A low-smoke halogen-free flame-retardant polyolefin sheath material and a preparation method thereof
By in-situ ring-opening esterification reaction of POE-g-GMA and EVOH and multi-stage side-feeding process, a continuous intrinsic polymeric skeleton carbon layer was constructed, which solved the interfacial compatibility and rheological stability problems of polyolefin materials in the flame retardant process, and achieved the improvement of high flame retardant performance and mechanical reliability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- KAIKAI CABLE TECH
- Filing Date
- 2026-05-14
- Publication Date
- 2026-06-12
AI Technical Summary
Existing polyolefin materials suffer from contradictions between interfacial compatibility and mechanical properties, as well as conflicts between the char-forming ability of matrix macromolecules and melt rheological stability during the flame retardant process. This leads to the materials becoming brittle and fracturing at high temperatures, making it difficult to achieve high flame retardant performance and good mechanical reliability.
A three-dimensional macromolecular network was constructed by in-situ ring-opening esterification reaction of POE-g-GMA and EVOH. Combined with multi-stage side-feeding process and confined catalyst, a continuous intrinsic polymeric framework carbon layer was formed. Modified hydroxide and nanotube structure were used to improve the mechanical properties and flame retardant performance of the material.
This invention enables materials with high-filling flame-retardant systems to maintain high flame-retardant performance and excellent elongation at break at high temperatures, solving the problems of brittle fracture and melt fracture in traditional methods, and improving the long-term reliability and processing rheology of cables.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of polyolefin materials technology, specifically to a low-smoke, halogen-free flame-retardant polyolefin sheath material and its preparation method. Background Technology
[0002] With the increasing demand for high-performance materials in extreme environments, the flame retardant safety of polyolefin materials has become a research focus. Traditional halogen-containing polyolefin systems are gradually being replaced by environmentally friendly flame-retardant polyolefin compositions due to the secondary pollution problems caused by thermal degradation products. Currently, the technical approach of constructing flame-retardant systems through multi-component polymer blending still faces two key technical challenges in achieving a comprehensive performance balance of the polyolefin material itself:
[0003] First, there is a contradiction between the interfacial compatibility and mechanical properties of polymer components. To improve the flame retardancy of polyolefin compositions, a large number of heterogeneous dispersed phases are usually introduced into the system. However, in the multi-component blending process of existing polyolefin compositions, the interfacial tension between polymer components of different polarities (such as non-polar polyolefin elastomers and polar compatibilizers) is high, making it difficult to form a stable interpenetrating network structure. This imbalance in the microstructure leads to a significant decrease in the effective entanglement density of the matrix macromolecular chains at the heterogeneous phase interface, making the polyolefin composition prone to stress concentration under macroscopic stress fields. This results in a precipitous drop in the elongation at break and tensile strength of the bulk, seriously affecting the mechanical reliability of the polyolefin composition.
[0004] Second, there is a conflict between the intrinsic char-forming ability of the matrix macromolecules and the rheological stability of the melt. When heated, the matrix macromolecular chains of existing polyolefin compositions tend to undergo random breakage, resulting in loose amorphous structures with insufficient cohesion, which cannot form a skeletal carbon layer with continuous physical barrier performance at high temperatures. In addition, due to the poor wettability between the various polymer phases and functional components in the polyolefin composition, micro-phase separation and component segregation are easily induced. This unstable multiphase interface not only weakens the shielding effectiveness of the carbon layer, but also causes the melt of the composition to exhibit violent rheological fluctuations during processing, inducing surface melt fracture and making it difficult to obtain polyolefin materials with smooth surfaces.
[0005] To this end, a low-smoke, halogen-free flame-retardant polyolefin sheath material and its preparation method are proposed. Summary of the Invention
[0006] The purpose of this invention is to provide a low-smoke, halogen-free, flame-retardant polyolefin sheath material and its preparation method.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] Unless otherwise specified, all parts in this invention are parts by weight.
[0009] This invention provides a method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material. The method for preparing the polyolefin sheath material is as follows:
[0010] Add 45-55 parts of ethylene-vinyl acetate copolymer (EVA, P992759, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 12-18 parts of POE-g-GMA, 8-12 parts of ethylene-vinyl alcohol copolymer (EVOH), and 1.5 parts of composite antioxidant through the main feed port of the eccentric rotor stretch rheological extruder. Set the screw speed to 180 rpm and the temperature of this section (front section of the extruder) to 170-180℃. After the matrix resin passes through the reaction section, add 25-35 parts of bilayer modified hydroxide, 10-15 parts of ammonium polyphosphate (APP), and 3 parts of composite lubricant through the first side feed port (middle section of the extruder). Reduce the temperature of this section to 150-155℃ and maintain the speed at 180 rpm. Magnesium hydroxide is highly prone to agglomeration and must be forcibly dispersed by the screw speed to ensure it is uniformly coated by the previously generated crosslinked network. When the EVOH at the main feed port has just melted and begun to react with POE-g-GMA, the viscosity has not yet reached its maximum, and there is still a long distance to the outlet. APP enters together with magnesium hydroxide. In the strong tensile rheological field, APP has enough time to complete "wetting" and "penetration" in the molten EVOH matrix. 3-6 parts of confined catalyst (AOM@HNTs) are added to the second feed port (rear section of the extruder), the temperature is set to 135-145℃, and the local mixing element in the corresponding area of the second feed port is replaced with a distributed mixing element for non-destructive dispersion to obtain polyolefin material. After passing through the vacuum exhaust port (to remove residual volatiles and physically adsorbed water), the polyolefin material is extruded from the die head. The die head temperature is set to 140℃, and a water ring pelletizing process is used. After pelleting, the material is centrifuged and dehydrated, and then dried in a forced-air dryer at 70℃ for 5 hours to obtain the polyolefin sheath material.
[0011] Preferably, the preparation method of POE-g-GMA is as follows: 100 parts of polyolefin elastomer (ethylene-octene copolymer POE, Engage) are added... 8200) was fed into a high-speed mixer, and 2.5 parts glycidyl methacrylate, 1.5 parts styrene and 0.1 parts initiator dicumyl peroxide were added. The mixture was mixed at 400 rpm for 5 minutes at room temperature, and then allowed to stand for 2 hours to allow the monomers and initiator to fully penetrate into the POE particles, resulting in swollen material. The swollen material was fed into a co-rotating twin-screw extruder for reactive extrusion. The temperature zones of the extruder were set as follows: Zone 1 feeding section 150℃, Zones 2 to 4 reaction sections 170℃-185℃-185℃, Zones 5 to 6 homogenization and venting sections 175℃-170℃, and the die head 165℃. The screw speed was set to 200 rpm. During the extrusion process, unreacted monomers were removed by vacuuming (vacuum degree -0.08 MPa). The material was then water-cooled, stretched, and pelletized, and vacuum dried at 60℃ for 8 hours to obtain POE-g-GMA with a grafting rate of 1.8%.
[0012] Preferably, the ethylene-vinyl alcohol copolymer has a melt index of 1.9 g / 10 min at 190℃ and 2.16 kg, and a vinyl alcohol content of 38 mol%. At this value, the hydroxyl groups on the EVOH molecular chain can form a spatially uniform elastic network with the epoxy groups in POE-g-GMA, avoiding compatibilization failure due to insufficient hydroxyl groups and overcoming excessive cross-linking embrittlement caused by excessive hydroxyl groups. Moreover, EVOH at this value can form the best dynamic mechanical coupling with the matrix, ensuring that the material has elastomeric characteristics under high flame retardant filling, while providing a graphitized carbonization precursor with optimal structural continuity for the fire stage.
[0013] The preferred method for preparing the double-layer modified hydroxide is as follows: 100 parts of magnesium hydroxide (M675888, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) are added to a reaction vessel, along with 300 parts of anhydrous ethanol. Mechanical stirring is started at 800 rpm, and the temperature is raised to 75°C. 2.5 parts of titanate coupling agent NDZ-201 are added dropwise, and the reaction is maintained at this temperature for 25-35 minutes. The stirring speed is increased to 1200 rpm, and 1.5 parts of silane coupling agent KH-550 are added dropwise. The reaction is continued at 1200 rpm for 40-55 minutes. After the reaction, the mixture is filtered, and the filter cake is dried in a vacuum drying oven at 105°C for 4 hours. An air jet mill is used, with a grinding pressure set to 0.8 MPa and a classifying wheel speed set to 3000 rpm. The particle size D of the powder after grinding is... 50 By controlling the thickness to 2.0 μm, a bilayer modified hydroxide was obtained.
[0014] Preferably, the composite lubricant is obtained by compounding oxidized polyethylene wax (OPE wax, model Honeywell AC-629) and zinc stearate in a mass ratio of 2:1. Zinc stearate provides internal lubrication, while OPE wax forms an isolation film (external lubrication) on the mold surface, synergistically improving the rheology of the high-filler system and making the extrusion surface smooth.
[0015] The preferred method for preparing the confined catalyst is as follows: 100 parts of halloysite nanotubes (H698168, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) are added to 400 parts of an aqueous solution of ammonium octamolate with a mass concentration of 10-16 wt%. The solution is placed in a vacuum reactor, stirred at 500 rpm, and the vacuum degree is maintained at -0.09 MPa. The gas is evacuated and released 3 times to allow the ammonium octamolate aqueous solution to enter the tube cavity. The negative pressure is maintained for 15 min each time to ensure that the air in the tube cavity is completely discharged and the drug solution enters. The product is centrifuged and dried at 90°C to constant weight. Then it is redispersed in 400 parts of anhydrous ethanol, heated to 80°C, and 3 parts of silane coupling agent KH-560 are added. The reaction is carried out for 1.8-2.6 h. After the reaction is completed, the product is centrifuged, dried at 90°C, and then ground in a planetary ball mill at 300 rpm for 30 min. The mixture is then passed through a 300-mesh sieve to obtain the confined catalyst.
[0016] Preferably, the composite antioxidant is obtained by compounding a hindered phenolic primary antioxidant (antioxidant 1010) and a phosphite secondary antioxidant (antioxidant 168) in a mass ratio of 1:2. Antioxidant 1010 is responsible for capturing carbon and oxygen free radicals generated during polymer processing; antioxidant 168 is responsible for decomposing peroxides generated in the system (reducing them to alcohols).
[0017] Another aspect of the present invention provides a low-smoke, halogen-free, flame-retardant polyolefin sheath material, wherein the polyolefin sheath material is prepared by any of the above-described preparation methods.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0019] 1. This invention overcomes the technical bottleneck of highly filled flame-retardant systems easily leading to brittle fracture of the material's mechanical properties. By introducing POE-g-GMA with highly active epoxy groups and ethylene-vinyl alcohol copolymer containing dense hydroxyl groups, a "second-level" in-situ ring-opening esterification reaction is induced between the two in the high-temperature section of the tensile rheological field. This reaction constructs a three-dimensional macromolecular dynamic network that penetrates the interface between the matrix resin and the modified powder within the material. The high degree of matching between the ring-opening esterification rate of GMA and the tensile rheological field is the key to achieving high mechanical properties. This "chemical anchoring" effect effectively replaces traditional physical blending, enabling the material to absorb a large amount of impact energy through the slippage and deformation of the interfacial macromolecular chains when subjected to external bending or impact stress. While maintaining high flame-retardant performance, it endows the sheath material with extremely excellent elongation at break.
[0020] 2. This invention resolves the contradiction between strong shear dispersion and the easy degradation of heat-sensitive flame retardants. Traditional internal mixing or twin-screw extrusion processes, with their high shear, easily sever the polymer backbone or cause foaming of heat-sensitive components. This invention employs a stretch rheological extruder based on an eccentric rotor, combined with a multi-stage side-feeding process: in the front section of the extruder, a high-temperature, high-stretch force field is used to complete the in-situ reaction; in the middle section, medium-temperature forced degradation of powder agglomeration is used; and in the rear section, a low-temperature, distributed mixing element gently incorporates a hollow-structured confined catalyst. Through continuous volumetric stretching, the dispersed phase is coated, eliminating not only the micro-agglomeration of the flame retardant but also protecting the integrity of the nanotube structure, resulting in a smooth, defect-free surface on the extruded cable.
[0021] 3. Traditional systems using small molecules such as pentaerythritol are highly hygroscopic and tend to precipitate on the cable surface (blooming), resulting in an extremely loose char layer structure during combustion. This invention utilizes EVOH as a macromolecular char source. The high-density hydroxyl groups on its main chain can directly undergo cross-linking and dehydration under the catalysis of polyphosphoric acid, forming a continuous intrinsic polymeric framework char layer. Because EVOH itself participates in the early in-situ cross-linking network construction, this char layer derived from the polymer main chain possesses extremely high cohesive force and mechanical strength, fundamentally solving the migration and failure problem of small molecule flame retardants and greatly improving the long-term reliability of cables.
[0022] 4. This invention constructs a "nano-confined slow-release" catalytic mechanism, significantly improving the material's survivability in extreme fire conditions. Ammonium octamolybdate, possessing char-forming catalytic activity, is encapsulated within the hollow cavity of halloysite nanotubes (HNTs), effectively preventing premature consumption and agglomeration of free catalyst during high-temperature extrusion. During combustion, the rigid HNTs embed into the char layer formed by EVOH dehydration, creating a physically reinforcing microstructure similar to "reinforced concrete." Simultaneously, the molybdenum-based catalyst within the cavity is slowly released at high temperatures, achieving continuous catalysis throughout the entire combustion process. This deep integration of chemical slow release and physical reinforcement ensures the char layer remains intact even under extremely high temperatures and strong airflow impacts, effectively suppressing melting and dripping.
[0023] 5. This invention significantly improves the flame retardant efficiency and processing rheology of inorganic hydroxides. Magnesium hydroxide undergoes a "titanium ester-silane" bilayer graft modification, with the inner layer reducing surface energy and the outer layer providing active crosslinking sites, constructing a flexible buffer layer on the powder surface. During processing, the bilayer modification, combined with an internal / external lubrication system of OPE wax and zinc stearate, greatly reduces the dynamic viscosity of the highly filled melt. During combustion, the bilayer modified MDH releases water vapor for physical cooling during solid-phase decomposition, while simultaneously undergoing gas-solid biphase flame retardant synergy with the confined release of a molybdenum-based catalyst. This multi-dimensional synergistic mechanism significantly reduces the total filler content of the inorganic powder, achieving a leap in the overall material performance. Attached Figure Description
[0024] Figure 1 The graph shows the test results of limiting oxygen index and smoke density level for Examples 1-4 and Comparative Examples 1, 3-4 and 8 of the present invention. Detailed Implementation
[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0026] Please see Figure 1 This invention provides a low-smoke, halogen-free, flame-retardant polyolefin sheath material and its preparation method, the technical solution of which is as follows:
[0027] Example 1
[0028] 100 parts of polyolefin elastomer were added to a high-speed mixer, along with 2.5 parts of glycidyl methacrylate, 1.5 parts of styrene, and 0.1 parts of initiator dicumyl peroxide. The mixture was stirred at 400 rpm for 5 minutes at room temperature, and then allowed to stand for 2 hours to allow the monomers and initiator to fully penetrate into the POE particles, resulting in swollen material. The swollen material was then fed into a co-rotating twin-screw extruder for reactive extrusion. The extruder temperature zones were set as follows: Zone 1 (feeding section) 150℃, Zones 2 to 4 (reaction section) 170℃-185℃-185℃, Zones 5 to 6 (homogenization and venting section) 175℃-170℃, and the die head 165℃. The screw speed was set to 200 rpm. During extrusion, unreacted monomers were removed by vacuuming (vacuum degree -0.08 MPa). The material was then water-cooled, stretched, and pelletized, and vacuum-dried at 60℃ for 8 hours to obtain POE-g-GMA with a grafting rate of 1.8%.
[0029] 100 parts of magnesium hydroxide were added to a reaction vessel, along with 300 parts of anhydrous ethanol. Mechanical stirring was started at 800 rpm, and the temperature was raised to 75°C. 2.5 parts of titanate coupling agent NDZ-201 were added dropwise, and the reaction was maintained at this temperature for 25 minutes. The stirring speed was then increased to 1200 rpm, and 1.5 parts of silane coupling agent KH-550 were added dropwise. The reaction was continued at 1200 rpm for another 40 minutes. After the reaction, the mixture was filtered, and the filter cake was dried in a vacuum drying oven at 105°C for 4 hours. An air jet mill was then used, with a grinding pressure set to 0.8 MPa and a classifying wheel speed set to 3000 rpm. The particle size D of the powder after grinding was determined. 50 By controlling the thickness to 2.0 μm, a bilayer modified hydroxide was obtained.
[0030] 100 parts of halloysite nanotubes were added to 400 parts of a 10 wt% ammonium octamolate aqueous solution and placed in a vacuum reactor. The reactor was stirred at 500 rpm and the vacuum was maintained at -0.09 MPa. The gas was evacuated and released three times, maintaining the negative pressure for 15 min each time. The product was centrifuged and dried at 90 °C to constant weight. Then it was redispersed in 400 parts of anhydrous ethanol, heated to 80 °C, and 3 parts of silane coupling agent KH-560 were added. The reaction was carried out for 1.8 h. After the reaction was completed, the product was centrifuged, dried at 90 °C, and then ground in a planetary ball mill at 300 rpm for 30 min. The resulting confined catalyst was obtained by passing the material through a 300-mesh sieve.
[0031] The composite lubricant is obtained by compounding oxidized polyethylene wax (OPE wax) and zinc stearate in a mass ratio of 2:1; the composite antioxidant is obtained by compounding hindered phenolic primary antioxidant (antioxidant 1010) and phosphite secondary antioxidant (antioxidant 168) in a mass ratio of 1:2.
[0032] 45 parts of ethylene-vinyl acetate copolymer, 12 parts of POE-g-GMA, 8 parts of ethylene-vinyl alcohol copolymer (EVOH, 38 mol% vinyl alcohol content), and 1.5 parts of composite antioxidant were added through the main feed port of the eccentric rotor stretch rheological extruder. The screw speed was set to 180 rpm, and the temperature of this section (front section of the extruder) was set to 170-180℃. After the matrix resin passed through the reaction section, 25 parts of bilayer modified hydroxide, 10 parts of ammonium polyphosphate (APP), and 3 parts of composite lubricant were added through the first side feed port (middle section of the extruder). The temperature of this section was reduced to 150-155℃. The temperature was maintained at 180 rpm. Three parts of confined catalyst (AOM@HNTs) were added to the second side feed port (rear section of the extruder). The temperature was set to 135-145℃. The local mixing element in this area was replaced with a distributed mixing element (toothed disc mixing element TME). The length of the distributed mixing element section was three times the screw diameter to obtain polyolefin material. After passing through the vacuum exhaust port, the polyolefin material was extruded from the die head. The die head temperature was set to 140℃. A water ring pelletizing process was adopted. After pelleting, the material was centrifuged and dehydrated, and then dried in a forced-air dryer at 70℃ for 5 hours to obtain polyolefin sheath material.
[0033] Example 2
[0034] The preparation method and parameters were the same as in Example 1, except that: 48 parts of EVA, 14 parts of POE-g-GMA, 9 parts of EVOH, 28 parts of bilayer modified hydroxide, 12 parts of APP, and 4 parts of AOM@HNTs were used; the mass concentration of ammonium octamolate aqueous solution was 12 wt%; when preparing the bilayer modified hydroxide, titanate coupling agent NDZ-201 was added and reacted at a constant temperature for 28 min, followed by the addition of silane coupling agent KH-550 and then reacted at a constant temperature for 45 min; when preparing the confined catalyst, silane coupling agent KH-560 was added and reacted for 2.0 h.
[0035] Example 3
[0036] The preparation method and parameters were the same as in Example 1, except that: 52 parts EVA, 16 parts POE-g-GMA, 11 parts EVOH, 32 parts bilayer modified hydroxide, 14 parts APP, and 5 parts AOM@HNTs were used; the mass concentration of ammonium octamolate aqueous solution was 14 wt%; when preparing the bilayer modified hydroxide, titanate coupling agent NDZ-201 was added and reacted at a constant temperature for 32 min, followed by the addition of silane coupling agent KH-550 and then reacted at a constant temperature for 50 min; when preparing the confined catalyst, silane coupling agent KH-560 was added and reacted for 2.4 h.
[0037] Example 4
[0038] The preparation method and parameters were the same as in Example 1, except that: EVA 55 parts, POE-g-GMA 18 parts, EVOH 12 parts, bilayer modified hydroxide 35 parts, APP 15 parts, AOM@HNTs 6 parts; the mass concentration of ammonium octamolate aqueous solution was 16 wt%; when preparing the bilayer modified hydroxide, titanate coupling agent NDZ-201 was added and reacted at a constant temperature for 35 min, and silane coupling agent KH-550 was added dropwise and reacted at a constant temperature for 55 min; when preparing the confined catalyst, silane coupling agent KH-560 was added and reacted for 2.6 h.
[0039] Comparative Example 1
[0040] The preparation method and parameters of Example 1 are the same, except that EVOH and POE-g-GMA are not added, and are replaced with 15 parts of matrix resin EVA and 5 parts of conventional small molecule char-forming agent pentaerythritol.
[0041] Comparative Example 2
[0042] The preparation method and parameters of Example 1 were used, except that POE-g-GMA was replaced with commercially available POE-g-MAH (Dow Fusabond N493).
[0043] Comparative Example 3
[0044] The preparation method and parameters of Example 1 are the same, except that AOM@HNTs are not prepared. Instead, ammonium octamolate powder and halloysite nanotubes are directly physically mixed and then added to an extruder.
[0045] Comparative Example 4
[0046] The preparation method and parameters of Example 1 are the same, except that a conventional co-rotating twin-screw extruder is used, and all materials are added at once from the main feed port and mixed and extruded at 170°C.
[0047] Comparative Example 5
[0048] The preparation method and parameters of Example 1 were used, except that the magnesium hydroxide was not modified with a "titanium ester-silane" bilayer.
[0049] Comparative Example 6
[0050] The preparation method and parameters of Example 1 are the same, except that the phosphite-based auxiliary antioxidants are removed from the composite antioxidant, and only the hindered phenolic primary antioxidant is retained.
[0051] Comparative Example 7
[0052] The preparation method and parameters of Example 1 are the same, except that no comonomer styrene was added when preparing POE-g-GMA.
[0053] Comparative Example 8
[0054] The preparation method and parameters of Example 1 are the same, except that ammonium polyphosphate is removed and replaced with an equal amount of magnesium hydroxide.
[0055] Experimental Example 1: Mechanical Property Testing
[0056] Tensile strength and elongation at break: Referring to standard GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers", the tensile speed was set to 250 mm / min; the results are shown in Table 1.
[0057] Table 1 Mechanical property tests of Examples 1-4 and Comparative Examples 1-2 and 4-7
[0058] Group Tensile strength / MPa Elongation at break / % Example 1 13.5 265 Example 2 14.2 256 Example 3 15.3 248 Example 4 14.9 250 Comparative Example 1 9.5 120 Comparative Example 2 11.0 155 Comparative Example 4 6.5 75 Comparative Example 5 8.2 105 Comparative Example 6 10.2 135 Comparative Example 7 9.8 145
[0059] Experiment Example 2: Flame Retardant Performance Test
[0060] Limiting Oxygen Index (LOI): Tested according to standard GB / T 2406.2-2009;
[0061] Vertical flammability rating: Based on UL94 standard, the test strip thickness is 3.2 mm;
[0062] Smoke density rating: The maximum specific optical density in flame mode was tested according to standard GB / T 8323.2-2008. The sample size was 75mm×75mm×2mm and the radiation intensity was 25kW / m².
[0063] The results are shown in Table 2.
[0064] Table 2 Flame retardant performance tests of Examples 1-4 and Comparative Examples 1, 3-4, and 8
[0065] Group Limiting oxygen index / % Vertical flammability rating Smoke density level Example 1 32.5 V-0 45 Example 2 33.2 V-0 40 Example 3 34.8 V-0 33 Example 4 35.0 V-0 36 Comparative Example 1 28.0 V-1 65 Comparative Example 3 27.5 V-1 78 Comparative Example 4 23.0 Combustion ratingless 85 Comparative Example 8 21.8 Burning drips ignite the absorbent cotton. 88
[0066] As shown in Tables 1 and 2, in Examples 1-4, this invention constructs a deep three-dimensional synergistic barrier of "microstructure-chemical reaction-macro force field". Utilizing highly active GMA grafting and in-situ ring-opening esterification of macromolecular EVOH, supplemented by acid source catalysis of APP, a dynamic network with both "high tensile deformation capacity" and "high-strength intrinsic carbon layer" is constructed, solving the problem of embrittlement caused by high filling of flame retardants. Simultaneously, the AOM@HNTs nano-confined structure in this invention, relying on a multi-stage tensile rheological temperature control process, can achieve non-destructive dispersion, resulting in a qualitative leap in flame retardancy and smoke suppression capabilities. In Example 4, although the amount of confined catalyst increased and the concentration of ammonium octamolate aqueous solution increased, the content of EVOH (char source) in the matrix had reached its upper limit, and the stoichiometric ratio of acid source-carbon source-catalyst source tended to saturate. The excess catalytic sites could not further significantly increase the oxygen index.
[0067] In Comparative Example 1, pentaerythritol, as a small-molecule char-forming agent, readily aggregates and debonds at the interface within the EVA matrix. This not only acts as a stress concentration point, leading to a significant decrease in elongation at break and failing to meet application requirements, but also readily volatilizes with flue gas at high temperatures, resulting in a loose and fragile char layer that cannot form the high-strength, dense char layer with large molecular crosslinks like EVOH, significantly reducing its anti-dripping ability. In Comparative Example 2, the esterification reaction rate of MAH (maleic anhydride) with hydroxyl groups is much lower than the ring-opening reaction of GMA (epoxy group). Within the limited extrusion residence time, commercially available POE-g-MAH cannot form a highly interpenetrating three-dimensional crosslinked network with EVOH, resulting in low compatibilization and stress transfer efficiency, and significantly impairing the material's flexibility and tensile deformation capacity. In Comparative Example 3, without the hollow confinement protection of nanotubes, ammonium octamolate was prematurely lost during high-temperature processing and easily lost with heat waves in the strong convection of the fire. The system lost its "slow-release catalysis" mechanism, which not only led to a decrease in char formation rate and the initiation of dripping in the later stage of combustion, but also completely failed in its ability to physically adsorb and catalytically degrade toxic smoke macromolecules, resulting in a surge in smoke density. In Comparative Example 4, the strong shear force of the conventional twin-screw extruder and the one-step high temperature of 170°C directly caused the heat-sensitive APP to decompose prematurely and foam in the barrel. At the same time, the brittle halloysite nanotubes were completely sheared, and the extrudate was filled with microporous defects and had a rough surface. Its mechanical structure and flame-retardant defense were physically destroyed during the molding stage. In Comparative Example 5, the surface of unmodified magnesium hydroxide was extremely polar, and it severely agglomerated in the non-polar polyolefin matrix. These agglomerates were like pebbles in a sponge, which easily caused interfacial voids under tensile stress, leading to brittle fracture of the material with minimal deformation; at the same time, it also caused abnormally high melt viscosity during processing. In Comparative Example 6, the lack of phosphite-based antioxidants decomposed peroxides generated during polymer processing, leading to the rapid depletion of the hindered phenolic antioxidant. This resulted in partial irreversible thermo-oxidative degradation and chain breakage of the EVA matrix during the high-temperature in-situ crosslinking stage, fundamentally weakening the intrinsic load-bearing capacity of the polymer matrix. In Comparative Example 7, the absence of styrene's charge-transfer complexation protection caused severe homopolymerization (self-polymerization into small particles) of the GMA monomer during grafting, resulting in very few effective epoxy groups grafted onto the POE backbone. This resulted in a severe shortage of interfacial "anchoring" points, leading to micro-phase separation in the multiphase composite system. In Comparative Example 8, although the equivalent replacement of magnesium hydroxide maintained good mechanical reinforcement, the system completely lost ammonium polyphosphate, a crucial "acid source." Without strong acid-catalyzed dehydration, the EVOH macromolecules could not undergo crosslinking to form char in the fire, preventing the formation of the "intrinsic polymeric skeleton char layer." Ultimately, the flame-retardant properties failed due to matrix melting and dripping.
[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material, characterized in that: The polyolefin sheath material is prepared as follows: Ethylene-vinyl acetate copolymer, POE-g-GMA, ethylene-vinyl alcohol copolymer, and composite antioxidant are added through the main feed port of an eccentric rotor stretch rheological extruder; a double-layer modified hydroxide, ammonium polyphosphate, and composite lubricant are added through the first side feed port; a confined catalyst is added through the second side feed port, and the local mixing element in the corresponding area of the second side feed port is replaced with a distributed mixing element to obtain polyolefin material; the polyolefin material is extruded and pelletized after passing through a vacuum exhaust port, and then centrifuged, dehydrated, and dried by forced air to obtain the polyolefin sheath material; The confined catalyst was prepared from halloysite nanotubes, an aqueous solution of ammonium octamolate, and a silane coupling agent.
2. The method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material according to claim 1, characterized in that: The preparation method of POE-g-GMA is as follows: Polyolefin elastomer is put into a high-speed mixer, glycidyl methacrylate, styrene and diisopropylbenzene peroxide are added, and after mixing at room temperature, the mixture is allowed to swell to obtain swollen material; The swollen material is added to a co-rotating twin-screw extruder for reactive extrusion, and after water cooling, it is granulated and vacuum dried to obtain POE-g-GMA.
3. The method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material according to claim 1, characterized in that: The preparation method of the bilayer modified hydroxide is as follows: magnesium hydroxide is added to a reaction vessel, anhydrous ethanol is added, mechanical stirring is started, and titanate coupling agent is added dropwise after heating; the stirring speed is increased, and silane coupling agent KH-550 is added dropwise; after the reaction is completed, the mixture is filtered and dried, and then pulverized and ground to obtain the bilayer modified hydroxide.
4. The method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material according to claim 1, characterized in that: The composite lubricant is obtained by compounding oxidized polyethylene wax and zinc stearate.
5. The method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material according to claim 1, characterized in that: The confined catalyst is prepared as follows: Halloysite nanotubes are added to the ammonium octamolate aqueous solution, placed in a vacuum reactor, stirred, and after circulating and evacuating the gas, the temperature is raised, silane coupling agent KH-560 is added to react, the product is centrifuged, dried, ground and sieved to obtain the confined catalyst.
6. The method for preparing a low-smoke, halogen-free, flame-retardant polyolefin sheath material according to claim 1, characterized in that: The composite antioxidant is obtained by combining a hindered phenolic primary antioxidant with a phosphite secondary antioxidant.
7. A low-smoke, halogen-free, flame-retardant polyolefin sheath material, characterized in that: The polyolefin sheath material is prepared by the preparation method according to any one of claims 1-6.