A highly elastic polyester-based degradable plastic film and its preparation method

Abstract

The present invention relates to the technical field of polyester materials, and specifically relates to a highly elastic polyester-based degradable plastic film and a preparation method thereof. The film comprises the following components: 45-55 parts by weight of modified polylactic acid, 12-16 parts by weight of tributyl citrate, 0.3-0.5 parts by weight of bile acid, 1-5 parts by weight of nano-silica, 0.5-0.9 parts by weight of cellulose nanofibers, 0.1-0.5 parts by weight of vitamin E antioxidant, 0.1-0.3 parts by weight of UV-326 ultraviolet absorber, and 2-6 parts by weight of talc powder. Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:0.6-1.2. By using sphinganine to modify polylactic acid, a long carbon-hydrogen chain is introduced through an amide bond to improve the elastic properties of the film. Utilizing the hydrophobicity of the long carbon-hydrogen chain structure, the application of the polylactic acid film in a high-humidity environment is improved. By using the natural emulsifier bile acid, the compatibility problem between the modified polylactic acid and other components is overcome, and the mechanical properties of the film are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester materials, and specifically, to a highly elastic polyester-based degradable plastic film and a preparation method thereof. Background Art

[0002] The main feature of degradable plastic films is that they can gradually decompose in the natural environment through the action of microorganisms or physical and chemical processes such as photooxidation and hydrolysis, and ultimately be converted into harmless substances such as carbon dioxide, water, and biomass, significantly reducing the long-term environmental pollution problem caused by traditional plastic films. Traditional plastic films, such as polyethylene (PE), polypropylene (PP), etc., have a wide range of applications in multiple fields such as agricultural production, packaging, and construction. However, their non-degradable characteristics have led to serious "white pollution". These plastic wastes accumulate in the natural environment for a long time, not only damaging the soil structure and affecting crop growth, but also being accidentally eaten by wild animals, posing a threat to the ecological system. In contrast, the emergence of degradable plastic films provides an effective way to solve the above problems.

[0003] Existing degradable plastic films are mainly prepared from bio-based degradable plastics. Polylactic acid is one of the commonly used raw materials. Polylactic acid itself has good biodegradability, but its mechanical properties and elasticity are relatively poor, and it has certain hygroscopicity and water vapor sensitivity. Especially under high humidity conditions, it will accelerate the aging and degradation of the material, resulting in a decline in material properties. In view of this, we propose a highly elastic polyester-based degradable plastic film and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a highly elastic polyester-based degradable plastic film and a preparation method thereof to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides a highly elastic polyester-based degradable plastic film, which includes the following components: 45 - 55 parts by weight of modified polylactic acid, 12 - 16 parts by weight of tributyl citrate, 0.3 - 0.5 parts by weight of bile acid, 1 - 5 parts by weight of nano-silica, 0.5 - 0.9 parts by weight of cellulose nanofibers, 0.1 - 0.5 parts by weight of vitamin E antioxidant, 0.1 - 0.3 parts by weight of UV-326 ultraviolet absorber, and 2 - 6 parts by weight of talcum powder;

[0006] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:0.6 - 1.2.

[0007] Preferably, the preparation method of the modified polylactic acid is as follows:

[0008] Dissolve sphinganine in N,N-dimethylformamide to form a sphinganine solution. Then add polylactic acid into a three-neck flask equipped with a condenser, and add N,N-dimethylformamide. Heat it to 50 - 70 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine. Subsequently, dropwise add the sphinganine solution while maintaining stirring, and heat it to 50 - 60 °C. React for 6 - 12 h, stop heating. Pour the reaction mixture into water to precipitate the product. Filter and collect the solid product with a Buchner funnel, wash the product with pure water, put the washed product into a vacuum drying oven, and dry it to a constant weight at 60 - 70 °C to obtain the product, modified polylactic acid.

[0009] The carbonyl group in the polylactic acid molecular chain is coplanar with the adjacent oxygen atom and is very close to the adjacent carbon atom, making it difficult to rotate. Therefore, the molecular chain has poor flexibility, and the material shows the characteristics of being hard and brittle with poor impact resistance. Polylactic acid is polymerized from lactic acid monomers and is relatively sensitive to humidity. A large number of ester bonds are contained in its main chain, and these ester bonds are prone to hydrolysis reactions in water, resulting in the breakage of the molecular chain. When the polylactic acid film is exposed to a high-humidity environment, as the moisture content increases, the hydrolysis rate will accelerate, leading to the rapid decomposition of the film and increasing the water vapor permeability, affecting its water vapor barrier performance and resulting in significant changes in the material's properties in the short term, such as becoming brittle, losing strength, and having poor sealing performance, thereby affecting the shelf life and quality of the items inside the package.

[0010] Dihydrosphingosine, namely D-threonine dihydrosphingosine, is a long-chain amino alcohol and an amphiphilic molecule. Its head contains an amino group and a hydroxyl group, and these functional groups can form hydrogen bonds with water molecules, so it has hydrophilicity. Its tail is a long hydrocarbon chain, and this part of the structure does not interact with water, so it has hydrophobicity. The primary amino group of dihydrosphingosine can form an amide bond through a condensation reaction with the carboxyl group of polylactic acid, thus linking a long hydrocarbon chain to polylactic acid. Due to the good flexibility and ductility of the long hydrocarbon chain, they can fill the gaps between polymer molecular chains, increase the spacing between polymer chains to a certain extent, reduce the intermolecular interaction force, and reduce the close packing between molecules, thereby making the material softer and more elastic. When subjected to external force, it can absorb and disperse stress, thus improving the elasticity of the material. Therefore, the flexibility of polylactic acid can be improved. At the same time, the long hydrocarbon chain structure can form a hydrophobic barrier, reducing the chance of water penetrating into the polymer interior, thereby slowing down the hydrolysis rate of the ester bond and improving the application of the polylactic acid film in a high-humidity environment, expanding the application range. However, although the improvement of hydrophobicity effectively reduces the water sensitivity of polylactic acid, there is a problem of poor compatibility with other materials. Therefore, bile acid is added. Since bile acid is a natural emulsifier and has amphiphilicity, it can effectively improve the compatibility problem between the modified polylactic acid and other components, reduce the phase separation phenomenon, and enhance the interfacial binding force, making the mechanical properties of the film significantly improved.

[0011] Preferably, the concentration of the dihydrosphingosine solution is 0.1 - 0.5 M.

[0012] Preferably, the concentration of the polylactic acid solution is 1 - 5% w / v.

[0013] Preferably, the molar ratio of dihydrosphingosine to N,N'-dicyclohexylcarbodiimide is 1:1 - 1.2.

[0014] Preferably, 4-dimethylaminopyridine accounts for 1 - 10% of the mass of N,N'-dicyclohexylcarbodiimide.

[0015] On the other hand, the present invention provides a preparation method of a highly elastic polyester-based degradable plastic film for a highly elastic polyester-based degradable plastic film described in any one of the above, including the following steps:

[0016] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talcum powder, stir and mix at room temperature for 5-10 min. After making it fully uniform, add the mixed material into a twin-screw extruder, set the extrusion temperature and extrusion speed. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10-20 °C. Place the cooled film on a stretching machine for biaxial stretching treatment. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a high-elastic polyester-based degradable plastic film.

[0017] Preferably, the extrusion temperature is 160-180 °C, and the extrusion speed is 20-30 revolutions per minute.

[0018] Preferably, the draw ratio of the biaxial stretching treatment is set to 3-5:1.

[0019] Preferably, the stretching speed of the biaxial stretching treatment is controlled at a strain rate of 5-10% per second.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In this high-elastic polyester-based degradable plastic film and its preparation method, sphinganine is used to modify polylactic acid. The amino group and carboxyl group on sphinganine form an amide bond, so that sphinganine is linked to polylactic acid. Due to the good flexibility and ductility of the long carbon-hydrogen chain of sphinganine, the elastic properties of polylactic acid are improved. Combining with the hydrophobicity of the long carbon-hydrogen chain structure, the opportunity for moisture to penetrate into the interior of the polymer is reduced, thereby slowing down the hydrolysis rate of the ester bond and improving the application of the polylactic acid film in a high-humidity environment, expanding the application range. At the same time, the natural emulsifier bile acid is used to overcome the compatibility problem between the modified polylactic acid and other components, reduce the phase separation phenomenon, enhance the interfacial bonding force, and improve the mechanical properties of the film. Specific Embodiments

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] A highly elastic polyester-based degradable plastic film of the present invention comprises the following components: 45-55 parts by weight of modified polylactic acid, 12-16 parts by weight of tributyl citrate, 0.3-0.5 parts by weight of bile acid, 1-5 parts by weight of nano-silica, 0.5-0.9 parts by weight of cellulose nanofibers, 0.1-0.5 parts by weight of vitamin E antioxidant, 0.1-0.3 parts by weight of UV-326 ultraviolet absorber, and 2-6 parts by weight of talcum powder;

[0024] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:0.6-1.2.

[0025] Example 1: A highly elastic polyester-based degradable plastic film and its preparation method, comprising the following steps:

[0026] Prepare the components: 55 parts by weight of modified polylactic acid, 16 parts by weight of tributyl citrate, 0.5 parts by weight of bile acid, 5 parts by weight of nano-silica, 0.9 parts by weight of cellulose nanofibers, 0.5 parts by weight of vitamin E antioxidant, 0.3 parts by weight of UV-326 ultraviolet absorber, and 6 parts by weight of talcum powder;

[0027] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:0.6; the molar ratio of sphinganine to N,N'-dicyclohexylcarbodiimide is 1:1.2; 4-dimethylaminopyridine accounts for 10% of the mass of N,N'-dicyclohexylcarbodiimide;

[0028] Dissolve sphinganine in N,N-dimethylformamide to form a 0.5M sphinganine solution, then add polylactic acid to a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a 5% w / v polylactic acid solution. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then dropwise add the sphinganine solution while maintaining stirring and heating to 50 °C. React for 8 h, stop heating, pour the reaction mixture into water to precipitate the product, filter and collect the solid product with a Buchner funnel, wash the product with pure water, and put the washed product into a vacuum drying oven and dry it to constant weight at 70 °C to obtain the product modified polylactic acid;

[0029] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talc powder, stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder, set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment, set the stretching ratio at 3:1, and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0030] Example 2: A highly elastic polyester-based degradable plastic film and its preparation method, including the following steps:

[0031] Prepare components: 55 parts by weight of modified polylactic acid, 16 parts by weight of tributyl citrate, 0.5 parts by weight of bile acid, 5 parts by weight of nano-silica, 0.9 parts by weight of cellulose nanofibers, 0.5 parts by weight of vitamin E antioxidant, 0.3 parts by weight of UV-326 ultraviolet absorber and 6 parts by weight of talc powder;

[0032] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:0.9; the molar ratio of sphinganine to N,N'-dicyclohexylcarbodiimide is 1:1.2; 4-dimethylaminopyridine accounts for 10% of the mass of N,N'-dicyclohexylcarbodiimide;

[0033] Dissolve sphinganine in N,N-dimethylformamide to form a sphinganine solution with a concentration of 0.5 M. Then add polylactic acid into a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat it to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution with a concentration of 5% w / v. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then dropwise add the sphinganine solution while maintaining stirring and heating to 50 °C. React for 8 h, stop heating. Pour the reaction mixture into water to precipitate the product, filter and collect the solid product with a Buchner funnel, wash the product with pure water, and put the washed product into a vacuum drying oven and dry it to constant weight at 70 °C to obtain the product modified polylactic acid;

[0034] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talc powder, stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder, set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment, set the stretching ratio at 3:1, and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0035] Example 3: A highly elastic polyester-based degradable plastic film and its preparation method, including the following steps:

[0036] Prepare components: 55 parts by weight of modified polylactic acid, 16 parts by weight of tributyl citrate, 0.5 parts by weight of bile acid, 5 parts by weight of nano-silica, 0.9 parts by weight of cellulose nanofibers, 0.5 parts by weight of vitamin E antioxidant, 0.3 parts by weight of UV-326 ultraviolet absorber and 6 parts by weight of talc powder;

[0037] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:1.2; the molar ratio of sphinganine to N,N'-dicyclohexylcarbodiimide is 1:1.2; 4-dimethylaminopyridine accounts for 10% of the mass of N,N'-dicyclohexylcarbodiimide;

[0038] Dissolve sphinganine in N,N-dimethylformamide to form a sphinganine solution with a concentration of 0.5 M. Then add polylactic acid into a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat it to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution with a concentration of 5% w / v. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then dropwise add the sphinganine solution while maintaining stirring and heating to 50 °C. React for 8 h, stop heating, pour the reaction mixture into water to precipitate the product, filter and collect the solid product with a Buchner funnel, wash the product with pure water, and place the washed product in a vacuum drying oven and dry it to constant weight at 70 °C to obtain the product modified polylactic acid;

[0039] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talc powder, stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder, set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment, set the stretching ratio at 3:1, and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0040] Example 4: A highly elastic polyester-based degradable plastic film and its preparation method, including the following steps:

[0041] Prepare components: 55 parts by weight of modified polylactic acid, 12 parts by weight of tributyl citrate, 0.3 parts by weight of bile acid, 1 part by weight of nano-silica, 0.5 parts by weight of cellulose nanofibers, 0.1 parts by weight of vitamin E antioxidant, 0.1 parts by weight of UV-326 ultraviolet absorber and 2 parts by weight of talc powder;

[0042] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:1.2; the molar ratio of sphinganine to N,N'-dicyclohexylcarbodiimide is 1:1; 4-dimethylaminopyridine accounts for 1% of the mass of N,N'-dicyclohexylcarbodiimide;

[0043] Dissolve sphinganine in N,N-dimethylformamide to form a sphinganine solution with a concentration of 0.5 M. Then add polylactic acid into a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat it to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution with a concentration of 5% w / v. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then dropwise add the sphinganine solution while maintaining stirring and heating to 50 °C. React for 8 h, stop heating. Pour the reaction mixture into water to precipitate the product, filter and collect the solid product with a Buchner funnel, wash the product with pure water, and put the washed product into a vacuum drying oven and dry it to a constant weight at 70 °C to obtain the product modified polylactic acid;

[0044] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber, and talcum powder, and stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder. Set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment. Set the stretching ratio at 3:1 and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0045] Example 5: A highly elastic polyester-based degradable plastic film and its preparation method, comprising the following steps:

[0046] Prepare components: 45 parts by weight of modified polylactic acid, 16 parts by weight of tributyl citrate, 0.5 parts by weight of bile acid, 5 parts by weight of nano-silica, 0.9 parts by weight of cellulose nanofibers, 0.5 parts by weight of vitamin E antioxidant, 0.3 parts by weight of UV-326 ultraviolet absorber, and 6 parts by weight of talcum powder;

[0047] Among them, the modified polylactic acid is prepared by mixing polylactic acid and dihydrosphingosine in a mass ratio of 10:1.2; the molar ratio of dihydrosphingosine to N,N'-dicyclohexylcarbodiimide is 1:1.2; 4-dimethylaminopyridine accounts for 10% of the mass of N,N'-dicyclohexylcarbodiimide;

[0048] Dissolve dihydrosphingosine in N,N-dimethylformamide to form a dihydrosphingosine solution with a concentration of 0.5 M. Then add polylactic acid into a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat it to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution with a concentration of 5% w / v. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then dropwise add the dihydrosphingosine solution while maintaining stirring and heating to 50 °C. React for 8 h, stop heating, pour the reaction mixture into water to precipitate the product, filter and collect the solid product with a Buchner funnel, wash the product with pure water, and put the washed product into a vacuum drying oven and dry it to constant weight at 70 °C to obtain the product modified polylactic acid;

[0049] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talc powder, stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder. Set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die. Use a cooling roller to rapidly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment. Set the stretching ratio at 3:1 and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0050] Example 6: A highly elastic polyester-based degradable plastic film and its preparation method, comprising the following steps:

[0051] Prepare components: 50 parts by weight of modified polylactic acid, 16 parts by weight of tributyl citrate, 0.5 parts by weight of bile acid, 5 parts by weight of nano-silica, 0.9 parts by weight of cellulose nanofibers, 0.5 parts by weight of vitamin E antioxidant, 0.3 parts by weight of UV-326 ultraviolet absorber and 6 parts by weight of talc powder;

[0052] Among them, the modified polylactic acid is prepared by mixing polylactic acid and sphinganine in a mass ratio of 10:1.2; the molar ratio of sphinganine to N,N'-dicyclohexylcarbodiimide is 1:1.2; 4-dimethylaminopyridine accounts for 10% of the mass of N,N'-dicyclohexylcarbodiimide;

[0053] Dissolve sphinganine in N,N-dimethylformamide to form a sphinganine solution with a concentration of 0.5 M. Then add polylactic acid into a three-neck flask equipped with a condenser tube, and add N,N-dimethylformamide. Heat to 50 °C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution with a concentration of 5% w / v. Then add N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine. Subsequently, dropwise add the sphinganine solution while maintaining stirring and heat to 50 °C. React for 8 h, stop heating. Pour the reaction mixture into water to precipitate the product. Filter and collect the solid product with a Buchner funnel. Wash the product with pure water. Put the washed product into a vacuum drying oven and dry it to constant weight at 70 °C to obtain the product modified polylactic acid;

[0054] Using a high-speed mixer, add modified polylactic acid, tributyl citrate, nano-silica, cellulose nanofibers, vitamin E antioxidant, UV-326 ultraviolet absorber and talcum powder, stir and mix at room temperature for 10 min. After making it fully uniform, add the mixed material into a twin-screw extruder. Set the extrusion temperature at 180 °C and the extrusion speed at 30 revolutions per minute. During the extrusion process, press the melt into a thin sheet through a die, and use a cooling roller to quickly cool the film just coming out of the extruder to make it solidify. Control the temperature of the cooling medium at 10 °C. Place the cooled film on a stretching machine for biaxial stretching treatment. Set the stretching ratio at 3:1 and control the stretching speed at a strain rate of 10% per second. Finally, cut and surface-treat the film. After completion, roll up and package the finished film to obtain a highly elastic polyester-based degradable plastic film.

[0055] Comparative Example 1: Using the method of Example 3, dihydrosphingosine-modified polylactic acid was not added.

[0056] Comparative Example 2: Using the method of Example 3, polycaprolactone and polylactic acid were used for mixed modification.

[0057] Comparative Example 3: Using the method of Example 3, bile acid was not added.

[0058] The present invention relates to a highly elastic polyester-based degradable plastic film prepared by using modified polylactic acid. Among them, the performance index test items and test standards of the highly elastic polyester-based degradable plastic film are as follows:

[0059] Test the moisture resistance of the plastic film. The specific test steps are as follows: First, record the mass of the sample before the test, and then place the sample in an environment with the same humidity and temperature. Set the conditions at 40 °C and 90% relative humidity. After 30 days, record the remaining mass of the sample, and calculate the degradation residual rate. Degradation residual rate (%) = (mass before the test - mass after 30 days) / mass before the test. In a high-humidity environment, the faster the degradation rate, the worse the moisture resistance.

[0060] According to GB / T 1040.3-2006 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets", test the tensile strength and elongation at break of the material. Tensile strength refers to the maximum stress that the material can withstand during the tensile process, that is, the maximum force per unit area that the material can withstand before fracture; elongation at break refers to the ratio of the increase in the gauge length at fracture to the original gauge length during the tensile process of the specimen. Tensile strength is an important parameter to measure the ability of the material to resist external tensile force. For elastic materials, good tensile strength means that the material can remain intact under a large stress and is not prone to fracture; elongation at break directly reflects the ductility and elasticity of the material. A high elongation at break indicates that the material can withstand a large deformation without breaking.

[0061] The tear strength of the material was tested according to GB / T 16578-2008 "Plastics - Determination of tear resistance of films and sheets". Tear strength refers to the ability of a material to resist tear propagation, which is the force required to apply on a specimen with a specific shape until the tear is fully developed. Tear strength is related to the overall toughness of the material. Especially for film and sheet materials, good tear strength means that the material can still maintain its integrity after local damage.

[0062] Through the above standard, the high - elastic polyester - based degradable plastic films prepared in Examples 1 - 6 and Comparative Examples 1 - 3 were tested, and the obtained data are shown in Table 1:

[0063] Table 1 Performance data of Examples 1 - 6 and Comparative Examples 1 - 3

[0064]

[0065] The above data fully show that compared with Comparative Examples 1 - 3, Examples 1 - 6 can fully demonstrate the role of modified polylactic acid in the elasticity and moisture - resistance performance of high - elastic polyester - based degradable plastic films.

[0066] Since the present invention uses modified polylactic acid to prepare high - elastic polyester - based degradable plastic films, the performance of high - elastic polyester - based degradable plastic films is effectively improved by modified polylactic acid, as follows:

[0067] It can be seen from Examples 1 - 3 that as the proportion of the modified polylactic acid component continuously increases, the elasticity and moisture - resistance performance are significantly improved. This shows that the reaction between sphinganine and polylactic acid can effectively improve the mechanical properties and elasticity of polylactic acid. The flexible long hydrocarbon chain of sphinganine can fill the voids between polymer molecular chains, increase the spacing between polymer chains, reduce the close packing between molecules, so that the film is more elastic. At the same time, the hydrophobic structure of the long hydrocarbon chain of sphinganine reduces the chance of moisture penetrating into the polymer interior, slows down the degradation rate of the polylactic acid film in a high - humidity environment, and thus effectively expands the application range. Therefore, the elasticity and moisture - resistance performance of the film are significantly improved.

[0068] It can be seen from Example 2 and Example 4 that as the content of other components continuously increases, the elasticity and moisture - resistance performance show no obvious change. This indicates that small - scale changes within a certain range of other components are not sufficient to significantly affect the elasticity and moisture - resistance performance of high - elastic polyester - based degradable plastic films. Therefore, there is no obvious change.

[0069] It can be seen from Example 2, Example 5 and Example 6 that with the continuous increase of the content of modified polylactic acid, the elasticity and moisture resistance are significantly improved, which further supports the conclusion that the reaction between sphinganine and polylactic acid can effectively improve the mechanical properties and elasticity of polylactic acid. It shows that after the modification of polylactic acid by sphinganine, on the one hand, the flexible long hydrocarbon chain can help polylactic acid reduce the intermolecular interaction force, provide free space for the movement of molecular chains, and improve the elastic properties of the film. On the other hand, it can form a hydrophobic barrier to reduce the contact between ester groups and water molecules, thereby improving its water resistance.

[0070] According to the above test experiments, the high-elastic polyester-based degradable plastic film prepared according to Example 3 has the optimal performance, so Example 3 is taken as the optimal example.

[0071] It can be seen from the comparison between Example 3 and Comparative Examples 1-3:

[0072] In Comparative Example 1, sphinganine-modified polylactic acid is not added, and the elasticity and moisture resistance of the high-elastic polyester-based degradable plastic film are worse. Sphinganine forms an amide bond through a condensation reaction with the carboxyl group of polylactic acid, which not only weakens the intermolecular interaction force and improves the elastic properties of the film, but also introduces a long hydrocarbon chain and increases the hydrophobicity of the material. Therefore, without sphinganine, the polylactic acid film lacks these structural improvements, shows higher rigidity and brittleness, and the characteristics of rapid hydrolysis in a high-humidity environment, cannot effectively resist moisture, and cannot be effectively applied in a high-humidity environment, with a narrow application range.

[0073] In Comparative Example 2, polycaprolactone and polylactic acid are added for mixed modification, and the elasticity and moisture resistance of the high-elastic polyester-based degradable plastic film are poor. The mixed modification of polycaprolactone and polylactic acid can improve the elasticity of the material to a certain extent, but the modification of polycaprolactone mainly relies on physical mixing to improve, rather than sphinganine enhancing the material properties through chemical structure changes. In addition, new chemical bonds are formed, and sphinganine can be more evenly distributed in polylactic acid. Therefore, compared with the mixed modification of polycaprolactone and polylactic acid, the performance of sphinganine-modified polylactic acid is better.

[0074] In Comparative Example 3, bile acid is not added. As a natural emulsifier, bile acid can promote good dispersion and interfacial combination between different components. A good dispersion state helps to reduce the phase separation phenomenon and enhance the synergistic effect between various components. Therefore, when bile acid is lacking, it will lead to poor distribution of additives or fillers, resulting in local enrichment or depletion, affecting the overall consistency.

[0075] In summary, by modifying polylactic acid with sphinganine, a flexible long hydrocarbon chain is introduced into polylactic acid, improving the flexibility and hydrophobicity of polylactic acid. The amphiphilic bile acid is used to improve the compatibility between components and enhance the uniformity of the film. Moreover, the added sphinganine and bile acid are both natural components with good biocompatibility, which not only effectively improve the elastic properties of polylactic acid but also enhance the application of polylactic acid in a high-humidity environment.

[0076] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A highly elastic polyester degradable plastic film, characterized in that: The invention comprises the following components: 45-55 parts by weight of modified polylactic acid, 12-16 parts by weight of tributyl citrate, 0.3-0.5 parts by weight of bile acid, 1-5 parts by weight of nano-silicon dioxide, 0.5-0.9 parts by weight of cellulose nanofiber, 0.1-0.5 parts by weight of vitamin E antioxidant, 0.1-0.3 parts by weight of UV-326 ultraviolet absorber and 2-6 parts by weight of talc; The modified polylactic acid is prepared by mixing polylactic acid and dihydrosphingosine in a mass ratio of 10:0.6-1.2; The preparation method of the modified polylactic acid is as follows: The dihydrosphingosine is dissolved in N,N-dimethylformamide to form a dihydrosphingosine solution, and then polylactic acid is added to a three-necked flask with a condenser, and N,N-dimethylformamide is added, and the mixture is heated to 50-70°C under magnetic stirring until the polylactic acid is completely dissolved to obtain a polylactic acid solution, and then N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added, and then the dihydrosphingosine solution is added dropwise while stirring and heating to 50-60°C. The reaction is carried out for 6-12 hours, and the heating is stopped. The reaction mixture is poured into water to precipitate the product, and the solid product is collected by filtration using a Buchner funnel. The product is washed with pure water, and the washed product is placed in a vacuum drying oven and dried at 60-70°C to constant weight to obtain the product modified polylactic acid.

2. The highly elastic polyester degradable plastic film according to claim 1, characterized in that: The concentration of the dihydrosphingosine solution is 0.1-0.5M.

3. The highly elastic polyester degradable plastic film according to claim 1, characterized in that: The concentration of the polylactic acid solution is 1-5% w / v.

4. The highly elastic polyester degradable plastic film according to claim 1, characterized in that: The molar ratio of the dihydrosphingosine to N,N'-dicyclohexylcarbodiimide is 1:1-1.

2.

5. The highly elastic polyester degradable plastic film according to claim 1, characterized in that: The 4-dimethylaminopyridine accounts for 1-10% of the mass of N,N'-dicyclohexylcarbodiimide.

6. A method for preparing a highly elastic polyester-based degradable plastic film, for preparing the highly elastic polyester-based degradable plastic film according to any one of claims 1 to 5, characterized in that: The steps include: Use a high-speed mixer to add modified polylactic acid, tributyl citrate, bile acid, nano-silica, cellulose nanofiber, vitamin E antioxidant, UV-326 ultraviolet absorber and talc, stir and mix at room temperature for 5-10 minutes to make it fully uniform, then add the mixed materials into a twin-screw extruder, set the extrusion temperature and extrusion speed, and during the extrusion process, press the melt into a thin sheet through a mold, use a cooling roller to quickly cool the film just out of the extruder to solidify it, control the cooling medium temperature at 10-20°C, place the cooled film on a stretching machine for biaxial stretching treatment, and finally cut and surface-treat the film. After completion, the finished film is rolled up and packaged to obtain a high-elasticity polyester biodegradable plastic film.

7. The method for preparing a highly elastic polyester degradable plastic film according to claim 6, wherein: The extrusion temperature is 160-180° C., and the extrusion speed is 20-30 rpm.

8. The method for preparing a highly elastic polyester degradable plastic film according to claim 6, wherein: The stretching ratio of the biaxial stretching process is set to 3 to 5:

1.

9. The method for preparing a highly elastic polyester degradable plastic film according to claim 6, wherein: The stretching speed of the biaxial stretching process is controlled at a strain rate of 5-10% per second.

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