A method for preparing composite flame-retardant fibers by synergistic flame retardancy modification of aluminum hypophosphite based on a sym-triazine ring

Abstract

A method for preparing composite flame-retardant fibers by synergistic flame-retardant modification of melamine ring-based aluminum hypophosphite includes: adding benzoguanamine and p-methoxybenzaldehyde into a reaction vessel equipped with a water separator, adding toluene as a solvent and p-toluenesulfonic acid as a catalyst, and carrying out a stirring reaction under heating conditions; cooling the reaction vessel after the reaction is completed to room temperature, filtering off the liquid in the reaction vessel, and washing and drying to obtain a first flame retardant with a melamine ring and Schiff base structure; using aluminum hypophosphite as a second flame retardant, and melt-blending the first flame retardant and the second flame retardant with polyamide 6 at mass fractions of 2-10% and 0.25-1.25% respectively through an extruder, and spinning the obtained blend material through a melt spinning machine to obtain composite flame-retardant fibers. The present invention aims at problems such as continuous combustion and melt dripping caused by the breakage of the molecular chain induced by high-temperature oxidation of PA6, and utilizes the property of the melamine ring structure to expand and form carbon to promote the formation of a stable carbon layer on PA6.

Description

Technical Field

[0001] The present invention relates to the technical field of polyamides and their flame-retardant fibers, and particularly relates to a method for preparing composite flame-retardant fibers by synergistic flame-retardant modification of polyamide 6 with inorganic aluminum hypophosphite based on a s-triazine ring. Background Art

[0002] Polyamide is a general term for thermoplastic resins with amide groups as repeating units on the main polymer chain. Polyamide was invented by American chemist Carothers and his research team. DuPont of the United States was the first to develop and apply resins to fibers and achieved industrial production of polyamide in 1939. After that, injection-molded products of polyamide were also developed and applied, replacing some metal products due to their light weight and low cost. In 1943, IG Farben produced polyamide 6 (PA6), and they believed that monomer polymerization was simpler and the cost was lower, so they preferred to develop PA6. PA6 is a semi-crystalline polymer with excellent mechanical strength, elasticity, wear resistance, and chemical corrosion resistance. PA6 is the most widely used type of polyamide product and is widely used as an engineering plastic and textile fiber. However, in actual production and application, since the limiting oxygen index of PA6 is only 22% and the vertical burning rating is UL-94 V-2, it is prone to dripping during combustion, belongs to a flammable material, and is likely to cause a fire, posing a great threat to personal safety and property safety. Therefore, preparing and developing PA6 materials with excellent comprehensive properties and a flame-retardant rating meeting national standards is of great significance for reducing the harm of fires.

[0003] Two very important application directions of flame-retardant PA6 are composite materials and synthetic fibers. For applications in electricity, high temperatures, or places where there may be a fire hazard, such as transportation tracks, electronic appliances, mechanical engineering, and electrical equipment, the flame-retardant requirements for PA6 are higher; the structural characteristics of PA6 synthetic fibers make them more easily ignited and more harmful compared to PA6 resins, especially in fields such as curtains, carpets, and special clothing in public places.

[0004] Therefore, it is of great significance to study the flame-retardant and anti-dripping properties of PA6 and prepare halogen-free flame-retardant PA6 for application in fibers. Summary of the Invention

[0005] Based on this, the present invention provides a method for preparing composite flame-retardant fibers by synergistic flame-retardant modification with inorganic aluminum hypophosphite based on a s-triazine ring to solve the technical problem that the fiber fabric of polyamide 6 in the prior art is prone to dripping during combustion and is likely to cause a fire.

[0006] To achieve the above object, the present invention provides a method for preparing composite flame-retardant fibers by synergistic flame-retardant modification with inorganic aluminum hypophosphite based on a s-triazine ring, which comprises the following steps:

[0007] S1. Add benzoguanamine and p-methoxybenzaldehyde into a reaction vessel equipped with a water separator, add toluene as the solvent and p-toluenesulfonic acid as the catalyst, and carry out a stirring reaction under heating conditions;

[0008] S2. Cool the reaction vessel after the reaction is completed to room temperature, filter off the liquid in the reaction vessel by suction, and obtain the first flame retardant with a melamine ring and a Schiff base structure after washing and drying;

[0009] S3. Use aluminum hypophosphite as the second flame retardant, melt-blend the first flame retardant and the second flame retardant with polyamide 6 at mass fractions of 2-10% and 0.25-1.25% respectively through an extruder, and spin the obtained blended material through a melt spinning machine to obtain composite flame retardant fibers.

[0010] As a further preferred technical solution of the present invention, the dosages of each component in step S1 are: 6.0 g of benzoguanamine, 13.056 g of p-methoxybenzaldehyde, 200-300 ml of toluene, and 15-20 ml of p-toluenesulfonic acid.

[0011] As a further preferred technical solution of the present invention, the heating temperature for the stirring reaction in step S1 under heating conditions is 120 °C, and the stirring time is 6 hours.

[0012] As a further preferred technical solution of the present invention, a spherical condenser for introducing condensed water is connected to the water separator.

[0013] As a further preferred technical solution of the present invention, in step S2, the filtered reactants are washed with absolute ethanol at least three times, and then dried in a vacuum oven at 40-50 °C for at least 12 hours.

[0014] As a further preferred technical solution of the present invention, in step S3, the temperature for melt blending is 230 °C; the temperature for spinning by the melt spinning machine is 245 °C, the spinning speed is 500-2000 m / min, and the draw ratio is 1.2-2.0.

[0015] In view of the problems of continuous combustion and melt dripping caused by the high-temperature oxidation-induced molecular chain breakage of PA6, the present invention utilizes the property of the s-triazine ring structure to expand into carbon, promoting the formation of a stable carbon layer in PA6. Meanwhile, combined with the property that the Schiff base structure can undergo irreversible chemical cross-linking at high temperatures, a flame retardant DPTAA with both s-triazine ring and Schiff base structures is synthesized through an aldehyde-amine condensation reaction to solve the melt dripping problem of PA6. When applied to the flame retardant modification of PA6, DPTAA improves the vertical burning performance of PA6 from UL-94 V-2 grade to V-0 grade. At the same time, the peak heat release of PA6 decreases by 10.4%, and the smoke release decreases by 2.9%. However, the limiting oxygen index of PA6 / DPTAA is relatively low, and the overall heat release performance is not improved. Therefore, the present invention adopts a phosphorus-nitrogen synergistic flame retardant method, combining DPTAA with aluminum hypophosphite (synergistic flame retardant of s-triazine ring and aluminum hypophosphite DPTAA-ALHP) to co-modify PA6. The limiting oxygen index of the composite PA6 / DPTAA-ALHP can reach 30.9%. At the same time, the vertical burning performance is also greatly improved, from UL-94 V-2 grade to V-0 grade, and the melt dripping phenomenon also disappears significantly, with the heat release decreasing by 9.23%.

[0016] The present invention can achieve the following beneficial effects:

[0017] 1) By using a phosphorus-nitrogen synergistic flame retardant method, DPTAA and aluminum hypophosphite are blended into PA6 to obtain a PA6 / DPTAA-ALHP composite resin, and melt spinning is carried out. The vertical burning grade of PA6 / DPTAA-ALHP reaches V-0 grade. At the same time, the melt dripping problem of PA6 is solved, and the limiting oxygen index is increased from 24.5% to 30.9%. Moreover, compared with the limiting oxygen index of 28.6% of PA6 / DPTAA8, there is a significant improvement. The peak heat release PHRR decreases by 4.3%, and the total heat release THR decreases by 9.23%. The study of the flame retardant mechanism shows that the dilution effect of non-combustible gases in the gas phase, the capture effect of phosphorus-oxygen free radicals, and the barrier effect of the carbon layer in the condensed phase jointly play a role during the combustion process. The flame retardant fiber is obtained by the melt spinning method, and the breaking strength of the fiber decreases with the addition of the flame retardant, from 2.53 cN / dtex to 1.45 cN / dtex.

[0018] 2) The s-triazine ring structural unit of the present invention is rich in tertiary nitrogen structure and has excellent charring effect. When burning, it releases non-combustible gases such as nitrogen, which can promote the formation of an expanded structure of the carbon layer, enabling the modified resin to have the functions of blocking combustible gases and heat conduction and diffusion. There is also a stable conjugated structure in the s-triazine ring, which gives it high thermal stability. Some triazine derivatives have good hydrogen bond assembly ability and can form hydrogen bond interactions with groups such as carbonyl and imino groups in the PA6 molecular chain intermolecularly or intramolecularly. The two have potential structural matching, which is beneficial to improving the comprehensive performance of the flame-retardant polymer. Therefore, the s-triazine ring structure can provide a functional structural unit for flame-retardant PA6.

[0019] 3) The vertical burning grade of the PA6 resin of the present invention reaches V-0 level after adding the DPTAA-ALHP flame retardant. At the same time, the sample after adding the flame retardant either has only one small melt droplet or none at all, indicating that the DPTAA-ALHP flame retardant greatly improves the anti-melt droplet performance of PA6. The limiting oxygen index is increased from 24.5% to 30.9%. Compared with the limiting oxygen index of 28.6% of PA6 / DPTAA8 in the previous chapter, there is a significant improvement. The peak heat release rate PHRR is decreased by 4.3%, and the total heat release THR is decreased by 9.23%. This shows that DPTAA-ALHP coordinates the flame retardant performance of PA6 in multiple aspects, not only improving the flame retardant and anti-melt droplet performance of PA6, but also reducing the heat release. In the air atmosphere, the char yield of PA6 after adding DPTAA-ALHP is increased by more than 3 times compared with pure PA6, from 5.41% to 18.77%, playing a good role in isolating oxygen and heat. Therefore, the composite flame-retardant fiber of the present invention has better comprehensive protection performance when applied to wearable protective clothing and other fabrics such as curtain and carpet. Description of the Drawings

[0020] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0021] Figure 1 It is a schematic diagram of the synthesis process and synthesis mechanism of DPTAA;

[0022] Figure 2 It is the 1H NMR spectrum and infrared spectrum of DPTAA;

[0023] Figure 3 It is the Py-GC-MS curve and pyrolysis diagram of DPTAA;

[0024] Figure 4 It is a video screenshot of the vertical burning process of pure PA6 and PA6 / DPTAA8;

[0025] Figure 5CCT-related curves of pure PA6 and PA6 / DPTAA, a) HRR; b) THR; c) SPR; d) TSR;

[0026] Figure 6 For pure PA6 and PA6 / DPTAA8ALHP 1.00 Video screenshot of the vertical combustion process;

[0027] Figure 7 CCT-related curves of pure PA6 and PA6 / DPTAA-ALHP, a) HRR; b) THR; c) SPR; d) TSR;

[0028] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0029] The following is a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustration and explanation of the present invention, and are not intended to limit the present invention.

[0030] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods used are all conventional methods unless otherwise specified.

[0031] Experimental raw materials: Benzoguanamine was purchased from Wendong (Shanghai) Chemical Co., Ltd.; p-Methoxybenzaldehyde was purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd.; p-Toluenesulfonic acid was purchased from the Shanghai Branch of Beijing Innochem Science & Technology Co., Ltd.; Toluene was purchased from Sinopharm Chemical Reagent Co., Ltd.; Absolute ethanol was purchased from Sinopharm Chemical Reagent Co., Ltd.; Polyamide 6 (PA6) chips were purchased from Jiangsu Haiyang Nylon New Materials Co., Ltd.; Inorganic aluminum hypophosphite was purchased from Henan Senjie Chemical Products Co., Ltd.

[0032] Comparative Example 1

[0033] The PA6 chips were melted using a CTE20 PLUS twin-screw extruder produced by Coperion (Nanjing) Machinery Co., Ltd. at a temperature of 230 °C, and the obtained sample was named Pure PA6; after being vacuum dried at 120 °C for 48 h, the Pure PA6 was spun using a C-type melt spinning machine produced by Fuji Corporation of Japan at a spinning temperature of 245 °C to obtain Pure PA6 fibers.

[0034] Comparative Examples 2-6

[0035] 1) Preparation of the first flame retardant (DPTAA):

[0036] Refer toFigure 1 , add 6.0000 g of benzoguanamine and 13.0560 g of p-methoxybenzaldehyde into a 500 ml single-necked round-bottom flask equipped with a water separator, stir evenly, then add 300 ml of toluene as a solvent, and finally add 20 ml of p-toluenesulfonic acid as a catalyst into the flask and stir evenly. Place the round-bottom flask in an oil bath, start stirring, first connect the water separator above the round-bottom flask, then connect a spherical condenser. After fixing, turn on the cooling water and heat the round-bottom flask, set the temperature to 120 °C, and cover the water separator and the surface of the oil bath with tin foil to ensure that the temperature will not drop significantly. Stir and react for 6 hours, then remove the device and let the round-bottom flask cool naturally to room temperature. Finally, filter off the liquid, wash it 3 times with absolute ethanol, and dry it in a vacuum oven at 50 °C for 16 hours to obtain about 6.5 g of the first flame retardant with a s-triazine ring and Schiff base structure in the form of a pale yellow powder.

[0037] 2) Melt blending:

[0038] Respectively blend DPTAA with PA6 chips at mass fractions of 2%, 4%, 6%, 8%, and 10% using a CTE20 PLUS twin-screw extruder produced by Coperion (Nanjing) Machinery Co., Ltd. to obtain flame-retardant blends. The blending temperature is 230 °C to obtain PA6 / DPTAA series samples, which are respectively named PA6 / DPTAA2, PA6 / DPTAA4, PA6 / DPTAA6, PA6 / DPTAA8, and PA6 / DPTAA 10 .

[0039] 3) Melt spinning:

[0040] The PA6 / DPTAA series samples (PA6 / DPTAA2, PA6 / DPTAA4, PA6 / DPTAA6, PA6 / DPTAA8, and PA6 / DPTAA 10 ) are respectively dried in vacuum at 120 °C for 48 h and then spun using a Type C melt spinning machine produced by Fuji Company of Japan. The spinning temperature is 245 °C, and finally PA6 / DPTAA composite flame-retardant fibers are obtained.

[0041] Perform nuclear magnetic resonance hydrogen spectrum analysis and infrared spectrum analysis on DPTAA:

[0042] Through Figure 2From the proton nuclear magnetic resonance spectrum, it can be seen that peaks a, c, and e are the peaks corresponding to p-methoxybenzaldehyde on the product, peaks d and f are the peaks corresponding to benzoguanamine in the product, and peak b is the peak of -HC=N-. Since the amino group reacts with the aldehyde group, there is a shift compared to the amino peak of the raw material. Analyzing from the perspective of the raw materials, benzoguanamine is a white powder, and p-methoxybenzaldehyde is a colorless transparent liquid. The substance after reaction synthesis becomes a light yellow powder, and the yield reaches 6.6 - 6.7 g. Analyze the synthesis results from both macroscopic and microscopic perspectives. From the infrared spectrum, we can see that 770 - 825 cm -1 is caused by the out-of-plane bending vibration of the benzene ring, and 1171 cm -1 is due to the in-plane bending vibration of the benzene ring. 1652 cm -1 and 1615 cm -1 are two absorption peaks resulting from the conjugation splitting of the benzene ring and -C=N-. Through infrared, we further confirm the formation of DPTAA.

[0043] Analysis of the gas-phase pyrolysis products of DPTAA:

[0044] Through Figure 3 the gas-phase pyrolysis mass spectrometry and the pyrolysis products in Table 1, it is analyzed that the structure of the flame retardant is a molecule with a s-triazine ring and a Schiff base structure. At the same time, based on the structure of DPTAA, we deduce a schematic diagram of the molecular bond breakage during the pyrolysis of the DPTAA flame retardant. Besides carbon dioxide generated in the gas phase, benzoguanamine, 2-cyano-4'-methylbiphenyl, and benzonitrile are mainly generated. Benzoguanamine containing a s-triazine ring structure mainly serves the purpose of promoting char formation during high-temperature processes, while the carbon-nitrogen unsaturated bond promotes irreversible chemical cross-linking between the broken molecular chains of PA6 during high-temperature processes, thus endowing PA6 with the anti-dripping property.

[0045] Table 1. Pyrolysis product information of DPTAA

[0046]

[0047] Flame retardancy analysis of PA6 / DPTAA

[0048] The PA6 / DPTAA fiber product or fabric obtained by melt spinning is passed through Figure 5From the UL-94 vertical burning test and the results in Table 2, we can see that Pure PA6 burns violently during the first ignition, and there are continuous molten drops dripping, immediately igniting the absorbent cotton. During the second ignition, because a carbon layer is formed on the surface after the first combustion, the burning stops after 2 seconds. For PA6 / DPTAA2, it burns violently during the first ignition, with molten drops dripping and igniting the absorbent cotton. After the second ignition, the burning time is slightly shortened. For PA6 / DPTAA4, it can already be seen that the flame retardancy performance has been improved. It is not easy to burn during the first ignition and is not ignited during the second ignition. For PA6 / DPTAA6, it is not ignited during the first ignition, but because the carbon layer formed due to non-combustion during the first time is not sufficient to resist the flame, it burns for 2 seconds and then goes out during the second ignition. For PA6 / DPTAA8, it is not ignited during both the first and second ignitions, and the absorbent cotton does not burn. According to the national standard, it reaches the V-0 level. PA6 / DPTAA8 realizes the anti-melting drop performance of PA6. PA6 / DPTAA 10 During injection molding, the fluidity is too good, and the addition of the flame retardant has a greater impact on PA6 itself, so the flame retardancy performance also decreases. However, because the proportion of the s-triazine ring structure decreases, the ability of PA6 to expand and form carbon decreases, resulting in a not very high limiting oxygen index for PA6 / DPTAA. The LOI of PA6 / DPTAA8 that meets the flame retardant standard is only 28.6%, and the highest LOI among them for PA6 / DPTAA 10 can reach 30.0%.

[0049] Table 2. LOI and UL-94 test results

[0050]

[0051] Note: av-t1 and av-t2 are both the average values of five test samples

[0052] To further explore the flame retardant effect of the PA6 / DPTAA composite material in a real fire, the cone calorimetry method was used for testing. From Figure 6 and Table 3, it can be seen that the ignition time of the material is extended from 63 s to a maximum of 77 s, which means that the material is less likely to be ignited. With the addition of the DPTAA flame retardant, the PHRR is reduced by 10.4%. PHRR is a very important index for flame retardancy, which also shows that DPTAA improves the heat release performance of PA6, but the total heat release does not decrease. At the same time, the total smoke release of PA6 / DPTAA8 that meets the flame retardant standard is reduced by 2.9% compared with pure PA6, which also indicates that the DPTAA flame retardant also improves the reduction of the smoke release amount.

[0053] Table 3. Test results of cone calorimetry

[0054]

[0055] A flame retardant (DPTAA) with a s-triazine ring and a Schiff base structure combines the characteristics of the s-triazine ring expanding to form carbon and the Schiff base structure generating irreversible chemical cross-linking at high temperatures, achieving the flame retardant and anti-melting drip properties of PA6, but with a relatively low limiting oxygen index.

[0056] Example 1

[0057] 1) Preparation of the first flame retardant (DPTAA):

[0058] Refer to Figure 1 , add 6.0000 g of benzoguanamine and 13.0560 g of p-methoxybenzaldehyde into a 500 ml single-necked round-bottom flask equipped with a water separator, stir evenly, then add 300 ml of toluene as a solvent, and finally add 20 ml of p-toluenesulfonic acid as a catalyst into the flask and stir evenly. Place the round-bottom flask in an oil bath, start stirring, first connect the water separator above the round-bottom flask, then connect a spherical condenser. After fixing, turn on the cooling water and heat the round-bottom flask, set the temperature to 120 °C, cover the water separator and the surface of the oil bath with tin foil to ensure that the temperature will not drop significantly. Stir and react for 6 hours, then remove the device and let the round-bottom flask cool naturally to room temperature. Finally, filter off the liquid, wash it 3 times with absolute ethanol, and dry it in a vacuum oven at 50 °C for 16 hours to obtain the first flame retardant with a s-triazine ring and a Schiff base structure in the form of a pale yellow powder, about 6.5 g.

[0059] 2) Melt blending:

[0060] Using aluminum hypophosphite (ALHP) as the second flame retardant, DPTAA and ALHP are melt-blended with PA6 chips at mass fractions of 8% and 0.25% respectively using a CTE20 PLUS twin-screw extruder produced by Coperion (Nanjing) Machinery Co., Ltd. to obtain a flame-retardant blend. The blending temperature is 230 °C to obtain a PA6 / DPTAA-ALHP sample, named PA6 / DPTAA8ALHP according to the mass fractions of DPTAA and ALHP. 0.25 .

[0061] 3) Melt spinning:

[0062] After the PA6 / DPTAA-ALHP sample is vacuum-dried at 120 °C for 48 h, it is spun using a C-type melt spinning machine produced by Fuji Corporation of Japan. The spinning temperature is 245 °C, and finally a PA6 / DPTAA-ALHP composite flame-retardant fiber is obtained.

[0063] Examples 2 - 5

[0064] Using the same preparation method as in Example 1, only changing the mass fraction of ALHP in the melt blending (DPTAA was kept at 8%), the respective examples were 0.50%; 0.75%; 1.00%; 1.25%, and a series of PA6 / DPTAA-ALHP samples were obtained, named PA6 / DPTAA8ALHP 0.25 、PA6 / DPTAA8ALHP 0.50 、PA6 / DPTAA8ALHP 0.75 、PA6 / DPTAA8ALHP 1.00 、PA6 / DPTAA8ALHP 1.25 。Finally, the PA6 / DPTAA-ALHP series of samples were melt-spun to obtain PA6 / DPTAA-ALHP composite flame-retardant fibers.

[0065] The flame-retardant properties of the PA6 / DPTAA-ALHP series of samples in the above examples were tested:

[0066] As Figure 6 and shown in Table 4, taking pure PA6 as the control group, Pure PA6 burned violently, and molten droplets continuously dripped. PA6 / DPTAA8ALHP 0.25 was not ignited during the first ignition, burned for 3 seconds after the second ignition, and the flame went out after one molten droplet dripped. PA6 / DPTAA8ALHP 0.50 、PA6 / DPTAA8ALHP 0.75 and PA6 / DPTAA8ALHP 0.25 had basically the same experimental results. Although there was finally one molten droplet, the molten droplet quickly dripped away to take away the heat, and the sample bar stopped burning. PA6 / DPTAA8ALHP 1.00 was not ignited during the first ignition or the second ignition, and the absorbent cotton did not burn. We judged that it reached the V-0 level according to the national standard. At the same time, PA6 / DPTAA8ALHP 1.00 had no molten droplet phenomenon. PA6 / DPTAA8ALHP 1.25 was not ignited during the first ignition, had one molten droplet during the second ignition, but the molten droplet did not ignite the absorbent cotton. It was judged to reach the V-0 level according to the national standard. At the same time, after adding ALHP, the limiting oxygen index increased compared with adding only DPTAA, and the LOI could finally reach 30.9%. Comparing with the limiting oxygen index of 28.6% of PA6 / DPTAA8, the limiting oxygen index had a relatively large increase.

[0067] Table 4. LOI and UL-94 test results

[0068]

[0069] Note: av-t1 and av-t2 are the average values ​​of five test samples.

[0070] LOI and UL-94 are only applicable to the small flame mode test method. In order to further explore the flame retardant effect of PA6 / DPTAA-ALHP composite materials in real fire, we used cone calorimetry to test. Figure 7 As can be seen from Table 5, for heat release and total heat release, PA6 / DPTAA8ALHP 1.25 The PHRR was reduced by 4.3% and the total heat release was reduced by 9.23%, which proves that the addition of ALHP has improved the reduction of heat release. As for smoke release and total smoke release, ALHP belongs to phosphorus flame retardant, so there is a problem of increased smoke volume. PA6 / DPTAA8ALHP 1.25 The total smoke release increased by 17.4%, and after adding the flame retardant, the initial ignition time was shortened. When modifying the flame retardant, we must comprehensively consider various indicators and strive to obtain the optimal formula.

[0071] Table 5. Cone calorimetry test results

[0072]

[0073] In summary, the purpose of mixing DPTAA and ALHP in a certain proportion is to ensure a good anti-melting effect and improve the limiting oxygen index and heat release performance of PA6. Similarly, the prepared composite flame retardant fiber has the same flame retardant properties.

[0074] Spinnability and mechanical properties test:

[0075] Pure PA6 is also used as the control group. Its spinnability is good and the spinning speed can reach 2000m / min. However, the edge collapse phenomenon occurs during the winding process. The spinnability of the PA6 / DPTAA-ALHP series samples is not greatly affected, and the spinning speed can still reach 2000m / min. When the ALHP content is greater than 1.25%, the breaking strength is reduced to 1.45cN / dtex, and the spinnability is affected. Because of the addition of DPTAA, the fiber has a certain viscosity, the mechanical properties are improved, and the edge collapse phenomenon does not occur. At the same time, the fiber's breaking strength will decrease with the addition of ALHP. In order to ensure good flame retardant effect and mechanical properties, as well as spinnability, the mass fractions of DPTAA and ALHP in the composite masterbatch for melt spinning are in the range of 2-10% and 0.25-1.25%, respectively.

[0076] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this embodiment without departing from the principle and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a s-triazine ring, characterized in that, It includes the following steps: S1. Add benzoguanamine and p-methoxybenzaldehyde into a reaction vessel with a water separator, add toluene as a solvent and p-toluenesulfonic acid as a catalyst, and carry out a stirring reaction under heating conditions; S2. Cool the reaction vessel after the reaction is completed to room temperature, filter off the liquid in the reaction vessel by suction, and obtain the first flame retardant with a melamine ring and a Schiff base structure after washing and drying; S3. Use aluminum hypophosphite as the second flame retardant, and melt-blend the first flame retardant and the second flame retardant with polyamide 6 at mass fractions of 8% and 1.0 - 1.25% respectively through an extruder, and spin the blended material through a melt spinning machine to obtain composite flame retardant fibers; In step S1, the heating temperature for the stirring reaction under heating conditions is 120 °C.

2. The method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a s-triazine ring as claimed in claim 1, wherein In step S1, the feeding ratio of each component is: 6.0 g of benzoguanamine, 13.056 g of p-methoxybenzaldehyde, 200 - 300 mL of toluene, and 15 - 20 mL of p-toluenesulfonic acid.

3. The method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a sym-triazine ring as claimed in claim 1, wherein In step S1, the stirring time for the stirring reaction under heating conditions is 6 hours.

4. The method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a melamine ring, as claimed in claim 1, wherein A spherical condenser for introducing condensed water is connected to the water separator.

5. The method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a sym-triazine ring as claimed in claim 1, wherein In step S2, the filtered reactants are washed with absolute ethanol at least three times, and then dried in a vacuum oven at 40 - 50 °C for at least 12 hours.

6. The method for preparing a composite flame-retardant fiber by synergistic flame-retardant modification of aluminum hypophosphite based on a sym-triazine ring as claimed in any one of claims 1 to 5, characterized in that In step S3, the temperature for melt blending is 230 °C; the temperature for spinning by the melt spinning machine is 245 °C, the spinning speed is 500 - 2000 m / min, and the draw ratio is 1.2 - 2.0.

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