A kind of afterglow flame-retardant microcapsule and its application in polypropylene material

Abstract

This invention relates to the field of polymer materials technology, and discloses a afterglow flame-retardant microcapsule and its application in polypropylene materials. The afterglow flame-retardant microcapsule comprises a core containing a phosphorus-nitrogen intumescent flame retardant, and a shell coating the surface of the core. The shell is a melamine-formaldehyde resin doped with organic room-temperature phosphorescent molecules. The dense resin shell of this microcapsule significantly reduces the water solubility of the phosphorus-nitrogen intumescent flame retardant, effectively solving the defects of traditional phosphorus-nitrogen intumescent flame retardants being easily water-soluble and prone to leakage. The water resistance of the microcapsule is greatly improved. Simultaneously, the rigid three-dimensional network structure can inhibit the movement of luminescent molecules, isolate oxygen, effectively stabilize triplet excitons, and endow the material with stable room-temperature phosphorescence properties. Its phosphorescence emission peak is located at 550 nm, and the afterglow lifetime is 0.14 s. The microcapsule has a uniform particle size distribution, good dispersibility, and a stable overall structure, simultaneously achieving both flame retardancy and long afterglow luminescence functions, making it suitable for polymer material modification applications.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a glow-retardant microcapsule and its application in polypropylene materials. Background Technology

[0002] The functional integration of polymer materials is a significant development direction in the field of materials science. In scenarios such as public safety, emergency protection, and high-end equipment manufacturing, polymer products are no longer merely structural supports but are expected to possess multi-faceted environmental responsiveness. Photoluminescence, due to its unique advantages in passive lighting, safety warnings, and visual traceability, has become a hot topic for adding value to polymer materials. Especially in practical applications such as safe storage boxes, outdoor warning signs, underground pipeline sheathing, and emergency evacuation facilities, the spontaneous visibility of materials in low-light or even dark environments is crucial for ensuring personnel safety and improving rescue efficiency.

[0003] Organic room-temperature phosphorescence (RTP) materials have become a research hotspot in the field of functional materials due to their advantages such as low cost, simple synthesis, good biocompatibility, flexibility, and easy modification of functional groups. However, due to the weak spin-orbit coupling effect of organic materials, obtaining efficient organic room-temperature phosphorescence materials with both long phosphorescence lifetime and high phosphorescence quantum yield remains a challenge, hindering their application in functionalized polymers.

[0004] Polypropylene (PP) is polymerized from propylene monomers through an addition polymerization reaction. It not only boasts high cost-effectiveness, lightweight, non-toxicity, and odorless properties, but also exhibits good corrosion resistance and considerable mechanical strength, making it an ideal matrix for preparing functionalized polymer materials. However, in expanding its application to high-safety-level scenarios, polypropylene faces a critical technical bottleneck: its inherent flammability poses a fundamental safety hazard. Pure polypropylene has a limiting oxygen index of only about 18%, releasing a large amount of heat and producing severe dripping during combustion, making it highly susceptible to becoming a fire propagation medium. This makes it difficult for ordinary polypropylene products to meet the mandatory flame-retardant requirements for applications such as fire emergency boxes and electronic equipment protective housings.

[0005] Adding phosphorus-nitrogen intumescent flame retardants such as ammonium polyphosphate (APP) is the most economical and efficient method in industry to improve the flame retardant properties of polypropylene. However, the presence of numerous hydrophilic groups in the APP molecule results in high hygroscopicity and poor water resistance. In humid or temperature-fluctuating environments, APP readily migrates and precipitates from the interior of the polypropylene matrix to the surface. This migration not only causes a continuous decline in flame retardant efficacy, but the precipitated white powder spots also severely scatter and absorb excitation and emission light, hindering the energy absorption of the luminescent components and significantly reducing the emission intensity, thereby lowering both flame retardant and luminescent properties. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a glow-retardant microcapsule.

[0007] The second objective of this invention is to provide a method for preparing such afterglow flame-retardant microcapsules.

[0008] The third objective of this invention is to provide applications for these afterglow flame-retardant microcapsules.

[0009] The fourth objective of this invention is to provide a functionalized polypropylene composite material.

[0010] The fifth objective of this invention is to provide applications of this functionalized polypropylene composite material.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a glow-retardant microcapsule comprising a core containing a phosphorus-nitrogen intumescent flame retardant and a shell coating the surface of the core, wherein the shell is a melamine-formaldehyde resin doped with organic room-temperature phosphorescent molecules.

[0012] In some embodiments of the present invention, the phosphorus-nitrogen intumescent flame retardant is selected from at least one of ammonium polyphosphate (APP), melamine polyphosphate (MPP), and piperazine pyrophosphate (PAPP).

[0013] In some preferred embodiments of the present invention, the phosphorus-nitrogen intumescent flame retardant is ammonium polyphosphate.

[0014] In some embodiments of the present invention, the organic room-temperature phosphorescent molecule is selected from at least one of the compounds shown in formula (I) or formula (II): Equation (Ⅰ); Formula (II).

[0015] In some embodiments of the present invention, the mass ratio of the phosphorus-nitrogen intumescent flame retardant to the melamine-formaldehyde resin is (1-3):1.

[0016] In some preferred embodiments of the present invention, the mass ratio of the phosphorus-nitrogen intumescent flame retardant to the melamine-formaldehyde resin is (1.5-2.5):1.

[0017] In some embodiments of the present invention, the amount of organic room temperature phosphorescent molecules doped in melamine-formaldehyde resin is 0.01wt%-1.0wt%.

[0018] In some preferred embodiments of the present invention, the amount of organic room temperature phosphorescent molecules doped in melamine-formaldehyde resin is 0.4wt%-0.7wt%.

[0019] A second aspect of the present invention provides a method for preparing the afterglow flame-retardant microcapsules described in the first aspect of the present invention, comprising the following steps: A suspension of a phosphorus-nitrogen intumescent flame retardant, an organic room-temperature phosphorescent molecule solution, and a melamine-formaldehyde resin prepolymer solution were mixed and reacted to obtain the afterglow flame retardant microcapsules.

[0020] In some embodiments of the present invention, the preparation method of the afterglow flame-retardant microcapsules specifically includes the following steps: First, a suspension of phosphorus-nitrogen intumescent flame retardant is mixed with an organic room-temperature phosphorescent molecule solution, then a melamine-formaldehyde resin prepolymer solution is added and reacted to obtain the afterglow flame retardant microcapsules.

[0021] In some embodiments of the present invention, the solvent in the suspension of the phosphorus-nitrogen intumescent flame retardant includes an ethanol / water mixture with a volume ratio of 1:(1-2).

[0022] In some preferred embodiments of the present invention, the solvent in the suspension of the phosphorus-nitrogen intumescent flame retardant includes an ethanol / water mixture with a volume ratio of 1:(1.2-1.8).

[0023] In some embodiments of the present invention, the concentration of phosphorus-nitrogen intumescent flame retardant in the phosphorus-nitrogen intumescent flame retardant suspension is 0.08-0.12 g / mL.

[0024] In some preferred embodiments of the present invention, the concentration of phosphorus-nitrogen intumescent flame retardant in the phosphorus-nitrogen intumescent flame retardant suspension is 0.09-0.11 g / mL.

[0025] In some embodiments of the present invention, the solvent in the organic room temperature phosphorescent molecular solution is selected from at least one of tetrahydrofuran, 1,4-dioxane, and acetone.

[0026] In some preferred embodiments of the present invention, the solvent in the organic room temperature phosphorescent molecular solution is tetrahydrofuran.

[0027] In some embodiments of the present invention, the melamine-formaldehyde resin prepolymer solution is prepared by heating and reacting melamine and formaldehyde aqueous solution.

[0028] In some embodiments of the present invention, the concentration of the formaldehyde aqueous solution is 30wt%-40wt%.

[0029] In some preferred embodiments of the present invention, the concentration of the formaldehyde aqueous solution is 35wt%-40wt%.

[0030] In some embodiments of the present invention, the molar ratio of melamine to formaldehyde is 1:(2-5).

[0031] In some preferred embodiments of the present invention, the molar ratio of melamine to formaldehyde is 1:(2-4).

[0032] In some embodiments of the present invention, the pH of the system for the heating reaction is 8-9.

[0033] In some embodiments of the present invention, the pH of the heating reaction system is adjusted by adding at least one of an amine, an alkali metal hydroxide, and an alkali metal carbonate.

[0034] In some preferred embodiments of the present invention, the pH of the heating reaction system is adjusted by adding at least one of diethylamine, triethylamine, triethanolamine, sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0035] In some embodiments of the present invention, the heating reaction is carried out at a temperature of 100-120°C for a duration of 1-3 hours.

[0036] In some preferred embodiments of the present invention, the heating reaction is carried out at a temperature of 105-115°C for 1-2 hours.

[0037] The third aspect of the present invention provides the application of the afterglow flame-retardant microcapsules described in the first aspect of the present invention in the preparation of functionalized polymer materials.

[0038] A fourth aspect of the present invention provides a functionalized polypropylene composite material comprising a polypropylene matrix and afterglow flame-retardant microcapsules of the first aspect of the present invention dispersed in the polypropylene matrix.

[0039] In some embodiments of the present invention, the mass fraction of the afterglow flame-retardant microcapsules in the functionalized polypropylene composite material is 20%-40%.

[0040] In some preferred embodiments of the present invention, the mass fraction of the afterglow flame retardant microcapsules in the functionalized polypropylene composite material is 25%-35%.

[0041] In some embodiments of the present invention, the functionalized polypropylene composite material is prepared by a method comprising the following steps: Polypropylene was melt-blended with afterglow flame-retardant microcapsules and then extruded and granulated to obtain the functionalized polypropylene composite material.

[0042] In some embodiments of the present invention, the temperature of the melt blending is 150-230°C.

[0043] In some preferred embodiments of the present invention, the melt blending temperature is 170-210°C.

[0044] The fifth aspect of the present invention provides the application of the functionalized polypropylene composite material described in the fourth aspect of the present invention in the preparation of safety storage boxes, outdoor warning signs, underground pipeline sheaths or emergency evacuation facilities.

[0045] Compared with the prior art, the beneficial effects of the present invention are: The afterglow flame-retardant microcapsules provided by this invention use melamine-formaldehyde resin as the core material for in-situ encapsulation of a phosphorus-nitrogen intumescent flame retardant, and uniformly dope organic room-temperature phosphorescent molecules inside the shell. The dense resin shell significantly reduces the water solubility of the phosphorus-nitrogen intumescent flame retardant, effectively solving the defects of traditional phosphorus-nitrogen intumescent flame retardants that are easy to dissolve in water and easily lost, and greatly improving the water resistance of the microcapsules. At the same time, the rigid three-dimensional network structure can inhibit the movement of luminescent molecules and isolate oxygen, effectively stabilizing triplet excitons and giving the material stable room-temperature phosphorescence properties. Its phosphorescence emission peak is located at 550nm and the afterglow lifetime can reach 0.14s. The afterglow flame-retardant microcapsules have uniform particle size distribution, good dispersibility, and stable overall structure, and can simultaneously achieve the two functions of flame retardancy and long afterglow luminescence. They are suitable for subsequent polymer material modification applications and have strong practicality and versatility.

[0046] The functionalized polypropylene composite material provided by this invention adds afterglow flame-retardant microcapsules to the polypropylene matrix, achieving simultaneous improvement in flame retardancy, long afterglow luminescence, and mechanical properties. Compared with pure polypropylene, the limiting oxygen index of the material increases from 19.5% to 26.3%, and the flame retardancy rating reaches UL-94 V-1. The flame retardant performance remains basically unchanged after immersion in water, with outstanding water resistance and long-term flame retardant ability. During combustion, the material can form a dense, expanded char layer, effectively blocking heat and oxygen transfer, and the flame retardant mechanism is stable and reliable. The nominal strain at fracture and the notched impact strength of the cantilever beam of this composite material are significantly improved, and the toughening effect is obvious, making up for the lack of toughness of traditional inorganic flame-retardant fillers that easily degrade plastics. In addition, the composite material can stably emit green room temperature phosphorescence, with uniform and visible light emission and improved thermal stability. The preparation process of this composite material is mature, and it also has added value such as safety warnings, emergency signs, and anti-counterfeiting, and has broad application prospects in the fields of safe storage boxes, outdoor warning signs, underground pipeline sheaths, or emergency evacuation facilities. Attached Figure Description

[0047] Figure 1 The 1H NMR spectrum of compound (II) is shown. Figure 2 The carbon NMR spectrum of compound (II) is shown below. Figure 3 Here is the high-resolution mass spectrum of compound (II); Figure 4 FTIR spectra of ammonium polyphosphate and the afterglow flame-retardant microcapsules in Examples 1-3; Figure 5 The results are for water solubility tests of ammonium polyphosphate and the afterglow flame-retardant microcapsules in Examples 1-3; Figure 6 The steady-state fluorescence emission spectra of the afterglow flame-retardant microcapsules in Examples 1-3; Figure 7 The phosphorescent delayed emission spectra of the afterglow flame-retardant microcapsules in Examples 1-3; Figure 8 The phosphorescence emission decay curves of the afterglow flame-retardant microcapsules in Examples 1-3 are shown. Figure 9 The combustion behavior of pure polypropylene injection-molded specimens; Figure 10 The combustion behavior of injection-molded specimens of functionalized polypropylene composite material with a flame-retardant microcapsule content of 10 wt% was studied. Figure 11 Combustion behavior of injection-molded specimens of functionalized polypropylene composite material with a flame-retardant microcapsule content of 30 wt% was studied. Figure 12 Thermogravimetric curves of injection-molded specimens of functionalized polypropylene composite material with a polypropylene and afterglow flame retardant microcapsule content of 30 wt%; Figure 13 Thermogravimetric curves of injection-molded specimens of functionalized polypropylene composite material with a polypropylene and afterglow flame retardant microcapsule content of 30 wt% were obtained. Figure 14 The image shows the luminescence effect of an injection-molded sample of a functionalized polypropylene composite material with a flame-retardant microcapsule content of 30 wt%. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to specific accompanying drawings and embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0049] The compounds of formula (I) used in the following examples Purchased from Bid Pharmaceuticals.

[0050] Compound of formula (II) To make this yourself, the synthesis method is as follows: 1) Under argon protection, 0.75 g (4.62 mmol), phenylboronic acid (0.64 g, 5.21 mmol), and 20 mL of 1,4-dioxane were added to a 250 mL three-necked flask, followed by 5.5 mL of 2 mol / L K₂CO₃ aqueous solution. The mixture was bubbled and ventilated for 30 min. Then, 14.8 mg of tetra(triphenylphosphine)palladium was added, and the mixture was heated to 100 °C and reacted for 10 h. The solvent in the filtrate was removed by rotary evaporation under reduced pressure. The crude product was purified by silica gel column chromatography using n-hexane as the eluent to obtain 0.90 g of intermediate product, which was a colorless oily liquid with a yield of 93.07%. 2) The intermediate product (0.90 g, 4.32 mmol), 1,2-dibromobenzene (0.96 g, 4.08 mmol), potassium carbonate (1.46 g, 10.56 mmol), and 20 mL of N,N-dimethylacetamide were added to a 250 mL three-necked flask. The mixture was bubbled and aerated for 30 min. Then, tricyclohexylphosphine fluoroborate (0.08 g, 0.22 mmol) and palladium acetate (0.04 g, 0.19 mmol) were added. The mixture was stirred at 130 °C for 10 h. After the reaction was completed, the solvent in the filtrate was removed by rotary evaporation. The crude product was purified by silica gel column chromatography using dichloromethane and petroleum ether (v / v = 1: 19) as eluents. The obtained solid was further recrystallized once from dichloromethane / methanol under ultrasonic treatment to obtain 0.50 g of solid powder of compound (II), with a yield of 42.71%.

[0051] Figure 1 The 1H NMR spectrum of compound (II) is shown below. The deuterated solvent used is CDCl3, and the corresponding 1H NMR data are as follows: 1 ¹H NMR (600MHz, deuterated chloroform) δ 9.05–9.00 (m, 1H), 8.84–8.78 (m, 2H), 8.72 (m, J=10.0, 7.7, 3.1Hz, 1H), 8.19 (m, J=8.7, 6.4, 1.8Hz, 1H), 8.03 (m, J=8.1, 4.3Hz, 1H), 7.79–7.74 (m, 1H), 7.71–7.64 (m, 3H), 7.58 (m, J=8.3, 7.1, 3.0, 1.4Hz, 1H), 7.52–7.47 (m, 1H). Figure 2 The carbon NMR spectrum of compound (II) is shown below, with deuterated solvent CDCl3 used. The corresponding carbon NMR data are as follows: 13C NMR (151MHz, deuterated chloroform) δ 139.29, 138.39, 137.67, 129.97, 129.66, 129.47 128.04, 128.02, 127.36, 127.33, 127.32, 125.64, 125.20, 125.14, 124.99, 124.72, 123.97, 123.86, 123.42, 123.26. Figure 3 The high-resolution mass spectrum of compound (II) is shown below. The corresponding high-resolution mass spectrometry data is: ESI-HRMS [M+H]. + m / z: C 20 H 13 S + Theoretical calculated value: 285.0737; Measured value: 285.0732. Depend on Figure 1 , Figure 2 and Figure 3 It can be seen that the compound of formula (II) has the target structure and can be used for the preparation of afterglow flame retardant microcapsules.

[0052] Example 1 This embodiment prepares a glow-retardant microcapsule, and the steps are as follows: S1. Add 43.2g of melamine to a three-necked flask, then add 57.7g of formaldehyde solution with a mass fraction of 37% (the molar ratio of melamine to formaldehyde is 1:3). Adjust the pH to 8-9 using triethanolamine, and heat to 110℃ while stirring. Heat and stir for 1 hour to make the solution change from turbid to clear and transparent, thus obtaining a melamine-formaldehyde resin prepolymer solution. S2. First, grind the ammonium polyphosphate into powder using a mortar and pestle, then add it to a planetary ball mill for further grinding to obtain micron-sized powder. Mix the ammonium polyphosphate powder with an ethanol / water solution (1:1.5, v / v) and disperse it evenly using an ultrasonic disperser to form a suspension of ammonium polyphosphate with a concentration of 0.1 g / mL. S3. Dissolve the compound of formula (Ⅰ) in tetrahydrofuran to prepare an organic room temperature phosphorescent molecular solution with a concentration of 5 mg / mL; S4. Take ammonium polyphosphate suspension, add about 5 mL of organic room temperature phosphorescent molecular solution, stir evenly, and then add melamine-formaldehyde resin prepolymer solution to make the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin 1:1. During stirring, add glacial acetic acid dropwise to adjust the pH of the system to 6.0, react in an 80℃ water bath for 1 h, centrifuge to precipitate, filter to collect the solid phase, and dry for 48 h to obtain afterglow flame retardant microcapsules.

[0053] Example 2 This embodiment prepares a glow-retardant microcapsule, and the steps are as follows: S1. Add 43.2g of melamine to a three-necked flask, then add 57.7g of formaldehyde solution with a mass fraction of 37% (the molar ratio of melamine to formaldehyde is 1:3). Adjust the pH to 8-9 using triethanolamine, and heat to 110℃ while stirring. Heat and stir for 1 hour to make the solution change from turbid to clear and transparent, thus obtaining a melamine-formaldehyde resin prepolymer solution. S2. First, grind the ammonium polyphosphate into powder using a mortar and pestle, then add it to a planetary ball mill for further grinding to obtain micron-sized powder. Mix the ammonium polyphosphate powder with an ethanol / water solution (1:1.5, v / v) and disperse it evenly using an ultrasonic disperser to form a suspension of ammonium polyphosphate with a concentration of 0.1 g / mL. S3. Dissolve the compound of formula (Ⅰ) in tetrahydrofuran to prepare an organic room temperature phosphorescent molecular solution with a concentration of 5 mg / mL; S4. Take ammonium polyphosphate suspension, add about 5 mL of organic room temperature phosphorescent molecular solution, stir evenly, and then add melamine-formaldehyde resin prepolymer solution to make the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin 2:1. During stirring, add glacial acetic acid dropwise to adjust the pH of the system to 6.0, react in an 80℃ water bath for 1 h, centrifuge to precipitate, filter to collect the solid phase, and dry for 48 h to obtain afterglow flame retardant microcapsules.

[0054] Example 3 This embodiment prepares a glow-retardant microcapsule, and the steps are as follows: S1. Add 43.2g of melamine to a three-necked flask, then add 57.7g of formaldehyde solution with a mass fraction of 37% (the molar ratio of melamine to formaldehyde is 1:3). Adjust the pH to 8-9 using triethanolamine, and heat to 110℃ while stirring. Heat and stir for 1 hour to make the solution change from turbid to clear and transparent, thus obtaining a melamine-formaldehyde resin prepolymer solution. S2. First, grind the ammonium polyphosphate into powder using a mortar and pestle, then add it to a planetary ball mill for further grinding to obtain micron-sized powder. Mix the ammonium polyphosphate powder with an ethanol / water solution (1:1.5, v / v) and disperse it evenly using an ultrasonic disperser to form a suspension of ammonium polyphosphate with a concentration of 0.1 g / mL. S3. Dissolve the compound of formula (Ⅰ) in tetrahydrofuran to prepare an organic room temperature phosphorescent molecular solution with a concentration of 5 mg / mL; S4. Take ammonium polyphosphate suspension, add about 5 mL of organic room temperature phosphorescent molecular solution, stir evenly, and then add melamine-formaldehyde resin prepolymer solution to make the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin 3:1. During stirring, add glacial acetic acid dropwise to adjust the pH of the system to 6.0, react in an 80℃ water bath for 1 h, centrifuge to precipitate, filter to collect the solid phase, and dry for 48 h to obtain afterglow flame retardant microcapsules.

[0055] Example 4 This embodiment prepares a glow-retardant microcapsule, and the steps are as follows: S1. Add 43.2g of melamine to a three-necked flask, then add 57.7g of formaldehyde solution with a mass fraction of 37% (the molar ratio of melamine to formaldehyde is 1:3). Adjust the pH to 8-9 using triethanolamine, and heat to 110℃ while stirring. Heat and stir for 1 hour to make the solution change from turbid to clear and transparent, thus obtaining a melamine-formaldehyde resin prepolymer solution. S2. First, grind the ammonium polyphosphate into powder using a mortar and pestle, then add it to a planetary ball mill for further grinding to obtain micron-sized powder. Mix the ammonium polyphosphate powder with an ethanol / water solution (1:1.5, v / v) and disperse it evenly using an ultrasonic disperser to form a suspension of ammonium polyphosphate with a concentration of 0.1 g / mL. S3. Dissolve the compound of formula (II) in tetrahydrofuran to prepare an organic room temperature phosphorescent molecular solution with a concentration of 5 mg / mL; S4. Take ammonium polyphosphate suspension, add about 5 mL of organic room temperature phosphorescent molecular solution, stir evenly, and then add melamine-formaldehyde resin prepolymer solution to make the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin 2:1. During stirring, add glacial acetic acid dropwise to adjust the pH of the system to 6.0, react in an 80℃ water bath for 1 h, centrifuge to precipitate, filter to collect the solid phase, and dry for 48 h to obtain afterglow flame retardant microcapsules.

[0056] Application examples The afterglow flame-retardant microcapsules prepared in Example 2 were used to prepare functionalized polypropylene composite materials, and the steps are as follows: Keeping the total addition amount constant at 200g, the polypropylene and the afterglow flame retardant microcapsules from Example 2 were melt-blended in a twin-screw extruder at 190°C. The main extruder speed was set to 40rpm, and the mixture was extruded and granulated to obtain a functionalized polypropylene composite material. The addition amounts of the afterglow flame retardant microcapsules were 10%, 20%, and 30% of the total mass of the functionalized polypropylene composite material, respectively.

[0057] Characterization and performance testing 1. Fourier transform infrared spectroscopy characterization was performed on ammonium polyphosphate and the afterglow flame-retardant microcapsules prepared in Examples 1-3: Figure 4The FTIR spectra of ammonium polyphosphate and the afterglow flame-retardant microcapsules in Examples 1-3 are shown below. Figure 4 It can be seen that ammonium polyphosphate at 3200cm -1 (NH stretching vibration), 1256cm -1 (P=O stretching vibration), 1075cm -1 and 880cm -1 (PO stretching vibration), and 1520cm -1 Strong absorption is observed at the (ammonium ion bending vibration) site. In Examples 1-3, the afterglow flame-retardant microcapsules, in addition to possessing all the characteristic peaks of ammonium polyphosphate, also exhibit strong absorption at 1560 cm⁻¹. -1 and 1340cm -1 An absorption peak of the triazine ring appears at 3050 cm⁻¹. -1 The presence of an aromatic ring CH absorption peak from compound (I) confirms that melamine-formaldehyde resin successfully coated ammonium polyphosphate and that organic room-temperature phosphorescent molecule compound (I) was successfully doped. Since ammonium polyphosphate is a hydrophilic particle and compound (I) is a hydrophobic organic molecule, the two are incompatible in the preparation system. Therefore, compound (I) cannot enter the interior of the ammonium polyphosphate lattice, but is instead doped into the shell of melamine-formaldehyde resin.

[0058] 2. Water solubility test of ammonium polyphosphate and the afterglow flame retardant microcapsules prepared in Examples 1-3: 2g of sample was dissolved in 50mL of deionized water at 25℃, ultrasonically dispersed for 15min, and the conductivity was measured after standing for 24h.

[0059] Figure 5 The water solubility test results for ammonium polyphosphate and the afterglow flame-retardant microcapsules in Examples 1-3 are provided by... Figure 5 It is known that the electrical conductivity of ammonium polyphosphate is about 800 μS / cm. In Examples 1-3, the electrical conductivity of the afterglow flame retardant microcapsules decreased to about 180 μS / cm, 150 μS / cm and 200 μS / cm, respectively. In Example 2, the electrical conductivity of the afterglow flame retardant microcapsules was the lowest. This indicates that when the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin is 2:1, the shell density of the afterglow flame retardant microcapsules is optimal, the hydrophobic barrier effect is the best, and the water resistance is the best.

[0060] 3. Dynamic light scattering (DLS) particle size analysis of ammonium polyphosphate and the afterglow flame retardant microcapsules prepared in Examples 1-3: The samples were prepared into 1 mg / mL ethanol solutions, ultrasonically dispersed, and then the particle size was measured using a dynamic light scattering particle size analyzer. The results are shown in Table 1.

[0061] Table 1. Comparison of particle size distribution and dispersibility of ammonium polyphosphate and afterglow flame retardant microcapsules in Examples 1-3

[0062] Table 1 compares the particle size distribution and dispersibility of ammonium polyphosphate and the afterglow flame-retardant microcapsules in Examples 1-3. As shown in Table 1, the average particle size of ammonium polyphosphate is 2280 nm, and the polydispersity index is 0.445, indicating severe agglomeration in ethanol medium and a wide particle size distribution. This is mainly attributed to the strong hydrogen bond interactions induced by the polar groups on the surface of the polyphosphate particles. Compared with polyphosphate particles, the particle size distribution and dispersibility of the afterglow flame-retardant microcapsules in Examples 1-3 show significant changes. Specifically, the average particle size of the afterglow flame-retardant microcapsules in Example 1 is 2047 nm. The polydispersity index was 0.257. In Example 2, the average particle size of the afterglow flame retardant microcapsules was 2143 nm and the polydispersity index was 0.285. In Example 3, the average particle size of the afterglow flame retardant microcapsules was 2532 nm and the polydispersity index was 0.336. It can be seen that after being coated with melamine-formaldehyde resin, the particle size distribution of the afterglow flame retardant microcapsules in Examples 1 and 2 became narrower and the dispersibility was significantly improved. In Example 3, the afterglow flame retardant microcapsules, due to insufficient amount of melamine-formaldehyde resin as the coating material, instead acted as an adhesive, resulting in particle agglomeration and increased particle size.

[0063] 4. Optical performance testing of the afterglow flame retardant microcapsules prepared in Examples 1-3: The samples were excited at 330nm / 550nm.

[0064] Figure 6 The steady-state fluorescence emission spectra of the afterglow flame-retardant microcapsules in Examples 1-3 are obtained from... Figure 6 It can be seen that under 330nm wavelength excitation, the afterglow flame retardant microcapsules in Examples 1-3 all showed a strong fluorescence emission peak at 370nm, belonging to the organic room temperature phosphorescent molecular formula (Ⅰ) compound, proving that the organic room temperature phosphorescent molecule maintains fluorescence activity in the microcapsule. Among them, the fluorescence intensity of the afterglow flame retardant microcapsule in Example 1 was the highest, followed by Example 2, and the lowest in Example 3. That is, the fluorescence intensity of the afterglow flame retardant microcapsule is inversely proportional to the content of ammonium polyphosphate. This is because as the content of ammonium polyphosphate increases, microcrystals will form in the matrix, which will easily cause the excitation light to be scattered and dissipated. In addition, the increase of ammonium polyphosphate content and the decrease of melamine-formaldehyde resin content will also lead to agglomeration, reducing the optical transparency of the afterglow flame retardant microcapsule, making it difficult for the excitation light to reach its interior and thus excite the fluorescence of the organic room temperature phosphorescent molecule.

[0065] Figure 7 The phosphorescent delayed emission spectra of the afterglow flame-retardant microcapsules in Examples 1-3 are obtained from... Figure 7It can be seen that under the test conditions of excitation wavelength of 330nm and delay time of 1ms, the afterglow flame retardant microcapsules in Examples 1-3 all showed obvious green phosphorescence peaks at 550nm, proving that the afterglow flame retardant microcapsules have organic room temperature phosphorescence properties. Among them, the afterglow flame retardant microcapsules in Example 2 had the highest phosphorescence intensity, which represents the best triplet exciton stability and the best confinement and oxygen isolation effect of the shell for organic room temperature phosphorescent molecules.

[0066] Figure 8 The phosphorescence emission decay curves of the afterglow flame-retardant microcapsules in Examples 1-3 are shown below. Figure 8 It can be seen that by performing a double exponential fitting on the phosphorescence emission decay curves obtained under 550nm wavelength excitation, the phosphorescence afterglow lifetimes of the afterglow flame-retardant microcapsules in Examples 1-3 were 0.06s, 0.14s, and 0.29s, respectively. This indicates that the afterglow flame-retardant microcapsules in Example 1 had the fastest afterglow lifetime decay and weak phosphorescence. The afterglow flame-retardant microcapsules in Example 2 showed stable afterglow visible to the naked eye. The afterglow flame-retardant microcapsules in Example 3 had the longest afterglow lifetime. However, considering that the shell of the afterglow flame-retardant microcapsules in Example 3 was too thin and had poor water resistance, it is believed that when the mass ratio of ammonium polyphosphate to melamine-formaldehyde resin is 2:1, the four major indicators of phosphorescence intensity, afterglow lifetime, water resistance, and particle size of the afterglow flame-retardant microcapsules can achieve the optimal balance.

[0067] 5. The functionalized polypropylene composite material prepared in the application example was injection molded into a standard test specimen. After standing for 24 hours, its mechanical properties were tested, using ammonium polyphosphate or polypropylene specimens as controls. The test items included: 1) Mechanical property testing: a. Tensile test: The test shall be conducted in accordance with GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". The sample shall be stretched at a rate of 100 mm / min until it breaks. The tensile strength and nominal strain at break of the test specimen shall be measured. Each test shall be repeated 6 times and the arithmetic mean shall be taken. b. Bending test: Refer to B / T 9341-2008 "Test method for bending properties of plastics" and keep the span at 64mm. Bend at a rate of 5mm / min until 10mm. Test the bending strength and bending modulus. Repeat each test 6 times and take the arithmetic mean. c. Impact test: The test shall be conducted in accordance with GB / T 1843-2008 "Determination of impact strength of plastic cantilever beams". Each test shall be repeated 6 times and the arithmetic mean shall be taken.

[0068] Table 2. Test results of mechanical properties of injection-molded specimens of polypropylene and functionalized polypropylene composites.

[0069] Table 2 shows the mechanical property test results of injection-molded specimens of polypropylene and functionalized polypropylene composites. As can be seen from Table 2, when the content of afterglow flame retardant microcapsules in the functionalized polypropylene composite is 10wt%, the mechanical properties of the injection-molded specimens are not much different from those of pure polypropylene specimens. When the content of afterglow flame retardant microcapsules increases to 30wt%, the tensile strength and flexural strength of the specimens decrease. This is because afterglow flame retardant microcapsules are rigid particles, and their interfacial bonding with polypropylene is not as tight as that between polypropylene particles, which easily causes stress concentration points. However, at this time, the nominal strain at break, flexural modulus and notched impact strength of the specimens are significantly improved. This is because the melamine-formaldehyde resin layer has good flexibility and can induce the craze-shear band mechanism. Under stress, afterglow flame retardant microcapsules, as rigid particles, are easy to act as crack initiation points. The generation and propagation of cracks require a lot of energy, which allows the specimens to absorb a lot of energy under external force, especially under impact, thus achieving a toughening effect.

[0070] 2) Flame retardant performance test: a. Limiting Oxygen Index (LOI): The limiting oxygen index of the samples was tested before and after immersion in water, in accordance with GB / T 2406.2-2009 "Plastics - Determination of Combustion Behavior by Oxygen Index Method - Part 2: Room Temperature Test". b. Vertical burning (UL-94) test: The test shall be conducted in accordance with GB / T 2408-2021 "Determination of the flammability of plastics - Horizontal and Vertical Methods", and the flammability rating of the sample before and after immersion in water shall be recorded.

[0071] Table 3. Test results of flame retardant properties of injection-molded specimens of polypropylene and functionalized polypropylene composites.

[0072] Table 3 shows the test results of the flame retardant properties of injection-molded polypropylene and functionalized polypropylene composite samples. Figure 9 The combustion behavior of pure polypropylene injection-molded specimens. Figure 10 The combustion behavior of injection-molded specimens of functionalized polypropylene composite material with a afterglow flame-retardant microcapsule content of 10 wt% was studied. Figure 11 The combustion behavior of injection-molded specimens of functionalized polypropylene composite material with a afterglow flame-retardant microcapsule content of 30 wt% is shown in Table 3. Figure 9 , Figure 10 and Figure 11It can be seen that the limiting oxygen index of pure polypropylene injection molding samples is only 19.5%, making them extremely flammable. The flame spreads continuously, accompanied by a large amount of molten dripping, with no char layer formed, indicating complete combustion. As the content of afterglow flame-retardant microcapsules in the polypropylene matrix increases, the limiting oxygen index of the samples gradually increases, and the flame retardant grade gradually improves from F to V-2 and V-1. During combustion, the combustion rate slows down, the molten dripping decreases, and the amount of char formation increases. In the functionalized polypropylene composite injection molding samples with an afterglow flame-retardant microcapsule content of 30wt%, a significant char layer expansion phenomenon can be observed during combustion, which effectively blocks oxygen and delays combustion, indicating that the afterglow flame-retardant microcapsules endow the polypropylene material with flame-retardant properties. In addition, the limiting oxygen index and flame retardant grade of the samples before and after immersion in water are basically the same, and the flame retardant performance hardly decreases, proving that the water resistance of the afterglow flame-retardant microcapsules improves the long-term flame retardant effect.

[0073] 3) Thermal stability test: The thermal stability of the sample is tested using a thermogravimetric analyzer. 5-20 mg of sample is weighed into an alumina crucible and tested under a nitrogen atmosphere. The test temperature is 40-800℃ and the heating rate is 10℃ / min. The thermogravimetric curve and differential thermogravimetric curve are recorded. The characteristic decomposition temperature and the char residue at 800℃ are analyzed.

[0074] Figure 12 Thermogravimetric curves of injection-molded specimens of functionalized polypropylene composite material with a polypropylene and afterglow flame-retardant microcapsule content of 30 wt% are obtained from... Figure 12 It can be seen that, taking a 5% mass loss as the standard, the thermal decomposition temperature of the functionalized polypropylene composite injection molding specimens with a polypropylene and afterglow flame retardant microcapsule content of 30wt% is around 390℃. At this time, the main process is the decomposition of polypropylene, generating alkanes and olefins. At the same time, the afterglow flame retardant microcapsules also decompose to generate gases such as ammonia, nitric oxide, and carbon dioxide, as well as water and phosphoric acid. The first stage of decomposition ends at around 480℃. Subsequently, the functionalized polypropylene composite injection molding specimens begin the second stage of decomposition, which is mainly the decomposition of the carbon layer. This process ends at around 700℃, and there is still mass residue after the decomposition, which fully proves the formation of the expanded carbon layer. The residual carbon rate is about 2.05%.

[0075] Figure 13 Thermogravimetric curves of injection-molded specimens of functionalized polypropylene composite material with a polypropylene and afterglow flame retardant microcapsule content of 30 wt% are obtained from... Figure 13 It can be seen that the maximum thermal decomposition rates of the functionalized polypropylene composite injection molding specimens with a polypropylene content of 30wt% and a residual flame retardant microcapsule content are 24% / min and 19% / min, respectively, corresponding to temperatures of approximately 450℃ and 470℃, respectively. This proves that the residual flame retardant microcapsule increases the thermal decomposition temperature of polypropylene, reduces the thermal decomposition rate, enhances the thermal stability and resistance to high-temperature thermo-oxidative aging of the material, and further improves its flame retardant safety.

[0076] 4) Luminescence effect test: Irradiate the sample with a 365nm ultraviolet lamp and observe the luminescence behavior.

[0077] Figure 14 The image shows the luminescence effect of an injection-molded sample of a functionalized polypropylene composite material with a afterglow flame-retardant microcapsule content of 30 wt%. Figure 14 Image (a) in the image is taken under normal natural light conditions. Figure 14 Image (b) is taken 0.01 seconds after excitation by a 365nm ultraviolet lamp and removal of the light source. Figure 14 It can be seen that under normal natural light conditions, the functionalized polypropylene composite injection-molded sample is a common white polypropylene profile with no luminescence. After excitation by a 365nm ultraviolet lamp, the sample exhibits a uniform green afterglow, with full coverage of the luminescent area and no local dark areas. This proves that the afterglow flame-retardant microcapsules are well dispersed in the polypropylene matrix, and the organic room-temperature phosphorescent molecules are uniformly distributed within the shell without aggregation or segregation. The green phosphorescence corresponds to the 550nm emission peak in the spectrum, and the afterglow is identifiable to the naked eye, consistent with the 0.14s lifetime data. This luminescence effect, which shows no abnormalities under normal conditions and exhibits afterglow after ultraviolet excitation, is suitable for core scenarios such as emergency marking and anti-counterfeiting packaging.

[0078] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A glow-retardant microcapsule, characterized in that, It includes a core containing a phosphorus-nitrogen intumescent flame retardant, and a shell layer covering the surface of the core, wherein the shell layer is a melamine-formaldehyde resin doped with organic room-temperature phosphorescent molecules; wherein, The mass ratio of the phosphorus-nitrogen intumescent flame retardant to the melamine-formaldehyde resin is (1-3):1; the doping amount of the organic room-temperature phosphorescent molecule in the melamine-formaldehyde resin is 0.01wt%-1.0wt%. The organic room-temperature phosphorescent molecule is selected from at least one of the compounds shown in formula (I) or formula (II): Equation (Ⅰ); Formula (II).

2. The afterglow flame-retardant microcapsule according to claim 1, characterized in that, The phosphorus-nitrogen intumescent flame retardant is selected from at least one of ammonium polyphosphate, melamine polyphosphate, and piperazine pyrophosphate.

3. The method for preparing the afterglow flame-retardant microcapsules according to claim 1 or 2, characterized in that, Includes the following steps: A suspension of a phosphorus-nitrogen intumescent flame retardant, an organic room-temperature phosphorescent molecule solution, and a melamine-formaldehyde resin prepolymer solution were mixed and reacted to obtain the afterglow flame retardant microcapsules.

4. The preparation method according to claim 3, characterized in that, The pH of the reaction system is 5.0-7.0; And / or, the reaction is carried out at a temperature of 65-95°C for a time of 0.5-2 hours.

5. The application of the afterglow flame-retardant microcapsules according to claim 1 or 2 in the preparation of functionalized polymer materials.

6. A functionalized polypropylene composite material, characterized in that, The functionalized polypropylene composite material comprises a polypropylene matrix and afterglow flame-retardant microcapsules as described in claim 1 or 2 dispersed in the polypropylene matrix.

7. The functionalized polypropylene composite material according to claim 6, characterized in that, In the functionalized polypropylene composite material, the mass fraction of the afterglow flame-retardant microcapsules is 20%-40%.

8. The application of the functionalized polypropylene composite material according to claim 6 or 7 in the preparation of safety storage boxes, outdoor warning signs, underground pipeline sheaths or emergency evacuation facilities.

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