A bio-based flame retardant nylon material and a method of making the same

Abstract

This invention belongs to the field of composite polymer materials technology, specifically relating to a bio-based flame-retardant nylon material and its preparation method. This invention achieves full bio-based flame-retardant components and multi-source synergistic flame retardancy. The material is composed of bio-based nylon resin, tannic acid-phytic acid coordinated modified montmorillonite, chitosan microencapsulated ammonium polyphosphate, sodium lignosulfonate, etc. Through the physical barrier of montmorillonite and the synergistic effect of the tannic acid-phytic acid expanded char layer, combined with the chitosan-APP carbon-nitrogen synergistic system, a dense multi-layered char layer is formed during combustion, effectively suppressing dripping. Sodium lignosulfonate improves filler dispersion and interfacial bonding through multiple hydrogen bonds and ion pair interactions, resulting in high retention of mechanical properties. The chitosan microencapsulation layer blocks moisture erosion, and the coordination network reduces migration and precipitation, exhibiting excellent resistance to damp heat aging. The preparation method uses conventional melt blending extrusion, offering good process compatibility and suitability for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of composite polymer materials technology, specifically relating to a bio-based flame-retardant nylon material and its preparation method. Background Technology

[0002] Nylon, as one of the most produced engineering plastics, is widely used in automobiles, electronics, rail transportation and other fields. However, the limiting oxygen index (LOI) of pure nylon is only about 24%, and its UL94 flame retardant rating can only reach V-2 level. It is prone to producing molten droplets when burning, making it difficult to meet the stringent flame retardant performance requirements of high-end safety fields such as interiors of new energy vehicles and housings of electronic devices.

[0003] Traditional halogen-free flame retardant systems often use phosphorus and nitrogen flame retardants and inorganic fillers for compound modification, which generally have the following problems: (1) Petroleum-based flame retardants account for a high proportion, resulting in a large carbon footprint, which does not conform to the development trend of bio-based materials; (2) Small molecule flame retardants are prone to migration and precipitation in use and humid and hot environments, leading to a significant decrease in flame retardant performance; (3) The interface between flame retardant fillers and nylon matrix is ​​poor, and the tensile strength and toughness of composite materials decrease significantly after addition; (4) Conventional compound flame retardants have low synergistic efficiency, and the carbon layer formed by combustion is loose and easy to break, with insufficient hot melt dripping effect.

[0004] Most of the bio-based flame-retardant nylons reported so far are simple blends of bio-based resins and petroleum-based flame retardants, and have not achieved a fully bio-based flame-retardant system.

[0005] Therefore, developing a flame-retardant nylon material with high flame retardancy, anti-dripping properties, high mechanical property retention, and resistance to humid heat migration has significant industrial value and environmental significance. Summary of the Invention

[0006] The purpose of this invention is to address existing problems by providing a bio-based flame-retardant nylon material and its preparation method.

[0007] This invention is achieved through the following technical solution: A bio-based flame-retardant nylon material, comprising the following components by weight: 65-80 parts of bio-based nylon resin, 6-15 parts of tannic acid-phytic acid coordination-modified montmorillonite, 4-10 parts of chitosan microencapsulated ammonium polyphosphate, 1-4 parts of sodium lignosulfonate, 0.8-2.5 parts of maleic anhydride graft compatibilizer, and 0.2-0.8 parts of antioxidant. All weight parts are based on the mass of the components after drying.

[0008] Furthermore, the bio-based nylon resin is selected from one or more of bio-based PA56, PA510, PA610, PA1010, and PA11.

[0009] Furthermore, in the tannic acid-phytic acid coordination-modified montmorillonite, the montmorillonite is sodium-based montmorillonite with a cation exchange capacity of 80~110 meq / 100g, a modified interlayer spacing of 2.2~3.2nm, and an organic matter content of 12~25wt%.

[0010] Furthermore, the preparation of the tannic acid-phytic acid coordination-modified montmorillonite includes the following steps: (A) Disperse sodium montmorillonite in deionized water and ultrasonically disperse for 30-45 min to prepare a suspension of 2-4 wt%; (B) Prepare a 10-15 wt% tannic acid aqueous solution and adjust the pH to 7.2-8.0 with dilute ammonia. (C) Under stirring conditions, tannic acid solution is slowly added dropwise to montmorillonite suspension, and stirring is continued for 1.5 to 3 hours to allow tannic acid to be loaded onto the surface and interlayer of montmorillonite sheets through hydrogen bonding and electrostatic interaction. (D) Add phytic acid aqueous solution to the mixed system and continue stirring for 1-2 hours. Phosphate groups of phytic acid and phenolic hydroxyl groups of tannic acid form a stable coordination and hydrogen bond network, and at the same time form hydrogen bonds with the edge hydroxyl groups of montmorillonite to build a stable interfacial composite structure. (E) After the reaction is complete, centrifuge and wash with deionized water until neutral. Dry under vacuum at 60~70℃ to constant weight to obtain the tannic acid-phytic acid coordination modified montmorillonite.

[0011] The two-dimensional montmorillonite sheets form a physical barrier during combustion, inhibiting melt flow and droplets; phytic acid decomposes upon heating to form phosphoric acid, which catalyzes char formation; tannic acid, as a natural polyphenol, rapidly pyrolyzes to form a continuous and dense char layer; the three components form a stable composite structure through coordination and hydrogen bonding, preventing phase separation of flame-retardant components and broadening the synergistic flame-retardant temperature window.

[0012] Furthermore, in the chitosan microencapsulated ammonium polyphosphate, the degree of polymerization of ammonium polyphosphate is n≥200.

[0013] Furthermore, the preparation of the chitosan microencapsulated ammonium polyphosphate includes the following steps: (a) Dissolve chitosan in a 1.5-2.5 vol% dilute acetic acid aqueous solution to prepare a 1.5-3 wt% chitosan solution; (b) Using ammonium polyphosphate (APP) as the core material, the ammonium polyphosphate is dispersed in a chitosan solution, the pH is adjusted to 4.5~5.5, a small amount of phytic acid is added as an ionic crosslinking agent, the amount of phytic acid added is 10%~30% of the mass of chitosan, and the reaction is stirred for 1~2 hours to allow chitosan to be deposited on the surface of the ammonium polyphosphate particles to form a dense shell layer. (c) After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol, and dry under vacuum at 50~60℃ to obtain chitosan microencapsulated ammonium polyphosphate.

[0014] APP, acting as both an acid and gas source, decomposes upon heating to generate polyphosphoric acid and release non-flammable gases such as ammonia, catalyzing char formation and diluting oxygen; chitosan, as a nitrogen-rich bio-based char-forming agent, combines with APP to form phosphorus... Nitrogen-synergistic expansion flame retardant system; chitosan shell can block moisture, improve the APP's resistance to humid heat migration, and at the same time improve its compatibility with nylon matrix.

[0015] Furthermore, the maleic anhydride graft compatibilizer is POE-g-MAH or PP-g-MAH, with a grafting rate of 0.6% to 1.5%.

[0016] Furthermore, the antioxidant is a hindered phenolic antioxidant (such as antioxidant 1010) or a phosphite antioxidant (such as antioxidant 168).

[0017] A method for preparing the bio-based flame-retardant nylon material includes the following steps: (1) Vacuum dry the bio-based nylon resin at 85~95℃ for 8~10h until the water content is less than 0.05wt%; Tannic acid-phytic acid-modified montmorillonite and chitosan microencapsulated ammonium polyphosphate were vacuum dried at 60-70℃ for 4-5 hours. (2) The dried tannic acid-phytic acid coordination modified montmorillonite, sodium lignosulfonate and maleic anhydride graft compatibilizer were mixed in a high-speed mixer at 800-1200 rpm for 5-8 min to obtain the first premix. (3) The dried bio-based nylon resin, chitosan microencapsulated ammonium polyphosphate and the first premix obtained in step (2) and the antioxidant are fed into a twin-screw extruder for melt blending and extrusion. The extruder barrel temperature is 210~255℃ and the screw speed is 180~250rpm. (4) The extrudate is cooled and pelletized to obtain the bio-based flame-retardant nylon material.

[0018] Furthermore, the temperature of the twin-screw extruder in step (3) is set to gradually increase from the feed port to the die head, with the maximum temperature not exceeding 255°C.

[0019] The present invention has the following advantages over the prior art: 1. This invention achieves fully bio-based flame retardant components and multi-source synergistic flame retardancy. The tannic acid, phytic acid, chitosan, and sodium lignosulfonate used in this invention are all derived from renewable resources. Montmorillonite is a natural mineral with high overall bio-based carbon content, and is halogen-free, low-smoke, and low-toxicity. A synergistic structure of physical barrier and expanded char layer is constructed by coordinating montmorillonite with tannic acid and phytic acid. Combined with the phosphorus-nitrogen synergistic system provided by chitosan microencapsulated ammonium polyphosphate, a dense, continuous multi-layered char layer is formed during combustion, effectively inhibiting dripping.

[0020] 2. The bio-based flame-retardant nylon material of this invention exhibits excellent interfacial compatibility and high retention of mechanical properties. Sodium lignosulfonate is rich in phenolic hydroxyl groups, carboxyl groups, and sulfonate groups, which can form multiple hydrogen bonds and ion pairs with the hydroxyl groups on the surface of modified montmorillonite, the amino groups of chitosan, and the amide bonds of the nylon matrix. This significantly improves the dispersion uniformity of the flame-retardant filler in the nylon matrix and reduces interfacial defects.

[0021] 3. The bio-based flame-retardant nylon material of this invention exhibits strong heat migration resistance and good process compatibility. The chitosan microcapsule layer effectively blocks moisture from eroding ammonium polyphosphate, and the tannic acid-phytic acid coordination network reduces the migration and precipitation tendency of flame-retardant components, significantly improving the flame-retardant performance retention rate after hygrothermal aging. Furthermore, the preparation method of this invention employs a conventional melt blending extrusion process, with the extrusion temperature controlled at 210~255℃, avoiding thermal decomposition of the flame retardant and allowing for direct implementation on existing plastic processing lines, demonstrating promising prospects for industrial application. Detailed Implementation

[0022] To further explain the present invention, the following specific embodiments are described.

[0023] Example 1 A method for preparing the bio-based flame-retardant nylon material includes the following steps: (1) Vacuum dry the bio-based nylon resin at 85°C for 10 hours until the water content is less than 0.05 wt%; Tannic acid-phytic acid-modified montmorillonite and chitosan microencapsulated ammonium polyphosphate were vacuum dried at 60℃ for 5 h. (2) Weigh out the corresponding weight parts of 65 parts of bio-based nylon resin, 6 parts of tannic acid-phytic acid coordination modified montmorillonite, 4 parts of chitosan microencapsulated ammonium polyphosphate, 1 part of sodium lignosulfonate, 0.8 parts of maleic anhydride graft compatibilizer, and 0.2 parts of antioxidant for later use. (3) The dried tannic acid-phytic acid coordination modified montmorillonite, sodium lignosulfonate and maleic anhydride graft compatibilizer were mixed in a high-speed mixer at 800 rpm for 8 min to obtain the first premix. (4) The dried bio-based nylon resin, chitosan microencapsulated ammonium polyphosphate, and the first premix obtained in step (3) and antioxidant are fed into a twin-screw extruder for melt blending and extrusion. The extruder barrel temperature is 210°C and the screw speed is 180 rpm. (5) The extrudate is cooled and pelletized to obtain the bio-based flame-retardant nylon material.

[0024] The bio-based nylon resin is selected from bio-based PA56.

[0025] The tannic acid-phytic acid coordination-modified montmorillonite is sodium-based montmorillonite with a cation exchange capacity of 80 meq / 100g, a modified interlayer spacing of 2.2 nm, and an organic matter content of 12 wt%.

[0026] The preparation of the tannic acid-phytic acid coordination-modified montmorillonite includes the following steps: (A) Disperse sodium montmorillonite in deionized water and sonicate for 30 min to prepare a 2 wt% suspension; (B) Prepare a 10wt% tannic acid aqueous solution and adjust the pH to 7.2 with dilute ammonia. (C) Under stirring conditions, tannic acid solution was slowly added dropwise to montmorillonite suspension, and stirring was continued for 1.5 h for adsorption, so that tannic acid was loaded on the surface and between layers of montmorillonite sheets through hydrogen bonding and electrostatic interaction. (D) Add phytic acid aqueous solution to the mixed system and continue stirring for 1 hour. Phosphate groups of phytic acid and phenolic hydroxyl groups of tannic acid form a stable coordination and hydrogen bond network, and at the same time form hydrogen bonds with the edge hydroxyl groups of montmorillonite to build a stable interfacial composite structure. (E) After the reaction is complete, centrifuge and wash with deionized water until neutral. Dry under vacuum at 60°C to constant weight to obtain the tannic acid-phytic acid coordination modified montmorillonite.

[0027] In the chitosan microencapsulated ammonium polyphosphate, the degree of polymerization of ammonium polyphosphate n≥200.

[0028] The preparation of the chitosan microencapsulated ammonium polyphosphate includes the following steps: (a) Dissolve chitosan in a 1.5 vol% dilute acetic acid aqueous solution to prepare a 1.5 wt% chitosan solution; (b) Using ammonium polyphosphate (APP) as the core material, the ammonium polyphosphate is dispersed in a chitosan solution, the pH is adjusted to 4.5, a small amount of phytic acid is added as an ionic crosslinking agent, the amount of phytic acid added is 10% of the mass of chitosan, and the reaction is stirred for 1 hour to allow chitosan to be deposited on the surface of the ammonium polyphosphate particles to form a dense shell layer. (c) After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol, and dry under vacuum at 50°C to obtain chitosan microencapsulated ammonium polyphosphate.

[0029] The maleic anhydride graft compatibilizer is POE-g-MAH.

[0030] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 (mass ratio 1:1).

[0031] Example 2 A method for preparing the bio-based flame-retardant nylon material includes the following steps: (1) The bio-based nylon resin was vacuum dried at 90°C for 9 hours until the water content was less than 0.05 wt%. Tannic acid-phytic acid-modified montmorillonite and chitosan microencapsulated ammonium polyphosphate were vacuum dried at 65℃ for 4.5 h. (2) Weigh out the corresponding weight parts of 72 parts of bio-based nylon resin, 10 parts of tannic acid-phytic acid coordination modified montmorillonite, 7 parts of chitosan microencapsulated ammonium polyphosphate, 3 parts of sodium lignosulfonate, 1.3 parts of maleic anhydride graft compatibilizer, and 0.5 parts of antioxidant for later use. (3) The dried tannic acid-phytic acid coordination modified montmorillonite, sodium lignosulfonate and maleic anhydride graft compatibilizer were mixed in a high-speed mixer at 1000 rpm for 6 min to obtain the first premix. (4) The dried bio-based nylon resin, chitosan microencapsulated ammonium polyphosphate and the first premix obtained in step (3) and the antioxidant are fed into a twin-screw extruder for melt blending and extrusion. The extruder barrel temperature is 230°C and the screw speed is 210 rpm. (5) The extrudate is cooled and pelletized to obtain the bio-based flame-retardant nylon material.

[0032] The bio-based nylon resin is selected from bio-based PA56.

[0033] The tannic acid-phytic acid coordination-modified montmorillonite is sodium-based montmorillonite with a cation exchange capacity of 90 meq / 100g, a layer spacing of 2.7 nm after modification, and an organic matter content of 20 wt%.

[0034] The preparation of the tannic acid-phytic acid coordination-modified montmorillonite includes the following steps: (A) Disperse sodium montmorillonite in deionized water and sonicate for 37 min to prepare a 3 wt% suspension; (B) Prepare a 12.5 wt% tannic acid aqueous solution and adjust the pH to 7.6 with dilute ammonia. (C) Under stirring conditions, tannic acid solution was slowly added dropwise to montmorillonite suspension, and stirring was continued for 2.2 h for adsorption, so that tannic acid was loaded on the surface and between layers of montmorillonite sheets through hydrogen bonding and electrostatic interaction. (D) Add phytic acid aqueous solution to the mixed system and continue stirring for 1.5 h. The phosphate group of phytic acid forms a stable coordination and hydrogen bond network with the phenolic hydroxyl group of tannic acid, and at the same time forms hydrogen bonds with the edge hydroxyl group of montmorillonite to build a stable interfacial composite structure. (E) After the reaction is complete, centrifuge and wash with deionized water until neutral. Dry under vacuum at 65°C to constant weight to obtain the tannic acid-phytic acid coordination modified montmorillonite.

[0035] In the chitosan microencapsulated ammonium polyphosphate, the degree of polymerization of ammonium polyphosphate n≥200.

[0036] The preparation of the chitosan microencapsulated ammonium polyphosphate includes the following steps: (a) Dissolve chitosan in a 2 vol% dilute acetic acid aqueous solution to prepare a 2.2 wt% chitosan solution; (b) Using ammonium polyphosphate (APP) as the core material, the ammonium polyphosphate is dispersed in a chitosan solution, the pH is adjusted to 5.0, a small amount of phytic acid is added as an ionic crosslinking agent, the amount of phytic acid added is 20% of the mass of chitosan, and the reaction is stirred for 1.5 h to allow chitosan to be deposited on the surface of the ammonium polyphosphate particles to form a dense shell layer. (c) After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol, and dry under vacuum at 55°C to obtain chitosan microencapsulated ammonium polyphosphate.

[0037] The maleic anhydride graft compatibilizer is POE-g-MAH.

[0038] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 (mass ratio 1:1).

[0039] Example 3 A method for preparing the bio-based flame-retardant nylon material includes the following steps: (1) The bio-based nylon resin was vacuum dried at 95°C for 8 hours until the water content was less than 0.05 wt%. Tannic acid-phytic acid-modified montmorillonite and chitosan microencapsulated ammonium polyphosphate were vacuum dried at 70℃ for 4 hours. (2) Weigh out the corresponding weight parts of 80 parts of bio-based nylon resin, 15 parts of tannic acid-phytic acid coordination modified montmorillonite, 10 parts of chitosan microencapsulated ammonium polyphosphate, 4 parts of sodium lignosulfonate, 2.5 parts of maleic anhydride graft compatibilizer, and 0.8 parts of antioxidant for later use. (3) The dried tannic acid-phytic acid coordination modified montmorillonite, sodium lignosulfonate and maleic anhydride graft compatibilizer were mixed in a high-speed mixer at 1200 rpm for 5 min to obtain the first premix. (4) The dried bio-based nylon resin, chitosan microencapsulated ammonium polyphosphate, and the first premix obtained in step (3) and antioxidant are fed into a twin-screw extruder for melt blending and extrusion. The extruder barrel temperature is 255°C and the screw speed is 250 rpm. (5) The extrudate is cooled and pelletized to obtain the bio-based flame-retardant nylon material.

[0040] The bio-based nylon resin is selected from bio-based PA56.

[0041] The tannic acid-phytic acid coordination-modified montmorillonite is sodium-based montmorillonite with a cation exchange capacity of 110 meq / 100g, a modified interlayer spacing of 3.2 nm, and an organic matter content of 25 wt%.

[0042] The preparation of the tannic acid-phytic acid coordination-modified montmorillonite includes the following steps: (A) Disperse sodium montmorillonite in deionized water and sonicate for 45 min to prepare a 4 wt% suspension; (B) Prepare a 15wt% tannic acid aqueous solution and adjust the pH to 8.0 with dilute ammonia. (C) Under stirring conditions, tannic acid solution was slowly added dropwise to montmorillonite suspension, and stirring was continued for 3 hours to allow tannic acid to be loaded onto the surface and interlayer of montmorillonite sheets through hydrogen bonding and electrostatic interaction. (D) Add phytic acid aqueous solution to the mixed system and continue stirring for 2 hours. Phosphate groups of phytic acid and phenolic hydroxyl groups of tannic acid form a stable coordination and hydrogen bond network, and at the same time form hydrogen bonds with the edge hydroxyl groups of montmorillonite to build a stable interfacial composite structure. (E) After the reaction is complete, centrifuge and wash with deionized water until neutral. Dry under vacuum at 70°C to constant weight to obtain the tannic acid-phytic acid coordination modified montmorillonite.

[0043] In the chitosan microencapsulated ammonium polyphosphate, the degree of polymerization of ammonium polyphosphate n≥200.

[0044] The preparation of the chitosan microencapsulated ammonium polyphosphate includes the following steps: (a) Dissolve chitosan in a 2.5 vol% dilute acetic acid aqueous solution to prepare a 3 wt% chitosan solution; (b) Using ammonium polyphosphate (APP) as the core material, the ammonium polyphosphate is dispersed in a chitosan solution, the pH is adjusted to 5.5, a small amount of phytic acid is added as an ionic crosslinking agent, the amount of phytic acid added is 30% of the mass of chitosan, and the reaction is stirred for 2 hours to allow chitosan to be deposited on the surface of the ammonium polyphosphate particles to form a dense shell layer. (c) After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol, and dry under vacuum at 60°C to obtain chitosan microencapsulated ammonium polyphosphate.

[0045] The maleic anhydride graft compatibilizer is POE-g-MAH.

[0046] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 (mass ratio 1:1).

[0047] Example 4 Compared with Example 2, Example 4 replaces bio-based PA56 with an equal amount of PA510, while the rest of the formulation and process are the same as in Example 2.

[0048] Example 5 Compared with Example 2, Example 4 replaces bio-based PA56 with an equal amount of PA610, while the rest of the formulation and process are the same as in Example 2.

[0049] Example 6 Compared with Example 2, Example 4 replaces bio-based PA56 with an equal amount of PA1010, while the rest of the formulation and process are the same as in Example 2.

[0050] Example 7 Compared with Example 2, Example 4 replaces bio-based PA56 with an equal amount of PA11, while the rest of the formulation and process are the same as in Example 2.

[0051] Comparative Example 1 Compared with Example 2, Comparative Example 1 does not add tannic acid-phytic acid modified montmorillonite, and its weight part is made up by PA56. The rest of the formula and process are the same as in Example 2.

[0052] Comparative Example 2 Compared with Example 2, Comparative Example 2 replaces chitosan microencapsulated ammonium polyphosphate with an equal weight of ordinary APP (degree of polymerization n=200), while the rest of the formulation and process are the same as in Example 2.

[0053] Comparative Example 3 Comparative Example 3 uses a commercially available brand of halogen-free flame-retardant reinforced bio-based PA56 composite material as a reference. The composition of this reference sample is: 78 parts of bio-based PA56 resin, 15 parts of organic aluminum phosphonate flame retardant (petroleum-based), 7 parts of glass fiber, and an appropriate amount of antioxidant. It is prepared using a conventional melt blending extrusion process.

[0054] 1. Experimental testing 1.1 Flame retardant performance test 1.1.1 Limiting Oxygen Index (LOI) The determination was carried out in accordance with GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test".

[0055] This experiment used Type I specimens (size: 80mm×10mm×4mm). Five specimens were tested in each group, and the arithmetic mean was taken as the final LOI value.

[0056] 1.1.2 Vertical flammability rating (UL94) The test was conducted in accordance with GB / T 2408-2021 "Determination of the flammability of plastics - Horizontal and Vertical Methods".

[0057] The sample was vertically mounted on the test frame, and ignited with a 50W Bunsen burner flame for 10 seconds. The first afterflame time (t1) was recorded. The flame was removed, and after the sample extinguished, a second 10-second ignition was immediately applied. The second afterflame time (t2) and the second afterburner time (t3) were recorded. Simultaneously, it was observed whether molten droplets ignited the lower layer of absorbent cotton during combustion. The flame retardancy rating (V-0, V-1, or V-2) was determined based on the combustion behavior. The evaluation criteria for the flame retardancy rating are shown in Table 1 below.

[0058] Table 1 Flame Retardant Rating Standards

[0059] The test specimens were 125mm × 13mm × 1.6mm in size. Five specimens were tested for each sample, and the highest grade among all specimens was used as the final judgment result. The droplet behavior was also recorded. 1.2 Mechanical property testing 1.2.1 Tensile properties The test was conducted in accordance with GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0060] This test uses a type 1A dumbbell-shaped specimen with the following dimensions: total length ≥ 150 mm, narrow section length 75 mm, narrow section width 10 mm, and thickness 4 mm.

[0061] Sample speed: 50 mm / min, test temperature: (23±2)℃, relative humidity: (50±5)%.

[0062] Five samples were tested in each group, and the arithmetic mean was taken.

[0063] The formula for calculating the tensile strength retention rate is:

[0064] The tensile strength of the pure PA56 matrix was determined by testing pure PA56 resin without flame retardant prepared using the same injection molding process under the same conditions.

[0065] 1.2.2 Bending performance The test was conducted in accordance with GB / T 9341-2008 "Determination of Flexural Properties of Plastics".

[0066] The test specimen dimensions were 80mm × 10mm × 4mm, and the support span was 64mm.

[0067] Test speed: L2mm / min, test temperature: (23±2)℃.

[0068] The flexural modulus and flexural strength were determined. Five specimens were tested for each group of samples, and the arithmetic mean was taken.

[0069] 1.3 Performance testing after damp heat aging The test was conducted in accordance with the provisions for "damp heat test" in GB / T 2573-2008 "Test Method for Aging Performance of Glass Fiber Reinforced Plastics".

[0070] Humid heat aging conditions: temperature (85±2)℃, relative humidity (85±5)%, aging time 168h.

[0071] Place the test strips in a constant temperature and humidity chamber, ensuring sufficient spacing between the samples to allow for air circulation.

[0072] After aging, the sample was removed and placed under standard environmental conditions of (23±2)℃ and (50±5)% relative humidity for 24 hours for conditioning. Then, the LOI and tensile strength were tested.

[0073] The formulas for calculating the flame retardant retention rate and tensile strength retention rate are as follows:

[0074]

[0075] 2. Experimental Results 2.1 Flame retardant properties The flame retardant performance test results are shown in Table 2 below.

[0076] Table 2 Comparison of flame retardant performance of each embodiment and comparative example

[0077] As shown in Table 2 above, the LOI of Examples 1-3 increased with the increase of flame retardant addition, all reaching UL94 V-0 rating with no dripping. Examples 4-7 maintained V-0 rating in different bio-based nylon matrices, indicating that the flame retardant system of the present invention has good matrix universality. Comparative Example 1, without the addition of modified montmorillonite, had an LOI of 25.8%, reaching only V-2 rating with dripping, indicating that the two-dimensional physical barrier of montmorillonite is indispensable for improving the flame retardant rating and anti-dripping properties. Comparative Example 2, using ordinary APP instead of microcapsule APP, had an LOI decrease by 3.3 percentage points and a small amount of dripping, confirming the necessity of chitosan microencapsulation for improving flame retardant efficiency. Comparative Example 3, a commercially available reference sample, had an LOI of 31.2% and a V-0 rating, comparable to Example 1, but the flame retardant was petroleum-based and non-renewable.

[0078] 2.2 Mechanical Properties The mechanical performance test results are shown in Table 3 below.

[0079] Table 3 Comparison of mechanical properties of each embodiment and comparative example

[0080] As shown in Table 3 above, the tensile strength retention rates of Examples 1-3 were 85.8%–89.2%, elongation at break were 15.2%–18.5%, and flexural modulus was 2.15–2.42 GPa. The excellent mechanical properties maintained even with high flame retardant loadings are attributed to the multiple hydrogen bonds and ion-pair interfacial bridging effects of sodium lignosulfonate. Examples 4-7 all achieved retention rates of over 86% in different nylon matrices. In Comparative Example 2, after using ordinary APP, the tensile strength retention rate decreased to 76.8%, and the elongation at break was only 14.1%, confirming the crucial contribution of microencapsulation to interfacial compatibility. The tensile strength retention rate of the commercially available reference in Comparative Example 3 was only 79.9%, lower than the 89.2% of Example 2 of this invention, indicating that the fully bio-based flame retardant system of this invention is superior to the traditional petroleum-based flame retardant / glass fiber system in terms of interfacial bonding.

[0081] 2.3 Performance after damp heat aging The performance test results after damp heat aging are shown in Table 4 below.

[0082] Table 4. Performance Comparison Results of Each Example and Comparative Example After Damp Heat Aging

[0083] As shown in Table 4 above, after 168 hours of humid heat aging at 85℃ / 85% RH, Examples 1-7 all exhibited LOI retention rates greater than 96% and tensile strength retention rates greater than 95.5%, demonstrating excellent resistance to humid heat migration. Example 2 achieved an LOI retention rate of 97.3% and a tensile strength retention rate of 96.3%. This is attributed to the effective protection of APP by the chitosan microcapsule layer and the inhibition of flame retardant component migration by the tannic acid-phytic acid coordination network. In Comparative Example 2, after using ordinary APP, the LOI retention rate decreased to 91.9%, and the tensile strength retention rate was only 90.1%, far lower than Example 2, fully demonstrating the necessity of microencapsulation modification. Comparative Example 3, a commercially available reference, had an LOI retention rate of 92.3% and a tensile strength retention rate of 90.4%, both lower than the examples of this invention, indicating that the humid heat aging resistance of this invention is superior to that of commercially available petroleum-based flame retardant systems.

[0084] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bio-based flame-retardant nylon material, characterized in that, By mass, it includes the following components: 65-80 parts of bio-based nylon resin, 6-15 parts of tannic acid-phytic acid coordination-modified montmorillonite, 4-10 parts of chitosan microencapsulated ammonium polyphosphate, 1-4 parts of sodium lignosulfonate, 0.8-2.5 parts of maleic anhydride graft compatibilizer, and 0.2-0.8 parts of antioxidant.

2. The bio-based flame-retardant nylon material according to claim 1, characterized in that, The bio-based nylon resin is selected from one or more of bio-based PA56, PA510, PA610, PA1010, and PA11.

3. The bio-based flame-retardant nylon material according to claim 1, characterized in that, The tannic acid-phytic acid coordination-modified montmorillonite is sodium-based montmorillonite with a cation exchange capacity of 80~110 meq / 100g, a modified interlayer spacing of 2.2~3.2nm, and an organic matter content of 12~25wt%.

4. The bio-based flame-retardant nylon material according to claim 3, characterized in that, The preparation of the tannic acid-phytic acid coordination-modified montmorillonite includes the following steps: (A) Disperse sodium montmorillonite in deionized water and ultrasonically disperse for 30-45 min to prepare a suspension of 2-4 wt%; (B) Prepare a 10-15 wt% tannic acid aqueous solution and adjust the pH to 7.2-8.0 with dilute ammonia. (C) Under stirring conditions, tannic acid solution was added dropwise to montmorillonite suspension, and stirring was continued for 1.5 to 3 hours for adsorption. (D) Add phytic acid aqueous solution to the mixture and continue stirring for 1-2 hours; (E) After the reaction is complete, centrifuge and wash with deionized water until neutral. Dry under vacuum at 60~70℃ to constant weight to obtain the tannic acid-phytic acid coordination modified montmorillonite.

5. The bio-based flame-retardant nylon material according to claim 1, characterized in that, In the chitosan microencapsulated ammonium polyphosphate, the degree of polymerization of ammonium polyphosphate n≥200.

6. The bio-based flame-retardant nylon material according to claim 5, characterized in that, The preparation of the chitosan microencapsulated ammonium polyphosphate includes the following steps: (a) Dissolve chitosan in a 1.5-2.5 vol% dilute acetic acid aqueous solution to prepare a 1.5-3 wt% chitosan solution; (b) Using ammonium polyphosphate as the core material, the ammonium polyphosphate is dispersed in a chitosan solution, the pH is adjusted to 4.5-5.5, phytic acid is added as an ionic crosslinking agent, the amount of phytic acid added is 10%-30% of the mass of chitosan, and the reaction is stirred for 1-2 hours to allow chitosan to be deposited on the surface of the ammonium polyphosphate particles to form a dense shell layer. (c) After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol, and dry under vacuum at 50~60℃ to obtain chitosan microencapsulated ammonium polyphosphate.

7. The bio-based flame-retardant nylon material according to claim 1, characterized in that, The maleic anhydride graft compatibilizer is POE-g-MAH or PP-g-MAH, with a grafting rate of 0.6% to 1.5%.

8. The bio-based flame-retardant nylon material according to claim 1, characterized in that, The antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant.

9. A method for preparing the bio-based flame-retardant nylon material according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Vacuum dry the bio-based nylon resin at 85~95℃ for 8~10h until the water content is less than 0.05wt%; Tannic acid-phytic acid-modified montmorillonite and chitosan microencapsulated ammonium polyphosphate were vacuum dried at 60-70℃ for 4-5 hours. (2) The dried tannic acid-phytic acid coordination modified montmorillonite, sodium lignosulfonate and maleic anhydride graft compatibilizer were mixed in a high-speed mixer at 800-1200 rpm for 5-8 min to obtain the first premix. (3) The dried bio-based nylon resin, chitosan microencapsulated ammonium polyphosphate, and the first premix obtained in step (2) and the antioxidant are fed into a twin-screw extruder for melt blending and extrusion. (4) The extrudate is cooled and pelletized to obtain the bio-based flame-retardant nylon material.

10. The preparation method according to claim 9, characterized in that, The extruder barrel temperature in step (3) is 210~255℃ and the screw speed is 180~250rpm.

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