Preparation method and application of modified fish scale single-component intumescent flame retardant

Abstract

The present invention discloses a modified fish scale single-component intumescent flame retardant, its preparation method and application. The present invention uses sodium alginate, fish scale, phytic acid, aluminum salt and melamine as raw materials, and prepares a "three-source-in-one" modified fish scale single-component intumescent flame retardant through a one-pot process. The preparation process of the flame retardant of the present invention is simple and safe. Most of the raw materials are derived from low-cost fishery waste and green renewable biomass materials. It is environmentally friendly and highly compatible with polymers. It has little effect on the mechanical properties of composite materials. It has high flame retardant efficiency when applied to PLA and can effectively suppress its melt dripping.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-biomass-based polymer flame retardant, and specifically relates to a modified fish scale single-component intumescent flame retardant, and a preparation method and application thereof. Background Art

[0002] Polylactic acid (PLA) is a linear aliphatic polyester extracted from agricultural crops. It is abundant and renewable, and can be completely degraded into CO2 and H2O, making it an environmentally friendly green resource. Its excellent biocompatibility and processability have led to its widespread application in food packaging, biomedicine, and industrial and agricultural production. However, PLA's thermal stability is inferior to that of traditional thermoplastics, and its limiting oxygen index (LOI) is very low (only around 20%). At high temperatures, it burns, producing large amounts of molten droplets and inducing secondary combustion. This makes it a flammable material, posing a significant safety hazard in daily life and industrial production, limiting its application. Therefore, research on flame-retardant modification of PLA is extremely important.

[0003] Flame retardants commonly used to enhance the flame retardancy of PLA include halogen-based flame retardants, phosphorus-based flame retardants, metal hydroxide flame retardants, and intumescent flame retardants (IFRs). Halogen-based flame retardants are gradually being phased out due to their high toxicity and pollution. Intumescent flame retardants, which combine carbon, phosphorus, and nitrogen, have emerged as promising candidates due to their low dosage, high flame retardancy, and low toxicity. Among these, new biomass-based intumescent flame retardants are attracting attention from researchers due to their excellent biocompatibility, environmental friendliness, and renewable nature.

[0004] Phytic acid (PA) contains 28% phosphorus and is primarily found in plant seeds and rhizomes. It is an important phosphorus-containing substance and a green, renewable natural resource. Its structural formula contains six negatively charged phosphate groups, which can chelate with metal ions in aqueous solution and react with ammonium ions to form a large amount of precipitate. As an emerging biomass material, PA has significant development potential in flame-retardant polymers. PA can be used alone as a phosphorus-based flame retardant or as an acid source in conjunction with other flame retardants. During combustion and heating, polyphosphates are released in the condensed phase, promoting the expansion of the matrix to form a protective carbon layer, terminating the chain reaction in the gas phase, and promoting the generation of inert gas from the gas source.

[0005] Sodium alginate (SA) is the sodium salt of the natural polysaccharide alginic acid, primarily extracted from the cell walls of brown algae. It appears as a pale yellow powder that dissolves readily in water to form a viscous liquid. It is characterized by high biocompatibility, environmental friendliness, low toxicity, and relatively low cost. Although sodium alginate has excellent carbon-forming properties as a carbon source, its thermal stability is poor and requires modification for use in flame-retardant materials. Alginate forms an "egg-box" microstructure with divalent and trivalent metal ions, allowing for mild gelation modification. By varying the metal ion content and pH value, the pyrolysis behavior and flame retardancy of sodium alginate can be adjusted, effectively suppressing the formation of molten droplets.

[0006] Fish scales (FS), a crucial byproduct of fishery processing, have long been wasted as waste, with immature processing and recycling methods causing significant environmental pollution. Fish scales are primarily composed of collagen and hydroxyapatite. Scale proteins, as polymers of various amino acids, possess diverse structures and excellent biocompatibility. They can form flame-retardant systems through strong electrostatic attraction with biomass compounds, making them a natural nitrogen-containing flame retardant. Scale proteins produce non-combustible gases such as NH3 and H2O during combustion and possess excellent carbon-promoting properties. In the condensed phase, they can cross-link with PLA degradation products to form char, effectively suppressing the dense smoke produced by combustion. Therefore, they can be developed into a biomass flame retardant for PLA, offering low cost, abundant resources, and sustainability.

[0007] The present invention uses sodium alginate and phytic acid to chemically modify fish scales, with sodium alginate as a carbonizing agent, phytic acid as an acid source, and fish scale protein as a nitrogen source and a "bridge", synergistically melamine and active Al 3+ The synthesis of a biomass-based intumescent flame retardant is conducted. This new flame retardant is low-cost, has appropriate amounts of C, N, and P, has high flame retardancy, can effectively suppress smoke and prevent secondary combustion caused by molten droplets, and its raw materials are renewable green resources, with broad application prospects and economic value. Summary of the Invention

[0008] The present invention aims to provide a preparation method and application of a modified fish scale single-component intumescent flame retardant. The obtained flame retardant has the advantages of using renewable materials, good thermal stability, strong compatibility with PLA, high flame retardant efficiency and anti-drip, and has broad application prospects and application value in PLA.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for preparing a modified fish scale single-component intumescent flame retardant, comprising the following steps:

[0011] (1) washing the fish scales with clean water, drying, and crushing them to obtain fish scale powder;

[0012] (2) Slowly add sodium alginate into deionized water and stir to dissolve at 50-70°C to obtain a sodium alginate solution;

[0013] (3) Add fish scale powder to deionized water to form a suspension, stir evenly, and then add 1 mol / L dilute acid solution at 70-100 °C and react for 0.5-1.0 h to obtain a fish scale solution;

[0014] (4) Adding sodium alginate solution dropwise to the fish scale solution obtained in step (3), stirring and reacting at 70-100°C for 1.0-2.0 h to obtain an alginate-modified fish scale suspension;

[0015] (5) Slowly add phytic acid to the sodium carbonate solution, stir evenly, and let it stand at room temperature for 5-10 minutes to obtain a sodium phytate solution;

[0016] (6) Sodium phytate solution was added dropwise to the alginate-modified fish scale suspension obtained in step (4), and the mixture was stirred at 70-100°C for 3.0-4.0 h. Aluminum salt and melamine were added and stirred for 1.0-2.0 h.

[0017] (7) Adding 5% by mass of sodium carbonate solution to the solution obtained in step (6) to adjust the pH to neutral, aging and then washing, vacuum filtering, and drying, crushing and sieving the filtered product to obtain the modified fish scale single-component intumescent flame retardant.

[0018] Furthermore, the fish scales in step (1) are one or more of mackerel scales and crucian carp scales; the drying temperature is 60-80°C and the drying time is 24-36 hours.

[0019] Furthermore, the amount of the dilute acid solution used in step (3) is 12-15 mL per 5 g of fish scales; the acid used is one or more of acetic acid, hydrochloric acid, and nitric acid; and the fish scales are one or more of mackerel scales and crucian carp scales.

[0020] Furthermore, the amount of phytic acid used in step (5) is such that the mass ratio of phytic acid to sodium alginate and fish scale is (6.6-9.9):5:5; the mass concentration of the sodium carbonate solution is 10%, and the amount used is 65-75 mL per 10 g of phytic acid.

[0021] Furthermore, the amount of aluminum salt and melamine used in step (6) is as follows: 3+ , the molar ratio of melamine to phytic acid is 1:2:1; the aluminum salt is one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0022] Furthermore, the aging time in step (7) is 12-24 h; the drying temperature is 70-100 °C and the drying time is 12-24 h.

[0023] Furthermore, the stirring rate in steps (2) to (7) is 200-500 rpm.

[0024] The present invention also provides a modified fish scale single-component intumescent flame retardant.

[0025] The modified fish scale one-component intumescent flame retardant can be applied to PLA flame retardancy, and the steps are: adding the modified fish scale one-component intumescent flame retardant to PLA, and the addition amount is 3%-10% of the mass of PLA.

[0026] The beneficial effects of the present invention are:

[0027] (1) The raw materials of the present invention are mainly low-cost fishery waste and green renewable biomass materials, which are environmentally friendly and have a wide range of sources.

[0028] (2) The present invention prepares the modified fish scale single-component intumescent flame retardant by a one-pot method. The entire reaction is carried out in the aqueous phase, and there is no need to separate the intermediate product. The final product is a large amount of white precipitate that is easy to extract. The processing performance is good, the preparation process is simple and safe, and no toxic and harmful gases are generated, which makes it easy to realize industrial production.

[0029] (3) When the modified fish scale single-component intumescent flame retardant is added to PLA at a concentration of 10 wt%, its flame retardant grade can reach UL94 V-0. It has high flame retardant efficiency, can effectively prevent molten dripping, has strong compatibility with polymers, and has little effect on the mechanical properties of composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Synthesis process diagram of the all-biobased single-component intumescent flame retardant of the present invention.

[0031] Figure 2 : FT-IR images of the fully bio-based single-component intumescent flame retardants prepared in Examples 1 and 2.

[0032] Figure 3 : SEM image of the carbon layer after combustion of the sample prepared in Example 1.

[0033] Figure 4 : SEM image of the carbon layer after combustion of the sample prepared in Example 2.

[0034] Figure 5 : SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 1.

[0035] Figure 6: SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 2.

[0036] Figure 7 : SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 3.

[0037] Figure 8 : SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 4. DETAILED DESCRIPTION

[0038] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0039] Example 1

[0040] Mackerel scales were washed with clean water, dried in an oven at 80°C for 24 h, and then crushed using a wall crusher to obtain mackerel scale powder. 5 g of sodium alginate was slowly added to a beaker containing 200 mL of deionized water. The sodium alginate was dissolved at 60°C using magnetic stirring at 400 rpm and ultrasonic vibration to obtain a sodium alginate solution. 5 g of mackerel scale powder was added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. 200 mL of deionized water was poured into the flask to form a suspension. After stirring at 300 rpm, 12 mL of acetic acid (1 mol / L) was added and the mixture was reacted at 70°C for 1 h to obtain a milky white fish scale solution. The above sodium alginate solution was then added dropwise and the mixture was reacted at 80°C and 500 rpm for 1 h to obtain a sodium alginate-modified fish scale suspension. 9.43 g (70 wt %, 0.01 mol) of phytic acid was added dropwise to 63.6 mL of 10% Na2CO3 solution. The mixture was stirred evenly with a magnetic stirrer at 200 rpm and allowed to stand at room temperature for 5 min. The mixture was then slowly added to the sodium alginate-modified fish scale suspension through a separatory funnel and reacted at 90°C for 4.0 h. 3.33 g (0.005 mol) of aluminum sulfate 18hydrate and 2.52 g (0.02 mol) of melamine were then added and the reaction was continued with stirring for 1.5 h. Finally, 5 wt % sodium carbonate solution was added to adjust the pH to neutral. The resulting reaction suspension was aged for 12.0 h, vacuum filtered, and washed with anhydrous ethanol. The filtered product was dried in an oven at 70°C for 24.0 h, crushed, and passed through a 200-mesh sieve to obtain a modified fish scale single-component intumescent flame retardant.

[0041] Example 2

[0042] Crucian carp scales were washed with clean water, dried in an oven at 60°C for 36.0 h, and then crushed using a wall-breaking machine to obtain crucian carp scale powder. 5 g of sodium alginate was slowly added to a beaker containing 200 mL of deionized water. The sodium alginate was dissolved at 60°C using magnetic stirring at 400 rpm and ultrasonic vibration to obtain a sodium alginate solution. 5 g of crucian carp scale powder was added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. 200 mL of deionized water was poured into the flask to form a suspension. After stirring at 300 rpm, 12 mL of citric acid solution (1 mol / L) was added and the mixture was reacted at 70°C for 1.0 h to obtain a milky white fish scale solution. The above sodium alginate solution was then added dropwise and the mixture was reacted at 80°C and 500 rpm for 1.0 h to obtain a sodium alginate-modified fish scale suspension. 9.43 g (70 wt %, 0.01 mol) of phytic acid was added dropwise to 63.6 mL of 10% Na2CO3 solution. The mixture was stirred evenly at 200 rpm and allowed to stand at room temperature for 5 min. The mixture was then slowly added to the sodium alginate-modified fish scale suspension through a separatory funnel and reacted at 90°C for 4.0 h. 3.33 g (0.005 mol) of aluminum sulfate 18hydrate and 2.52 g (0.02 mol) of melamine were then added and the reaction was continued with stirring for 1.5 h. Finally, 5 wt % sodium carbonate solution was added to adjust the pH to neutral. The resulting reaction suspension was aged for 12.0 h, vacuum filtered, and washed with anhydrous ethanol. The filtered product was dried in an oven at 80°C for 12.0 h, crushed, and passed through a 200-mesh sieve to obtain a modified fish scale single-component intumescent flame retardant.

[0043] Figure 2 The FT-IR images of the modified fish scale single-component intumescent flame retardant prepared in Examples 1 and 2 are shown in Figure 1. Compared with the fish scale, the flame retardants prepared in Examples 1 and 2 have a high FT-IR value at 3150 cm -1 A new broad peak appeared near the NH stretching vibration absorption peak of melamine. -1 and 1541 cm -1 The C=O and NH stretching vibration absorption peaks of fish scale amide appear at 1663 cm -1 A PO absorption peak appears near 1145 cm -1 A P=O absorption peak appeared near the surface of the fish scale, which is the characteristic absorption peak of phytic acid. The above results indicate that the modified fish scale single-component intumescent flame retardant was successfully prepared.

[0044] Comparative Example 1

[0045] 5 g of sodium alginate was slowly added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. 200 mL of deionized water was then poured in. The sodium alginate was dissolved at 60°C using magnetic stirring at 400 rpm and ultrasonic vibration. 12 mL of 1 mol / L acetic acid solution was added to the sodium alginate solution, and the reaction was continued at 80°C and 500 rpm for 1.0 h. 9.43 g (70 wt%, 0.01 mol) of phytic acid was then added dropwise to 63.6 mL of 10% Na₂CO₃ solution. The mixture was stirred at 200 rpm and allowed to stand at room temperature for 5 min. The mixture was then slowly added dropwise to the sodium alginate solution via a separatory funnel and allowed to react at 90°C for 4.0 h to obtain an alginic acid / phytic acid solution. 3.33 g (0.005 mol) of aluminum sulfate 18hydrate and 2.52 g (0.02 mol) of melamine were then added to the three-necked flask and the reaction was continued with stirring for 1.5 hours. Finally, 5 wt% sodium carbonate solution was added to the solution to adjust the pH to neutral. The resulting reaction suspension was aged for 12 hours, vacuum filtered, and washed with anhydrous ethanol. The filtered product was dried in an oven at 70°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain a phytic acid-modified sodium alginate intumescent flame retardant.

[0046] Comparative Example 2

[0047] Mackerel scales were washed with water, dried in an oven at 80°C for 24 h, and then crushed using a wall-breaking machine to obtain mackerel scale powder. 5 g of mackerel scales were weighed and added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. 200 mL of deionized water was poured into the flask to form a suspension. After magnetic stirring at 300 rpm, 12 mL of 1 mol / L acetic acid solution was added. The mixture was reacted at 70°C for 1 h to obtain a milky white fish scale suspension. The reaction was then continued at 80°C and 500 rpm for 1 h. 9.43 g (70 wt%, 0.01 mol) of phytic acid was added dropwise to 63.6 mL of 10% Na₂CO₃ solution. The mixture was magnetically stirred at 200 rpm and allowed to stand at room temperature for 5 min. The mixture was then slowly added to the fish scale suspension via a separatory funnel and reacted at 90°C for 4 h to obtain a phytic acid-modified fish scale suspension. 3.33 g (0.005 mol) of aluminum sulfate 18hydrate and 2.52 g (0.02 mol) of melamine were then added, and the reaction was stirred for another 1.5 hours. Finally, 5 wt% sodium carbonate solution was added to the solution to adjust the pH to neutral. The resulting reaction suspension was aged for 12 hours, vacuum filtered, and washed with anhydrous ethanol. The filtered product was dried in an oven at 80°C for 12 hours, crushed, and passed through a 200-mesh sieve to obtain a phytic acid-modified fish scale single-component intumescent flame retardant.

[0048] Application Example 1

[0049] 10 parts (by mass) of the modified fish scale one-component intumescent flame retardant obtained in Example 1 and 90 parts (by mass) of PLA were weighed and stirred and uniformly mixed. The mixture was then extruded into granules and injection molded using a twin-screw extruder to produce flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and mechanical property standard test specimens for testing.

[0050] Application Example 2

[0051] 10 parts (by mass) of the modified fish scale one-component intumescent flame retardant obtained in Example 2 and 90 parts (by mass) of PLA were weighed and stirred and evenly mixed. The mixture was extruded into granules and injection molded using a twin-screw extruder to prepare flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and mechanical property standard test specimens for testing.

[0052] Figure 3 、 4 The SEM images of the char layer after combustion of the sample strips prepared in Example 1 and 2 are shown. As can be seen from the figure, the char layer has protrusions on the surface but no large number of holes are formed. It is generally uniform and smooth, indicating that it plays a role in blocking the heat source. Therefore, the sample has good flame retardant properties.

[0053] Comparative Application Example 1

[0054] Polylactic acid pellets were injection molded to produce flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and mechanical property standard test specimens for testing.

[0055] Figure 5 This is a SEM image of the char layer after combustion of the sample prepared in Comparative Example 1. As can be seen from the figure, the char layer is rough and has large holes, which cannot effectively block the heat source and does not achieve the ideal flame retardant effect.

[0056] Application Comparative Example 2

[0057] 10 parts by mass of a commercially available ammonium polyphosphate (DP>1000, phosphorus content of 30%-32%, and nitrogen content of 14%-16%) flame retardant were weighed and mixed with 90 parts by mass of PLA. The mixture was then extruded into pellets using a twin-screw extruder and injection molded to produce flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and standard mechanical property test specimens for testing.

[0058] Figure 6 This is an SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 2. As can be seen from the figure, the carbon layer has a large number of micropores, which cannot effectively block the heat source and does not achieve the ideal flame retardant effect.

[0059] Application Comparative Example 3

[0060] 10 parts (by mass) of the phytic acid-modified sodium alginate intumescent flame retardant obtained in Comparative Example 1 and 90 parts (by mass) of PLA were weighed and stirred, and then extruded into granules and injection molded using a twin-screw extruder to prepare flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and mechanical property standard test specimens for testing.

[0061] Figure 7 This is an SEM image of the char layer after combustion of the sample prepared in Comparative Example 3. As can be seen from the figure, the char layer has large pores and cannot block heat, and the ideal flame retardant effect is not achieved.

[0062] Comparative Application Example 4

[0063] 10 parts (by mass) of the phytic acid-modified fish scale single-component intumescent flame retardant obtained in Comparative Example 2 were weighed and mixed with 90 parts (by mass) of PLA, and then extruded into granules and injection molded using a twin-screw extruder to produce flame retardant test specimens (length × width × thickness = 130 mm × 10 mm × 3.2 mm) and mechanical property standard test specimens for testing.

[0064] Figure 8 This is an SEM image of the char layer after burning the sample prepared in Comparative Example 4. The char layer has large pores and cannot block heat, and the ideal flame retardant effect is not achieved.

[0065] The results of the performance tests of Application Examples 1-2 and Application Comparative Examples 1-4 are shown in Table 1.

[0066] Table 1 Flame retardant test results

[0067]

[0068] Vertical combustion tests and limiting oxygen index tests indicate that the commercially available ammonium polyphosphate flame retardant in Comparative Example 2 exhibits poor compatibility when used alone in PLA. The flame retardant effect of the burning strips is limited compared to pure PLA (Comparative Example 1), and the severe droplet formation is not significantly improved. Furthermore, the flame retardant in Comparative Example 2 may contain insufficient nitrogen, resulting in a low phosphorus-nitrogen synergistic efficiency, which prevents sufficient dilution of oxygen and combustible products in the gas phase. However, as can be seen in Examples 1 and 2, the flame retardant of the present invention exhibits excellent compatibility in PLA, resulting in significantly improved flame retardancy in the burning strips compared to Comparative Example 1.

[0069] Compared with Application Examples 1 and 2, the droplet rate of the flame-retardant strips in Application Comparative Examples 3 and 4 accelerated during combustion, the residual carbon rate was low, and the overall flame retardant effect was not ideal. Application Comparative Example 3 may be due to the fact that alginate failed to effectively compound phytate, making it difficult to catalyze the dehydration of sodium alginate to form an aromatic ring structure, and the flame retardant and PLA could not cross-link in the condensed phase to form a dense carbon layer; Application Comparative Example 4 is due to the low carbon content of the fish scales themselves, resulting in a small carbon layer formed during combustion, and the melt flowed faster during combustion. Fish scales can act as a "bridge" to connect alginate and phytate, allowing the flame retardant to integrate acid source, carbon source and gas source. Therefore, Application Examples 1 and 2 have higher flame retardant efficiency and effectively suppress the problem of melt dripping during PLA combustion.

[0070] The modified fish scale single-component intumescent flame retardant prepared by the present invention belongs to a high molecular biomass material, has good compatibility with a polylactic acid matrix, is easy to form intermolecular hydrogen bonds with polylactic acid active groups, and has little effect on the mechanical properties of the composite material.

[0071] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a modified fish scale one-component intumescent flame retardant, characterized in that: The following steps are involved: (1) washing the fish scales with clean water, drying, and crushing them to obtain fish scale powder; (2) Slowly add sodium alginate into deionized water and stir to dissolve at 50-70°C to obtain a sodium alginate solution; (3) Add fish scale powder to deionized water to form a suspension, stir evenly, and then add 1 mol / L dilute acid solution at 70-100 °C for 0.5-1.0 h to obtain a fish scale solution; (4) Adding sodium alginate solution dropwise to the fish scale solution obtained in step (3), stirring and reacting at 70-100°C for 1.0-2.0h to obtain a sodium alginate modified fish scale suspension; (5) Slowly add phytic acid to the sodium carbonate solution, stir evenly, and let it stand at room temperature for 5 minutes to obtain a sodium phytate solution; (6) Sodium phytate solution was added dropwise to the sodium alginate modified fish scale suspension obtained in step (4), and the mixture was stirred at 70-100°C for 3.0-4.0 h, and then aluminum salt and melamine were added and stirred for 1.0-2.0 h; (7) Adding 5% by mass of sodium carbonate solution to the solution obtained in step (6) to adjust the pH to neutral, aging, vacuum filtering, drying, crushing, and sieving to obtain the modified fish scale single-component intumescent flame retardant.

2. The preparation method according to claim 1, wherein: The fish scales in step (1) are one or more of mackerel scales and crucian carp scales; the drying temperature is 60-80°C and the drying time is 24-36 hours.

3. The preparation method according to claim 1, wherein: The amount of the dilute acid solution used in step (3) is 12-15 mL per 5 g of fish scale powder; the acid used is one or more of acetic acid, hydrochloric acid, and citric acid.

4. The preparation method according to claim 1, wherein: The amount of phytic acid used in step (5) is such that the mass ratio of phytic acid to sodium alginate and fish scale powder is (6.6-9.9):5:

5.

5. The preparation method according to claim 1, wherein: The mass concentration of the sodium carbonate solution in step (5) is 10%, and the dosage is 65-75 mL per 10 g of phytic acid.

6. The preparation method according to claim 1, wherein: The amount of aluminum salt and melamine used in step (6) is as follows: 3+ , the molar ratio of melamine to phytic acid is 1:2:1; the aluminum salt is one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride.

7. The preparation method according to claim 1, wherein: The aging time in step (7) is 12-24 h; the drying temperature is 70-100 °C and the drying time is 12-24 h.

8. The preparation method according to claim 1, wherein: The stirring rate in steps (2) to (7) is 200-500 rpm.

9. A modified fish scale one-component intumescent flame retardant prepared by the method according to any one of claims 1 to 8.

10. Use of the modified fish scale one-component intumescent flame retardant according to claim 9 in PLA, characterized in that: The modified fish scale single-component intumescent flame retardant is added to PLA in an amount of 3% to 10% of the mass of the PLA.

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