Flame-retardant cable material based on recycled pet modification and preparation method thereof

Abstract

The application relates to the technical field of cable recycling, and discloses a flame-retardant cable material based on recycled PET modification and a preparation method thereof. The method comprises the following steps: sequentially performing hydraulic cleaning, eddy current sorting and hot air drying on recycled polyethylene terephthalate (PET) material, and controlling the water content of the material to be lower than 0.02%; under the protection of inert gas, performing solid-state pre-reaction on the dried PET, a styrene-acrylonitrile-glycidyl methacrylate copolymer containing an epoxy functional group, microencapsulated red phosphorus and a silane coupling agent in a high-speed stirred tank at 180-190 DEG C to form a pretreated composite; and feeding the pretreated composite, ethylene-vinyl acetate copolymer, an aluminum hypophosphite salt and an anti-dripping agent into a co-rotating parallel twin-screw extruder to realize dynamic crosslinking under the action of a reasonable temperature gradient and high shear, and obtaining modified regenerated particles with a diameter of 2-3 mm through water ring pelletization. The method realizes high-value regeneration of recycled PET, is environmentally friendly and can be produced on a large scale.

Description

Technical Field

[0001] This invention relates to the field of cable recycling technology, specifically to a flame-retardant cable material based on recycled PET and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET), a high-performance general-purpose thermoplastic polyester, is widely used in packaging, textiles, electronics, and other fields due to its high mechanical strength, good chemical resistance, and stable processing properties. With the continuous growth in PET product consumption, the environmental pressure caused by large amounts of waste PET products is becoming increasingly prominent, making recycling an important way to alleviate resource shortages and environmental problems. Among these efforts, modifying recycled PET for use in cable material production is one effective direction for achieving high-value utilization.

[0003] As a key component of power transmission and communication systems, the flame-retardant properties of cable materials directly affect the operational safety of power facilities and communication equipment. In densely populated areas such as buildings, subways, and high-rise buildings, the flame-retardant requirements for cable materials are even more stringent. Traditional flame-retardant cable materials are mostly prepared using virgin polymer base materials combined with flame retardants, which not only results in high raw material costs but also fails to achieve resource recycling. Therefore, utilizing recycled PET to prepare flame-retardant cable materials, which combines the dual benefits of resource recycling and safety protection, has become a hot research topic in the industry.

[0004] However, recycled PET is prone to introducing impurities during the recycling process, and its molecular weight decreases and crystallinity changes, leading to reduced mechanical properties and processing stability, directly affecting the performance of subsequent modified materials. Simultaneously, during flame-retardant modification, recycled PET exhibits poor compatibility with flame retardants and other polymeric substrates, easily resulting in uneven dispersion and weak interfacial bonding, thus impacting the material's flame-retardant effect and overall performance. Currently, existing technologies for modifying recycled PET to prepare cable materials suffer from problems such as simple pretreatment processes and incomplete impurity removal, leading to insufficient raw material purity; a lack of effective pre-reaction control methods during component compounding, resulting in poor interfacial compatibility among components; unreasonable cross-linking process design, making precise control of material properties difficult; and some technologies use halogenated flame retardants, which, while achieving a certain flame-retardant effect, release toxic and harmful gases during combustion, failing to meet environmental protection requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant cable material based on recycled PET and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this invention provides a flame-retardant cable material based on recycled PET and its preparation method, which sequentially performs the following steps:

[0007] Process A: The recycled polyethylene terephthalate (PET) material is subjected to hydraulic cleaning, eddy current separation, and hot air drying to control its moisture content to below 0.02%;

[0008] Step B: Under inert gas protection, the PET obtained in Step A is subjected to solid-state pre-reaction with styrene-acrylonitrile-glycidyl methacrylate copolymer containing epoxy functional groups, microencapsulated red phosphorus and silane coupling agent in a high-speed stirred tank at 180-190℃ to form a pretreated composite.

[0009] Step C: The pretreated composite, ethylene-vinyl acetate copolymer, aluminum hypophosphite and anti-dripping agent are fed into a co-rotating parallel twin-screw extruder to achieve dynamic cross-linking under a specific temperature gradient and high shear. Modified recycled granules with a diameter of 2-3 mm are obtained by water ring pelletizing.

[0010] Process D: Modified recycled granules, linear low-density polyethylene, elastomers, and processing aids are extruded through a double-layer co-extrusion die head to simultaneously form an inner adhesive layer and an outer flame-retardant sheath layer on the outer periphery of the conductor.

[0011] Preferably, in step A, the hydraulic cleaning adopts a two-stage countercurrent rinsing, and the rinsing solution contains 1.5% sodium hydroxide and 0.3% nonionic surfactant by mass fraction; the hot air drying adopts a segmented method, first rapidly dehydrating at 100-105℃ for 30 minutes, and then drying at a constant temperature of 75-80℃ for 4 hours.

[0012] Preferably, in step B, the components by weight are: 100 parts of recycled PET material, 8-15 parts of the copolymer containing epoxy functional groups, 12-18 parts of microencapsulated red phosphorus, and 0.5-1.5 parts of silane coupling agent KH-550; the solid pre-reaction time is 25-40 minutes, and the stirring speed is 600-800 rpm.

[0013] Preferably, in step C, the temperature field of the co-rotating parallel twin-screw extruder is set as follows: from the feed port to the die head, the temperatures of the six temperature zones are 185℃, 235℃, 245℃, 250℃, 248℃, and 245℃ respectively; during the dynamic crosslinking process, the length-to-diameter ratio of the screw is 40:1, and the rotation speed is 280-320 rpm.

[0014] Preferably, in step C, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 28%-33% by mass, and the melt index is 6g / 10min; the average particle size D50 of the aluminum hypophosphite is ≤5μm, and its addition amount is 8%-12% of the total weight of the pretreated composite.

[0015] Preferably, in step D, the structural design of the double-layer co-extrusion die head enables partial interpenetration at the molecular level between the inner adhesive layer material and the outer flame-retardant sheath material at the die opening; the inner layer extrusion temperature is set to 215-225℃, and the outer layer extrusion temperature is set to 230-240℃.

[0016] Preferably, in step D, the weight ratio of the linear low-density polyethylene to the modified recycled granules is 1:2 to 1:3; the elastomer is a polyolefin elastomer, and its addition amount is 5-8 parts by weight based on 100 parts by weight of the modified recycled granules.

[0017] Preferably, in step E, the irradiation dose of the electron irradiation crosslinking is 12-15 Mrad, and the beam energy is 1.5-2.0 MeV; the circulating water cooling adopts a three-stage gradient cooling, with the water temperature gradually decreasing from 80°C to 25°C.

[0018] Preferably, after step E, the procedure further includes:

[0019] Process E: The formed cable is subjected to circulating water cooling and electron irradiation cross-linking, and a bundled combustion test is conducted according to IEC 60332-1 standard to confirm its flame retardant rating;

[0020] Process F: Online defect detection and closed-loop control process, which utilizes the X-ray real-time detection system and near-infrared spectroscopy analysis system integrated into the production line to monitor the uniformity of sheath thickness and the consistency of material composition, and feeds the data back to the extruder screw speed and temperature control system to achieve automatic fine-tuning of process parameters.

[0021] The present invention also includes a flame-retardant cable material based on recycled PET modification, which is produced by the above-mentioned preparation method of a flame-retardant cable material based on recycled PET modification.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This method achieves efficient recycling of PET in the field of flame-retardant cable materials through a precisely designed multi-stage synergistic process. The synergistic effect of each stage gives the method and product multiple advantages. First, stage A adopts a pretreatment method that combines hydraulic cleaning, eddy current separation and hot air drying, which can effectively remove impurities such as metal scraps, paper, and dirt mixed in the recycled PET material. At the same time, the moisture content is strictly controlled to be below 0.02%, reducing the adverse effects of impurities and moisture on the subsequent reaction process, improving the purity and stability of the raw materials, and providing a high-quality raw material guarantee for the smooth implementation of the subsequent modification process.

[0024] Process B involves a solid-state pre-reaction under inert gas protection. This inert gas environment prevents oxidative degradation of PET and other components at high temperatures, ensuring the directional conduction of the pre-reaction. The epoxy functional groups in the styrene-acrylonitrile-glycidyl methacrylate copolymer containing epoxy functional groups can react with the hydroxyl and carboxyl groups at the ends of the PET molecular chains to form chemical bonds. Simultaneously, microencapsulated red phosphorus, under the action of a silane coupling agent, achieves good bonding with the PET matrix. The resulting pretreated composite effectively improves the interfacial compatibility between the components, avoiding uneven component dispersion during subsequent processing.

[0025] Process C utilizes a co-rotating parallel twin-screw extruder to achieve dynamic crosslinking. Specific temperature gradients and high shear forces promote thorough mixing and reaction between the pretreated composite, ethylene-vinyl acetate copolymer, aluminum hypophosphite, and anti-dripping agent. This dynamic crosslinking process constructs a dense crosslinked network structure, enhancing the material's structural stability and mechanical properties. The 2-3mm modified recycled granules prepared by the water ring pelletizing process exhibit uniform particle size, good flowability, and facilitate precise control in subsequent molding processes.

[0026] Process D employs a dual-layer co-extrusion die to simultaneously form the inner adhesive layer and the outer flame-retardant sheath layer. This allows for precise control of the component ratios and processing parameters of each layer according to their different performance requirements, achieving simultaneous molding of the two layers. This enhances the tightness of the interlayer interface bonding and avoids the interlayer delamination problem that easily occurs in traditional step-by-step molding processes. The inner adhesive layer improves the adhesion between the cable material and the conductor, while the outer flame-retardant sheath layer directly provides flame-retardant protection. The synergistic effect of the two layers enhances the overall performance of the cable.

[0027] The circulating water cooling in process E enables rapid and uniform cooling of the formed cable, improving the crystallinity of the material and reducing internal stress. Electron irradiation crosslinking further optimizes the crosslinking network structure of the material, enhancing its heat resistance, aging resistance, and mechanical strength. Bundled burning tests conducted according to IEC 60332-1 standards accurately verify the flame-retardant performance of the finished cable, ensuring that the product meets industry safety standards. Attached Figure Description

[0028] Figure 1 This diagram illustrates the working steps of a method for preparing flame-retardant cable material based on recycled PET modification, as described in this invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are only for illustrating the present invention and not for limiting the scope of the present invention. It should be noted that, unless otherwise specified, the raw materials used in this embodiment are all conventional commercially available products; the equipment used are all conventional industrial production equipment; and the test methods involved are all performed in accordance with relevant national or industry standards. Among them, the flame retardant performance is tested by bundle burning according to IEC 60332-1 standard, the mechanical properties are tested by tensile testing according to GB / T 1040.2-2006 standard, and the processing performance is characterized by melt flow rate (MFR) and tested according to GB / T3682.1-2018 standard.

[0030] The core of this invention lies in achieving efficient recycling and flame-retardant modification of PET through the synergistic cooperation of processes A to F, thereby producing high-performance cable materials. Specifically, process A is crucial in ensuring the purity and low moisture content of the recycled PET through multi-stage cleaning and segmented drying; process B achieves preliminary bonding between the flame-retardant components and PET through solid-state pre-reaction, improving compatibility; process C's dynamic cross-linking and precise temperature control ensure the material's processability and basic flame-retardant properties; process D's double-layer co-extrusion process achieves synergistic effects between the adhesive layer and the sheath layer; process E's electron irradiation cross-linking and gradient water cooling enhance the material's structural stability and flame-retardant durability; and process F's online defect detection achieves closed-loop process control, ensuring product consistency. The following detailed descriptions, through specific embodiments and comparative examples, illustrate this process.

[0031] I. Example 1

[0032] 1.1 Raw material preparation

[0033] Recycled PET material: Selected waste bottled PET recycled material, initially crushed to particles with a diameter of 5-10mm; Styrene-acrylonitrile-glycidyl methacrylate copolymer (SAN-GMA) containing epoxy functional groups: epoxy value 0.35eq / 100g, molecular weight 50000; Microencapsulated red phosphorus: coating layer is melamine-formaldehyde resin, particle size D50=8μm, phosphorus content 85%; Silane coupling agent KH-550: industrial grade; Ethylene-vinyl acetate copolymer (EVA): vinyl acetate mass content 28%, melt index 6 g / 10 min (190℃, 2.16 kg); Aluminum hypophosphite: average particle size D50=3 μm, purity 99%; Anti-dripping agent: polytetrafluoroethylene micro powder, particle size 1 μm; Linear low-density polyethylene (LLDPE): melt flow rate 2 g / 10 min (190℃, 2.16 kg); Polyolefin elastomer (POE): melt index 1.5 g / 10 min (190℃, 2.16 kg); Processing aids: calcium stearate (lubricant), antioxidant 1010 and antioxidant 168 compound system (mass ratio 1:1).

[0034] 1.2 Specific procedures

[0035] Process A: Purification of recycled PET material. A two-stage countercurrent rinsing device is used. In the first-stage rinsing tank, a mixed rinsing solution with a mass fraction of 1.5% sodium hydroxide and 0.3% nonionic surfactant (fatty alcohol polyoxyethylene ether) is added, with the temperature controlled at 50℃, rinsing time at 20 min, and stirring speed at 150 r / min. In the second-stage rinsing tank, deionized water is added, with a rinsing time of 15 min, temperature at 40℃, and stirring speed at 120 r / min. After rinsing, the PET material is sent to a segmented hot air drying oven. The first stage is set at 100℃ for 30 min to achieve rapid dehydration; the second stage is set at 75℃ for 4 h of constant temperature drying, ultimately controlling the moisture content of the PET material to 0.015% (measured by a Karl Fischer moisture analyzer).

[0036] Step B: Solid-state pre-reaction preparation of pretreated composite. 100 parts by weight of dried recycled PET material, 8 parts by weight of SAN-GMA copolymer, 12 parts by weight of microencapsulated red phosphorus, and 0.5 parts by weight of silane coupling agent KH-550 were added to a high-speed stirred tank. Nitrogen gas was introduced as an inert protective gas (gas flow rate 0.5 L / min). After closing the tank door, the temperature was raised to 180°C, stirring was started, and the speed was set to 600 r / min. This temperature and speed were maintained for solid-state pre-reaction for 25 min. After the reaction was completed, the mixture was allowed to cool naturally to below 80°C, and the material was discharged to obtain pretreated composite particles.

[0037] Step C: Dynamic crosslinking and granulation. The pretreated composite is mixed evenly with EVA, aluminum hypophosphite, antioxidant, lubricant, and anti-dripping agent. The amount of aluminum hypophosphite added is 8% of the total weight of the pretreated composite, the amount of EVA added is 20% of the total weight of the pretreated composite, the amount of the antioxidant compound system added is 0.3 parts by weight, the amount of calcium stearate added is 0.2 parts by weight, and the amount of anti-dripping agent added is 0.5 parts by weight. The mixture is fed into a co-rotating parallel twin-screw extruder (model: TSE-75, length-to-diameter ratio 40:1). The temperature gradient from the feed port to the die head is set as follows: 185℃, 235℃, 245℃, 250℃, 248℃, 245℃. The screw speed is 280 r / min. The material undergoes a dynamic cross-linking reaction under high shear in the barrel. After being extruded from the die head, it is granulated by a water ring pelletizer (cooling water temperature 25℃, cutter speed 800 r / min) to obtain modified recycled granules with a diameter of 2 mm. The moisture content of the granules is controlled below 0.02%.

[0038] Process D: Double-layer co-extrusion molding. Modified recycled granules are mixed with LLDPE, POE, and processing aids to prepare the inner adhesive layer and the outer flame-retardant sheath layer. The formula for the inner adhesive layer is: modified recycled granules:LLDPE:POE = 2:1:5 (weight ratio), with 0.2 parts by weight of processing aids. The formula for the outer flame-retardant sheath layer is: modified recycled granules:LLDPE:POE = 3:1:5 (weight ratio), with 0.2 parts by weight of processing aids. The two materials are fed into two single-screw extruders and simultaneously extruded through a double-layer co-extrusion die (10mm die diameter) around a copper conductor (2.5mm diameter). The inner layer extrusion temperature is set at 215℃, and the outer layer extrusion temperature at 230℃. The extrusion rate is controlled at 1.5m / min to ensure that the inner adhesive layer thickness is 0.8mm and the outer flame-retardant sheath layer thickness is 1.2mm, with partial interpenetration at the molecular level between the two layers at the die.

[0039] Step E: Post-treatment and Flame Retardant Performance Verification. The formed cable is fed into a circulating water cooling system using a three-stage gradient cooling method: first stage cooling water temperature 80℃, second stage 50℃, and third stage 25℃, with each stage having a cooling length of 3m. The cable running speed is consistent with the extrusion speed. After water cooling, the cable is fed into an electron irradiation device (accelerator model: EB-150, beam energy 1.5MeV), with an irradiation dose set to 12Mrad, to complete the cross-linking treatment. The irradiated cable undergoes a bundled combustion test according to IEC 60332-1 standard. The sample length is 1.5m, the number of strands in a bundle is 30, the ignition time is 4 minutes, and the combustion phenomenon is observed and the extinguishing time is recorded.

[0040] Process F: Online Defect Detection and Closed-Loop Control. The cross-linked cable undergoing irradiation is sequentially passed through a real-time X-ray detection system (detection accuracy 0.01mm) and a near-infrared spectroscopy analysis system. The X-ray detection system monitors the thickness uniformity of the inner adhesive layer and the outer flame-retardant sheath layer, while the near-infrared spectroscopy analysis system monitors the consistency of material composition (characteristic peak intensity deviation controlled within ±5%). The detection data is fed back to the extruder screw speed and temperature control system in real time. When a sheath thickness deviation exceeds 0.05mm, the system automatically fine-tunes the screw speed (adjustment range ±5r / min); when a characteristic peak deviation in material composition exceeds 5%, it automatically fine-tunes the temperature of each temperature zone of the extruder (adjustment range ±2℃), achieving closed-loop control of process parameters.

[0041] II. Example 2

[0042] 2.1 Raw material preparation

[0043] Similar to Example 1, only some material parameters were adjusted: the epoxy value of the SAN-GMA copolymer was 0.40 eq / 100g; the microencapsulated red phosphorus particle size D50 was 10 μm, and the phosphorus content was 86%; the average particle size of the aluminum hypophosphite was D50 was 4 μm.

[0044] 2.2 Specific procedures

[0045] Process A: Same as in Example 1, the final moisture content of the PET material is controlled to be 0.012%.

[0046] Step B: 100 parts by weight of recycled PET material, 10 parts by weight of SAN-GMA copolymer, 14 parts by weight of microencapsulated red phosphorus, and 1.0 part by weight of silane coupling agent KH-550 are added to a high-speed stirred tank, nitrogen gas is introduced for protection (flow rate 0.6L / min), the temperature is raised to 185℃, the stirring speed is 700r / min, the solid pre-reaction is carried out for 30min, and the pretreated composite is obtained after cooling.

[0047] Step C: In the mixture, the amount of aluminum hypophosphite added is 10% of the total weight of the pretreated composite, the amount of EVA added is 25% of the total weight of the pretreated composite, the amount of antioxidant added is 0.4 parts by weight, the amount of calcium stearate is 0.25 parts by weight, and the amount of anti-dripping agent is 0.6 parts by weight. The temperature gradient of the twin-screw extruder is the same as in Example 1, the screw speed is 300 r / min, and the modified recycled particles with a diameter of 2.5 mm are obtained by water ring pelletizing.

[0048] Process D: Inner adhesive layer material formulation: modified recycled granules:LLDPE:POE=2.5:1:6 (weight ratio); Outer flame-retardant sheath material formulation: modified recycled granules:LLDPE:POE=3:1:6 (weight ratio). Inner layer extrusion temperature: 220℃, outer layer extrusion temperature: 235℃, extrusion rate: 1.8m / min, inner adhesive layer thickness: 0.9mm, outer flame-retardant sheath thickness: 1.3mm.

[0049] Step E: Circulating water cooling employs a three-stage gradient cooling (80℃→55℃→25℃), with an electron beam energy of 1.8 MeV and an irradiation dose of 13.5 Mrad. The beam combustion test conditions are consistent with those in Example 1.

[0050] Process F: Same as in Example 1, with characteristic peak intensity deviation controlled within ±4%.

[0051] III. Example 3

[0052] 3.1 Raw material preparation

[0053] Recycled PET material: Waste textile PET recycled material, crushed to a particle size of 3-8mm; SAN-GMA copolymer: epoxy value 0.45eq / 100g, molecular weight 60000; microencapsulated red phosphorus: coating layer is urea-formaldehyde resin, particle size D50=12μm, phosphorus content 87%; other raw materials are the same as in Example 1.

[0054] 3.2 Specific procedures

[0055] Process A: The parameters for the two-stage countercurrent rinsing are the same as in Example 1. The temperature of the first stage of the segmented hot air drying is 102°C, and the temperature of the second stage is 78°C. The final moisture content of the PET material is 0.01%.

[0056] Step B: 100 parts by weight of recycled PET material, 12 parts by weight of SAN-GMA copolymer, 15 parts by weight of microencapsulated red phosphorus, 1.0 part by weight of silane coupling agent KH-550, nitrogen flow rate 0.8L / min, temperature raised to 185℃, stirring speed 750r / min, solid pre-reaction for 35min, cooling to obtain pretreated composite.

[0057] Step C: The amount of aluminum hypophosphite added is 10% of the total weight of the pretreated composite, the amount of EVA added is 22% of the total weight of the pretreated composite, the amount of antioxidant added is 0.4 parts by weight, the amount of calcium stearate is 0.25 parts by weight, and the amount of anti-dripping agent is 0.6 parts by weight. The temperature gradient of the twin-screw extruder is the same as in Example 1, the screw speed is 300 r / min, and the modified recycled granules with a diameter of 2.5 mm are obtained by water ring pelletizing.

[0058] Process D: Inner adhesive layer material formulation: modified recycled granules:LLDPE:POE=2.5:1:6 (weight ratio); Outer flame-retardant sheath material formulation: modified recycled granules:LLDPE:POE=3:1:6 (weight ratio). Inner layer extrusion temperature: 220℃, outer layer extrusion temperature: 235℃, extrusion rate: 1.8m / min, inner adhesive layer thickness: 0.9mm, outer flame-retardant sheath thickness: 1.3mm.

[0059] Step E: Circulating water cooling employs a three-stage gradient cooling (80℃→55℃→25℃), with an electron beam energy of 1.8 MeV and an irradiation dose of 13.5 Mrad. The beam combustion test conditions are consistent with those in Example 1.

[0060] Process F: Same as in Example 1, with characteristic peak intensity deviation controlled within ±4%.

[0061] IV. Example 4

[0062] 4.1 Raw material preparation

[0063] Consistent with Example 1, except that the average particle size of aluminum phosphate salt is D50=5μm and the particle size of microencapsulated red phosphorus is D50=15μm.

[0064] 4.2 Specific procedures

[0065] Process A: Two-stage countercurrent rinsing, first stage temperature 55℃, second stage temperature 45℃; segmented hot air drying, first stage temperature 105℃, second stage temperature 80℃; final PET material moisture content 0.018%.

[0066] Step B: 100 parts by weight of recycled PET material, 15 parts by weight of SAN-GMA copolymer, 18 parts by weight of microencapsulated red phosphorus, 1.5 parts by weight of silane coupling agent KH-550, nitrogen flow rate 1.0 L / min, temperature raised to 190℃, stirring speed 800 r / min, solid pre-reaction for 40 min, cooling to obtain pretreated composite.

[0067] Step C: The amount of aluminum hypophosphite added is 12% of the total weight of the pretreated composite, the amount of EVA added is 25% of the total weight of the pretreated composite, the amount of antioxidant added is 0.5 parts by weight, the amount of calcium stearate is 0.3 parts by weight, and the amount of anti-dripping agent is 0.8 parts by weight. The temperature gradient of the twin-screw extruder is the same as in Example 1, the screw speed is 320 r / min, and the modified recycled granules with a diameter of 3 mm are obtained by water ring pelletizing.

[0068] Process D: Inner adhesive layer material formulation: modified recycled granules:LLDPE:POE=3:1:8 (weight ratio); Outer flame-retardant sheath material formulation: modified recycled granules:LLDPE:POE=3:1:8 (weight ratio). Inner layer extrusion temperature: 225℃, outer layer extrusion temperature: 240℃, extrusion rate: 2.0m / min, inner adhesive layer thickness: 1.0mm, outer flame-retardant sheath thickness: 1.5mm.

[0069] Step E: Three-stage gradient cooling with circulating water (80℃→60℃→25℃), electron beam energy 2.0MeV, irradiation dose 15Mrad. The beam combustion test conditions are the same as in Example 1.

[0070] Process F: Same as in Example 1, with characteristic peak intensity deviation controlled within ±3%.

[0071] V. Comparative Example 1 (Missing Process B: Solid Pre-reaction)

[0072] 5.1 Raw material preparation

[0073] Completely consistent with Example 2.

[0074] 5.2 Specific procedures

[0075] Process A: Completely consistent with Example 2, with a final PET material moisture content of 0.012%.

[0076] Step B is omitted: The dried recycled PET material is directly mixed with SAN-GMA copolymer, microencapsulated red phosphorus, silane coupling agent KH-550, and EVA, aluminum hypophosphite, processing aids, etc. from step C, and the mixing ratio is the same as the material ratio in step C of Example 2.

[0077] Process C: Completely consistent with Example 2, including twin-screw extruder parameters, granulation parameters, etc.

[0078] Processes D through F are completely identical to those in Example 2.

[0079] VI. Comparative Example 2 (without microencapsulated red phosphorus)

[0080] 6.1 Raw material preparation

[0081] Except for the absence of microencapsulated red phosphorus, the other raw materials are completely identical to those in Example 2.

[0082] 6.2 Specific procedures

[0083] Process A: Completely consistent with Example 2.

[0084] Step B: 100 parts by weight of recycled PET material, 10 parts by weight of SAN-GMA copolymer, and 1.0 part by weight of silane coupling agent KH-550 are prepared. The remaining parameters are the same as in Step B of Example 2. A pretreated composite (without microencapsulated red phosphorus) is prepared.

[0085] Step C: The amount of aluminum hypophosphite added is adjusted to 20% of the total weight of the pretreated composite (to compensate for the lack of flame retardant effect of microencapsulated red phosphorus), and the proportions of other materials, extruder parameters, and granulation parameters are the same as in Example 2.

[0086] Processes D through F are completely identical to those in Example 2.

[0087] Multiple performance tests were conducted on the cable samples prepared in the four embodiments and two comparative examples mentioned above, including flame retardancy (based on IEC 60332-1 bundled burning test, evaluation indicators are flame retardancy rating and extinguishing time), mechanical properties (tensile strength and elongation at break, test samples are sheath layer cut pieces, dumbbell-shaped specimens, tensile rate 50 mm / min), processing performance (melt flow rate MFR, test temperature 230℃, load 2.16 kg), bonding performance (peel strength, tested according to GB / T 29510-2013 standard, test rate 50 mm / min), and long-term stability (thermal aging test, after aging in a 100℃ oven for 72 h, the retention rate of tensile strength and elongation at break were tested). The test results are shown in the table below.

[0088]

[0089] Examples 1-4 were designed to create gradient formulations by adjusting the amounts of SAN-GMA, microencapsulated red phosphorus, and aluminum hypophosphite, as well as the ratio of LLDPE to modified recycled granules, to explore the impact of each component's content on the final performance. Example 1 used lower amounts of flame-retardant components and compatibilizers, Example 4 used the highest amounts, and Examples 2 and 3 used intermediate values. Comparative Example 1 had the same formulation components as Example 2, except for the absence of step B (solid-state pre-reaction), which was used to verify the necessity of this step. Comparative Example 2 removed microencapsulated red phosphorus and doubled the amount of aluminum hypophosphite to verify the synergistic effect of microencapsulated red phosphorus in the flame-retardant system and the rationality of the flame-retardant system of this invention. From the perspective of formulation design logic, this invention improves compatibility by reacting the epoxy functional groups of SAN-GMA with the terminal hydroxyl and carboxyl groups of PET. Simultaneously, microencapsulated red phosphorus and aluminum hypophosphite form a phosphorus-aluminum synergistic flame-retardant system, reducing the amount of a single flame retardant and balancing flame-retardant and mechanical properties.

[0090]

[0091] The flame retardant performance test results show that all four examples achieved the Class A flame retardant rating of the IEC 60332-1 standard. Furthermore, with the increase in the amount of SAN-GMA, microencapsulated red phosphorus, and aluminum hypophosphite added, the extinguishing time gradually shortened, the dripping phenomenon gradually lessened and eventually disappeared, and the integrity of the char layer continuously improved. Example 4, due to the use of the highest amount of flame retardant components and compatibilizer, exhibited the best flame retardant performance, with an extinguishing time of only 40 seconds, no dripping phenomenon, and a thick, dense char layer with a certain strength. This is because the synergistic flame retardant system formed by microencapsulated red phosphorus and aluminum hypophosphite can rapidly decompose during combustion to produce substances such as phosphoric acid and metaphosphoric acid, catalyzing the dehydration of PET and EVA substrates into char. Simultaneously, the high addition amount of SAN-GMA improved the compatibility of the components, ensuring that the char layer could continuously and densely cover the material surface, isolating oxygen and heat transfer.

[0092] Comparing Example 2 with Comparative Example 1, it can be found that after omitting the solid-state pre-reaction step B, the flame retardancy rating of the cable sample drops to Grade B, the extinguishing time is prolonged to 120s, severe dripping occurs, and the char layer is discontinuous and easily detaches. This is because the solid-state pre-reaction enables the epoxy functional groups of SAN-GMA to react with the end groups of PET in advance, while the silane coupling agent achieves preliminary bonding between the flame retardant components and the PET substrate at high temperature, improving the compatibility and dispersion uniformity of each component. However, after omitting this step, it is difficult for each component to achieve uniform dispersion during extrusion, the flame retardant components are prone to agglomeration, resulting in a decrease in flame retardancy efficiency. At the same time, the interfacial bonding force between the substrate and the flame retardant components is poor, and dripping easily occurs during combustion, making it impossible for the char layer to form a continuous structure.

[0093] Comparative Example 2, by removing microencapsulated red phosphorus and doubling the amount of aluminum hypophosphite, still maintained a flame retardant rating of B, with a quenching time of 105 s and significant dripping. This indicates a significant synergistic flame retardant effect between microencapsulated red phosphorus and aluminum hypophosphite, and simply increasing the amount of aluminum hypophosphite cannot replace this synergistic effect. The coating layer of microencapsulated red phosphorus can prevent the red phosphorus from oxidizing and decomposing during processing, while slowly releasing phosphorus during combustion. This synergistic effect with the aluminum compounds produced by the decomposition of aluminum hypophosphite further improves char formation efficiency and char layer quality. In contrast, the single aluminum hypophosphite flame retardant system has low char formation efficiency and is difficult to form an effective barrier char layer, resulting in a decrease in flame retardant performance.

[0094]

[0095] In terms of mechanical properties, the tensile strength and elongation at break of Examples 1-4 were superior to those of Comparative Examples 1 and 2. Furthermore, the tensile strength gradually increased with the increase of SAN-GMA content, reaching a maximum of 16.3 MPa in Example 4. The elongation at break peaked at 350% in Example 3, but decreased slightly in Example 4. This is because SAN-GMA, as a compatibilizer, allows its epoxy functional groups to chemically react with substrates such as PET and EVA, forming crosslinking points and enhancing interfacial bonding, thereby improving the mechanical properties of the material. However, when the amount of SAN-GMA added is too high (Example 4, 15 parts by weight), excessive crosslinking leads to a slight decrease in material toughness and a slight reduction in elongation at break. Comparative Example 1, lacking a solid-state pre-reaction, exhibited poor compatibility among its components and weak interfacial bonding, resulting in a tensile strength of only 8.6 MPa and an elongation at break of 185%, far lower than Example 2. Comparative Example 2, due to the use of a high content of aluminum hypophosphite alone, experienced easy agglomeration of flame retardant particles, disrupting the continuity of the substrate and significantly reducing mechanical properties.

[0096] Regarding processing performance, the MFR values ​​of Examples 1-4 were all within the range of 1.8-2.1 g / 10 min, which is within the ideal processing range, indicating that the material has good flowability and can meet the process requirements of twin-screw extrusion and bilayer co-extrusion. This is due to the solid pre-reaction in step B, which initially dispersed the components evenly, and the addition of EVA, which improved the processing flowability of the material. The MFR of Comparative Example 1 was only 1.2 g / 10 min, indicating poor processing flowability. This is because the components have poor compatibility, generating large internal friction during melting, which leads to increased melt flow resistance. The MFR of Comparative Example 2 was 1.5 g / 10 min, slightly better than Comparative Example 1, but still lower than Example 2, indicating that the high content of aluminum hypophosphite has a certain negative impact on the material's flowability.

[0097] Regarding adhesion performance, the peel strength of Examples 1-4 was all above 1.2 N / mm, with Example 4 reaching 1.7 N / mm, indicating a good adhesion between the inner adhesive layer and the outer flame-retardant sheath layer. This is because the structural design of the double-layer co-extrusion die head allows for partial interpenetration at the molecular level between the two layers at the die orifice. Furthermore, the addition of LLDPE and POE improves the compatibility of the two layers. Comparative Examples 1 and 2 showed peel strengths of 0.8 N / mm and 0.9 N / mm, respectively, indicating poor adhesion. This was mainly due to the poor compatibility of the components in Comparative Example 1, and the alteration of the flame-retardant system in Comparative Example 2 affecting the interfacial bonding between the two layers.

[0098] Regarding long-term stability, the tensile strength retention rate after thermal aging in Examples 1-4 was all above 92%, and the elongation at break retention rate was all above 88%, with Example 4 showing the best performance, indicating that the material has good thermal stability. This is attributed to the effect of the antioxidant system and the stable cross-linked structure formed by electron irradiation cross-linking. The thermal aging retention rates of Comparative Examples 1 and 2 were both below 90%, especially the elongation at break retention rate of Comparative Example 1, which was only 78.3%, indicating poor long-term stability.

[0099] The comparative tests of the above four examples and two comparative examples demonstrate that the method for preparing flame-retardant cable materials based on recycled PET modification provided by this invention, through the synergistic cooperation of processes A to F, effectively enhances the recycling value of recycled PET, producing cable materials with excellent flame-retardant, mechanical, processing, and bonding properties. Specifically, the solid-state pre-reaction in process B is a key step in ensuring the compatibility and flame-retardant performance of each component. The synergistic flame-retardant system of microencapsulated red phosphorus and aluminum hypophosphite achieves Class A flame-retardant effect at a relatively low addition amount. The double-layer co-extrusion process and electron irradiation crosslinking further improve the structural stability and reliability of the material. Examples 3 and 4 exhibit the best overall performance, especially Example 4, which demonstrates outstanding flame-retardant performance and long-term stability, making it suitable for cable products with high requirements for flame-retardant rating and service life. Examples 1 and 2 offer cost advantages and are suitable for the production of conventional flame-retardant cables. This invention not only realizes the resource utilization of waste PET and reduces the production cost of cable materials but also has significant environmental benefits and broad industrial application prospects.

[0100] 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 flame-retardant cable material based on recycled PET modification, characterized in that, This method performs the following steps sequentially: Process A: The recovered polyethylene terephthalate material is subjected to hydraulic cleaning, eddy current separation, and hot air drying to control its moisture content to below 0.02%; Step B: Under inert gas protection, the PET obtained in Step A is subjected to solid-state pre-reaction with styrene-acrylonitrile-glycidyl methacrylate copolymer containing epoxy functional groups, microencapsulated red phosphorus and silane coupling agent in a high-speed stirred tank at 180-190℃ to form a pretreated composite. Step C: The pretreated composite, ethylene-vinyl acetate copolymer, aluminum hypophosphite and anti-dripping agent are fed into a co-rotating parallel twin-screw extruder to achieve dynamic cross-linking under temperature gradient and high shear. Modified recycled granules with a diameter of 2-3 mm are obtained by water ring pelletizing. Process D: Modified recycled granules, linear low-density polyethylene, elastomers, and processing aids are extruded through a double-layer co-extrusion die head to simultaneously form an inner adhesive layer and an outer flame-retardant sheath layer on the outer periphery of the conductor.

2. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In step A, the hydraulic cleaning adopts a two-stage countercurrent rinsing process, and the rinsing solution contains 1.5% sodium hydroxide and 0.3% nonionic surfactant by mass. The hot air drying adopts a segmented process, first rapidly dehydrating at 100-105℃ for 30 minutes, and then drying at a constant temperature of 75-80℃ for 4 hours.

3. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In step B, the components by weight are as follows: 100 parts of recycled PET material, 8-15 parts of copolymer containing epoxy functional groups, 12-18 parts of microencapsulated red phosphorus, and 0.5-1.5 parts of silane coupling agent KH-550; the solid pre-reaction time is 25-40 minutes, and the stirring speed is 600-800 rpm.

4. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In process C, the temperature field of the co-rotating parallel twin-screw extruder is set as follows: from the feed port to the die head, the temperatures of the six temperature zones are 185℃, 235℃, 245℃, 250℃, 248℃, and 245℃ respectively; during the dynamic crosslinking process, the length-to-diameter ratio of the screw is 40:1, and the rotation speed is 280-320 rpm.

5. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In step C, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 28%-33% by mass, and the melt index is 6g / 10min; the average particle size D50 of the aluminum hypophosphite is ≤5μm, and its addition amount is 8%-12% of the total weight of the pretreated composite.

6. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In process D, the inner layer extrusion temperature is set to 215-225℃, and the outer layer extrusion temperature is set to 230-240℃.

7. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, In step D, the weight ratio of the linear low-density polyethylene to the modified recycled granules is 1:2 to 1:3; the elastomer is a polyolefin elastomer, and its addition amount is 5-8 parts by weight based on 100 parts by weight of the modified recycled granules.

8. The method for preparing a flame-retardant cable material based on recycled PET modification according to claim 1, characterized in that, Following step D, the process further includes: Process E: The formed cable is subjected to circulating water cooling and electron irradiation cross-linking, and a bundled combustion test is conducted according to IEC 60332-1 standard to confirm its flame retardant rating; Process F: Online defect detection and closed-loop control process, which utilizes the X-ray real-time detection system and near-infrared spectroscopy analysis system integrated into the production line to monitor the uniformity of sheath thickness and the consistency of material composition, and feeds the data back to the extruder screw speed and temperature control system to achieve automatic fine-tuning of process parameters.

9. A method for preparing flame-retardant cable material based on recycled PET modification according to claim 8, characterized in that, In step E, the irradiation dose of the electron irradiation crosslinking is 12-15 Mrad, and the beam energy is 1.5-2.0 MeV; the circulating water cooling adopts a three-stage gradient cooling, with the water temperature gradually decreasing from 80°C to 25°C.

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