A hydrophobic and biodegradable polylactic acid cast film and its preparation method

Abstract

This invention discloses a hydrophobic and biodegradable polylactic acid (PLA) cast film and its preparation method, belonging to the field of PLA film technology. The raw materials of the hydrophobic and biodegradable PLA cast film include the following components: 88-92 parts PLA, 8-12 parts poly(butylene terephthalate-adipate), 0.8-1.2 parts reinforcing agent, 0.3-0.8 parts compatibilizer, 2.5-3.5 parts toughening agent, and 0.2-0.5 parts antioxidant; wherein the reinforcing agent is obtained by modifying nano-titanium dioxide with n-octane bromide. The preparation method provided by this invention is simple to operate and suitable for industrial production. The resulting hydrophobic and biodegradable PLA cast film has high mechanical strength and elongation at break, while also possessing good hydrophobic properties. Furthermore, this film material is entirely made of biodegradable polymer materials, conforming to the current trend of green and environmentally friendly development, and providing an effective way to solve the environmental problems caused by traditional film products.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid (PLA) film technology. Specifically, it relates to a hydrophobic and biodegradable PLA cast film and its preparation method. Background Technology

[0002] The widespread use of traditional petroleum-based plastics has led to severe "white pollution," placing immense pressure on the ecological environment. Developing biodegradable polymers has become a global research hotspot in the materials science field. Polylactic acid (PLA), as a typical bio-based biodegradable polymer, is considered one of the ideal materials to replace traditional petroleum-based plastics due to its excellent biocompatibility, biodegradability, and renewability.

[0003] Polylactic acid (PLA) has a highly regular molecular chain structure, resulting in a densely packed chain segment arrangement that imparts a certain tensile strength to the material. However, its rigid molecular chains and low mobility lead to high brittleness and low elongation at break. Polybutylene terephthalate (PBAT) is a well-balanced, biodegradable, and environmentally friendly plastic with good flexibility and ductility, achieving an elongation at break of up to 500%. Currently, blending PLA with PBAT to improve the flexibility and elongation of PLA is one of the mainstream technical routes for developing biodegradable materials and achieving complementary properties. However, PLA and PBAT differ significantly in molecular structure and polarity, resulting in poor thermodynamic compatibility during melt blending and a tendency for phase separation. This limits the toughening effect and may cause an imbalance between strength and toughness, making it difficult to obtain high-performance blends. Furthermore, PLA's poor hydrophobic properties lead to insufficient self-cleaning ability and a tendency to cause membrane fouling, thus limiting its application range.

[0004] Therefore, how to effectively improve the elongation at break while ensuring mechanical strength, achieve a balance of "strong and tough" mechanical properties, and at the same time have good hydrophobic properties, is a technical problem that urgently needs to be solved in the field of polylactic acid film technology. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a hydrophobic and biodegradable polylactic acid cast film and its preparation method, which can improve the mechanical strength and elongation at break of the polylactic acid film, while also having good hydrophobic properties.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A hydrophobic and biodegradable polylactic acid cast film, comprising the following components by weight: 88-92 parts polylactic acid (PLA), 8-12 parts polybutylene terephthalate (PBAT), 0.8-1.2 parts reinforcing agent, 0.3-0.8 parts compatibilizer, 2.5-3.5 parts toughening agent, and 0.2-0.5 parts antioxidant; wherein the reinforcing agent is prepared by modifying nano-titanium dioxide with n-octane bromide.

[0008] PLA molecular chains are highly polar, while PBAT molecular chains contain long aliphatic flexible segments and aromatic rigid side groups, resulting in overall weaker polarity. This difference in polarity leads to thermodynamic incompatibility and high interfacial tension during melt blending. In the above scheme, by adding reinforcing agents, nano-titanium dioxide can act as a heterogeneous nucleating agent for PLA, improving crystallinity and crystallization rate, and refining grain size, which helps to enhance the strength and toughness of the material. Modifying nano-titanium dioxide with bromooctane introduces hydrophobic segments, enabling it to bond well with the hydrophobic PBAT matrix. The nano-titanium dioxide acts as an intermediate "bridge," effectively improving the compatibility and interfacial bonding between PLA and PBAT, ensuring a dual improvement in both strength and toughness in mechanical properties. In addition, the carbon chains introduced by bromooctane can achieve hydrophobic treatment, improving hydrophobic properties and preventing the formation of hydrophobic defects in the nano-titanium dioxide, which serves as a connection site. Through the synergistic effect of multiple mechanisms of PLA, PBAT, and reinforcing agents, the strength and toughness are significantly improved while maintaining hydrophobic properties, thus enhancing the overall performance of the composite material.

[0009] Furthermore, the preparation method of the reinforcing agent is as follows:

[0010] A1. By weight, add 10 parts of nano titanium dioxide to 80-150 parts of anhydrous ethanol, stir evenly, heat to 50-60℃, add 0.08-0.12 parts of triethylamine, stir for 2-5 minutes to obtain a premixed solution;

[0011] A2. Add a mixture of 1-2 parts of bromooctane and 0.1-0.2 parts of tetraethoxysilane dropwise to the premixed solution, heat to 70-80℃, stir for 3-5 hours, cool, filter, wash with ethanol and deionized water, filter under vacuum, and dry to obtain the reinforcing agent.

[0012] In the above scheme, grafting modification of anionic active sites with n-octane bromide gives the modified nano-titanium dioxide strong polarity and good hydrophobic properties. The addition of the crosslinking agent tetraethoxysilane can simultaneously modify the surface of the nano-titanium dioxide, making it uniformly dispersed, and giving the long-chain structure of n-octane bromide high crosslinking activity. It can form a complex and dense network structure between PLA and PBAT, so that the nanoparticles form "fishing net nodes" in the polyester matrix, supporting and connecting the entire material. At the same time, it can also act as elastic buffer sites to achieve a rigid-elastic combination, ultimately forming a continuous three-dimensional network structure that runs through the entire material, effectively improving the mechanical properties of the material.

[0013] Furthermore, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2.

[0014] In the above scheme, antioxidant 1010 can achieve slow oxidative degradation during long-term storage and use, while antioxidant 168 can improve thermal stability. In high-temperature melting and heat treatment, it strongly inhibits melt yellowing and molecular chain degradation caused by thermal oxidation, ensuring the processing stability and initial performance of the film. Through the combined use of antioxidant 1010 and antioxidant 168, a complete and efficient antioxidant system can be constructed for PLA.

[0015] A method for preparing a hydrophobic and biodegradable polylactic acid (PLA) cast film, used to prepare the hydrophobic and biodegradable PLA cast film described above, includes the following steps:

[0016] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0017] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0018] S3. Add polylactic acid composite masterbatch to the casting machine, control the temperature of each temperature control zone, and after melting, extrude it from the die head position for casting, cooling, and winding to obtain a hydrophobic and biodegradable polylactic acid cast film.

[0019] By premixing polybutylene terephthalate (PBAT) with compatibilizers and reinforcing agents, the reinforcing agents are pre-anchored to the PBAT polymer matrix, forming a preliminary adhesive system. This makes PBAT easier to "tear apart," providing conditions for PLA to be uniformly dispersed in PBAT. This avoids excessive aggregation and phase separation tendencies during direct blending, thereby obtaining a uniform and continuous blended adhesive system and effectively improving the mechanical properties of the material.

[0020] Furthermore, in step S3: during the casting to winding process, when the cast material passes through the casting roll, the temperature of the casting roll is 50-60℃.

[0021] In conventional casting processes, the cooling rate often exceeds the crystallization rate, resulting in some amorphous (glassy) material remaining in the film. The glass transition temperature (Tg) of this amorphous PLA is approximately 55-65°C. By controlling the casting roll temperature to 50-60°C, heat treatment of the film material can be achieved, optimizing the amorphous morphology and inducing crystallization. Simultaneously, it promotes the transformation of the amorphous state around the modified titanium dioxide into "flat" fine crystals, forming dense and strong "rivets" at the interface between PLA and PBAT, strengthening the bonding interface and achieving multiple functions such as reinforcement and nucleation. Utilizing the synergistic effect of the roll temperature design and the modified titanium dioxide, the phase separation problem caused by excessively rapid cooling during the casting of blended films is completely solved, effectively improving the mechanical properties of the blended material.

[0022] Furthermore, in step S3: during the casting to winding process, the surface of the casting roller has a micro-nano-scale rough structure.

[0023] When the film passes through a casting roller (50-60℃) with a surface roughened structure, the film can be roughened during the heat treatment process to obtain a film with uniform structure and good hydrophobic properties.

[0024] Further, in step S3: during the casting to winding process, when passing through the casting roller, a nano silica dispersion with a concentration of 0.3-1wt% is sprayed on the surface of the cast material.

[0025] In the above scheme, silica particles can be deposited on the film surface to form a roughened structure, giving the film certain hydrophobic properties. At the same time, due to the presence of modified nano-titanium dioxide in the polyester matrix, a bonding effect is formed with nano-silica, which can improve the dispersion performance of silica and enhance its adhesion to the film surface, further improving the hydrophobic properties of the film.

[0026] Furthermore, the solvent for the nano-silica dispersion is ethanol, and the particle size range of the nano-silica is 80-300 nm.

[0027] Furthermore, the thickness of the hydrophobic biodegradable polylactic acid cast film is 0.01-0.1 mm.

[0028] In the above scheme, the thickness of the hydrophobic biodegradable polylactic acid cast film is controlled to be 0.01-0.1 mm, which can achieve good processing performance and mechanical strength, and can withstand the physical or chemical effects during the roughening process, thus ensuring the film's formability, strength and reliability of subsequent processing.

[0029] In the above scheme, the roller temperature (50-60℃) can make the ethanol evaporate quickly, allowing the nano-silica to quickly adhere to the film surface. At the same time, the rapid evaporation of the solvent will cause the film to shrink slightly, which will have a certain intercalation effect on the nano-silica, making the nano-silica particles form a denser and more stable arrangement on the film surface, further improving the hydrophobic properties of the film.

[0030] Furthermore, the temperature control parameters for each temperature range of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 195-205℃, and the temperature of barrel 1 and barrel 2 is 185-195℃.

[0031] The technical solution of the present invention achieves the following beneficial technical effects:

[0032] 1. This invention, by adding reinforcing agents, allows nano-titanium dioxide to act as a heterogeneous nucleating agent for PLA, improving crystallinity and crystallization rate, and refining grain size, thus contributing to enhanced strength and toughness of the material. Modification of nano-titanium dioxide with n-octane introduces hydrophobic segments, enabling good bonding between it and the hydrophobic PBAT matrix. Nano-titanium dioxide acts as an intermediate "bridge," effectively improving the compatibility and interfacial bonding between PLA and PBAT, ensuring a dual improvement in both strength and toughness in mechanical properties. Furthermore, the carbon chains introduced by n-octane achieve hydrophobicity treatment, improving hydrophobic properties and preventing the formation of hydrophobic defects in nano-titanium dioxide, which serves as a bonding site. Through the synergistic effect of multiple mechanisms involving PLA, PBAT, and reinforcing agents, while maintaining hydrophobic properties, strength and toughness are significantly improved, enhancing the overall performance of the composite material.

[0033] 2. This invention modifies the surface of nano-titanium dioxide by grafting n-octane bromide, supplemented by the crosslinking agent tetraethoxysilane. The modified nano-titanium dioxide acts as a heterogeneous nucleating agent for PLA, refining grain size and improving crystallinity. The hydrophobic long chains grafted onto its surface bond well with the PBAT matrix, constructing an effective "bridge" between PLA and PBAT. This significantly improves the thermodynamic incompatibility caused by their polarity difference, effectively suppressing phase separation. Simultaneously, the crosslinking network structure promoted by tetraethoxysilane allows the nanoparticles to form "fishing net nodes"-like support and connections within the polyester matrix, providing elastic buffering and achieving a rigid-elastic three-dimensional network structure. This effectively improves the tensile strength and elongation at break of the material, achieving a "strong and tough" mechanical balance.

[0034] 3. During the casting stage, precisely controlling the casting roller temperature to 50-60℃, which is close to the glass transition temperature of PLA, enables heat treatment of the film material, optimizes the amorphous structure, induces crystallization, and promotes the formation of "flat" fine microcrystals around the modified titanium dioxide. These microcrystals cause the nano-titanium dioxide to form "rivets" at the PLA-PBAT interface, strengthening the interfacial bonding and effectively improving the phase separation problem that may be caused by excessively rapid cooling. Furthermore, spraying a specific concentration of nano-silica dispersion onto the surface of the cast material and using the roller temperature to rapidly evaporate the solvent ethanol causes the nano-silica particles to form a stable and tightly packed roughened structure on the film surface. The modified nano-titanium dioxide in the polyester matrix forms bonds with the surface nano-silica, further improving the adhesion of nano-silica to the film surface, thus significantly enhancing the hydrophobic properties of the film. This gives the material excellent mechanical properties as well as good self-cleaning ability, expanding its application prospects. Detailed Implementation

[0035] Example 1

[0036] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 90 parts polylactic acid, 10 parts polybutylene terephthalate (PET), 1.0 part reinforcing agent, 0.5 parts compatibilizer (BASF ADR-4468), 3.0 parts toughening agent (Jindaquan A-6649), and 0.3 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0037] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0038] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0039] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm. During the casting to winding process, when the cast material passes through the casting roller, a nano silica dispersion with a concentration of 0.5wt% is sprayed on the surface of the cast material. The temperature of the casting roller is 55℃.

[0040] The preparation method of the reinforcing agent is as follows:

[0041] A1. By weight, add 10 parts of nano titanium dioxide to 100 parts of anhydrous ethanol, stir evenly, heat to 55°C, add 0.10 parts of triethylamine, stir for 3 min, and obtain a premixed solution.

[0042] A2. A mixture of 1.5 parts of bromooctane and 0.15 parts of tetraethoxysilane was added dropwise to the premixed solution, heated to 75°C, stirred for 4 hours, cooled, filtered, washed with ethanol and deionized water, filtered under vacuum, and dried to obtain the reinforcing agent.

[0043] Example 2

[0044] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 88 parts polylactic acid, 12 parts polybutylene terephthalate (PET), 0.8 parts reinforcing agent, 0.3 parts compatibilizer (BASF ADR-4468), 2.5 parts toughening agent (Jindaquan A-6649), and 0.2 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0045] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0046] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0047] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm. Among them, during the casting to winding process, when the cast material passes through the casting roller, the temperature of the casting roller is 60℃, and the surface of the casting roller has a micro-nano-level rough structure.

[0048] The preparation method of the reinforcing agent is as follows:

[0049] A1. By weight, add 10 parts of nano titanium dioxide to 80 parts of anhydrous ethanol, stir evenly, heat to 50°C, add 0.08 parts of triethylamine, stir for 5 min, and obtain a premixed solution;

[0050] A2. A mixture of 1 part bromooctane and 0.1 part tetraethoxysilane was added dropwise to the premixed solution, heated to 70°C, stirred for 5 hours, cooled, filtered, washed with ethanol and deionized water, filtered under vacuum, and dried to obtain the reinforcing agent.

[0051] Example 3

[0052] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 92 parts polylactic acid, 8 parts polybutylene terephthalate (PET), 1.2 parts reinforcing agent, 0.8 parts compatibilizer (BASF ADR-4468), 3.5 parts toughening agent (Jindaquan A-6649), and 0.5 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0053] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0054] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0055] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm. During the casting to winding process, when the cast material passes through the casting roller, a nano silica dispersion with a concentration of 0.3wt% is sprayed on the surface of the cast material. The temperature of the casting roller is 60℃.

[0056] The preparation method of the reinforcing agent is as follows:

[0057] A1. By weight, add 10 parts of nano titanium dioxide to 150 parts of anhydrous ethanol, stir evenly, heat to 60°C, add 0.12 parts of triethylamine, stir for 2 min, and obtain a premixed solution.

[0058] A2. A mixture of 2 parts of bromooctane and 0.2 parts of tetraethoxysilane was added dropwise to the premixed solution, heated to 80°C, stirred for 3 hours, cooled, filtered, washed with ethanol and deionized water, filtered under vacuum, and dried to obtain the reinforcing agent.

[0059] Example 4

[0060] The only difference between this embodiment and Embodiment 1 is that the casting roller is not heated, as detailed below:

[0061] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 90 parts polylactic acid, 10 parts polybutylene terephthalate (PET), 1.0 part reinforcing agent, 0.5 parts compatibilizer (BASF ADR-4468), 3.0 parts toughening agent (Jindaquan A-6649), and 0.3 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0062] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0063] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0064] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm. During the casting to winding process, when the cast material passes through the casting roller, a nano silica dispersion with a concentration of 0.5wt% is sprayed on the surface of the cast material. The temperature of the casting roller is room temperature 22℃.

[0065] The preparation method of the reinforcing agent is as follows:

[0066] A1. By weight, add 10 parts of nano titanium dioxide to 100 parts of anhydrous ethanol, stir evenly, heat to 55°C, add 0.10 parts of triethylamine, stir for 3 min, and obtain a premixed solution.

[0067] A2. A mixture of 1.5 parts of bromooctane and 0.15 parts of tetraethoxysilane was added dropwise to the premixed solution, heated to 75°C, stirred for 4 hours, cooled, filtered, washed with ethanol and deionized water, filtered under vacuum, and dried to obtain the reinforcing agent.

[0068] Comparative Example 1

[0069] The only difference between this comparative example and Example 1 is that the reinforcing agent is nano-titanium dioxide, as detailed below:

[0070] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 90 parts polylactic acid, 10 parts polybutylene terephthalate (PET), 1.0 part nano-titanium dioxide, 0.5 parts compatibilizer (BASF ADR-4468), 3.0 parts toughening agent (Jindaquan A-6649), and 0.3 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0071] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0072] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0073] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm. During the casting to winding process, when the cast material passes through the casting roller, a nano silica dispersion with a concentration of 0.5wt% is sprayed on the surface of the cast material. The temperature of the casting roller is 55℃.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that, during the casting process, the nano-silica dispersion was not sprayed, as detailed below:

[0076] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 90 parts polylactic acid, 10 parts polybutylene terephthalate (PET), 1.0 part reinforcing agent, 0.5 parts compatibilizer (BASF ADR-4468), 3.0 parts toughening agent (Jindaquan A-6649), and 0.3 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0077] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0078] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0079] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound up to obtain a hydrophobic biodegradable polylactic acid cast film with a thickness of 0.03mm; the temperature of the casting roller is 55℃.

[0080] The preparation method of the reinforcing agent is as follows:

[0081] A1. By weight, add 10 parts of nano titanium dioxide to 100 parts of anhydrous ethanol, stir evenly, heat to 55°C, add 0.10 parts of triethylamine, stir for 3 min, and obtain a premixed solution.

[0082] A2. A mixture of 1.5 parts of bromooctane and 0.15 parts of tetraethoxysilane was added dropwise to the premixed solution, heated to 75°C, stirred for 4 hours, cooled, filtered, washed with ethanol and deionized water, filtered under vacuum, and dried to obtain the reinforcing agent.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that the reinforcing agent is nano-titanium dioxide, and the nano-silica dispersion was not sprayed, as detailed below:

[0085] A hydrophobic and biodegradable polylactic acid (PLA) cast film is prepared from the following raw materials in parts by weight: 90 parts polylactic acid, 10 parts polybutylene terephthalate (PET), 1.0 part nano-titanium dioxide, 0.5 parts compatibilizer (BASF ADR-4468), 3.0 parts toughening agent (Jindaquan A-6649), and 0.3 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio). The specific steps include:

[0086] S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix;

[0087] S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch;

[0088] S3. Add polylactic acid composite masterbatch to the casting machine. The temperature control parameters of each zone of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 200℃, the temperature of barrel 1 and barrel 2 is 190℃. After melting, it is extruded from the die head position, cast, cooled and wound to obtain a hydrophobic biodegradable polylactic acid casting film with a thickness of 0.03mm; the temperature of the casting roller is 55℃.

[0089] Proof of effectiveness

[0090] The polylactic acid composite masterbatches and hydrophobic biodegradable polylactic acid cast films prepared in Examples 1-4 and Comparative Examples 1-3 were used to prepare samples. Tensile strength and elongation at break were determined according to the standard method of GB / T 1040-2006, with a tensile rate of 20 mm / min. Specific test results are shown in Table 1.

[0091] Table 1

[0092]

[0093] Results Analysis

[0094] As can be seen from Examples 1-4 and Comparative Examples 1-3, and in conjunction with the data in Table 1, the tensile strength of Examples 1-4 reaches above 45.6 MPa, the elongation at break reaches above 62.7%, and the contact angle reaches above 123.6°. The overall performance is better than that of the comparative examples, indicating that the hydrophobic biodegradable polylactic acid cast film provided by the present invention has high mechanical strength and elongation at break, while also having good hydrophobic properties.

[0095] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A hydrophobic and biodegradable polylactic acid cast film, characterized in that, By weight, the raw materials used include the following components: 88-92 parts polylactic acid, 8-12 parts polybutylene terephthalate (PET), 0.8-1.2 parts reinforcing agent, 0.3-0.8 parts compatibilizer, 2.5-3.5 parts toughening agent, and 0.2-0.5 parts antioxidant; wherein the reinforcing agent is prepared by modifying nano-titanium dioxide with n-octane bromide.

2. The hydrophobic biodegradable polylactic acid cast film according to claim 1, characterized in that, The preparation method of the reinforcing agent is as follows: A1. By weight, add 10 parts of nano titanium dioxide to 80-150 parts of anhydrous ethanol, stir evenly, heat to 50-60℃, add 0.08-0.12 parts of triethylamine, stir for 2-5 minutes to obtain a premixed solution; A2. Add a mixture of 1-2 parts of bromooctane and 0.1-0.2 parts of tetraethoxysilane dropwise to the premixed solution, heat to 70-80℃, stir for 3-5 hours, cool, filter, wash with ethanol and deionized water, filter under vacuum, and dry to obtain the reinforcing agent.

3. The hydrophobic biodegradable polylactic acid cast film according to claim 1, characterized in that, The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:

2.

4. A method for preparing a hydrophobic biodegradable polylactic acid (PLA) cast film, used to prepare the hydrophobic biodegradable PLA cast film according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Add poly(butylene terephthalate), reinforcing agent and compatibilizer to a high-speed mixer and mix evenly to obtain a premix; S2. The premix and all other raw materials are melt-blended by twin screw extruder and then extruded and granulated to obtain polylactic acid composite masterbatch; S3. Add polylactic acid composite masterbatch to the casting machine, control the temperature of each temperature control zone, and after melting, extrude it from the die head position for casting, cooling, and winding to obtain a hydrophobic and biodegradable polylactic acid cast film.

5. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 4, characterized in that, In step S3: During the casting to winding process, when the cast material passes through the casting roll, the temperature of the casting roll is 50-60℃.

6. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 5, characterized in that, In step S3: During the casting to winding process, the surface of the casting roller has a micro-nano-scale rough structure.

7. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 5, characterized in that, In step S3: During the casting to winding process, when passing through the casting roller, a nano silica dispersion with a concentration of 0.3-1wt% is sprayed on the surface of the cast material.

8. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 4, characterized in that, The solvent for the nano-silica dispersion is ethanol, and the particle size range of the nano-silica is 80-300nm.

9. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 4, characterized in that, The thickness of the hydrophobic and biodegradable polylactic acid cast film is 0.01-0.1 mm.

10. The method for preparing the hydrophobic biodegradable polylactic acid cast film according to claim 4, characterized in that, The temperature control parameters for each temperature range of the casting machine are as follows: the temperature of the die head, connector and barrel 3 is 195-205℃, and the temperature of barrel 1 and barrel 2 is 185-195℃.

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