Flame retardant containing diisobutyl aluminum hypophosphite, nylon flame-retardant material and preparation methods of flame retardant and nylon flame-retardant material

Abstract

The invention provides a flame retardant containing diisobutyl aluminum hypophosphite, a nylon flame-retardant material and a preparation method, and belongs to the technical field of flame-retardant materials. The preparation method comprises the following steps: wrapping diisobutyl aluminum hypophosphite with a melamine-formaldehyde resin shell layer to prepare a flame retardant microcapsule, pre-blending a flame retardant with a furan functional group and a cross-linking agent with a maleimide group, and co-doping the mixture, the microcapsule and boron nitride into a nylon 66 matrix to prepare the nylon flame-retardant material. The self-repairing flame retardant property is given to the material while the flame retardant property of the material is further improved, meanwhile, the boron nitride forms a three-dimensional network structure in a matrix, the mechanical property of the material is improved, and the problems that a conventional flame retardant material is poor in flame retardant efficiency and mechanical property and must be scrapped after being used are solved. The nylon flame-retardant material disclosed by the invention has excellent flame-retardant property and mechanical property, also has unique self-repairing capability, and shows great application potential.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials technology, specifically to the design of a flame retardant containing diisobutyl aluminum hypophosphite, a nylon flame retardant material, and a preparation method thereof. Background Technology

[0002] Nylon 66, as one of the common engineering plastics, has excellent mechanical strength, corrosion resistance and self-lubricating properties, and is widely used in the automotive industry, electronics and electrical, aerospace and other fields. However, the limiting oxygen index of nylon 66 is only 20%~24%, and the UL-94 vertical burning test can usually only reach V-2 level. It is a flammable material and will burn rapidly when it comes into contact with a fire source, accompanied by melting and dripping, which greatly limits the application of nylon 66 in scenarios with higher safety requirements.

[0003] To meet safety regulations, flame retardants are typically added to nylon to improve its flame retardancy. Traditional halogenated flame retardants (such as decabromodiphenyl ether, tetrabromobisphenol A, chlorinated paraffin, and Declone), while possessing excellent flame retardant efficiency, release large amounts of toxic fumes, such as dioxins, during combustion, causing serious harm to the environment and human health. Therefore, halogenated flame retardants are strictly limited or prohibited by regulations such as the EU RoHS Directive. In contrast, phosphorus-based flame retardants, especially hypophosphite-based ones (such as diethylaluminum hypophosphite and diisobutylaluminum hypophosphite), are considered an ideal halogen-free flame retardant system due to their efficient char formation and gas-phase flame retardant properties. Diisobutylaluminum hypophosphite (AlPi) can capture free radicals in the gas phase, interrupting the combustion chain reaction, while the condensed phase promotes char formation in nylon, forming a dense char layer to insulate against heat and oxygen. CN118165369B discloses a flame retardant containing diisobutyl aluminum hypophosphite, a nylon flame retardant material, and a preparation method thereof. The invention involves compounding phenol-aryl epoxy resin, diisobutyl aluminum hypophosphite, and diethyl aluminum hypophosphite to prepare a flame retardant, which is then mixed with nylon 6 and nylon 66 to prepare a nylon flame retardant material. Two compounding methods are used: one is to directly stir and mix the three components to obtain the flame retardant; the other is to first dissolve the phenol-aryl epoxy resin and then compound it with diisobutyl aluminum hypophosphite and diethyl aluminum hypophosphite, subsequently removing the solvent to obtain the flame retardant. Both compounding methods yield flame retardants with good compatibility with the nylon matrix, which can improve the flame retardancy and mechanical properties of the nylon flame retardant material. However, in this invention, the amount of diisobutyl aluminum hypophosphite added is too high. While diisobutyl aluminum hypophosphite alone can indeed provide excellent flame retardancy to nylon materials, it also reduces the toughness of the nylon material, making the material brittle and prone to cracking or fragmentation.

[0004] Furthermore, flame-retardant materials that rely on a single flame retardant face a problem: when exposed to fire, the material is easily rendered unusable due to excessive consumption of the flame retardant. This one-time flame-retardant approach is not only inefficient but also wasteful of resources. Even when the fire is not severe, although the base material may not be damaged, the flame-retardant material may still become unusable due to the consumption of the flame retardant, resulting in unnecessary losses. Therefore, flame retardants not only need to improve the flame retardancy of the material at low addition levels but also need to maintain the material's mechanical strength and toughness as much as possible. In addition, developing a renewable flame retardant that can fully or partially restore its flame-retardant function after exposure to fire is also a key technical challenge in the preparation of flame-retardant materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a flame retardant containing diisobutylaluminum hypophosphite. This invention achieves controlled release of AlPi within the matrix upon exposure to fire or heat by encapsulating AlPi into microcapsules and injecting them into a nylon 66 matrix, without affecting the mechanical properties of the nylon flame retardant material.

[0006] Another objective of this invention is to provide a recycled nylon flame-retardant material comprising the aforementioned AlPi. This invention involves injecting a furan-containing phosphorus-nitrogen flame retardant and a maleimide-containing crosslinking agent into a nylon 66 matrix. Upon heating, these react to undergo a Diels-Alder reaction, generating a six-membered ring. When the material is exposed to fire and heated, the temperature rises, and the six-membered ring absorbs heat and breaks down into furan groups and maleimide, thus cooling the surrounding area. As the fire subsides and the material temperature gradually decreases, the furan groups and maleimide undergo a renewed Diels-Alder reaction to generate another six-membered ring. Furthermore, this invention incorporates boron nitride into the nylon 66 matrix, creating a thermally conductive network that disperses heat when heated, further enhancing flame retardancy in conjunction with the flame-retardant microcapsules.

[0007] This invention discloses a flame retardant microcapsule containing diisobutyl aluminum hypophosphite, the technical solution of which is as follows: Melamine and formaldehyde aqueous solution are reacted under weakly alkaline conditions to generate a water-soluble prepolymer. AlPi powder is then dispersed in the aqueous phase of anionic surfactant and a uniformly dispersed suspension is formed by high-speed shearing. The prepolymer is added to the suspension and the pH is adjusted to acidity, so that the prepolymer is deposited on the surface of diisobutyl aluminum hypophosphite and a melamine-formaldehyde resin shell is formed by cross-linking and curing.

[0008] The present invention also discloses a nylon flame retardant material comprising the following components: nylon 66 matrix material, antioxidant, flame retardant microcapsules containing AlPi, self-healing phosphorus-nitrogen flame retardant precursor, and boron nitride filler.

[0009] This invention also discloses a method for preparing nylon flame-retardant materials, the technical solution of which is as follows: Step 1: Disperse boron nitride in anhydrous ethanol and sonicate it to form a suspension. Then add silane coupling agent to the suspension, heat and stir, centrifuge to separate the solid, wash with ethanol, and dry to obtain the surface-pretreated boron nitride filler.

[0010] Step 2: Add hexachlorocyclotriphosphazene to a solvent, use hexamethylenetetramine as a ring-opening agent, heat and stir to induce a ring-opening polymerization reaction, then cool and add a mixed solution of furan-methanol and triethylamine dropwise while stirring, then filter and remove the solvent by vacuum distillation of the filtrate, wash the obtained solid with ethanol and dry it to obtain polyphosphazene with furan functional groups at the end, then stir and mix it evenly with a crosslinking agent with maleimide groups to obtain a self-healing phosphorus nitrogen flame retardant precursor.

[0011] Step 3: Nylon 66 matrix, antioxidant, flame retardant microcapsules, self-healing phosphorus-nitrogen flame retardant precursor, and surface-pretreated boron nitride are melt-blended in a twin-screw extruder, extruded and pelletized, and heated in an oven to obtain nylon composite flame retardant granules.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. AlPi exists in the form of microcapsules in the nylon matrix. The resin shell on the surface of the microcapsules provides a certain degree of flexibility, reducing the destructive effect of AlPi on the structure in the matrix. Compared with directly adding flame retardant powder, the microcapsules have better interfacial compatibility, which can reduce stress concentration and mitigate the adverse effects on the mechanical properties of the material. In addition, the matrix is ​​filled with a three-dimensional boron nitride network. Due to the high rigidity of boron nitride, it can improve the tensile modulus and strength of the material. At the same time, boron nitride inhibits crack propagation and induces nylon 66 crystallization, which can also significantly improve the fracture and impact strength of the material.

[0013] 2. AlPi microcapsules, self-healing phosphorus and nitrogen flame retardants, and boron nitride-filled networks form a triple synergistic flame retardant mechanism in nylon flame-retardant materials. When the material initially comes into contact with a fire source, the phosphorus and nitrogen flame retardants dispersed in the nylon matrix can sense the temperature change, thereby triggering the Diels-Alder reverse reaction and causing the six-membered ring to break. Since this reaction is a strongly endothermic process, the external temperature of the material will drop rapidly, delaying the heating and decomposition of the nylon matrix. When the fire is too large to be extinguished by simply relying on the cooling effect of the endothermic reaction, heat is transferred through the coating to the nylon matrix. The internally filled boron nitride network structure can quickly conduct heat to the entire system, effectively preventing the material from burning. Excessive local temperature can lead to decomposition or ignition, prolonging the ignition time of the entire material. If the fire spreads further, the excessive heat is conducted through the boron nitride network, causing the microcapsule shell filled in the matrix to decompose and release the AlPi flame retardant inside the microcapsule. The flame retardant decomposes at high temperature to produce phosphorus-containing free radical scavengers. At the same time, the phosphorus-nitrogen flame retardant also releases free radicals due to high temperature, producing N / P free radicals. These free radicals interrupt the chain reaction of combustion and promote the dehydration and carbonization of the nylon matrix to form a dense carbon layer, which isolates the heat source and oxygen. Furthermore, the microcapsule resin shell itself decomposes and releases non-flammable gases such as nitrogen when heated, further enhancing the flame retardant and smoke-suppressing effects.

[0014] 3. Traditional flame-retardant materials often suffer from depletion of the flame retardant after a single fire, forcing the material to be scrapped and replaced. Alternatively, adding large amounts of flame retardant can extend its lifespan, but this significantly reduces the material's mechanical properties. The nylon flame retardant proposed in this invention utilizes a self-healing flame retardant filled into the nylon matrix, leveraging the Diels-Alder reversible reaction to give the material a certain degree of regeneration. When the fire is small and the material experiences relatively low temperatures, the flame retardant's six-membered rings break down, absorbing heat to cool the surrounding area and prevent the fire from spreading. After the fire subsides and the temperature drops, the six-membered rings spontaneously recombine within a certain timeframe, restoring the original flame-retardant capability. When the fire is moderate, the heat absorbed by the broken six-membered rings is insufficient to rapidly lower the material's temperature. AlPi microcapsules then come into play, achieving a flame-retardant effect through the consumption of some microcapsules and a small amount of phosphorus-nitrogen flame retardant. Although some AlPi microcapsules and phosphorus-nitrogen flame retardant are consumed, some remain, maintaining the material's flame-retardant effect. The effect is slightly reduced but it can still be used. Only when the fire is large will the AlPi microcapsules and phosphorus nitrogen flame retardants be completely consumed and decomposed. At this time, it will be directly scrapped like traditional flame retardant materials. However, because the material is filled with a boron nitride network, it can quickly transfer heat to the entire system when the fire is large. This causes all microcapsules to rupture and release the flame retardant inside almost simultaneously, achieving the effect of controlling the fire to a minimum in the shortest time with the lowest consumption. In contrast, the flame retardant in traditional materials is gradually consumed. During the consumption process, it cannot effectively suppress the growth of the fire, which can easily cause the fire to spread and increase the unnecessary consumption of flame retardant. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the preparation process of the nylon flame-retardant material of the present invention. Figure 2 A comparison chart of the tensile properties of samples from each experimental group; Figure 3 A comparison chart of notched impact strength of samples from different experimental groups; Figure 4 A comparison chart of the bending properties of samples from each experimental group; Figure 5 A comparison chart of the limiting oxygen index of samples from each experimental group. Detailed Implementation

[0016] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0017] This invention proposes a flame retardant containing aluminum diisobutylphosphite, which uses melamine-formaldehyde as a shell to encapsulate AlPi into microcapsules. The specific technical solution is as follows: Under weakly alkaline conditions, melamine and formaldehyde aqueous solutions form a water-soluble prepolymer. The prepolymer is then mixed with AlPi in an aqueous system containing anionic surfactants. Under emulsified dispersion conditions, the melamine-formaldehyde prepolymer coats the outer layer of AlPi. When the system pH decreases to acidic, the prepolymer undergoes condensation polymerization, and the resulting hydrophobic oligomers migrate and deposit on the surface of AlPi particles, cross-linking and solidifying to form complete AlPi flame retardant microcapsules encapsulated by the melamine-formaldehyde shell. The dense, cross-linked network shell effectively seals AlPi, preventing its migration or moisture absorption. Simultaneously, the melamine-formaldehyde shell itself acts as a nitrogen-based flame retardant, synergistically interacting with the AlPi core. Upon thermal decomposition, the shell releases non-flammable gases to expand into a char layer, and AlPi promotes the decomposition of the matrix into char, jointly constructing a highly efficient expansion barrier system.

[0018] The present invention also proposes a nylon flame retardant material comprising the following components: matrix, flame retardant, antioxidant, and filler.

[0019] The matrix is ​​nylon 66 resin matrix, the flame retardant is AlPi flame retardant microcapsules and self-healing phosphorus and nitrogen flame retardant, the antioxidant is a compound system composed of hindered phenolic antioxidant and phosphite antioxidant, and the filler is boron nitride.

[0020] This invention also proposes a method for preparing nylon flame-retardant materials, the specific technical solution of which is as follows: 1. Boron nitride surface pretreatment Boron nitride was dispersed in anhydrous ethanol, and its surface was pretreated with a silane coupling agent to enhance the interfacial bonding between boron nitride and the nylon matrix. During subsequent melt blending, sufficient shearing action allowed the boron nitride sheets to be uniformly dispersed and overlapped within the nylon matrix, forming a continuous three-dimensional network. Due to boron nitride's extremely high in-plane thermal conductivity, this three-dimensional network rapidly conducts and disperses heat from impact points throughout the system, preventing localized heat accumulation. Simultaneously, as a two-dimensional nanomaterial, boron nitride possesses extremely high modulus and strength. When the material is subjected to external forces, the boron nitride filler can bear most of the load, thus significantly improving the material's tensile strength and flexural modulus.

[0021] 2. Preparation of self-healing phosphorus-nitrogen flame retardant precursor Hexachlorocyclotriphosphazene was added to an anhydrous organic solvent and heated under the action of the ring-opening agent hexamethylenetetramine to produce linear polydichlorophosphazene. Subsequently, a mixed solution of furanol and triethylamine was slowly added dropwise to the system while stirring, allowing furanol to replace the chlorine atoms in the main chain and ends of the polydichlorophosphazene through a nucleophilic substitution reaction. After the reaction was completed, the mixture was filtered and the filtrate was collected. The solvent was removed by vacuum distillation of the filtrate, and the resulting solid was washed with ethanol and dried under vacuum to remove unreacted monomers on the surface. Then, it was mixed with a dried crosslinking agent with maleimide groups at room temperature and stirred evenly to obtain a self-healing phosphorus-nitrogen flame retardant precursor. The precursor contains a 4π electron system of furan ring and a 2π electron system of maleimide. The two can undergo a [4+2] cycloaddition reaction at a relatively low temperature, namely the Diels-Alder reaction. When the Diels-Alder reaction is completed, a new six-membered ring is generated. When this six-membered ring is exposed to the high temperature of a fire, it will break to generate furan ring and maleimide. When the fire ends and the temperature drops, it will turn back into a six-membered ring, thus regenerating the flame retardant effect of cooling by endothermic reaction.

[0022] 3. Melt blending molding of nylon flame retardant materials The matrix, filler, antioxidant, microcapsules, and flame retardant precursor are fed into a twin-screw extruder. At high temperature, the shear force of the screws uniformly disperses the flame retardant precursor, boron nitride, and microcapsules within the nylon matrix. The molten mixture is then extruded and cooled to form the final product. Because the melamine-formaldehyde shell, flame retardant precursor, and surface-pretreated boron nitride all exhibit good interfacial compatibility with the nylon matrix, melt blending allows these components to be smoothly and uniformly dispersed within the nylon matrix. The formed nylon composite material is then placed in an oven for heating and heat preservation. After a period of time, the material is removed and cooled to obtain the molded renewable nylon flame-retardant material. Because the furan ring and maleimide in the self-healing flame retardant precursor of the material are in an unlinked state during the high temperature of the melting stage, the nylon flame retardant material needs to be kept at a low temperature for a period of time after preparation to ensure that the furan ring and maleimide inside the material react to generate a six-membered ring that can be broken. Moreover, the temperature of the nylon flame retardant material during melt injection molding is much lower than the escape temperature of the N / P free radicals in the flame retardant. Therefore, the melt injection molding temperature has not reached the starting point that would cause irreversible consumption of the flame retardant. Therefore, when the material is subsequently subjected to secondary injection molding, it is only necessary to place the material at a low temperature after injection molding to allow the Diels-Alder reaction to proceed again and generate a six-membered ring to restore most of its self-healing flame retardant function.

[0023] The following are some specific embodiments of the present invention: Example 1 S1: Take 5g of melamine and 10g of 37% formaldehyde aqueous solution, add to 100mL of deionized water, adjust the temperature to 60℃, slowly add 10% NaOH solution to adjust the pH to 8.5, stir for 30min to form melamine-formaldehyde prepolymer. Separately weigh 2g of sodium dodecylbenzenesulfonate and add to 200mL of deionized water, adjust the temperature to 50℃ and stir, while slowly adding 20g of aluminum diisobutylphosphite (AlPi) powder, continue stirring for 30min to form a uniform and stable white suspension. Then pour the prepolymer into the white suspension, continue stirring for 15min, then adjust the pH to 4.0 with 10% citric acid aqueous solution, adjust the temperature to 70℃ and continue the reaction for 3h, adjust the pH to 7.0 with 10% NaOH aqueous solution, filter the reactants, wash with deionized water and ethanol, and vacuum dry at 60℃ for 12h to obtain white AlPi flame retardant microcapsule powder.

[0024] S2: Disperse 10g of boron nitride powder in 100g of anhydrous ethanol, sonicate for 30min to make it uniformly dispersed into a suspension, then add 0.2g of silane coupling agent KH-550 to the suspension, stir at 80℃ for 3h, separate the solid with a high-speed centrifuge, wash with anhydrous ethanol to remove unreacted silane coupling agent, and vacuum dry the solid at 80℃ for 6h to obtain surface-pretreated boron nitride.

[0025] S3: Weigh 2.86 g of hexachlorocyclotriphosphazene and 1.68 g of hexamethylenetetramine, and add them sequentially to a three-necked flask. Then, slowly add 25 mL of anhydrous 1,4-dioxane to the flask, start stirring at 300 rpm, and purge the flask with nitrogen gas. Place the flask in an oil bath and adjust the temperature to 105 °C for 6 h. Then, lower the temperature to 50 °C, weigh 0.98 g of furanol and 1.21 g of triethylamine, mix them thoroughly, and slowly add them to the flask. Then, raise the temperature to 65 °C and stir for 3 h. After the reaction is complete, filter the reactants and collect the filtrate. Distill the filtrate under reduced pressure at 0.1 MPa and 50 °C to obtain a pale yellow viscous solid. Wash it three times with anhydrous ethanol, and then transfer it to a vacuum drying oven at 60 °C for 4 h to obtain a pale yellow polyphosphazene powder with furan groups at the ends.

[0026] S4: Weigh 2.0g of the pale yellow powder obtained in S3 and 2.46g of 4,4'-diphenylmethane bismaleimide, add them to a 50mL beaker and stir with a magnetic stirrer at room temperature for 60min to obtain a self-healing phosphorus-nitrogen flame retardant precursor powder. Take 70g of dry nylon 66 resin powder, 10g of flame retardant microcapsule powder, 3.5g of precursor powder, 10g of surface-pretreated boron nitride powder, and 0.3g of antioxidant, wherein the mass ratio of hindered phenolic antioxidant to phosphite antioxidant is 1:1. Put all materials into a twin-screw extruder for blending and granulation. The extruder temperature is set to 250℃ at the front and gradually increased to 275℃ at the back, and the screw speed is 300rpm. After shearing and blending in the extruder for 1min, the material is extruded, cooled in a water bath, and pelletized to obtain nylon composite granules. The nylon composite granules were then placed in a 90℃ oven and kept warm for 12 hours to obtain a self-healing nylon flame-retardant material.

[0027] Example 2 The preparation method is the same as in Example 1, except that: S1: After adding the citric acid aqueous solution, adjust the temperature to 55℃; S3: Place the three-necked flask in an oil bath and react at 80°C for 4 hours; S4: The amount of flame retardant microcapsule powder added is 20g, and the amount of boron nitride powder added after surface pretreatment is 5g. The remaining steps are the same.

[0028] Example 3 The preparation method is the same as in Example 1, except that: S1: After adding the citric acid aqueous solution, adjust the temperature to 80℃; S3: Place the three-necked flask in an oil bath and react at 120°C for 8 hours; S4: The amount of flame retardant microcapsule powder added is 5g, and the amount of boron nitride powder added after surface pretreatment is 15g. All other steps are the same.

[0029] Example 4 The preparation method is the same as in Example 1, except that: S1: After adding the citric acid aqueous solution, adjust the temperature to 65℃; S3: Place the three-necked flask in an oil bath and react at 90°C for 5 hours. S4: The amount of flame retardant microcapsule powder added is 15g, and the amount of boron nitride powder added after surface pretreatment is 12g. The remaining steps are the same.

[0030] Comparative Example 1 The preparation method is the same as in Example 1, except that: Weigh 70g of dry nylon 66 resin, 10g of dry AlPi powder, 3.5g of precursor powder, and 0.3g of antioxidant, and prepare nylon flame retardant material step by step according to steps S3 and S4.

[0031] This comparative preparation does not add boron nitride filler, and does not prepare AlPi flame retardant into microcapsules but adds it directly into the nylon matrix, thus forming a nylon flame retardant material.

[0032] Comparative Example 2 The preparation method is the same as in Example 1, except that: AlPi was prepared into flame retardant microcapsules in step S1. Then, 70g of dry nylon 66 resin, 10g of flame retardant microcapsule powder, and 0.3g of antioxidant were weighed and prepared into nylon flame retardant material in step S4.

[0033] This comparative preparation relies solely on AlPi flame retardant microcapsules for flame retardancy. The resulting nylon flame retardant material lacks a boron nitride thermal conductive network and does not contain self-healing phosphorus-nitrogen flame retardants.

[0034] Comparative Example 3 The preparation method is the same as in Example 1, except that: Weigh 70g of dry nylon 66 resin, 10g of dry AlPi powder, 10g of surface-pretreated boron nitride, and 0.3g of antioxidant, and prepare nylon flame retardant material according to step S4.

[0035] This comparative preparation involved directly injecting AlPi into the nylon matrix, and the material contained no self-healing phosphorus-nitrogen flame retardants.

[0036] Experimental Example 1 The nylon flame-retardant granules prepared in step S3 of Examples 1-4 and Comparative Examples 1-3 were added to an injection molding machine. The barrel temperature was adjusted to 270°C and the mold temperature to 80°C. The granules were melted at high temperature and injected into the mold to prepare standard test specimens. Tensile strength and elongation at break: According to ASTM D638 "Standard for Test Methods of Tensile Properties of Plastics", the specimen is 165 mm long, 10 mm wide, and 6.4 mm thick, and is dumbbell-shaped.

[0037] Notched impact strength: According to ASTM D256, "Standard Test Method for Determination of the Resistance of Plastics to Cantilever Pendulum Impact", the specimen is 80 mm long, 10 mm wide, and 4 mm thick.

[0038] Flexural strength and flexural modulus: according to ASTM D790 "Plastics Flexural Properties Test and Other Mechanical Properties Test Standards", the specimen is 80 mm long, 10 mm wide and 4 mm thick.

[0039] The mechanical properties of the specimens were tested using a universal testing machine, and the test results are shown in Table 1.

[0040] Table 1 Mechanical properties of the experimental group samples From Table 1 and Figures 2-4 As can be seen from the data, the mechanical properties of the sample in the example are generally higher than those of the comparative sample, indicating that the presence of flame retardant microcapsules and boron nitride filler can significantly improve the mechanical properties of the material. Furthermore, the self-healing phosphorus-nitrogen flame retardant has good compatibility with the nylon matrix and does not significantly affect the mechanical properties of the material. In Comparative Example 1, AlPi was directly injected into the nylon 66 matrix, resulting in a large number of rigid flame retardant particles dispersed within the matrix, making it brittle. In Comparative Example 2, AlPi was prepared into flame retardant microcapsules and mixed with the nylon 66 matrix. It can be seen that the flame retardant was encapsulated within the melamine-formaldehyde resin and would not be released without the influence of heat. This enhanced the flame retardant properties of the material without significantly affecting its mechanical properties. However, without the support of the boron nitride network, the mechanical properties of the material were still far inferior to those of the example samples. In Comparative Example 3, AlPi particles were directly mixed into the nylon 66 matrix, and the matrix contained the support of a three-dimensional boron nitride network. It can be seen that even with the enhancement effect of boron nitride on the mechanical properties of the material, the directly added AlPi particles still had a strong negative impact on the mechanical properties.

[0041] Experiment Example 2 The nylon flame-retardant materials prepared in Examples 1-4 and Comparative Examples 1-3 were injection molded into standard samples for flame-retardant performance testing. Vertical burning test: According to UL-94 "Flammability of Plastic Materials for Equipment and Electrical Components", the sample is 125 mm long, 13 mm wide, and 1.6 mm thick. The sample is placed at 25°C and 50% relative humidity for 48 hours, then placed in an oven at 70°C for 168 hours, and then transferred to a desiccator to cool to room temperature before burning on an alcohol lamp.

[0042] Limiting Oxygen Index (LOI): Measured according to ASTM D2863, "Method for determination of the minimum oxygen concentration required for combustion of a plastic-like candle (oxygen index)". The sample is 150 mm long, 10 mm wide, and 4 mm thick. The sample is placed in a glass combustion chamber, and a mixture of oxygen and nitrogen at different concentrations is introduced into the chamber from the bottom. The top of the sample is ignited, and the combustion of the sample at different oxygen concentrations is observed.

[0043] Regeneration Capacity Test: The sample was placed over an alcohol lamp flame to ignite its coating surface for 30 seconds, then removed, and the ignition status was recorded. The material was then placed at 35°C for 24 hours, and the LOI test was performed again to observe the recovery of the LOI value. This process was repeated until the LOI value dropped below 28%, and the number of cycles was recorded.

[0044] The test results are shown in Table 2.

[0045] Table 2 Flame retardant performance test of experimental group samples From Table 2 and Figure 5As can be seen, the flame retardant performance of the sample in the examples is significantly better than that of the comparative sample, indicating that the triple synergistic effect of flame retardant microcapsules, boron nitride, and self-healing phosphorus-nitrogen flame retardant can significantly improve the flame retardant ability of nylon, and the flame retardant performance of the sample in the examples all have excellent renewability. Comparative Example 1 directly injects AlPi into the nylon 66 matrix as the main flame retardant in the nylon flame retardant material. Due to the presence of the self-healing flame retardant, the sample has a certain regenerability. However, without a boron nitride network, when all the six-membered rings of the self-healing flame retardant break, the internal heat cannot dissipate in a short time, resulting in excessively high local temperatures and affecting the flame retardant effect. Comparative Example 2 mixes AlPi into flame retardant microcapsules with the nylon 66 matrix, relying solely on the effect of AlPi flame retardant to produce a nylon flame retardant material. Due to the lack of internal boron nitride support, the sample produces burning drips during combustion, resulting in poor flame retardant effect and almost no regenerability. In Comparative Example 3, the AlPi in the sample is directly mixed into the nylon 66 matrix, and the matrix contains a three-dimensional boron nitride network for support. It can be seen that the sample has a certain flame retardant ability, but since the flame retardant effect is achieved solely through the consumption of the AlPi flame retardant microcapsules filled inside the sample, the regenerability of the sample is poor.

Claims

1. A flame retardant containing aluminum diisobutylphosphite, characterized in that: The flame retardant is a core-shell structured aluminum diisobutylphosphite microcapsule, with aluminum diisobutylphosphite as the core and a resin shell layer deposited on the surface of aluminum diisobutylphosphite through interfacial polymerization of melamine and formaldehyde.

2. The flame retardant containing diisobutylaluminum hypophosphite according to claim 1, characterized in that: The microcapsules are prepared by melamine-formaldehyde prepolymer under weakly alkaline conditions. Diethyl aluminum hypophosphite is dispersed in an aqueous phase of an anionic surfactant to form a suspension. The two are mixed under acidic conditions and deposited through interfacial polymerization to form core-shell structured microcapsules.

3. The flame retardant containing diisobutylaluminum hypophosphite according to claim 1, characterized in that: The reaction temperature during the interfacial polymerization deposition is 55~80℃.

4. A nylon flame-retardant material, characterized in that: The flame retardant comprising aluminum diisobutylphosphite as described in any one of claims 1 to 3 further comprises a matrix, a self-healing flame retardant, an antioxidant, and reinforcing fillers.

5. The nylon flame-retardant material according to claim 4, characterized in that: The matrix is ​​nylon 66 resin, the self-healing flame retardant is composed of a phosphorus-nitrogen flame retardant with furan functional groups and a crosslinking agent with maleimide groups, the antioxidant is one or more of a compound composition of hindered phenolic antioxidants and phosphite antioxidants, and the reinforcing filler is boron nitride.

6. The nylon flame-retardant material according to claim 5, characterized in that: The furan-functionalized phosphorus-nitrogen flame retardant is a terminal furan-functionalized polyphosphazene, and the maleimide-functionalized crosslinking agent is bismaleimide.

7. A method for preparing a nylon flame-retardant material according to any one of claims 4 to 6, characterized in that, The specific steps are as follows: S1. Melamine and formaldehyde aqueous solution are reacted under weakly alkaline conditions to generate a water-soluble prepolymer. AlPi powder is then dispersed in the aqueous phase of anionic surfactant and a uniformly dispersed suspension is formed by high-speed shearing. The prepolymer is added to the suspension and the pH is adjusted to acidity so that the prepolymer is deposited on the surface of diisobutyl aluminum hypophosphite and a melamine-formaldehyde resin shell is formed by cross-linking and curing. S2. Disperse boron nitride in anhydrous ethanol and ultrasonically disperse it to form a suspension. Then add silane coupling agent to the suspension, heat and stir, centrifuge to separate the solid, wash with ethanol, and dry to obtain the surface-pretreated boron nitride filler. S3. Hexachlorocyclotriphosphazene is subjected to ring-opening polymerization to generate linear polydichlorophosphazene, which is then subjected to nucleophilic substitution reaction with triethylamine. After precipitation, washing and drying, a phosphorus-nitrogen flame retardant with furan groups is obtained. It is then stirred evenly with a crosslinking agent with maleimide groups to obtain a self-healing phosphorus-nitrogen flame retardant precursor. S4. Nylon 66 matrix, antioxidant, flame retardant microcapsules, self-healing phosphorus-nitrogen flame retardant precursor, and surface-pretreated boron nitride are melt-blended in a twin-screw extruder, extruded, pelletized, and heated to obtain self-healing nylon composite flame retardant granules.

8. The method for preparing a nylon flame-retardant material according to claim 7, characterized in that: The reaction temperature of the ring-opening polymerization reaction in S3 is 80~120℃, and the reaction time is 4~8h. The mass ratio of the flame retardant microcapsules and the surface-pretreated boron nitride in S4 is 4:1~1:

3.

9. The method for preparing a nylon flame-retardant material according to claim 7, characterized in that: In the twin-screw extruder described in S4, the barrel temperature gradually increases from the front to the back during melt blending, with a temperature range of 250~275℃ and a screw speed of 300rpm.

10. A method for preparing a nylon flame-retardant material according to claim 7, characterized in that: The nylon flame retardant material is a renewable flame retardant material, which can be recycled at least 3 times.

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