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

Abstract

The invention belongs to the technical field of polypropylene, and particularly relates to flame-retardant environment-friendly polypropylene plastic and a preparation method thereof. The flame-retardant polypropylene composite material is prepared from the following raw materials: polypropylene resin, a core-shell structure flame retardant, nano reinforcement master batch and an auxiliary agent, according to the core-shell structure flame retardant, ammonium polyphosphate and aluminum hypophosphite serve as a composite core, and the surface of the composite core is coated with a silicon-boron co-modified hyperbranched polymer shell layer through an in-situ polymerization method; the nano reinforcement master batch is a master batch prepared by melt blending of a graft modified magnesium-aluminum layered double hydroxide, maleic anhydride grafted polypropylene and a polypropylene carrier. Wide-temperature-range concerted catalytic charring is achieved through the composite core, a ceramic phase reinforced carbon layer is generated on a shell layer in situ, efficient flame retardance is achieved through a multiple chemical bond bridging network, meanwhile, the industrial problem that the mechanical property is degraded under high filling is remarkably solved, and high efficiency and high toughness are achieved.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene technology, specifically relating to flame-retardant and environmentally friendly polypropylene plastics and their preparation methods. Background Technology

[0002] Polypropylene (PP) is widely used in automobiles, home appliances, electronics, construction, and daily necessities due to its low cost, excellent processing performance, balanced mechanical properties, and resistance to chemical corrosion. However, PP is an extremely flammable polymer material with a limiting oxygen index (LOI) of only 17-18%. It ignites upon contact with air and produces a large amount of molten droplets during combustion, which can easily cause secondary fires. This greatly limits its application in high-end fields.

[0003] To improve the safety of polypropylene (PP), flame retardant modification is usually required. Traditional flame retardant technologies often use halogenated flame retardants such as brominated epoxy resins and decabromodiphenyl ethane. Although these have high flame retardant efficiency, they release toxic and corrosive hydrogen halide gases and carcinogenic substances such as dioxins and furans during combustion, posing a serious threat to the environment and human health. With increasingly stringent global environmental regulations, the development of efficient and environmentally friendly halogen-free flame retardant technologies has become an inevitable trend in the industry.

[0004] Currently, intumescent flame retardant (IFR) system is one of the mainstream technologies for halogen-free flame-retardant PP. A typical IFR system consists 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. At the same time, the gas source decomposes to produce non-combustible gas, which plays a role in diluting oxygen and cooling.

[0005] However, existing flame-retardant PP technologies based on the IFR system still suffer from the following technical drawbacks: The components in the IFR system are mostly highly polar inorganic or small-molecule organic compounds, exhibiting extremely poor compatibility with the non-polar PP matrix. To achieve flame retardancy, the amount of IFR added is typically as high as 25-30 wt%, leading to a significant decrease in the mechanical properties of the composite material, particularly impact strength and elongation at break, making the material brittle and limiting its applications. Components such as ammonium polyphosphate (APP) are hygroscopic, causing hydrolysis during processing, affecting flame retardant performance and long-term material stability. Simultaneously, small-molecule components tend to migrate to the material surface ("blooming"), affecting the appearance and durability of the product. The char layer formed by traditional IFR systems is relatively loose, easily cracking and detaching during combustion due to airflow impact or melt mechanics, exposing fresh PP matrix for continued combustion, making it difficult to maintain the flame-retardant effect for long.

[0006] Furthermore, the narrow decomposition temperature range of single acid sources (such as ammonium polyphosphate) in IFR leads to an inconsistent and unstable char formation process, making the char layer prone to oxidation and burn-through at high temperatures. Traditional organic polymer char layers lack sufficient mechanical strength and oxidation resistance at temperatures exceeding 700°C, making it difficult to form a durable and effective protection. Although nanofillers can enhance the char layer, their aggregation in the polypropylene matrix and weak interfacial interactions with the flame retardant system limit their full potential.

[0007] Therefore, there is an urgent need in this field for a new technical solution that can achieve efficient char formation across the entire temperature range, construct an ultra-stable ceramicized carbon layer, and ensure strong interfacial coupling of all components at the nanoscale, in order to break through the performance bottleneck of existing environmentally friendly flame-retardant PP materials. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a flame-retardant and environmentally friendly polypropylene plastic with good flame-retardant properties and mechanical properties.

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

[0010] The flame-retardant and environmentally friendly polypropylene plastic of this invention is made from the following raw materials in parts by weight:

[0011] Polypropylene resin: 60-82 parts;

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

[0013] Nano-reinforced masterbatch: 3-8 parts;

[0014] Additives: 0.5-1 part;

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

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

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

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

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

[0020] Ammonium polyphosphate and aluminum hypophosphite were blended to form a composite core. The composite core was dispersed in a solvent and heated to 80-100℃. Monomers, namely pentaerythritol phosphate, melamine, vinyltriethoxysilane, and trimethyl borate, were added dropwise in sequence. A catalyst was added and the temperature was raised to 130-160℃. The reaction was carried out for 5-8 hours. After the reaction was completed, the mixture was washed with ethanol and dried under vacuum at 80℃ 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 to 3.

[0022] The mass ratio of 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 is used in an amount of 0.1-0.5% of the total mass of the monomers.

[0024] The grafted modified magnesium-aluminum layered double hydroxide is an aminosilane-grafted modified magnesium-aluminum hydrotalcite.

[0025] The preparation method of aminosilane-grafted modified magnesium aluminum hydrotalcite is as follows:

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

[0027] Magnesium aluminum hydrotalcite powder was dried in a vacuum drying oven at 80℃ for 12 hours to completely remove physically adsorbed water. 10.0g of the dried LDH was weighed and dispersed in 200mL of anhydrous ethanol. The mixture was sonicated for 30 minutes to ensure full dispersion, resulting in suspension A.

[0028] Preparation of silane hydrolysate:

[0029] Mix 100 mL of anhydrous ethanol with 10 mL of deionized water, and adjust the pH of the ethanol-water mixture to 4.0-5.0 with glacial acetic acid. While stirring, slowly add 3.0 g of γ-aminopropyltriethoxysilane (30% of the LDH mass). Continue stirring for at least 2 hours to allow the γ-aminopropyltriethoxysilane to fully hydrolyze into a more reactive silanol (Si-OH), thus obtaining the silane hydrolysate.

[0030] Surface grafting reaction:

[0031] The silane hydrolysate was added dropwise to suspension A through a constant pressure dropping funnel. Under nitrogen protection, the mixture was heated to 78°C and refluxed with continuous mechanical stirring for 12-24 hours.

[0032] Post-processing and purification:

[0033] After the reaction is complete, cool to room temperature. Centrifuge the product and discard the supernatant. Wash the precipitate repeatedly with anhydrous ethanol by centrifugation at least four times until no white precipitate (Cl-) is found in the last wash solution when tested with AgNO3 solution. Dry the washed product in a vacuum drying oven at 80℃ for 24 hours, then grind it to obtain aminosilane-grafted modified magnesium aluminum hydrotalcite.

[0034] The preparation method of the nano-reinforced masterbatch is as follows: grafted modified magnesium aluminum layered double hydroxide, maleic anhydride grafted polypropylene, and polypropylene carrier are premixed in a high-speed mixer, with a preferred ratio of LDH:PP-g-MAH:PP = 20:40:40. Then, the mixture is added to a co-rotating twin-screw extruder and subjected to high-shear melt blending at 180-200℃ and a high screw speed of 400-600 rpm, followed by extrusion granulation to obtain the nano-reinforced masterbatch.

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

[0036] The additive is one or both of antioxidants and lubricants.

[0037] The method for preparing the flame-retardant and environmentally friendly polypropylene plastic of the present invention comprises the following steps:

[0038] Polypropylene resin, core-shell flame retardant, nano-reinforcing masterbatch, and additives are mixed evenly and then fed into a twin-screw extruder for melt extrusion granulation. The temperature of each zone of the extruder is set to 170-210℃, and the screw speed is 200-400 rpm. The resulting particles are then dried and injection molded.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1) This invention uses ammonium polyphosphate and aluminum hypophosphite as the composite core of a core-shell flame retardant, providing a continuous acid source over a wide temperature range from 300℃ to over 450℃. At low temperatures, ammonium polyphosphate decomposes to initiate initial carbonization, while at high temperatures, the more stable aluminum hypophosphite continues the decomposition, not only continuously catalyzing char formation, but its decomposition product PH3 also has the effect of quenching free radicals in the gas phase. This "relay" catalytic mechanism ensures a stable and continuous char formation process, avoiding the "window period" defect in the char layer caused by a single acid source.

[0041] 2) During combustion, the organic portion of the core-shell structured flame retardant shell layer of the present invention forms a basic carbon structure, while silicon and boron elements are transformed in situ into Si-OC, SiO2 ceramic phase, and B2O3 glass phase. These inorganic phases are dispersed at the nanoscale or form a continuous network, which greatly improves the mechanical strength, structural integrity at high temperatures, and resistance to oxidation and ablation of the carbon layer. This fundamentally improves the quality of the carbon layer.

[0042] 3) The active group -NH2 of the aminosilane-grafted modified magnesium aluminum layered double hydroxide (MLD) described in this invention can chemically react with the anhydride groups of maleic anhydride-grafted polypropylene (PP-g-MAH) and the groups on the core-shell structure flame retardant shell, forming a multi-layered chemical bond bridge of "PP matrix → PP-g-MAH → aminosilane-grafted modified magnesium aluminum layered double hydroxide → core-shell structure flame retardant shell". Combined with masterbatch technology to ensure uniform dispersion, stress can be efficiently transferred, and the reinforcing and toughening effect of the nano-reinforcement masterbatch is maximized, thus maintaining excellent mechanical properties even under extremely high filling conditions. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments.

[0044] Unless otherwise specified, all raw materials used in the examples were commercially available.

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

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

[0047] PP resin: Grade T30S, China Petroleum & Chemical Corporation.

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

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

[0050] Preparation of aminosilane-grafted modified magnesium aluminum hydrotalcite:

[0051] Pretreatment and activation of magnesium-aluminum hydrotalcite (Mg-Al-LDH):

[0052] Magnesium aluminum hydrotalcite powder was dried in a vacuum drying oven at 80℃ for 12 hours to completely remove physically adsorbed water. 10.0g of the dried LDH was weighed and dispersed in 200mL of anhydrous ethanol. The mixture was sonicated for 30 minutes to ensure full dispersion, resulting in suspension A.

[0053] Preparation of silane hydrolysate:

[0054] Mix 100 mL of anhydrous ethanol with 10 mL of deionized water, and adjust the pH of the ethanol-water mixture to 4.5 with glacial acetic acid. Add 3.0 g of γ-aminopropyltriethoxysilane while stirring at 400 rpm. Continue stirring for 2 hours to allow the γ-aminopropyltriethoxysilane to fully hydrolyze into a more reactive silanol (Si-OH), thus obtaining the silane hydrolysate.

[0055] Surface grafting reaction:

[0056] The silane hydrolysate was added dropwise to suspension A through a constant pressure dropping funnel. Under nitrogen protection, the mixture was heated to 78°C and refluxed with continuous mechanical stirring for 20 hours.

[0057] Post-processing and purification:

[0058] After the reaction was complete, the mixture was cooled to room temperature. The product was centrifuged and the supernatant was discarded. The precipitate was washed four times with anhydrous ethanol by repeated centrifugation. The final washing solution was tested with AgNO3 solution and no white precipitate (Cl-) was found. The washed product was dried in a vacuum drying oven at 80℃ for 24 hours, ground, and passed through a 200-mesh sieve to obtain aminosilane-grafted modified magnesium aluminum hydrotalcite.

[0059] Example 1

[0060] The method for preparing the flame-retardant and environmentally friendly polypropylene plastic comprises the following steps:

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

[0062] 140g of ammonium polyphosphate (APP) and 60g of aluminum hypophosphite (AHP) were weighed and placed in a planetary ball mill. Under argon protection, they were mechanically mixed at 300 rpm for 3 hours to obtain 200g of APP / AHP (mass ratio 7:3) composite core powder. 500mL of xylene was added to a 1000mL three-necked flask equipped with mechanical stirring, a reflux condenser, and nitrogen protection. Mechanical stirring was started, and the above 200g of composite core powder was added. The temperature was raised to 90℃ to ensure uniform dispersion. The monomers were added dropwise in sequence: 40g of pentaerythritol phosphate, 25g of melamine, 10g of vinyltriethoxysilane, and 5g of trimethyl borate (total monomer mass 80g, core mass ratio 1:2.5). After the addition was complete, a catalyst mixture (0.2g of p-toluenesulfonic acid and 0.2g of dibutyltin dilaurate, totaling 0.5% of the total monomer mass) was added. Under nitrogen protection, the reaction system was slowly heated to 145°C and refluxed at this temperature for 6 hours. After the reaction was completed, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The product was filtered, and the resulting filter cake was washed three times with 300 mL of anhydrous ethanol. Then, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of core-shell flame retardant FR-1.

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

[0064] 20g of aminosilane-grafted modified magnesium aluminum hydrotalcite powder, 40g of PP-g-MAH, and 40g of PP resin were premixed in a high-speed mixer for 5 minutes. The mixture was then added to a co-rotating twin-screw extruder (L / D = 40), with the extrusion temperature set at 190℃ and the screw speed at 500rpm for high-shear melt blending. The mixture was then extruded and granulated to obtain a nano-reinforced masterbatch MB-1 with an A-LDH content of 20wt%.

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

[0066] 71.5 parts (by weight, the same below) of PP resin, 23 parts of FR-1, 5 parts of MB-1, 0.5 parts of antioxidant 1010, and 0.5 parts of calcium stearate were mixed evenly in a high-speed mixer. The mixture was then fed into a twin-screw extruder, with the temperature of each zone set to 170℃-180℃-190℃-200℃-190℃ and the screw speed at 300 rpm for melt extrusion granulation. The resulting particles were dried at 80℃ for 4 hours and then injection molded into standard test strips for performance testing.

[0067] Example 2

[0068] The method for preparing the flame-retardant and environmentally friendly polypropylene plastic comprises the following steps:

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

[0070] 180g of ammonium polyphosphate (APP) and 20g of aluminum hypophosphite (AHP) were weighed and placed in a planetary ball mill. Under argon protection, they were mechanically mixed at 300 rpm for 3 hours to obtain 200g of APP / AHP (mass ratio 9:1) composite core powder. 500mL of xylene was added to a 1000mL three-necked flask equipped with mechanical stirring, a reflux condenser, and nitrogen protection. Mechanical stirring was started, and the above 200g of composite core powder was added. The temperature was raised to 90℃ to ensure uniform dispersion. The monomers were added dropwise in sequence: 45g of pentaerythritol phosphate, 20g of melamine, 3g of vinyltriethoxysilane, and 2g of trimethyl borate (total monomer mass 70g, core mass ratio 1:2.8). After the addition was complete, a catalyst mixture (0.035g of p-toluenesulfonic acid and 0.035g of dibutyltin dilaurate, totaling 0.1% of the total monomer mass) was added. Under nitrogen protection, the reaction system was slowly heated to 130°C and refluxed at this temperature for 8 hours. After the reaction was completed, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The product was filtered, and the resulting filter cake was washed three times with 300 mL of anhydrous ethanol. Then, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of core-shell flame retardant FR-2.

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

[0072] 10g of aminosilane-grafted modified magnesium aluminum hydrotalcite powder, 30g of PP-g-MAH, and 60g of PP resin were premixed in a high-speed mixer for 5 minutes. The mixture was then added to a co-rotating twin-screw extruder (L / D = 40), and the extrusion temperature was set to 190℃ and the screw speed to 500rpm for high-shear melt blending. The mixture was then extruded and granulated to obtain a nano-reinforced masterbatch MB-2 with an A-LDH content of 10wt%.

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

[0074] 81.5 parts (by weight, the same below) of PP resin, 15 parts of FR-2, 3 parts of MB-2, and 0.5 parts of antioxidant 1010 were mixed evenly in a high-speed mixer. The mixture was then fed into a twin-screw extruder, with the temperature of each zone set to 170℃-180℃-190℃-200℃-190℃ and the screw speed at 200 rpm for melt extrusion granulation. The resulting particles were dried at 80℃ for 4 hours and then injection molded into standard test strips 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 retardants

[0078] 120g of ammonium polyphosphate (APP) and 80g of aluminum hypophosphite (AHP) were weighed and placed in a planetary ball mill. Under argon protection, they were mechanically mixed at 300 rpm for 3 hours to obtain 200g of APP / AHP (mass ratio 6:4) composite core powder. 500mL of xylene was added to a 1000mL three-necked flask equipped with mechanical stirring, a reflux condenser, and nitrogen protection. Mechanical stirring was started, and the above 200g of composite core powder was added. The temperature was raised to 90℃ to ensure uniform dispersion. The monomers were added dropwise in the following order: 55g of pentaerythritol phosphate, 30g of melamine, 12g of vinyltriethoxysilane, and 3g of trimethyl borate (total monomer mass 100g, core mass ratio 1:2). After the addition was complete, a catalyst mixture (0.25g of p-toluenesulfonic acid and 0.25g of dibutyltin dilaurate, totaling 0.5% of the total monomer mass) was added. Under nitrogen protection, the reaction system was slowly heated to 160°C and refluxed at this temperature for 5 hours. After the reaction was completed, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The product was filtered, and the resulting filter cake was washed three times with 300 mL of anhydrous ethanol. Then, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of core-shell flame retardant FR-3.

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

[0080] 30g of aminosilane-grafted modified magnesium aluminum hydrotalcite powder, 50g of PP-g-MAH, and 20g of PP resin were premixed in a high-speed mixer for 5 minutes. The mixture was then added to a co-rotating twin-screw extruder (L / D = 40), with the extrusion temperature set at 190℃ and the screw speed at 500rpm for high-shear melt blending. The mixture was then extruded and granulated to obtain MB-3, a nano-reinforced masterbatch with an A-LDH content of 20wt%.

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

[0082] 60.5 parts (by weight, 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 were mixed evenly in a high-speed mixer. The mixture was then fed into a twin-screw extruder, with the temperature of each zone set to 170℃-180℃-190℃-200℃-190℃ and the screw speed at 400 rpm for melt extrusion granulation. The resulting particles were dried at 80℃ for 4 hours and then injection molded into standard test strips for performance testing.

[0083] Comparative Example 1

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

[0085] Comparative Example 2

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

[0087] Comparative Example 3

[0088] Replace the nano-reinforcement masterbatch with an equal mass of PP-g-MAH, and follow the same steps as in Example 1.

[0089] Comparative Example 4

[0090] Masterbatch was prepared by blending 20g of unmodified Mg-Al-LDH powder with 40g of PP-g-MAH and 40g of PP resin. The remaining steps were the same as in Example 1.

[0091] Comparative Example 5

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

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

[0094] Table 1 Test Results

[0095]

[0096]

[0097] With the increase in the total amount of flame retardant system, the fire safety performance (high LOI, low pHRR / THR, high char residue) is significantly and systematically improved. Example 3 achieved an LOI of nearly 40% and below 100 kW / m². 2 The pHRR is top-tier among PP materials, fully demonstrating the high efficiency of the technical solution of this invention.

[0098] Mechanical properties are inversely proportional to the filler content. However, it is worth emphasizing that this invention achieves an excellent balance between fire resistance and mechanical properties. Example 1 shows that while the pHRR is significantly reduced compared to the traditional IFR system, the impact strength remains at 11.5 kJ / m². 2 It is far superior to ordinary flame-retardant PP.

[0099] Comparative Example 1, using a pure APP core, showed inferior performance in key fire resistance indicators such as LOI, char residue, and pHRR compared to Example 1. This directly demonstrates that the APP / AHP composite core, through "relay" catalysis and gas-phase synergy, constructs a more effective flame-retardant barrier, validating the creativity of the composite core design. Comparative Example 2, using a pure HPPN shell without Si-B modification, exhibited a pHRR of 175 kW / m³. 2 The char yield and residual char rate (27.8%) were significantly worse than in Example 1. This clearly demonstrates that the in-situ ceramicized network formed by the introduction of Si-B elements is the core of constructing the ultra-stable char layer, greatly enhancing the structural integrity of the char layer under real flame impact. Comparative Example 3 shows the most significant performance decline. Its UL-94 dropped to V-1 with dripping, pHRR increased sharply, and mechanical properties also decreased significantly. This proves that the nano-reinforcement masterbatch is indispensable to this system. It not only enhances the mechanical strength of the char layer as a skeleton and works synergistically with the flame retardant, but also significantly improves the mechanical properties of the composite material itself as a reinforcing filler. Compared with Example 1, the mechanical properties of Comparative Example 4, especially the impact strength, decreased significantly, and the flame retardant performance was also weakened. This is because the LDH without aminosilane modification lacks effective chemical bonding with the PP matrix and PP-g-MAH, resulting in weak interfacial bonding and poor stress transmission, making the nanoparticles prone to becoming defect points. This highlights the importance of LDH surface functionalization for achieving strong interfacial coupling. The mechanical properties and flame retardant performance of Comparative Example 5 both decreased to some extent. This demonstrates the necessity of masterbatch technology. Due to their enormous specific surface area and surface energy, nanoparticles are highly prone to agglomeration during melt blending. By pre-preparing masterbatches and utilizing high shear forces to fully exfoliate and disperse nanoparticles in a small amount of carrier before diluting them into a large system, agglomeration can be effectively avoided, ensuring their uniform distribution at the nanoscale and thus maximizing their reinforcing and char-forming framework effects.

Claims

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

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

4.

3. The flame-retardant and environmentally friendly polypropylene plastic according to claim 1, characterized in that, The preparation method of the core-shell structure flame retardant is as follows: Ammonium polyphosphate and aluminum hypophosphite were blended to form a composite core. The composite core was dispersed in a solvent, heated, and monomers were added dropwise in sequence: pentaerythritol phosphate, melamine, vinyltriethoxysilane, and trimethyl borate. A catalyst was added, and the reaction was heated. After the reaction was completed, the mixture was washed and dried to obtain a core-shell structured flame retardant.

4. The flame-retardant and environmentally friendly polypropylene plastic according to claim 3, characterized in that, 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 to 3.

5. The flame-retardant and environmentally friendly polypropylene plastic according to claim 3, characterized in that, The catalyst is a mixture of p-toluenesulfonic acid and dibutyltin dilaurate.

6. The flame-retardant and environmentally friendly polypropylene plastic according to claim 1, characterized in that, The grafted modified magnesium-aluminum layered double hydroxide is an aminosilane-grafted modified magnesium-aluminum hydrotalcite.

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

8. The flame-retardant and environmentally friendly polypropylene plastic according to claim 1, characterized in that, The grafted modified magnesium-aluminum layered double hydroxide accounts for 10-30 wt% of the nano-reinforcement masterbatch.

9. The flame-retardant and environmentally friendly polypropylene plastic according to claim 1, characterized in that, The additive is one or both of antioxidants and lubricants.

10. A method for preparing flame-retardant and environmentally friendly polypropylene plastic according to any one of claims 1-9, characterized in that, It is prepared by the following steps: Polypropylene resin, core-shell structure flame retardant, nano-reinforcing masterbatch, and additives are mixed evenly and then fed into a twin-screw extruder for melt extrusion granulation. The resulting particles are dried and then injection molded.

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