Graft-modified anti-aging flame-retardant polypropylene and preparation method thereof

Abstract

The invention belongs to the technical field of flame-retardant polymers, and particularly relates to graft modified anti-aging flame-retardant polypropylene and a preparation method thereof. The grafted modified anti-aging flame-retardant polypropylene comprises the following raw materials in parts by mass: 100 parts of polyolefin, 4-7 parts of a vinyl silane coupling agent and 8-15 parts of a reactive flame retardant as shown in a formula (I). According to the invention, the self-made nitrogen-phosphine synergistic reactive flame retardant and the vinyl silane coupling agent are added into the polypropylene, and the polypropylene is modified through melt grafting, so that the flame retardance of the polypropylene is remarkably improved, the flame retardance has excellent weather resistance, and the flame retardance is basically not reduced after long-time double 85 high-temperature and high-humidity aging. The nitrogen-phosphine synergistic reaction type flame retardant improves the flame retardant property and the weather resistance, and also has the advantages of small addition amount and small influence on the mechanical property of polyolefin.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame-retardant polymers, and particularly relates to a graft-modified anti-aging flame-retardant polypropylene and a preparation method thereof. Background Art

[0002] Polyolefins are currently widely used thermoplastic polymers, with excellent properties such as non-toxicity, low density, and chemical corrosion resistance. However, polyolefins are flammable materials. For example, the LOI of polyethylene and polypropylene is only 17 - 18.5%, with a high heat release rate during combustion and easy generation of molten droplets. Therefore, it is necessary to carry out flame-retardant treatment on them.

[0003] Currently, the common method for flame-retardant treatment of polypropylene is physical blending. For example, a flame retardant and a polyolefin matrix are melt co-extruded together. The flame retardants include inorganic fillers and organic flame retardants. However, the method of improving the flame retardancy of polyolefins by physical blending has drawbacks: on the one hand, a large addition amount is required to achieve a suitable flame-retardant effect. For example, 20% of an intumescent flame retardant, or more than 40% of a metal hydroxide flame retardant, increases the manufacturing cost and affects the mechanical properties of the polyolefin material. CN119505412A discloses a flame-retardant high-modulus polypropylene composite material, comprising the following components in parts by weight: 50 - 60 parts of polypropylene, 30 - 40 parts of a phosphorus-nitrogen-based flame retardant, 3 - 5 parts of a compatibilizer, and 0.5 - 1.5 parts of a dispersant; the dispersant is an imidized isobutene-maleic anhydride copolymer, and the compatibilizer is a polystyrene-oxazoline graft polymer. This patent uses a large amount of flame retardants and also requires a compatibilizer to improve the compatibility between the flame retardant and the polyolefin. This method of improving flame retardancy by physical blending has the above-mentioned drawbacks.

[0004] Polyolefins are non-polar polymer materials with poor compatibility with conventional flame retardant systems. In a humid and hot environment, the physically blended flame retardants are prone to migration, precipitation, and failure, resulting in a decline in the flame retardant effect. This restricts the application of polypropylene materials in fields that require flame retardancy and are under high-temperature conditions for a long time. For example, in the flame retardant modification of polyolefins, and adding reactive flame retardants to chemically modify polypropylene to obtain polyolefins with excellent weather resistance. Polyolefins are prepared by the photopolymerization or thermal polymerization of polyolefins and functional monomers. For example, CN119639163A discloses a method for preparing a flame retardant and anti-aging polyolefin plastic, which includes the following steps: S1. Add pretreated polypropylene, aqueous acrylic acid solution, and benzophenone solution to a glass reaction kettle, transfer it to an ultraviolet cross-linking instrument, and carry out ultraviolet grafting reaction, and then post-treat to obtain modified polypropylene; S2. Add [(6-oxo-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)methyl]succinic acid, isophorone diisocyanate, triethylamine, and xylene to a reaction kettle and stir. Under nitrogen protection, raise the temperature of the reaction kettle to 40-60 °C, keep the temperature for 2-3 h, add 2-cyclopropylacetamide, and react for 10-12 h, and then post-treat to obtain a flame retardant; S3. Add the modified polypropylene, modified anti-aging agent, flame retardant, and compound nucleating agent to a twin-screw extruder for melt extrusion, and inject it into a single-screw granulator to obtain a composite polypropylene plastic. This patent still needs to separately prepare a modified anti-aging agent and modified polypropylene and extrude them together in a twin-screw extruder, and the preparation process is complicated and not suitable for industrial production.

[0005] CN119144080A discloses an intrinsically flame retardant, antioxidant, and cross-linked polyolefin composite material. The raw materials are composed of the following parts by mass: 34-82 parts of polyolefin, 10-40 parts of flame retardant unit side-chain grafted polyethylene, 16-30 parts of halogen-free flame retardant, and 1-2.5 parts of cross-linking agent; the flame retardant unit side-chain grafted polyethylene is composed of EVA hydrolytically grafted with a flame retardant containing a flame retardant structural unit. The flame retardant containing a flame retardant structural unit is selected from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphinous chloride, or anthraceneformic acid. However, this patent still needs to add a halogen-free flame retardant to have the required flame retardant performance.

[0006] CN118599204A discloses a high-strength flame retardant and antistatic polyethylene polymer material, which includes the following components in parts by weight: 100 parts of ultra-high molecular weight polyethylene, 10-25 parts of carboxylated graphene, 3-15 parts of flame retardant and antistatic cross-linking agent, 4-8 parts of polyethylene grafted maleic anhydride, 0.8-1.5 parts of antioxidant, and 0.1-1 part of nucleating agent. The structural formula of the flame retardant and antistatic cross-linking agent is as follows: By utilizing the hydroxyl and alkenyl groups on its surface to chemically crosslink with the carboxyl groups of polyethylene, polyethylene grafted maleic anhydride, and carboxylated graphene, a continuous crosslinked network structure is formed to obtain a high-strength flame-retardant and antistatic polyethylene polymer material. However, the preparation process of the flame retardant used in this patent is complex, requiring three-step reactions to prepare the flame retardant, and the raw materials are expensive with a low yield, which is not suitable for large-scale industrial production. Summary of the Invention

[0007] To solve the existing technologies. Specifically, the present invention provides the following technical solutions to solve the above technical problems: A graft-modified anti-aging flame-retardant polypropylene, comprising the following raw materials in parts by mass: 100 parts of polyolefin, 4 - 7 parts of vinyl silane coupling agent, 8 - 15 parts of a reactive flame retardant represented by formula (I): (I).

[0008] Preferably, the graft-modified anti-aging flame-retardant polypropylene comprises the following raw materials in parts by mass: 100 parts of polyolefin, 4 - 7 parts of vinyl silane coupling agent, 10 - 12 parts of a reactive flame retardant represented by formula (I) The inventors' previous patent disclosed a nitrogen-phosphorus synergistic flame retardant represented by formula (I). Through the Atherton-Todd reaction of maleic hydrazide with DOPO, the coupling of DOPO with hydrazide compounds was achieved, obtaining a new type of nitrogen-phosphorus synergistic flame retardant. The inventors found that this flame retardant can endow PBT with excellent flame retardant effects even at a relatively low addition amount, confirming that this flame retardant is a flame retardant with excellent performance. Since the flame retardant represented by formula (I) has polymerizable double bonds, it is expected to become a reactive flame retardant. The present invention conducts melt graft modification on the flame retardant represented by formula (I), polyolefin, and vinyl silane coupling agent together to prepare a polyolefin material with excellent flame retardant performance, and the obtained flame-retardant polyolefin has excellent flame retardant and anti-aging properties. After undergoing long-term aging in a humid and hot environment, the flame retardant performance basically does not decline.

[0009] Furthermore, the polyolefin is selected from at least one of polyethylene and polypropylene, and the melt index of the polyolefin is 5 - 100 g / 10 min under the conditions of 230 °C and 2.16 kg; and / or the vinyl silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0010] Preferably, the melt index of the polyolefin is 5 - 10 g / 10 min under the conditions of 230 °C and 2.16 kg.

[0011] Furthermore, the graft-modified anti-aging flame-retardant polypropylene further comprises the following raw materials in parts by mass: 1-3 parts of a toughening agent, 0.1-1 part of an antioxidant, and 0.1-1 part of a lubricant.

[0012] The toughening agent is selected from at least one of ethylene-propylene-diene terpolymers; the antioxidant is selected from at least one of antioxidant 1076, antioxidant 168, antioxidant 1098, antioxidant 1010, and antioxidant BHT; the lubricant is selected from at least one of magnesium stearate, zinc stearate, and polyethylene wax.

[0013] Furthermore, the reactive flame retardant represented by formula (I) is prepared by a preparation method including the following steps: maleic hydrazide and DOPO react in the presence of an acid-binding agent and a halogenating agent, and then are post-treated; the synthesis route is as follows: 。

[0014] Furthermore, the acid-binding agent is selected from at least one of triethylamine, N,N-diisopropylethylamine, pyridine, and tetramethylguanidine; the halogenating agent is carbon tetrachloride. Further, the molar ratio of maleic hydrazide, DOPO, the acid-binding agent, and the halogenating agent is 1:2.1-2.5:50-100:50-100. The slight excess of DOPO and the far excess of the acid-binding agent and the halogenating agent are both for the purpose of increasing the yield of the DOPO disubstituted product.

[0015] Furthermore, the reaction solvent is a halogenated hydrocarbon, and the halogenated hydrocarbon is selected from at least one of dichloromethane and dichloroethane. The reaction conditions are to react at 50-80 °C for 5-15 h. After the reaction is completed, the solvent and the halogenating agent are evaporated, and the remaining product is slurried and purified with ethanol to remove the salt formed by the acid-binding agent (such as triethylamine hydrochloride) and other impurities.

[0016] Furthermore, in the reaction, while adding the acid-binding agent, a halogenated salt with a molar amount of 0.05-0.1 times that of maleic hydrazide is added, and the reaction solvent is a mixed solvent of a halogenated hydrocarbon and an alcohol with 1-3 carbon atoms in a volume ratio of 10:1-2. Preferably, the halogenated salt is selected from lithium chloride, zinc chloride, ferric chloride, and aluminum trichloride.

[0017] There are two reactive N-H groups on maleic hydrazide that can react with DOPO. However, after one DOPO is substituted, due to the large size of the DOPO group, the remaining N-H activity decreases due to steric hindrance, and the yield of the double-substituted DOPO product is affected. The inventors also found that the product with single DOPO substitution has an important impact on the performance of the flame retardant, and even a small amount will affect the flame retardant effect of the flame retardant. Therefore, it is necessary to improve the yield of the double-DOPO product. Unexpectedly, the inventors found that when a small amount of halogenated salt is added during the reaction and the solvent is a mixture of halogenated hydrocarbon and lower alcohol, the yield of the double-DOPO substitution product can be significantly improved. The inventors speculate that the possible reason is that the halogenated salt can accelerate the formation of acyl chloride in the first stage and react with another substrate faster; in addition, it can also increase the nucleophilicity of hydroxylamine in the acyl hydrazide, which helps to form the double-substituted product.

[0018] Furthermore, the present invention also provides a method for preparing the graft-modified anti-aging flame-retardant polypropylene as described above, comprising the following steps: (S1) React maleic hydrazide and DOPO in the presence of an acid-binding agent and a halogenating reagent to prepare the reactive flame retardant of formula (I); (S2) Mix 100 parts by mass of polyolefin, 8-15 parts by mass of the reactive flame retardant of formula (I), 4-7 parts by mass of vinyl silane coupling agent, and 0.1-0.5 parts by mass of initiator evenly, add them to a twin-screw extruder, and melt-extrude and pelletize to obtain the graft-modified anti-aging flame-retardant polypropylene.

[0019] Furthermore, the initiator is selected from at least one of dicumyl peroxide, diisopropylbenzene peroxide, dicyclohexyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, and tert-butyl perpivalate.

[0020] Furthermore, in step (S2), the method of mixing evenly is a high-speed mixer; the process conditions for melt-extrusion and pelletization are 190-230 °C and a screw speed of 200-300 rpm.

[0021] Furthermore, in step (S2), when adding the reactive flame retardant of formula (I), 1-3 parts by mass of a toughening agent, 0.1-1 part by mass of an antioxidant, and 0.1-1 part by mass of a lubricant are also added.

[0022] Furthermore, in step (S1), the acid-binding agent is selected from at least one of triethylamine, N,N-diisopropylethylamine, pyridine, and tetramethylguanidine; the halogenating reagent is carbon tetrachloride. Further, the molar ratio of maleic hydrazide, DOPO, acid-binding agent, and halogenating reagent is 1:2.1-2.5:50-100:50-100. The slight excess of DOPO and the far excess of acid-binding agent and halogenating reagent are both for the purpose of improving the yield of the DOPO double-substituted product.

[0023] Further, in step (S1), the reaction solvent is a halogenated hydrocarbon, and the halogenated hydrocarbon is selected from at least one of dichloromethane and dichloroethane. The reaction conditions are to react at 50 - 80 °C for 5 - 15 h. After the reaction, the solvent and the halogenating reagent are distilled off, and the remaining product is slurried and purified with ethanol to remove the salts formed by the acid-binding agent (such as triethylamine hydrochloride) and other impurities.

[0024] Further, in step (S1), while adding the acid-binding agent, a halogenated salt with a molar amount of 0.05 - 0.1 times that of maleic hydrazide is also added, and the reaction solvent is a mixed solvent of a halogenated hydrocarbon and an alcohol with C1 - 3 in a volume ratio of 10:1 - 2. Preferably, the halogenated salt is selected from lithium chloride, zinc chloride, ferric trichloride, and aluminum trichloride.

[0025] In the present invention, by adding a self-made nitrogen-phosphorus synergistic reactive flame retardant and a vinyl silane coupling agent to polypropylene, the polypropylene is modified by melt grafting, significantly improving the flame retardancy of the polypropylene, and the flame retardancy has excellent weather resistance. After long-term high-temperature and high-humidity aging at double 85, the flame retardant performance basically does not decrease. In addition to improving the weather resistance of the flame retardant performance, the nitrogen-phosphorus synergistic reactive flame retardant of the present invention also has the advantages of less addition amount and little influence on the mechanical properties of polyolefins. Description of the Drawings

[0026] Figure 1 is the 1 1H NMR spectrum of the product obtained in Preparation Example 1; Figure 2 is the 31 31P NMR spectrum of the product obtained in Preparation Example 1; Figure 3 is the mass spectrum of the product obtained in Preparation Example 1; Figure 4 is the DSC chart of the product obtained in Preparation Example 1; Figure 5 is the TGA chart of the product obtained in Preparation Example 1. Detailed Embodiments

[0027] The following specific examples are used to further explain and illustrate the technical solutions of the present invention.

[0028] The polypropylene is K8009, and the melt index is 8.5 g / 10 min under the conditions of 230 °C and 2.16 kg.

[0029] Preparation Example 1 .

[0030] Add 10 ml of dichloromethane, 0.5 mol of carbon tetrachloride, 5 mmol of maleic hydrazide, and 11 mmol of DOPO to the reaction vessel. Dropwise add 0.5 mol of triethylamine at room temperature and react at 70 °C for 6 h. After the reaction is completed, rotary evaporate to remove dichloromethane and carbon tetrachloride. The remaining solid is slurried with ethanol and purified twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and recrystallize to obtain a white powdery sample with a yield of 86.3% and an HPLC purity of 99.4%.

[0031] Figure 1 is the 1 1H NMR spectrum of the product obtained in Preparation Example 1. Figure 2 is the 31 31P NMR spectrum of the product obtained in Preparation Example 1. Doublets appear at 6.52 ppm and 6.72 ppm with similar chemical shifts, indicating that the compound is a pair of diastereoisomers. Figure 3 is the mass spectrum of the product obtained in Preparation Example 1. The molecular ion peak with a mass-to-charge ratio (m / z) of 541.1 is used to finally determine the relative molecular weight of the compound, with two DOPOs coupled to maleic hydrazide. Figure 4 is the DSC chart of the product obtained in Preparation Example 1. Figure 5 is the TGA chart of the product obtained in Preparation Example 1. The compound has two melting points, further indicating that the compound is a pair of diastereoisomers. The compound structure contains a carbon-carbon double bond, so it is prone to break and decompose at the carbon-carbon double bond during thermogravimetric analysis.

[0032] Preparation Example 2 Add 10 ml of dichloromethane, 1 ml of methanol, 0.5 mol of carbon tetrachloride, 5 mmol of maleic hydrazide, 11 mmol of DOPO, and 0.5 mmol of lithium chloride to the reaction vessel. Dropwise add 0.5 mol of triethylamine at room temperature and react at 70 °C for 6 h. After the reaction is completed, rotary evaporate to remove dichloromethane, methanol, and carbon tetrachloride. The remaining solid is slurried with ethanol and purified twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and recrystallize to obtain a white powdery sample with a yield of 94.2% and an HPLC purity of 99.6%.

[0033] That is, compared with Preparation Example 1, Preparation Example 2 also added 0.5 mmol of lithium chloride and 1 ml of methanol.

[0034] Preparation Example 3 Add 10 ml of dichloromethane, 0.5 mol of carbon tetrachloride, 5 mmol of maleic hydrazide, 11 mmol of DOPO, and 0.5 mmol of lithium chloride to the reaction vessel. Dropwise add 0.5 mol of triethylamine at room temperature and react at 70 °C for 6 h. After the reaction, rotary evaporate to remove dichloromethane, methanol, and carbon tetrachloride. Purify the remaining solid by slurrying with ethanol twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and recrystallize to obtain a white powdery sample with a yield of 90.7% and an HPLC purity of 99.4%.

[0035] That is, compared with Preparation Example 1, Preparation Example 3 also added 0.5 mmol of lithium chloride.

[0036] Preparation Example 4 Add 10 ml of dichloromethane, 1 ml of methanol, 0.5 mol of carbon tetrachloride, 5 mmol of maleic hydrazide, and 11 mmol of DOPO to the reaction vessel. Dropwise add 0.5 mol of triethylamine at room temperature and react at 70 °C for 6 h. After the reaction, rotary evaporate to remove dichloromethane, methanol, and carbon tetrachloride. Purify the remaining solid by slurrying with ethanol twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and recrystallize to obtain a white powdery sample with a yield of 86.8% and an HPLC purity of 99.4%.

[0037] That is, compared with Preparation Example 1, Preparation Example 4 also added 1 ml of methanol.

[0038] From the comparison of Examples 1-4, it can be seen that adding metal chlorides and methanol can significantly improve the product yield. Adding only metal chlorides can also increase the yield, but not significantly; only increasing C1-3 alcohols results in a small increase in yield.

[0039] Example 1 100 parts by mass of polypropylene K8009, 8 parts by mass of the reactive flame retardant prepared in Preparation Example 1, 5 parts by mass of vinyltriethoxysilane, and 0.3 parts by mass of dicumyl peroxide are mixed evenly by a high-speed mixer and added to a twin-screw extruder. Melt-extrude and pelletize at 190-230 °C and a screw speed of 300 rpm to obtain graft-modified anti-aging flame-retardant polypropylene.

[0040] Example 2 Other conditions are the same as in Example 1, except that the amount of the reactive flame retardant described in formula (I) is 10 parts by mass.

[0041] Example 3 Other conditions are the same as in Example 1, except that the amount of the reactive flame retardant described in formula (I) is 12 parts by mass.

[0042] Comparative Example 1 Other conditions are the same as those in Example 1, except that the reactive flame retardant described in formula (I) is not added.

[0043] Comparative Example 2 Other conditions are the same as those in Example 1, except that vinyltriethoxysilane is not added.

[0044] Comparative Example 3 100 parts by mass of polypropylene K8009 and 26 parts by mass of tris(2-hydroxyethyl)aminomethyl phosphate are uniformly mixed by a high-speed mixer and then added to a twin-screw extruder. Melting extrusion granulation is carried out at 190 - 230 °C with a screw speed of 300 rpm to obtain flame-retardant polypropylene.

[0045] Application Example The flame retardancy of the polypropylene obtained in the above examples and comparative examples was tested, and the results are shown in Table 1 below: The double 85 laboratory samples were placed at 85 °C and 85% RH for 30 days, and the limiting oxygen index (LOI) was tested after drying.

[0046] Table 1 Polypropylene Flame Retardancy and Mechanical Property Tests .

[0047] It can be seen from the data in Table 1 that by adding the self-made nitrogen-phosphorus synergistic reactive flame retardant and vinyl silane coupling agent to polypropylene and modifying polypropylene through melt grafting, the flame retardancy of polypropylene is significantly improved, and the flame retardancy has excellent weather resistance. After long-term high-temperature and high-humidity aging under double 85 conditions, the flame retardancy hardly decreases. In addition to improving the weather resistance of the flame retardancy, the nitrogen-phosphorus synergistic reactive flame retardant of the present invention also has the advantages of less addition amount and little influence on the mechanical properties of polyolefins.

Claims

1. A graft-modified anti-aging flame-retardant polypropylene, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of polyolefin, 4-7 parts of vinyl silane coupling agent, and 8-15 parts of reactive flame retardant represented by formula (I): (I)。 2. The graft-modified anti-aging flame-retardant polypropylene according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of polyolefin, 4-7 parts of vinyl silane coupling agent, and 10-12 parts of reactive flame retardant represented by formula (I).

3. The graft-modified anti-aging flame-retardant polypropylene according to claim 1, characterized in that: The polyolefin is selected from at least one of polyethylene and polypropylene; the polyolefin has a melt index of 5-100 g / 10 min at 230° C. and 2.16 kg; and / or the vinyl silane coupling agent is selected from at least one of vinyl triethoxysilane, vinyl trimethoxysilane, vinyl triisopropoxysilane, and γ-methacryloxypropyl trimethoxysilane.

4. The graft-modified anti-aging flame-retardant polypropylene according to claim 1, characterized in that: The reactive flame retardant represented by formula (I) is prepared by a preparation method comprising the following steps: maleic hydrazide and DOPO react in the presence of an acid binding agent and a halogenating agent, and then undergo post-treatment to obtain the flame retardant; the synthetic route is as follows: 。 5. The graft-modified anti-aging flame-retardant polypropylene according to claim 4, characterized in that: The acid binding agent is selected from at least one of triethylamine, N,N-diisopropylethylamine, pyridine and tetramethylguanidine; and the halogenating agent is carbon tetrachloride.

6. The graft-modified anti-aging flame-retardant polypropylene according to claim 4, characterized in that: The molar ratio of maleic hydrazide, DOPO, acid binding agent and halogenating agent is 1:2.1-2.5:50-100:50-100.

7. The graft-modified anti-aging flame-retardant polypropylene according to claim 4, characterized in that: The reaction solvent is a halogenated hydrocarbon, which is selected from at least one of dichloromethane and dichloroethane. The reaction conditions are 50-80° C. for 5-15 hours.

8. The graft-modified anti-aging flame-retardant polypropylene according to claim 4, characterized in that: When the acid binding agent is added, a halogenated salt with a molar amount of 0.05-0.1 times of maleic hydrazide is also added, and the reaction solvent is a mixed solvent of a halogenated hydrocarbon and a C1-3 alcohol in a volume ratio of 10:1-2; the halogenated salt is selected from lithium chloride, zinc chloride, ferric chloride, and aluminum chloride.

9. The method for preparing the graft modified anti-aging flame-retardant polypropylene according to any one of claims 1 to 8, characterized in that: The following steps are involved: (S1) maleic hydrazide and DOPO react in the presence of an acid binding agent and a halogenating agent to prepare a reactive flame retardant of formula (I); (S2) 100 parts by mass of polyolefin, 8-15 parts by mass of the reactive flame retardant of formula (I), 4-7 parts by mass of vinyl silane coupling agent, and 0.1-0.5 parts by mass of initiator are mixed uniformly, added into a twin-screw extruder, melt-extruded and granulated to obtain graft-modified anti-aging flame-retardant polypropylene.

10. The preparation method according to claim 9, characterized in that: The initiator is at least one selected from dicumyl peroxide, di-tert-butyl cumyl peroxide, dicyclohexyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, and tert-butyl peroxypivalate; In step (S2), the uniform mixing method is a high-speed mixer; the process conditions for melt extrusion granulation are 190-230° C. and a screw speed of 200-300 rpm.

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