the reaction. Timing was started after the set temperature was reached, and the reaction was maintained at 70 °C for 12 h.

[0079] b) Product separation and post-processing

[0080] After the reaction was complete, the reactor was quickly transferred to an ice-water bath, and coolant was introduced through the internal cooling coil to rapidly cool the system to below 40°C. The pressure inside the reactor was slowly released to atmospheric pressure, and then the reactor was opened, and the mixed product was removed. The product was placed in a vacuum oven and dried at 40°C and -0.1 MPa for 10 h to remove unreacted propylene oxide and residual carbon dioxide, finally yielding a PPC / PLA block copolymer. Analysis showed that the copolymer had a number-average molecular weight of 100 kg / mol, a molecular weight distribution of 3.0, a PPC segment molar content of 87.1%, and a PLA segment molar content of 3.0%.

[0081] Preparation Example 3

[0082] a) Polymerization reaction

[0083] In a 5000 mL high-pressure reactor pretreated with anhydrous and oxygen-free materials, 4.3 g of a self-made porphyrin aluminum system catalyst (freeze-dried to remove solvent), 1500 mL of diethyl carbonate, 1500 mL of propylene oxide, and 35 g of lactide were added sequentially, followed by the introduction of 2100 g of carbon dioxide. The reactor was heated to 70 °C, and the pressure inside the reactor reached a maximum of 7 MPa during the reaction. Timing was started after the set temperature was reached, and the reaction was maintained at 70 °C for 12 h.

[0084] b) Product separation and post-processing

[0085] After the reaction was complete, the reactor was quickly transferred to an ice-water bath, and coolant was introduced through the internal cooling coil to rapidly cool the system to below 40°C. The pressure inside the reactor was slowly released to atmospheric pressure, and then the reactor was opened, and the mixed product was removed. The product was placed in a vacuum oven and dried at 40°C and -0.1 MPa for 10 h to remove unreacted propylene oxide and residual carbon dioxide, finally yielding a PPC / PLA block copolymer. Analysis showed that the copolymer had a number-average molecular weight of 120 kg / mol, a molecular weight distribution of 1.7, a PPC segment molar content of 89.0%, and a PLA segment molar content of 4.0%.

[0086] Example 1

[0087] This embodiment provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0088] Take 2 kg of PPC with a number-average molecular weight of 190 kg / mol, a molecular weight distribution of 2.5, a carbonate content of 89%, a catalyst residue of 10 ppm, and a melt index of 0.5 g / 10 min; take 1.3 kg of PPC with a number-average molecular weight of 180 kg / mol, a molecular weight distribution of 1.6, and a density of 1.2 g / cm³. 3PLA with a melt index of 7 g / 10 min (190℃), a melting point of 173℃, and a glass transition temperature of 55℃; and 0.03 kg of a compatibilizer with a number-average molecular weight of 130 kg / mol, a molecular weight distribution of 3.1, a PPC segment molar content of 88.2%, and a PLA segment molar content of 3.5% (Preparation Example 1). The above raw materials were mixed evenly in a mixer, and then granulated in a twin-screw extruder to prepare granular material. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granular material was then added to a casting machine equipped with a biaxial stretching unit to prepare a biodegradable mulch film. The screw unit temperature of the casting machine is set to 150℃ in zone one, 160℃ in zone two, and 175℃ in zone three; the die head unit temperature is 190℃; and the front-end filter screen is 1000 mesh. The performance test results for the mulch film are shown in Table 1, and the test standard refers to GB / T 1040.2-2006.

[0089] Example 2

[0090] This embodiment provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0091] Take 2 kg of PPC with a number-average molecular weight of 180 kg / mol, a molecular weight distribution of 2.8, a carbonate content of 90%, a catalyst residue of 20 ppm, and a melt index of 0.8 g / 10 min; take 2.95 kg of PPC with a number-average molecular weight of 200 kg / mol, a molecular weight distribution of 1.6, and a density of 1.3 g / cm³. 3 PLA with a melt index of 6 g / 10 min (190℃), a melting point of 175℃, and a glass transition temperature of 56℃; and 0.05 kg of a compatibilizer with a number-average molecular weight of 100 kg / mol, a molecular weight distribution of 3.0, a PPC segment molar content of 87.1%, and a PLA segment molar content of 3.0% (Preparation Example 2). The above raw materials were mixed evenly in a mixer, and then granulated in a twin-screw extruder to prepare granular material. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granular material was then added to a casting machine equipped with a biaxial stretching unit to prepare a biodegradable mulch film. The screw unit temperature of the casting machine is set to 150℃ in zone one, 160℃ in zone two, and 175℃ in zone three; the die head unit temperature is 190℃; and the front-end filter screen is 1000 mesh. The performance test results for the mulch film are shown in Table 1, and the test standard refers to GB / T 1040.2-2006.

[0092] Example 3

[0093] This embodiment provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0094] Take 2 kg of PPC with a number-average molecular weight of 170 kg / mol, a molecular weight distribution of 2.8, a carbonate content of 93%, a catalyst residue of 40 ppm, and a melt index of 1.2 g / 10 min; take 1.96 kg of PPC with a number-average molecular weight of 175 kg / mol, a molecular weight distribution of 1.9, and a density of 1.35 g / cm³. 3 PLA with a melt index of 5.7 g / 10 min (190℃), a melting point of 177℃, and a glass transition temperature of 56.5℃ was prepared; 0.04 kg of a compatibilizer with a number-average molecular weight of 120 kg / mol, a molecular weight distribution of 1.7, a PPC segment molar content of 89.0%, and a PLA segment molar content of 4.0% (Preparation Example 3) was also prepared. The above raw materials were mixed evenly in a mixer, and then granulated in a twin-screw extruder to prepare granular material. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granular material was then added to a casting machine equipped with a biaxial stretching unit to prepare a biodegradable mulch film. The screw unit temperature of the casting machine is set to 150℃ in zone one, 160℃ in zone two, and 175℃ in zone three; the die head unit temperature is 190℃; and the front-end filter screen is 1000 mesh. The performance test results for the mulch film are shown in Table 1, and the test standard refers to GB / T 1040.2-2006.

[0095] Comparative Example 1

[0096] This comparative example provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0097] Take 2 kg of PPC with a number-average molecular weight of 190 kg / mol, a molecular weight distribution of 2.5, a carbonate content of 89%, a catalyst residue of 10 ppm, and a melt index of 0.5 g / 10 min; take 1.3 kg of PPC with a number-average molecular weight of 180 kg / mol, a molecular weight distribution of 1.6, and a density of 1.2 g / cm³. 3PLA with a melt index of 7 g / 10 min (190℃), a melting point of 173℃, and a glass transition temperature of 55℃ was prepared. The raw materials were mixed evenly in a mixer, then granulated in a twin-screw extruder to produce granular material. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granular material was then fed into a casting machine equipped with a biaxial stretching unit to prepare biodegradable mulch film. The casting machine screw unit temperatures were set as follows: Zone 1: 150℃, Zone 2: 160℃, Zone 3: 175℃, Die Head unit temperature: 190℃, and front-end filter screen: 1000 mesh. The performance of the plastic film is shown in Table 1, and the testing standard refers to GB / T 1040.2-2006.

[0098] Comparative Example 2

[0099] This comparative example provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0100] Take 2 kg of PPC with a number-average molecular weight of 180 kg / mol, a molecular weight distribution of 2.8, a carbonate content of 90%, a catalyst residue of 20 ppm, and a melt index of 0.8 g / 10 min; take 2.95 kg of PPC with a number-average molecular weight of 200 kg / mol, a molecular weight distribution of 1.6, and a density of 1.3 g / cm³. 3 PLA with a melt index of 6 g / 10 min (190℃), a melting point of 175℃, and a glass transition temperature of 56℃ was prepared. The raw materials were mixed evenly in a mixer, then granulated in a twin-screw extruder to produce granular material. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granular material was then fed into a casting machine equipped with a biaxial stretching unit to prepare a biodegradable mulch film. The casting machine screw unit temperatures were set as follows: Zone 1: 150℃, Zone 2: 160℃, Zone 3: 175℃, Die Head unit temperature: 190℃, and the front-end filter screen was 1000 mesh. The performance of the plastic film is shown in Table 1, and the testing standard refers to GB / T 1040.2-2006.

[0101] Comparative Example 3

[0102] This embodiment provides a carbon dioxide-based biodegradable mulch film, the preparation method of which is as follows:

[0103] Take 2 kg of PPC with a number-average molecular weight of 170 kg / mol, a molecular weight distribution of 2.8, a carbonate content of 93%, a catalyst residue of 40 ppm, and a melt index of 1.2 g / 10 min; take 1.96 kg of PPC with a number-average molecular weight of 175 kg / mol, a molecular weight distribution of 1.9, and a density of 1.35 g / cm³. 3 PLA with a melt index of 5.7 g / 10 min (190℃), a melting point of 177℃, and a glass transition temperature of 56.5℃ was prepared. The raw materials were mixed evenly in a mixer, then fed into a twin-screw extruder for granulation. The twin-screw extruder temperatures were set as follows: Zone 1: 120℃, Zone 2: 125℃, Zone 3: 135℃, Zone 4: 150℃, Zone 5: 150℃, Zone 6: 150℃, Zone 7: 165℃, Zone 8: 165℃, Zone 9: 170℃, Zone 10: 170℃, Zone 11: 145℃, and Die Head: 140℃. The granulated material was then fed into a casting machine equipped with a biaxial stretching unit to prepare a biodegradable mulch film. The casting machine screw unit temperatures were set as follows: Zone 1: 150℃, Zone 2: 160℃, Zone 3: 175℃, Die Head unit temperature: 190℃, and the front-end filter screen was 1000 mesh. The performance of the plastic film is shown in Table 1, and the testing standard refers to GB / T 1040.2-2006.

[0104] In this invention, the corresponding test standards for the carbon dioxide-based biodegradable mulch film prepared in the examples and the carbon dioxide-based biodegradable mulch film prepared in the comparative examples are all in accordance with GB / T 1040.2-2006.

[0105] The test results are shown in Table 1 below:

[0106] Table 1

[0107]

[0108] Table 1 lists the test results of tensile strength and elongation at break for the examples and comparative examples. The results show that the tensile strength of all examples (23.72~24.17 MPa) is significantly higher than that of the comparative examples (14.96~16.32 MPa). In terms of average tensile strength, the present invention increases the tensile strength from approximately 15.47 MPa in the comparative examples to approximately 24.00 MPa in the examples, an increase of approximately 55%. The results indicate that the compatibilizer provided by the present invention effectively enhances the interfacial adhesion between the PPC and PLA phases, enabling the blend to withstand higher loads.

[0109] Meanwhile, the elongation at break of the embodiments (215.33%~344.86%) far exceeded that of the comparative examples (89.13%~102.51%). In terms of average elongation at break, the present invention increased from approximately 95.99% in the comparative example to approximately 275.54% in the embodiments, an increase of approximately 187%. This result fully demonstrates that the compatibilizer (hydrogen NMR spectrum as shown in the figure) is effective. Figure 1 The addition of (Example 1) greatly improves the toughness of the material, enabling it to undergo greater deformation before fracture, thus fundamentally overcoming the brittle weakness of simple blends.

[0110] It should be noted that the significant differences in data between the above embodiments and comparative examples are fundamentally due to the "molecular bridging" effect of the core component of this invention—the PPC / PLA copolymer compatibilizer. In the comparative examples, due to the lack of this compatibilizer, the interface between the PPC and PLA phases is clear, and the adhesion is weak (SEM images as shown). Figure 2 In example b (Comparative Example 1), stress cannot be effectively transferred, and cracks easily form and propagate rapidly at micro-defects, resulting in low strength and high brittleness. However, in the embodiments of this invention, the compatibilizer, through its special molecular structure, anchors itself at the interface between the two phases, greatly enhancing interfacial compatibility, promoting the refinement of the dispersed phase and the formation of a stable co-continuous structure (SEM image as shown). Figure 2 (as in Example 1), thereby achieving a synergistic improvement in strength and toughness on a macroscopic level.

[0111] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compatibilizer for carbon dioxide-based biodegradable mulch films, characterized in that, The compatibilizer includes a PPC / PLA block copolymer.

2. The compatibilizer according to claim 1, characterized in that, The PPC / PLA block copolymer has a PPC segment molar content of 75% to 95% and a PLA segment molar content of 2% to 5%.

3. The compatibilizer according to claim 1 or 2, characterized in that, The PPC / PLA block copolymer has a number-average molecular weight of 80-170 kg / mol and a molecular weight distribution of 1.5-3.

5.

4. A method for preparing a compatibilizer as described in any one of claims 1 to 3, characterized in that, Includes the following steps: A compatibilizer is prepared by copolymerization of carbon dioxide, propylene oxide, and lactide under the action of a catalyst.

5. A carbon dioxide-based biodegradable mulch film, characterized in that, By weight, it includes: 40-60 parts PPC, 40-60 parts PLA, and 0.5-2 parts compatibilizer; The compatibilizer is any one of the compatibilizers according to claims 1 to 3 or the compatibilizer prepared by the preparation method according to claim 4.

6. The carbon dioxide-based biodegradable mulch film according to claim 5, characterized in that, The PPC has a number-average molecular weight of 80-220 kg / mol and a molecular weight distribution of 2.1-3.

2. The PLA has a number-average molecular weight of 90-200 kg / mol and a molecular weight distribution of 1.5-2.

5.

7. The carbon dioxide-based biodegradable mulch film according to claim 5 or 6, characterized in that, The carbon dioxide-based biodegradable mulch film also includes functional additives; The functional additives include, but are not limited to, any one or more of ultraviolet absorbers, antioxidants, or inorganic fillers; The thickness of the carbon dioxide-based biodegradable mulch film is 6~15 μm.

8. A method for preparing a carbon dioxide-based biodegradable mulch film as described in any one of claims 5 to 7, characterized in that, Includes the following steps: S1: Mix PPC, PLA and compatibilizer, and then melt-blend, extrude, cool and granulate the resulting mixture in a twin-screw extruder to obtain the material; S2: The material is processed into a film to obtain a carbon dioxide-based biodegradable mulch film.

9. The preparation method according to claim 8, characterized in that, The processing temperature range of the twin-screw extruder is 120~170℃.

10. The preparation method according to claim 8 or 9, characterized in that, The film-forming process includes, but is not limited to, casting and stretching film formation or blow molding film formation.

Images