PBAT / PLA composite degradable plastic and preparation process thereof

Abstract

The invention belongs to the technical field of polyester degradable plastics, and particularly relates to a PBAT / PLA composite degradable plastic and a preparation process thereof. The invention aims to solve the problems of poor weather resistance and insufficient mechanical properties of the existing PBAT / PLA composite material. The preparation method comprises the following steps: preheating PBAT resin particles, and carrying out melt grafting treatment to obtain modified PBAT; hydroxyl-terminated PBS is obtained through ester exchange polycondensation treatment, and a triblock compatilizer is further obtained through bulk polymerization; the preparation method comprises the following steps: carrying out acetylation modification on nano cellulose to obtain a dispersion enhancer, and carrying out melt blending on the dispersion enhancer and PLA resin particles to obtain enhanced master batches; and carrying out reactive blending on the modified PBAT, the reinforced master batch and the triblock compatilizer, and carrying out vacuum drying to obtain the degradable plastic. The degradable plastic provided by the invention keeps excellent degradability while having good mechanical strength.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyester degradable plastics, and particularly relates to a PBAT / PLA composite degradable plastic and a preparation process thereof. BACKGROUND

[0002] Polybutylene adipate terephthalate, namely PBAT, is a new type of biodegradable polymer material that can be completely decomposed by microorganisms under specific conditions. PBAT has excellent flexibility and good processing performance, and particularly exhibits unique advantages in the field of thin films, which can meet the requirements of material ductility and tear resistance in application scenarios such as packaging and tableware. However, the mechanical strength and rigidity of PBAT are relatively low, which limits its use in some applications that require higher load capacity. On the other hand, polylactic acid, namely PLA, is also a biodegradable plastic known for its high strength, high modulus and good rigidity, and is widely used in fields such as injection molding, fibers and films. However, its inherent brittleness and low elongation at break limit its application in scenarios that require good toughness.

[0003] In order to overcome the shortcomings of PBAT and PLA and fully utilize their advantages, blending modification of the two has become an important research direction. Through blending modification, the flexibility of PBAT and the strength of PLA can be effectively combined to obtain a composite material with more excellent comprehensive performance. Such a composite material can generally exhibit better impact strength, tensile performance and processing performance, thereby expanding its application range. However, the existing PBAT / PLA composite materials still have some problems in technology. Due to the differences in polarity and melt viscosity between PBAT and PLA, the compatibility of the two is poor, which easily leads to phase separation and affects the mechanical properties and degradation performance of the final material. In order to improve the compatibility of the two, researchers usually need to introduce a compatibilizer or use other modification methods. In addition, the existing PBAT / PLA composite materials still need to be further improved in terms of heat resistance, barrier property and processing performance, in order to meet the requirements of more extensive applications.

[0004] At present, the poor weather resistance and insufficient mechanical properties of the existing PBAT / PLA composite materials are still important problems faced by the industry.

[0005] Therefore, a PBAT / PLA composite degradable plastic and a preparation process thereof are provided. SUMMARY

[0006] The application aims to provide a PBAT / PLA composite degradable plastic and a preparation process thereof. The application obtains modified PBAT by preheating PBAT resin particles and then performing melt grafting treatment; obtains hydroxyl-terminated PBS by ester exchange polycondensation treatment, and further obtains a triblock compatibilizer by bulk polymerization; obtains a dispersion enhancer by acetylation modification of nanocellulose, and obtains an enhanced master batch by melt blending the dispersion enhancer with PLA resin particles; and obtains the degradable plastic by reactive blending of the modified PBAT, the enhanced master batch and the triblock compatibilizer, and vacuum drying.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme. A preparation process of a PBAT / PLA composite degradable plastic, comprising the following steps: Unless otherwise specified, the parts in the application refer to mass parts, and the average molecular weight refers to the average molecular weight.

[0008] The PBAT resin particles are preheated and then subjected to melt grafting treatment to obtain modified PBAT. The BA unit of the PBAT resin particles accounts for 70%, the BT unit accounts for 30%, and the average molecular weight is 45000.

[0009] Dimethyl succinate and 1,4-butanediol are mixed and subjected to ester exchange polycondensation treatment to obtain hydroxyl-terminated PBS.

[0010] The hydroxyl-terminated PBS and lactide monomers are mixed, and the triblock compatibilizer is obtained after bulk polymerization treatment.

[0011] The lactide monomer is racemic 3,6-dimethyl-1,4-dioxane-2,5-dione, and the CAS is 95-96-5.

[0012] The nanocellulose is acetylated and modified to obtain a dispersion enhancer.

[0013] The average molecular weight of the nanocellulose is 10000, the average length-diameter ratio is 100-200, and the average diameter is 10-20 nm.

[0014] The PLA resin particles are dried and then melt blended with the dispersion enhancer to obtain an enhanced master batch.

[0015] The average molecular weight of the PLA resin particles is 65000.

[0016] The modified PBAT, the enhanced master batch and the triblock compatibilizer are subjected to reactive blending to obtain a composite resin precursor.

[0017] The composite resin precursor is vacuum dried at a temperature of 60°C and an operating pressure of 1 mbar for 12 hours to obtain the degradable plastic.

[0018] Preferably, the process of melt grafting treatment is as follows: 100 parts of PBAT resin particles are preheated at 80-85°C for 4 hours, mixed with 2-4 parts of glycidyl methacrylate and 0.2-0.5 parts of dicumyl peroxide, fed into an extruder at 140-150°C, the screw rotation speed is maintained at 150-200 rpm, treated at 170°C for 10 min, heated to 190°C for 20 min, and extruded at 180°C to obtain the modified PBAT.

[0019] Preferably, the process of ester exchange polycondensation treatment is as follows: dimethyl succinate and 1,4-butanediol are mixed in a molar ratio of 1:1.1-1.3, titanium tetrabutoxide and triphenyl phosphite are added, heated to 160-190°C under nitrogen protection, heated to 220°C at a heating rate of 5°C / min after 3 hours of continuous reaction, and the pressure of the reaction system is reduced to 1 mbar, and the reaction is continued for 5 hours to obtain the hydroxyl-terminated PBS.

[0020] Preferably, the process of ester exchange polycondensation treatment is as follows: dimethyl succinate and 1,4-butanediol are mixed in a molar ratio of 1:1.1-1.3, titanium tetrabutoxide and triphenyl phosphite are added, heated to 160-190°C under nitrogen protection, heated to 220°C at a heating rate of 5°C / min after 3 hours of continuous reaction, and the pressure of the reaction system is reduced to 1 mbar, and the reaction is continued for 5 hours to obtain the hydroxyl-terminated PBS.

[0021] Preferably, the process of bulk polymerization treatment is as follows: the hydroxyl-terminated PBS and lactide monomers are mixed in a molar ratio of 1:100-170, and then a toluene solution of stannous octoate is added, and the reaction is carried out at 130-160°C for 8 hours, and then the reaction solution is cooled and recrystallized with methanol to obtain the triblock compatibilizer.

[0022] Preferably, the process of bulk polymerization treatment is as follows: the hydroxyl-terminated PBS and lactide monomers are mixed in a molar ratio of 1:100-170, and then a toluene solution of stannous octoate is added, and the reaction is carried out at 130-160°C for 8 hours, and then the reaction solution is cooled and recrystallized with methanol to obtain the triblock compatibilizer.

[0023] Preferably, the process of acetylation modification is as follows: 0.5-1 parts of nanocellulose are dispersed in 80 parts of glacial acetic acid, and then stirred and reacted at 50°C, and then 120-160 parts of acetic anhydride and 0.01 parts of iodine are added, and then stirred and reacted at 80-100°C for 3 hours, and then the obtained precipitate is washed and dried to obtain the dispersion enhancer.

[0024] Preferably, the process of melt blending is as follows: 100 parts of PLA resin particles are mixed with 5-18 parts of dispersion enhancer, and then extruded at 185°C with a screw rotation speed of 200-400 rpm to obtain the enhanced masterbatch.

[0025] Preferably, the process of reactive blending is: the modified PBAT and the reinforcing masterbatch are fed at 160 DEG C, mixed at 200 DEG C, and the dispersion reinforcing agent is added, the screw rotation speed is controlled at 220 rpm, after the reaction is completed, the extrusion is carried out at 180 DEG C, and the composite resin precursor is obtained; wherein the mass ratio of the modified PBAT, the reinforcing masterbatch and the triblock compatibilizer is 40:30-55:5-9.

[0026] A degradable plastic based on PBAT / PLA blending modification comprises modified PBAT, reinforcing masterbatch and dispersion reinforcing agent.

[0027] Compared with the prior art, the beneficial effects of the present application are: 1. The PBAT resin particles are modified by melt grafting treatment, and the modified PBAT, the reinforcing masterbatch and the triblock compatibilizer are chemically bonded in the blending process through the process of reactive blending, a synergistic system of chemical bonding and physical compatibility is constructed, a PBAT / PLA blended composite material with better compatibility is obtained, and the toughness and weather resistance of the degradable plastic product are improved.

[0028] 2. The acetylation modification process is used to activate the nanocellulose, which significantly improves the compatibility of the nanocellulose with the hydrophobic polyester matrix, and the acetylated dispersion reinforcing agent is dispersed in the PLA matrix before the final reactive blending, which ensures the full combination of the dispersion reinforcing agent with the PLA matrix, and significantly improves the compatibility with the PBAT phase in the process of reactive blending, thereby improving the weather resistance of the degradable plastic product.

[0029] 3. The ester exchange polycondensation process is used to prepare hydroxyl-terminated PBS, and the PLA-b-PBS-b-PLA triblock copolymer is synthesized through bulk polymerization treatment with lactide monomers, and is used as a triblock compatibilizer to fully combine the PBAT phase and the PLA phase in the process of reactive mixing, thereby significantly improving the strength of the degradable plastic product.

[0030] 4. By adjusting the components of the triblock compatibilizer and the melt grafting treatment of PBAT, it is ensured that the fully combined PBAT / PLA mixed phase still has good degradability. At the same time, the added triblock compatibilizer and reinforcing masterbatch are degradable, and the components synergistically improve the strength and weather resistance of the degradable plastic product, and at the same time, no non-degradable segments are introduced, so that the degradable plastic product has excellent degradability. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The flow chart of the preparation process of the degradable plastic in the present application. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention are described clearly and completely below through some embodiments and experimental examples. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] Reference Figure 1 As shown in the process flow chart, the present invention provides a PBAT / PLA composite biodegradable plastic and its preparation process, and the technical solution is as follows: Example 1

[0034] After preheating 100 parts of PBAT resin particles at 80-85°C for 4 hours, they were mixed with 2 parts of glycidyl methacrylate and 0.2 parts of dicumyl peroxide, fed into an extruder at 140°C, the screw speed was maintained at 150 rpm, treated at 170°C for 10 minutes, heated to 190°C for 20 minutes, and extruded at 180°C to obtain modified PBAT.

[0035] Dimethyl succinate and 1,4-butanediol were mixed in a molar ratio of 1:1.1, tetrabutyl titanate and triphenyl phosphite were added, and the temperature was raised to 160°C under nitrogen protection. After the reaction was continued for 3 hours, the temperature was raised to 220°C at a heating rate of 5°C / min, and the pressure of the reaction system was reduced to 1 mbar. The reaction was continued for 5 hours to obtain hydroxyl-terminated PBS.

[0036] The addition amount of tetrabutyl titanate is 0.02 wt % of the total mass of dimethyl succinate and 1,4-butanediol, and the addition amount of triphenyl phosphite is 0.6 wt % of the total mass of dimethyl succinate and 1,4-butanediol.

[0037] After mixing hydroxyl-terminated PBS and lactide monomer at a molar ratio of 1:100, a toluene solution of stannous octoate was added, and the mixture was reacted at 130°C for 8 hours. The reaction solution was cooled and recrystallized using methanol to obtain a triblock compatibilizer.

[0038] The mass concentration of the toluene solution of stannous octoate is 2.5 wt %, and the amount added is 0.5 wt % of the mass of lactide.

[0039] 0.5 parts of nanocellulose was dispersed in 80 parts of glacial acetic acid, and after stirring at 50°C, 120 parts of acetic anhydride and 0.01 parts of iodine were added, and after stirring at 80°C for 3 hours, the obtained precipitate was washed and dried to obtain a dispersion enhancer.

[0040] 100 parts of PLA resin particles were mixed with 5 parts of dispersion enhancer, and extruded at 185° C. with a screw speed of 200 rpm to obtain a reinforced masterbatch.

[0041] The modified PBAT and the reinforcing masterbatch are fed at 160°C, mixed at 200°C, and the dispersion reinforcing agent is added, with the screw rotation speed controlled at 220 rpm, and after the reaction is completed, the composite resin precursor is extruded at 180°C; wherein the mass ratio of the modified PBAT, the reinforcing masterbatch, and the triblock compatibilizer is 40:30:5.

[0042] The composite resin precursor is vacuum dried at a temperature of 60°C for 12 hours at an operating pressure of 1 mbar to obtain the degradable plastic.

[0043] Example 2-20 differs from Example 1 in the operating parameters, but is completely identical in the process steps. The relevant operating parameter changes are summarized in Tables 1, 2, and 3.

[0044] Table 1 Operating parameter changes of Examples 1-20 (I)

[0045]

[0046] Table 2 Operating parameter changes of Examples 1-20 (II)

[0047]

[0048] Table 3 Operating parameter changes of Examples 1-20 (III)

[0049] Comparative Example 1 Unlike Example 1, no melt grafting treatment is performed, and the other process parameters are the same.

[0050] Comparative Example 2 Unlike Example 1, no triblock compatibilizer is added, and the other process parameters are the same.

[0051] Comparative Example 3 Unlike Example 1, a blend of PBS and PLA is used instead of the triblock compatibilizer, with the molar ratio of the added PBS and PLA being 1:100, wherein the average molecular weight of the PBS is 35,000, and the average molecular weight of the PLA is 65,000, and the other process parameters are the same.

[0052] Comparative Example 4 Unlike Example 6, no acetylation modification is performed, and the other process parameters are the same.

[0053] Comparative Example 5 Different from Example 6, the dispersing reinforcing agent was directly blended with other components in the reactive blending process without the step of preparing the reinforcing master batch by melt blending, and other process parameters were the same.

[0054] Comparative Example 6 Different from Example 11, the ester exchange polycondensation treatment was not performed, and PBS with an average molecular weight of 35000 was directly used instead of the hydroxyl-terminated PBS to participate in the bulk polymerization treatment, and other process parameters were the same.

[0055] Comparative Example 7 Different from Example 11, the bulk polymerization treatment was not performed, and PLA with an average molecular weight of 65000 was blended with the hydroxyl-terminated PBS, and other process parameters were the same.

[0056] Comparative Example 8 Different from Example 11, epoxidized linseed oil was used instead of the triblock compatibilizer, and other process parameters were the same.

[0057] Comparative Example 9 Different from Example 16, an equal amount of talc powder was used instead of acetylated nanocellulose, and other process parameters were the same.

[0058] Comparative Example 10 Different from Example 16, no reinforcing master batch was added, and other process parameters were the same.

[0059] Experimental Example 1 The toughness and weather resistance of the degradable plastic products prepared in Examples 1-5 and Comparative Examples 1-3 were tested, and the related results are summarized in Table 4.

[0060] The test method for toughness was as follows: a sample of 0.5 mm x 100 mm x 20 mm was used to perform tensile property testing along the long axis, and the maximum breaking strength (N / m) and elongation at break (%) were recorded.

[0061] The test method for weather resistance was as follows: the initial toughness data of the sample were recorded, and the sample was irradiated with 340 nm ultraviolet light with a power of 0.55 W / m 2 After irradiation for 100 hours at 40°C, the retention rate (%) of the maximum breaking strength and elongation at break was tested, and the higher the retention rate, the better the weather resistance.

[0062] Table 4 Toughness and Weather Resistance of Degradable Plastic Products Prepared in Examples 1-5 and Comparative Examples 1-3

[0063] As shown in the data of Table 4, the degradable plastic products prepared in Examples 1-5 have good toughness and good toughness retention rate after UV treatment, and good weather resistance. Comparative Example 1 is not subjected to melt grafting treatment, and the toughness decreases significantly, but the weather resistance does not decrease significantly, indicating that melt grafting modification is crucial for improving the toughness of the material and provides a basis for subsequent chemical bonding. Comparative Example 2 does not add a triblock compatibilizer, and the toughness decreases significantly, and the weather resistance also decreases significantly, indicating that the triblock compatibilizer effectively improves the compatibility of PBAT / PLA, and significantly improves the toughness and weather resistance of the material. Comparative Example 3 uses a blend of PBS and PLA instead of a triblock compatibilizer, and the toughness decreases significantly, but the weather resistance is not significantly affected, indicating that the pre-synthesized PLA-b-PBS-b-PLA triblock compatibilizer with a specific structure is much better than a simple physical blend in improving compatibility and improving performance.

[0064] In summary, the reaction sites provided by the modified PBAT in the present application, the bridging of the triblock compatibilizer and the process conditions of reactive blending work together to form a synergistic system of chemical bonding and physical compatibility, strengthen the interfacial bonding, and have significant advantages in toughness and weather resistance. It is a strong proof of the effectiveness of melt grafting modified PBAT, adding PLA-b-PBS-b-PLA triblock compatibilizer and constructing a synergistic system of chemical bonding and physical compatibility through reactive blending, which improves the toughness and weather resistance of the degradable plastic product.

[0065] Experimental Example 2 The weather resistance and acid resistance of the degradable plastic products prepared in Examples 6-10 and Comparative Examples 4-5 were tested, and the related results are summarized in Table 5.

[0066] The test method for weather resistance refers to Experimental Example 1, and the test method for acid resistance is as follows: record the initial toughness data of the sample, after soaking in 10wt% hydrochloric acid for 7 days, record the retention rate (%) of the maximum breaking strength and elongation at break, the higher the retention rate, the better the acid resistance.

[0067] Table 5 Weather resistance and acid resistance of degradable plastic products prepared in Examples 6-10 and Comparative Examples 4-5

[0068] As shown in the data of Table 5, the degradable plastic products prepared in Examples 6-10 have better performance in both weather resistance and acid resistance. The acetylation modification of nanocellulose is not performed in Comparative Example 4, resulting in the decrease of both UV aging resistance and acid resistance, indicating that the acetylation treatment effectively reduces the hydrophilicity of nanocellulose, enhances the interfacial compatibility of the hydrophobic PLA matrix, and thus improves the ability of the composite to resist environmental aging. In Comparative Example 5, the step of preparing the reinforcing masterbatch by melt blending is not performed, and the dispersing reinforcing agent is directly added in the reactive blending. The weather resistance has a small decrease, and the acid resistance also has the same trend, indicating that the acetylation nanocellulose is dispersed in PLA by melt blending to prepare a masterbatch in advance, which helps to overcome the agglomeration problem of nanocellulose, achieve more uniform dispersion in the PLA matrix, and thus more effectively play its reinforcing and stabilizing role, further improving the weather resistance of the material.

[0069] In summary, acetylation improves the intrinsic compatibility of nanocellulose and PLA, and the step of preparing a masterbatch optimizes its physical dispersion state. The combination of the two ensures that the activated reinforcing agent can be fully and uniformly combined in the PLA matrix. This not only stabilizes the PLA phase, but in the final reactive blending, this well-dispersed and compatibility-improved PLA-nanocellulose composite phase can also better interact with PBAT to form a more stable overall structure, thereby maximizing the weather resistance of the product.

[0070] Experimental Example 3 The mechanical strength of the degradable plastic products prepared in Examples 11-15 and Comparative Examples 6-8 was tested, and the related results are summarized in Table 6.

[0071] The mechanical strength includes toughness and puncture resistance, wherein the test method of toughness refers to Experimental Example 1, and the test method of puncture resistance is as follows: a sample of 0.5 mm x 100 mm x 100 mm is prepared, a hemispherical probe with a diameter of 3.2 mm is used to press at a speed of 25 mm / min, and the peak puncture force (N) is recorded. The greater the peak puncture force, the better the puncture resistance of the sample.

[0072] Table 6 Mechanical strength of degradable plastic products prepared in Examples 11-15 and Comparative Examples 6-8

[0073] As shown in the data of Table 6, the degradable plastic products prepared in Examples 11-15 and Examples 1-10 have similar toughness and good puncture resistance, and are suitable for use as base materials for products such as packaging bags, straws, tableware, etc. Comparative Example 6 directly uses ordinary PBS instead of the hydroxyl-terminated PBS prepared by ester exchange polycondensation to participate in subsequent bulk polymerization, and the mechanical strength of the product prepared in Example 11 is lower, indicating that the hydroxyl-terminated PBS synthesized by precise control through ester exchange polycondensation is the basis for the subsequent successful preparation of a tri-block copolymer with excellent compatibility effect, and is crucial to improve the strength of the final material. Comparative Example 7 does not perform bulk polymerization treatment, and only blends PLA with hydroxyl-terminated PBS, and the toughness decreases significantly, but the puncture resistance decreases less, which proves that the hydroxyl-terminated PBS must be connected with lactide monomers through bulk polymerization to form a specific PLA-b-PBS-b-PLA block structure, in order to effectively bridge the PBAT and PLA two phases, and physical blending cannot achieve the same compatibility effect and strength improvement. Comparative Example 8 uses epoxidized linseed oil instead of the tri-block compatibilizer synthesized in the present application, and the toughness decreases less, but the puncture resistance decreases significantly, indicating that the PLA-b-PBS-b-PLA tri-block copolymer synthesized by the specific method in the present application can more effectively improve the compatibility of the PBAT / PLA system and significantly improve the tensile strength and puncture resistance of the material, compared with epoxidized linseed oil.

[0074] In summary, the present application can effectively combine PBAT and PLA phases by preparing hydroxyl-terminated PBS through ester exchange polycondensation, and then performing bulk polymerization to generate a PLA-b-PBS-b-PLA tri-block copolymer as a compatibilizer, which can significantly improve the toughness and puncture resistance of the degradable plastic product.

[0075] Experimental Example 4 The degradability and weather resistance of the degradable plastic products prepared in Examples 16-20 and Comparative Examples 9-10 were tested, and the related results are summarized in Table 7.

[0076] The test method for weather resistance refers to Experimental Example 1, and the test method for degradability is as follows: the sample is made into a fragment with a particle size of less than 2 mm, buried in humus soil at a temperature of 25°C, and the residual sample mass is measured after 30 days of treatment to calculate the biodegradation rate (%) of the sample within 30 days. The higher the biodegradation rate, the better the degradability.

[0077] The humus soil used has a pH value in the range of 6.0-7.0, an organic matter content of 55%, and a natural water content of 25%.

[0078] Table 7 Degradability and weather resistance of the degradable plastic products prepared in Examples 16-20 and Comparative Examples 9-10

[0079] As shown in the data of Table 7, the degradable plastic products prepared in Examples 16-20 have good degradability and better weather resistance. The humus soil environment at 25℃ is not a specialized composting environment, and the decomposition effect of degradable materials is poor, but Examples 16-20 can still decompose more than 20% in 30 days, and have excellent biodegradability. Comparative Example 9 uses an equal amount of non-biodegradable talc powder to replace the biodegradable acetylated nanocellulose as a reinforcing filler, and the weather resistance decreases to some extent, and the biodegradation rate is significantly reduced, which directly proves that the introduction of non-degradable segments will significantly reduce the overall biodegradation performance of the material. Comparative Example 10 does not add a reinforcing master batch, and the weather resistance decreases slightly, and the biodegradation rate also decreases slightly, indicating that the addition of the degradable reinforcing master batch in the present application not only synergistically improves the weather resistance performance of the material, but also does not sacrifice its own degradability and the influence on the morphology of the matrix, but helps to maintain the overall biodegradation rate of the material.

[0080] In summary, by selecting and synergistically controlling each component, the present application successfully improves the strength and weather resistance of the material while avoiding the introduction of non-degradable components, ensuring the overall excellent degradability of the composite material.

[0081] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a PBAT / PLA composite biodegradable plastic, characterized by: The preparation process is as follows: The PBAT resin particles are preheated and then melt-grafted to obtain modified PBAT; Dimethyl succinate and 1,4-butanediol are mixed in a molar ratio of 1:1.1-1.3, and subjected to transesterification and polycondensation to obtain hydroxyl-terminated PBS; The hydroxyl-terminated PBS and lactide monomer are mixed and subjected to bulk polymerization to obtain a triblock compatibilizer; The nanocellulose is modified by acetylation to obtain a dispersion enhancer; drying the PLA resin particles and melt-blending them with the dispersion enhancer to obtain a reinforced masterbatch; Reactively blending the modified PBAT, the reinforcing masterbatch and the triblock compatibilizer to obtain a composite resin precursor; Wherein, the added mass ratio of the modified PBAT, the reinforcing masterbatch and the dispersion enhancer is 40:30-55:5-9; The composite resin precursor is vacuum dried to obtain the degradable plastic.

2. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, wherein: The melt grafting process is as follows: 100 parts by mass of the PBAT resin particles are preheated at 80-85°C for 4 hours, mixed with 2-4 parts of glycidyl methacrylate and 0.2-0.5 parts of dicumyl peroxide, and fed into an extruder at 140-150°C, maintaining the screw speed at 150-200 rpm, treating at 170°C for 10 minutes, heating to 190°C for 20 minutes, and extruding at 180°C to obtain the modified PBAT.

3. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, characterized in that: The transesterification and polycondensation process is as follows: the dimethyl succinate and the 1,4-butanediol are mixed, tetrabutyl titanate and triphenyl phosphite are added, the temperature is raised to 160-190° C. under nitrogen protection, the temperature is raised to 220° C. at a heating rate of 5° C. / min after continuous reaction, and the pressure of the reaction system is reduced to 1 mbar. The reaction is continued for 5 hours to obtain the hydroxyl-terminated PBS.

4. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, wherein: The bulk polymerization process is as follows: mixing the hydroxyl-terminated PBS and the lactide monomer in a molar ratio of 1:100-170, adding a toluene solution of stannous octoate, reacting at 130-160° C., cooling the reaction solution, and then recrystallizing it with methanol to obtain the triblock compatibilizer.

5. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, wherein: The acetylation modification process is as follows: by mass, 0.5-1 parts of the nanocellulose are dispersed in 80 parts of glacial acetic acid, stirred for reaction, 120-160 parts of acetic anhydride and 0.01 parts of iodine are added, stirred for reaction at 80-100° C., and the resulting precipitate is washed and dried to obtain the dispersion enhancer.

6. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, characterized in that: The melt blending process is as follows: 100 parts of the PLA resin particles are mixed with 5-18 parts of the dispersion enhancer by mass, and the mixture is extruded at 185° C. at a screw speed of 200-400 rpm to obtain the enhanced masterbatch.

7. The process for preparing a PBAT / PLA composite biodegradable plastic according to claim 1, characterized in that: The reactive blending process is as follows: the modified PBAT and the reinforcing masterbatch are fed and mixed, and the dispersion enhancer is added. After the reaction is completed, the mixture is extruded at 180° C. to obtain the composite resin precursor.

8. A biodegradable plastic based on PBAT / PLA blend modification, characterized by: The degradable plastic is prepared by the preparation process according to any one of claims 1 to 7; The degradable plastic comprises: modified PBAT, reinforcing masterbatch and triblock compatibilizer.

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