Degradable high-barrier polylactic acid film and preparation method thereof

Abstract

The application discloses a degradable high-barrier polylactic acid film and a preparation method thereof. Raw materials for preparing the degradable high-barrier polylactic acid film include 60-80 parts of PLA, 20-40 parts of PPC, 1-5 parts of maleic anhydride modified starch and 1-5 parts of a chain extender in terms of weight. The degradable high-barrier polylactic acid film prepared by the application adds maleic anhydride modified starch, the surface of the modified starch has hydrophobic groups, i.e. maleic anhydride derivatives, which effectively avoid the agglomeration of starch due to the water absorption characteristics, improve the dispersion effect of the starch in the PLA, and the modified starch has a carbonyl group similar to the polarity of the ester group in the PLA molecule. In addition, the unreacted carboxyl group of the modified starch can occur ester exchange reaction with the terminal hydroxyl group of the PLA molecular chain in the blending extrusion to form a maleic anhydride modified starch-PLA graft copolymer, effectively improving the compatibility of the PLA and the modified starch, so that the modified starch can effectively improve the mechanical properties of the PLA film.

Description

Technical Field

[0001] This invention relates to the field of composite film preparation technology, and in particular to a biodegradable high-barrier polylactic acid film and its preparation method. Background Technology

[0002] With the increasing prevalence of white pollution and the depletion of petroleum resources, researching new biodegradable packaging materials to replace traditional petroleum-based materials has become an inevitable trend. Currently, the most common barrier films used in food packaging are made of polyolefins, such as polypropylene (PP) and polyethylene (PE). PP has generally poor barrier properties, while PE has good moisture resistance but poor gas barrier properties, and polyolefin materials are not biodegradable in nature. Polylactic acid (PLA) possesses both good mechanical properties and excellent biodegradability, but its barrier properties are poor, it is hard and brittle, has low melt strength, and is difficult to blown into film.

[0003] Patent CN118027476A discloses a method for preparing a heat-resistant and antibacterial PLA / polypropylene carbonate (PPC) barrier film. The method involves co-extruding PLA, PPC, and dextrorotatory polylactic acid grafted glycidyl methacrylate (PDLA-g-GMA) to obtain a masterbatch. The masterbatch is then dissolved in an organic solvent, while nano-zinc oxide is dispersed into the solution. Finally, the solution is coated onto a glass plate using a doctor blade. After solvent evaporation, a heat-resistant and antibacterial PLA / PPC barrier film with a thickness of 115 µm and an oxygen permeability of less than 100 cm⁻¹ is obtained. 3 / m 2 The method, which operates at 24h / 0.1MPa, requires the use of organic solvents such as chloroform, making the process quite cumbersome. Furthermore, it is only suitable as an experimental method and not for industrial-scale mass production.

[0004] Therefore, there is an urgent need to develop a biodegradable PLA film that can be industrially produced and simultaneously possesses excellent barrier and mechanical properties. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing traditional composite film materials have poor barrier properties, so this invention provides a biodegradable high-barrier polylactic acid film and its preparation method.

[0006] Therefore, in a first aspect, the present invention provides a biodegradable high-barrier polylactic acid film, characterized in that, by weight, the raw materials for preparing the biodegradable high-barrier polylactic acid film include: 60-80 parts PLA, 20-40 parts PPC, 1-5 parts maleic anhydride modified starch, and 1-5 parts chain extender.

[0007] Furthermore, the method for preparing maleic anhydride-modified starch is as follows: starch is mixed with water to form a suspension, the starch suspension is added to hydrolyzed maleic anhydride and dispersed, and the mixture is dried to obtain maleic anhydride-modified starch.

[0008] Furthermore, the specific preparation method of the maleic anhydride modified starch is as follows: starch and water are mixed at a mass ratio of 1:1 and then ultrasonically dispersed to form a suspension. After hydrolyzing maleic anhydride, the starch suspension is added to it for high-speed dispersion and mixing. The mixture is dried to remove moisture and then pulverized and ground to obtain maleic anhydride modified starch.

[0009] Furthermore, the hydrolysis temperature of the maleic anhydride is 60~80℃, and the hydrolysis time is 10~15min.

[0010] Furthermore, the drying temperature of the mixture is 90~120℃, and the drying time is 10~15h.

[0011] Furthermore, the chain extender is one of epoxy-functionalized acrylate chain extenders or epoxidized soybean oil.

[0012] Secondly, the present invention provides a method for preparing a biodegradable high-barrier polylactic acid film, characterized by comprising the following steps:

[0013] PLA, PPC, and maleic anhydride-modified starch were dried, mixed, melt-blended, granulated, dried, and blown into a film to obtain the biodegradable high-barrier polylactic acid film.

[0014] Furthermore, the preparation method is as follows:

[0015] (1) The PLA, PPC and maleic anhydride modified starch were dried at 70℃ for 12h to remove moisture, mixed evenly, melt-blended by a twin-screw extruder and then granulated. The resulting particles were placed in a 70℃ oven and dried for 12h to remove moisture for later use.

[0016] (2) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0017] The technical solution provided by this invention has the following advantages:

[0018] 1. The biodegradable high-barrier polylactic acid film prepared by this invention contains maleic anhydride-modified starch. The modified starch has hydrophobic groups, namely maleic anhydride derivatives, on its surface, which effectively prevents starch from agglomerating due to its easy water absorption and improves its dispersion effect in PLA. In addition, the modified starch has carbonyl groups with polarity similar to the ester groups in PLA molecules. Furthermore, the unreacted carboxyl groups of the modified starch can undergo transesterification with the terminal hydroxyl groups of PLA molecular chains during blending and extrusion to form maleic anhydride-modified starch-PLA graft copolymer, which effectively improves the compatibility between PLA and modified starch, thereby enabling the modified starch to effectively improve the mechanical properties of PLA film.

[0019] 2. The method used in this invention for starch modification involves heating maleic anhydride to hydrolyze it into maleic acid. The maleic acid is adsorbed onto the surface and pores of the starch granules. Simultaneously, under acidic conditions, the starch undergoes partial hydrolysis, producing more hydroxyl groups. During drying, as the water evaporates, the concentration of maleic acid in the system continuously increases, thus acting as a catalyst for the esterification reaction. At this point, two reactions occur: first, the hydroxyl groups on the starch surface attack one of the carboxyl groups of maleic acid, resulting in an acid-catalyzed esterification reaction; second, the residual maleic anhydride directly reacts with the hydroxyl groups of starch, i.e., the hydroxyl groups of starch attack the carbonyl carbon of the anhydride, forming a ring-opening half-ester, while the other carboxyl group exists in the form of a free acid. Ultimately, some of the hydroxyl groups on the starch molecule are grafted with maleic acid groups containing carboxyl groups and carbon-carbon double bonds, resulting in hydrophobicity. Existing technologies typically involve extruding a mixture of starch and maleic anhydride. However, this method suffers from short reaction times in the extruder, leading to incomplete esterification. Furthermore, the high shear forces exerted by the extruder at high temperatures cause starch molecular chains to break and maleic anhydride to decompose, hindering the esterification reaction. Maleic anhydride is also corrosive, and its reaction in the extruder can damage the equipment. To avoid corrosion, a corrosion-resistant screw and liquid injection system are required, significantly increasing production costs. This application employs a post-processing method to modify starch, eliminating the need for organic solvents, simplifying the process, making it suitable for industrial mass production, and offering low cost and high output.

[0020] 3. The biodegradable high-barrier polylactic acid film prepared by this invention involves blending PPC with PLA. PPC forms a sheet structure in the PLA matrix and has excellent gas barrier properties. There is a strong interaction between the polar ester / carbonate groups of PLA and PPC, resulting in a tight bond at the interface between the two phases. This gives the biodegradable high-barrier polylactic acid film excellent gas barrier properties. Furthermore, maleic anhydride-modified starch is uniformly dispersed in the PLA / PPC matrix, further improving the barrier properties and mechanical properties of the film. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade. For example, in the embodiments and comparative examples of this invention, the epoxy-functionalized acrylate chain extenders used include ADR-4370 / 4468.

[0023] Example 1

[0024] This embodiment provides a method for preparing a biodegradable high-barrier polylactic acid film, including the following steps:

[0025] (1) Mix starch and water at a mass ratio of 1:1 and then ultrasonically disperse for 30 minutes to prepare a suspension. Hydrolyze maleic anhydride at 70°C for 12 minutes. Then add the starch suspension to it and disperse and mix at high speed for 30 minutes. Place the mixture in a 100°C oven to dry for 12 hours to remove moisture. After crushing and grinding, obtain maleic anhydride modified starch.

[0026] (2) Take 80 parts by weight of PLA, 20 parts by weight of PPC, 5 parts by weight of maleic anhydride modified starch and 3 parts by weight of chain extender ADR-4370, dry them at 70℃ for 12h to remove moisture, mix them evenly, add them to a twin-screw extruder, set the extruder temperature to 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, 180℃, melt, blend, extrude, water cool, pelletize, dry and pelletize, put the obtained particles into a 70℃ oven to dry for 12h to remove moisture, and set aside for later use;

[0027] (3) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0028] Example 2

[0029] This embodiment provides a method for preparing a biodegradable high-barrier polylactic acid film, including the following steps:

[0030] (1) Mix starch and water at a mass ratio of 1:1 and then ultrasonically disperse for 40 minutes to prepare a suspension. Hydrolyze maleic anhydride at 60℃ for 15 minutes. Then add the starch suspension to it and disperse and mix at high speed for 40 minutes. Place the mixture in an oven at 120℃ to dry for 10 hours to remove moisture. After crushing and grinding, obtain maleic anhydride modified starch.

[0031] (2) Take 60 parts by weight of PLA, 40 parts by weight of PPC, 2 parts by weight of maleic anhydride modified starch and 1 part by weight of chain extender ADR-4468, dry them at 70℃ for 12h to remove moisture, mix them evenly, add them to a twin-screw extruder, set the extruder temperature to 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, 180℃, melt, blend, extrude, water cool, pelletize, dry and pelletize, put the obtained particles into a 70℃ oven to dry for 12h to remove moisture, and set aside for later use;

[0032] (3) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0033] Example 3

[0034] This embodiment provides a method for preparing a biodegradable high-barrier polylactic acid film, including the following steps:

[0035] (1) Mix starch and water at a mass ratio of 1:1 and then ultrasonically disperse for 20 minutes to prepare a suspension. Hydrolyze maleic anhydride at 80°C for 10 minutes. Then add the starch suspension to the suspension and disperse and mix at high speed for 20 minutes. Place the mixture in a 90°C oven to dry for 15 hours to remove moisture. After crushing and grinding, obtain maleic anhydride modified starch.

[0036] (2) Take 70 parts by weight of PLA, 30 parts by weight of PPC, 1 part by weight of maleic anhydride modified starch and 5 parts by weight of chain extender epoxidized soybean oil, dry them at 70℃ for 12h to remove moisture, mix them evenly, add them to a twin-screw extruder, set the extruder temperature to 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, 180℃, melt, blend, extrude, water cool, pelletize, dry and pelletize, put the obtained particles into a 70℃ oven to dry for 12h to remove moisture, and set aside for later use;

[0037] (3) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0038] Example 4

[0039] This embodiment provides a method for preparing a biodegradable high-barrier polylactic acid film, including the following steps:

[0040] (1) Mix starch and water at a mass ratio of 1:1 and then ultrasonically disperse for 25 minutes to prepare a suspension. Hydrolyze maleic anhydride at 75°C for 11 minutes. Then add the starch suspension and disperse and mix at high speed for 35 minutes. Place the mixture in an oven at 110°C and dry for 11 hours to remove moisture. After crushing and grinding, obtain maleic anhydride modified starch.

[0041] (2) Take 65 parts by weight of PLA, 35 parts by weight of PPC, 4 parts by weight of maleic anhydride modified starch and 4 parts by weight of chain extender ADR-4468, dry them at 70℃ for 12h to remove moisture, mix them evenly, add them to a twin-screw extruder, set the extruder temperature to 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, 180℃, melt, blend, extrude, water cool, pelletize, dry and pelletize, put the obtained particles into a 70℃ oven to dry for 12h to remove moisture, and set aside for later use;

[0042] (3) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0043] Example 5

[0044] This embodiment provides a method for preparing a biodegradable high-barrier polylactic acid film, including the following steps:

[0045] (1) Mix starch and water at a mass ratio of 1:1 and then ultrasonically disperse for 35 minutes to prepare a suspension. Hydrolyze maleic anhydride at 65°C for 13 minutes. Then add the starch suspension and disperse and mix at high speed for 25 minutes. Place the mixture in a 100°C oven to dry for 13 hours to remove moisture. After crushing and grinding, obtain maleic anhydride modified starch.

[0046] (2) Take 75 parts by weight of PLA, 25 parts by weight of PPC, 3 parts by weight of maleic anhydride modified starch and 2 parts by weight of chain extender ADR-4370, dry them at 70℃ for 12h to remove moisture, mix them evenly, add them to a twin-screw extruder, set the extruder temperature to 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, 180℃, melt, blend, extrude, water cool, pelletize, dry and pelletize, put the obtained particles into a 70℃ oven to dry for 12h to remove moisture, and set aside for later use;

[0047] (3) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.

[0048] Comparative Example 1

[0049] Comparative Example 1 follows the same implementation method as Example 1, except that PPC is replaced with PBAT in the formulation to prepare comparative polylactic acid film 1.

[0050] Comparative Example 2

[0051] Comparative Example 2 follows the same implementation method as Example 1, except that the maleic anhydride modified starch in the formulation is replaced with unmodified ordinary starch, and comparative polylactic acid film 2 is prepared.

[0052] Experimental Example

[0053] The PLA films prepared in the above embodiments and comparative examples had a blow-up ratio of approximately 3.0 and a thickness of 30 µm, and the following performance tests were performed. The specific results are shown in Table 1.

[0054] Test 1. Tensile strength: According to standard GB / T1040.3-2006 Determination of tensile properties of plastics (Part 3), the obtained polylactic acid film was cut into test samples of 100mm×15mm, the tensile rate was set to 100mm / min, and the transverse and longitudinal tensile strength of the film was tested. Three data points were tested for each group and the average value was taken.

[0055] Test 2. Oxygen permeability: According to GB / T-1038.1-2022, the oxygen permeability of polylactic acid film is tested using the pressure difference method. Three data points are collected for each test and the average value is taken.

[0056] Test 3. Transmittance: The obtained polylactic acid film was cut into 100mm×100mm samples and tested according to the spectrophotometer method of GB / T-2410-2008. The transmittance in the spectral range of 400-700nm was tested using a transmittance tester. Three data points were tested for each group and the average value was taken.

[0057] Table 1. Test results of Examples 1-5 and Comparative Examples 1-2

[0058] Example 1 58 54 497 95 Example 2 55 46 593 94.5 Example 3 57 48 599 94 Example 4 54 50 521 94.5 Example 5 57 48 574 94 Comparative Example 1 38 43 956 90 Comparative Example 2 25 31 1425 94

[0059] The above performance tests show that, compared with Comparative Example 2, the polylactic acid films prepared in Examples 1-5 all have a transverse strength > 50 MPa and a longitudinal strength > 40 MPa. Since maleic anhydride modified starch has high compatibility with PLA, it effectively improves the mechanical properties of polylactic acid films.

[0060] Compared with Comparative Example 1, the polylactic acid films prepared in Examples 1-5, using high-barrier PPC blend blown film, have better oxygen barrier effect and lower oxygen permeability. Furthermore, the maleic anhydride modified starch, as a filler, enhances mechanical properties while being uniformly dispersed in the PLA / PPC matrix, further improving barrier performance.

[0061] Meanwhile, in Comparative Example 1, the light transmittance of the blown film made by blending PBAT was only 90%, while the light transmittance of the other films was all >94%. This indicates that the polylactic acid film prepared by the method of this application has both excellent barrier properties and light transmittance, and can be used for the industrial production of highly transparent, highly barrier biodegradable blown films.

[0062] 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 this invention.

Claims

1. A biodegradable high-barrier polylactic acid film, characterized in that, The raw materials for preparing the biodegradable high-barrier polylactic acid film, by weight, include: 60-80 parts PLA, 20-40 parts PPC, 1-5 parts maleic anhydride modified starch, and 1-5 parts chain extender.

2. The biodegradable high-barrier polylactic acid film according to claim 1, characterized in that, The method for preparing maleic anhydride-modified starch is as follows: starch is mixed with water to form a suspension, the starch suspension is added to hydrolyzed maleic anhydride and dispersed, and the mixture is dried to obtain maleic anhydride-modified starch.

3. The biodegradable high-barrier polylactic acid film according to claim 2, characterized in that, The specific preparation method of the maleic anhydride modified starch is as follows: starch and water are mixed at a mass ratio of 1:1 and then ultrasonically dispersed to form a suspension. After hydrolyzing maleic anhydride, the starch suspension is added to it for high-speed dispersion and mixing. The mixture is dried to remove moisture and then pulverized and ground to obtain maleic anhydride modified starch.

4. The biodegradable high-barrier polylactic acid film according to claim 3, characterized in that, The hydrolysis temperature of the maleic anhydride is 60~80℃.

5. The biodegradable high-barrier polylactic acid film according to claim 3, characterized in that, The drying temperature of the mixture is 90~120℃, and the drying time is 10~15h.

6. The biodegradable high-barrier polylactic acid film according to claim 1, characterized in that, The chain extender is one of epoxy-functionalized acrylate chain extenders or epoxidized soybean oil.

7. A method for preparing a biodegradable high-barrier polylactic acid film, characterized in that, Includes the following steps: PLA, PPC, and maleic anhydride-modified starch were dried, mixed, melt-blended, granulated, dried, and blown into a film to obtain the biodegradable high-barrier polylactic acid film.

8. The method for preparing a biodegradable high-barrier polylactic acid film according to claim 7, characterized in that, The specific preparation method is as follows: (1) The PLA, PPC and maleic anhydride modified starch were dried at 70℃ for 12h to remove moisture, mixed evenly, melt-blended by a twin-screw extruder and then granulated. The resulting particles were placed in a 70℃ oven and dried for 12h to remove moisture for later use. (2) The particles prepared above are added to a blown film machine. The temperature of the blown film machine is set in segments of 180°C, 180°C, 170°C, 170°C and 150°C to obtain the biodegradable high-barrier polylactic acid film.