Environmentally friendly flame-retardant polypropylene composition and process for its preparation

Abstract

The application belongs to the technical field of flame retardant aids, and particularly relates to an organosilane modified graphite-based flame retardant, a flame-retardant polypropylene and a preparation method and application thereof. A phenyl silane coupling agent and an isocyanurate ring compound with a terminal siloxane group are introduced into expandable graphite, Si-O-Si structure is formed through hydrolysis and condensation of the siloxane group, the phenyl group, the isocyanurate ring and the urea bond are introduced into the expandable graphite, and thus the organosilane modified graphite-based flame retardant is obtained, so that the interface modification of the surface of the expandable graphite is more optimized, and the flame-retardant effect is strengthened to V-0 level. The modified graphite-based flame retardant is added into a polypropylene matrix, when combustion occurs, the expandable graphite can expand more uniformly and quickly, a denser, continuous and firm expanded carbon layer is formed, heat and oxygen are more effectively isolated, and combustion is delayed, so that the amount of the flame retardant is reduced, the flame retardancy of the polypropylene is improved, and the mechanical properties of the polypropylene are maintained.

Description

Technical Field

[0001] This application belongs to the field of flame retardant additives technology, specifically relating to an organosilane modified graphite-based flame retardant, flame-retardant polypropylene, its preparation method and application. Background Technology

[0002] Polypropylene (PP), as a classic general-purpose plastic, is characterized by high production volume, low price, and wide application. In terms of performance, it boasts excellent electrical insulation, chemical resistance, and processing properties. Moreover, among general-purpose plastics, polypropylene has the highest mechanical properties and heat resistance. Similar to most organic hydrocarbon polymers, polypropylene is flammable and produces large amounts of toxic fumes during combustion. Literature reports that the limiting oxygen index (LOI) of polypropylene without flame retardants is approximately 17.4%. Therefore, polypropylene is highly flammable, producing molten droplets that can spread the flame and trigger secondary combustion in the air, posing a significant environmental hazard and limiting its application in fields requiring high safety standards.

[0003] Furthermore, halogenated flame retardants used in polyolefins (such as brominated and chlorinated flame retardants) are difficult to degrade, can accumulate in the environment and organisms over long periods, and bioaccumulate through the food chain, posing a long-term risk to ecosystems. Halogenated flame retardants also release toxins during combustion; when decomposed at high temperatures or in fires, they may produce highly toxic carcinogens such as dioxins and furans. Therefore, many countries have restricted or banned some halogenated flame retardants, and the industry is developing various halogen-free flame retardants to replace halogenated ones.

[0004] Based on the concept of halogen-free environmental protection, adding intumescent flame retardants to polypropylene matrices is a rapidly developing flame retardant technology. Among them, expandable graphite (EG) has good flame retardancy and is widely used in polypropylene, polyethylene, polybutylene succinate, epoxy resin, and polyurethane. During combustion, expandable graphite expands rapidly, forming a loose, porous "worm-like" structure, resulting in a large amount of char residue covering the polymer surface. This char layer reduces heat and mass transfer, ultimately interrupting the pyrolysis of the polymer matrix. During the expansion of expandable graphite, compounds including CO2, H2O, and SO2 are produced, which dilute the concentration of flammable gases released in the flame zone. As a simple flame retardant and smoke suppressant, the expansion process of expandable graphite also consumes a large amount of heat, reducing the heat of combustion and the combustion rate, while also causing its expansion direction to be irregular; the resulting char layer is very loose and easily detached. This highlights the current limitations of using expandable graphite as a flame retardant in polypropylene. Modification is necessary, involving the addition of other halogen-free flame retardants, such as phosphorus-based, nitrogen-based, or silicone-based flame retardants, in synergistic use. This aims to improve the flame retardant's own effectiveness, reduce its dosage in polypropylene to below 20 wt%, and ensure that the mechanical properties of polypropylene remain unaffected. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art by using a mixture of terminal siloxane isocyanurate ring compounds and phenylsilane coupling agents with expandable graphite, followed by a hydrolysis-condensation reaction to obtain an organosilane-modified graphite-based flame retardant. The modified graphite-based flame retardant is then added to a polypropylene matrix to achieve a V-0 flame retardant effect at a dosage lower than 20 wt% of the polypropylene matrix, while also taking into account the mechanical properties of the polypropylene composite material.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] Firstly, organosilane-modified graphite-based flame retardants, whose raw materials include: isocyanurate ring compounds with terminal siloxane groups, phenylsilane coupling agents, and expandable graphite;

[0008] The general structural formula of the terminal siloxane-based isocyanurate ring compound is as follows:

[0009] ;

[0010] R0 is selected from methyl, ethyl, or isopropyl;

[0011] R1 is selected from straight-chain alkyl, branched alkyl, or cycloalkyl groups having 1 to 12 carbon atoms;

[0012] R2 is selected from straight-chain alkyl, branched alkyl, or cycloalkyl groups with 1 to 6 carbon atoms;

[0013] The terminal siloxane isocyanurate ring compound comprises an isocyanurate ring and a urea bond;

[0014] The phenylsilane coupling agent is selected from one or both of phenyltrimethoxysilane and phenyltriethoxysilane;

[0015] Preferably, the method for preparing the siloxane-terminated isocyanurate ring compound includes: reacting a diisocyanate trimer with an aminosilane coupling agent;

[0016] Preferably, the reaction temperature of the diisocyanate trimer with the aminosilane coupling agent is room temperature to 60°C;

[0017] Preferably, the diisocyanate trimer is selected from aliphatic diisocyanate trimers or aromatic diisocyanate trimers;

[0018] Preferably, the aminosilane coupling agent is selected from 3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane.

[0019] Preferably, the expansion ratio of the expandable graphite is greater than 100 times.

[0020] Furthermore, by weight, the raw materials for the organosilane-modified graphite-based flame retardant include the following components in parts by weight: 90-110 parts by weight of expandable graphite, 10-16 parts by weight of phenylsilane coupling agent, and 3-8 parts by weight of isocyanurate ring compound with terminal siloxane groups.

[0021] The sum of the mass of the phenylsilane coupling agent and the isocyanurate ring compound with terminal siloxane is 15-25 wt% of the expandable graphite.

[0022] Preferably, the mass ratio of the phenylsilane coupling agent to the terminal siloxane isocyanurate ring compound is (2-3):1.

[0023] Secondly, a method for preparing an organosilane-modified graphite-based flame retardant as described above includes: dispersing expandable graphite in an alcohol / water mixed solution, adding a terminal siloxane-based isocyanurate cyclic compound and a phenylsilane coupling agent, mixing and then hydrolyzing to obtain the product.

[0024] The alcohol in the alcohol / water mixture is selected from any one of methanol, ethanol, or isopropanol.

[0025] Preferably, the mass ratio of alcohol to water in the alcohol / water mixed solution is (10-20):1;

[0026] Preferably, the mass ratio of the alcohol / water mixture to expandable graphite is (1-1.5):1.

[0027] Furthermore, the preparation method specifically includes the following steps:

[0028] S1. Expandable graphite is vacuum dried and then dispersed in an alcohol / water mixed solution to obtain a uniform suspension.

[0029] S2. Adjust the pH of the suspension to 7.5-8.5;

[0030] S3. At 40-60℃, add dropwise a mixture of terminal siloxane isocyanurate ring compound and phenylsilane coupling agent to the suspension.

[0031] S4. After the addition is complete, maintain the temperature at 40-60℃ for the reaction.

[0032] S5. After the heat preservation reaction is completed, filter the solution, wash the filtrate until neutral, and take the filter cake for vacuum drying to obtain organosilane modified graphite-based flame retardant.

[0033] Thirdly, the application of the organosilane-modified graphite-based flame retardants mentioned above in the preparation of polyolefins.

[0034] Fourthly, a flame-retardant polypropylene, the raw materials of which include: the organosilane-modified graphite-based flame retardant described above, polypropylene, lubricant and antioxidant;

[0035] Preferably, the polypropylene is selected from polypropylene with a melt flow index of 1.0-5.0 g / 10 min (according to GB / T 3682 standard) to ensure melt strength, prevent sagging, and ensure the flatness of the building panels;

[0036] More preferably, the polypropylene is selected from polypropylene with a melt flow index of 2.0-4.0 g / 10 min (according to GB / T 3682 standard);

[0037] The antioxidant is selected from one or two of hindered phenolic antioxidants and phosphite antioxidants;

[0038] Preferably, the hindered phenolic antioxidant is selected from antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]);

[0039] Preferably, the phosphite antioxidant is selected from antioxidant 168 (tris[2,4-di-tert-butylphenyl]phosphite);

[0040] The lubricant is selected from one or more of stearic acid, metal soaps of stearic acid, erucamide, oleamide, ethylene bis-stearamide, polyethylene wax, Fischer-Tropsch wax and polytetrafluoroethylene micro powder;

[0041] Preferably, the lubricant is selected from erucamide or oleamide.

[0042] Furthermore, by weight, the flame-retardant polypropylene comprises the following raw material formulation in parts by weight: 90-110 parts by weight of polypropylene, 10-20 parts by weight of organosilane modified graphite-based flame retardant, 1-3 parts by weight of lubricant, and 3-5 parts by weight of antioxidant.

[0043] Preferably, the flame-retardant polypropylene comprises the following raw material formulation in parts by weight: 90-110 parts by weight of polypropylene, 12-18 parts by weight of organosilane modified graphite-based flame retardant, 1-3 parts by weight of lubricant, and 3-5 parts by weight of antioxidant.

[0044] Further preferred, by weight, the flame-retardant polypropylene comprises the following raw material formulation in parts by weight: 90-110 parts by weight of polypropylene, 14-16 parts by weight of organosilane modified graphite-based flame retardant, 1-3 parts by weight of lubricant, and 3-5 parts by weight of antioxidant.

[0045] Fifthly, a method for preparing flame-retardant polypropylene as described above includes: mixing the component raw materials of the flame-retardant polypropylene described above and then processing and molding them to obtain the product.

[0046] The processing and forming steps include:

[0047] S1. Premix all raw materials to obtain a premix;

[0048] S2. The premixed material is melt-blended and extruded at 150-250℃;

[0049] S3. The melt blend extrusion product is cooled, granulated, and the granules are dried for later use.

[0050] S4. Add the dried granules to the injection molding machine and injection mold to obtain flame-retardant polypropylene.

[0051] Sixthly, the application of the flame-retardant polypropylene described above in building panels.

[0052] The beneficial effects of the technical solutions proposed above in this application are:

[0053] 1. Based on expandable graphite, a phenylsilane coupling agent and a siloxane-terminated isocyanurate ring compound are introduced. After hydrolysis and condensation of the siloxane, Si-O-Si bonds are obtained, forming a heat insulation layer between expandable graphite particles and improving the flame retardant effect. At the same time, phenyl, isocyanurate rings and urea bonds are introduced into expandable graphite to obtain an organosilane-modified graphite-based flame retardant. This provides a more optimized interface modification of the expandable graphite surface and enhances the flame retardant effect of polypropylene to V-0 level.

[0054] 2. The modification process of expandable graphite using organosilanes does not require the use of highly toxic solvents. It directly hydrolyzes and condenses in an alcohol aqueous solution to form Si-O-Si bonds, connecting the phenylsilane coupling agent and the isocyanurate ring compound with terminal siloxane.

[0055] 3. Adding organosilane-modified graphite-based flame retardants to the polypropylene matrix, with a dosage of less than 20 wt% of the polypropylene matrix, allows the expandable graphite to expand more uniformly and rapidly during combustion, forming a denser, continuous, and firm expanded char layer. This more effectively isolates heat and oxygen, delays combustion, thereby improving the flame retardancy of polypropylene and maintaining its mechanical properties. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1ATR-FTIR spectra of the terminal siloxane toluene diisocyanate trimer (red), terminal siloxane hexamethylene diisocyanate trimer (blue), and terminal siloxane isophorone diisocyanate trimer (green) prepared in Examples 1, 3, and 5.

[0058] Figure 2 These are photographs of UL-94 vertical burning tests for Examples 11, 3, and 4. Detailed Implementation

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention. It should be noted that the terminology used herein is only for describing specific implementation methods and is not intended to limit the exemplary implementation methods according to the present invention.

[0060] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially.

[0061] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0062] The terms "and / or," "or / and," and "and / or" as used herein include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that in this application, the technical solution undoubtedly includes technical solutions connected by "logical AND," and also undoubtedly includes technical solutions connected by "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0063] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0064] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0065] In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions containing the listed features.

[0066] The polypropylene grade PPH-T03 has a melt flow index of 2.6 g / 10 min (according to GB / T 3682 standard) and is mainly used in building materials. It is produced by Sinopec Maoming.

[0067] Expandable graphite with a particle size of 200 mesh, an expansion ratio of 120 times, and a carbon content of 93.53%, produced by Nanjing Jicang Nano.

[0068] 3-Aminopropyltrimethoxysilane (KH540), phenyltrimethoxysilane, Jianghan New Materials.

[0069] Hexamethylene diisocyanate urea dione Desmodur N3400, hexamethylene diisocyanate trimer Desmodur N3390 BA / SN, isophorone diisocyanate trimer Desmodur Z4470 BA, Covestro.

[0070] Toluene diisocyanate trimer Takenate D-260, Mitsui Chemicals, Japan.

[0071] Example 1

[0072] Synthesis of terminal siloxane precursor: Takenate D-260 toluene diisocyanate trimer and 3-aminopropyltrimethoxysilane (KH540) were used as raw materials, with 112 parts by mass of Takenate D-260 (NCO content 7.5%) and 35.9 parts by mass of KH540. The reaction was carried out at room temperature for 2 hours under nitrogen protection to obtain terminal siloxane toluene diisocyanate trimer.

[0073] The structure of the terminal siloxane-alkyl toluene diisocyanate trimer was characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and the results are as follows: Figure 1 As shown.

[0074] Pretreatment of expandable graphite: Expandable graphite was vacuum dried at 60℃ for 8 hours. Then, 100 parts by weight of expandable graphite were weighed and added to 120 parts by weight of anhydrous ethanol / water mixed solution (ethanol / water mass ratio 11:1). The solution was ultrasonically dispersed for 1 hour to form a uniform suspension. The suspension was then transferred to a three-necked flask, and the pH of the system was adjusted to between 8.0 and 8.5 with ammonia. The temperature was controlled at 50℃ in a water bath, and a mixture of 12 parts by weight of phenyltrimethoxysilane and 6 parts by weight of terminal siloxane toluene diisocyanate trimer was added dropwise over 4 hours. After the addition was complete, the reaction was maintained at 50℃ for 1 hour. The product was then filtered and washed with ethanol solution until neutral. Unreacted monomers were removed by filtration. The filter cake was vacuum dried at 50℃ for 12 hours to obtain an organosilane-modified graphite-based flame retardant.

[0075] Example 2

[0076] The preparation steps of the organosilane modified graphite-based flame retardant are the same as in Example 1, except that a mixture of 15 parts by mass of phenyltrimethoxysilane and 5 parts by mass of terminal siloxane toluene diisocyanate trimer is added dropwise.

[0077] Example 3

[0078] Synthesis of terminal siloxane precursor: Using hexamethylene diisocyanate trimer Desmodur N3390 and 3-aminopropyltrimethoxysilane (KH540) as raw materials, with 41 parts by mass of Desmodur N3390 (NCO content 19.5%) and 35.9 parts by mass of KH540, the two were reacted at 40°C for 2 hours under nitrogen protection to obtain terminal siloxane hexamethylene diisocyanate trimer.

[0079] The structure of the terminal siloxane-alkyl hexamethylene diisocyanate trimer was characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and the results are as follows: Figure 1 As shown.

[0080] The subsequent steps are the same as in Example 1, except that a mixture of 6 parts by mass of terminal siloxane hexamethylene diisocyanate trimer and 12 parts by mass of phenyltrimethoxysilane is added dropwise.

[0081] Example 4

[0082] The synthesis steps of the terminal siloxane precursor and subsequent steps are the same as in Example 3, except that a mixture of 5 parts by mass of terminal siloxane hexamethylene diisocyanate trimer and 15 parts by mass of phenyltrimethoxysilane is added dropwise.

[0083] Example 5

[0084] Synthesis of terminal siloxane precursor: using isophorone diisocyanate trimer Desmodur Z4470 BA and 3-aminopropyltrimethoxysilane (KH540) as raw materials, wherein the amount of Desmodur Z4470 BA is 66.5 parts by mass (NCO content 12.0%) and the amount of KH540 is 35.9 parts by mass, the two are reacted at 45°C for 2 hours under nitrogen protection to obtain terminal siloxane isophorone diisocyanate trimer.

[0085] The structure of the terminal siloxane-alkyl isophorone diisocyanate trimer was characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and the results are as follows: Figure 1 As shown.

[0086] The subsequent steps are the same as in Example 1, except that a mixture of 6 parts by mass of terminal siloxane isophorone diisocyanate trimer and 12 parts by mass of phenyltrimethoxysilane is added dropwise.

[0087] Example 6

[0088] The synthesis steps of the terminal siloxane precursor and subsequent steps are the same as in Example 3, except that a mixture of 5 parts by mass of terminal siloxane isophorone diisocyanate trimer and 15 parts by mass of phenyltrimethoxysilane is added dropwise.

[0089] Example 7

[0090] Polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of organosilane-modified graphite-based flame retardant of Example 1, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0091] The processing and forming steps include:

[0092] S1. Premix all raw materials to ensure that flame retardants, lubricants and antioxidants are uniformly dispersed in the polypropylene matrix;

[0093] S2. Add the premix to a twin-screw extruder and melt-blend and extrude at 160-210℃ and 160rpm.

[0094] S3. The melt blend extrusion product is cooled in a water bath and then pelletized. The pellets are dried in a drying oven at 60°C for 24 hours.

[0095] S4. Injection molding: The dried granules are added to the injection molding machine to obtain a series of standard specimens of different sizes for subsequent performance testing.

[0096] Example 8

[0097] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of organosilane-modified graphite-based flame retardant of Example 2, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0098] The processing and molding steps are the same as in Example 7.

[0099] Example 9

[0100] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 14 parts by weight of organosilane-modified graphite-based flame retardant of Example 2, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0101] The processing and molding steps are the same as in Example 7.

[0102] Example 10

[0103] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of the organosilane-modified graphite-based flame retardant of Example 3, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0104] The processing and molding steps are the same as in Example 7.

[0105] Example 11

[0106] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of the organosilane-modified graphite-based flame retardant of Example 4, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0107] The processing and molding steps are the same as in Example 7.

[0108] Example 12

[0109] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 14 parts by weight of the organosilane-modified graphite-based flame retardant of Example 4, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0110] The processing and molding steps are the same as in Example 7.

[0111] Example 13

[0112] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of the organosilane-modified graphite-based flame retardant of Example 5, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0113] The processing and molding steps are the same as in Example 7.

[0114] Example 14

[0115] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of the organosilane-modified graphite-based flame retardant of Example 6, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0116] The processing and molding steps are the same as in Example 7.

[0117] Example 15

[0118] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 14 parts by weight of the organosilane-modified graphite-based flame retardant of Example 6, 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0119] The processing and molding steps are the same as in Example 7.

[0120] Comparative Example 1

[0121] Pretreatment of expandable graphite: Expandable graphite was vacuum dried at 60℃ for 8 hours. Then, 100 parts by weight of expandable graphite were weighed and added to 120 parts by weight of anhydrous ethanol / water mixed solution (ethanol / water mass ratio 11:1). The solution was ultrasonically dispersed for 1 hour to form a uniform suspension. The suspension was then transferred to a three-necked flask, and the pH of the system was adjusted to between 8.0 and 8.5 with ammonia. The temperature was controlled at 50℃ in a water bath, and 20 parts by weight of phenyltrimethoxysilane were added dropwise over 4 hours. After the addition was completed, the reaction was maintained at 50℃ for 1 hour. The product was then filtered and washed with ethanol solution until neutral. Unreacted monomers were removed by filtration. The filter cake was vacuum dried at 50℃ for 12 hours to obtain an organosilane-modified graphite-based flame retardant.

[0122] Comparative Example 2

[0123] Synthesis of terminal siloxane precursor: Hexamethylene diisocyanate urea dione (HDI urea dione) Desmodur N3400 and 3-aminopropyltrimethoxysilane (KH540) were used as raw materials, wherein the amount of HDI urea dione was 38.2 parts by mass (NCO content 22.0%) and the amount of KH540 was 35.9 parts by mass. The two were reacted at 40°C for 2 hours under nitrogen protection to obtain terminal siloxane hexamethylene diisocyanate urea dione.

[0124] The subsequent steps are the same as in Example 1, except that 5 parts by mass of a mixture of terminal siloxane hexamethylene diisocyanate urea dione and 15 parts by mass of phenyltrimethoxysilane are added dropwise.

[0125] Comparative Example 3

[0126] Polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of organosilane-modified graphite-based flame retardant (Comparative Example 1), 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0127] The processing and molding steps are the same as in Example 7.

[0128] Comparative Example 4

[0129] The polypropylene doped with organosilane-modified graphite-based flame retardant comprises the following raw materials: 100 parts by weight of PPH-T03 polypropylene granules, 16 parts by weight of organosilane-modified graphite-based flame retardant (Comparative Example 2), 2 parts by weight of lubricant erucamide, 2.5 parts by weight of hindered phenolic antioxidant 1010, and 1.5 parts by weight of phosphite antioxidant 168.

[0130] The processing and molding steps are the same as in Example 7.

[0131] Performance testing

[0132] Tensile breaking strength and elongation at break were tested in accordance with GB / T 1040.2-2022, where the tensile speed was set at 50 mm / min.

[0133] Notched impact strength of cantilever beam: The notched impact strength of the cantilever beam at 23℃ was tested in accordance with ISO 180:2023.

[0134] Limiting Oxygen Index (LOI) Test: Referencing the ASTM D 2863-2013 standard, the Limiting Oxygen Index (LOI) is tested. The LOI value measures the minimum oxygen concentration required for a material to burn. The higher the LOI value, the stronger the corresponding flame retardancy.

[0135] UL-94 Vertical Burning Test: Referencing ASTM D3801 standard, the flame retardancy rating of the material is assessed by observing the burning time, dripping pattern, and whether it ignites the cotton pad below.

[0136] The test results of polypropylene doped with organosilane-modified graphite-based flame retardants in Examples 7-15 and Comparative Examples 3-4 are listed in Table 1.

[0137] Table 1

[0138]

[0139] Examples 1-6 use the reaction products of TDI trimer, HDI trimer, or IPDI trimer with KH540 (terminated siloxane TDI trimer, siloxane HDI trimer, or siloxane IPDI trimer) as precursors, which are hydrolyzed and condensed with phenyltrimethoxysilane under alkaline conditions, thereby introducing an isocyanurate ring. The N-(C=O)-N bond or -NH-(C=O)-NH urea bond therein is coupled with the polar groups on the surface of expandable graphite after chemical oxidation intercalation through hydrogen bonding. The phenyltrimethoxysilane forms a Si-O-Si structure after hydrolysis. Its own benzene ring binds to the delocalized large π bond formed by the unhybridized p electrons in the sp2 hybridized carbon atoms on the graphite surface through π-π interactions. Thus, the phenyltrimethoxysilane and the precursor hydrolysis product are coupled on the surface of expandable graphite to prepare organosilanes modified graphite-based flame retardants. The organosilane-modified graphite-based flame retardant was further incorporated into polypropylene, and the flame-retardant polypropylene of Examples 7-15 was prepared by injection molding.

[0140] Analysis of the test results in Table 1 shows that the amount of organosilane-modified graphite-based flame retardant in the formulations of Examples 7-15 is 14-16 wt% of polypropylene, corresponding to a limiting oxygen index (LOI) of ≥26% for polypropylene. The flame retardant effect is V-0 in the UL-94 test, and it has no significant impact on the mechanical properties of flame-retardant polypropylene.

[0141] Comparative Example 1 uses phenyltrimethoxysilane alone for hydrolysis and couples it with expandable graphite to prepare an organosilane-modified graphite-based flame retardant. Lacking nitrogen, isocyanurate rings, and urea bonds, the polypropylene prepared in Comparative Example 3 has poor flame retardant effect. In the UL-94 vertical burning test, it produces molten droplets that ignite cotton, and the flame retardant rating is only V-2.

[0142] Comparative Example 2 used HDI urea diketone instead of the HDI trimer in Example 3, but the resulting organosilane-modified graphite-based flame retardant did not perform well. The reason for this was that the urea diketone ring in HDI urea diketone was formed by the reaction of two isocyanates (-NCO) of two HDI molecules to create a cyclic dimer structure. This dimer structure is unstable in alkaline aqueous solutions and easily decomposes, thus failing to form a stable structure during subsequent hydrolysis. The lack of isocyanurate rings resulted in poor flame retardancy in the polypropylene of Comparative Example 4. While no droplets were observed in the UL-94 vertical burning test, the sample had a long burning time and a flame retardancy rating of only V-1.

[0143] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of them. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Although the specific embodiments of the present invention have been described above, they are not intended to limit the protection scope of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An organosilane-modified graphite-based flame retardant, characterized in that, The raw materials include: isocyanurate ring compounds with terminal siloxanes, phenylsilane coupling agents, and expandable graphite; The general structural formula of the terminal siloxane-based isocyanurate ring compound is as follows: ； R0 is selected from methyl, ethyl, or isopropyl. R1 is selected from straight-chain alkyl, branched alkyl, or cycloalkyl groups having 1 to 12 carbon atoms; R2 is selected from straight-chain alkyl, branched alkyl, or cycloalkyl groups with 1 to 6 carbon atoms; The terminal siloxane isocyanurate ring compound comprises an isocyanurate ring and a urea bond; The phenylsilane coupling agent is selected from one or both of phenyltrimethoxysilane and phenyltriethoxysilane.

2. The organosilane-modified graphite-based flame retardant according to claim 1, characterized in that, The raw materials for organosilane-modified graphite-based flame retardants, by weight, include the following components: 90-110 parts by weight of expandable graphite, 10-16 parts by weight of phenylsilane coupling agent, and 3-8 parts by weight of isocyanurate ring compound with terminal siloxane. The sum of the mass of the phenylsilane coupling agent and the isocyanurate cyclic compound with terminal siloxane is 15-25 wt% of the expandable graphite.

3. A method for preparing an organosilane-modified graphite-based flame retardant as described in any one of claims 1-2, comprising: Expandable graphite is dispersed in an alcohol / water mixture, and a terminal siloxane isocyanurate cyclic compound and a phenylsilane coupling agent are added. The mixture is then hydrolyzed to obtain the product. The alcohol in the alcohol / water mixture is selected from any one of methanol, ethanol, or isopropanol.

4. The method for preparing the organosilane-modified graphite-based flame retardant according to claim 3, characterized in that, The mass ratio of alcohol to water in the alcohol / water mixed solution is (10-20):1; And / or, the mass ratio of the alcohol / water mixture to expandable graphite is (1-1.5):

1.

5. The method for preparing the organosilane-modified graphite-based flame retardant according to claim 3, characterized in that, The preparation method specifically includes the following steps: S1. Expandable graphite is vacuum dried and then dispersed in an alcohol / water mixed solution to obtain a uniform suspension. S2. Adjust the pH of the suspension to 7.5-8.5; S3. At 40-60℃, add dropwise a mixture of terminal siloxane isocyanurate ring compound and phenylsilane coupling agent to the suspension. S4. After the addition is complete, maintain the temperature at 40-60℃ for the reaction. S5. After the heat preservation reaction is completed, filter the solution, wash the filtrate until neutral, and take the filter cake for vacuum drying to obtain organosilane modified graphite-based flame retardant.

6. The application of the organosilane-modified graphite-based flame retardant as described in any one of claims 1-2 in the preparation of polyolefins.

7. A flame-retardant polypropylene, characterized in that, The raw materials include: the organosilane-modified graphite-based flame retardant as described in any one of claims 1-2, polypropylene, lubricant, and antioxidant; The antioxidant is selected from one or two of hindered phenolic antioxidants and phosphite antioxidants; The lubricant is selected from one or more of stearic acid, metal soaps of stearic acid, erucamide, oleamide, ethylene bis-stearamide, polyethylene wax, Fischer-Tropsch wax, and polytetrafluoroethylene micro powder.

8. The flame-retardant polypropylene according to claim 7, characterized in that, By weight, flame-retardant polypropylene comprises the following raw material formulation in parts by weight: 90-110 parts by weight of polypropylene, 10-20 parts by weight of organosilane modified graphite-based flame retardant, 1-3 parts by weight of lubricant, and 3-5 parts by weight of antioxidant.

9. A method for preparing flame-retardant polypropylene as described in any one of claims 7-8, characterized in that, The flame-retardant polypropylene is obtained by mixing the components of the above-mentioned raw materials and then processing and molding them. The processing and forming steps include: S1. Premix all raw materials to obtain a premix; S2. The premixed material is melt-blended and extruded at 150-250℃; S3. The melt blend extrusion product is cooled, granulated, and the granules are dried for later use. S4. Add the dried granules to the injection molding machine and injection mold to obtain flame-retardant polypropylene.

10. The application of flame-retardant polypropylene as described in any one of claims 7-8 in building panels.

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