Halogen-free intrinsic flame-retardant copolymerized polyamide 66 and preparation method thereof

Abstract

The invention discloses halogen-free intrinsic flame-retardant copolymerized polyamide 66 and a preparation method thereof, the halogen-free intrinsic flame-retardant copolymerized polyamide 66 is prepared by copolymerizing an intrinsic flame retardant DDP, caprolactam, adipic acid and hexamethylenediamine, and the molecular structure comprises the following structural units: (1); (2); (3). And the quantitative relation x: y: z of the structural units (1), the structural units (2) and the structural units (3) is (60-90): (5-20): (5-20). The DDP is introduced into the copolymerized polyamide 66, so that the flame retardant property of the material is greatly improved; meanwhile, due to the introduced caprolactam, the polymerization temperature is reduced, the DDP is protected, and the toughness of the material is improved, so that the material has flame retardance and toughness and can be used for spinning. Besides, the DDP flame retardant is tightly linked with a PA66 molecular chain in a copolymerization manner, so that the flame retardant property of the nylon 66 is improved, the flame retardant cannot be separated out due to poor compatibility of the flame retardant, and the durability of the flame-retardant material is improved.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant polyamides, specifically, it relates to a halogen-free intrinsically flame-retardant copolyamide 66 and its preparation method. Background Technology

[0002] Polyamide (PA) materials, also known as nylon materials, are thermoplastic engineering plastics containing amide bonds (-CO-NH-) in their molecular chains. Polyhexamethylene adipamide resin (PA66) is the most widely used polyamide material. Due to its excellent mechanical properties, heat resistance, chemical resistance, and abrasion resistance, as well as its ease of modification and processing, it is widely used in the automotive, electronics, chemical, and construction industries, making it one of the world's most produced and widely applied engineering plastics. However, PA66 has an oxygen index of only 24%, classifying it as a flammable material that is easily ignited. Furthermore, due to its low melt strength, PA66 is prone to molten dripping during combustion, achieving a vertical burning rating of only V-2, which can cause the spread of fire during use and severely limits its applications. Therefore, improving the flame retardant properties of PA66 is a very important research topic.

[0003] Currently, flame retardant modification of PA66 is mainly divided into two methods: physical blending and chemical copolymerization. Physical blending involves melt-blending the flame retardant with the PA66 matrix. While simple to operate, it suffers from problems such as high flame retardant dosage, poor compatibility with the matrix, easy migration and precipitation leading to flame retardant performance degradation, and severe damage to the material's mechanical properties (especially toughness). Chemical copolymerization (also known as intrinsic flame retardant modification or copolymer flame retardant modification) uses the flame retardant as a reactive unit, chemically binding it to the macromolecular chain, making it an intrinsic structural unit. This avoids problems such as reduced flame retardant efficiency due to migration and precipitation. Furthermore, intrinsic flame retardant modification has the specific characteristic of high flame retardant efficiency, thus greatly reducing the amount of flame retardant used and minimizing damage to the original physical and mechanical properties of the polymer. However, intrinsic flame retardant modification faces significant challenges in terms of technology, equipment, and cost due to the change in polymerization process.

[0004] DDP is a commonly used intrinsic flame retardant with two reactive carboxyl groups, making it widely used in the intrinsic flame retardancy of polyamides and polyesters. However, applying DDP to the intrinsic flame retardancy of PA66 faces two major technical challenges: (1) Contradictory thermal stability: DDP has a low thermal degradation initiation temperature (about 215℃), while the conventional polymerization temperature of PA66 (especially in the late pre-condensation and final condensation stages) is usually as high as 250-280℃. At this high temperature, DDP is very prone to thermal decomposition, which not only leads to a decrease in flame retardant efficiency, but its decomposition products also interfere with the polymerization reaction, resulting in low polymer molecular weight, difficulty in viscosity growth, and darkening of color. It may also cause side reactions such as crosslinking, which seriously damages the performance and processability of the final product.

[0005] (2) Toughness loss: DDP molecules contain rigid phenanthrene ring structures. Their introduction will disrupt the regularity of PA66 molecular chains and reduce crystallinity, which usually leads to increased brittleness and a significant decrease in elongation at break, thus losing its value as a fiber or tough engineering plastic.

[0006] In the prior art, Chinese invention patent CN120424331A discloses a flame-retardant and stain-resistant copolymer nylon 6, its preparation method, and its applications. This patent utilizes flame retardants such as DDP to copolymerize with caprolactam and amino-terminated polysiloxanes to prepare a series of flame-retardant copolymer nylons. Because PA6 has a relatively low polymerization temperature, and the addition of amino-terminated polysiloxanes further lowers the polymerization temperature, DDP can remain stable at the polymerization temperature for a long time, thus enabling the preparation of intrinsically flame-retardant copolymer PA6. However, due to the higher polymerization temperature of PA66, this method cannot meet the requirements for the copolymerization of PA66.

[0007] Chinese invention patent application number CN98807508.3 discloses a reactive phosphorus-based flame retardant CEPPA for polyamides, which is obtained by melt copolymerization with PA66 salt. However, due to the low phosphoamide bond energy formed by CEPPA and hexamethylenediamine, the copolymer has poor heat resistance and is at risk of thermal degradation during hot processing. Furthermore, the introduction of CEPPA with benzene ring side groups impairs the toughness of the material, which greatly affects the application range of the copolyamide and makes it more difficult to achieve spinning.

[0008] Therefore, developing an intrinsic flame-retardant modification method that can effectively protect DDP from decomposition during the high-temperature polymerization of PA66 while maintaining or even improving the toughness of PA66 material is a technical problem that urgently needs to be solved in this field.

[0009] In view of this, the present invention is proposed. Summary of the Invention

[0010] The technical problem to be solved by this invention is to overcome at least one of the shortcomings of the prior art and provide a halogen-free intrinsically flame-retardant copolymer polyamide 66 and its preparation method. This invention introduces a third monomer—caprolactam—to ternary copolymerize with PA66 salt (adipic acid and hexamethylenediamine) and DDP flame retardant, and improves the polymerization process, successfully completing the polymerization reaction within a temperature window that does not cause significant thermal decomposition of DDP, while simultaneously achieving flame retardancy and toughening.

[0011] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a halogen-free intrinsically flame-retardant copolyamide 66, which is obtained by copolymerization of intrinsic flame retardant DDP, caprolactam, adipic acid and hexamethylenediamine, and whose molecular structure includes the following structural units: (1) ; (2) ; (3) .

[0012] As one possible approach, the molecular chain structure is as follows: Formula I In a further scheme, the quantitative relationship x:y:z of structural unit (1), structural unit (2) and structural unit (3) is (60-90):(5-20):(5-20); Preferably, x:y:z is (80-90):(5-10):(5-10).

[0013] The polymerization temperature of pure PA66 is typically above 220°C, while the thermal degradation temperature of DDP is approximately 215°C. Direct polymerization of DDP at high temperatures leads to polymerization failure and performance degradation. This invention introduces a third monomer—caprolactam—with a lower ring-opening polymerization temperature (180-200°C). A ternary random copolymer of "PA6 / PA66 / DDP" is formed by copolymerizing caprolactam with DDP and hexamethylenediamine adipic acid salt. This copolymer has a lower overall melting point, allowing the reaction temperature during the entire prepolymerization and polycondensation stages to be controlled within a range that does not cause significant decomposition of DDP (e.g., prepolymerization at 180-200°C).

[0014] Meanwhile, the introduction of caprolactam units disrupts the regularity of the PA66 molecular chain, which can improve the toughness (elongation at break) of the material under certain ratios, offsetting the brittleness caused by the rigid benzene ring structure of DDP, thus taking into account both flame retardancy and spinnability.

[0015] Therefore, in the polymer of this invention, the introduction of DDP significantly improves the flame retardant properties of the material, while the introduction of caprolactam lowers the prepolymerization temperature and improves the toughness of the material, making the material possess both flame retardancy and toughness, enabling it to be spun. Furthermore, the DDP flame retardant is copolymerized and tightly linked to the PA66 molecular chain, improving the flame retardant properties of nylon 66 without precipitation due to poor compatibility, thus enhancing the durability of the flame-retardant material.

[0016] A further option is a halogen-free intrinsically flame-retardant copolyamide 66 with a limiting oxygen index of 26.0-30.0%, an elongation at break of >40%, a yield strength of 45-60 MPa, and a melt flow index of 13-18 g / 10 min.

[0017] Preferably, the elongation at break is >100%.

[0018] Secondly, the present invention provides a method for preparing the halogen-free intrinsically flame-retardant copolyamide 66, comprising: S1. Under an inert atmosphere, an aqueous solution of DDP, caprolactam, adipic acid and hexamethylenediamine is mixed and prepolymerized at a first preset temperature to obtain an aqueous prepolymer. S2. Heat the prepolymer aqueous solution while controlling dehydration, maintain the first preset pressure, until the temperature reaches the second preset temperature, stop dehydration, and obtain the concentrated prepolymer aqueous solution. S3. The concentrated prepolymer aqueous solution is heated and pressurized to reach the second preset pressure; then the pressure is released to atmospheric pressure or near atmospheric pressure, and the temperature is raised to the third preset temperature during the pressure release process. S4. The product obtained in S3 is kept at a third preset temperature and subjected to reduced pressure to carry out a final polycondensation reaction to obtain a halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0019] The preparation method of this invention achieves "thermal-sensitive flame retardant protection", "flame retardant-toughness balance", and "controllable synthesis of high molecular weight" through a synergistic process path of "low-temperature prepolymerization and fixation of DDP - controlled temperature rise and dehydration - pressure rise and depressurization transition - high-temperature vacuum thickening".

[0020] In this invention, the initial reaction temperature (first preset temperature) is set in the lower range of 180-220℃. At this temperature, DDP is stable, and the reactions of caprolactam ring opening and PA66 salt preliminary condensation can be initiated to form a preliminary prepolymer network, "fixing" DDP molecules to the growing molecular chain through chemical bonds.

[0021] Then, through the slow heating and controlled dehydration in S2, and the pressurization-depressurization process in S3, a smooth and controllable transition of the system temperature from the prepolymerization temperature (first preset temperature) to the final polycondensation temperature (third preset temperature) is achieved. Crucially, when the temperature rises to a range potentially risky for DDP, DDP has already been bonded to the polymer backbone through the prepolymerization reaction, significantly improving its thermal stability compared to its free monomer state. This successfully protects the chemical structure of DDP, allowing it to integrate into the PA66 molecular backbone as a complete reactive monomer, forming stable covalent bonds, thus achieving true "intrinsic flame retardancy."

[0022] By controlling drainage and pressure (first preset pressure), water is removed smoothly, avoiding system boiling or drastic viscosity fluctuations caused by sudden large-scale evaporation of water, thus ensuring a uniform increase in prepolymer concentration. The pressurization stage (to the second preset pressure) helps water molecules remain within the system at high temperatures, acting as an "internal plasticizer" and promoting molecular chain movement and further growth. Subsequent slow depressurization smoothly removes this water, guiding the reaction towards polycondensation. Finally, applying a high vacuum (-0.10 MPa) at a high temperature (third preset temperature range) completely removes residual small molecules, strongly driving the polycondensation reaction equilibrium to the right, significantly increasing the polymer's molecular weight (intrinsic viscosity). This results in a polymer with high relative viscosity and controllable molecular weight distribution. High molecular weight means better mechanical strength and melt strength, giving the material excellent spinnability, enabling stable melt spinning into high-strength flame-retardant fibers.

[0023] A further solution, step S1, specifically involves: Under an inert atmosphere, DDP, caprolactam, adipic acid and hexamethylenediamine are prepared into corresponding aqueous solutions according to the specified ratio. The aqueous solutions are then mixed and added into a pressure-resistant reaction vessel with a drain valve. Prepolymerization is carried out at a first preset temperature to obtain a prepolymer aqueous solution.

[0024] In a further proposed scheme, DDP, caprolactam, adipic acid, and hexamethylenediamine are homogeneous solid raw materials, and the total mass of the four is the total mass of the solid raw materials.

[0025] In step S1, the proportion of each solid raw material in the total mass of solid raw materials is as follows: The mass fractions of caprolactam, DDP, adipic acid, and hexamethylenediamine are 5wt%-20wt%, 60wt%-90wt%, respectively. Preferably, the mass fraction of caprolactam is 5wt%-10wt%, the mass fraction of DDP is 5wt%-10wt%, and the mass fraction of adipic acid and hexamethylenediamine is 80wt%-90wt%.

[0026] A further proposed scheme involves the total mass of solid raw materials accounting for 40wt%-60wt% of the total mass of the aqueous solution. In other words, the aqueous solutions of each raw material are mixed to form a mixture, wherein the total mass of DDP, caprolactam, adipic acid, and hexamethylenediamine accounts for 40wt%-60wt% of the total mass of the mixture.

[0027] In a further embodiment, in step S1, the first preset temperature is lower than the thermal degradation temperature of DDP; Preferably, the first preset temperature is 180-200℃, and the prepolymerization reaction time is 2-4 hours; Preferably, the first preset temperature is 180-190℃, and the prepolymerization reaction time is 2-3h.

[0028] A further solution, step S2, specifically involves: The prepolymer aqueous solution obtained in S1 is heated further. During this process, the drain valve is opened to remove a certain proportion of water from the system, and the pressure is kept within the first preset pressure range until the temperature reaches the second preset temperature. Then the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0029] In a further step, in step S2, 60-80 wt% of the water in the system is removed through controlled dehydration; Preferably, 60 wt% of the water in the system is removed.

[0030] In a further step, in step S2, the first preset pressure is 0.3-0.5 MPa.

[0031] Preferably, the first preset pressure is 0.35-0.45 MPa.

[0032] In a further step, in step S2, the second preset temperature is 210-215℃. This second preset temperature is as close as possible to the thermal degradation temperature of DDP to balance reaction efficiency and thermal degradation issues.

[0033] A further solution, step S3, specifically involves: The concentrated prepolymer aqueous solution obtained from S2 is further heated, causing the temperature and pressure to rise continuously until the pressure reaches the second preset pressure range. Then, the drain valve is opened, causing the pressure to drop continuously to 0 MPa, and the temperature is adjusted to reach the third preset temperature range.

[0034] In a further step, in step S3, the second preset pressure is 1.7-1.9 MPa; Preferably, the second preset pressure is 1.7-1.8 MPa.

[0035] In a further step, the third preset temperature in step S3 is 250-270℃; In step S3, the third preset temperature is 250-260℃.

[0036] A further solution, step S4, specifically involves: The solution obtained by S3 is sealed in a reactor, the temperature is maintained within the third preset temperature range, a vacuum is drawn, and the final polycondensation is carried out for a certain period of time before the material is discharged to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0037] In a further step, in step S4, the third preset temperature is 250-270℃; Preferably, in step S4, the third preset temperature is 260-270℃.

[0038] In a further step, in step S4, a vacuum is drawn to reduce the pressure to -0.10 MPa. In a further embodiment, in step S4, the final polycondensation reaction is carried out for 10-120 minutes.

[0039] In the preparation method of this invention, by introducing a third monomer (caprolactam), the prepolymerization temperature is lowered, allowing polymerization to take place below the thermal decomposition temperature of DDP, reducing the occurrence of side reactions and improving the quality of the polymer. The introduction of DDP and the third monomer lowers the melting point of the polymer, which significantly reduces the final polycondensation temperature, further avoiding the thermal degradation of DDP, ensuring the efficiency of the flame retardant, and improving the product quality.

[0040] The above-mentioned ratio range of raw materials is a relatively preferred technical solution obtained by technicians based on extensive research. Since DDP flame retardant and caprolactam enter the molecular chain of nylon 66, they inevitably affect the performance of nylon 66. By controlling the mass ratio of nylon 66 salt to flame retardant salt and caprolactam within the above-mentioned range, it is possible to significantly improve the flame retardant performance of nylon 66 while minimizing the impact of the introduction of flame retardant on the mechanical properties of nylon 66, so that the obtained intrinsically flame-retardant nylon 66 has excellent comprehensive performance.

[0041] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. Solved the problem of DDP thermal decomposition: By introducing caprolactam monomer with a lower polymerization temperature, and performing ternary copolymerization with PA66 salt and DDP, the reaction temperature of the entire prepolymerization stage was effectively lowered (controlled at 180-200℃). This temperature is much lower than the significant thermal decomposition temperature of DDP (215℃), thereby maximizing the protection of the chemical structure of DDP, thus achieving the bonding between DDP and PA66 without thermal degradation, and ensuring its flame retardant efficiency.

[0042] 2. Synergistic Achievement of Flame Retardancy and High Toughness: The introduction of DDP endows the material with efficient and permanent intrinsic flame retardancy. Simultaneously, the introduction of caprolactam units acts as an internal plasticizer, disrupting the overly regular arrangement of the PA66 molecular chains, significantly improving the material's elongation at break and toughness. This effectively offsets the brittleness caused by the rigid structure of DDP, enabling the material to possess both flame retardancy and excellent mechanical properties. This achieves the preparation of intrinsically flame-retardant PA66, meeting the application requirements of spinning and high-toughness plastics.

[0043] 3. In this invention, DDP is copolymerized and bonded to the PA66 main chain, ensuring that the flame retardant will not precipitate due to poor compatibility, thus improving the durability of the material.

[0044] 4. Compared with the blending modification method using traditional DOPO-based flame retardants, the present invention has better flame retardant effect and better mechanical properties when the same amount of flame retardant is added.

[0045] 5. The preparation method of the present invention is based on the conventional polyamide pressurized aqueous solution polymerization process. It does not require large-scale modification of existing PA66 production equipment, nor does it require the pre-synthesis of complex flame-retardant prepolymers. The process is simple, controllable, and easy to realize industrial production.

[0046] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0047] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 The image shows the 1H-NMR spectrum of the copolymer obtained in Example 1 of this invention.

[0048] Among them, PA66-5PA6-5DDP represents a feed composition of 5wt% DDP + 5wt% caprolactam + 90wt% hexamethylenediamine adipic acid.

[0049] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0051] It should be noted that the specific testing method for the performance of the high elongation at break halogen-free intrinsically flame-retardant copolyamide 66 prepared by this invention is as follows: 1. Limiting Oxygen Index (LOI) testing was conducted according to ASTM D 2863 on a Fire Testing Technology instrument (FTT, West Sussex, UK). The sample size was 80.0 × 10.0 × 4.0 mm. 3 .

[0052] 2. The UL-94 vertical burning test was conducted according to ASTM D 3801 on a CZF-5 instrument (Jiangning Analytical Instruments Co., Ltd., Jiangning, China). The specimen size was 80.0 × 13.0 × 3.2 mm. 3 .

[0053] 3. 1 H NMR spectra were measured using an Avance III 400 MHz spectrometer (Bruker, Switzerland). The copolymer sample was dissolved in TFA-d solvent at a concentration of 5 mg / mL.

[0054] 4. Tensile properties were tested using a tensile testing machine (Instron 3365). Test samples with a thickness of approximately 0.5-0.8 mm were cut into dumbbell shapes. The test conditions for all samples were as follows: strain rate of 100 mm / min, spacing of 4 mm, testing at room temperature, and relative humidity of 60±3%. Each sample was tested five times, and the average value was taken as the final test result of the sample.

[0055] The present invention will now be described in further detail with reference to specific embodiments.

[0056] Example 1 S1. Under an inert atmosphere, 30.0 g DDP (5 wt%), 30.0 g caprolactam (5 wt%), 295.2 g adipic acid and 244.8 g hexamethylenediamine (90 wt%) were mixed to prepare a 60 wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 180 °C and reacted for 2 h to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0057] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0058] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0059] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0060] The 1H-NMR spectrum of the copolymer obtained in this embodiment is shown below. Figure 1 As shown.

[0061] Example 2 S1. Under an inert atmosphere, 60.0g of DDP (10wt%), 30.0g of caprolactam (5wt%), 272.9g of adipic acid and 237.1g of hexamethylenediamine (85wt%) were mixed to prepare a 50wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 190℃ and reacted for 2 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0062] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0063] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.8 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 270℃ during this process.

[0064] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 30 minutes before discharging to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0065] Example 3 S1. Under an inert atmosphere, 60.0g of DDP (10wt%), 60.0g of caprolactam (10wt%), 256.2g of adipic acid and 223.8g of hexamethylenediamine (80wt%) were mixed to prepare a 50wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 190℃ and reacted for 3 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0066] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.5MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0067] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.8 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0068] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, evacuate the vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 60 minutes before discharging the material to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0069] Example 4 S1. Under an inert atmosphere, 120.0g of DDP (20wt%), 120.0g of caprolactam (20wt%), 178.1g of adipic acid and 181.9g of hexamethylenediamine (60wt%) were mixed to prepare a 40wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 200℃ and reacted for 4 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0070] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 80wt% of the water in the system, and the pressure is kept at around 0.3MPa until the temperature reaches 210℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0071] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.9 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 250℃ during this process.

[0072] S4. Finally, seal the reactor, maintain the temperature within 250-260℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 120 minutes before discharging to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0073] Example 5 S1. Under an inert atmosphere, mix 30.0g DDP (5wt%), 60.0g caprolactam (10wt%), 278.5g adipic acid and 231.5g hexamethylenediamine (85wt%) in an aqueous solution to prepare a 50wt% aqueous solution. Add the solution to a pressure-resistant reaction vessel with a drain valve, heat to 190℃ and react for 3 hours to carry out prepolymerization and obtain a prepolymer aqueous solution.

[0074] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0075] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.8 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0076] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, evacuate the vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 60 minutes before discharging the material to obtain halogen-free intrinsic flame-retardant copolyamide 66 with high elongation at break.

[0077] Comparative Example 1 This comparative example prepared pure PA66 without the addition of DDP and caprolactam, as detailed below: S1. Under an inert atmosphere, 334.4 g of adipic acid and 265.6 g of hexamethylenediamine aqueous solution were mixed to prepare a 50 wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 220 °C and reacted for 2 h to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0078] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 250℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0079] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 275°C during this process.

[0080] S4. Finally, seal the reactor, maintain the temperature within 275-285℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain the polymer.

[0081] Comparative Example 2 The difference between this comparative example and Example 1 is that DDP was not added, as detailed below: S1. Under an inert atmosphere, 60.0 g of caprolactam (10 wt%), 300.8 g of adipic acid and 239.2 g of hexamethylenediamine aqueous solution were mixed to prepare a 60 wt% aqueous solution, which was added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 180 °C and reacted for 2 h to carry out prepolymerization and obtain a prepolymer aqueous solution.

[0082] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0083] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0084] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain the polymer.

[0085] Comparative Example 3 The difference between this comparative example and Example 1 is that caprolactam was not added, as detailed below: S1. Under an inert atmosphere, 30.0g of DDP (10wt%), 317.5g of adipic acid and 252.5g of hexamethylenediamine aqueous solution are mixed to prepare a 60wt% aqueous solution, which is then added to a pressure-resistant reaction vessel with a drain valve. The mixture is heated to 180℃ and reacted for 2 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0086] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0087] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0088] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain the polymer.

[0089] Comparative Example 4 The difference between this comparative example and Example 1 is that the polymerization temperature was increased, as detailed below: S1. Under an inert atmosphere, 30.0g DDP (5wt%), 30.0g caprolactam (5wt%), 295.2g adipic acid and 244.8g hexamethylenediamine aqueous solution were mixed to prepare a 60wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 220℃ and reacted for 2 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0090] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 240℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0091] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 275°C during this process.

[0092] S4. Finally, seal the reactor, maintain the temperature within 275-285℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain the polymer.

[0093] Comparative Example 5 The difference between this comparative example and Example 1 is that caprolactam in Example 1 was replaced with an equal mass of laurolactam monomer.

[0094] S1. Under an inert atmosphere, 30.0g of DDP (5wt%), 30.0g of laurolactam (5wt%), 295.2g of adipic acid and 244.8g of hexamethylenediamine (90wt%) were mixed to prepare a 60wt% aqueous solution, which was then added to a pressure-resistant reaction vessel with a drain valve. The mixture was heated to 180℃ and reacted for 2 hours to carry out prepolymerization, thereby obtaining a prepolymer aqueous solution.

[0095] S2. The obtained prepolymer aqueous solution is then continuously heated. During this process, the drain valve is opened to remove about 60wt% of the water in the system, and the pressure is kept at around 0.4MPa until the temperature reaches 215℃. At this point, the drain valve is closed to obtain the concentrated prepolymer aqueous solution.

[0096] S3. Then continue heating it, allowing the temperature and pressure to rise continuously until the pressure reaches 1.7 MPa. Then open the drain valve, allowing the pressure to drop continuously to 0 MPa, while adjusting the temperature to reach 260℃ during this process.

[0097] S4. Finally, seal the reactor, maintain the temperature within 260-270℃, draw a vacuum to make the pressure reach -0.10MPa, and maintain this pressure for 10 minutes before discharging to obtain the polymer.

[0098] The main raw material dosages and condition parameters for each embodiment and comparative example are summarized below: Table 1 condition Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 DDPwt% 5 10 10 20 5 - - 5 5 5 caprolactam wt% 5 5 10 20 10 - 10 - 5 - laurolactam wt% - - - - - - - - - 5 adipic acid and hexamethylenediamine wt% 90 85 80 60 85 100 90 90 90 90 aqueous solution mass concentration (wt%) 60 50 50 40 50 50 60 　60 60 60 First preset temperature ℃ 180 190 190 200 190 220 180 180 220 180 Prepolymerization time h 2 2 3 4 3 2 2 2 2 2 Dehydration ratio (wt%) 60 60 60 80 60 60 60 60 60 60 First preset pressure (MPa) 0.4 0.4 0.5 0.3 0.4 0.4 0.4 0.4 0.4 0.4 Second preset temperature ℃ 215 215 215 210 215 250 215 215 240 215 Second preset pressure (MPa) 1.7 1.8 1.8 1.9 1.8 1.7 1.7 1.7 1.7 1.7 Third preset temperature ℃ 260 270 260 250 260 275 260 260 275 260 Polycondensation time min 10 30 60 120 60 10 10 10 10 10 Experimental Example 1 This experimental example tests the mechanical and flame-retardant properties of the polymers obtained in the above embodiments and comparative examples, and the results are summarized below: Table 2 Results analysis: Comparative Example 1 prepared pure PA66, which has high regularity and high strength but is flammable.

[0099] Comparative Example 2 added caprolactam but not DDP. Compared with pure PA66, the elongation at break was increased (344.7%), indicating that the introduction of caprolactam had a significant toughening effect on PA66, but the flame retardancy was only average (V-2, LOI 22%).

[0100] Comparative Example 3 added DDP but not caprolactam, which slightly improved the flame retardant properties, but the final polycondensation temperature was relatively low for this polymerization, making it difficult to increase the molecular weight to a high level. The elongation at break was extremely low, it lacked toughness, and the process was difficult.

[0101] Comparative Example 4 included both DDP and caprolactam, but the polymerization temperature was too high. Although the limiting oxygen index and vertical burning performance of Comparative Example 4 were slightly better than those of Example 1, its mechanical properties decreased significantly, with the elongation at break plummeting to 14.5% and the strength dropping to 22.4 MPa. This was due to the cross-linking reaction of the polymer caused by the higher polymerization temperature. From an application perspective, although the flame retardant properties were slightly improved, the damage to the mechanical properties severely limited the application range of the nylon material, making it largely insignificant. This demonstrates that adjusting the appropriate polymerization temperature is crucial for this system.

[0102] In Comparative Example 5, caprolactam in Example 1 was replaced with an equal mass of laurolactam monomer. The introduction of long-chain monomers not only impaired the flame retardant properties but also reduced the reactivity of the system, resulting in poorer polymer chain regularity. This is because the rigidity and polarity of the two molecular chains differ greatly, and dodecyllactam has lower ring-opening reactivity than caprolactam. Therefore, the co-condensation reaction with nylon salts is prone to chain segment inhomogeneity, significantly increasing the difficulty of implementation and resulting in low economic efficiency.

[0103] In Examples 1-5 of this invention, different amounts of DDP and caprolactam were added, resulting in a significant improvement in flame retardancy compared to pure PA66, while maintaining high toughness, with an elongation at break >40%, preferably >100%. In these embodiments, caprolactam was used to toughen and counteract the brittleness of DDP in the formulation; and low-temperature polymerization was employed to protect DDP and its molecular chains, achieving both flame retardancy and toughening. Furthermore, the strength of all examples (45.2 - 59.3 MPa) was between that of the high-toughness Comparative Example 2 (42.4 MPa) and the high-strength pure PA66 Comparative Example 1 (64.4 MPa). This indicates that although the crystallinity and regularity of the material decreased with the introduction of DDP and caprolactam, they remained within an acceptable or even excellent range.

[0104] In Examples 1-4 (DDP content 5%-20%), the elongation at break gradually decreased from 186.1% (5% DDP) to 43.1% (20% DDP). This indicates that as the DDP content increases, flame retardancy improves, but rigidity increases while toughness decreases. However, even at a high addition of 20% (Example 4), the material still maintained a certain degree of ductility (>40%), which is far superior to the brittle material in Comparative Example 2.

[0105] In Example 5, even after adding a flame retardant, the elongation at break was still maintained at an ultra-high value of 262.5%, indicating that the formulation (appropriate amount of caprolactam) and process of the present invention can retain the excellent toughness brought by caprolactam to the greatest extent while introducing the rigid flame retardant DDP.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A halogen-free intrinsically flame retardant copolyamide 66 characterized in that, It is prepared from intrinsic flame retardant DDP, caprolactam, adipic acid and hexamethylene diamine, and includes the following structural units in the molecular structure: （1） ； （2） ； （3） 。 2. The halogen-free intrinsically flame retardant copolyamide 66 according to claim 1, characterized in that, The quantity relationship of the structural unit (1), the structural unit (2) and the structural unit (3) is (60-90):(5-20):(5-20); Preferably, the quantity relationship of the structural unit (1), the structural unit (2) and the structural unit (3) is (80-90):(5-10):(5-10).

3. The halogen-free intrinsically flame retardant copolyamide 66 according to claim 1 or 2, characterized in that, The limiting oxygen index of the halogen-free intrinsic flame-retardant copolymer polyamide 66 is 26.0-30.0%, the elongation at break is >40%, the yield strength is 45-60 MPa, and the melt index is 13-18 g / 10 min. Preferably, the elongation at break is >100%.

4. A process for the preparation of a halogen-free intrinsically flame retardant copolyamide 66 according to any one of claims 1 to 3, characterized in that, It comprises: S1, mixing the aqueous solution of DDP, caprolactam, adipic acid and hexamethylene diamine under an inert atmosphere, pre-polymerizing at a first preset temperature to obtain a pre-polymer aqueous solution; S2, heating the pre-polymer aqueous solution and accompanying controllable dehydration, maintaining a first preset pressure until the temperature reaches a second preset temperature, stopping the dehydration to obtain a concentrated pre-polymer aqueous solution; S3, heating and pressurizing the concentrated pre-polymer aqueous solution to reach a second preset pressure, then depressurizing to normal pressure or near normal pressure, and heating to a third preset temperature during the depressurization process; S4, maintaining the product prepared in S3 at the third preset temperature, reducing the pressure, and performing a final polycondensation reaction to obtain a high-elongation halogen-free intrinsic flame-retardant copolymer polyamide 66.

5. The preparation method according to claim 4, characterized in that, In step S1, the proportion of each solid raw material in the total mass of solid raw materials is: The mass fraction of caprolactam is 5wt%-20wt%, the mass fraction of DDP is 5wt%-20wt%, and the mass fraction of adipic acid and hexamethylene diamine is 60wt%-90wt%; Preferably, the mass fraction of caprolactam is 5wt%-10wt%, the mass fraction of DDP is 5wt%-10wt%, and the mass fraction of adipic acid and hexamethylene diamine is 80wt%-90wt%.

6. The production method according to claim 4 or 5, characterized by, In step S1, the first preset temperature is lower than the thermal degradation temperature of DDP; Preferably, the first preset temperature is 180-200℃, and the reaction time of pre-polymerization is 2-4h; Preferably, the first preset temperature is 180-190℃, and the reaction time of pre-polymerization is 2-3h.

7. The method of any one of claims 4-6, wherein the method further comprises, In step S2, 60-80wt% of water in the system is removed by controllable dehydration; Preferably, 60wt% of water in the system is removed.

8. The method of any one of claims 4-7, wherein, In step S2, the first preset pressure is 0.3-0.5MPa, and the second preset temperature is 210-215℃; Preferably, the first preset pressure is 0.35-0.45Mpa.

9. The method of any one of claims 4-8, wherein, In step S3, the second preset pressure is 1.7-1.9MPa; Preferably, the second preset pressure is 1.7-1.8Mpa.

10. The method of any one of claims 4-9, wherein, In steps S3 and S4, the third preset temperature is 250-270℃; Preferably, in step S4, vacuum and pressure reduction are performed so that the pressure reaches -0.10Mpa; Preferably, in step S4, the time for performing the final polycondensation reaction is 10-120min.

Images