Flame-retardant weather-resistant thermoplastic elastomer and preparation method thereof

Abstract

The invention relates to a flame-retardant weather-resistant thermoplastic elastomer and a preparation method thereof, and belongs to the technical field of flame-retardant material preparation, and the preparation method specifically comprises the following preparation steps: S1, collecting a lignin raw material, crushing, sieving, and sequentially carrying out enzymolysis treatment and acidolysis treatment on the lignin raw material to obtain pretreated lignin; and S2, mixing the pretreated lignin, polyester polyol, a chain extender and a flame retardant, uniformly stirring, adding isocyanate, raising the temperature of a system, reacting for 2-3 hours, transferring the system into a mold, and balancing at room temperature to obtain the flame-retardant weather-resistant thermoplastic elastomer. The prepared elastomer has the characteristics of good weather resistance, good flame retardant effect, simple preparation and no pollution.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant material preparation, and more specifically, to a flame retardant and weather-resistant thermoplastic elastomer and a preparation method thereof. Background Art

[0002] As a kind of polymer material with both the elasticity of rubber and the processing performance of plastic, thermoplastic elastomer (TPE) is widely used in the fields of automobile, construction, electronics, aerospace, etc. However, with the continuous improvement of material performance requirements, traditional TPE seems to be unable to meet the requirements in terms of flame retardancy and weather resistance. Therefore, the development of a thermoplastic elastomer with both flame retardancy and weather resistance has become a hot topic in current research.

[0003] Lignin, as a natural polymer material second only to cellulose in content in nature, has a unique chemical structure and physical properties. It mainly exists in plant cell walls and together with cellulose and hemicellulose constitutes the skeleton of the plant body. Lignin molecules contain a large number of functional groups such as hydroxyl and methoxy groups, which provide the possibility for chemical modification of lignin. Through specific chemical reactions such as oxidation, methylation, acetylation, etc., lignin can be converted into flame-retardant lignin with excellent flame retardant properties. However, a large amount of polluted wastewater is generated in the process, and the modification process increases the preparation cost of the elastomer.

[0004] Based on the above statements, the present invention provides a flame retardant and weather resistant thermoplastic elastomer and a preparation method thereof. Summary of the invention

[0005] In order to solve the problems raised in the background technology, the present invention provides a flame retardant and weather resistant thermoplastic elastomer and a preparation method thereof.

[0006] A method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing and screening them, and then performing enzymatic hydrolysis and acid hydrolysis treatment on them to obtain pretreated lignin; Wherein, the specific operation of the enzymatic hydrolysis treatment is: Mix the crushed lignin raw material with the complex enzyme, add sterile deionized water, add an oxidant to the system, increase the system temperature to 60°C-80°C, and stir for 12-24 hours; S2. Mix 15-20 parts of the pretreated lignin obtained in step S1, 5-10 parts of polyester polyol, 3-7 parts of chain extender and 1-3 parts of flame retardant by mass, stir evenly and add 10-15 parts of isocyanate, increase the system temperature to 60-80°C, react for 2-3 hours, transfer the system to a mold, and balance at room temperature to obtain a flame retardant and weather-resistant thermoplastic elastomer.

[0007] Furthermore, a method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing them through an 80-mesh sieve, and then performing enzymatic hydrolysis and acid hydrolysis on them in sequence to obtain pretreated lignin; Wherein, the specific operation of enzymolysis treatment is: The crushed lignin raw material is mixed with the complex enzyme at a mass ratio of 1:(0.01-0.02), sterile deionized water is added at a mass volume ratio of 1g:5ml, an oxidant is added to the system, the system temperature is increased to 60°C-80°C, and stirred at a rate of 30-60rpm for 12-24 hours.

[0008] In the above reaction process, a composite enzyme is used to enzymatically hydrolyze the lignin raw material, and a small amount of solvent system is used. During the enzymatic hydrolysis process, an appropriate amount of oxidant is added to promote oxidation reactions of functional groups such as alcohol groups, ether groups and methyl groups on aromatic rings in the lignin molecules, thereby generating soluble oxidation products, making the lignin easier to be enzymatically hydrolyzed and further converted.

[0009] S2. Mix 15-20 parts of the pretreated lignin obtained in step S1, 5-10 parts of polyester polyol, 3-7 parts of chain extender and 1-3 parts of flame retardant by mass, stir evenly and add 10-15 parts of isocyanate, increase the system temperature to 60°C-80°C, react for 2-3 hours, transfer the system to a mold, and equilibrate at room temperature for 12-24 hours to obtain a flame retardant and weather-resistant thermoplastic elastomer.

[0010] Furthermore, the composite enzyme is obtained by mixing ligninase and peroxidase in a mass ratio of 1:(0.2-0.5).

[0011] Furthermore, in step S1, the oxidant is at least one of hydrogen peroxide, sodium peroxide and potassium permanganate.

[0012] Further, in step S1, the specific operation of the acid hydrolysis treatment is: The pH value of the lignin raw material system after enzymatic hydrolysis is adjusted to 5-6 with acid solution, a reducing agent is added to the system, the system temperature is increased to 70° C.-90° C., and the acid treatment time is 4-6 hours.

[0013] In the above reaction process, a small amount of reducing agent is used in the acid hydrolysis process. The reducing agent promotes the breaking of carbon-oxygen bonds and carbon-carbon bonds in lignin molecules, promotes the degradation of lignin, and increases the content of lignin monomers in the system. It reduces the excessive oxidation or polymerization reaction of aromatic rings in the enzymatic hydrolysis and acid hydrolysis of lignin, thereby maintaining the stability of the system. At the same time, the use of reducing agents can reduce the conversion of phenolic substances in the system to quinones, improve the chelating effect of the lignin system on metal ions, and improve the flame retardant effect and weather resistance of the final elastomer product.

[0014] Furthermore, it is characterized in that the reducing agent is a ferrous salt, and the usage amount is 1-5wt% of the lignin raw material.

[0015] Furthermore, in step S2, the polyester polyol is at least one of polyethylene adipate diol and polybutylene adipate diol.

[0016] Furthermore, in step S2, the isocyanate is at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and xylylene diisocyanate.

[0017] Furthermore, in step S2, the flame retardant is aluminum hypophosphite.

[0018] Furthermore, the chain extender is an alicyclic alcohol chain extender and an aromatic alcohol chain extender.

[0019] Furthermore, the alicyclic alcohol chain extender is at least one of 1,4-cyclohexanediol and hydrogenated bisphenol A; the aromatic alcohol chain extender is at least one of dimethylene phenyl glycol and resorcinol hydroxy ether.

[0020] In summary, the present invention has the following beneficial effects: In the technical solution of the present invention, the lignin raw material is subjected to enzymatic hydrolysis and then acid hydrolysis to prepare pretreated lignin. In addition, during the enzymatic hydrolysis and acid hydrolysis processes, an oxidant and a reductant are used to enhance the decomposition of lignin, respectively. During the process, a relatively small amount of solvent is used, and the separation and purification process of conventional lignin materials for enhancing thermoplastic elastomers is omitted. The process does not involve complex modification of lignin, thus avoiding the treatment of lignin-contaminated water. While reducing costs, this pretreatment method is used to convert other substances in the lignin raw material into humic acid substances, chelate trace elements in the pretreated lignin system, and other components act as carbon sources, which can better exert flame retardant properties in thermoplastic elastomers.

[0021] In the technical solution of the present invention, a composite enzyme is used to enzymolyze the lignin raw material, and the amount of solvent system used is small. During the enzymolysis process, a small amount of oxidant is added to promote the oxidation reaction of functional groups such as alcohol groups, ether groups and methyl groups on aromatic rings in the lignin molecules, thereby generating soluble oxidation products, making the lignin easier to be enzymolyzed and further converted. Subsequently, the lignin raw material is acid-lyzed to further promote the decomposition of lignin, refine the molecular weight of lignin, and use the method of compounding the composite enzyme with acid solution to reduce the preparation cost. During the acidolysis process, an appropriate amount of reducing agent is also used, which can promote the breaking of covalent bonds in lignin molecules, especially those stable structures such as β-O-4 bonds connecting phenylpropane units, so that lignin is more easily decomposed into smaller molecular fragments, and improve the carbonization effect of lignin. At the same time, a small amount of reducing agent is used during the acidolysis process, and the reducing agent promotes the breaking of carbon-oxygen bonds and carbon-carbon bonds in lignin molecules, promotes the degradation of lignin, and increases the content of lignin monomers in the system. Reduce excessive oxidation or polymerization of aromatic rings during enzymatic and acid hydrolysis of lignin, thereby maintaining the stability of the system. At the same time, the use of reducing agents can reduce the conversion of phenolic substances in the system to quinones, improve the chelating effect of the lignin system on metal ions, and improve the flame retardant and weather resistance of the final elastomer product.

[0022] In the technical solution of the present invention, aluminum hypophosphite and lignin-based materials are used to synergistically flame retard the thermoplastic elastomer, and they jointly play the role of condensed phase flame retardancy and gas phase flame retardancy during the combustion process. The glassy compound formed when aluminum hypophosphite burns will cover the surface of the substrate, playing a role of heat insulation and oxygen isolation. The carbon layer formed by enzymatic lignin during the combustion process also has the role of heat insulation and oxygen isolation. This physical barrier layer can further inhibit the combustion reaction. The acidic substances in the modified lignin system can also promote the dehydration process, and the generated glassy compound can increase the density of the carbon layer, thereby quickly reducing the heat conduction and heat radiation on the surface of the substrate, while isolating oxygen, thereby effectively preventing the spread of flames. Enzymatic lignin may also have a certain stabilizing effect on the PO· free radicals generated by aluminum hypophosphite, thereby extending the survival time of the PO· free radicals in the gas phase, enhancing its ability to capture HO· free radicals, and further improving the flame retardant effect on the elastomer. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The specific embodiments of the present invention relate to: The lignin raw material used was corn stover; Ligninase: provided by Shandong Nuojie Biotechnology Co., Ltd., model PW380; Peroxidase: provided by Shanghai Yuanye Biotechnology, CAS No. 9009-99-0, RZ>3, ≧300U / mg; Commercially available enzymatic lignin: provided by Wuhan Jiyesheng Chemical Co., Ltd., CAS number 86855-54-1; Aluminum hypophosphite: provided by Dazhan Jiyuan New Material Technology Co., Ltd., model 8206, active ingredient content is 96%.

[0025] Aluminum hydroxide: provided by Hangzhou Haihong Fine Chemical Co., Ltd., CAS No. 21645-51-3, average particle size 3-6μm.

[0026] Example 1 The present invention provides a method for preparing a flame retardant and weather-resistant thermoplastic elastomer, which adopts the following technical scheme: A method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing them through an 80-mesh sieve, and then performing enzymatic hydrolysis and acid hydrolysis on them in sequence to obtain pretreated lignin; Wherein, the specific operation of enzymolysis treatment is: The crushed lignin raw material is mixed with the composite enzyme in a mass ratio of 1:0.01, sterile deionized water is added in a mass volume ratio of 1g:5ml, 30wt% hydrogen peroxide solution is added to the system, the system temperature is increased to 60°C, and stirred at a speed of 30rpm for 12 hours; the composite enzyme is obtained by mixing ligninase and peroxidase in a mass ratio of 1:0.2; the mass volume ratio of lignin raw material and 30wt% hydrogen peroxide solution is 1g:0.5mL.

[0027] Wherein, the specific operation of acid hydrolysis treatment is: The pH value of the lignin raw material system after enzymatic hydrolysis was adjusted to 5 using 1 mol / L sulfuric acid solution, and a reducing agent was added to the system, the system temperature was increased to 70°C, and the acid treatment time was 4 hours; the reducing agent was ferrous sulfate, and the amount used was 1wt% of the lignin raw material.

[0028] S2. Mix 15 parts of the pretreated lignin obtained in step S1, 5 parts of polyester polyol, 3 parts of chain extender and 1 part of flame retardant by mass, add 10 parts of isocyanate after stirring evenly, increase the system temperature to 50°C, react for 2 hours, transfer the system to a mold, and balance at room temperature for 12 hours to obtain a flame retardant and weather-resistant thermoplastic elastomer; Wherein, the polyester polyol is polyethylene adipate diol; the isocyanate is toluene diisocyanate; the chain extender is 1,4-cyclohexanediol; and the flame retardant is aluminum hypophosphite.

[0029] Example 2 The present invention provides a method for preparing a flame retardant and weather-resistant thermoplastic elastomer, which adopts the following technical scheme: A method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing them through an 80-mesh sieve, and then performing enzymatic hydrolysis and acid hydrolysis on them in sequence to obtain pretreated lignin; Wherein, the specific operation of enzymolysis treatment is: The crushed lignin raw material is mixed with the composite enzyme in a mass ratio of 1:0.015, sterile deionized water is added in a mass volume ratio of 1g:5ml, 30wt% hydrogen peroxide solution is added to the system, the system temperature is increased to 70°C, and stirred at a speed of 45rpm for 18 hours; the composite enzyme is obtained by mixing ligninase and peroxidase in a mass ratio of 1:0.3; the mass volume ratio of lignin raw material and 30wt% hydrogen peroxide solution is 1g:0.7mL.

[0030] Wherein, the specific operation of acid hydrolysis treatment is: The pH value of the lignin raw material system after enzymatic hydrolysis was adjusted to 5.5 using 1 mol / L sulfuric acid solution, and a reducing agent was added to the system, the system temperature was increased to 80°C, and the acid treatment time was 5 hours; the reducing agent was ferrous sulfate, and the amount used was 3wt% of the lignin raw material.

[0031] S2, by weight, 18 parts of the pretreated lignin obtained in step S1, 8 parts of polyester polyol, 5 parts of chain extender and 2 parts of flame retardant were mixed, 12 parts of isocyanate were added after stirring evenly, the system temperature was increased to 55°C, after reacting for 2 hours, the system was transferred to a mold, and balanced at room temperature for 18 hours to obtain a flame retardant and weather-resistant thermoplastic elastomer; Wherein, the polyester polyol is polyethylene adipate diol; the isocyanate is toluene diisocyanate; the chain extender is 1,4-cyclohexanediol; and the flame retardant is aluminum hypophosphite.

[0032] Example 3 The present invention provides a method for preparing a flame retardant and weather-resistant thermoplastic elastomer, which adopts the following technical scheme: A method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing them through an 80-mesh sieve, and then performing enzymatic hydrolysis and acid hydrolysis on them in sequence to obtain pretreated lignin; Wherein, the specific operation of enzymolysis treatment is: The crushed lignin raw material is mixed with the composite enzyme in a mass ratio of 1:0.02, sterile deionized water is added in a mass volume ratio of 1g:5ml, 30wt% hydrogen peroxide solution is added to the system, the system temperature is increased to 80°C, and stirred at a speed of 60rpm for 24 hours; the composite enzyme is obtained by mixing ligninase and peroxidase in a mass ratio of 1:0.5; the mass volume ratio of lignin raw material and 30wt% hydrogen peroxide solution is 1g:1mL.

[0033] Wherein, the specific operation of acid hydrolysis treatment is: The pH value of the lignin raw material system after enzymatic hydrolysis was adjusted to 6 using 1 mol / L sulfuric acid solution, a reducing agent was added to the system, the system temperature was increased to 90°C, and the acid treatment time was 6 hours; the reducing agent was ferrous sulfate, and the amount used was 5wt% of the lignin raw material.

[0034] S2, by weight, 20 parts of the pretreated lignin obtained in step S1, 10 parts of polyester polyol, 7 parts of chain extender and 3 parts of flame retardant were mixed, 15 parts of isocyanate were added after stirring evenly, the system temperature was increased to 60°C, after reacting for 3 hours, the system was transferred to a mold, and balanced at room temperature for 24 hours to obtain a flame retardant and weather-resistant thermoplastic elastomer; Wherein, the polyester polyol is polybutylene adipate diol; the isocyanate is diphenylmethane diisocyanate; the chain extender is resorcinol hydroxy ether; and the flame retardant is aluminum hypophosphite.

[0035] Comparative Example 1 A method for preparing a flame retardant and weather-resistant thermoplastic elastomer comprises the following preparation steps: S1, collecting lignin raw materials, crushing them through an 80-mesh sieve, and then performing acid hydrolysis and enzymolysis treatment on them in sequence to obtain pretreated lignin; Wherein, the specific operation of acid hydrolysis treatment is: The lignin raw material system was added into sterile deionized water at a mass volume ratio of 1g:5ml, the pH value of the system was adjusted to 5 with 1mol / L sulfuric acid solution, a reducing agent was added to the system, the system temperature was increased to 60°C, and the acid treatment time was 4 hours; the reducing agent was ferrous sulfate, and the amount used was 1wt% of the lignin raw material.

[0036] Wherein, the specific operation of enzymolysis treatment is: A composite enzyme was added to the acid-hydrolyzed lignin raw material at a mass ratio of 1:0.01, and then a 30wt% hydrogen peroxide solution was added to the system, the system temperature was increased to 50°C, and the system was stirred at a rate of 30rpm for 12 hours; the composite enzyme was obtained by mixing ligninase and peroxidase at a mass ratio of 1:0.2; the mass volume ratio of the lignin raw material to the 30wt% hydrogen peroxide solution was 1g:0.5mL.

[0037] S2. Mix 15 parts of the pretreated lignin obtained in step S1, 5 parts of polyester polyol, 3 parts of chain extender and 1 part of flame retardant by mass, add 10 parts of isocyanate after stirring evenly, increase the system temperature to 50°C, react for 2 hours, transfer the system to a mold, and balance at room temperature for 12 hours to obtain a flame retardant and weather-resistant thermoplastic elastomer; Wherein, the polyester polyol is polyethylene adipate diol; the isocyanate is toluene diisocyanate; the chain extender is 1,4-cyclohexanediol; and the flame retardant is aluminum hypophosphite.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is that ligninase is used instead of composite enzyme.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that commercially available enzymatically hydrolyzed lignin is used instead of pretreated lignin.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S2 of this comparative example, the flame retardant used is aluminum hydroxide.

[0041] Comparative Example 5 The difference between this comparative example and Example 1 is that in step S2 of this comparative example, the amount of the flame retardant added is 5 parts.

[0042] Performance Testing Now the mechanical properties of the thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 are tested. The hardness, tensile strength and elongation of the thermoplastic elastomers prepared in different groups are tested. Samples with a size of 125 mm × 10 mm × 2 mm are taken and tested on a universal tensile testing machine at room temperature. The specific testing method refers to the contents described in GB / T1040.1-2006 and GB / T 2411-2008. Each sample is tested 5 times, and the average value is recorded. The specific performance test results are shown in Table 1 below.

[0043] Table 1 Mechanical properties test of thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 Group Hardness(Shore) Tensile strength(MPa) Elongation at break (%) Example 1 75A 42.0 642 Example 2 70A 44.3 655 Example 3 73A 42.5 650 Comparative Example 1 82A 38.0 628 Comparative Example 2 80A 38.5 630 Comparative Example 3 85A 36.4 622 Comparative Example 4 80A 40.3 636 Comparative Example 5 87A 33.6 546 From the results shown in Table 1 above, it can be seen that the thermoplastic elastomer prepared in Example 2 has the best mechanical properties. From the results in Comparative Example 1, it can be seen that the order of oxidant and reductant and enzymatic hydrolysis and acid hydrolysis determines the binding effect of the final pre-treated lignin system with the elastomer matrix. From the results in Comparative Examples 2-3, it can be seen that the use of a composite enzyme can better improve the reinforcing effect of pre-treated lignin on the matrix. From the results in Comparative Examples 4 and 5, it can be seen that other flame retardants or flame retardants are used in large amounts, and their compatibility with polyurethane elastomers may be poor, and interface defects are easily formed, thereby affecting the stability of the carbon layer.

[0044] The flame retardant effect of the thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 is now tested. A sample with a size of 125 mm × 10 mm × 2 mm is fixed vertically in a combustion test box, one end of the sample is ignited with a flame, and the burning time and length of the sample are recorded. Each sample is tested 5 times, and the average value is recorded. The specific test results are shown in Table 2 below.

[0045] Table 2 Flame retardant effect test of thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 Group Burning time(s) Burning length(mm) Example 1 1.6 2.6 Example 2 1.0 2.3 Example 3 1.1 2.5 Comparative Example 1 3.0 2.8 Comparative Example 2 3.0 2.7 Comparative Example 3 2.6 2.5 Comparative Example 4 2.0 2.2 Comparative Example 5 1.7 2.0 From the results in Table 2, it can be seen that the thermoplastic elastomer prepared in Example 2 has the best flame retardant effect.

[0046] The weather resistance of the thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 is now tested. The samples in different groups are placed in an ultraviolet aging box, using a UVA-340 lamp, with a wavelength range set to 340nm and an irradiance set to 1.0W / m 2 The ambient temperature was set to 50°C. After aging for 7 days, the mechanical properties of the material were tested and the percentage changes in hardness, tensile strength and elongation were recorded. Each sample was tested 5 times and the average value was recorded. The specific test results are shown in Table 3 below.

[0047] Table 3 Weathering resistance test of thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-5 Group Hardness change (%) Change in tensile strength (%) Change in elongation at break (%) Example 1 +6.0 -9.1 -10.4 Example 2 +3.5 -5.3 -6.1 Example 3 +4.4 -6.0 -7.4 Comparative Example 1 +6.5 -9.0 -12.3 Comparative Example 2 +6.6 -9.3 -12.9 Comparative Example 3 +6.5 -9.1 -12.4 Comparative Example 4 +6.2 -8.6 -11.3 Comparative Example 5 +11.3 -16.3 -17.0 It can be seen from the results in Table 2 and Table 3 that the flame retardant properties and weather resistance of the thermoplastic elastomers prepared in Examples 1-3 of the present invention are significantly better than those of the thermoplastic elastomers prepared in Comparative Examples 1-5, that is, within the technical solution defined in the present invention, the comprehensive performance of the prepared thermoplastic elastomers is excellent.

[0048] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0049] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a flame retardant and weather-resistant thermoplastic elastomer, characterized in that: The method comprises the following preparation steps: S1, collecting lignin raw materials, crushing and screening them, and then performing enzymatic hydrolysis and acid hydrolysis treatment on them to obtain pretreated lignin; Wherein, the specific operation of the enzymatic hydrolysis treatment is: Mix the crushed lignin raw material with the complex enzyme, add sterile deionized water, add an oxidant to the system, increase the system temperature to 60°C-80°C, and stir for 12-24 hours; S2. Mix 15-20 parts of the pretreated lignin obtained in step S1, 5-10 parts of polyester polyol, 3-7 parts of chain extender and 1-3 parts of flame retardant by mass, stir evenly and add 10-15 parts of isocyanate, increase the system temperature to 60°C-80°C, react for 2-3 hours, transfer the system to a mold, and balance at room temperature to obtain a flame retardant and weather-resistant thermoplastic elastomer.

2. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S1, the oxidant is at least one of hydrogen peroxide, sodium peroxide and potassium permanganate.

3. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 2, characterized in that: The composite enzyme is obtained by mixing ligninase and peroxidase in a mass ratio of 1:(0.2-0.5).

4. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S1, the specific operation of the acid hydrolysis treatment is: The pH value of the lignin raw material system after enzymatic hydrolysis is adjusted to 5-6 with acid solution, a reducing agent is added to the system, the system temperature is increased to 70° C.-90° C., and the acid treatment time is 4-6 hours.

5. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 4, characterized in that: The reducing agent is ferrous salt, and the usage amount is 1-5wt% of the lignin raw material.

6. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S2, the polyester polyol is at least one of polyethylene adipate diol and polybutylene adipate diol.

7. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S2, the isocyanate is at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and xylylene diisocyanate.

8. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S2, the chain extender is an alicyclic alcohol chain extender and an aromatic alcohol chain extender.

9. The method for preparing a flame retardant and weather resistant thermoplastic elastomer according to claim 1, characterized in that: In step S2, the flame retardant is aluminum hypophosphite.

10. A thermoplastic elastomer obtained by the method for preparing a flame retardant and weather resistant thermoplastic elastomer according to any one of claims 1 to 9.