Environment-friendly flame-retardant composite material for pipes and preparation method thereof

Abstract

The application belongs to the technical field of composite materials, and particularly relates to an environment-friendly flame-retardant composite material for pipes and a preparation method thereof. The composite material comprises the following components in parts by weight: 80-100 parts of aliphatic polyamide, 10-15 parts of toughening agent, 20-30 parts of inorganic fiber filler, 8-14 parts of alkyl phosphinic acid salt, 6-10 parts of attapulgite, 2-4 parts of brominated polystyrene, 1-3 parts of coupling agent, 1-3 parts of lubricant, and 1-3 parts of antioxidant. The aliphatic polyamide is used as a base resin, and the alkyl phosphinic acid salt, the attapulgite and the brominated polystyrene are ternary compounded, so that multiple targets of improving flame-retardant efficiency, maintaining mechanical properties and improving processing stability are achieved. Technical defects such as large single flame-retardant additive amount, limited flame-retardant effect and easy precipitation of the alkyl phosphinic acid salt are effectively overcome, so that the composite material achieves a more optimal comprehensive balance in flame retardancy, mechanical strength and use reliability.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to an environmentally friendly flame-retardant composite material for pipes and its preparation method. Background Technology

[0002] Fiber-reinforced composites based on thermoplastics, especially inorganic fiber-reinforced thermoplastics, are a novel type of lightweight material. Their application in engineering components helps achieve energy conservation and emission reduction goals. Inorganic fiber-reinforced thermoplastics can be rapidly processed through injection molding, resulting in high production efficiency and lower unit costs. Furthermore, inorganic fiber-reinforced thermoplastics exhibit good ductility and impact resistance, and the random orientation of the fibers makes them isotropic. Since thermoplastics can be repeatedly processed by heating and melting, fiber-reinforced thermoplastic parts can be repaired through heating, saving time and costs. In addition, manufacturing engineering components with thermoplastics allows components that were originally composed of multiple parts to be integrated into a single unit, reducing component weight and simplifying production lines, thereby improving production efficiency and reducing production costs.

[0003] Fiber-reinforced polyamide composites are thermoplastic composites made by compounding fibers as the reinforcing phase and thermoplastic polyamide resin as the matrix in a specific ratio. The reinforcing fiber not only possesses high strength but also exhibits excellent properties such as chemical corrosion resistance, impact load resistance, high temperature resistance, electrical insulation, and fire resistance. The matrix material, polyamide, has good processability and mechanical properties. Fiber-reinforced polyamide composites, composed of these two materials, not only possess excellent specific strength, specific stiffness, and corrosion resistance but are also inexpensive and have high production efficiency, making them potentially valuable for achieving lightweight engineering devices.

[0004] Existing technologies have extensively studied polyamide composite materials. CN106751784A discloses a high-rigidity, corrosion-resistant nylon alloy pipe material and its preparation method. By weight, it comprises 50-60 parts nylon 6, 20-30 parts modified PPO, 3-6 parts SEBS grafted material, 15-20 parts inorganic reinforcing material, and 1-2 parts additives as raw materials. The high-rigidity, corrosion-resistant nylon alloy material obtained by this selection and combination exhibits good processability and excellent mechanical properties. It boasts high strength, good corrosion resistance, and safe use, meeting the demands of harsh environments and showing broad market application prospects. Pipes made from this material exhibit good high-temperature resistance, high-pressure resistance, and corrosion resistance, making them suitable for mining, oil extraction, and other fields. The material is widely available, environmentally friendly, and performs ideally. However, the aforementioned patent technology does not address improvements in the flame-retardant properties of pipe materials. CN119432066A also discloses a high-strength flame-retardant composite material for pipes and its preparation method. The high-strength flame-retardant composite material for this pipeline comprises the following components by weight: 70-80 parts PA12T, 10-15 parts toughening agent, 20-30 parts fiber-reinforced filler, 8-16 parts melamine polyphosphate, 1-6 parts attapulgite, 2-4 parts graphene, 0-3 parts coupling agent, 0-3 parts lubricant, and 0-3 parts antioxidant. While the aforementioned patented technology improves the flame-retardant properties of polyamide to some extent, it uses aromatic nylon as the matrix resin, resulting in poor processing performance. In particular, it employs melamine polyphosphate flame retardant, which has a certain degree of toxicity and does not meet environmental protection requirements. Furthermore, melamine polyphosphate flame retardant is highly hygroscopic and easily hydrolyzed; with long-term use, its insulation resistance and tracking index decrease significantly, making it unsuitable for humid, outdoor, and high-voltage electrical environments. Summary of the Invention

[0005] The purpose of this invention is to prepare an environmentally friendly flame-retardant composite material for pipes. It uses a non-nitrogen-containing flame retardant, which overcomes the technical problems of low mechanical strength and poor flame retardancy of polyamide. It has a smooth surface and is suitable for use as a pipe material.

[0006] The objective of this invention is achieved through the following technical solution: An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: 80-100 parts aliphatic polyamide, 10-15 parts toughening agent, 20-30 parts inorganic fiber filler, 8-14 parts alkyl phosphonates, 6-10 parts attapulgite, 2-4 parts brominated polystyrene, 1-3 parts coupling agent, 1-3 parts lubricant, and 1-3 parts antioxidant.

[0007] This invention uses aliphatic polyamide as the matrix resin, relying on its excellent mechanical strength, wear resistance and processing fluidity to provide basic structural support and molding adaptability for composite materials. Inorganic fibers are used as reinforcing fillers, which can significantly improve the tensile strength, flexural modulus and heat distortion temperature of polyamide, make up for the deficiencies of aliphatic polyamide in rigidity, dimensional stability and high temperature load-bearing capacity, and provide skeletal support for the overall improvement of mechanical properties.

[0008] Meanwhile, this invention abandons the traditional melamine polyphosphate flame retardant and uses alkyl phosphinate as the core flame retardant component. With its excellent compatibility, high thermal stability and efficient gas phase flame retardant effect in the polyamide system, it can quickly capture combustion free radicals and inhibit flame spread. At the same time, it promotes the formation of a stable char layer in the matrix during combustion, achieving a high flame retardant level with low addition amount.

[0009] Attapulgite acts as an inorganic synergist, working synergistically with alkyl phosphinates to further strengthen the char layer structure during combustion, improving its density and high-temperature resistance, and reducing dripping. It also complements inorganic fibers, mitigating potential strength reduction and insufficient toughness after flame retardant addition, while lowering system costs and improving thermal and processing stability. Brominated polystyrene, as an organic polymer flame retardant, enhances flame retardant efficiency through both gas and condensed phase pathways, compensating for the performance limitations of single halogen-free flame retardants in high-flame-retardant applications, particularly in improving the limiting oxygen index and shortening flame retardant time. Furthermore, as a polymeric flame retardant, brominated polystyrene improves the compatibility of alkyl phosphinate flame retardants with polyamides, enhancing their dispersion properties. These three flame-retardant components effectively reduce the total amount of a single flame retardant while meeting high flame retardant requirements, minimizing the weakening effect of high additions on the polyamide matrix and inorganic fiber reinforcement, and avoiding problems such as poor interfacial bonding and significant mechanical property degradation caused by excessive flame retardant.

[0010] In one embodiment, the aliphatic polyamide is at least one of polyamide 6, polyamide 66, and polyamide 56. Using short-chain aliphatic polyamides can balance reinforcement and processing performance, and better promote the dispersion of fillers in the matrix resin.

[0011] In one embodiment, the toughening agent is at least one of maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, maleic anhydride-grafted ethylene-octene copolymer, maleic anhydride-grafted ethylene propylene diene monomer (EPDM) rubber, maleic anhydride-grafted polyphenylene ether, and maleic anhydride-grafted polystyrene.

[0012] In one embodiment, the inorganic fiber filler is at least one of glass fiber and carbon fiber. Specifically, glass fiber may be selected. Further, alkali-free glass fiber may be used as the reinforcing filler.

[0013] In one embodiment, the alkylphosphinate is aluminum diethylphosphinate.

[0014] It is worth mentioning that although alkyl phosphinates have good flame retardant effects, they are prone to migration and precipitation during high-temperature processing, which not only affects surface quality but also leads to a decrease in the mechanical properties of the product due to uneven dispersion. Attapulgite, on the other hand, has a unique rod-shaped crystal structure and high specific surface area, and its porous structure also endows it with excellent adsorption properties. It can form a physical barrier and network anchoring effect in the system, effectively binding alkyl phosphinate molecules, reducing their migration and precipitation to the surface, while improving the density of the char layer, enhancing the synergistic effect of flame retardancy and improving heat resistance. Brominated polystyrene, with its highly efficient gas-phase flame retardant effect, improves the overall flame retardant level, reduces dependence on alkyl phosphinates, further reduces the precipitation risk caused by their addition, and maintains good compatibility with polyamides and inorganic fibers, avoiding a significant decrease in mechanical properties. The combination of the two creates a significant synergistic effect, which not only enhances the flame retardant mechanism in both the condensed and gas phases, enabling the system to achieve a high flame retardant rating at a lower effective flame retardant concentration, but also inhibits the precipitation of alkyl phosphinates from both physical anchoring and chemical compatibility aspects, significantly improving processing stability and effectively solving the technical problem of easy precipitation when alkyl phosphinates are used alone.

[0015] In one embodiment, an environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: 85-95 parts aliphatic polyamide, 12-14 parts toughening agent, 23-27 parts inorganic fiber filler, 10-13 parts alkyl phosphinate, 7-9 parts attapulgite, 2-4 parts brominated polystyrene, 1-3 parts coupling agent, 1-3 parts lubricant, and 1-3 parts antioxidant. An appropriate amount of alkyl phosphinate can improve the flame-retardant properties of the composite material while avoiding excessive alkyl phosphinate from negatively impacting the product's mechanical and surface properties. Attapulgite and brominated polystyrene serve as flame-retardant and reinforcing additives. Adjusting their amounts can further improve the composite material's performance. Attapulgite, as an inorganic filler, combines both reinforcing and flame-retardant effects. The type of attapulgite is not particularly limited; any commonly used material in the art is acceptable. Specifically, its size can be 1-20 µm. Specifically, considering dispersion reinforcement and flame retardant effects, the particle size should be 5-15µm. Sizes that are too large or too small are detrimental to the utilization of its structural characteristics, weakening adsorption and reinforcement effects. In particular, excessively small sizes hinder dispersion in the polyamide system, making it impossible to construct an adsorption-reinforced network, resulting in minimal improvement in product performance. Furthermore, combining 7-9 parts of attapulgite with 2-4 parts of brominated polystyrene can better improve the flame retardant and mechanical properties of the composite material, avoiding the processing difficulties caused by excessive attapulgite usage. Overall, this system, while ensuring mechanical properties through inorganic fiber reinforcement, achieves multiple objectives—improved flame retardant efficiency, maintained mechanical properties, and improved processing stability—through the ternary compounding of alkyl phosphine, attapulgite, and brominated polystyrene. This effectively overcomes the technical shortcomings of single flame retardants, such as large addition amounts, limited flame retardant effects, and the easy precipitation of alkyl phosphine, resulting in a better overall balance between flame retardancy, mechanical strength, and reliability in the composite material.

[0016] In one embodiment, the coupling agent is at least one of KH550, KH560, and KH570.

[0017] In one embodiment, the lubricant is at least one of silicone powder, polytetrafluoroethylene, amide wax, talc, calcium stearate, and zinc stearate.

[0018] In one embodiment, the antioxidant is at least one of antioxidant 1024, antioxidant 264, antioxidant 565, antioxidant 168, and antioxidant 1010.

[0019] On the other hand, the present invention also provides a method for preparing an environmentally friendly flame-retardant composite material for pipes, comprising the following steps: (1) Mix aliphatic polyamide, toughening agent, alkyl phosphinate, attapulgite, brominated polystyrene, coupling agent, lubricant and antioxidant evenly to obtain a mixture; (2) The mixture is added to the twin-screw extruder through the main feed port, and the inorganic fiber filler is added to the twin-screw extruder through the side feed port. The mixture is extruded and granulated to obtain the environmentally friendly flame-retardant pipe composite material.

[0020] In one embodiment, the twin-screw extruder has a screw speed of 300-600 r / min and an extrusion temperature of 230-300°C.

[0021] Beneficial effects: This invention uses aliphatic polyamide as the matrix resin, leveraging its excellent mechanical strength, wear resistance, and processing fluidity to provide fundamental structural support and molding adaptability for the composite material. Inorganic fibers, as reinforcing fillers, significantly improve the tensile strength, flexural modulus, and heat distortion temperature of the polyamide, compensating for the deficiencies of aliphatic polyamide in rigidity, dimensional stability, and high-temperature load-bearing capacity, thus providing skeletal support for the overall improvement in mechanical properties. Under the premise of ensuring mechanical properties through inorganic fiber reinforcement, this system achieves multiple objectives—improved flame retardancy efficiency, maintenance of mechanical properties, and improved processing stability—through a ternary compound of alkyl phosphinate, attapulgite, and brominated polystyrene. This effectively overcomes the technical defects of single flame retardants, such as large addition amounts, limited flame retardant effects, and easy precipitation of alkyl phosphinates. The resulting composite material achieves a better overall balance in flame retardancy, mechanical strength, and reliability, making it suitable for use as a material for water supply pipes and other applications. Detailed Implementation

[0022] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] The following examples and comparative methods for preparing environmentally friendly flame-retardant pipe composite materials include the following steps: (1) Mix polyamide 66 (or polyamide 6), toughening agent, aluminum diethylphosphinate, attapulgite, brominated polystyrene, coupling agent, lubricant and antioxidant evenly to obtain a mixture; (2) The mixture is added to the twin-screw extruder through the main feed port, and the glass fiber filler is added to the twin-screw extruder through the side feed port. The mixture is extruded and granulated to obtain an environmentally friendly flame-retardant composite material for pipes. The screw speed of the twin-screw extruder is 400 r / min and the extrusion temperature is 270℃.

[0026] Performance testing: The tensile strength (ISO 527-2), notched impact strength (ISO 179), and flame retardant performance (UL94) of the environmentally friendly flame-retardant composite pipe samples prepared in the following examples and comparative examples were tested respectively, and the surface precipitation of the samples was observed. The surface precipitation was divided into four levels: 1, 2, 3, and 4, with 1 to 4 indicating increasingly severe precipitation. Example 1

[0027] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 80 parts polyamide 66, 10 parts toughening agent (maleic anhydride-grafted polypropylene), 20 parts glass fiber, 8 parts aluminum diethylphosphinate, 9 parts attapulgite with an average size of 5µm, 4 parts brominated polystyrene, 1 part coupling agent KH550, 3 parts lubricant (silicone powder), and 1 part antioxidant 1010. Tests showed that the tensile strength of this composite material is 168MPa, and the notched impact strength is 13.6kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1. Example 2

[0028] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 100 parts polyamide 66, 15 parts maleic anhydride-grafted polyethylene (toughening agent), 30 parts glass fiber, 14 parts aluminum diethylphosphinate, 6 parts attapulgite with an average size of 15 µm, 2 parts brominated polystyrene, 3 parts coupling agent KH550, 1 part polytetrafluoroethylene (PTFE) lubricant, and 3 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 186 MPa, and the notched impact strength is 14.8 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 2. Example 3

[0029] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts maleic anhydride-grafted ethylene-octene copolymer (toughening agent), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 10 parts attapulgite with an average size of 10 µm, 3 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts talc (lubricant), and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 184 MPa, and the notched impact strength is 14.1 kJ / m². 2It has a flame retardant rating of V-0 and a surface grade of 2. Example 4

[0030] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 83 parts polyamide 6, 13 parts maleic anhydride-grafted EPDM rubber (toughening agent), 22 parts glass fiber, 13 parts aluminum diethylphosphinate, 6.5 parts attapulgite with an average size of 7µm, 2.2 parts brominated polystyrene, 1.5 parts coupling agent KH550, 1 part calcium stearate (lubricant), and 1 part antioxidant 1010. Tests showed that the tensile strength of this composite material is 174 MPa, and the notched impact strength is 14.6 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1. Example 5

[0031] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts maleic anhydride-grafted ethylene-octene copolymer (toughening agent), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 8 parts attapulgite with an average size of 5 µm, 3 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts talc (lubricant), and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 180 MPa, and the notched impact strength is 14.7 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 2. Example 6

[0032] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 86 parts polyamide 6, 12 parts maleic anhydride-grafted polypropylene toughening agent, 23 parts glass fiber, 9 parts aluminum diethylphosphinate, 7 parts attapulgite with an average size of 12µm, 2.5 parts brominated polystyrene, 2 parts coupling agent KH550, 1 part zinc stearate lubricant, and 1.5 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 169MPa, and the notched impact strength is 13.8kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1. Example 7

[0033] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts maleic anhydride-grafted ethylene-octene copolymer (toughening agent), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 8 parts attapulgite with an average size of 15 µm, 3 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts talc (lubricant), and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 173 MPa, and the notched impact strength is 13.9 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 2. Example 8

[0034] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 95 parts polyamide 6, 14 parts toughening agent (maleic anhydride-grafted ethylene-octene copolymer), 27 parts glass fiber, 11 parts aluminum diethylphosphinate, 8.5 parts attapulgite with an average size of 7µm, 3.5 parts brominated polystyrene, 2.5 parts coupling agent KH550, 1.5 parts lubricant silicone powder, and 1.6 parts antioxidant 1010. The tensile strength of this composite material is 172MPa, and the notched impact strength is 15.0kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1. Example 9

[0035] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 92 parts polyamide 66, 13 parts maleic anhydride-grafted polyethylene (toughening agent), 26 parts glass fiber, 10.5 parts aluminum diethylphosphinate, 7.5 parts attapulgite with an average size of 12 µm, 3.2 parts brominated polystyrene, 1.7 parts coupling agent KH550, 2.2 parts polytetrafluoroethylene (PTFE) lubricant, and 2.5 parts antioxidant 1010. Tests showed that the composite material has a tensile strength of 177 MPa and a notched impact strength of 14.4 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1. Example 10

[0036] An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts toughening agent (maleic anhydride-grafted ethylene-octene copolymer), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 8 parts attapulgite with an average size of 10 µm, 3 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts lubricant talc, and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 183 MPa, and the notched impact strength is 15.2 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 1.

[0037] Comparative Example 1 An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts toughening agent (maleic anhydride-grafted ethylene-octene copolymer), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 0 parts attapulgite with an average size of 10µm, 11 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts lubricant talc, and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 151MPa, and the notched impact strength is 10.3kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 4.

[0038] Comparative Example 2 An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts toughening agent (maleic anhydride-grafted ethylene-octene copolymer), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 11 parts attapulgite with an average size of 10 µm, 0 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts lubricant talc, and 2 parts antioxidant 1010. Tests showed that the composite material has a tensile strength of 171 MPa and a notched impact strength of 12.6 kJ / m². 2 It has a flame retardant rating of V-1 and a surface grade of 2.

[0039] Comparative Example 3 An environmentally friendly flame-retardant composite material for pipes comprises the following components in parts by weight: The composite material consists of 90 parts polyamide 66, 13 parts maleic anhydride-grafted ethylene-octene copolymer (toughening agent), 25 parts glass fiber, 12 parts aluminum diethylphosphinate, 8 parts attapulgite with an average size of 10 µm, 7 parts brominated polystyrene, 2 parts coupling agent KH550, 2 parts talc (lubricant), and 2 parts antioxidant 1010. Tests showed that the tensile strength of this composite material is 168 MPa, and the notched impact strength is 12.1 kJ / m². 2 It has a flame retardant rating of V-0 and a surface grade of 3.

[0040] As can be seen from the above examples and comparative examples, this invention abandons the traditional melamine polyphosphate flame retardant and uses alkyl phosphinate as the core flame retardant component. Leveraging its excellent compatibility, high thermal stability, and efficient gas-phase flame retardant effect in the polyamide system, it can quickly capture combustion free radicals and inhibit flame spread. Simultaneously, it promotes the formation of a stable char layer in the matrix during combustion, achieving a high flame retardant rating with low addition amounts. Attapulgite acts as an inorganic synergist, forming a synergistic effect with alkyl phosphinate, further strengthening the char layer structure during combustion, improving the density and high-temperature resistance of the char layer, and reducing dripping. Furthermore, it can form a complementary reinforcing effect with inorganic fibers, improving problems such as decreased strength and insufficient toughness that may occur after adding flame retardants, while reducing system costs and improving the system's thermal and processing stability. Brominated polystyrene, as an organic polymer flame retardant, can improve flame retardant efficiency through both gas-phase and condensed-phase pathways, compensating for the performance shortcomings of single halogen-free flame retardants in high-flame-retardant application scenarios. Furthermore, brominated polystyrene, as a polymeric flame retardant, can improve the compatibility of alkyl phosphinate flame retardants with polyamides and enhance their dispersion properties. These three flame-retardant components can effectively reduce the total amount of a single flame retardant while meeting high flame retardant ratings, minimizing the weakening effect of high addition levels on the polyamide matrix and inorganic fiber reinforcement, and avoiding problems such as poor interfacial bonding and significant degradation of mechanical properties caused by excessive flame retardant.

[0041] Specifically, compared to Example 10, Comparative Examples 1 and 2 lacked attapulgite and brominated polystyrene, respectively, resulting in decreased impact toughness and surface properties. This is because although alkyl phosphinates have good flame retardant effects, they are prone to migration and precipitation during high-temperature processing, which not only affects surface quality but also hinders the improvement of flame retardancy and mechanical properties due to uneven dispersion. Attapulgite, with its unique rod-shaped structure and high specific surface area, can form physical barriers and network anchoring effects in the system, effectively binding alkyl phosphinate molecules, reducing their migration and precipitation to the surface, while improving the density of the char layer, enhancing the synergistic flame retardant effect, and improving heat resistance. Brominated polystyrene, on the other hand, improves the overall flame retardant level with its efficient gas-phase flame retardant effect, reduces dependence on alkyl phosphinates, further reduces the precipitation risk caused by their addition, and maintains good compatibility with polyamides and inorganic fibers, avoiding a significant decrease in mechanical properties. The combination of the two creates a significant synergistic effect, which not only enhances the flame retardant mechanism in both the condensed and gas phases, enabling the system to achieve a high flame retardant rating at a lower effective flame retardant concentration, but also inhibits the precipitation of alkyl phosphinates from both physical anchoring and chemical compatibility aspects, significantly improving processing stability. Based on solving the problem of easy precipitation of alkyl phosphinates, it further improves their mechanical properties.

[0042] Compared to Example 10, Comparative Example 3 used excessive amounts of brominated polystyrene. Although this had little impact on its flame retardant effect, its mechanical and surface properties were significantly reduced. This is because brominated polystyrene, as an organic flame retardant, mainly relies on gas-phase flame retardancy to improve its flame retardant efficiency; it does not possess the functions of physical anchoring, interface reinforcement, or inhibition of small molecule migration. When the amount of brominated polystyrene is excessively increased, on the one hand, it will significantly increase the proportion of organic flame retardant components in the system. These large-molecule organic flame retardants will weaken the interaction forces between polyamide molecular chains and reduce the interfacial bonding strength between the matrix and glass fiber and attapulgite, resulting in a significant deterioration in the tensile and impact properties of the composite material. On the other hand, excessive brominated polystyrene will increase the free volume of the system during melt processing, providing more migration channels for alkyl phosphinate molecules, weakening the original anchoring and blocking effect of attapulgite, making it easier for alkyl phosphinates to diffuse, accumulate, and precipitate to the material surface, thereby affecting the appearance and long-term reliability of the product. Therefore, the amount of brominated polystyrene added in this compound system needs to be controlled within a reasonable range and cannot be increased excessively. Otherwise, it will not only fail to further improve the flame retardant effect, but also damage the original mechanical properties and processing stability of the system and aggravate the precipitation problem of alkylphosphinates.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An environmentally friendly flame-retardant composite material for pipes, characterized in that, The product comprises the following components in parts by weight: 80-100 parts aliphatic polyamide, 10-15 parts toughening agent, 20-30 parts inorganic fiber filler, 8-14 parts alkyl phosphonate, 7-9 parts attapulgite, 2-4 parts brominated polystyrene, 1-3 parts coupling agent, 1-3 parts lubricant, and 1-3 parts antioxidant; wherein the aliphatic polyamide is at least one of polyamide 6, polyamide 66, and polyamide 56; and the inorganic fiber filler is glass fiber.

2. The environmentally friendly flame-retardant composite material for pipes as described in claim 1, characterized in that, The toughening agent is at least one of maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, maleic anhydride-grafted ethylene-octene copolymer, maleic anhydride-grafted ethylene propylene diene monomer (EPDM) rubber, maleic anhydride-grafted polyphenylene ether, and maleic anhydride-grafted polystyrene.

3. The environmentally friendly flame-retardant composite material for pipes as described in claim 1, characterized in that, The alkylphosphinate is aluminum diethylphosphinate.

4. The environmentally friendly flame-retardant composite material for pipes as described in claim 1, characterized in that, The coupling agent is at least one of KH550, KH560, and KH570.

5. The environmentally friendly flame-retardant composite material for pipes as described in claim 1, characterized in that, The lubricant is at least one of silicone powder, polytetrafluoroethylene, amide wax, talc, calcium stearate, and zinc stearate.

6. The environmentally friendly flame-retardant composite material for pipes as described in claim 1, characterized in that, The antioxidant is at least one of antioxidant 1024, antioxidant 264, antioxidant 565, antioxidant 168, and antioxidant 1010.

7. A method for preparing an environmentally friendly flame-retardant composite material for pipes according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Mix aliphatic polyamide, toughening agent, alkyl phosphinate, attapulgite, brominated polystyrene, coupling agent, lubricant and antioxidant evenly to obtain a mixture; (2) The mixture is added to the twin-screw extruder through the main feed port, and the inorganic fiber filler is added to the twin-screw extruder through the side feed port. The mixture is extruded and granulated to obtain the environmentally friendly flame-retardant pipe composite material.

8. The method for preparing an environmentally friendly flame-retardant composite material for pipes according to claim 7, characterized in that, The twin-screw extruder has a screw speed of 300-600 r / min and an extrusion temperature of 230-300℃.