Phosphorus-silicon synergistic efficient flame-retardant polylactic acid and preparation method thereof

Abstract

The preparation method comprises the following steps: S1, in a nitrogen atmosphere, dissolving vinyltriethoxysilane and a flame-retardant intermediate containing a P-H bond in an organic solvent, carrying out heating and stirring reaction, and carrying out reduced pressure distillation to obtain a phosphorus-silicon flame-retardant intermediate; s2, dissolving a water-soluble polyphenol compound in deionized water, adding the phosphorus-silicon flame-retardant intermediate dispersed by an ethanol water solution, uniformly mixing, adding a pH regulator until the system is weakly alkaline, and in a nitrogen atmosphere, carrying out heating and stirring reaction, reduced pressure distillation and drying to obtain a phosphorus-silicon modified polyphenol flame retardant; and S3, mixing 98-99 parts by weight of polylactic acid and 1-2 parts by weight of the phosphorus-silicon modified polyphenol flame retardant, heating and drying, carrying out melt blending and extrusion granulation in an extruder, and heating and pressurizing by an injection molding machine to obtain the phosphorus-silicon synergistic efficient flame-retardant polylactic acid. The flame retardant has the advantages of mature preparation process, convenience in operation, good compatibility, high flame retardant efficiency and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardant materials, and in particular relates to a phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA), a biodegradable material, has become one of the most widely researched and promising bio-based materials due to its excellent processing properties, biocompatibility, biodegradability, and environmental friendliness. Currently, PLA has been successfully applied in a variety of fields, including medicine, chemical fiber textiles, green packaging, agriculture, and electronics. However, its inherent flammability severely restricts its further application, necessitating the development of efficient flame-retardant modification technologies for PLA.

[0003] Existing PLA flame retardant systems primarily include halogen-based, phosphorus-based, nitrogen-based, silicon-based, intumescent flame retardants, inorganic flame retardants, nanocomposites, and multi-component synergistic flame retardant systems. Halogen-based flame retardants, however, have been gradually phased out of the industry due to the release of toxic fumes and corrosive gases during combustion. While inorganic flame retardants are inexpensive, they typically require high addition levels, inevitably degrading the material's processing and mechanical properties. In recent years, a growing body of research has demonstrated that combining two or more flame retardants together often exhibits superior flame retardancy compared to a single component. This not only reduces the amount of flame retardant added, but also mitigates the impact on the mechanical properties, processing, and cost of PLA materials.

[0004] Chinese patent CN117364473A discloses "a boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric and its finishing process." The fabric is obtained by treating a polylactic acid nonwoven fabric with a flame-retardant treatment solution. The main component of the flame-retardant treatment solution is a boron-doped phosphorus-nitrogen synergistic flame retardant BTP, which is prepared by reacting the following components by weight: 6.2 parts boric acid, 44.7 parts triethanolamine, 264 parts phytic acid, 240 parts urea, and 830-840 parts water. Chinese patent CN118028991A discloses "a fully bio-based multi-component synergistic anti-drip flame retardant, its preparation method, and its application in flame-retardant polylactic acid fibers." This anti-drip flame retardant is a phosphorus-sulfur synergistic flame retardant system composed of 30-35 parts chitosan, 55-60 parts aminotrimethylenephosphonic acid, and 10-15 parts sulfur-containing amino acids.

[0005] While the development of multi-component synergistic flame-retardant systems is increasing, they still suffer from common issues such as low flame retardancy, high addition levels, and impacts on PLA mechanical properties. Regarding flame retardancy mechanisms, phosphorus-based flame retardants are primarily used in the preparation of vapor-phase flame retardants, but lack condensed-phase flame retardancy. Silicon-based flame retardants, on the other hand, possess excellent condensed-phase flame retardancy, generating a dense char residue during heating that insulates heat transfer. Therefore, the synergistic effect of phosphorus-based and silicon-based flame retardants is expected to achieve highly effective flame retardancy for PLA. Summary of the Invention

[0006] In order to solve the deficiencies in the prior art, the present invention provides a phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid and a preparation method thereof.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: The preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid comprises: S1: Under a nitrogen atmosphere, vinyltriethoxysilane and a flame retardant intermediate containing a PH bond are dissolved in an organic solvent, heated and stirred to react, and then distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: dissolving a water-soluble polyphenol compound in deionized water, adding a phosphorus-silicon flame retardant intermediate dispersed in an ethanol aqueous solution, mixing uniformly, adding a pH adjuster until the system becomes weakly alkaline, heating and stirring the reaction under a nitrogen atmosphere, distilling under reduced pressure, and drying to obtain a phosphorus-silicon modified polyphenol flame retardant; S3: In parts by weight, 98-99 parts of polylactic acid and 1-2 parts of phosphorus-silicon modified polyphenol flame retardant are mixed, heated and dried, melt-blended and extruded into granules in an extruder, and then heated and pressurized by an injection molding machine to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0008] Preferably, in step S1, the molar ratio of vinyltriethoxysilane to the flame retardant intermediate containing a PH bond is 1:1, and the flame retardant intermediate containing a PH bond is any one of diphenylphosphine and diphenylphosphine oxide.

[0009] Preferably, in step S1, the organic solvent is any one of dichloromethane, chloroform, and ethanol.

[0010] Preferably, in step S1, the temperature range of the heating and stirring reaction is 40° C. to 80° C., and the time range of the heating and stirring reaction is 6 h to 12 h.

[0011] Preferably, the water-soluble polyphenol compound in step S2 is any one of tannic acid, epicatechin gallate, and epigallocatechin gallate.

[0012] Preferably, the molar ratio of the water-soluble polyphenol compound to the phosphorus silicon flame retardant intermediate in step S2 is in the range of 1:2 to 1:5, and the volume ratio of ethanol to water in the ethanol aqueous solution is in the range of 1:1 to 3:1.

[0013] Preferably, the pH regulator in step S2 is any one of ammonia water, sodium carbonate, sodium bicarbonate, disodium hydrogen phosphate, and tris(hydroxymethyl)aminomethane, and the pH of the system is adjusted to a range of 8 to 9.

[0014] Preferably, the temperature range of the heating and stirring reaction in S2 is 40°C to 80°C, and the time range of the heating and stirring reaction is 4h to 24h; The heating and drying temperature in S3 is 80° C., and the heating and drying time ranges from 4 hours to 8 hours.

[0015] Preferably, the temperature of the melt blending in S3 is 170° C., the speed of the extruder is in the range of 60 to 80 r / min, and the time of the melt blending is in the range of 5 to 10 min; The injection molding heating temperature is 175° C. and the pressurizing pressure is 10 MPa.

[0016] The invention also discloses phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, which is prepared by the preparation method of the phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The present invention first prepares a phosphorus-silicon flame retardant intermediate and then prepares a phosphorus-silicon modified polyphenol flame retardant. The phosphorus-silicon modified polyphenol flame retardant not only contains phosphorus-silicon flame retardant elements, but also its natural plant polyphenol compounds have free radical capture and carbonization effects, which can simultaneously exert a synergistic flame retardant mechanism of the condensed phase and the gas phase, making up for the low flame retardant efficiency of a single flame retardant element or a simple compound of a multi-component synergistic system. The overall solution of the present invention has a mature preparation process, is easy to operate, and is suitable for industrial production and promotion and application; (2) The phosphorus-silicon modified polyphenol flame retardant provided by the present invention has good compatibility with polylactic acid and high flame retardant efficiency. When the addition amount is less than 2.0%, polylactic acid can pass the UL-94 vertical combustion test V-0 grade, the limiting oxygen index is greater than 28%, and the physical and chemical properties of polylactic acid itself are well maintained; In summary, the present invention has the advantages of mature preparation technology, convenient operation, good compatibility, high flame retardant efficiency, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the process for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid of the present invention; Figure 2 This is a scanning electron microscope comparison of the phosphorus-silicon modified polyphenol flame retardant and tannic acid in specific embodiment 1 of the present invention; Figure 3 Video screenshots comparing the phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid prepared in specific example 1 of the present invention and the polylactic acid provided in comparative example 1 during the vertical combustion test. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0020] The components of the embodiments of the present invention generally described and shown in the drawings herein may be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention.

[0021] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0022] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0024] In the following embodiments, the present invention will provide a method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, and prepare phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid. The phosphorus-silicon modified polyphenol flame retardant provided by the present invention not only contains phosphorus-silicon flame retardant elements, but also introduces the free radical capture and carbonization effect of natural plant polyphenol compounds, which can simultaneously exert the synergistic flame retardant mechanism of the condensed phase and the gas phase, and only requires an extremely low addition amount to give the polylactic acid material high flame retardant efficiency.

[0025] The raw materials used in the following examples of the present invention are described as follows: vinyltriethoxysilane, a flame retardant intermediate containing a pH bond, an organic solvent, a water-soluble polyphenol compound, and a pH regulator are all conventional commercial products; the polylactic acid brand is LX-175.

[0026] The performance measurement methods involved in the following embodiments listed in the present invention are described as follows: UL-94 vertical combustion test is in accordance with GB / T2408-2008 standard; limiting oxygen index measurement is in accordance with GB / T2406.1-2008 standard; mechanical properties are in accordance with GB / T1040.2-2006 standard.

[0027] Example 1 The preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid of the present invention comprises: S1: Under a nitrogen atmosphere, vinyltriethoxysilane and a flame retardant intermediate containing a PH bond are dissolved in an organic solvent, heated and stirred to react, and then distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: dissolving a water-soluble polyphenol compound in deionized water, adding a phosphorus-silicon flame retardant intermediate dispersed in an ethanol aqueous solution, mixing uniformly, adding a pH adjuster until the system becomes weakly alkaline, heating and stirring the reaction under a nitrogen atmosphere, distilling under reduced pressure, and drying to obtain a phosphorus-silicon modified polyphenol flame retardant; S3: In parts by weight, 98-99 parts of polylactic acid and 1-2 parts of phosphorus-silicon modified polyphenol flame retardant are mixed, heated and dried, melt-blended and extruded into granules in an extruder, and then heated and pressurized by an injection molding machine to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0028] In the above scheme, the flame retardant intermediate containing PH bonds mainly adopts a gas phase flame retardant mechanism. The phosphorus-containing free radicals generated during the combustion process can effectively capture free radicals such as hydrogen and hydroxyl, thereby preventing the chain decomposition reaction of polylactic acid during the combustion process. Vinyltriethoxysilane mainly adopts a condensed phase flame retardant mechanism. During combustion, a carbon layer is formed on the surface of polylactic acid, which prevents the exchange of matter and energy from the burning part to the internal unburned part, thereby preventing further decomposition of the material. The PH bonds contained in the structure of the flame retardant intermediate containing PH bonds are highly reactive and easily undergo nucleophilic addition reactions with carbon-carbon double bonds.

[0029] In the above scheme, the water-soluble polyphenol compounds are mainly natural plant polyphenols, which are a class of polyphenolic hydroxyl compounds widely present in plants, such as plant bark, shells, roots, leaves and pulp. Their unique polyphenol structure gives them high reactivity and good high-temperature thermal stability. At the same time, phenol is easily dehydrogenated to form phenoxy free radicals, thereby capturing other free radicals. The phenolic hydroxyl groups of polyphenol compounds have high reactivity and can undergo dehydration condensation reaction with silanol and the like in a weakly alkaline environment, thereby introducing flame retardant elements.

[0030] In the step S1, the molar ratio of vinyltriethoxysilane to the flame retardant intermediate containing a PH bond is 1:1, and the flame retardant intermediate containing a PH bond is any one of diphenylphosphine and diphenylphosphine oxide.

[0031] In step S1, the organic solvent is any one of dichloromethane, chloroform, and ethanol.

[0032] In step S1, the temperature range of the heating and stirring reaction is 40° C. to 80° C., and the time range of the heating and stirring reaction is 6 h to 12 h.

[0033] The water-soluble polyphenol compound in step S2 is any one of tannic acid, epicatechin gallate, and epigallocatechin gallate.

[0034] The molar ratio of the water-soluble polyphenol compound to the phosphorus silicon flame retardant intermediate in step S2 is in the range of 1:2 to 1:5, and the volume ratio of ethanol to water in the ethanol aqueous solution is in the range of 1:1 to 3:1.

[0035] In step S2, the pH regulator is any one of ammonia water, sodium carbonate, sodium bicarbonate, disodium hydrogen phosphate, and tris(hydroxymethyl)aminomethane, and the pH of the system is adjusted to a range of 8 to 9.

[0036] The temperature range of the heating and stirring reaction in S2 is 40°C to 80°C, and the time range of the heating and stirring reaction is 4h to 24h; The heating and drying temperature in S3 is 80° C., and the heating and drying time ranges from 4 hours to 8 hours.

[0037] The temperature of the melt blending in S3 is 170° C., the speed of the extruder is in the range of 60 to 80 r / min, and the time of the melt blending is in the range of 5 to 10 min; The injection molding heating temperature is 175° C. and the pressurizing pressure is 10 MPa.

[0038] The invention also discloses phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, which is prepared by the preparation method of the phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid.

[0039] The above is a general method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid. Specifically, in this embodiment, the following specific values ​​of each raw material are used to prepare phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid; Specifically, this embodiment provides a method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, the steps of which are as follows: S1: Under nitrogen atmosphere, 0.2 mol of vinyltriethoxysilane and 0.2 mol of diphenylphosphine were dissolved in chloroform, stirred at 60°C for 8 h, and distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: Dissolve 0.01 mol of tannic acid in deionized water, add 0.05 mol of a phosphorus-silicon flame retardant intermediate dispersed in an ethanol-water solution (volume ratio 1:1), mix well, add sodium bicarbonate solution to adjust the pH of the system to 8, react with stirring at 60°C under a nitrogen atmosphere for 8 hours, distill under reduced pressure, and dry to obtain a phosphorus-silicon modified polyphenol flame retardant; S3: In parts by weight, 99 parts of polylactic acid and 1 part of phosphorus-silicon modified polyphenol flame retardant were mixed, heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0040] Example 2 The preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid in this embodiment is basically similar to that in Example 1. Specifically, this embodiment provides a preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, and the steps are as follows: S1: Under nitrogen atmosphere, 0.2 mol of vinyltriethoxysilane and 0.2 mol of diphenylphosphine were dissolved in chloroform, stirred at 60°C for 8 h, and distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: Dissolve 0.01 mol of tannic acid in deionized water, add 0.05 mol of a phosphorus-silicon flame retardant intermediate dispersed in an ethanol-water solution (volume ratio 1:1), mix well, add sodium bicarbonate solution to adjust the pH of the system to 8, react with stirring at 60°C under a nitrogen atmosphere for 8 h, distill under reduced pressure, and dry to obtain a phosphorus-silicon modified polyphenol flame retardant; S3: In parts by weight, 99 parts of polylactic acid and 1 part of phosphorus-silicon modified polyphenol flame retardant were mixed, heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0041] Example 3 The preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid in this embodiment is basically similar to that in Example 1. Specifically, this embodiment provides a preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, and the steps are as follows: S1: Under nitrogen atmosphere, 0.2 mol of vinyltriethoxysilane and 0.2 mol of diphenylphosphine were dissolved in dichloromethane, stirred at 40°C for 12 h, and distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: Dissolve 0.01 mol of epicatechin gallate in deionized water, add 0.02 mol of a phosphosilicate flame retardant intermediate dispersed in an ethanol-water solution (volume ratio 3:1), mix well, add tris(hydroxymethyl)aminomethane solution to adjust the pH of the system to 9, react at 80°C under nitrogen atmosphere with stirring for 4 h, distill under reduced pressure, and dry to obtain a phosphosilicate modified polyphenol flame retardant; S3: In parts by weight, 98 parts of polylactic acid and 2 parts of phosphorus-silicon modified polyphenol flame retardant were mixed, heated and dried at 80°C for 8 hours, melt-blended in a micro extruder (temperature 170°C, speed 60r / min, time 10min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0042] Example 4 The preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid in this embodiment is basically similar to that in Example 1. Specifically, this embodiment provides a preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, and the steps are as follows: S1: Under nitrogen atmosphere, 0.2 mol of vinyltriethoxysilane and 0.2 mol of diphenylphosphine were dissolved in ethanol, stirred at 80°C for 6 h, and distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: Dissolve 0.01 mol of epigallocatechin gallate in deionized water, add 0.03 mol of a phosphosilicate flame retardant intermediate dispersed in an ethanol aqueous solution (volume ratio 2:1), mix well, add an ammonia aqueous solution to adjust the pH of the system to 8.5, react with stirring at 40°C under a nitrogen atmosphere for 24 hours, distill under reduced pressure, and dry to obtain a phosphosilicate modified polyphenol flame retardant; S3: In parts by weight, 98.5 parts of polylactic acid and 1.5 parts of phosphorus-silicon modified polyphenol flame retardant were mixed, heated and dried at 80°C for 6 hours, melt-blended in a micro extruder (temperature 170°C, speed 70r / min, time 8min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0043] The present invention also provides the following comparative examples for comparison with Examples 1-4.

[0044] Comparative Example 1 This comparative example provides a method for preparing pure polylactic acid: The polylactic acid was heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain pure polylactic acid material.

[0045] Comparative Example 2 This comparative example provides a method for preparing vinyltriethoxysilane-modified polylactic acid: In parts by weight, 99 parts of polylactic acid and 1 part of vinyltriethoxysilane were mixed, heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid.

[0046] Comparative Example 3 This comparative example provides a method for preparing diphenylphosphine-modified polylactic acid: In parts by weight, 99 parts of polylactic acid and 1 part of diphenylphosphine are mixed, heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid.

[0047] Comparative Example 4 This comparative example provides a method for preparing tannic acid-modified polylactic acid: In parts by weight, 99 parts of polylactic acid and 1 part of tannic acid are mixed, heated and dried at 80°C for 4 hours, melt-blended in a micro extruder (temperature 170°C, speed 80r / min, time 5min), extruded into granules, and then heated and pressurized by a micro injection molding machine (temperature 175°C, pressure 10MPa) to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

[0048] The comparison of the phosphorus silicon modified polyphenol flame retardant prepared in Example 1 and tannic acid is shown in FIG. Figure 2 As shown in the figure, tannic acid presents a relatively regular spherical shape with a smooth surface, while the phospho-silicon modified polyphenol flame retardant obtained by the dehydration condensation reaction after the introduction of the phospho-silicon flame retardant intermediate presents an irregular rough surface, indicating that the phospho-silicon flame retardant has been successfully modified onto the surface of tannic acid.

[0049] Comparison of video screenshots of the phosphorus-silicon synergistic high-efficiency polylactic acid prepared in Example 1 and the pure polylactic acid prepared in Comparative Example 1 during the vertical combustion test Figure 3 As shown in the figure, the pure polylactic acid sample burns completely after the first ignition, and the combustion process is accompanied by a large amount of molten dripping; while the flame retardant polylactic acid prepared in Example 1 can be extinguished within 2 seconds after the first ignition, and immediately extinguishes itself after the second ignition, and no molten dripping phenomenon is observed, indicating that it has excellent flame retardant effect.

[0050] The performance test results of the flame retardant polylactic acid materials prepared in Examples 1-4 and Comparative Examples 1-4 were statistically analyzed and the results are shown in the following table:

[0051] As can be seen from the above table, the flame-retardant polylactic acid prepared by Examples 1-4 of the present invention can pass the UL-94 vertical burning test V-0 grade when the addition amount is only 1-2 parts, the limiting oxygen index is greater than 28%, and the physical and chemical properties of the polylactic acid itself are well maintained. Compared with Examples 1-2, Comparative Examples 2-4, at the same addition amount, only vinyltriethoxysilane, a flame retardant intermediate containing a PH bond, or a natural plant polyphenol compound are added. The prepared polylactic acid materials cannot obtain the vertical burning test grade, and the limiting oxygen index is only lower than 22%, which further illustrates that the flame retardant provided by the present invention exerts a phosphorus-silicon synergistic flame retardant mechanism and improves the flame retardant efficiency.

[0052] This embodiment does not impose any formal restrictions on the shape, material, structure, etc. of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid, characterized in that: include: S1: Under a nitrogen atmosphere, vinyltriethoxysilane and a flame retardant intermediate containing a PH bond are dissolved in an organic solvent, heated and stirred to react, and then distilled under reduced pressure to obtain a phosphorus silicon flame retardant intermediate; S2: dissolving a water-soluble polyphenol compound in deionized water, adding a phosphorus-silicon flame retardant intermediate dispersed in an ethanol aqueous solution, mixing uniformly, adding a pH adjuster until the system becomes weakly alkaline, heating and stirring the reaction under a nitrogen atmosphere, distilling under reduced pressure, and drying to obtain a phosphorus-silicon modified polyphenol flame retardant; S3: In parts by weight, 98-99 parts of polylactic acid and 1-2 parts of phosphorus-silicon modified polyphenol flame retardant are mixed, heated and dried, melt-blended and extruded into granules in an extruder, and then heated and pressurized by an injection molding machine to obtain phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid.

2. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: In the step S1, the molar ratio of vinyltriethoxysilane to the flame retardant intermediate containing a PH bond is 1:1, and the flame retardant intermediate containing a PH bond is any one of diphenylphosphine and diphenylphosphine oxide.

3. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: In step S1, the organic solvent is any one of dichloromethane, chloroform, and ethanol.

4. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: In step S1, the temperature range of the heating and stirring reaction is 40° C. to 80° C., and the time range of the heating and stirring reaction is 6 h to 12 h.

5. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: The water-soluble polyphenol compound in step S2 is any one of tannic acid, epicatechin gallate, and epigallocatechin gallate.

6. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: The molar ratio of the water-soluble polyphenol compound to the phosphorus silicon flame retardant intermediate in step S2 is in the range of 1:2 to 1:5, and the volume ratio of ethanol to water in the ethanol aqueous solution is in the range of 1:1 to 3:

1.

7. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: In step S2, the pH regulator is any one of ammonia water, sodium carbonate, sodium bicarbonate, disodium hydrogen phosphate, and tris(hydroxymethyl)aminomethane, and the pH of the system is adjusted to a range of 8 to 9.

8. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: The temperature range of the heating and stirring reaction in S2 is 40°C to 80°C, and the time range of the heating and stirring reaction is 4h to 24h; The heating and drying temperature in S3 is 80° C., and the heating and drying time ranges from 4 hours to 8 hours.

9. The method for preparing phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to claim 1, characterized in that: The temperature of the melt blending in S3 is 170° C., the speed of the extruder is in the range of 60 to 80 r / min, and the time of the melt blending is in the range of 5 to 10 min; The injection molding heating temperature is 175° C. and the pressurizing pressure is 10 MPa.

10. Phosphorus-silicon synergistic high-efficiency flame retardant polylactic acid, characterized by: The invention is prepared by the preparation method of phosphorus-silicon synergistic high-efficiency flame-retardant polylactic acid according to any one of claims 1 to 9.

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