Preparation method of conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material

Abstract

The invention relates to the technical field of high polymer materials, in particular to a preparation method of a conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material. The invention aims to solve the problems of high material hardness, obvious friction noise and unstable conductive network caused by dependence on high-filling carbon black in the prior art. The method comprises the following steps: carrying out carboxylation and acylating chlorination treatment on a multi-walled carbon nanotube, and carrying out segmented graft modification on the multi-walled carbon nanotube and fluorine-containing short-chain amine, saturated long-chain amine and unsaturated long-chain amine to improve the compatibility of the multi-walled carbon nanotube with a polyethylene matrix; preparing master batches from the modified carbon nanotubes and a polyolefin elastomer, carrying out total mixing and extrusion on the master batches, high-density polyethylene and an auxiliary agent, and carrying out thermal aging treatment. According to the method, a stable conductive network is constructed under the low addition amount (0.5%-0.8%), the surface resistivity, the friction coefficient and the noise fluctuation are remarkably reduced, and meanwhile the wear resistance and the long-acting antistatic performance are improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a method for preparing a conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material. Background Technology

[0002] In the field of cable sheathing materials, polyethylene-based materials are widely used due to their excellent insulation and processing performance, but they do not inherently possess antistatic capabilities. To meet the antistatic requirements of cables in harsh environments such as rail transit and underground operations, traditional methods typically employ the addition of conductive agents to achieve charge dissipation. Among these, carbon black, due to its low cost and good conductivity, has become the most commonly used conductive filler phase. However, a relatively high proportion of carbon black (e.g., 15%-20% or more) is required to form a continuous conductive network. This high filler content directly leads to a significant increase in the hardness of the polyethylene matrix and a decrease in the material's flexibility, making it prone to rigid contact with cable trays or pipes during cable laying and operation.

[0003] High filler content also increases the material's coefficient of friction, making it more prone to intermittent stick-slip phenomena during dynamic friction. This stick-slip not only exacerbates wear but also generates harsh whistling and scraping noises, causing noise pollution in enclosed or sensitive environments (such as subway tunnels), affecting equipment lifespan and personnel comfort. Simultaneously, carbon black particles have poor dispersibility in polyethylene melt, easily agglomerating and forming localized conductive enrichment areas and non-uniform networks. During extrusion processing, high shear forces can disrupt these fragile conductive pathways, leading to increased surface resistivity fluctuations and even resistance decay in the early stages of use.

[0004] A more profound problem lies in the insufficient thermal stability of carbon black-based conductive networks. During long-term operation, cables accumulate heat due to current load or changes in ambient temperature. The weak interfacial bonding between carbon black and polyethylene, coupled with differences in thermal expansion, easily leads to the migration or rearrangement of conductive phases. This causes a significant shift in surface resistivity over time, making it difficult to maintain antistatic properties. Furthermore, high-hardness materials are more prone to generating abrasive debris during friction, exacerbating the interfacial ploughing effect. This not only increases noise fluctuations but also accelerates material wear, creating a vicious cycle.

[0005] Existing technologies have attempted to replace conductive agents with metal powders or carbon fibers, but metal fillers have high density and are prone to oxidation, while carbon fibers have a large aspect ratio and are easily broken during processing, making it difficult to achieve stable conductivity at low addition levels. Some improvement schemes reduce noise by adding lubricants, but often sacrifice antistatic properties or durability. In short, existing strategies with high-filler conductive agents struggle to overcome the trade-off between material hardness, frictional noise, and conductivity stability, failing to meet the comprehensive requirements of modern cables for long-term antistatic performance, low-noise operation, and high wear resistance. Summary of the Invention

[0006] The purpose of this invention is to propose a method for preparing conductive carbon nanotube polyethylene antistatic and low-noise cable sheath material, in order to solve the problems of existing cable sheath materials that rely on high filler carbon black and other conductive agents, resulting in high material hardness, significant frictional noise, and easy damage to the conductive network during processing and operation, making it difficult to achieve both long-term antistatic effect and low noise wear resistance.

[0007] To achieve the above objectives, the present invention provides a method for preparing conductive carbon nanotube / polyethylene antistatic and low-noise cable sheath material, comprising the following steps: (1) Under nitrogen protection, acyl chloride multi-walled conductive carbon nanotubes are subjected to an amidation reaction with amines, and alkyl segments are grafted onto amide bonds to obtain modified conductive carbon nanotubes. (2) Modified conductive carbon nanotubes are melt-blended with polyolefin elastomers to obtain modified conductive carbon nanotube masterbatch; (3) The modified conductive carbon nanotube masterbatch is mixed with polyolefin elastomer, high-density polyethylene and additives, diluted and melt-extruded into granules, and then subjected to heat aging treatment to obtain conductive carbon nanotube / polyethylene antistatic low noise cable sheath material.

[0008] Furthermore, in step (1), the amines include at least fluorinated short-chain amines, saturated long-chain amines and unsaturated long-chain amines, and are added in stages in the order of fluorinated short-chain amines, saturated long-chain amines and unsaturated long-chain amines for reaction; the molar fraction of the fluorinated short-chain amines in the amines is 8% to 12%, and the molar fraction of the saturated long-chain amines in the amines is 50% to 55%.

[0009] Preferably, in step (1), the acyl chloride multi-walled conductive carbon nanotubes are obtained by acyl chloride treatment of carboxylated multi-walled conductive carbon nanotubes; the carboxylated multi-walled conductive carbon nanotubes are obtained by carboxylation treatment of multi-walled conductive carbon nanotubes.

[0010] Preferably, the multi-walled conductive carbon nanotubes have an average diameter of 7–15 nm and an average length of 1.0–2.0 μm.

[0011] Preferably, the carboxylation treatment employs mixed acid oxidation, wherein the mixed acid consists of 98% sulfuric acid and 65% nitric acid by mass, with the mass ratio of sulfuric acid to nitric acid being 2:1 to 4:1.

[0012] Preferably, the acyl chloride treatment uses thionyl chloride as the acyl chloride reagent and anhydrous N,N-dimethylformamide is added as an accelerator; the mass ratio of carboxylated multi-walled conductive carbon nanotubes to thionyl chloride is 1:8 to 1:12, and the amount of the accelerator is 1% to 5% of the mass of the carboxylated multi-walled conductive carbon nanotubes.

[0013] Preferably, the fluorinated short-chain amine is selected from one or more of 2,2,3,3,4,4,4-heptafluorobutylamine, 2,2,3,3-tetrafluoropropylamine, and 1H,1H,2H,2H-perfluorohexylamine; the saturated long-chain amine is selected from one or more of dodecylamine, hexadecylamine, octadecylamine, and eicosamine; and the unsaturated long-chain amine is selected from one or more of oleylamine, linoleylamine, and erucic acid amine.

[0014] Preferably, in the modified conductive carbon nanotube masterbatch obtained in step (2), the mass fraction of modified conductive carbon nanotubes is 8% to 12%; in the conductive carbon nanotube / polyethylene antistatic low noise cable sheath material, the mass fraction of modified conductive carbon nanotubes is 0.5% to 0.8%.

[0015] Preferably, in step (3), anhydride-modified high-density polyethylene is added as a compatibilizer, and the amount of the compatibilizer is 0.5% to 2.0% of the total mass of the cable sheath material.

[0016] Preferably, the temperature of the heat aging treatment in step (3) is 70-90°C and the aging time is 4-10h.

[0017] Preferably, the adjuvants in step (3) include hindered phenolic antioxidants, phosphite antioxidants, and calcium stearate.

[0018] The beneficial effects of this invention are: This invention utilizes modified conductive carbon nanotubes as the conductive phase to construct a stable and continuous conductive network within a polyethylene matrix at low addition levels. After low-density alkylation grafting of carbon nanotubes with amide bonds, the introduced alkyl segments on their surface exhibit improved compatibility with the polyethylene molecular chains, significantly enhancing the wettability and dispersion stability of the carbon nanotubes in the melt. This uniform dispersion avoids localized stress concentration caused by conductive phase agglomeration, resulting in smoother interfacial contact during friction and effectively reducing the ploughing effect and intermittent stick-slip caused by hard points, thereby reducing howling noise.

[0019] In the grafting system, fluorine-containing short chains are preferentially introduced to form preferential sites on the carbon nanotube surface, creating a surface energy gradient. The low surface energy of the fluorine-containing segments promotes the formation of a oriented, low-friction layer on the material surface during friction, which not only reduces the sliding friction coefficient but also suppresses local charge accumulation and reduces electrostatic discharge noise. Simultaneously, this gradient structure delays the reorganization of the conductive network under thermo-mechanical coupling conditions, ensuring stable surface resistivity during long-term use and more durable antistatic properties.

[0020] In the segmented grafting sequence, saturated long-chain amines (such as octadecylamine) are grafted first, followed by unsaturated long-chain amines (such as oleylamine), forming a compliance gradient on the carbon nanotube surface. This synergistic effect enables the material to maintain toughness and wear resistance under long-term friction conditions. The energy release at the friction interface is more uniform, avoiding noise peaks caused by sudden stick-slip, and significantly reducing noise fluctuations.

[0021] Anhydride-modified high-density polyethylene (HDPE) is used as a compatibilizer to enhance the interfacial interaction between the polyethylene matrix and modified carbon nanotubes. The anhydride groups form chemical bonds with residual functional groups on the carbon nanotube surface, reducing the risk of phase separation and allowing the conductive network to be more uniformly embedded in the matrix. This interfacial strengthening reduces the initiation of microcracks during friction, improves the overall wear resistance of the material, and prevents resistivity drift caused by conductive phase migration.

[0022] The masterbatch pre-dispersion process ensures that the modified conductive carbon nanotubes are pre-homogenized at the microscale before final mixing. The masterbatch acts as a carrier, protecting the carbon nanotubes from excessive shear damage during secondary extrusion and maintaining the integrity of the conductive pathways. This process design results in a final sheath material with highly consistent conductivity and tribological properties, stable noise output, and suitability for high-reliability applications. In summary, this invention, through material modification and process optimization, synergistically improves antistatic properties, reduces noise, and enhances wear resistance at multiple scales. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0024] This invention provides a method for preparing conductive carbon nanotube / polyethylene antistatic and low-noise cable sheath material. The core of this method is to use modified conductive carbon nanotubes as the conductive phase to construct a stable conductive pathway at a low addition amount, while taking into account the requirements of antistatic properties, low noise, and wear resistance.

[0025] The preparation method provided by the present invention preferably includes the following steps: Step S1 involves carboxylating multi-walled conductive carbon nanotubes; Step S2 involves acyl chloride treatment of the carboxylated product; Step S3 involves reacting the acyl chlorided multi-walled conductive carbon nanotubes with amines under nitrogen protection to obtain modified conductive carbon nanotubes via low-density alkylation of amide bonds; Step S4 involves melt blending the modified conductive carbon nanotubes with polyolefin elastomer to obtain masterbatch; Step S5 involves mixing and diluting the masterbatch with polyolefin elastomer, high-density polyethylene, and additives, followed by melt extrusion granulation and heat aging treatment at 80°C to obtain sheath material; Step S6 involves extruding the sheath material into a sheath.

[0026] In the preparation method provided by the present invention, the multi-walled conductive carbon nanotubes are preferably commercially available multi-walled conductive carbon nanotube materials, more preferably with an average diameter of 7-15 nm, more preferably 9-11 nm, specifically 7 nm, 8 nm, 9 nm, 9.5 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm or 15 nm; the average length is preferably 1.0-2.0 μm, more preferably 1.3-1.7 μm, specifically 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm or 2.0 μm.

[0027] In the sheath material system provided by this invention, the polyethylene matrix preferably includes a polyolefin elastomer and high-density polyethylene, wherein the polyolefin elastomer is preferably an α-olefin ethylene copolymer-type polyolefin elastomer; the high-density polyethylene is used to provide the sheath molding strength and environmental resistance. Further, anhydride-modified high-density polyethylene is preferably added as a compatibility component to improve the interfacial interaction between the modified conductive carbon nanotubes and the polyethylene matrix and reduce the risk of agglomeration; this improved interfacial compatibility can reduce the "ploughing effect" during friction, thereby reducing the risk of howling and scratching noise and contributing to the long-term stability of surface resistance.

[0028] In the sheathing material system provided by this invention, the additives preferably include antioxidants and lubricating / stabilizing agents; the antioxidants preferably include a combination of hindered phenolic antioxidants and phosphite antioxidants, and the lubricating / stabilizing agent is preferably calcium stearate. The above-mentioned additive system can suppress the oxidative degradation of polyethylene caused by extrusion heat and reduce the accumulation of processing frictional heat, thereby reducing the probability of the conductive network being damaged during extrusion and helping to reduce noise fluctuations under long-term frictional operating conditions.

[0029] In step S1 provided by this invention, carboxylation is preferably carried out using a mixed acid oxidation method. The mixed acid is preferably composed of 98% sulfuric acid and 65% nitric acid by mass. The mass ratio of sulfuric acid to nitric acid is preferably 2:1 to 4:1, more preferably 2.5:1 to 3.5:1, specifically 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. This ratio affects the oxidation intensity and defect introduction rate, thereby affecting the density of carboxyl functional groups and the subsequent acylation efficiency. An excessively high proportion of nitric acid can easily lead to over-cleavage, while an excessively high proportion of sulfuric acid may cause insufficient oxidation, thus affecting the subsequent grafting efficiency.

[0030] In step S1 provided by this invention, the mixed acid preparation is preferably carried out under ice-water bath conditions, and the system temperature is preferably below 20°C; the mechanical stirring speed is preferably 300-700 rpm, more preferably 450-550 rpm, specifically 300 rpm, 400 rpm, 500 rpm, 600 rpm, or 700 rpm; the stirring time is preferably 5-20 min, more preferably 8-12 min. These temperature control and stirring conditions affect the uniformity of the mixed acid and the controllability of the initial exothermic reaction, thereby affecting the risk of localized peroxidation and aggregation after the addition of carbon nanotubes.

[0031] In step S1 provided by the present invention, the multi-walled conductive carbon nanotubes are preferably added in batches, with the number of batches preferably being 2 to 5 times, more preferably 3 to 4 times; after each addition, ultrasonic dispersion is preferably performed, with the ultrasonic power preferably being 200 to 600W, more preferably 350 to 450W, and the ultrasonic time preferably being 5 to 15 minutes, more preferably 8 to 12 minutes.

[0032] In step S1 provided by the present invention, the carboxylation reaction temperature is preferably 50-70°C, more preferably 58-62°C; the reaction time is preferably 1-3 h, more preferably 1.5-2.5 h.

[0033] In step S1 provided by this invention, after the reaction is completed, the reaction slurry is preferably quenched in ice water and stirred. The amount of ice water is preferably 80 to 120 times the mass of the carbon nanotubes, more preferably 90 to 110 times. The stirring time is preferably 20 to 40 minutes, more preferably 25 to 35 minutes. Subsequently, the mixture is filtered and washed with deionized water until the pH of the filtrate is 6.5 to 7.0, more preferably 6.7 to 6.9. This quenching, washing, and pH control can effectively terminate the oxidation reaction, reduce the risk of subsequent side reactions caused by acid residue, and thus improve the controllability and repeatability of the acyl chloride and grafting steps.

[0034] In step S2 of this invention, the acyl chloride reagent is preferably thionyl chloride, and a small amount of anhydrous N,N-dimethylformamide may be added as a promoter; the mass ratio of carboxylated multi-walled conductive carbon nanotubes to thionyl chloride is preferably 1:8 to 1:12, more preferably 1:9 to 1:11, specifically 1:8, 1:9, 1:10, 1:11 or 1:12; the amount of promoter is preferably 1% to 5% of the mass of carboxylated multi-walled conductive carbon nanotubes, more preferably 2% to 4%. This ratio affects the completeness of the conversion of carboxyl groups to acyl chloride, and thus affects the grafting efficiency and grafting density of amide bond formation in step S3; insufficient acyl chloride will lead to insufficient grafting sites, while excessive grafting or residual acyl chloride / acidic components may affect the stability of subsequent melt processing.

[0035] In step S2 provided by the present invention, the reaction is preferably carried out under nitrogen protection, the nitrogen replacement flow rate is preferably 50-150 mL / min, more preferably 80-120 mL / min; the replacement time is preferably 10-30 min, more preferably 12-18 min; the reflux temperature is preferably 70-80℃, more preferably 74-76℃; and the reflux time is preferably 4-8 h, more preferably 5-7 h.

[0036] In step S2 provided by the present invention, after the reaction is completed, excess thionyl chloride and volatile byproducts are preferably removed under reduced pressure. The removal temperature is preferably 30-50°C, more preferably 38-42°C. Subsequently, the product is washed with anhydrous toluene and vacuum dried at 50-70°C for 4-10 hours, more preferably at 58-62°C for 5-7 hours.

[0037] In step S3 provided by the present invention, a segmented grafting sequence of "fluorine-containing short chain preferentially occupying the site, saturated long chain, and unsaturated long chain" is preferably adopted.

[0038] In this invention, the preferential occupancy of fluorine-containing short chains can form a surface energy gradient, promote the formation of a low-friction orientation layer on the surface and suppress the decay of surface resistance over time, thereby contributing to low noise and long-term antistatic stability; the sequential grafting of saturated and unsaturated long chains can obtain a chain segment flexibility gradient, improving the sustainability of wear resistance and low noise performance.

[0039] In step S3 provided by the present invention, the solvent is preferably anhydrous toluene; the mass ratio of acyl chloride multi-walled conductive carbon nanotubes to anhydrous toluene is preferably 1:8 to 1:12, more preferably 1:9 to 1:11; the ultrasonic dispersion power is preferably 200 to 600 W, more preferably 350 to 450 W; the ultrasonic dispersion time is preferably 10 to 30 min, more preferably 15 to 25 min; and the stirring speed is preferably 400 to 800 rpm, more preferably 550 to 650 rpm.

[0040] In step S3 provided by the present invention, based on 65g of acyl chloride multi-walled conductive carbon nanotubes, the total molar amount of fluorinated short-chain amines, saturated long-chain amines and unsaturated long-chain amines is preferably 0.08 to 0.12 mol; and the molar fraction of fluorinated short-chain amines among the three types of amines is preferably 8% to 12%, and the molar fraction of saturated long-chain amines is preferably 50% to 55%.

[0041] In step S3 of this invention, the acid scavenger is preferably triethylamine; the amount of acid scavenger is preferably matched with the total amount of amines to ensure that the amidation reaction can proceed continuously and to reduce the impact of acidic byproducts on the surface of carbon nanotubes and subsequent extrusion stability. As an alternative, the acid scavenger may also be selected from one or more of pyridine and diisopropylethylamine; as long as it can achieve the technical effects of this invention, it falls within the protection scope of this invention.

[0042] In step S3 of this invention, the fluorinated short-chain amine is preferably 2,2,3,3,4,4,4-heptafluorobutylamine; as alternative raw materials, the fluorinated short-chain amine can also be selected from 2,2,3,3-tetrafluoropropylamine, 1H,1H,2H,2H-perfluorohexylamine, etc.; the saturated long-chain amine is preferably octadecylamine, but can also be selected from dodecylamine, hexadecylamine, eicosamine, etc.; the unsaturated long-chain amine is preferably oleylamine, but can also be selected from linoleylamine, erucic acid amine, etc. The above combination of short-chain fluorinated and long-chain hydrocarbon groups achieves both surface energy regulation and improved compatibility with polyethylene melt.

[0043] In step S4 of this invention, it is preferable to prepare a modified conductive carbon nanotube masterbatch. The mass fraction of modified conductive carbon nanotubes in the masterbatch is preferably 8% to 12%, more preferably 9% to 11%, and can specifically be 8%, 9%, 10%, 11%, or 12%. The mass fraction of the masterbatch affects the pre-dispersion degree and feeding uniformity of the conductive phase in the subsequent total mixing and dilution: too low a mass fraction will increase the amount of masterbatch used and increase the mixing error; too high a mass fraction may increase the risk of agglomeration inside the masterbatch and form local stress concentration in the secondary extrusion.

[0044] In step S4 provided by the present invention, the high-speed dry mixing speed is preferably 600-1000 rpm, more preferably 750-850 rpm; the dry mixing time is preferably 3-10 min, more preferably 4-6 min; the twin-screw extrusion temperature zone is preferably set in a gradient of 110-180°C; the screw speed is preferably 150-250 rpm, more preferably 180-220 rpm; and vacuum exhaust is turned on in the middle and later stages.

[0045] In step S5 of this invention, it is preferable to pre-coat the material with masterbatch before total mixing and dilution, and then extrude granulation and heat aging treatment at 80°C to form a sheath material. The mass percentage of modified conductive carbon nanotubes in the sheath material is preferably 0.4%–1.0%, more preferably 0.5%–0.8%, and even more preferably 0.6%. This addition amount directly affects the formation of the conductive network and frictional noise: too low an addition amount may make it difficult to form a through-network, resulting in high surface resistance; too high an addition amount may increase hardness and friction factor, thereby increasing noise risk. Using modified conductive carbon nanotubes and controlling them within the preferred range is beneficial for achieving antistatic requirements while reducing the increase in hardness and the source of frictional noise caused by high filler content.

[0046] In step S5 of this invention, anhydride-modified high-density polyethylene is preferably added as a compatible component during the total dilution process. Its dosage is preferably 0.5% to 2.0% of the total mass of the sheath material, more preferably 0.8% to 1.2%. Simultaneously, antioxidants and calcium stearate are preferably added to inhibit thermo-oxidative aging and improve processing lubrication. The extrusion temperature range for the total dilution is preferably set in a gradient of 145 to 190°C, the screw speed is preferably 120 to 200 rpm, and vacuum venting is activated after the melt homogenization section. This vacuum venting facilitates the removal of volatiles and low-molecular-weight substances, reduces the risk of bubbles and resistance fluctuations, and thereby improves the apparent quality and surface resistance stability of the extruded sheath material.

[0047] In step S5 provided by this invention, the thermal aging temperature is preferably 70–90°C, more preferably 78–82°C; the thermal aging time is preferably 4–10 h, more preferably 5–7 h; and the material thickness is preferably 10–30 mm, more preferably 15–25 mm. These aging parameters affect the stress release and a certain degree of self-recovery / re-overlapping of the conductive network, thereby affecting the risk of resistance drift and noise stability. Insufficient thermal aging may lead to network breakage caused by extrusion shearing that is difficult to recover, while excessive thermal aging may cause unnecessary accumulation of thermal history.

[0048] In step S6 provided by this invention, the extrusion barrel temperature is preferably set in segments of 150–190°C, the die head temperature is preferably 175–185°C, the screw speed is preferably 40–60 rpm, and the traction speed is matched with 10–30 m / min; after demolding, it is preferably cooled and shaped in a water bath at 15–30°C. These extrusion and cooling conditions affect the surface density and uniformity of the conductive phase distribution of the sheath, thereby affecting the consistency of surface resistance and fluctuations in operating friction noise.

[0049] The following description, in conjunction with embodiments, is intended to further illustrate the invention, but should not be construed as limiting the scope of protection of the invention. Example 1

[0050] The multi-walled conductive carbon nanotubes used in this embodiment are Nanocyl NC7000 from Nanocyl, with an average diameter of 9.5 nm and an average length of 1.5 μm; the polyolefin elastomer is ENGAGE 8200 from Dow Chemical, with a density of 0.870 g / cm³. 3 The melt flow rate was 5 g / 10 min at 190℃ / 2.16 kg; the high-density polyethylene used was Dow Chemical Company's DOW DGDK-6862NT; and the anhydride-modified high-density polyethylene used was DuPont's FUSABOND E100.

[0051] Step S1: Under ventilated conditions, add 900g of 98% sulfuric acid and 300g of 65% nitric acid to a three-necked flask in an ice-water bath. Control the system temperature below 20℃ and mechanically stir at 500rpm for 10min to form a homogeneous mixed acid. Then, add 80g of multi-walled conductive carbon nanotubes in three portions. After each addition, ultrasonically disperse the nanotubes at 400W for 10min while maintaining stirring. After the addition is complete, raise the temperature to 60℃ and stir at 500rpm for 2h. After the reaction is complete, pour the reaction slurry into 8000g of ice water to quench it and stir for 30min. Then filter to separate the solid. Wash the solid in batches with deionized water until the pH of the filtrate is 6.8. Finally, vacuum dry at 80℃ for 12h to obtain carboxylated multi-walled conductive carbon nanotubes. Step S2: Add 70g of carboxylated multi-walled conductive carbon nanotubes, 700g of thionyl chloride and 2g of anhydrous N,N-dimethylformamide to a dry three-necked flask. Purge with nitrogen gas at 100mL / min for 15min, maintain nitrogen protection and reflux at 75℃ for 6h. After the reaction is complete, remove excess thionyl chloride and volatile byproducts under reduced pressure at 40℃. Rinse the inner wall of the flask with anhydrous toluene and filter the solid. Wash the solid twice with anhydrous toluene and dry under vacuum at 60℃ for 6h to obtain acyl chloride multi-walled conductive carbon nanotubes. Step S3: Add 65g of acyl chloride multi-walled conductive carbon nanotubes and 650g of anhydrous toluene to a dry three-necked flask. First, disperse the mixture by ultrasonication at 400W for 20min, then stir at 600rpm under nitrogen protection and control the system temperature at 25℃. Next, add 2g of 2,2,3,3,4,4,4-heptafluorobutylamine and 6g of triethylamine, and maintain the reaction temperature at 25℃ for 1h. Then, raise the temperature to 75℃ and add 15g of octadecylamine and 12g of triethylamine, and maintain the reaction temperature at 75℃ for 4h. Then, cool the system to 60℃ and add 10g of oleylamine and 6g of triethylamine, and maintain the reaction temperature at 60℃ for 2h. After the reaction is complete, cool to room temperature and filter. Wash the modified conductive carbon nanotubes three times with anhydrous toluene, twice with anhydrous ethanol, and then with deionized water until there is no amine odor. Finally, vacuum dry at 80℃ for 12h to obtain the modified conductive carbon nanotubes. Step S4: Add 60g of modified conductive carbon nanotubes and 540g of polyolefin elastomer to a high-speed mixer and dry mix at 800rpm for 5min. Then feed the mixture into a twin-screw extruder for melt mixing and granulation. The extrusion temperature zones are set sequentially to 120℃, 140℃, 160℃, 170℃, 170℃, and 160℃. The screw speed is set to 200rpm, and vacuum exhaust is turned on in the middle and later stages. The extruded strip is water-cooled and pelletized to obtain modified conductive carbon nanotube masterbatch. Step S5: Add 600g of modified conductive carbon nanotube masterbatch, 5460g of polyolefin elastomer, 3800g of high-density polyethylene, 100g of anhydride-modified high-density polyethylene, 20g of antioxidant 1010, 10g of antioxidant 168 and 10g of calcium stearate to a mixer and dry mix at 500rpm for 10min to obtain a premix. Add the premix to a twin-screw extruder and set the extrusion temperature zones sequentially to 150℃, 165℃, 175℃, 180℃, 180℃ and 175℃. Set the screw speed to 160rpm and turn on vacuum exhaust after the melt homogenization section. The extruded strip is water-cooled, pelletized, and then evenly laid in a metal tray with a thickness of 20mm. Heat-age at 80℃ for 6h and naturally cool to room temperature to obtain conductive carbon nanotube polyethylene antistatic low-noise cable sheath material.

[0052] Step S6: Add conductive carbon nanotube polyethylene antistatic low noise cable sheath material to a single screw cable sheath extruder. Set the barrel temperature to 160℃, 170℃, 180℃, and 180℃ in sequence. Set the die head temperature to 180℃. Set the screw speed to 50 rpm and match the traction speed to 20 m / min. Extrude the material to cover the wire core to form a sheath layer. After demolding, cool and shape the material in a 25℃ water bath and then wind it up. Example 2

[0053] The difference from Example 1 is as follows: In step S5, the amount of modified conductive carbon nanotube masterbatch added is 400g (40g of modified conductive carbon nanotubes and 360g of polyolefin elastomer in the masterbatch), the amount of polyolefin elastomer (excluding the masterbatch) added is 5640g, and the amount of high-density polyethylene added is 3820g; the amount of anhydride-modified high-density polyethylene is 100g, antioxidant 1010 is 20g, antioxidant 168 is 10g, and calcium stearate is 10g, making the total mass of the ingredients 10000g, thus the mass percentage of modified conductive carbon nanotubes in the sheath material is 0.4%. All other conditions are the same as in Example 1. Example 3

[0054] The difference from Example 1 is as follows: In step S5, the amount of modified conductive carbon nanotube masterbatch added is 800g (80g of modified conductive carbon nanotubes and 720g of polyolefin elastomer in the masterbatch), the amount of polyolefin elastomer (excluding the masterbatch) added is 5280g, and the amount of high-density polyethylene added is 3780g; the amount of anhydride-modified high-density polyethylene is 100g, antioxidant 1010 is 20g, antioxidant 168 is 10g, and calcium stearate is 10g, making the total mass of the ingredients 10000g, thus the mass percentage of modified conductive carbon nanotubes in the sheath material is 0.8%. All other conditions are the same as in Example 1. Example 4

[0055] The difference from Example 1 is that in step S3, the fluorinated short-chain amine is replaced by 2,2,3,3,4,4,4-heptafluorobutylamine with 1.5 g of 2,2,3,3-tetrafluoropropylamine, and the reaction is still carried out at 25°C for 1 hour. The subsequent stepwise grafting sequence of octadecylamine and oleylamine, the amount of triethylamine, and the reaction temperature / time remain unchanged. All other conditions are the same as in Example 1.

[0056] Comparative Example 1: The difference from Example 1 is that the carboxylation treatment in step S1, the acyl chloride treatment in step S2, and the amine grafting treatment in step S3 are omitted. Instead, Nanocyl's NANOCYL NC7000 multi-walled conductive carbon nanotubes are directly used as the conductive phase in step S4 to prepare conductive carbon nanotube masterbatch and in step S5 to prepare cable sheath material; the remaining conditions are the same as in Example 1.

[0057] Comparative Example 2: The difference from Example 1 is that, in step S3, 2,2,3,3,4,4,4-heptafluorobutylamine is not added for the fluorinated short-chain occupancy reaction. Instead, while keeping the other reagents and process conditions unchanged in step S3, the grafting reaction between saturated and unsaturated long-chain amines is directly initiated to obtain modified conductive carbon nanotubes without fluorinated short-chain occupancy structures. The remaining conditions are the same as in Example 1.

[0058] Comparative Example 3: The difference from Example 1 is that the order of adding saturated long-chain amines and unsaturated long-chain amines in step S3 is reversed compared to Example 1. That is, after the fluorinated short-chain amine occupancy is completed, the oleylamine grafting reaction is carried out first, followed by the octadecylamine grafting reaction. The remaining conditions are the same as in Example 1.

[0059] Comparative Example 4: The difference from Example 1 is that in step S5, anhydride-modified high-density polyethylene is not added as a compatibilizer, and the amount of anhydride-modified high-density polyethylene is adjusted from 100g to 0g, while the amount of high-density polyethylene is increased by 100g to maintain a total batch weight of 10000g. All other conditions are the same as in Example 1.

[0060] Comparative Example 5: The difference from Example 1 is that the modified conductive carbon nanotube masterbatch is not prepared using the masterbatch pre-dispersion process in step S4. Instead, in step S5, the modified conductive carbon nanotubes are directly mixed with polyolefin elastomer, high-density polyethylene, and additives, and then extruded and granulated. The remaining conditions are the same as in Example 1.

[0061] The present invention conducts the following performance tests on the sheath materials prepared in Examples 1-4 and Comparative Examples 1-5, and the test methods are as follows: Sample preparation: Two types of samples were prepared by hot pressing. The first type was a sheet with a thickness of 2.0 mm (used for volume resistivity, surface resistivity, tensile and tribo-wear). The hot pressing temperature was 180℃, preheating for 5 min, pressure was applied at 10 MPa and held for 8 min, and then water-cooled to 40℃ under pressure before demolding. The second type was a film with a thickness of 0.10 mm (used for electrostatic half-life). The hot pressing temperature was 180℃, preheating for 3 min, pressure was applied at 5 MPa and held for 3 min, and then water-cooled to 40℃ under pressure before demolding. All samples were conditioned in a standard environment of 23℃ and 50% relative humidity for 48 h before testing.

[0062] Tensile properties (GB / T 1040.2-2022): The 2.0 mm hot-pressed sheets of the examples and comparative examples were prepared into dumbbell-shaped specimens with a gauge length of 50 mm, a test temperature of 23 °C, and a tensile speed of 50 mm / min. Five specimens were tested for each sample and the average value was taken. The tensile strength and elongation at break were recorded.

[0063] Surface resistivity (GB / T 31838.3-2019): 2.0 mm hot-pressed sheets from the examples and comparative examples were used to measure the surface resistivity using the ring electrode method. The test voltage was 100 V DC, and the reading was taken 60 s after the voltage was applied. Five test points were evenly selected on the sheet for each sample, and the average value was taken. The ratio of the maximum value to the minimum value was calculated as a uniformity index. At the same time, the same sheet was placed in a hot air environment at 80 °C for 168 h and the above test was repeated, and the change rate of surface resistivity was calculated.

[0064] Electrostatic half-life (GB / T 14447-1993): Take 0.10 mm thin film samples from the examples and comparative examples, cut them into 100 mm × 100 mm pieces, and place them in an environment of 23°C and 50% relative humidity for 48 h before testing; apply a 10 kV electrostatic voltage to the surface of the thin film using the half-life method and record the time required for the electrostatic voltage to decay to 50% of its initial value as the electrostatic half-life. Each sample is tested 5 times and the average value is taken.

[0065] Sliding friction coefficient and wear volume (GB / T 3960-2016): The pin-disc sliding friction and wear test was adopted. The disc sample was a hot-pressed sheet of the example and comparative example, processed into a circular disc with a diameter of 30 mm and a thickness of 3.0 mm. The pin was a stainless steel ball with a diameter of 6 mm. The normal load was 10 N, the sliding radius was 10 mm, the linear velocity was 0.10 m / s, and the test time was 1800 s. During the test, the friction coefficient curve was recorded in real time, and the average value of the stable stage (600~1800 s) was taken as the sliding friction coefficient. The mass difference of the disc sample before and after the test was weighed and the wear volume was calculated by combining the density.

[0066] Friction noise (GB / T 3785.1-2023 and GB / T 3767-2016): Under the same friction and wear test apparatus and operating conditions for sliding friction coefficient and wear volume testing, a Class 1 sound level meter microphone is placed 0.50m outside the test bench, with the microphone height equal to the friction contact point. Sampling is performed in A-weighted, time-weighted "fast" mode, and the friction noise level is characterized by the equivalent continuous sound pressure level. The A-weighted equivalent continuous sound pressure level and the standard deviation of the sound pressure level are recorded for the entire time period (0-1800 seconds) to characterize noise fluctuations. The sound level meter is calibrated using a sound calibrator before the test. The test results are shown in Table 1.

[0067] Table 1 Performance test results of the examples and comparative examples

[0068] Data Analysis: As can be seen from the data in Table 1, the cable sheath material prepared by this invention exhibits a trend of more continuous conductive network and faster electrostatic decay with increasing amount of modified conductive carbon nanotubes in terms of surface resistivity, electrostatic half-life, and uniformity. Simultaneously, the surface resistivity change becomes more stable after aging. Regarding friction, wear, and noise, the sliding friction coefficient, wear volume, and noise fluctuations remain at low levels, demonstrating a more stable friction interface and more uniform energy release. This may be because the conductive carbon nanotubes form a surface energy gradient after preferential occupancy by fluorinated short chains, and further, through segmented grafting with octadecylamine and oleylamine, they possess both wetting and dispersion stability in polyolefin elastomers and high-density polyethylene. Simultaneously, the anhydride-modified high-density polyethylene provides synergistic chemical and physical compatibility at the phase interface, and the pre-dispersion process of the masterbatch inhibits agglomeration and migration, allowing the conductive network to maintain continuity under long-term friction and thermal conditions, thereby achieving a synergistic improvement in antistatic, low-noise, and wear-resistant properties.

[0069] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, when the conductive carbon nanotubes were not subjected to fluorine-containing short-chain occupancy and long-chain amine segmentation grafting, and were directly mixed with polyolefin elastomers, the surface resistivity uniformity deteriorated significantly, the resistance stability decreased after aging, the electrostatic decay slowed down, and higher wear and noise fluctuations occurred. The main reason is that the surface energy of the unmodified conductive carbon nanotubes is not well matched with the polyolefin system, making it easy to form agglomerates and resulting in a discrete structure of locally connected and locally broken conductive pathways. During friction, the agglomerates are more likely to induce furrows and intermittent stick-slip, increasing the fluctuation of the friction coefficient curve, which in turn manifests as stronger friction noise and more unstable sound pressure level fluctuations.

[0070] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 2 and 3, when the fluorinated short-chain preferential occupancy is not introduced in step S3, or when the grafting order of octadecylamine and oleylamine is reversed, the material can still establish a certain conductive network, but the resistance stability, wear, and noise performance all deteriorate to varying degrees. This may be because the fluorinated short-chain occupancy is beneficial for forming a lower surface energy orientation layer on the surface of the conductive carbon nanotubes and inhibiting interface rearrangement, thereby reducing the risk of resistance drift and stick-slip during long-term use. However, changing the segmented grafting order affects the arrangement and coverage integrity of long-chain amines on the surface, reducing the synergy of wetting-dispersion-boundary lubrication, making the conductive network more susceptible to heat and frictional disturbances, leading to localized disconnection and stronger transient energy release at the friction interface, resulting in more significant noise fluctuations.

[0071] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 4 and 5, when no anhydride-modified high-density polyethylene is added as a compatibilizer, or when the modified conductive carbon nanotubes are directly dry-mixed and extruded without masterbatch pre-dispersion, the uniformity and aging stability of conductivity-related indicators decrease simultaneously, while wear and noise levels increase and fluctuate more. The main reason is that the lack of compatibilizer weakens the interfacial bonding between the polyolefin elastomer and high-density polyethylene, making it easier for conductive carbon nanotubes to accumulate at the interfacial and form micro-defect channels, resulting in the conductive network being more prone to rearrangement under thermo-mechanical coupling conditions; while the lack of masterbatch pre-dispersion amplifies the initial agglomeration and feed dispersion, causing local unevenness in the composition and hardness of the friction interface material.

[0072] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material, characterized in that, Includes the following steps: (1) Under nitrogen protection, acyl chloride multi-walled conductive carbon nanotubes are subjected to an amidation reaction with amines, and alkyl segments are grafted onto amide bonds to obtain modified conductive carbon nanotubes. (2) Modified conductive carbon nanotubes are melt-blended with polyolefin elastomers to obtain modified conductive carbon nanotube masterbatch; (3) Modified conductive carbon nanotube masterbatch is mixed with polyolefin elastomer, high-density polyethylene and additives, diluted and melt-extruded into granules, and then subjected to heat aging treatment to obtain conductive carbon nanotube / polyethylene antistatic low noise cable sheath material. In step (1), the amines include at least fluorinated short-chain amines, saturated long-chain amines and unsaturated long-chain amines, and are added in stages in the order of fluorinated short-chain amines, saturated long-chain amines and unsaturated long-chain amines for reaction; the molar fraction of the fluorinated short-chain amines in the amines is 8% to 12%, and the molar fraction of the saturated long-chain amines in the amines is 50% to 55%.

2. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, In step (1), the acyl chloride multi-walled conductive carbon nanotubes are obtained by acyl chloride treatment of carboxylated multi-walled conductive carbon nanotubes; the carboxylated multi-walled conductive carbon nanotubes are obtained by carboxylation treatment of multi-walled conductive carbon nanotubes.

3. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 2, characterized in that, The average diameter of the multi-walled conductive carbon nanotubes is 7–15 nm, and the average length is 1.0–2.0 μm.

4. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 2, characterized in that, The carboxylation treatment employs mixed acid oxidation, wherein the mixed acid consists of 98% sulfuric acid and 65% nitric acid by mass, with the mass ratio of sulfuric acid to nitric acid being 2:1 to 4:

1.

5. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 2, characterized in that, The acyl chloride treatment uses thionyl chloride as the acyl chloride reagent and anhydrous N,N-dimethylformamide as the accelerator; the mass ratio of carboxylated multi-walled conductive carbon nanotubes to thionyl chloride is 1:8 to 1:12, and the amount of the accelerator is 1% to 5% of the mass of the carboxylated multi-walled conductive carbon nanotubes.

6. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, The fluorinated short-chain amine is selected from one or more of 2,2,3,3,4,4,4-heptafluorobutylamine, 2,2,3,3-tetrafluoropropylamine, and 1H,1H,2H,2H-perfluorohexylamine; the saturated long-chain amine is selected from one or more of dodecylamine, hexadecylamine, octadecylamine, and eicosamine; and the unsaturated long-chain amine is selected from one or more of oleylamine, linoleylamine, and erucic acid amine.

7. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, In the modified conductive carbon nanotube masterbatch obtained in step (2), the mass fraction of modified conductive carbon nanotubes is 8% to 12%; in the conductive carbon nanotube / polyethylene antistatic low noise cable sheath material, the mass fraction of modified conductive carbon nanotubes is 0.5% to 0.8%.

8. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, In step (3), anhydride-modified high-density polyethylene is added as a compatibilizer, and the amount of the compatibilizer is 0.5% to 2.0% of the total mass of the cable sheath material.

9. The preparation method of the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, The temperature of the heat aging treatment in step (3) is 70-90℃ and the aging time is 4-10h.

10. The method for preparing the conductive carbon nanotube / polyethylene antistatic low-noise cable sheath material according to claim 1, characterized in that, The adjuvants in step (3) include hindered phenolic antioxidants, phosphite antioxidants, and calcium stearate.

Images