Flame-retardant environment-friendly polypropylene plastic and preparation method thereof

Abstract

The application belongs to the technical field of polypropylene, and particularly relates to a flame-retardant environment-friendly polypropylene plastic and a preparation method thereof. The flame-retardant environment-friendly polypropylene plastic is prepared from the following raw materials: polypropylene resin, core-shell structure flame retardant, nano reinforcing body master batch and auxiliary agent. The core-shell structure flame retardant is a composite core of polyphosphoric acid ammonium and aluminum hypophosphite, and a silicon-boron co-modified hyperbranched polymer shell layer is coated on the surface of the composite core through an in-situ polymerization method. The nano reinforcing body master batch is a master batch prepared by melt blending of grafted magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene and a polypropylene carrier. The application realizes wide temperature range synergistic catalytic carbonization through the composite core, the shell layer generates a ceramic phase reinforced carbon layer in-situ, and relies on a multiple chemical bond bridging network, so that the industry problem of mechanical property degradation under high filling is solved, and high efficiency and high toughness are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polypropylene, and particularly relates to a flame-retardant environment-friendly polypropylene plastic and a preparation method thereof. BACKGROUND

[0002] Polypropylene (PP) is widely used in the fields of automobiles, household appliances, electronics, building and daily necessities due to its low cost, excellent processing performance, balanced mechanical properties, chemical corrosion resistance and other advantages. However, PP is a highly flammable polymer material, with a limiting oxygen index (LOI) of only 17-18%, which ignites in air and produces a large amount of molten dripping during combustion, which easily causes secondary fires, greatly limiting its application in high-end fields.

[0003] In order to improve the safety of PP, it is usually necessary to modify it with flame retardants. Traditional flame-retardant technologies often use halogen-based flame retardants such as brominated epoxy resin and decabromodiphenyl ethane, which have high flame-retardant efficiency, but release toxic and corrosive hydrogen halide gas and carcinogenic dioxin and furan substances during combustion, posing a serious threat to the environment and human health. With the increasing strictness of global environmental protection, the development of efficient and environmentally friendly halogen-free flame-retardant technology has become an inevitable trend in the industry.

[0004] At present, intumescent flame retardant (IFR) system is one of the mainstream technologies for halogen-free flame-retardant PP. A typical IFR system is composed of an acid source, a carbon source and a gas source. Its mechanism of action is that at high temperatures, the acid source decomposes to produce phosphoric acid, which catalyzes the dehydration and carbonization of the carbon source to form a dense carbon layer, while the gas source decomposes to produce non-combustible gas, which plays a role in diluting oxygen and cooling.

[0005] However, the existing flame-retardant PP technology based on IFR system still has the following technical defects: the components in the IFR system are mostly inorganic or small molecular organic substances with strong polarity, and have poor compatibility with the non-polar PP matrix. In order to achieve flame-retardant effect, the addition amount of IFR is usually as high as 25-30wt%, which leads to a significant decrease in the mechanical properties of the composite material, especially the impact strength and elongation at break, and the material becomes brittle, limiting its application. Components such as ammonium polyphosphate (APP) are easily hygroscopic, which leads to their hydrolysis during processing, affecting the flame-retardant performance and long-term stability of the material. At the same time, small molecular components are easily migrated to the surface of the material ("blooming"), affecting the appearance and durability of the product. The carbon layer formed by the traditional IFR system is relatively loose, which is easily broken and detached during the combustion process due to the impact of air flow or the mechanical action of the melt, leading to the exposure of fresh PP matrix for continuous combustion, and the flame-retardant effect is difficult to be persistent.

[0006] Further, the decomposition temperature range of single acid source (such as ammonium polyphosphate) in IFR is narrow, resulting in that the carbonization process is not continuous and stable enough, and the carbon layer is easy to be oxidized and burned through at high temperature. The mechanical strength and oxidation resistance of the traditional organic polymer carbon layer are insufficient at high temperature of more than 700 DEG C, and it is difficult to form a persistent and effective protection. Although the nano filler can enhance the carbon layer, the agglomeration problem of the nano filler in the polypropylene matrix and the weak interfacial force with the flame retardant system limit the full play of its potential.

[0007] Therefore, there is an urgent need in the art for a new technical solution capable of realizing efficient carbonization in the whole temperature range, constructing an ultra-stable ceramic carbon layer, and ensuring strong interface coupling of all components at the nanoscale, to break through the performance bottleneck of the existing environmentally friendly flame-retardant PP materials. SUMMARY

[0008] In view of the deficiencies of the prior art, the purpose of the present application is to provide an environmentally friendly flame-retardant polypropylene plastic with good flame-retardant performance and mechanical properties.

[0009] The present application also provides a preparation method, which is simple and easy to implement, and suitable for large-scale production.

[0010] The environmentally friendly flame-retardant polypropylene plastic according to the present application is prepared from the following raw materials in parts by mass:

[0011] Polypropylene resin: 60-82 parts;

[0012] Core-shell structure flame retardant: 15-35 parts;

[0013] Nano reinforcing agent masterbatch: 3-8 parts;

[0014] Auxiliary agent: 0.5-1 part;

[0015] The core-shell structure flame retardant is ammonium polyphosphate and aluminum hypophosphite as a composite core, and a silicon-boron co-modified hyperbranched polymer shell layer is coated on the surface of the composite core by in-situ polymerization;

[0016] The shell layer is copolymerized from phosphorus-containing monomers, nitrogen-containing monomers, silicon-containing monomers and boron-containing compounds, and has five functions of compatibilization, carbon source, gas source, carbonization crosslinking and in-situ ceramization.

[0017] The nano reinforcing agent masterbatch is a masterbatch prepared by melt blending of a graft-modified magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene (PP-g-MAH) and a polypropylene carrier.

[0018] The mass ratio of the ammonium polyphosphate and aluminum hypophosphite is 9:1 to 6:4.

[0019] The preparation method of the core-shell structure flame retardant is:

[0020] The ammonium polyphosphate and aluminum hypophosphite are blended to form a composite core, the composite core is dispersed in a solvent, and the temperature is raised to 80-100℃. The monomers, namely, pentaerythritol phosphate, melamine, vinyltriethoxysilane, and trimethyl borate, are added dropwise in sequence, a catalyst is added, the temperature is raised to 130-160℃, and the reaction is carried out for 5-8 hours. After the reaction is completed, the product is washed with ethanol and dried at 80℃ in a vacuum for 12 hours to obtain the core-shell structure flame retardant.

[0021] The ratio of the total mass of the pentaerythritol phosphate, melamine, vinyltriethoxysilane, and trimethyl borate to the total mass of the composite core is 1:2-3.

[0022] The mass ratio of the pentaerythritol phosphate, melamine, vinyltriethoxysilane, and trimethyl borate is (40-55):(20-30):(3-12):(2-5).

[0023] The catalyst is a mixture of p-toluenesulfonic acid and dibutyltin dilaurate, and the amount used is 0.1-0.5% of the total mass of the monomers.

[0024] The graft-modified magnesium-aluminum layered double hydroxide is an amino silane graft-modified magnesium-aluminum hydrotalcite.

[0025] The preparation method of the amino silane graft-modified magnesium-aluminum hydrotalcite is as follows:

[0026] Pretreatment and activation of the magnesium-aluminum hydrotalcite (LDH):

[0027] The magnesium-aluminum hydrotalcite powder is dried in a vacuum drying oven at 80℃ for 12 hours to completely remove the physically adsorbed water. 10.0g of the dried LDH is dispersed in 200mL of anhydrous ethanol, and ultrasonic treatment is carried out for 30 minutes to obtain a suspension A.

[0028] Preparation of the silane hydrolysis solution:

[0029] 100mL of anhydrous ethanol and 10mL of deionized water are mixed, and the pH of the ethanol-water mixture is adjusted to 4.0-5.0 with glacial acetic acid. Under stirring, 3.0g of γ-aminopropyl triethoxysilane (30% of the mass of the LDH) is slowly added. The stirring is continued for at least 2 hours to allow the γ-aminopropyl triethoxysilane to be completely hydrolyzed to form a more reactive silanol (Si-OH), and a silane hydrolysis solution is obtained.

[0030] Surface grafting reaction:

[0031] The silane hydrolysis solution is added dropwise to the suspension A through a constant pressure dropping funnel, and the temperature is raised to 78℃ under nitrogen protection for a mechanical stirring reflux reaction for 12-24 hours.

[0032] Post-treatment and purification:

[0033] After the reaction is completed, it is cooled to room temperature. The product is centrifuged to separate the supernatant. The precipitate is repeatedly washed by centrifugation with anhydrous ethanol at least 4 times until the last washing liquid is tested by AgNO3 solution without white precipitate (Cl-). The washed product is placed in a vacuum drying oven at 80℃ for 24 hours, and ground to obtain the amino silane grafted modified magnesium-aluminum hydrotalcite.

[0034] The preparation method of the nanoreinforcement masterbatch is that the grafted modified magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene and polypropylene carrier are premixed in a high-speed mixer, preferably in a ratio of LDH:PP-g-MAH:PP=20:40:40. Then it is added into a co-rotating twin-screw extruder for high-shear melt blending at 180-200℃ and high screw speed of 400-600rpm, and extruded and granulated to obtain the nanoreinforcement masterbatch.

[0035] The grafted modified magnesium-aluminum layered double hydroxide accounts for 10-30wt% in the nanoreinforcement masterbatch.

[0036] The auxiliary agent is one or both of an antioxidant and a lubricant.

[0037] The preparation method of the flame-retardant environment-friendly polypropylene plastic according to the present application is prepared by the following steps:

[0038] The polypropylene resin, core-shell structure flame retardant, nanoreinforcement masterbatch and auxiliary agent are uniformly mixed, and then added into a twin-screw extruder for melt extrusion and granulation. The temperature of each zone of the extruder is set to 170-210℃, and the screw speed is 200-400rpm. The obtained particles are dried and injection molded.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] 1) The present application uses ammonium polyphosphate and aluminum hypophosphite as the composite core of the core-shell structure flame retardant, which provides a wide temperature range of 300℃ to 450℃ or above for continuous acid source. At low temperature, ammonium polyphosphate decomposes to initiate initial carbonization, and at high temperature, more stable aluminum hypophosphite decomposes to not only continuously catalyze carbonization, but also PH3, which has the effect of gas phase quenching free radicals. This "relay" catalytic mechanism ensures the smooth and continuous carbonization process, avoiding the "window period" defect of the carbon layer caused by a single acid source.

[0041] 2) The shell layer of the core-shell structure flame retardant according to the present application forms a basic carbon structure when burning, and at the same time, silicon and boron elements are in-situ converted into Si-O-C, SiO2 ceramic phase and B2O3 glass phase. These inorganic phases are dispersedly distributed or form a continuous network at the nanoscale, which greatly improves the mechanical strength, structural integrity at high temperature and anti-ablation oxidation ability of the carbon layer, and essentially improves the quality of the carbon layer.

[0042] 3) The active group -NH2 of the amino silane grafted modified Mg-Al-LDH can react with the anhydride group of maleic anhydride grafted polypropylene (PP-g-MAH) and the group on the shell of the core-shell flame retardant, forming a multiple chemical bond bridge of "PP matrix→PP-g-MAH→amino silane grafted modified Mg-Al-LDH→core-shell flame retardant shell". Combined with the master batch technology to ensure uniform dispersion, the stress can be efficiently transmitted, and the reinforcing and toughening effect of the nano reinforcing master batch is maximized, so as to maintain excellent mechanical properties under extremely high filling. DETAILED DESCRIPTION

[0043] The application will be further described below in combination with examples.

[0044] All raw materials used in the examples are commercially available, except for special instructions.

[0045] Ammonium polyphosphate: degree of polymerization n = 2000, industrial grade, Jinan Mingde Chemical Co., Ltd.;

[0046] PP-g-MAH: QB510 brand, Mitsui Chemicals, Japan;

[0047] PP resin: T30S brand, China Petroleum Chemical Co., Ltd.

[0048] Mg-Al-LDH: Mg4Al2(OH) 12 CO3]·3H2O, Shanghai Maikelin Biochemical Technology Co., Ltd.;

[0049] γ-aminopropyl triethoxysilane, KH-550, Hangzhou Jessica Chemical Co., Ltd.

[0050] Preparation of amino silane grafted modified Mg-Al-LDH:

[0051] Pretreatment and activation of Mg-Al-LDH:

[0052] The Mg-Al-LDH powder was dried in a vacuum drying oven at 80°C for 12 hours to completely remove the physically adsorbed water. 10.0 g of dried LDH was weighed and dispersed in 200 mL of anhydrous ethanol, and ultrasonic treatment was performed for 30 minutes to obtain a suspension A.

[0053] Preparation of silane hydrolysis solution:

[0054] Mix 100 mL of absolute ethanol with 10 mL of deionized water, and adjust the pH of the above ethanol-water mixture to 4.5 with glacial acetic acid. Under stirring at 400 rpm, add 3.0 g of γ-aminopropyltriethoxysilane. Continue stirring for 2 hours to allow the γ-aminopropyltriethoxysilane to hydrolyze completely to form more reactive silanol (Si-OH), and obtain a silane hydrolysis solution.

[0055] Surface grafting reaction:

[0056] Add the silane hydrolysis solution to the suspension A through a constant pressure dropping funnel, and under nitrogen protection, heat to 78°C and continue mechanical stirring to reflux for 20 hours.

[0057] Post-treatment and purification:

[0058] After the reaction is completed, cool to room temperature. Centrifuge the product, and discard the supernatant. Wash the precipitate repeatedly with absolute ethanol for 4 times, and test the last washing liquid with AgNO3 solution to check if there is white precipitate (Cl-). Dry the washed product in a vacuum drying oven at 80°C for 24 hours, grind, and pass through a 200 mesh sieve to obtain the amino-silane grafted modified Mg-Al hydrotalcite.

[0059] Example 1

[0060] The preparation method of the environmentally friendly flame-retardant polypropylene plastic comprises the following steps:

[0061] (1) Preparation of a core-shell structure flame retardant

[0062] Weigh 140 g of ammonium polyphosphate (APP) and 60 g of aluminum hypophosphite (AHP), and place them in a planetary ball mill. Under argon protection, mechanically blend at a speed of 300 rpm for 3 hours to obtain a total weight of 200 g of APP / AHP (mass ratio 7:3) composite core powder. In a 1000 mL three-necked flask equipped with mechanical stirring, reflux condenser and nitrogen protection, add 500 mL of xylene, start mechanical stirring, add the above-mentioned 200 g of composite core powder, and heat to 90°C to disperse uniformly. Add the monomers in turn: pentaerythritol phosphate 40 g, melamine 25 g, vinyltriethoxysilane 10 g and trimethyl borate 5 g (total mass of monomers 80 g, mass ratio to core 1:2.5). After the addition is completed, add the catalyst mixture (p-toluenesulfonic acid 0.2 g, dibutyltin dilaurate 0.2 g, total amount is 0.5% of the total mass of monomers). Under nitrogen protection, slowly heat the reaction system to 145°C, and reflux at this temperature for 6 hours. After the reaction is completed, stop heating and naturally cool to room temperature. Filter the product, wash the obtained filter cake with 300 mL of absolute ethanol for three times, and then place it in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of core-shell structure flame retardant FR-1.

[0063] (2) Preparation of nano-reinforcement masterbatch

[0064] 20 g of amino-silane grafted modified Mg-Al hydrotalcite powder, 40 g of PP-g-MAH and 40 g of PP resin were pre-mixed in a high-speed mixer for 5 minutes. Then the mixture was fed into a co-rotating twin-screw extruder (L / D = 40) with the temperature set at 190 °C and the screw rotation speed at 500 rpm for high shear melt blending, extrusion and pelletization to obtain a nano-reinforcement masterbatch MB-1 with A-LDH content of 20 wt%.

[0065] (3) Preparation of environmentally friendly flame-retardant polypropylene plastic

[0066] 71.5 parts (mass parts, the same below) of PP resin, 23 parts of FR-1, 5 parts of MB-1, 0.5 part of antioxidant 1010 and 0.5 part of calcium stearate were uniformly mixed in a high-speed mixer. The mixture was fed into a twin-screw extruder with the temperature set at 170 °C-180 °C-190 °C-200 °C-190 °C and the screw rotation speed at 300 rpm for melt extrusion and pelletization. The obtained particles were dried at 80 °C for 4 hours and then injected into standard samples using an injection molding machine for performance testing.

[0067] Example 2

[0068] The preparation method of the environmentally friendly flame-retardant polypropylene plastic comprises the following steps:

[0069] (1) Preparation of core-shell structure flame retardant

[0070] Ammonium polyphosphate (APP) 180 g and aluminum hypophosphite (AHP) 20 g were weighed and placed in a planetary ball mill for mechanical blending at a rotation speed of 300 rpm for 3 hours under argon protection to obtain a total weight of 200 g of APP / AHP (mass ratio 9:1) composite core powder; a 1000 mL three-necked flask equipped with a mechanical stirrer, a reflux condenser and nitrogen protection was charged with 500 mL of xylene, the mechanical stirring was started, and the above-mentioned 200 g of composite core powder was added and uniformly dispersed by heating to 90 °C; monomers were added in sequence: pentaerythritol phosphate 45 g, melamine 20 g, vinyl triethoxy silane 3 g and trimethyl borate 2 g (total mass of monomers 70 g, mass ratio to core 1:2.8); after the addition was completed, a catalyst mixture (p-toluenesulfonic acid 0.035 g, dibutyltin dilaurate 0.035 g, total amount 0.1% of the total mass of monomers) was added. The reaction system was slowly heated to 130 °C under nitrogen protection, and refluxed at this temperature for 8 hours; after the reaction was completed, the heating was stopped and the system was naturally cooled to room temperature. The product was filtered, the obtained filter cake was washed with 300 mL of anhydrous ethanol for three times, and then placed in a vacuum drying oven at 80 °C for drying for 12 hours to obtain a core-shell structure flame retardant white powder FR-2.

[0071] (2) Preparation of nano-reinforced masterbatch

[0072] 10 g of amino-silane grafted modified Mg-Al hydrotalcite powder, 30 g of PP-g-MAH and 60 g of PP resin were pre-mixed in a high speed mixer for 5 minutes. Then the mixture was fed into a co-rotating twin screw extruder (L / D = 40) with the temperature set at 190 °C and screw rotation speed at 500 rpm for high shear melt blending and extrusion granulation. A nano-reinforced masterbatch MB-2 with 10 wt% of A-LDH content was obtained.

[0073] (3) Preparation of flame-retardant and environmentally friendly polypropylene plastic

[0074] 81.5 parts of PP resin, 15 parts of FR-2, 3 parts of MB-2 and 0.5 part of antioxidant 1010 were mixed uniformly in a high speed mixer. The mixture was fed into a twin screw extruder with the temperature set at 170 °C-180 °C-190 °C-200 °C-190 °C and screw rotation speed at 200 rpm for melt extrusion granulation. The obtained granules were dried at 80 °C for 4 hours and then injected into standard samples using an injection molding machine for performance testing.

[0075] Example 3

[0076] The method for preparing the flame-retardant and environmentally friendly polypropylene plastic comprises the following steps:

[0077] (1) Preparation of core-shell structure flame retardant

[0078] Take 120 g of ammonium polyphosphate (APP) and 80 g of aluminum hypophosphite (AHP), put them in a planetary ball mill, mechanically blend under argon protection at a speed of 300 rpm for 3 hours, to obtain a total weight of 200 g of APP / AHP (mass ratio 6:4) composite core powder; add 500 mL of xylene to a 1000 mL three-necked flask equipped with mechanical stirring, reflux condenser and nitrogen protection, start the mechanical stirring, add the above 200 g of composite core powder, and heat to 90°C to make it uniformly dispersed; add the monomers: pentaerythritol phosphate 55 g, melamine 30 g, vinyl triethoxy silane 12 g and trimethyl borate 3 g (total mass of monomers 100 g, mass ratio to core 1:2) in sequence; after the addition is completed, add the catalyst mixture (p-toluenesulfonic acid 0.25 g, dibutyltin dilaurate 0.25 g, total amount 0.5% of the total mass of monomers). Slowly heat the reaction system to 160°C under nitrogen protection, and reflux at this temperature for 5 hours; after the reaction is completed, stop heating and naturally cool to room temperature. Filter the product, wash the filter cake with 300 mL of anhydrous ethanol three times, and then place it in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of the core-shell structure flame retardant FR-3.

[0079] (2) Preparation of nano-reinforcement masterbatch

[0080] Pre-mix 30 g of amino silane grafted modified Mg-Al hydrotalcite powder, 50 g of PP-g-MAH and 20 g of PP resin in a high-speed mixer for 5 minutes. Then add the mixture to a co-rotating twin-screw extruder (L / D = 40), set the extrusion temperature to 190°C and the screw speed to 500 rpm, perform high-shear melt blending, and extrude and granulate to obtain a nano-reinforcement masterbatch MB-3 with an A-LDH content of 20 wt%.

[0081] (3) Preparation of environmentally friendly flame-retardant polypropylene plastic

[0082] Mix 60.5 parts (mass parts, the same below) of PP resin, 35 parts of FR-3, 3.5 parts of MB-1, 0.5 parts of antioxidant 1010 and 0.5 parts of calcium stearate in a high-speed mixer. Add the mixture to a twin-screw extruder, set the temperature of each zone to 170°C-180°C-190°C-200°C-190°C, and the screw speed to 400 rpm, melt extrude and granulate. After drying the particles at 80°C for 4 hours, use an injection molding machine to inject them into standard bars for performance testing.

[0083] Comparative Example 1

[0084] The core of step (1) is 200 g of pure ammonium polyphosphate, and the remaining steps are the same as in Example 1.

[0085] Comparative Example 2

[0086] The core of step (1) is the same as Example 1, but the shell coating monomers are only pentaerythritol phosphate 50 g and melamine 30 g (total mass 80 g), without the addition of silicon-containing and boron-containing monomers, and the remaining steps are the same as Example 1.

[0087] Comparative Example 3

[0088] The nanoreinforced masterbatch is replaced with an equal mass of PP-g-MAH, and the remaining steps are the same as Example 1.

[0089] Comparative Example 4

[0090] A masterbatch is prepared by blending 20 g of original Mg-Al-LDH powder without amino silane modification with 40 g of PP-g-MAH and 40 g of PP resin. The remaining steps are the same as Example 1.

[0091] Comparative Example 5

[0092] This comparative example verifies the necessity of the masterbatch technology. The components in MB-1 are split and directly added to the final blending step in proportion, and the remaining steps are the same as Example 1.

[0093] The products prepared in the examples and comparative examples are subjected to performance testing, and the test results are shown in Table 1 below:

[0094] Table 1 Test Results Table

[0095]

[0096]

[0097] With the increase of the total amount of the flame retardant system, the fire safety performance (high LOI, low pHRR / THR, high char yield) is significantly and systematically improved. Example 3 achieves an LOI of nearly 40% and a pHRR of less than 100 kW / m 2 , which is at the top level in PP materials, fully demonstrating the high efficiency of the technical solution of the present application.

[0098] The mechanical properties are inversely proportional to the filling amount. However, it is worth emphasizing that the present application achieves an excellent balance between fire safety and mechanical properties. Example 1, while significantly reducing the pHRR compared to traditional IFR systems, still maintains an impact strength of 11.5 kJ / m 2 , which is much higher than ordinary flame-retardant PP.

[0099] Comparative Example 1 uses pure APP core, which is inferior to Example 1 in key fireproof indicators such as LOI, char yield and pHRR. This directly proves that the APP / AHP composite core builds a more effective flame barrier through "relay" catalysis and gas-phase synergy, verifying the creativity of the composite core design. Comparative Example 2 uses pure HPPN shell without Si-B modification, which is far inferior to Example 1 in pHRR (175 kW / m 2 ) and char yield (27.8%). This clearly shows that the in-situ ceramic network formed by the introduction of Si-B elements is the core of building an ultra-stable carbon layer, greatly enhancing the structural integrity of the carbon layer under real flame impact. Comparative Example 3 is the most significant performance decline. Its UL-94 drops to V-1 level with dripping, pHRR increases sharply, and mechanical properties also decrease significantly. This proves that the nano-reinforced masterbatch is indispensable to the system. It not only enhances the mechanical strength of the carbon layer as a skeleton, but also synergizes with the flame retardant, and significantly improves the mechanical properties of the composite itself as a reinforcing filler. Compared with Example 1, the mechanical properties of Comparative Example 4, especially the impact strength, decrease significantly, and the flame retardant performance also weakens. This is because the LDH without amino silane modification lacks effective chemical bonding between the PP matrix and PP-g-MAH, the interfacial bonding force is weak, leading to poor stress transfer, and the nanoparticles are easy to become defect points. This highlights the importance of LDH surface functionalization for achieving strong interfacial coupling. Comparative Example 5 has a certain degree of decline in mechanical properties and flame retardant properties. This proves the necessity of masterbatch technology. Due to its large specific surface area and surface energy, nanoparticles are prone to agglomeration during melt blending. By preparing masterbatch in advance, using high shear force to fully exfoliate and disperse the nanoparticles in a small amount of carrier, and then diluting them into a large system, agglomeration can be effectively avoided, ensuring uniform distribution at the nanoscale, thereby maximizing its reinforcing and carbon skeleton effect.

Claims

1. An environmentally friendly flame retardant polypropylene plastic, characterized in that, It is prepared from the following raw materials in mass fraction: Polypropylene resin: 60-82 parts; Core-shell structure flame retardant: 15-35 parts; Nano-reinforced masterbatch: 3-8 parts; Auxiliary agent: 0.5-1 part; The core-shell structure flame retardant is a composite core of ammonium polyphosphate and aluminum hypophosphite, and a shell layer of silicon-boron co-modified hyperbranched polymer is coated on the surface of the composite core by in-situ polymerization; The nano-reinforced masterbatch is a masterbatch prepared by melt blending of grafted modified magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene and polypropylene carrier; The grafted modified magnesium-aluminum layered double hydroxide is amino silane grafted modified magnesium-aluminum hydrotalcite.

2. The flame retardant eco-friendly polypropylene plastic according to claim 1, characterized in that, The mass ratio of the ammonium polyphosphate and aluminum hypophosphite is 9:1~6:

4.

3. The flame retardant eco-friendly polypropylene plastic according to claim 1, characterized in that, The preparation method of the core-shell structure flame retardant is: The ammonium polyphosphate and aluminum hypophosphite are blended to form a composite core, the composite core is dispersed in a solvent, the temperature is raised, and the monomers: pentaerythritol phosphate, melamine, vinyl triethoxysilane and trimethyl borate are sequentially added dropwise, a catalyst is added, the temperature is raised for reaction, and after the reaction is completed, washing and drying are performed to obtain the core-shell structure flame retardant.

4. The flame retardant eco-friendly polypropylene plastic according to claim 3, characterized in that, The total mass of the pentaerythritol phosphate, melamine, vinyl triethoxysilane and trimethyl borate to the total mass of the composite core is 1:2~3.

5. The flame retardant eco-friendly polypropylene plastic according to claim 3, wherein the flame retardant eco-friendly polypropylene plastic is a flame retardant eco-friendly polypropylene plastic for a refrigerator. The catalyst is a mixture of p-toluenesulfonic acid and dibutyltin dilaurate.

6. The flame retardant eco-friendly polypropylene plastic according to claim 1, wherein the flame retardant eco-friendly polypropylene plastic is a flame retardant eco-friendly polypropylene plastic for a refrigerator. The preparation method of the nano-reinforced masterbatch is: the grafted modified magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene and polypropylene carrier are premixed in a high-speed mixer, then added into a co-rotating twin-screw extruder, melt blended, extruded and granulated to obtain the nano-reinforced masterbatch.

7. The flame retardant eco-friendly polypropylene plastic according to claim 1, wherein the flame retardant eco-friendly polypropylene plastic is a flame retardant eco-friendly polypropylene plastic for a refrigerator. The grafted modified magnesium-aluminum layered double hydroxide accounts for 10-30wt% in the nano-reinforced masterbatch.

8. The flame retardant eco-friendly polypropylene plastic according to claim 1, wherein the flame retardant eco-friendly polypropylene plastic is a flame retardant eco-friendly polypropylene plastic for a refrigerator. The auxiliary agent is one or both of an antioxidant and a lubricant.

9. A method for preparing the flame-retardant environmentally friendly polypropylene plastic according to any one of claims 1-8, characterized in that, It is prepared by the following steps: The polypropylene resin, core-shell structure flame retardant, nano-reinforced masterbatch and auxiliary agent are uniformly mixed, then added into a twin-screw extruder for melt extrusion and granulation, and the obtained particles are dried and injection molded.

Images