Biodegradable plastic packaging film material and preparation method thereof

Abstract

The invention discloses a biodegradable plastic packaging film material and a preparation method thereof, and belongs to the technical field of polyester materials. The biodegradable plastic packaging film material is prepared from the following substances in parts by weight: 85-95 parts of poly (terephthalic acid) / side chain aliphatic diacid butanediol copolyester, 3-10 parts of polylactic acid, 2-10 parts of a compatilizer, 1-20 parts of an inorganic filler, 0.01-2 parts of an epoxy chain extender and 0.5-2 parts of a lubricant, the compatilizer is a triblock copolymer of polylactic acid-poly (butylene adipate) with a side chain and polylactic acid, and the number-average molecular weight of the triblock copolymer is 2000 to 3500 g / mol. According to the preparation method, terephthalic acid / aliphatic diacid butanediol copolyester with side chains is adopted as a base material to be blended with PLA, the triblock compatilizer is added, and the mixture is matched with the epoxy chain extender, the lubricant and the inorganic filler in a synergistic effect mode, so that the prepared packaging film material is excellent in mechanical property, the damp-heat aging resistance and the water vapor barrier property are improved, and the packaging film material is suitable for large-scale popularization and application. And the application environment is wider.

Description

Technical Field

[0001] The present application relates to a biodegradable plastic packaging film material and a preparation method thereof, belonging to the technical field of polyester materials. Background Art

[0002] Traditional plastic film materials are often mainly made of petroleum-based raw materials such as polypropylene (PP) and polyethylene (PE), and it is difficult to be degraded in the natural environment after use, which brings great harm and impact to the environment. With the improvement of environmental protection requirements, biodegradable materials have received more and more attention in the field of packaging film materials. Therefore, traditional non-degradable plastics are gradually being replaced by biodegradable materials.

[0003] At present, the more commonly used degradable polyester materials, such as poly(butylene adipate-co-terephthalate) (PBAT), belong to thermoplastic biodegradable plastics, which have good ductility, elongation at break and good heat resistance. However, PBAT has problems of insufficient tensile strength and rigidity. In order to make up for its disadvantages, PBAT often needs to be blended with other biodegradable materials, such as polylactic acid (PLA) for use. And there is an aromatic structure in the PBAT molecule, and PLA is an aliphatic structure with a methyl side group. The mixing enthalpy of the two is relatively high. Therefore, generally, the compatibility of PBAT and PLA is poor, which limits their wide application.

[0004] In addition, most of the current polyester plastic packaging film products have problems of poor heat aging resistance and water vapor barrier performance. Therefore, on the one hand, it is necessary to develop new polyester products with sufficient strength and toughness, and high heat aging resistance and high water vapor barrier performance; on the other hand, good solutions also need to be proposed for the problem of poor compatibility of polyester materials during blending. Summary of the Invention

[0005] In order to solve the above problems, the present application proposes a biodegradable plastic packaging film material and a preparation method thereof. By using poly(butylene terephthalate-co-fatty acid with side chain) as the matrix material and adding a block copolymer as the compatibilizer between the matrix material and PLA, the compatibility of each component in the packaging film material is improved, so that the comprehensive properties such as mechanical properties, heat aging resistance and water vapor barrier performance are enhanced.

[0006] According to one aspect of the present application, there is provided a biodegradable plastic packaging film material, which is prepared from the following substances in parts by weight: 85-95 parts of poly(butylene terephthalate-co-fatty acid with side chain), 3-10 parts of polylactic acid, 2-10 parts of compatibilizer, 1-20 parts of inorganic filler, 0.01-2 parts of epoxy chain extender, and 0.5-2 parts of lubricant;

[0007] The compatibilizer is a triblock copolymer of polylactic acid - poly(butylene adipate with side-chain fatty diacid) - polylactic acid, and the number-average molecular weight of the triblock copolymer is 2000 - 3500 g / mol.

[0008] Specifically, the number-average molecular weight of the poly(terephthalic acid / butylene adipate with side-chain fatty diacid) copolymer is 3×10 4 g / mol - 12×10 4 g / mol; the number-average molecular weight of PLA is 2×10 4 g / mol - 11×10 4 g / mol.

[0009] The side-chain alkyl groups in the copolyester reduce the regularity and crystallinity of the polymer molecular chains, thereby enhancing the structural stability of the copolyester molecular chains, and further improving the tensile properties of the packaging film material; in addition, the side-chain alkyl groups can effectively increase the density of the non-crystalline region, so that the heat aging resistance and water vapor barrier properties of the packaging film material are improved;

[0010] This setting is achieved by adding a triblock copolymer of polylactic acid - poly(butylene adipate with side-chain fatty diacid) - polylactic acid. Since the block copolymer compatibilizer has the same chain segments as PLA and poly(terephthalic acid / butylene adipate with side-chain fatty diacid), self-assembly will occur at the interface during the blending process. Therefore, it can more effectively reduce the interfacial tension between the two, avoid the occurrence of phase separation, improve the uniformity of the packaging film material, and achieve the enhancement and toughening of PLA and poly(terephthalic acid / butylene adipate with side-chain fatty diacid); at the same time, the introduction of side chains in the matrix polyester is beneficial to increasing the density of the non-crystalline region of the polyester material, thereby enhancing the barrier properties of the film material. Finally, the obtained biodegradable plastic packaging film material has excellent mechanical properties, heat aging resistance and water vapor barrier properties.

[0011] Optionally, the synthesis process of the triblock copolymer is as follows:

[0012] Using a fatty diacid with side chains and 1,4-butanediol as polymerization monomers, a poly(butylene adipate with side-chain fatty diacid) macromolecular initiator is prepared by an esterification-polycondensation process;

[0013] The macromolecular initiator undergoes an esterification-polycondensation reaction with lactic acid under the action of a catalyst to obtain a triblock copolymer;

[0014] Among them, the structural formula of the fatty diacid with side chains is shown in Formula I, the structural formula of the macromolecular initiator is shown in Formula II, and the structural formula of the triblock polymer is shown in Formula Ш:

[0015]

[0016] Among them, in Formula I, x is an integer from 1 to 5, and y is an integer from 1 to 4; in Formula Ш, m is the number of polylactic acid structural units, m' is the number of polylactic acid structural units, and n is the number of structural units of poly(butylene adipate) with side chains; m, m', and n are integers, and the molar ratio of (m + m'):n is (1 - 2):(3 - 6).

[0017] The block length of the block compatibilizer can endow good compatibility between the polyester matrix material and lactic acid within a certain range. If the block length is too long, it will affect the migration ability of the block compatibilizer and cannot achieve a good compatibilizing effect at the interface; if the block length is too short, it cannot form an effective entanglement with the matrix material, which will also affect the compatibilizing effect.

[0018] Optionally, the poly(terephthalic acid / butylene adipate with side chains) is obtained by an esterification-polycondensation process using adipic acid with side chains, terephthalic acid, and 1,4-butanediol as polymerization monomers;

[0019] Among them, the molar ratio of terephthalic acid to adipic acid with side chains is 1:1 - 5, and the ratio of the sum of the molar numbers of terephthalic acid and adipic acid with side chains to 1,4-butanediol is 1:1 - 2.

[0020] The ratio between various monomers will affect the tensile strength of the packaging film material: when the content of the hard segment monomer terephthalic acid is relatively high, the overall strength of the copolyester increases, and the strength of the obtained packaging film material is correspondingly enhanced, while the elongation at break will decrease to a certain extent; when the content of the hard segment monomer terephthalic acid is relatively low, the toughness of the copolyester increases, and the tensile strength of the obtained packaging film material decreases.

[0021] Optionally, the side chain of the adipic acid monomer with side chains has 2 - 5 carbon atoms, and the main chain has 4 - 8 carbon atoms.

[0022] Optionally, the epoxy chain extender is an epoxy chain extender with a bio-based aconitic acid as the backbone, and the structural general formula is shown in Formula IV:

[0023]

[0024] Among them, in Formula IV, p is an integer from 1 to 4.

[0025] The epoxy chain extender with a biobased aconitic acid backbone contains three epoxy groups, which can undergo a polymerization reaction with the hydroxyl groups at the chain ends of the copolyester. It can not only increase the molecular weight of the copolyester but also crosslink linear polymers into a network structure, improving the thermal aging resistance and water vapor barrier properties of the packaging film material. By limiting the number of carbon atoms in the carbon chain of the epoxy alcohol, the molecular structure of the crosslinking sites of the chain extender can be controlled, playing a role in regulating the spatial density of the crosslinking sites. Relying on the double bond structure in the aconitic acid ester, it can play a good rigid support role, which is beneficial to enhancing the rigidity of the crosslinking sites, thereby promoting the improvement of its mechanical properties. The epoxy chain extender with a biobased aconitic acid backbone has higher green environmental protection compared to other chemically sourced epoxy chain extenders.

[0026] Optionally, the inorganic filler is one or more of calcium carbonate, talcum powder, silica, zinc stearate, and hydrotalcite.

[0027] Optionally, the lubricant is one or more of zinc stearate, ethylene bisstearamide, erucamide, and oleamide.

[0028] According to another aspect of the present application, there is provided a method for preparing a biodegradable plastic packaging film material, including the following steps:

[0029] (1) Put the poly(butylene terephthalate / copolyesters of aliphatic dicarboxylic acids with side chains) and polylactic acid into an oven for drying and reserve.

[0030] (2) Weigh the epoxy chain extender and the dried poly(butylene terephthalate / copolyesters of aliphatic dicarboxylic acids with side chains) according to the amount, add them to a high-speed mixer, and then add the compatibilizer, polylactic acid, inorganic filler, and lubricant and mix them evenly together.

[0031] (3) Add the above-mentioned evenly mixed materials to a screw extruder for extrusion granulation, and after extrusion granulation, blow film to obtain the packaging film material.

[0032] Optionally, in step (1), the drying temperature is 30 - 80 °C and the drying time is 1 - 6 h.

[0033] Optionally, in step (2), the speed setting of the high-speed mixer is to stir at a low speed of 180 r / min for 10 min first, and then stir at a high speed of 1000 r / min for 20 min;

[0034] The temperature of the screw extrusion in step (3) is 180 - 220 °C and the screw rotation speed is 250 r / min.

[0035] The beneficial effects that can be produced by the present application include but are not limited to:

[0036] 1. The biodegradable plastic packaging film material provided by this application blends poly(butylene terephthalate / alkane-substituted aliphatic dicarboxylate) as the matrix material with polylactic acid, and adds a triblock copolymer of polylactic acid - poly(alkane-substituted aliphatic dicarboxylate)-polylactic acid as a compatibilizer, reducing the interfacial strength between the copolyester and polylactic acid and improving their compatibility; meanwhile, under the synergistic action of an epoxy chain extender, inorganic filler, and lubricant, the overall uniformity of the packaging film material is good, and the mechanical properties, heat resistance, and water vapor barrier properties of the obtained packaging film material are all improved.

[0037] 2. The biodegradable plastic packaging film material provided by this application uses poly(butylene terephthalate / alkane-substituted aliphatic dicarboxylate) as the matrix material. The alkyl side chains in the copolyester reduce the regularity and crystallinity of the polymer molecular chains, thereby enhancing the structural stability of the copolyester molecular chains and further improving the tensile properties of the packaging film material; in addition, the alkyl side chains can effectively increase the density of the amorphous region, thus enhancing the thermal aging resistance and water vapor barrier properties of the packaging film material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of this application and form a part of this application. The schematic embodiments and descriptions thereof are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0039] Figure 1 It is the tensile test diagram of the film material in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The following describes this application in detail with reference to the embodiments, but this application is not limited to these embodiments.

[0041] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be obtained through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in the conventional manner in the art or according to the product instructions. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention. The preferred implementation methods and materials described in this patent are only for demonstration purposes.

[0042] In the following preparation method of the biodegradable packaging film material, the preparation method of the epoxy chain extender used is:

[0043] T1. React aconitic acid with thionyl chloride at 100 °C to obtain an acyl chloride intermediate;

[0044] T2. React the acyl chloride intermediate with epoxy alcohol at 20 °C to obtain an epoxy chain extender with a bio-based aconitic acid backbone;

[0045] The structural formula of the obtained epoxy alcohol is as shown in the following formula,

[0046]

[0047] wherein p is an integer from 1 to 4, and p depends on the type of epoxy alcohol. For example, when it is epoxy butanol, p is 2.

[0048] Example 1

[0049] The preparation method of the biodegradable plastic packaging film material includes the following steps:

[0050] (1) Put the poly(butylene terephthalate / cyclic aliphatic dicarboxylate) and polylactic acid into an oven and dry them at 40 °C for 4 h for later use;

[0051] (2) Add 1.2 parts of epoxy chain extender and 90 parts of poly(butylene terephthalate / methylsuccinic acid) to a high-speed mixer and mix evenly. Then add 6 parts of compatibilizer, 7 parts of polylactic acid, 1.5 parts of calcium carbonate, and 1.2 parts of zinc stearate and mix evenly together. The mixing speed of the high-speed mixer is set to stir at a low speed of 180 r / min for 10 min first, and then stir at a high speed of 1000 r / min for 20 min;

[0052] Among them, the molar ratio of terephthalic acid to methylsuccinic acid in the poly(butylene terephthalate / methylsuccinic acid) monomer is 1:3, the molar ratio of the sum of the moles of terephthalic acid and methylsuccinic acid to 1,4-butanediol is 1:1.5, and the molecular weight of the obtained poly(butylene terephthalate / methylsuccinic acid) is 8×10 4 g / mol; the molecular weight of polylactic acid is 9×10 4 g / mol; the compatibilizer is a PLA-poly(butylene methylsuccinate)-PLA block copolymer with a number-average molecular weight of 2600 g / mol; the epoxy chain extender is an epoxy chain extender with a biobased aconitic acid as the backbone, the number of carbon atoms in its aliphatic chain p = 3, and the type of epoxy alcohol used is epoxy pentanol;

[0053] (3) Add the above-mentioned evenly mixed materials into a screw extruder for extrusion granulation. The temperature of the screw extrusion is 180 °C, the screw speed is 250 r / min, and after extrusion granulation, blow molding is carried out to obtain the packaging film material 1#.

[0054] Example 2

[0055] The preparation method of the biodegradable plastic packaging film material includes the following steps:

[0056] (1) Put the poly(butylene terephthalate / cyclic aliphatic dicarboxylate) and polylactic acid into an oven and dry them at 30 °C for 1 h for later use;

[0057] (2) Add 0.01 part of epoxy chain extender, 85 parts of poly(butylene terephthalate / ethylene butanedioate) into a high-speed mixer and mix evenly. Then add 2 parts of compatibilizer, 3 parts of polylactic acid, 1 part of talcum powder, and 0.5 part of ethylene bisstearamide and mix evenly together. The mixing speed of the high-speed mixer is set to stir at a low speed of 180 r / min for 10 min first, and then stir at a high speed of 1000 r / min for 20 min;

[0058] Among them, the molar ratio of terephthalic acid to methylmalonic acid in the monomers of poly(butylene terephthalate / ethylene butanedioate) is 1:1, the sum of the molar numbers of terephthalic acid and ethyl succinic acid to 1,4-butanediol is 1:1, and the molecular weight of the obtained poly(butylene terephthalate / ethylene butanedioate) is 3×10 4 g / mol; the molecular weight of polylactic acid is 2×10 4 g / mol; the compatibilizer is a PLA-poly(butylene 2-butyladipate)-PLA block copolymer with a number-average molecular weight of 2000 g / mol; the epoxy chain extender is an epoxy chain extender with a bio-based aconitic acid as the backbone, the number of carbon atoms p in its aliphatic chain is 1, and the type of epoxy alcohol used is glycidol;

[0059] (3) Add the above-mentioned evenly mixed material into a screw extruder for extrusion granulation. The temperature of the screw extrusion is 220 °C, the screw speed is 250 r / min, and after extrusion granulation, blow molding is carried out to obtain the packaging film material 2#.

[0060] Example 3

[0061] The preparation method of the biodegradable plastic packaging film material includes the following steps:

[0062] (1) Put poly(butylene terephthalate / side-chain fatty diacid) and polylactic acid into an oven and dry at 80 °C for 6 h for standby;

[0063] (2) Add 2 parts of epoxy chain extender, 95 parts of poly(butylene terephthalate / 2-butyladipate) into a high-speed mixer and mix evenly. Then add 10 parts of compatibilizer, 10 parts of polylactic acid, 20 parts of hydrotalcite, and 2 parts of oleamide and mix evenly together. The mixing speed of the high-speed mixer is set to stir at a low speed of 180 r / min for 10 min first, and then stir at a high speed of 1000 r / min for 20 min;

[0064] Among them, the molar ratio of terephthalic acid to methyl succinic acid in the monomers of poly(butylene terephthalate / 2-butyladipate) is 1:5, the sum of the molar numbers of terephthalic acid and 2-butyl succinic acid to 1,4-butanediol is 1:2, and the molecular weight of the obtained poly(butylene terephthalate / 2-butyladipate) is 12×10 4 g / mol; the molecular weight of polylactic acid is 11×104 g / mol; The compatibilizer is a PLA-polybutylene methylmalonate-PLA block copolymer with a number-average molecular weight of 3500 g / mol; The epoxy chain extender is an epoxy chain extender with a biobased aconitic acid backbone, where the number of carbon atoms in the aliphatic chain p = 4, and the type of epoxy alcohol used is epoxyhexanol;

[0065] (3) Add the above uniformly mixed materials into a screw extruder for extrusion granulation. The temperature of the screw extrusion is 180 - 220 °C, the screw speed is 250 r / min, and after extrusion granulation, blow molding is performed to obtain the packaging film material 3#.

[0066] Example 4

[0067] The difference from Example 1 is that the PLA-polybutylene methylsuccinate-PLA block copolymer is replaced with a PLA-poly(2-methylsuberic acid)butylene glycol-PLA block copolymer to prepare the packaging film material 4#.

[0068] Example 5

[0069] The difference from Example 1 is that the PLA-polybutylene methylsuccinate-PLA block copolymer is replaced with a PLA-poly(2-heptyladipic acid)butylene glycol copolymer-PLA block copolymer to prepare the packaging film material 5#.

[0070] Example 6

[0071] The difference from Example 1 is that the molar ratio of terephthalic acid to methylsuccinic acid, the monomers of poly(terephthalic acid / methylsuccinic acid)butylene glycol copolymer, is 1:0.5, and the ratio of the sum of the molar numbers of terephthalic acid and methylsuccinic acid to 1,4-butanediol is 1:2 to prepare the packaging film material 6#.

[0072] Example 7

[0073] The difference from Example 1 is that the molar ratio of terephthalic acid to methylsuccinic acid, the monomers of poly(terephthalic acid / methylsuccinic acid)butylene glycol copolymer, is 1:10, and the ratio of the sum of the molar numbers of terephthalic acid and methylsuccinic acid to 1,4-butanediol is 1:2 to prepare the packaging film material 7#.

[0074] Example 8

[0075] The difference from Example 1 is that poly(terephthalic acid / methylsuccinic acid)butylene glycol copolymer is replaced with poly(terephthalic acid / 2-heptyladipic acid)butylene glycol to prepare the packaging film material 8#.

[0076] Example 9

[0077] The difference from Example 1 is that poly(butylene terephthalate-co-methyl succinate) is replaced by poly(butylene terephthalate-co-2-methyl suberate), and packaging film material 9# is prepared.

[0078] Example 10

[0079] The difference from Example 1 is that the type of epoxy alcohol used as the epoxy chain extender, which is epoxy pentanol, is replaced by epoxy decanol, and packaging film material 10# is prepared.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that poly(butylene terephthalate-co-methyl succinate) is replaced by poly(butylene adipate-co-terephthalate) (PBAT), and packaging film material D1# is prepared.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that 6 parts of the compatibilizer are replaced by 20 parts, and packaging film material D2# is prepared.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that the number average molecular weight of the compatibilizer is replaced from 2600 g / mol to 5000 g / mol, and packaging film material D3# is prepared.

[0086] Comparative Example 4

[0087] The difference from Example 1 is that 7 parts of polylactic acid are replaced by 20 parts of polylactic acid, and packaging film material D4# is prepared.

[0088] Test Example

[0089] The film materials prepared in the above Examples 1 to 10 and Comparative Examples 1 to 4 were used to test the water vapor barrier performance and the tensile properties before and after thermal aging of the polyester copolymers prepared in the above Examples and Comparative Examples. The test results are shown in Table 1. Among them, the thermal aging was carried out according to GB / T 141-2008 "Test Method for Thermal Aging of Plastics"; the tensile property test was carried out according to GB / T 1040-92 "Test Method for Tensile Properties of Plastics", and the shape of the test sample was a Type II dumbbell-shaped specimen in the execution standard; the water vapor transmission rate was measured according to GB / T 1037-2021 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Cup Method for Weight Gain and Weight Loss".

[0090] Table 1

[0091]

[0092] As can be seen from the test results in the above table, the packaging film material prepared in this application has excellent mechanical properties and water vapor barrier properties. At the same time, the retention rate of the tensile strength of the packaging film material after heat aging treatment can reach more than 80%, and the retention rate of the elongation at break of the packaging film material after heat aging treatment can reach more than 70%, indicating good heat aging resistance.

[0093] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other, and the key point of each embodiment is to illustrate the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the description of the method embodiment.

[0094] The above description is only for the embodiments of this application and is not intended to limit this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of the claims of this application.

Claims

1. A biodegradable plastic packaging film material, characterized in that: The method is prepared from the following materials in parts by weight: 85-95 parts of polyterephthalic acid / butylene glycol copolyester with side chain fatty diacid, 3-10 parts of polylactic acid, 2-10 parts of compatibilizer, 1-20 parts of inorganic filler, 0.01-2 parts of epoxy chain extender, and 0.5-2 parts of lubricant; The compatibilizer is a triblock copolymer of polylactic acid-polybutylene glycol ester with side chain fatty acid-polylactic acid, and the number average molecular weight of the triblock copolymer is 2000-3500 g / mol.

2. The biodegradable plastic packaging film material according to claim 1, characterized in that: The synthesis process of the triblock copolymer is: Using side chain fatty dibasic acid and 1,4-butanediol as polymerization monomers, polybutylene glycol ester with side chain fatty dibasic acid was prepared through esterification-polycondensation process as macromolecular initiator; The macromolecular initiator undergoes an esterification-polycondensation reaction with lactic acid under the action of a catalyst to obtain a triblock copolymer; The structural formula of the side chain fatty dibasic acid is shown in Formula I, the structural formula of the macromolecular initiator is shown in Formula II, and the structural formula of the triblock polymer is shown in Formula Ш: Wherein, in formula I, x is an integer of 1 to 5, and y is an integer of 1 to 4; in formula Ш, m is the number of polylactic acid structural units, m' is the number of polylactic acid structural units, and n is the number of polybutylene glycol side chain fatty diacid ester structural units; m, m' and n are integers, and the ratio of (m+m'):n is (1 to 2):(3 to 6).

3. The biodegradable plastic packaging film material according to claim 1, characterized in that: The poly(terephthalic acid) / butylene glycol copolyester with side chain fatty diacid is obtained by using side chain fatty diacid, terephthalic acid and 1,4-butanediol as polymerization monomers through an esterification-polycondensation process; The molar ratio of terephthalic acid to a fatty diacid with a side chain is 1:1-5, and the molar ratio of the sum of the moles of terephthalic acid and a fatty diacid with a side chain to 1,4-butanediol is 1:1-2.

4. The biodegradable plastic packaging film material according to claim 3, characterized in that: The side chain carbon number of the fatty diacid monomer with side chain is 2-5, and the main chain carbon number is 4-7.

5. The biodegradable plastic packaging film material according to claim 1, characterized in that: The epoxy chain extender is an epoxy chain extender with bio-based aconitic acid as the skeleton, and the general structural formula is shown in Formula IV: Here, p is an integer from 1 to 4.

6. The biodegradable plastic packaging film material according to claim 1, characterized in that: The inorganic filler is one or more of calcium carbonate, talcum powder, silicon dioxide, zinc stearate and hydrotalcite.

7. The biodegradable plastic packaging film material according to claim 6, characterized in that: The lubricant is one or more of zinc stearate, ethylene bisstearamide, erucic acid amide and oleic acid amide.

8. A method for preparing the biodegradable plastic packaging film material according to any one of claims 1 to 7, characterized in that: The steps include: (1) putting poly(terephthalic acid) / butylene glycol copolyester with side chain fatty diacid and poly(lactic acid) into an oven for drying; (2) adding epoxy chain extender and dried poly(terephthalic acid) / poly(butylene glycol) copolyester with side chain fatty acid to a high-speed mixer according to the amount, and then adding compatibilizer, polylactic acid, inorganic filler and lubricant to mix evenly; (3) adding the above-mentioned uniformly mixed materials into a screw extruder for extrusion granulation, and blowing film after extrusion granulation to obtain packaging film material.

9. The method for preparing the biodegradable plastic packaging film material according to claim 8, characterized in that: In step (1), the drying temperature is 30 to 80° C. and the drying time is 1 to 6 hours.

10. The method for preparing the biodegradable plastic packaging film material according to claim 8, characterized in that: In step (2), the speed of the high-speed mixer is set to first stir at a low speed of 180 r / min for 10 min, and then stir at a high speed of 1000 r / min for 20 min; The temperature of the screw extrusion in step (3) is 180-220° C., and the screw speed is 250 r / min.

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