Low-smoke halogen-free heat conduction pipe material and preparation method thereof

Abstract

The invention belongs to the technical field of polymer composite materials, and particularly discloses a low-smoke halogen-free heat-conducting pipe material and a preparation method thereof.The low-smoke halogen-free heat-conducting pipe material is prepared by taking polypropylene as a matrix and adding a functional polyolefin compatilizer, a composite flame-retardant system, modified heat-conducting flame-retardant filler, high-temperature-resistant resin and a cross-linking system; the material is prepared through interface modification blending, melt blending and extrusion molding. The APTES grafted inorganic filler, the compatilizer and the matrix resin form a chemical molecule bonding interface, interface gaps are eliminated, the polyether sulfone resin and a composite cross-linking system are added to synergistically improve the high-temperature stability, and the material can stably work at 150 DEG C for a long time. The material disclosed by the invention has the advantages of low smoke, no halogen, efficient flame retardance, excellent mechanical property and high heat conduction efficiency, is suitable for harsh scenes such as cable protection pipes and the like, is simple in preparation process and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically a low-smoke halogen-free heat pipe material and its preparation method. Background Technology

[0002] Cable protection conduits, as core protective components of electrical systems, are widely used in construction, industrial manufacturing, rail transportation, new energy, and other fields. Their core function is to isolate external mechanical damage and environmental corrosion, and to suppress the spread of flames in dangerous scenarios such as fires, thus protecting the safety of internal cables. Traditional cable protection conduits are mostly made of polyvinyl chloride (PVC). Although they have advantages such as low processing costs and acceptable flame retardancy, they release large amounts of dense black smoke and toxic and corrosive gases such as hydrogen chloride (HCl) during fires, seriously hindering personnel evacuation and fire rescue. They also corrode precision electronic equipment, causing secondary disasters, and are no longer able to meet modern safety and environmental protection standards.

[0003] With increasingly stringent safety and environmental regulations, low-smoke halogen-free (HFLS) materials have become the mainstream development direction for cable protection pipes. Polypropylene (PP) has become an ideal substrate to replace PVC due to its balanced mechanical properties, excellent chemical stability, environmental friendliness, non-toxicity, and good processing fluidity. However, pure PP material has two major drawbacks as a cable protection pipe material: firstly, it is flammable and cannot meet fire safety requirements without flame-retardant modification; secondly, it has poor thermal conductivity, with a thermal conductivity of only 0.2-0.3 W / (m·K), which easily leads to the accumulation of heat generated during cable operation, accelerating material aging and cable insulation failure.

[0004] In existing technologies, the flame retardant modification of low-smoke halogen-free PP materials mainly involves adding inorganic metal hydroxides (such as aluminum hydroxide ATH and magnesium hydroxide MDH) and thermally conductive fillers. This can increase the thermal conductivity and flame retardant properties of the material, but this method has the following drawbacks: 1. High addition amount: Generally, inorganic metal hydroxides need to be added at more than 50 wt.% to achieve V0 flame retardancy, which leads to a significant decrease in the mechanical properties of the material and a deterioration in processing fluidity; 2. Poor interfacial compatibility: There are molecular-level gaps between the inorganic flame retardant / thermal conductive filler and the PP resin matrix, resulting in poor compatibility between the two. This not only causes fluctuations in the mechanical properties of the material and uneven dispersion during processing, but also generates significant interfacial thermal resistance, disrupts the continuity of the thermal conductive network, and reduces thermal conductivity. 3. Insufficient high-temperature stability: The long-term operating temperature of existing low-smoke halogen-free PP materials is mostly below 120℃. Under high-temperature conditions of 150℃ (such as around industrial kilns, outdoor wiring in high-temperature areas, and inside new energy equipment cabins), they are prone to thermal deformation and rapid degradation of mechanical properties, which cannot meet the needs of special application scenarios.

[0005] Therefore, developing a cable protection pipe material that combines low smoke and halogen-free properties, high efficiency flame retardancy, excellent mechanical properties, high thermal conductivity, and stable operation at 150℃ has become the key to solving the industry's pain points. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-smoke halogen-free heat pipe material and its preparation method. Through synergistic design such as interface modification, composite flame retardancy, high-temperature enhancement and cross-linking regulation, the technical problems of poor compatibility between inorganic fillers and resin matrix and insufficient high-temperature stability of materials are solved. The invention achieves a breakthrough in the comprehensive performance of the material in terms of low smoke halogen-free, high efficiency flame retardancy, excellent mechanical properties, high thermal conductivity and stable operation at 150℃. It is suitable for cable protection scenarios with stringent requirements for safety, heat dissipation and high temperature resistance.

[0007] A low-smoke halogen-free heat pipe material comprises the following components by weight: 55-80 parts polypropylene matrix, 3-8 parts polyethersulfone resin, 15-25 parts composite filler, 5-10 parts compatibilizer, 0.5-2 parts crosslinking agent, 0.5-2 parts co-crosslinking agent, 0.5-1 part anti-aging agent, and 8-15 parts flame retardant.

[0008] Furthermore, the compatibilizer is any one or more of polypropylene block copolymer-maleic anhydride graft (PP-g-MAH), dibutyl maleate grafted polyethylene (PE-g-DBM), or dibutyl maleate grafted ethylene propylene diene monomer (EPDM-g-DBM).

[0009] Furthermore, the composite filler comprises aluminum hydroxide (Al(OH)3) and boron nitride (hBN) in a mass ratio of 2:1 to 3:1; the aluminum hydroxide and boron nitride are grafted with APTES (3-aminopropyltriethoxysilane) at a grafting rate of 3-5%. In this invention, the surface of Al(OH)3 treated with APTES grafting is grafted with an APTES molecular layer via Al-O-Si covalent bonds, and the molecular layer thickness is precisely controlled at 2-3 nm; the amino terminus (-NH2) of APTES can form a stable NH•••O=C hydrogen bond network with the maleic anhydride group (-COO-) in PP-g-MAH, constructing a "sandwich-type" molecular bonding interface; h-BN and Al(OH)3 maintain a distance of more than 20 nm in the matrix to avoid phonon scattering caused by direct contact and ensure the continuity of the thermally conductive network.

[0010] Furthermore, the glass transition temperature of the polyethersulfone resin is ≥220℃; the polyethersulfone resin is modified by grafting maleic anhydride, and the grafting rate is 1.5-2%.

[0011] Furthermore, the crosslinking agent is a peroxide crosslinking agent, including any one or two of dicumyl peroxide (DCP) and di-tert-butyl peroxide (BIBP), and the co-crosslinking agent includes any one or more of triallyl isocyanurate (TAIC), high vinyl 1,2-polybutadiene (HVPBD), trimethylolpropane trimethacrylate (TMPTMA), and zinc dimethacrylate (ZDMA).

[0012] Furthermore, the flame retardant comprises a cyclic phosphonate and a monomeric N-alkoxy hindered amine in a mass ratio of 3:1 to 4:1.

[0013] Furthermore, the anti-aging agent includes any one or more of antioxidant 168, antioxidant 1010, and UV327.

[0014] This invention provides a method for preparing a low-smoke, halogen-free heat pipe material, comprising the following steps: S1. Dry the raw materials to remove surface moisture and set aside; S2. Add polypropylene matrix, composite filler, compatibilizer and polyethersulfone resin to a mixing unit, set parameters and mix to obtain pre-dispersion material; S3. Add the pre-dispersed material, crosslinking agent, co-crosslinking agent, flame retardant and anti-aging agent to the mixing device, set the parameters and mix to obtain the premixed material; S4. The premixed material is fed into an extruder for extrusion and granulation, and then placed into a molding machine for processing and molding to obtain a low-smoke halogen-free heat pipe material.

[0015] Furthermore, in step S2, the mixing temperature is 150–170°C, the mixing time is 10–20 min, and the shear force of the mixing device is 5–8 MPa.

[0016] Furthermore, in step S3, the mixing device rotates at a speed of 1000–1500 rpm, and the mixing time is 5–10 min.

[0017] Furthermore, in step S4, the extrusion temperature of the extruder is 160-200℃ and the rotation speed is 40-60 rpm; the processing temperature is 180-200℃ and the rotation speed is 30-50 rpm.

[0018] Beneficial effects: I. This invention constructs a molecular bonding interface of "Al-O-Si covalent bonds + hydrogen bonds" by grafting inorganic fillers with APTES, compatibilizers, and matrix resins, eliminating the interfacial voids between inorganic materials and organic resins in traditional composite materials, reducing the interfacial thermal resistance to below 0.02 m²·K / W; at the same time, h-BN and Al(OH)3 can be reasonably spaced to construct a continuous thermally conductive network, and the thermal conductivity of the material reaches 0.8-0.85 W / (m·K), which is 2-3 times higher than that of pure PP.

[0019] Second, the halogen-free synergistic flame retardant system using cyclic phosphonates and NOR-HAS requires only 8-15 parts to achieve UL94 V0 rating, with a minimum light transmittance of ≥60% and HCl release of <7% during combustion, fully meeting the stringent requirements for low-smoke halogen-free cable protection materials.

[0020] Third, by using polyethersulfone resin and composite crosslinking system, the material can work stably for a long time at 150℃. After heat aging at 150℃, the tensile strength retention rate is ≥90% and the impact strength retention rate is ≥88%. The performance change rate is far lower than the industry standard of ±25%, which solves the technical pain point of high temperature failure of existing low smoke halogen-free materials.

[0021] IV. The functionalized compatibilizer and crosslinking system synergistically enhance the interfacial bonding force between the resin and the inorganic filler. The material has a tensile strength ≥12MPa, an elongation at break ≥110%, and an impact strength (unnotched) ≥9kJ / m², meeting the mechanical protection requirements of cable protection pipes.

[0022] V. Excellent processing performance and environmental protection: The composite system has good compatibility and a melt flow rate of 2.0-3.0 g / 10 min. It can be produced by conventional twin-screw extrusion and pipe forming processes without the need for special equipment. All raw materials are halogen-free and environmentally friendly, with no release of toxic or harmful substances, and meet environmental protection standards. Detailed Implementation

[0023] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Example 1 This embodiment provides a low-smoke halogen-free heat pipe material, comprising the following parts by weight: 70 parts polypropylene matrix, 5 parts polyethersulfone resin, 18 parts composite filler, 8 parts compatibilizer, 1.2 parts crosslinking agent, 0.8 parts co-crosslinking agent, 0.5 parts anti-aging agent, and 12 parts flame retardant. The composite filler contains aluminum hydroxide (Al(OH)3) in a mass ratio of 2.5:1 to boron nitride (BN). The compatibilizer is a polypropylene block copolymer-maleic anhydride graft (PP-g-MAH). The crosslinking agent is dicumyl peroxide, the co-crosslinking agent is triallyl isocyanurate, the anti-aging agent is antioxidant 1010, and the flame retardant contains a cyclic phosphonate in a mass ratio of 3:1 to the monomer N-alkoxyhedral amine (NOR-HAS).

[0024] The modification steps of Al(OH)3 and h-BN in the composite filler in this embodiment are as follows: The purchased Al(OH)3 has a particle size of 80-100 nm. The Al(OH)3 nanoparticles are pre-ground in a ball mill to remove the surface oxide layer. Then, the Al(OH)3 nanoparticles are dispersed in a mixed solvent of ethanol and water at a volume ratio of 7:3. 55 g of Al(OH)3 nanoparticles are added to 100 ml of the mixed solvent. Then, the pH of the system is adjusted to 4.5 with acetic acid, and stirred for 30 minutes in a 60°C water bath. After stirring, deionized water is added for centrifugation and washing at 8000 rpm for 10 minutes. This process is repeated three times to completely remove residual acetic acid and obtain activated Al(OH)3.

[0025] An ethanol solution of APTES (2% by mass) was added dropwise to an activated Al(OH)3 dispersion at 70°C and 500 rpm. After stirring and reflux for 2 hours, the mixture was washed three times by centrifugation with ethanol, and then dried under vacuum at 60°C to obtain APTES-modified Al(OH)3 particles. The modification method for h-BN was the same as described above.

[0026] This embodiment also provides a method for preparing a low-smoke halogen-free heat pipe material, including the following steps: S1. The polypropylene matrix and PP-g-MAH were vacuum dried at 80℃ for 4 hours, the composite filler was dried at 120℃ for 6 hours, and other raw materials were dried at room temperature for 2 hours. S2. Add the polypropylene matrix, composite filler, compatibilizer, and polyethersulfone resin to a mixer and blend for 10 minutes at 150°C and 5MPa shear stress to obtain a pre-dispersion. S3. Add the pre-dispersed material, crosslinking agent, co-crosslinking agent, flame retardant and anti-aging agent to a high-speed mixer and stir at 1200 rpm for 8 minutes to obtain the premix. S4. Add the premixed material to a twin-screw extruder, set the extrusion temperature (from hopper to die) to 160℃, 170℃, 180℃, 190℃, and 200℃, and the screw speed to 50 rpm. After the material undergoes melt shearing, cross-linking reaction, and uniform dispersion in the extruder, it is extruded through the die, cooled to room temperature in a water bath, and then pelletized by a pelletizer to obtain composite material particles. Place the composite material particles in a vacuum drying oven and dry at 90℃ for 2 hours to remove the moisture adsorbed during processing. Then, add the dried particles to an extrusion molding machine, set the molding temperature to 180-200℃, and the screw speed to 40 rpm, and extrude them through the corresponding die. After cooling, shaping, and traction cutting, the finished low-smoke halogen-free heat-conducting pipe is obtained.

[0027] Example 2 This embodiment provides a low-smoke halogen-free heat pipe material, comprising the following parts by weight: 65 parts polypropylene matrix, 6 parts polyethersulfone resin, 20 parts composite filler, 10 parts compatibilizer, 1.4 parts crosslinking agent, 0.6 parts co-crosslinking agent, 0.6 parts anti-aging agent, and 10 parts flame retardant. The composite filler contains aluminum hydroxide (Al(OH)3) and boron nitride (BN) in a mass ratio of 2:1. The modification steps for aluminum hydroxide and boron nitride are the same as in Example 1. The compatibilizer is dibutyl maleate grafted ethylene propylene diene monomer (EPDMgDBM), the crosslinking agent is dicumyl peroxide, the co-crosslinking agent is zinc dimethacrylate, the anti-aging agent is antioxidant 1010, and the flame retardant contains cyclic phosphonate and N-alkoxy hindered amine monomer in a mass ratio of 3:1.

[0028] This embodiment also provides a method for preparing a low-smoke halogen-free heat pipe material, including the following steps: S1. The polypropylene matrix and EPDMGDBM were vacuum dried at 80℃ for 4 hours, the composite filler was dried at 120℃ for 6 hours, and the other raw materials were dried at room temperature for 2 hours. S2. Add the polypropylene matrix, composite filler, compatibilizer, and polyethersulfone resin to a mixer and blend for 10 minutes at 150°C and 5MPa shear stress to obtain a pre-dispersion. S3. Add the pre-dispersed material, crosslinking agent, co-crosslinking agent, flame retardant and anti-aging agent to a high-speed mixer and stir at 1200 rpm for 8 minutes to obtain the premix. S4. Add the premixed material to a twin-screw extruder, set the extrusion temperature (from hopper to die) to 160℃, 170℃, 180℃, 190℃, and 200℃, and the screw speed to 50 rpm. After the material undergoes melt shearing, cross-linking reaction, and uniform dispersion in the extruder, it is extruded through the die, cooled to room temperature in a water bath, and then pelletized by a pelletizer to obtain composite material particles. Place the composite material particles in a vacuum drying oven and dry at 90℃ for 2 hours to remove the moisture adsorbed during processing. Then, add the dried particles to an extrusion molding machine, set the molding temperature to 180-200℃, and the screw speed to 40 rpm, and extrude them through the corresponding die. After cooling, shaping, and traction cutting, the finished low-smoke halogen-free heat-conducting pipe is obtained.

[0029] Example 3 This embodiment provides a low-smoke, halogen-free heat pipe material, comprising the following parts by weight: 58 parts polypropylene matrix, 7 parts polyethersulfone resin, 22 parts composite filler, 12 parts compatibilizer, 1 part crosslinking agent, 1 part co-crosslinking agent, 0.7 parts anti-aging agent, and 14 parts flame retardant. The composite filler contains aluminum hydroxide (Al(OH)3) and boron nitride (BN) in a 3:1 mass ratio. The modification steps for aluminum hydroxide and boron nitride are the same as in Example 1. The compatibilizer is a 1:1 weight mixture of polypropylene block copolymer-maleic anhydride graft and dibutyl maleate grafted polyethylene. The crosslinking agent is dicumyl peroxide, the co-crosslinking agent is zinc dimethacrylate, the anti-aging agent is antioxidant 168, and the flame retardant contains a 4:1 mass ratio of cyclic phosphonate and N-alkoxy hindered amine monomer.

[0030] This embodiment also provides a method for preparing a low-smoke halogen-free heat pipe material, including the following steps: S1. The polypropylene matrix and compatibilizer are vacuum dried at 80℃ for 4 hours, the composite filler is dried at 120℃ for 6 hours, and other raw materials are dried at room temperature for 2 hours. S2. Add the polypropylene matrix, composite filler, compatibilizer, and polyethersulfone resin to a mixer and blend for 10 minutes at 150°C and 5MPa shear stress to obtain a pre-dispersion. S3. Add the pre-dispersed material, crosslinking agent, co-crosslinking agent, flame retardant and anti-aging agent to a high-speed mixer and stir at 1200 rpm for 8 minutes to obtain the premix. S4. Add the premixed material to a twin-screw extruder, set the extrusion temperature (from hopper to die) to 160℃, 170℃, 180℃, 190℃, and 200℃, and the screw speed to 50 rpm. After the material undergoes melt shearing, cross-linking reaction, and uniform dispersion in the extruder, it is extruded through the die, cooled to room temperature in a water bath, and then pelletized by a pelletizer to obtain composite material particles. Place the composite material particles in a vacuum drying oven and dry at 90℃ for 2 hours to remove the moisture adsorbed during processing. Then, add the dried particles to an extrusion molding machine, set the molding temperature to 180-200℃, and the screw speed to 40 rpm, and extrude them through the corresponding die. After cooling, shaping, and traction cutting, the finished low-smoke halogen-free heat-conducting pipe is obtained.

[0031] Comparative Example 1 The difference between this comparative example and the embodiment is that polyethersulfone resin was not added to the raw materials. Specifically, the raw materials include the following parts by weight: 75 parts polypropylene matrix, 18 parts composite filler, 8 parts compatibilizer, 1.2 parts crosslinking agent, 0.8 parts co-crosslinking agent, 0.5 parts anti-aging agent, and 12 parts flame retardant. The composite filler contains aluminum hydroxide (Al(OH)3) in a mass ratio of 2.5:1 to boron nitride (BN). The compatibilizer is a polypropylene block copolymer-maleic anhydride graft (PP-g-MAH). The crosslinking agent is dicumyl peroxide, the co-crosslinking agent is triallyl isocyanurate, the anti-aging agent is antioxidant 1010, and the flame retardant contains a cyclic phosphonate in a mass ratio of 3:1 to the monomer N-alkoxyhedral amine. Other preparation methods are consistent with the embodiment.

[0032] Comparative Example 2 The difference between this comparative example and the embodiment is that the boron nitride and aluminum hydroxide in the composite filler have not been modified, while the other components and preparation methods are the same as in Example 1.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that no compatibilizer was added. Specifically, it comprises the following components by weight: 70 parts polypropylene matrix, 5 parts polyethersulfone resin, 18 parts composite filler, 1.2 parts crosslinking agent, 0.8 parts co-crosslinking agent, 0.5 parts anti-aging agent, and 12 parts flame retardant. Other components and preparation methods are the same as in Example 1.

[0034] Comparative Example 4 The difference between this comparative example and Example 1 is that no crosslinking agent or co-crosslinking agent was added. Specifically, it includes the following components by weight: 70 parts polypropylene matrix, 5 parts polyethersulfone resin, 18 parts composite filler, 8 parts compatibilizer, 0.5 parts anti-aging agent, and 12 parts flame retardant. Other components and preparation methods are the same as in Example 1.

[0035] Comparative Example 5 The difference between this comparative example and Example 1 lies in the weight proportions of the raw material components. Specifically, it includes the following weight proportions: 70 parts polypropylene matrix, 5 parts polyethersulfone resin, 30 parts composite filler, 13 parts compatibilizer, 1.2 parts crosslinking agent, 0.8 parts co-crosslinking agent, 0.5 parts anti-aging agent, and 5 parts flame retardant. Other components and preparation methods are the same as in Example 1.

[0036] The materials prepared in the above embodiments and comparative examples were tested for their properties. The test results are shown in Tables 1 and 2 below. The test standards are as follows: tensile strength and elongation at break GB / T 1040.2-2006; unnotched impact strength GB / T1043.1-2008; flame retardant rating GB / T 2408-2021; HCl release GB / T 17650.1; thermal conductivity GB / T10294-2008; interfacial thermal resistance GB / T32064-2015; performance retention rate after heat aging GB / T 7141-2021; melt flow rate GB / T 3682.1-2018; heat distortion temperature GB / T 1633-2000.

[0037] Table 1. Performance Test Table of Low-Smoke Halogen-Free Heat Pipe Materials Prepared in the Examples Performance index Example 1 Example 2 Example 3 Tensile strength (MPa) 13.2 12.5 13.8 Elongation at break (%) 172 178 165 Notched impact strength (kJ / m²) 9.8 9.2 10.5 Flame retardant grade V0 V0 V0 Minimum light transmittance (%) 70 65 72 HCl release amount (%) 6.2 6.8 5.9 Thermal conductivity (W / (m·K)) 0.81 0.82 0.85 Interface thermal resistance (m²·K / W) 0.018 0.019 0.017 Tensile strength retention rate after heat aging (%) 92 91 93 Impact strength retention rate after heat aging (%) 89 88 90 Melt flow rate (g / 10min) 2.5 2.3 2.4 Heat distortion temperature (℃) 165 162 168 Table 2. Performance Test Table of Low-Smoke Halogen-Free Heat Pipe Materials Prepared in the Comparative Example Performance index Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Tensile strength (MPa) 12.8 8.5 7.8 10.1 9.2 Elongation at break (%) 158 85 68 142 72 Notched impact strength (kJ / m²) 8.5 5.2 4.5 6.8 5.8 Flame retardant grade V0 V1 V1 V0 V2 Minimum light transmittance (%) 68 45 42 62 50 HCl release amount (%) 6.3 6.5 6.8 6.1 7.5 Thermal conductivity (W / (m·K)) 0.79 0.45 0.38 0.65 0.52 Interface thermal resistance (m²·K / W) 0.019 0.052 0.058 0.025 0.045 Tensile strength retention rate after heat aging (%) 60 75 72 78 70 Impact strength retention rate after heat aging (%) 55 68 65 70 63 Melt flow rate (g / 10min) 2.6 2.2 1.8 2.8 1.5 Heat distortion temperature (℃) 135 152 150 158 155 As shown in Table 1, the heat pipe material obtained in this embodiment has a higher thermal conductivity and lower smoke density than the comparative example, and the rate of change of interfacial thermal resistance is significantly reduced after thermal aging.

[0038] Compared to the examples, Comparative Example 1 did not add polyethersulfone resin and relied solely on the heat resistance of the PP matrix itself. However, the heat distortion temperature of pure PP is only around 100°C, and significant thermal oxidative degradation occurs at 150°C. The molecular chain breakage leads to a sharp decline in mechanical properties: after 1000 hours of heat aging at 150°C, the tensile strength retention rate decreased from 92% to 60%, the impact strength retention rate decreased from 89% to 55%, and the heat distortion temperature decreased from 165°C to 135°C, failing to meet the requirements for high-temperature applications. Furthermore, PP degradation at high temperatures exacerbates the generation of flue gas during combustion, reducing the minimum light transmittance from 70% to 68%.

[0039] Compared to the examples, Comparative Example 2 did not involve modification of boron nitride and aluminum hydroxide. In this invention, APTES was used to graft Al(OH)3 onto PP-g-MAH to construct a molecular bonding interface of "Al-O-Si covalent bonds + hydrogen bonds". This interface can eliminate interfacial voids in traditional composite materials, allowing the inorganic filler to form a tight molecular-level bond with the resin matrix. In contrast, Comparative Example 2 did not undergo APTES grafting treatment and did not contain PP-g-MAH. The Al(OH)3 and h-BN surfaces are inert groups, and only weak van der Waals forces exist between them and the PP matrix. A large number of interfacial voids exist, resulting in a sharp increase in interfacial thermal resistance. The air in the voids becomes a thermal conduction barrier. At the same time, direct contact between the fillers causes severe phonon scattering, disrupting the continuity of the thermal conduction network and causing a decrease in thermal conductivity. Meanwhile, due to insufficient interfacial bonding, stress concentration easily occurs at the interface under stress, leading to a significant decrease in mechanical properties. Tensile strength drops from 13.2 MPa to 8.5 MPa, elongation at break from 172% to 85%, and unnotched impact strength from 9.8 kJ / m² to 5.2 kJ / m². Furthermore, interfacial voids exacerbate smoke generation during combustion, reducing minimum light transmittance from 70% to 45% and significantly increasing smoke density.

[0040] Comparative Example 3 did not contain a compatibilizer. In this invention, the functionalized polyolefin compatibilizer is the core medium for constructing the interface. Without any compatibilizer, the polar groups on the surface of APTES-grafted Al(OH)3 and h-BN cannot effectively combine with the non-polar PP matrix, resulting in more severe interfacial porosity than in Comparative Example 1, thus reducing the thermal conductivity. Simultaneously, under stress, the filler is prone to delamination from the matrix, and stress concentration is far greater than in other comparative examples. The tensile strength drops to 7.8 MPa, the elongation at break is only 68%, and the unnotched impact strength is 4.5 kJ / m², failing to meet the basic mechanical protection requirements for cable protection pipes. Furthermore, the lack of a compatibilizer leads to decreased melt flowability, uneven material dispersion during processing, easy filler detachment during combustion, discontinuous char layer formation, a flame retardant rating reduced to V1, a minimum light transmittance of only 42%, a significantly increased smoke density, and an increase in HCl release to 6.8%, weakening the low-smoke halogen-free performance.

[0041] Compared to the examples, Comparative Example 4 did not include any crosslinking agent or co-crosslinking agent. The core function of the composite crosslinking system (peroxide crosslinking agent + co-crosslinking agent) of this invention is to construct a three-dimensional crosslinking network, strengthening interfacial bonding and material structural stability: the peroxide decomposes at the extrusion temperature to generate free radicals, initiating a crosslinking reaction between the PP molecular chains, PES molecular chains, and modified groups on the filler surface, thus upgrading the interfacial bonding from "molecular bonding" to "chemical crosslinking bonding"; the co-crosslinking agent can improve crosslinking efficiency, reduce crosslinking side reactions, and make the crosslinking network more uniform and dense. Comparative Example 4 does not contain a crosslinking system, lacks a three-dimensional crosslinking network support, and lacks chemical crosslinking reinforcement. Under stress, the interface is prone to slippage, the tensile strength decreases from 13.2 MPa to 10.1 MPa, and the elongation at break decreases from 172% to 142%. At the same time, the filler is prone to agglomeration in the matrix, leading to a decrease in thermal conductivity and an increase in interfacial thermal resistance. Furthermore, the material structure is prone to deformation at high temperatures. After 1000 hours of heat aging at 150℃, the tensile strength retention rate drops from 92% to 78%, the impact strength retention rate drops from 89% to 70%, and the heat distortion temperature drops from 165℃ to 158℃.

[0042] Comparative Example 5 altered the raw material ratios. The proportions of each component in this invention were precisely optimized to form a synergistic system of "matrix-filler-flame retardant-crosslinking." Comparative Example 5 disrupted this synergistic balance by increasing the filler content and decreasing the flame retardant content. Excessive composite filler tends to agglomerate in the matrix, disrupting the continuity of the thermally conductive network, increasing the interfacial thermal resistance to 0.045 m²·K / W, and decreasing the thermal conductivity. Simultaneously, excessive filler occupies matrix space, hindering the movement of PP molecular chains, reducing the elongation at break to 70%, and increasing melt viscosity during processing, with the MFR decreasing to 1.5 g / 10 min. Insufficient flame retardant content prevents the synergistic effect of the composite flame retardant system from being realized. The concentration of PO· free radicals released from the cyclic phosphonate is insufficient, weakening the quenching and charring effects of NOR-HAS, failing to effectively suppress flame spread, and reducing the flame retardant rating to V2. Furthermore, polymer degradation is more severe during combustion, with HCl release increasing to 7.5%, minimum light transmittance at only 50%, and low-smoke halogen-free performance failing to meet standards. Furthermore, excessive filler will hinder the cross-linking reaction, resulting in a decrease in cross-linking density, a less dense three-dimensional network structure, and a decrease in tensile strength retention rate to 70% and impact strength retention rate to 63% after 1000 hours of heat aging at 150℃. The heat distortion temperature is 155℃, and the high-temperature stability is reduced.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-smoke, halogen-free heat pipe material, characterized in that: It comprises the following components by weight: 55-80 parts polypropylene matrix, 3-8 parts polyethersulfone resin, 15-25 parts composite filler, 5-10 parts compatibilizer, 0.5-2 parts crosslinking agent, 0.5-2 parts co-crosslinking agent, 0.5-1 part anti-aging agent, and 8-15 parts flame retardant.

2. The low-smoke halogen-free heat pipe material according to claim 1, characterized in that: The compatibilizer is any one or more of polypropylene block copolymer-maleic anhydride graft, dibutyl maleate grafted polyethylene, or dibutyl maleate grafted ethylene propylene diene monomer (EPDM) rubber; the polyethersulfone resin is modified by maleic anhydride grafting, and the grafting rate is 1.5-2%.

3. The low-smoke halogen-free heat pipe material according to claim 1, characterized in that: The composite filler comprises aluminum hydroxide and boron nitride in a mass ratio of 2:1 to 3:1; the aluminum hydroxide and boron nitride are modified by APTES grafting with an APTES grafting rate of 3 to 5%.

4. The low-smoke halogen-free heat pipe material according to claim 1, characterized in that: The crosslinking agent is a peroxide crosslinking agent, including any one or two of dicumyl peroxide and di-tert-butyl peroxide, and the co-crosslinking agent includes any one or more of triallyl isocyanurate, high vinyl 1,2-polybutadiene, trimethylolpropane trimethacrylate and zinc dimethacrylate.

5. The low-smoke halogen-free heat pipe material according to claim 1, characterized in that: The polyethersulfone resin has a glass transition temperature ≥220℃; the flame retardant comprises cyclic phosphonates and N-alkoxy hindered amine monomers in a mass ratio of 3:1 to 4:

1.

6. A low-smoke, halogen-free heat pipe material, characterized in that: The anti-aging agent includes any one or more of antioxidant 168, antioxidant 1010, and UV327.

7. The method for preparing the low-smoke halogen-free heat pipe material according to any one of claims 1-6, characterized in that: Includes the following steps: S1. Dry the raw materials to remove surface moisture and set aside; S2. Add polypropylene matrix, composite filler, compatibilizer and polyethersulfone resin to a mixing unit, set parameters and mix to obtain pre-dispersion material; S3. Add the pre-dispersed material, crosslinking agent, co-crosslinking agent, flame retardant and anti-aging agent to the mixing device, set the parameters and mix to obtain the premixed material; S4. The premixed material is fed into an extruder for extrusion and granulation, and then placed into a molding machine for processing and molding to obtain a low-smoke halogen-free heat pipe material.

8. The method for preparing the low-smoke halogen-free heat pipe material as described in claim 7, characterized in that: In step S2, the mixing temperature is 150–170°C, the mixing time is 10–20 min, and the shear force of the mixing device is 5–8 MPa.

9. The method for preparing the low-smoke halogen-free heat pipe material as described in claim 7, characterized in that: In step S3, the mixing device rotates at 1000-1500 rpm and the mixing time is 5-10 min.

10. The method for preparing the low-smoke halogen-free heat pipe material as described in claim 7, characterized in that: In step S4, the extrusion temperature of the extruder is 160-200℃ and the rotation speed is 40-60 rpm; the processing temperature is 180-200℃ and the rotation speed is 30-50 rpm.