CN117384445A - Halogen-free flame-retardant antioxidant crosslinked polyolefin composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a halogen-free flame-retardant antioxidant crosslinked polyolefin composite material and a preparation method thereof, wherein the composite material comprises the following raw materials in parts by mass: 45-75 parts of polyolefin, 25-55 parts of microencapsulated flame retardant and 1-2.5 parts of cross-linking agent. The microcapsule flame retardant added in the composite material takes flame-retardant polyurethane formed by polymerizing DOPO derivatives and isocyanate as a shell layer, can not only play a role in core-shell synergistic flame retardance with the core flame retardant, but also have synergistic effects of various flame retarding mechanisms such as gas phase and condensation. In addition, the halogen-free flame-retardant antioxidant crosslinked polyolefin composite material provided by the invention still has excellent ageing resistance under the condition that no antioxidant is added, can prolong the service life of the material while improving the flame retardant property of the material, and can be widely applied to the fields of aerospace, national defense, construction, medical treatment, chemical industry and the like.

Description

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

Technical field

The invention relates to the technical field of flame-retardant cross-linked polyolefin composite materials, and in particular to a halogen-free flame-retardant and antioxidant cross-linked polyolefin composite material and a preparation method thereof.

Background technique

Polyolefin has excellent mechanical properties, electrical insulation properties, low temperature resistance, chemical corrosion resistance, heat aging resistance, UV aging resistance, good compatibility with filling materials, easy processing, suitable price, and large variety and output, making polyolefin materials Widely used in insulation and sheathing materials for wires and cables. According to statistics, electrical fires that occur in our country every year account for about 30% of the total fires in the year. Among electrical fires, there are overload, wire short circuit, poor contact, equipment aging and other reasons. These reasons are important to the aging of cable materials. connect. Cable materials will face various special service environments during the service process. Under the coupling effect of complex environmental factors (high temperature, light, rain, wind and sand, vibration, etc.), the material properties gradually deteriorate. The flame retardants added to the materials interact with other The additives will also migrate and precipitate, directly causing the mechanical and flame retardant properties of the material to decrease, resulting in a decrease in the safe service performance and service life of the cable material. Therefore, the design and preparation of halogen-free flame retardant and antioxidant polyolefin composite materials has broad development prospects.

Research reports show that microencapsulation of flame retardants through microencapsulation technology can not only solve the migration problem of flame retardants, but also improve the comprehensive physical properties, weather resistance and durability of the material.

Antioxidants commonly used in polyolefins are divided into main antioxidants and auxiliary antioxidants. The main antioxidants are antioxidants that can eliminate free radicals, which are divided into aromatic amines (due to color pollution and toxicity, they are more common among polyolefins). Use less) and hindered phenols (such as antioxidant 1010) and other types of compounds and their derivatives with similar structures; auxiliary antioxidants are compounds that can decompose hydroperoxides, including phosphites and sulfur-containing (such as antioxidants agent 168 and DLTP) and other compounds. It is reported in the literature that phosphite in the +3 valence state is a commonly used auxiliary antioxidant. Its mechanism of action is as a hydroperoxide decomposer. It can reduce the hydroperoxides released by polymer materials into alcohols, while itself It is oxidized to phosphate. In addition, since phosphorus-containing compounds are excellent flame retardants, +3-valent phosphites are often used as halogen-free flame retardants and antioxidants. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO, phosphorus is in the +1 valence state) is a new flame retardant intermediate. Because its structure contains P-H bonds, It can react with certain compounds containing double bonds, carbonyl groups, and epoxy bonds to produce a variety of derivatives. However, DOPO and its derivatives mainly improve flame retardant properties through the gas phase flame retardant mechanism. They are often used in flame retardant epoxy resins and generally have poor flame retardant effects on polyolefin composites. There are no reports on the antioxidant research of +1 valence state phosphorus-containing DOPO and its derivatives. Therefore, it is of great significance to apply DOPO and its derivatives containing +1 valence phosphorus element to the flame retardant and anti-oxidation research of polyolefin composite materials.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention provides a halogen-free flame retardant and antioxidant cross-linked polyolefin composite material and a preparation method thereof, which can not only give the polyolefin composite material good flame retardant and antioxidant properties, but also solve the problem of Issues with the long-term durability of flame-retardant polyolefin composites.

The halogen-free flame retardant and antioxidant cross-linked polyolefin composite material of the present invention has the following raw materials in terms of parts by mass:

45-75 parts of polyolefin, 25-55 parts of microencapsulated flame retardant, 1-2.5 parts of cross-linking agent.

The polyolefin is selected from the group consisting of ethylene-vinyl acetate copolymer, polyethylene, ethylene-propylene diene rubber, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, and maleic anhydride-grafted ternary rubber. Ethylene-propylene rubber, ethylene-octene copolymer, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, maleic anhydride grafted hydrogenated styrene-butadiene One or more of the diene-styrene block copolymers are mixed in any proportion. The above raw materials are all commercially available.

The cross-linking agent is selected from the group consisting of dicumyl peroxide, triallyl cyanurate, triallyl isocyanurate, trimethylolpropyl trimethacrylate, and trimethylol triacrylate. One or more of ester, pentaerythritol triacrylate, and pentaerythritol tetraacrylate are mixed in any proportion.

The microencapsulated flame retardant is composed of a core layer and a shell structure, wherein the core layer structure is a flame retardant, and the shell layer structure is a flame retardant polyurethane formed by the polymerization of DOPO derivatives and isocyanate; the core layer and the shell layer structure The mass ratio is 75~85:15~25. A ratio that is too high or too low will have an adverse effect on the flame retardant effect.

The raw materials of the microencapsulated flame retardant are composed as follows in terms of parts by mass:

10-15 parts of DOPO derivatives, 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.

The DOPO derivative is selected from DOPO compounds containing a hydroxyl structure, such as DOPO-GY, DOPO-DH, DOPO-GD, etc., and the corresponding structural formula is as follows:

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

The flame retardant is selected from ammonium polyphosphate, piperazine pyrophosphate, magnesium hydroxide, aluminum hydroxide, hydrotalcite, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, aluminum hypophosphite, phosphine One or more of aluminum phosphate, expandable graphite, zinc borate, graphene, transition metal disulfides, carbon nanotubes, halloysite, sepiolite, and kaolin are mixed in any proportion.

The isocyanate is selected from toluene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, o-phenyl diisocyanate, m-xylylene diisocyanate, 4,4-diisocyanate dicyclohexylmethane, 1,5-naphthalene Diisocyanate, 1,6-hexane diisocyanate, dimethylbiphenyl diisocyanate, 4,4'-methylene bis(phenyl isocyanate), polymethylene polyphenyl polyisocyanate or trithiophosphoric acid Phenyl isocyanate.

The catalyst used was dibutyltin silicate.

The surfactant is selected from any one or more of triton and OP-10.

The microencapsulated flame retardant is prepared through the following steps:

Add the DOPO derivative to the solvent, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add isocyanate and stir at this temperature for 15-25 minutes. Then add flame retardants, catalysts and surfactants for coating, and at the same time Raise the temperature to 85°C and react for 6-10 hours, then cool to room temperature, filter with suction, and put the obtained filter cake into an 80°C oven to dry for 12 hours. The obtained product is a microencapsulated flame retardant.

The preparation method of the halogen-free flame retardant and antioxidant cross-linked polyolefin composite material of the present invention includes the following steps:

Add 25-55 parts of microencapsulated flame retardant to 45-75 parts of polyolefin, mix in an internal mixer or extruder at 120-180°C until uniform, then add 1-2.5 parts of cross-linking agent, and mix After uniformity, it is pressed into a plate in a flat vulcanizer, and cross-linked polyolefin composite materials are prepared through thermal vulcanization cross-linking or radiation cross-linking.

When using thermal vulcanization cross-linking, vulcanize in a flat vulcanizer at 160-200°C for 15 minutes.

When radiation cross-linking is used, radiation cross-linking is carried out under high-energy electron beam or cobalt source irradiation at a radiation dose of 200KGy to produce radiation-cross-linked polyolefin sheets or plates.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

1. The halogen-free flame retardant and antioxidant cross-linked polyolefin composite material provided by the present invention has excellent flame retardant properties. The selected flame retardant uses flame-retardant polyurethane formed by the 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 a benzene ring structure with carbon-forming function and nitrogen, phosphorus, etc. Flame retardant elements can play a core-shell synergistic flame retardant role with the core flame retardant. (2) The phosphorus element in the low valence state (+1 valence) in the shell layer can exert a gas phase flame retardant mechanism. Core flame retardants such as ammonium polyphosphate or metal hydroxide can exert a condensed phase flame retardant mechanism. The layer and core exert a synergistic effect on 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 polyolefin composite materials. (3) The core-shell structure not only improves the water resistance of the core flame retardant, but also greatly improves the dispersion and interface compatibility problems of the flame retardant in polyolefin composite materials, reducing the problem of flame retardant in the polyolefin composite material. The agglomeration during processing and good dispersion further enhance the mechanical properties and flame retardant properties of polyolefin composites.

2. The halogen-free flame retardant and antioxidant cross-linked polyolefin composite material provided by the present invention still has excellent anti-aging properties without adding any antioxidants, which can be proved by the following tests: (1) Passing the free radical scavenging test It is proved that the core-shell structure flame retardant has excellent free radical scavenging ability; (2) The oxidation induction time test can show that the composite material has good antioxidant effect; (3) Cross-linking through high temperature ovens of 180℃ and 150℃ When the polyolefin composite material is subjected to a long-term accelerated thermal aging test, it can be found that the halogen-free flame retardant and antioxidant cross-linked 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 the present invention. The phosphorus element in the low valence state (+1 valence) of the shell can decompose the hydroperoxide generated by free radicals into a high valence state (+3 or +5 valence) phosphorus element, so it can consume more free radicals than traditional phosphites; in addition, the benzene ring in the DOPO structure is connected to the phosphorus element, and the benzene ring structure can quench free radicals and has a higher thermal decomposition temperature , which can stabilize the DOPO structure in the low valence state (+1 valence) so that it can exist stably during long-term high-temperature thermal aging, thereby improving the flame retardant properties of polyolefin composite materials and giving the polyolefin composite materials good Long term antioxidant properties.

Description of the drawings

Figure 1 is the relationship curve of the retention rate of the elongation at break at 180°C (a) and 150°C (b) of the sample of Example 1 as a function of time.

Figure 2 is the relationship curve of the retention rate of the elongation at break at 180°C (a) and 150°C (b) of the sample of Example 2 as a function of time.

Figure 3 is the relationship curve of the retention rate of the elongation at break at 180°C (a) and 150°C (b) of the sample of Example 3 as a function of time.

Figure 4 is the relationship curve of the retention rate of the elongation at break at 180°C (a) and 150°C (b) of the sample of Example 4 as a function of time.

Figure 5 is the relationship curve of the retention rate of the elongation at break at 180°C (a) and 150°C (b) of the sample of Example 5 as a function of time.

Figure 6 shows the test results of DPPH·free radical scavenging by flame retardants in Examples 1-5 of the present invention.

Figure 7 shows the oxidation induction time test results of the samples in Examples 1-5 of the present invention.

Detailed ways

In order to further illustrate the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1:

a. Preparation of DOPO-GY

Take a 500ml three-necked bottle and react with DOPO and glyoxal molar ratio of 1:0.5 as the raw material. First, dissolve 108.08g of DOPO in the acetonitrile solution, then slowly add the glyoxal solution dropwise, and apply a reflux condensation device. Under mechanical stirring conditions, react at 90°C for 6 hours. When the reaction is completed, filter with suction, wash three times with acetonitrile, and dry the product at 55°C for 12 hours.

b. DOPO-GY reacts with toluene diisocyanate (TDI) and coats ammonium polyphosphate (APP)

Take a 500ml three-necked flask, add 10.26g of DOPO-GY and 80ml of DMF, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add 4.74g of TDI and 40ml of DMF, stir for 15-25min, and then add 85g of APP, 200ml DMF, 1g triton and 0.3g dibutyltin silicate, then raise the temperature to 85℃ and react for 6-10h. When the reaction is completed, filter, wash with ethanol, and then dry at 80℃ for 12h. .

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

In order to further verify the performance of microencapsulated flame retardants with DOPO-GY as the shell layer, we designed comparative formulas as shown in Tables 1 and 2 and Figures 1, 6 and 7 to compare the comprehensive physical property testing results of the two. Table 1 shows the addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 2 shows the mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample ) test results; Figure 1 is the relationship curve of the retention rate of the elongation at break with time when the samples were placed in a 180°C heat aging oven for 7 days and a 150°C heat aging oven for about 10 weeks respectively; Figure 6 It is a free radical scavenging test on the model. 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) is a very stable nitrogen-centered free radical. Its stability mainly comes from the three benzene rings. The resonance stabilization effect prevents the unpaired electrons on the nitrogen atoms sandwiched in the middle from playing their due electron pairing role. As a stable free radical, DPPH can capture ("scavenge") other free radicals. Therefore, after adding DPPH, it is observed whether a certain compound has the nature of free radical elimination reaction. Since DPPH has strong absorption centered at 520nm, it appears deep purple in the solution, and after being neutralized, it becomes a stable free radical in organic solvents. Its alcohol solution appears purple and needs to be protected from light at low temperature. Storage, has maximum absorption peak at 517nm. The single electrons of DPPH scavenged by free radicals are captured to make the color lighter, the absorbance value at the maximum light absorption wavelength decreases, and the decrease in absorbance level indicates an increase in antioxidant properties, so that the antioxidant properties of the test sample can be evaluated. Figure 7 shows the oxidation induction time test of the sample. The oxidation induction time (OIT) is the time when the sample begins to undergo an autocatalytic oxidation reaction under high-temperature (200°C) oxygen conditions. It is used to evaluate the performance of polymer materials in molding, processing, storage and An indicator of resistance to thermal oxygen degradation during use. The Oxidation Induction Period (OIT) method is a method that uses differential thermal analysis (DTA) to test the accelerated aging of plastics in high-temperature oxygen based on the exothermic reaction when the plastic molecular chain breaks. The longer the oxidation induction time is, the better the antioxidant effect of the polymer material is.

Table 1 The addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI)

Table 2 Test results of mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample

Example 2:

a. Preparation of DOPO-DH

Take a 500ml three-necked bottle and dissolve 71.33g of DOPO in 300ml of chloroform solution. After DOPO is completely dissolved, add 29.73g of paraformaldehyde, then slowly add 34.69g of diethanolamine solution dropwise, and apply a reflux condensation device. Under mechanical stirring conditions, react at 55°C for 12 hours. When the reaction is completed, the solution is cooled to room temperature, filtered, washed with chloroform, and then dried in a vacuum oven at 100°C for 12 hours.

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

Take a 500ml three-necked flask, add 14.88g of DOPO-DH and 80ml of THF, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add 10.12g of TDI and 40ml of THF, stir for 15-25min, and then add 75g of PAPP, 200ml THF, 1g triton and 0.3g dibutyltin silicate, then raise the temperature to 85°C and react for 6-10h. When the reaction is completed, filter, wash with ethanol, and then dry at 80°C for 12h. .

c. Add 25 parts of microencapsulated flame retardant (DOPO-DH@PAPP) to 75 parts of polyethylene (PE) according to the mass ratio, then mix it in an internal mixer or extruder at 180°C until uniform, and then Add 1 part of trimethylolpropyl trimethacrylate (PETA), mix evenly, and conduct radiation cross-linking under high-energy electron beam irradiation at a radiation dose of 200KGy to make a radiation-cross-linked polyethylene sheet. or plates.

In order to further verify the performance of microencapsulated flame retardants with DOPO-DH as the shell layer, we designed comparative formulas as shown in Tables 3, 4 and Figure 2 to compare the comprehensive physical property testing results of the two. Table 3 shows the addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 4 shows the mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample ) Test results; Figure 2 is the relationship curve of the retention rate of the elongation at break with time when each sample was placed in a 180°C heat aging oven for 7 days and a 150°C heat aging oven for about 10 weeks;

Table 3 Addition of each component in the mixing formula and test results of vertical combustion (UL-94) and limiting oxygen index (LOI)

Table 4 Test results of mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample

Example 3:

a. Preparation of DOPO-GD

Take a 500ml three-necked bottle and dissolve 54g of DOPO in 150ml of toluene solution. After the DOPO is completely dissolved, use a dropping funnel to add 50g of glutaraldehyde aqueous solution dropwise within 20 minutes, and apply a reflux condensation device while mechanically stirring. Under the conditions, react at 85°C for 5 hours. When the reaction is completed, the solution is cooled to room temperature, filtered with suction, washed with toluene, and then dried at 80°C for 12 hours.

b. DOPO-GD reacts with toluene diisocyanate (TDI) and wraps aluminum hydroxide (ATH)

Take a 500ml three-necked bottle, add 14.03g of DOPO-GD and 80ml of 1,4-dioxane, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add 5.97g of TDI and 40ml of 1,4-dioxane. Dioxane, stir for 15-25 minutes, then add 80g of ATH, 200ml of 1,4-dioxane, 1g of triton and 0.3g of dibutyltin silicate, then heat up to 85°C, react 6 -10h, wait until the reaction is completed, filter with suction, wash with ethanol, and then dry at 80°C for 12h.

c. Add 55 parts of microencapsulated flame retardant (DOPO-GD@ATH) to 45 parts of ethylene propylene diene rubber (EPDM) according to the mass ratio, and then mix it in an internal mixer or extruder at 140°C until the Evenly, then add 1.5 parts of triallyl cyanurate (TAIC) and 0.7 parts of dicumyl peroxide (DCP), mix evenly and then vulcanize in a 160°C vulcanizer for 15 minutes to make a plate.

In order to further verify the performance of microencapsulated flame retardants with DOPO-GD as the shell layer, we designed comparative formulas as shown in Tables 5, 6 and Figure 3 to compare the comprehensive physical property testing results of the two. Table 5 shows the addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 6 shows the mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample ) test results; Figure 3 is the relationship curve of the retention rate of the elongation at break with time when each sample was placed in a 180°C heat aging oven for 7 days and a 150°C heat aging oven for about 10 weeks;

Table 5 The addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI)

Table 6 Test results of mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample

Example 4:

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

Take a 500ml three-necked flask, add 10.37g of DOPO-GY and 80ml of THF, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add 4.63g of HDI and 40ml of THF, stir for 15-25min, and then add 85g of PAPP, 200ml THF, 1g triton and 0.3g dibutyltin silicate, then raise the temperature to 85°C and react for 6-10h. When the reaction is completed, filter, wash with ethanol, and then dry at 80°C for 12h. .

b. Add 25 parts of microencapsulated flame retardant (DOPO-GY@PAPP) to 75 parts of ethylene vinyl acetate (EVA) according to the mass ratio, and then mix it in an internal mixer or extruder at 150°C until uniform , then add 1.4 parts of triallyl cyanurate (TAIC), mix evenly, and perform radiation cross-linking under cobalt source irradiation at a radiation dose of 200KGy to make a radiation cross-linked EVA sheet or plate. .

In order to further verify the performance of the microencapsulated flame retardant with DOPO-GY as the shell layer, we replaced TDI with HDI and changed the type of flame retardant, and then designed the comparison shown in Tables 7, 8 and Figure 4 formula, and compare the comprehensive physical property testing results of the two. Table 7 shows the addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 8 shows the mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample ) Test results; Figure 4 is the relationship curve of the retention rate of the elongation at break with time when each sample was placed in a 180°C heat aging oven for 7 days and a 150°C heat aging oven for about 10 weeks;

Table 7 Addition of each component in the mixing formula and test results of vertical combustion (UL-94) and limiting oxygen index (LOI)

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

Example 5:

a. DOPO-DH reacts with diphenylmethane diisocyanate (MDI) and wraps APP

Take a 500ml three-necked flask, add 12.65g of DOPO-DH and 80ml of DMF, stir and raise the temperature to 40°C. After the reactants are completely dissolved, add 12.35g of MDI and 40ml of DMF, stir for 15-25min, and then add 75g of PAPP, 200ml DMF, 1g triton and 0.3g dibutyltin silicate, then raise the temperature to 85°C and react for 6-10h. When the reaction is completed, filter, wash with ethanol, and then dry at 80°C for 12h. .

c. Add 25 parts of microencapsulated flame retardant (DOPO-DH@APP) to 75 parts of polyethylene (PE) according to the mass ratio, and then mix it in an internal mixer or extruder at 140°C until uniform, and then Add 0.8 parts of trimethylolpropyl trimethacrylate (PETA) and 0.4 parts of dicumyl peroxide (DCP), and then use a flat vulcanizer to vulcanize at 170°C for 15 minutes to prepare a cross-linked polyethylene sheet or plate. .

In order to further verify the performance of microencapsulated flame retardants with DOPO-DH as the shell layer, we replaced TDI with MDI and changed the type of flame retardant, and then designed comparisons as shown in Tables 9, 10 and Figure 5 formula, and compare the comprehensive physical property testing results of the two. Table 9 shows the addition amount of each component in the mixing formula and the test results of vertical combustion (UL-94) and limiting oxygen index (LOI); Table 10 shows the mechanical properties, combustion performance (Cone) and smoke density (Ds) of the sample ) test results; Figure 5 is the relationship curve of the retention rate of elongation at break with time when each sample was placed in a 180°C heat aging oven for 7 days and a 150°C heat aging oven for about 10 weeks.

Table 9 Addition of each component in the mixing formula and test results of vertical combustion (UL-94) and limiting oxygen index (LOI)

Table 10 Test results of mechanical properties, combustion performance (Cone) and smoke density (Ds) of each sample

Based on the above experimental results, the following conclusions are drawn:

(1) When microencapsulated flame retardants with DOPO derivatives as the shell layer are added to polyolefin composite materials, their mechanical properties and flame retardant properties are better than those of the control group with unwrapped flame retardants.

(2) Through the free radical scavenging test and the oxidation induction time test, it is proved that the structural flame retardant has a certain free radical capturing function and can exert a long-term antioxidant effect during the service life of the polymer material. After adding a microencapsulated flame retardant with a DOPO derivative as a shell layer, the polyolefin composite material underwent a heat aging test at 150°C for 10 weeks. The degree of mechanical property degradation was significantly better than that of the control group. Therefore, the halogen-free flame retardant and antioxidant cross-linked polyolefin composite material and its preparation method provided by the present invention not only endow the polyolefin material with good flame retardant properties, but also improve the long-term heat aging resistance of the polyolefin composite material.

The above are only the preferred embodiments of the present invention. It should be pointed out that those of ordinary skill in the art can also make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications can also be made. should be regarded as the protection scope of the present invention.

Claims (9)

1. The halogen-free flame-retardant antioxidant cross-linked polyolefin composite material comprises the following raw materials in parts by weight:

45-75 parts of polyolefin, 25-55 parts of microencapsulated flame retardant and 1-2.5 parts of cross-linking agent;

the microencapsulated flame retardant consists of a core layer and a shell layer structure, wherein the core layer structure is the flame retardant, and the shell layer structure is flame retardant polyurethane formed by polymerizing DOPO derivatives and isocyanate; the mass ratio of the core layer to the shell layer structure is 75-85:15-25.

2. The halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 1, wherein:

the polyolefin is selected from one or more of ethylene-vinyl acetate copolymer, polyethylene, ethylene propylene diene monomer, maleic anhydride grafted ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, maleic anhydride grafted ethylene propylene diene monomer, ethylene-octene copolymer, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer and maleic anhydride grafted hydrogenated styrene-butadiene-styrene block copolymer.

3. The halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 1, wherein:

the cross-linking agent is selected from one or more of dicumyl peroxide, triallyl cyanurate, triallyl isocyanurate, trimethylol propyl methacrylate, trimethylol triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate, and the cross-linking agent is mixed according to any proportion.

4. The halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 1, wherein:

the microencapsulated flame retardant comprises the following raw materials in 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 part of catalyst and 0.5-1.5 parts of surfactant.

5. The halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 4, wherein:

the DOPO derivative is selected from DOPO compounds containing hydroxyl structures.

6. The halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 5, wherein:

the DOPO derivative is selected from compounds with the following structures:

7. the halogen-free flame retardant antioxidant crosslinked polyolefin composite of claim 4, wherein:

the flame retardant is one or more selected from ammonium polyphosphate, piperazine pyrophosphate, magnesium hydroxide, aluminum hydroxide, hydrotalcite, melamine phosphate, melamine polyphosphate, melamine cyanurate, pentaerythritol, aluminum hypophosphite, aluminum phosphinate, expandable graphite, zinc borate, graphene, transition metal disulfide, carbon nano tube, halloysite, sepiolite and kaolin which are mixed according to any proportion.

8. The halogen-free flame retardant antioxidant crosslinked polyolefin composite material according to claim 4, characterized in that the microencapsulated flame retardant is prepared by the following method:

adding DOPO derivative into solvent, stirring and heating to 40 ℃, adding isocyanate after the reactant is completely dissolved, stirring for 15-25min at the temperature, then adding flame retardant, catalyst and surfactant for wrapping, heating to 85 ℃ for reaction for 6-10h, cooling to room temperature, suction filtering, and drying the obtained filter cake in an oven at 80 ℃ for 12h to obtain the microencapsulated flame retardant.

9. A method for preparing the halogen-free flame retardant antioxidant crosslinked polyolefin composite material according to claim 1, which is characterized by comprising the following steps:

adding 25-55 parts of microencapsulated flame retardant into 45-75 parts of polyolefin, mixing in an internal mixer or an extruder at 120-180 ℃ until the mixture is uniform, adding 1-2.5 parts of cross-linking agent, pressing the mixture into a plate in a flat vulcanizing machine after the uniform mixing, and preparing the cross-linked polyolefin composite material through thermal vulcanization cross-linking or irradiation cross-linking.