Degradable high-transparency polyester resin and preparation method thereof

Abstract

The invention relates to the technical field of degradable polyester, in particular to degradable high-transparency polyester resin and a preparation method thereof. The problem that the light transmittance and the mechanical property of the degradable high-transmittance polyester resin are difficult to achieve at the same time is solved. A high-transmittance polyester matrix is prepared, and a random structure is constructed to refine a crystal region, so that the problem of opaque due to crystallization is solved; meanwhile, in-situ polymerization is utilized to prepare modified nano cellulose with matched refractive index, and a hyperbranched polymer is introduced in blending; in the twin-screw extrusion process, a chain extender two-stage gradient feeding process is adopted, and supercritical carbon dioxide is assisted to reduce the processing temperature and promote dispersion; according to the preparation method disclosed by the invention, thermosensitive yellowing and generation of gel points are avoided, and the biodegradable polyester material with high light transmittance and excellent mechanical strength is prepared through dual effects of a hydrogen bond physical network and chemical crosslinking.

Description

Technical Field

[0001] This invention relates to the field of biodegradable polyester technology, specifically to a biodegradable high-permeability polyester resin and its preparation method. Background Technology

[0002] With increasing global attention focused on the problem of white pollution, the research and application of biodegradable polymer materials has become a hot topic in materials science. Among numerous biodegradable materials, polybutylene succinate and polybutylene adipate / terephthalate are highly favored due to their excellent processing and mechanical properties. However, these semi-crystalline polyesters face a significant challenge in practical applications: achieving both high light transmittance and excellent mechanical properties is difficult.

[0003] Polybutylene succinate (PBS) and polybutylene adipate / terephthalate (PBT) exhibit extremely high crystallinity and crystallinity. While high crystallinity imparts high strength and modulus to the materials, the resulting spherulites are often larger than the wavelength of visible light, causing light scattering and giving the materials an opaque, milky-white, or waxy appearance. This significantly limits their application in high-end transparent packaging, agricultural greenhouse films, and transparent sheets.

[0004] To improve transparency, existing technologies typically employ two approaches: one is to introduce a random structure through copolymerization to disrupt crystallization, but this often leads to a significant decrease in the material's melting point, weakened strength, and excessive softness or even stickiness; the other is to add nucleating agents to refine spherulites, but conventional nucleating agents (such as talc) are themselves opaque fillers, and adding too much can introduce new haze. Furthermore, inorganic nanofillers added to improve mechanical properties often agglomerate due to surface energy differences, compromising transparency and creating stress concentration points. Therefore, developing a biodegradable polyester resin that can precisely control crystallization behavior while maintaining or even improving mechanical strength and achieving high light transmittance is a pressing technical problem that needs to be solved.

[0005] To address this, a biodegradable high-permeability polyester resin and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a biodegradable, high-permeability polyester resin and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all parts in this invention are parts by weight.

[0008] This invention provides a method for preparing a biodegradable, highly permeable polyester resin. The method is as follows: 100 parts of a highly permeable polyester matrix, 0.2 parts of an anti-hydrolysis agent bis(2,6-diisopropylphenyl)carbodiimide, and 1-5 parts of a hyperbranched polymer are mixed uniformly in a high-speed mixer to obtain a highly permeable polyester composition; the highly permeable polyester composition is added to the main feed port (first zone) of a twin-screw extruder with an aspect ratio (L / D) of 48:1, and 1-3.5 parts of modified nanocellulose and a styrene-glycidyl acrylate copolymer chain extender (Joncryl) are added through the side feed port (fourth zone). ADR-4368), supercritical carbon dioxide is injected in zone 6, and styrene-glycidyl acrylate copolymer chain extender (JoncrylADR-4368) is added to side feed port 2 (zone 9). Vacuum devolatilization is performed in zone 11. The extruded strip is cooled in a 45°C water bath, pelletized, and vacuum dried at 60°C for 8 hours to obtain polyester resin. The screw speed is 220 rpm. The temperature settings are as follows: zone 1 160°C, zones 2-5 180°C, zones 6-8 170°C, zones 9-11 180°C, and die head 175°C.

[0009] The preferred method for preparing the high-permeability polyester matrix is ​​as follows: 118 parts of succinic acid, 90 parts of 1,4-butanediol, 14.4 parts of 1,4-cyclohexanediethanol, 14.6 parts of isosorbide, and 0.1 parts of tetrabutyl titanate are added to a reactor equipped with a distillation column. The temperature is raised to 190°C, the stirring speed is 150 rpm, and the reaction is carried out for 3.5 h. The temperature is then raised to 225-245°C, a vacuum is drawn, and the pressure drops below 50 Pa within 40 min. The stirring speed is adjusted to 80 rpm, and the reaction is continued for 3 h. Nitrogen gas is then introduced for discharge, and the material is water-cooled and pelletized to obtain the high-permeability polyester matrix.

[0010] The preferred method for preparing the hyperbranched polymer is as follows: 19.2 parts of anhydrous citric acid, 17 parts of isophorone diamine and 9 parts of 1,4-butanediol are added to a reaction vessel equipped with mechanical stirring and nitrogen protection. The temperature is raised to 140°C, the stirring speed is 200 rpm, and the reaction is carried out under nitrogen protection for 1.5 h. The temperature is then raised to 160°C, the vacuum is drawn to 500 Pa, and the reaction is continued for 2 h. The acid value is monitored. When the acid value drops to 70-110 mg KOH / g, the heating is stopped immediately, the mixture is poured out while hot, cooled and pulverized to obtain the hyperbranched polymer.

[0011] The preferred method for preparing modified nanocellulose is as follows: 10 parts of cellulose nanocrystals (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., C909405) are dispersed in 200 parts of N,N-dimethylformamide and ultrasonically treated at 400W and 20kHz for 30min to obtain a suspension; 50 parts of L-lactide and 0.05 parts of stannous octoate are added, nitrogen gas is introduced to replace the precipitate three times, the temperature is raised to 110℃, and the reaction is carried out at 300rpm for 10-15h; after the reaction is completed, the product is washed three times by centrifugation with anhydrous ethanol (8000rpm, 10min / time), dried in a vacuum oven at 50℃ for 24h, and ground through a 200-mesh sieve to obtain modified nanocellulose.

[0012] Preferably, the supercritical carbon dioxide injection amount is 1.2wt%-2.0wt% of the high-permeability polyester matrix, and the injection pressure is set to 10MPa.

[0013] Preferably, the total amount of chain extender is 0.6 parts; the amount added in the first stage accounts for 15%-30% of the total amount, and the amount added in the second stage accounts for 70%-85% of the total amount.

[0014] Another aspect of the present invention provides a biodegradable high-permeability polyester resin, which is prepared by any of the above preparation methods; the raw materials for preparing the biodegradable high-permeability polyester resin include a high-permeability polyester matrix, an anti-hydrolysis agent, a hyperbranched polymer, and modified nanocellulose.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention constructs a random copolymer structure by introducing bio-based isosorbide and 1,4-cyclohexanediethanol into the polyester backbone. The unique rigid bicyclic structure of bio-based isosorbide possesses a strong steric hindrance effect, effectively disrupting the regularity of the polyester molecular chain and preventing chain segments from folding into the crystal lattice. This modification fundamentally reduces the crystallization rate of the polyester and strictly limits the size of the generated spherulites to below the visible light wavelength, thereby eliminating light scattering caused by the crystalline region and endowing the material with extremely high light transmittance. Simultaneously, traditional decrystallization methods often lead to material softening, while the rigid framework inherent in bio-based isosorbide and 1,4-cyclohexanediethanol perfectly compensates for the modulus loss due to decreased crystallinity, allowing the resin to maintain a fully transparent appearance while still possessing excellent structural rigidity.

[0016] 2. This invention employs in-situ ring-opening polymerization to graft and modify cellulose nanocrystals, successfully coating their surface with low-molecular-weight polylactic acid segments. This material modification technology has dual beneficial effects: Firstly, through molecular structure design, the refractive index of the grafted nanocellulose surface is highly matched with the refractive index of the amorphous region of the polyester matrix, eliminating the common light reflection and scattering problems at the interface between inorganic nanofillers and the polymer matrix, achieving the "invisibility" of the nano-reinforcing phase, and ensuring the high light transmittance of the material; secondly, the grafted layer endows the nanocellulose with excellent hydrophobicity and compatibility, completely solving the problem of its agglomeration in the matrix, allowing its high axial strength skeletal function to be fully utilized, and significantly improving the tensile strength of the material.

[0017] 3. This invention creatively introduces a hyperbranched polymer synthesized from citric acid and isophorone diamine. Due to the highly branched, spherical amorphous structure of the hyperbranched polymer, its addition does not induce crystallization or light scattering, maintaining the resin's high transparency. More importantly, the hyperbranched polymer molecule contains a large number of amide bonds, which can form a high-density hydrogen-bonded physical cross-linking network in the polyester matrix, providing an excellent "sacrificial bond" toughening mechanism. Simultaneously, its abundant terminal functional groups, through subsequent chain extension reactions, form a stable chemical cross-linking network with the matrix and modified nanocellulose. This dual-network structure provides the matrix with a large free volume and energy absorption pathway, toughening without reducing strength.

[0018] 4. This invention employs a synergistic process in which multifunctional chain extenders are added in two stages with a gradient. A small amount of chain extender is added at the front end of extrusion, primarily to preferentially react with the terminal carboxyl groups generated from polyester degradation and the end groups of hyperbranched polymers when the melt viscosity is low. This serves to repair molecular weight and seal the ends, and to initially enhance the affinity between the phases. At the rear end of extrusion, after the nanomaterials and hyperbranched components have been uniformly dispersed, a sufficient amount of chain extender is added to construct a macroscopic three-dimensional chemical cross-linking network. This time-difference feeding design effectively avoids the phenomenon of excessively rapid local cross-linking caused by adding a large amount of chain extender in the early stage, fundamentally eliminating the formation of "fisheyes" and gel points in the resin, ensuring the uniformity of melt strength and the excellent optical quality of the finished product.

[0019] 5. This invention introduces a supercritical carbon dioxide fluid-assisted processing technology into the twin-screw extrusion process. Supercritical carbon dioxide acts as an excellent temporary plasticizer in the polymer melt, significantly reducing the melt viscosity of the system and allowing the extruder to operate at lower temperatures. This is crucial for systems containing heat-sensitive substances such as isosorbide and hyperbranched polyamides, effectively preventing thermal degradation and yellowing caused by high-temperature shearing and ensuring the resin's clear and transparent hue. Furthermore, the supercritical carbon dioxide fluid has extremely high permeability, penetrating deep into the interior of nanocellulose aggregates. When the melt advances to the mid-stage atmospheric pressure relief zone, the pressure is released instantaneously. The huge pressure difference causes the supercritical carbon dioxide permeating the aggregates to generate a violent volume expansion force. Combined with screw shearing, this achieves complete individual peeling and uniform dispersion of the nanomaterials before the extended chain network is fully locked. Attached Figure Description

[0020] Figure 1 The figures show the tensile strength test results of Examples 1-4 and Comparative Examples 2-8 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1 This invention provides a biodegradable, high-permeability polyester resin and its preparation method, the technical solution of which is as follows: 118 parts of succinic acid, 90 parts of 1,4-butanediol, 14.4 parts of 1,4-cyclohexanediethanol, 14.6 parts of isosorbide, 0.1 parts of tetrabutyl titanate, and 0.15 parts of antioxidant (antioxidant 1010 and antioxidant 168 were compounded in a 1:1 mass ratio) were added to a reactor equipped with a distillation column. The temperature was raised to 190°C, the stirring speed was 150 rpm, and the reaction was carried out for 3.5 h. The temperature was raised to 225°C, a vacuum was drawn, and the pressure dropped to below 50 Pa within 40 min. The stirring speed was adjusted to 80 rpm, and the reaction was continued for 3 h. Nitrogen gas was purged and the product was discharged. The product was then water-cooled and pelletized to obtain a high-permeability polyester matrix.

[0023] 19.2 parts of anhydrous citric acid, 17 parts of isophorone diamine, and 9 parts of 1,4-butanediol were added to a reactor equipped with mechanical stirring and nitrogen protection. The temperature was raised to 140°C, the stirring speed was 200 rpm, and the reaction was carried out under nitrogen protection for 1.5 h. The temperature was then raised to 160°C, the vacuum was drawn to 500 Pa, and the reaction was continued for 2 h. The acid value was monitored. When the acid value dropped to 70 mg KOH / g, the heating was stopped immediately, the mixture was poured out while hot, cooled and pulverized to obtain the hyperbranched polymer.

[0024] Ten parts of cellulose nanocrystals were dispersed in 200 parts of N,N-dimethylformamide and sonicated at 400W and 20kHz for 30 min to obtain a suspension. 50 parts of L-lactide and 0.05 parts of stannous octoate were added, and nitrogen gas was introduced to replace the precipitate three times. The temperature was raised to 110℃ and reacted at 300rpm for 10 h. After the reaction was completed, the product was washed three times by centrifugation with anhydrous ethanol (8000rpm, 10 min / time), dried in a vacuum oven at 50℃ for 24 h, and ground through a 200-mesh sieve to obtain modified nanocellulose.

[0025] 100 parts of high-permeability polyester matrix, 0.2 parts of anti-hydrolysis agent bis(2,6-diisopropylphenyl)carbodiimide, and 1 part of hyperbranched polymer were mixed evenly in a high-speed mixer to obtain a high-permeability polyester composition. The high-permeability polyester composition was added to the main feed port (zone 1) of a twin-screw extruder with an aspect ratio (L / D) of 48:1 at a main feed rate of 10 kg / h. One part of modified nanocellulose and chain extender Joncryl ADR-4368 were added through side feed port 1 (zone 4). Supercritical carbon dioxide was injected into zone 6 at a rate of 1.2 wt% of the high-permeability polyester matrix and an injection pressure of 10 MPa. A normal pressure vent was installed in zone 8 for pressure relief. The chain extender Joncryl was added through side feed port 2 (zone 9). ADR-4368 was vacuum devolatilized in zone 11, with the vacuum level maintained between -0.08 MPa and -0.1 MPa. The extruded strip was cooled in a 45°C water bath, pelletized, and then vacuum dried at 60°C for 8 hours to obtain polyester resin. The screw speed was 220 rpm. The temperature settings were as follows: zone 1 160°C, zones 2-5 180°C, zones 6-8 170°C, zones 9-11 180°C, and die head 175°C. The total amount of chain extender was 0.6 parts. The first stage addition accounted for 15% of the total amount, and the second stage addition accounted for 85% of the total amount.

[0026] Example 2 The preparation method and parameters were the same as in Example 1, except that the second heating temperature was 230°C when preparing the high-permeability polyester matrix; the heating was stopped when the acid value dropped to 85 mg KOH / g when preparing the hyperbranched polymer; the reaction was carried out at 300 rpm for 12 h when preparing the modified nanocellulose; the amount of hyperbranched polymer was 2 parts, the amount of modified nanocellulose was 2 parts, the amount of supercritical carbon dioxide injected was 1.4 wt% of the high-permeability polyester matrix, and the amount of chain extender added in the first stage accounted for 20% of the total amount and the amount added in the second stage accounted for 80% of the total amount.

[0027] Example 3 The preparation method and parameters were the same as in Example 1, except that the second heating temperature was 235°C when preparing the high-permeability polyester matrix; the heating was stopped when the acid value dropped to 95 mg KOH / g when preparing the hyperbranched polymer; the reaction was carried out at 300 rpm for 13 h when preparing the modified nanocellulose; the amount of hyperbranched polymer was 3 parts, the amount of modified nanocellulose was 2.5 parts, the amount of supercritical carbon dioxide injected was 1.6 wt% of the high-permeability polyester matrix, and the amount of chain extender added in the first stage accounted for 25% of the total amount and the amount added in the second stage accounted for 75% of the total amount.

[0028] Example 4 The preparation method and parameters were the same as in Example 1, except that the second heating temperature was 245°C when preparing the high-permeability polyester matrix; the heating was stopped when the acid value dropped to 110 mg KOH / g when preparing the hyperbranched polymer; the reaction was carried out at 300 rpm for 15 h when preparing the modified nanocellulose; the amount of hyperbranched polymer was 5 parts, the amount of modified nanocellulose was 3.5 parts, the amount of supercritical carbon dioxide injected was 2.0 wt% of the high-permeability polyester matrix, and the amount of chain extender added in the first stage accounted for 30% of the total amount and the amount added in the second stage accounted for 70% of the total amount.

[0029] Comparative Example 1 The preparation method and parameters of Example 1 are the same, except that 1,4-cyclohexanediethanol and isosorbide are not added when preparing the high-transparency polyester matrix.

[0030] Comparative Example 2 The preparation method and parameters were the same as in Example 1, except that the cellulose nanocrystals were not modified.

[0031] Comparative Example 3 The preparation method and parameters of Example 1 were used, except that no modified nanocellulose was added.

[0032] Comparative Example 4 The preparation method and parameters were the same as in Example 1, except that no hyperbranched polymer was added.

[0033] Comparative Example 5 The preparation method and parameters of Example 1 were used as reference, except that the feeding method of the chain extender was changed. All of the total amount of 0.6 parts of Joncryl ADR-4368 was added at once in the fourth zone (side feed port 1), and no addition was made in the ninth zone.

[0034] Comparative Example 6 The preparation method and parameters of Example 1 are the same, except that the supercritical carbon dioxide injection in the sixth zone is turned off, and the overall temperature from the sixth zone to the head is increased by 15°C.

[0035] Comparative Example 7 Referring to the preparation method and parameters of Example 1, the difference is that the preparation method of modified nanocellulose is changed to: cellulose nanocrystals and low molecular weight polylactic acid (weight average molecular weight of 4000, L-lactic acid monomer content ≥99%) are directly physically blended in N,N-dimethylformamide and then dried for use, instead of in-situ polymerization.

[0036] Comparative Example 8 The preparation method and parameters are the same as in Example 1, except that no chain extender is added.

[0037] Experimental Example 1: Mechanical Property Testing Tensile strength and elongation at break were determined according to the national standard GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics". Extruded and dried resin pellets were prepared into standard type 1A dumbbell-shaped specimens using an injection molding machine and tested on a universal testing machine. The tensile speed was set to 50 mm / min, the test temperature to 23±2℃, and the relative humidity to 50±5%. The results are shown in Table 1 and... Figure 1 As shown.

[0038] Table 1 Mechanical property tests of Examples 1-4 and Comparative Examples 2-8 Experiment Example 2: Transmittance Test Referring to the national standard GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics", the resin was pressed into a flat sheet with a thickness of 1.0 mm by a hot press at 180℃. The transmittance and haze were tested using an integrating sphere transmittance and haze meter, and the visible light transmittance (%) and haze (%) were recorded. The results are shown in Table 2.

[0039] Table 2. Transmittance tests of Examples 1-4 and Comparative Examples 1-2 and 5-7 Experiment Example 3: Degradation Performance Test Referring to the national standard GB / T 19277.1-2011 "Determination of final aerobic biodegradability of materials under controlled composting conditions", the samples were crushed to less than 2 mm, mixed with standard compost inoculum, and tested for 90 days in a high-temperature aerobic composting environment of 58±2℃. The biodegradation rate was calculated by measuring the amount of carbon dioxide released. The results are shown in Table 3.

[0040] Table 3 Degradation performance tests of Examples 1-4 As can be seen from Tables 1-3, in Examples 1-4, firstly, alicyclic rigid monomers were introduced into the molecular backbone to block crystallization and ensure extremely high light transmittance; secondly, in-situ ring-opening polymerization was used to achieve refractive index matching between the modified nanocellulose and the amorphous matrix; in addition, hyperbranched polymers were introduced into the system, and combined with a two-stage gradient chain extension process and supercritical fluid assistance, a uniform and gel-free "physical hydrogen bond-chemical crosslinking" dual network was constructed at low temperature. All features support each other and are indispensable, ultimately achieving a unity of high strength, high toughness, high transmittance and biodegradability of the material. The biodegradability of the materials prepared in the examples of this invention is all above 90%.

[0041] In Comparative Example 1, when preparing the high-transmittance polyester matrix, 1,4-cyclohexanediethanol and isosorbide were not added. Removing isosorbide and 1,4-cyclohexanediethanol, which hinder the regular folding of chain segments, resulted in a rapidly increasing crystallization rate in the matrix, forming large spherulites larger than the wavelength of visible light. This led to severe light scattering, a sharp drop in transmittance, and a surge in haze. In Comparative Example 2, the unmodified cellulose nanocrystals contained a large number of polar hydroxyl groups on their surface, causing severe aggregation in the weakly polar polyester. These aggregates not only became light scattering centers but also led to stress concentration, resulting in lower tensile strength and elongation at break compared to the examples. In Comparative Example 3, no modified nanocellulose was added, and the high-strength rigid framework of nanocellulose was lost, leading to a significant decrease in the tensile strength of the material. In Comparative Example 4, no hyperbranched polymer was added, resulting in a lack of the free volume and high-density hydrogen-bonded "sacrificial bond" network provided by the hyperbranched polymer. The material could not effectively absorb deformation energy, becoming relatively brittle, and the elongation at break dropped significantly. In Comparative Example 5, changing the feeding method of the chain extender and adding all the chain extender at once led to excessively rapid local cross-linking, forming a large number of visible gel points. These gel points not only impaired light transmission but also became weak points during the material's tensile process, resulting in a sharp drop in elongation at break. In Comparative Example 6, shutting off the supercritical fluid and increasing the temperature during processing caused the heat-sensitive isosorbide to yellow, reducing light transmittance. Simultaneously, the loss of the expansion and exfoliation assistance from supercritical carbon dioxide resulted in poorer dispersion of the components, and the tensile strength and toughness were inferior to those of the examples. In Comparative Example 7, changing the preparation method of the modified nanocellulose resulted in physical blending failing to achieve a strong bond between polylactic acid segments and the surface of cellulose nanocrystals. Under the high shear of a twin-screw extruder, these segments easily detached, leading to an imperfect refractive index match at the interface and weak interfacial bonding between the two phases. This prevented the effective transfer of matrix stress to the cellulose nanocrystals, resulting in mechanical properties inferior to those of the examples. In Comparative Example 8, no chain extender was added. Without the coupling effect of the chain extender, the matrix, nanocellulose and hyperbranched polymer were only bound by weak van der Waals forces or a small number of hydrogen bonds, which could not form a macroscopic three-dimensional chemical cross-linking network, resulting in a decrease in tensile strength and elongation at break.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a biodegradable, highly permeable polyester resin, characterized in that: The preparation method is as follows: a high-permeability polyester matrix, an anti-hydrolysis agent, and a hyperbranched polymer are mixed evenly in a mixer to obtain a high-permeability polyester composition; the high-permeability polyester composition is added to the main feed port of a twin-screw extruder, modified nanocellulose is added through a side feed port, supercritical carbon dioxide is injected in the sixth zone, vacuum devolatilization is performed in the eleventh zone, and after water cooling and pelletizing, vacuum drying is performed to obtain the polyester resin. The modified nanocellulose is obtained by coating polylactic acid segments onto the surface of cellulose nanocrystals, and the refractive index of the modified cellulose nanocrystals matches that of the high-transparency polyester matrix.

2. The method for preparing a biodegradable high-permeability polyester resin according to claim 1, characterized in that: The high-permeability polyester matrix is ​​prepared as follows: succinic acid, 1,4-butanediol, 1,4-cyclohexanediethanol, isosorbide, and tetrabutyl titanate are added to a reaction vessel, heated, and stirred to react; the temperature is increased, a vacuum is drawn, the stirring speed is reduced, and the reaction continues; nitrogen gas is purged and the material is discharged; water is used to cool and pelletize the material to obtain the high-permeability polyester matrix.

3. The method for preparing a biodegradable high-permeability polyester resin according to claim 1, characterized in that: The hyperbranched polymer is prepared as follows: anhydrous citric acid, isophorone diamine and 1,4-butanediol are added to a reaction vessel, heated, and reacted under nitrogen protection. The temperature is increased, and the reaction is continued under vacuum. The acid value is monitored. When the acid value drops to 70-110 mg KOH / g, heating is stopped immediately. The mixture is poured out, cooled and pulverized to obtain the hyperbranched polymer.

4. The method for preparing a biodegradable high-permeability polyester resin according to claim 1, characterized in that: The modified nanocellulose is prepared as follows: the cellulose nanocrystals are dispersed in N,N-dimethylformamide and ultrasonically treated to obtain a suspension; L-lactide and stannous octoate are added, nitrogen gas is introduced for replacement, and the temperature is raised for reaction; after the reaction is completed, the nanocellulose is washed, dried and ground to obtain the modified nanocellulose.

5. The method for preparing a biodegradable high-permeability polyester resin according to claim 1, characterized in that: The amount of supercritical carbon dioxide injected is 1.2wt%-2.0wt% of the high-permeability polyester matrix.

6. The method for preparing a biodegradable high-permeability polyester resin according to claim 1, characterized in that: The polyester resin preparation process also requires the addition of a chain extender; the chain extender is added in two stages. In the first stage, it is added through side feed port one, with an addition amount accounting for 15%-30% of the total amount. In the second stage, it is added through side feed port two, with an addition amount accounting for 70%-85% of the total amount.

7. A biodegradable, high-permeability polyester resin, characterized in that: The biodegradable high-permeability polyester resin is prepared by the preparation method according to any one of claims 1-6; the raw materials for preparing the biodegradable high-permeability polyester resin include a high-permeability polyester matrix, an anti-hydrolysis agent, a hyperbranched polymer, and modified nanocellulose.

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