A method to simultaneously improve the mechanical and barrier properties of modified polylactic acid films

Abstract

This invention discloses a method for simultaneously improving the mechanical and barrier properties of modified polylactic acid (PLA) films. The method involves adding an epoxy glycerol ester, obtained from a double-bonded glycerol ester, as a bio-based crosslinking agent to the raw material system of the modified PLA film. The resulting composite system comprises the following components by weight: 60-80 parts PLA; 10-30 parts biodegradable polyester elastomer; 1-10 parts bio-based crosslinking agent; 1-30 parts light calcium carbonate; and 0.1-2 parts antioxidant. After melt-blending and granulation of each component using a twin-screw extruder, the mixture is blow-molded into a film to obtain a high-performance modified PLA film. This invention, by adding a bio-based crosslinking agent to the modified PLA film material, improves the compatibility between the PLA film material components and simultaneously enhances the material's mechanical and barrier properties. The resulting PLA film possesses high strength, high toughness, high barrier properties, and complete biodegradability, meeting the requirements of food, pharmaceutical packaging, and agricultural films.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymer material modification technology, specifically relating to a method that can simultaneously improve the mechanical and barrier properties of modified polylactic acid films. Background Technology

[0002] Traditional plastic packaging materials are mainly derived from petroleum and coal-based polymers, such as polypropylene, polyethylene, and polyvinyl chloride. While these materials offer excellent overall performance as packaging materials, they are not easily degraded in the environment, leading to environmental hazards such as microplastics. Therefore, the development of bio-based and environmentally degradable packaging materials is a trend. In recent years, polylactic acid (PLA) and its blends have seen rapid development and application in the packaging materials field, demonstrating enormous potential. To further improve the performance of PLA packaging materials and expand their application range, it is necessary to develop PLA packaging materials with excellent comprehensive properties, including mechanical and barrier properties.

[0003] Regarding the research and development of PLA packaging materials, several related invention patents have been published to date. For example, Chinese patent CN113527854A discloses a high-strength and high-toughness polylactic acid composite material. This involves first reacting a diamine with a diacid to obtain a polyamide copolymer, which is then blended with polylactic acid to prepare the polylactic acid composite material. This composite material exhibits a significant toughening effect compared to PLA, improving the toughness and elongation at break of the PLA composite material, but its barrier properties are not improved. Chinese patent CN115433383B discloses a biodegradable polylactic acid barrier film and its preparation method. This method involves first grafting D-lactide with cellulose diacetate to obtain a CDA-g-PDLA graft copolymer, and then using polylactic acid and CDA-g-PDLA as raw materials to prepare a multilayer barrier film. This method has a complex production process, and the mechanical and barrier properties of the resulting film still do not meet the requirements. Chinese patent CN117946502A discloses a polylactic acid toughening composition, preparation method, and obtained polylactic acid resin. The chain extender in the composition is a styrene-glycidyl methacrylate oligomer chain extender with epoxy functional groups. It only improves the mechanical properties of polylactic acid resin, but does not improve the barrier properties, which is difficult to meet the current production needs for PLA packaging materials.

[0004] In summary, existing literature reports that PLA packaging materials generally suffer from problems such as the inability to simultaneously improve the comprehensive properties of film materials, including mechanical and barrier properties, and complex manufacturing processes. Summary of the Invention

[0005] This invention proposes a method to simultaneously improve the mechanical and barrier properties of modified polylactic acid (PLA) films. This is achieved by introducing epoxy groups into glycerol esters through molecular design and then incorporating them into a PLA / biodegradable polyester elastomer blend. The interfacial reaction is used to regulate the interface and aggregated structure of the PLA / biodegradable polyester elastomer. This method enhances the interaction force and compatibility between the PLA and biodegradable polyester elastomer phases while retaining the basic properties of the PLA / biodegradable polyester elastomer blend, and introduces a crosslinked network, resulting in a high-strength, high-toughness, and high-barrier modified PLA film.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention first provides a method for simultaneously improving the mechanical and barrier properties of modified polylactic acid (PLA) films. The method is characterized by adding a bio-based crosslinking agent to the raw material system of the modified PLA film, thereby simultaneously improving the mechanical and barrier properties of the modified PLA film. The bio-based crosslinking agent is an epoxy glycerol ester obtained from a glycerol ester containing double bonds. By structurally designing the glycerol ester, a low-biotoxicity, highly biocompatible bio-based crosslinking agent is obtained. The epoxy groups contained in this agent can react with PLA and biodegradable polyester elastomer through an epoxy ring-opening reaction during the melt blending process to form macromolecular segments of PLA and biodegradable polyester elastomer in the blend system. The physical entanglement between these macromolecular segments and the biodegradable polyester elastomer and PLA matrix forms a crosslinking network. Furthermore, the interfacial reaction regulates the interfacial and aggregated structure of PBAT / PLA, effectively improving the compatibility of the PLA / biodegradable polyester elastomer blend and simultaneously enhancing the mechanical and barrier properties of the modified PLA film. High-performance PLA packaging materials are of great significance for reducing microplastic pollution and protecting the ecological environment.

[0008] Based on the above method, the present invention further provides a modified polylactic acid film with excellent mechanical and barrier properties, which is made by adding a bio-based crosslinking agent to the raw material system of the film.

[0009] Furthermore, in the raw material system of the modified polylactic acid film with added bio-based crosslinking agent, the composition of each component by weight is as follows:

[0010] Polylactic acid 60-80 parts;

[0011] 10-30 parts of biodegradable polyester elastomer;

[0012] 1-10 parts of bio-based crosslinking agent;

[0013] 1-30 parts of light calcium carbonate;

[0014] Antioxidant 0.1-2 parts.

[0015] Furthermore, the polylactic acid has a weight-average molecular weight of 50,000–300,000 g / mol and a density of 1.24–1.28 g / cm³. 3 The melt flow index is 6-8 g / 10 min.

[0016] Furthermore, the biodegradable polyester elastomer is one or more polymers selected from polybutylene adipate terephthalate, polycaprolactone, polypropylene carbonate, polybutylene succinate, bio-based thermoplastic polyurethane, polyglycerol sebacate and its derivatives, and poly(1,8-octanediol-citric acid) and its derivatives.

[0017] Further, the antioxidant is one or more of antioxidant 168, antioxidant 300, antioxidant 618, antioxidant 626, antioxidant 1010, antioxidant 1076, antioxidant TBHQ, antioxidant AT-10, antioxidant BHT, etc.

[0018] Furthermore, the structure of the bio-based crosslinking agent is shown in formula (1):

[0019]

[0020] In the formula, R is H or OH, x is any integer from 7 to 11, and y is any integer from 4 to 6.

[0021] The present invention also provides a method for preparing the modified polylactic acid film with excellent mechanical and barrier properties, comprising the following steps:

[0022] Step 1: Synthesize bio-based cross-linking agents

[0023] A solution of glycerol ester containing double bonds, formic acid, and hydrogen peroxide is added to a reactor and stirred at 50-80℃ for 8-24 hours to obtain an unseparated epoxy glycerol ester solution (containing unreacted formic acid and hydrogen peroxide).

[0024] Add chloroform to the unseparated epoxy glycerol ester solution, then wash with alkaline solution until neutral (after adding alkaline solution, the layers separate, the upper layer is formic acid and hydrogen peroxide, remove the upper layer, and wash repeatedly), then rotary evaporate at 45-80℃ for 1-5 hours using a rotary evaporator, and dry the oily substance obtained after rotary evaporation in a vacuum oven at -0.1MPa and 40-80℃ for 6-24 hours to obtain epoxy glycerol ester as a bio-based crosslinking agent.

[0025] Step 2: Prepare thin film

[0026] After drying the bio-based crosslinking agent, polylactic acid, biodegradable polyester elastomer, light calcium carbonate and antioxidant separately, they were melt-blended and extruded in a twin-screw extruder at a melt-blending temperature of 180-230℃ and a speed of 190-250 rpm / min. The modified polylactic acid material was then obtained by cooling, stretching, air-drying and pelletizing.

[0027] The modified polylactic acid material is added to a blow molding machine to blow a film. The temperature of each section of the blow molding machine is 170-200℃, and the main screw speed is 50-100 rpm / min, to obtain a modified polylactic acid film with excellent mechanical and barrier properties.

[0028] Preferably, in step 1, the double-bonded glyceride is one or more of castor oil, trioleate, tripalmitate and trierucic acid triglyceride.

[0029] Preferably, in step 1, the mass ratio of the double-bonded glycerol ester to formic acid is 1:0.5-1.0, and the mass ratio of the double-bonded glycerol ester to the hydrogen peroxide is 1:0.3-0.6.

[0030] Preferably, in step 2, before melt blending and extrusion, each raw material needs to be dried, such as by placing it in a vacuum oven for vacuum drying. The drying temperature can be set to 50℃-100℃ and the drying time can be set to 6-24h.

[0031] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0032] This invention adds a bio-based crosslinking agent to modified polylactic acid (PLA) film materials, which improves the compatibility between PLA film material components and enhances the mechanical and barrier properties of the material. The resulting PLA film has high strength, high toughness, high barrier properties, and is fully biodegradable, meeting the requirements of food, pharmaceutical packaging, and agricultural films. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the epoxidized castor oil prepared in the examples.

[0034] Figure 2 The image shows the infrared spectrum of the epoxy castor oil prepared in the examples. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to several embodiments and accompanying drawings. 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.

[0036] The raw materials used to prepare the modified polylactic acid films in each embodiment and comparative example are shown in Table 1:

[0037] Table 1. Raw materials and amounts used in the preparation of modified polylactic acid films in each example and comparative example (by weight parts)

[0038] Components Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 PLA 70.0 70.0 70.0 70.0 70.0 70.0 PBAT 30.0 30.0 30.0 30.0 30.0 30.0 Bio-based crosslinking agent \ 1.0 3.0 5.0 7.0 9.0 Light calcium carbonate 10.0 10.0 10.0 10.0 10.0 10.0 Antioxidant 1010 0.1 0.1 0.1 0.1 0.1 0.1

[0039] The polylactic acid used in each embodiment had a weight-average molecular weight of 230,000 g / mol and a density of 1.24 g / cm³. 3 The melt flow index is 7 g / 10 min.

[0040] The preparation steps of the bio-based crosslinking agent epoxidized castor oil used in each embodiment are as follows:

[0041] 1) Add 10g castor oil, 8g formic acid solution and 3.6g hydrogen peroxide solution with a mass concentration of 30% to the reactor, and stir the reaction at 60℃ for 12h to obtain unseparated epoxy castor oil solution.

[0042] 2) Add chloroform to the unseparated epoxy glycerol ester solution, then wash with a saturated sodium bicarbonate aqueous solution until neutral, and then rotary evaporate at 50°C for 2 hours. Dry the resulting oily substance in a vacuum oven at -0.1 MPa and 60°C for 12 hours to obtain epoxy castor oil as a bio-based crosslinking agent. Its structural formula and infrared spectrum are shown below. Figure 1 and Figure 2 As shown.

[0043] The preparation steps of the high-strength, high-toughness, and high-barrier modified polylactic acid films in each embodiment and comparative example are as follows:

[0044] 1) First, polylactic acid, polybutylene adipate terephthalate, bio-based crosslinking agent, light calcium carbonate and antioxidant are vacuum dried at 60°C for 12 hours.

[0045] 2) According to the weight ratio in Table 1, polylactic acid, polybutylene adipate terephthalate, bio-based crosslinking agent, light calcium carbonate and antioxidant 1010 are mixed evenly and then added to a twin-screw extruder with a speed of 220 rpm / min. The mixture is melt-blended and extruded at 190°C, and then cooled, stretched, air-dried and pelletized to obtain modified polylactic acid material.

[0046] 3) The modified polylactic acid material obtained above is added to a blow molding machine to blow a film. The temperature of each section of the blow molding machine is 180℃ and the main screw speed is 70rpm / min. After melt blow molding, a high-strength, high-toughness, and high-barrier modified polylactic acid film material is obtained.

[0047] The modified polylactic acid materials prepared in the above comparative examples and embodiments were hot-pressed into test strips for mechanical property testing. The resulting modified polylactic acid film materials were also tested for barrier properties. The testing standards are as follows:

[0048] Tensile strength, tested according to ISO 527 standard, at a speed of 50 mm / min.

[0049] The notched impact strength of the cantilever beam was tested according to ISO 180 standard.

[0050] Barrier performance was tested according to GB / T 1037-2021 standard.

[0051] The test results are shown in Table 2.

[0052] Table 2. Test results of composite material properties in each example and comparative example.

[0053]

[0054] Comparing Comparative Example 1 with Examples 1-5, it can be seen that the bio-based crosslinking agent prepared in this invention can effectively improve the compatibility, mechanical properties, and barrier properties of polylactic acid (PLA) / polybutylene adipate terephthalate (PBAT) composite materials. Furthermore, the higher the content of the bio-based crosslinking agent, the better the compatibility enhancement effect on the PLA / PBAT composite material, and the higher the tensile strength, elongation at break, and impact strength of the prepared PLA composite material, as well as the better its barrier properties. These results indicate that the bio-based crosslinking agent synthesized in this invention can effectively improve the compatibility and interfacial bonding force between PLA and biodegradable polyester elastomers, significantly improve the strength and toughness of PLA film materials, and simultaneously enhance the barrier properties of PLA film materials, demonstrating high application value in various fields.

[0055] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

Claims

1. A method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film, characterized in that, The raw material system of the modified polylactic acid film is added with a bio-based crosslinking agent, so as to simultaneously improve the mechanical property and barrier property of the modified polylactic acid film, the bio-based crosslinking agent being an epoxy glyceride prepared from a double-bond-containing glyceride; the raw material system of the modified polylactic acid film added with the bio-based crosslinking agent comprises the following components in parts by weight: Polylactic acid 60-80 parts; Biodegradable polyester elastomer 10-30 parts; Bio-based crosslinking agent 1-10 parts; Light calcium carbonate 1-30 parts; Antioxidant 0.1-2 parts; The structure of the bio-based crosslinking agent is shown in formula (1): （1） In the formula, R is H or OH, x is any integer in 7-11, and y is any integer in 4-6.

2. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1, characterized in that, The weight average molecular weight of the polylactic acid is 50,000 to 300,000 g / mol, the density is 1.24 to 1.28 g / cm 3 , and the melt index is 6 to 8 g / 10 min.

3. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1, characterized in that, The biodegradable polyester elastomer is one or more polymers selected from the group consisting of polybutylene adipate terephthalate, polycaprolactone, polypropylene carbonate, polybutylene succinate, bio-based thermoplastic polyurethane, polyglycerol sebacate and poly(1,8-octanediol-limonene dicarboxylate).

4. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1, characterized in that, The synthesis steps of the bio-based crosslinking agent include: The double-bond-containing glyceride, formic acid and hydrogen peroxide solution are added into a reactor, and stirred at 50-80 ℃ for 8-24 h to obtain an unseparated epoxy glyceride solution; Trichloromethane is added into the unseparated epoxy glyceride solution, and then washed with lye until neutral, and then rotary evaporated at 45-80 ℃ for 1-5 h using a rotary evaporator; the oily substance obtained after rotary evaporation is dried in a vacuum oven at a vacuum degree of -0.1 MPa and a temperature of 40-80 ℃ for 6-24 h to obtain the epoxy glyceride as the bio-based crosslinking agent.

5. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1, characterized in that, The double-bond-containing glyceride is a mixture of one or more of castor oil, glycerol trioleate, glycerol tripalmitate and trierucin.

6. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 4, characterized in that, The mass ratio of the double-bond-containing glyceride to formic acid is 1:0.5-1.0, and the mass ratio of the double-bond-containing glyceride to the hydrogen peroxide is 1:0.3-0.

6.

7. A modified polylactic acid film having excellent mechanical and barrier properties, obtained by the method according to any one of claims 1 to 6, characterized in that, The bio-based crosslinking agent is added into the raw material system of the film.

8. A preparation method of the modified polylactic acid film with excellent mechanical and barrier properties according to claim 7, characterized in that: The bio-based crosslinking agent, polylactic acid, biodegradable polyester elastomer, light calcium carbonate and antioxidant are dried respectively, and then melt blended and extruded in a double-screw extruder, the melt blending temperature being 180-230 ℃ and the rotation speed being 190-250 rpm / min, and then the modified polylactic acid material is obtained through cooling, drawing, air drying and granulation; The modified polylactic acid material is blown into a film in a blowing machine, the temperature of each section of the blowing machine being 170-200 ℃, and the rotation speed of the main screw being 50-100 rpm / min, so as to obtain the modified polylactic acid film with excellent mechanical and barrier properties.

9. Use of the modified polylactic acid film with excellent mechanical and barrier properties according to claim 7 in food packaging, medicine packaging or agricultural film.

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