Flame-retardant plastic for electric tricycles and its preparation method

Abstract

This application relates to the field of polymer modified materials technology, and discloses a flame-retardant plastic for electric tricycles and its preparation method. The flame-retardant plastic is made from copolymer polypropylene, polyolefin elastomer, maleic anhydride-grafted polypropylene, interfacial reactant, first-stage catalyst, piperazine pyrophosphate, aluminum hypophosphite, interfacial flexible end-capping agent, second-stage catalyst, antioxidant, and lubricant. The preparation method involves: premixing the resin base material and feeding it into a co-rotating twin-screw extruder; injecting the interfacial reactant and catalyst for in-situ grafting; then laterally feeding in flame-retardant powder; injecting the end-capping agent system and subjecting the extruder barrel section to reverse step cooling treatment; and finally, venting and pelletizing. This invention improves the mechanical properties of the material while maintaining the flame-retardant rating by constructing chemical bonds between the resin and the flame-retardant powder and forming a hydrophobic flexible coating layer around the powder. Simultaneously, it reduces the hygroscopic tendency of the flame retardant, which is beneficial for improving the long-term stability of the material.

Description

Technical Field

[0001] This invention relates to the field of polymer modified materials technology, specifically to a flame-retardant plastic for electric tricycles and its preparation method. Background Technology

[0002] With the widespread use of electric tricycles in short-distance logistics and daily commuting, the requirements for their overall safety performance have also increased. The battery casing, water flaps, and body panels of electric tricycles are mostly made of plastics such as polypropylene. Because polypropylene is inherently flammable, it poses a fire risk in the event of an electrical short circuit or battery thermal runaway. Therefore, it typically requires flame-retardant modification during the production process.

[0003] Currently, the industry commonly uses the addition of phosphorus-containing flame retardants or inorganic flame-retardant powders to improve the flame retardancy rating of polypropylene products. To meet flame retardancy standards, a relatively large proportion of polar flame retardant powder is usually added to the resin matrix. However, these polar powders have poor compatibility with non-polar polypropylene polymer segments, and the powder particles are prone to agglomeration during melt blending. This agglomeration can disrupt the integrity of the polymer continuous phase. When plastic parts are subjected to external impact, the agglomeration points are prone to local stress concentration, leading to a decrease in the mechanical impact strength and elongation at break of the modified material. Furthermore, commonly used phosphorus- and nitrogen-containing flame retardants generally possess certain hydrophilic and hygroscopic properties. Electric tricycles often face high humidity outdoor environments and rainy / snowy weather during actual service. Due to the lack of effective physical or chemical barriers, the flame retardants inside the material easily absorb moisture from the environment, causing the flame retardant particles to swell or even precipitate onto the surface of the plastic parts. This will not only further weaken the original mechanical strength of the material, but also cause the surface of the product to turn white and the flame retardant efficiency to decrease, making it difficult to maintain the stability and service life of vehicle plastic parts under long-term complex working conditions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a flame-retardant plastic for electric tricycles and its preparation method, which solves the problem that when a large amount of inorganic and phosphorus-containing flame retardants are added to existing flame-retardant plastics, the flame retardant powder tends to agglomerate in the resin matrix, often leading to a decrease in the mechanical properties of the material.

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a flame-retardant plastic for an electric tricycle, employing the following technical solution:

[0007] A flame-retardant plastic for an electric tricycle is made from raw materials comprising the following parts by weight:

[0008] 60.0–70.0 parts of copolymerized polypropylene;

[0009] 8.0–12.0 parts of polyolefin elastomer;

[0010] 3.0–5.0 parts of maleic anhydride-grafted polypropylene;

[0011] 0.5–1.0 parts of interfacial reactant;

[0012] 0.05–0.10 parts of the first-stage catalyst;

[0013] Piperazine pyrophosphate, 12.0–15.0 parts;

[0014] 4.0–6.0 parts of aluminum hypophosphite;

[0015] 0.5–1.0 parts of a flexible interface capping agent;

[0016] Secondary catalyst: 0.02–0.05 parts;

[0017] Antioxidant 0.2–0.4 parts;

[0018] Lubricant 0.2-0.3 parts;

[0019] The flame-retardant plastic is prepared by first mixing the copolymer polypropylene, polyolefin elastomer, and maleic anhydride-grafted polypropylene with the interfacial reactant, and then using a first-stage catalyst to catalyze the ring-opening esterification grafting reaction between the interfacial reactant and the maleic anhydride-grafted polypropylene; subsequently, piperazine pyrophosphate and aluminum hypophosphite are mixed in; finally, the interfacial flexible end-capping agent is added, and a second-stage catalyst is used to promote the de-alcoholization polycondensation crosslinking reaction between the interfacial flexible end-capping agent and the active groups in the previous system, thereby generating a flexible polymer coating network around the particles of piperazine pyrophosphate and aluminum hypophosphite.

[0020] By adopting the above technical solution, the system of the present invention mainly undergoes a multi-stage in-situ interfacial reaction process during the mixing and processing stage. Specifically, the epoxy groups in the interfacial reactant structure and the maleic anhydride groups on the maleic anhydride-grafted polypropylene molecular chains undergo a ring-opening esterification reaction under the catalysis of the first-stage catalyst. The main purpose of this process is to graft silane molecular chain segments carrying alkoxy groups onto the polypropylene polymer backbone. With the continuous advancement of melt blending, the alkoxy-grafted polypropylene segments come into full contact with the dispersed piperazine pyrophosphate and aluminum hypophosphite particles in the system. The silane end groups react with the active groups on the powder surface and form chemical bonds, thereby initially constructing the interface between the polymer resin phase and the inorganic phase of the flame retardant. Subsequently, with the participation of the second-stage catalyst, the terminal hydroxyl groups carried by the interfacial flexible end-capping agent undergo an in-situ de-alcoholization condensation reaction with the residual alkoxy groups at the powder interface, thereby crosslinking and generating a polydimethylsiloxane network on the outer layer of the flame retardant particles. Because polydimethylsiloxane molecules have certain hydrophobic properties, the coating layer formed by this network structure on the powder surface helps to prevent environmental moisture from penetrating into the flame retardant phase, which can reduce the tendency of the material to absorb moisture and exude in humid environments to a certain extent. At the same time, because the coating layer has relatively flexible polymer structure characteristics and retains a certain degree of freedom of chain segment movement, it can play a certain buffering role when subjected to external impact, which helps to alleviate the stress concentration phenomenon at the rigid particle interface, and thus helps to improve the elongation at break and impact resistance of the high-filling system.

[0021] Preferably, the interfacial reactant is γ-glycidoxypropyltrimethoxysilane, the first-stage catalyst is N,N-dimethylbenzylamine, the interfacial flexible end-capping agent is hydroxyl-terminated polydimethylsiloxane, and the second-stage catalyst is dibutyltin dilaurate.

[0022] By employing the above technical solution, γ-glycidoxypropyltrimethoxysilane possesses suitable ring-opening reactivity. Combined with N,N-dimethylbenzylamine, it can reduce the activation energy of the esterification reaction to a certain extent, which is beneficial for achieving the required grafting rate within a shorter residence time in the front section of the extruder. The hydroxyl-terminated polydimethylsiloxane molecular chain has good flexibility and, under the catalysis of dibutyltin dilaurate, can generally undergo good dealcoholization polycondensation with the siloxane groups on the powder surface. This combination ratio provides an effective interfacial crosslinking density while helping to reduce the risk of localized gelation of the matrix caused by excessive self-polymerization of free silanes.

[0023] Preferably, the antioxidant is a mixture of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite; the lubricant is calcium stearate.

[0024] By adopting the above technical solution, the combination of phenolic primary antioxidant and phosphite secondary antioxidant can synergistically capture free radicals generated during the melt blending stage and decompose hydrogen peroxide, which is beneficial to delaying the thermo-oxidative degradation process of the polymer matrix; calcium stearate helps to improve the processing fluidity of polymer melt, and can also absorb trace amounts of acidic byproducts in the system to a certain extent.

[0025] Preferably, the copolymer polypropylene is a block copolymer polypropylene with a melt flow rate of 10g / 10min to 15g / 10min at 230℃ and 2.16kg; the polyolefin elastomer is an ethylene-octene copolymer; and the maleic anhydride grafting rate of the maleic anhydride grafted polypropylene is 0.8wt% to 1.2wt%.

[0026] By adopting the above technical solutions, block copolymer polypropylene with a melt flow rate in the range of 10 g / 10 min to 15 g / 10 min provides basic mechanical strength while better adapting to the shear dispersion requirements in a twin-screw extruder; the ethylene-octene copolymer, as an elastic phase, can, to a certain extent, synergistically enhance the low-temperature toughness of the material with the silane flexible coating layer; and maleic anhydride-grafted polypropylene with a grafting rate of 0.8 wt% to 1.2 wt% provides corresponding reactive sites, which is beneficial to maintaining the conversion base for subsequent interfacial reactions.

[0027] Preferably, the flame-retardant plastic is produced by extrusion granulation using a co-rotating twin-screw extruder, and the flame-retardant plastic is in the form of cylindrical granules with a length of 3.0 mm.

[0028] By adopting the above technical solutions, the forced shear flow field of the co-rotating twin-screw extruder helps to promote the uniform distribution of the multiphase system, and the cylindrical granules of limited size help to maintain the continuity of material feeding and plasticization consistency in the subsequent injection molding process.

[0029] Secondly, the present invention provides a method for preparing flame-retardant plastics for electric tricycles, employing the following technical solution:

[0030] A method for preparing flame-retardant plastic for electric tricycles includes the following steps:

[0031] S1. Material premixing and feeding: Copolymer polypropylene, polyolefin elastomer, maleic anhydride grafted polypropylene, antioxidant and lubricant are premixed and continuously fed into the co-rotating twin-screw extruder.

[0032] S2, Front-end in-situ grafting: In the material feeding section of the co-rotating twin-screw extruder, a first mixture consisting of an interfacial reactant and a first-stage catalyst is continuously injected;

[0033] S3, Flame retardant intervention: In the barrel section after the first mixture is injected, premixed piperazine pyrophosphate and aluminum hypophosphite are forcibly fed laterally into the melt inside the extruder;

[0034] S4. Rear flexible end capping and reverse cooling: In the reaction section after the flame retardant is fed in, a second mixture consisting of an interface flexible end capping agent and a second-stage catalyst is injected, and at the same time, the barrel in which the reaction section is located is subjected to reverse step cooling treatment.

[0035] S5 Extrusion, Cooling and Pelletizing: The mixture is pushed backward, and after exhausting and removing by-products, it is extruded, cooled and pelletized to obtain the flame-retardant plastic for electric tricycles.

[0036] By adopting the above technical solution, the reaction steps are sequentially planned in the longitudinal space of the extruder, allowing the grafting of silane macromolecules onto the resin matrix to be completed in the front section. This reduces the steric hindrance caused by the large amount of solid powder hindering the expansion of polymer molecular chains. Subsequently, the powder is fed laterally in the middle section, which not only reduces the mechanical wear of hard particles on the screw feeding section but also utilizes the dispersing force provided by the melt itself. When the material enters the rear section, a reverse step cooling is implemented simultaneously with the injection of the end-capping agent. The increase in melt viscous resistance caused by the local temperature drop in the barrel increases the shear work of the screw elements on the material. This combination of physical shearing and chemical reaction is beneficial for guiding the de-alcoholization polycondensation reaction to occur directionally on the powder surface, thereby promoting the formation of in-situ coating structures.

[0037] Preferably, in step S2, the first mixture is prepared by adding the first-stage catalyst to the interfacial reactant at 20℃~25℃ and stirring at 150rpm~250rpm for 10 to 15 minutes; in step S4, the second mixture is prepared by adding the second-stage catalyst to the interfacial flexible end-capping agent at 20℃~25℃ and stirring at 150rpm~250rpm for 10 to 15 minutes. The stirring speed can preferably be 200rpm.

[0038] By adopting the above technical solution, the main agent and trace catalyst are mechanically pre-dispersed at room temperature within a specified rotation speed range, which helps the catalyst to be homogeneously distributed in the reaction solution, reduces the local concentration difference that may be generated by directly adding trace amounts of liquid to the polymer melt, and helps maintain the stability of the reaction system.

[0039] Preferably, the co-rotating twin-screw extruder has 10 independent temperature control zones; S1 is the main feeder in zone 1; S2 is the first mixture injected in zone 3 by a liquid metering pump; S3 is the piperazine pyrophosphate and aluminum hypophosphite pressed in zone 5 by a side feeder; S4 is the second mixture injected in zone 6 by a liquid metering pump, and the specific areas for the reverse step cooling treatment are zones 6 and 7, and the screw assembly in these two zones is equipped with three sets of kneading blocks with staggered angles of 45° and 90°.

[0040] By adopting the above technical solution, zones 3 to 5 are reserved for corresponding barrel sections for the ring-opening esterification grafting reaction; in addition, kneading blocks with 45° and 90° staggered are configured in zones 6 and 7, which are mainly used to provide transverse and longitudinal tensile shear fields during the pressure building stage. In conjunction with the polymer melt, the agglomerated powder particles can be better peeled off, thereby promoting the relatively uniform coating of the newly injected end-capping mixture on the powder surface.

[0041] Preferably, in S4, the reverse step cooling process is as follows: the barrel cooling water circulation system of Zone 6 and Zone 7 is forcibly opened to dynamically maintain the barrel temperature of Zone 6 and Zone 7 at 180℃~190℃.

[0042] By adopting the above technical solution, when the material enters the 6th and 7th zones from the higher initial temperature, forced cooling water circulation lowers the local ambient temperature to 180℃~190℃. The decrease in temperature leads to an increase in the shear viscosity of the mixed melt, which to some extent enhances the mechanical dispersion efficiency of the kneaded blocks. Simultaneously, this cooling environment is also conducive to the release of subsequent trace reaction byproducts.

[0043] Preferably, the barrel temperatures of the remaining zones of the co-rotating twin-screw extruder are set sequentially as follows: Zone 1: 175℃~185℃, Zone 2: 180℃~190℃, Zones 3 to 5: 195℃~205℃, Zone 8: 195℃~205℃, Zone 9: 200℃~210℃, and Zone 10: 205℃~215℃. In S5, the vacuum exhaust system is activated in Zone 9 to maintain the system vacuum at -0.08MPa~-0.09MPa. The extruded material is then cooled and shaped in a 20℃~30℃ water bath and dried by a high-pressure air knife before being pelletized by a traction pelletizer.

[0044] By adopting the above technical solution, after undergoing mid-stage cooling and high-shear treatment, the temperature in zones 8 to 10 gradually rises to the range of 205℃ to 215℃, mainly to maintain the rheological smoothness of the polymer at the end of the flow channel; zone 9 maintains a negative pressure state of -0.08MPa to -0.09MPa to remove trace amounts of volatile substances such as alcohols generated by the polycondensation reaction, which helps to reduce the probability of micropores in the final granules; and water cooling at 20℃ to 30℃ is conducive to stable extrusion molding and maintains the morphological regularity of continuous pellet cutting to a certain extent.

[0045] This invention provides a flame-retardant plastic for electric tricycles and a method for preparing the same. It offers the following advantages:

[0046] 1. This invention establishes a chemical bond between a polypropylene resin matrix and flame-retardant powders such as piperazine pyrophosphate and aluminum hypophosphite through the compounding of an interfacial reactant, a flexible interfacial end-capping agent, and a matching catalyst. The flexible polydimethylsiloxane network generated on the powder surface by in-situ polycondensation effectively buffers the stress concentration caused by rigid particles on the polymer chain segments, thereby mitigating the negative impact of high-filling-content inorganic powders on the material's mechanical properties while maintaining the system's flame-retardant performance.

[0047] 2. This invention uses hydroxyl-terminated polydimethylsiloxane to construct the interface end-capping layer, giving the outer side of the flame retardant particles hydrophobic characteristics. This coating structure reduces the channel area for phosphorus-containing flame retardant components to contact environmental moisture, inhibiting their moisture absorption and swelling under humid conditions, and also significantly improving the long-term physicochemical stability of flame-retardant plastic products in complex environments.

[0048] 3. The preparation method of this invention optimizes the extrusion process by combining spatial segment planning with reverse step cooling. Specifically, in the barrel section after the flame retardant powder and end-capping agent are mixed, the temperature is forcibly lowered to 180℃~190℃. The increased melt viscosity caused by the temperature drop, combined with the mechanical action of the screw kneading block, applies greater shear stress. This process step helps to peel off agglomerated powder particles and promotes effective interfacial reactions on the powder surface, which is beneficial to improving the internal uniformity and molding quality of the final plastic granules. Attached Figure Description

[0049] Figure 1 Fourier transform infrared spectra of composite material samples after Soxhlet extraction in Examples 1, 2, and 3 of the present invention;

[0050] Figure 2 This is a time-scan rheological curve showing the evolution of the complex viscosity of polymer melts over time in Example 1 and Comparative Example 4 of the present invention.

[0051] Figure 3 Figure 1 shows a comparison of the extrusion process stability of Examples 1 and 5 of the present invention with that of Comparative Example 6. Figure 2(a) shows the change of the torque load rate of the main motor of the extruder with running time, and Figure 3(b) shows the change of the vacuum degree of the vacuum exhaust port in Zone 9 with running time. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0054] The copolymer polypropylene is a heterogeneous block copolymer polypropylene with an ethylene mass fraction of 8wt% to 12wt% and a melt flow rate of 10g / 10min to 15g / 10min (test conditions of 230℃ / 2.16kg). The CAS number is 9010-79-1.

[0055] The polyolefin elastomer is an ethylene-octene copolymer with an octene comonomer mass fraction of 20wt% to 30wt%, a Mooney viscosity (ML(1+4)) of 10 to 20 at 121°C, and a CAS number of 26221-73-8.

[0056] The maleic anhydride grafting rate of the maleic anhydride-grafted polypropylene is 0.8wt% to 1.2wt%, and the melt index is 50g / 10min to 100g / 10min (230℃ / 2.16kg test conditions).

[0057] The average particle size (D50) of piperazine pyrophosphate is 5.0 μm to 10.0 μm, the pH value in a 1 wt% aqueous suspension is 5.0 to 7.0, and the CAS number is 66034-17-1.

[0058] The aluminum hypophosphite has a phosphorus mass fraction greater than or equal to 40 wt%, an average particle size D50 of 10.0 μm to 15.0 μm, and CAS number 7784-22-7.

[0059] The CAS number for γ-glycidyl etheroxypropyltrimethoxysilane is 2530-83-8.

[0060] The kinematic viscosity of hydroxyl-terminated polydimethylsiloxane at 25°C is 500 cSt to 1000 cSt, and its CAS number is 70131-67-8.

[0061] The CAS number for N,N-dimethylbenzylamine is 103-83-3.

[0062] The CAS number for dibutyltin dilaurate is 77-58-7.

[0063] The CAS number for pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 6683-19-8.

[0064] Tris(2,4-di-tert-butylphenyl) phosphite has the CAS number 31570-04-4.

[0065] The CAS number for calcium stearate is 1592-23-0.

[0066] Preparation Example 1:

[0067] This preparation example provides a method for preparing a mixture of interfacial reactant and first-stage catalyst (hereinafter referred to as Solution A) and a mixture of interfacial flexible end-capping agent and second-stage catalyst (hereinafter referred to as Solution B), specifically including the following steps:

[0068] (1) Preparation of solution A: At room temperature (20℃~25℃), add 0.075 kg of N,N-dimethylbenzylamine to 0.75 kg of γ-glycidyl etheroxypropyltrimethoxysilane and stir with a mechanical stirrer at 200 rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution A.

[0069] (2) Preparation of solution B: At room temperature (20℃~25℃), add 0.035kg of dibutyltin dilaurate to 0.75kg of hydroxyl-terminated polydimethylsiloxane, and stir with a mechanical stirrer at 200rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution B.

[0070] Preparation Example 2:

[0071] This preparation example provides a method for preparing a mixture of interfacial reactant and first-stage catalyst (hereinafter referred to as Solution A) and a mixture of interfacial flexible end-capping agent and second-stage catalyst (hereinafter referred to as Solution B), specifically including the following steps:

[0072] (1) Preparation of solution A: At room temperature (20℃~25℃), add 0.05kg of N,N-dimethylbenzylamine to 0.5kg of γ-glycidyl etheroxypropyltrimethoxysilane and stir with a mechanical stirrer at 200rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution A.

[0073] (2) Preparation of solution B: At room temperature (20℃~25℃), add 0.02kg of dibutyltin dilaurate to 0.5kg of hydroxyl-terminated polydimethylsiloxane, and stir with a mechanical stirrer at 200rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution B.

[0074] Preparation Example 3:

[0075] This preparation example provides a method for preparing a mixture of interfacial reactant and first-stage catalyst (hereinafter referred to as Solution A) and a mixture of interfacial flexible end-capping agent and second-stage catalyst (hereinafter referred to as Solution B), specifically including the following steps:

[0076] (1) Preparation of solution A: At room temperature (20℃~25℃), add 0.10 kg of N,N-dimethylbenzylamine to 1.0 kg of γ-glycidyl etheroxypropyltrimethoxysilane and stir with a mechanical stirrer at 200 rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution A.

[0077] (2) Preparation of solution B: At room temperature (20℃~25℃), add 0.05kg of dibutyltin dilaurate to 1.0kg of hydroxyl-terminated polydimethylsiloxane and stir with a mechanical stirrer at 200rpm for 10 to 15 minutes to make the system uniformly mixed to obtain solution B.

[0078] Example 1:

[0079] This embodiment provides a method for preparing flame-retardant plastic for electric tricycles, specifically including the following steps:

[0080] (1) Resin base premixing and main feed: 65.0 kg of copolymer polypropylene, 10.0 kg of polyolefin elastomer, 4.0 kg of maleic anhydride grafted polypropylene, 0.15 kg of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.15 kg of tris(2,4-di-tert-butylphenyl) phosphite, and 0.25 kg of calcium stearate were added to a high-speed mixer and mixed at 400 rpm for 4 minutes. After mixing, the mixture was continuously fed into the first zone of a co-rotating twin-screw extruder through the main feeder. The co-rotating twin-screw extruder has 10 independent temperature control zones, and the screw assembly in zones 6 to 7 is equipped with three sets of kneading blocks with staggered angles of 45° and 90°. The screw speed was set to 350 rpm, the barrel temperature in zone 1 was 180°C, and the barrel temperature in zone 2 was 185°C.

[0081] (2) Injection of Liquid A: When the material is pushed to Zone 3, 0.825 kg of Liquid A prepared in Preparation Example 1 is continuously injected into the barrel through the first set of liquid metering pumps. The barrel temperature in Zones 3 and 4 is set to 200°C.

[0082] (3) Flame retardant side feeding: 13.5 kg piperazine pyrophosphate and 5.0 kg aluminum hypophosphate are premixed and then forced into the melt in zone 5 by a side feeder. The barrel temperature in zone 5 is set to 200℃.

[0083] (4) Injection of liquid B and reverse cooling: When the material is pushed to zone 6, 0.785 kg of liquid B prepared in preparation example 1 is injected into the barrel through the second set of liquid metering pumps. The barrel cooling water circulation system of zone 6 and zone 7 is forcibly turned on, and the barrel temperature of the two zones is set and dynamically maintained at 185°C.

[0084] (5) Extrusion, cooling and pelletizing: Set the barrel temperature of zone 8 to 200℃, zone 9 to 205℃, and zone 10 to 210℃. In zone 9, turn on the vacuum exhaust system and maintain the system vacuum at -0.085MPa. The melt is extruded through a multi-hole die set at 210℃ to form a strip, cooled and shaped in a 25℃ water bath, dried by a high-pressure air knife, and then cut into cylindrical pellets with a length of 3.0mm by a traction pelletizer.

[0085] Example 2:

[0086] This embodiment provides a method for preparing flame-retardant plastic for electric tricycles, specifically including the following steps:

[0087] (1) Resin base premixing and main feed: 60.0 kg of copolymer polypropylene, 8.0 kg of polyolefin elastomer, 3.0 kg of maleic anhydride-grafted polypropylene, 0.1 kg of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.1 kg of tris(2,4-di-tert-butylphenyl) phosphite, and 0.2 kg of calcium stearate were added to a high-speed mixer and mixed at 400 rpm for 4 minutes. After mixing, the mixture was fed into the first zone of a co-rotating twin-screw extruder with the same configuration as in Example 1. The screw speed was set to 350 rpm, the barrel temperature of the first zone was 180°C, and the barrel temperature of the second zone was 185°C.

[0088] (2) Injection of Liquid A: When the material is pushed to Zone 3, 0.55 kg of Liquid A prepared in Preparation Example 2 is continuously injected into the barrel through the first set of liquid metering pumps. The barrel temperature in Zones 3 and 4 is set to 200°C.

[0089] (3) Flame retardant side feeding: 12.0 kg piperazine pyrophosphate and 4.0 kg aluminum hypophosphate are premixed and then forced into the melt in zone 5 by a side feeder. The barrel temperature in zone 5 is set to 200℃.

[0090] (4) Injection of liquid B and reverse cooling: When the material is pushed to zone 6, 0.52 kg of liquid B prepared in preparation example 2 is injected into the barrel through the second set of liquid metering pumps. The barrel cooling water circulation system of zone 6 and zone 7 is forcibly turned on, and the barrel temperature of the two zones is set and dynamically maintained at 185°C.

[0091] (5) Extrusion, cooling and pelletizing: The barrel temperature in zone 8 is set to 200°C, the barrel temperature in zone 9 is set to 205°C, and the barrel temperature in zone 10 is set to 210°C. The vacuum exhaust system is turned on in zone 9 to maintain the system vacuum at -0.085MPa. The melt is extruded through a multi-hole die set to 210°C, and after water cooling and air drying, it is pelletized. The process parameters are the same as in Example 1.

[0092] Example 3:

[0093] This embodiment provides a method for preparing flame-retardant plastic for electric tricycles, specifically including the following steps:

[0094] (1) Resin base premixing and main feed: 70.0 kg of copolymer polypropylene, 12.0 kg of polyolefin elastomer, 5.0 kg of maleic anhydride-grafted polypropylene, 0.2 kg of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.2 kg of tris(2,4-di-tert-butylphenyl) phosphite, and 0.3 kg of calcium stearate were added to a high-speed mixer and mixed at 400 rpm for 4 minutes. After mixing, the mixture was fed into the first zone of a co-rotating twin-screw extruder with the same configuration as in Example 1. The screw speed was set to 350 rpm, the barrel temperature of the first zone was 180°C, and the barrel temperature of the second zone was 185°C.

[0095] (2) Injection of liquid A: When the material is pushed to zone 3, 1.1 kg of liquid A prepared in preparation example 3 is continuously injected into the barrel through the first set of liquid metering pumps. The barrel temperature in zones 3 and 4 is set to 200°C.

[0096] (3) Flame retardant side feeding: 15.0 kg piperazine pyrophosphate and 6.0 kg aluminum hypophosphate are premixed and then forced into the melt in zone 5 by a side feeder. The barrel temperature in zone 5 is set to 200℃.

[0097] (4) Injection of liquid B and reverse cooling: When the material is pushed to zone 6, 1.05 kg of liquid B prepared in preparation example 3 is injected into the barrel through the second set of liquid metering pumps. The barrel cooling water circulation system of zone 6 and zone 7 is forcibly turned on, and the barrel temperature of the two zones is set and dynamically maintained at 185°C.

[0098] (5) Extrusion, cooling and pelletizing: The barrel temperature in zone 8 is set to 200°C, the barrel temperature in zone 9 is set to 205°C, and the barrel temperature in zone 10 is set to 210°C. The vacuum exhaust system is turned on in zone 9 to maintain the system vacuum at -0.085MPa. The melt is extruded through a multi-hole die set to 210°C, and after water cooling and air drying, it is pelletized. The process parameters are the same as in Example 1.

[0099] Example 4:

[0100] This embodiment provides a method for preparing flame-retardant plastic for electric tricycles, specifically including the following steps:

[0101] (1) Premixing of resin base material, injection of liquid A and side feeding of flame retardant: The types of materials, the amount of addition and the process operation and temperature settings of the extruder from zone 1 to zone 5 are exactly the same as in Example 1.

[0102] (2) Injection of liquid B and reverse cooling: When the material is pushed to zone 6, 0.785 kg of liquid B prepared in preparation example 1 is injected into the barrel through the second set of liquid metering pumps. The barrel cooling water circulation system of zone 6 and zone 7 is forcibly turned on, and the barrel temperature of the two zones is set and dynamically maintained at 190°C.

[0103] (3) Extrusion, cooling and pelletizing: The process operation and temperature setting of the extrusion and pelletizing steps are exactly the same as those in Example 1.

[0104] Example 5:

[0105] This embodiment provides a method for preparing flame-retardant plastic for electric tricycles, specifically including the following steps:

[0106] (1) Premixing of resin base material, injection of liquid A and side feeding of flame retardant: The types of materials, the amount of addition and the process operation and temperature settings of the extruder from zone 1 to zone 5 are exactly the same as in Example 1.

[0107] (2) Injection of liquid B and reverse cooling: When the material is pushed to zone 6, 0.785 kg of liquid B prepared in preparation example 1 is injected into the barrel through the second set of liquid metering pumps. The barrel cooling water circulation system of zone 6 and zone 7 is forcibly turned on, and the barrel temperature of the two zones is set and dynamically maintained at 180°C.

[0108] (3) Extrusion, cooling and pelletizing: The process operation and temperature setting of the extrusion and pelletizing steps are exactly the same as those in Example 1.

[0109] Comparative Example 1:

[0110] Compared with Example 1, the difference is that maleic anhydride-grafted polypropylene, liquid A and liquid B are not added to the formulation. The mass of the above-mentioned unadded components is made up by the equal amount of copolymer polypropylene. At the same time, the liquid injection steps in zones 3 and 6 and the reverse step cooling steps from zone 6 to zone 7 are not performed in the process. The conventional powder and resin direct blending extrusion process is used. All other aspects are the same.

[0111] Comparative Example 2:

[0112] Compared with Example 1, the difference is that liquid A is not added to the formula, and the corresponding mass of liquid A is made up by an equal amount of copolymer polypropylene. The injection step of liquid A in zone 3 is not performed in the process, but all other aspects are the same.

[0113] Comparative Example 3:

[0114] Compared with Example 1, the difference is that liquid B is not added to the formula, and the corresponding mass of liquid B is made up by an equal amount of copolymer polypropylene. The injection step of liquid B in zone 6 is not performed in the process, but all other aspects are the same.

[0115] Comparative Example 4:

[0116] Compared with Example 1, the difference is that no first-stage catalyst (N,N-dimethylbenzylamine) was added to solution A, and no second-stage catalyst (dibutyltin dilaurate) was added to solution B. Specifically, 0.75 kg of pure γ-glycidoxypropyltrimethoxysilane was injected into zone 3, and 0.075 kg of N,N-dimethylbenzylamine was not added; 0.75 kg of pure hydroxyl-terminated polydimethylsiloxane was injected into zone 6, and 0.035 kg of dibutyltin dilaurate was not added. The mass of the catalysts not added was made up by an equal amount of copolymer polypropylene, and all other aspects were the same.

[0117] Comparative Example 5:

[0118] Compared with Example 1, the difference lies in the order of material feeding. Specifically, liquid A and liquid B are sprayed at room temperature onto piperazine pyrophosphate and aluminum hypophosphite powder for high-speed mixing and pretreatment. Then, the pretreated powder is added to the extruder in zone 5 via a side feeder. The independent liquid injection steps in the melt stage of zones 3 and 6 are not performed. All other steps are the same.

[0119] Comparative Example 6:

[0120] Compared with Example 1, the difference lies in the different process parameter settings. Specifically, the barrel cooling water circulation system in Zones 6 and 7 was not activated for reverse step cooling intervention. Instead, the barrel temperature in these two zones was continuously set and maintained at 200°C. All other parameters are the same.

[0121] Test Example 1:

[0122] This test example provides a method for characterizing changes in the organic interface structure of extruded products. The main test objects are the cylindrical granules prepared in Example 1, Comparative Example 2, and Comparative Example 3. The specific experimental steps are as follows:

[0123] (1) Sample crushing: Weigh 10.0g of each of the cylindrical granules prepared in Example 1, Comparative Example 2 and Comparative Example 3, and crush them into powder at low temperature in a crusher so that the powder can pass through a 40-mesh standard sieve.

[0124] (2) Soxhlet extraction: Wrap each group of pulverized powders separately with filter paper and place them in a Soxhlet extractor. Add an appropriate amount of analytical grade acetone solvent to a round-bottom flask, heat to boiling, and maintain reflux for 24 hours. This step is used to fully extract free small molecule components in the system that have not undergone chemical bonding or have not been stably retained by the interfacial structure, including unreacted γ-glycidoxypropyltrimethoxysilane, hydroxyl-terminated polydimethylsiloxane, and catalyst, so as to reduce the influence of free small molecules on the subsequent infrared spectroscopy test results.

[0125] (3) Drying treatment: The extracted powder sample was placed in a vacuum drying oven and vacuum dried at 80°C for 12 hours to remove the residual acetone solvent and obtain the composite material residual powder after the removal of free small molecules.

[0126] (4) Preparation of thin film sample: Take an appropriate amount of the residual powder of the composite material after removing free small molecules, place it between two polytetrafluoroethylene films, and use a flat vulcanizing machine to hot press at 190°C and 10MPa pressure for 2 minutes, and then cold press to form a thin film test sample with a thickness of 0.05mm to 0.1mm.

[0127] (5) Infrared spectroscopy test: A Fourier transform infrared spectrometer was used to scan the thin film sample under test in transmission mode. The scanning range was set to 4000 cm⁻¹. -1 Up to 400cm -1 The resolution is 4cm. -1 The total number of scans was 32.

[0128] (6) Data Processing: Baseline calibration was performed on the obtained infrared spectra. A 1456 cm⁻¹ baseline was selected. -1 The absorption peak at 1735 cm⁻¹, which is the bending vibration peak of methyl groups in the polypropylene matrix, was used as the internal standard reference peak. The readings were taken at 1735 cm⁻¹. -1 1090cm -1 And 910cm -1 The absorbance at 1735 cm⁻¹ was calculated, and the absorbance ratio of each characteristic peak to the internal standard peak was also calculated. -1 The absorption peak at 1090 cm⁻¹ is used to characterize the C=O stretching vibration of the carbonyl group in the ester group. -1 The absorption peak at 910 cm⁻¹ is mainly used to characterize the asymmetric stretching vibrations of Si-O-Si and Si-OC structures. -1 The absorption peak is used to characterize the characteristic vibrations of epoxy groups.

[0129] Table 1. Relative absorbance ratios of infrared characteristic peaks in composite material samples after removal of free small molecules:

[0130] Sample Name Relative absorbance peak ratio (I 1735 / I 1456 ) of ester group Siloxane absorption peak relative ratio (I 1090 / I 1456 )]]> <![CDATA[Relative ratio of epoxy group absorption peaks (I 910 / I 1456 )]]> Example 1 0.453 0.812 0.012 Comparative Example 2 0.021 0.063 0.004 Comparative Example 3 0.428 0.231 0.015

[0131] Based on the data in Table 1 and the appendix Figure 1 It can be seen that the composite material sample of Example 1 after removing free small molecules has a growth rate of 1735 cm⁻¹. -1 A distinct absorption peak was observed at 1735 cm⁻¹, which can be attributed to the carbonyl vibration of the ester group generated during the ring-opening esterification reaction. In contrast, Comparative Example 2, without the addition of solution A, showed a peak at 1735 cm⁻¹. -1The relative absorbance ratio at the point was 0.021, close to the baseline level. These results indicate that, under the test conditions, after the introduction of solution A, a ring-opening esterification reaction may have occurred between the epoxy group in γ-glycidoxypropyltrimethoxysilane and the maleic anhydride group on the maleic anhydride-grafted polypropylene segment, forming an ester structure recognizable by infrared spectroscopy in the composite material system.

[0132] Meanwhile, 910cm in the three groups of samples -1 The relatively low relative ratios of the absorption peaks for epoxy groups indicate that the content of detectable residual epoxy groups in the sample is low after Soxhlet extraction. This result is consistent with the assumption that epoxy groups in the system participate in interfacial reactions or that unreacted small molecules are extracted and removed.

[0133] At 1090cm -1 The nearby absorption peaks can mainly be attributed to the asymmetric stretching vibrations of the Si-O-Si and Si-OC structures, while partial superposition with the absorption of the phosphorus-oxygen structure in the flame retardant cannot be ruled out. Therefore, this peak is more suitable as a basis for relative comparison of different samples under the same test conditions. Comparative Example 3, without the addition of solution B, has a peak at 1090 cm⁻¹. -1 The relative absorbance ratio at 1090 cm⁻¹ was 0.231, indicating that a certain amount of siloxane-related structures still exist in the system. These structures may originate from the hydrolytic condensation of the silane coupling agent and its interfacial interaction with the flame retardant surface. Example 1 showed absorbance at 1090 cm⁻¹. -1 The relative absorbance ratio at the point increased to 0.812, indicating that the structural signal related to siloxane in the sample was significantly enhanced after the addition of solution B.

[0134] Hydroxyl-terminated polydimethylsiloxane can undergo a dealcohydride condensation reaction with residual Si-OCH3 groups in the system under the presence of a secondary catalyst. Combined with the Soxhlet extraction results, the 1090 cm⁻¹ in Example 1... -1 The high relative absorbance ratio indicates that the hydroxyl-terminated polydimethylsiloxane segments are largely retained in the composite material system after extraction. This result supports the formation of in-situ interfacial polycondensation and flexible end-capped structures in this invention. However, this infrared result is mainly used to reflect the relative variation trend between different samples and should not be construed as a limitation on specific bonding ratios or interfacial structure morphology.

[0135] Test Example 2:

[0136] This test example provides a rheological verification method for the reaction kinetics of a dual-catalyst system. The main test object is a mixture of the formulation systems corresponding to Example 1 and Comparative Example 4. The specific experimental steps are as follows:

[0137] (1) Material premixing: The copolymer polypropylene, polyolefin elastomer, maleic anhydride-grafted polypropylene and various conventional additives in the corresponding proportions of the formulations in Example 1 and Comparative Example 4 were extracted and uniformly premixed in a high-speed mixer. At the same time, the corresponding piperazine pyrophosphate and aluminum hypophosphite powders were mixed in proportion.

[0138] (2) Rheological test sample loading: A rotational rheometer was used, equipped with a parallel plate fixture with a diameter of 25 mm, and the test environment temperature was set to 200℃. The premixed resin base material was placed on the lower test plate and heated to melt. After the material melted, the premixed flame retardant powder was added, and micro-in-situ stirring was performed to initially disperse the flame retardant powder in the melt. Then the upper test plate was pressed down, the test gap was set to 1.0 mm, and the overflow material at the edge of the fixture was cleaned.

[0139] (3) Liquid component addition: After the system temperature re-equilibrates to 200°C, a microsyringe is used to rapidly inject the mixture of liquid A and liquid B corresponding to Example 1, and the mixture of pure γ-glycidoxypropyltrimethoxysilane and pure hydroxyl-terminated polydimethylsiloxane corresponding to Comparative Example 4, into the melt edge of the parallel plate test area. The effective addition amounts of pure γ-glycidoxypropyltrimethoxysilane and pure hydroxyl-terminated polydimethylsiloxane in Comparative Example 4 are consistent with the effective addition amounts of the corresponding reactants in Example 1, but the first-stage catalyst and the second-stage catalyst are not added.

[0140] (4) Time scan test: Immediately start the time scan test mode of the rotational rheometer. Set the test angular frequency to 10 rad / s and the test strain to 1% to ensure that the test process is within the linear viscoelastic region of the material. Continuously collect data on the change of complex viscosity of the melt over time. Set the total test duration to 120 seconds and record the rheological behavior changes of different systems under isothermal conditions.

[0141] Table 2. Evolution of complex viscosity of polymer melt under isothermal conditions at 200℃:

[0142] 5 1482.3 1475.6 15 1531.7 1481.2 25 1856.4 1488.5 35 2412.9 1502.1 45 2987.5 1511.4 60 3354.2 1528.9 80 3512.8 1553.2 100 3581.4 1587.6 120 3605.1 1612.3

[0143] Based on the data in Table 2 and the appendix Figure 2 It can be seen that, under constant temperature conditions of 200℃, the complex viscosity of Example 1 and Comparative Example 4 showed different trends over time. In the 120-second test cycle, the complex viscosity of the material system in Comparative Example 4 increased from 1475.6 Pa·s to 1612.3 Pa·s, with a relatively small overall change. This indicates that without the addition of the first-stage catalyst and the second-stage catalyst, the reactions or structural changes that could cause viscosity increases within the system were relatively slow.

[0144] In the initial stage of testing (5 to 15 seconds), the complex viscosity of the material system in Example 1 showed minimal change. Subsequently, between 25 and 60 seconds, the complex viscosity increased from 1856.4 Pa·s to 3354.2 Pa·s, and the rate of increase slowed down after 80 seconds. This trend indicates that the addition of the first and second stage catalysts significantly accelerated the structural changes related to grafting, polycondensation, or interfacial interactions in the system, leading to increased melt flow resistance.

[0145] The comparison between Example 1 and Comparative Example 4 shows that the addition of N,N-dimethylbenzylamine and dibutyltin dilaurate promotes the ring-opening esterification reaction between the epoxy group and the maleic anhydride group, as well as the dealcoholization condensation reaction between the silicon-containing components, thereby resulting in a more significant increase in complex viscosity of the system in a shorter time. This result can serve as supplementary evidence to illustrate the promoting effect of the dual-catalyst system on interfacial reaction kinetics.

[0146] Test Example 3:

[0147] This test example provides a test method for the impact of reverse cooling process on the operational stability of continuous extrusion process. The main test objects are the material systems of Example 1, Example 5 and Comparative Example 6 in the continuous extrusion process. The specific experimental steps are as follows:

[0148] (1) Equipment preparation: Clean the co-rotating twin-screw extruder to ensure that there is no residual material from the previous experiment in the screw and barrel. Connect the programmable logic controller (PLC) data port of the equipment control system and configure the data acquisition software to record the main motor torque load rate and the gauge pressure vacuum degree of the vacuum exhaust port in zone 9. The vacuum degree is expressed in absolute value and the unit is MPa.

[0149] (2) Start-up and stable operation: According to the process settings of Example 1, Example 5 and Comparative Example 6, preheat each temperature control zone of the extruder. After the actual temperature of each zone reaches the set value and is kept constant for 30 minutes, start the main motor of the main machine, each stage of the feeder and the liquid injection metering pump in sequence, and feed continuously according to the formula set rate.

[0150] (3) Data Acquisition: After the extruder head discharges material evenly and the traction pelletizing system runs smoothly, mark this point as the test start point, i.e., 0 minutes, and begin recording the operating status continuously for 2 hours. During the 120-minute test cycle, the system automatically collects the main motor torque load rate and the absolute value of the vacuum degree at the vacuum exhaust port every 10 seconds. At the same time, record whether there is a phenomenon of melt escaping with gas at the vacuum exhaust port of zone 9.

[0151] (4) Data processing: After the test is completed, export the running data collected in the background and extract the data at specific time points for comparative analysis.

[0152] Table 3. Sampling data of torque load rate and vacuum degree during continuous operation of the extruder:

[0153] Sampling time (min) Example 1 Torque load rate (%) Example 1: Absolute value of vacuum (MPa) Example 5 Torque Load Rate (%) Example 5: Absolute value of vacuum (MPa) Comparative Example 6: Torque Load Rate (%) Comparative Example 6: Absolute value of vacuum degree (MPa) 10 73.2 0.084 88.5 0.085 61.4 0.071 30 75.8 0.086 91.2 0.086 62.8 0.052 50 72.1 0.083 87.4 0.083 60.9 0.078 70 74.6 0.085 92.1 0.085 63.5 0.046 90 76.5 0.084 89.8 0.084 61.7 0.065 110 73.9 0.085 90.6 0.086 62.2 0.058

[0154] Based on the data in Table 3 and the appendix Figure 3 It can be seen that, in Example 1, after adopting a reverse cooling setting of 185°C in zones 6 and 7, the torque load rate of the extruder main motor remained between 72.1% and 76.5% during 2 hours of continuous operation, and no shutdowns due to excessive torque load were observed during the operation. These results indicate that under these process conditions, the melt can still maintain a continuous conveying state and has good operational stability.

[0155] The absolute value of the vacuum degree in Example 1 remained basically around 0.084 MPa, that is, the gauge pressure vacuum degree was approximately -0.084 MPa. This result indicates that under the reverse cooling condition of 185℃, the pumping state of the vacuum exhaust port in Zone 9 is relatively stable, and small molecule components such as condensation byproducts can enter the exhaust section and be extracted relatively smoothly.

[0156] Comparative Example 6 did not execute the reverse cooling procedure from Zones 6 to 7; instead, the temperatures in these two zones were maintained at 200℃. The main motor torque load rate of this group of samples remained around 60%, indicating relatively low melt flow resistance; however, the absolute value of its vacuum fluctuated significantly, dropping to 0.046 MPa to 0.052 MPa at certain time points. These results indicate that under higher temperature and lower pressure conditions in the exhaust section, small molecule byproducts in the system are more likely to escape rapidly, potentially leading to fluctuations in the vacuum exhaust state. During the test, intermittent melt entrainment occurred at the exhaust port, indicating relatively poor continuous exhaust stability under these process conditions.

[0157] In Example 5, the temperature of zones 6 and 7 was set to 180°C, and the main motor torque load rate remained between 87.4% and 92.1%, higher than in Example 1. This result indicates that further reducing the temperature in this zone increases the apparent viscosity of the melt and the flow resistance, resulting in a corresponding increase in equipment load. Under the conditions of this test equipment, this group of samples did not trigger the main unit overload protection, and the absolute value of the vacuum degree remained between 0.083 MPa and 0.086 MPa, indicating that continuous extrusion and stable venting can still be maintained at 180°C, but the equipment load margin is lower than that at 185°C.

[0158] Based on the test results of Examples 1, 5, and Comparative Example 6, it can be seen that setting the temperature in zones 6 to 7 within the range of 180°C to 190°C is beneficial for balancing melt shear dispersion, equipment torque load, and vacuum exhaust stability. In particular, the system exhibited a relatively balanced operating state at 185°C in this test system.

[0159] Test Example 4:

[0160] This test example provides a test method for normal mechanical properties and flame retardant properties. The main test objects are the cylindrical granules prepared in Examples 1 to 5, Comparative Example 1 and Comparative Example 5. The specific experimental steps are as follows:

[0161] (1) Drying treatment: The cylindrical granules prepared in Examples 1 to 5, Comparative Example 1 and Comparative Example 5 were placed in a forced-air drying oven and dried continuously at 85°C for 4 hours to remove moisture from the material.

[0162] (2) Injection Molding: The dried granules were injection molded using an injection molding machine. The temperature distribution of the injection molding machine barrel was set as follows: feeding section 190℃, compression section 205℃, metering section 210℃, nozzle 210℃; the mold temperature was set to 40℃, the injection pressure was set to 75MPa, and the holding time was set to 15 seconds. Notched impact specimens conforming to ISO179 standard, tensile specimens conforming to ISO527 standard, and vertical burning specimens conforming to UL-94 test requirements were prepared respectively. The thickness of the vertical burning specimens was 3.2mm.

[0163] (3) Conditioning: The standard test specimens after injection molding are placed in a constant temperature and humidity environment of 23℃ and 50% for conditioning for 48 hours.

[0164] (4) Notched impact strength test: The notched impact strength of the simply supported beam was tested using a pendulum impact testing machine. A V-shaped notch with a depth of 2.0 mm was milled at the center of the spline, and the radius of curvature at the bottom of the notch was 0.25 mm. Ten splines were tested in each group, and the energy consumed by the impact failure was recorded and the arithmetic mean was calculated.

[0165] (5) Elongation at break test: The elongation at break was tested using an electronic universal testing machine. The initial gauge length between the fixtures was set to 50 mm, and the tensile test rate was 50 mm / min. Five specimens were tested in each group, and the gauge length elongation at break was recorded. The arithmetic mean of the elongation at break was calculated.

[0166] (6) Flame retardant performance test: The UL-94 vertical burning test was carried out on the 3.2mm thick sample using a vertical burning tester. Two flame ignitions lasting 10 seconds were applied to each sample, and the afterflame time and afterglow time were recorded. It was observed whether there was any phenomenon of molten droplets igniting the degreased cotton below during the burning process, and the flame retardant rating of each group of samples was determined.

[0167] Table 4 Summary of test data for normal mechanical properties and flame retardant properties:

[0168] Sample Name <![CDATA[Notched impact strength (kJ / m -2 )]]> Elongation at break (%) UL-94 flame retardant rating (3.2mm) Example 1 12.8 154.6 V-0 Example 2 16.4 182.3 V-0 Example 3 9.7 91.8 V-0 Example 4 11.9 143.2 V-0 Example 5 12.2 148.5 V-0 Comparative Example 1 3.9 24.1 V-0 Comparative Example 5 6.8 58.7 V-0

[0169] According to the data in Table 4, Examples 1 to 5, Comparative Example 1 and Comparative Example 5 all achieved UL-94V-0 rating under a thickness of 3.2 mm, indicating that the flame retardant system used can meet the corresponding flame retardant rating requirements under the above formulation and process conditions.

[0170] In terms of normal mechanical properties, the notched impact strength and elongation at break of Examples 1 to 5 were generally higher than those of Comparative Example 1 and Comparative Example 5. Comparative Example 1 was prepared by direct blending of powder and resin, and its notched impact strength was 3.9 kJ·m. -2 The elongation at break was 24.1%. This result indicates that, without interfacial reaction treatment, the interfacial bonding between the flame retardant powder and the polypropylene matrix is ​​relatively insufficient, resulting in low material toughness.

[0171] Comparative Example 5, which involved pre-spraying liquids A and B into the flame retardant powder, achieved a notched impact strength of 6.8 kJ·m. -2 The elongation at break was 58.7%, which is higher than that of Comparative Example 1, but still lower than that of Examples 1 to 5. This result indicates that the pretreatment method can improve the interfacial compatibility between the powder and the resin to a certain extent, but its improvement effect is lower than that of the stepwise injection of liquid A and liquid B in the melt stage.

[0172] The notched impact strength of Example 1 is 12.8 kJ·m. -2 The elongation at break was 154.6%, which was higher than that of Comparative Example 1 and Comparative Example 5. Combined with the aforementioned preparation process, in Example 1, liquids A and B were added in different regions of the extrusion process, which facilitated the formation of a more stable interfacial structure between γ-glycidyl etheroxypropyltrimethoxysilane, maleic anhydride-grafted polypropylene, the flame retardant interface, and the hydroxyl-terminated polydimethylsiloxane, thereby improving the mechanical properties of the highly filled flame-retardant system.

[0173] Example 2 shows a notched impact strength of 16.4 kJ·m under relatively low flame retardant dosage conditions. -2 The elongation at break was 182.3%, exhibiting a high level of toughness. In Example 3, after increasing the amounts of resin and flame retardant, the notched impact strength was 9.7 kJ·m. -2 The elongation at break was 91.8%, which was lower than that of Examples 1 and 2, but still higher than that of Comparative Examples 1 and 5. This result indicates that the interface treatment process can improve the mechanical properties of the material under different formulation ratios, but changes in the flame retardant content and system composition will affect the final mechanical properties.

[0174] In Examples 4 and 5, the temperatures of zones 6 and 7 were set to 190°C and 180°C, respectively, and their notched impact strengths were 11.9 kJ·m.-2 and 12.2 kJ·m -2 The elongation at break was 143.2% and 148.5%, respectively. These results are similar to those of Example 1, indicating that the obtained material can maintain relatively stable normal mechanical properties within the reverse cooling range of 180°C to 190°C.

[0175] Test Example 5:

[0176] This test example provides a test method for the anti-precipitation performance of materials under high temperature and high humidity conditions. The main test objects are the material samples prepared in Example 1, Comparative Example 1, and Comparative Example 3. The specific experimental steps are as follows:

[0177] (1) Damp heat aging treatment: Standard samples with dimensions of 80mm×10mm×4mm were cut from the injection molded samples of Example 1, Comparative Example 1 and Comparative Example 3 and placed on the sample rack of the constant temperature and humidity test chamber. The internal ambient temperature of the test chamber was set to 85℃ and the relative humidity to 85%, and the test chamber was run continuously for 1000 hours under these conditions to accelerate the damp heat aging treatment of the samples.

[0178] (2) Boiling extraction: After aging, each group of samples was taken out, the sample surface was rinsed with deionized water, and air-dried at room temperature. Then, each group of samples was placed in a round-bottom flask equipped with a reflux condenser, and 500 mL of ultrapure water was accurately added to each flask. The round-bottom flasks were placed in a constant temperature oil bath and heated to a temperature of 100°C and maintained for continuous boiling extraction of the samples. The total extraction time was set to 72 hours.

[0179] (3) Extraction sample collection: At the time points of 12 hours, 24 hours, 48 ​​hours and 72 hours of the extraction process, 5.0 mL of extract sample was transferred from each flask. Immediately after sampling, 5.0 mL of boiling ultrapure water was added to maintain a constant total volume of extract.

[0180] (4) Sample digestion and testing: The extract samples obtained at each time point were cooled to room temperature, filtered through a polytetrafluoroethylene microporous membrane with a pore size of 0.22 μm, and an appropriate amount of 65% nitric acid solution was added to the filtrate. The samples were then digested using a microwave digester to convert the phosphorus-containing components in the extract into inorganic phosphorus forms suitable for measurement. Subsequently, the total phosphorus concentration in the digested solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) at a wavelength of 213.618 nm. The total phosphorus concentration in each sample was calculated based on the standard working curve.

[0181] Table 5. Data on the change of total phosphorus concentration in the extract of the samples after 1000 hours of wet heat aging over time:

[0182] 12 0.23 17.42 3.86 24 0.35 38.65 11.24 48 0.51 71.39 26.58 72 0.68 92.14 45.71

[0183] According to the data in Table 5, after humid heat aging and boiling water extraction, the total phosphorus concentration in the extracts of Examples 1, 1, and 3 all showed an increasing trend with prolonged extraction time, but the magnitude of the increase varied significantly among different samples. This result can be used to characterize the migration and precipitation of phosphorus-containing components in different material systems under humid heat conditions and subsequent water extraction.

[0184] The total phosphorus concentration in Comparative Example 1 remained high at all extraction time points, increasing rapidly with extraction time, reaching 92.14 mg / L after 72 hours. This result indicates that the phosphorus-containing components in Comparative Example 1 are more likely to migrate into the aqueous phase under humid heat aging and subsequent water extraction conditions. Considering its preparation method, without interfacial reaction treatment, the interfacial bonding between the flame retardant and the polypropylene matrix is ​​relatively weak, which may lead to more frequent migration and precipitation of phosphorus-containing components under long-term humid heat.

[0185] In Comparative Example 3, the total phosphorus concentration increased from 3.86 mg / L to 45.71 mg / L over the 12-72 hour period, which was lower than that of Comparative Example 1 but significantly higher than that of Example 1. This result indicates that after introducing γ-glycidoxypropyltrimethoxysilane for the first-stage interface treatment in Comparative Example 3, the precipitation degree of phosphorus-containing components was reduced, but a significant dissolution trend still existed during long-term extraction. This phenomenon may be related to the lack of further end-capping treatment with terminal hydroxyl polydimethylsiloxane in the system; that is, the residual Si-OCH3 groups at the interface may hydrolyze in a humid and hot environment, reducing the stability of the interface structure and thus increasing the possibility of migration of phosphorus-containing components.

[0186] In Example 1, the total phosphorus concentration remained at a low level at each extraction time point, at 0.23 mg / L at 12 hours and 0.68 mg / L at 72 hours, significantly lower than that of Comparative Examples 1 and 3. This result indicates that the phosphorus-containing components in Example 1 exhibit low migration and precipitation tendencies under humid heat aging and subsequent water extraction conditions. Combined with the analysis of the preparation process in Example 1, this result demonstrates that the interfacial structure formed by the stepwise introduction of solution A and solution B is beneficial for improving the stable retention of the flame retardant in the polymer system and reducing the risk of phosphorus-containing component precipitation under high temperature and high humidity conditions.

[0187] As shown in Table 5, compared with Comparative Example 1, which did not undergo interface reaction treatment, and Comparative Example 3, which only underwent the first stage of interface treatment, Example 1 exhibited a lower total phosphorus leaching level under high temperature and humidity conditions and subsequent boiling water extraction, indicating that it has better anti-precipitation performance.

[0188] Test Example 6:

[0189] This test example provides a test method for assessing the retention of mechanical properties after damp heat aging. The main test objects are the cylindrical granules prepared in Example 1, Comparative Example 1, and Comparative Example 3. The specific experimental steps are as follows:

[0190] (1) Sample preparation: After drying the cylindrical granules prepared in Example 1, Comparative Example 1 and Comparative Example 3, they were molded by injection molding machine to prepare notched impact samples of simply supported beams conforming to ISO179 standard. 60 samples were processed in each group.

[0191] (2) Damp heat aging treatment: Place the molded specimens on the shelf of the constant temperature and humidity test chamber, keeping a distance between the specimens to ensure that the specimens are subjected to the damp heat environment more evenly. Set the internal temperature of the constant temperature and humidity test chamber to 85℃ and the relative humidity to 85%.

[0192] (3) Sampling in stages: 10 samples were taken from the test chamber at the aging time of 0 hours, 250 hours, 500 hours, 750 hours and 1000 hours respectively. Among them, the 0-hour sample is the initial sample that has not undergone damp heat aging treatment.

[0193] (4) Conditioning: Transfer the extracted samples to a standard laboratory environment and place them at a temperature of 23°C and a relative humidity of 50% for 48 hours to condition them.

[0194] (5) Notched impact strength test: A V-shaped notch with a depth of 2.0 mm was milled at the center of the specimen, and the notched impact strength of the specimen was tested using a pendulum impact testing machine. The test values ​​of each group of specimens were recorded, and the arithmetic mean was calculated.

[0195] (6) Calculation of mechanical retention rate: Divide the average notched impact strength of the 1000-hour aging node by the average notched impact strength of the 0-hour node to calculate the mechanical retention rate of the sample.

[0196] Table 6. Notched impact strength and retention rate of samples at different hygrothermal aging time points:

[0197] Sample Name <![CDATA[0h impact strength (kJ / m -2 )]]> <![CDATA[250h Impact Strength (kJ / m -2 )]]> <![CDATA[500h impact strength (kJ / m -2 )]]> <![CDATA[750h impact strength (kJ / m -2 )]]> <![CDATA[1000h Impact Strength (kJ / m -2 )]]> Mechanical retention rate (%) Example 1 12.8 12.6 12.3 11.9 11.8 92.2 Comparative Example 1 3.9 3.8 3.4 3.0 2.5 64.1 Comparative Example 3 11.7 10.4 8.7 6.2 4.6 39.3

[0198] According to the data in Table 6, Example 1, Comparative Example 1, and Comparative Example 3 all showed varying degrees of decrease in notched impact strength during the damp heat aging process, but the magnitude of the decrease differed. The initial notched impact strength of Example 1 was 12.8 kJ·m. -2 After 1000 hours of damp heat aging, the energy content was 11.8 kJ·m. -2 The mechanical retention rate was 92.2%, indicating that it could maintain high impact performance under the test conditions.

[0199] The initial notched impact strength of Comparative Example 1 is 3.9 kJ·m. -2 After 1000 hours of damp heat aging, the efficiency decreased to 2.5 kJ·m. -2 The mechanical retention rate was 64.1%. This result indicates that the initial impact strength of the sample was low without interfacial reaction treatment, and the impact performance further decreased after damp heat aging.

[0200] The initial notched impact strength of Comparative Example 3 is 11.7 kJ·m. -2 The efficiency was similar to that of Example 1, but decreased to 4.6 kJ·m after 1000 hours of damp heat aging. -2 The mechanical retention rate was 39.3%. This result indicates that although Comparative Example 3 improved the initial impact performance by introducing γ-glycidoxypropyltrimethoxysilane, its impact performance decreased significantly under long-term humid and hot conditions.

[0201] Based on the formulation and process analysis of Comparative Example 3, which did not include terminally hydroxyl-terminated polydimethylsiloxane for subsequent end-capping treatment, unreacted residual Si-OCH3 groups may exist in the system. In a humid and hot environment of 85℃ / 85%RH, these groups may hydrolyze to generate silanols, which then undergo further polycondensation, resulting in a relatively rigid siloxane polycondensation structure at the interface. These changes may reduce the flexibility and stability of the interface layer, leading to a decrease in the impact strength of the sample after aging.

[0202] In Example 1, liquids A and B were introduced stepwise during the extrusion process. The terminal hydroxyl polydimethylsiloxane could undergo a polycondensation reaction with the residual Si-OCH3 groups in the system, which helps reduce the possibility of further hydrolysis or polycondensation of active groups in the subsequent humid and hot environment. Simultaneously, the introduction of polydimethylsiloxane segments helps improve the flexibility and hydrophobicity of the flame retardant interface layer, thereby reducing the adverse effects of humid and hot aging on impact performance.

[0203] As can be seen from the results in Table 6, Example 1 maintained a high notched impact strength and mechanical retention rate after 1000 hours of damp heat aging, indicating that it has good mechanical property stability after damp heat aging under the test conditions.

[0204] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flame-retardant plastic for an electric tricycle, characterized in that, Made from the following ingredients in parts by weight: 60.0–70.0 parts of copolymerized polypropylene; 8.0–12.0 parts of polyolefin elastomer; 3.0–5.0 parts of maleic anhydride-grafted polypropylene; 0.5–1.0 parts of interfacial reactant; 0.05–0.10 parts of the first-stage catalyst; Piperazine pyrophosphate, 12.0–15.0 parts; 4.0–6.0 parts of aluminum hypophosphite; 0.5–1.0 parts of a flexible interface capping agent; Secondary catalyst: 0.02–0.05 parts; Antioxidant 0.2–0.4 parts; Lubricant 0.2-0.3 parts; The flame-retardant plastic is prepared by first mixing the copolymer polypropylene, polyolefin elastomer, and maleic anhydride-grafted polypropylene with the interfacial reactant, and then using a first-stage catalyst to catalyze the ring-opening esterification grafting reaction between the interfacial reactant and the maleic anhydride-grafted polypropylene; subsequently, piperazine pyrophosphate and aluminum hypophosphite are mixed in; finally, the interfacial flexible end-capping agent is added, and a second-stage catalyst is used to promote the de-alcoholization polycondensation crosslinking reaction between the interfacial flexible end-capping agent and the active groups in the previous system, thereby generating a flexible polymer coating network around the particles of piperazine pyrophosphate and aluminum hypophosphite.

2. The flame-retardant plastic for an electric tricycle according to claim 1, characterized in that, The interfacial reactant is γ-glycidoxypropyltrimethoxysilane, and the first-stage catalyst is N,N-dimethylbenzylamine. The interface flexible end-capping agent is hydroxyl-terminated polydimethylsiloxane, and the second-stage catalyst is dibutyltin dilaurate.

3. The flame-retardant plastic for an electric tricycle according to claim 1, characterized in that, The antioxidant is a mixture of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite; the lubricant is calcium stearate.

4. The flame-retardant plastic for an electric tricycle according to claim 1, characterized in that, The copolymer polypropylene is a block copolymer polypropylene, and its melt flow rate at 230℃ and 2.16kg is 10g / 10min to 15g / 10min. The polyolefin elastomer is an ethylene-octene copolymer; The maleic anhydride grafting rate of the maleic anhydride-grafted polypropylene is 0.8wt% to 1.2wt%.

5. The flame-retardant plastic for an electric tricycle according to claim 1, characterized in that, The flame-retardant plastic is produced by extrusion granulation using a co-rotating twin-screw extruder, and the flame-retardant plastic is in the form of cylindrical granules with a length of 3.0 mm.

6. A method for preparing flame-retardant plastic for an electric tricycle, used to prepare the flame-retardant plastic for an electric tricycle as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Material premixing and feeding: After premixing the copolymer polypropylene, polyolefin elastomer, maleic anhydride grafted polypropylene, antioxidant and lubricant, the mixture is continuously fed into the co-rotating twin-screw extruder. S2, Front-end in-situ grafting: In the material feeding section of the co-rotating twin-screw extruder, a first mixture consisting of an interfacial reactant and a first-stage catalyst is continuously injected; S3, Flame retardant intervention: In the barrel section after the first mixture is injected, premixed piperazine pyrophosphate and aluminum hypophosphite are forcibly fed laterally into the melt inside the extruder; S4. Rear flexible end capping and reverse cooling: In the reaction section after the flame retardant is fed in, a second mixture consisting of an interface flexible end capping agent and a second-stage catalyst is injected, and at the same time, the barrel in which the reaction section is located is subjected to reverse step cooling treatment. S5. Extrusion, Cooling and Pelletizing: The mixture is pushed backward, and after exhausting and removing by-products, it is extruded, cooled and pelletized to obtain the flame-retardant plastic for electric tricycles.

7. A method for preparing flame-retardant plastic for an electric tricycle according to claim 6, characterized in that, In S2, the first mixture is prepared by adding the first-stage catalyst to the interfacial reactant at 20°C to 25°C and stirring at 150 rpm to 250 rpm for 10 to 15 minutes. In S4, the second mixture is prepared by adding the second-stage catalyst to the interfacial flexible capping agent at 20°C to 25°C and stirring at 150 rpm to 250 rpm for 10 to 15 minutes.

8. A method for preparing flame-retardant plastic for an electric tricycle according to claim 6, characterized in that, The co-rotating twin-screw extruder has 10 independent temperature control zones; S1 performs main feeding in zone 1; S2 injects the first mixture into zone 3 via a liquid metering pump; S3 presses in the piperazine pyrophosphate and aluminum hypophosphite in zone 5 via a side feeder; S4 injects the second mixture into zone 6 via a liquid metering pump, and the specific areas of the reverse step cooling process are zones 6 and 7, in which the screw assembly of these two zones is equipped with three sets of kneading blocks with staggered angles of 45° and 90°.

9. A method for preparing flame-retardant plastic for an electric tricycle according to claim 6, characterized in that, In S4, the reverse step cooling process is as follows: the barrel cooling water circulation system of Zone 6 and Zone 7 is forcibly opened to dynamically maintain the barrel temperature of Zone 6 and Zone 7 at 180℃~190℃.

10. A method for preparing flame-retardant plastic for an electric tricycle according to claim 9, characterized in that, The barrel temperatures of the remaining zones of the co-rotating twin-screw extruder are set sequentially as follows: Zone 1: 175℃~185℃, Zone 2: 180℃~190℃, Zones 3 to 5: 195℃~205℃, Zone 8: 195℃~205℃, Zone 9: 200℃~210℃, and Zone 10: 205℃~215℃. In S5, the vacuum exhaust system is activated in zone 9 to maintain the system vacuum at -0.08MPa to -0.09MPa. The extruded material is then cooled and shaped in a water bath at 20℃ to 30℃ and dried by a high-pressure air knife before being pelletized by a traction pelletizer.

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