Degradable bio-based TPU (thermoplastic polyurethane) for agricultural mulching film and preparation method of degradable bio-based TPU

Abstract

The invention belongs to the technical field of polyurethane elastomers, and particularly relates to degradable bio-based TPU for an agricultural mulching film and a preparation method of the degradable bio-based TPU. The flame-retardant polyurethane elastomer is prepared from the following raw materials: diisocyanate, polyol, a chain extender, an antioxidant, a hydrolysis stabilizer, a light stabilizer, a main flame retardant, a synergistic flame retardant and a catalyst. The polyhydric alcohol is a mixture of bio-based polyhydric alcohol and polycaprolactone; the main flame retardant is ammonium polyphosphate; the synergistic flame retardant is thiophene-2-formaldehyde modified chitosan. The polycaprolactone is introduced in the TPU synthesis process, so that on one hand, the degradation of the TPU material can be promoted due to the biodegradability of the polycaprolactone; on the other hand, the flexibility of the material can be improved. According to the invention, the biological flame retardant is selected, and through the matching effect between the main flame retardant and the synergistic flame retardant, the generated intumescent flame retardant forms the thermal insulation and oxygen isolation effects of a compact carbon layer and the gas phase capture effect of phosphorus free radicals, so that an excellent flame retardant effect can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane elastomers, and particularly relates to a degradable bio-based TPU for agricultural mulch and a preparation method thereof. Background Art

[0002] With the rapid development of modern agriculture, agricultural mulching technology has been widely used in agricultural production because of its advantages of significantly increasing soil temperature, maintaining soil moisture, inhibiting weed growth, and promoting early maturity and yield increase of crops. However, traditional mulch materials such as polyethylene (PE) are difficult to degrade, and a large amount of discarded mulch accumulates in the soil after use, causing serious "white pollution" and posing a long-term threat to the agricultural ecological environment. Therefore, the development of a mulch material that is both environmentally friendly and degradable has become an urgent need for current agricultural development.

[0003] As a new type of organic functional polymer synthetic material, thermoplastic polyurethane elastomer (TPU) has attracted widespread attention in recent years due to its excellent physical properties and processability. TPU not only has rubber properties such as high strength and high wear resistance, but also has good thermoplastic properties, which makes it have broad application prospects in the field of plastics. More importantly, bio-based TPU materials are based on raw materials from natural plants or microorganisms, such as algae and non-edible plants, and are prepared through advanced synthesis technology. This material not only retains the excellent properties of traditional TPU, but also gives it biodegradable properties, providing a new idea for solving the problem of "white pollution".

[0004] The main problems with bio-based TPU include that the bio-based content of bio-based TPU is limited by the source of raw materials and the preparation process, but further increasing the bio-based content still faces challenges. In terms of flame retardancy, bio-based TPU is usually not as good as traditional petroleum-based TPU. The difficulty lies in finding a flame retardant that can effectively improve the flame retardancy without affecting other properties of the material (such as mechanical properties, processing properties, etc.). At the same time, the amount and dispersibility of the flame retardant are also key factors affecting the flame retardant effect. Summary of the invention

[0005] In view of the deficiencies of the prior art, the object of the present invention is to provide a degradable bio-based TPU for agricultural mulch film, which has a high bio-based content and good flame retardant properties.

[0006] The present invention uses bio-based material chitosan as a flame retardant to improve the flame retardant properties of bio-based TPU and simultaneously increase the bio-based content. Chitosan, as a natural polymer material, not only has good flame retardant properties, but is also well compatible with the bio-based TPU system, improving the overall performance of the material.

[0007] As a biodegradable polyester, polycaprolactone has good biocompatibility and environmental friendliness. When it is added to the synthesis process of TPU, it can promote the degradation of TPU materials because it is biodegradable. This feature makes TPU materials containing polycaprolactone have advantages in environmental protection and sustainability. In addition, the addition of polycaprolactone may also affect certain properties of TPU, such as improving the flexibility and wear resistance of the material.

[0008] The invention also provides a preparation method thereof, which is suitable for large-scale production.

[0009] The biodegradable bio-based TPU for agricultural mulch film of the present invention is made of the following raw materials in parts by weight: Diisocyanate: 9-16 parts; Polyol: 50-55 parts; Chain extender: 3-6 parts; Antioxidant: 0.1-0.2 parts; Hydrolysis stabilizer: 0.1-0.2 parts; Light stabilizer: 0.1-0.2 parts; Main flame retardant: 15-20 parts; Synergistic flame retardant: 10-15 parts; Catalyst: 0.1-0.5 parts; The polyol is a mixture of bio-based polyol and polycaprolactone in a mass ratio of 1:(0.1-0.15); The bio-based polyol has a functionality of 2 and a number average molecular weight of 1000-4000 g / mol; The main flame retardant is ammonium polyphosphate; The synergistic flame retardant is thiophene-2-carboxaldehyde modified chitosan.

[0010] The bio-based polyol is one of bio-based poly(propylene succinate) diol, bio-based poly(propylene sebacate) diol, and bio-based poly(propylene sebacate-succinate) diol.

[0011] The preparation method of the bio-based polyol is as follows: bio-based polysuccinic acid, bio-based sebacic acid or bio-based polysebacic acid-succinic acid and bio-based propylene glycol in a molar ratio of 1: (1.1-1.2) are put into a reactor, heated by nitrogen, and the temperature is raised to 140-150° C. in a first program, and kept warm for 1-3 hours; then a second program is set to heat the temperature to 210-230° C. in 2-4 hours, and kept warm for 2-4 hours; then the program vacuum is entered, and 10-100 ppm of tetrabutyl titanate is added, and the pressure in the reactor is evacuated from normal pressure to a relative vacuum of less than -0.098 MPa within 3-5 hours; when the detected acid value is less than 0.5 mgKOH, the color value is less than 30 APHA, the moisture is less than 300 ppm, and the hydroxyl value and viscosity reach the target value, the product is qualified, the vacuum is broken by nitrogen, and the temperature is lowered to less than 120° C. to obtain the bio-based polyol.

[0012] The diisocyanate is one of 1,6-hexamethylene diisocyanate and 4,4'-diphenylmethane diisocyanate.

[0013] The chain extender is bio-based 1,4-butanediol.

[0014] The antioxidant is antioxidant 1010, the hydrolysis stabilizer is polycarbodiimide, the light stabilizer is Tinuvin 144 (BASF), and the catalyst is an organic bismuth catalyst.

[0015] The preparation method of the thiophene-2-carboxaldehyde modified chitosan is as follows: chitosan and ethanol are put into a reaction container, thiophene-2-carboxaldehyde is added dropwise, the temperature is raised and stirred for reaction, and the chitosan is obtained after filtering, washing and drying. Figure 1 shown.

[0016] The temperature of the heating and stirring reaction is 85-95°C and the time is 12 hours.

[0017] Further, 0.1 mol chitosan and 60 ml ethanol were added to a 250 ml round-bottom flask, and 0.2 mol thiophene-2-carboxaldehyde was immediately dripped into the flask at a drip rate of 3 seconds per drop. The mixture was stirred at 85°C for 12 h. After the reaction was completed, the crude product was filtered and washed with ethanol several times, and the final product (yellow powder) thiophene-2-carboxaldehyde-modified chitosan was dried in vacuum at 60°C for 12 h.

[0018] The method for preparing the degradable bio-based TPU for agricultural mulch film of the present invention comprises the following steps: (1) Mixing the polyol and the chain extender, then adding the antioxidant, the hydrolysis stabilizer, and the light stabilizer, heating and stirring to obtain a premix; (2) After drying the main flame retardant and the synergistic flame retardant, compounding them into an intumescent flame retardant system; (3) Add diisocyanate and catalyst into storage tank A, add premix and expansion flame retardant system into storage tank B, react in a twin-screw extruder, and granulate to obtain TPU particles.

[0019] The temperature of the heating and stirring in step (1) is 80-110°C.

[0020] The drying temperature in step (2) is 75-85°C, and the drying time is 5 hours. The reaction temperature of the twin-screw extruder in step (3) is 180-190°C.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention introduces polycaprolactone in the TPU synthesis process. On the one hand, since polycaprolactone is biodegradable, it can promote the degradation of TPU materials; on the other hand, it can improve the flexibility of the material.

[0022] 2. The present invention uses bio-type flame retardants. Through the coordination between the main flame retardant and the synergistic flame retardant, the generated expansion flame retardant forms a dense carbon layer with heat preservation and oxygen isolation effect and the gas phase capture effect of phosphorus free radicals, which can achieve excellent flame retardant effect. While giving the material flame retardancy, chitosan has a high degree of crystallinity and therefore has very stable physical and chemical properties, which also provides a basis for its aging resistance.

[0023] 3. Thiophene-2-carboxaldehyde, as a modifier, can react chemically with chitosan, thereby changing the original chemical structure of chitosan. This change in chemical structure enables the modified chitosan to form a more stable carbon layer when burning, preventing the further spread of flames. At the same time, the introduction of thiophene-2-carboxaldehyde may also increase the cross-linking degree between chitosan molecules, improve the thermal stability and mechanical strength of the material, and further enhance its flame retardant properties.

[0024] 4. The bio-based content of the present invention can be higher than 60%. The product is processed by extrusion and injection molding. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the synthetic route of thiophene-2-carboxaldehyde modified chitosan. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the embodiments.

[0027] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0028] Light stabilizer Tinuvin 144 is a commercial product of BASF; Antioxidant 1010 is a commercially available product of BASF; Polycarbodiimide is a commercial product of BASF; Ammonium polyphosphate is a commercially available product of Jinan Jinyingtai Chemical Co., Ltd. with a degree of polymerization n≥1000; Bio-based succinic acid is a commercially available product of Kingfa Science & Technology Co., Ltd.; Bio-based propylene glycol is a commercial product of Kingfa Science & Technology Co., Ltd.; Bio-based sebacic acid is a commercially available product of Kingfa Science & Technology Co., Ltd.; Polylactone (Mw=2000) is a commercially available product of Juren New Materials; Bio-based 1,4-butanediol is a commercially available product of Kingfa Science & Technology Co., Ltd.; Chitosan (Mw = 60000) is a commercially available product of Sinopharm Chemical Reagent Company; Thiophene-2-carboxaldehyde is a commercial product of Aladdin.

[0029] Preparation method of thiophene-2-carboxaldehyde modified chitosan: Add 0.1 mol chitosan and 60 ml ethanol into a 250 ml round-bottom flask, and immediately drip 0.2 mol thiophene-2-carboxaldehyde into the flask at a drip rate of 3 seconds per drop. Stir at 90±5℃ for 12 h. After the reaction is completed, the crude product is filtered and washed with ethanol. The final product (yellow powder) thiophene-2-carboxaldehyde-modified chitosan is dried in vacuum at 60℃ for 12 h.

[0030] Example 1 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: 1,6-hexamethylene diisocyanate: 13.8 parts; Polyol (number average molecular weight 2000 g / mol): 54.8 parts; Chain extender: bio-based 1,4-butanediol: 5.4 parts; Antioxidant 1010: 0.2 parts; Light stabilizer Tinuvin 144: 0.2 parts; Hydrolysis stabilizer: polycarbodiimide: 0.1 part; Synergistic flame retardant: thiophene-2-carboxaldehyde modified chitosan: 10 parts; Main flame retardant: ammonium polyphosphate: 15 parts; Organic bismuth catalyst (DY-20): 0.5 parts.

[0031] The polyol is a mixture of bio-based polypropylene succinate diol and polycaprolactone, wherein the number average molecular weight of the bio-based polypropylene succinate diol is 2000 g / mol; the number average molecular weight of the polycaprolactone is 2000 g / mol, and the mass ratio of the bio-based polypropylene succinate diol to the polycaprolactone is 1:0.1.

[0032] The total biobased content of the system is 64.7%.

[0033] The preparation method of the bio-based polypropylene succinate diol: Bio-based polysuccinic acid and bio-propylene glycol in a molar ratio of 1:1.2 are put into a reactor, heated by nitrogen, and the temperature is raised to 140°C in the first program and kept for 1 hour; then the temperature is raised to 210°C in 2 hours and kept for 2 hours; then the reactor enters the program vacuum, and 10ppm tetrabutyl titanate is added, and the pressure in the reactor is evacuated from normal pressure to a relative vacuum below -0.098MPa within 3 hours; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, the product is qualified, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polysuccinic acid propylene glycol ester diol.

[0034] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 80°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and thiophene-2-carboxaldehyde modified chitosan at 85°C for 5 hours to compound into an intumescent flame retardant system; (3) Add 1,6-hexamethylene diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 180° C., and granulate to obtain TPU particles.

[0035] Example 2 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: 1,6-hexamethylene diisocyanate: 14.5 parts; Polyol (number average molecular weight 1000 g / mol): 51.4 parts; Chain extender: bio-based 1,4-butanediol: 3.4 parts; Antioxidant 1010: 0.2 parts; Light stabilizer Tinuvin 144: 0.1 part; Hydrolysis stabilizer: polycarbodiimide: 0.2 parts; Synergistic flame retardant: thiophene-2-carboxaldehyde modified chitosan: 12.5 parts; Main flame retardant: ammonium polyphosphate: 17.5 parts; Organic bismuth catalyst (DY-20): 0.2 parts.

[0036] The polyol is a mixture of bio-based polypropylene sebacate diol and polycaprolactone, wherein the number average molecular weight of the bio-based polypropylene sebacate diol is 1000 g / mol; the number average molecular weight of the polycaprolactone is 1000 g / mol, and the mass ratio of the bio-based polypropylene sebacate diol to the polycaprolactone is 1:0.12.

[0037] The total biobased content of the system is 61.3%.

[0038] The preparation method of the bio-based polypropylene sebacate diol: Bio-based polysebacic acid and bio-propylene glycol in a molar ratio of 1:1.1 are put into a reactor, heated by nitrogen, and the temperature is raised to 145°C in the first stage and kept warm for 2 hours; then the temperature is raised to 220°C in 3 hours and kept warm for 3 hours; then the reactor enters the vacuum program, and 50ppm tetrabutyl titanate is added, and the pressure in the reactor is evacuated from normal pressure to a relative vacuum of less than -0.098MPa within 4 hours; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, the product is qualified, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polypropylene sebacic acid diol.

[0039] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 95°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and thiophene-2-carboxaldehyde modified chitosan at 75°C for 5 hours to compound into an intumescent flame retardant system; (3) Add 1,6-hexamethylene diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 185°C, and granulate to obtain TPU particles.

[0040] Example 3 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: 1,6-hexamethylene diisocyanate: 9.9 parts; Polyol (number average molecular weight 4000 g / mol): 50.8 parts; Chain extender: bio-based 1,4-butanediol: 3.7 parts; Antioxidant 1010: 0.1 part; Light stabilizer Tinuvin 144: 0.2 parts; Hydrolysis stabilizer: polycarbodiimide: 0.2 parts; Synergistic flame retardant: thiophene-2-carboxaldehyde modified chitosan: 15 parts; Main flame retardant: ammonium polyphosphate: 20 parts; Organic bismuth catalyst (DY-20): 0.1 parts. The polyol is a mixture of bio-based poly(propylene sebacate-succinate) diol and polycaprolactone, wherein the number average molecular weight of the bio-based poly(propylene sebacate-succinate) diol is 4000 g / mol; the number average molecular weight of the polycaprolactone is 4000 g / mol, and the mass ratio of the bio-based poly(propylene sebacate-succinate) diol to the polycaprolactone is 1:0.15.

[0041] The total biobased content of the system is 61.9%.

[0042] The preparation method of the bio-based polypropylene sebacate diol: Bio-based polysebacic acid-succinic acid and bio-propylene glycol in a molar ratio of 1:1.1 are put into a reactor, heated by nitrogen, and the temperature is raised to 150°C in the first program and kept for 3 hours; then the temperature is raised to 230°C in 4 hours and kept for 4 hours; then the program vacuum is entered, and 100ppm tetrabutyl titanate is added. Within 5 hours, the pressure in the reactor is evacuated from normal pressure to a relative vacuum of less than -0.098MPa; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, it is a qualified product, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polypropylene sebacic acid diol.

[0043] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 110°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and thiophene-2-carboxaldehyde modified chitosan at 80°C for 5 hours to compound into an intumescent flame retardant system; (3) Add 1,6-hexamethylene diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 190° C., and granulate to obtain TPU particles.

[0044] Example 4 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: Diphenylmethane-4,4'-diisocyanate: 15.6 parts; Polyol (number average molecular weight 2000 g / mol): 54.8 parts; Chain extender: bio-based 1,4-butanediol: 3.6 parts; Antioxidant 1010: 0.2 parts; Light stabilizer Tinuvin 144: 0.2 parts; Hydrolysis stabilizer: polycarbodiimide: 0.1 part; Synergistic flame retardant: thiophene-2-carboxaldehyde modified chitosan: 10 parts; Main flame retardant: ammonium polyphosphate: 15 parts; Organic bismuth catalyst (DY-20): 0.5 parts. The polyol is a mixture of bio-based polypropylene succinate diol and polycaprolactone, wherein the number average molecular weight of the bio-based polypropylene succinate diol is 2000 g / mol; the number average molecular weight of the polycaprolactone is 2000 g / mol, and the mass ratio of the bio-based polypropylene succinate diol to the polycaprolactone is 1:0.1.

[0045] The total biobased content of the system is 62.9%.

[0046] The preparation method of the bio-based polypropylene succinate diol: Bio-based polysuccinic acid and bio-propylene glycol in a molar ratio of 1:1.2 are put into a reactor, heated by nitrogen, and the temperature is raised to 140°C in the first program and kept for 1 hour; then the temperature is raised to 210°C in 2 hours and kept for 2 hours; then the reactor enters the program vacuum, and 10ppm tetrabutyl titanate is added, and the pressure in the reactor is evacuated from normal pressure to a relative vacuum below -0.098MPa within 3 hours; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, the product is qualified, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polysuccinic acid propylene glycol ester diol.

[0047] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 80°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and thiophene-2-carboxaldehyde modified chitosan at 85°C for 5 hours to compound into an intumescent flame retardant system; (3) Add diphenylmethane-4,4'-diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 180°C, and granulate to obtain TPU particles.

[0048] Comparative Example 1 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: 1,6-hexamethylene diisocyanate: 12.2 parts; Polyol (number average molecular weight 1000 g / mol): 54.5 parts; Chain extender: bio-based 1,4-butanediol: 2.6 parts; Antioxidant 1010: 0.2 parts; Light stabilizer Tinuvin 144: 0.1 part; Hydrolysis stabilizer: polycarbodiimide: 0.2 parts; Synergistic flame retardant: chitosan: 12.5 parts; Main flame retardant: ammonium polyphosphate: 17.5 parts; Organic bismuth catalyst (DY-20): 0.2 parts. The polyol is a mixture of bio-based polypropylene sebacate diol and polycaprolactone, wherein the number average molecular weight of the bio-based polypropylene sebacate diol is 1000 g / mol; the number average molecular weight of the polycaprolactone is 1000 g / mol, and the mass ratio of the bio-based polypropylene sebacate diol to the polycaprolactone is 1:0.12.

[0049] The total biobased content of the system is 62.8%.

[0050] The preparation method of the bio-based polypropylene sebacate diol: Bio-based polysebacic acid and bio-propylene glycol in a molar ratio of 1:1.15 are put into a reactor, heated by nitrogen, and the temperature is raised to 145°C in the first program and kept warm for 2 hours; then the temperature is raised to 220°C in 3 hours and kept warm for 3 hours; then the reactor enters the program vacuum, and 50ppm tetrabutyl titanate is added, and the pressure in the reactor is evacuated from normal pressure to a relative vacuum of less than -0.098MPa within 4 hours; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, the product is qualified, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polypropylene sebacic acid diol.

[0051] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 95°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and chitosan at 75°C for 5 hours to form an intumescent flame retardant system; (3) Add 1,6-hexamethylene diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 185°C, and granulate to obtain TPU particles.

[0052] Comparative Example 2 The biodegradable bio-based TPU for agricultural mulch film is made of the following raw materials in parts by weight: 1,6-hexamethylene diisocyanate: 11.7 parts; Polyol (number average molecular weight 4000 g / mol): 48.4 parts; Chain extender: bio-based 1,4-butanediol: 4.4 parts; Antioxidant 1010: 0.1 part; Light stabilizer Tinuvin 144: 0.2 parts; Hydrolysis stabilizer: polycarbodiimide: 0.2 parts; Synergistic flame retardant: thiophene-2-carboxaldehyde modified chitosan: 15 parts; Main flame retardant: ammonium polyphosphate: 20 parts; Organic bismuth catalyst (DY-20): 0.1 parts.

[0053] The polyol is bio-based polypropylene glycol sebacate-succinate diol with a number average molecular weight of 4000 g / mol.

[0054] The total biobased content of the system is 67.8%.

[0055] The preparation method of the bio-based polypropylene sebacate diol: Bio-based polysebacic acid-succinic acid and bio-propylene glycol in a molar ratio of 1:1.1 are put into a reactor, heated by nitrogen, and the temperature is raised to 150°C in the first program and kept for 3 hours; then the temperature is raised to 230°C in 4 hours and kept for 4 hours; then the program vacuum is entered, and 100ppm tetrabutyl titanate is added. Within 5 hours, the pressure in the reactor is evacuated from normal pressure to a relative vacuum of less than -0.098MPa; when the detected acid value is less than 0.5mgKOH, the color value is less than 30APHA, the moisture is less than 300ppm, and the hydroxyl value and viscosity reach the target values, it is a qualified product, the vacuum is broken with nitrogen, and the temperature is lowered to below 120°C to obtain bio-based polypropylene sebacic acid diol.

[0056] The method for preparing the degradable bio-based TPU for agricultural mulch film comprises the following steps: (1) Mix the polyol and the chain extender, then add the antioxidant 1010, the hydrolysis stabilizer and the light stabilizer, raise the temperature to 110°C and stir to obtain a premix; (2) Drying ammonium polyphosphate and thiophene-2-carboxaldehyde modified chitosan at 80°C for 5 hours to compound into an intumescent flame retardant system; (3) Add 1,6-hexamethylene diisocyanate and catalyst DY-20 into storage tank A, add the premix and the intumescent flame retardant system into storage tank B, react in a twin-screw extruder at 190° C., and granulate to obtain TPU particles.

[0057] The TPU products obtained in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests according to the following standards. The results are shown in Tables 1 and 2.

[0058] (1) Biodegradability: The particles obtained in the test were subjected to film blowing to obtain a film with a thickness of 0.2 mm. The composting test was carried out according to the method specified in GB / T19277.2-2013. After 50 days of testing, the biodegradation rate of the samples was tested by gravimetric analysis.

[0059] (2) Mechanical properties: According to the ASTM-D412 method, the obtained particle injection molding test pieces were cut into dumbbell-shaped specimens that met the standard for data testing.

[0060] (3) Hardness test: Hardness test is carried out in accordance with ASTM-D2240.

[0061] (4) Flame retardant performance: tested in accordance with UL94 standard. (5) Aging resistance test: The obtained particle injection molded test piece was cut into dumbbell-shaped specimens that meet the standard and placed under 340nm 1.50W / m 2 The ultraviolet light was continuously irradiated, and samples were taken out at regular intervals for mechanical property testing.

[0062] Table 1 Test results of biodegradability, hardness and flame retardancy of products of Examples and Comparative Examples

[0063] Table 2 Aging resistance test results of the products of the embodiments and comparative examples

[0064] It can be seen from the test data in Table 1 and Table 2 that the present invention can realize the synthesis of bio-based thermoplastic polyurethane elastomer, and the bio-based content is higher than 60%, and the product has a highly efficient biodegradable effect. By comparing Example 1 with Example 4, HDI has better degradability than MDI; by comparing Example 2 with Comparative Example 1, thiophene-2-carboxaldehyde-modified chitosan has a synergistic effect, and the generated expanded carbon layer can effectively isolate heat and reduce the volatilization of combustible substances to have a flame retardant and aging-resistant effect on TPU; by comparing Example 3 with Comparative Example 2, polycaprolactone promotes the degradation of TPU.

Claims

1. A biodegradable bio-based TPU for agricultural mulch film, characterized in that: Made from the following raw materials in parts by weight: Diisocyanate: 9-16 parts; Polyol: 50-55 parts; Chain extender: 3-6 parts; Antioxidant: 0.1-0.2 parts; Hydrolysis stabilizer: 0.1-0.2 parts; Light stabilizer: 0.1-0.2 parts; Main flame retardant: 15-20 parts; Synergistic flame retardant: 10-15 parts; Catalyst: 0.1-0.5 parts; The polyol is a mixture of bio-based polyol and polycaprolactone in a mass ratio of 1:(0.1-0.15); The bio-based polyol has a functionality of 2 and a number average molecular weight of 1000-4000 g / mol; The main flame retardant is ammonium polyphosphate; The synergistic flame retardant is thiophene-2-carboxaldehyde modified chitosan.

2. The biodegradable bio-based TPU for agricultural mulch film according to claim 1, characterized in that: The bio-based polyol is one of bio-based polypropylene succinate diol, bio-based polypropylene sebacate diol, and bio-based polypropylene sebacate-succinate diol.

3. The biodegradable bio-based TPU for agricultural mulch film according to claim 1, characterized in that: The diisocyanate is one of 1,6-hexamethylene diisocyanate and 4,4'-diphenylmethane diisocyanate.

4. The biodegradable bio-based TPU for agricultural mulch film according to claim 1, characterized in that: The chain extender is bio-based 1,4-butanediol.

5. The biodegradable bio-based TPU for agricultural mulch film according to claim 1, characterized in that: The antioxidant is antioxidant 1010, the hydrolysis stabilizer is polycarbodiimide, the light stabilizer is Tinuvin 144, and the catalyst is an organic bismuth catalyst.

6. The biodegradable bio-based TPU for agricultural mulch film according to claim 1, characterized in that: The preparation method of the thiophene-2-carboxaldehyde modified chitosan comprises: putting chitosan and ethanol into a reaction container, dropping thiophene-2-carboxaldehyde, heating and stirring to react, filtering, washing and drying to obtain the chitosan.

7. The biodegradable bio-based TPU for agricultural mulch film according to claim 6, characterized in that: The temperature of the heating and stirring reaction is 85-95°C.

8. A method for preparing the degradable bio-based TPU for agricultural mulch film according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Mixing the polyol and the chain extender, then adding the antioxidant, the hydrolysis stabilizer, and the light stabilizer, heating and stirring to obtain a premix; (2) After drying the main flame retardant and the synergistic flame retardant, compounding them into an intumescent flame retardant system; (3) Add diisocyanate and catalyst into storage tank A, add premix and expansion flame retardant system into storage tank B, react in a twin-screw extruder, and granulate to obtain TPU particles.

9. The method for preparing the degradable bio-based TPU for agricultural mulch film according to claim 8, characterized in that: The temperature of the heating and stirring in step (1) is 80-110°C.

10. The method for preparing the degradable bio-based TPU for agricultural mulch film according to claim 8, characterized in that: The drying temperature in step (2) is 75-85°C, and the reaction temperature of the twin-screw extruder in step (3) is 180-190°C.

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