Degradable environment-friendly flame retardant and preparation method thereof

Abstract

The invention relates to the field of flame-retardant materials, and discloses a degradable environment-friendly flame retardant and a preparation method thereof, and the flame retardant is composed of a dynamic covalent network component, a phosphorus-nitrogen synergistic flame-retardant system, a nano self-assembly material and a catalytic component. Through staged response of a dynamic network, a compact carbon layer and flame-retardant gas are synergistically generated, and the flame-retardant efficiency is improved; the phosphorus-nitrogen synergistic effect and the nano material provide excellent thermal stability and smoke suppression performance; the catalytic component obviously enhances the mechanical property and the heat insulation effect of the carbon layer. The preparation method comprises the steps of dynamic network construction, flame-retardant system compounding, nano material preparation and blending molding. The flame retardant is excellent in flame retardance, the oxygen index reaches 37% or above, UL-94 reaches V-0 level, the degradation rate exceeds 95% within 90 days, and the flame retardant has environment friendliness, flame retardance and mechanical stability.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant materials, in particular to a degradable and environment-friendly flame retardant and a preparation method thereof. Background Art

[0002] In the current field of flame retardant material technology, the design of flame retardants needs to meet multiple requirements of material performance at the same time, including excellent flame retardancy, environmental friendliness, biodegradability, and stability of mechanical properties. However, existing flame retardant technology has significant deficiencies in taking these properties into account, which limits its application in environmental protection and functional material development.

[0003] The contradiction between flame retardant performance and environmental protection performance

[0004] Among traditional flame retardants, halogen flame retardants are widely used due to their high flame retardant efficiency. However, halogen flame retardants release toxic gases and corrosive products during combustion, causing serious environmental pollution and safety hazards. Therefore, environmentally friendly flame retardants such as phosphorus and nitrogen flame retardants have become the focus of research in recent years. However, such flame retardants often face the problem of insufficient flame retardant efficiency, especially in high-temperature combustion, it is difficult to form a flame-retardant carbon layer with high stability, which makes the material prone to secondary combustion. In the existing technology, how to improve the flame retardant efficiency of environmentally friendly flame retardants, especially through the synergistic generation of dense carbon layers through chemical reactions inside the material, is still a major problem.

[0005] The Difficulty of Balancing Biodegradability and Flame Retardancy

[0006] In recent years, with the rise of degradable materials, biodegradable flame retardants have gradually received attention. However, in the existing technology, the degradation performance of flame retardants often conflicts significantly with their flame retardant properties. On the one hand, many degradable materials (such as polylactic acid PLA) are easily decomposed into combustible gases when burned, which increases the flammability of the materials; on the other hand, traditional methods of enhancing flame retardant properties (such as by adding a high proportion of metal oxides or inorganic fillers) usually inhibit the degradation process, making it difficult for the materials to be completely decomposed in the natural environment. Therefore, how to optimize the composition and structure of flame retardants to improve flame retardant properties while taking into account their degradability is an important technical bottleneck in the current industry.

[0007] Insufficient dynamic network function in material structure

[0008] Existing flame retardant designs usually rely on physical filling of materials (such as adding layered double hydroxides (LDH) or phosphorus fillers) to improve flame retardancy, but such designs often lack chemical functions with dynamic responses. Especially in high-temperature environments, existing flame retardants lack adjustable dynamic bond structures, making it difficult to achieve multi-stage synergistic flame retardant effects during combustion. For example, after a single-component flame retardant material releases a small amount of flame retardant gas at the beginning of combustion, its flame retardant effect rapidly decays, making subsequent combustion difficult to control. How to release flame retardant gases and form a dense carbon layer at different stages of combustion through material chemical structure design is one of the key research directions for improving flame retardancy.

[0009] Therefore, the present invention provides a degradable and environmentally friendly flame retardant and a preparation method thereof to solve the deficiencies of the prior art. Summary of the invention

[0010] In view of the shortcomings of the prior art, the present invention proposes a degradable and environmentally friendly flame retardant and a preparation method thereof. The flame retardant achieves an optimized balance between flame retardant efficiency, degradability and material mechanical properties through innovative design of dynamic network components, phosphorus-nitrogen synergistic flame retardant system, nanostructure and catalytic components.

[0011] To achieve the above objectives, the present invention is implemented by the following technical scheme: a degradable and environmentally friendly flame retardant, the flame retardant is composed of the following components in proportion by mass:

[0012] Dynamic covalent network components: 20-40 parts;

[0013] It includes 5 to 15 parts of acylhydrazone monomer, 5 to 10 parts of disulfide bond monomer, and 5 to 10 parts of boron-oxygen bond monomer;

[0014] Acylhydrazone bond (C=N bond): Preferentially breaks under humid or acidic conditions, releasing small molecules (such as ammonia) and diluting combustible gases.

[0015] Disulfide bond (SS bond): breaks under high temperature conditions, releasing sulfur radicals (S·), effectively inhibiting the free radical chain reaction in combustion.

[0016] Boron-oxygen bond (BO bond): formed during combustion 2 O 3 , further promoting the formation of a high-density carbon layer and isolating oxygen and heat transfer.

[0017] Phosphorus-nitrogen synergistic flame retardant system: 20-35 parts;

[0018] It includes 10 to 20 parts of ammonium polyphosphate, 5 to 15 parts of quaternary ammonium salt modified chitosan, and 1 to 5 parts of borate;

[0019] The core of the phosphorus-nitrogen synergistic flame retardant system lies in the synergistic effect of phosphorus and nitrogen elements, which exhibits the dual effects of gas phase and condensed phase flame retardancy during the combustion process:

[0020] Gas phase flame retardant effect:

[0021] Ammonium polyphosphate (APP) decomposes at high temperature to generate phosphoric acid and polyphosphoric acid, which react with ammonia (NH 3 ) react to form inert gas, which inhibits the spread of flame.

[0022] Condensed phase flame retardant effect:

[0023] Chitosan modification enhances the carbon-forming ability of APP, and the carbon layer generated by decomposition further enhances its density and thermal isolation through the action of zinc borate, thereby effectively preventing oxygen diffusion and heat conduction.

[0024] The charring and gas release mechanisms in the phosphorus-nitrogen synergistic flame retardant system enable the flame retardant to exhibit excellent thermal insulation properties during flame propagation.

[0025] Nano self-assembly material: 5-10 parts;

[0026] Catalytic component: 0.1-1 part;

[0027] Biodegradable polymer matrix: 40-60 parts.

[0028] Preferably, the acylhydrazone monomer is a reaction product of p-hydroxybenzaldehyde and hydrazine, and its addition ratio is 25-50% of the total mass of the dynamic covalent network component.

[0029] Preferably, the disulfide bond monomer is dithioacetic acid or dithiopropionic acid.

[0030] Preferably, the quaternary ammonium salt modified chitosan in the phosphorus-nitrogen synergistic flame retardant system is prepared by the following method: dissolving chitosan in 10-20wt% acetic acid solution, adding quaternary ammonium salt and reacting for 60-90 minutes before neutralizing to a pH of 7-8.

[0031] Preferably, the nano self-assembly material is magnesium aluminum layered double hydroxide (LDH), wherein the molar ratio of magnesium ions to aluminum ions is 2.5 to 3.5:1.

[0032] As a nanosheet material, LDH's nanostructure has the following functions in flame retardants:

[0033] During the combustion process, LDH forms a physical barrier that prevents oxygen diffusion and the escape of combustible gases, reducing the heat transfer rate.

[0034] The metal oxides generated by the decomposition of LDH further enhance the mechanical strength and thermal stability of the carbon layer.

[0035] The physical barrier effect of the nanosheet layer works synergistically with the chemical reaction, making the material exhibit higher thermal stability and flame retardant properties.

[0036] Preferably, the catalytic component comprises Zn 2+ or Fe 3+ The addition form is 0.1-1M metal salt solution, which is introduced into the dynamic network by adsorption method.

[0037] Zn 2+ or Fe 3+ Metal ions play a catalytic role in the combustion process of materials:

[0038] Promote carbonization reaction at high temperature to improve the density and thermal insulation performance of the carbon layer.

[0039] Participate in redox reactions and further enhance the stability of the dynamic covalent network under high temperature conditions.

[0040] The introduction of catalytic components not only optimizes the carbon layer structure of the flame retardant, but also effectively improves its flame retardant efficiency during the pyrolysis process.

[0041] Preferably, the biodegradable polymer matrix is ​​a copolymer of polylactic acid (PLA) and polyhydroxyalkanoate (PHA), and the mass ratio of the copolymer of polylactic acid and polyhydroxyalkanoate is 1:1 to 3:1.

[0042] PLA and PHA copolymers are used as matrix materials to give flame retardants controllable degradation properties:

[0043] PLA provides high mechanical strength and rigidity.

[0044] The introduction of PHA improves the toughness and degradation resistance of the material.

[0045] This matrix design can achieve an optimal balance between the mechanical properties and degradation properties of the material by adjusting the ratio of PLA to PHA.

[0046] Preferably, a method for preparing a degradable environmentally friendly flame retardant comprises the following steps:

[0047] S1. Construction of dynamic network: mixing acylhydrazone monomer, disulfide bond monomer and boron-oxygen bond monomer at a temperature of 50 to 90° C. and a pH of 6 to 8, and stirring for 1 to 2 hours;

[0048] S2. Compounding of phosphorus-nitrogen synergistic groups: Mix ammonium polyphosphate solution and quaternary ammonium salt modified chitosan solution in a mass ratio of 1:2, add borate, and stir at 50-70° C. for reaction for 90-120 minutes;

[0049] S3, preparation of nanosheet material: preparing magnesium aluminum layered double hydroxide by solution coprecipitation method at pH 10, washing, drying and grinding into powder;

[0050] S4, blending and molding: blending the materials obtained in steps S1, S2 and S3 with a biodegradable polymer matrix to prepare flame retardant particles at 170-200° C. by melt blending;

[0051] S5. Catalyst introduction: Add Zn at the end of blending 2+ or Fe 3+ Salt solution, mix evenly and solidify into shape.

[0052] Preferably, in step S1, the amount of acylhydrazone monomer added is 25-50% of the total mass of the dynamic network, and the amount of disulfide bond monomer added is 10-30%.

[0053] Preferably, the blending shear rate in step S4 is 20 to 50 rpm, the pressure is 5 to 10 MPa, and the time is 5 to 10 minutes.

[0054] The above preparation method ensures the uniformity and synergy of the distribution of each component in the flame retardant system through the rational design of the dynamic network components and precise process control; through the melt blending technology, the full integration of the dynamic network and the matrix material is achieved, so that the flame retardant has both excellent mechanical properties and flame retardant properties, and can achieve controllable degradation under environmental conditions.

[0055] The present invention provides a degradable and environment-friendly flame retardant and a preparation method thereof, which has the following beneficial effects:

[0056] 1. The present invention adopts dynamic covalent network components, and realizes graded degradation of materials under different environmental conditions through the coordinated design of acylhydrazone bonds, disulfide bonds and boron-oxygen bonds, while maintaining the structural stability of the flame retardant during combustion. Compared with the solution in the prior art that the flame retardant performance decreases rapidly after degradation, the present invention successfully solves the technical problem of the difficulty in balancing the degradation and flame retardant performance of flame retardants.

[0057] 2. The present invention combines ammonium polyphosphate with quaternary ammonium salt-modified chitosan, and utilizes the phosphorus-nitrogen synergistic effect to enhance the comprehensive effect of gas phase flame retardancy and condensed phase carbonization. Compared with the limitations of single phosphorus or nitrogen flame retardants in the prior art, the present invention not only improves the limiting oxygen index of the flame retardant, but also solves the problem of insufficient density of the flame retardant layer, and significantly enhances the thermal insulation performance.

[0058] 3. The present invention uses a nano-sheet design of magnesium-aluminum layered double hydroxide (LDH) to enable the flame retardant to form a multi-layered heat insulation barrier during the combustion process. This design makes up for the defects of poor dispersibility and limited flame retardant effect of nano flame retardant materials in the prior art, and significantly improves the oxygen isolation effect and the stability of combustion residues.

[0059] 4. The present invention adopts Zn 2+ or Fe 3+ As a catalytic component, the carbonization efficiency in a high-temperature environment is improved by introducing the reaction process of a metal ion catalytic dynamic network. Compared with the technology of traditional flame retardants that fail to fully utilize the catalytic effect, the present invention effectively solves the problem of insufficient thermal stability of flame retardants while ensuring a high-density carbon layer, and improves the overall flame retardant performance of the material during combustion. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The present invention is a flow chart of the preparation method of a degradable and environment-friendly flame retardant. DETAILED DESCRIPTION

[0061] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] Please refer to the attached Figure 1 :

[0063] Embodiment 1:

[0064] Raw material ratio:

[0065] The flame retardant components are prepared according to the following ratios (by mass):

[0066] Acylhydrazone monomer (reaction product of p-hydroxybenzaldehyde and hydrazine): 10 parts

[0067] Dithioacetic acid: 8 parts

[0068] Diethyl borate: 7 parts

[0069] Ammonium polyphosphate: 15 parts

[0070] Quaternary ammonium salt modified chitosan: 10 parts

[0071] Zinc borate: 3 parts

[0072] Magnesium aluminum layered double hydroxide: 6 parts

[0073] Polylactic acid (PLA) and polyhydroxyalkanoate (PHA) copolymer: 50 parts (PLA:PHA=2:1)

[0074] Zn2+ solution (0.5M): 0.3 parts

[0075] Preparation steps:

[0076] Dynamic network construction

[0077] Dissolve p-hydroxybenzaldehyde (2 g) in 50 mL of ethanol, add hydrazine solution (5 wt %, 1.5 g), stir until uniform, control the pH to 7.5, react for 1.5 hours, and form an acylhydrazone monomer solution at 60° C.

[0078] Add dithioacetic acid (1.6 g) to the acylhydrazone solution, mix well, adjust the pH to 8.0, stir and react for 1 hour, add diethyl borate (1.4 g), continue stirring at 70° C. for 45 minutes to obtain a dynamic network prepolymer.

[0079] Phosphorus-nitrogen synergistic group complex

[0080] A 10 wt % ammonium polyphosphate solution (15 g APP dissolved in 150 mL water) was prepared and mixed with a quaternary ammonium salt-modified chitosan solution (10 g chitosan dissolved in 15 wt % acetic acid and 3 g quaternary ammonium salt added) at a mass ratio of 1:2.

[0081] Zinc borate (0.6 g) was added at 60° C. and the mixture was stirred for reaction for 90 minutes to form a phosphorus-nitrogen synergistic complex.

[0082] Preparation of nanosheet materials

[0083] Preparation of Mg 2+ With Al 3+ The precursor solution (3:1 molar ratio, 0.1M) was added dropwise to the coprecipitate at pH 10 and reacted for 2 hours. After washing and drying (60°C, 12 hours), the product was ground to 200 mesh to obtain magnesium aluminum layered double hydroxide (6 g).

[0084] Flame retardant molding

[0085] Dynamic network prepolymer (25 g), phosphorus-nitrogen complex (28 g), nanosheet material (6 g) and PLA / PHA copolymer (50 g) were blended at a melt blending temperature of 180° C. and a shear rate of 30 rpm. The mixture was stirred for 30 minutes to form particles.

[0086] Add Zn at the end of blending 2+ The solution (0.5 g) was uniformly mixed and pressed into sheets (200° C., 8 MPa, 8 min) to obtain a flame retardant sheet.

[0087] Embodiment 2:

[0088] Raw material ratio:

[0089] The flame retardant components are formulated according to the following mass parts:

[0090] Acylhydrazone monomer (reaction product of p-hydroxybenzaldehyde and hydrazine): 8 parts

[0091] Dithiopropionic acid: 6 parts

[0092] Diethyl borate: 6 parts

[0093] Ammonium polyphosphate: 20 parts

[0094] Quaternary ammonium salt modified chitosan: 12 parts

[0095] Zinc borate: 2 parts

[0096] Magnesium aluminum layered double hydroxide: 7 parts

[0097] Polylactic acid and polyhydroxyalkanoate copolymer: 45 parts (PLA:PHA=3:1)

[0098] Fe3+ solution (0.2M): 0.5 parts

[0099] Preparation steps:

[0100] Dynamic network construction

[0101] p-Hydroxybenzaldehyde (1.6 g) was dissolved in 50 mL of ethanol, and a hydrazine solution (5 wt %, 1.2 g) was added dropwise. The mixture was stirred and reacted for 2 hours to form an acylhydrazone monomer solution at 65°C.

[0102] Dithiopropionic acid (1.2 g) was added, stirred evenly, and the reaction temperature was maintained at 70° C. After 1 hour, diethyl borate (1.2 g) was added, and stirred for 45 minutes to obtain a dynamic network precursor.

[0103] Phosphorus-nitrogen synergistic group complex

[0104] A 15 wt% ammonium polyphosphate solution (20 g dissolved in water) was prepared, and a modified chitosan solution (12 g chitosan, 3.5 g quaternary ammonium salt dissolved in acetic acid) was added.

[0105] Zinc borate (0.4 g) was added at 70° C. and reacted for 120 minutes to form a synergistic flame retardant group complex.

[0106] Nanosheet material preparation

[0107] The magnesium salt and aluminum salt precursor solutions were prepared at a molar ratio of 2.5:1 (0.1M solution), and NaOH solution was added to adjust the pH to 10, and the mixture was reacted at room temperature for 3 hours to obtain a precipitate, which was then dried and ground into 100 mesh powder.

[0108] Flame retardant molding

[0109] The dynamic network (20 g), phosphorus-nitrogen complex (34 g), nanomaterial (7 g) and PLA / PHA matrix (45 g) were blended at a melt blending temperature of 190° C., a shear rate of 40 rpm, and a reaction time of 25 minutes.

[0110] Add Fe at the end 3+ The solution (0.5 g) was mixed evenly and then tableted (temperature 190°C, pressure 7 MPa, time 10 minutes).

[0111] Embodiment 3:

[0112] Raw material ratio:

[0113] Prepare according to the following proportions:

[0114] Acylhydrazone monomer (reaction product of p-hydroxybenzaldehyde and hydrazine): 12 parts

[0115] Dithioacetic acid: 9 parts

[0116] Diethyl borate: 5 parts

[0117] Ammonium polyphosphate: 18 parts

[0118] Quaternary ammonium salt modified chitosan: 8 parts

[0119] Zinc borate: 2 parts

[0120] Magnesium aluminum layered double hydroxide: 8 parts

[0121] Polylactic acid and polyhydroxyalkanoate copolymer: 48 parts (PLA:PHA=1:1)

[0122] Zn2+ solution (0.5M): 0.6 parts

[0123] Preparation steps

[0124] Dynamic network construction

[0125] Dissolve p-hydroxybenzaldehyde (2.4 g) in ethanol, add hydrazine solution (5 wt%, 1.8 g), react for 1.5 hours, add dithioacetic acid (1.8 g), continue the reaction, keep at 70°C for 1 hour, finally add diethyl borate (1 g), continue stirring for 30 minutes.

[0126] Synergistic flame retardant group composite

[0127] 18 g of ammonium polyphosphate was dissolved in water, and chitosan solution (8 g of chitosan, 2.5 g of quaternary ammonium salt) was added. Zinc borate was added and the mixture was reacted at 60° C. for 90 minutes.

[0128] Nanomaterial preparation

[0129] The magnesium-aluminum precursor solution was reacted at pH 10 for 2 hours to prepare a layered material, which was then dried to obtain a 200-mesh powder.

[0130] Flame retardant preparation

[0131] The above components were blended with PLA / PHA matrix at a melting temperature of 200°C, a shear rate of 25 rpm, and a time of 30 minutes. 2+ The solution (0.6 g) was mixed and then pressed into a mold (8 MPa, 10 min).

[0132] Comparative Example:

[0133] Comparative Example 1: Omitting disulfide bond monomers in a dynamic covalent network

[0134] Corresponding Example 1

[0135] In this comparative example, the disulfide bond monomer in the dynamic covalent network is omitted, and only the acylhydrazone monomer and the boron-oxygen bond monomer are retained. The remaining components and steps remain the same as those in Example 1.

[0136] Preparation process:

[0137] Dynamic network construction

[0138] Dissolve p-hydroxybenzaldehyde (2 g) in 50 mL of ethanol, add hydrazine solution (5 wt %, 1.5 g), stir until uniform, adjust the pH to 7.5, and react at 60° C. for 1.5 hours to form an acylhydrazone monomer solution.

[0139] Diethyl borate (1.4 g) was added to the acylhydrazone monomer solution and the reaction was continued at 70° C. for 45 minutes to generate a dynamic network precursor solution without adding disulfide bond monomers.

[0140] Phosphorus-nitrogen synergistic group complex

[0141] Preparation of phosphorus-nitrogen synergistic flame retardant system: 10wt% ammonium polyphosphate solution (15g dissolved in 150mL water) and quaternary ammonium salt modified chitosan solution (10g chitosan and 3g quaternary ammonium salt modified) were mixed in a mass ratio of 1:2, zinc borate (0.6g) was added at 60°C, and the reaction was stirred for 90 minutes.

[0142] Nanosheet material preparation

[0143] Magnesium aluminum layered double hydroxide (Mg-Al LDH) was prepared by preparing a precursor solution at a molar ratio of 3:1 and reacting for 2 hours at pH = 10. The precipitate was washed, dried (60° C., 12 hours) and ground into 200 mesh powder.

[0144] Flame retardant molding

[0145] The dynamic network precursor (25g), phosphorus-nitrogen synergistic system (28g), nanosheet material (6g) and PLA / PHA copolymer (50g, PLA:PHA=2:1) ​​were blended at a melt blending temperature of 180°C, a shear rate of 30rpm, stirring for 30 minutes, and pressed into sheets (200°C, 8MPa, 8 minutes).

[0146] Without Zn 2+ or Fe 3+ Catalytic components.

[0147] Comparative Example 2: Unmodified chitosan in phosphorus-nitrogen synergistic system

[0148] Corresponding Example 2

[0149] In this comparative example, the quaternary ammonium salt-modified chitosan in the phosphorus-nitrogen synergistic system was replaced with unmodified ordinary chitosan, and the other components and processes were consistent with those in Example 2.

[0150] Preparation process:

[0151] Dynamic network construction

[0152] According to the process of Example 2, the acylhydrazone monomer and the disulfide bond monomer are reacted to prepare a dynamic network precursor solution, and the specific operations remain the same.

[0153] Phosphorus-nitrogen synergistic group complex

[0154] Ammonium polyphosphate solution (20 g APP dissolved in 200 mL water) was mixed with ordinary chitosan solution (12 g chitosan dissolved in 10 wt % acetic acid), and zinc borate (0.4 g) was added at 70° C. and stirred for 120 minutes. No modified chitosan was used.

[0155] Nanosheet material preparation

[0156] The LDH preparation process was carried out according to the process of Example 2, including precipitation reaction, washing, drying and grinding steps.

[0157] Flame retardant molding

[0158] According to the process of Example 2, the dynamic network precursor, phosphorus-nitrogen synergistic group complex and PLA / PHA were blended (PLA:PHA=3:1), the melt blending temperature was 190°C, the shear rate was 40rpm, stirring was carried out for 25 minutes, and the tablets were pressed (190°C, 7MPa, 10 minutes).

[0159] Comparative Example 3: Nanosheet material omitted

[0160] Corresponding Example 1

[0161] In this comparative example, the nanosheet material (LDH) is completely omitted, and the remaining components and preparation process are consistent with those in Example 1.

[0162] Preparation process:

[0163] Dynamic network construction

[0164] The dynamic network precursor solution was prepared according to the process of Example 1, and the specific operations remained the same.

[0165] Phosphorus-nitrogen synergistic group complex

[0166] Preparation of phosphorus-nitrogen synergistic flame retardant system: 10wt% ammonium polyphosphate solution (15g dissolved in 150mL water) and quaternary ammonium salt modified chitosan solution (10g chitosan and 3g quaternary ammonium salt modified) were mixed in a mass ratio of 1:2, zinc borate (0.6g) was added at 60°C, and the reaction was stirred for 90 minutes.

[0167] Flame retardant molding

[0168] The dynamic network precursor (25 g), phosphorus-nitrogen synergistic system (28 g) and PLA / PHA copolymer (50 g, PLA:PHA=2:1) ​​were blended at a melt blending temperature of 180°C, a shear rate of 30 rpm, and stirred for 30 minutes, and pressed into sheets (200°C, 8 MPa, 8 minutes).

[0169] No magnesium aluminum layered double hydroxide was added.

[0170] Comparative Example 4: Omitting the Catalytic Component

[0171] Corresponding Example 3

[0172] This comparative example omits Zn 2+ or Fe 3+ The catalytic component, other components and preparation process remain the same as in Example 3.

[0173] Preparation process:

[0174] Dynamic network construction

[0175] Dissolve p-hydroxybenzaldehyde (2.4 g) in 50 mL of ethanol, add hydrazine solution (5 wt %, 1.8 g), stir evenly, control the pH to 7.5, and react for 1.5 hours.

[0176] After adding dithioacetic acid (1.8 g), stirring was continued and maintained at 70° C. for 1 hour. Finally, diethyl borate (1 g) was added and stirred for 30 minutes to obtain a dynamic network precursor solution.

[0177] Phosphorus-nitrogen synergistic group complex

[0178] According to the process of Example 3, the phosphorus-nitrogen synergistic group complex was prepared, and the specific operations remained the same.

[0179] Nanosheet material preparation

[0180] The LDH nanosheet material was prepared in the same manner as in Example 3.

[0181] Flame retardant molding

[0182] According to the process of Example 3, the dynamic network precursor, phosphorus-nitrogen synergistic group complex, LDH and PLA / PHA (PLA:PHA=1:1) were blended at a melt blending temperature of 200°C and a shear rate of 25 rpm. The mixture was stirred for 30 minutes and pressed into sheets (200°C, 8 MPa, 10 minutes).

[0183] Without Zn 2+ or Fe 3+ catalyst.

[0184] Test experiment:

[0185] Experiment 1:

[0186] Purpose

[0187] The effect of the introduction of disulfide bond monomers in the dynamic covalent network component on the flame retardant properties of the flame retardant was verified by comparing Example 1 with Comparative Example 1 to test the oxygen index, vertical combustion performance and thermal stability.

[0188] Experimental materials and equipment

[0189] Sample: The flame retardant sheet prepared in Example 1 and Comparative Example 1, with a size of 100 mm×10 mm×3 mm.

[0190] equipment:

[0191] Oxygen Index Tester: Used to determine the minimum oxygen concentration of a sample that supports combustion.

[0192] UL-94 combustion tester: used for vertical combustion performance test.

[0193] Thermogravimetric Analyzer (TGA): used to analyze thermal decomposition characteristics and carbon residue rate.

[0194] Experimental procedures

[0195] Oxygen Index Test (LOI)

[0196] According to ASTM D2863 standard, the sample is fixed in the oxygen index tester.

[0197] Adjust the oxygen concentration in the oxygen-nitrogen mixed gas flow and start igniting the sample from a lower oxygen concentration.

[0198] Record the lowest oxygen concentration (LOI value) at which the sample can continue to burn.

[0199] UL-94 vertical burning test

[0200] According to UL-94 standard, fix the sample in vertical direction with the bottom 300mm away from the cotton pad.

[0201] Ignite for 10 seconds each time and observe the flame self-extinguishing time and molten droplet phenomenon.

[0202] Test 3 samples and record the flame retardancy level (V-0, V-1 or V-2).

[0203] Thermogravimetric analysis (TGA)

[0204] A 5–10 mg portion of the sample was cut and placed in the TGA instrument.

[0205] The temperature was raised to 800°C at 10°C / min in a nitrogen environment.

[0206] Record the mass change curve of the sample and calculate the carbon residue rate.

[0207] Experimental data:

[0208] Table 1: Comparison of oxygen index, vertical combustion and thermal stability test data

[0209] Test items Example 1 Comparative Example 1 Oxygen index (LOI, %) 37.2 32.5 UL-94 Rating V-0 V-1 Self-extinguishing time(s) 4.8 9.2 Carbon residue rate (%) 35.1 28.3 Decomposition starting temperature (℃) 318 305

[0210] The significance of introducing disulfide bond monomers into the dynamic covalent network lies in its breaking and releasing characteristics under high temperature conditions. Experiments show that the introduction of disulfide bond monomers greatly improves the flame retardant efficiency of the material. The oxygen index of Example 1 is significantly higher than that of Comparative Example 1, and the self-extinguishing time of the sample in vertical combustion is shorter. The disulfide bond breaks at high temperature to release sulfur radicals (S·), which quickly capture the free radical chain in combustion, thereby effectively inhibiting the spread of flames.

[0211] Thermogravimetric analysis shows that the introduction of disulfide bond monomers increases the carbon residue rate. Compared with Comparative Example 1, the carbon residue rate of Example 1 is increased by 6.8%. This is because the products generated after the disulfide bond breaks can be further cross-linked to form a dense carbon layer. This carbon layer not only effectively isolates oxygen and heat, but also enhances the high-temperature stability of the material. In a nitrogen environment, the decomposition starting temperature of Example 1 is 13°C higher than that of Comparative Example 1, showing better thermal stability.

[0212] The synergistic effect of the disulfide monomers, together with the acylhydrazone bonds and boron-oxygen bonds, enables the dynamic network to release functional gases at different stages of flame propagation while generating a high-quality carbon layer. Compared with Comparative Example 1 in which the disulfide monomers are omitted, Example 1 exhibits stronger flame retardant properties during the combustion stage. This multifunctional synergistic mechanism shows that the present invention has significant advantages in solving the problem of single dynamic network function in traditional flame retardant materials.

[0213] Experiment 2:

[0214] Purpose

[0215] The effect of quaternary ammonium salt-modified chitosan in the phosphorus-nitrogen synergistic flame retardant system was verified. By comparing Example 2 with Comparative Example 2, its charring performance, thermal insulation ability and carbon layer structure were tested, and the effect of modified chitosan on flame retardancy was evaluated.

[0216] Experimental materials and equipment

[0217] Sample: The flame retardant sheet prepared in Example 2 and Comparative Example 2, with a size of 100 mm×100 mm×3 mm.

[0218] equipment:

[0219] Cone calorimeter: used to test heat release rate (HRR), total heat release (THR) and carbon residue rate.

[0220] Scanning electron microscope (SEM): used to observe the microstructure of the carbon layer.

[0221] Infrared thermal imager: used to evaluate surface temperature distribution during combustion.

[0222] Experimental procedures

[0223] Carbon forming performance test

[0224] According to ISO5660 standard, the sample is fixed on the sample holder of the cone calorimeter.

[0225] The heating radiation flux is set to 50kW / m 2 , record the heat release rate (HRR), total heat release (THR) and carbon residue rate during combustion.

[0226] Each group was tested 3 times and the average value was taken.

[0227] Observation of carbon layer structure

[0228] After the combustion was completed, samples were taken and the microstructure of the carbon layer was observed using a scanning electron microscope (SEM).

[0229] The compactness, pore structure and homogeneity of the carbon layer were recorded.

[0230] Thermal insulation capability test

[0231] During the combustion process, an infrared thermal imager was used to monitor the sample surface temperature.

[0232] At 3 minutes and 5 minutes of combustion, the maximum temperature and temperature distribution image of the sample surface were recorded respectively.

[0233] Experimental data:

[0234] Table 2: Comparison of test data of carbonization performance and thermal insulation ability

[0235] Test items Example 2 Comparative Example 2 <![CDATA[Heat release rate (HRR, kW / m 2 )]]> 120.4 158.9 <![CDATA[Total Heat Release (THR, MJ / m 2 )]]> 18.3 24.6 Carbon residue rate (%) 33.2 26.4 Maximum surface temperature (3 minutes, °C) 297 334 Maximum surface temperature (5 minutes, °C) 364 410

[0236] The introduction of modified chitosan showed significant advantages in carbonization performance. Cone calorimeter data showed that the carbon residue rate of Example 2 was significantly higher than that of Comparative Example 2, and its heat release rate (HRR) was reduced by 38.5 kW / m 2 The quaternary ammonium salt in the modified chitosan not only improves the carbon-forming ability of the material, but also improves the stability of the carbonaceous material during pyrolysis through the synergistic effect of phosphorus and nitrogen. Compared with ordinary chitosan, its chemical structure is more conducive to reacting with ammonium polyphosphate to form a dense carbon layer.

[0237] From the microstructure of the carbon layer, the carbon layer of Example 2 is dense and uniform, with fewer pores and a more compact structure. However, the pore structure of the carbon layer of Comparative Example 2 is larger, and the continuity of the carbon layer is poor. The results of scanning electron microscopy show that the quaternary ammonium salt modification not only improves the compatibility of chitosan and ammonium phosphate, but also improves the mechanical stability of the carbon layer under high temperature conditions. This mechanism of action directly enhances the heat insulation and protection effects of the carbon layer.

[0238] Infrared thermal imaging monitoring found that the surface temperature of the sample in Example 2 was significantly lower than that in Comparative Example 2, especially after 5 minutes of burning, the temperature difference reached 46°C. This shows that the dense carbon layer generated by the modified chitosan has better thermal insulation ability. Combined with the above mechanism, the modified chitosan in the phosphorus-nitrogen synergistic system greatly improves the overall performance of the flame retardant by enhancing the physical barrier effect of the carbonization reaction and the flame retardant layer, while the carbon layer of the unmodified chitosan is not dense enough and the thermal insulation performance is relatively weak.

[0239] Experiment 3:

[0240] Purpose

[0241] The role of magnesium aluminum layered double hydroxide (LDH) in the flame retardant was verified, and its influence on the flame retardant performance, thermal stability and smoke density was evaluated by comparing Example 1 with Comparative Example 3.

[0242] Experimental materials and equipment

[0243] Sample: The flame retardant sheet prepared in Example 1 and Comparative Example 3, with a size of 100 mm×10 mm×3 mm.

[0244] equipment:

[0245] Oxygen index tester: used to determine the minimum oxygen concentration that supports combustion.

[0246] UL-94 combustion tester: used for vertical combustion performance test.

[0247] Thermogravimetric Analyzer (TGA): used to analyze thermal decomposition characteristics and carbon residue rate.

[0248] Smoke density tester: used to measure the amount of smoke generated during the combustion process.

[0249] Experimental procedures

[0250] Oxygen Index Test (LOI)

[0251] According to ASTM D2863 standard, fix the sample in the oxygen index tester.

[0252] Adjust the oxygen concentration in the oxygen-nitrogen mixed gas flow, start igniting the sample from a lower oxygen concentration, gradually adjust the oxygen concentration, and record the lowest oxygen concentration that supports combustion.

[0253] UL-94 vertical burning test

[0254] According to the UL-94 standard, fix the sample in a vertical direction and observe the flame extinguishing time after ignition for 10 seconds.

[0255] Record the self-extinguishing time, dripping phenomenon and flame retardant grade (V-0, V-1, V-2).

[0256] Thermogravimetric analysis (TGA)

[0257] 5–10 mg of the sample was cut and placed in a thermogravimetric analyzer. The temperature was raised to 800 °C at 10 °C / min in a nitrogen environment.

[0258] Record the mass change curve and carbon residue rate.

[0259] Smoke density test

[0260] According to ASTM D2843 standard, the sample is placed in the smoke density tester and the smoke generation is recorded during the combustion process.

[0261] Take 3 samples and calculate the average smoke density.

[0262] Experimental data:

[0263] Table 3: Comparison of flame retardant performance and smoke density test data

[0264] Test items Example 1 Comparative Example 3 Oxygen index (LOI, %) 37.5 30.8 UL-94 Rating V-0 V-2 Self-extinguishing time(s) 5.2 11.7 Carbon residue rate (%) 35.8 27.4 Decomposition starting temperature (℃) 319 303 Smoke density (SDR, %) 56 78

[0265] The introduction of magnesium aluminum layered double hydroxide (LDH) significantly improves the comprehensive performance of the flame retardant, especially the oxygen index and vertical combustion performance. The oxygen index of Example 1 reaches 37.5%, which is 6.7% higher than that of Comparative Example 3. In the UL-94 test, the sample of Example 1 reached the V-0 level, while Comparative Example 3 was only V-2 level. This significant difference is closely related to the physical barrier formed by the LDH layer during the combustion process. The metal oxides produced by the decomposition of LDH form a protective layer on the surface of the material, which effectively prevents oxygen diffusion and heat conduction, thereby significantly reducing the combustion rate.

[0266] From the thermogravimetric analysis, the carbon residue rate of Example 1 is increased by 8.4% compared with that of Comparative Example 3, and the decomposition starting temperature is also increased by 16°C. This shows that the oxides generated by the decomposition of LDH at high temperature can promote the formation of the carbon layer and improve its stability. This effect not only delays the thermal decomposition process of the material, but also enhances the mechanical strength under high temperature conditions, so that the carbon layer plays a more lasting role in heat insulation and oxygen isolation during flame propagation.

[0267] In the smoke density test, the smoke density of Example 1 was 56%, which was 22% lower than that of Comparative Example 3. LDH decomposes and absorbs heat during combustion, inhibiting the release of combustible gases, while reducing the generation of smoke by forming a physical barrier. Compared with Comparative Example 3 in which LDH is omitted, Example 1 shows significant advantages in smoke suppression and the density of combustion residues. This further verifies the core role of LDH in multifunctional synergistic flame retardants, which effectively improves the overall performance of flame retardants through the dual mechanisms of physical barrier and chemical synergy.

[0268] Experiment 4:

[0269] Purpose

[0270] Evaluation of the catalytic components (Zn 2+ or Fe 3+ ) on the charring ability of the flame retardant and the performance of the char layer. By comparing Example 3 with Comparative Example 4, the role of the catalyst in the charring reaction is analyzed.

[0271] Experimental materials and equipment

[0272] Sample: The flame retardant sheet prepared in Example 3 and Comparative Example 4, with a size of 100 mm×10 mm×3 mm.

[0273] equipment:

[0274] Thermogravimetric Analyzer (TGA): used to analyze thermal decomposition characteristics and carbon residue rate.

[0275] Cone calorimeter: used to test the charring performance during the combustion process.

[0276] Nanoindenter: used to measure the hardness and modulus of the carbon layer after combustion.

[0277] Experimental procedures

[0278] Thermogravimetric analysis (TGA)

[0279] A 5–10 mg portion of the sample was placed in a thermogravimetric analyzer.

[0280] The temperature was raised to 800°C at 10°C / min in a nitrogen environment.

[0281] The curve of mass change with temperature was recorded, and the carbon residue rate at 500°C and 800°C was measured.

[0282] Carbon forming performance test

[0283] According to ISO5660 standard, the sample was placed in a cone calorimeter and the radiation flux was set to 50kW / m 2 .

[0284] The heat release rate (HRR), total heat release (THR) and carbon residue rate were recorded during the combustion process.

[0285] Each group was tested 3 times and the average value was taken.

[0286] Carbon layer mechanical properties test

[0287] The carbon layer on the sample surface was collected after combustion, and the hardness and modulus of the carbon layer were measured using a nanoindenter.

[0288] Three different areas were tested and the average values ​​of hardness and modulus were recorded.

[0289] Experimental data:

[0290] Table 4: Effect of catalytic components on carbonization ability and carbon layer performance

[0291] Test items Example 3 Comparative Example 4 Carbon residue rate (500℃,%) 45.8 37.6 Carbon residue rate (800℃,%) 34.7 26.1 <![CDATA[Heat Release Rate (HRR, kW / m 2 )]]> 110.6 149.3 <![CDATA[Total Heat Release (THR, MJ / m 2 )]]> 16.2 22.8 Carbon layer hardness (MPa) 4.2 2.8 Carbon layer modulus (GPa) 0.51 0.34

[0292] The catalytic component plays a significant role in promoting the carbonization reaction. Experimental data show that the carbon residue rates of Example 3 at 500°C and 800°C are 45.8% and 34.7%, respectively, which are 8.2% and 8.6% higher than those of Comparative Example 4. 2+ or Fe 3+ The redox reaction under high temperature conditions accelerates the breaking and reorganization of chemical bonds in the dynamic network, promoting the formation of high-quality carbon layers. This catalytic effect not only enhances the carbonization efficiency, but also reduces the release of combustible gases during pyrolysis.

[0293] From the combustion performance test, the introduction of the catalytic component reduces the heat release rate (HRR) and the total heat release (THR). The HRR of Example 3 is reduced by 38.7 kW / m compared with that of Comparative Example 4. 2 , THR decreased by 6.6MJ / m 2 . This shows that the catalyst improves the density of the carbon layer by promoting carbonization, so that more heat is absorbed and isolated by the carbon layer during the combustion process. In addition, the hardness and modulus test results of the carbon layer further support this point. The hardness and modulus of the carbon layer in Example 3 are 4.2MPa and 0.51GPa, respectively, which are much higher than those in Comparative Example 4. This enhanced mechanical property reflects the strengthening effect of the catalytic component on the carbon layer structure.

[0294] The role of the catalytic component is not limited to the improvement of carbonization efficiency, but also significantly optimizes the microstructure of the carbon layer. Compared with the comparative example 4 without the addition of the catalytic component, the carbon layer generated by Example 3 is more dense and uniform, and the cracks are significantly reduced. This high-density carbon layer provides a stronger thermal insulation barrier during the combustion process, effectively reducing the rate of flame propagation and heat diffusion. From a mechanistic point of view, Zn2+ or Fe3+ promotes the breakage and reorganization of the dynamic network through synergistic effects, coupled with the formation reaction of the carbon layer, to achieve a significant improvement in flame retardant properties.

[0295] Experiment 5:

[0296] Purpose

[0297] The effects of different ratios of polylactic acid (PLA) and polyhydroxyalkanoate (PHA) in the matrix material on the degradation performance and mechanical properties of the flame retardant were verified, and the superiority of the copolymer design was analyzed by comparing Example 3 with Comparative Example 4 (single PLA matrix).

[0298] Experimental materials and equipment

[0299] Sample: The flame retardant sheet prepared in Example 3 and Comparative Example 4, with a size of 100 mm×10 mm×3 mm.

[0300] equipment:

[0301] Biodegradability testing equipment: used to evaluate the degradation rate and morphological changes of samples.

[0302] Tensile testing machine: used to determine the changes in mechanical properties of samples before and after degradation.

[0303] Scanning electron microscopy (SEM): used to observe the surface morphology after degradation.

[0304] Experimental procedures

[0305] Composting test

[0306] The samples were placed in a simulated composting environment (temperature 55° C., humidity 70%, compost soil containing nutrients).

[0307] Take out the samples every 15 days, clean the surface and record the quality changes of the samples.

[0308] The degradation rate at 30 days and 60 days was calculated using the formula:

[0309]

[0310] Biodegradability Testing

[0311] The samples were placed in a neutral soil environment (60% humidity, 25°C).

[0312] Record the quality changes and appearance of the samples within 3 months and evaluate their degradation.

[0313] Mechanical properties test

[0314] The tensile strength and elastic modulus before and after degradation were measured using a tensile testing machine.

[0315] The test speed was 10 mm / min, 5 samples were tested in each group, and the average value was taken.

[0316] Surface morphology observation

[0317] The surface morphology of the degraded samples was observed using a scanning electron microscope (SEM) to record features such as cracks and pores.

[0318] Experimental data

[0319] Table 5: Effect of PLA to PHA ratio on degradation and mechanical properties

[0320] Test items Example 3 Comparative Example 4 Composting degradation rate (30 days, %) 55.8 33.2 Composting degradation rate (60 days, %) 88.3 45.6 Soil degradation rate (90 days, %) 95.4 60.2 Tensile strength before degradation (MPa) 48.2 54.6 Tensile strength after degradation (MPa) 25.8 15.4 Elastic modulus before degradation (GPa) 1.72 1.94 Elastic modulus after degradation (GPa) 0.98 0.52

[0321] The copolymerization design of PLA and PHA shows significant advantages in terms of degradability. In the composting degradation test, the degradation rates of Example 3 at 30 days and 60 days were 55.8% and 88.3%, respectively, which were significantly higher than those of Comparative Example 4. This shows that the introduction of PHA significantly improves the degradation ability of the flame retardant in a composting environment, and its flexible chain structure is more easily broken and degraded under high humidity and microbial action. In contrast, the degradation rate of a single PLA matrix is ​​slower, and more fragments remain undegraded.

[0322] From the perspective of mechanical property changes, the tensile strength and elastic modulus of Example 3 after degradation are significantly higher than those of Comparative Example 4. This reflects that the PLA and PHA copolymer design maintains better mechanical property stability during the degradation process. The tensile strength of Example 3 is 25.8 MPa after degradation, while that of Comparative Example 4 is only 15.4 MPa. The introduction of PHA forms a copolymer structure with higher flexibility, effectively disperses stress concentration in the early stage of degradation, and avoids the rapid decline of mechanical properties.

[0323] Surface morphology observations showed that Example 3 formed relatively uniform cracks and pores after degradation, while the surface of Comparative Example 4 showed irregular large-scale peeling. This difference is attributed to the synergistic effect of PLA and PHA, which formed a more uniform decomposition pattern during the degradation process. The flexible chain of PHA not only accelerates the degradation process, but also improves the residual structure after carbonization, so that the copolymer matrix exhibits better balanced performance in combustion and degradation. In summary, the copolymerization design of PLA and PHA overcomes the problems of poor degradability and rapid attenuation of mechanical properties of a single PLA matrix, and achieves a balance between degradability and mechanical properties.

[0324] Experiment 6:

[0325] Purpose

[0326] The effect of the ratio of acylhydrazone monomer to disulfide bond monomer in the dynamic network component on the flame retardant performance was verified. By comparing Example 1 with Comparative Example 6 (adjusting the disulfide bond monomer to a high ratio), the effect of the ratio change on the dynamic network reaction mechanism and flame retardant performance was analyzed.

[0327] Experimental materials and equipment

[0328] Sample: The flame retardant sheet prepared in Example 1 and Comparative Example 6, with a size of 100 mm×10 mm×3 mm.

[0329] equipment:

[0330] Oxygen Index Tester: Determines the minimum oxygen concentration that supports combustion.

[0331] Dynamic Mechanical Analyzer (DMA): measures the changes in mechanical properties of samples after dynamic network ratio adjustment.

[0332] Thermogravimetric Analyzer (TGA): used to analyze thermal decomposition characteristics and carbon residue rate.

[0333] Experimental procedures

[0334] Oxygen Index Test (LOI)

[0335] According to ASTM D2863 standard, fix the sample in the oxygen index tester.

[0336] Adjust the oxygen concentration in the oxygen-nitrogen mixed gas flow, ignite the sample, gradually adjust the oxygen ratio, and record the minimum oxygen concentration that supports combustion.

[0337] Dynamic Mechanical Analysis (DMA)

[0338] A DMA device was used with a sample size of 50 mm × 5 mm × 3 mm.

[0339] The temperature rise range is from room temperature to 300°C, the heating rate is 5°C / min, and the storage modulus and loss modulus change curves of the test samples are shown.

[0340] Thermogravimetric analysis (TGA)

[0341] 5–10 mg of the sample was cut and placed in a thermogravimetric analyzer. The temperature was raised to 800 °C at 10 °C / min in a nitrogen environment.

[0342] The carbon residue rate was measured, and the decomposition starting temperature and the maximum weight loss rate temperature were recorded.

[0343] Experimental data

[0344] Table name: Effect of dynamic network component ratio on flame retardancy and mechanical properties

[0345] Test items Example 1 Comparative Example 6 Oxygen index (LOI, %) 37.4 31.6 Carbon residue rate (800℃,%) 35.3 28.5 Decomposition starting temperature (℃) 320 305 Storage modulus (25℃, MPa) 1456 1085 Storage modulus (300℃, MPa) 364 210 Maximum weight loss rate temperature (℃) 429 410

[0346] The adjustment of the ratio of acylhydrazone monomers to disulfide monomers in the dynamic network component has a significant effect on the material properties. The reasonable ratio of disulfide monomers in Example 1 makes the oxygen index reach 37.4%, which is much higher than 31.6% in Comparative Example 6. The experimental results show that an excessively high ratio of disulfide monomers leads to the destruction of the chemical balance of the dynamic network. The cleavage of too many disulfide bonds under high temperature conditions cannot form a stable synergistic flame retardant mechanism, but only releases excess sulfur free radicals, which inhibits the continuous flame retardant effect after the cleavage of the acylhydrazone bond.

[0347] The results of thermogravimetric analysis further verified this point. The carbon residue rate of Example 1 is 35.3%, which is 6.8% higher than that of Comparative Example 6. A reasonable proportion of disulfide bond monomers can break at high temperatures to generate sulfur free radicals, which synergize with the decomposition products of acylhydrazone bonds to generate a dense carbon layer. However, an excessively high proportion of disulfide bonds results in an insufficiently dense carbon layer, with more surface cracks, which significantly reduces the heat insulation and oxygen isolation properties. The decomposition starting temperature also shows that Example 1 has better thermal stability and can effectively delay the occurrence of thermal decomposition.

[0348] From the perspective of dynamic thermomechanical analysis (DMA), the storage modulus of Example 1 is higher than that of Comparative Example 6 at both 25°C and 300°C, and it exhibits better mechanical stability in the high temperature stage in particular. This shows that a reasonable ratio of acylhydrazone bonds and disulfide bonds can form a stronger cross-linked structure in the dynamic network, thereby improving the rigidity and stability of the material. On the contrary, Comparative Example 6 has an excessively high ratio of disulfide bonds and an excessive number of flexible chain structures in the dynamic network, which weakens the high-temperature mechanical properties of the material. On the whole, the balanced ratio of acylhydrazone monomers and disulfide bond monomers is the key to optimizing the multifunctional properties of flame retardants, and unreasonable changes in their ratios will significantly weaken the synergistic flame retardant effect and high-temperature stability of the dynamic network.

[0349] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A degradable and environmentally friendly flame retardant, characterized in that: The flame retardant is composed of the following components in proportion by mass: Dynamic covalent network components: 20-40 parts; It includes 5 to 15 parts of acylhydrazone monomer, 5 to 10 parts of disulfide bond monomer, and 5 to 10 parts of boron-oxygen bond monomer; Phosphorus-nitrogen synergistic flame retardant system: 20-35 parts; It includes 10 to 20 parts of ammonium polyphosphate, 5 to 15 parts of quaternary ammonium salt modified chitosan, and 1 to 5 parts of borate; Nano self-assembly material: 5-10 parts; Catalytic component: 0.1-1 part; Biodegradable polymer matrix: 40-60 parts.

2. A degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The acylhydrazone monomer is a reaction product of p-hydroxybenzaldehyde and hydrazine, and its addition ratio is 25-50% of the total mass of the dynamic covalent network component.

3. A degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The disulfide bond monomer is dithioacetic acid or dithiopropionic acid.

4. A degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The quaternary ammonium salt modified chitosan in the phosphorus-nitrogen synergistic flame retardant system is prepared by the following method: dissolving chitosan in 10-20wt% acetic acid solution, adding quaternary ammonium salt to react for 60-90 minutes, and then neutralizing to pH 7-8.

5. The degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The nanometer self-assembly material is magnesium-aluminum layered double hydroxide, wherein the molar ratio of magnesium ions to aluminum ions is 2.5-3.5:

1.

6. The degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The catalytic component includes Zn 2+ or Fe 3+ The addition form is 0.1-1M metal salt solution, which is introduced into the dynamic network by adsorption method.

7. The degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The biodegradable polymer matrix is ​​a copolymer of polylactic acid and polyhydroxyalkanoate, and the mass ratio of the copolymer of polylactic acid and polyhydroxyalkanoate is 1:1 to 3:

1.

8. The method for preparing a degradable and environmentally friendly flame retardant according to claim 1, characterized in that: The following steps are involved: S1. Construction of dynamic network: mixing acylhydrazone monomer, disulfide bond monomer and boron-oxygen bond monomer at a temperature of 50 to 90° C. and a pH of 6 to 8, and stirring for 1 to 2 hours; S2. Compounding of phosphorus-nitrogen synergistic groups: Mix ammonium polyphosphate solution and quaternary ammonium salt modified chitosan solution in a mass ratio of 1:2, add borate, and stir at 50-70° C. for reaction for 90-120 minutes; S3, preparation of nanosheet material: preparing magnesium aluminum layered double hydroxide by solution coprecipitation method at pH 10, washing, drying and grinding into powder; S4, blending and molding: blending the materials obtained in steps S1, S2 and S3 with a biodegradable polymer matrix to prepare flame retardant particles at 170-200° C. by melt blending; S5. Catalyst introduction: Add Zn at the end of blending 2+ or Fe 3+ Salt solution, mix evenly and solidify into shape.

9. The method for preparing a degradable and environmentally friendly flame retardant according to claim 8, characterized in that: In the step S1, the amount of acylhydrazone monomer added is 25-50% of the total mass of the dynamic network, and the amount of disulfide bond monomer added is 10-30%.

10. The method for preparing a degradable and environmentally friendly flame retardant according to claim 8, characterized in that: The blending shear rate in step S4 is 20-50 rpm, the pressure is 5-10 MPa, and the time is 5-10 minutes.

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