High-strength and high-toughness PBAT-PLA dynamic crosslinking material capable of being repeatedly processed and preparation method of high-strength and high-toughness PBAT-PLA dynamic crosslinking material

Abstract

The invention relates to the technical field of high polymer materials, and provides a high-strength and high-toughness PBAT-PLA dynamic crosslinking material capable of being repeatedly processed and a preparation method thereof, the material comprises PBAT, PLA, a diisocyanate coupling agent and modified lignin; the modified lignin is obtained through high-hydroxyl-value modification and sulfydryl modification in sequence, the high-hydroxyl-value modification adopts graded extraction of components with high hydroxyl group content in the lignin, and sulfydryl is introduced through a grafting reaction in the sulfydryl modification; the diisocyanate coupling agent comprises an isocyanate group; the hydroxyl reacts with an isocyanate group to form a urethane bond; the sulfydryl reacts with the isocyanate group to form a thionocarbamate bond; the preparation method comprises the following steps: proportionally blending PBAT, PLA, a diisocyanate coupling agent and modified lignin to prepare a composite material; carrying out hot-pressing plasticizing on the composite material to obtain a finished composite material; the preparation method is green and environment-friendly and is convenient for industrialization, and the obtained dynamic crosslinking composite material has excellent mechanical property and reprocessing remolding property.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a repeatedly processable high-strength and high-toughness PBAT-PLA dynamic crosslinking material and a preparation method thereof. BACKGROUND

[0002] At present, the global plastic pollution problem continues to intensify, and the persistence of traditional plastics in the environment and the risk of microplastics generated thereby pose a serious threat to the ecological system. Under this background, polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) as the double core of biodegradable materials are promoting plastic substitution transformation through differentiated paths.

[0003] PBAT can be prepared through an oil-based, bio-based or mixed path, has excellent ductility, and its elongation at break can reach 300%-900%, the film forming flexibility is close to low density polyethylene (LDPE), and occupies a dominant position in soft packaging scenes such as ground cover and shopping bags; however, its tensile strength is not high (only 15-25 MPa), the heat distortion resistance temperature is low (<100℃), and the aromatic structure in the molecular chain leads to a slow degradation rate in the natural environment, and it needs to rely on industrial composting conditions (58-68℃) to achieve efficient decomposition.

[0004] PLA is mainly bio-based, and the main raw material is renewable resources such as corn starch, and can be formed by direct polycondensation of lactic acid or ring-opening polymerization of lactide, which is a hard thermoplastic material, has high transparency (transmittance >90%), high tensile strength (50-70 MPa) and high melting point (170-180℃), and is suitable for hard product fields such as tableware, fibers and 3D printing; but its molecular chain rigidity leads to significant brittleness, elongation at break is less than 10%, and low melt strength and slow crystallization rate limit its application in blown film processing and flexible packaging.

[0005] The strong complementarity of the properties of the two gives rise to the large-scale application of PBAT / PLA composite materials, and the high rigidity of PLA can make up for the insufficient strength of PBAT, and the chain segment flexibility of PBAT can effectively inhibit the brittle fracture of PLA. However, due to the significant difference in solubility parameters and melt viscosity between the two, their compatibility is poor, the interface adhesion is weak, and direct physical blending easily causes phase separation, so that the composite material is difficult to effectively achieve the expected synergistic strengthening and toughening effect.

[0006] To solve the compatibility problem, the prior art usually adopts the method of adding a compatibilizer (such as a maleic anhydride graft) or an inorganic filler (such as nano-clay), but there are problems such as high cost of modifier, introduction of non-bio-based components to reduce the degradability of the material, and still unsatisfactory strength and toughness. Covalent cross-linking strategy can effectively improve the compatibility and significantly improve the strength and toughness, but the formation of chemical cross-linking structure will lead to difficulty in recycling and reprocessing.

[0007] Therefore, based on the above description, it is urgent to develop a biologically based high-strength and high-toughness PBAT-PLA dynamic cross-linking material and a preparation method thereof. SUMMARY

[0008] Technical problems solved by the present application The prior art uses a compatibilizer to improve the compatibility of PBAT and PLA, and there are problems such as high cost of modifier, introduction of non-bio-based components to reduce the degradability of the material, and unsatisfactory strength and toughness. Covalent cross-linking also has technical problems such as difficulty in remolding.

[0009] Technical scheme adopted by the present application In view of the above shortcomings, the purpose of the present application is to provide a high-strength and high-toughness PBAT-PLA dynamic cross-linking material and a preparation method thereof.

[0010] The specific content is as follows: First, the present application provides a high-strength and high-toughness PBAT-PLA dynamic cross-linking material which can be repeatedly processed, comprising the following raw materials in parts by weight: PBAT 60-100 parts, PLA 0-40 parts, diisocyanate coupling agent 2.5-14 parts, and modified lignin 0.25-5 parts; The modified lignin is obtained by high-hydroxyl-value modification and thiol modification in sequence, the high-hydroxyl-value modification is a component with a hydroxyl content of >5.8 mmol / g in the fractionally extracted lignin, and the thiol modification introduces thiol groups through grafting reaction; The hydroxyl groups in the modified lignin react with the isocyanate groups of the diisocyanate coupling agent to form urethane bonds; The thiol groups in the modified lignin react with the isocyanate groups of the diisocyanate coupling agent to form thio urethane bonds.

[0011] Preferably, the weight average molecular weight of the high-hydroxyl-value modified lignin is 600-1000 g / mol.

[0012] Preferably, the high-hydroxyl-value modification is a component with a hydroxyl content of 5.8-6.3 mmol / g in the fractionally extracted lignin.

[0013] Preferably, the high-hydroxyl-value modification is a component with a hydroxyl content of 5.8-6.3 mmol / g in the fractionally extracted lignin.

[0014] Secondly, the application provides a preparation method of a high-strength and high-toughness PBAT-PLA dynamic crosslinking material which can be repeatedly processed, comprising the following steps: S1 dissolving alkali lignin in anhydrous ethanol, stirring, suction filtering and drying, and then crushing to obtain polyhydroxy lignin; S2 dissolving the polyhydroxy lignin and mercaptoacetic acid in acetone in a certain proportion, adding 4-dimethylaminopyridine and choline chloride, stirring, washing with dichloromethane, and then drying to obtain modified lignin; S3 blending PBAT, PLA, diisocyanate coupling agent and the modified lignin in a certain proportion to obtain a composite material; S4 hot-pressing and plasticizing the composite material to obtain a finished composite material.

[0015] Technical mechanism and beneficial effects of the application The high-strength and high-toughness PBAT-PLA dynamic crosslinking material provided by the application uses PBAT and PLA as main matrixes, so that the composite material has excellent strength and fracture toughness; in order to overcome the limitations of traditional blending and compatibilization methods, a small amount of alkali lignin is innovatively introduced, and multifunctional synergy is realized. The rigid benzene ring structure contained in the lignin molecule can effectively enhance the mechanical strength of the matrix material; the compatibilization function: the benzene and propanol structure unit of lignin has the effect of the benzene ring of PBAT, and the side group methoxy and polyhydroxypropyl enhance the compatibility with PLA; the dynamic crosslinking function: lignin is rich in hydroxyl (-OH) functional groups, and in the presence of diisocyanate coupling agent, the isocyanate group (-NCO) can react with the hydroxyl group of lignin, the hydroxyl group (-OH) or carboxyl group (-COOH) at the molecular chain end of PBAT and PLA, to form a crosslinking network with urethane bond (-NHCOO-) as the connecting point, to "bridge" PBAT and PLA, further strengthen the interface interaction, and form a "rigid and flexible" synergistic system; on the other hand, the urethane bond in the crosslinking network has dynamic reversibility at high temperature, which can promote the dynamic exchange and reconstruction of the dynamic crosslinking network during the hot-pressing forming process, and endow the material with excellent reworkability.

[0016] Further, the core of the present application is that the lignin is modified. Firstly, the present application modifies the lignin raw material with high hydroxyl value. This modification operation can form more hydroxyl groups to react with the isocyanate groups (-NCO) of diisocyanate to form more dynamic urethane bonds, thereby enhancing the dynamic reversibility of the material at high temperature. On the other hand, the increase of the hydroxyl content also provides sufficient reaction sites for the thiol grafting modification. Subsequently, the present application further introduces thiol groups by reacting mercaptoacetic acid with hydroxyl groups to modify the lignin into thiol-containing functional group-containing thiol lignin. Then, by reacting the thiol groups (-SH) with the isocyanate groups of diisocyanate, sulfur amine ester bonds (-NHCO-S-) are formed, which can act as "dynamic crosslinking points" and can undergo reversible bond exchange at high temperature, thereby imparting the material with repeatable processability.

[0017] In summary, the present application selects lignin with low molecular weight and high hydroxyl content as a multifunctional compatibilizer of biological origin, which can achieve good reinforcement and compatibilization functions, so that the material has high strength and high toughness. Meanwhile, the present application further modifies the lignin with high hydroxyl content by introducing thiol groups to obtain modified lignin, which can act as a multifunctional crosslinking agent. The dynamic crosslinking network containing dynamic urethane bonds and dynamic sulfur amine ester bonds can be formed by hot pressing, thereby not only imparting the composite material with remarkable mechanical properties of high strength, high toughness and high stability, but also having solvent resistance and reprocessability of thermoplastic materials. That is, the dynamic crosslinked material of the present application can still maintain good mechanical properties after being reshaped by hot pressing multiple times, so that it has remarkable practical application value in the field of controllable degradation structural materials such as disposable packaging, disposable tableware and mulch.

[0018] Further, the materials used in the present application have degradable properties. PBAT and PLA are both biodegradable polyesters and can be degraded by microorganisms in the natural environment. The modified lignin still has the property of biological origin and can maintain the overall degradability through the synergistic effect with PBAT and PLA. In addition, by purification with anhydrous ethanol and modification with mercaptoacetic acid, the industrial by-product lignin is converted into low molecular weight lignin with high reactivity, so that it changes from waste to "multifunctional crosslinking agent" to participate in the construction of dynamic crosslinking network, thereby improving the mechanical properties of the material and realizing the high-value application of waste. Moreover, the present application has no solvent pollution, is green and environmentally friendly, and the raw materials are easy to obtain, which can promote the development of the upstream industry.

[0019] Further, the method of introducing modified lignin and biological coupling agent to jointly construct a dynamic crosslinking network is also applicable to the reinforcement and toughening of PBAT. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0021] Figure 1 Stress-strain curves of the composite materials prepared for Example 1 to Example 3 and Comparative Example 4.

[0022] Figure 2 Stress-strain curves of the composite materials prepared for Example 4 to Example 6 and Comparative Example 5.

[0023] Figure 3 Stress-strain curves of the composite materials prepared for Example 11 and Comparative Example 7.

[0024] Figure 4 Remoldability test stress-strain curve of the composite material prepared for Example 1. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, they are all the conventional products that can be purchased in the market.

[0026] Example 1 In this embodiment, PBAT (purchased from Jinfa Technology Co., Ltd., weight average molecular weight 80000-100000 g / mol), PLA (purchased from NatureWorks Co., Ltd. in the United States, weight average molecular weight 100000-200000 g / mol).

[0027] High-hydroxyl-value modified lignin: Dissolve the alkali lignin in anhydrous ethanol, mechanically stir at room temperature for 2 h, the solid-liquid ratio of alkali lignin to anhydrous ethanol is 100 g: 500-600 mL, obtain a mixed solution, perform suction filtration on the mixed solution, concentrate the filtrate to 100 mL by rotary evaporation, pour the concentrated solution into an evaporating dish for volatilization, after volatilizing the solvent, put the obtained solid into a vacuum oven for drying for 4 days, then perform crushing, obtain high-hydroxyl low-molecular-weight lignin, the molecular weight of the high-hydroxyl low-molecular-weight lignin is 600-1000 g / mol; the hydroxyl content is 5.8-6.3 mmol / g.

[0028] Modified high-hydroxyl low-molecular-weight lignin: Pre-quantitative by weight parts: mercaptoacetic acid 5 parts, the above high-hydroxyl low-molecular-weight lignin 70 parts, 4-dimethylaminopyridine 0.5 parts, acetone 100 parts, choline chloride 10 parts, stirring at 40°C for 2 days, followed by spin-drying, washing with dichloromethane, and then drying to obtain modified lignin with a weight average molecular weight of 600-1000 g / mol to prepare a dynamic cross-linked material.

[0029] Preparation of a composite material: PBAT, PLA and modified lignin were placed in a vacuum oven and dried for 10 h to remove residual water.

[0030] PBAT 35 g and PLA 15 g were weighed and added to a Banbury mixer for melt plasticization for 1 min, followed by the addition of 1.26 g of pentamethylene diisocyanate (PDI) for melt blending for 10 min, and then the addition of 0.5 g of modified lignin for blending for 5 min to obtain a composite material.

[0031] Hot-press plasticization: The above composite material was placed in a 10 mm x 10 mm x 0.5 mm hollow mold, and vulcanization and cross-linking were performed using a vacuum press machine with the following specific parameter conditions: plasticization at 175°C for 25 min, and vulcanization at a pressurized pressure of 5 MPa for 2 h.

[0032] Example 2 The difference between this example and Example 1 is that in the step of preparing a composite material, the amount of PDI added is 3.15 g, and the amount of modified lignin added is 1.5 g.

[0033] Example 3 The difference between this example and Example 1 is that in the step of preparing a composite material, the amount of PDI added is 7.04 g, and the amount of modified lignin added is 2.5 g.

[0034] Example 4 The difference between this example and Example 1 is that PBAT (purchased from Tongcheng New Material Co., Ltd., weight average molecular weight 90000-110000 g / mol) and PLA (purchased from Nanjing Well Co., Ltd., weight average molecular weight 96000-150000 g / mol) are used; the amount of PDI added is 1.37 g, and the amount of modified lignin added is 0.5 g.

[0035] Example 5 The difference between this example and Example 4 is that the amount of PDI added is 3.26 g, and the amount of modified lignin added is 1.5 g.

[0036] Example 6 The difference between this example and Example 4 is that the amount of PDI added is 6.83 g, and the amount of modified lignin added is 2.5 g.

[0037] Example 7 The difference between this example and Example 1 is that in the step of preparing the composite material, PDI is replaced by isophorone diisocyanate.

[0038] Example 8 The difference between this example and Example 1 is that in the step of preparing the composite material, PDI is replaced by diphenylmethane-4,4'-diisocyanate.

[0039] Example 9 The difference between this example and Example 1 is that the solid-liquid ratio of alkali lignin to anhydrous ethanol is 100g:550mL; mercaptoacetic acid 20 parts, high-hydroxyl low-molecular-weight lignin 85 parts, 4-dimethylamino pyridine 2.5 parts, acetone 250 parts, choline chloride 15 parts, and stirring reaction at 40°C for 52h.

[0040] In the step of preparing the composite material, the amount of PBAT is 30g, the amount of PLA is 20g, the amount of PDI is 1.26g, and the amount of modified lignin is 0.72g.

[0041] In the step of hot-pressing plasticization, the specific parameter conditions are: plasticization at 180°C for 22min, and vulcanization at a pressurized pressure of 6MPa for 2h.

[0042] Example 10 The difference between this example and Example 1 is that the solid-liquid ratio of alkali lignin to anhydrous ethanol is 100g:600mL; mercaptoacetic acid 30 parts, high-hydroxyl low-molecular-weight lignin 95 parts, 4-dimethylamino pyridine 5 parts, acetone 500 parts, choline chloride 30 parts, and stirring reaction at 45°C for 60h.

[0043] In the step of preparing the composite material, the amount of PBAT is 45g, the amount of PLA is 5g, the amount of PDI is 3.36g, and the amount of modified lignin is 0.13g.

[0044] In the step of hot-pressing plasticization, the specific parameter conditions are: plasticization at 185°C for 22min, and vulcanization at a pressurized pressure of 8MPa for 2.5h.

[0045] Example 11 The difference between this example and Example 1 is that in the step of preparing the composite material, PBAT and modified lignin are placed in a vacuum oven for drying for 10h to remove residual water. Then PBAT 50g is weighed and added to the internal mixer for melt plasticization for 1min, followed by the addition of 3.36g of PDI for melt blending for 10min, and then the introduction of 1.50g of modified lignin for blending for 5min.

[0046] Hot-pressing plasticization: The above composite material was placed in a 10 mm x 10 mm x 0.5 mm hollow mold, and vulcanization and crosslinking were performed by using a vacuum press machine, with specific parameter conditions being: plasticization for 25 min at 180°C, and vulcanization for 2.5 h under a pressurized pressure of 5 MPa.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that no modified lignin is added in the step of preparing the composite material.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that no thiol modification is performed on the high-hydroxyl low-molecular-weight lignin, and the high-hydroxyl low-molecular-weight lignin is directly used to prepare the composite material.

[0049] Comparative Example 3 The difference between this comparative example and Example 1 is that no purification treatment of the alkali lignin by using anhydrous ethanol is performed, and the alkali lignin is directly used to prepare the composite material.

[0050] Comparative Example 4 The difference between this comparative example and Example 1 is that neither PDI nor modified lignin is added in the step of preparing the composite material.

[0051] Comparative Example 5 The difference between this comparative example and Example 4 is that neither PDI nor modified lignin is added in the step of preparing the composite material.

[0052] Comparative Example 6 The difference between this comparative example and Example 11 is that no modified lignin is added in the step of preparing the composite material.

[0053] Comparative Example 7 The difference between this comparative example and Example 11 is that neither PDI nor modified lignin is added in the step of preparing the composite material.

[0054] Test Example 1 The mechanical properties and solvent resistance of the samples of Examples 1-11 and Comparative Examples 1-7 were determined; wherein the mechanical properties were determined by a tensile test, with the tensile test conditions being: a temperature of 25°C; a load of 50 N; and a pulling speed of 50 mm / min; and wherein the test and calculation methods for the swelling rate and the gel content were as follows: the sample was hot-pressed into a sheet, and each fixed disc was cut and accurately weighed (W0) W d ). The weighed sample was completely immersed in excess solvent (dichloromethane), and the container was placed in a constant temperature (25°C) environment, and the sample was taken out regularly, the excess solvent on the surface was absorbed with filter paper, and the mass of the sample in the swelling state was quickly weighed until the swelling reached a constant mass (W1) Ws ), and then the swollen sample was taken out and dried to obtain the net weight (W2) W n ), and the swelling rate was W s / W d , and the gel content was W n / W d The determination results are shown in Table 1.

[0055] Table 1: Performance determination results of samples

[0056] As shown in Table 1, the tensile strength of the modified lignin in Examples 1 to 11 is 36.5-56.3 MPa, the elongation at break is 643-1873%, the swelling rate is 1921-5611%, and the gel content is 38-81.1%. It can be seen that the introduction of modified lignin in the examples significantly improves the mechanical strength, toughness and solvent resistance of the material.

[0057] In Comparative Example 1, no modified lignin is added, and the hydroxyl and mercapto groups of the modified lignin can react with the isocyanate groups of the diisocyanate coupling agent to form urethane bonds and thio urethane bonds, enhancing the interfacial bonding of PBAT and PLA and constructing a dynamic crosslinking network. Without the addition, the crosslinking effect is missing, the interfacial compatibility is reduced, and the tensile strength (25.3 MPa) and elongation at break (350%) are significantly lower than those of Example 1 (40.3 MPa, 805%).

[0058] In Comparative Example 2, only the hydroxyl group is modified, and the mercapto group is not modified. In the examples, the modified lignin is modified by "hydroxyl + mercapto" groups, which can react with the coupling agent through two groups to improve the crosslinking density. When only the hydroxyl group is modified, the reaction sites are reduced (lacking thio urethane bonds between mercapto groups and isocyanate groups), and the crosslinking degree is insufficient, so the gel content (31%) is lower than that of Example 1 (38.4%), and the elongation at break (700%) is also slightly lower.

[0059] In Comparative Example 3, the alkali lignin is not purified, and the alkali lignin not purified with anhydrous ethanol has low purity, low hydroxyl content, and wide molecular weight distribution, which cannot effectively react with the coupling agent, resulting in weak interfacial bonding, and the tensile strength (30.6 MPa) and elongation at break (450%) are much lower than those of Example 1.

[0060] Without coupling agent and modified lignin in Comparative Example 4 and Comparative Example 5, PBAT and PLA are not compatible by itself, and the mechanical properties are greatly reduced due to the lack of crosslinking network support. For example, the tensile strength (20.2 MPa) of Comparative Example 4 is only 50% of that of Example 1, and the elongation at break (466%) is less than 60% of that of Example 1.

[0061] Without modified lignin in Comparative Example 6, based on Example 11, Example 11 has the best performance (tensile strength 56.3 MPa, elongation at break 1874%) due to the strong crosslinking effect of modified lignin and coupling agent; without modified lignin, the crosslinking is insufficient, and the elongation at break is reduced to 900%, and the tensile strength is reduced to 25.3 MPa.

[0062] Without coupling agent and modified lignin in Comparative Example 7, based on Example 11, the crosslinking agent and modified lignin are completely missing, and there is no chain extension reaction between the amine ester bond segments of PBAT molecules, resulting in the worst mechanical properties (tensile strength 22.1 MPa, elongation at break 822.6%), which are much lower than those of Example 11.

[0063] Figure 1 In Table 2, PABT / PLA, PBAT / PLA / L1, PBAT / PLA / L3 and PBAT / PLA / L5 correspond to the composite materials prepared in Comparative Example 4, Example 1, Example 2 and Example 3, respectively; and Figure 1 It can be seen that the tensile strength and elongation at break of PBAT / PLA / L1, PBAT / PLA / L3 and PBAT / PLA / L5 are significantly higher than those of PBAT / PLA.

[0064] Figure 2 In Table 3, PABT / PLA, PBAT / PLA / L1, PBAT / PLA / L3 and PBAT / PLA / L5 correspond to the composite materials prepared in Comparative Example 5, Example 4, Example 5 and Example 6, respectively; and Figure 2 It can be seen that the tensile strength and elongation at break of PBAT / PLA / L1, PBAT / PLA / L3 and PBAT / PLA / L5 are significantly higher than those of PBAT / PLA.

[0065] Figure 3 In Table 4, PBAT corresponds to Comparative Example 7, and PBAT / L1 corresponds to Example 11, and Figure 3 It can be seen that the use of modified lignin can significantly improve the tensile strength and elongation at break of PBAT.

[0066] Test Example 2 With the sample of Example 1, its remolding performance was determined, and the specific test method was as follows: the sample after hot pressing or tension was cut into fragments, and then was placed into a hollow mold with a size of 10mmx10mmx0.5mm again, and then was subjected to melt hot pressing to promote rearrangement of the topological network by using a vacuum pressing machine, and the specific parameter conditions were as follows: plasticization for 25min at 180℃, and vulcanization for 30min under a pressing pressure of 5MPa, and the test result was as shown in Figure 4 .

[0067] Figure 4 In the figure, the stress-strain curves of the initial sample (i.e. the initial sample without repeated test, recycling or other special treatment), the once-remolded sample, the twice-remolded sample and the thrice-remolded sample were compared.

[0068] According to Figure 4 , the stress-strain curves of the multiple remolding were consistent with the overall trend of the stress-strain curve of the initial sample, which indicated that the material had similar response rules in the whole process of stress deformation, and thus it could be seen that the composite material prepared by the application still had excellent mechanical properties such as high strength and high toughness after multiple remolding.

[0069] The above is only the preferred embodiment of the application, and is not used to limit the application, and for those skilled in the art, the application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material, characterized in that: The raw materials include, by weight: 60-100 parts of PBAT, 0-40 parts of PLA, 2.5-14 parts of diisocyanate coupling agent and 0.25-5 parts of modified lignin; The modified lignin is obtained by sequentially high hydroxyl value modification and thiol modification, wherein the high hydroxyl value modification is to fractionally extract components with a hydroxyl content greater than 5.8 mmol / g in the lignin, and the thiol modification is to introduce thiol groups through a grafting reaction; The hydroxyl groups in the modified lignin react with the isocyanate groups in the diisocyanate coupling agent to form urethane bonds; The mercapto groups in the modified lignin react with the isocyanate groups of the diisocyanate coupling agent to form a thiourethane bond.

2. A method for preparing the reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 1, characterized in that: The steps include: S1: dissolving alkali lignin in anhydrous ethanol, stirring, filtering and drying, and then crushing polyhydroxy lignin; S2: dissolving the polyhydroxy lignin and thioglycolic acid in acetone in a certain proportion, adding 4-dimethylaminopyridine and choline chloride, stirring, washing with dichloromethane, and drying to obtain modified lignin; S3: PBAT, PLA, a diisocyanate coupling agent, and the modified lignin are mixed in proportion to prepare a composite material; S4: hot pressing and plasticizing the composite material to obtain a finished composite material.

3. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S1, the solid-liquid ratio of the alkali lignin to the anhydrous ethanol is 100 g:500-600 mL.

4. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 3, characterized in that: In step S2, the weight average molecular weight of the modified lignin is 540 to 1900 g / mol.

5. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S2, the polyhydroxy lignin is 70 to 95 parts, the thioglycolic acid is 5 to 30 parts, the acetone is 100 to 500 parts, the 4-dimethylaminopyridine is 0.5 to 5 parts, and the choline chloride is 10 to 30 parts in parts by weight.

6. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S2, the stirring reaction temperature is 40-45° C.; the stirring reaction time is 48-60 h.

7. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S3, the diisocyanate coupling agent includes at least one of pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane-4,4'-diisocyanate or toluene diisocyanate.

8. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S3, by weight, the PBAT is 60 to 100 parts, the PLA is 0 to 40 parts, the diisocyanate coupling agent is 2.5 to 14 parts, and the modified lignin is 0.25 to 5 parts.

9. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: In step S4, the hot pressing plasticization includes the following parameters: heating temperature of 180-185° C., plasticization time of 22-25 min, pressure of 5-8 MPa, and pressurization time of 2-2.5 h.

10. The method for preparing a reproducible high-strength and high-toughness PBAT-PLA dynamic cross-linked material according to claim 2, characterized in that: The invention has the characteristics of being repeatable, and the repeatable molding conditions include: a heating temperature of 180 to 185° C., a plasticizing time of 22 to 25 minutes, a pressure of 5 MPa, and a pressurized vulcanization time of 30 minutes.

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