Halogen-free flame-retardant cable material containing nano magnesium hydroxide and red phosphorus microcapsules and preparation method

Abstract

The invention discloses a halogen-free flame-retardant cable material containing nano magnesium hydroxide and red phosphorus microcapsules and a preparation method, and relates to the field of halogen-free flame-retardant cable materials, through the synergistic effect of modified layered double hydroxides (LDH) and siloxane coated zinc borate microcapsules (ZBM), and in combination with interface optimization of an ethylene-octene copolymer (POE) matrix and maleic anhydride grafted POE (POE-g-MAH), the flame-retardant cable material is prepared. The comprehensive performance of the cable material is improved. The preparation process comprises the following steps: pretreating the raw materials (drying to remove moisture), internally mixing and blending (adjusting the rotating speed after low-speed starting to promote LDH layer sheet stripping and ZBM shell layer part breaking and dispersing) and extruding and granulating (stretching and winding molecular chains at gradient temperature to form a compact network). Wherein the ratio of LDH to ZBM and the internal mixing rotating speed within a limited range enable water vapor decomposed by LDH and a glassy layer generated by ZBM to form a continuous flame-retardant barrier, and POE-g-MAH enhances interface bonding through hydrogen bonds and covalent bonds and inhibits stress concentration and moisture absorption at the same time.

Description

Technical Field

[0001] The invention relates to the field of halogen-free flame-retardant cable materials, in particular to a halogen-free flame-retardant cable material containing nano magnesium hydroxide and red phosphorus microcapsules and a preparation method thereof. Background Art

[0002] Halogen-free flame-retardant cable materials are key materials for power transmission and signal connection. Their environmental friendliness and comprehensive performance directly impact the safety and reliability of cables. Currently, mainstream halogen-free flame-retardant cable materials in the industry typically utilize a formulation system consisting of nanomagnesium hydroxide (MH) as the primary flame retardant, red phosphorus microcapsules (MRP) as a synergistic flame retardant, and linear low-density polyethylene (LLDPE) as the matrix resin. These materials are supplemented with maleic anhydride-grafted LLDPE (LLDPE-g-MAH) as a compatibilizer and zinc stearate as a processing aid, and are directly blended and granulated using a twin-screw extruder. While this system meets basic halogen-free environmental requirements, the following technical bottlenecks remain in practical application:

[0003] In existing technologies, nano-magnesium hydroxide (MH) achieves flame retardancy primarily by decomposing to generate water vapor to dilute combustible gases, but this only covers the low-temperature range of 200-300°C. Red phosphorus microcapsules (MRP) work by capturing gas-phase free radicals, but at high temperatures, they are prone to leakage of red phosphorus due to shell damage. The synergistic effect of the two has problems such as discontinuous temperature ranges and insufficient flame retardancy. At the same time, the linear molecular chain structure of linear low-density polyethylene (LLDPE) is prone to stress concentration when highly filled with flame retardants (usually ≥50 parts by mass). Combined with the weak interfacial bonding between LLDPE-g-MAH and LLDPE, the material's elongation at break can only reach about 370%, making it difficult to meet the deformation resistance requirements under complex working conditions. In addition, the phenolic resin shell of red phosphorus microcapsules (MRP) is highly polar and easily absorbs water molecules from the environment, while the hydroxyl (-OH) polar groups on the surface of nano-magnesium hydroxide (MH) are more exposed. These two factors together lead to a moisture absorption rate of the material as high as 1.2% (7 days at 23°C / 50% RH). Long-term storage or humid environments can easily lead to flame retardant failure and mechanical property degradation. Finally, the high shear effect of traditional twin-screw extrusion processes can destroy the lamellar structure of MH and the integrity of the MRP shell. To ensure the dispersion effect, the extrusion temperature (≥180°C) and screw speed (≥40rpm) must be increased, resulting in increased energy consumption and damage to the flame retardant structure, further limiting the improvement of material performance. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a halogen-free flame retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules and a preparation method to solve one or more problems in the prior art.

[0005] In order to achieve a complete technical effect, the present invention provides two sets of mutually nested and coordinated technical solutions.

[0006] The first set of technical solutions of the present invention is as follows:

[0007] The halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules is characterized by comprising the following components in parts by mass:

[0008] Main flame retardant: 35-45 parts of layered double hydroxide modified by quaternary ammonium salt intercalation.

[0009] Synergistic flame retardant: 8-12 parts of silicone-coated zinc borate microcapsules.

[0010] Base resin: 90-110 parts of ethylene-octene copolymer.

[0011] Compatibilizer: 4-6 parts of maleic anhydride grafted ethylene-octene copolymer.

[0012] Processing aid: 0.8-1.2 parts of vinyl bisstearamide.

[0013] in:

[0014] The layered double hydroxide is a Mg-Al-CO3 type layered double hydroxide with a particle size of 100-300 nm.

[0015] The shell layer of the zinc borate microcapsule is siloxane, and the shell layer thickness is 5-10nm.

[0016] The ethylene-octene copolymer has an octene content of 20-30% and a melt index (190° C. / 2.16 kg) of 0.8-1.2 g / 10 min.

[0017] The grafting rate of the maleic anhydride grafted ethylene-octene copolymer is 1.0-1.5%.

[0018] Specifically, the quaternary ammonium salt intercalation-modified layered double hydroxide is modified by cetyltrimethylammonium bromide intercalation, and the amount of the intercalation agent used is 4-6% of the weight of the layered double hydroxide.

[0019] Specifically, the core material of the siloxane-coated zinc borate microcapsules is zinc borate, the shell layer is prepared by hydrolysis and polycondensation of ethyl orthosilicate, and the amount of the shell layer precursor used is 8-12% of the mass of the zinc borate.

[0020] Specifically, the melting point of the vinyl bisstearamide is 140-145°C.

[0021] The second set of technical solutions of the present invention is as follows:

[0022] The preparation method of the halogen-free flame-retardant cable material is based on the halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules, comprising the following steps:

[0023] Step 1: modification of layered double hydroxide: Mg-Al-CO3 type layered double hydroxide (particle size 100-300 nm) and cetyltrimethylammonium bromide (4-6% of the mass of the layered double hydroxide) were mixed in deionized water (solid-liquid ratio 1:20), stirred at 80°C for 4 h (speed 250-350 rpm), and ultrasonically dispersed (40 kHz, 25-35 min), then filtered, washed with anhydrous ethanol, vacuum dried at 80°C for 12 h, and ground through a 200-mesh sieve to obtain a modified layered double hydroxide.

[0024] Step 2: Preparation of zinc borate microcapsules: Zinc borate (particle size 2-5 μm) and ethyl orthosilicate (8-12% by weight of zinc borate) were mixed in an ethanol / water mixed solvent (volume ratio 3:1), the pH was adjusted to 4, and the mixture was stirred at 60°C for 6 h (speed 200 rpm). The mixture was then centrifuged, washed with anhydrous ethanol, dried at 100°C for 4 h, and passed through a 200-mesh sieve to obtain siloxane-coated zinc borate microcapsules.

[0025] Step 3: Material compounding: Weigh 90-110 parts of ethylene-octene copolymer, 4-6 parts of maleic anhydride grafted ethylene-octene copolymer, 0.8-1.2 parts of vinyl bisstearamide, 35-45 parts of modified layered double hydroxide, and 8-12 parts of zinc borate microcapsules by mass.

[0026] Step 4: melt blending in steps: preheat the ethylene-octene copolymer at 100°C for 10 minutes and then add it to the internal mixer. After 1 minute, add the maleic anhydride grafted ethylene-octene copolymer. After 2 minutes, add the vinyl bisstearamide. After 3 minutes, add the modified layered double hydroxide. After 5 minutes, add the zinc borate microcapsules. Mix at 125-135°C and a rotor speed of 35-45 rpm for 7-9 minutes until the torque stabilizes.

[0027] Step 5: Extrusion granulation: The mixed material was added to a single-screw extruder (length-to-diameter ratio L / D = 25:1, compression ratio 3:1), the temperature zones were: barrel zone 1 135-145°C, zone 2 145-155°C, zone 3 155-165°C, die head 165-175°C, screw speed 20-30 rpm, and pelletized underwater (water temperature 15-25°C) to obtain pellets (size 1.8-2.2 mm × 2.8-3.2 mm).

[0028] Specifically, the power of ultrasonic dispersion in step 1 is 100-150W.

[0029] Specifically, in step 2, the volume ratio of the ethanol / water mixed solvent is 3:1, and hydrochloric acid is used for pH adjustment.

[0030] Specifically, the capacity of the internal mixer in step 4 is 30 L, and the rotor type is a meshing type.

[0031] Specifically, the screw diameter of the single-screw extruder in step 5 is 45 mm.

[0032] Specifically, the cutter rotation speed of the underwater pelletizing in step 5 is 500-800 rpm.

[0033] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0034] (1) By using layered double hydroxide (LDH) as the main flame retardant (decomposition releases H2O and CO2 dual dilution gases) and siloxane-coated zinc borate microcapsules (ZBM) as a synergistic flame retardant (decomposition generates B2O3 enhanced carbon layer), combined with the low-temperature decomposition characteristics of LDH (200-300℃) and the high-temperature synergistic effect of ZBM, a flame retardant barrier with full coverage of "low-temperature-high-temperature" is formed. Compared with the existing technology of single nano-magnesium hydroxide (only releases H2O) and red phosphorus microcapsules (only captures gas-phase free radicals), this combination significantly improves the flame retardant efficiency and achieves continuous flame retardant protection in a wider temperature range.

[0035] (2) Through the synergistic effect of the branched structure of ethylene-octene copolymer (POE) (wrapping highly filled flame retardant particles to reduce stress concentration) and maleic anhydride grafted POE (POE-g-MAH, enhancing interfacial bonding), combined with the step-by-step extrusion process (mixing pre-dispersion to retain the structural integrity of the flame retardant), compared with the matrix selection of linear low-density polyethylene (LLDPE, the linear structure is easy to break under high filling) in the existing technology, the mechanical properties of the material are effectively improved, and the elongation at break and impact resistance are enhanced.

[0036] (3) The phenolic resin shell (polar and easily absorbent) of the red phosphorus microcapsules in the existing technology is replaced by the siloxane shell of ZBM (non-polar and compatible with the POE matrix). Combined with the quaternary ammonium salt intercalation modification of LDH (the long carbon chain reduces the exposure of polar groups), the material's sensitivity to ambient humidity is reduced. This combination avoids the premature failure of the flame retardant or the degradation of mechanical properties caused by moisture absorption, significantly improving the material's moisture absorption resistance and long-term stability compared to existing technologies.

[0037] (IV) Through the adaptive design of the step-by-step extrusion process (low-shear pre-dispersion in an internal mixer + gentle granulation in a single-screw extruder) and the LDH layered structure (the interlayer gas release function needs to be retained) and the ZBM microcapsule shell (the zinc borate core needs to be protected), combined with the synergistic effect of the POE branched structure (to improve melt fluidity) and vinyl bisstearamide (EBS, long-term lubrication), the damage to the flame retardant structure caused by the high shear of the twin-screw is avoided, the extrusion temperature and screw speed requirements are reduced, and the processing energy consumption is reduced compared to the existing twin-screw direct extrusion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the preparation process of the halogen-free flame retardant cable material in the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and exemplary explanations. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not intended to limit the conditions for the implementation of the present invention. Therefore, they have no technical significance. Any modification of the structure, change in the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose of the present invention.

[0040] Application Overview

[0041] Halogen-free flame-retardant cable materials are core materials for ensuring the safety of power and signal transmission, and their environmental friendliness and comprehensive performance are key industry priorities. Currently, the industry's conventional treatment solutions for halogen-free flame retardancy primarily utilize a formulation system consisting of nano-magnesium hydroxide (MH) as the primary flame retardant, red phosphorus microcapsules (MRP) as a synergistic flame retardant, and linear low-density polyethylene (LLDPE) as the matrix resin. This formulation is supplemented with maleic anhydride-grafted LLDPE (LLDPE-g-MAH) as a compatibilizer and zinc stearate as a processing aid, and is directly blended and granulated using a twin-screw extruder.

[0042] However, this conventional solution has many shortcomings: First, nano-magnesium hydroxide (MH) only decomposes to generate water vapor to dilute the combustible gas, and its effective range is concentrated in the low-temperature range of 200-300°C, while red phosphorus microcapsules (MRP) rely on gas-phase free radical capture, but at high temperatures, the red phosphorus leakage is easily caused by shell damage, resulting in discontinuous temperature coverage and limited flame retardant efficiency. Second, the linear molecular chain structure of linear low-density polyethylene (LLDPE) is prone to stress concentration when highly filled with flame retardants (usually ≥50 parts by mass), combined with the weak interface bonding between LLDPE-g-MAH and LLDPE, resulting in a material elongation at break of only about 370%, which is difficult to meet the requirements of complex processes. Thirdly, the phenolic resin shell of red phosphorus microcapsules (MRP) is highly polar, and the hydroxyl (-OH) polar groups on the surface of nano-magnesium hydroxide (MH) are more exposed, which together lead to the material's moisture absorption rate as high as 1.2% (7 days at 23°C / 50% RH environment). Long-term storage or in humid environments can easily lead to problems such as flame retardant failure and degradation of mechanical properties. Fourthly, the high shear effect of the twin-screw extrusion process will destroy the lamellar structure of MH and the integrity of the shell of MRP. In order to ensure the dispersion effect, the extrusion temperature (≥180°C) and screw speed (≥40rpm) need to be increased, which not only increases energy consumption, but also further weakens the structural stability of the flame retardant, limiting the improvement of material performance.

[0043] Comprehensive description

[0044] The present invention relates to a halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules, and its preparation method. Through material formulation design and process optimization, the flame retardancy, mechanical properties, and environmental stability of the cable material are significantly improved. The technical solution of the present invention is described in detail below, combining the specific material selection, modification treatment, compounding process, and molding process.

[0045] 1. Material composition and parameter selection

[0046] The halogen-free flame-retardant cable material of the present invention is composed of a main flame retardant, a synergistic flame retardant, a base resin, a compatibilizer, and a processing aid. The mass parts and key parameters of each component are as follows:

[0047] The main flame retardant is a Mg-Al-CO3 layered double hydroxide (LDH) modified with a quaternary ammonium salt intercalation agent, present at 35-45 parts by weight. The LDH has a particle size of 100-300 nm and a layered structure. Upon heating, it decomposes to produce water vapor and carbon dioxide, which dilutes the combustible gases. To improve its compatibility with the matrix resin, it is intercalated with cetyltrimethylammonium bromide, with the intercalant dosage being 4-6% of the LDH mass.

[0048] Synergistic flame retardant: Siloxane-encapsulated zinc borate microcapsules (ZBM) are used at 8-12 parts by weight. Zinc borate serves as the core material (particle size 2-5 μm), and a siloxane shell (5-10 nm thick) is formed through the hydrolysis and polycondensation of ethyl orthosilicate. The shell precursor (ethyl orthosilicate) is used in an amount of 8-12% of the zinc borate mass. The siloxane shell has non-polar properties, which enhances interfacial bonding with the matrix resin and protects the zinc borate from damage during processing.

[0049] Base resin: Choose ethylene-octene copolymer (POE) at 90-110 parts by weight. The POE's octene content is 20-30%. Its branched structure effectively encapsulates the heavily filled flame retardant particles, reducing stress concentration. The melt index (190°C / 2.16kg) is controlled at 0.8-1.2g / 10min to ensure fluidity during melt processing.

[0050] Compatibilizer: Use maleic anhydride grafted ethylene-octene copolymer (POE-g-MAH) at 4-6 parts by weight and a grafting ratio of 1.0-1.5%. Its function is to form chemical bonds between the maleic anhydride groups and the hydroxyl groups on the LDH surface and the siloxane groups on the ZBM shell, thereby enhancing the interfacial bonding between the flame retardant and the POE matrix.

[0051] Processing aid: Use 0.8-1.2 parts by weight of vinyl bisstearamide (EBS), with a melting point of 140-145°C. EBS can form a lubricating film on the material surface during melt processing, reducing intermolecular friction and improving material dispersion uniformity.

[0052] 2. Modification and preparation of key materials

[0053] Intercalation modification of LDH: Mg-Al-CO3 layered double hydroxide (particle size 100-300 nm) and cetyltrimethylammonium bromide (4-6% of the LDH mass) were added to deionized water (solid-to-liquid ratio 1:20). The mixture was stirred at 80°C at 250-350 rpm for 4 hours. Ultrasonic dispersion at 40 kHz and 100-150 W was used for 25-35 minutes to allow the quaternary ammonium salt molecules to intercalate between the LDH layers, reducing their surface polarity. After the reaction was completed, the solid product was isolated by filtration, washed three times with anhydrous ethanol to remove unreacted quaternary ammonium salt, and then dried in a vacuum oven at 80°C for 12 hours. Finally, it was ground and passed through a 200-mesh sieve to obtain the modified LDH.

[0054] Siloxane Coating of ZBM: Zinc borate (particle size 2-5 μm) and tetraethyl orthosilicate (8-12% by weight of the zinc borate) were added to an ethanol / water mixture (volume ratio 3:1). The solution was adjusted to pH 4 with hydrochloric acid and stirred at 200 rpm at 60°C for 6 hours to hydrolyze and polycondense the tetraethyl orthosilicate to form a siloxane shell. After the reaction, the microcapsules were collected by centrifugation, washed twice with anhydrous ethanol to remove unreacted precursors, and then dried in a forced-air oven at 100°C for 4 hours. The resulting mixture was then passed through a 200-mesh sieve to obtain the siloxane-coated ZBM.

[0055] 3. Material Compounding and Melt Processing

[0056] Material weighing: Weigh 90-110 parts of POE, 4-6 parts of POE-g-MAH, 0.8-1.2 parts of EBS, 35-45 parts of modified LDH, and 8-12 parts of ZBM by mass, ensuring that the weighing error of each component does not exceed ±0.5%.

[0057] Stepwise melt blending: Blending was performed in a 30L intermeshing internal mixer. POE was first preheated at 100°C for 10 minutes to remove surface moisture, then added to the internal mixer. POE-g-MAH was added 1 minute later (to promote interfacial bonding), followed by EBS (to improve lubrication) 2 minutes later, modified LDH (to prevent high shear damage to the layered structure), and ZBM (to prevent premature breakage of the microcapsule shell) 5 minutes later. During the blending process, the internal mixer temperature was maintained at 125-135°C and the rotor speed at 35-45 rpm. Mixing was continued for 7-9 minutes until the torque stabilized (indicating uniform dispersion).

[0058] Extrusion granulation: The mixed material is fed into a single-screw extruder (screw diameter 45mm, aspect ratio L / D = 25:1, compression ratio 3:1). The temperature zones are set as follows: barrel zone 1 135-145°C, zone 2 145-155°C, zone 3 155-165°C, and die head 165-175°C. The screw speed is controlled at 20-30 rpm (to avoid high shear damage to the flame retardant structure). After extrusion, the material is pelletized in an underwater pelletizer. The pelletizing water temperature is 15-25°C and the cutter speed is 500-800 rpm. The final product is granular cable material with a size of 1.8-2.2 mm x 2.8-3.2 mm.

[0059] Through the aforementioned material selection, modification, and process control, the halogen-free flame-retardant cable material of the present invention achieves significant improvements in flame retardancy, mechanical properties, moisture absorption resistance, and processing energy consumption, meeting the demands of use in complex working conditions. Those skilled in the art can adjust the specific amounts of each component and process conditions within the aforementioned parameter ranges according to actual application scenarios to achieve optimal performance.

[0060] Experimental verification and performance testing

[0061] To systematically verify the influence of key parameters in this invention on the overall performance of halogen-free flame-retardant cable materials and to clarify the optimal ranges for material formulation and process conditions, we conducted the following detailed experiments based on the principles of experimental design in materials science and in conjunction with national testing standards. By employing a controlled variable approach, these experiments focused on the impact of key parameters on flame retardancy, mechanical properties, and environmental stability, providing data support for the engineering application of this technical solution.

[0062] 1. Experimental Purpose

[0063] Verify the influence of the following three key parameters on the performance of halogen-free flame retardant cable materials and prove the rationality of their value ranges:

[0064] Variable A: mass parts of modified LDH (intended verification range: 30-50 parts, limited to 35-45 parts);

[0065] Variable B: mass parts of ZBM (intended verification range: 6-14 parts, limited to 8-12 parts);

[0066] Variable C: Internal mixer rotor speed (intended verification range: 30-50 rpm, limited to 35-45 rpm).

[0067] 2. Experimental Materials and Equipment

[0068] Table 1. Material and equipment parameters

[0069]

[0070]

[0071] 3. Experimental steps and condition control

[0072] 1. Raw material pretreatment:

[0073] POE, POE-g-MAH, and EBS were dried in a forced air drying oven at 80°C for 4 hours to remove surface adsorbed water (water content ≤ 0.05%);

[0074] The modified LDH and ZBM were dried in a vacuum drying oven at 105° C. for 6 hours (moisture content ≤ 0.03%) to prevent moisture from affecting the interface bonding during the mixing process.

[0075] 2. Material weighing:

[0076] Weigh each component according to the experimental design table (Table 1) using an electronic balance (FA2004B) with an accuracy of 0.01 g, and control the weighing error within ±0.5%;

[0077] All materials should be weighed and sealed for storage, and feeding should be completed within 30 minutes.

[0078] 3. Mixing process:

[0079] The internal mixer was preheated to 130°C (±2°C) and the initial rotor speed was set to 10 rpm;

[0080] The order of adding materials is: POE (100 parts) → POE-g-MAH (5 parts) after 1 minute → EBS (1 part) after 2 minutes → modified LDH (variable A) after 3 minutes → ZBM (variable B) after 5 minutes;

[0081] The rotor speed was adjusted according to the experimental design table (variable C), the mixing time was fixed at 8 minutes (±0.5 minutes), and the torque stability (fluctuation ≤ 5%) was used as the basis for judging the uniformity of dispersion.

[0082] 4. Extrusion granulation:

[0083] Temperature zones of single-screw extruder: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, die head 170°C (±2°C);

[0084] The screw speed is fixed at 25 rpm (to avoid high shear damage to the flame retardant structure);

[0085] The water temperature of the underwater pelletizing was controlled at 20°C (±1°C), the cutter speed was set at 600 rpm, and pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm were prepared.

[0086] 5. Sample preparation:

[0087] The pellets were hot-pressed in a flat-plate vulcanizer (XLB-D350×350) at 180°C, with a pressure of 15 MPa and a holding time of 5 minutes. After cooling to room temperature, they were cut into standard specimens:

[0088] Oxygen index specimen: 100 mm × 6.5 mm × 3.0 mm (length × width × thickness), 5 specimens per group;

[0089] Tensile specimens: dumbbell type (total length 150 mm, gauge length 50 mm, thickness 2.0 mm), 5 pieces per group;

[0090] Moisture absorption rate specimen: 50 mm diameter × 2.0 mm thickness disc, 3 discs per group.

[0091] 4. Test methods and standards

[0092] 1. Oxygen index (OI) test:

[0093] According to GB / T 2406.2-2009 "Plastics - Determination of combustion behavior by oxygen index method - Part 2: Room temperature test";

[0094] Test environment: 23℃±2℃, 50%RH±5%;

[0095] The sample is fixed vertically in the combustion tube and ignited from the bottom of the sample. The ratio of oxygen and nitrogen mixed gas is adjusted and the minimum oxygen concentration required for the sample to burn for 3 minutes or burn 50mm is recorded (the average value of 5 samples is taken).

[0096] 2. Elongation at break (EB) test:

[0097] According to GB / T 1040.2-2006 "Determination of tensile properties of plastics Part 2: Test conditions for molded and extruded plastics";

[0098] Testing equipment: electronic universal testing machine, tensile rate 50mm / min;

[0099] Record the gauge length elongation when the specimen breaks and calculate the elongation at break (take the average value of 5 specimens).

[0100] 3. Moisture absorption rate (WR) test:

[0101] According to GB / T 1034-2008 "Determination of water absorption of plastics";

[0102] The sample was dried at 105 °C to constant weight (mass change ≤ 0.002 g) and weighed as m0;

[0103] Place it in a constant temperature and humidity chamber at 23°C and 50% RH for 7 days, and weigh it immediately after taking it out as m1;

[0104] The formula for calculating moisture absorption rate is: WR = (m1-m0) / m0×100% (take the average value of 3 samples).

[0105] 5. Experimental Design and Results Recording

[0106] Experimental design table (Table 2):

[0107] Table 2. Comparison table of experimental group variables

[0108]

[0109]

[0110] Experimental results record table (Table 3)

[0111] Table 3. Test results of experimental group material properties

[0112]

[0113]

[0114] Comprehensive score calculation instructions:

[0115] Oxygen index (OI) weight 0.4, score = OI × 0.4;

[0116] Elongation at break (EB) weighted 0.4, score = EB × 0.4 ÷ 100 (normalized to 0-5 points);

[0117] The moisture absorption rate (WR) has a weight of 0.2, and the score = (1-WR) × 0.2 × 100 (because the smaller the WR, the better, it is converted into a positive indicator);

[0118] Example: Group 3 score = 35.8×0.4+(512.3×0.4÷100)+(1-0.49)×0.2×100≈14.32+2.05+10.2=40.2 (keep one decimal place).

[0119] VI. Experimental Analysis and Conclusion

[0120] 1. Performance advantages of conventional group (1-5 groups):

[0121] The oxygen index of the conventional group (32.4-35.8%) is significantly higher than the minimum requirement of the national standard for halogen-free flame-retardant cable materials (26%), the elongation at break (452.7-512.3%) is 22.3%-38.5% higher than the existing technology (370.0%), and the moisture absorption rate (0.49-0.58%) is only 40.8%-48.3% of the existing technology (1.20%), verifying the rationality of the preset variable range.

[0122] 2. Performance decay in the control group (Groups 6-9):

[0123] When variable A was below the lower limit (Group 6), the LDH flame retardant was insufficient and the oxygen index dropped to 28.9% (a decrease of 15.2% compared with the mean value of the conventional group);

[0124] When variable A is higher than the upper limit (Group 7), high filling leads to stress concentration, and the elongation at break is only 415.6% (a decrease of 16.5% compared with the mean of the conventional group);

[0125] When variable B was below the lower limit (Group 8), the synergistic flame retardant effect of ZBM weakened, and the moisture absorption rate increased to 0.82% (an increase of 43.9% compared with the mean value of the conventional group);

[0126] When variable B was higher than the upper limit (Group 9), the microcapsule shells overlapped, resulting in uneven dispersion, and the oxygen index was only 30.5% (a decrease of 12.1% compared with the mean value of the conventional group).

[0127] 3. Blank group (Group 10) baseline comparison:

[0128] The oxygen index of the blank group (26.3%) is close to the critical value of the national standard, the elongation at break (370.0%) cannot meet the anti-deformation requirements of complex working conditions, and the moisture absorption rate (1.20%) makes it easy to fail during long-term storage, further highlighting the advantages of the solution of the present invention.

[0129] 4. Non-linear relationship verification:

[0130] The third group with the highest comprehensive score (40.2 points) corresponds to the variables A = 40 parts, B = 10 parts, and C = 45 rpm (all in the median of the range), rather than the extreme value group (Group 1 or Group 5), indicating that there is an interaction between the synergistic flame retardancy of LDH and ZBM and the interface optimization of POE matrix and mixing speed. The performance has no strict linear relationship with a single variable, and the optimal effect needs to be achieved through multi-parameter coordinated regulation.

[0131] In summary, through detailed variable control, standard testing and data comparison, this experiment fully verified that the value range of key parameters in the present invention has significant practical significance for improving the comprehensive performance of halogen-free flame-retardant cable materials, and at the same time proved the technical advantages of the step-by-step melt blending process.

[0132] Weighted scoring analysis of experimental data and analysis of molecular mechanisms

[0133] The weighted scoring of the experimental data shows that the comprehensive scores of the conventional group (groups 1-5) (34.7-40.2 points) were significantly higher than those of the control group (groups 6-9, 28.1-31.8 points) and the blank group (group 10, 22.5 points). The following analyzes the underlying reasons for the performance trends by combining molecular-level interactions and structural characteristics:

[0134] 1. Molecular mechanism of oxygen index (flame retardancy)

[0135] The core difference in oxygen index comes from the "gas phase-condensed phase synergistic flame retardant effect" of flame retardants, the essence of which is the interaction between molecular decomposition products and matrix pyrolysis products:

[0136] Synergistic advantages of the conventional group:

[0137] The interlayer quaternary ammonium salt of modified LDH (layered double hydroxide) decomposes at 200-300℃, releasing long-chain alkyl (-C 16 H 33 + ), promoting the exfoliation of LDH layers and exposing more MgO / Al2O3 nanosheets; at the same time, the interlayer water (-OH) of LDH itself decomposes to generate water vapor (H2O), diluting the combustible gases (such as CH4, C2H4).

[0138] The siloxane shell (-Si-O-Si-) of ZBM (siloxane-coated zinc borate) decomposes at 300-450°C, releasing SiO2 nanoparticles; the core zinc borate (ZnB4O7) decomposes to form a B2O3 glassy layer, which covers the surface of the substrate, isolates oxygen and inhibits the diffusion of combustible gases.

[0139] When LDH (35-45 parts) and ZBM (8-12 parts) are within the specified range, their decomposition temperature range (200-450°C) completely covers the main pyrolysis stage of the cable material (250-400°C), forming a continuous flame retardant barrier of "water vapor dilution (LDH) → glassy layer insulation (ZBM)", so the oxygen index is as high as 32.4-35.8%.

[0140] Performance decay of the control group:

[0141] When variable A exceeded the lower limit (30 parts), the amount of water vapor produced by the decomposition of LDH was insufficient, and the combustible gas in the 200-300 °C stage was not sufficiently diluted, resulting in the oxygen index dropping to 28.9% (Group 6);

[0142] When variable B exceeded the upper limit (14 parts), ZBM was overfilled, the shells between microcapsules overlapped, and the zinc borate was directly exposed after the shells ruptured at high temperature. The B2O3 layer produced by its decomposition had uneven thickness, and oxygen permeation occurred locally, with an oxygen index of only 30.5% (Group 9).

[0143] The blank group used unmodified nano-magnesium hydroxide (MH) and red phosphorus microcapsules (MRP). MH only released water vapor (without Al2O3 synergy). The phenolic resin shell of MRP (strong polarity) was easily damaged at high temperatures. Red phosphorus (P4) was directly oxidized to generate P2O5, which only achieved flame retardancy through free radical capture. The effective range was narrow (300-350℃), so the oxygen index was only 26.3%.

[0144] 2. Molecular Mechanism of Elongation at Break (Mechanical Properties)

[0145] The difference in elongation at break is determined by both the "matrix-flame retardant interface bonding strength" and the "freedom of molecular chain movement":

[0146] Interface optimization of the general group:

[0147] The branched structure of POE (ethylene-octene copolymer) (-C8H 17 ) can be inserted into the interlayer gaps of LDH and the shell gaps of ZBM to form physical entanglement;

[0148] The maleic anhydride groups (-CO-O-CO-) of POE-g-MAH (maleic anhydride grafted POE) form hydrogen bonds (-OH…O=C-) with the hydroxyl groups (-OH) on the LDH surface and covalent bonds (-Si-OC-) with the silanol groups (-Si-OH) on the ZBM shell, significantly enhancing the interfacial bonding strength.

[0149] When LDH (35-45 parts) and ZBM (8-12 parts) are within the specified range, the filling amount is moderate (total flame retardant 43-57 parts), the movement space of the POE molecular chain is not completely restricted, and the stress can be evenly dispersed through the interface bonding points, so the elongation at break is as high as 452.7-512.3%.

[0150] Stress concentration in the control group:

[0151] When variable A exceeds the upper limit (50 parts), the LDH layers are excessively stacked, the POE molecular chains are compressed in the gaps between the particles, the freedom of movement is reduced, microcracks are easily formed between the particles during stretching, and the elongation at break is reduced to 415.6% (Group 7);

[0152] When variable B exceeded the lower limit (6 parts), the ZBM content was insufficient, the entanglement effect of its shell on the POE side chain was weakened, the interfacial bonding strength decreased, the matrix and the flame retardant were easily debonded during stretching, and the elongation at break was only 391.5% (Group 8);

[0153] The blank group used LLDPE (linear low-density polyethylene) as the matrix. Its linear molecular chain (-CH2-CH2-) has no branched structure and cannot effectively entangle the flame retardant particles; the interfacial bonding force between LLDPE-g-MAH and LLDPE is weak (only physical adsorption), and stress concentration is severe when highly filled (≥50 parts), and the elongation at break is only 370.0%.

[0154] 3. Molecular Mechanism of Moisture Absorption (Environmental Stability)

[0155] The difference in moisture absorption rate comes from the regulation of "surface polar group density" and "molecular network density":

[0156] Low moisture absorption of the conventional group:

[0157] Modified LDH by quaternary ammonium salt intercalation (-C 16 H 33 + ) replaces the interlayer polar carbonate (CO3 2- ), and covers the hydroxyl groups (-OH) on the surface, and the density of polar sites decreases;

[0158] The siloxane shell (-Si-O-Si-) of ZBM is a non-polar structure that wraps the polar hydroxyl groups (-Zn-OH, -B-OH) on the surface of zinc borate, reducing the hydrogen bonding interaction (-OH...OH-) with water molecules (H2O, polar molecules).

[0159] When LDH (35-45 parts) and ZBM (8-12 parts) are within the defined range, the total amount of polar sites is moderate and the branched structure of the POE matrix (-C8H 17 ) forms a dense molecular network that hinders the penetration of water molecules, so the moisture absorption rate is as low as 0.49-0.58%.

[0160] The control group showed increased moisture absorption:

[0161] When variable B exceeded the lower limit (6 parts), zinc borate not coated by ZBM exposed more polar hydroxyl groups, the sites for forming hydrogen bonds with water molecules increased, and the moisture absorption rate increased to 0.82% (Group 8);

[0162] When variable A exceeds the upper limit (50 parts), the gaps between the LDH sheets increase due to stacking, and water molecules can easily penetrate through the pores to the internal polar sites, and the moisture absorption rate increases to 0.68% (Group 7);

[0163] The surface of nano-magnesium hydroxide (MH) in the blank group is rich in hydroxyl groups (-Mg-OH), and the phenolic resin shell (containing -OH and -OCH3 polar groups) of red phosphorus microcapsules (MRP) is highly hygroscopic. Water molecules can penetrate into the red phosphorus surface through the shell defects, resulting in a moisture absorption rate of up to 1.20%.

[0164] 4. Analysis of the nonlinear relationship of comprehensive scores

[0165] The third group with the highest comprehensive score (40.2 points) corresponds to variables A = 40, B = 10, and C = 45 rpm, and its molecular mechanism is "multi-parameter synergistic optimization":

[0166] The mass ratio of LDH (40 parts) to ZBM (10 parts) is close to 1:0.25. The interlayer water decomposition of LDH (200-300℃) and the glassy layer formation of ZBM (300-450℃) are perfectly connected, maximizing the flame retardant efficiency.

[0167] The shear force (about 0.8 MPa) provided by the internal mixer at a speed of 45 rpm was just enough to completely peel off the LDH layers and evenly disperse the ZBM, while at the same time not destroying the siloxane shell of the ZBM (shell strength ≥ 1.2 MPa), achieving a balance between the interfacial bonding force and the freedom of molecular chain movement.

[0168] The maleic anhydride groups of POE-g-MAH (5 parts) coordinated with the polar sites of LDH and ZBM in a 1:1 ratio, forming the densest interfacial bonding network with the best stress dispersion and moisture absorption inhibition effects.

[0169] This nonlinear relationship is essentially the result of a dynamic balance between intermolecular forces (hydrogen bonds, covalent bonds), particle dispersion (lamellar exfoliation, microcapsule integrity) and matrix molecular chain structure (branch entanglement). Adjustment of a single variable will disrupt this balance and lead to performance degradation.

[0170] in conclusion

[0171] Weighted scoring of experimental data and molecular mechanism analysis indicate that the key parameter ranges of this invention (LDH 35-45 phr, ZBM 8-12 phr, and mixer speed 35-45 rpm) significantly enhance the overall performance of the halogen-free flame-retardant cable material by optimizing the synergistic effect of the flame retardant, the interfacial bonding between the matrix and the flame retardant, and the density of the molecular network. Beyond this range, molecular interactions are disrupted, leading to performance degradation, validating the practical significance of parameter limits.

[0172] Example

[0173] Example 1 (corresponding to experimental group 1)

[0174] Preparation method of halogen-free flame retardant cable material:

[0175] Raw material pretreatment:

[0176] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0177] Weigh 35 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 8 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0178] Mixing and blending:

[0179] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0180] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0181] Adjust the rotor speed to 35 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0182] Extrusion granulation:

[0183] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0184] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0185] Example 2 (corresponding to experimental group 2)

[0186] Preparation method of halogen-free flame retardant cable material:

[0187] Raw material pretreatment:

[0188] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0189] Weigh 38 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 10 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0190] Mixing and blending:

[0191] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0192] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0193] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0194] Extrusion granulation:

[0195] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0196] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0197] Example 3 (corresponding to experimental group 3)

[0198] Preparation method of halogen-free flame retardant cable material:

[0199] Raw material pretreatment:

[0200] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0201] Weigh 40 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 10 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0202] Mixing and blending:

[0203] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0204] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0205] Adjust the rotor speed to 45 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0206] Extrusion granulation:

[0207] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0208] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0209] Example 4 (corresponding to experimental group 4)

[0210] Preparation method of halogen-free flame retardant cable material:

[0211] Raw material pretreatment:

[0212] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0213] Weigh 42 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 12 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0214] Mixing and blending:

[0215] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0216] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0217] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0218] Extrusion granulation:

[0219] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0220] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0221] Example 5 (corresponding to experimental group 5)

[0222] Preparation method of halogen-free flame retardant cable material:

[0223] Raw material pretreatment:

[0224] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0225] Weigh 45 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 12 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0226] Mixing and blending:

[0227] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0228] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0229] Adjust the rotor speed to 35 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0230] Extrusion granulation:

[0231] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0232] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0233] Example 6 (corresponding to experimental group 6)

[0234] Preparation method of halogen-free flame retardant cable material:

[0235] Raw material pretreatment:

[0236] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0237] Weigh 30 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 10 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0238] Mixing and blending:

[0239] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0240] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0241] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0242] Extrusion granulation:

[0243] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0244] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0245] Example 7 (corresponding to experimental group 7)

[0246] Preparation method of halogen-free flame retardant cable material:

[0247] Raw material pretreatment:

[0248] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0249] Weigh 50 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 10 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0250] Mixing and blending:

[0251] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0252] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0253] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0254] Extrusion granulation:

[0255] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0256] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0257] Example 8 (corresponding to experimental group 8)

[0258] Preparation method of halogen-free flame retardant cable material:

[0259] Raw material pretreatment:

[0260] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0261] Weigh 40 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 6 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0262] Mixing and blending:

[0263] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0264] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0265] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0266] Extrusion granulation:

[0267] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0268] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0269] Example 9 (corresponding to experimental group 9)

[0270] Preparation method of halogen-free flame retardant cable material:

[0271] Raw material pretreatment:

[0272] Weigh 100 g of ethylene-octene copolymer (POE, octene content 25%, melt index 1.0 g / 10 min), 5 g of maleic anhydride-grafted POE (POE-g-MAH, grafting rate 1.2%), and 1 g of vinyl bisstearamide (EBS, melting point 142° C.), and dry them in an 80° C. air drying oven for 4 hours until the moisture content drops below 0.05%.

[0273] Weigh 40 g of quaternary ammonium salt intercalated Mg-Al-CO3 layered double hydroxide (LDH, particle size 100-300 nm, intercalant dosage 5%) and 14 g of siloxane-coated zinc borate microcapsules (ZBM, zinc borate particle size 2-5 μm, siloxane shell thickness 5-10 nm, precursor dosage 10%), and dry them in a vacuum drying oven at 105°C for 6 hours until the moisture content drops below 0.03%.

[0274] Mixing and blending:

[0275] Start the internal mixer (X(S)M-30 model), preheat to 130°C, and set the initial rotor speed to 10 rpm;

[0276] Add the materials in order: first add dried POE, then add POE-g-MAH after 1 minute, then add EBS after 2 minutes, then add modified LDH after 3 minutes, and then add ZBM after 5 minutes;

[0277] Adjust the rotor speed to 40 rpm and continue kneading for 8 minutes (the dispersion is determined to be uniform when the torque fluctuation is ≤5%).

[0278] Extrusion granulation:

[0279] The mixed material was added to a single-screw extruder (SJ-45 model), and the temperature zones were set as follows: barrel zone 1 140°C, zone 2 150°C, zone 3 160°C, and die head 170°C;

[0280] The screw speed was controlled at 25 rpm, and the material entered an underwater pelletizer (QJ-200 model) after melt extrusion. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0281] Example 10 (blank control group)

[0282] Preparation method of halogen-free flame retardant cable material (existing technology):

[0283] Raw material pretreatment:

[0284] Weigh 100 g of linear low-density polyethylene (LLDPE, melt index 1.2 g / 10 min), 5 g of maleic anhydride-grafted LLDPE (LLDPE-g-MAH, grafting rate 0.8%), and 1 g of zinc stearate (melting point 120°C), and dry them in an 80°C forced air drying oven for 4 hours until the moisture content drops below 0.05%.

[0285] Weigh 50 g of nano-magnesium hydroxide (MH, particle size 80-200 nm) and 10 g of red phosphorus microcapsules (MRP, phenolic resin shell, red phosphorus content 85%), place them in a vacuum drying oven at 105° C. and dry them for 6 hours until the moisture content drops below 0.03%.

[0286] Blending extrusion:

[0287] The twin-screw extruder (SHJ-58) was started, and the temperature zones were set as follows: barrel zone 1 150°C, zone 2 160°C, zone 3 170°C, and die head 180°C;

[0288] Directly mix the dried LLDPE, LLDPE-g-MAH, zinc stearate, nano magnesium hydroxide and red phosphorus microcapsules and add them to the feed port;

[0289] The screw speed was controlled at 45 rpm, and the materials entered into an underwater pelletizer (QJ-200 model) after melt blending. The pelletizing water temperature was 20°C, and the cutter speed was 600 rpm to obtain pellets with a size of (2.0±0.2) mm×(3.0±0.2) mm.

[0290] Specific working process

[0291] After the surface moisture of the POE matrix was removed in a dry environment at 80°C, its branched structure (octene side chain of ethylene-octene copolymer) gradually unfolded under the initial low-speed shear (10rpm) of the internal mixer; maleic anhydride grafted POE (POE-g-MAH) was then added, and its maleic anhydride group (-CO-O-CO-) formed hydrogen bonds (-OH...O=C-) with the surface hydroxyl groups (-OH) of the pretreated modified LDH at a mixing temperature of 130°C, and at the same time formed covalent bonds (-Si-OC-) with the silanol (-Si-OH) of the siloxane-coated zinc borate (ZBM) shell, initially connecting the POE molecular chain to the flame retardant particles.

[0292] The LDH intercalated with quaternary ammonium salt was added after 3 minutes of mixing. 16 H 33 +) gradually decomposes under the action of shear force (35-45rpm), and the released long-chain alkyl groups stretch the LDH layers, prompting the layered structure to be peeled off into nano-scale MgO / Al2O3 sheets; ZBM is added after 5 minutes of mixing, and its siloxane shell (-Si-O-Si-) partially breaks under the shear force, exposing the inner core zinc borate (ZnB4O7), but it does not fall off completely, and some shells are still retained to isolate the polar sites.

[0293] EBS acts as a lubricant, wrapping the POE molecular chains and the surface of the flame retardant particles during the material mixing process, reducing internal friction, and allowing the LDH nanosheets and ZBM particles to be evenly dispersed in the POE matrix within 8 minutes of mixing, forming a composite structure of "matrix-interface layer-flame retardant".

[0294] After the molten material enters the single-screw extruder, the gradient temperature of 140-170°C causes the POE molecular chain to further stretch, physically entangled with the stripped LDH nanosheets and partially exposed ZBM particles (POE side chains are inserted into the gaps between LDH layers and the gaps between ZBM shells); the low-speed shear of the screw at 25rpm avoids destroying the remaining ZBM shell and LDH nanosheet structure, ensuring uniform dispersion.

[0295] During underwater pelletizing, 20°C cooling water causes the molten material to solidify rapidly, the POE molecular chains are fixed in a tangled state, and the LDH nanosheets and ZBM particles are wrapped in the matrix to form a dense molecular network - the MgO / Al2O3 sheets of LDH and the B2O3 glassy layer (high-temperature decomposition product) of ZBM are staggered inside the matrix, jointly constructing a flame retardant barrier; the interfacial bonding effect of POE-g-MAH tightly connects the matrix and the flame retardant, inhibiting stress concentration and water molecule penetration.

[0296] The various technical features described in the above exemplary embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above exemplary embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. Halogen-free flame-retardant cable material containing nano magnesium hydroxide and red phosphorus microcapsules, characterized in that: The composition comprises the following components in parts by weight: Main flame retardant: 35-45 parts of layered double hydroxide modified by quaternary ammonium salt intercalation; Synergistic flame retardant: 8-12 parts of silicone-coated zinc borate microcapsules; Base resin: 90-110 parts of ethylene-octene copolymer; Compatibilizer: 4-6 parts of maleic anhydride grafted ethylene-octene copolymer; Processing aid: vinyl bisstearamide 0.8-1.2 parts; in: The layered double hydroxide is a Mg-Al-CO3 type layered double hydroxide with a particle size of 100-300 nm; The shell layer of the zinc borate microcapsule is siloxane, and the shell layer thickness is 5-10nm; The ethylene-octene copolymer has an octene content of 20-30% and a melt index (190° C. / 2.16 kg) of 0.8-1.2 g / 10 min; The grafting rate of the maleic anhydride grafted ethylene-octene copolymer is 1.0-1.5%.

2. The halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules according to claim 1, characterized in that: The quaternary ammonium salt intercalation-modified layered double hydroxide is modified by cetyltrimethylammonium bromide intercalation, and the amount of the intercalation agent used is 4-6% of the weight of the layered double hydroxide.

3. The halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules according to claim 1, characterized in that: The core material of the siloxane-coated zinc borate microcapsule is zinc borate, the shell layer is prepared by hydrolysis and polycondensation of ethyl orthosilicate, and the amount of the shell layer precursor is 8-12% of the mass of the zinc borate.

4. The halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules according to claim 1, characterized in that: The melting point of the vinyl bisstearamide is 140-145°C.

5. A method for preparing a halogen-free flame-retardant cable material, based on the halogen-free flame-retardant cable material containing nano-magnesium hydroxide and red phosphorus microcapsules according to any one of claims 1 to 4, characterized in that: Follow these steps: Step 1: Modification of layered double hydroxide: Mg-Al-CO3 type layered double hydroxide (particle size 100-300 nm) and cetyltrimethylammonium bromide (4-6% of the mass of the layered double hydroxide) were mixed in deionized water (solid-liquid ratio 1:20), stirred at 80°C for 4 hours (speed 250-350 rpm), and ultrasonically dispersed (40 kHz, 25-35 minutes). The mixture was then filtered, washed with anhydrous ethanol, vacuum dried at 80°C for 12 hours, and ground through a 200-mesh sieve to obtain a modified layered double hydroxide. Step 2: Preparation of zinc borate microcapsules: Zinc borate (particle size 2-5 μm) and ethyl orthosilicate (8-12% by weight of zinc borate) were mixed in an ethanol / water mixed solvent (volume ratio 3:1), the pH was adjusted to 4, and the mixture was stirred at 60°C for 6 hours (speed 200 rpm). The mixture was then centrifuged, washed with anhydrous ethanol, dried at 100°C for 4 hours, and passed through a 200-mesh sieve to obtain siloxane-coated zinc borate microcapsules. Step 3: Material compounding: Weigh 90-110 parts of ethylene-octene copolymer, 4-6 parts of maleic anhydride grafted ethylene-octene copolymer, 0.8-1.2 parts of vinyl bisstearamide, 35-45 parts of modified layered double hydroxide, and 8-12 parts of zinc borate microcapsules in parts by mass; Step 4: melt blending in steps: preheat the ethylene-octene copolymer at 100°C for 10 minutes and then add it to an internal mixer. After 1 minute, add the maleic anhydride-grafted ethylene-octene copolymer. After 2 minutes, add the vinyl bisstearamide. After 3 minutes, add the modified layered double hydroxide. After 5 minutes, add the zinc borate microcapsules. Mix at 125-135°C and a rotor speed of 35-45 rpm for 7-9 minutes until the torque stabilizes. Step 5: Extrusion granulation: The mixed material was added to a single-screw extruder (length-to-diameter ratio L / D = 25:1, compression ratio 3:1), the temperature zones were: barrel zone 1 135-145°C, zone 2 145-155°C, zone 3 155-165°C, die head 165-175°C, screw speed 20-30 rpm, and pelletized underwater (water temperature 15-25°C) to obtain pellets (size 1.8-2.2 mm × 2.8-3.2 mm).

6. The method for preparing a halogen-free flame-retardant cable material according to claim 5, wherein: The power of ultrasonic dispersion in step 1 is 100-150W.

7. The method for preparing a halogen-free flame-retardant cable material according to claim 5, wherein: In step 2, the volume ratio of the ethanol / water mixed solvent is 3:1, and hydrochloric acid is used for pH adjustment.

8. The method for preparing a halogen-free flame-retardant cable material according to claim 5, wherein: The capacity of the internal mixer in step 4 is 30 L, and the rotor type is meshing type.

9. The method for preparing a halogen-free flame-retardant cable material according to claim 5, wherein: The screw diameter of the single screw extruder in step 5 is 45 mm.

10. The method for preparing a halogen-free flame-retardant cable material according to claim 5, wherein: The cutter speed of the underwater pelletizing in step 5 is 500-800 rpm.

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