P / n / si multi-element reactive halogen-free flame retardant, and preparation method and application thereof

Abstract

The application discloses a preparation method of a P / N / Si multi-element reactive halogen-free flame retardant, specifically comprising the following steps: preparing DOPO grafted 3-chloropropyl trimethoxysilane, which is denoted as PPTMS; preparing a cage-like POSS containing DOPO, which is denoted as PSC; mixing the PSC with toluene to obtain a PSC solution; uniformly mixing maleimide MI with toluene, dropwise adding the PSC solution into the maleimide MI solution to perform a condensation reflux reaction, and performing vacuum rotary evaporation to obtain the P / N / Si multi-element reactive halogen-free flame retardant. The phosphorus-containing monomer, the nitrogen-containing monomer and the silicon-containing monomer in the flame retardant are covalently bonded, and the multi-elements in the molecule exist in the form of a collection acid source, a carbon source, a gas source and a ceramicization, wherein the phosphorus-containing monomer is dehydrated into carbon, the nitrogen-containing monomer releases non-combustible gas to dilute the gas phase, and the silicon-containing monomer forms a dense ceramic barrier layer to improve the triple synergy of carbon residue strength and anti-dripping property, thereby greatly improving the flame retardant efficiency.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant preparation technology, specifically relating to a method for preparing a P / N / Si multi-element reactive halogen-free flame retardant, and also relating to the P / N / Si multi-element reactive halogen-free flame retardant and its applications. Background Technology

[0002] Polypropylene (PP) boasts numerous advantages, including low density, low cost, good processing performance, mechanical properties, and chemical resistance. As one of the most widely produced and applied general-purpose plastics, it is extensively used in core fields such as automotive lightweighting, electronics, and building materials. However, PP, composed of carbon and hydrogen atoms, has a limiting oxygen index (LOI) of only 17.4-18%, far lower than the oxygen content in air (21%). This makes PP highly susceptible to continuous combustion in air, accompanied by molten dripping, posing a serious safety hazard and severely limiting its application in scenarios requiring combustion. While traditional halogenated flame retardants exhibit excellent flame-retardant effects, they release large amounts of toxic and corrosive gases and fumes such as dioxins and hydrogen halides during combustion.

[0003] Currently, conventional halogen-free flame retardants are mainly classified into phosphorus-based, nitrogen-based, silicon-based, and metal compound-based systems. Single-system approaches often suffer from drawbacks such as poor flame retardancy, excessively high dosage requirements, and difficulty in achieving optimal mechanical properties. For example, phosphorus-based flame retardants primarily achieve flame retardancy through condensed carbon formation, but suffer from drawbacks such as high dosage and easy precipitation. Nitrogen-based flame retardants achieve flame retardancy by releasing non-combustible gases and diluting the gas phase. Silicon-based flame retardants achieve flame retardancy by forming a ceramic insulating layer on the surface, but their flame retardant effect is very limited when used alone, making it difficult to meet the flame retardant requirements of high-end applications. Metal compound flame retardants only achieve effective flame retardancy when added at a dosage greater than 40%, but this proportion causes PP embrittlement and a significant decrease in mechanical properties. Therefore, developing a multi-system synergistic flame retardant with low dosage, good compatibility with PP, and high flame retardant effect is of great industrial significance. Summary of the Invention

[0004] The primary objective of this invention is to provide a method for preparing a P / N / Si multi-element reactive halogen-free flame retardant, which solves the problems of poor mechanical properties and low flame retardant efficiency of existing flame retardants.

[0005] A second objective of this invention is to provide a P / N / Si multi-element reactive halogen-free flame retardant.

[0006] A third objective of this invention is to provide the application of a P / N / Si multi-element reactive halogen-free flame retardant in the preparation of PSMI-modified polypropylene materials.

[0007] The first technical solution adopted in this invention is a method for preparing a P / N / Si multi-element reactive halogen-free flame retardant, specifically implemented according to the following steps: Step 1: Prepare DOPO-grafted 3-chloropropyltrimethoxysilane, denoted as PPTMS; Step 2: Prepare cage-like POSS containing DOPO, denoted as PSC; Step 3: Mix PSC with toluene to obtain a PSC solution; mix maleimide MI with toluene evenly, add it dropwise to the PSC solution for reflux reaction, and evaporate under reduced pressure to obtain oil droplet-shaped product PSMI, which is a P / N / Si multi-element reactive halogen-free flame retardant.

[0008] The invention is further characterized in that, Step 1 specifically involves: Dissolve OH-DOPO in N,N-dimethylformamide and stir at 70-80℃ for 30-40 min to obtain an OH-DOPO solution; CPTMS was dissolved in DMF and added to an OH-DOPO solution under a N2 atmosphere. The reaction was carried out at 100-110℃ for 14-16 h. The solvent was removed by rotary evaporation under reduced pressure, and the product was dried to obtain DOPO-grafted 3-chloropropyltrimethoxysilane PPTMS. The molar ratio of OH-DOPO to CPTMS was 1-1.2:1.

[0009] Step 2 specifically involves: PPTMS was added to tetrahydrofuran under N2 atmosphere, followed by deionized water, and the reaction was carried out under reflux at a temperature of 50-55℃ for 30-40 min. Sodium hydroxide was then added and the mixture was stirred for 15-20 h. The solvent was removed by vacuum distillation and dried to obtain a pale yellow solid. Under a nitrogen atmosphere, a pale yellow solid was mixed with anhydrous tetrahydrofuran and refluxed at -5℃ to 0℃ for 20-30 minutes to obtain a reaction solution. 2-Chloroethyltrichlorosilane was diluted in anhydrous tetrahydrofuran and added dropwise to the reaction solution at a uniform rate over 60-70 minutes. After the addition was complete, triethylamine was added, and the mixture was stirred at -5°C to 0°C for 18-20 hours. After the reaction was complete, the product was washed with cold anhydrous tetrahydrofuran and dried under vacuum to obtain PSC. The molar ratio of PPTMS to sodium hydroxide was 6-7:1; the molar ratio of the pale yellow solid product, triethylamine, and 2-chloroethyltrichlorosilane was 1-1.2:3-4:10-11.

[0010] Step 3 specifically involves: Under a nitrogen atmosphere, PSC and toluene are mixed and stirred at 60-70℃ for 20-30 minutes to obtain a PSC solution. Maleimide (MI) was mixed with toluene and added dropwise to a PSC solution at 80-90°C. The mixture was then subjected to reflux for 10-12 hours. The solvent was removed by rotary evaporation under reduced pressure to obtain the oil droplet product PSMI. The molar ratio of PSC to MI was 1-1.2:1.

[0011] The second technical solution adopted in this invention is a method for preparing a P / N / Si multi-element reactive halogen-free flame retardant.

[0012] The third technical solution adopted in this invention is a method for preparing PSMI-modified polypropylene material, specifically as follows: Weigh out the following components by mass percentage: 2%-14% PSMI, 0.2% primary antioxidant 1010, 0.1% secondary antioxidant 168, 0.3% lubricant calcium stearate, 0.1% initiator dicumyl peroxide, 2% KT-1, and the balance is polypropylene. The sum of the mass percentages of the above components is 100%. Polypropylene, PSMI, primary antioxidant 1010, secondary antioxidant 168, calcium stearate, DCP, and KT-1 are mixed in a high-speed mixer; the resulting mixture is added to a twin-screw extruder for melt blending, cooled, and then granulated; it is then fed into the heated barrel of an injection molding machine for plasticization, finally yielding PSMI-modified polypropylene material.

[0013] The beneficial effects of this invention are: (1) In the P, N and Si multi-element flame retardant (PSMI) of the present invention, the phosphorus-containing monomer, nitrogen-containing monomer and silicon-containing monomer are covalently bonded. The multi-element existence in the molecule combines acid source, carbon source, gas source and ceramicization. Among them, the phosphorus-containing monomer dehydrates into carbon, the nitrogen-containing monomer releases non-combustible gas and dilutes the gas phase, and the silicon-containing monomer forms a dense ceramic barrier layer, which improves the residual char strength and anti-dripping properties in a triple synergistic effect, greatly improving the flame retardant efficiency. (2) The halogen-free flame retardant of the present invention has better compatibility with non-polar PP. The silicon chain segment has good flexibility and steric hindrance effect. The addition of maleimide group in the flame retardant can be grafted onto the PP molecular chain through chemical reaction, resulting in a larger interfacial contact area with PP, further improving interfacial bonding, making it less prone to precipitation and frosting, and having a high mechanical property retention rate. Attached Figure Description

[0014] Figure 1 This is a flowchart of the preparation process of PPTMS in the method of this invention; Figure 2 This is a flowchart of the PSC preparation process in the method of this invention; Figure 3This is a flowchart of the preparation process of PSMI in the method of this invention; Figure 4 These are test diagrams of the bending strength and bending modulus of the sample in the embodiment of the present invention and the comparative sample; Figure 5 These are limiting oxygen index test graphs of the samples in the embodiments of the present invention and the comparative samples; Figure 6 These are test graphs of the char residue rate of the sample in the embodiment of the present invention and the comparative sample; Figure 7 These are impact strength test diagrams of the sample in the embodiment of the present invention and the comparative sample. Detailed Implementation

[0015] The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant of the present invention is carried out according to the following steps: Step 1, preparing DOPO-grafted 3-chloropropyltrimethoxysilane CPTMS (PPTMS), specifically: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-ethanol 10-oxide (OH-DOPO) was dissolved in N,N-dimethylformamide (DMF) and stirred uniformly at 70-80℃ for 30-40 min to obtain an OH-DOPO solution. 3-Chloropropyltrimethoxysilane (CPTMS) was dissolved in DMF and slowly added to an OH-DOPO solution under a N2 atmosphere. The reaction was carried out at 100-110℃ for 14-16 h. Finally, the solvent was removed by rotary evaporation under reduced pressure and the solution was dried to obtain DOPO-grafted 3-chloropropyltrimethoxysilane (PPTMS). The molar ratio of OH-DOPO to CPTMS is 1-1.2:1; The synthesis of PPTMS mainly involves an SN2 nucleophilic substitution reaction, which causes the oxygen atom of the hydroxyl group on OH-DOPO to acquire a lone pair of electrons. This lone pair acts as a nucleophile to attack the C-Cl bond on CPTMS, forming a CO ether bond, thus enabling the phosphorus-containing monomer to be successfully grafted onto the silicon-containing monomer.

[0016] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-ethanol 10-oxide (OH-DOPO) was purchased from Henan Weitixi Chemical Technology Co., Ltd. Step 2, prepare cage-like POSS (PSC) containing DOPO, specifically as follows: PPTMS was added to tetrahydrofuran under N2 atmosphere, followed by deionized water, and the reaction was carried out under reflux at a temperature of 50-55℃ for 30-40 min. Sodium hydroxide was then added and the mixture was stirred for 15-20 h. Finally, the solvent was removed by vacuum distillation and dried to obtain a pale yellow solid. The molar ratio of DOPO-grafted 3-chloropropyltrimethoxysilane (PPTMS) to sodium hydroxide (NaOH) is 6-7:1; Under a nitrogen atmosphere, a pale yellow solid was mixed with anhydrous tetrahydrofuran and refluxed at -5℃ to 0℃ for 20-30 minutes to obtain a reaction solution. 2-Chloroethyltrichlorosilane was diluted in anhydrous tetrahydrofuran and added dropwise to the reaction solution at a uniform rate over 60-70 minutes. After the addition was complete, triethylamine was added, and the mixture was stirred at -5°C to 0°C for 18-20 hours. After the reaction was complete, the product was washed multiple times with cold anhydrous tetrahydrofuran to remove impurities. Finally, it was vacuum dried at 50°C for 24 hours to obtain DOPO-containing cage-like POSS (PSC).

[0017] The molar ratio of the pale yellow solid product, triethylamine, and 2-chloroethyltrichlorosilane is 1-1.2:3-4:10-11. Trimethoxysilane on PPTMS undergoes hydrolysis and self-condensation under THF and NaOH conditions to generate a cage-like POSS sodium salt intermediate with silicon oxide anions. Then, through low temperature and triethylamine binding acid, the POSS silicon oxide anions attack the chlorinated carbon of 2-chloroethyltrichlorosilane, removing the chlorine atom. Silicon oxide then bonds with silane to obtain PSC, thus successfully preparing the POSS structure carrying phosphorus-containing monomers.

[0018] Step 3: Prepare cage-like POSS (PSMI) containing DOPO and maleimide (MI), which is a P / N / Si multi-element reactive halogen-free flame retardant; specifically: Under a nitrogen atmosphere, PSC and toluene are mixed and stirred uniformly at 60-70℃ for 20-30 minutes to obtain a PSC solution. Maleimide (MI) was mixed with toluene and added dropwise to a PSC solution at 80-90°C. The mixture was then subjected to reflux for 10-12 hours. Finally, the solvent was removed by rotary evaporation under reduced pressure to obtain the oil droplet product PSMI.

[0019] The molar ratio of PSC to MI is 1-1.2:1; The reaction of PSC with maleamide monomer is also an SN2 nucleophilic substitution reaction. The maleamide monomer provides a nucleophilic nitrogen atom to attack the alkyl carbon bonded to chlorine on PSC. The C-Cl bond breaks, the chlorine atom is released, and maleimide is finally grafted onto the phosphorus-containing monomer PSC.

[0020] The halogen-free flame retardant of the present invention introduces phosphorus, nitrogen and silicon elements, and the maleamide monomer has double bonds. Under the catalysis of the peroxide initiator, the polypropylene main chain is melt-grafted to form a tertiary carbon macromolecular active free radical with a single electron. This radical readily undergoes an electrophilic addition reaction with the double bonds on the maleamide group, so that the flame retardant is successfully grafted onto the polypropylene.

[0021] The preparation method of the PSMI-modified polypropylene material of the present invention is as follows: Weigh out the following components by mass percentage: 2%-14% PSMI, 0.2% primary antioxidant 1010, 0.1% secondary antioxidant 168, 0.3% lubricant calcium stearate, 0.1% initiator dicumyl peroxide, 2% KT-1 (PP grafted maleic anhydride compatibilizer), with the balance being polypropylene. The sum of the mass percentages of the above components is 100%. Polypropylene, PSMI, primary antioxidant 1010, secondary antioxidant 168, calcium stearate, DCP, and KT-1 were mixed in a high-speed mixer. The resulting mixture was then melt-blended in a twin-screw extruder, cooled, and granulated. The granulated mixture was then fed into the heated barrel of an injection molding machine for plasticization, ultimately yielding PSMI-modified polypropylene material. The high-speed mixer operates at 300-400 rpm and the mixing time is 10-20 minutes. The temperatures of the ten zones of the twin-screw extruder are as follows: Zone 1: 150-160℃, Zone 2: 190-200℃, Zone 3: 210-220℃, Zone 4: 220-230℃, Zone 5: 220-230℃, Zone 6: 220-230℃, Zone 7: 220-230℃, Zone 8: 220-230℃, Zone 9: 210-220℃, Zone 10: 220-230℃; The main motor speed of the twin-screw extruder is 300-350 rpm, and the main feed speed is 500-550 rpm. The barrel temperature of the injection molding machine is 210-230℃, and the plasticizing time is 6-8s; The density of polypropylene is 0.9 g / cm³. 3 Under test conditions of 230℃ / 2.16kg, the melt flow rate was 26 g / 10min, and the impact strength at room temperature was 40KJ / m. 2 The tensile strength is 18 MPa, the flexural strength is 21 MPa, and the flexural modulus is 800 MPa. In the flame retardant of the present invention, the phosphorus-containing monomer, nitrogen-containing monomer, and silicon-containing monomer are covalently bonded. The presence of multiple elements within the molecule integrates acid source, carbon source, gas source, and ceramization. Among them, the phosphorus-containing monomer dehydrates to form carbon, the nitrogen-containing monomer releases non-combustible gas to dilute the gas phase, and the silicon-containing monomer forms a dense ceramized barrier layer, which enhances the residual char strength and anti-dripping properties in a triple synergistic effect, resulting in high flame retardant efficiency. The halogen-free flame retardant of this invention has better compatibility with non-polar PP. The silicon segments have good flexibility and steric hindrance effect. Furthermore, the addition of maleimide groups in the flame retardant can be grafted onto the PP molecular chain through chemical reaction, resulting in a larger interfacial contact area with PP, further enhancing interfacial bonding, making it less prone to precipitation and blooming, and maintaining high mechanical properties.

[0022] Example 1 The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant of the present invention is carried out according to the following steps: Step 1, the preparation method of DOPO grafted with 3-chloropropyltrimethoxysilane (CPTMS) (i.e., PPTMS), specifically includes the following steps: First, 14.6 g of OH-DOPO was dissolved in 150 mL of N,N-dimethylformamide (DMF) solution and poured into a 250 mL three-necked flask. The mixture was stirred uniformly at 75 °C for 30 min. Then, a nitrogen atmosphere was established in the system. 11.16 g of CPTMS was dissolved in DMF and slowly added to the system. The reaction was carried out at 100 °C for 14 h. The solvent was removed by rotary evaporation under reduced pressure, and the product was dried to obtain PPTMS. The reaction equation is as follows: Figure 1 As shown; Step 2, the preparation method of DOPO-containing cage-like POSS (PSC), specifically includes the following steps: In a reaction vessel, 18.5 g of PPTMS was added to 50 mL of tetrahydrofuran solution, and a reflux emplacement and N2 atmosphere were established. Then, 1.05 mL of deionized water was added, and the mixture was vigorously stirred at 50 °C for 30 min. Next, 0.79 g of sodium hydroxide was added, and stirring continued for 15 h. Finally, the solvent was removed by vacuum distillation, and the resulting pale yellow solid was dried. This pale yellow solid and anhydrous tetrahydrofuran were then simultaneously added to a reaction vessel prepared with reflux and N2 atmosphere, and stirred while maintaining the system temperature at -5 °C to 0 °C. Subsequently, 12.3 g of 2-chloroethyltrichlorosilane was diluted with 20 mL of anhydrous tetrahydrofuran and added dropwise to the reaction system under a nitrogen atmosphere over a period of 1 hour. After the addition was complete, 16.4 mL of triethylamine was added, and stirring continued at -5 °C to 0 °C for 20 hours. After the reaction was complete, the product was washed multiple times with cold anhydrous tetrahydrofuran to remove impurities, and finally dried under low-temperature vacuum to obtain PSC. The reaction equation is as follows: Figure 2 As shown; Step 3, the preparation method of cage-like POSS (PSMI) containing DOPO and maleimide (MI), specifically includes the following steps: 24.1 g PSC and 120 mL toluene solution were added to a 250 mL three-necked flask. The mixture was stirred uniformly at 60 °C, and nitrogen gas was bubbled through the system, with a reflux purging device in place. Simultaneously, 10.2 g MI was added to the homogeneous solution for further dissolution. The temperature was then raised to 90 °C, and the solution was added dropwise to the system through a separatory funnel. The reaction was allowed to proceed for 10 h. Finally, the solvent was removed by rotary evaporation under reduced pressure to obtain the oil droplet product (PSMI). The reaction equation is as follows: Figure 3 As shown.

[0023] Example 2 The mechanical and flame retardant properties of the PSMI reactive flame retardant modified PP obtained in Example 1 were tested, as follows: 86%-98% polypropylene (CNOOC Shell Petrochemicals Co., Ltd., melt flow index 26 g / 10min), X parts PSMI, 0.2% primary antioxidant 1010, 0.1% secondary antioxidant 168, 0.3% calcium stearate, 0.1% DCP, and 2% KT-1 were mixed in a high-speed mixer (300 rpm, 10 min). The resulting mixture was then melt-blended in a twin-screw extruder, which had 10 temperature zones: Zone 1: 150℃, Zone 2: 190℃, Zone 3: 210℃, Zone 4: 220℃, Zone 5: 220℃, Zone 6: 220℃, Zone 7: 220℃, Zone 8: 220℃, Zone 9: 210℃, Zone 10: 220℃. The main extruder speed was 450 rpm, and the main feed speed was 550 rpm. After cooling, the mixture was granulated. The sample was plasticized in the heated barrel of the injection molding machine using the injection molding method. The barrel temperature was 220℃. Finally, a standard sample was made and placed in a constant temperature and humidity test chamber at 23℃ and 50% humidity for 24 hours before performance testing.

[0024] The following seven groups of samples were set up: Sample A is a PSMI-modified polypropylene material with 2 wt% added PSMI; Sample B is a PSMI-modified polypropylene material with 4 wt% added PSMI; Sample C is a PSMI-modified polypropylene material with 6 wt% added PSMI; Sample D is a PSMI-modified polypropylene material with 8 wt% added PSMI; Sample E is a PSMI-modified polypropylene material with 10 wt% added PSMI; Sample F is a PSMI-modified polypropylene material with 12 wt% added PSMI; Sample G is a PSMI-modified polypropylene material with 14 wt% added PSMI; Comparative Example 1 sample was made of pure polypropylene; Comparative Example 2 sample was a modified polypropylene material with 14 wt% OH-DOPO added; that is, OH-DOPO was added to polypropylene as a flame retardant. Comparative Example 3 was a modified polypropylene material with 14 wt% POSS added; that is, 14% POSS was added to polypropylene as a flame retardant. Comparative Example 4 is a modified polypropylene material with 14 wt% MI added; that is, 14% MI is added to polypropylene as a flame retardant. Example 3 The mechanical property test results of all proportion samples are shown in Table 1. Table 1. Test results of mechanical properties of the samples

[0025] The melt flow index was tested at 230℃ and 2.16kg, the flexural strength and flexural modulus were tested at 2mm / min, and the tensile strength was tested at 50mm / min.

[0026] like Figure 4 , Figure 7 As shown, pure PP and flame retardants containing single elements of N, P, and Si were used as comparative examples. The experimental results showed that in the AG sample of this invention, as the proportion of flame retardant increased, the impact strength decreased slightly, but the melt flow index, flexural strength, and flexural modulus all significantly improved. On one hand, small-molecule phosphides act as internal lubricants, while organosilicon acts as external lubricants, improving material flowability. On the other hand, the Si-O-Si rigid framework contained in the PSMI flame retardant is added to the PP system, restricting molecular chain movement and increasing the overall rigidity of the material. Furthermore, because PSMI can undergo a grafting reaction with PP, unlike simple composites, its compatibility is better, thus reducing the possibility of agglomeration and making the decrease in impact strength less significant.

[0027] Example 4 The flame retardant performance test results for all proportions of samples are shown in Table 2. Table 2 Flame retardant performance test results

[0028] Using pure PP and flame retardants containing single elements of N, P, and Si as comparative examples, the experimental results showed that in the AG sample of this invention, the flame retardant decomposed prematurely, releasing acid / gas sources, which catalyzed the premature carbonization of PP, thus causing the temperature at which the weight loss of 5% gradually decreased. In contrast, single phosphorus-based flame retardants (Comparative Example 2) and single nitrogen-based flame retardants (Comparative Example 4) were prone to decomposition at low temperatures, leading to premature decomposition and damage to PP segments, resulting in a decrease in the initial thermal stability of the material. In contrast, the single silicon flame retardant (Comparative Example 3) exhibited high thermal stability, remained inert and heat-resistant throughout the process, and did not decompose at low temperatures. Therefore, the temperature at which Comparative Example 3 lost 5% of its weight gradually decreased. 5% Comparison of T values ​​in ratios 2 and 4 5% The rate is higher than that of the embodiment containing PSMI flame retardant with P, N, and Si elements, mainly due to the premature decomposition of P and N elements in the flame retardant. Furthermore, in the sample AG of this invention, the maximum decomposition rate T increases with the increase of the proportion of flame retardant. max% As the process progresses, the maximum decomposition rate Rmax decreases. This is also due to the formation of a stable SiO2 network by silicon, which increases stability at high temperatures, thus reducing the maximum decomposition rate and mitigating the severe cracking caused by P and N elements. Furthermore, compared to the increase in flame retardants, the char residue at 700℃ also gradually increases. This is mainly attributed to the catalytic dehydration of P and N elements leading to carbonization, and the formation of a dense silicon-carbon composite layer after Si combustion, resulting in a gradual increase in char residue. Figure 6 As shown above, the results indicate that the PSMI flame retardant material containing P, N, and Si exhibits improved thermal stability and flame retardant performance due to the combined effect of the three elements, and is significantly superior to the performance of a single flame retardant.

[0029] Example 5 The combustion performance test results of all samples are shown in Table 3. Table 3 Combustion performance test results

[0030] Using pure PP and flame retardants containing single elements of N, P, and Si as comparative examples, the experimental results clearly show that in the AG sample of this invention, the limiting oxygen index (LOI value) continuously increases with the increase of the proportion of flame retardant. Figure 5 As shown; and when more than 12% PSMI flame retardant is added, UL94 can reach V0 level. This is also the effective result of the synergistic effect of the three elements P, N and Si. Other single-element flame retardants are difficult to achieve such an effect.

[0031] Example 6 This invention relates to a P / N / Si multi-element reactive halogen-free flame retardant that combines the advantages of multiple flame-retardant elements to achieve a significant "1+1>2" effect, overcoming the performance deficiencies of single-system flame retardants. It simultaneously leverages the characteristics of phosphorus, nitrogen, and silicon flame-retardant systems, and utilizes the double bonds on PSMI to react with PP to form a reactive flame retardant. This achieves high flame-retardant performance across multiple systems. Furthermore, the presence of non-polar Si-O-Si chains acts as a "bridge" within the system, significantly adjusting interfacial compatibility. Additionally, direct grafting onto the PP molecular chain improves the compatibility between the flame retardant and PP, preventing detachment during use and ensuring excellent performance.

Claims

1. A method for preparing a P / N / Si multi-element reactive halogen-free flame retardant, characterized in that, The specific steps are as follows: Step 1: Prepare DOPO-grafted 3-chloropropyltrimethoxysilane, denoted as PPTMS; Step 2: Prepare cage-like POSS containing DOPO, denoted as PSC; Step 3: Mix PSC with toluene to obtain a PSC solution; mix maleimide MI with toluene evenly, add it dropwise to the PSC solution for reflux reaction, and evaporate under reduced pressure to obtain oil droplet-shaped product PSMI, which is a P / N / Si multi-element reactive halogen-free flame retardant.

2. The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in claim 1, characterized in that, In step 1, specifically: Dissolve OH-DOPO in N,N-dimethylformamide and stir at 70-80℃ for 30-40 min to obtain an OH-DOPO solution; CPTMS was dissolved in DMF and added to an OH-DOPO solution under a N2 atmosphere. The reaction was carried out at 100-110℃ for 14-16 h. The solvent was removed by rotary evaporation under reduced pressure and the solution was dried to obtain DOPO-grafted 3-chloropropyltrimethoxysilane PPTMS.

3. The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in claim 2, characterized in that, The molar ratio of OH-DOPO to CPTMS is 1-1.2:

1.

4. The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in claim 1, characterized in that, Step 2 specifically involves: PPTMS was added to tetrahydrofuran under N2 atmosphere, followed by deionized water, and the reaction was carried out under reflux at a temperature of 50-55℃ for 30-40 min. Sodium hydroxide was then added and the mixture was stirred for 15-20 h. The solvent was removed by vacuum distillation and dried to obtain a pale yellow solid. Under a nitrogen atmosphere, a pale yellow solid was mixed with anhydrous tetrahydrofuran and refluxed at -5℃ to 0℃ for 20-30 minutes to obtain a reaction solution. 2-Chloroethyltrichlorosilane was diluted in anhydrous tetrahydrofuran and added dropwise to the reaction solution at a constant rate over a period of 60-70 minutes. After the addition was complete, triethylamine was added, and the mixture was stirred at -5°C to 0°C for 18-20 hours. After the reaction was completed, the product was washed with cold anhydrous tetrahydrofuran and dried under vacuum to obtain PSC.

5. The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in claim 4, characterized in that, The molar ratio of PPTMS to sodium hydroxide is 6-7:1; The molar ratio of the pale yellow solid product, triethylamine, and 2-chloroethyltrichlorosilane is 1-1.2:3-4:10-11.

6. The preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in claim 1, characterized in that, Step 3 specifically involves: Under a nitrogen atmosphere, PSC and toluene are mixed and stirred at 60-70℃ for 20-30 minutes to obtain a PSC solution. Maleimide (MI) was mixed with toluene and added dropwise to a PSC solution at 80-90°C. The mixture was then subjected to reflux for 10-12 hours. The solvent was removed by rotary evaporation under reduced pressure to obtain the oil droplet product PSMI. The molar ratio of PSC to MI was 1-1.2:

1.

7. The P / N / Si multi-element reactive halogen-free flame retardant prepared by the preparation method of any one of claims 1-6.

8. The application of the preparation method of the P / N / Si multi-element reactive halogen-free flame retardant as described in any one of claims 1-6 in the preparation of PSMI modified polypropylene materials.

9. The application as described in claim 8, characterized in that, The preparation method of PSMI-modified polypropylene material is as follows: Weigh out the following components by mass percentage: 2%-14% PSMI, 0.2% primary antioxidant 1010, 0.1% secondary antioxidant 168, 0.3% lubricant calcium stearate, 0.1% initiator dicumyl peroxide, 2% KT-1, and the balance is polypropylene. The sum of the mass percentages of the above components is 100%. Polypropylene, PSMI, primary antioxidant 1010, secondary antioxidant 168, calcium stearate, DCP, and KT-1 are mixed in a high-speed mixer; the resulting mixture is added to a twin-screw extruder for melt blending, cooled, and then granulated; it is then fed into the heated barrel of an injection molding machine for plasticization, finally yielding PSMI-modified polypropylene material.

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