High-impact-resistance flame-retardant polypropylene foam material and preparation method thereof

Abstract

The invention relates to a high-impact-resistance flame-retardant polypropylene foam material and a preparation method thereof. The high-impact-resistance flame-retardant polypropylene foam material is prepared from the following raw materials in parts by weight: 70-85 parts of modified polypropylene resin, 10-15 parts of ethylene / octylene copolymer, 3-8 parts of chemical foaming agent, 0.5-2 parts of nucleating agent, 0.3-1 part of antioxidant and 0.5-2 parts of lubricant, the modified polypropylene resin is maleic anhydride grafted polypropylene resin of which the surface contains a phosphorus heterocyclic ring structure and a triazine ring structure. The modified grafted polypropylene resin with the surface containing the phosphorus heterocyclic ring structure and the triazine ring structure is adopted to cooperate with the ethylene / octylene copolymer, so that the polypropylene foam material has the excellent effects of flame retardance and impact resistance, and the flame retardance and the impact resistance are enhanced in a foam structure at the same time.

Description

Technical Field

[0001] This application relates to the field of high-performance polypropylene materials technology, and in particular to a high-impact flame-retardant polypropylene foam material and its preparation method. Background Technology

[0002] With the globalization of the automotive industry and the widespread adoption of lean manufacturing models, long-distance, multimodal transport of automotive parts has become commonplace. Precision components, vulnerable parts, and high-value assemblies are highly susceptible to damage from vibration, drops, or compression during complex logistics processes, leading to significant economic losses. Simultaneously, the potential fire risks during warehousing and transportation pose a serious challenge to the safety of packaging materials. Therefore, the market urgently needs packaging materials that simultaneously provide superior shock absorption and reliable flame retardant protection to ensure supply chain security and meet increasingly stringent environmental and safety regulations.

[0003] Currently, the materials widely used in automotive parts packaging mainly include the following categories: first, traditional foam plastics represented by polystyrene and polyethylene, which are low in cost and lightweight; second, paper products such as corrugated cardboard and honeycomb cardboard, as well as wooden packaging; and third, polyurethane foam with good cushioning properties. In addition, polypropylene foam, as an emerging option, has also attracted attention due to its advantages such as heat resistance and recyclability. These materials constitute the main means by which current technology solves packaging problems.

[0004] However, all of the aforementioned existing technologies have significant drawbacks and cannot meet the dual requirements of high-end automotive parts packaging. Polystyrene has insufficient impact resistance and is brittle; polyethylene and polypropylene have extremely poor inherent flame retardancy, are flammable, and drip easily; paper products and wooden packaging have shortcomings in terms of moisture resistance, consistent cushioning, and fire resistance; polyurethane foam often relies on halogenated flame retardants, posing environmental and toxicity risks. Crucially, polypropylene foam, the most promising material, has its own bottlenecks: pure polypropylene foam has high brittleness and poor impact resistance; while simply blending and adding flame retardants or toughening agents often results in mutual constraints, leading to a deterioration in toughness when flame retardancy is improved, or a decrease in flame retardancy efficiency and processability when toughness is improved, making it impossible to achieve a balance between high performance and low performance.

[0005] In summary, existing packaging materials present a fundamental contradiction: they cannot simultaneously achieve high impact resistance and high flame retardancy. Therefore, there is an urgent need to develop a novel foaming material that can synergistically improve both impact resistance and flame retardancy to address the safety challenges in the transportation of automotive parts. Summary of the Invention

[0006] In order to simultaneously improve the impact resistance and flame retardant properties of foamed materials, this application provides a high impact resistance and flame retardant polypropylene foamed material and its preparation method.

[0007] In a first aspect, this application provides a high-impact, flame-retardant polypropylene foam material, employing the following technical solution: A high-impact flame-retardant polypropylene foam material comprises the following components in parts by weight: 70-85 parts modified polypropylene resin, 10-15 parts ethylene / octene copolymer, 3-8 parts chemical foaming agent, 0.5-2 parts nucleating agent, 0.3-1 parts antioxidant, and 0.5-2 parts lubricant; wherein the modified polypropylene resin is a maleic anhydride-grafted polypropylene resin with a surface containing phosphorus-containing heterocyclic structures and triazine ring structures.

[0008] The inventors discovered that modified grafted polypropylene resin with phosphorus-containing heterocyclic and triazine ring structures on its surface, in synergy with ethylene / octene copolymers, enables polypropylene foam materials to simultaneously enhance both flame retardancy and impact resistance within the cell structure.

[0009] Specifically, the phosphorus-containing heterocyclic structure and triazine ring structure introduced into the polypropylene resin molecular chain through chemical bonds can achieve a synergistic flame-retardant effect of phosphorus and nitrogen within the resin matrix. The phosphorus-containing heterocyclic structure in the modified polypropylene resin molecule decomposes during combustion to produce acidic substances such as phosphoric acid and metaphosphoric acid, which catalyze the dehydration and char formation of the polypropylene resin, forming a dense char layer that prevents oxygen and heat from transferring into the material and inhibits the release of combustible gases. Meanwhile, the triazine ring structure possesses extremely high thermal stability and flame-retardant activity. During combustion, it is not only difficult to decompose itself but also synergistically enhances the density and high-temperature resistance of the char layer with phosphorus-based flame-retardant components. Both structures simultaneously and efficiently exert gas-solid dual-phase flame-retardant functions at the molecular level, overcoming the shortcomings of physically added flame retardants, such as easy migration, low efficiency, and deterioration of matrix properties.

[0010] Ethylene / octene copolymer, as an elastomer component, has molecular chains with good flexibility and flowability, which can form a small elastic dispersed phase in the polypropylene resin matrix. When the material is impacted, the elastic dispersed phase can absorb the impact energy and prevent the generation and propagation of cracks. After grafting modification, the molecular chain polarity of the modified polypropylene resin increases, and the interfacial compatibility with ethylene / octene copolymer is significantly improved, avoiding the decline in impact performance caused by phase separation. The synergistic effect of the two greatly improves the impact strength of the material.

[0011] This application utilizes modified polypropylene resin with phosphorus-containing heterocyclic and triazine ring structures on its surface, along with ethylene / octene copolymer, chemical foaming agent, nucleating agent, antioxidant, and lubricant to synergistically enhance the polypropylene foam material's excellent impact resistance and flame retardancy, while also maintaining good foaming molding stability and mechanical structural integrity.

[0012] In one specific feasible implementation, the preparation steps of the above-mentioned modified polypropylene resin are as follows: S1-1 Under nitrogen protection, maleic anhydride-grafted polypropylene resin was added to a solvent and mixed. A DMF solution of 6-aminohexanol was added to initiate a ring-opening reaction. After post-treatment, PP-g-OH was obtained. S2-1 Under nitrogen protection, the PP-g-OH obtained in step S1-1 was added to DMF and mixed. Under ice bath, a premixed solution of 2-bromoisobutyryl bromide and triethylamine was added to carry out an esterification reaction. After post-treatment, PP-g-Br was obtained. S3-1. Under nitrogen protection, 2,4-dichloro-1,3,5-triazine was dissolved in a solvent, and KI was added to form a triazine solution. DOPO and triethylamine were dissolved in a solvent and added to the triazine solution under ice bath conditions to react. GMA was dissolved in a solvent, and sodium hydride was added to react and form a sodium alkoxide solution of GMA, which was then added to the reaction solution to react. After post-treatment, DOPO-triazine-GMA was obtained. S4-1 Under nitrogen protection, PP-g-Br, butyl methacrylate, copper catalyst, and ligand obtained in step S2-1 are added to a solvent, and DOPO-triazine-GMA obtained in step S3-1 is added and mixed before polymerization. The modified polypropylene resin is then obtained after post-treatment.

[0013] By adopting the above steps, the modified polypropylene resin grafted with maleic anhydride is modified through a stepwise modification process of "ring-esterification-intermediate synthesis-polymerization" so that the final modified polypropylene resin can accurately introduce phosphorus-containing heterocyclic structures and triazine ring structures. Moreover, the grafting rate of the two flame-retardant structures on the resin molecular chain is controllable and the distribution is uniform, thereby ensuring that it can synergistically exert excellent flame-retardant and interfacial compatibility effects with other components.

[0014] Specifically, in the first ring-opening reaction, the anhydride groups of maleic anhydride-grafted polypropylene resin undergo a ring-opening reaction with 6-aminohexanol to generate PP-g-OH. The core function of this step is to introduce hydroxyl active sites onto the polypropylene molecular chain, providing reaction sites for the subsequent esterification reaction. The introduction of hydroxyl groups can also slightly increase the polarity of polypropylene, laying the foundation for subsequent bonding with polar flame-retardant intermediates. In the second esterification reaction, PP-g-OH undergoes an esterification reaction with 2-bromoisobutyryl bromide to generate PP-g-Br. The bromo group acts as an active initiation site, possessing extremely high initiation activity, which can efficiently initiate the subsequent polymerization reaction, ensuring the flame retardancy of the intermediate. The intermediate can be stably grafted onto the polypropylene molecular chain, avoiding the migration and loss problems caused by the physical mixing of flame retardant components. In the third step of intermediate synthesis, the stepwise reaction of 2,4-dichloro-1,3,5-triazine with DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and GMA (glycidyl methacrylate) can accurately construct a dual flame retardant intermediate (DOPO-triazine-GMA) containing phosphorus heterocycles and triazine rings. The epoxy group of GMA provides active sites for the subsequent polymerization reaction with PP-g-Br, ensuring that the dual flame retardant structure can be directionally grafted onto the polypropylene molecular chain. In the fourth polymerization step, PP-g-Br acts as an initiator, undergoing polymerization with DOPO-triazine-GMA and butyl methacrylate under the action of a copper catalyst and ligands. The introduction of butyl methacrylate further modifies the flexibility of the modified resin, and synergistically with DOPO-triazine-GMA, ensures that the flame-retardant structure is uniformly distributed on the polypropylene molecular chain. The synergistic cooperation of each reaction step achieves precise modification through "active site introduction - initiator preparation - synthesis of dual flame-retardant intermediates - directional graft polymerization." The resulting modified polypropylene resin not only exhibits excellent flame-retardant properties but also forms good interfacial bonds with other components, ensuring the overall stability of the material's performance.

[0015] In one specific implementation scheme, the above-mentioned chemical foaming agent is selected from one or two of azodicarbonamide and sodium bicarbonate; more preferably, the above-mentioned chemical foaming agent includes azodicarbonamide and sodium bicarbonate, wherein the mass ratio of azodicarbonamide to sodium bicarbonate is (2.5-3.5):1.

[0016] Azodicarbonamide has a high decomposition temperature and a slow decomposition rate, enabling it to continuously generate gas during the later stages of material melt blending and foaming, providing a continuous driving force for cell growth and stability. Sodium bicarbonate has a low decomposition temperature and a fast decomposition rate, enabling it to rapidly generate a small amount of gas in the early stages of melt blending, providing initial gas nuclei for the nucleating agent and promoting the formation of more nucleation sites. The inventors discovered that mixing the two at a mass ratio of (2.5-3.5):1 achieves a synergistic effect of "rapid initial nucleation + continuous later foaming," avoiding the problems of insufficient nucleation or excessive gas escape caused by a single foaming agent, thereby forming a cell structure with uniform pore size and dense distribution.

[0017] If the proportion of azodicarbonamide is too high, the initial nucleation sites provided by sodium bicarbonate will be insufficient. The gas produced by the decomposition of azodicarbonamide will have difficulty finding uniform nucleation sites in the melt, leading to the aggregation and growth of bubbles, forming a large-pore, non-uniform bubble structure. The material will have many voids and defects, making it prone to cracking at these defects upon impact, thus reducing its impact resistance. At the same time, the non-uniform bubble structure will also reduce the flame retardant stability of the material. If the proportion of sodium bicarbonate is too high, due to its low decomposition temperature and fast decomposition rate, a large amount of gas will be generated during the initial stage of melt blending. At this time, the melt has not yet been fully plasticized and homogeneous, and the melt strength is insufficient to effectively encapsulate the gas, resulting in a large amount of gas escaping. This will not only reduce the foaming ratio, but also cause irregular bubbles due to excessive concentration of nucleation sites and gas escape, significantly reducing the mechanical properties of the material.

[0018] In one specific implementation, the nucleating agent comprises talc and an organic nucleating agent; more preferably, the mass ratio of the talc to the organic nucleating agent is 1:(0.5-1); more preferably, the organic nucleating agent is selected from dibenzyl sorbitol or a dibenzyl sorbitol derivative.

[0019] Talc, as an inorganic nucleating agent, possesses a high specific surface area and surface energy, providing numerous heterogeneous nucleation sites for the gases generated by the decomposition of foaming agents, thus promoting uniform gas nucleation. Organic nucleating agents, such as dibenzyl sorbitol and its derivatives, are typical α-crystal nucleating agents with good compatibility. Their molecular structure contains multiple hydroxyl groups and benzene rings. The hydroxyl groups can form hydrogen bonds with polar groups such as phosphorus-containing heterocycles and triazine rings on the modified polypropylene resin molecular chain, while the benzene rings can bind to the resin molecular chain through π-π interactions. This allows for uniform dispersion in the polypropylene melt, further refining the nucleation sites. Simultaneously, it can regulate the crystal morphology of polypropylene, making the crystals more uniform and refined. The synergistic effect of both significantly increases the number and uniformity of nucleation sites, preventing gas aggregation at a few sites and the formation of large pores, ensuring uniform pore size and dense distribution.

[0020] When acting synergistically with talc, dibenzyl sorbitol or its derivatives can adsorb onto the surface of talc, reducing its surface energy and agglomeration, thus allowing the nucleation sites to be more evenly distributed in the melt. Simultaneously, the inorganic rigidity of talc synergistically with the crystallization-refining properties of the organic nucleating agent further enhances the crystallinity and uniformity of the material, resulting in more stable melt strength and better encapsulation of foaming gas, forming a uniform and dense cell structure. Furthermore, the refined crystalline structure and good interfacial compatibility enable the crystalline particles to effectively disperse impact energy upon impact, reducing the likelihood of delamination at the interface and significantly improving the material's impact resistance and mechanical stability.

[0021] If the proportion of talc is too high, the organic nucleating agent cannot adequately improve the dispersibility of the talc, causing it to easily agglomerate in the melt, forming locally high-density nucleation sites and locally non-nucleation sites. This results in large differences in cell size and uneven distribution, leading to defects within the material. Simultaneously, the organic nucleating agent's crystallization refining effect is insufficient, resulting in coarse polypropylene crystal particles, reduced material toughness, and decreased impact resistance. If the proportion of organic nucleating agent is too high, on the one hand, the high cost of the organic nucleating agent itself increases the material preparation cost; on the other hand, excessive organic nucleating agent significantly increases the melt viscosity, making it difficult for the gas generated by the decomposition of the foaming agent to diffuse and grow in the high-viscosity melt, leading to a decrease in foaming ratio, excessively high cell density, and poor lightweighting effect. Furthermore, excessive organic nucleating agent may precipitate on the material surface, affecting the material's surface properties and compatibility.

[0022] In one specific implementation, the antioxidant includes hindered phenolic oxidant 1010 and phosphite oxidant 168, wherein the mass ratio of hindered phenolic oxidant 1010 to phosphite oxidant 168 is 1:(1-2).

[0023] Hindered phenolic antioxidant 1010 is a primary antioxidant. Its mechanism of action is to capture free radicals generated during material oxidation, terminating the free radical chain reaction and thus preventing oxidative degradation of the material. Phosphite antioxidant 168 is a secondary antioxidant. Its mechanism of action is to decompose hydroperoxides generated during material oxidation, converting them into stable compounds and preventing the decomposition of hydroperoxides from generating new free radicals. It can also react with the oxidation products of the primary antioxidant, regenerating the primary antioxidant and extending its lifespan. The two work synergistically to form a complete antioxidant system of "free radical capture + hydroperoxide decomposition + primary antioxidant regeneration," which can comprehensively inhibit the oxidative degradation of materials under high-temperature environments.

[0024] The synergistic advantage of this mass ratio of 1:(1-2) lies in the fact that the proportion of phosphite antioxidant 168 is slightly higher than or equal to that of hindered phenolic antioxidant 1010. This allows for the full decomposition of the large amount of hydroperoxides generated during high-temperature melting and foaming, preventing the explosive growth of free radicals caused by the accumulation of hydroperoxides. Simultaneously, it provides ample regeneration opportunities for 1010, ensuring that the main antioxidant can continuously exert its free radical scavenging effect. During the high-temperature processing of the material, this synergistic antioxidant system effectively protects the polypropylene molecular chains from breakage, preventing foaming instability caused by a decrease in melt strength. It also protects the flame-retardant structure in the modified resin from oxidative damage, ensuring the stability of the material's flame-retardant and mechanical properties.

[0025] In one specific implementation, the lubricant comprises calcium stearate and polyethylene wax, wherein the mass ratio of calcium stearate to polyethylene wax is (1-2):1.

[0026] By using the above-mentioned mass ratio of calcium stearate and polyethylene wax, the synergistic effect significantly improves the dispersion uniformity of the components in the polypropylene foam material, while reducing melt processing resistance and improving the material's molding fluidity and surface smoothness. Calcium stearate, a metal soap-type lubricant, has both internal and external lubrication functions: For internal lubrication, its polar groups interact with the polar groups of modified polypropylene resin, ethylene / octene copolymer, and other components, reducing internal friction between molecular chains and improving melt fluidity; for external lubrication, its non-polar portion migrates to the melt surface, forming a lubricating film that reduces external friction between the melt and processing equipment (such as screws and barrels), thus reducing equipment wear. Polyethylene wax, a non-polar lubricant, primarily functions as an external lubricant. Its molecular chains possess good flexibility and fluidity, enabling it to form a more uniform and stable lubricating film on the melt surface, further reducing external friction resistance.

[0027] If the proportion of calcium stearate is too high, although the internal lubrication effect is enhanced, the external lubrication effect is insufficient. This increases the frictional resistance between the melt and the equipment, leading to a rise in melt processing temperature and increasing the risk of material oxidation and degradation. Simultaneously, excessive calcium stearate may precipitate on the material surface, affecting surface properties and compatibility, and reducing the material's impact resistance. If the proportion of polyethylene wax is too high, the external lubrication effect is too strong, resulting in insufficient adhesion between the melt and the equipment, reduced screw conveying efficiency, and impact on extrusion stability. Furthermore, excessive polyethylene wax reduces the melt viscosity and strength, preventing effective gas encapsulation during foaming, leading to cell collapse, a decrease in foaming ratio, and insufficient rigidity in the material's mechanical properties due to excessive polyethylene wax addition.

[0028] Secondly, this application provides a method for preparing a high-impact, flame-retardant polypropylene foam material, employing the following technical solution: A method for preparing a high-impact, flame-retardant polypropylene foam material includes the following steps: S1-2, Premix: Modified polypropylene resin, ethylene / octene copolymer, nucleating agent, antioxidant and lubricant are mixed at 60-80℃ to obtain a premix; S2-2, Melt Blending and Extrusion: The premix obtained in step S1-2 is added to the main feed port of a twin-screw extruder, and the chemical foaming agent is added through the side feed port. The mixture is then blended and extruded at a melting temperature of 150-180℃ to obtain an expandable melt. S3-2, Foaming and Molding: The expandable melt obtained in step S2-2 is extruded into a foaming and molding zone heated to 190-210℃ to decompose and foam, and then cooled and shaped to obtain the high impact-resistant flame-retardant polypropylene foam material.

[0029] The above preparation method can be used to obtain polypropylene foam materials with uniform cell structure, excellent flame retardant properties and impact resistance.

[0030] The premixing stage involves mixing the modified polypropylene resin, ethylene / octene copolymer, nucleating agent, antioxidant, and lubricant at 60-80℃. This temperature is below the melting point of each component, preventing premature melting and agglomeration. Simultaneously, the appropriate temperature increases the molecular activity of the components, promoting initial dispersion and laying the foundation for subsequent melt blending. The core function of this step is to achieve initial uniform dispersion of the components, preventing agglomeration due to insufficient melt blending time.

[0031] Melt blending and extrusion stage: The premix is ​​added through the main feed port, and the chemical foaming agent is added through the side feed port. The mixture is then blended and extruded at a melting temperature of 150-180℃. This temperature range allows the modified polypropylene resin and ethylene / octene copolymer to be fully plasticized and melted, forming a uniform melt matrix. Adding the chemical foaming agent through the side feed port avoids premature decomposition caused by prolonged high-temperature residence after addition through the main feed port, ensuring the foaming agent remains stable before entering the foaming molding zone. This coordinated feeding method of the main and side feed ports, combined with the appropriate melting temperature, achieves a synergistic effect of sufficient melt plasticization and stable dispersion of the foaming agent, resulting in uniform dispersion of the foaming agent within the melt.

[0032] Foaming and molding stage: The expandable melt is extruded into a foaming and molding zone at 190-210℃. This temperature, higher than the melting temperature, allows the chemical foaming agent to decompose rapidly and fully, generating gas. Simultaneously, it gives the melt suitable viscosity and elasticity to encapsulate the gas and allow for cell growth. The subsequent cooling and setting step quickly fixes the cell structure, preventing cell shrinkage or collapse during melt cooling. The synergistic matching of the foaming and molding temperature with the melting temperature achieves a three-way synergistic effect: efficient decomposition of the foaming agent, stable cell growth, and rapid structural setting, ensuring the final foamed material with uniform cells and a stable structure.

[0033] The synergistic effect of the entire process steps and parameters ensures that the entire process, from initial dispersion to complete uniform mixing of components, from stable dispersion of the foaming agent to efficient decomposition and foaming, and from nucleation and growth of cells to stable shaping, is controllable. Ultimately, this allows the material's various properties to reach an optimal balance: uniform mixing of components ensures the uniformity of flame retardant and impact resistance; a stable foaming process ensures the uniformity of cell structure; and suitable temperature parameters prevent oxidative degradation of the material and premature decomposition of the foaming agent, ensuring the stability of the material's performance.

[0034] In summary, this application includes at least one of the following beneficial technical effects: 1. This application utilizes modified grafted polypropylene resin with phosphorus-containing heterocyclic and triazine ring structures on its surface, in synergy with ethylene / octene copolymer, to achieve the excellent effect of simultaneously enhancing the flame retardancy and impact resistance of polypropylene foam material in the cell structure.

[0035] 2. This application uses a chemical foaming agent composed of azodicarbonamide and sodium bicarbonate to enable polypropylene foam material to form a cell structure with uniform pore size and dense distribution. Detailed Implementation

[0036] The present application will be further described in detail below with reference to embodiments and comparative examples: Some of the raw materials used in the examples and comparative examples: Maleic anhydride-grafted polypropylene resin (model: MP101, purchased from Dongguan Kangjin New Material Technology Co., Ltd.); 2,4-dichloro-1,3,5-triazine (CAS: 2831-66-5); DOPO (full name: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, model: 850214, purchased from Shandong Gaotai Chemical Technology Co., Ltd.); GMA (full name: glycidyl methacrylate, model: yaner, purchased from Zhongshan Dixing Chemical Co., Ltd.); ethylene / octene copolymer (brand name) Product No.: C0560 (purchased from Shanghai Sufa Import & Export Co., Ltd.); Talc powder (product No.: Talcum12, purchased from Guangdong Yongfeng Chemical Co., Ltd.); Dibenzyl sorbitol (CAS: 32647-67-9); Hindered phenolic oxidant 1010 and phosphite oxidant 168 were both purchased from Dongguan Kangjin New Material Technology Co., Ltd.; Calcium stearate (model: KJ-101, purchased from Dongguan Kangjin New Material Technology Co., Ltd.); Polyethylene wax (model: TS-5204, purchased from Shandong Yousuo Chemical Technology Co., Ltd.).

[0037] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available products.

[0038] Preparation Example 1 The preparation steps of modified polypropylene resin are as follows: S1-1 Under nitrogen protection, 100g of maleic anhydride-grafted polypropylene resin was added to 300mL of p-xylene, heated to 150°C and stirred under reflux for 5 hours, then 10g of 6-aminohexanol was added, and the mixture was kept at 150°C and refluxed for another 2 hours. After the reaction was completed, the reaction solution was poured into excess methanol to precipitate a solid product, which was then filtered, washed, and dried under vacuum at 60°C for 12 hours to obtain PP-g-OH. S2-1 Under nitrogen protection, 100g of PP-g-OH obtained in step S1-1 was added to 300mL of p-xylene, heated to 150°C and stirred under reflux for 5 hours. Under ice bath conditions, 17.5g of 2-bromoisobutyryl bromide was diluted with 20mL of p-xylene and then added to 15g of triethylamine to form a premix. The premix was slowly added dropwise to the above solution through a constant pressure dropping funnel. The mixture was stirred at room temperature for 0.5 hours, and then heated to 150°C and refluxed for 5 hours. After the reaction was completed, the mixture was filtered, and the filtrate was poured into methanol to precipitate a solid product. The product was then filtered, washed, and dried under vacuum at 60°C for 12 hours to obtain PP-g-Br. S3-1. Under nitrogen protection, 1.84 g of 2,4-dichloro-1,3,5-triazine was dissolved in 20 mL of DMF, and 0.1 g of KI was added to form a triazine solution. 2.16 g of DOPO and 1.01 g of triethylamine were dissolved in 15 mL of DMF and added to the triazine solution under ice bath conditions. After the addition was complete, the temperature was raised to 40°C and stirred for 4 hours. 1.42 g of GMA was dissolved in 15 mL of tetrahydrofuran, and 0.24 g of sodium hydride was added under ice bath conditions. The mixture was stirred at room temperature for 0.5 hours to generate a sodium GMA alkoxide solution. The sodium GMA alkoxide solution was added to the reaction mixture, and the temperature was raised to 40°C and stirred for 12 hours. After the reaction was completed, the mixture was filtered, and the filtrate was extracted by vacuum distillation. The organic phase was dried over anhydrous magnesium sulfate, concentrated, and purified by column chromatography to obtain DOPO-triazine-GMA. S4-1 Under nitrogen protection, 1g of PP-g-Br obtained in step S2-1, 0.71g of butyl methacrylate, 14.4mg of cuprous bromide, and 46.8mg of bipyridine were added to 10mL of toluene, and 2.58g of DOPO-triazine-GMA obtained in step S3-1 were added. The mixture was heated to 80°C and polymerized for 24 hours. After the reaction was completed, the reaction solution was poured into a large amount of methanol to precipitate the solid product. The product was filtered, washed, and dried under vacuum at 40°C for 12 hours to obtain the modified polypropylene resin. Example

[0039] Example 1 The preparation of high-impact flame-retardant polypropylene foam material is as follows: S1-2, Premix: 77.5 parts by weight of the modified polypropylene resin prepared in Preparation Example 1, 12.5 parts by weight of the ethylene / octene copolymer, 0.7 parts by weight of talc and 0.55 parts by weight of dibenzyl sorbitol, 0.26 parts by weight of hindered phenolic oxidant 1010 and 0.39 parts by weight of phosphite oxidant 168, 0.75 parts by weight of calcium stearate and 0.5 parts by weight of polyethylene wax are mixed at 70°C to obtain a premix. S2-2, Melt Blending and Extrusion: The premix obtained in step S1-2 is added to the main feed port of a twin-screw extruder, and 4.125 parts by weight of azodicarbonamide and 1.375 parts by weight of sodium bicarbonate are added through the side feed port. The mixture is then blended and extruded at a melting temperature of 165°C to obtain an expandable melt. S3-2, Foaming Molding: The expandable melt obtained in step S2-2 is extruded into a foaming molding zone heated to 200°C to decompose and foam, and then cooled and shaped to obtain a high-impact flame-retardant polypropylene foam material.

[0040] Example 2 The only difference between Example 2 and Example 1 is that in step S1-2 of Example 2, 0.7 parts by weight of talc and 0.55 parts by weight of dibenzyl sorbitol are replaced with 1.25 parts by weight of talc.

[0041] Example 3 The difference between Example 3 and Example 1 is that in step S1-2 of Example 3, 0.7 parts by weight of talc and 0.55 parts by weight of dibenzyl sorbitol are replaced with 1.25 parts by weight of dibenzyl sorbitol.

[0042] Example 4 The only difference between Example 4 and Example 1 is that in step S1-2 of Example 4, 0.7 parts by weight of talc and 0.55 parts by weight of dibenzyl sorbitol are replaced with 1 part by weight of talc and 0.25 parts by weight of dibenzyl sorbitol.

[0043] Example 5 The difference between Example 5 and Example 1 is that in step S1-2 of Example 5, 0.7 parts by weight of talc and 0.55 parts by weight of dibenzyl sorbitol are replaced with 0.4 parts by weight of talc and 0.85 parts by weight of dibenzyl sorbitol.

[0044] Example 6 The difference between Example 6 and Example 1 is that in step S1-2 of Example 6, 0.26 parts by weight of hindered phenolic oxidant 1010 and 0.39 parts by weight of phosphite oxidant 168 are replaced with 0.65 parts by weight of hindered phenolic oxidant 1010.

[0045] Example 7 The difference between Example 7 and Example 1 is that in step S1-2 of Example 7, 0.26 parts by weight of hindered phenolic oxidant 1010 and 0.39 parts by weight of phosphite oxidant 168 are replaced with 0.65 parts by weight of phosphite oxidant 168.

[0046] Example 8 The difference between Example 8 and Example 1 is that in step S1-2 of Example 8, 0.26 parts by weight of hindered phenolic oxidant 1010 and 0.39 parts by weight of phosphite oxidant 168 are replaced with 0.5 parts by weight of hindered phenolic oxidant 1010 and 0.15 parts by weight of phosphite oxidant 168.

[0047] Example 9 The difference between Example 9 and Example 1 is that in step S1-2 of Example 9, 0.26 parts by weight of hindered phenolic oxidant 1010 and 0.39 parts by weight of phosphite oxidant 168 are replaced with 0.15 parts by weight of hindered phenolic oxidant 1010 and 0.5 parts by weight of phosphite oxidant 168.

[0048] Example 10 The difference between Example 10 and Example 1 is that in step S1-2 of Example 10, 0.75 parts by weight of calcium stearate and 0.5 parts by weight of polyethylene wax are replaced with 1.25 parts by weight of calcium stearate.

[0049] Example 11 The difference between Example 11 and Example 1 is that in step S1-2 of Example 11, 0.75 parts by weight of calcium stearate and 0.5 parts by weight of polyethylene wax are replaced with 1.25 parts by weight of polyethylene wax.

[0050] Example 12 The difference between Example 12 and Example 1 is that in step S1-2 of Example 12, 0.75 parts by weight of calcium stearate and 0.5 parts by weight of polyethylene wax are replaced with 1 part by weight of calcium stearate and 0.25 parts by weight of polyethylene wax.

[0051] Example 13 The difference between Example 13 and Example 1 is that in step S1-2 of Example 13, 0.75 parts by weight of calcium stearate and 0.5 parts by weight of polyethylene wax are replaced with 0.4 parts by weight of calcium stearate and 0.85 parts by weight of polyethylene wax.

[0052] Example 14 The only difference between Example 14 and Example 1 is that in step S2-2 of Example 14, 4.125 parts by weight of azodicarbonamide and 1.375 parts by weight of sodium bicarbonate are replaced with 5.5 parts by weight of azodicarbonamide.

[0053] Example 15 The difference between Example 15 and Example 1 is that in step S2-2 of Example 15, 4.125 parts by weight of azodicarbonamide and 1.375 parts by weight of sodium bicarbonate are replaced with 5.5 parts by weight of sodium bicarbonate.

[0054] Example 16 The only difference between Example 16 and Example 1 is that in step S2-2 of Example 16, 4.125 parts by weight of azodicarbonamide and 1.375 parts by weight of sodium bicarbonate are replaced with 4.5 parts by weight of azodicarbonamide and 1 part by weight of sodium bicarbonate.

[0055] Example 17 The difference between Example 17 and Example 1 is that in step S2-2 of Example 17, 4.125 parts by weight of azodicarbonamide and 1.375 parts by weight of sodium bicarbonate are replaced with 2 parts by weight of azodicarbonamide and 3.5 parts by weight of sodium bicarbonate.

[0056] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that in steps S1-2 of Comparative Example 1, 77.5 parts by weight of the modified polypropylene resin prepared in Example 1 is replaced with 70 parts by weight of maleic anhydride-grafted polypropylene resin, 3.5 parts by weight of 2,4-dichloro-1,3,5-triazine, and 4 parts by weight of DOPO.

[0057] According to GB / T1843-1996 Plastics Cantilever Beam Impact Test Method, GB / T1040-1992 Plastics Tensile Properties Test Method, and GB / T8332-2008 Foamed Plastics Burning Performance Test Method (Horizontal Burning Method), the samples of Examples 1-17 and Comparative Example 1 were tested, and the results are shown in the table below (all samples were molded parts of the same specification, and the test environment was 23℃ and 50% relative humidity): The test standard according to GB / T8332-2008 "Test Method for Burning Performance of Foamed Plastics - Horizontal Burning Method" is as follows: The UL94HF-1 standard requires that at least four out of a set of five specimens have an open flame time of 2 seconds or less, and the open flame time of any single specimen does not exceed 10 seconds. The specimen must not be damaged after being marked with a 60mm marker. After the ignition source is removed, or after being marked with a 60mm marker, the specimen's burning time must not exceed 30 seconds, with no molten droplets. The UL94HF-2 standard requires that at least four out of a set of five specimens have an open flame time of 2 seconds or less, and the open flame time of any single specimen does not exceed 10 seconds. The specimen must not be damaged after being marked with a 60mm marker. After the ignition source is removed, or after being marked with a 60mm marker, the specimen's burning time must not exceed 30 seconds, and the molten droplets must ignite the absorbent cotton. The UL94HBF standard states that the burning rate of the material between the 25mm and 125mm marks should not exceed 40mm / min, or it should self-extinguish before the 125mm mark, but it does not meet the requirements of UL94HF-1 and UL94HF-2.

[0058] The stringency of flame retardant standards is HF-1 > HF-2 > HBF.

[0059] Table 1. Test data of notched impact strength, elongation at break and flame retardancy rating of polypropylene foam. Test Project Notched impact strength (kJ / m²) Elongation at break (%) Flame retardant rating (UL94) Example 1 17.2 69.2 HF-1 Example 2 14.1 55.3 HF-1 Example 3 13.5 52.1 HF-1 Example 4 15.6 61.8 HF-1 Example 5 15.2 60.3 HF-1 Example 6 12.8 43.7 HF-2 Example 7 13.3 45.9 HF-2 Example 8 14.8 58.6 HF-1 Example 9 15.1 59.4 HF-1 Example 10 13.6 49.8 HF-1 Example 14 13.0 48.2 HF-1 Example 12 15.0 62.5 HF-1 Example 13 14.7 61.2 HF-1 Example 14 11.5 38.7 HF-2 Example 15 9.8 33.5 HBF Example 16 15.3 60.5 HF-1 Example 17 12.8 42.8 HF-2 Comparative Example 1 7.6 24.3 HBF Combining Examples 1 and 2-5, and referring to Table 1, it can be seen that the impact resistance of Example 1 is better than that of Examples 2-5. This may be because the inorganic nucleating agent and the organic nucleating agent under the preferred ratio have a synergistic effect. Talc provides a large number of heterogeneous nucleation sites, and the organic nucleating agent improves the dispersibility of talc and refines the crystals, making the foam cells more refined and uniform. As a result, the polypropylene foam material prepared in Example 1 has the best support and toughness among them.

[0060] Combining Examples 1 and 6-9, and referring to Table 1, it can be seen that the impact resistance and flame retardant properties of Example 1 are superior to those of Examples 6-9. This may be because the hindered phenolic antioxidant 1010 and the phosphite antioxidant 168, in the preferred ratio, synergistically enhance each other. 1010 efficiently captures free radicals generated during the high-temperature processing of the material to terminate the oxidation chain reaction, while 168 decomposes the hydroperoxides generated during oxidation and regenerates 1010, forming a complete antioxidant system. This effectively avoids the degradation of the resin matrix and the destruction of the flame-retardant structure. In contrast, Examples 6-9 use a single antioxidant or a compound system that deviates from the preferred ratio, resulting in a lack or weakening of the antioxidant synergistic effect. This fails to fully inhibit high-temperature oxidation damage, leading to a decrease in the integrity of the material matrix and the stability of the flame-retardant structure, thus making the impact resistance and flame retardant properties inferior to those of Examples 6-9.

[0061] Combining Examples 1 and 10-13, and referring to Table 1, it can be seen that the impact resistance of Example 1 is better than that of Examples 10-13. This may be because the calcium stearate and polyethylene wax in the preferred ratio have a synergistic effect. Calcium stearate takes into account both internal lubrication (reducing internal friction between resin molecular chains) and external lubrication (reducing external friction between the melt and processing equipment), while polyethylene wax strengthens external lubrication and forms a stable lubricating film, ensuring that each component is uniformly dispersed in the melt, while ensuring the stability of the melt processing process, so that the cell structure is intact and without defects. In contrast, Examples 10-13 use a single lubricant or a compound system that deviates from the preferred ratio, resulting in an imbalance of lubrication function, uneven dispersion of components, or fluctuations in melt processing, making the cell structure prone to defects, thus making the impact resistance less than that of Example 1.

[0062] Combining Examples 1 and 14-17, and referring to Table 1, it can be seen that the impact resistance and flame retardant properties of Example 1 are superior to those of Examples 14-17. This may be because the azodicarbonamide and sodium bicarbonate in the preferred ratio have a synergistic effect. Sodium bicarbonate provides initial nucleation sites through rapid decomposition in the early stage of melt blending, while azodicarbonamide provides stable foaming power through continuous decomposition in the foaming stage, achieving a synergistic effect of "rapid initial nucleation + continuous later foaming", forming a uniform and densely distributed cell structure. In contrast, Examples 14-17 use a single foaming agent or a compound system that deviates from the preferred ratio, which cannot achieve a synergistic match between nucleation and foaming. A single foaming agent is prone to insufficient nucleation or excessive gas escape, while deviation from the ratio will destroy the synergistic effect, resulting in an uneven or collapsed cell structure. This reduces the impact resistance of the material and destroys the integrity of the char layer during the flame retardant process, thus making the impact resistance and flame retardant properties inferior to those of Example 1.

[0063] Combining Example 1 and Comparative Example 1, and referring to Table 1, it can be seen that the impact resistance and flame retardant properties of Example 1 are superior to those of Comparative Example 1. This may be because the modified polypropylene resin used in Example 1 achieves intramolecular phosphorus-nitrogen synergistic flame retardancy by grafting phosphorus-containing heterocyclic and triazine ring structures through molecular chain chemical bonds. At the same time, it improves the interfacial compatibility with ethylene / octene copolymer, making the elastic dispersed phase uniformly dispersed to enhance toughness. In contrast, Comparative Example 1 uses a physical mixing method for flame retardants, which has poor compatibility with the resin matrix, is prone to agglomeration, and cannot achieve efficient phosphorus-nitrogen synergistic flame retardancy. Furthermore, the agglomerated flame retardant will destroy the resin matrix structure, causing the elastomer toughening effect to fail, thus making the impact resistance and flame retardant properties far inferior to those of Example 1.

[0064] This application utilizes a modified polypropylene resin with molecularly linked phosphorus-containing heterocyclic and triazine ring structures, which is synergistically toughened with an ethylene / octene copolymer. Simultaneously, it incorporates a preferred ratio of compounded chemical foaming agents, compounded nucleating agents, compounded antioxidants, and compounded lubricants. The synergistic effect of these components optimizes the cell structure, ensures matrix integrity, and achieves highly efficient phosphorus-nitrogen synergistic flame retardancy. This results in a polypropylene foam material with excellent high impact resistance, highly efficient flame retardancy, and also exhibits good molding stability and excellent mechanical structural integrity.

[0065] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-impact, flame-retardant polypropylene foam material, characterized in that, It includes the following components in parts by weight: 70-85 parts modified polypropylene resin, 10-15 parts ethylene / octene copolymer, 3-8 parts chemical foaming agent, 0.5-2 parts nucleating agent, 0.3-1 parts antioxidant and 0.5-2 parts lubricant; The modified polypropylene resin is a maleic anhydride-grafted polypropylene resin with a surface containing phosphorus-containing heterocyclic structures and triazine ring structures.

2. The high impact-resistant flame-retardant polypropylene foam material according to claim 1, characterized in that, The preparation steps of the modified polypropylene resin are as follows: S1-1 Under nitrogen protection, maleic anhydride-grafted polypropylene resin was added to a solvent and mixed. A DMF solution of 6-aminohexanol was added to initiate a ring-opening reaction. After post-treatment, PP-g-OH was obtained. S2-1 Under nitrogen protection, the PP-g-OH obtained in step S1-1 was added to DMF and mixed. Under ice bath, a premixed solution of 2-bromoisobutyryl bromide and triethylamine was added to carry out an esterification reaction. After post-treatment, PP-g-Br was obtained. S3-1. Under nitrogen protection, 2,4-dichloro-1,3,5-triazine was dissolved in a solvent, and KI was added to form a triazine solution. DOPO and triethylamine were dissolved in a solvent and added to the triazine solution under ice bath conditions to react. GMA was dissolved in a solvent, and sodium hydride was added to react and form a sodium alkoxide solution of GMA, which was then added to the reaction solution to react. After post-treatment, DOPO-triazine-GMA was obtained. S4-1 Under nitrogen protection, PP-g-Br, butyl methacrylate, copper catalyst, and ligand obtained in step S2-1 are added to a solvent, and DOPO-triazine-GMA obtained in step S3-1 is added and mixed before polymerization. The modified polypropylene resin is then obtained after post-treatment.

3. The high impact-resistant flame-retardant polypropylene foam material according to claim 1, characterized in that, The chemical foaming agent is selected from one or two of azodicarbonamide and sodium bicarbonate.

4. The high impact-resistant flame-retardant polypropylene foam material according to claim 3, characterized in that, The chemical foaming agent includes azodicarbonamide and sodium bicarbonate, wherein the mass ratio of azodicarbonamide to sodium bicarbonate is (2.5-3.5):

1.

5. The high impact-resistant flame-retardant polypropylene foam material according to claim 1, characterized in that, The nucleating agent includes talc and organic nucleating agents.

6. The high impact-resistant flame-retardant polypropylene foam material according to claim 5, characterized in that, The mass ratio of talc to organic nucleating agent is 1:(0.5-1).

7. The high impact-resistant flame-retardant polypropylene foam material according to claim 6, characterized in that, The organic nucleating agent is selected from one of dibenzyl sorbitol or a dibenzyl sorbitol derivative.

8. The high impact-resistant flame-retardant polypropylene foam material according to claim 1, characterized in that, The antioxidants include hindered phenolic oxidant 1010 and phosphite oxidant 168, wherein the mass ratio of hindered phenolic oxidant 1010 to phosphite oxidant 168 is 1:(1-2).

9. The high impact-resistant flame-retardant polypropylene foam material according to claim 1, characterized in that, The lubricant comprises calcium stearate and polyethylene wax, wherein the mass ratio of calcium stearate to polyethylene wax is (1-2):

1.

10. A method for preparing a high-impact flame-retardant polypropylene foam material according to any one of claims 1-9, characterized in that, Includes the following steps: S1-2, Premix: Modified polypropylene resin, ethylene / octene copolymer, nucleating agent, antioxidant, and lubricant are mixed at 60-80℃ to obtain a premix; S2-2, Melt Blending and Extrusion: The premix obtained in step S1-2 is added to the main feed port of a twin-screw extruder, and the chemical foaming agent is added through the side feed port. The mixture is then blended and extruded at a melting temperature of 150-180℃ to obtain an expandable melt. S3-2, Foaming and Molding: The expandable melt obtained in step S2-2 is extruded into a foaming and molding zone heated to 190-210℃ to decompose and foam, and then cooled and shaped to obtain the high impact-resistant flame-retardant polypropylene foam material.