A halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material and its preparation method

Abstract

This invention discloses a halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material and its preparation method. The raw materials of the composite material are composed of the following components by mass: 45-75 parts polyolefin, 25-55 parts microencapsulated flame retardant, and 1-2.5 parts crosslinking agent. The microencapsulated flame retardant added to the composite material uses a flame-retardant polyurethane formed by polymerizing DOPO derivatives and isocyanates as a shell. This not only exerts a synergistic flame-retardant effect with the core flame retardant but also exhibits synergistic effects from multiple flame-retardant mechanisms, including gas-phase and condensed-phase processes. Furthermore, the halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material provided by this invention still possesses excellent anti-aging properties without the addition of any antioxidants. It improves the flame-retardant performance of the material while extending its service life, making it widely applicable in aerospace, defense, construction, medical, and chemical industries.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant cross-linked polyolefin composite materials, specifically to a halogen-free flame-retardant and antioxidant cross-linked polyolefin composite material and its preparation method. Background Technology

[0002] Polyolefins possess excellent mechanical properties, electrical insulation properties, low-temperature resistance, chemical corrosion resistance, heat aging resistance, UV aging resistance, good compatibility with fillers, ease of processing, reasonable price, and large variety and output, making them widely used in the insulation and sheathing materials of wires and cables. Statistics show that electrical fires account for approximately 30% of all fires in my country annually. These electrical fires are caused by factors such as overload, short circuits, poor contact, and equipment aging, all of which are significantly related to the aging of cable materials. During service, cable materials face various special operating environments. Under the coupled effects of complex environmental factors (high temperature, sunlight, rain, wind, sand, vibration, etc.), material performance gradually deteriorates. Flame retardants and other additives added to the materials can also migrate and precipitate, directly causing a decline in the mechanical and flame-retardant properties of the material, leading to a reduction in the safe service performance and service life of the cable. Therefore, the design and preparation of halogen-free flame-retardant and antioxidant polyolefin composite materials has broad development prospects.

[0003] Research reports indicate that microencapsulation of flame retardants can not only solve the migration problem of flame retardants, but also improve the overall physical properties, weather resistance, and durability of materials.

[0004] Antioxidants commonly used in polyolefins are divided into primary antioxidants and secondary antioxidants. Primary antioxidants are those that eliminate free radicals, and they include aromatic amines (rarely used in polyolefins due to color pollution and toxicity) and hindered phenols (such as antioxidant 1010), as well as their structurally similar derivatives. Secondary antioxidants are compounds that decompose hydroperoxides, including phosphite esters and sulfur-containing compounds (such as antioxidant 168 and DLTP). Literature reports that +3 valent phosphite esters are a commonly used class of secondary antioxidants. Their mechanism of action is as a hydroperoxide decomposer, reducing the hydroperoxides released from polymer materials to alcohols, while being oxidized to phosphate esters themselves. Furthermore, because phosphorus-containing compounds are excellent flame retardants, +3 valent phosphite esters are often used as halogen-free flame-retardant antioxidants. 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO, with phosphorus in the +1 valence state) is a novel flame retardant intermediate. Due to the presence of a PH bond in its structure, it can react with certain compounds containing double bonds, carbonyl groups, and epoxy bonds to generate various derivatives. However, DOPO and its derivatives mainly improve flame retardant properties through a gas-phase flame retardant mechanism and are commonly used for flame-retardant epoxy resins, but their flame retardant effect on polyolefin composites is generally poor. Furthermore, there are no reports on the antioxidant properties of +1 valence phosphorus-containing DOPO and its derivatives. Therefore, applying +1 valence phosphorus-containing DOPO and its derivatives to the flame retardant and antioxidant research of polyolefin composites is of great significance. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material and its preparation method. This not only endows the polyolefin composite material with good flame-retardant and antioxidant properties, but also solves the problem of long-term durability of flame-retardant polyolefin composite materials.

[0006] The present invention relates to a halogen-free flame-retardant and antioxidant cross-linked polyolefin composite material, the raw materials of which are composed of the following parts by mass:

[0007] 45-75 parts polyolefin, 25-55 parts microencapsulated flame retardant, and 1-2.5 parts crosslinking agent.

[0008] The polyolefin is selected from one or more of the following: ethylene-vinyl acetate copolymer, polyethylene, ethylene propylene diene monomer (EPDM) rubber, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, maleic anhydride-grafted EPDM rubber, ethylene-octene copolymer, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, and maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer, mixed in any proportion. All raw materials are commercially available.

[0009] The crosslinking agent is selected from one or more of dicumyl peroxide, triallyl cyanurate, triallyl isocyanurate, trimethylolpropene trimethacrylate, trimethylolpropene triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate, mixed in any proportion.

[0010] The microencapsulated flame retardant consists of a core layer and a shell layer structure. The core layer structure is the flame retardant, and the shell layer structure is a flame-retardant polyurethane formed by polymerizing a DOPO derivative with an isocyanate. The mass ratio of the core layer to the shell layer structure is 75–85:15–25. A ratio that is too high or too low will adversely affect the flame retardant effect.

[0011] The microencapsulated flame retardant comprises the following raw materials in parts by mass:

[0012] 10-15 parts of DOPO derivative, 200-300 parts of solvent, 75-85 parts of flame retardant, 4-13 parts of isocyanate, 0.1-0.3 parts of catalyst, and 0.5-1.5 parts of surfactant.

[0013] The DOPO derivatives are selected from DOPO compounds containing hydroxyl groups, such as DOPO-GY, DOPO-DH, DOPO-GD, etc., with the corresponding structural formulas shown below:

[0014]

[0015] The solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, chloroform, and 1,4-dioxane.

[0016] The flame retardant is selected from one or more of the following: ammonium polyphosphate, piperazine pyrophosphate, magnesium hydroxide, aluminum hydroxide, hydrotalcite, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, aluminum hypophosphite, aluminum phosphonate, expandable graphite, zinc borate, graphene, transition metal disulfides, carbon nanotubes, halloysite, sepiolite, and kaolin, mixed in any proportion.

[0017] The isocyanate is selected from toluene diisocyanate, terephthalic diisocyanate, isophorone diisocyanate, o-phenyl diisocyanate, m-phenylenedimethyl isocyanate, 4,4-diisocyanate dicyclohexylmethane, 1,5-naphthalene diisocyanate, 1,6-hexane diisocyanate, dimethylbiphenyl diisocyanate, 4,4'-methylenebis(phenyl isocyanate), polymethylene polyphenyl polyisocyanate, or triphenyl isocyanate thiophosphate.

[0018] The catalyst used is dibutyltin disilicate.

[0019] The surfactant is selected from one or more of Triton and OP-10.

[0020] The microencapsulated flame retardant is prepared through the following steps:

[0021] The DOPO derivative is added to a solvent, stirred, and heated to 40°C. After the reactants are completely dissolved, isocyanate is added and stirred at this temperature for 15-25 minutes. Then, flame retardant, catalyst, and surfactant are added for encapsulation. The temperature is raised to 85°C and reacted for 6-10 hours. The mixture is then cooled to room temperature, filtered, and the resulting filter cake is placed in an 80°C oven and dried for 12 hours. The product obtained is the microencapsulated flame retardant.

[0022] The present invention discloses a method for preparing a halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material, comprising the following steps:

[0023] Add 25-55 parts of microencapsulated flame retardant to 45-75 parts of polyolefin, mix them in an internal mixer or extruder at 120-180℃ until uniform, then add 1-2.5 parts of crosslinking agent, mix them evenly, and press them into sheets in a flat vulcanizing machine. Prepare crosslinked polyolefin composite materials by hot vulcanization crosslinking or irradiation crosslinking.

[0024] When using hot vulcanization crosslinking, vulcanize at 160-200℃ for 15 minutes in a flat vulcanizing machine.

[0025] When using irradiation crosslinking, irradiation crosslinking is carried out under the irradiation of a high-energy electron beam or cobalt source at an irradiation dose of 200 KGy to produce irradiated crosslinked polyolefin sheets or plates.

[0026] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0027] 1. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material provided by the present invention has excellent flame-retardant properties. The selected flame retardant uses flame-retardant polyurethane formed by polymerization of DOPO derivatives and isocyanates as the shell layer. Its advantages are mainly reflected in the following three aspects: (1) The shell layer contains benzene ring structures with char-forming function and flame-retardant elements such as nitrogen and phosphorus, which can play a core-shell synergistic flame-retardant role with the core flame retardant. (2) The low-valence (+1 valence) phosphorus element in the shell layer can play a gas-phase flame-retardant mechanism, and the core flame retardant such as ammonium polyphosphate or metal hydroxide can play a condensed-phase flame-retardant mechanism. The shell layer and the core play a synergistic effect of multiple flame-retardant mechanisms, improve the flame-retardant efficiency of the flame retardant, and help improve the flame-retardant level and flame-retardant performance of the polyolefin composite material. (3) The core-shell structure not only improves the water resistance of the core flame retardant, but also greatly improves the problem of the dispersion and interfacial compatibility of the flame retardant in polyolefin composites, reduces the agglomeration of the flame retardant during processing, and the good dispersion further enhances the mechanical properties and flame retardant properties of polyolefin composites.

[0028] 2. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material provided by the present invention still has excellent anti-aging properties without the addition of any antioxidants, which can be proven by the following tests: (1) the free radical scavenging test proves that the core-shell structure flame retardant has excellent free radical scavenging ability; (2) the oxidation induction time test shows that the composite material has good antioxidant effect; (3) the long-term accelerated thermal aging test of the crosslinked polyolefin composite material by high temperature ovens at 180℃ and 150℃ shows that the halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material of the present invention has excellent thermal aging performance and long-term anti-aging performance. This is mainly due to the core-shell structure microencapsulated flame retardant used in this invention. The low-valence (+1) phosphorus element in the shell can decompose the hydroperoxide generated by free radicals into a high-valence (+3 or +5) phosphorus element, thus consuming more free radicals than traditional phosphites. In addition, the benzene ring in the DOPO structure is connected to the phosphorus element. The benzene ring structure can quench free radicals and has a high thermal decomposition temperature, thereby stabilizing the low-valence (+1) DOPO structure and ensuring its stability during long-term high-temperature thermal aging. This not only improves the flame retardant performance of polyolefin composites but also endows them with good long-term antioxidant properties. Attached Figure Description

[0029] Figure 1 The curves show the relationship between the retention rate of elongation at break and time for the sample of Example 1 at 180℃ (a) and 150℃ (b).

[0030] Figure 2 The curves show the relationship between the retention rate of elongation at break and time for the sample of Example 2 at 180℃ (a) and 150℃ (b).

[0031] Figure 3 The curves show the relationship between the retention rate of elongation at break and time for the sample of Example 3 at 180℃ (a) and 150℃ (b).

[0032] Figure 4 The curves show the relationship between the retention rate of elongation at break and time for the sample of Example 4 at 180℃ (a) and 150℃ (b).

[0033] Figure 5 The curves show the relationship between the retention rate of elongation at break and time for the sample of Example 5 at 180℃ (a) and 150℃ (b).

[0034] Figure 6 The results of the flame retardant scavenging of DPPH free radicals in Examples 1-5 of this invention are shown.

[0035] Figure 7 The results are the oxidation induction time test results of the samples in Examples 1-5 of this invention. Detailed Implementation

[0036] To further illustrate the technical solution of the present invention, preferred embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0037] Example 1:

[0038] a. Preparation of DOPO-GY

[0039] Take a 500ml three-necked flask and use DOPO and glyoxal in a molar ratio of 1:0.5 as raw materials for the reaction. First, dissolve 108.08g of DOPO in acetonitrile solution, then slowly add glyoxal solution dropwise, and apply a reflux condenser. Under mechanical stirring, react at 90℃ for 6h. After the reaction is completed, filter, wash three times with acetonitrile, and dry the product at 55℃ for 12h.

[0040] b. DOPO-GY reacts with toluene diisocyanate (TDI) and encapsulates ammonium polyphosphate (APP).

[0041] Take a 500ml three-necked flask, add 10.26g of DOPO-GY and 80ml of DMF, stir and heat to 40℃. After the reactants are completely dissolved, add 4.74g of TDI and 40ml of DMF, stir for 15-25min, then add 85g of APP, 200ml of DMF, 1g of Triton and 0.3g of dibutyltin disterite, then heat to 85℃ and react for 6-10h. After the reaction is complete, filter, wash with ethanol, and then dry at 80℃ for 12h.

[0042] c. Add 25 parts of microencapsulated flame retardant (DOPO-GY@APP) to 75 parts of ethylene-vinyl acetate copolymer (EVA) by mass ratio, and then mix them in an internal mixer or extruder at 130°C until uniform. Then add 1.4 parts of triallyl cyanurate (TAIC) and 0.6 parts of dicumyl peroxide (DCP), mix them evenly, and then vulcanize them in a vulcanizing machine at 165°C for 15 minutes to make the sheet.

[0043] To further verify the performance of microencapsulated flame retardants with DOPO-GY as the shell, we designed the following as shown in Tables 1 and 2. Figure 1 , 6The comparative formulations shown in Tables 7 and 8 are compared to examine their overall physical property test results. Table 1 shows the addition amount of each component in the compound formulation and the results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests; Table 2 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples. Figure 1 The curves show the relationship between the retention rate of elongation at break and time when the samples were placed in a 180℃ heat aging oven for 7 days and in a 150℃ heat aging oven for about 10 weeks. Figure 6 This test involves free radical scavenging of a sample. 1,1-Diphenyl-2-trinitrophenylhydrazine (DPPH) is a very stable nitrogen-centered free radical. Its stability mainly comes from the resonance stabilization of the three benzene rings, which prevents the unpaired electrons on the central nitrogen atom from performing their proper electron pairing function. As a stable free radical, DPPH can capture ("scaveng") other free radicals. Therefore, the addition of DPPH is used to observe whether a compound possesses the essential properties of free radical scavenging. Because DPPH has a strong absorption centered at 520 nm, it appears deep purple in solution. After neutralization, it remains a stable free radical in organic solvents, with its alcoholic solution also appearing purple and requiring low-temperature, light-protected storage. It has a maximum absorption peak at 517 nm. When free radicals scaveng, the single electrons of DPPH are captured, causing its color to lighten and the absorbance at the maximum absorption wavelength to decrease. This decrease in absorbance level indicates an increase in antioxidant activity, thus allowing evaluation of the antioxidant properties of the test sample. Figure 7 The oxidation induction time (OIT) test is performed on samples. OIT measures the time it takes for a sample to begin an autocatalytic oxidation reaction under high-temperature (200°C) oxygen conditions. It is an indicator of the resistance of polymer materials to heat-induced oxygen degradation during molding, processing, storage, and use. The OIT method uses differential thermal analysis (DTA) based on the exothermic reaction during the breakage of plastic molecular chains to test the degree of accelerated aging of plastics in high-temperature oxygen. A longer OIT indicates a better antioxidant effect of the polymer material.

[0044] Table 1. Addition amount of each component in the compound formulation and results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests.

[0045]

[0046] Table 2. Test results of mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples.

[0047]

[0048] Example 2:

[0049] a. Preparation of DOPO-DH

[0050] Take a 500ml three-necked flask, dissolve 71.33g of DOPO in 300ml of chloroform solution. After the DOPO is completely dissolved, add 29.73g of paraformaldehyde, then slowly add 34.69g of diethanolamine solution, and apply a reflux condenser. Under mechanical stirring, react at 55℃ for 12h. After the reaction is complete, cool the solution to room temperature, filter, wash with chloroform, and then dry in a vacuum oven at 100℃ for 12h.

[0051] b. DOPO-DH reacts with toluene diisocyanate (TDI) and encapsulates piperazine pyrophosphate (PAPP).

[0052] Take a 500ml three-necked flask, add 14.88g of DOPO-DH and 80ml of THF, stir and heat to 40℃. After the reactants are completely dissolved, add 10.12g of TDI and 40ml of THF, stir for 15-25min, then add 75g of PAPP, 200ml of THF, 1g of Triton and 0.3g of dibutyltin disilicate, then heat to 85℃ and react for 6-10h. After the reaction is complete, filter, wash with ethanol, and then dry at 80℃ for 12h.

[0053] c. Add 25 parts of microencapsulated flame retardant (DOPO-DH@PAPP) to 75 parts of polyethylene (PE) by mass ratio, then mix them in an internal mixer or extruder at 180°C until uniform. Then add 1 part of trimethylolpropionic acid (PETA), mix them evenly, and then irradiate them under high-energy electron beam irradiation at an irradiation dose of 200KGy to produce irradiated crosslinked polyethylene sheets or plates.

[0054] To further verify the performance of microencapsulated flame retardants with DOPO-DH as the shell, we designed the following as shown in Tables 3 and 4. Figure 2 The comparative formulations shown are compared to their comprehensive physical property test results. Table 3 shows the addition amount of each component in the compound formulation and the results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests; Table 4 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples; Figure 2 The curves show the relationship between the retention rate of elongation at break and time when each sample was placed in a 180℃ heat aging oven for 7 days and in a 150℃ heat aging oven for about 10 weeks.

[0055] Table 3. Addition amount of each component in the compound formulation and results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests.

[0056]

[0057] Table 4. Test results of mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples.

[0058]

[0059] Example 3:

[0060] a. Preparation of DOPO-GD

[0061] Take a 500ml three-necked flask and dissolve 54g of DOPO in 150ml of toluene solution. After the DOPO is completely dissolved, add 50g of glutaraldehyde aqueous solution dropwise over 20min using a dropping funnel, and apply a reflux condenser. Under mechanical stirring, react at 85℃ for 5h. After the reaction is complete, cool the solution to room temperature, filter it, wash it with toluene, and then dry it at 80℃ for 12h.

[0062] b. DOPO-GD reacts with toluene diisocyanate (TDI) and encapsulates aluminum hydroxide (ATH).

[0063] Take a 500ml three-necked flask, add 14.03g of DOPO-GD and 80ml of 1,4-dioxane, stir and heat to 40℃. After the reactants are completely dissolved, add 5.97g of TDI and 40ml of 1,4-dioxane, stir for 15-25min, then add 80g of ATH, 200ml of 1,4-dioxane, 1g of Triton, and 0.3g of dibutyltin dihexylsilicate. Then heat to 85℃ and react for 6-10h. After the reaction is complete, filter, wash with ethanol, and then dry at 80℃ for 12h.

[0064] c. Add 55 parts of microencapsulated flame retardant (DOPO-GD@ATH) to 45 parts of EPDM rubber by mass ratio, then mix them in an internal mixer or extruder at 140°C until uniform. Then add 1.5 parts of triallyl cyanurate (TAIC) and 0.7 parts of dicumyl peroxide (DCP), mix them evenly, and vulcanize them in a vulcanizing machine at 160°C for 15 minutes to make sheets.

[0065] To further verify the performance of microencapsulated flame retardants with DOPO-GD as the shell, we designed the following as shown in Tables 5 and 6. Figure 3 The comparative formulations shown are compared to their comprehensive physical property test results. Table 5 shows the addition amount of each component in the compound formulation and the results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests; Table 6 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples; Figure 3The curves show the relationship between the retention rate of elongation at break and time when each sample was placed in a 180℃ heat aging oven for 7 days and in a 150℃ heat aging oven for about 10 weeks.

[0066] Table 5. Addition amount of each component in the compound formulation and results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests.

[0067]

[0068] Table 6. Test results of mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples.

[0069]

[0070] Example 4:

[0071] a. DOPO-GY reacts with hexamethylene diisocyanate (HDI) and encapsulates piperazine pyrophosphate (PAPP).

[0072] Take a 500ml three-necked flask, add 10.37g of DOPO-GY and 80ml of THF, stir and heat to 40℃. After the reactants are completely dissolved, add 4.63g of HDI and 40ml of THF, stir for 15-25min, then add 85g of PAPP, 200ml of THF, 1g of Triton and 0.3g of dibutyltin disilicate, then heat to 85℃ and react for 6-10h. After the reaction is complete, filter, wash with ethanol, and then dry at 80℃ for 12h.

[0073] b. Add 25 parts of microencapsulated flame retardant (DOPO-GY@PAPP) to 75 parts of ethylene vinyl acetate (EVA) by mass ratio, and then mix them in an internal mixer or extruder at 150°C until uniform. Then add 1.4 parts of triallyl cyanurate (TAIC), mix them evenly, and then irradiate them under cobalt source irradiation at an irradiation dose of 200KGy to produce irradiated crosslinked EVA sheets or plates.

[0074] To further verify the performance of the microencapsulated flame retardant with DOPO-GY as the shell, we replaced TDI with HDI and changed the type of flame retardant, and then designed the flame retardants shown in Tables 7 and 8. Figure 4 The comparative formulations shown are compared to their comprehensive physical property test results. Table 7 shows the addition amount of each component in the compound formulation and the results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests; Table 8 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples; Figure 4The curves show the relationship between the retention rate of elongation at break and time when each sample was placed in a 180℃ heat aging oven for 7 days and in a 150℃ heat aging oven for about 10 weeks.

[0075] Table 7. Addition amount of each component in the compound formulation and results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests.

[0076]

[0077]

[0078] Table 8. Test results of mechanical properties, combustion performance (Cone), and smoke density (Ds) of each sample.

[0079]

[0080] Example 5:

[0081] a. DOPO-DH reacts with diphenylmethane diisocyanate (MDI) and encapsulates APP.

[0082] Take a 500ml three-necked flask, add 12.65g of DOPO-DH and 80ml of DMF, stir and heat to 40℃. After the reactants are completely dissolved, add 12.35g of MDI and 40ml of DMF, stir for 15-25min, then add 75g of PAPP, 200ml of DMF, 1g of Triton and 0.3g of dibutyltin disterite, then heat to 85℃ and react for 6-10h. After the reaction is complete, filter, wash with ethanol, and then dry at 80℃ for 12h.

[0083] c. Add 25 parts of microencapsulated flame retardant (DOPO-DH@APP) to 75 parts of polyethylene (PE) by mass ratio, then mix them in an internal mixer or extruder at 140°C until uniform, then add 0.8 parts of trimethylolpropionic acid (PETA) and 0.4 parts of dicumyl peroxide (DCP), and then vulcanize at 170°C for 15 minutes using a flat vulcanizing machine to obtain cross-linked polyethylene sheets or plates.

[0084] To further verify the performance of the microencapsulated flame retardant with DOPO-DH as the shell, we replaced TDI with MDI and changed the type of flame retardant, and then designed the flame retardants shown in Tables 9 and 10. Figure 5 The comparative formulations shown are compared to their comprehensive physical property test results. Table 9 shows the addition amount of each component in the compound formulation and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 10 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of the samples; Figure 5The curves show the relationship between the retention rate of elongation at break and time when each sample was placed in a 180℃ heat aging oven for 7 days and in a 150℃ heat aging oven for about 10 weeks.

[0085] Table 9. Addition amounts of each component in the compound formulation and results of vertical combustion (UL-94) and limiting oxygen index (LOI) tests.

[0086]

[0087] Table 10 shows the test results of the mechanical properties, combustion performance (Cone), and smoke density (Ds) of each sample.

[0088]

[0089] Based on the above experimental results, the following conclusions can be drawn:

[0090] (1) Adding microencapsulated flame retardants with DOPO derivatives as shells to polyolefin composites results in better mechanical and flame retardant properties than the control group with unencapsulated flame retardants.

[0091] (2) Free radical scavenging and oxidation induction time tests demonstrated that the flame retardant with this structure possesses a certain free radical scavenging function, exhibiting long-term antioxidant effects throughout the service life of the polymer material. The polyolefin composite material with a microencapsulated flame retardant containing a DOPO derivative as the shell showed a significantly better decrease in mechanical properties than the control group after a long-term heat aging test at 150℃ for 10 weeks. Therefore, the halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material and its preparation method provided by this invention not only endow polyolefin materials with excellent flame retardant properties but also improve the long-term heat aging resistance of the polyolefin composite material.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A halogen-free flame-retardant and antioxidant cross-linked polyolefin composite material, wherein the raw materials are composed of the following parts by mass: 45-75 parts polyolefin, 25-55 parts microencapsulated flame retardant, and 1-2.5 parts crosslinking agent; The microencapsulated flame retardant is composed of a core layer and a shell layer structure, wherein the core layer structure is a flame retardant and the shell layer structure is a flame-retardant polyurethane formed by polymerizing DOPO derivatives and isocyanates; the mass ratio of the core layer to the shell layer structure is 75~85:15~25. The DOPO derivatives are selected from compounds with the following structures: ； The flame retardant is selected from one or more of the following: ammonium polyphosphate, piperazine pyrophosphate, magnesium hydroxide, aluminum hydroxide, hydrotalcite, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, aluminum hypophosphite, aluminum phosphonate, expandable graphite, zinc borate, graphene, transition metal disulfides, carbon nanotubes, halloysite, sepiolite, and kaolin, mixed in any proportion.

2. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material according to claim 1, characterized in that: The polyolefin is selected from one or more of the following: ethylene-vinyl acetate copolymer, polyethylene, ethylene propylene diene monomer (EPDM) rubber, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, maleic anhydride-grafted EPDM rubber, ethylene-octene copolymer, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, and maleic anhydride-grafted hydrogenated styrene-butadiene-styrene block copolymer, mixed in any proportion.

3. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material according to claim 1, characterized in that: The crosslinking agent is selected from one or more of dicumyl peroxide, triallyl cyanurate, triallyl isocyanurate, trimethylolpropene trimethacrylate, trimethylolpropene triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate, mixed in any proportion.

4. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material according to claim 1, characterized in that: The raw materials of the microencapsulated flame retardant are composed of the following parts by mass: 10-15 parts of DOPO derivative, 200-300 parts of solvent, 75-85 parts of flame retardant, 4-13 parts of isocyanate, 0.1-0.3 parts of catalyst, and 0.5-1.5 parts of surfactant.

5. The halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material according to claim 4, characterized in that... The microencapsulated flame retardant was prepared by the following method: The DOPO derivative is added to a solvent, stirred, and heated to 40°C. After the reactants are completely dissolved, isocyanate is added and stirred at this temperature for 15-25 minutes. Then, flame retardant, catalyst, and surfactant are added for encapsulation. The temperature is raised to 85°C and reacted for 6-10 hours. The mixture is then cooled to room temperature, filtered, and the resulting filter cake is placed in an 80°C oven and dried for 12 hours. The product obtained is the microencapsulated flame retardant.

6. A method for preparing the halogen-free flame-retardant and antioxidant crosslinked polyolefin composite material according to claim 1, characterized in that... Includes the following steps: Add 25-55 parts of microencapsulated flame retardant to 45-75 parts of polyolefin, mix until uniform in a mixer or extruder at 120-180℃, then add 1-2.5 parts of crosslinking agent, mix evenly, and press into sheets in a flat vulcanizing machine. Prepare crosslinked polyolefin composite materials by hot vulcanization crosslinking or irradiation crosslinking.

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