Phytic acid-modified pyrophosphoryl piperazine and zinc borate synergistic flame-retardant polypropylene and preparation method thereof

Abstract

This invention belongs to the field of flame retardant polymer materials, and specifically relates to a phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame retardant polypropylene and its preparation method. The composition by mass percentage is: polypropylene (PP): 73-75%; phytic acid-modified piperazine pyrophosphate (PM@PAPP): 24-26%; zinc borate: 0.5-2%. This invention uses piperazine pyrophosphate as the core and, through a liquid-phase supramolecular self-assembly process, in-situ coats the surface with a supramolecular network formed by phytic acid and melamine to prepare a core-shell structured phytic acid-modified piperazine pyrophosphate. This core-shell structure is then compounded with zinc borate, and melt-blended and hot-pressed to obtain a flame-retardant polypropylene composite material. This composite material improves the compatibility between the material and the flame retardant, inhibits the release of toxic fumes, and forms a continuous, dense char layer, enhancing the material's thermal stability and fire safety performance. It solves the problems of traditional flame retardants, such as large dosage requirements, easy migration, insufficient foaming, and poor smoke suppression effects.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant polymer materials, and specifically relates to a plant acid-modified piperazine pyrophosphate and zinc borate synergistic flame retardant polypropylene and its preparation method. Background Technology

[0002] Polypropylene (PP), as a general-purpose thermoplastic, is widely used in building materials, electronic and electrical enclosures, and automotive parts due to its low cost, ease of processing, and excellent mechanical and chemical stability. However, PP has a limiting oxygen index of only about 17.2%, making it extremely flammable. The combustion process is accompanied by molten droplets, a large amount of toxic fumes, and the release of heat, which severely limits its application in scenarios with high fire safety requirements.

[0003] Intumescent flame retardants (IFR) are the mainstream halogen-free flame retardant solution for polypropylene. They consist of an acid source, a gas source, and a carbon source. When heated, they can form an expanded porous carbon layer on the material surface, isolating heat and oxygen and inhibiting dripping. Traditional IFRs use ammonium polyphosphate (APP) as the acid source, melamine (MEL) as the gas source, and pentaerythritol as the carbon source. They have drawbacks such as large addition amounts, easy migration, poor water resistance, and low flame retardant efficiency.

[0004] Piperazine pyrophosphate (PAPP) is a three-in-one intumescent flame retardant containing phosphorus, nitrogen, and carbon elements. It exhibits excellent thermal stability, charring ability, and water resistance, and can replace traditional APP-based flame retardants. However, it suffers from insufficient foaming ability and requires the addition of a foaming agent to enhance its flame retardant effect. Phytic acid (PA) is a green bio-based flame retardant with high phosphorus content and strong charring ability, making it a highly efficient acid source. Melamine (MEL) is a classic gas source that releases inert gas upon heating to dilute the flammable concentration. Zinc borate (ZB) is a non-toxic smoke suppressant that forms a glassy char layer at high temperatures, inhibiting smoke release and enhancing the density of the char layer.

[0005] In the prior art, phytic acid-melamine supramolecular self-assembled flame retardants have been disclosed. Firstly, such as the phytic acid supramolecular flame retardant disclosed in patent CN202210462889.X, which only involves the simple self-assembly of phytic acid and organic amine compounds to form small molecule salts, and is merely a physical blending of powders or a single supramolecular salt formation, without core-shell structure modification using PAPP as the core and PA-MEL as the shell. This type of system has poor interfacial compatibility with the PP matrix, the flame retardant is prone to agglomeration and migration, and cannot form a continuous, dense char layer, resulting in limited flame retardant and smoke suppression effects. Secondly, such as the PAPP / melamine cyanurate disclosed in patent CN202111239160.8. The (MCA) compound flame retardant uses ball milling to physically mix PAPP and MCA, which is only a mechanical and physical blending process without a supramolecular self-assembly coating structure. Furthermore, MCA is a hydrogen-bonded complex of melamine and cyanuric acid. In the MCA compound system, MCA has a low thermal decomposition temperature, low char yield, and a loose and porous char layer, which cannot effectively block heat and smoke. Its smoke suppression performance is far inferior to that of the PA-MEL supramolecular shell layer. Thirdly, existing technologies do not disclose a "core-shell structure PM@PAPP with PAPP as the core and PA-MEL supramolecular layer as the shell," nor do they disclose a phosphorus-nitrogen-boron synergistic flame retardant system combining this core-shell structure flame retardant with zinc borate (ZB). Moreover, the single PA-MEL self-assembly system lacks the support of the PAPP core, resulting in low synergistic efficiency of acid, gas, and carbon sources, requiring large addition amounts to achieve a flame retardant effect and significantly reducing the mechanical properties of the PP matrix.

[0006] Currently, single flame retardants struggle to simultaneously achieve high flame retardancy, smoke suppression, thermal stability, and environmental friendliness. Physical blending suffers from uneven dispersion, poor interfacial compatibility, and a loose char layer. Specifically, conventional physical blending methods, such as melt-mixing phytic acid and melamine into polypropylene, result in macroscopic phase separation and agglomeration of the flame retardant components within the polypropylene matrix due to their polarity differences. During combustion, the physically separated acid, gas, and char sources cannot undergo simultaneous dehydration, foaming, and cross-linking reactions, leading to a char layer with large, easily ruptured pores that cannot effectively block heat and oxygen. This explains why traditional compounded flame retardants require large dosages and still exhibit poor flame retardant efficiency.

[0007] The key technological direction for solving the shortcomings of polypropylene flame retardancy and overcoming the defects of existing technologies is to construct the core-shell structure PM@PAPP through supramolecular self-assembly and combine it with ZB to achieve synergistic effects of phosphorus-nitrogen-boron multi-element. Summary of the Invention

[0008] The purpose of this invention is to provide a phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene and its preparation method, which solves the problems of low flame retardant efficiency, poor smoke suppression, easy melting and dripping, and poor dispersibility of traditional polypropylene flame retardant materials. Through supramolecular self-assembly and multi-element synergy, it achieves integrated high-efficiency flame retardancy, smoke suppression, and thermal stability.

[0009] This invention relates to a phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame retardant polypropylene. The raw material composition, by mass percentage, is as follows: polypropylene (PP): 73-75%; phytic acid-modified piperazine pyrophosphate (PM@PAPP): 24-26%; zinc borate (ZB): 0.5-2%.

[0010] Preferably, other additives can be added to the flame-retardant polypropylene as needed; preferably, a compatibilizer is added, the compatibilizer accounting for 1-1.5% of the total mass of PP and flame retardant, and the compatibilizer is maleic anhydride-grafted polypropylene.

[0011] This invention employs a supramolecular self-assembly method to prepare an integrated flame retardant of phytic acid-modified piperazine pyrophosphate (PM@PAPP). Phytic acid (PA) and melamine (MEL) are used to encapsulate piperazine pyrophosphate (PAPP). Then, it is compounded with zinc borate (ZB) to construct a highly efficient intumescent flame retardant system through phosphorus-nitrogen-boron synergistic effects. The flame-retardant PP composite material is prepared by melt blending and hot pressing, resulting in a material with no dripping, achieving a V-0 flame retardancy rating, and exhibiting excellent smoke suppression performance.

[0012] PM@PAPP is a core-shell flame retardant with piperazine pyrophosphate as the core and phytic acid-melamine supramolecular network as the shell.

[0013] The specific preparation steps for PM@PAPP are as follows:

[0014] (1) Disperse melamine (MEL) in deionized water and mechanically stir at 70-80℃ until homogeneous;

[0015] (2) Disperse phytic acid (PA) in deionized water and add it dropwise to the MEL solution at a rate of 3-5 drops / s. Stir at 70-80℃ for 30 min to obtain PA-MEL mixture.

[0016] (3) Disperse piperazine pyrophosphate (PAPP) in a mixture of deionized water and anhydrous ethanol with a volume ratio of 3:2. Add PA-MEL mixture dropwise and stir at 400-600 rpm for 2-4 hours at 70-80℃.

[0017] (4) Centrifuge to collect the product, dry at 70-80℃ to constant weight to obtain PM@PAPP powder.

[0018] The molar ratio of phytic acid to melamine is 1:3~6; the total mass ratio of phytic acid and melamine to piperazine pyrophosphate is 1:1-7.

[0019] The preparation steps for phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene are as follows:

[0020] (a) Place PP, PM@PAPP, and ZB in a drying oven at 70-80℃ for 8-12 hours to remove moisture;

[0021] (b) Heat the internal mixer to 175-180℃, add PP, PM@PAPP, ZB and maleic anhydride-grafted polypropylene according to the formula, and melt-blend for 8-10 minutes until uniform.

[0022] (c) The blended material is hot-pressed at 175-180℃ for 3 minutes and cold-pressed at room temperature for 2 minutes in a flat vulcanizing machine, and then cut into standard strips.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) This invention first uses a simple supramolecular self-assembly method to coat phytic acid and melamine with piperazine pyrophosphate to form a core-shell structure, achieving a tight combination of acid source, gas source, and carbon source. Compared with conventional physical mixing, the PA-MEL supramolecular network coated on the shell can degrade in situ, directly releasing acidic catalysts and inert gases on the surface of the PAPP core, instantly inducing the PAPP and matrix to expand and char, thus improving its synergistic effect of flame retardancy and smoke suppression. This preparation method can obtain the desired target product through simple non-covalent interactions, and does not require complex reaction conditions and steps in the experiment.

[0025] (2) The prepared phytic acid modified piperazine pyrophosphate (PM@PAPP) is used as the acid source and gas source of the intumescent flame retardant, and zinc borate (ZB) is used as the synergistic smoke suppressant to form a new type of high-efficiency flame retardant. Through melt blending, flame retardant PP composite material is prepared by mixing with PP and pressing into tablets. The whole preparation process is highly efficient.

[0026] (3) The supramolecular self-assembly employed in this invention can interact with phytic acid and melamine, which are rich in active groups, to form a supramolecular assembly layer as a coating shell, thereby encapsulating the core material piperazine pyrophosphate. This supramolecularly assembled shell is tightly packed, not easily damaged during processing, and has higher stability. The supramolecularly assembled shell not only acts as a char-forming agent during combustion but also improves the dispersion performance of modified piperazine pyrophosphate in the matrix material, thereby improving its compatibility with the polymer matrix material. At the same time, the synergistic effect of phosphorus-nitrogen-boron can significantly enhance the flame retardant and smoke-suppressing properties of the material. Attached Figure Description

[0027] Figure 1 SEM images of (a) PAPP and (b) PM@PAPP;

[0028] Figure 2 (a)FT-IR, (b)XRD, and (ci)XPS spectra of PAPP and PM@PAPP;

[0029] Figure 3 (a) TGA and (b) DTG curves for PAPP and PM@PAPP (PA-MEL@PAPP);

[0030] Figure 4 (a) TGA and (b) DTG curves of PP and its composites;

[0031] Figure 5 CCT test curves for PP and its composites;

[0032] Figure 6 Digital photographs, SEM images, and Raman spectroscopy results of residual carbon in PP flame-retardant composite materials. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] Comparative Example 1:

[0035] The flame-retardant polypropylene is composed of the following mass percentages: PP: 75%, PAPP: 25%. Maleic anhydride-grafted polypropylene accounts for 1% of the total mass of PP and PAPP flame retardants. The preparation process is as follows:

[0036] (1) Place the above PP and PAPP in an oven at 80℃ for 12 hours to dry and remove moisture.

[0037] (2) Set the mixing temperature of the internal mixer to 180℃. After the temperature stabilizes, start feeding.

[0038] (3) First, slowly pour the dried PP into the internal mixer through the feeding port, and then slowly add PAPP and maleic anhydride grafted polypropylene in sequence. Under the action of the dual rotors, fully extrude, shear, and melt-blend for 10 minutes until fully mixed. Then, the blended material is hot-pressed for 3 minutes and cold-pressed at room temperature for 2 minutes in a flat vulcanizing machine to obtain PP / PAPP (PP1) material.

[0039] Comparative Example 2

[0040] The phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene consists of the following mass percentages: PP: 75%, PM@PAPP: 25%. Maleic anhydride-grafted polypropylene accounts for 1% of the total mass of PP and PM@PAPP flame retardants. The preparation process is as follows:

[0041] (1) Add 2.67g of MEL and 50mL of deionized water to a 250mL round-bottom flask, place it in an oil bath at 80℃, and then dissolve the MEL completely under mechanical stirring to obtain a MEL solution.

[0042] (2) Add 3.33g PA (calculated based on the pure weight of phytic acid) and disperse it in deionized water. Add it dropwise to the MEL solution at a rate of 3-5 drops / s. Stir at 70-80℃ for 30 min to obtain PA-MEL mixture. Then disperse piperazine pyrophosphate (PAPP) in deionized water and anhydrous ethanol (volume ratio of deionized water and anhydrous ethanol is 3:2) to obtain PAPP suspension. Add PA-MEL mixture dropwise to the suspension containing 30g PAPP. Stir at 500rpm at 80℃ for 2 h. After the reaction is completed, cool the mixture to room temperature, centrifuge, and dry at 70℃ to obtain PM@PAPP white powder.

[0043] (3) The dried and weighed PP, PM@PAPP and maleic anhydride grafted polypropylene were processed according to the mixing and hot pressing conditions of Comparative Example 1 to obtain PP / PM@PAPP (PP2) material.

[0044] The properties of the material in this embodiment are shown in Table 1.

[0045] Example 1

[0046] The phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene consists of the following mass percentages: PP: 74.5%, PM@PAPP: 25%, ZB: 0.5%. Maleic anhydride-grafted polypropylene comprises 1% of the total mass of PP, PM@PAPP, and ZB. The preparation process is as follows:

[0047] (1) Add 2.67g of MEL and 50mL of deionized water to a 250mL round-bottom flask, place it in an oil bath at 80℃, and then dissolve the MEL completely under mechanical stirring to obtain a MEL solution.

[0048] (2) Add 3.33g PA (calculated based on the pure weight of phytic acid) and disperse it in deionized water. Add it dropwise to the MEL solution at a rate of 3-5 drops / s. Stir at 70-80℃ for 30 min to obtain PA-MEL mixture. Then disperse piperazine pyrophosphate (PAPP) in deionized water and anhydrous ethanol (volume ratio of deionized water and anhydrous ethanol is 3:2) to obtain PAPP suspension. Add PA-MEL mixture dropwise to the suspension containing 30g PAPP. Stir at 500rpm at 80℃ for 2 h. After the reaction is completed, cool the mixture to room temperature, centrifuge, and dry at 70℃ to obtain PM@PAPP white powder.

[0049] (3) The dried and weighed PP, PM@PAPP, ZB and maleic anhydride grafted polypropylene were repeatedly subjected to the mixing and hot pressing conditions of Comparative Example 1 to obtain PP / PM@PAPP / ZB (PP3) material.

[0050] The properties of the material in this embodiment are shown in Table 1.

[0051] Example 2

[0052] The phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene consists of the following mass percentages: PP: 74%, PM@PAPP: 25%, ZB: 1%. Maleic anhydride-grafted polypropylene comprises 1% of the total mass of PP, PM@PAPP, and ZB. The preparation process is as follows:

[0053] (1) Add 2.67g of MEL and 50mL of deionized water to a 250mL round-bottom flask, place it in an oil bath at 80℃, and then dissolve the MEL completely under mechanical stirring.

[0054] (2) The preparation of PM@PAPP is the same as in Example 1.

[0055] (3) Repeat the mixing and hot pressing steps of Comparative Example 1 with the dried and weighed PP, PM@PAPP, ZB and maleic anhydride grafted polypropylene to obtain PP / PM@PAPP / ZB (PP4) material.

[0056] The properties of the material in this embodiment are shown in Table 1.

[0057] Example 3

[0058] The phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene consists of the following mass percentages: PP: 73.5%, PM@PAPP: 25%, ZB: 1.5%. Maleic anhydride-grafted polypropylene comprises 1% of the total mass of PP, PM@PAPP, and ZB. The preparation process is as follows:

[0059] (1) Add 2.67g of MEL and 50mL of deionized water to a 250mL round-bottom flask, place it in an oil bath at 80℃, and then dissolve the MEL completely under mechanical stirring.

[0060] (2) The preparation of PM@PAPP is the same as in Example 1.

[0061] (3) The dried and weighed PP, PM@PAPP, ZB and maleic anhydride grafted polypropylene were repeatedly subjected to the mixing and hot pressing conditions of Comparative Example 1 to obtain PP / PM@PAPP / ZB (PP5) material.

[0062] The properties of the material in this embodiment are shown in Table 1.

[0063] Example 4

[0064] The phytic acid-modified piperazine pyrophosphate and zinc borate synergistic flame-retardant polypropylene consists of the following mass percentages: PP: 73%, PM@PAPP: 25%, ZB: 2%. Maleic anhydride-grafted polypropylene comprises 1% of the total mass of PP, PM@PAPP, and ZB. The preparation process is as follows:

[0065] (1) Add 2.67g of MEL and 50mL of deionized water to a 250mL round-bottom flask, place it in an oil bath at 80℃, and then dissolve the MEL completely under mechanical stirring.

[0066] (2) The preparation of PM@PAPP is the same as in Example 1.

[0067] (3) The dried and weighed PP, PM@PAPP, ZB and maleic anhydride grafted polypropylene were repeatedly subjected to the mixing and hot pressing conditions of Comparative Example 1 to obtain PP / PM@PAPP / ZB (PP6) material.

[0068] The properties of the material in this embodiment are shown in Table 1.

[0069] Limiting oxygen index (LOI), UL-94, and mechanical properties were tested on pure PP and comparative examples 1-2 and 1-4. The results are shown in Table 1.

[0070] Table 1 Summary of Performance Characterization of Pure PP and Flame-Retardant PP Composite Materials

[0071] Performance parameters Pure PP Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Flammability rating UL-94 NR V-0 V-0 V-0 V-0 V-0 V-0 Limiting Oxygen Index (LOI) 17.2 30.4 32.5 33.1 33.5 35.3 34.9 Tensile strength (MPa) 37.01 26.61 27.96 28.40 27.76 27.44 27.25 Elongation at break (%) 158.00 32.28 32.95 27.43 23.13 21.65 21.79 Residual mass ratio (%) 1.50 11.53 12.37 8.52 9.93 11.80 12.76

[0072] Test results show that the optimal formulation of PP5 in this invention achieves a LOI of 35.3%, a UL-94 V-0 rating, and no dripping. pHRR, pSPR, and pCOP are reduced by 91%, 93%, and 81% respectively compared to pure PP, with significantly improved thermal stability and char residue. It also exhibits optimal flame retardant and smoke suppression performance. The combination of PM@PAPP and ZB can catalyze the formation of a continuous, dense char layer, effectively blocking heat and smoke, and enhancing the fire safety of polypropylene.

[0073] Figure 1 SEM images of (a) PAPP and (b) PM@PAPP are shown. It can be seen that the untreated PAPP surface is relatively smooth. After modification with PA and MEL, many sheet-like structures are attached to the PM@PAPP surface. This is due to the ion attraction between PA and MEL and the π-π stacking self-assembly of the triazine rings, resulting in a layered structure aggregation. The surface structure before and after modification exhibits a clear encapsulation state, proving the formation of a core-shell structure with PAPP as the core and the PA-MEL supramolecular network as the shell.

[0074] Figure 2The following are the (a) FT-IR, (b) XRD, and (c) XPS spectra of PAPP and PM@PAPP. PAPP at 886 cm⁻¹... -1 and 980cm -1 The characteristic absorption peaks of P–O–P and P–OH are observed at 1502 cm⁻¹, respectively. Due to the ionic interactions between MEL and PAPP / PA, the FT-IR of PM@PAPP shows significant changes. PM@PAPP exhibits a peak at 1502 cm⁻¹. -1 A new peak appears at 3370 cm⁻¹, originating from the shift of the characteristic peak of the MEL triazine ring due to nitrogen protonation. -1 The appearance of a new broad absorption peak at this point corresponds to a shift and broadening of the –NH2 characteristic peak in the MEL, indicating the formation of –NH3 in the system. + O - Structure. 990cm -1 The broadening of the peak shape is related to the P–O bond in PA. PM@PAPP retains the characteristic peaks of PAPP, MEL, and PA, confirming that MEL and PA have been successfully coated on the PAPP surface through supramolecular self-assembly. The XRD diffraction peaks of PM@PAPP and PAPP are basically consistent, indicating that the modification of PA and MEL has not changed the original crystal structure of PAPP. Both PAPP and PM@PAPP show characteristic peaks of O1s, N1s, C1s, P2p, and P2s, indicating that the samples are mainly composed of four elements: C, N, O, and P. The C1s, O1s, and N1s of PAPP correspond to the CN and CC structures in the piperazine ring, the POP and P=O structures in phosphoric acid, and the protonated nitrogen atom (–NH2), respectively. + –). In addition to the characteristic peaks of PAPP, PM@PAPP exhibits distinct new characteristic peaks at 288.6 eV (C1s), 531.5 eV (O1s), and 399.4 eV (N1s), corresponding to the C=N of MEL, the oxygen atom in the incompletely salted phosphate group and hydrogen bond network of the phytic acid molecule, and the C=N–C nitrogen atom on the triazine ring of MEL, respectively. XPS results confirm the successful modification of PAPP by PA and MEL.

[0075] Figure 3 The images show (a) TGA and (b) DTG curves for PAPP and PM@PAPP. The thermal decomposition of PAPP generally occurs in three stages. The first stage, at 50-300℃, involves the reaction of P-OH and NH2 in PAPP. + -OP dehydration releases H2O. In the second stage (300-460℃), char is formed under the catalysis of phosphoric acid and its derivatives. In the third stage (300-460℃), the char further degrades. The residual char mass at 800℃ is 41.94wt%, exhibiting good char-forming ability and thermal stability. The introduction of PA and MEL, and the T of PM@PAPP... -5wt%The temperature dropped to 279.94℃, attributed to the pyrolysis of PA-MEL. High-temperature decomposition of PA produces polyphosphoric acid and H3PO4, which, in synergistic catalysis with PAPP, generate more carbon, further increasing the carbon content to 47.57% at 800℃. PM@PAPP exhibits stronger carbonization capabilities, effectively suppressing smoke and improving the material's flame-retardant properties.

[0076] Figure 4 The figures show (a) TGA and (b) DTG curves of PP and its composites. Pure PP begins to decompose at 413.38℃. -50wt% and T max The char residue at 452.27℃, 460.04℃, and 800℃ was only 1.5%. With the addition of IFR, the PP flame-retardant composite material decomposes before PP. The phosphoric acid and other substances produced by the thermal decomposition of PA and PAPP can catalyze the esterification reaction, thereby inducing the matrix to char prematurely. The thermal decomposition of PP composite material is divided into two stages. At around 370℃, PAPP releases small molecules such as H2O. In the second stage, PA and PAPP begin to decompose to produce polyphosphoric acid and phosphoric acid derivatives, which react with piperazine to promote the dehydration and char formation of PP. With the addition of 25wt% PAPP, the char residue of PP1 composite material at 800℃ increased to 11.53wt%. With the addition of ZB, the char formation ability of PP composite material is further enhanced, and the T of PP6... max The char residue at 473.58℃ and 800℃ is 12.76%. The high-temperature decomposition of ZB produces ZnO and B2O3, which synergistically promote the formation of a high-quality char layer with PM@PAPP, effectively inhibiting thermal decomposition and significantly enhancing the thermal stability and char residue of the composite material.

[0077] Figure 5The CCT test curves for PP and its composites are shown. The initial ignition time of the composites is shorter than that of pure PP, which is due to the PP matrix disintegration induced by IFR at low temperatures. Compared to PP1, PP2, and PP5, the peak heat release rates decreased by 85%, 76%, and 91%, respectively. The total heat release of PP5 decreased by 59%. The peak smoke release rate and total smoke generation of pure PP were 0.097 m² / s and 11.3 m², respectively. The peak smoke release rate of PP5 decreased by 93%, and the total smoke generation decreased to 4.87 m². The peak CO release of pure PP was 0.0078 g / s, while the peak CO release of PP5 decreased by 81%. ZB and PM@PAPP exhibit excellent synergistic smoke and toxicity suppression effects. The dense carbon layer effectively enhances the barrier ability against smoke and heat; this is due to the core-shell structure of PM@PAPP. If PA, MEL, and PAPP are merely physically blended within a PP matrix, phase separation occurs during melt processing due to their different polarities, preventing simultaneous foaming into char when heated. This results in a char layer with large, easily broken pores, failing to effectively block heat and oxygen.

[0078] Figure 6 Digital photographs, SEM images, and Raman spectroscopy results of the char residue from PP flame-retardant composite materials. An expanded char layer forms on the surface of the material after combustion, resulting from the cross-linking of the flame retardant with the matrix under heat. Char layers produced by a single flame retardant are insufficient in strength, leading to surface cracks and voids. PP2 char layers exhibit closed char bubbles, resulting in a more continuous char layer. PP5 char layers have a smoother, more continuous surface, forming a glassy char layer with denser char bubbles. The Raman spectrum at 1350 cm⁻¹... -1 The nearby D peak corresponds to a disordered carbon structure, 1600 cm⁻¹ -1 The nearby G peak corresponds to the vibration of sp² bonded carbon in hexagonal graphite, and the I peak of the PP composite material... D / I G The ratios are sorted as follows: PP1 > PP2 > PP5, and the I of PP5 is... D / I G With a value of only 1.85, it has the highest graphitized carbon content and a stronger carbon layer barrier effect.

[0079] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A synergistic flame retardant polypropylene of phytic acid modified pyrophosphoryl piperazine and zinc borate, characterized in that, The synergistic flame-retardant polypropylene is composed of polypropylene (PP): 73-75%; phytic acid modified pyrophosphoryl piperazine (PM@PAPP): 24-26%; zinc borate (ZB): 0.5-2% by mass percentage. The phytic acid modified pyrophosphoryl piperazine is a core-shell structure flame retardant with pyrophosphoryl piperazine as the core and a phytic acid-melamine supermolecular network as the shell layer.

2. The synergistic flame retardant polypropylene of phytic acid modified pyrophosphoryl piperazine and zinc borate according to claim 1, characterized in that, The preparation steps of the phytic acid modified pyrophosphoryl piperazine are as follows:

3. The synergistic flame retardant polypropylene of phytic acid modified pyrophosphoryl piperazine and zinc borate according to claim 2, characterized in that, (1) Disperse melamine in deionized water, uniformly mechanically stir at 70-80℃, and obtain a melamine solution; (2) Disperse phytic acid in deionized water, add dropwise to the melamine solution of step (1), and stir and react at 70-80℃ to obtain a phytic acid-melamine mixed solution; (3) Disperse pyrophosphoryl piperazine in a mixture of deionized water and ethanol, slowly add the phytic acid-melamine mixed solution of step (2), and stir and react at 70-80℃ for 2-4 hours; (4) Centrifuge and dry the reaction product of step (3) to obtain the phytic acid modified pyrophosphoryl piperazine. In step (2), the molar ratio of phytic acid to melamine is 1:3-6.

4. The synergistic flame retardant polypropylene of phytic acid modified pyrophosphoryl piperazine and zinc borate according to claim 3, characterized in that, In step (3), the mass ratio of the total mass of phytic acid and melamine to the mass of pyrophosphoryl piperazine is 1:1-7; the volume ratio of deionized water to anhydrous ethanol is 3:2; and the stirring speed is 400-600 rpm.

5. The synergistic flame retardant polypropylene of phytic acid modified pyrophosphoryl piperazine and zinc borate according to claim 3, characterized in that, The steps are as follows:

6. The method of preparing the phytic acid modified pyrophosphoryl piperazine and zinc borate synergistic flame retardant polypropylene according to claim 1, characterized in that, (a) Dry polypropylene, phytic acid modified pyrophosphoryl piperazine and zinc borate in a 70-80℃ air drying oven for 8-12 hours to remove water; (b) melt blend the dried raw materials, and then hot press form. The melt blending temperature is 175-180℃, the hot pressing temperature is 175-180℃, and during the melt blending process of step (b), 1-1.5% of maleic anhydride grafted polypropylene is additionally added as a compatibilizer based on the total mass of polypropylene, phytic acid modified pyrophosphoryl piperazine and zinc borate.

7. The production method according to claim 6, wherein ​

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