Intrinsic flame-retardant polyamide and preparation method thereof

Abstract

The preparation method comprises the following steps: step 1, fully mixing a polymeric monomer, a catalyst and a modified flame-retardant salt monomer, and carrying out a prepolymerization reaction in a protective atmosphere under the condition of 1.4-1.6 MPa; step 2, reducing the pressure to normal pressure, fully carrying out polymerization reaction, reducing the pressure and removing impurities to obtain the required intrinsic flame-retardant polyamide; the phosphorus-containing flame-retardant salt monomer is modified by diamine, so that the thermal stability of the phosphorus-containing flame-retardant salt monomer is improved, the intrinsic flame-retardant polyamide thermoplastic elastomer can be synthesized by a one-step method, and the synthesis process is simple.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer synthesis, and in particular to an intrinsic flame-retardant polyamide and a preparation method thereof. Background Art

[0002] Polyamides are widely used in the automotive, electronics, textile, and other fields due to their excellent mechanical properties, chemical resistance, and processability. However, traditional TPAE materials have significant flammability issues, posing a high risk of fire under high temperature or open flame conditions, severely limiting their application in applications with strict fire safety requirements.

[0003] In the existing technology, flame retardants are often introduced by physical blending or surface coating to improve flammability, but such methods have obvious shortcomings: 1) Physical blending leads to uneven dispersion of flame retardants, easy migration and precipitation, and poor flame retardancy; 2) The added flame retardant has poor compatibility with the matrix, which significantly deteriorates the mechanical properties of the material (such as toughness and tensile strength); 3) Some flame retardant systems require multi-step composite processes or complex post-processing, which increases production costs and process difficulty.

[0004] Currently, conventional phosphorus-based flame retardants rely on a single gas-phase or condensed-phase flame retardant mechanism, prioritizing flame retardant efficiency and making it difficult to balance high efficiency with overall material performance. There is an urgent need to develop a novel flame-retardant modification strategy that can achieve stable immobilization of flame-retardant ingredients through chemical bonding to prevent migration failure, while simultaneously retaining the inherent performance advantages of polyamide and simplifying the preparation process to meet the needs of industrial production. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides an intrinsic flame retardant polyamide and a preparation method thereof.

[0006] The technical solution adopted by the present invention is: a method for preparing an intrinsic flame retardant polyamide, comprising the following steps:

[0007] Step 1: fully mix the polymerization monomer, catalyst and modified flame retardant salt monomer, and carry out prepolymerization reaction under protective atmosphere at 1.4-1.6 MPa;

[0008] Step 2: Reduce the pressure to normal pressure to fully carry out the polymerization reaction, and after reducing the pressure and removing impurities, the desired intrinsic flame retardant polyamide can be obtained;

[0009] The modified flame retardant salt monomer is produced by reacting a carboxyl-containing phosphorus-based flame retardant monomer with a diamine having 5 to 12 carbon atoms; the flame retardant salt monomer accounts for 4 to 8 wt.% of the mass of the polymerized monomer; the carboxyl-containing phosphorus-based flame retardant monomer is one of 2-carboxyethylphenyl hypophosphorous acid, bis(4-carboxyphenyl)phenylphosphine oxide, and 2-(diphenylphosphinomethyl)succinic acid.

[0010] Furthermore, the preparation process of the modified flame retardant salt monomer is as follows:

[0011] Adding a carboxyl group-containing phosphorus-based flame retardant monomer to a diamine monomer solution; wherein the molar ratio of the carboxyl group-containing phosphorus-based flame retardant monomer to hexamethylenediamine is 1:1.05-1.1;

[0012] The reaction is fully carried out under stirring conditions, the product is separated by filtration under reduced pressure, and the desired modified flame retardant salt monomer is obtained after recrystallization and drying.

[0013] Furthermore, in step 1, the prepolymerization reaction temperature is 220-250° C., and the reaction time is 2-4 hours.

[0014] Furthermore, in step 2, the polymerization reaction temperature is 255-270° C., and the reaction time is 2-5 hours.

[0015] Furthermore, the catalyst is composed of one or two or more of titanium trioxide, zinc acetate, and tetrabutyl titanate mixed in any proportion.

[0016] Furthermore, the step 1 further comprises polyether polyol, and the polyether polyol accounts for 10 to 50 wt.% of the mass of the reaction monomers.

[0017] Furthermore, the polyether polyol is one of polytetramethylene glycol and polyethylene glycol.

[0018] Furthermore, the polymerization monomers in step 1 are lactam monomers having amide characteristics and dibasic acids capable of participating in copolymerization.

[0019] An intrinsic flame retardant polyamide has a limiting oxygen index ranging from 24 to 30 vol.%.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention modifies the phosphorus-containing flame retardant salt monomer with a diamine, thereby improving the thermal stability of the phosphorus-containing flame retardant salt monomer and preventing its thermal decomposition during the polymerization process; the obtained modified phosphorus-containing flame retardant salt can be pyrolyzed under high temperature conditions to produce polyphosphoric acid, which catalyzes the dehydration of the polymer to form a dense carbon layer covering the polymer surface, forming a physical barrier that isolates the polymer from oxygen; the phosphorus-containing free radicals formed during the phase degradation process can inhibit the active free radicals formed during the combustion process, terminate the chain reaction, and achieve a good flame retardant effect;

[0022] (2) The present invention adopts a one-step method to synthesize the intrinsic flame-retardant polyamide thermoplastic elastomer, which does not require a two-step method of adding materials. The reaction raw materials are added in one step, thereby simplifying the polymerization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1is the synthetic chemical reaction formula of the modified flame retardant salt monomer in Example 1 of the present invention.

[0024] Figure 2 This is the synthetic chemical reaction formula for the intrinsic flame retardant polyamide thermoplastic elastomer in Example 1 of the present invention.

[0025] Figure 3 These are the vertical burning test results of the intrinsic flame retardant polyamide thermoplastic elastomers obtained in Examples 1 to 3 of the present invention and Comparative Example 1, where a is the result of Comparative Example 1, b is the result of Example 1, c is the result of Example 2, d is the result of Example 3, and e is the statistical result.

[0026] Figure 4 These are cone calorimetry test curves of the intrinsic flame retardant polyamide thermoplastic elastomers obtained in Examples 2 and 3 of the present invention and Comparative Example 1, where a is the HRR result, b is the THR result, c is the TSR result, and d is the CO production.

[0027] Figure 5 These are SEM images of the intrinsic flame retardant polyamide thermoplastic elastomers obtained in Examples 2 and 3 of the present invention and Comparative Example 1 after cone calorimetry testing, where a is the result of Comparative Example 1, b is the result of Example 2, and c is the result of Example 3.

[0028] Figure 6 The mechanical properties of the intrinsic flame retardant polyamide thermoplastic elastomers obtained in Examples 1 to 3 of the present invention and Comparative Example 1 are shown in Figures a and b, respectively. The mechanical properties after qualitative characterization at 1 times stretching are shown in Figures b and c, respectively.

[0029] Figure 7 This is the synthetic chemical reaction formula for the modified flame retardant salt monomer in Example 4 of the present invention.

[0030] Figure 8 This is the synthetic chemical reaction formula for the intrinsic flame retardant polyamide in Example 4 of the present invention.

[0031] Figure 9 These are the vertical burning test results of the intrinsic flame retardant polyamide obtained in Examples 4 to 7 of the present invention and Comparative Example 1, where a is the result of Comparative Example 1, b is the result of Example 4, c is the result of Example 5, d is the result of Example 6, e is the result of Example 7, and f is the statistical result.

[0032] Figure 10 These are cone calorimetry test curves of the intrinsic flame retardant polyamide obtained in Examples 4 and 6 of the present invention and Comparative Example 1, where a is the HRR result, b is the THR result, c is the TSR result, and d is the CO production.

[0033] Figure 11These are SEM images of the intrinsic flame retardant polyamides obtained in Examples 4 and 6 of the present invention and Comparative Example 1 after cone calorimetry testing, with a being the result of Comparative Example 1, b being the result of Example 4, and c being the result of Example 6.

[0034] Figure 12 The mechanical properties test results of Examples 4 and 6 and Comparative Example 1 are shown in Figures a and b, respectively. The strain and tensile strength curves are shown in Figures b and c, respectively. The tensile and elongation at break of Example 6 at different stretching times are shown in Figures 4 and 6 and Comparative Example 1.

[0035] Figure 13 Schematic diagram of thermogravimetric curves of the modified flame retardant salt monomer and CEPPA before modification used in Example 1 of the present invention, a is the mass retention rate curve, and b is the DTG curve.

[0036] Figure 14 Schematic diagram of thermogravimetric curves of intrinsic flame-retardant polyamides obtained in Examples 8 to 10 of the present invention and Comparative Example 2, where a represents the weight retention rate and b represents the DTG curve. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] A method for preparing an intrinsic flame-retardant polyamide comprises the following steps:

[0039] Step 1: Thoroughly mix the polymerization monomer, catalyst, and modified flame retardant salt monomer, and conduct a prepolymerization reaction under a protective atmosphere at 1.4-1.6 MPa. The prepolymerization temperature is 220-250°C, and the reaction time is 2-4 hours. The catalyst is one or more of the following: tantalum trioxide, zinc acetate, and tetrabutyl titanate, mixed in any proportion. The amount of catalyst added can be adjusted according to actual needs. The polymerization monomers are a lactam monomer with amide characteristics and a dibasic acid capable of copolymerization. Any monomer that meets these requirements can be used; in the following examples, caprolactam and adipic acid are selected as the polymerization monomers.

[0040] The modified flame retardant salt monomer is produced by reacting a carboxyl-containing phosphorus-based flame retardant monomer with a diamine having 5 to 10 carbon atoms; the flame retardant salt monomer accounts for 4 to 8 wt.% of the mass of the polymerized monomer; the carboxyl-containing phosphorus-based flame retardant monomer is one of 2-carboxyethylphenyl hypophosphite CEPPA, bis(4-carboxyphenyl)phenylphosphine oxide BCPPO, and 2-(diphenylphosphinomethyl)succinic acid DPOSA, and the structure is shown below.

[0041]

[0042] The preparation process of modified flame retardant salt monomer is as follows:

[0043] Dissolve the diamine monomer in a polar solvent to obtain a diamine solution, wherein the polar solvent is one of ethanol, methanol, and N,N-dimethylformamide. Add a carboxyl group-containing phosphorus-based flame retardant monomer to the diamine monomer solution and mix; the molar ratio of the carboxyl group-containing phosphorus-based flame retardant monomer to hexamethylenediamine is 1:1.05-1.1;

[0044] The mixture was stirred for 5 h to generate white crystals, which were separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. The obtained crystals were vacuum dried at 70° C. for 12 h.

[0045] Modified flame-retardant salt monomers are introduced into polyamide segments. Under high-temperature conditions, they pyrolyze to produce polyphosphoric acid, which catalyzes the dehydration of the polymer to form a dense char layer that covers the polymer surface, forming a physical barrier between the polymer and oxygen. Furthermore, phosphorus-containing free radicals formed during gas-phase degradation inhibit active free radicals formed during combustion, terminating the chain reaction and providing a strong flame-retardant effect.

[0046] In addition, due to the modification, the flame retardant salt monomer is introduced into the polyamide chain segment through diamine, which greatly improves its thermal stability.

[0047] Step 2: Reduce the pressure to normal pressure, continue heating to 255-270°C, and carry out polymerization reaction for 2-5 hours; then reduce the pressure of the reaction system to 100-1000 Pa, remove small molecule water and unreacted monomers, and obtain the target product with a sufficiently high molecular weight. Discharge, cool, and pelletize under nitrogen protection to obtain copolymerized flame-retardant polyamide.

[0048] Alternatively, polyether polyol can be added as a soft segment to the polyamide during the addition process to obtain a polyamide thermoplastic elastomer. The preparation can be completed in a one-pot process, which is simple.

[0049] Example 1

[0050] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0051] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polytetramethylene ether glycol, 8.3 g of modified flame retardant salt monomer and 0.5 g of tritium trioxide were added into a reactor.

[0052] The chemical formula of the modification reaction is as follows Figure 1 As shown:

[0053] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0054] The above reaction system was prepolymerized under nitrogen atmosphere at 230° C. and 1.5 MPa for 3 hours.

[0055] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 265°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-2CEPPA.

[0056] Example 2

[0057] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0058] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polytetramethylene ether glycol, 16.6 g of modified flame retardant salt monomer and 0.5 g of tritium trioxide were added into a reactor.

[0059] The chemical formula of the modification reaction is as follows Figure 1 As shown:

[0060] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0061] The above reaction system was prepolymerized under nitrogen atmosphere at 230° C. and 1.5 MPa for 3 hours.

[0062] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 265°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-4CEPPA.

[0063] Example 3

[0064] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0065] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polytetramethylene ether glycol, 24.9 g of modified flame retardant salt monomer and 0.5 g of tritium trioxide were added into a reactor.

[0066] The chemical formula of the modification reaction is as follows Figure 1 As shown:

[0067] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0068] The above reaction system was prepolymerized under nitrogen atmosphere at 230° C. and 1.5 MPa for 3 hours.

[0069] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 265°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-6CEPPA.

[0070] Figure 3 The vertical burning test results for the intrinsically flame-retardant polyamides obtained in Examples 1-3 of the present invention and Comparative Example 1 are shown. a is the result for Comparative Example 1, b is the result for Example 1, c is the result for Example 2, d is the result for Example 3, and e is the statistical result. The figure shows that during the test, pure TPAE readily ignited under atmospheric conditions, with significant molten dripping produced, but failed to self-extinguish. Consequently, the dripping easily ignited the underlying cotton substrate, resulting in an NR rating. Meanwhile, TPAE-2CEPPA ignited within 10 seconds but self-extinguished after 7 seconds, with significantly less dripping during subsequent ignition. However, the cotton could still ignite and extinguish within 3 seconds. In contrast, TPAE-4CEPPA ignited within the initial 10 seconds but then immediately extinguished, producing minimal molten dripping and failing to ignite the underlying cotton. Furthermore, it did not ignite within the subsequent 10 seconds, thus receiving a V-0 rating. TPAE-6CEPPA did not ignite within 10 seconds and produced only minimal dripping, earning a V-0 rating.

[0071] The introduction of CEPPA destroys the molecular chain regularity of TPAE, reduces the hydrogen bonding between molecular chains, and enhances the melt fluidity. Therefore, when ignited, the material produces less dripping, and the melt phase transition occurs quickly, promoting the rapid dissipation of heat. This characteristic reduces the heat content in the dripping and accelerates its release, thus effectively preventing the cotton substrate underneath from being ignited. Figure 3 Figure e shows the comparison before and after combustion, indicating that the length of the sample after combustion does not exceed 5 cm. This shows that the introduction of CEPPA significantly improves the flame retardancy of polyamide.

[0072] Figure 4 The cone-type thermal test curves of Examples 1 to 3 and Comparative Example 1 show a comparison of heat release rate (HRR), total heat release (THR), total smoke release (TSR), and CO emissions. Figures a and b show that CEPPA exhibits a significant inhibitory effect on heat release. The peak heat release rate (PHRR) of TPAE-6CEPPA increases from 923.2 kW / m 2 Significantly reduced to 799.5kW / m 2 Correspondingly, the THR of TPAE-6CEPPA is from 96.3MJ / m 2 Dropped to 76.8MJ / m 2 , a 20.2% reduction compared to TPAE. EHC, a key indicator of material combustion intensity, was reduced from 29.2MJ / kg to 27.1MJ / kg for TPAE-6CEPPA, a 7.2% reduction. Compared to TPAE, the addition of CEPPA showed higher TSR and CO generation. In particular, the TSR value of TPAE-6CEPPA was reduced from 1029.4m 2 / m 2 Rising to 1800.4m 2 / m 2 . The increase in total smoke and CO emissions indicates that smoke generation and incomplete combustion are enhanced during the combustion of TPAE-6CEPPA. Therefore, this may lead to the dilution of oxygen, combustible gases and active free radicals, thereby inhibiting the further spread of the fire and achieving a gas-phase flame retardant effect. It can be seen that the flame-retardant polyamide obtained in the embodiment of the present invention can hinder the heat transfer of TPAE and effectively inhibit the formation of high-energy free radicals during the combustion of TPAE. In addition, it improves the smoke generation performance of the material, indicating the combustion inhibition of TPAE.

[0073] Figure 5 The SEM images after the cone calorimetry test show that the residual carbon in Comparative Example 1 is very small, while Examples 2 and 3 have significant carbon layers. In particular, Example 3 has a continuous and dense carbon layer.

[0074] This indicates that CEPPA exerts dual flame retardancy mechanisms on TPAE, both in the gas phase and the condensed phase. The primary flame retardant mechanism involves the generation of phosphorus-containing free radicals upon combustion, which promote the formation of phosphoric acid, which coats the polymer melt surface, forming a barrier that isolates the melt from oxygen and inhibits further combustion. Furthermore, the reduction of combustible gas emissions during degradation is also a key aspect of flame retardancy, as it reduces the fuel required to sustain flame combustion. These combined effects significantly enhance the material's flame retardancy.

[0075] Figure 6 The mechanical properties of the intrinsic copolymer flame-retardant polyamide thermoplastic elastomers obtained in Examples 1-3 and Comparative Example 1 are shown. a is the strain and tensile strength curve of the elastic fiber after one stretching and subsequent heat treatment at 70°C. Compared with TPAE, the tensile strength is slightly reduced. The flame-retardant polyamide obtained in Example 2 has good tensile properties. With the increase of the stretch ratio, the mechanical strength of the TPAE-4CEPPA fiber increases from 0.83 cN / dtex to 1.57 cN / dtex, and the elongation at break decreases from 335.4% to 83.3%. Compared with the unstretched fiber, the orientation and crystallinity of the fiber increase with the increase of the stretch ratio. It can be seen that the addition of CEPPA can enhance its mechanical properties.

[0076] Example 4

[0077] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 8 shown

[0078] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polyethylene glycol, 16.6 g of DPOSA modified flame retardant salt monomer and 1.0 g of zinc acetate were added to a reactor.

[0079] The chemical formula of DPOSA modification reaction is as follows: Figure 7 As shown:

[0080] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. DPOSA was then slowly added to the solution and stirred for 5 hours. The molar ratio of DPOSA to hexamethylenediamine was 1:1.1. After white crystals precipitated, CHS was isolated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0081] The above reaction system was prepolymerized under nitrogen atmosphere at 220° C. and 1.6 MPa for 2 hours.

[0082] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 270°C for polymerization for 4 hours. Reduce the reaction system pressure to 1000 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-4DPOSA.

[0083] Example 5

[0084] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 8 shown

[0085] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polyethylene glycol, 24.9 g of DPOSA modified flame retardant salt monomer and 1.0 g of zinc acetate were added to a reactor.

[0086] The chemical formula of DPOSA modification reaction is as follows: Figure 7 As shown:

[0087] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. DPOSA was then slowly added to the solution and stirred for 5 hours. The molar ratio of DPOSA to hexamethylenediamine was 1:1.1. After white crystals precipitated, CHS was isolated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0088] The above reaction system was prepolymerized under nitrogen atmosphere at 220° C. and 1.6 MPa for 2 hours.

[0089] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 270°C for polymerization for 4 hours. Reduce the reaction system pressure to 1000 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-6DPOSA.

[0090] Example 6

[0091] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 8 shown

[0092] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polyethylene glycol, 33.2 g of DPOSA modified flame retardant salt monomer and 1.0 g of zinc acetate were added to a reactor.

[0093] The chemical formula of DPOSA modification reaction is as follows: Figure 7 As shown:

[0094] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. DPOSA was then slowly added to the solution and stirred for 5 hours. The molar ratio of DPOSA to hexamethylenediamine was 1:1.1. After white crystals precipitated, CHS was isolated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0095] The above reaction system was prepolymerized under nitrogen atmosphere at 220° C. and 1.6 MPa for 2 hours.

[0096] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 270°C for polymerization for 4 hours. Reduce the reaction system pressure to 1000 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-8DPOSA.

[0097] Example 7

[0098] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 8 shown

[0099] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 100 g of polyethylene glycol, 41.5 g of DPOSA modified flame retardant salt monomer and 1.0 g of zinc acetate were added to a reactor.

[0100] The chemical formula of DPOSA modification reaction is as follows: Figure 7 As shown:

[0101] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. DPOSA was then slowly added to the solution and stirred for 5 hours. The molar ratio of DPOSA to hexamethylenediamine was 1:1.1. After white crystals precipitated, CHS was isolated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0102] The above reaction system was prepolymerized under nitrogen atmosphere at 220° C. and 1.6 MPa for 2 hours.

[0103] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 270°C for polymerization for 4 hours. Reduce the reaction system pressure to 1000 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer TPAE-10DPOSA.

[0104] Figure 9Schematic diagrams of vertical combustion for Examples 4 to 7 and Comparative Example 1 show that TPAE-4DPOSA can be ignited within 10 seconds but extinguishes itself after 8 seconds. However, the cotton can still be ignited. After the second ignition, the flame is removed and extinguished within 5 seconds. In contrast, TPAE-8DPOSA can be ignited within the initial 10 seconds, but then immediately extinguishes, producing very little molten dripping and failing to ignite the cotton cloth below. In addition, it does not ignite within the subsequent 10 seconds, thus obtaining a V-0 rating. Notably, TPAE-10DPOSA does not ignite within 10 seconds and no molten dripping is produced, obtaining a V-0 rating.

[0105] The introduction of DPOSA disrupts the regularity of TPAE, resulting in fewer hydrogen bonds between subchains and enhanced melt fluidity. Consequently, less dripping occurs during ignition, and the melt phase transition rapidly dissipates heat. This property reduces the heat content in the dripping material, facilitating its release and preventing ignition of the underlying cotton substrate. As can be seen in Figure f, the burn length never exceeds 5 cm. This demonstrates that the introduction of DPOSA significantly improves flame retardancy.

[0106] Figure 10 The cone calorimetry data curves of Examples 4, 6 and Comparative Example 1 show that DPOSA exhibits a significant inhibitory effect on heat release. 2 Significantly reduced to 599.6kW / m 2 Correspondingly, the THR of TPAE-8DPOSA is 101.1MJ / m 2 Down to 50.3MJ / m 2 , which is 50.2% lower than that of TPAE. EHC, a key indicator of material combustion intensity, is reduced from 30.7MJ / kg to 23.4MJ / kg for TPAE-8DPOSA, a decrease of 23.8%. From c and d, it can be seen that compared with TPAE, the introduction of DPOSA shows lower TSR and higher CO generation. In particular, the TSR value of TPAE-8DPOSA is reduced from 1039.7m 2 / m 2 Descend to 950.0m 2 / m 2 , CO production increased from 0.0332 kg / kg to 0.1180 kg / kg. The increase in total smoke and CO emissions indicates that smoke generation and incomplete combustion are enhanced during the combustion of TPAE-8DPOSA.

[0107] After cone calorimetry test, SEM images are shown as follows: Figure 11 As shown in the figure, it can be seen that Examples 4 and 6 have a significant carbon layer on the surface.

[0108] Figure 12 Figure 1 shows the mechanical property test results for Examples 4 and 6 and Comparative Example 1. (a) shows the strain and tensile strength curves, and (b) shows the tensile strength and elongation at break of Example 6 at different stretching times. The figure shows that the addition of DPOSA slightly decreases the tensile strength and elongation at break compared to TPAE. The fiber obtained in Example 6 exhibits excellent mechanical properties, with a tensile strength maintained at 1.19 cN / dtex and an elongation at break of 278.2%, indicating that the introduction of DPOSA has little effect on the mechanical properties of the fiber.

[0109] Example 8

[0110] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0111] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 8.3 g of CEPPA modified flame retardant salt monomer and 0.5 g of tritium trioxide were added to a reactor.

[0112] The chemical formula of CEPPA modification reaction is as follows Figure 1 As shown:

[0113] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0114] The above reaction system was prepolymerized under nitrogen atmosphere at 250° C. and 1.4 MPa for 4 hours.

[0115] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 255°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide TPA-2CEPPA.

[0116] Example 9

[0117] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0118] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 16.6 g of CEPPA modified flame retardant salt monomer and 0.5 g of tritium trioxide were added to a reactor.

[0119] The chemical formula of CEPPA modification reaction is as follows Figure 1 As shown:

[0120] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0121] The above reaction system was prepolymerized under nitrogen atmosphere at 250° C. and 1.4 MPa for 4 hours.

[0122] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 255°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecule water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide TPA-4CEPPA.

[0123] Example 10

[0124] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0125] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 24.9 g of CEPPA modified flame retardant salt monomer and 0.5 g of tritium trioxide were added to a reactor.

[0126] The chemical formula of CEPPA modification reaction is as follows Figure 1 As shown:

[0127] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0128] The above reaction system was prepolymerized under nitrogen atmosphere at 250° C. and 1.4 MPa for 4 hours.

[0129] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 255°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen and pelletize it to obtain the flame-retardant copolymerized polyamide TPA-6CEPPA.

[0130] Example 11

[0131] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0132] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 40 g of polytetramethylene ether glycol, 16.6 g of CEPPA modified flame retardant salt monomer and 0.5 g of tritium trioxide were added into a reactor.

[0133] The chemical formula of CEPPA modification reaction is as follows Figure 1 As shown:

[0134] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0135] The above reaction system was prepolymerized under nitrogen atmosphere at 230° C. and 1.5 MPa for 3 hours.

[0136] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 265°C for polymerization for 5 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen protection and pelletize it to obtain a flame-retardant copolymerized polyamide thermoplastic elastomer.

[0137] Example 12

[0138] A method for preparing an intrinsic flame-retardant copolymer polyamide comprises the following steps: Figure 2 shown

[0139] Step 1: 400 g of caprolactam, 14.6 g of adipic acid, 200 g of polytetramethylene ether glycol, 16.6 g of modified flame retardant salt monomer (the flame retardant salt monomer is CEPPA) and 0.5 g of titanate trioxide are added into a reactor.

[0140] The chemical formula of the modification reaction is as follows Figure 1 As shown:

[0141] Hexamethylenediamine was dissolved in the polar solvent methanol and stirred. CEPPA was then slowly added to the solution and stirred for 5 hours. The molar ratio of CEPPA to hexamethylenediamine was 1:1.05. After white crystals precipitated, CHS was separated by filtration under reduced pressure and recrystallized to obtain powdery crystals. Finally, pure CHS was vacuum-dried at 70°C for 12 hours to obtain a yield of approximately 93.6%.

[0142] The above reaction system was prepolymerized under nitrogen atmosphere at 230° C. and 1.5 MPa for 3 hours.

[0143] Step 2: Reduce the reaction system to atmospheric pressure and continue heating to 265°C for polymerization for 2 hours. Reduce the reaction system pressure to 500 Pa to remove small molecules of water and unreacted monomers until the target product with a sufficiently high molecular weight is obtained. Cool the product under nitrogen protection and pelletize it to obtain the flame-retardant copolymerized polyamide thermoplastic elastomer.

[0144] Comparative Example 1

[0145] The other steps of this comparative example are the same as those of Example 1, except that no modified flame retardant salt monomer is contained, and the obtained copolymerized flame retardant polyamide thermoplastic elastomer is TPAE.

[0146] Comparative Example 2

[0147] The other steps of this comparative example are the same as those of Example 8, except that the modified flame retardant salt monomer is not contained, and the obtained copolymerized flame retardant polyamide is TPA.

[0148] The vertical burning test and limit index test data of the flame retardant copolymer polyamide obtained in Examples 1 to 12 and Comparative Examples 1 and 2

[0149]

[0150]

[0151] Figure 13 The thermal gravimetric curves of flame retardant salt CEPPA before and after modification. It can be seen from the figure that its thermal stability can be significantly improved after modification.

[0152] Figure 14 2 are thermogravimetric curves of Comparative Example 2 and Examples 8 to 10. It can be seen from the figure that introducing CEPPA into the intrinsic copolymer flame-retardant polyamide thermoplastic elastomer can significantly improve its thermal stability.

[0153] The present invention introduces a modified phosphorus-containing flame-retardant monomer into polyamide through a one-step melt polymerization process, resulting in an intrinsically flame-retardant polyamide. The phosphorus-containing groups introduced into the polymer side chains significantly enhance the flame retardancy of TPA while maintaining excellent thermal stability and mechanical properties. Furthermore, the introduction of soft segments yields a polyamide thermoplastic elastomer, which also exhibits excellent flame retardancy and mechanical properties.

Claims

1. A method for preparing an intrinsic flame retardant polyamide, characterized in that: The following steps are involved: Step 1: fully mix the polymerization monomer, catalyst and modified flame retardant salt monomer, and carry out prepolymerization reaction under protective atmosphere at 1.4-1.6 MPa; Step 2: Reduce the pressure to normal pressure to fully carry out the polymerization reaction, and after reducing the pressure and removing impurities, the desired intrinsic flame retardant polyamide can be obtained; The modified flame retardant salt monomer is produced by reacting a carboxyl-containing phosphorus-based flame retardant monomer with a diamine having 5 to 12 carbon atoms; the flame retardant salt monomer accounts for 2 to 8 wt.% of the mass of the polymerized monomer; the carboxyl-containing phosphorus-based flame retardant monomer is one of 2-carboxyethylphenyl hypophosphorous acid, bis(4-carboxyphenyl)phenylphosphine oxide, and 2-(diphenylphosphinomethyl)succinic acid.

2. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: The preparation process of the modified flame retardant salt monomer is as follows: Adding a carboxyl group-containing phosphorus-based flame retardant monomer to a diamine monomer solution; wherein the molar ratio of the carboxyl group-containing phosphorus-based flame retardant monomer to hexamethylenediamine is 1:1.05-1.1; The reaction is fully carried out under stirring conditions, the product is separated by filtration under reduced pressure, and the desired modified flame retardant salt monomer is obtained after recrystallization and drying.

3. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: The prepolymerization reaction temperature in step 1 is 220-250° C., and the reaction time is 2-4 hours.

4. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: In the step 2, the polymerization reaction temperature is 255-270° C., and the reaction time is 2-5 hours.

5. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: The catalyst is composed of one or two or more of titanium trioxide, zinc acetate, and tetrabutyl titanate mixed in any proportion.

6. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: The step 1 further comprises polyether polyol, which accounts for 10 to 50 wt.% of the mass of the reaction monomers.

7. The method for preparing an intrinsic flame retardant polyamide according to claim 6, characterized in that: The polyether polyol is one of polytetramethylene glycol and polyethylene glycol.

8. The method for preparing an intrinsic flame retardant polyamide according to claim 1, characterized in that: The polymerization monomers in step 1 are lactam monomers having amide characteristics and dibasic acids capable of participating in copolymerization.

9. The intrinsic flame retardant polyamide obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The limiting oxygen index of the intrinsic flame retardant polyamide is in the range of 24 to 30 vol.%.

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