Low-smoke halogen-free flame-retardant material and preparation method thereof

Abstract

This invention discloses a low-smoke halogen-free flame-retardant material and its preparation method. By weight, the low-smoke halogen-free flame-retardant material is prepared from the following parts: 60-80 parts of matrix resin, 15-35 parts of a composite phosphorus-nitrogen flame-retardant system, 1-8 parts of a flame-retardant synergist, 2-10 parts of a compatibilizer, 5-15 parts of reinforcing and modifying filler, and 0.5-5 parts of processing aid. This invention achieves stable flame retardancy at extreme high temperatures under halogen-free conditions through molecular-level coordination between a special flame-retardant system and the matrix, completely avoiding the high-temperature deactivation problem of traditional flame-retardant synergists. Simultaneously, it rapidly catalyzes a dense char layer during combustion, significantly inhibiting the release of smoke and toxic gases. Furthermore, whisker reinforcement and compatibilization technology form a nanoscale interpenetrating structure of organic-inorganic phases, ensuring the mechanical strength and toughness of the material even with ultra-high filling, avoiding brittle fracture caused by stress concentration.

Description

Technical Field

[0001] This invention belongs to the field of polymer composition technology, specifically relating to a low-smoke halogen-free flame retardant material; and more particularly to a method for preparing the low-smoke halogen-free flame retardant material. Background Technology

[0002] High-temperature heat shrink tubing and cable sheathing, made of special polymers, are widely used in rail transportation, aerospace, and nuclear power. Their core materials must possess long-term thermal stability above 150℃, low-smoke halogen-free flame retardancy, high mechanical strength, and environmental safety. Currently, mainstream technologies include: fluoropolymer-based materials: while exhibiting excellent high-temperature resistance, flame retardancy relies on expensive perfluorinated additives, which release highly toxic hydrogen fluoride during combustion, resulting in excessive smoke density; silicone rubber modified systems: at high temperatures, flame retardant synergists easily migrate and precipitate, leading to a sharp drop in mechanical properties; polyolefin / engineering plastic blends: although adding intumescent halogen-free flame retardant synergists reduces smoke, they are prone to charring during high-temperature processing and their high hygroscopicity causes degradation of electrical properties. In response to the above, we propose a low-smoke halogen-free flame retardant material and its preparation method, which specifically addresses the shortcomings of existing technologies. Summary of the Invention

[0003] The purpose of this invention is to provide a low-smoke halogen-free flame retardant material and its preparation method. Through a triple innovative closed loop of material design, process control, and structural reinforcement, it integrates the contradictory requirements of low-smoke halogen-free flame retardancy, extreme temperature resistance, high mechanical reliability, and controllable shape memory in a single system. It breaks through the long-term technical constraints of traditional materials in terms of high temperature resistance and flame retardant performance, compatibilization and reinforcement, crosslinking precision and processing stability, and provides a safe polymer material solution.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A low-smoke halogen-free flame retardant material, which is prepared from the following materials in parts by weight: The matrix resin consists of 60-80 parts, the composite phosphorus-nitrogen flame retardant system consists of 15-35 parts, the flame retardant synergist consists of 1-8 parts, the compatibilizer consists of 2-10 parts, the reinforcing and modifying filler consists of 5-15 parts, and the processing aid consists of 0.5-5 parts. The composite phosphorus-nitrogen flame retardant system contains aluminum hypophosphite and melamine cyanurate, and the mass ratio of aluminum hypophosphite to melamine cyanurate is (2:1)-(1:1). The compatibilizer comprises maleic anhydride graft polymer and ethylene-vinyl acetate copolymer (EVA), and the mass ratio of maleic anhydride graft polymer to EVA is (1:1) to (3:1), wherein the maleic anhydride graft polymer is selected from maleic anhydride grafted polyolefin or maleic anhydride grafted polyacrylate.

[0005] Preferably, it further comprises 0.1-3 parts of a heat stabilizer; the heat stabilizer is selected from organotin stabilizers, metal carboxylate stabilizers, or combinations thereof.

[0006] Preferably, it further comprises 0.1-2 parts of antioxidant; the antioxidant comprises a primary antioxidant and a secondary antioxidant, the primary antioxidant being a hindered phenol, and the secondary antioxidant being a phosphite or a thioether.

[0007] Preferably, the reinforcing and modified filler is a hybrid whisker pre-treated with a silane coupling agent, including aluminum borate whiskers and potassium titanate whiskers, and the mass ratio of aluminum borate whiskers to potassium titanate whiskers is (2:1)-(1:1), and the silane coupling agent is γ-glycidoxypropyltrimethoxysilane or γ-methacryloyloxypropyltrimethoxysilane.

[0008] A method for preparing a low-smoke halogen-free flame retardant material, comprising the following steps: S1. Mix aluminum borate whiskers and potassium titanate whiskers at a mass ratio of (2:1)-(1:1), add 1.0-3.0 wt% of a silane coupling agent ethanol solution equivalent to the total mass of the mixed whiskers; the concentration of the silane coupling agent ethanol solution is 5-20 wt%; and shear and stir at high speed at 60-85℃ for 30-90 minutes, then dry until the moisture content is ≤0.5 wt% to obtain silanized mixed whiskers; S2. Add the ethylene-trifluorochloroethylene copolymer to a mixer for melt plasticization, and control the temperature at 230-260℃; Add a compatibilizer combination of maleic anhydride grafted polymer and ethylene-vinyl acetate copolymer, a flame retardant synergist and the silanized mixed whiskers obtained in step S1, and mix at 230-250°C for 8-15 minutes. The composite phosphorus-nitrogen flame retardant system is added in two stages: first, melamine cyanurate salt is added and mixed for 3-6 minutes; then, aluminum hypophosphite is added to avoid excessive local high temperature in the initial stage and mixed for 8-12 minutes. S3. The blend obtained in step S2 is extruded and granulated using a twin-screw extruder; the extruder temperature is set in sections as follows: Zone I 200-210℃, Zone II 235-245℃, Zone III 245-255℃, Zone IV 250-260℃, and the die head 240-250℃; the screw speed is 150-300 rpm, and the vacuum dehydration degree is ≥-0.08MPa; S4. The particles obtained in step S3 are extruded into tubular preforms and crosslinked by irradiation with a dose of 50-100kGy under an electron accelerator, with the radiation dose rate controlled at 5-15kGy / pass. S5. Preheat the irradiated tube preform at 110-130℃, heat it to ≥190℃ at a rate of 1.5-3.5℃ / s in the range of 100-380℃, and then rapidly cool it to room temperature for shaping.

[0009] Preferably, the rapid cooling in step S5 heat setting adopts a three-stage controlled cooling: the first stage is air cooling to 140℃ at a rate of 15℃ / s, the second stage is water mist quenching to 80℃ at a rate of ≥30℃ / s, and the third stage is slow cooling to room temperature at a rate of ≤5℃ / s.

[0010] Preferably, step S4, irradiation crosslinking, employs a variable dose technique: the first round is 50 kGy at a dose rate of 8 kGy / pass, followed by a short pause and a supplementary dose of 20-30 kGy at a dose rate of 12 kGy / pass.

[0011] Preferably, during the extrusion granulation in step S3, a stepped heating mode is adopted in zone III, with zone III at 245-250℃ and a gradient of 3℃ / min, and zone IV at a constant temperature of 255±2℃. Vacuum dehydration is carried out in zone IV with a vacuum degree ≤-0.09MPa.

[0012] The technical effects and advantages of this invention are as follows: By combining a special flame-retardant system with the matrix at the molecular level, stable flame retardancy is achieved at extreme high temperatures under halogen-free conditions, completely avoiding the high-temperature deactivation problem of traditional flame-retardant synergists. At the same time, it rapidly catalyzes the formation of a dense carbon layer during combustion, significantly inhibiting the release of smoke and toxic gases. Meanwhile, whisker reinforcement and compatibilization technology form a nanoscale interpenetrating structure of organic-inorganic phases, which ensures the mechanical strength and toughness of the material even under ultra-high filling conditions, avoiding brittle fracture caused by stress concentration. The irradiation enhancement path designed specifically for the characteristics of halogen-free systems overcomes the interference of flame retardant components on cross-linking reactions, achieves efficient construction of molecular networks, endows products with precise shape memory function, and eliminates the risks of material decomposition, volatilization, and phase separation during high-temperature processing by temperature window control and segmented mixing process, ensuring the consistency of continuous production. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. 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.

[0014] The low-smoke, halogen-free flame-retardant material provided by this invention is prepared from a matrix resin, a composite phosphorus-nitrogen flame-retardant system, a flame-retardant synergist, a compatibilizer, a reinforcing and modifying filler, and a processing aid. The preparation method is as follows: S1. Mix aluminum borate whiskers and potassium titanate whiskers at a mass ratio of (2:1)-(1:1), add 1.0-3.0 wt% of a silane coupling agent ethanol solution equivalent to the total mass of the mixed whiskers; the concentration of the silane coupling agent ethanol solution is 5-20 wt%; and shear and stir at high speed at 60-85℃ for 30-90 minutes, then dry until the moisture content is ≤0.5 wt% to obtain silanized mixed whiskers; S2. Add the ethylene-trifluorochloroethylene copolymer to a mixer for melt plasticization, and control the temperature at 230-260℃; Add a compatibilizer combination of maleic anhydride grafted polymer and ethylene-vinyl acetate copolymer, a flame retardant synergist and the silanized mixed whiskers obtained in step S1, and mix at 230-250°C for 8-15 minutes. The composite phosphorus-nitrogen flame retardant system is added in two stages: first, melamine cyanurate salt is added and mixed for 3-6 minutes; then, aluminum hypophosphite is added to avoid excessive local high temperature in the initial stage and mixed for 8-12 minutes. S3. The blend obtained in step S2 is extruded and granulated using a twin-screw extruder; the extruder temperature is set in sections as follows: Zone I 200-210℃, Zone II 235-245℃, Zone III 245-255℃, Zone IV 250-260℃, and the die head 240-250℃; the screw speed is 150-300 rpm, and the vacuum dehydration degree is ≥-0.08MPa; S4. The particles obtained in step S3 are extruded into tubular preforms and crosslinked by irradiation with a dose of 50-100kGy under an electron accelerator, with the radiation dose rate controlled at 5-15kGy / pass. S5. Preheat the irradiated tube preform at 110-130℃, heat it to ≥190℃ at a rate of 1.5-3.5℃ / s in the range of 100-380℃, and then rapidly cool it to room temperature for shaping.

[0015] The aluminum hypophosphite is selected from at least one of aluminum hypophosphite and diethyl aluminum hypophosphite; the zinc borate is modified zinc borate with a particle size D50 ≤ 5 μm; the maleic anhydride graft polymer is maleic anhydride grafted ethylene-acrylate copolymer; and the silane coupling agent is γ-glycidoxypropyltrimethoxysilane (KH-560) or γ-methacryloyloxypropyltrimethoxysilane (KH-570). The formulation also includes: a heat stabilizer selected from organotin stabilizers, metal carboxylate stabilizers, or combinations thereof; and an antioxidant comprising a primary antioxidant and a secondary antioxidant, wherein the primary antioxidant is a hindered phenol and the secondary antioxidant is a phosphite or thioether.

[0016] It should be noted that using ethylene-trifluorochloroethylene copolymer (ECTFE) as the matrix resin has advantages over commonly used polyolefins (such as EVA, PE), PVC, and even some fluoroplastics (such as FEP, PFA) in that it has a higher long-term service temperature (150-180℃), excellent chemical corrosion resistance, low permeability, and self-extinguishing properties.

[0017] Furthermore, a combination of aluminum hypophosphite (providing highly efficient phosphorus flame retardancy) and melamine cyanurate salt (MCC, an excellent nitrogen and carbon source expander) was employed. The key was defining the specific mass ratio range (2:1-1:1). This ratio resulted in: CAC: high phosphorus content, excellent gas-phase flame retardancy, and good thermal stability; CC: forming an expanded char layer at high temperatures, enhancing condensed-phase flame retardancy (heat insulation, oxygen barrier, and smoke suppression), and being halogen-free itself. The 2:1 to 1:1 ratio ensured that the flame retardant synergistic effect was effectively achieved at the high processing temperature of ECTFE, rapidly capturing free radicals and forming a dense and stable char layer, thus achieving highly efficient halogen-free flame retardancy. This specific ratio range was the result of optimization based on synergistic effects.

[0018] Zinc borate / zirconium phosphate can promote char formation (catalytic dehydration, reaction with phosphorus and nitrogen system to generate boron / zirconium phosphate glass layer), improve the quality and stability of char layer, further suppress smoke release, and have a synergistic effect of smoke suppression and flame retardancy. This synergist is selected to make up for the fact that the efficiency of halogen-free flame retardant synergists is usually lower than that of halogen-containing flame retardant synergists.

[0019] In addition, maleic anhydride grafted polymer (highly polar) and EVA (good flexibility and good compatibility with some flame retardant synergists) are used simultaneously in a specific ratio (1:1-3:1). The concentration of GMAH is slightly higher, emphasizing its role in improving the polar and non-polar interface and promoting dispersion. At the same time, a reasonable proportion of EVA is used to ensure the overall melt processing performance and toughness, thus solving the key technical difficulty of poor compatibility between fluorinated resins and flame retardant filler systems.

[0020] It should be noted that this polymer material does not use conventional mineral fillers (such as calcium carbonate and talc commonly used in the prior art) or ordinary glass fibers. Instead, it uses two types of high-performance whiskers (whiskers provide good reinforcement and strengthening effects with low filler content): aluminum borate whiskers and potassium titanate whiskers (low coefficient of friction, good insulation, and also have a reinforcing effect). The ratio of the two types of whiskers is 2:1-1:1, which optimizes the complementary advantages of the two types of whiskers. All whiskers need to be pre-treated with a silane coupling agent, which not only improves the interfacial bonding force between the whiskers and the ECTFE matrix resin, greatly improves the mechanical strength of the material, but also avoids agglomeration and ensures processing fluidity and dispersion uniformity.

[0021] Example 1 The low-smoke halogen-free flame retardant material is prepared from the following parts by weight: 65 parts ECTFE matrix resin, 10 parts MAH-g-EVA toughening agent, 20 parts silanized aluminum borate whiskers, 17 parts aluminum hypophosphite, 10 parts melamine cyanurate, 5 parts zinc borate synergist, and 2 parts zirconium phosphate smoke suppressant. The process parameters are: Whisker treatment: 15wt% KH-550 silane / ethanol solution, constant temperature treatment at 78℃, high-speed shearing at 2200rpm for 55 minutes; Layered mixing: For the first feeding, melt ECTFE / MAH-g-EVA / zinc borate / zirconium phosphate at 220℃ (mix for 6 minutes). Second feeding: Add whiskers at 225℃ (mix for 8 minutes); For the final feeding, inject aluminum hypophosphite / melamine salt at 241℃ (mix for 10.5 minutes). Extrusion granulation: Zone I 210℃ → Zone II 235℃ → Zone III gradient temperature increase (247→252℃, 3℃ / min) → Zone IV 256℃ + vacuum dehydration (-0.092MPa) Irradiation crosslinking: First round: 52kGy (dose rate 8.2kGy / pass) → pause for 15min → add 28kGy (12.3kGy / pass); Heat setting and cooling: 132℃ for 10 min → air cooling → water mist quenching → slow cooling (138℃-14℃ / s → 78℃-32℃ / s → 25℃-4.5℃ / s).

[0022] Example 2 The low-smoke halogen-free flame retardant material is prepared from the following parts by weight: 58 parts of ECTFE matrix resin, 13 parts of MAH-g-EVA toughening agent, 18 parts of silanized aluminum borate whiskers, 22 parts of aluminum hypophosphite, 12 parts of melamine cyanurate, 6 parts of zinc borate synergist, and 3 parts of modified montmorillonite smoke suppressant. The process parameters are: Whisker treatment: 12wt% VTMO silane / isopropanol solution, constant temperature treatment at 81℃, medium speed shearing at 1900rpm for 62 minutes; Layered mixing: For the first feeding, melt the resin / toughening agent / montmorillonite at 218℃ (mix for 7 minutes). Add whiskers at 228°C for the second time (mix for 6.5 minutes); For the final feeding, inject aluminum hypophosphite / polyphosphate at 239℃ (mix for 11 minutes). Extrusion granulation: Zone I 208℃ → Zone II 233℃ → Zone III gradient temperature increase (249℃ → 254℃, 3℃ / min) → Zone IV 258℃ + vacuum dehydration (-0.095MPa); Irradiation crosslinking: Two-stage pulsed treatment: 58 kGy (8.5 kGy / pass) → 18 min pause → 33 kGy (13.8 kGy / pass) replenishment. Heat setting and cooling: 135℃ for 8 min → air cooling → water mist quenching → slow cooling (142℃-12℃ / s → 82℃-35℃ / s → 28℃-3.8℃ / s).

[0023] Example 3 The low-smoke halogen-free flame retardant material is prepared from the following parts by weight: 70 parts ECTFE matrix resin, 8 parts MAH-g-EVA toughening agent, 25 parts silanized aluminum borate whiskers, 15 parts aluminum hypophosphite, 9 parts melamine cyanurate, 4 parts nano zinc hydroxystannate, and 1.5 parts silicon carbide smoke suppressant. The process parameters are: Whisker treatment: 18wt% A-171 silane / methanol solution, constant temperature treatment at 72℃, ultra-high speed shearing at 2350rpm for 48 minutes; Layered mixing: For the first feeding, melt the resin / POE / zinc stannate at 223℃ (mix for 5.5 minutes). Secondary feeding: Add whiskers / silicon carbide at 232℃ (mix for 9 minutes); For the final feeding, aluminum hypophosphate / borate was injected at 243°C (mixed for 9.8 minutes). Extrusion granulation: Step temperature control, Zone I 215℃ → Zone II 242℃ → Zone III gradient (254→259℃, 3℃ / min) → Zone IV 261℃ + deep dehydration (-0.098MPa); Irradiation crosslinking: High-intensity pulse, 62kGy (9kGy / pass) → pause for 22min → replenish 37kGy (15kGy / pass); Heat setting and cooling: 128℃ setting for 12min → three-control cold strengthening, air cooling → water mist quenching → slow cooling (136℃-16℃ / s → 76℃-28℃ / s → 22℃-2.5℃ / s); Comparative Example 1 The flame retardant material consists of 75 parts FEP resin, 12 parts perfluorooctanoic acid ammonium, 8 parts antimony trioxide, 15 parts glass fiber, and 10 parts calcium carbonate filler. The preparation process is as follows: Mixing: Add all components to a high-speed mixer at once and mix at room temperature for 15 minutes; Extrusion granulation: single-temperature zone screw (constant temperature 280℃), no vacuum dehydration; Irradiation crosslinking: Single through irradiation (total dose 85 kGy, dose rate 11 kGy / pass). Molding and cooling: Hot pressing (145℃×15MPa×10min) → direct air cooling to room temperature.

[0024] Comparative Example 2 60 parts PPO resin, 25 parts ammonium polyphosphate, 15 parts pentaerythritol, 12 parts nylon, 18 parts ordinary potassium titanate whiskers, and 2 parts zinc stearate lubricant. The preparation process is as follows: mixing: resin / flame retardant synergist / whiskers are fed in simultaneously and mixed at 200℃ for 18 minutes; Extrusion granulation: Three-stage temperature control (Zone I 200℃ / Zone II 228℃ / Zone III 242℃), no gradient temperature rise; Irradiation crosslinking: single irradiation (70 kGy constant dose rate); Cooling treatment: After molding, the material is rapidly cooled in a room temperature water bath (water temperature 25℃).

[0025] The specific formulation data of the embodiments and comparative examples of the present invention are shown in Table 1 below: Table 1

[0026] Based on the above 3 sets of examples, 2 sets of comparative examples, and Table 1: Mechanism and effect of Example 1: The flame retardant synergistic mechanism is that aluminum hypophosphite, melamine salt, and zinc borate form a triple firewall of gas phase, condensed phase, and free radicals: high-temperature dehydration of hypophosphite initiates molecular cross-linking; melamine salt expands upon heating, releasing inert gas to dilute oxygen; zinc borate melts and covers the cracks in the char layer, and zirconium phosphate catalyzes and improves char formation efficiency (compared to systems without smoke suppressants). The interface strengthening pathway involves the amino (-NH2) groups grafted onto the surface of aluminum silanized borate whiskers forming an ion-dipole interaction with the ECTFE chain segments. Simultaneously, the anhydride groups of MAH-g-EVA bond with the hydroxyl groups of the whiskers during the mixing process, achieving organic-inorganic phase nano-interpenetration and improving stress transfer efficiency. The principle of irradiation anti-interference and the segmented feeding strategy isolate the flame retardant synergist from competing with the crosslinking active sites. The first mixing makes the toughening agent and resin form a continuous phase, and the flame retardant synergist added in the last addition is physically dispersed in it. During irradiation, the electron beam preferentially attacks the double bonds of the matrix to build the network skeleton.

[0027] Mechanism and effect of Example 2: With its low toxicity, aluminum hypophosphate and montmorillonite form a layered double metal hydroxide (LDH) analog. During combustion, the montmorillonite sheets are oriented to intercalate into the carbon layer, and the aluminum hypophosphate is pyrolyzed to generate an AlPO4 framework. The two form a nano-closed unit that inhibits the escape of small toxic molecules of benzene.

[0028] Cross-linking precision control core, pulse irradiation strategy (first round 58kGy → relaxation 18min → supplementary irradiation 33kGy) solves the energy absorption interference of flame retardant synergist: the first round of irradiation establishes a primary network at the whisker / resin interface, the thermal motion of flame retardant synergist molecules during the relaxation period releases captured free radicals, and supplementary irradiation strengthens the density of cross-linking points of phase domains. For protection against thermo-oxidative aging, calcium silicate whiskers-modified montmorillonite form a Si-O-Al inorganic network on the material surface, which preferentially captures free radicals during long-term service and delays the breakage of the resin main chain.

[0029] Mechanism and Effects of Example 3: Extreme temperature tolerance: the siloxane bonds (Si-O-Ti) on the surface of potassium silanized titanate whiskers are transformed into a ceramic phase framework above 300℃, and nano-silicon carbide is dispersed to fill the pores; melamine borate melts to form B2O3 glass, which has a dual effect of locking the thermal motion of molecular chains. Radiation damage suppression: Ultra-high dose pulsed irradiation (total 99kGy) is achieved through two-stage energy loading: the first stage of 62kGy constructs high-density cross-linking points, followed by a 22-minute pause to relax the stress around the whiskers, and a supplementary irradiation of 37kGy to complete interpenetration of the phase interface, thus avoiding microcracks around the whiskers caused by a single high peak dose.

[0030] The cooling stress dissipation technique, a three-control cooling process (air cooling → water mist quenching → gradient slow cooling), allows the material to pass through a decreasing rate curve of 16℃ / s → 28℃ / s → 2.5℃ / s in the Tg temperature range (136→76℃), matching the difference in thermal shrinkage between whiskers and resin, and eliminating internal stress concentration points.

[0031] Comparative Example 1 Interface failure mechanism: Untreated glass fiber and FEP resin are only bonded by van der Waals forces. At temperatures above 220°C, the dehydration and condensation of the silanol groups (-SiOH) in the glass fiber initiates agglomeration, and the stress field forms voids-fiber microcrack sources (size > 500 nm). Flame retardancy efficiency collapses: PFOA pyrolysis (>250℃) produces perfluoroisobutylene gas, and antimony trioxide (Sb2O3) simultaneously catalyzes the generation of highly toxic fluorinated fumes; its gas-phase flame retardant mechanism completely collapses in the absence of solid-phase synergists. Crosslinking network distortion: Sb3 + Ion trapping irradiated free radicals to form [Sb] + -e - The stable structure leads to the loss of crosslinking points (effective crosslinking density decreases by 54%).

[0032] Comparative Example 2 Autophagy effect of flame retardant synergists: APP (decomposition temperature ≈220℃) releases NH3 and H2O prematurely when mixed at 228℃, which not only destroys the integrity of the molecular chain, but also induces pentaerythritol (PER) to hydrolyze and generate acrolein (a precursor to tobacco poisoning). Reinforcement phase failure mechanism: Unmodified potassium titanate whiskers form a weak interface layer in nylon 6 (interfacial energy < 3 mJ / m). 2 The rapid cooling process leads to a difference in thermal shrinkage between the two (whisker CTE≈6×10). -6 / K vs PA6≈80×10 -6 / K), inducing whisker pull-out-matrix tearing failure; The dilemma of irradiation shielding: The phosphorus oxy group (P=O) of APP strongly absorbs electron beam energy and converts it into heat energy. The local temperature of the flame retardant synergist reaches 290℃, which triggers the chain breakage and degradation of PA6 molecules.

[0033] The effects of Examples 1-3 and Comparative Examples 1-2 are compared in Table 2 below: Table 2

[0034] From the above, it can be seen that in terms of flame retardancy, the proportion of physical hybrid flame retardants (fluoride poisons the flame / expansion system self-damages and forms char) is relatively high. However, the example constructs a gas-solid-liquid three-state flame retardant ecosystem through molecular-level synergy of aluminum hypophosphite metal coordination bonds, zinc borate molten film, and melamine gas generator, which completely avoids thermal decomposition runaway.

[0035] In terms of reinforcement, the comparative example uses geometric fiber filling reinforcement (glass fiber / unmodified whiskers), with interface defect size > material fracture critical value (dc≈100nm); the example uses silane coupling agent to construct grafted polymer brushes, forming a 50-200nm progressive modulus transition region around the whiskers to homogenize the stress field.

[0036] In terms of process control, traditional processes (comparative example) treat materials as static black boxes, leading to thermal degradation of flame retardant synergists and distortion of crosslinking points. This invention responds to material phase transitions through dynamic process control: temperature window tuning: the final feeding temperature gradient (E1241℃→E3243℃) matches the activation energy of the flame retardant synergist; irradiation energy distribution: the relaxation mechanism during the rest period releases the frozen stress of the molecular chains; and cooling rate programming: the slow cooling curve avoids abrupt changes in the free volume of the glass transition region.

[0037] In summary, this invention achieves stable flame retardancy at extreme high temperatures under halogen-free conditions through a special flame retardant system and molecular-level coordination with the matrix, completely avoiding the high-temperature deactivation problem of traditional flame retardant synergists; at the same time, it rapidly catalyzes the formation of a dense carbon layer during combustion, significantly inhibiting the release of smoke and toxic gases; furthermore, whisker reinforcement and compatibilization technology form a nanoscale interpenetrating structure of organic-inorganic phases, ensuring the mechanical strength and toughness of the material even under ultra-high filling conditions, and avoiding brittle fracture caused by stress concentration; The irradiation enhancement path designed specifically for the characteristics of halogen-free systems overcomes the interference of flame retardant components on cross-linking reactions, achieves efficient construction of molecular networks, endows products with precise shape memory function, and eliminates the risks of material decomposition, volatilization, and phase separation during high-temperature processing by temperature window control and segmented mixing process, ensuring the consistency of continuous production.

[0038] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-smoke, halogen-free flame-retardant material, characterized in that: This low-smoke halogen-free flame retardant material is prepared from the following parts by weight: The matrix resin consists of 60-80 parts, the composite phosphorus-nitrogen flame retardant system consists of 15-35 parts, the flame retardant synergist consists of 1-8 parts, the compatibilizer consists of 2-10 parts, the reinforcing and modifying filler consists of 5-15 parts, and the processing aid consists of 0.5-5 parts. The composite phosphorus-nitrogen flame retardant system contains aluminum hypophosphite and melamine cyanurate, and the mass ratio of aluminum hypophosphite to melamine cyanurate is (2:1)-(1:1). The compatibilizer comprises maleic anhydride graft polymer and ethylene-vinyl acetate copolymer (EVA), and the mass ratio of maleic anhydride graft polymer to EVA is (1:1) to (3:1), wherein the maleic anhydride graft polymer is selected from maleic anhydride grafted polyolefin or maleic anhydride grafted polyacrylate.

2. The low-smoke halogen-free flame retardant material according to claim 1, characterized in that, It also contains 0.1-3 parts of a heat stabilizer; the heat stabilizer is selected from organotin stabilizers, metal carboxylate stabilizers, or combinations thereof.

3. The low-smoke halogen-free flame retardant material according to claim 1, characterized in that, It also contains 0.1-2 parts of antioxidant; the antioxidant includes a primary antioxidant and a secondary antioxidant, the primary antioxidant being hindered phenols, and the secondary antioxidant being phosphites or thioethers.

4. The low-smoke halogen-free flame retardant material according to claim 1, characterized in that, The reinforcing and modified filler is a hybrid whisker pre-treated with a silane coupling agent, including aluminum borate whiskers and potassium titanate whiskers, with a mass ratio of aluminum borate whiskers to potassium titanate whiskers of (2:1)-(1:1). The silane coupling agent is γ-glycidoxypropyltrimethoxysilane or γ-methacryloyloxypropyltrimethoxysilane.

5. A method for preparing a low-smoke halogen-free flame retardant material, the method being used to prepare the low-smoke halogen-free flame retardant material according to any one of claims 1-4, characterized in that, It is prepared by the following steps: S1. Mix aluminum borate whiskers and potassium titanate whiskers at a mass ratio of (2:1)-(1:1), add 1.0-3.0 wt% of a silane coupling agent ethanol solution equivalent to the total mass of the mixed whiskers; the concentration of the silane coupling agent ethanol solution is 5-20 wt%; and shear and stir at high speed at 60-85℃ for 30-90 minutes, then dry until the moisture content is ≤0.5 wt% to obtain silanized mixed whiskers; S2. Add the ethylene-trifluorochloroethylene copolymer to a mixer for melt plasticization, and control the temperature at 230-260℃; Add a compatibilizer combination of maleic anhydride grafted polymer and ethylene-vinyl acetate copolymer, a flame retardant synergist and the silanized mixed whiskers obtained in step S1, and mix at 230-250°C for 8-15 minutes. The composite phosphorus-nitrogen flame retardant system is added in two stages: first, melamine cyanurate salt is added and mixed for 3-6 minutes; then, aluminum hypophosphite is added to avoid excessive local high temperature in the initial stage and mixed for 8-12 minutes. S3. The blend obtained in step S2 is extruded and granulated using a twin-screw extruder; the extruder temperature is set in sections as follows: Zone I 200-210℃, Zone II 235-245℃, Zone III 245-255℃, Zone IV 250-260℃, and the die head 240-250℃; the screw speed is 150-300 rpm, and the vacuum dehydration degree is ≥-0.08MPa; S4. The particles obtained in step S3 are extruded into tubular preforms and crosslinked by irradiation with a dose of 50-100kGy under an electron accelerator, with the radiation dose rate controlled at 5-15kGy / pass. S5. Preheat the irradiated tube preform at 110-130℃, heat it to ≥190℃ at a rate of 1.5-3.5℃ / s in the range of 100-380℃, and then rapidly cool it to room temperature for shaping.

6. The method for preparing a low-smoke halogen-free flame retardant material according to claim 5, characterized in that, In step S5 heat setting, rapid cooling is achieved using a three-stage controlled cooling system: the first stage is air cooling to 140℃ at a rate of 15℃ / s; the second stage is water mist quenching to 80℃ at a rate of ≥30℃ / s; and the third stage is slow cooling to room temperature at a rate of ≤5℃ / s.

7. The method for preparing a low-smoke halogen-free flame retardant material according to claim 6, characterized in that, Step S4, irradiation crosslinking, employs variable dose technology: the first round is 50 kGy at a dose rate of 8 kGy / pass, followed by a short pause and a supplementary dose of 20-30 kGy at a dose rate of 12 kGy / pass.

8. The method for preparing a low-smoke halogen-free flame retardant material according to claim 7, characterized in that, During the extrusion granulation in step S3, a stepped heating mode is adopted in zone III, with a temperature of 245-250℃ and a gradient of 3℃ / min. Zone IV is kept at a constant temperature of 255±2℃, and vacuum dehydration is carried out in zone IV with a vacuum degree ≤-0.09MPa.

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