A full-bio-based multi-component synergistic anti-dripping flame retardant, a preparation method thereof and application thereof in flame-retardant polylactic acid fibers

Abstract

The present application relates to the field of flame retardant, disclose a kind of full biological base multi-component synergistic anti-dripping flame retardant and its preparation method, application in flame-retardant polylactic acid fiber.The anti-dripping flame retardant includes by electrostatic adsorption combination chitosan, aminotri (methylenephosphonic acid) and sulfur-containing amino acid;Chitosan, aminotri (methylenephosphonic acid) and sulfur-containing amino acid mass fraction is as follows:chitosan 30-35 parts, aminotri (methylenephosphonic acid) 55-60 parts, sulfur-containing amino acid 10-15 parts, total 100 parts.The anti-dripping flame retardant of the present application uses aminotri (methylenephosphonic acid) as biological base acid source with high flame-retardant efficiency, then sulfur-containing amino acid is used as sulfur source to introduce phosphorus-sulfur synergistic flame-retardant system, on the one hand, improve the efficiency of free radical generated in the combustion process of flame retardant, on the other hand, improve the rate of heat-insulating, oxygen-insulating carbon layer formed in the combustion process of flame retardant, so as to further improve the flame-retardant efficiency of flame retardant.

Description

Technical Field

[0001] The present invention relates to the field of flame retardants, and in particular to a fully bio-based multi-component synergistic anti-drip flame retardant and a preparation method thereof, and application thereof in flame-retardant polylactic acid fibers. Background Art

[0002] Due to its excellent mechanical properties, biocompatibility, spinnability and degradability, polylactic acid has become a biodegradable material that is expected to replace traditional petroleum-based polymer materials. It is one of the bio-based biodegradable materials with great application potential. However, like most conventional polymer materials, polylactic acid has the disadvantage of being extremely flammable, which limits its application in some fields with high flame retardancy requirements. There are currently two options for flame retardant modification of polylactic acid. One is to introduce flame retardants into the polylactic acid molecular chain through chemical reactions in the form of grafting or blocking. This option is often complex and costly, making it difficult to achieve industrial application. Therefore, the flame retardant modification of polylactic acid is usually carried out using the second option, that is, introducing flame retardants into the polylactic acid material through physical blending to produce a flame retardant polylactic acid composite material.

[0003] Patent CN111057357 discloses a polylactic acid halogen-free flame-retardant composite material, its preparation method, and plastic products. The flame retardant used is mainly composed of acrylate-modified casein. When used in the flame-retardant modification of polylactic acid, this flame retardant has good flame retardant efficiency and does not significantly reduce the mechanical properties of polylactic acid. However, its inherent petroleum-based components greatly reduce the biodegradability advantage of polylactic acid, creating certain obstacles to the recycling of polylactic acid materials. Patent CN111848893 discloses a phosphorus-nitrogen intumescent flame retardant, its preparation, and application in polylactic acid. The flame retardant is a copolymer of vanillin and phenylphosphoryl dichloride. Although this phosphorus-nitrogen intumescent flame retardant contains bio-based components and is relatively simple to prepare, its application in flame-retardant polylactic acid has problems such as excessive addition and poor flame retardant efficiency. Patent CN114855298 discloses a flame-retardant polylactic acid fiber using a two-dimensional inorganic nanomaterial as a flame retardant. This flame-retardant polylactic acid fiber has the advantages of being green, environmentally friendly, and highly flame-retardant. However, the synthesis and loading steps of the flame retardant are very complex, and the flame retardant is expensive, making it difficult to achieve industrial production and application. Patent CN107022804 discloses a flame-retardant, biodegradable, and antibacterial polylactic acid elastic fiber. The main components of the flame retardant used are phosphate, cobalt oxide, and diammonium phosphate. The raw materials used are non-toxic, but the flame retardant effect is limited. Increasing the limiting oxygen index of the polylactic acid fiber to 30% requires a 10wt% flame retardant addition.

[0004] Overall, the petroleum-based flame retardants currently used in PLA fibers are difficult to degrade and pose serious pollution risks, while bio-based flame retardants have issues such as low flame retardancy, high cost, complex synthesis steps, and significant damage to PLA fiber properties. Therefore, it is difficult for current flame retardants to achieve both biodegradability and flame retardancy. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a fully bio-based multi-component synergistic anti-drip flame retardant and its preparation method, and its application in flame-retardant polylactic acid fiber. The anti-drip flame retardant of the present invention uses aminotrimethylenephosphonic acid with high flame retardant efficiency as a bio-based acid source, and then uses sulfur-containing amino acids as a sulfur source to introduce a phosphorus-sulfur synergistic flame retardant system. On the one hand, it improves the efficiency of the flame retardant in generating free radicals during the combustion process, and on the other hand, it improves the rate at which the flame retardant forms a heat-insulating and oxygen-isolating carbon layer during the combustion process, thereby further improving the flame retardant efficiency of the flame retardant. Compared with most of the current bio-based flame retardants, it has less addition, lower cost, higher flame retardant efficiency and a simpler synthesis process; compared with the petroleum-based flame retardants currently on the market, it has less pollution and higher degradability.

[0006] The specific technical solutions of the present invention are:

[0007] A fully bio-based multi-component synergistic anti-dripping flame retardant comprises positively charged chitosan, negatively charged aminotrimethylene phosphonic acid, and positively charged sulfur-containing amino acids; the chitosan and aminotrimethylene phosphonic acid are bonded via electrostatic adsorption, and the sulfur-containing amino acids and aminotrimethylene phosphonic acid are bonded via electrostatic adsorption.

[0008] The present invention uses chemical means to synthesize a fully bio-based multi-component synergistic anti-drip flame retardant, the main components of which are chitosan, aminotrimethylenephosphonic acid and sulfur-containing amino acids. The three components can be ionized in the solution to form ionic bonds and bonded together in a self-assembled manner.

[0009] For the first time, the raw materials of the present invention are all bio-based degradable materials with excellent biodegradability, and therefore do not affect the biodegradability of polylactic acid.

[0010] Secondly, it addresses the problem that current bio-based flame retardants are difficult to achieve both biodegradability and flame retardancy. The present invention introduces a phosphorus-sulfur synergistic flame retardant effect on the basis of a single phosphorus-based flame retardant, further improving the flame retardant efficiency of the flame retardant and reducing the amount of flame retardant added. Among them, the mechanism of the phosphorus-sulfur synergistic flame retardant effect of the present invention is: during the combustion process, the phosphate group decomposes into a variety of phosphorus-based free radicals after being heated, and these free radicals react with carbon-sulfur bonds to form sulfur free radicals; sulfur free radicals can act as a cross-linking agent, quickly causing a cross-linking reaction between the polylactic acid molecular chain and the chitosan molecular chain to form a cross-linked network structure, thereby improving the shear strength of the polylactic acid melt during combustion, inhibiting the generation of molten droplets, and at the same time promoting the carbonization of chitosan, accelerating the formation of heat-insulating and oxygen-isolating carbon layers, which is different from the mechanism of the existing phosphorus-sulfur synergistic flame retardant effect. The synergistic effect formed between the three components greatly improves the flame retardant efficiency of the flame retardant.

[0011] The mass proportions of the chitosan, aminotrimethylene phosphonic acid and sulfur-containing amino acid are: 30-35 parts of chitosan, 55-60 parts of aminotrimethylene phosphonic acid, 10-15 parts of sulfur-containing amino acid, and a total of 100 parts.

[0012] The present invention found that it is not possible to obtain a fully bio-based multi-component synergistic anti-drip flame retardant with similar performance simply by mixing chitosan, aminotrimethylenephosphonic acid and sulfur-containing amino acids. The ratio between the three is crucial, and it was finally found that the effect is best within the above ratio range.

[0013] Furthermore, the sulfur-containing amino acid is selected from one or more of methionine, cysteine, and cystine.

[0014] Furthermore, the mass ratio of the chitosan, aminotrimethylenephosphonic acid and sulfur-containing amino acid is preferably 30 parts of chitosan, 60 parts of aminotrimethylenephosphonic acid and 10 parts of sulfur-containing amino acid.

[0015] A method for preparing a fully bio-based multi-component synergistic anti-dripping flame retardant comprises: dissolving chitosan in an acetic acid or formic acid solution, adding aminotrimethylenephosphonic acid after sufficient dissolution, and reacting under stirring; then adding a sulfur-containing amino acid and reacting under stirring; after the reaction is completed, removing the solvent by rotary evaporation, and vacuum drying the resulting product to obtain the fully bio-based multi-component synergistic anti-dripping flame retardant.

[0016] The present invention discovered that the order in which chitosan, aminotrimethylenephosphonic acid, and sulfur-containing amino acids are added during the preparation process is crucial. If aminotrimethylenephosphonic acid is combined with the sulfur-containing amino acid first, followed by chitosan and aminotrimethylenephosphonic acid, the number of aminotrimethylenephosphonic acid reaction sites that react with methionine is reduced, thereby reducing the efficiency of the reaction between the three components. Under this reaction sequence, the anti-drip flame retardant contains a large number of free aminotrimethylenephosphonic acid molecules. The presence of these small molecules can cause acid corrosion of the polylactic acid matrix during melt blending of the anti-drip flame retardant and polylactic acid, significantly affecting the mechanical properties of the polylactic acid fiber.

[0017] Furthermore, the concentration of the acetic acid or formic acid solution is 0.5-1.5 wt%.

[0018] Furthermore, the two stirring reaction times are 10-60 min; the rotary evaporation temperature is 70-90° C.; the vacuum drying temperature is 75-95° C., and the time is 10-24 h.

[0019] The application of the above-mentioned all-biobased multi-component synergistic anti-drip flame retardant in the preparation of flame-retardant polylactic acid fiber: the all-biobased multi-component synergistic anti-drip flame retardant is vacuum dried to a moisture content of ≤80ppm, ground into powder, and then melt-blended with polylactic acid in a mass ratio of 97:3-99:1 to obtain a flame-retardant polylactic acid composite material, and the flame-retardant polylactic acid composite material is formed by melt spinning to obtain flame-retardant polylactic acid fiber.

[0020] Furthermore, the polylactic acid is vacuum dried before mixing, and the melt blending temperature is 170-190° C. and the time is 4-10 minutes.

[0021] Furthermore, the melt spinning conditions are: temperature 190-250° C., spinneret aperture 0.10-0.20 mm, side wind temperature 20-30° C., wind speed 0.3-0.7 m / s, and humidity 65-75%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] First, compared with traditional single-component flame retardants, the bio-based multi-component synergistic flame retardant provided by the present invention introduces a phosphorus-sulfur synergistic flame retardant system. On the basis of selecting flame retardant components that are all non-toxic and degradable bio-based compounds, the flame retardant efficiency of the flame retardant is significantly improved by introducing a new flame retardant mechanism.

[0024] Second, the main components of the all-biobased multi-component synergistic anti-drip flame retardant provided by the present invention are all bio-based degradable compounds, which will not damage the degradable properties of polylactic acid fibers. In addition, the synthesis method is simple and the cost of raw materials is low.

[0025] Third, the flame-retardant polylactic acid fiber prepared by the present invention has excellent flame retardant properties. The small amount of flame retardant added means that the polylactic acid fiber does not suffer excessive loss of mechanical properties. It can be used in the textile field with high requirements for flame retardant properties and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a graph showing the XPS test results of the bio-based multi-component synergistic anti-dripping flame retardant of Example 1;

[0027] Figure 2 Thermal stability analysis diagram of polylactic acid flame retardant fiber in different cases. DETAILED DESCRIPTION

[0028] Example 1:

[0029] The fully bio-based multi-component synergistic anti-dripping flame retardant provided in this embodiment has the following specific preparation steps: dissolving chitosan in a 1wt% acetic acid solution, adding aminotrimethylenephosphonic acid after it is completely dissolved, stirring and reacting at room temperature for 1 hour, then adding methionine, stirring and reacting at room temperature for 1 hour, after the reaction is completed, placing the solution in a rotary evaporator, and rotary evaporating at 85°C to remove most of the acetic acid solution, and finally vacuum drying the product at 80°C for 24 hours to obtain a fully bio-based multi-component synergistic anti-dripping flame retardant, wherein the main components include, by mass, 30 parts of chitosan, 60 parts of aminotrimethylenephosphonic acid, and 10 parts of methionine.

[0030] The structural formula of the anti-drip flame retardant is as follows:

[0031]

[0032] After polylactic acid was dried at 80°C for 12 hours, 99.5 parts of polylactic acid and 0.5 parts of a fully bio-based multi-component synergistic anti-dripping flame retardant were taken by weight and blended in an internal mixer at 180°C for 6 minutes to obtain a flame-retardant polylactic acid composite material.

[0033] The flame-retardant polylactic acid composite material is put into a melt spinning machine to obtain flame-retardant polylactic acid fiber by melt spinning, wherein the spinning machine temperature is 200°C, the spinneret aperture is 0.15mm, the crosswind temperature is 25°C, the wind speed is 0.5m / s, and the humidity is 70%.

[0034] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 3.4 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-2; according to GB / T5454-1997 "Textile combustion performance test oxygen index method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 22.6%.

[0035] Example 2:

[0036] The flame-retardant polylactic acid fiber provided in this embodiment has substantially the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the all-biobased multi-component synergistic anti-drip flame retardant used is 1 part.

[0037] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 3.3 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 24.2%.

[0038] Example 3:

[0039] The flame-retardant polylactic acid fiber provided in this embodiment has substantially the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the all-biobased multi-component synergistic anti-drip flame retardant used is 1.5 parts.

[0040] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 3.3 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 25.1%.

[0041] Example 4:

[0042] The flame-retardant polylactic acid fiber provided in this embodiment has substantially the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the fully bio-based multi-component synergistic anti-drip flame retardant used is 2 parts.

[0043] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 3.2 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 26.0%.

[0044] Example 5:

[0045] The flame-retardant polylactic acid fiber provided in this embodiment has substantially the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the fully bio-based multi-component synergistic anti-drip flame retardant used is 2.5 parts.

[0046] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 3.0 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 27.1%.

[0047] Example 6:

[0048] The flame-retardant polylactic acid fiber provided in this embodiment has substantially the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the all-biobased multi-component synergistic anti-drip flame retardant used is 3 parts.

[0049] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 2.9 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 28.3%.

[0050] Example 7:

[0051] The flame-retardant polylactic acid fiber provided in this embodiment has roughly the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the all-biobased multi-component synergistic anti-drip flame retardant used is 3 parts, and its main components and mass ratio are chitosan: aminotrimethylenephosphonic acid: methionine = 35:55:10.

[0052] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 2.9 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 27.8%.

[0053] Example 8:

[0054] The flame-retardant polylactic acid fiber provided in this embodiment has roughly the same raw materials and preparation method as in Example 1, with the difference being that, in this embodiment, the mass fraction of the all-biobased multi-component synergistic anti-drip flame retardant used is 3 parts, and its main components and mass ratio are chitosan: aminotrimethylenephosphonic acid: methionine = 30:55:15.

[0055] The obtained flame-retardant polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame-retardant polylactic acid fiber was measured to be 2.9 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textiles burning performance test vertical method" standard, the LOI value of the flame-retardant polylactic acid fiber of this embodiment was measured to be 28.0%.

[0056] Comparative Example 1:

[0057] The all-biobased multi-component synergistic anti-drip flame retardant in Example 1 was omitted, and the other raw materials and preparation process were the same.

[0058] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame retardant polylactic acid fiber was measured to be 3.4 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was no grade; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 19.2%.

[0059] Comparative Example 2:

[0060] The methionine in the raw materials of the all-biobased multi-component synergistic anti-drip flame retardant in Example 2 was omitted, and the remaining raw materials were the same as the preparation method.

[0061] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame retardant polylactic acid fiber was measured to be 3.1 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-2; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 23.8%.

[0062] Comparative Example 3:

[0063] The methionine in the raw materials of the all-biobased multi-component synergistic anti-drip flame retardant in Example 3 was omitted, and the remaining raw materials were the same as the preparation method.

[0064] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame retardant polylactic acid fiber was measured to be 2.9 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-1; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 24.6%.

[0065] Comparative Example 4:

[0066] The methionine in the raw materials of the all-biobased multi-component synergistic anti-drip flame retardant in Example 4 was omitted, and the remaining raw materials were the same as the preparation method.

[0067] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the flame retardant polylactic acid fiber was measured to be 2.8 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was V-0; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 25.6%.

[0068] Comparative Example 5:

[0069] The all-biobased multi-component synergistic anti-drip flame retardant in Example 4 was replaced with chitosan, and the remaining raw materials were the same as the preparation method.

[0070] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the polylactic acid fiber was measured to be 2.5 cN / dtex; according to the UL-94 vertical burning test results, its flame retardancy grade was no grade; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 19.5%.

[0071] Comparative Example 6:

[0072] The component ratio of the all-biobased multi-component synergistic anti-drip flame retardant in Example 6 was changed to chitosan: aminotrimethylenephosphonic acid: methionine = 30:50:20, and the remaining raw materials were the same as the preparation method.

[0073] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the polylactic acid fiber was measured to be 2.2 cN / dtex; according to the UL-94 vertical burning test results, its flame retardant grade was no grade; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 26.8%.

[0074] Comparative Example 7:

[0075] The component ratio of the all-biobased multi-component synergistic anti-drip flame retardant in Example 6 was changed to chitosan: aminotrimethylenephosphonic acid: methionine = 20:70:10, and the remaining raw materials were the same as the preparation method.

[0076] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the polylactic acid fiber was measured to be 2.8 cN / dtex; according to the UL-94 vertical burning test results, its flame retardant grade was no grade; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 27.0%.

[0077] Comparative Example 8:

[0078] The synthesis sequence of the all-biobased, multi-component, synergistic anti-drip flame retardant in Example 6 was replaced by first reacting aminotrimethylenephosphonic acid with methionine, and then adding the reaction product to the chitosan solution. The raw material ratios, flame retardant dosage, and other processes for the flame retardant synthesis were the same as in Example 6.

[0079] The obtained polylactic acid fiber was subjected to performance testing. According to GB / T 14344-2008 "Test method for tensile properties of chemical fiber filaments", the strength of the polylactic acid fiber was measured to be 2.4 cN / dtex; according to the UL-94 vertical burning test results, its flame retardant grade was V-0; according to GB / T5455-1997 "Textile combustion performance test vertical method" standard, the LOI value of the polylactic acid fiber of this comparative example was measured to be 26.8%.

[0080] Performance Testing

[0081] Figure 1This is the XPS test chart of the anti-dripping flame retardant used in Examples 1-6. From the quantitative analysis results of the three elements N, P, and S, it can be seen that the proportion of the flame retardant finished product components is basically consistent with the raw material input ratio, indicating that no single component is lost during the synthesis process of the anti-dripping flame retardant, and the synthesis process is feasible.

[0082] Figure 2 This is the thermal stability analysis data chart of polylactic acid flame retardant fiber. It can be seen that the addition of anti-dripping flame retardant can improve the thermal stability of polylactic acid fiber. When the flame retardant addition amount is 1.5wt%, the thermal stability of polylactic acid fiber is improved to the highest level. In addition, with the increase of the addition amount of anti-dripping flame retardant, the residual amount of polylactic acid fiber is significantly increased, proving that the anti-dripping flame retardant is beneficial to the charring of polylactic acid fiber.

[0083] Table 1: Limiting oxygen index, vertical combustion, and fiber tensile test results for Examples 2-6 and Comparative Examples 1-5

[0084]

[0085] From the table above we can see that:

[0086] In Example 2, chitosan / aminotrimethylenephosphonic acid / methionine at a feed amount of 1.0 wt% can make the flame retardant grade of the polylactic acid fiber reach V-0. In comparison, the limiting oxygen index and vertical burning test results of Comparative Example 2 without adding methionine are relatively poor.

[0087] Vertical combustion tests of Example 2 and Comparative Example 3 show that while Comparative Example 3 has a higher limiting oxygen index, its flame retardancy rating is only V-1. This is due to the high generation of droplets during combustion. In comparison, Example 2 forms fewer droplets during combustion. This is because the addition of methionine introduces sulfur, which readily forms free radicals during combustion, triggering a crosslinking reaction. This increases the viscosity of the melt after crosslinking, thereby inhibiting the formation of droplets. Phosphate groups and sulfur can mutually induce phosphorus and sulfur radicals under high temperature conditions, forming a synergistic effect that increases the efficiency of free radical generation during combustion and enhances the flame retardant effect.

[0088] By comparing Comparative Example 6 with Example 6, it can be seen that the addition of too much methionine will reduce the flame retardant efficiency of the flame retardant. This is because the addition of too much methionine will cause the synergistic effect of free radicals formed between phosphorus and sulfur to shift towards the generation direction of sulfur radicals, thereby resulting in a decrease in the relative content of phosphorus-based free radicals, thereby reducing the efficiency of capturing hydroxyl radicals during the combustion of the flame retardant; on the other hand, the addition of too much methionine will cause excessive cross-linking to form during the melt blending of the flame retardant and polylactic acid, thereby reducing the toughness of the polylactic acid fiber.

[0089] By comparing Comparative Example 7 with Example 6, it can be seen that excessive addition of aminotrimethylenephosphonic acid will also reduce the flame retardant efficiency of the flame retardant. This is because there is an excess of aminotrimethylenephosphonic acid and a large amount of aminotrimethylenephosphonic acid does not react.

[0090] Comparison of Example 6 and Comparative Example 8 shows that changing the synthesis sequence of the anti-drip flame retardant reduces flame retardancy and significantly impairs the mechanical properties of the flame-retardant polylactic acid fiber. This is due to the altered synthesis sequence of the anti-drip flame retardant in Comparative Example 8, which reduces the number of aminotrimethylenephosphonic acid reaction sites that react first with methionine, thereby reducing the reaction efficiency among the three components. Under this reaction sequence, the anti-drip flame retardant contains a relatively large number of free aminotrimethylenephosphonic acid molecules. The presence of these small molecules causes acid corrosion of the polylactic acid matrix during melt blending of the anti-drip flame retardant and polylactic acid, significantly impacting the mechanical properties of the polylactic acid fiber.

[0091] In summary, the phosphorus-sulfur synergistic flame retardant effect has a more obvious influence on the flame retardant efficiency of the flame retardant. The phosphorus-sulfur synergistic flame retardant effect can reduce the amount of flame retardant added, thereby reducing the impact of the flame retardant on the mechanical properties of polylactic acid fiber.

Claims

1. A fully bio-based multi-component synergistic anti-drip flame retardant, characterized by: The invention comprises positively charged chitosan, negatively charged aminotrimethylenephosphonic acid, and positively charged sulfur-containing amino acid; the chitosan and aminotrimethylenephosphonic acid are combined by electrostatic adsorption, and the sulfur-containing amino acid and aminotrimethylenephosphonic acid are combined by electrostatic adsorption; The mass parts of the chitosan, aminotrimethylenephosphonic acid and sulfur-containing amino acid are: 30-35 parts of chitosan, 55-60 parts of aminotrimethylenephosphonic acid, 10-15 parts of sulfur-containing amino acid, and the total is 100 parts; The preparation method of the fully bio-based multi-component synergistic anti-dripping flame retardant includes: dissolving chitosan in an acetic acid or formic acid solution, adding aminotrimethylenephosphonic acid after sufficient dissolution, and reacting under stirring; then adding a sulfur-containing amino acid and reacting under stirring; after the reaction is completed, removing the solvent by rotary evaporation, and vacuum drying the resulting product to obtain the fully bio-based multi-component synergistic anti-dripping flame retardant.

2. The all-biobased multi-component synergistic anti-drip flame retardant according to claim 1, characterized in that: The sulfur-containing amino acid is selected from one or more of methionine, cysteine ​​and cystine.

3. The all-biobased multi-component synergistic anti-drip flame retardant according to claim 1, characterized in that: The mass proportions of the chitosan, aminotrimethylenephosphonic acid and sulfur-containing amino acid are: 30 parts of chitosan, 60 parts of aminotrimethylenephosphonic acid, 10 parts of sulfur-containing amino acid, and a total of 100 parts.

4. A method for preparing the all-biobased multi-component synergistic anti-drip flame retardant according to any one of claims 1 to 3, characterized in that include: Chitosan is dissolved in acetic acid or formic acid solution, and aminotrimethylenephosphonic acid is added after it is fully dissolved, and the mixture is reacted under stirring; a sulfur-containing amino acid is then added, and the mixture is reacted under stirring; after the reaction is completed, the solvent is removed by rotary evaporation, and the resulting product is vacuum dried to obtain a fully bio-based multi-component synergistic anti-dripping flame retardant.

5. The preparation method according to claim 4, characterized in that: The concentration of the acetic acid or formic acid solution is 0.5-1.5 wt %.

6. The preparation method according to claim 4, characterized in that: The stirring reaction time is 10-60min; The rotary evaporation temperature is 70-90°C; The vacuum drying temperature is 75-95° C. and the time is 10-24 hours.

7. Use of the all-biobased multi-component synergistic anti-drip flame retardant according to any one of claims 1-3 or the all-biobased multi-component synergistic anti-drip flame retardant obtained by the preparation method according to any one of claims 4-6 in the preparation of flame-retardant polylactic acid fiber.

8. The use according to claim 7, characterized in that: The fully bio-based multi-component synergistic anti-drip flame retardant is vacuum dried to a moisture content of ≤80ppm, ground into powder, and then melt-blended with polylactic acid at a mass ratio of 97:3-99:1 to obtain a flame-retardant polylactic acid composite material. The flame-retardant polylactic acid composite material is then melt-spinned to obtain flame-retardant polylactic acid fiber.

9. The use according to claim 8, characterized in that: The polylactic acid is vacuum dried before mixing, and the melt blending temperature is 170-190° C. and the time is 4-10 minutes.

10. The use according to claim 8, characterized in that: The melt spinning conditions are: temperature 190-250° C., spinneret aperture 0.10-0.20 mm, crosswind temperature 20-30° C., wind speed 0.3-0.7 m / s, and humidity 65-75%.

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