Durable flame-retardant tpe composite based on click chemistry and preparation method thereof

Abstract

This invention provides a click chemistry-based durable flame-retardant TPE composite material and its preparation method, belonging to the field of polymer material modification technology. The material includes: 10-60 parts of modified SBS prepared by click chemistry, 5-40 parts of filler oil, 2-15 parts of polypropylene, and 10-20 parts of silazane-modified microencapsulated flame retardant. This invention imparts flame-retardant and anti-aging properties to the matrix through click chemistry modification of SBS. Simultaneously, the silazane-modified microencapsulated flame retardant shell contains a benzene ring structure with char-forming function and flame-retardant elements such as silicon, nitrogen, and phosphorus, which work synergistically with the core flame retardant to improve the flame-retardant performance and flame-retardant rating of the material. Furthermore, the microencapsulated organic shell improves the compatibility of the flame retardant and the mechanical and durability properties of the flame-retardant TPE material. The benzene rings and phosphorus-carbon bonds in the flame retardant also enhance the heat aging resistance of the TPE, further strengthening the flame-retardant and heat-aging properties of the TPE material.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and in particular to a click chemistry-based durable flame-retardant TPE composite material and its preparation method. Background Technology

[0002] Thermoplastic elastomers (TPEs) combine the high elasticity of rubber with the processability of plastics, making them widely used in automotive parts, building seals, and electronic packaging. Among them, styrene-butadiene-styrene block copolymers (SBS), as an important type of TPE material, have become one of the most in-demand varieties due to their excellent mechanical properties and controllable cost. However, pure SBS material has a low limiting oxygen index, is easily flammable, and melts and drips during combustion. Furthermore, its poor resistance to oxidative aging significantly limits its adoption in high-end applications where stringent requirements for flame retardancy and durability are present.

[0003] To further expand the application range of SBS materials, flame retardant modification is currently mainly achieved through chemical modification or physical filling. From a chemical modification perspective, traditional methods primarily employ peroxide-initiated free radical grafting reactions to introduce phosphorus- and nitrogen-containing flame-retardant functional groups into the SBS molecular chain. However, this type of reaction has significant drawbacks: poor selectivity of free radical reactions, easy initiation of cross-linking and chain scission side reactions in the SBS molecular chain, leading to excessive cross-linking and loss of processability; and harsh reaction conditions with low controllability, making it difficult to stably regulate the grafting rate and product structure. From a physical filling perspective, while directly adding flame retardants (such as ammonium polyphosphate and magnesium hydroxide) is simple, the flame retardants have poor compatibility with the SBS matrix and are prone to agglomeration. This not only significantly degrades the material's mechanical, elastic, and processing properties but also results in low flame retardant efficiency and poor flame retardant durability, making it difficult to achieve efficient and durable flame retardant effects.

[0004] To address compatibility issues, existing technologies employ microencapsulation of flame retardants for modification. This involves coating the flame retardant surface with a polymer shell to improve its inherent shortcomings and compatibility with the matrix. However, current microencapsulation modification techniques often focus solely on enhancing flame retardancy and compatibility, neglecting the synergistic maintenance of the modified material's antioxidant and mechanical properties. This leads to an imbalance in the overall performance of the modified SBS thermoplastic elastomer material, failing to meet the demands of high-end applications for multifunctional material integration.

[0005] Furthermore, thiol-olefin click chemistry, as an efficient and controllable organic synthesis method, has advantages such as mild reaction conditions, high selectivity, and few byproducts, and has been gradually applied in the field of polymer material modification. However, there are currently no reports on combining thiol-olefin click chemistry with microencapsulation flame retardant technology to prepare SBS thermoplastic elastomer materials with high flame retardancy, excellent mechanical properties, and durability through precise control of the reaction process. There is also a lack of systematic technical solutions to effectively avoid excessive crosslinking and loss of processability of the product during SBS modification.

[0006] Given the shortcomings of the existing technologies, there is an urgent need to develop an SBS modification method with mild reaction conditions, high controllability, and the ability to effectively avoid excessive crosslinking. By constructing functionalized graft structures and high-performance microcapsule flame-retardant systems, the synergistic optimization of flame retardancy and mechanical properties can be achieved, and SBS-based TPE composite materials with excellent comprehensive performance can be prepared to meet the application requirements of high-end fields for multifunctional and highly reliable materials. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a click chemistry-based durable flame-retardant TPE composite material and its preparation method. By modifying SBS with click chemistry, the matrix is ​​endowed with intrinsic flame retardant and anti-aging properties. Combined with silazane-modified microcapsule flame retardants, core-shell synergistic flame retardancy is achieved, taking into account the material's mechanical properties, flame retardant efficiency, and durability, and significantly improving its heat aging resistance. It can be widely used in fields such as construction, transportation, chemical industry, machinery, communications, and energy.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] On one hand, the present invention provides a click chemistry-based durable flame-retardant TPE composite material, the raw materials of which are composed of the following components by mass parts: 10-60 parts of modified SBS prepared by click chemistry, 5-40 parts of filler oil, 2-15 parts of polypropylene, and 10-20 parts of silazane-modified microencapsulated flame retardant; the modified SBS prepared by click chemistry is phosphorus-sulfur-grafted SBS obtained by thiol-ene click chemistry reaction; the silazane-modified microencapsulated flame retardant has a core-shell structure, the core layer is a flame retardant modified by silane coupling agent, and the shell layer is a coating layer formed by a double-bonded silazane precursor, a double-bonded flame-retardant monomer, and a mercapto-containing monomer through a thiol-ene click chemistry reaction.

[0010] Preferably, the filler oil is selected from one or more of paraffin oil, naphthenic oil, and aromatic oil; the polypropylene is selected from one or more of homopolymer polypropylene and copolymer polypropylene.

[0011] Preferably, the raw materials of the silazane-modified microencapsulated flame retardant are composed of the following components by mass parts: 85 parts flame retardant, 1-10 parts silazane precursor containing double bonds, 1-10 parts flame retardant monomer containing double bonds, and 1-10 parts mercapto monomer.

[0012] Preferably, the flame retardant is selected from one or more of magnesium hydroxide, aluminum hydroxide, dihydroxide, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, charring agent, ammonium polyphosphate, piperazine pyrophosphate, aluminum hypophosphite, aluminum phosphonate, expandable graphite, zinc borate, graphene, transition metal disulfides, carbon nanotubes, halloysite, sepiolite, and kaolin; the silane coupling agent is γ-mercaptopropyltrimethoxysilane; the double-bonded silazane precursor is trivinyltrimethylcyclotrisilazane; and the double-bonded flame-retardant monomer is diphenylphosphine chloride grafted with hydroxyethyl acrylate.

[0013] Preferably, the mercapto-containing monomer is selected from one or more of 4,4'-dimercaptobiphenyl, 4,4'-dimercaptodiphenyl ether, trimercaptotriazine, trimethylolpropane tris(3-mercaptopropionic acid) ester, 1,2,4,5-tetramercaptobenzene, and pentaerythritol tetramercaptopropionate.

[0014] Preferably, the modified SBS prepared based on click chemistry is obtained by a method comprising the following steps:

[0015] Step 1, Pre-reaction: A polyfunctional thiol compound and a monofunctional compound containing double bonds are dissolved in an organic solvent, a photoinitiator is added, and a thiol-ene click chemical reaction occurs under ultraviolet light irradiation in an inert atmosphere to obtain a pre-reaction solution; the molar ratio of the polyfunctional thiol compound to the monofunctional compound containing double bonds is 1:2.

[0016] Step 2, Grafting reaction: SBS is dissolved in an organic solvent to obtain an SBS solution; the SBS solution is added to the pre-reaction solution, and a grafting reaction is carried out under light irradiation. After the reaction is completed, modified SBS is obtained through post-treatment; the ratio of the number of moles of double bonds in the SBS to the number of moles of remaining thiol groups in the pre-reaction solution is 1.5~2.0:1.

[0017] Preferably, the polyfunctional thiol compound is trimethylolpropane tris(3-mercaptopropionic acid) ester; the monofunctional compound containing a double bond is diphenylphosphine chloride grafted hydroxyethyl acrylate; the SBS is linear or star-shaped SBS; the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; a phenolic antioxidant is added to the reaction system as a polymerization inhibitor, and the amount of the polymerization inhibitor added is 0.1% to 1% of the total mass of the reaction system; the organic solvent is selected from one or two of toluene and xylene.

[0018] Preferably, the silazane-modified microencapsulated flame retardant is prepared by a method comprising the following steps:

[0019] Step A: Prepare flame retardant monomers containing double bonds and flame retardants modified with silane coupling agents;

[0020] Step B: Disperse the silane coupling agent modified flame retardant in a solvent, add a flame retardant monomer containing double bonds, a silazane precursor containing double bonds, and a mercapto monomer, add a photoinitiator under a nitrogen atmosphere, and conduct a thiol-ene click chemical reaction under ultraviolet light irradiation. After the reaction is completed, the silazane modified microencapsulated flame retardant is obtained through post-treatment.

[0021] Preferably, the specific preparation process of step A includes:

[0022] Preparation of flame-retardant monomers containing double bonds: Hydroxyethyl acrylate and triethylamine were added to anhydrous dichloromethane to form a reaction system. Diphenylphosphine chloride was dissolved in dichloromethane and added dropwise to the reaction system. After the addition was complete, the reaction was stirred for 4-6 hours under a nitrogen atmosphere and at room temperature. After post-treatment, flame-retardant monomers containing double bonds were obtained.

[0023] Preparation of flame retardant modified with silane coupling agent: Flame retardant, silane coupling agent and ethanol-water mixed solvent are added to the reaction system, the pH is adjusted to 10, emulsifier is added, the temperature is raised to 40~60℃ and reacted for 4~8h. After the reaction is completed, the flame retardant modified with silane coupling agent is obtained through post-treatment.

[0024] On the other hand, the present invention also provides a method for preparing the above-mentioned click chemistry-based durable flame-retardant TPE composite material, comprising the following steps: mixing modified SBS prepared based on click chemistry with filler oil in parts by mass, then adding polypropylene and silazane-modified microencapsulated flame retardant and mixing them in a uniform manner; mixing the mixture in a uniform manner at 170~200℃, and then pressing it into shape to obtain the TPE composite material.

[0025] Compared with the prior art, the present invention discloses at least the following technical effects:

[0026] 1. This invention uses a thiol-olefin click chemistry route to modify SBS. By controlling the molar ratio of multifunctional thiols to phosphorus-containing acrylates through pre-reaction, a pre-grafted molecule with only one remaining thiol group is generated. The ratio of SBS double bonds to the remaining thiol group is precisely controlled in the main reaction, which can avoid the problems of intramolecular cyclization or excessive cross-linking of multiple chains caused by the pre-reaction molecule. Soluble functionalized grafted products can be stably obtained, significantly improving the repeatability and controllability of the modification reaction. It effectively solves the technical problems of cross-linking runaway, poor product solubility and loss of processability that are prone to occur in traditional free radical grafting processes.

[0027] 2. This invention innovatively prepares a silazane-modified microencapsulated flame retardant. A core-shell structure is constructed using a silane coupling agent-modified flame retardant as the core and a phosphorus-containing flame-retardant monomer and a multi-thiol compound as the shell, achieving synergistic integration of multiple flame-retardant elements including phosphorus, nitrogen, silicon, and sulfur. This microcapsule can exert dual flame-retardant effects in both the gas and condensed phases. Combined with modified SBS containing phosphorus and sulfur flame-retardant elements, it forms a synergistic flame-retardant system, significantly enhancing flame-retardant performance. Furthermore, the benzene ring and phosphorus-carbon bond structures in the modified SBS and the microencapsulated flame retardant can significantly improve the oxidation and thermal aging resistance of TPE composite materials.

[0028] 3. This invention utilizes thiol-olefin click chemistry to prepare modified SBS and silazane-modified microencapsulated flame retardants. Room temperature is the primary reaction temperature, and the reaction is initiated by ultraviolet light. No high-temperature, high-pressure equipment is required; the single-step reaction can be completed in 60-120 minutes, resulting in a rapid reaction rate. The product can be purified simply by washing and rotary evaporation. The solvent used in microencapsulation preparation can be recycled and reused. Compared to traditional SBS modification processes, this method consumes less energy, produces fewer byproducts, and simultaneously improves product purity and functional retention. The preparation process is green and efficient.

[0029] 4. In this invention, the phosphorus-sulfur-grafted SBS structure and the silazane-modified microcapsules form a synergistic effect. The microencapsulated organic shell improves the compatibility between the flame retardant and the SBS matrix, effectively solving the problem of significant decrease in mechanical properties after traditional SBS flame retardant modification. At the same time, it endows the composite material with comprehensive properties of high-efficiency flame retardancy, oxidation resistance and durability, breaking through the limitation of the single function of existing SBS materials. The prepared TPE composite material can be widely used in construction, transportation, chemical industry, machinery, communication, energy and other fields, with a wider range of applications and stronger practicality. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram illustrating the reaction of the flame retardant modified with the double-bonded flame retardant monomer DPOEA and the silane coupling agent KH590 provided by the present invention; wherein, Figure 1 In the diagram, 'a' represents the reaction of the flame-retardant monomer DPOEA containing a double bond. Figure 1 In the diagram, b represents the reaction of the flame retardant modified by the silane coupling agent KH590.

[0032] Figure 2The diagram illustrates the preparation of the silazane-modified microencapsulated flame retardant (Si-N@FR) provided by this invention and the click chemical reaction of thiols and olefins.

[0033] Figure 3 This is a schematic diagram of the reaction of modified SBS (SBS-PS) prepared based on click chemistry, as provided by the present invention.

[0034] Figure 4 XPS full spectrum and FTIR spectrum of SBS and SBS-PS provided for this invention; wherein, Figure 4 In the figure, 'a' represents the XPS full spectrum of SBS and SBS-PS. Figure 4 In the diagram, b represents the FTIR spectra of SBS and SBS-PS.

[0035] Figure 5 The present invention provides TGA and DTG curves for SBS and SBS-PS; wherein, Figure 5 In the figure, 'a' represents the TGA curves for SBS and SBS-PS. Figure 5 In the figure, b represents the DTG curves of SBS and SBS-PS.

[0036] Figure 6 XPS spectra, Si and S contents, TGA curves, and DTG curves of APP and its modified microencapsulated flame retardant provided by this invention; wherein, Figure 6 In the figure, 'a' represents the XPS spectrum of APP and its modified microencapsulated flame retardant. Figure 6 In the figure, b represents the Si and S content of APP and its modified microencapsulated flame retardant. Figure 6 In the figure, 'c' represents the TGA curve of APP and its modified microencapsulated flame retardant. Figure 6 In the figure, d represents the DTG curve of APP and its modified microencapsulated flame retardant.

[0037] Figure 7 SEM images, WCA optical images, and surface element distribution maps of APP, SiAPP, Si-N@APP, and comparative modified samples provided by this invention; wherein, Figure 7 In the image, 'a' represents the SEM image of the app. Figure 7 In the image, b represents the SEM image from SiAPP. Figure 7 In the image, c represents the SEM image of Si-N@APP. Figure 7 In the image, d represents the SEM image of the modified sample for comparison. Figure 7 In this context, 'g' represents the WCA optical image of the APP. Figure 7 In the image, h represents the WCA optical image from SiAPP. Figure 7 In the image, i represents the WCA optical image of the comparative modified sample. Figure 7In this context, j represents the WCA optical image of Si-N@APP. Figure 7 e1-e6 in the diagram represent the surface elemental distribution of Si-N@APP. Figure 7 f1-f6 in the diagram represent the surface elemental distribution of the comparative modified samples.

[0038] Figure 8 The free radical scavenging efficiency diagrams for APP, SiAPP, and Si-N@APP provided by this invention are shown. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The English abbreviations in this invention correspond to the following: APP is ammonium polyphosphate, TPE is thermoplastic elastomer, SBS is styrene-butadiene-styrene block copolymer, SBS-PS is phosphorus-sulfur-grafted modified SBS prepared based on click chemistry, SiFR is flame retardant modified with silane coupling agent KH590, SiAPP is ammonium polyphosphate modified with silane coupling agent KH590, Si-N@FR is silazane-modified microencapsulated flame retardant, Si-N@APP is silazane-modified microencapsulated ammonium polyphosphate, DPOEA is diphenylphosphine chloride grafted with hydroxyethyl acrylate, DPO is diphenylphosphine chloride, EA is hydroxyethyl acrylate, Si-N is trivinyltrimethylcyclotrisilazane, TMPMP is trimethylolpropane tris(3-mercaptopropionic acid) ester, TPO is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and BHT is butylated hydroxytoluene.

[0041] This invention aims to provide a method for modifying SBS based on thiol-olefin click chemistry, characterized by mild reaction conditions, high controllability, and effective avoidance of excessive crosslinking. This method is used to prepare a high-performance flame-retardant TPE composite material by blending the modified SBS with a microencapsulated flame retardant. The raw materials, by mass, consist of the following components: 10-60 parts of modified SBS prepared based on click chemistry, 5-40 parts of filler oil, 2-15 parts of polypropylene, and 10-20 parts of silazane-modified microencapsulated flame retardant. The modified SBS prepared based on click chemistry is a phosphorus-sulfur-grafted SBS obtained through a thiol-olefin click chemistry reaction. The silazane-modified microencapsulated flame retardant has a core-shell structure; the core layer is a flame retardant modified with a silane coupling agent, and the shell layer is a coating layer formed by a double-bonded silazane precursor, a double-bonded flame-retardant monomer, and a mercapto-containing monomer through a thiol-olefin click chemistry reaction.

[0042] Furthermore, this invention imparts flame-retardant and anti-aging properties to the matrix itself through click chemical modification of SBS. At the same time, the shell layer of the silazane-modified microencapsulated flame retardant contains a benzene ring structure with char-forming function and flame-retardant elements such as silicon, nitrogen, and phosphorus. It works synergistically with the core flame retardant to enhance the flame-retardant performance and flame-retardant level of the flame-retardant material. In addition, the microencapsulated organic shell layer can also improve the compatibility of the flame retardant and the mechanical and durability properties of the flame-retardant TPE material. Moreover, the benzene ring and phosphorus-carbon bond in the flame retardant can also improve the heat aging resistance of TPE, further enhancing the flame-retardant and heat aging performance of the TPE material.

[0043] The above content will be further explained below through specific implementation methods. The provided embodiments are only some embodiments of the present invention.

[0044] Example 1

[0045] This embodiment aims to prepare a silazane-modified microencapsulated flame retardant, such as... Figure 1 As shown, it includes the following steps:

[0046] like Figure 1 As shown in a, DPOEA was first prepared as follows: 11.6 g of hydroxyethyl acrylate (EA) (116, 0.1 mol), 300 mL of anhydrous dichloromethane, and 10.1 g of triethylamine (101, 0.1 mol) were added to the reaction system; then 23.6 g of diphenylphosphine chloride (236, 0.1 mol) was dissolved in dichloromethane to prepare a DPO solution, which was then slowly added dropwise to the above reaction system through a constant pressure dropping funnel; after the addition was complete, the reaction temperature was raised to room temperature (25 °C) while maintaining a nitrogen atmosphere, and the reaction was stirred for 4-6 h. The mixture was then washed, separated, and rotary evaporated to obtain DPOEA.

[0047] like Figure 1 As shown in b, the next step is to prepare a flame retardant modified with silane coupling agent KH590. The specific process is as follows: using 100g of flame retardant FR as raw material, 10g of silane coupling agent KH590 and 400mL of mixed solvent (ethanol and water 3:1) are added to the reaction system. The pH is adjusted to 10, and 1g of OP-10 emulsifier is added. The temperature is raised to 40-60℃ and reacted for 4-8 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed, and dried. The resulting product is dried in an oven at 50℃ to constant weight to obtain a white solid product (SiFR). In this embodiment, ammonium polyphosphate (APP) is used as the flame retardant FR, and the obtained product is SiAPP.

[0048] like Figure 2 As shown, the final preparation of the silazane-modified microencapsulated flame retardant (Si-N@FR) involves the following process: ... Figure 1 The white solid 85g of SiFR obtained from b was dispersed in 300mL of solvent. Figure 1The product DPOEA, trivinyltrimethylcyclotrisilazane (Si-N), and 15g of mercapto-containing monomer were added dropwise to the reaction system. The mixture was heated to 25°C under a nitrogen atmosphere, and then a photoinitiator was added. The mixture was then irradiated with ultraviolet light for 1 hour to induce a thiol-ene click chemical reaction, and the solution gradually turned yellow. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried. The resulting product was dried in an oven at 50°C to constant weight to obtain the silazane-modified microencapsulated flame retardant Si-N@FR.

[0049] Specifically, in this embodiment, when ammonium polyphosphate (APP) is selected as the flame retardant, the preparation process of the modified microencapsulated flame retardant is as follows: 85g of SiAPP and 200mL of dichloromethane are added to a 500mL three-necked flask. 1.5g of DPOEA (306, 0.005mol), 5.2g of trivinyltrimethylcyclotrisilazane (Si-N) (258, 0.02mol), and 8.3g of pentaerythritol tetramercaptopropionate (488, 0.017mol) are added dropwise to the reaction system and stirred and heated to 25°C under a nitrogen atmosphere. Subsequently, photoinitiator TPO (5% of the total mass, approximately 0.5g) and polymerization inhibitor BHT (0.5% of the total mass, approximately 0.05g) are added. After reacting for 60min, the mixture is cooled to room temperature, filtered, washed with water and dichloromethane, and then dried at 80°C to obtain the product Si-N@APP.

[0050] In addition, such as Figure 6 As shown, XPS spectra, elemental analysis, and TGA-DTG thermal characterization comprehensively verify the successful preparation of the silazane-modified microencapsulated flame retardant (Si-N@APP) in this embodiment. The changes in elemental composition and improved thermal properties of the modified flame retardant are clearly demonstrated, providing direct evidence for the formation of the core-shell structure and the enhancement of flame retardant efficacy. Specific characterization results are as follows:

[0051] Figure 6 In the figure, 'a' represents the XPS spectrum of APP and its modified microencapsulated flame retardant. Compared with pure APP, the spectra of SiAPP and Si-N@APP show characteristic peaks of Si element, and Si-N@APP also shows obvious characteristic peaks of S element. This directly proves that the silane coupling agent KH590 successfully modified APP. Furthermore, the precursor containing double bond silazane, the flame retardant monomer containing double bond, and the mercapto monomer successfully formed a coating shell on the surface of SiAPP through a thiol-ene click chemical reaction, achieving effective integration of multiple flame retardant elements such as Si, N, P, and S, which is consistent with the design goal of the core-shell structure.

[0052] Figure 6Figure b shows the Si and S content of APP and its modified microencapsulated flame retardant. It can be clearly seen that pure APP contains almost no Si and S elements, while the Si content in SiAPP is significantly increased, and the Si and S content in Si-N@APP are both greatly increased. This quantitatively confirms the degree of reaction of silane coupling agent modification and subsequent click chemical coating, proving the successful grafting of shell monomers on the surface of SiAPP, and that the elemental composition of the core-shell structure meets the design requirements.

[0053] Figure 6 In the figure, c represents the TGA curve of APP and its modified microencapsulated flame retardant. Compared with pure APP, SiAPP has a slightly higher initial thermal decomposition temperature and a slightly higher char rate. In contrast, Si-N@APP has a significantly higher initial thermal decomposition temperature and a much higher char rate throughout the entire thermal decomposition range than pure APP and SiAPP. This demonstrates that the formation of the core-shell structure effectively improves the thermal stability of the flame retardant and slows down the thermal decomposition process. At the same time, the synergistic effect of multiple flame retardant elements can promote the formation of a dense char layer and enhance the flame retardant effect of the condensed phase.

[0054] Figure 6 In the figure, d represents the DTG curve of APP and its modified microencapsulated flame retardant. Pure APP has a high peak value of maximum thermal decomposition rate and a low peak temperature. The maximum thermal decomposition rate of SiAPP is slightly reduced and the peak temperature is slightly shifted later. In contrast, the maximum thermal decomposition rate of Si-N@APP is significantly reduced and the corresponding peak temperature is significantly shifted later. This phenomenon confirms from the perspective of thermal decomposition kinetics that the core-shell structure of silazane-modified microencapsulated flame retardant can effectively inhibit the thermal decomposition rate of the flame retardant, making the thermal decomposition process smoother and reducing the rapid release of thermal decomposition products. This lays the foundation for the synergistic effect of gas-phase flame retardancy and condensed-phase flame retardancy. It also proves that the modification process of this embodiment can stably prepare microencapsulated flame retardants with excellent thermal properties.

[0055] Example 2

[0056] This embodiment aims to provide a modified SBS (SBS-PS) prepared based on click chemistry, as follows:

[0057] like Figure 3 As shown, step one, pre-reaction: a multifunctional thiol compound and a monofunctional compound containing a double bond are dissolved in a first organic solvent, a photoinitiator is added, and under an inert atmosphere, the mixture is irradiated with ultraviolet light to induce a thiol-ene click chemical reaction, resulting in a pre-reaction solution;

[0058] Step 2, Grafting reaction: SBS is dissolved in a second organic solvent to obtain an SBS solution; the SBS solution is added to the pre-reaction solution obtained in Step 1, and the grafting reaction is carried out by stirring under light irradiation. After the reaction is completed, the SBS composite material based on click chemistry modification (SBS-PS) is obtained by precipitation, washing and drying.

[0059] Further, in step one, the multifunctional thiol compound is preferably trimethylolpropane tris(3-mercaptopropionate) (TMPMP), and the monofunctional compound containing double bonds is preferably diphenylphosphine chloride-grafted hydroxyethyl acrylate (DPOEA). The molar ratio of the two is controlled at 1:2, and the reaction time is 1 hour, forming a "pre-grafted molecule" with one remaining thiol group and an attached functional unit (such as a phosphorus-containing structure). When this molecule reacts with SBS subsequently, its remaining thiol group can connect to the SBS chain, minimizing the possibility of multiple thiol groups of a pre-reacted molecule connecting to the same SBS chain, which could lead to intramolecular cyclization, or excessive cross-linking due to the connection of multiple chains. The goal is to obtain a soluble graft-modified product.

[0060] Furthermore, in step 2, the key control lies in the amount of SBS added. The amount of SBS added, based on the number of moles of double bonds it contains, should be slightly higher than or equal to the number of moles of remaining thiol groups in the pre-reaction solution, with a preferred ratio of (1.5-2.0):1, and the reaction time is 1 hour.

[0061] The SBS is a commercially available linear or star-shaped product, whose polybutadiene segments provide ample reaction sites.

[0062] The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), which exhibits high pyrolysis efficiency under long-wave ultraviolet light (365 nm) and relatively good thermal stability. The polymerization inhibitor is a phenolic antioxidant, preferably butylated hydroxytoluene (BHT), added at 0.1%-1% of the total mass of the reaction system.

[0063] Furthermore, the first organic solvent and the second organic solvent may be the same or different, preferably toluene or xylene, which have good solubility for both the reactants and SBS.

[0064] Based on the above, the preparation process of this embodiment is as follows:

[0065] In a 250 mL three-necked flask equipped with a magnetic stirrer, reflux condenser, and nitrogen inlet tube, add 100 mL of anhydrous toluene. Under nitrogen protection, add trimethylolpropane tris(3-mercaptopropionic acid) ester (TMPMP, molecular weight 398.5, 0.01 mol, 3.985 g) and phosphorus-containing acrylate monomer DPOEA (molecular weight 316, 0.02 mol, 6.32 g) sequentially. After stirring and dissolving, add photoinitiator TPO (2% of total mass, approximately 0.2 g) and polymerization inhibitor BHT (0.5% of total mass, approximately 0.05 g). After continuously purging with nitrogen to remove oxygen for 15 minutes, expose the flask to 365 nm ultraviolet light (light intensity approximately 20 mW / cm²). 2 Under irradiation, the mixture was stirred and reacted in a 40°C water bath for 60 minutes. After irradiation was stopped, pre-reaction solution A was obtained.

[0066] In another container, linear SBS (with a double bond content of 1.2 mmol / g, requiring approximately 16.67 g of SBS to provide 0.02 mol of double bonds) was dissolved in 150 mL of xylene and stirred overnight at room temperature until completely dissolved, yielding a homogeneous viscous solution B. Under nitrogen protection, SBS solution B was slowly added dropwise to the pre-reaction solution A over approximately 30 min. After the addition was complete, the reaction was stirred for another 30 min. The reaction solution was cooled to room temperature, washed three times with methanol to remove unreacted small molecules and solvent, rotary evaporated at 50 °C, and finally dried in a vacuum oven at 50 °C to constant weight, yielding a white, elastic solid product, denoted as SBS-PS.

[0067] like Figure 4 As shown, XPS full-spectrum and FTIR spectral characterization directly verify the successful execution of the thiol-alkene click chemistry reaction in this embodiment, as well as the effective grafting of phosphorus and sulfur flame-retardant functional groups onto the SBS molecular chain, confirming the successful preparation of modified SBS (SBS-PS). Specific characterization results are as follows:

[0068] Figure 4 In the figure, 'a' represents the XPS full spectrum of SBS and SBS-PS. Compared with the XPS spectrum of pure SBS, the spectrum of SBS-PS shows characteristic absorption peaks of P and S elements, and the intensity of the characteristic peaks is obvious. This directly proves that in this embodiment, phosphorus- and sulfur-containing functional groups were successfully grafted onto the SBS molecular chain through the thiol-alkene click chemistry reaction, realizing the phosphorus and sulfur functionalization modification of SBS, which is consistent with the design goals of the pre-reaction and grafting reaction.

[0069] Figure 4 In Figure b, the FTIR spectra of SBS and SBS-PS are shown. Compared with pure SBS, SBS-PS exhibits new characteristic absorption peaks at characteristic wavenumbers, such as phosphorus-oxygen bonds and carbon-sulfur bonds. At the same time, the intensity of the characteristic absorption peaks of the double bonds in the SBS molecular chain is significantly weakened. This phenomenon is supported by the functional group structure: on the one hand, the pre-reaction product of multifunctional thiols and phosphorus-containing double bond monomers undergoes an effective thiol-alkene click grafting reaction with the double bonds on the SBS molecular chain through the remaining thiol groups; on the other hand, the reaction sites on the SBS molecular chain are fully utilized, the degree of grafting reaction is controllable, and no abnormal changes in the characteristic peaks of functional groups due to over-reaction occur. This further proves that the grafting reaction process controlled by the molar ratio in this embodiment can stably achieve the functionalization modification of SBS, and the product structure meets the design requirements.

[0070] In addition, such as Figure 5As shown, the thermal performance characterization by TGA and DTG directly verifies the optimization of thermal stability and thermal decomposition behavior of modified SBS (SBS-PS) compared to pure SBS. This further confirms the role of phosphorus and sulfur functional groups in improving the thermal properties of SBS, laying the foundation for the subsequent flame retardant and heat aging resistance properties of the composite material. Specific characterization results are as follows:

[0071] Figure 5 In Figure 'a', the TGA curves of SBS and SBS-PS are shown. Compared with the TGA curve of pure SBS, the initial thermal decomposition temperature of SBS-PS is significantly increased, and the char residue rate during the entire thermal decomposition process is significantly higher than that of pure SBS. This directly proves that the successful grafting of phosphorus and sulfur functional groups in this embodiment effectively improves the thermal stability of SBS and slows down the thermal decomposition process of the material. At the same time, phosphorus and sulfur elements can promote the formation of char layer and increase the char residue rate during the thermal decomposition process, providing a condensed phase flame retardant basis for the material.

[0072] Figure 5 In Figure b, the DTG curves for SBS and SBS-PS are shown. Compared with pure SBS, the temperature corresponding to the maximum thermal decomposition rate of SBS-PS is significantly delayed, and the maximum thermal decomposition rate is significantly reduced. This phenomenon is supported by thermal decomposition kinetics: on the one hand, the grafting of phosphorus and sulfur functional groups has a significant inhibitory effect on the thermal decomposition of SBS molecular chains, slowing down the thermal breakage rate of molecular chains; on the other hand, the thermal decomposition process of modified SBS is smoother, and there is no sudden thermal decomposition caused by structural defects. This further proves that the thiol-ene click grafting reaction with precise molar ratio control in this embodiment can achieve functional modification of SBS while ensuring the regularity of the product molecular structure, so that the modified SBS has better thermal decomposition characteristics.

[0073] Example 3

[0074] This embodiment aims to provide a method for preparing a click chemistry-based durable flame-retardant TPE composite material. The specific process is as follows: 50 parts of phosphorus-sulfur modified styrene-butadiene-styrene (SBS-PS) prepared in Example 2 are added to a high-speed mixer and stirred at a speed of 100 r / min. Then, 20 parts of filler oil (such as paraffin oil) are added and mixed at a speed of 100 r / min for 12 minutes. Then, 10 parts of polypropylene and 20 parts of Si-N@APP prepared in Example 1 are added and mixed at a speed of 100 r / min for 6 minutes. The mixed material is poured into the hopper of a 180°C twin-screw extruder, extruded and granulated. The granules are then pressed into sheets in a flat vulcanizing machine to obtain the flame-retardant TPE composite material for testing.

[0075] Comparative Example 1

[0076] The TPE composite material in this comparative example is the same as that in Example 1, except that phosphorus-containing SBS and silazane-modified microencapsulated flame retardant were not prepared. Instead, the SBS-PS in Example 3 was replaced with an equal proportion of SBS, an equal proportion of APP and an equal proportion of SiAPP in this comparative example. The relevant experimental formulations are listed in Table 1.

[0077] The TPE composite material of Example 3 and the TPE composite material of Comparative Example 1 were made into sheets, and the flame retardant properties of the TPE composite material were tested. The test results are shown in Table 1 below.

[0078] Table 1. Formulation of TPE and its composites, and test results of UL-94 and oxygen index.

[0079]

[0080] Table 1 shows that the TPE-PS / Si-N@APP composite material prepared in this invention exhibits a significant, stepwise improvement in flame retardant performance compared to pure TPE, TPE-PS with only SBS modification, TPE / APP with physically filled APP, and TPE-PS / APP with modified SBS and physically filled APP. This fully verifies the synergistic flame retardant effect of phosphorus-sulfur grafted modified SBS and silazane-modified microencapsulated flame retardant Si-N@APP. Specifically: pure TPE has no flame retardant rating (NR) and a limiting oxygen index of only 22±0.5%, indicating significant flammability; TPE-PS obtained through click chemical modification has a limiting oxygen index increased to 25±0.5%, but still has no flame retardant rating, indicating that the grafting of phosphorus-sulfur functional groups can only slightly improve the oxygen index of the material and cannot meet the requirements for flame retardant classification; the TPE / APP with directly physically filled APP has a limiting oxygen index increased to 26±0.5%, but still has no flame retardant rating, reflecting... Traditional methods of using physically filled flame retardants have low flame retardant efficiency. TPE-PS / APP, which combines modified SBS with physically filled APP, achieves a flame retardant rating of V-1 and a limiting oxygen index (LOI) of 28±0.5%, indicating a certain synergistic flame retardant effect between modified SBS and APP, but still does not achieve high-efficiency flame retardancy. However, this invention, which combines modified SBS with the silazane-modified microencapsulated flame retardant Si-N@APP, successfully achieves a flame retardant rating of V-0 and a further increased LIO of 30±0.5%, making it the sample with the highest flame retardant rating and LIO among all samples. This confirms that the core-shell synergistic flame retardant system of the silazane-modified microencapsulated flame retardant forms a highly efficient synergistic flame retardant effect with the intrinsic flame retardant properties of modified SBS, significantly improving the flame retardant performance and rating of the composite material. This effectively solves the technical problems of poor flame retardancy and low flame retardant rating in traditional SBS-based TPE materials.

[0081] To further investigate the flame retardant properties of the TPE composite material prepared in this invention, cone calorimeter tests were conducted on each sample to analyze key flame retardant indicators such as heat release, smoke release, and gas generation. The specific test results are shown in Table 2.

[0082] Table 2 Summary of main parameters of TPE and its composites tested by cone calorimeter

[0083]

[0084] Table 2 shows that the TPE-PS / Si-N@APP composite material prepared in this invention exhibits the best flame retardant effect in all cone calorimeter test indicators. Compared with pure TPE and other comparative samples, heat release, smoke release, and toxic gas generation are significantly suppressed, fully demonstrating the high efficiency of the synergistic flame retardant system of phosphorus-sulfur grafted modified SBS and silazane-modified microencapsulated flame retardant Si-N@APP. Specifically, the peak heat release rate (PHRR) of pure TPE is as high as 1066.56 kW / m. 2 The total heat release (THR) is 44.407 MJ / m³. 2 The smoke release and CO generation rates were also at a high level, exhibiting a strong combustion hazard. While the TPE-PS with modified SBS showed a decrease in various indicators, the reduction was limited, indicating that the intrinsic flame retardancy of the matrix alone had a weak inhibitory effect on heat release. The PHRR and THR of the physically filled APP TPE / APP showed a significant decrease, demonstrating the flame retardant effect of APP, but the improvement in smoke release and gas generation was only moderate. The TPE-PS / APP with modified SBS combined with physically filled APP showed further optimization of various indicators, proving that there is a certain synergistic effect between matrix modification and physical flame retardant filling, which can effectively reduce the heat release rate. The PHRR of the TPE-PS / Si-N@APP composite material of this invention was reduced to 275.2 kW / m³. 2 The THR is only 21.983 MJ / m 2 Compared to pure TPE, the emissions were reduced by 74.2% and 50.5% respectively. Furthermore, its peak smoke release rate (PSPR), total smoke release rate (TSR), and peak CO formation rate (PCOR) were the lowest among all samples, decreasing to 0.174 m... 2 / s, 500.2m 2 / m 222.02 mg / s. This result fully demonstrates that the core-shell structure of the silazane-modified microencapsulated flame retardant can exert a dual flame-retardant effect in both the gas phase and the condensed phase. It forms a highly efficient synergy with the intrinsic flame-retardant properties of phosphorus-sulfur grafted modified SBS. This not only significantly reduces the heat release level of the material, but also effectively inhibits the generation of smoke and toxic gases, significantly improving the flame-retardant safety of the composite material. It solves the technical problem of traditional flame-retardant modification that only focuses on heat release inhibition and neglects smoke and toxic gas control.

[0085] Meanwhile, the improvement of flame retardant performance needs to take into account the maintenance of mechanical properties and aging resistance, which is the key to measuring the comprehensive application value of composite materials. For this reason, the mechanical properties and heat aging resistance at 165℃ for 14 days of each sample were tested, and the specific results are shown in Table 3.

[0086] Table 3. Test results of mechanical properties and heat aging resistance (165℃, 14 days) of each sample.

[0087]

[0088] Table 3 shows that the TPE-PS / Si-N@APP composite material prepared in this invention maintains excellent flame retardant properties while also possessing outstanding mechanical properties and heat aging resistance. This effectively solves the industry pain points of significant deterioration in mechanical properties and poor aging resistance in traditional flame retardant modification. It fully verifies the synergistic effect of phosphorus-sulfur grafted modified SBS and silazane-modified microencapsulated flame retardant Si-N@APP on improving the overall performance of the composite material. Specifically, pure TPE exhibits excellent mechanical properties before aging, with a tensile strength of 23.8 MPa and an elongation at break of 854.1%, but its heat aging resistance is extremely poor. After 14 days of heat aging at 165℃, the tensile strength retention rate is only 5.5%, and the elongation at break retention rate is only 3.8%, indicating almost complete loss of mechanical properties. Only the SBS-modified TPE-PS shows a slight improvement in mechanical properties before aging, and the performance retention rate is significantly improved after heat aging, indicating that phosphorus... Grafting sulfur functional groups not only imparts flame retardancy to the matrix but also enhances its resistance to thermal aging. The mechanical properties of TPE / APP directly physically filled with APP plummeted before aging, with a tensile strength of only 11.7 MPa, and the performance retention rate after thermal aging was low. This demonstrates that traditional physically filled flame retardants, due to poor compatibility with the matrix, severely degrade the mechanical properties of the material, and offer limited improvement in aging resistance. The mechanical properties and aging resistance of TPE-PS / APP combined with modified SBS and physically filled APP were slightly improved compared to TPE / APP before aging, but still did not achieve good performance retention. In contrast, the TPE-PS / Si-N@APP composite material of this invention achieved a tensile strength of 15.8 MPa and an elongation at break of 694.6% before aging, maintaining excellent mechanical properties. After 14 days of thermal aging at 165℃, the tensile strength retention rate was as high as 84.2%, and the elongation at break retention rate was 82.5%, the highest among all samples. This result fully demonstrates that the organic shell of the silazane-modified microencapsulated flame retardant significantly improves the interfacial compatibility between the flame retardant and the SBS matrix, avoiding the mechanical property degradation caused by flame retardant agglomeration. At the same time, the modified SBS and the benzene rings, phosphorus-carbon bonds and other structures contained in Si-N@APP synergistically enhance the heat aging resistance of the composite material, achieving synergistic optimization of flame retardant performance, mechanical properties and heat aging resistance, giving the composite material excellent comprehensive application performance.

[0089] In addition, such as Figure 7 As shown, through SEM microscopic morphology observation, WCA surface wettability testing, and surface elemental distribution characterization, the successful construction of the Si-N@APP core-shell structure of the silazane-modified microencapsulated flame retardant can be comprehensively verified from the dimensions of microstructure, interface characteristics, and elemental distribution. Furthermore, by comparing with comparative modified samples, the significant advantages of the click chemistry process of this invention in terms of coating uniformity, interfacial compatibility, and integration of multiple flame-retardant elements are highlighted. Specific characterization results are as follows:

[0090] Figure 7In the images, a, b, c, and d represent SEM images of APP, SiAPP, Si-N@APP, and the comparative modified sample, respectively. Pure APP exhibits an irregular blocky morphology with a smooth surface and uneven particle size distribution, showing obvious agglomeration. After modification with KH590, the surface of SiAPP becomes rougher, and the edges of the blocky structure show subtle modifications, improving the agglomeration phenomenon. In contrast, Si-N@APP, after being microencapsulated with silazane, forms a uniform organic coating shell on its surface, with a more regular overall morphology and more uniform particle size distribution, completely eliminating the obvious agglomeration problem and clearly showing the microscopic features of the core-shell structure. This demonstrates that the double-bonded silazane precursor, the double-bonded flame-retardant monomer, and the mercapto monomer successfully form a dense coating layer on the surface of the SiAPP core layer through a thiol-ene click chemistry reaction. The comparative modified sample shows uneven coating thickness, local damage, and residual agglomeration, highlighting the advantages of the click chemistry process of this invention in terms of coating uniformity and structural integrity.

[0091] Figure 7 In the image, g, h, i, and j represent the WCA optical images of APP, SiAPP, the comparative modified sample, and Si-N@APP, respectively. Pure APP is an inorganic flame retardant with strong surface hydrophilicity and a water contact angle of 0°. After modification with a silane coupling agent, organic functional groups are introduced into the surface of SiAPP, increasing the water contact angle to 54.4°, reducing hydrophilicity and enhancing hydrophobicity. The water contact angle of the comparative modified sample is 98.6°, and although the hydrophobicity is improved, it is still lower than that of Si-N@APP. However, due to the organic shell coating on the surface, the water contact angle of Si-N@APP is further significantly increased to 111.6°, and the hydrophobicity and organic compatibility are significantly optimized. This result proves that the interfacial compatibility between the modified flame retardant and the SBS organic matrix is ​​greatly improved, which can effectively prevent the flame retardant from agglomerating in the matrix and lay a microscopic foundation for maintaining the mechanical properties of the composite material.

[0092] Figure 7 In the diagrams, e1-e6 represent the surface element distribution of Si-N@APP, and f1-f6 represent the surface element distribution of the comparative modified sample. C, O, N, S, P, and Si elements can be clearly detected on the surface of Si-N@APP, and each element is uniformly distributed across the entire flame retardant particle surface without obvious local enrichment. This fully demonstrates that the click chemical coating reaction of the double-bonded silazane precursor, DPOEA, and mercapto-containing monomer occurs uniformly on the SiAPP surface, achieving the synergistic integration of multiple flame retardant elements such as P, N, Si, and S on the flame retardant surface. Although C, O, P, and Si elements can be detected in the comparative modified sample, the distribution of N and S elements is uneven, and the content is low in some areas, indicating that the coating reaction is insufficient and the shell structure is not intact enough, making it difficult to achieve efficient synergistic flame retardancy.

[0093] Therefore, based on Figure 7Multiple characterization results corroborate each other, confirming at the microscopic level the successful preparation of the Si-N@APP core-shell structure of the silazane-modified microencapsulated flame retardant of this invention. Simultaneously, it demonstrates that this click chemistry modification process effectively optimizes the microstructure and surface wettability of the flame retardant, achieving a uniform distribution of multiple flame-retardant elements. Compared to traditional modification methods, it exhibits superior coating uniformity and structural integrity, providing crucial microstructural support for the synergistic optimization of flame retardancy and mechanical properties when combined with modified SBS.

[0094] like Figure 8 As shown, by testing the free radical scavenging efficiency of APP, SiAPP, and Si-N@APP, the effectiveness of silazane-modified microencapsulated flame retardants in the gas-phase flame retardant process can be directly verified. The modification process clearly demonstrates the improvement in the free radical scavenging ability of the flame retardant, providing direct experimental evidence for the gas-phase flame retardant effect of the core-shell synergistic flame retardant system. Specific characterization results are as follows:

[0095] Pure APP exhibits the lowest free radical scavenging efficiency among the three, capturing only a small amount of free radicals. This indicates that unmodified ammonium polyphosphate has a weak inhibitory effect on active free radicals in the gas phase during combustion, and relying solely on its condensed-phase charring flame retardant mechanism is insufficient to achieve high-efficiency flame retardancy. SiAPP modified with silane coupling agent KH590 shows a certain improvement in free radical scavenging efficiency compared to pure APP, indicating that the organic functional groups introduced after silane modification endow the flame retardant with a certain free radical capturing ability, and the gas phase flame retardant effect is initially improved. Si-N@APP, after being microencapsulated with silazane, achieves a significant improvement in free radical scavenging efficiency compared to pure APP and SiAPP, exhibiting extremely strong free radical capturing ability under the same test conditions, making it the sample with the best free radical scavenging effect among the three.

[0096] This test result fully demonstrates that the present invention, through a thiol-olefin click chemistry reaction, coats the surface of the SiAPP core layer with an organic shell composed of a silazane precursor containing double bonds, a flame-retardant monomer containing double bonds, and a mercapto monomer. This successfully integrates multiple flame-retardant elements with free radical scavenging capabilities, such as phosphorus, sulfur, nitrogen, and silicon, into the flame retardant. These elements can synergistically release active groups during material combustion, efficiently capturing active free radicals such as hydroxyl and hydrogen in the gas phase, interrupting the chain reaction of combustion, and thus exerting excellent gas-phase flame-retardant effects. Simultaneously, this result also corroborates the aforementioned cone calorimeter test results showing a significant reduction in heat release and smoke generation in the Si-N@APP composite material. This confirms that the silazane-modified microencapsulated flame retardant achieves highly efficient synergistic flame retardancy through the dual effects of gas-phase free radical capture and the formation of a dense condensed carbon layer. Combined with the intrinsic flame-retardant properties of phosphorus-sulfur grafted modified SBS, this further enhances the overall flame-retardant performance of the composite material.

[0097] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A click chemistry-based durable flame-retardant TPE composite material, characterized in that, The raw materials consist of the following components by mass: 10-60 parts of modified SBS prepared based on click chemistry, 5-40 parts of filler oil, 2-15 parts of polypropylene, and 10-20 parts of silazane-modified microencapsulated flame retardant; the modified SBS prepared based on click chemistry is phosphorus-sulfur-grafted SBS obtained through a thiol-olefin click chemistry reaction; the silazane-modified microencapsulated flame retardant has a core-shell structure, with the core layer being a silane coupling agent-modified flame retardant, and the shell layer being a coating layer formed by a double-bonded silazane precursor, a double-bonded flame-retardant monomer, and a mercapto-containing monomer through a thiol-olefin click chemistry reaction; The modified SBS prepared based on click chemistry is obtained by a method comprising the following steps: Step 1, Pre-reaction: A polyfunctional thiol compound and a monofunctional compound containing double bonds are dissolved in an organic solvent, a photoinitiator is added, and a thiol-ene click chemical reaction occurs under ultraviolet light irradiation in an inert atmosphere to obtain a pre-reaction solution; the molar ratio of the polyfunctional thiol compound to the monofunctional compound containing double bonds is 1:2; wherein the monofunctional compound containing double bonds is diphenylphosphine chloride grafted with hydroxyethyl acrylate; Step 2, Grafting reaction: SBS is dissolved in an organic solvent to obtain an SBS solution; the SBS solution is added to a pre-reaction solution, and a grafting reaction is carried out under light irradiation. After the reaction is completed, modified SBS is obtained through post-treatment. The SBS is linear or star-shaped SBS. The ratio of the number of moles of double bonds in the SBS to the number of moles of remaining thiol groups in the pre-reaction solution is 1.5~2.0:

1.

2. The click chemistry-based durable flame-retardant TPE composite material according to claim 1, characterized in that, The filler oil is selected from one or more of paraffin oil, naphthenic oil, and aromatic oil; the polypropylene is selected from one or more of homopolymer polypropylene and copolymer polypropylene.

3. The click chemistry-based durable flame-retardant TPE composite material according to claim 1, characterized in that, The raw materials of the silazane-modified microencapsulated flame retardant are composed of the following components by mass parts: 85 parts flame retardant, 1-10 parts silazane precursor containing double bonds, 1-10 parts flame retardant monomer containing double bonds, and 1-10 parts mercapto monomer.

4. The click chemistry-based durable flame-retardant TPE composite material according to claim 3, characterized in that, The flame retardant is selected from one or more of the following: magnesium hydroxide, aluminum hydroxide, dihydroxide, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, charring agent, ammonium polyphosphate, piperazine pyrophosphate, aluminum hypophosphite, aluminum phosphonate, expandable graphite, zinc borate, graphene, transition metal disulfides, carbon nanotubes, halloysite, sepiolite, and kaolin; the silane coupling agent is γ-mercaptopropyltrimethoxysilane; the double-bonded silazane precursor is trivinyltrimethylcyclotrisilazane; and the double-bonded flame retardant monomer is diphenylphosphine chloride grafted with hydroxyethyl acrylate.

5. The click chemistry-based durable flame-retardant TPE composite material according to claim 3, characterized in that, The thiol-containing monomer is selected from one or more of 4,4'-dimercaptobiphenyl, 4,4'-dimercaptodiphenyl ether, trimercaptotriazine, trimethylolpropane tri(3-mercaptopropionic acid) ester, 1,2,4,5-tetramercaptobenzene, and pentaerythritol tetramercaptopropionate.

6. The click chemistry-based durable flame-retardant TPE composite material according to claim 1, characterized in that, The multifunctional thiol compound is trimethylolpropane tris(3-mercaptopropionic acid) ester; the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; a phenolic antioxidant is added to the reaction system as a polymerization inhibitor, and the amount of the polymerization inhibitor added is 0.1% to 1% of the total mass of the reaction system; the organic solvent is selected from one or two of toluene and xylene.

7. The click chemistry-based durable flame-retardant TPE composite material according to claim 1, characterized in that, The silazane-modified microencapsulated flame retardant is prepared by a method comprising the following steps: Step A: Prepare flame retardant monomers containing double bonds and flame retardants modified with silane coupling agents; Step B: Disperse the silane coupling agent modified flame retardant in a solvent, add a flame retardant monomer containing double bonds, a silazane precursor containing double bonds, and a mercapto monomer, add a photoinitiator under a nitrogen atmosphere, and conduct a thiol-ene click chemical reaction under ultraviolet light irradiation. After the reaction is completed, the silazane modified microencapsulated flame retardant is obtained through post-treatment.

8. The click chemistry-based durable flame-retardant TPE composite material according to claim 7, characterized in that, The specific preparation process of step A includes: Preparation of flame-retardant monomers containing double bonds: Hydroxyethyl acrylate and triethylamine were added to anhydrous dichloromethane to form a reaction system. Diphenylphosphine chloride was dissolved in dichloromethane and added dropwise to the reaction system. After the addition was complete, the reaction was stirred for 4-6 hours under a nitrogen atmosphere and at room temperature. After post-treatment, flame-retardant monomers containing double bonds were obtained. Preparation of flame retardant modified with silane coupling agent: Flame retardant, silane coupling agent and ethanol-water mixed solvent are added to the reaction system, the pH is adjusted to 10, emulsifier is added, the temperature is raised to 40~60℃ and reacted for 4~8h. After the reaction is completed, the flame retardant modified with silane coupling agent is obtained through post-treatment.

9. A method for preparing a click chemistry-based durable flame-retardant TPE composite material as described in any one of claims 1 to 8, characterized in that, The process includes the following steps: mixing modified SBS prepared based on click chemistry with filler oil in parts by mass, then adding polypropylene and silazane-modified microencapsulated flame retardant and mixing them evenly; mixing the mixture evenly at 170~200℃, and then pressing it into shape to obtain TPE composite material.

Images