A reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinking material and its preparation method

Abstract

This invention relates to the field of polymer materials technology, and provides a reprocessable, high-strength, high-toughness PBAT-PLA dynamic crosslinked material and its preparation method. The material comprises PBAT, PLA, a diisocyanate coupling agent, and modified lignin. The modified lignin is obtained by sequentially modifying with high hydroxyl value and then with thiol groups. High hydroxyl value modification involves graded extraction of components with high hydroxyl group content from the lignin, while thiol group modification introduces thiol groups through a grafting reaction. The diisocyanate coupling agent contains isocyanate groups. Hydroxyl groups react with isocyanate groups to form urethane bonds; thiol groups react with isocyanate groups to form thiourethane bonds. The preparation method includes: blending PBAT, PLA, the diisocyanate coupling agent, and modified lignin in a specific ratio to obtain a composite material; and hot-pressing and plasticizing the composite material to obtain the finished composite material. This preparation method is green and environmentally friendly, easy to industrialize, and the obtained dynamic crosslinked composite material exhibits excellent mechanical properties and reprocessing and remodeling performance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically, it relates to a reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinked material and its preparation method. Background Technology

[0002] Currently, global plastic pollution continues to worsen, and the persistence of traditional plastics in the environment and the microplastic risks they generate pose a serious threat to ecosystems. Against this backdrop, polylactic acid (PLA) and polybutylene adipate / terephthalate (PBAT), as the dual cores of biodegradable materials, are driving the transformation towards plastic substitution through differentiated pathways.

[0003] PBAT can be prepared through petroleum-based, bio-based, or a combination of both. It has excellent ductility, with an elongation at break of 300%–900%. Its film-forming flexibility is close to that of low-density polyethylene (LDPE), making it dominant in flexible packaging applications such as mulch films and shopping bags. However, its tensile strength is not high (only 15–25 MPa), its heat distortion temperature is low (<100℃), and the aromatic structure in its molecular chain leads to a slow degradation rate in natural environments. It requires industrial composting conditions (58–68℃) to achieve efficient decomposition.

[0004] PLA is a rigid thermoplastic material primarily based on bio-based properties, with its main raw materials being renewable resources such as corn starch. It can be formed through direct polycondensation of lactic acid or ring-opening polymerization of lactide. It possesses high transparency (transmittance > 90%), high tensile strength (50–70 MPa), and a relatively high melting point (170–180°C), making it suitable for rigid products such as tableware, fibers, and 3D printing. However, its rigid molecular chain leads to significant brittleness, with an elongation at break of less than 10%, and its low melt strength and slow crystallization rate limit its application in blown film processing and flexible packaging.

[0005] The strong complementarity of the two properties has spurred the large-scale application of PBAT / PLA composites. The high rigidity of PLA can compensate for the insufficient strength of PBAT, while the segmental flexibility of PBAT can effectively suppress the brittle fracture of PLA. However, due to the significant differences in their solubility parameters and melt viscosity, their compatibility is poor, interfacial adhesion is weak, and direct physical blending easily leads to phase separation, making it difficult for the composites to effectively achieve the expected synergistic reinforcement and toughening effects.

[0006] To address compatibility issues, existing technologies often employ the addition of compatibilizers (such as maleic anhydride grafts) or inorganic fillers (such as nanoclay). However, these methods suffer from drawbacks such as high modifier costs, the introduction of non-biobased components reducing material biodegradability, and unsatisfactory strength and toughness. Covalent cross-linking strategies can effectively improve compatibility and significantly enhance strength and toughness; however, the formation of chemically cross-linked structures makes the material difficult to recycle and reuse.

[0007] Therefore, based on the above description, there is an urgent need to develop a reprocessable, high-strength, high-toughness PBAT-PLA dynamic crosslinking material and its preparation method based on bio-based materials. Summary of the Invention

[0008] Technical problem solved by the present invention

[0009] Existing methods use compatibilizers to improve the compatibility of PBAT and PLA, but these methods suffer from problems such as high cost of modifiers, introduction of non-bio-based components that reduce the biodegradability of materials, and insufficient strength and toughness. Covalent crosslinking also presents technical challenges such as difficulty in reshaping and processing.

[0010] The technical solution adopted in this invention

[0011] To address the aforementioned shortcomings, the present invention aims to provide a reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinking material and its preparation method.

[0012] The details are as follows:

[0013] First, the present invention provides a reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinking material, which, by weight, comprises the following raw materials: 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.

[0014] The modified lignin is obtained by sequentially modifying it with high hydroxyl value and then with thiol group. The high hydroxyl value modification is carried out by fractional extraction of lignin with a hydroxyl content >5.8 mmol / g, and the thiol group modification is carried out by introducing thiol groups through a grafting reaction.

[0015] The hydroxyl groups in the modified lignin react with the isocyanate groups of the diisocyanate coupling agent to form urethane bonds.

[0016] The thiol groups in the modified lignin react with the isocyanate groups in the diisocyanate coupling agent to form thiourethane bonds.

[0017] The weight-average molecular weight of the lignin modified with high hydroxyl value is 540–1900 g / mol.

[0018] Preferably, the weight-average molecular weight of the lignin modified with high hydroxyl value is 600-1000 g / mol.

[0019] Preferably, the high hydroxyl value modification is a fraction of lignin with a hydroxyl content of 5.8 to 6.3 mmol / g obtained from graded extraction.

[0020] Second, this invention provides a method for preparing a reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinked material, comprising the following steps:

[0021] S1 dissolves alkali lignin in anhydrous ethanol, and after stirring, filtration and drying, it is pulverized into polyhydroxy lignin.

[0022] S2 dissolves the polyhydroxy lignin and mercaptoacetic acid in acetone in a certain proportion, adds 4-dimethylaminopyridine and choline chloride, stirs, washes with dichloromethane, and then dries to obtain modified lignin.

[0023] S3 is prepared by blending PBAT, PLA, diisocyanate coupling agent and the modified lignin in proportion to obtain a composite material;

[0024] S4 involves hot-pressing and plasticizing the composite material to obtain the finished composite material.

[0025] Technical Mechanism and Beneficial Effects of the Invention

[0026] The high-strength and high-toughness PBAT-PLA dynamic crosslinked material provided by this invention uses PBAT and PLA as the main matrix, enabling the composite material to possess both excellent strength and fracture toughness. To overcome the limitations of traditional blending compatibilization methods, this invention innovatively introduces a small amount of alkaline lignin, achieving multifunctional synergy.

[0027] Enhancement function: The rigid benzene ring structure abundant in lignin molecules can effectively enhance the mechanical strength of the matrix material; Compatibilization function: Lignin can effectively improve the interfacial compatibility between the two, and its phenylpropane structural unit has similarity to the benzene ring of PBAT. The side groups methoxy and polyhydroxypropyl enhance compatibility with PLA; dynamic cross-linking function: lignin is rich in hydroxyl (-OH) functional groups. In the presence of diisocyanate coupling agents, its isocyanate groups (-NCO) can react with the hydroxyl groups of lignin, the hydroxyl (-OH) or carboxyl groups (-COOH) at the ends of the molecular chains of PBAT and PLA to form a cross-linking network with urethane bonds (-NHCOO-) as the connection points, "bridging" PBAT and PLA, further strengthening the interfacial interaction, and forming a synergistic system that combines rigidity and flexibility; on the other hand, the urethane bonds in this cross-linking network have dynamic reversibility at high temperatures, which can promote the dynamic exchange and reconstruction of the dynamic cross-linking network during hot pressing, giving the material excellent reprocessability.

[0028] Furthermore, the core of this invention is the modification of lignin. First, the lignin raw material is modified with a high hydroxyl value. This modification, on the one hand, allows for the formation of more dynamic urethane bonds by reacting more hydroxyl groups with the isocyanate groups (-NCO) of diisocyanate, enhancing the dynamic reversibility of the material at high temperatures; on the other hand, the increased hydroxyl content also provides sufficient reaction sites for thiol grafting modification. Subsequently, this invention further introduces thiol groups, modifying lignin into thiol-functionalized lignin through the reaction of thioglycolic acid with hydroxyl groups. Then, through the reaction of thiol groups (-SH) with the isocyanate groups of diisocyanate, thiourethane bonds (-NHCO-S-) are formed, which can act as "dynamic crosslinking points" and undergo reversible bond exchange at high temperatures, thereby endowing the material with reprocessability.

[0029] In summary, this invention selects low-molecular-weight lignin with high hydroxyl content as a bio-based multifunctional compatibilizer, achieving excellent reinforcement and compatibilization functions, resulting in materials with high strength and high toughness. Furthermore, this invention further modifies the high-hydroxyl-content lignin with thiol groups to obtain modified lignin, which can act as a multifunctional crosslinking agent. It can form a dynamic crosslinking network containing dynamic urethane and dynamic thiourethane bonds through hot pressing, thereby endowing the composite material with not only significant high strength, high toughness, and high stability mechanical properties, but also solvent resistance and the reprocessability of thermoplastic materials. That is, the dynamically crosslinked material of this invention can still maintain good mechanical properties after multiple hot-pressing reshaping, making it of significant practical application value in the field of controllable degradable structural materials such as disposable packaging, disposable tableware, and agricultural films.

[0030] Furthermore, the materials used in this invention possess biodegradable properties. Both PBAT and PLA are biodegradable polyesters that can be degraded by microorganisms in the natural environment. The modified lignin retains its bio-based properties and maintains overall biodegradability through synergistic effects with PBAT and PLA. In addition, through purification with anhydrous ethanol and modification with mercaptoacetic acid, industrial byproduct lignin is transformed into a highly reactive low-molecular-weight lignin, turning it from waste into a "multifunctional crosslinking agent" to participate in the construction of a dynamic crosslinking network. This not only improves the mechanical properties of the material but also enables the high-value application of waste. Moreover, this invention is solvent-free, environmentally friendly, and uses readily available raw materials, which can promote the development of upstream industries.

[0031] Furthermore, the method of constructing a dynamic cross-linked network by introducing modified lignin and bio-based coupling agents is also applicable to the reinforcement and toughening of PBAT. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 The stress-strain curves are for the composite materials prepared in Examples 1 to 3 and Comparative Example 4.

[0034] Figure 2 The stress-strain curves are for the composite materials prepared in Examples 4 to 6 and Comparative Example 5.

[0035] Figure 3 The stress-strain curves of the composite materials prepared in Example 11 and Comparative Example 7 are shown.

[0036] Figure 4 The stress-strain curves for remodeling tests of the composite material prepared in Example 1 are shown. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0038] Example 1

[0039] In this embodiment, PBAT (purchased from Kingfa Science & Technology Co., Ltd., with a weight-average molecular weight of 80,000-100,000 g / mol) and PLA (purchased from NatureWorks, Inc., with a weight-average molecular weight of 100,000-200,000 g / mol) were used.

[0040] High hydroxyl value modified lignin:

[0041] Alkali lignin was dissolved in anhydrous ethanol and mechanically stirred at room temperature for 2 hours. The solid-liquid ratio of alkali lignin to anhydrous ethanol was 100 g: 500–600 mL to obtain a mixed solution. The mixed solution was filtered, and the filtrate was concentrated to 100 mL by rotary evaporation. The concentrated solution was poured into an evaporating dish for evaporation. After the solvent was evaporated, the resulting solid was placed in a vacuum oven and dried for 4 days. Then it was pulverized to obtain high-hydroxyl low-molecular-weight lignin with a molecular weight of 600–1000 g / mol and a hydroxyl content of 5.8–6.3 mmol / g.

[0042] Modification of high-hydroxyl, low-molecular-weight lignin:

[0043] Based on the following weight proportions, pre-weigh 5 parts of thioglycolic acid, 70 parts of the above-mentioned high-hydroxyl low-molecular-weight lignin, 0.5 parts of 4-dimethylaminopyridine, 100 parts of acetone, and 10 parts of choline chloride. Stir and react at 40°C for 2 days, then evaporate to dryness, wash with dichloromethane, and dry again to obtain a modified lignin dynamic crosslinking material with a weight average molecular weight of 600-1000 g / mol.

[0044] Preparation of composite materials:

[0045] PBAT, PLA and modified lignin were placed in a vacuum oven and dried for 10 hours to remove residual water.

[0046] Weigh 35g of PBAT and 15g of PLA, add them to a mixer and melt-plasticize for 1 min. Then add 1.26g of pentamethylene diisocyanate (PDI) and melt-blend for 10 min. Next, add 0.5g of modified lignin and blend for 5 min to obtain the composite material.

[0047] Hot pressing plasticizing:

[0048] The above composite material was placed in a hollow mold of 10mm×10mm×0.5mm and vulcanized and crosslinked using a vacuum press. The specific parameters were: plasticizing at 175℃ for 25 minutes and vulcanizing at a pressure of 5MPa for 2 hours.

[0049] Example 2

[0050] The difference between this embodiment and Example 1 is that in the preparation of the composite material, the amount of PDI added is 3.15g and the amount of modified lignin added is 1.5g.

[0051] Example 3

[0052] The difference between this embodiment and Example 1 is that in the preparation of the composite material, the amount of PDI added is 7.04g and the amount of modified lignin added is 2.5g.

[0053] Example 4

[0054] The difference between this embodiment and Example 1 is that PBAT (purchased from Tongcheng New Materials Co., Ltd., weight average molecular weight 90000-110000 g / mol), PLA (purchased from Nanjing Weier Co., Ltd., weight average molecular weight 96000-150000 g / mol), PDI added amount is 1.37 g, and modified lignin added amount is 0.5 g.

[0055] Example 5

[0056] The difference between this embodiment and Embodiment 4 is that the amount of PDI added is 3.26g and the amount of modified lignin added is 1.5g.

[0057] Example 6

[0058] The difference between this embodiment and Embodiment 4 is that the amount of PDI added is 6.83g and the amount of modified lignin added is 2.5g.

[0059] Example 7

[0060] The difference between this implementation and Example 1 is that in the step of preparing the composite material, PDI is replaced with isophorone diisocyanate.

[0061] Example 8

[0062] The difference between this embodiment and Example 1 is that in the step of preparing the composite material, PDI is replaced with diphenylmethane-4,4'-diisocyanate.

[0063] Example 9

[0064] The difference between this embodiment and Example 1 is that the solid-liquid ratio of alkali lignin to anhydrous ethanol is 100g:550mL; 20 parts of thioglycolic acid, 85 parts of high hydroxyl low molecular weight lignin, 2.5 parts of 4-dimethylaminopyridine, 250 parts of acetone, 15 parts of choline chloride, and the reaction is stirred at 40°C for 52h.

[0065] In the preparation of the composite material, 30g of PBAT, 20g of PLA, 1.26g of PDI, and 0.72g of modified lignin were weighed.

[0066] In the hot pressing plasticizing step, the specific parameters are as follows: plasticizing at 180℃ for 22 minutes, and vulcanizing at a pressure of 6MPa for 2 hours.

[0067] Example 10

[0068] The difference between this embodiment and Example 1 is that the solid-liquid ratio of alkali lignin to anhydrous ethanol is 100g:600mL; 30 parts of thioglycolic acid, 95 parts of high hydroxyl low molecular weight lignin, 5 parts of 4-dimethylaminopyridine, 500 parts of acetone, 30 parts of choline chloride, and the reaction is carried out at 45°C for 60h.

[0069] In the preparation of the composite material, 45g of PBAT, 5g of PLA, 3.36g of PDI, and 0.13g of modified lignin were weighed.

[0070] In the hot pressing plasticizing step, the specific parameters are as follows: plasticizing at 185℃ for 22 minutes, and vulcanizing at 8MPa pressure for 2.5 hours.

[0071] Example 11

[0072] The difference between this embodiment and Embodiment 1 is that, in the preparation of the composite material, PBAT and modified lignin are dried in a vacuum oven for 10 hours to remove residual water. Then, 50g of PBAT is weighed and added to a mixer for melt plasticizing for 1 minute, followed by the addition of 3.36g of PDI for melt blending for 10 minutes, and then 1.50g of modified lignin is introduced and blended for 5 minutes.

[0073] Hot pressing plasticizing:

[0074] The above composite material was placed in a hollow mold of 10mm×10mm×0.5mm and vulcanized and crosslinked using a vacuum press. The specific parameters were: plasticizing at 180℃ for 25 minutes and vulcanizing at a pressure of 5MPa for 2.5 hours.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that no modified lignin was added in the steps of preparing the composite material.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that the high-hydroxyl low-molecular-weight lignin is not modified with thiol groups, and the high-hydroxyl low-molecular-weight lignin is directly used to prepare the composite material.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that alkali lignin is not purified with anhydrous ethanol, but is directly used to prepare the composite material.

[0081] Comparative Example 4

[0082] The difference between this comparative example and Example 1 is that neither PDI nor modified lignin was added in the steps of preparing the composite material.

[0083] Comparative Example 5

[0084] The difference between this comparative example and Example 4 is that neither PDI nor modified lignin was added in the steps of preparing the composite material.

[0085] Comparative Example 6

[0086] The difference between this comparative example and Example 11 is that no modified lignin was added in the steps of preparing the composite material.

[0087] Comparative Example 7

[0088] The difference between this comparative example and Example 11 is that neither PDI nor modified lignin was added in the steps of preparing the composite material.

[0089] Experimental Example 1

[0090] Using Examples 1-11 and Comparative Examples 1-7 as samples, the mechanical properties and solvent resistance of the samples were determined. The mechanical properties were determined by tensile testing under the following conditions: temperature 25°C; load 50 N; tensile speed 50 mm / min. The swelling rate and gel content were tested and calculated as follows: the samples were hot-pressed into sheets, cut into fixed circular pieces, and the initial mass of the circular samples was accurately weighed. W d Completely immerse the weighed sample in excess solvent (dichloromethane), place the container in a constant temperature (25°C) environment, periodically remove the sample, gently blot off excess solvent adhering to the surface with filter paper, and quickly weigh the sample in the swollen state until the swelling reaches a constant mass. W s Then, the swollen sample was removed, thoroughly dried, and the net weight was obtained. W n The swelling ratio is W s / W d The gel content is W n / W d The measurement results are shown in Table 1.

[0091] Table 1 Results of Sample Performance Measurement

[0092]

[0093] As shown in Table 1, the tensile strength of Examples 1 to 11 of the present invention 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%. This indicates that the introduction of modified lignin in the examples significantly improves the mechanical strength, toughness, and solvent resistance of the materials.

[0094] In Comparative Example 1, no modified lignin was added. The hydroxyl and thiol groups of the modified lignin could react with the isocyanate groups of the diisocyanate coupling agent to form urethane and thiourethane bonds, enhancing the interfacial bonding between PBAT and PLA and constructing a dynamic cross-linked network. Without the addition of lignin, the cross-linking effect was absent, the interfacial compatibility decreased, and the tensile strength (25.3 MPa) and elongation at break (350%) were significantly lower than those in Example 1 (40.3 MPa, 805%).

[0095] In Comparative Example 2, only hydroxyl modification was performed without thiol modification. In the example, the modified lignin underwent dual modification with "hydroxyl + thiol", which can increase the crosslinking density by reacting with the coupling agent through the two groups. However, when only hydroxyl modification was performed, the number of reaction sites decreased (the thiourethane bond between thiol and isocyanate group was lacking), the degree of crosslinking was insufficient, the gel content (31%) was lower than that of Example 1 (38.4%), and the elongation at break (700%) was also slightly lower.

[0096] In Comparative Example 3, the alkali lignin that was not purified with anhydrous ethanol had low purity, low hydroxyl content, and a wide molecular weight distribution, which made it unable to react effectively with the coupling agent. This resulted in weak interfacial bonding, and the tensile strength (30.6 MPa) and elongation at break (450%) were much lower than those in Example 1.

[0097] In Comparative Examples 4 and 5, no coupling agent or modified lignin was added. Without coupling agent and modified lignin, PBAT and PLA have poor compatibility, lack cross-linking network support, and their mechanical properties decrease significantly. For example, the tensile strength (20.2 MPa) of Comparative Example 4 is only 50% of that of Example 1, and its elongation at break (466%) is less than 60% of that of Example 1.

[0098] In Comparative Example 6, no modified lignin was added. Based on Example 11, Example 11 had the best performance (tensile strength 56.3 MPa, elongation at break 1874%) due to the strong cross-linking effect between the modified lignin and the coupling agent. Without the addition of modified lignin, the cross-linking was insufficient, and the elongation at break dropped to 900% and the tensile strength dropped to 25.3 MPa.

[0099] Comparative Example 7, without coupling agent and modified lignin, is based on Example 11. It completely lacks crosslinking agent and modified lignin, and the PBAT intermolecular amine ester bond segments have no chain extension reaction, resulting in the worst mechanical properties (tensile strength 22.1 MPa, elongation at break 822.6%), which are far lower than those of Example 11.

[0100] Figure 1 In this context, PABT / PLA, PBAT / PLA / L1, PBAT / PLA / L3, and PBAT / PLA / L5 correspond to the composite materials prepared in Example 4, Example 1, Example 2, and Example 3, respectively; [The remaining text appears to be a fragmented and incomplete sentence, possibly due to OCR errors. A more accurate translation would require the full context.] 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.

[0101] Figure 2 In this context, PABT / PLA, PBAT / PLA / L1, PBAT / PLA / L3, and PBAT / PLA / L5 correspond to the composite materials prepared in Example 5, Example 4, Example 5, and Example 6, respectively; [The remaining text appears to be incomplete and requires further context.] Figure 2It 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.

[0102] Figure 3 In the example, PBAT corresponds to Example 7, and PBAT / L1 corresponds to Example 11. Figure 3 It is known that the use of modified lignin can significantly improve the tensile strength and elongation at break of PBAT.

[0103] Experimental Example 2

[0104] Using Example 1 as the sample, its reshaping performance was determined. The specific test method was as follows: the sample after hot pressing or stretching was cut into fragments and placed back into a 10mm×10mm×0.5mm hollow mold. A vacuum press was used for melt hot pressing to promote topological network rearrangement. The specific parameters were: plasticizing at 180℃ for 25 minutes, and vulcanizing at a pressure of 5MPa for 30 minutes. The test results are as follows: Figure 4 As shown.

[0105] Figure 4 In the figure, “PBAT / PLA / L1” indicates that the test sample is the composite material prepared in Example 1; the figure compares the stress-strain curves of the initial sample (i.e., the initial sample that has not undergone repeated testing, recycling or other special treatment), the first reprocessed sample, the second reprocessed sample, and the third reprocessed sample.

[0106] according to Figure 4 It can be seen that the stress-strain curves of the reshaped samples have the same overall trend as those of the initial sample, indicating that the material has similar response laws throughout the entire process of deformation under stress. Thus, the composite material prepared by this invention still possesses excellent mechanical properties such as high strength and high toughness after multiple reshaping processes.

[0107] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A reprocessable, high-strength, high-toughness PBAT-PLA dynamic crosslinking material, characterized in that, By weight, it includes the following raw materials: 60-100 parts PBAT, 0-40 parts PLA, 2.5-14 parts diisocyanate coupling agent and 0.25-5 parts modified lignin; The modified lignin is obtained by sequentially modifying it with high hydroxyl value and then with thiol group. The high hydroxyl value modification is carried out by fractional extraction of lignin with a hydroxyl content >5.8 mmol / g, and the thiol group modification is carried out by introducing thiol groups through a 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 in the diisocyanate coupling agent to form thiourethane bonds.

2. A method for preparing a reprocessable high-strength, high-toughness PBAT-PLA dynamic crosslinked material as described in claim 1, characterized in that, Includes the following steps: S1 dissolves alkali lignin in anhydrous ethanol, and after stirring, filtration and drying, it is pulverized into polyhydroxy lignin. S2 dissolves the polyhydroxy lignin and mercaptoacetic acid in acetone in a certain proportion, adds 4-dimethylaminopyridine and choline chloride, stirs, washes with dichloromethane, and then dries to obtain modified lignin. S3. PBAT, PLA, diisocyanate coupling agent and the modified lignin are blended in proportion to prepare a composite material. S4 involves hot-pressing and plasticizing the composite material to obtain the finished composite material.

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

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

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

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

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

10. The method for preparing the reprocessable high-strength and high-toughness PBAT-PLA dynamic crosslinked material according to claim 2, characterized in that, It has the characteristic of being reprocessable. The reprocessing molding conditions include: heating temperature of 180-185℃, plasticizing time of 22-25min, pressure of 5MPa, and pressure vulcanization time of 30min.

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