Biodegradable plastic product for food contact and preparation method thereof

Abstract

The invention discloses a biodegradable plastic product for food contact and a preparation method thereof, and relates to the technical field of bio-based materials. The biodegradable plastic product for food contact is prepared by blow molding of composite starch into a film; the composite starch comprises modified starch and reinforcing filler; the modified starch is prepared by reacting corn starch with maleic anhydride hollow capsules and then adding poly (butylene succinate), the maleic anhydride hollow capsules are prepared by reacting vinyl ester resin with maleic anhydride to improve hydrophobicity and thermoplasticity, and the reinforcing filler is prepared by reacting plant fibers, calcium carbonate and polyhydroxystearate fatty amine to improve hydrophobicity and thermoplasticity. And the polyhydroxystearate fatty amine is prepared by reacting palmitic acid, 3-dimethylaminopropylamine and poly12-hydroxystearate, so that the mechanical property of the product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of bio-based materials, and specifically to a biodegradable plastic product for food contact and a preparation method thereof. Background Art

[0002] Biodegradable plastics are environmentally friendly plastics that have developed rapidly in recent years and have excellent application properties. They are a type of plastics caused by the action of microorganisms (such as bacteria, molds, and fungi) and algae. Such materials can be widely used in fields such as catering, packaging, and films. After use, they degrade into non-toxic and harmless small molecules in nature under suitable conditions, which not only avoids the waste of plastic products but also realizes the recycling of energy.

[0003] Among natural polymer materials, starch is the most widely used degradable material. However, there are hydrogen bonds between natural starch molecules, resulting in poor solubility and thermoplasticity. It has good hydrophilicity but is not easily soluble in water, and its melting temperature is higher than the decomposition temperature, making it impossible to perform melt extrusion hot processing. Usually, it needs to be modified by thermoplasticization to obtain thermoplastic starch TPS. Plasticizers are used in this process, including but not limited to water, glycerol, urea, sorbitol, and low molecular polysaccharides, etc. TPS has a low cost and excellent degradation performance, but its mechanical properties and processing performance are still not satisfactory; at the same time, its storage performance is insufficient and it is prone to retrogradation, which greatly limits its scope of use and still needs to be blended with synthetic polymers. Therefore, the present invention studies and prepares a biodegradable plastic product for food contact using starch as a raw material to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a biodegradable plastic product for food contact and a preparation method thereof to solve the problems raised in the above background art.

[0005] To solve the above technical problems, the present invention provides the following technical solution: A biodegradable plastic product for food contact is prepared by blow molding a composite starch, polyvinyl alcohol, and a toughening agent into a film; the composite starch includes modified starch and reinforcing filler.

[0006] Preferably, the modified starch is prepared by reacting corn starch with maleic anhydride hollow capsules and then adding polybutylene succinate; the maleic anhydride hollow capsules are prepared by reacting vinyl ester resin with maleic anhydride.

[0007] Preferably, the reinforcing filler is prepared by reacting plant fiber, calcium carbonate with polyhydroxystearate fatty amine; the polyhydroxystearate fatty amine is prepared by reacting palmitic acid, 3-dimethylaminopropylamine with poly-12-hydroxystearate.

[0008] Preferably, the toughening agent is one of ethylene glycol or glycerol.

[0009] Preferably, a method for preparing a biodegradable plastic product for food contact includes the following specific steps:

[0010] S1. Mix corn starch and dimethyl sulfoxide at a mass ratio of 1:30 - 50, stir evenly, add maleic anhydride hollow capsules in an amount of 0.2 - 0.4 times the mass of the corn starch, heat up to 60 - 70 °C, add catalyst N-methylimidazole in an amount of 0.02 - 0.04 times the mass of the corn starch, continue the reflux reaction for 4 - 6 h, then add polybutylene succinate in an amount of 0.2 - 0.3 times the mass of the corn starch, continue the reaction for 1 - 2 h, wash with absolute ethanol 3 - 5 times, filter by suction and dry to obtain modified starch.

[0011] S2. Mix the pretreated plant fiber with a calcium chloride solution of 0.2 - 0.3 mol / L at a material-liquid ratio of 1 - 2:32, stir at 400 - 600 rpm for 30 - 50 min, add polyhydroxystearic acid ester fatty amine in an amount of 0.04 - 0.06 times the mass of the pretreated plant fiber, adjust the pH to 8 - 9 with sodium hydroxide, heat up to 32 - 35 °C, react for 1 - 4 h, filter out and wash with deionized water 3 - 5 times, and dry to obtain the reinforcing filler.

[0012] S3. Mix the modified starch and the reinforcing filler at a mass ratio of 50:3 - 5, stir evenly to obtain a composite starch.

[0013] S4. Mix the composite starch, polyvinyl alcohol and toughening agent, stir evenly, then carry out hot melt extrusion and blow molding into a plastic film through a single-screw extrusion blow molding machine, and finally cut, wind and package to obtain a biodegradable plastic product for food contact.

[0014] Preferably, in the above step S1, the preparation method of the maleic anhydride hollow capsule is as follows: Under a nitrogen atmosphere, mix maleic anhydride, styrene, azobisisobutyronitrile and isopentyl acetate at a mass ratio of 2 - 2.4:1:0.03:25, heat up to 70 - 80 °C, react for 1 - 2 h, add vinyl ester resin with the same mass as styrene, n-heptane in an amount of 8 - 10 times the mass of styrene and azobisisobutyronitrile in an amount of 0.001 - 0.002 times the mass of styrene, continue to keep warm for 3 - 5 h, cool to room temperature and then centrifuge, wash with acetone and petroleum ether 3 - 5 times in sequence, air-dry naturally for 12 - 24 h, and then dry in an oven at 40 - 50 °C to obtain the maleic anhydride hollow capsule.

[0015] Preferably, in the above step S2, the preparation method of polyhydroxystearate fatty amine is as follows: Mix 12-hydroxystearic acid, stannous chloride, and xylene in a mass ratio of 10:0.3-0.4:3, heat up to 170-180 °C, react for 16-18 h, then add palmitic acid in an amount of 0.01-0.03 times the mass of 12-hydroxystearic acid, continue to react for 5-6 h, cool down to 120-130 °C, perform vacuum distillation, transfer to a nitrogen atmosphere, add 3-dimethylaminopropylamine in an amount of 0.15-0.25 times the mass of 12-hydroxystearic acid, heat up to 180-190 °C, and reflux and react for 6-8 h to obtain polyhydroxystearate fatty amine.

[0016] Preferably, in the above step S2, the process of pretreating plant fibers is as follows: Immerse softwood pulp in a sodium hydroxide solution with a mass fraction of 1-3%, heat up to 30-32 °C, react for 2-3 h, fish out and wash with deionized water 5-8 times.

[0017] Preferably, in the above step S4, the mass ratio of composite starch, polyvinyl alcohol, and toughening agent is 4-7:1:0.2-0.3.

[0018] Preferably, in the above step S4, the processing temperature of the blown film machine is 165-175 °C.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0020] The food-contact biodegradable plastic product prepared by the present invention is obtained by blow-molding composite starch into a film; the composite starch includes modified starch and reinforcing filler;

[0021] The modified starch is prepared by reacting corn starch with maleic anhydride hollow capsules and then adding polybutylene succinate. The maleic anhydride hollow capsules are prepared by reacting vinyl ester resin with maleic anhydride. After acylating the hydroxyl groups on the starch, the maleic anhydride hollow capsules form starch esters while introducing vinyl ester resin and maleic anhydride with a cross-linked structure, reducing the intermolecular force, thereby improving the hydrophobicity and thermoplasticity;

[0022] The reinforcing filler is prepared by reacting plant fibers, calcium carbonate, and polyhydroxystearate fatty amine. The polyhydroxystearate fatty amine is prepared by reacting palmitic acid, 3-dimethylaminopropylamine, and poly-12-hydroxystearate. By coating calcium carbonate on the surface of plant fibers with polyhydroxystearate fatty amine, while improving the hydrophobicity, the compatibility with the modified starch is improved, thereby enhancing the mechanical properties of the product. Detailed Embodiments

[0023] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0024] To more clearly illustrate the method provided by the present invention, the following examples are used for detailed description. The test methods for each index of the biodegradable plastic products for food contact prepared in the examples and comparative examples are as follows:

[0025] Mechanical properties: The elongation at break of the biodegradable plastic products for food contact prepared in the examples and comparative examples was tested with reference to ASTM-D638.

[0026] Hydrophobicity: The surface water contact angle of the biodegradable plastic products for food contact prepared in the examples and comparative examples was tested.

[0027] Example 1

[0028] S1. Under a nitrogen atmosphere, maleic anhydride, styrene, azobisisobutyronitrile and isopentyl acetate were mixed in a mass ratio of 2.4:1:0.03:25, heated to 80 °C, and reacted for 2 h. Then, vinyl ester resin with the same mass as styrene, n-heptane 10 times the mass of styrene, and azobisisobutyronitrile 0.002 times the mass of styrene were added, and the mixture was kept warm for 5 h. After cooling to room temperature, it was centrifuged, washed 5 times with acetone and petroleum ether in sequence, dried naturally in ventilation for 24 h, and then dried in an oven at 50 °C to obtain maleic anhydride hollow capsules. Corn starch and dimethyl sulfoxide were mixed in a mass ratio of 1:50, stirred evenly, and then maleic anhydride hollow capsules 0.4 times the mass of corn starch were added. After heating to 70 °C, catalyst N-methylimidazole 0.04 times the mass of corn starch was added, and the mixture was refluxed for 6 h. Then, polybutylene succinate 0.3 times the mass of corn starch was added, and the reaction continued for 1-2 h. It was washed 5 times with absolute ethanol, filtered by suction and dried to obtain modified starch.

[0029] S2. Immerse the softwood pulp in a 1% sodium hydroxide solution by mass, heat it to 30 °C, react for 2 h, take it out and wash it 5 times with deionized water to obtain pretreated plant fibers; mix 12-hydroxy stearic acid, stannous chloride and xylene according to a mass ratio of 10:0.3:3, heat it to 170 °C, react for 16 h, then add palmitic acid which is 0.01 times the mass of 12-hydroxy stearic acid, continue to react for 5 h, cool it to 120 °C, carry out vacuum distillation, transfer it to a nitrogen atmosphere, add 3-dimethylaminopropylamine which is 0.15 times the mass of 12-hydroxy stearic acid, heat it to 180 °C, and carry out reflux reaction for 6 h to prepare polyhydroxy stearate fatty amine; mix the pretreated plant fibers with a 0.2 mol / L calcium chloride solution according to a material-liquid ratio of 1:32, stir at 400 rpm for 30 min, add polyhydroxy stearate fatty amine which is 0.04 times the mass of the pretreated plant fibers, adjust the pH to 8 with sodium hydroxide, heat it to 32 °C, react for 1 h, filter it out and wash it 3 times with deionized water, and dry it to obtain the reinforcing filler;

[0030] S3. Mix the modified starch and the reinforcing filler according to a mass ratio of 50:3, stir evenly to obtain the composite starch;

[0031] S4. Mix the composite starch, polyvinyl alcohol and toughening agent according to a mass ratio of 4:1:0.2, stir evenly and then carry out hot melt extrusion and blow molding into a plastic film through a single-screw extrusion blow molding machine. The processing temperature of the blow molding machine is 165 °C, and finally cut, wind and package to obtain the biodegradable plastic product for food contact.

[0032] Example 2

[0033] S1. Under a nitrogen atmosphere, mix maleic anhydride, styrene, azodiisobutyronitrile and isoamyl acetate according to a mass ratio of 2.2:1:0.03:25, heat it to 75 °C, react for 1.5 h, add vinyl ester resin with the same mass as styrene, n-heptane which is 9 times the mass of styrene and azodiisobutyronitrile which is 0.0015 times the mass of styrene, continue to keep warm for 4 h, centrifuge after cooling to room temperature, wash it 4 times with acetone and petroleum ether in sequence, dry it naturally by ventilation for 18 h, and then dry it in an oven at 45 °C to obtain maleic anhydride hollow capsules; mix corn starch and dimethyl sulfoxide according to a mass ratio of 1:40, stir evenly and then add maleic anhydride hollow capsules which are 0.3 times the mass of corn starch, heat it to 65 °C, add catalyst N-methylimidazole which is 0.03 times the mass of corn starch, continue to carry out reflux reaction for 5 h, then add polybutylene succinate which is 0.25 times the mass of corn starch, continue to react for 1.5 h, wash it 4 times with absolute ethanol, filter it by suction and dry it to obtain the modified starch;

[0034] S2. Immerse the softwood pulp in a sodium hydroxide solution with a mass fraction of 2%, heat it up to 31 °C, react for 2.5 h, fish it out and wash it 6 times with deionized water to obtain pretreated plant fibers; mix 12 - hydroxystearic acid, stannous chloride and xylene in a mass ratio of 10:0.35:3, heat it up to 175 °C, react for 17 h, then add palmitic acid which is 0.02 times the mass of 12 - hydroxystearic acid, continue to react for 5.5 h, cool it down to 125 °C, carry out vacuum distillation, transfer it to a nitrogen atmosphere, add 3 - dimethylaminopropylamine which is 0.2 times the mass of 12 - hydroxystearic acid, heat it up to 185 °C, and carry out reflux reaction for 7 h to prepare polyhydroxystearate fatty amine; mix the pretreated plant fibers with a calcium chloride solution of 0.25 mol / L according to a material - to - liquid ratio of 1.5:32, stir at 500 rpm for 40 min, add polyhydroxystearate fatty amine which is 0.05 times the mass of the pretreated plant fibers, adjust the pH to 8.5 with sodium hydroxide, heat it up to 34 °C, react for 3 h, filter it out and wash it 4 times with deionized water, and dry it to obtain the reinforcing filler;

[0035] S3. Mix the modified starch and the reinforcing filler according to a mass ratio of 50:4, stir evenly to obtain the composite starch;

[0036] S4. Mix the composite starch, polyvinyl alcohol and toughening agent according to a mass ratio of 6:1:0.25, stir evenly and then carry out hot - melt extrusion and blow - molding into a plastic film through a single - screw extrusion blow - molding machine. The processing temperature of the blow - molding machine is 170 °C, and finally cut, roll and package to obtain the biodegradable plastic product for food contact.

[0037] Example 3

[0038] S1. Under a nitrogen atmosphere, mix maleic anhydride, styrene, azobisisobutyronitrile and isoamyl acetate in a mass ratio of 2.4:1:0.03:25, heat it up to 80 °C, react for 2 h, add vinyl ester resin with the same mass as styrene, n - heptane which is 10 times the mass of styrene and azobisisobutyronitrile which is 0.002 times the mass of styrene, continue to keep warm for 5 h, centrifuge after cooling to room temperature, wash it 5 times with acetone and petroleum ether in sequence, dry it naturally in ventilation for 24 h, and then dry it in an oven at 50 °C to obtain maleic anhydride hollow capsules; mix corn starch and dimethyl sulfoxide in a mass ratio of 1:50, stir evenly and then add maleic anhydride hollow capsules which are 0.4 times the mass of corn starch, heat it up to 70 °C, add catalyst N - methylimidazole which is 0.04 times the mass of corn starch, continue to carry out reflux reaction for 6 h, then add polybutylene succinate which is 0.03 times the mass of corn starch, continue to react for 2 h, wash it 5 times with absolute ethanol, filter by suction and dry it to obtain the modified starch;

[0039] S2. Immerse the softwood pulp in a sodium hydroxide solution with a mass fraction of 3%, heat it to 32°C, react for 3 h, fish it out and wash it 8 times with deionized water to obtain pretreated plant fibers; mix 12 - hydroxystearic acid, stannous chloride and xylene in a mass ratio of 10:0.4:3, heat it to 180°C, react for 18 h, then add palmitic acid which is 0.3 times the mass of 12 - hydroxystearic acid, continue to react for 6 h, cool it to 130°C, carry out vacuum distillation, transfer it to a nitrogen atmosphere, add 3 - dimethylaminopropylamine which is 0.25 times the mass of 12 - hydroxystearic acid, heat it to 190°C, and reflux and react for 8 h to prepare polyhydroxystearate fatty amine; mix the pretreated plant fibers with a calcium chloride solution of 0.3 mol / L in a material - to - liquid ratio of 2:32, stir at 600 rpm for 50 min, add polyhydroxystearate fatty amine which is 0.06 times the mass of the pretreated plant fibers, adjust the pH to 9 with sodium hydroxide, heat it to 35°C, react for 4 h, filter it out and wash it 5 times with deionized water, and dry it to obtain the reinforcing filler;

[0040] S3. Mix the modified starch and the reinforcing filler in a mass ratio of 50:5, stir evenly to obtain the composite starch;

[0041] S4. Mix the composite starch, polyvinyl alcohol and toughening agent in a mass ratio of 7:1:0.3, stir evenly and then carry out hot - melt extrusion and blow - molding into a plastic film through a single - screw extrusion blow - molding machine. The processing temperature of the blow - molding machine is 175°C, and finally cut, wind and package to obtain the biodegradable plastic products for food contact.

[0042] Comparative Example 1

[0043] The composition of Comparative Example 1 is the same as that of Example 2. The difference in the preparation method of the biodegradable plastic products for food contact between this and Example 2 is that the modified starch is prepared by reacting corn starch with maleic anhydride hollow capsules.

[0044] Comparative Example 2

[0045] The composition of Comparative Example 2 is the same as that of Example 2. The difference in the preparation method of the biodegradable plastic products for food contact between this and Example 2 is that the composite starch includes corn starch and the reinforcing filler.

[0046] Comparative Example 3

[0047] The composition of Comparative Example 3 is the same as that of Example 2. The difference in the preparation method of this food-contact biodegradable plastic product from that of Example 2 lies in Step S1. Step S1 is modified as follows: Corn starch and dimethyl sulfoxide are mixed at a mass ratio of 1:40, and after stirring evenly, the temperature is raised to 65°C. Then, a catalyst N-methylimidazole with a mass 0.03 times that of the corn starch is added, and the reflux reaction continues for 5 h. Next, polybutylene succinate with a mass 0.25 times that of the corn starch is added, and the reaction continues for 1.5 h. Then, it is washed 4 times with absolute ethanol, filtered by suction, and dried to obtain modified starch.

[0048] Comparative Example 4

[0049] The composition of Comparative Example 4 is the same as that of Example 2. The difference in the preparation method of this food-contact biodegradable plastic product from that of Example 2 lies in Step S2. Step S2 is modified as follows: Softwood pulp is immersed in a sodium hydroxide solution with a mass fraction of 2%, and the temperature is raised to 31°C. After reacting for 2.5 h, it is fished out and washed 6 times with deionized water to obtain pretreated plant fibers. The pretreated plant fibers are mixed with a calcium chloride solution of 0.25 mol / L at a material-liquid ratio of 1.5:32, stirred at 500 rpm for 40 min, the pH is adjusted to 8.5 with sodium hydroxide, the temperature is raised to 34°C, and the reaction continues for 3 h. Then, it is filtered out and washed 4 times with deionized water and dried to obtain the reinforcing filler.

[0050] Comparative Example 5

[0051] The composition of Comparative Example 5 is the same as that of Example 2. The difference in the preparation method of this food-contact biodegradable plastic product from that of Example 2 is that it is made by blow molding the modified starch, polyvinyl alcohol, and toughening agent into a film.

[0052] Effect Example

[0053] Table 1 below gives the performance analysis results of the food-contact biodegradable plastic products prepared using Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention:

[0054] Table 1

[0055]

[0056]

[0057] By comparing the experimental data of the examples and comparative examples in Table 1, it can be clearly found that the food-contact biodegradable plastic products prepared using Examples 1, 2, and 3 have higher mechanical properties and hydrophobicity.

[0058] From the comparison of the experimental data of Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be found that after the hydroxyl groups on the starch are acylated by maleic anhydride hollow capsules, while forming starch esters, vinyl ester resins and maleic anhydride with cross-linked structures are introduced, reducing the intermolecular force, thereby improving the hydrophobicity and thermoplasticity.

[0059] From the comparison of the experimental data of Example 1, Example 2, Example 3 and Comparative Example 3, Comparative Example 4, it can be found that by coating calcium carbonate on the surface of plant fibers with polyhydroxystearate fatty amines, while improving the hydrophobicity, the compatibility with modified starch is improved, thereby enhancing the mechanical properties of the product.

[0060] Obviously, the above embodiments are merely examples for clearly explaining the embodiments of the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the embodiments here. And these obvious changes or modifications derived from the spirit of the present invention are still within the protection scope of the present invention.

Claims

1. A biodegradable plastic product for food contact, characterized in that, It is prepared by blow molding a composite starch, polyvinyl alcohol and a toughening agent into a film; the composite starch includes a modified starch and a reinforcing filler.

2. The biodegradable plastic product for food contact according to claim 1, wherein, The modified starch is prepared by reacting corn starch with maleic anhydride hollow capsules and then adding polybutylene succinate; the maleic anhydride hollow capsules are prepared by reacting vinyl ester resin with maleic anhydride.

3. The biodegradable plastic product for food contact according to claim 1, wherein, The reinforcing filler is prepared by reacting plant fiber, calcium carbonate with polyhydroxystearate fatty amine; the polyhydroxystearate fatty amine is prepared by reacting palmitic acid, 3-dimethylaminopropylamine with poly-12-hydroxystearate.

4. A biodegradable plastic product for food contact according to claim 1, characterized in that, The toughening agent is one of ethylene glycol or glycerol.

5. The preparation method of a biodegradable plastic product for food contact according to claim 1, characterized in that, It includes the following specific steps: S1. Mix corn starch and dimethyl sulfoxide at a mass ratio of 1:30 - 50, stir evenly, add maleic anhydride hollow capsules at 0.2 - 0.4 times the mass of corn starch, heat up to 60 - 70 °C, add catalyst N-methylimidazole at 0.02 - 0.04 times the mass of corn starch, continue reflux reaction for 4 - 6 h, then add polybutylene succinate at 0.2 - 0.3 times the mass of corn starch, continue the reaction for 1 - 2 h, wash with absolute ethanol 3 - 5 times, filter by suction and dry to obtain the modified starch: S2. Mix the pretreated plant fiber and 0.2 - 0.3 mol / L calcium chloride solution at a material-liquid ratio of 1 - 2:32, stir at 400 - 600 rpm for 30 - 50 min, add polyhydroxystearate fatty amine at 0.04 - 0.06 times the mass of the pretreated plant fiber, adjust the pH to 8 - 9 with sodium hydroxide, heat up to 32 - 35 °C, react for 1 - 4 h, filter out and wash with deionized water 3 - 5 times, dry to obtain the reinforcing filler; S3. Mix the modified starch and the reinforcing filler at a mass ratio of 50:3 - 5, stir evenly to obtain the composite starch; S4. Mix the composite starch, polyvinyl alcohol and the toughening agent, stir evenly, then carry out hot melt extrusion and blow molding into a plastic film through a single-screw extrusion blow molding machine, and finally cut, wind and package to obtain the biodegradable plastic product for food contact.

6. The preparation method of a biodegradable plastic product for food contact according to claim 5, characterized in that, In the above step S1, the preparation method of the maleic anhydride hollow capsules is: under a nitrogen atmosphere, mix maleic anhydride, styrene, azobisisobutyronitrile and isopentyl acetate at a mass ratio of 2 - 2.4:1:0.03:25, heat up to 70 - 80 °C, react for 1 - 2 h, add vinyl ester resin with the same mass as styrene, n-heptane at 8 - 10 times the mass of styrene and azobisisobutyronitrile at 0.001 - 0.002 times the mass of styrene, continue to keep warm for 3 - 5 h, cool to room temperature and then centrifuge, wash with acetone and petroleum ether 3 - 5 times in sequence, dry naturally in ventilation for 12 - 24 h, and then dry in an oven at 40 - 50 °C to obtain the maleic anhydride hollow capsules.

7. The preparation method of a biodegradable plastic product for food contact according to claim 5, characterized in that, In the above step S2, the preparation method of polyhydroxystearate fatty amine is as follows: Mix 12-hydroxystearic acid, stannous chloride and xylene in a mass ratio of 10:0.3-0.4:3, heat up to 170-180 °C, react for 16-18 h, then add palmitic acid in an amount of 0.01-0.03 times the mass of 12-hydroxystearic acid, continue to react for 5-6 h, cool down to 120-130 °C, carry out vacuum distillation, transfer to a nitrogen atmosphere, add 3-dimethylaminopropylamine in an amount of 0.15-0.25 times the mass of 12-hydroxystearic acid, heat up to 180-190 °C, and carry out reflux reaction for 6-8 h to obtain polyhydroxystearate fatty amine.

8. The preparation method of a biodegradable plastic product for food contact according to claim 5, characterized in that, In the above step S2, the process of pre-treating plant fiber is as follows: Immerse softwood pulp in a sodium hydroxide solution with a mass fraction of 1-3%, heat up to 30-32 °C, react for 2-3 h, fish out and wash with deionized water for 5-8 times.

9. The preparation method of a biodegradable plastic product for food contact according to claim 5, characterized in that, In the above step S4, the mass ratio of composite starch, polyvinyl alcohol and toughening agent is 4-7:1:0.2-0.

3.

10. The preparation method of a biodegradable plastic product for food contact according to claim 5, wherein In the above step S4, the processing temperature of the blown film machine is 165-175 °C.

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