Method capable of simultaneously improving mechanical and barrier properties of modified polylactic acid film

Abstract

The invention discloses a method for simultaneously improving mechanical and barrier properties of a modified polylactic acid film, which comprises the following steps of: adding epoxy glyceride prepared by taking glyceride containing double bonds as a raw material into a raw material system of the modified polylactic acid film as a bio-based cross-linking agent; the formed composite system comprises the following components in parts by weight: 60-80 parts of polylactic acid; 10 to 30 parts of a biodegradable polyester elastomer; 1-10 parts of a bio-based cross-linking agent; 1-30 parts of light calcium carbonate; 0.1 to 2 parts of an antioxidant; the high-performance modified polylactic acid film is obtained by performing melt blending, extrusion and granulation on all the components through a double-screw extruder and then performing blow molding and film forming. The bio-based cross-linking agent is added into the modified polylactic acid film material, so that the compatibility among the components of the polylactic acid film material is improved, the mechanical property and barrier property of the material are improved, and the obtained polylactic acid film has high strength, high toughness, high barrier property and complete biodegradability; the requirements in the fields of food, medicine packaging, agricultural films and the like are met.

Description

Technical Field

[0001] The invention belongs to the technical field of modification of degradable polymer materials, and in particular relates to a method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film. Background Art

[0002] Traditional plastic packaging materials are mainly derived from petroleum and coal-based polymer materials, such as polypropylene, polyethylene and polyvinyl chloride. They have excellent comprehensive performance as packaging materials, but they are not easy to degrade in the environment and will produce ecological and environmental hazards such as "microplastics". Therefore, it is a trend to develop bio-based packaging materials and environmentally degradable packaging materials. In recent years, polylactic acid (PLA) and its blended composite materials have developed and applied rapidly in the field of packaging materials and have great development potential. In order to further improve the performance of PLA packaging materials and expand their scope of application, it is necessary to develop PLA packaging materials with excellent comprehensive properties such as mechanical and barrier properties.

[0003] Regarding the research and development of PLA packaging materials, some relevant invention patents have been disclosed so far. For example, Chinese patent CN113527854A discloses a high-strength and high-toughness polylactic acid composite material, which is first obtained by reacting diamine and dibasic acid to obtain a polyamide copolymer, and then mixed with polylactic acid to prepare a polylactic acid composite material. The composite material has a significant toughening effect relative to PLA, and improves the toughness and elongation at break of the PLA composite material, but the barrier performance is not improved. Chinese patent CN115433383B discloses a biodegradable polylactic acid barrier film and a preparation method thereof, in which D-lactide and diacetyl cellulose are first grafted to obtain a CDA-g-PDLA graft copolymer, and then a multilayer barrier film is prepared using polylactic acid and CDA-g-PDLA as raw materials. The production and processing technology of this method is complicated, and the mechanical and barrier properties of the resulting film still cannot meet the needs. Chinese patent CN117946502A discloses a polylactic acid toughening composition, a preparation method and the obtained polylactic acid resin. The chain extender in the component is a styrene-glycidyl methacrylate oligomer chain extender with an epoxy functional group. It only improves the mechanical properties of the polylactic acid resin, but does not improve the barrier properties, which makes it difficult to meet the current production demand for PLA packaging materials.

[0004] In summary, the PLA packaging materials reported in existing literature generally have problems such as the inability to simultaneously improve the comprehensive properties of film materials such as mechanics and barrier properties, and complex production processes. Summary of the invention

[0005] The present invention proposes a method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film. The method comprises the following steps: introducing epoxy groups through molecular design of glycerol ester, and introducing the epoxy groups into a polylactic acid / biodegradable polyester elastomer blend composite material. The interface and aggregate structure of the polylactic acid / biodegradable polyester elastomer are regulated through interfacial reaction. The basic properties of the polylactic acid / biodegradable polyester elastomer blend composite material are retained while the interaction force and compatibility between the two phases of polylactic acid and biodegradable polyester elastomer are improved. A cross-linked network is introduced to obtain a modified polylactic acid film with high strength, high toughness and high barrier properties.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention first provides a method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film, which is characterized in that a bio-based cross-linking agent is added to the raw material system of the modified polylactic acid film, thereby simultaneously improving the mechanical and barrier properties of the modified polylactic acid film, and the bio-based cross-linking agent is a glycidyl ester prepared from a glyceride containing a double bond as a raw material. A bio-based cross-linking agent with low biotoxicity and high biocompatibility is obtained by structurally designing the glyceride, and the epoxy groups contained in it can react with PLA and a biodegradable polyester elastomer through an epoxy ring-opening reaction during the melt blending process of preparing a film, forming macromolecular segments of polylactic acid and biodegradable polyester elastomer in the blending system, utilizing the physical entanglement between the macromolecular segments and the biodegradable polyester elastomer and the polylactic acid matrix to form a cross-linking network, and regulating the interface and aggregated structure of PBAT / PLA through interfacial reaction, effectively improving the compatibility of the polylactic acid / biodegradable polyester elastomer blend, and simultaneously improving the mechanical and barrier properties of the modified polylactic acid film. High-performance PLA packaging materials are of great significance to 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, wherein a bio-based cross-linking agent is added to the raw material system of the film.

[0009] Furthermore, in the raw material system of the modified polylactic acid film to which the bio-based cross-linking agent is added, the components are composed by weight as follows:

[0010] Polylactic acid 60-80 parts;

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

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

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

[0014] Antioxidant 0.1-2 parts.

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

[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, poly(1,8-octanediol-citric acid) and its derivatives.

[0017] Furthermore, the antioxidant is one or more mixtures 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 cross-linking 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 having excellent mechanical and barrier properties, comprising the following steps:

[0022] Step 1: Synthesis of bio-based cross-linking agent

[0023] Adding double-bond-containing glyceride, formic acid and hydrogen peroxide solution into a reactor, stirring and reacting at 50-80° C. for 8-24 hours to obtain an unseparated glycidyl ester solution (containing unreacted formic acid and hydrogen peroxide);

[0024] Chloroform is added to the unseparated glycidyl ester solution, and then washed with alkali solution until neutral (layering is carried out after adding alkali solution, the upper layer is formic acid and hydrogen peroxide, the upper layer is removed, and washing is repeated multiple times), and then rotary evaporation is carried out at 45-80° C. for 1-5 hours using a rotary evaporator, and 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° C. for 6-24 hours to obtain glycidyl ester as a bio-based cross-linking agent.

[0025] Step 2: Prepare the film

[0026] The bio-based cross-linking agent, polylactic acid, biodegradable polyester elastomer, light calcium carbonate and antioxidant are dried separately, melt-blended and extruded in a twin-screw extruder, the melt-blending temperature is 180-230° C., and the rotation speed is 190-250 rpm / min, and then the modified polylactic acid material is obtained by cooling, drawing, air-drying and pelletizing;

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

[0028] Preferably, in step 1, the double bond-containing glyceride is a mixture of one or more of castor oil, triolein, tripalmitin and trierucic acid triglyceride.

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

[0030] Preferably, in step 2, before melt blending and extrusion, the raw materials need to be dried, for example, they can be placed in a vacuum oven for vacuum drying, the drying temperature can be set to 50° C.-100° C., and the drying time can be set to 6-24 hours.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The present invention adds a bio-based cross-linking agent to the modified polylactic acid film material, thereby improving the compatibility between the components of the polylactic acid film material and simultaneously improving the mechanical properties and barrier properties of the material, so that the obtained polylactic acid film has high strength, high toughness, high barrier properties and complete biodegradability, meeting the requirements of the fields of food, pharmaceutical packaging and agricultural films. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of epoxy castor oil prepared in the example.

[0034] Figure 2 IR spectrum of the epoxy castor oil prepared in the example. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described in detail below in conjunction with several embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] The raw materials for preparing the modified polylactic acid films in various embodiments and comparative examples are shown in Table 1:

[0037] Table 1. Raw materials and dosages (by weight) for preparing modified polylactic acid films in various embodiments and comparative examples

[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 cross-linkers \ 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 weight average molecular weight of the polylactic acid used in each embodiment is 230000 g / mol and the density is 1.24 g / cm 3 , the melt index is 7g / 10min.

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

[0041] 1) 10 g of castor oil, 8 g of formic acid solution and a 30% hydrogen peroxide solution containing 3.6 g of hydrogen peroxide were added into a reactor, and stirred for reaction at 60° C. for 12 h to obtain an unseparated epoxy castor oil solution.

[0042] 2) Add chloroform to the unseparated epoxyglycerol solution, then wash with a saturated sodium bicarbonate aqueous solution until neutral, and then use a rotary evaporator to rotary evaporate for 2 hours at 50° C., and dry the oily substance obtained after rotary evaporation in a vacuum oven with a vacuum degree of -0.1 MPa and a temperature of 60° C. for 12 hours to obtain epoxy castor oil as a bio-based cross-linking agent, whose structural formula and infrared spectrum are shown in Figure 1 and Figure 2 shown.

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

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

[0045] 2) Polylactic acid, polybutylene adipate-terephthalate, bio-based crosslinking agent, light calcium carbonate and antioxidant 1010 were mixed uniformly according to the weight proportions in Table 1, added into a twin-screw extruder at a speed of 220 rpm / min, melt-blended and extruded at 190° C., and then cooled, drawn, air-dried and pelletized to obtain a 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° C., and the main machine screw speed is 70 rpm / 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 specimens for testing mechanical properties, and the obtained modified polylactic acid film materials were tested for barrier properties. The test standards are as follows:

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

[0049] Izod notched impact strength, tested according to ISO 180 standard.

[0050] Barrier properties are 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 various embodiments and comparative examples

[0053]

[0054] Comparing Comparative Example 1 with Examples 1-5, it can be seen that the bio-based cross-linking agent prepared by the present invention can effectively improve the compatibility, mechanical properties and barrier properties of the polylactic acid (PLA) / polybutylene adipate-terephthalate (PBAT) composite material. At the same time, the higher the content of the bio-based cross-linking agent, the better the volume expansion effect on the polylactic acid (PLA) / polybutylene adipate-terephthalate (PBAT) composite material, the higher the tensile strength, elongation at break and impact strength of the prepared polylactic acid composite material, and the better the barrier property. The above results show that the bio-based cross-linking agent synthesized by the present invention can effectively improve the compatibility and interfacial bonding force of polylactic acid (PLA) and biodegradable polyester elastomer, significantly improve the strength and toughness of polylactic acid film materials, and at the same time achieve the improvement of the barrier properties of polylactic acid film materials, and has high application value in various fields.

[0055] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution 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, such as a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film, characterized in that: A bio-based cross-linking agent is added to the raw material system of the modified polylactic acid film, thereby improving the mechanical and barrier properties of the modified polylactic acid film at the same time. The bio-based cross-linking agent is glycidyl glycidyl ester prepared from glycerol ester containing double bonds as raw material.

2. A method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1, characterized in that: The raw material system of the modified polylactic acid film with a bio-based cross-linking agent includes the following components in parts by weight: Polylactic acid 60-80 parts; 10-30 parts of biodegradable polyester elastomer; 1-10 parts of bio-based cross-linking agent; Light calcium carbonate 1-30 parts; Antioxidant 0.1-2 parts.

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

4. The method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 2, characterized in that: 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, poly(1,8-octanediol-citric acid) and its derivatives.

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 structure of the bio-based cross-linking agent is shown in formula (1): 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.

6. A method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1 or 5, characterized in that: The synthesis steps of the bio-based cross-linking agent include: Adding double-bond-containing glyceride, formic acid and hydrogen peroxide solution into a reactor, stirring and reacting at 50-80° C. for 8-24 hours to obtain an unseparated glycidyl ester solution; Chloroform is added to the unseparated glycidyl ester solution, and then washed with alkali solution until neutral, and then rotary evaporated at 45-80° C. for 1-5 hours using a rotary evaporator, and 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° C. for 6-24 hours to obtain glycidyl ester as a bio-based cross-linking agent.

7. A method for simultaneously improving the mechanical and barrier properties of a modified polylactic acid film according to claim 1 or 5, characterized in that: The double-bond-containing glyceride is a mixture of one or more of castor oil, triolein, tripalmitin and trierucic acid triglyceride.

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

6.

9. A modified polylactic acid film having excellent mechanical and barrier properties obtained by the method according to any one of claims 1 to 8, characterized in that: A bio-based cross-linking agent is added into the raw material system of the film.

10. A method for preparing the modified polylactic acid film having excellent mechanical and barrier properties as claimed in claim 9, characterized in that: The bio-based cross-linking agent, polylactic acid, biodegradable polyester elastomer, light calcium carbonate and antioxidant are dried separately, melt-blended and extruded in a twin-screw extruder, the melt-blending temperature is 180-230° C., and the rotation speed is 190-250 rpm / min, and then the modified polylactic acid material is obtained by cooling, drawing, air-drying and pelletizing; The modified polylactic acid material is added into a blow molding machine to blow a film, the temperature of each section of the blow molding machine is 170-200° C., and the main machine screw speed is 50-100 rpm / min, so as to obtain a modified polylactic acid film with excellent mechanical and barrier properties.

11. Use of the modified polylactic acid film having excellent mechanical and barrier properties as claimed in claim 9 in food packaging, pharmaceutical packaging or agricultural film.

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