A fully biodegradable film and a method for preparing the same

Abstract

The present application relates to the technical field of material, especially to a kind of polybutylene adipate terephthalate / starch / carbon dioxide-based thermoplastic polyurethane fully biodegradable film and preparation method thereof.The fully biodegradable film of the present application has the following formula composition: polybutylene adipate terephthalate resin (PBAT) 40-65 parts by weight, modified starch (TPS) 15-30 parts by weight, carbon dioxide-based thermoplastic polyurethane (PPCU) 9-40 parts by weight, opening agent 0.1-1 parts by weight, lubricant 0.1-2 parts by weight.The present application mixes polybutylene adipate terephthalate resin with modified starch, carbon dioxide-based thermoplastic polyurethane and other additives, and combines the above specific ratio, so that the film prepared by the finally prepared composition has the advantages of high tensile and tear strength, good elastic modulus, good elongation at break, good moisture and water resistance, good barrier property and good degradation performance.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a fully biodegradable poly(butylene terephthalate) / starch / carbon dioxide-based thermoplastic polyurethane film and its preparation method. Background Technology

[0002] The environmental pollution caused by petroleum-based plastics is becoming increasingly serious, necessitating the replacement with fully biodegradable plastics. Polybutylene terephthalate (PBAT) is a fully biodegradable plastic that has been widely studied both domestically and internationally. However, films made from pure PBAT are relatively soft, have low strength, and are expensive, limiting their application in many fields. Therefore, during application processing, PBAT is usually blended with other materials for modification to improve its performance.

[0003] The high cost of raw materials for PBAT is a major factor limiting its widespread use. Therefore, it is necessary to add low-cost fillers for blending modification during PBAT processing. Ning et al. reported on the study of starch-filled modified PBAT (Ning Ping, Chen Mingyue, Xiao Yunhe. Study on the structure and properties of starch-filled modified PBAT, New Chemical Materials, 2010, 38(7):116-119). With the addition of compatibilizer, the compatibility between starch and PBAT is significantly improved. In particular, when the content of compatibilizer (EMH4210) is 7 parts, the starch dosage of 10% can still maintain good performance. The addition of compatibilizer not only improves the dispersion effect of starch, but also greatly improves the compatibility between starch and PBAT. However, the compatibilizer does not degrade, which affects the degradation performance of the material.

[0004] Qiu Qiaoping et al. reported the preparation of biodegradable TPS / PBAT composite materials (Qiu Qiaoping, Xie Xinchun, Tan Lei, Xiang Ming. Preparation of Biodegradable TPS / PBAT Composite Materials, Synthetic Resins and Plastics, 2009, 26(3): 13-16). A fully biodegradable TPS / PBAT composite material was prepared by melt blending and extrusion of thermoplastic starch (TPS) and PBAT. After adding PBAT, the melt flowability of the composite material significantly improved; the tensile strength decreased from 6.36 MPa to 3.31 MPa, and then increased to 12.98 MPa. The addition of PBAT inhibited the recrystallization of amylopectin molecules and reduced the water absorption rate of the composite material. The TPS / PBAT composite material prepared by this technique has a relatively low tensile strength, making it unsuitable for preparing shopping bag films and limiting its application range.

[0005] Pan Hongwei, Zhang Huiliang, and others reported in the journal *Korean Journal Chemical Engineering* (2017, 34(5): 1294-1304) on the co-extrusion and blow molding of PBAT with carbon dioxide copolymer polypropylene carbonate (PPC) into films. The study showed that the addition of PPC increased the tensile strength and gas barrier properties of the PBAT / PPC film. The literature also reported the degradation of the film in soil, indicating that the PBAT / PPC film is particularly suitable for packaging bag applications. However, the application and promotion of the PBAT / PPC film prepared by this technology is limited by the high cost of PPC, approximately 20,000 yuan / ton.

[0006] Zhang Huiliang et al. disclosed an invention patent for "a ternary fully biodegradable film and its preparation method" (publication number CN113214615A). The invention involves blending and modifying PBAT with polypropylene carbonate (PPC) and thermoplastic starch (TPS), extruding and granulating the mixture, and then blowing the film using a blown film machine to prepare a PBAT / PPC / TPS ternary blend blown film. The tensile strength of this film is less than 20 MPa, and the technology still has the disadvantage of being unable to withstand large loads.

[0007] Zhang Ye, Zhang Huiliang, and others reported in the journal *Plastics Industry*, 2018, 46(1):99-103, 146., on the preparation of polylactic acid (PLA) / polybutylene succinate (PBS) / carbon dioxide-based thermoplastic polyurethane (PPCU) films using melt blending and extrusion blown film processes. The PLA / PBS / PPCU films prepared using this technology are expensive due to the high cost of PBS (30,000 RMB / ton) and PLA (20,000 RMB / ton), making widespread application difficult.

[0008] Yang Jia et al. disclosed an invention patent for "a highly transparent fully biodegradable film and its preparation method" (publication number CN113845761A). The invention involves the extrusion and granulation of PLA with toughening agents PBAT, PBS, PPC, and PPCU in a binary or multi-component blend, followed by blown film processing to prepare a binary or multi-component blend blown film. The PLA used in this film costs approximately 20,000 yuan / ton and has a content as high as 80%-97%, while the PBS costs approximately 30,000 yuan / ton. The high cost limits its application and promotion.

[0009] Lin Shuhong et al. disclosed an invention patent for "A Biodegradable Blown Film Resin Film and Its Preparation Method" (Publication No. CN114672139A). The method involves blending and extruding 60-100 parts of long-chain branched polylactic acid, 40-80 parts of PBAT, 12-25 parts of modified PPC, 1-6 parts of tetrabutyl titanate, 7-15 parts of ionic liquid, 5-15 parts of plasticizer, and 3-8 parts of compatibilizer to prepare a blown film resin. The resulting biodegradable film exhibits good toughness and high mechanical strength. However, the PLA used in this film is relatively expensive, costing approximately 20,000 yuan / ton, and its content is as high as 60-100 parts, limiting its application and promotion due to cost constraints.

[0010] Zhao Ruofei et al. disclosed an invention patent for "A biodegradable packaging material, packaging film bag, and preparation method" (publication number CN113185820A). This patent describes a biodegradable packaging material using PLA as the main material, supplemented with a quaternary blend system of PBAT, PBS, and PPCU. ADR is used as a chain extender, and a film with high transparency and excellent mechanical properties is prepared through cold crystallization. The PLA used in this film costs approximately 20,000 yuan / ton, and PBS costs approximately 30,000 yuan / ton, resulting in high costs; its application and promotion are limited by these costs.

[0011] How to make good use of these existing technologies to provide thin film products with better performance has become one of the important problems that urgently need to be solved in this field. Summary of the Invention

[0012] To address the problems existing in the prior art, this invention provides a low-cost, high-strength fully biodegradable film and its preparation method.

[0013] Existing technologies can significantly reduce material costs through blending modification with starch. Starch is also a biodegradable natural polymer. The cost of polybutylene terephthalate (PET) / starch films obtained through blending modification is greatly reduced. However, the films have poor water resistance and are not resistant to humid environments. The inventors have discovered for the first time that adding carbon dioxide-based thermoplastic polyurethane (PPCU) can improve the water and moisture resistance of the film, overcoming the moisture absorption disadvantage of starch and extending the film's shelf life. Furthermore, modifying starch improves the compatibility of starch with PBAT and PPCU. Existing literature has not found reports on the preparation of blown films by blending PBAT with carbon dioxide-based thermoplastic polyurethane (PPCU) and thermoplastic starch (TPS). The inventors have proposed this technical solution for the first time.

[0014] The technical solution of this invention to solve the technical problem is as follows:

[0015] In a first aspect of the invention, a fully biodegradable film is provided.

[0016] The fully biodegradable film of the present invention has the following composition: 40-65 parts by weight of polybutylene terephthalate-adipate resin (PBAT), 15-30 parts by weight of modified starch (TPS), 9-40 parts by weight of carbon dioxide-based thermoplastic polyurethane (PPCU), 0.1-1 parts by weight of opening agent, and 0.1-2 parts by weight of lubricant.

[0017] The modified starch is starch modified with a modifier and containing a plasticizer. The modifier is any one of citric acid or maleic anhydride, mixed with any one of titanate coupling agent, aluminate coupling agent, and silane coupling agent. The plasticizer is one or two of glycerol and sorbitol. The modified starch can be obtained by simply blending starch, plasticizer, and modifier.

[0018] The opening agent is erucamide or oleamide;

[0019] The lubricant is glyceryl monostearate.

[0020] Preferably, the modified starch is modified corn starch or cassava starch; the weight ratio of starch, plasticizer and modifier in the modified starch is 70-75:20-25:1-3.

[0021] Preferably, the weight ratio of any one of citric acid or maleic anhydride to any one of titanate coupling agent, aluminate coupling agent and silane coupling agent is 1:1 to 1:0.2.

[0022] Preferably, the weight-average molecular weight of the carbon dioxide-based thermoplastic polyurethane is 6 × 10⁻⁶. 4 g / mol to 5×10 5 g / mol.

[0023] More preferably, the fully biodegradable film of the present invention has the following composition: 45-60 parts by weight of polybutylene terephthalate-adipate resin, 17-22 parts by weight of modified starch, 20-30 parts by weight of carbon dioxide-based thermoplastic polyurethane, 0.2-0.5 parts by weight of opening agent, and 0.5-1.2 parts by weight of lubricant.

[0024] In a second aspect of the invention, a method for preparing a fully biodegradable thin film as described in the first aspect is provided, comprising the following steps:

[0025] 1) Starch, plasticizer, and modifier are mixed and modified to obtain modified starch;

[0026] 2) Polybutylene terephthalate-adipate resin, modified starch, carbon dioxide-based thermoplastic polyurethane, opening agent and lubricant are mixed and extruded to obtain a blown film resin;

[0027] 3) The film is blown with the film blowing resin to obtain a fully biodegradable poly(butylene terephthalate) / starch / carbon dioxide-based thermoplastic polyurethane film.

[0028] Preferably, the extrusion temperature is 80–185°C, the screw speed is 200–350 rpm, and the blown film processing temperature is 150–185°C.

[0029] Compared with the prior art, the present invention has the following technical effects:

[0030] 1) This invention involves mixing polybutylene terephthalate (PET) resin with modified starch, carbon dioxide-based thermoplastic polyurethane, and other additives in a specific ratio. Due to the compatibilizing effect of citric acid or maleic anhydride with titanate coupling agents, aluminate coupling agents, and silane coupling agents on PET resin, starch, and carbon dioxide-based thermoplastic polyurethane, the resulting film exhibits advantages such as high tensile and tear strength, good elastic modulus, good elongation at break, good barrier properties, good degradation performance, and strong water and moisture resistance. Furthermore, the addition of low-cost starch and plasticizers significantly reduces film costs, enabling a better reduction in the price of biodegradable films and their packaging products, thus meeting the market demands for shopping bags, express delivery bags, garbage bags, and agricultural films.

[0031] 2) This invention uses carbon dioxide-based thermoplastic polyurethane, whose chemical structure contains polyurethane segments. Existing PPC, commonly used in the prior art, is obtained by copolymerizing carbon dioxide and propylene oxide and does not contain polyurethane segments. Carbon dioxide-based thermoplastic polyurethane possesses certain elasticity and toughness, while PPC lacks these properties. Furthermore, the TPS used in this invention is relatively inexpensive, costing approximately 5000 yuan / ton, resulting in lower overall cost. Detailed Implementation

[0032] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a fully biodegradable poly(butylene terephthalate) / starch / carbon dioxide-based thermoplastic polyurethane film and its preparation method.

[0033] The PBAT used in the following examples was purchased from Xinjiang Lanshan Tunhe Polyester Co., Ltd., and its model is TH801T;

[0034] The starch was purchased from Shandong Shouguang Juneng Golden Corn Development Co., Ltd.

[0035] The carbon dioxide-based thermoplastic polyurethane was purchased from Jiangsu Zhongke Jinlong Environmental Protection New Materials Co., Ltd., model number T4.

[0036] The opening agent erucamide was purchased from Jiangxi Weike Oil & Chemical Co., Ltd.

[0037] The lubricant, glyceryl monostearate, was purchased from Liaocheng Ruijie Chemical Co., Ltd.; other additives were not restricted in their source of purchase.

[0038] In the following examples, the tensile properties of the film were tested according to GB / T 1010.3-2006; the tear strength was tested according to QB / T 1130-91; and the heat-sealing strength was tested according to ASTM F88-05.

[0039] Example 1

[0040] The fully biodegradable film of this embodiment is prepared by the following method:

[0041] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, titanate coupling agent, and glycerol in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0042] (2) Weigh out 63 parts of PBAT, 27 parts of modified starch, 9.3 parts of carbon dioxide-based thermoplastic polyurethane, 0.5 parts of glyceryl monostearate, and 0.2 parts of erucamide;

[0043] (3) Add each raw material to the high-speed mixer in a certain order. The order of addition is PBAT, modified starch, carbon dioxide-based thermoplastic polyurethane, glyceryl monostearate, and erucamide. Set the mixing speed to low and mix at low speed for about 3 minutes before discharging.

[0044] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0045] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0046] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0047] Example 2

[0048] The fully biodegradable film of this embodiment is prepared by the following method:

[0049] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, titanate coupling agent, and glycerol in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0050] (2) Weigh out 56 parts of PBAT, 24 parts of modified starch, 19 parts of carbon dioxide-based thermoplastic polyurethane, 0.8 parts of glyceryl monostearate, and 0.2 parts of erucamide.

[0051] (3) Add each raw material to the high-speed mixer in a certain order. The order of addition is PBAT, modified starch, carbon dioxide-based thermoplastic polyurethane, glyceryl monostearate, and erucamide. Set the mixing speed to low and mix at low speed for about 3 minutes before discharging.

[0052] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0053] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0054] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0055] Example 3

[0056] The fully biodegradable film of this embodiment is prepared by the following method:

[0057] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, titanate coupling agent, and glycerol in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0058] (2) Weigh out 49 parts of PBAT, 21 parts of modified starch, 29.3 parts of carbon dioxide-based thermoplastic polyurethane, 0.5 parts of glyceryl monostearate, and 0.2 parts of erucamide;

[0059] (3) Add each raw material to the high-speed mixer in a certain order. The order of addition is PBAT, modified starch, carbon dioxide-based thermoplastic polyurethane, glyceryl monostearate, and erucamide. Set the mixing speed to low and mix at low speed for about 3 minutes before discharging.

[0060] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0061] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0062] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0063] Example 4

[0064] The fully biodegradable film of this embodiment is prepared by the following method:

[0065] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, and titanate coupling agent in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0066] (2) Weigh 42 parts of PBAT, 18 parts of modified starch, 38.7 parts of carbon dioxide-based thermoplastic polyurethane, 1 part of glyceryl monostearate, and 0.3 parts of erucamide.

[0067] (3) Add each raw material to the high-speed mixer in a certain order. The order of addition is PBAT, modified starch, carbon dioxide-based thermoplastic polyurethane, glyceryl monostearate, and erucamide. Set the mixing speed to low and mix at low speed for about 3 minutes before discharging.

[0068] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0069] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0070] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0071] Comparative Example 1

[0072] The fully degraded film of this comparative example was prepared by the following method:

[0073] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, and titanate coupling agent in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0074] (2) Weigh 68.7 parts of PBAT, 30 parts of modified starch, 1 part of glyceryl monostearate, and 0.3 parts of erucamide;

[0075] (3) Add each raw material to the high-speed mixer in a certain order, namely PBAT, modified starch, glyceryl monostearate, and erucamide; turn the mixing speed to low speed and mix at low speed for about 3 minutes before discharging.

[0076] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0077] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0078] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0079] Comparative Example 2

[0080] The fully degraded film of this comparative example was prepared by the following method:

[0081] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, and titanate coupling agent in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0082] (2) Weigh out 69.7 parts of PBAT, 30 parts of modified starch, and 0.3 parts of erucamide;

[0083] (3) Add each raw material to the high-speed mixer in a certain order, namely PBAT, modified starch, and erucamide; turn the mixing speed to low speed and mix at low speed for about 3 minutes before discharging.

[0084] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0085] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0086] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0087] Comparative Example 3

[0088] The fully degraded film of this comparative example was prepared by the following method:

[0089] (1) Weigh 75 parts of starch, 1 part of maleic anhydride, 0.3 parts of titanate coupling agent, and 23.7 parts of glycerol; add starch, maleic anhydride, and titanate coupling agent in the following order; turn the mixing speed to high speed, stir at high speed to 90°C, continue stirring for about 3 minutes, and then discharge to obtain modified starch.

[0090] (2) Weigh out 70 parts of PBAT and 30 parts of modified starch;

[0091] (3) Add each raw material to the high-speed mixer in a certain order, namely PBAT and modified starch; turn the mixing speed to low speed and mix at low speed for about 3 minutes before discharging.

[0092] (4) Add the mixed raw materials into the hopper of the twin-screw extruder, set the processing temperature of each temperature zone of the extruder, and the operating temperature is 80, 120, 180, 180, 180, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, and obtain blown film modified resin by stretching, air cooling and pelletizing.

[0093] (5) The blown film modified resin is put into the blown film machine for blown film processing. The temperature of each temperature zone of the blown film machine is 145, 170, 175, 180 and 185℃. Finally, a fully degradable film can be obtained.

[0094] (6) The film thickness was controlled at 0.025 mm. The mechanical properties of the film were tested, and the test results are listed in Table 1.

[0095] Table 1 Mechanical and optical properties of the thin film

[0096]

[0097] As shown in Table 1, with the increase of CO2-based thermoplastic polyurethane content from 9.3% to 38.7%, the tensile strength, tear strength, and elongation at break all remained at relatively high values, indicating that the film exhibited good comprehensive mechanical properties. The maleic anhydride and coupling agent significantly improved the interfacial bonding between polybutylene terephthalate / starch / CO2-based thermoplastic polyurethane. Under the plasticizing effect of the plasticizer, the plasticizing effect on starch was effectively increased, resulting in a significant improvement in the mechanical properties of the material. With the synergistic effect of various additives, this ternary blend exhibited good compatibility.

[0098] As can be seen from Comparative Example 1, the lack of PPCU significantly reduces the tensile strength, elongation at break, tear strength, and heat-sealing strength of the film.

[0099] Comparative Examples 2 and 3 show that the absence of glyceryl monostearate and erucamide reduces the tensile strength, elongation at break, tear strength, and heat-sealing strength of the film. This indicates that glyceryl monostearate and erucamide can improve the compatibility of the components and significantly enhance the film's performance. This film has a simple processing technology, low cost, and is fully biodegradable, making it a viable alternative to non-degradable polyethylene films. It can be used in shopping bags, garbage bags, agricultural films, and other film and bag products, contributing to environmental protection and possessing significant application value.

[0100] This invention provides a fully biodegradable film and its preparation method, mainly composed of polybutylene terephthalate-adipate / starch / carbon dioxide-based thermoplastic polyurethane and its additives. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fully biodegradable film, characterized in that, The composition of its formula is as follows: 40-65 parts by weight of polybutylene terephthalate-adipate resin (PBAT), 15-30 parts by weight of modified starch (TPS), 9-40 parts by weight of carbon dioxide-based thermoplastic polyurethane (PPCU), 0.1-1 parts by weight of opening agent, and 0.1-2 parts by weight of lubricant. The modified starch is starch modified with a modifier and containing a plasticizer. The modifier is any one of citric acid or maleic anhydride, mixed with any one of titanate coupling agent, aluminate coupling agent, and silane coupling agent. The plasticizer is one or both of glycerol and sorbitol. The modified starch is obtained by simple blending of starch, plasticizer, and modifier. The opening agent is erucamide or oleamide; The lubricant is glyceryl monostearate; The modified starch is modified corn starch or cassava starch; the weight ratio of starch, plasticizer and modifier in the modified starch is 70-75:20-25:1~3; The weight ratio of any one of citric acid or maleic anhydride to any one of titanate coupling agent, aluminate coupling agent and silane coupling agent is 1:1 to 1:0.

2. The weight-average molecular weight of the carbon dioxide-based thermoplastic polyurethane is 6 × 10⁻⁶. 4 g / mol up to 5×10 5 g / mol.

2. The fully biodegradable film according to claim 1, characterized in that, The fully biodegradable film has the following composition: 45-60 parts by weight of polybutylene terephthalate-adipate resin, 17-22 parts by weight of modified starch, 20-30 parts by weight of carbon dioxide-based thermoplastic polyurethane, 0.2-0.5 parts by weight of opening agent, and 0.5-1.2 parts by weight of lubricant.

3. The method for preparing the fully biodegradable film according to any one of claims 1-2, comprising the following steps: 1) Starch, plasticizer, and modifier are mixed and modified to obtain modified starch; 2) Polybutylene terephthalate-adipate resin, modified starch, carbon dioxide-based thermoplastic polyurethane, opening agent and lubricant are mixed and extruded to obtain a resin for blown film. 3) The film is blown with the film blowing resin to obtain a fully biodegradable poly(butylene terephthalate) / starch / carbon dioxide-based thermoplastic polyurethane film.

4. The method for preparing a fully biodegradable thin film according to claim 3, characterized in that: In step 2), the extrusion temperature is 80~185℃ and the screw speed is 200~350 rpm.

5. The method for preparing a fully biodegradable thin film according to claim 3, characterized in that: In step 3), the blown film processing temperature is 150~185℃.

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