Plant-based degradable TPU agricultural film and preparation method thereof

Abstract

The present invention belongs to the technical field of polyurethane films, and specifically relates to plant-based degradable TPU agricultural films and preparation methods thereof. The following raw materials are included in mass fractions: plant-based polyester polyols: 44-69 parts; diisocyanates: 17-43 parts; chain extenders: 3-11 parts; lubricants: 0.1-1 parts; biodegradation agents: 1-10 parts; catalysts: 0.05-0.1 parts; the plant-based polyester polyols are prepared by polymerization of lignin, small molecule dibasic acids and small molecule diols. The present invention uses natural, renewable, inexpensive and widely available lignin as raw material, aiming to alleviate dependence on and consumption of petroleum resources, while ensuring the safety and environmental protection characteristics of the product; by optimizing the formula and preparation process, the obtained film has excellent biodegradability, high air permeability and easy processing.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane films, and in particular relates to a plant-based degradable TPU agricultural film and a preparation method thereof. Background Art

[0002] In agricultural production, ground film and greenhouse film are widely used to effectively regulate soil temperature and humidity. Currently, the widely used materials are non-biodegradable polyethylene products. However, these products are abandoned in the soil after use. Because they are difficult to remove, they pose a significant pollution threat to the agricultural soil environment. In view of this serious problem, it is particularly urgent to develop alternative bio-based degradable agricultural films. As an alternative material, thermoplastic polyurethane elastomer (TPU) exhibits advantages such as high elasticity, excellent flexibility, good film-forming properties and moisture permeability, but its raw materials are mainly derived from petrochemical resources, resulting in a significant increase in oil consumption. In addition, traditional TPU materials face the challenge of being unable to be completely degraded, which limits their wider application range. Therefore, the development of new bio-based and degradable agricultural film materials has become the key to solving current problems. Summary of the invention

[0003] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a plant-based degradable TPU agricultural film, which uses lignin, which is natural, renewable, inexpensive and widely available, as raw material, aiming to alleviate dependence on and consumption of petroleum resources while ensuring the safety and environmental protection characteristics of the product; by optimizing the formula and preparation process, the obtained film has excellent biodegradability, high air permeability and easy processing.

[0004] Another object of the present invention is to provide a method for preparing a plant-based degradable TPU agricultural film, which is scientific, reasonable, simple and easy to implement.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The plant-based degradable TPU agricultural film comprises the following raw materials in parts by weight:

[0007] Plant-based polyester polyol: 44-69 parts;

[0008] Diisocyanate: 17-43 parts;

[0009] Chain extender: 3-11 parts;

[0010] Lubricant: 0.1-1 part;

[0011] Biodegradation agent: 1-10 parts;

[0012] Catalyst: 0.05-0.1 parts;

[0013] The plant-based polyester polyol is prepared by polymerization reaction of lignin, small molecule dibasic acid and small molecule diol;

[0014] The preparation method of the plant-based degradable TPU agricultural film is as follows: a mixture of plant-based polyester polyol and lubricant, diisocyanate, chain extender and catalyst are mixed by metering, reacted in a twin-screw extruder, extruded and granulated, and the obtained pellets are added with a biodegradation agent during the film casting process and the film cooling and solidification stage to obtain the plant-based degradable TPU agricultural film.

[0015] The preparation method of the plant-based polyester polyol is as follows: lignin, a small molecule dibasic acid and a small molecule diol are added to a reaction kettle, heated and stirred, protected by nitrogen, heated to 140-150°C until water is produced by the reaction, the top temperature of the reflux tower is controlled at 100-105°C, tetrabutyl titanate is added, the temperature is raised to 220-250°C, the reaction is continued for 2-4 hours, and then the water produced by the polycondensation is removed by a nitrogen bubbling process. When the acid value of the material in the kettle drops below 0.6 mgKOH / g and the water content drops below 0.05 wt.%, the temperature is lowered and the material is discharged to obtain the plant-based polyester polyol.

[0016] The number average molecular weight of the plant-based polyester polyol is 500-3000, wherein the molar ratio of the small molecule dibasic acid to the small molecule diol is (1.1-5.1):1, the amount of lignin used is 5-50wt.% of the total amount of the plant-based polyester polyol, and the amount of tetrabutyl titanate added accounts for 0.005-0.01wt.% of the total amount of the plant-based polyester polyol.

[0017] The small molecule dibasic acid is a dibasic acid containing 4-10 carbon atoms; the small molecule diol is a diol containing 2-6 carbon atoms.

[0018] The diisocyanate is one of 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, 1,4-cyclohexane diisocyanate, dicyclohexylmethane diisocyanate or xylylene diisocyanate.

[0019] The chain extender is a diol containing 2 to 6 carbon atoms.

[0020] The lubricant is one of oleamide, stearic acid alcohol ester, stearic acid amide, stearic acid monoglyceride or butyl stearate.

[0021] The biodegradation agent is one of lactate dehydrogenase, catalase, amylase, citrate synthase or triose phosphate isomerase.

[0022] The catalyst is an organic tin or organic bismuth catalyst.

[0023] The method for preparing the plant-based degradable TPU agricultural film comprises the following steps:

[0024] 1) Add plant-based polyester polyol and lubricant to reactor A and stir at 100-120°C; add diisocyanate to reactor B and stir at 50-70°C; add chain extender to reactor C and keep the temperature at 40-60°C; mix the materials in reactors A, B and C through the perfusion system and inject them into the twin-screw extruder. At the same time, add the catalyst to the feeding port of the twin-screw extruder through a micro-injection pump. The mixed materials are uniformly reacted and transported in the twin-screw barrel. After the synthesis reaction is completed, TPU pellets are obtained through plasticization and granulation, wherein the screw temperature is 80-250°C;

[0025] 2) Add TPU pellets into the extruder, heat to a molten state, extrude the melt through the die, and then cool and solidify. During the cooling and solidification process, a biodegradable agent is sprayed on both ends of the film to finally obtain a plant-based degradable TPU agricultural film.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The lignin used in the present invention is a rich natural aromatic polymer with a structure rich in functional groups such as hydroxyl, methoxyl, carbonyl, and carboxyl. It can not only be used to synthesize polyols to replace petroleum-based polyols, but also has the characteristics of wide sources, low prices, high yields, and no pollution. In addition, the lignin does not need to be added with black masterbatch, and its inherent black film properties help to keep warm and moisturize, further improving the environmental protection and practicality of the material;

[0028] (2) The present invention significantly increases the bio-based content of the product by synthesizing TPU using lignin. At the same time, the added biodegradation agent can promote the TPU film to undergo a complex dehydrogenation reaction under the conditions of ultraviolet light, heat, and oxygen, reducing the molecular weight into short-chain molecules, which are eventually decomposed by enzymes and microorganisms into water and carbon dioxide to complete the degradation process. This process has no effect on the pH value of soil and groundwater, ensuring environmental friendliness.

[0029] (3) The present invention sprays the biodegradation agent during the cooling, shaping and winding process of the TPU film, which not only avoids the problem of degradation agent failure caused by high temperature, but also ensures the uniform distribution of the degradation agent on the surface of the film, thereby improving the degradation effect and ensuring that the biodegradation performance of the product is fully exerted;

[0030] (4) The preparation method of the present invention is scientific and reasonable. It adopts a one-step continuous production process of a twin-screw extruder, simplifies the operation process, and improves production efficiency. By adding a lubricant, the problem of roller sticking during the film forming process is effectively solved, and the processing efficiency is further improved. The prepared TPU film material has excellent moisture permeability and air permeability, and shows significant advantages in the field of agricultural films. DETAILED DESCRIPTION

[0031] The present invention is further described below with reference to the embodiments, but they do not limit the implementation of the present invention.

[0032] The raw materials used in the examples and comparative examples are conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are conventional methods in the art unless otherwise specified.

[0033] Some of the raw materials used in the examples and comparative examples are described as follows:

[0034] Plant-based polyester polyol A has a number average molecular weight of 500, and its preparation method is as follows: 1,10-sebacic acid and ethylene glycol in a molar ratio of 1.1:1 are added to a reactor, and then lignin accounting for 5wt.% of the total feed amount of the plant-based polyester polyol is added, heated and stirred, nitrogen protection, the temperature is raised to 140°C until water is produced by the reaction, the top temperature of the reflux tower is controlled at 100°C, tetrabutyl titanate accounting for 0.005wt.% of the total feed amount of the plant-based polyester polyol is added, the temperature is raised to 230°C, the reaction is continued for 2h, and then the water produced by the condensation is removed by a nitrogen bubbling process. When the acid value of the material in the reactor drops to 0.2mgKOH / g and the water content drops to 0.03wt.%, the product is qualified, the temperature is lowered and the material is discharged to obtain plant-based polyester polyol A.

[0035] Plant-based polyester polyol B has a number average molecular weight of 3000, and its preparation method is as follows: succinic acid and hexanediol with a molar ratio of 5.1:1 are added to a reactor, and then lignin accounting for 50wt.% of the total feed amount of the plant-based polyester polyol is added, heated and stirred, nitrogen protection, the temperature is raised to 145°C until water is produced by the reaction, the top temperature of the reflux tower is controlled at 102°C, tetrabutyl titanate accounting for 0.01wt.% of the total feed amount of the plant-based polyester polyol is added, the temperature is raised to 250°C, the reaction is continued for 3h, and then the water produced by the condensation is removed by a nitrogen bubbling process. When the acid value of the material in the reactor drops to 0.5mgKOH / g and the water content drops to 0.02wt.%, the product is qualified, the temperature is lowered and the material is discharged to obtain plant-based polyester polyol B.

[0036] Plant-based polyester polyol C has a number average molecular weight of 2000, and its preparation method is as follows: adipic acid and 1,4-butanediol in a molar ratio of 1.2:1 are added to a reactor, and then lignin accounting for 30wt.% of the total feed amount of the plant-based polyester polyol is added, heated and stirred, nitrogen protection, the temperature is raised to 150°C until water is reacted, the top temperature of the reflux tower is controlled at 105°C, tetrabutyl titanate accounting for 0.01wt.% of the total feed amount of the plant-based polyester polyol is added, the temperature is raised to 250°C, the reaction is continued for 4h, and then the water generated by the condensation is removed by a nitrogen bubbling process. When the acid value of the material in the reactor drops to 0.3mgKOH / g and the water content drops to 0.02wt.%, the product is qualified, the temperature is lowered and the material is discharged to obtain plant-based polyester polyol C.

[0037] Polyester polyol D has a number average molecular weight of 2000, and its preparation method is as follows: 1,6-hexanediol and 1,4-butanediol in a molar ratio of 1.2:1 are added to a reactor, heated and stirred, protected by nitrogen, and heated to 150°C until water is produced by the reaction, the top temperature of the reflux tower is controlled at 105°C, tetrabutyl titanate is added in an amount of 0.01wt.% of the total amount of plant-based polyester polyol, the temperature is raised to 250°C, the reaction is continued for 4h, and then the water produced by the condensation is removed by a nitrogen bubbling process. When the acid value of the material in the reactor drops to 0.3mgKOH / g and the water content drops to 0.02wt.%, the product is qualified, the temperature is lowered and the material is discharged to obtain polyester polyol D.

[0038] Example 1

[0039] The plant-based degradable TPU agricultural film is made of the following raw materials in parts by weight:

[0040] Plant-based polyester polyol A: 49.43 parts;

[0041] HDI: 40.52 parts;

[0042] Ethylene glycol: 8.9 parts;

[0043] Stearic acid monoglyceride: 0.1 part;

[0044] Lactate dehydrogenase: 1 part;

[0045] Stannous octoate: 0.05 parts;

[0046] The preparation method of the plant-based degradable TPU agricultural film comprises the following steps:

[0047] 1) Add plant-based polyester polyol A and stearic acid monoglyceride to reactor A and stir at 110±10℃; add MDI-100 to reactor B and stir at 60±10℃; add 1,4-butanediol to reactor C and keep the temperature at 50±10℃; mix the materials in reactors A, B and C through the perfusion system and inject them into the twin-screw extruder, and add stannous octoate to the feeding port of the twin-screw extruder through a micro-injection pump, and the mixed materials are uniformly reacted and transported in the twin-screw barrel. After the synthesis reaction is completed, TPU pellets are obtained by plasticization and granulation, wherein the screw temperature is 165±85℃;

[0048] 2) Add TPU pellets into the extruder, heat to a molten state, extrude the melt through a die, and then cool and solidify. During the cooling and solidification process, lactate dehydrogenase is sprayed on both ends of the film to finally obtain a plant-based biodegradable TPU agricultural film.

[0049] Example 2

[0050] The plant-based degradable TPU agricultural film is made of the following raw materials in parts by weight:

[0051] Plant-based polyester polyol B: 66.68 parts;

[0052] HMDI: 17.10 parts;

[0053] 1,6-Hexanediol: 5.12 parts;

[0054] Stearic acid amide: 1 part;

[0055] Citrate synthase: 10 parts;

[0056] Dibutyltin dilaurate: 0.1 part;

[0057] The preparation method of the plant-based degradable TPU agricultural film has the same steps as Example 1.

[0058] Example 3

[0059] The plant-based degradable TPU agricultural film is made of the following raw materials in parts by weight:

[0060] Plant-based polyester polyol C: 59.23 parts;

[0061] MDI-100: 25.37 parts;

[0062] 1,4-Butanediol: 6.52 parts;

[0063] Oleic acid amide: 0.8 parts;

[0064] Amylase: 8 parts;

[0065] Bismuth neodecanoate: 0.08 parts;

[0066] The preparation method of the plant-based degradable TPU agricultural film has the same steps as Example 1.

[0067] Comparative Example 1

[0068] The TPU film is made of the following raw materials in parts by weight:

[0069] Polyester polyol D: 59.23 parts;

[0070] MDI-100: 25.37 parts;

[0071] 1,4-Butanediol: 6.52 parts;

[0072] Oleic acid amide: 0.8 parts;

[0073] Amylase: 8 parts;

[0074] Bismuth neodecanoate: 0.08 parts;

[0075] The preparation method of the TPU film has the same steps as Example 1.

[0076] Comparative Example 2

[0077] The TPU film is made of the following raw materials in parts by weight:

[0078] Plant-based polyester polyol C: 64.43 parts;

[0079] MDI-100: 27.60 parts;

[0080] 1,4-Butanediol: 7.09 parts;

[0081] Oleic acid amide: 0.8 parts;

[0082] Bismuth neodecanoate: 0.08 parts;

[0083] The preparation method of the TPU film has the same steps as Example 1.

[0084] Comparative Example 3

[0085] The TPU film is made of the following raw materials in parts by weight:

[0086] Polyester polyol D: 64.43 parts;

[0087] MDI-100: 27.60 parts;

[0088] 1,4-Butanediol: 7.09 parts;

[0089] Oleic acid amide: 0.8 parts;

[0090] Bismuth neodecanoate: 0.08 parts;

[0091] The preparation method of the TPU film has the same steps as Example 1.

[0092] Comparative Example 4

[0093] The TPU film is made of the following raw materials in parts by weight:

[0094] Plant-based polyester polyol C: 59.23 parts;

[0095] MDI-100: 25.37 parts;

[0096] 1,4-Butanediol: 6.52 parts;

[0097] Oleic acid amide: 0.8 parts;

[0098] Amylase: 8 parts;

[0099] Bismuth neodecanoate: 0.08 parts;

[0100] The TPU film preparation method described above is different from that of Example 1 in that amylase is added into the reactor A simultaneously with the plant-based polyester polyol C and oleic acid amide, and stirred at 110±10° C. The rest is the same as that of Example 1.

[0101] The TPU films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test methods were as follows:

[0102] Hardness (Shore A): Refer to GB / T 531.1-2008;

[0103] Tensile strength (MPa): refer to GB / T 528-2009, recorded as initial tensile strength;

[0104] Tear strength (kN / m): refer to GB / T 529-2008;

[0105] Rebound rate (%): refer to GB / T 1681-2009;

[0106] Contact angle (°): refer to GB / T 30693-2014;

[0107] Tensile strength retention rate (%) / appearance after degradation: At a temperature of 16±4℃ and a humidity of 45±5%, a TPU film with a size of 10×12cm was buried in the soil to a depth of 20cm. After 30 days, the TPU film was taken out and its appearance was observed. At the same time, its tensile strength was measured, and the ratio of the tensile strength to the initial tensile strength was calculated. The ratio×100% is the tensile strength retention rate.

[0108] Insulation time (h): Use the prepared TPU film to seal a 30×20 cm culture dish filled with soil, then put the culture dish in a 30°C oven for 2 hours, and then put it in a cool place at 12°C. The time it takes for the soil to cool down to 12°C is the insulation time.

[0109] The test results are shown in Table 1:

[0110] Table 1 Performance test results

[0111]

[0112] It can be seen from the data in Table 1 that the TPU films prepared in Examples 1-3 have high tensile strength and tear strength, excellent resilience, a large number of holes appear on the film surface after degradation, high degradation efficiency, long heat preservation time, and good hydrophobic properties.

[0113] In Comparative Examples 1 and 3, since plant-based polyester polyols were not used, the degradation efficiency was low, the insulation time was short, and the hydrophobic performance was poor; in Comparative Example 2, since no biodegradation agent was added, and in Comparative Example 4, since the biodegradation agent was added at the front end and inactivated at high temperature, the degradation efficiency of the TPU film was low.

Claims

1. A plant-based degradable TPU agricultural film, characterized in that: Including the following raw materials by mass: Plant-based polyester polyol: 44-69 parts; Diisocyanate: 17-43 parts; Chain extender: 3-11 parts; Lubricant: 0.1-1 part; Biodegradation agent: 1-10 parts; Catalyst: 0.05-0.1 parts; The preparation method of the plant-based polyester polyol is as follows: lignin, a small molecule dibasic acid and a small molecule diol are added to a reaction kettle, heated and stirred, and the temperature is raised to 140-150° C. until water is produced by the reaction, the temperature of the top of the reflux tower is controlled at 100-105° C., tetrabutyl titanate is added, the temperature is raised to 220-250° C., the reaction is continued for 2-4 hours, and then the water produced by the polycondensation is removed by a nitrogen bubbling process. When the acid value of the material in the kettle drops below 0.6 mgKOH / g and the water content drops below 0.05 wt.%, the plant-based polyester polyol is obtained; The small molecule diol is one of ethylene glycol, hexanediol or 1,4-butanediol; The number average molecular weight of the plant-based polyester polyol is 500-3000, the molar ratio of the small molecule dibasic acid to the small molecule diol is (1.1-5.1):1, and the amount of lignin is 5-50wt.% of the total amount of the plant-based polyester polyol; The biodegradation agent is one of lactate dehydrogenase, catalase, amylase, citrate synthase or triose phosphate isomerase; The preparation method of the plant-based degradable TPU agricultural film is as follows: a mixture of plant-based polyester polyol and lubricant, diisocyanate, chain extender and catalyst are mixed by metering, reacted in a twin-screw extruder, extruded and granulated, and the obtained granules are added with a biodegradation agent during the film casting process and the film cooling and solidification stage to obtain the plant-based degradable TPU agricultural film; The method for preparing the plant-based degradable TPU agricultural film comprises the following steps: 1) Add plant-based polyester polyol and lubricant to reactor A and stir at 100-120°C; add diisocyanate to reactor B and stir at 50-70°C; add chain extender to reactor C and keep the temperature at 40-60°C; mix the materials in reactors A, B and C through the perfusion system and inject them into the twin-screw extruder. At the same time, add the catalyst through the micro-injection pump at the feeding port of the twin-screw extruder. The mixed materials are uniformly reacted and transported in the twin-screw barrel. After the synthesis reaction is completed, TPU pellets are obtained by plasticization and granulation; 2) Add TPU pellets into the extruder, heat to a molten state, extrude the melt through the die, and then cool and solidify. During the cooling and solidification process, a biodegradable agent is sprayed on both ends of the film to finally obtain a plant-based degradable TPU agricultural film.

2. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The small molecule dibasic acid is a dibasic acid containing 4 to 10 carbon atoms.

3. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The diisocyanate is one of 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, 1,4-cyclohexane diisocyanate, dicyclohexylmethane diisocyanate or xylylene diisocyanate.

4. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The chain extender is a diol containing 2 to 6 carbon atoms.

5. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The lubricant is one of oleic acid amide, stearic acid alcohol ester or stearic acid amide.

6. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The lubricant is stearic acid monoglyceride or butyl stearate.

7. The plant-based degradable TPU agricultural film according to claim 1, characterized in that: The catalyst is an organic tin or organic bismuth catalyst.

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