Preparation method of a biodegradable block-branched copolyester

Abstract

The present invention relates to the field of biodegradable materials, and discloses a preparation method of a biodegradable block-branched copolyester. The steps are as follows: (1) melt-blend a first resin, a second resin and a first chain extender to obtain a block copolyester; (2) melt-blend the block copolyester obtained in step (1) with a second chain extender to obtain a biodegradable block-branched copolyester; the second chain extender is an inorganic nanoparticle-based chain extender prepared by reacting an inorganic nanoparticle with a modifier. In the present invention, the first resin and the second resin are first formed into a block copolyester under the action of the first chain extender, and then the block copolyester is formed into a block-branched copolyester under the action of the second chain extender. The formed branched structure endows the polyester with better processing, mechanical and degradation properties; and the second chain extender uses an inorganic nanoparticle-based chain extender, which solves the problems of the dispersibility and compatibility of inorganic nanoparticles and further improves the degradation and mechanical properties of the polyester.

Description

Technical Field

[0001] The present invention relates to the field of biodegradable materials, and particularly to a method for preparing a biodegradable block-branched copolyester. Background Art

[0002] With the increasing aggravation of "white pollution", the preparation and application of biodegradable materials have received more and more attention. Polyethylene terephthalate (PET) is the polyester with the largest global usage at present. It is non-toxic, transparent and has stable thermal, mechanical and long-term usability, so it is widely used in the fields of textiles, food, packaging, medicine, information, electronics, etc. However, PET is non-degradable. In order to relieve the environmental pressure brought by the large amount of PET used, the development and preparation of degradable polyesters can effectively promote the sustainable development and progress of the polyester industry, and at the same time is of great significance for ecological environment protection and solving "white pollution".

[0003] Currently, the widely used biodegradable polymers mainly include poly(butylene adipate-co-terephthalate) (PBAT), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoates (PHAs), poly(butylene succinate) (PBS), polyglycolic acid (PGA), poly(propylene carbonate) (PPC), etc. However, because their prices are 2-3 times that of ordinary industrial plastics and their mechanical properties are poorer than those of traditional plastics such as PET and PP, they cannot be widely promoted and applied in the market. In addition, for aromatic polyesters, although the introduction of aliphatic polyesters can improve their degradability (such as the Chinese patent document with the publication number CN101016373), there is a balance among the degradability, mechanical strength and processing performance of the copolyester. For example, in the aliphatic-aromatic copolyester, when the aromatic component content is higher than 60%, the copolyester is non-biodegradable; while reducing the aromatic content and increasing the aliphatic content, the biodegradability is improved, but the heat resistance (glass transition temperature, melting point), processability, etc. of the copolyester all decrease. Therefore, the key to developing biodegradable polyesters is to balance the usability, processing performance and degradation performance.

[0004] The properties of polyesters can be adjusted by designing their chain structures. At present, various biodegradable polyesters have been developed by adjusting the polyester monomer composition, such as poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate-co-adipate) (PBSA), poly(butylene succinate-co-terephthalate) (PBST), etc. However, most of these polyesters are random copolymers with a linear structure. The introduction of random aliphatic chain segments can improve the degradability of the copolyester, but will reduce the mechanical properties of the material.

[0005] Introducing inorganic nanoparticles into polyester, using them as grafting points, can achieve chain extension of polyester, while also forming a branched structure, improving the processing, degradation, and mechanical properties of polyester. In addition, inorganic nanoparticles can serve as nucleation points to increase the crystallinity of polyester, further enhancing the mechanical properties of polyester, and also overcoming the problems of poor interfacial compatibility and difficult uniform dispersion between inorganic nanoparticles and polyester due to their large specific surface area. Summary of the Invention

[0006] The present invention aims to overcome the problem that it is difficult to balance the degradation performance and the use and processing performance of biodegradable polyesters in the prior art, and provides a preparation method of a biodegradable block-branched copolyester. First, a block copolymer is formed by reacting a first resin and a second resin under the action of a first chain extender, and then the block copolymer is further reacted under the action of a second chain extender to form a block-branched copolyester. The formed branched structure endows the polyester with better processing, mechanical, and degradation properties; and the second chain extender uses an inorganic nanoparticle-based chain extender, which solves the problems of the dispersibility and compatibility of inorganic nanoparticles, and further improves the degradation and mechanical properties of the polyester.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method of a biodegradable block-branched copolyester, comprising the following steps:

[0009] (1) First, melt-blend a first resin, a second resin, and a first chain extender to obtain a block copolymer; the first resin is selected from one or more of polylactic acid (PLA), polyglycolic acid (PGA), poly(propylene carbonate) (PPC), polycaprolactone (PCL), poly(vinyl acetate) (PVAc), polyethylene glycol (PEG), and poly(vinyl alcohol) (PVOH); the second resin is selected from one or more of poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS), poly(butylene succinate-co-terephthalate) (PBST), polyhydroxyalkanoates (PHA), poly(ethylene succinate-co-terephthalate) (PEST), and poly(ethylene adipate-co-terephthalate) (PEAT);

[0010] (2) Melt-blend the block copolymer obtained in step (1) with a second chain extender to obtain the biodegradable block-branched copolyester; the second chain extender is an inorganic nanoparticle-based chain extender prepared by reacting inorganic nanoparticles with a modifier.

[0011] In the present invention, the first resin and the second resin are first melt-blended under the action of a first chain extender to form a block copolyester. Compared with the random copolyester with a single topological structure, the block copolyester simultaneously has the characteristics of different chain segment polyesters. The second resin segment in the present invention is mainly a biodegradable polyester containing aromatic groups, and the first resin segment is mainly an aliphatic polyester and a carbon dioxide polyester, which increases the biodegradability and mechanical strength of the resin. Then, the block copolyester is secondarily chain-extended under the action of a second chain extender to further form a block-branched copolyester, and the formed branched structure endows the polyester with better processing, mechanical and degradation properties.

[0012] In the present invention, an inorganic nanoparticle-based chain extender is used as the second chain extender. After the inorganic particles are modified with a modifier and used as the second chain extender, the inorganic nanoparticles are directly introduced into the molecular structure of the block-branched copolyester. The inorganic nanoparticles can serve as a breakthrough point for biodegradation and accelerate the degradation efficiency of the polyester. At the same time, the inorganic nanoparticles can serve as nucleation points to improve the crystallinity of the polyester. After being modified, the inorganic nanoparticles are used as chain extenders and directly connected to the molecular structure of the polyester, solving the problems of the dispersibility of the inorganic nanoparticles and their compatibility with the polyester, and further improving the degradation performance and mechanical properties of the polyester.

[0013] Preferably, an antioxidant is also added in steps (1) and (2). The antioxidant added in step (1) accounts for 0.05-5.0% of the total mass of the first resin and the second resin. The antioxidant added in step (2) accounts for 0.05-5.0% of the mass of the block copolyester. The antioxidant is selected from one or more of BTH, DSTP, DLTP, 168, 264, 300, 425, 626, 627, 1010, 1076.

[0014] Preferably, the weight-average molecular weight of the first resin described is 5-500 kg / mol, and the weight-average molecular weight of the second resin is 10-500 kg / mol. The molar ratio of the first resin to the second resin is 90:10-10:90.

[0015] Preferably, the first chain extender is selected from one or more of bisphenol A diglycidyl ether, Joncryl ADR, glycidyl methacrylate (GMA), 2,4-toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), succinic anhydride, maleic anhydride, pyromellitic dianhydride (PMDA), 2,2'-bis(2-oxazoline), 1,4-phenyl-bis(2-oxazoline).

[0016] Preferably, the addition amount of the first chain extender in step (1) is 0.1-5.0% of the total mass of the first resin and the second resin.

[0017] Preferably, the melt blending time in step (1) is 3 to 15 min.

[0018] Preferably, when preparing the inorganic nanoparticle-based chain extender, the inorganic nanoparticles are selected from one or more of SiO2, TiO2, CaCO3, Al2O3, montmorillonite, talc powder, mica, soapstone, ZnO, etc., and the particle size of the inorganic nanoparticles is 5 to 1000 nm; the modifier is selected from one or more of bisphenol A diglycidyl ether, Joncryl ADR, GMA, 1,6-hexamethylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, pyromellitic dianhydride, succinic anhydride, maleic anhydride, etc. The modifier used in the present invention contains functional groups that can react with the hydroxyl groups on the surface of inorganic nanoparticles, and the modifier can be grafted onto the surface of inorganic nanoparticles through chemical reactions, so that the inorganic nanoparticles can participate in the chain extension reaction of block copolyester as a chain extender, thereby connecting the inorganic nanoparticles to the molecular structure of the product through chemical bonds, and solving the problems of its dispersibility and compatibility.

[0019] Preferably, when preparing the second chain extender, the mass ratio of the modifier to the inorganic nanoparticles is 1:1 to 10:1, the reaction temperature is 20 to 180 °C, the reaction time is 3 to 30 min, and the reaction is carried out under nitrogen protection.

[0020] Preferably, the addition amount of the second chain extender in step (2) is 0.1 to 5.0% of the total mass of the first resin and the second resin.

[0021] Preferably, the melt blending time in step (2) is 3 to 10 min.

[0022] Therefore, the present invention has the following beneficial effects:

[0023] (1) After modifying the inorganic particles with a modifier and using them as the second chain extender, the inorganic nanoparticles are directly introduced into the molecular structure of the block branched copolyester, solving the problems of poor compatibility and easy agglomeration between the inorganic nanoparticles and the polyester, improving the uniform dispersibility of the inorganic nanoparticles as a reinforcing body in the polyester, and at the same time increasing the biodegradable sites of the copolyester and enhancing the degradability;

[0024] (2) Through chain segment design, using the modified inorganic particles as the grafting points of multi-functional groups, a polyester containing both block and branched structures is prepared, simultaneously improving the mechanical properties and degradability of the copolyester;

[0025] (3) Through chain segment design, the synthesized polyester contains a branched structure, enhancing the melt strength and processing performance of the polyester. Description of the Drawings

[0026] Figure 1It is the curve of the mass of the copolyesters in Examples 1-2 and Comparative Examples 1-3 changing with time in a sodium hydroxide solution. Detailed implementation manners

[0027] The present invention will be further described below in conjunction with the accompanying drawings and detailed implementation manners.

[0028] In the present invention, unless otherwise specified, the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art unless otherwise specified.

[0029] Example 1:

[0030] A preparation method of a biodegradable block-branched copolyester, comprising the following steps:

[0031] (1) Mix the first resin, the second resin, the first chain extender and antioxidant 1010, and then add them to a twin-screw extruder for melt blending; wherein the first resin and the second resin are PLA and PEST respectively, the weight-average molecular weights of PLA and PEST are 41 kg / mol and 50 kg / mol respectively, and the molar ratio of the first resin to the second resin is 20:80; the first chain extender is IPDI, and the addition amounts of the first chain extender and antioxidant 1010 are 1.0% and 0.5% of the total mass of the first resin and the second resin respectively; the melt blending temperature in the twin-screw extruder is 230 °C, and the mixing time is 5 min; to obtain a PEST-b-PLA block copolyester;

[0032] (2) Mix the block copolyester obtained in step (1) with the second chain extender and antioxidant 1010, and add them to a twin-screw extruder for melt blending; wherein the second chain extender is an inorganic nanoparticle-based chain extender, and its preparation method is: mix IPDI and nano-SiO2 (average particle size 30 ± 5 nm) at a mass ratio of 2:1, and react at 30 °C for 10 min under nitrogen protection to obtain an inorganic nanoparticle-based chain extender; the addition amounts of the second chain extender and antioxidant 1010 are 0.5% and 0.5% of the mass of the block copolyester respectively; the melt blending temperature in the twin-screw extruder is 200 °C, and the mixing time is 5 min; to prepare a biodegradable PEST-b-PLA block-branched copolyester, and the polyester melt obtained has high strength and stable processing.

[0033] Example 2:

[0034] A preparation method of a biodegradable block-branched copolyester, comprising the following steps:

[0035] (1) Mix the first resin, the second resin, the first chain extender, and antioxidant 1010, and then add them to a twin-screw extruder for melt blending; wherein the first resin and the second resin are PLA and PEST respectively, the weight-average molecular weights of PLA and PEST are 41 kg / mol and 50 kg / mol respectively, and the molar ratio of the first resin to the second resin is 20:80; the first chain extender is IPDI, and the addition amounts of the first chain extender and antioxidant 1010 are 1.0% and 0.5% of the total mass of the first resin and the second resin respectively; the melt blending temperature in the twin-screw extruder is 230 °C, and the mixing time is 5 min; obtain the PEST-b-PLA block copolyester;

[0036] (2) Mix the block copolyester obtained in step (1) with the second chain extender and antioxidant 1010, and add them to a twin-screw extruder for melt blending; wherein the second chain extender is an inorganic nanoparticle-based chain extender, and its preparation method is: mix IPDI and nano-CaCO3 (average particle size 70 ± 10 nm) at a mass ratio of 2:1, and react at 30 °C for 10 min under nitrogen protection to obtain the inorganic nanoparticle-based chain extender; the addition amounts of the second chain extender and antioxidant 1010 are 0.5% and 0.5% of the mass of the block copolyester respectively; the melt blending temperature in the twin-screw extruder is 200 °C, and the mixing time is 5 min; prepare the biodegradable PEST-b-PLA block branched copolyester, and the polyester melt prepared has high strength and stable processing.

[0037] Example 3:

[0038] A preparation method of a biodegradable block branched copolyester, comprising the following steps:

[0039] (1) Mix the first resin, the second resin, the first chain extender, and antioxidant 1010, and then add them to a twin-screw extruder for melt blending; wherein the first resin and the second resin are PGA and PEST respectively, the weight-average molecular weights of PGA and PEST are 200 kg / mol and 50 kg / mol respectively, and the molar ratio of the first resin to the second resin is 20:80; the first chain extender is HDI, and the addition amounts of the first chain extender and antioxidant 1010 are 1.0% and 0.5% of the total mass of the first resin and the second resin respectively; the melt blending temperature in the twin-screw extruder is 230 °C, and the mixing time is 5 min; obtain the PEST-b-PGA block copolyester;

[0040] (2) Mix the block copolyester obtained in step (1) with a second chain extender and antioxidant 1010, and add them to a twin-screw extruder for melt blending; wherein the second chain extender is an inorganic nanoparticle-based chain extender, and its preparation method is: Mix maleic anhydride and nano-ZnO (average particle size 50±5 nm) at a mass ratio of 8:1, and react at 110°C for 30 min under nitrogen protection to obtain an inorganic nanoparticle-based chain extender; the addition amounts of the second chain extender and antioxidant 1010 are 4% and 0.5% of the mass of the block copolyester respectively; the melt blending temperature in the twin-screw extruder is 200°C, and the mixing time is 5 min; a biodegradable PEST-b-PGA block-branched copolyester is prepared, and the polyester obtained has high melt strength and stable processing.

[0041] Example 4:

[0042] A preparation method of a biodegradable block-branched copolyester, comprising the following steps:

[0043] (1) Mix the first resin, second resin, first chain extender and antioxidant 1076, and add them to a twin-screw extruder for melt blending; wherein the first resin and second resin are PGA and PBAT respectively, the weight-average molecular weights of PGA and PBAT are 15 kg / mol and 105 kg / mol respectively, and the molar ratio of the first resin to the second resin is 10:90; the first chain extender is Joncryl ADR, and the addition amounts of the first chain extender and antioxidant 1076 are 1.0% and 0.5% of the total mass of the first resin and second resin respectively; the melt blending temperature in the twin-screw extruder is 230°C, and the mixing time is 5 min; obtain a PBAT-b-PGA block copolyester;

[0044] (2) Mix the block copolyester obtained in step (1) with a second chain extender and antioxidant 1076, and add them to a twin-screw extruder for melt blending; wherein the second chain extender is an inorganic nanoparticle-based chain extender, and its preparation method is: Mix maleic anhydride and nano-ZnO (average particle size 50±5 nm) at a mass ratio of 5:1, and react at 110°C for 30 min under nitrogen protection to obtain an inorganic nanoparticle-based chain extender; the addition amounts of the second chain extender and antioxidant 1076 are 3% and 0.5% of the mass of the block copolyester respectively; the melt blending temperature in the twin-screw extruder is 230°C, and the mixing time is 5 min; a biodegradable PBAT-b-PGA block-branched copolyester is prepared, and the polyester obtained has high melt strength and stable processing.

[0045] Comparative Example 1:

[0046] A preparation method of a random copolyester PEST, comprising the following steps:

[0047] (1) Esterification reaction: 664 g of terephthalic acid, 118 mol of succinic acid, 372 g of ethylene glycol, and 0.423 g of antimony glycolate were put into a reaction kettle. After purging the air in the reaction kettle with nitrogen, the esterification reaction was carried out at 190 °C, 250 °C, and 3 MPa respectively. When the amount of esterification distillate reached about 80% of the theoretical value, the esterification reaction was terminated.

[0048] (2) Polycondensation reaction: The diol was removed by vacuum pumping. After 60 min, the vacuum degree was brought within 60 Pa. At the same time, the temperature was adjusted to 280 °C, and the polycondensation reaction was carried out for 2.5 h to obtain a random copolyester PEST with a weight-average molecular weight of 51 kg / mol. The polyester melt prepared had high strength and stable processing.

[0049] Comparative Example 2 (block copolyester synthesized only with the first chain extender):

[0050] A preparation method of a biodegradable block copolyester includes the following steps:

[0051] The first resin, the second resin, the first chain extender, and antioxidant 1010 were mixed and then added to a twin-screw extruder for melt blending. The first resin and the second resin were PLA and PEST respectively, with weight-average molecular weights of 41 kg / mol and 50 kg / mol. The molar ratio of the first resin to the second resin was 20:80. The first chain extender was IPDI, and the addition amounts of the first chain extender and antioxidant 1010 were 1.0% and 0.5% of the total mass of the first resin and the second resin respectively. The melt blending temperature in the twin-screw extruder was 230 °C, and the mixing time was 5 min. A PEST-b-PLA block copolyester was obtained, and the polyester melt prepared had low strength and was easy to break.

[0052] Comparative Example 3 (directly blending inorganic nanoparticles with the block copolyester):

[0053] A preparation method of a biodegradable block-branched copolyester includes the following steps:

[0054] (1) The first resin, the second resin, the first chain extender, and antioxidant 1010 were mixed and then added to a twin-screw extruder for melt blending. The first resin and the second resin were PLA and PEST respectively, with weight-average molecular weights of 41 kg / mol and 50 kg / mol. The molar ratio of the first resin to the second resin was 20:80. The first chain extender was IPDI, and the addition amounts of the first chain extender and antioxidant 1010 were 1.0% and 0.5% of the total mass of the first resin and the second resin respectively. The melt blending temperature in the twin-screw extruder was 230 °C, and the mixing time was 5 min. A PEST-b-PLA block copolyester was obtained;

[0055] (2) Mix the block copolyester obtained in step (1) with a second chain extender, antioxidant 1010, and inorganic nanoparticles, and add them to a twin-screw extruder for melt blending; wherein the second chain extender is IPDI, and the inorganic nanoparticles are nano-SiO2 (average particle size 30±5 nm); the addition amounts of the second chain extender, antioxidant 1010, and inorganic nanoparticles are 0.33%, 0.5%, and 0.17% of the mass of the block copolyester, respectively; the melt blending temperature in the twin-screw extruder is 200 °C, and the mixing time is 5 min; a biodegradable PEST-b-PLA block-branched copolyester is prepared, and the melt strength of the prepared polyester is low and it is easy to break.

[0056] Comparative Example 4

[0057] A random copolyester PBAT, sourced from Zhejiang Hangzhou Xinfu Technology Co., Ltd., has a weight-average molecular weight of 105 kg / mol.

[0058] Test the mechanical properties and degradation properties of the block-branched copolyesters prepared in the above examples and comparative examples. The results are shown in Table 1 and Figure 1 as shown below.

[0059] (1) Mechanical property test:

[0060] Prepare the block-branched copolyesters / block copolyesters prepared in the examples and comparative examples into fibers with a diameter of 15 μm respectively; use a 3345 type tensile testing machine (INSTRON, USA) to test the mechanical properties of the specimens. When testing, the pulling rate is 10 mm / min, and the actual thickness of the specimens is measured by a CT-100 type thickness gauge. At least 7 specimens are prepared for each group, and their average values are taken. The obtained mechanical properties are shown in Table 1.

[0061] Table 1: Test results of the mechanical properties of the block-branched copolyesters.

[0062] Sample Tensile strength (MPa) Elongation at break (%) Young's modulus (GPa) Example 1 310±20 300±40 15.1±4.2 Example 2 305±15 310±30 14.8±4.5 Example 3 265±25 237±45 12.9±3.0 Example 4 31±1 770±30 111.6±8.0 Comparative Example 1 200±20 270±20 10.1±0.5 Comparative Example 2 220±50 480±80 13.7±2.2 Comparative Example 3 160±20 370±50 12.1±1.0 Comparative Example 4 29±2 810±70 81.0±5.6

[0063] As can be seen from Table 1, the mechanical properties of the random copolyester PEST in Comparative Example 1 are poor. In Comparative Example 2, the block copolyester PEST-b-PLA retains the properties of the PEST and PLA segments, and its tensile strength, elongation at break, and Young's modulus are significantly improved compared to Comparative Example 1. After further synthesizing block-branched copolyesters (Examples 1 and 2), their strength and Young's modulus are further increased. The elongation at break slightly decreases due to the branched structure but is still significantly higher than that of the random copolyester, indicating that this structure is beneficial to improving the mechanical properties of the polyester. In Comparative Example 3, due to the poor compatibility between the nanoparticles and the polyester, the improvement in mechanical strength is limited. Similarly, in the PBAT system, compared with pure PBAT (Comparative Example 4), the block-branched copolyester PBAT-b-PGA (Example 4) has better mechanical strength and modulus.

[0064] (2) Degradation performance test:

[0065] Respectively, the block-branched copolyesters / block copolyesters obtained in Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were made into fibers with a diameter of 15 μm and placed in a 0.5 mol / L sodium hydroxide solution at a reaction temperature of 58 °C. The mass changes of the fibers were weighed at different time intervals, and the results of the mass loss rate are as Figure 1 shown.

[0066] From Figure 1 it can be seen that the alkali hydrolysis quality of the random PEST copolyester (Comparative Example 1) is low, and the alkali hydrolysis efficiency at 48 h is only 35%. However, after introducing PLA into the random PEST copolyester, the alkali hydrolysis efficiency of the block-structured PEST-b-PLA copolyester (Comparative Example 2) is greatly improved, and the alkali hydrolysis efficiency at 48 h reaches 87%. After introducing nanoparticles (Comparative Example 3), the alkali hydrolysis efficiency of the PEST-b-PLA copolyester is slightly improved. Further, by segment design, block-branched PEST-b-PLA copolyesters (Examples 1 and 2) are prepared, and the alkali hydrolysis efficiency is greatly improved. The alkali hydrolysis efficiency at 20 h reaches more than 90%, and complete degradation occurs at 48 h, and the alkali hydrolysis efficiency is close to 100%. This is because the introduction of 0.5% inorganic nanoparticles and the existence of a branched structure act together to significantly increase the alkali hydrolysis efficiency.

[0067] The above examples are used to explain and illustrate the present invention, rather than limiting the present invention. Any modifications and changes made to the present invention within the spirit and scope of the protection of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable block-branched copolyester, characterized in that, It includes the following steps: (1) First, melt-blend the first resin, the second resin, and the first chain extender to obtain a block copolyester; the first resin is selected from one or more of polylactic acid, polyglycolic acid, poly(propylene carbonate), polycaprolactone, poly(vinyl acetate), polyethylene glycol, and poly(vinyl alcohol); the second resin is selected from one or more of poly(butylene adipate-co-terephthalate), poly(butylene succinate), poly(butylene succinate-co-terephthalate), polyhydroxyalkanoate, poly(ethylene glycol succinate-co-terephthalate), and poly(ethylene glycol adipate-co-terephthalate); (2) Melt-blend the block copolyester obtained in step (1) with the second chain extender to obtain the biodegradable block-branched copolyester; the second chain extender is an inorganic nanoparticle-based chain extender prepared by reacting inorganic nanoparticles with a modifier; the modifier is selected from one or more of bisphenol A diglycidyl ether, Joncryl ADR, glycidyl methacrylate, 1,6-hexamethylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, pyromellitic dianhydride, succinic anhydride, and maleic anhydride.

2. The preparation method according to claim 1, characterized in that, An antioxidant is also added in steps (1) and (2). The antioxidant added in step (1) accounts for 0.05-5.0% of the total mass of the first resin and the second resin; the antioxidant added in step (2) accounts for 0.05-5.0% of the mass of the block copolyester; the antioxidant is selected from one or more of BTH, DSTP, DLTP, 168, 264, 300, 425, 626, 627, 1010, and 1076.

3. The preparation method according to claim 1, characterized in that, The weight-average molecular weight of the first resin is 5-500 kg / mol, and the weight-average molecular weight of the second resin is 10-500 kg / mol; the molar ratio of the first resin to the second resin is 90:10-10:

90.

4. The preparation method according to claim 1, characterized in that, The first chain extender is selected from one or more of bisphenol A diglycidyl ether, Joncryl ADR, glycidyl methacrylate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, succinic anhydride, maleic anhydride, pyromellitic dianhydride, 2,2'-bis(2-oxazoline), and 1,4-phenyl-bis(2-oxazoline).

5. The preparation method according to claim 1, characterized in that, The addition amount of the first chain extender in step (1) is 0.1-5.0% of the total mass of the first resin and the second resin.

6. The preparation method according to claim 1 or 2 or 4, characterized in that, The melt-blending time in step (1) is 3-15 min.

7. The preparation method according to claim 1, characterized in that, When preparing the inorganic nanoparticle-based chain extender, the inorganic nanoparticles are selected from one or more of SiO2, TiO2, CaCO3, Al2O3, montmorillonite, talc, mica, saponite, and ZnO, and the particle size of the inorganic nanoparticles is 5-1000 nm.

8. The preparation method according to claim 1 or 7, characterized in that, When preparing the second chain extender, the mass ratio of the modifier to the inorganic nanoparticles is 1:1-10:1, the reaction temperature is 20-180 °C, the reaction time is 3-30 min, and the reaction is carried out under nitrogen protection.

9. The preparation method according to claim 1 or 7, characterized in that, In step (2), the addition amount of the second chain extender is 0.1-5.0% of the total mass of the first resin and the second resin.

10. The preparation method according to claim 1 or 7, characterized in that, The melt blending time in step (2) is 3-10 min.

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