A cold-resistant polyvinyl chloride composite shielding material for the middle layer of a cable and its preparation method

Abstract

This application relates to the field of rubber materials, and in particular to a polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable and its preparation method. In this application, polylactic acid grafted carbon nanotubes (PLA-g-CNT) are used in combination with other conductive fillers. By utilizing the anchoring effect of PLA-g-CN on small molecule plasticizers, the migration of small molecule plasticizers is significantly suppressed while satisfying the overall electromagnetic shielding effect, so as to achieve a long-term cold-resistant effect. It has good application prospects in cable sheathing materials in extremely cold regions.

Description

Technical Field

[0001] This application relates to the field of rubber materials, and in particular to a polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable and its preparation method. Background Technology

[0002] With the further popularization of 5G technology, the demand for its supporting cable materials is increasing. Among the many 5G cable materials, polyvinyl chloride (PVC) has been widely used due to its significant advantages, and its industry acceptance has greatly improved. PVC is an amorphous material, usually a white powder with low branching degree and a relative density of about 1.4 g / cm³. It begins to decompose at around 140°C. The molecular weight of PVC is generally between 55,000 and 120,000, increasing as the polymerization temperature decreases, and it does not have a fixed melting point. PVC is widely used in communication cables, construction, and other industries, possessing many outstanding advantages. It not only has wear resistance comparable to vulcanized rubber, but also excellent flame retardancy, excellent light transmittance, and is almost insoluble in organic solvents, remaining stable in solvents such as gasoline and alcohol. Furthermore, it has good insulation and mechanical properties, offering a superior cost-performance ratio. However, PVC also has some drawbacks, mainly manifested in the following aspects:

[0003] (1) Polyvinyl chloride (PVC) used in cables needs to have a certain shielding function against electromagnetic waves. However, the inherent electrical insulation properties of PVC itself make it almost useless for shielding electromagnetic waves. Therefore, in order to expand the application scope of PVC composite materials in 5G system engineering and obtain high-performance, low-cost functional composite materials, it is usually necessary to modify PVC to give it efficient electromagnetic wave shielding function.

[0004] (2) Polyvinyl chloride (PVC) is a hard and brittle material with insufficient impact resistance. Temperature has a significant impact on its products. At low temperatures, PVC products rapidly become brittle, hardening and becoming increasingly fragile, making them prone to breakage under external force. The same phenomenon exists with flexible PVC materials. During the preparation of flexible PVC materials, a large amount of small-molecule plasticizers are added. These plasticizers migrate at low temperatures, causing PVC products to become brittle and hard over time. This is because the polar chlorine atoms in the PVC molecular chain create strong intermolecular forces, resulting in low impact strength. The products are easily broken under external impact, and this defect is more pronounced at low temperatures. When PVC reaches its embrittlement temperature, both its strength and toughness are very low. These defects make PVC coatings unsuitable for outdoor use in high-latitude regions, such as parts of northern my country, northern Russia, and Europe. While using macromolecular plasticizers can reduce plasticizer migration and meet the requirements for use under low-temperature conditions, it can also lead to slower system flow and higher processing temperatures. Furthermore, the poor bonding performance between macromolecular plasticizers and electromagnetic shielding materials can also cause a certain loss in the system's hardness and elasticity. Summary of the Invention

[0005] Based on the above problems, the main objective of this application is to provide a method for preparing soft PVC, which can achieve a glass transition temperature below -50°C while maintaining good electromagnetic shielding performance and long-term cold resistance.

[0006] First, this application provides a polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable, comprising the following components by weight:

[0007] 100 parts of polyvinyl chloride

[0008] 10-20 parts of inorganic composite conductive agent

[0009] 40-60 parts of small molecule plasticizer

[0010] 5-10 parts compatibilizer

[0011] 0-10 parts of excipients

[0012] The inorganic composite conductive agent comprises the following components:

[0013] 1-5 parts of polylactic acid-grafted carbon nanotubes

[0014] The balance is any one of carbon fiber, expanded graphite, conductive nickel powder, and antimony tin oxide;

[0015] The excipients include any number of stabilizers, antioxidants, impact modifiers, lubricants, release agents, and coupling agents.

[0016] In the above scheme, the system is first defined as a ternary synergistic structure of "PVC matrix - composite conductive agent - plasticizer / compressor system". The composite conductive agent is composed of "polylactic acid grafted carbon nanotubes (PLA-g-CNT)" and one of "carbon fiber, expanded graphite, conductive nickel powder, or tin-antimony oxide". PLA-g-CNT, as a nanoscale filler, can form a fine conductive network in the PVC matrix; while the micron-scale second component (such as carbon fiber) acts as a "conductive bridge", connecting the CNT network and constructing a multi-scale three-dimensional conductive pathway, significantly improving electromagnetic shielding effectiveness. Furthermore, the system uses a lower amount of carbon nanotubes, resulting in a lower overall price and a significant improvement in cost. In addition, the PLA chains on the PLA-g-CNT surface can anchor small-molecule plasticizers through hydrogen bonds, forming a "molecular anchoring" effect. Through physical entanglement and interfacial interactions, the migration and precipitation of small-molecule plasticizers to the material surface can be effectively inhibited, providing a good foundation for the PVC system to maintain good resilience and weather resistance at lower temperatures.

[0017] Preferably, the inorganic composite conductive agent is a combination of carbon fiber or expanded graphite and polymer-grafted carbon nanotubes, wherein the carbon fiber or expanded graphite is treated with a mixed acid containing nitric acid and / or sulfuric acid to introduce oxygen-containing functional groups.

[0018] In the aforementioned system, pretreatment of carbon fibers and expanded graphite with mixed acids introduces polar oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the inert surface. These functional groups significantly enhance the interaction forces (such as hydrogen bonding and dipole interactions) between the filler and the PVC matrix, as well as between the polylactic acid segments in PLA-g-CNT. This greatly improves the uniformity of filler dispersion and interfacial bonding strength in the matrix, which not only facilitates the stable construction of the conductive network but also effectively transfers external stress to the high-strength filler, enhancing the overall mechanical properties of the composite material. Furthermore, both can be compounded with PLA-g-CNT to produce an even stronger shielding effect.

[0019] Preferably, the mass ratio of the carbon fiber to the expanded graphite is 1:0.2 to 0.5.

[0020] In the above scheme, a specific ratio of carbon fiber to expanded graphite is used to construct a more complete "point-to-surface" synergistic conductive network. This ratio can avoid uneven dispersion or network structure defects caused by an excessive amount of any one component. At the same time, compared with other materials, expanded graphite can also better restrict the migration of plasticizers through its layered structure to provide better weather resistance, while carbon fiber provides better strength. Overall, the above configuration can achieve better weather resistance, mechanical strength, elasticity, and electromagnetic shielding performance.

[0021] Preferably, the step of treating the expanded graphite and carbon fiber with mixed acid is as follows:

[0022] Expanded graphite and carbon fiber were added to a mixed acid at a solid-liquid ratio of 1:10 to 30 and reacted at 40 to 80°C for 1 to 5 hours. The mixture was then washed with water until neutral and dried.

[0023] The carbon fiber is pretreated with acetone for desizing.

[0024] The above scheme limits the solid-liquid ratio, reaction temperature, and reaction time, ensuring the full introduction of oxygen-containing functional groups while avoiding excessive damage to the filler structure caused by overly vigorous reactions. Simultaneously, acetone desizing treatment of the carbon fibers aims to reduce the organic slurry adhering to the carbon fiber surface, thereby providing better reaction performance.

[0025] Preferably, the specific steps for grafting polylactic acid onto carbon nanotubes are as follows:

[0026] The carbon nanotube surface is hydroxylated, then an initiator is fixed to the surface of the carbon nanotube, and then grafted onto the surface of the carbon nanotube by in-situ polymerization of lactide.

[0027] In the above scheme, a surface-initiated in-situ polymerization method is used for preparation. This method directly initiates the reaction on the surface of carbon nanotubes, ensuring a high medium density and controllable chain length. At the same time, it improves the fixation performance and dispersion uniformity of PLA. In addition, the above preparation method has a relatively uniform and mild reaction, and the conditions are easy to achieve. It also has a good effect on reducing costs for industrial-scale production.

[0028] Preferably, the grafting rate of polylactic acid onto carbon nanotubes is 30-60%, and / or,

[0029] The initiator is 0.2 to 0.5% of the mass of lactide.

[0030] In the above scheme, a low grafting rate and a low initiator dosage were controlled overall. The overall purpose was to control the reaction rate and reduce the accumulation of polylactic acid on the surface of carbon nanotubes. It should be noted that in this system, excessive polylactic acid will make it difficult for CNTs to overlap, which will lead to a decrease in the overall electromagnetic shielding performance. On the other hand, too low a grafting rate will have a certain impact on the system's ability to restrict the plasticizer.

[0031] Preferably, the carbon nanotubes are multi-walled carbon nanotubes, and / or the initiator is stannous octoate.

[0032] Multi-walled carbon nanotubes have lower cost, better mechanical properties and more stable structure, while stannous octoate has better reactivity and fewer byproducts.

[0033] Preferably, the small molecule plasticizer comprises DOS and DOP, wherein the mass percentage of DOS in the small molecule plasticizer is 75-90%.

[0034] In the above scheme, DOS (dioctyl sebacate) has good cold resistance, while DOP (dioctyl phthalate) can improve the processing performance of PVC. The combination has better low temperature resistance and processing fluidity, and while having good plasticizing efficiency, it also reduces the cost of the system. Overall, it can better balance cold resistance and processing performance.

[0035] In addition, this application also relates to a method for preparing the aforementioned polyvinyl chloride composite shielding material for the middle layer of extremely cold-resistant cables, comprising the following steps:

[0036] S1. Polylactic acid-grafted carbon nanotubes are premixed with small molecule plasticizers to obtain the first premixed system;

[0037] S2. The remaining components are initially mixed at the gelation temperature of PVC to obtain a second mixed system;

[0038] S3. Mix the first and second mixing systems, and then discharge the material.

[0039] In the above system, the core step is to first mix PLA-g-CNT with the plasticizer, and then melt it into other components. This can achieve the effect of forming an anchoring system in advance, which can achieve the initial and gentle pre-dispersion of CNT in the plasticizer, avoiding the damage or poor dispersion of carbon nanotube structure caused by high shear when directly melt-blended with PVC. At the same time, it can also achieve the anchoring system between CNT and plasticizer in advance, and reduce the agglomeration effect between CNTs.

[0040] Preferably, in step S1, the first premixed system is aged for 6 to 12 hours after mixing.

[0041] The aging process allows small molecule plasticizers to fully penetrate and swell the polylactic acid grafted layer on the surface of carbon nanotubes, forming a more stable and reliable dispersion system and anchoring performance. Overall, it helps the first mixed system to form a more uniform dispersion system when mixed with PVC melt, which helps to build an efficient and stable conductive network, and also makes a more positive contribution to long-lasting cold resistance.

[0042] In summary, this application uses polylactic acid-grafted carbon nanotubes (PLA-g-CNT) in combination with other conductive fillers. By utilizing the anchoring effect of PLA-g-CN on small molecule plasticizers, the migration of small molecule plasticizers is significantly suppressed while satisfying the overall electromagnetic shielding effect, thereby achieving long-lasting cold resistance. This approach has good application prospects in cable sheathing materials in extremely cold regions. Detailed Implementation

[0043] The technical solutions in this application will be further described through the following specific embodiments.

[0044] First, the preparation example A series involves processing commercially available multi-walled carbon nanotubes to prepare polylactic acid-grafted multi-walled carbon nanotubes, with the specific design as follows:

[0045] Preparation of Example A1 specifically includes the following steps:

[0046] Acidification of carbon nanotubes: Multi-walled carbon nanotubes (average diameter 12 nm, average length 30 μm) were added to a mixed acid (concentrated H2SO4:concentrated HNO3 volume ratio 3:1) at a solid-liquid ratio of 1:20 and ultrasonically dispersed for 30 min. Then the temperature was raised to 70 °C and the reaction was carried out under mechanical stirring for 4 h. Subsequently, 5 times the volume of ice water mixture was poured into the mixture for dilution. After filtration, the mixture was washed with deionized water until neutral to obtain acidified carbon nanotubes.

[0047] Initiator fixation: Acidified carbon nanotubes were dispersed in toluene at a mass ratio of 1:50 and ultrasonically dispersed for 20 min. Then, 2% of the carbon nanotubes by mass of stannous octoate was added. The mixture was heated to 80 °C under nitrogen protection and mechanically stirred for 2 h. After centrifugation, the mixture was washed three times with anhydrous toluene and vacuum dried to obtain the initiator-carbon nanotube composite system.

[0048] In-situ polymerization: The initiator-carbon nanotube composite system was dispersed in anhydrous toluene at a mass ratio of 1:20. Lactide (5 times the mass of carbon nanotubes, i.e., the initiator mass was 0.4% of the lactide mass) was added, followed by polymerization at 130℃ under nitrogen protection for 24 h. The product was then washed with toluene, centrifuged, rinsed with deionized water, and dried to obtain polylactic acid-modified carbon nanotubes. Thermogravimetric analysis showed a grafting rate of 41.9%.

[0049] Preparation Example A2 differs from Preparation Example A1 in that the mass of stannous octoate is 3% of the mass of carbon nanotubes, and the mass of lactide is 7.5 times the mass of carbon nanotubes. The grafting rate was determined to be 58.1% by thermogravimetric analysis.

[0050] Preparation Example A3 differs from Preparation Example A1 in that the mass of stannous octoate is 4% of the mass of carbon nanotubes, and the mass of lactide is 10 times the mass of carbon nanotubes. The grafting rate was determined to be 69.4% by thermogravimetric analysis.

[0051] Preparation Example A4 differs from Preparation Example A1 in that the mass of stannous octoate is 1.2% of the mass of carbon nanotubes, and the mass of lactide is 3 times the mass of carbon nanotubes. The grafting rate was determined to be 32.0% by thermogravimetric analysis.

[0052] Preparation Example A5 differs from Preparation Example A1 in that the mass of stannous octoate is 0.8% of the mass of carbon nanotubes, and the mass of lactide is twice the mass of carbon nanotubes. The grafting rate was determined to be 24.1% by thermogravimetric analysis.

[0053] It should be noted that in the above embodiments, the final grafting rate is only the goal. The same grafting rate can be achieved by different amounts of polylactic acid, initiator, system concentration, and reaction time.

[0054] The preparation of Example B series involves treating the remaining conductive filler with mixed acid, as detailed below:

[0055] In Preparation Example B1, the remaining conductive fillers were carbon fibers (average length 3 mm, average aspect ratio 500) and expanded graphite (carbon content > 99%, 100 mesh) in a mass ratio of 1:0.2, which were added to a system of 98% sulfuric acid and 68% nitric acid in a volume ratio of 3:1 at a solid-liquid ratio of 1:20. The mixture was reacted at 60°C for 3 h, then filtered, washed with water until neutral, and dried in a vacuum drying oven at 50°C.

[0056] Preparation Example B2 differs from Preparation Example B1 in that the mass ratio of carbon fiber to expanded graphite in the conductive filler is 1:0.1.

[0057] Preparation Example B3 differs from Preparation Example B1 in that the mass ratio of carbon fiber to expanded graphite in the conductive filler is 1:0.3.

[0058] Preparation Example B4 differs from Preparation Example B1 in that the mass ratio of carbon fiber to expanded graphite in the conductive filler is 1:0.5.

[0059] Preparation Example B5 differs from Preparation Example B1 in that the mass ratio of carbon fiber to expanded graphite in the conductive filler is 1:1.

[0060] Preparation Example B6 differs from Preparation Example B1 in that the composition of the conductive filler remains the same, but no mixed acid treatment is performed.

[0061] Example 1: This application describes the preparation of a polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable, which can be used as a protective sheath for optical cables in Northeast China or Russia. The material comprises the following components by weight:

[0062] SG-3 PVC Masterbatch 100 parts

[0063] Preparation Example A1 3 parts

[0064] Preparation Example B1 (12 portions)

[0065] 30 parts of DOS plasticizer

[0066] 6 parts DOP plasticizer

[0067] Glycidyl methacrylate grafted with chlorinated polyethylene (compatibilizer) 8 parts

[0068] It also includes auxiliary materials, as follows:

[0069] Calcium and zinc stabilizer (Baerostab CZ 118) 4 parts

[0070] Calcium stearate (lubricant) 1 part

[0071] Zinc stearate (lubricant) 0.5 parts

[0072] Polyethylene wax (release agent) 0.5 parts

[0073] DURASTRENGTH-200 (Impact Modifier) ​​2 parts

[0074] The preparation steps in this embodiment are as follows:

[0075] S1. The modified multi-walled carbon nanotubes in preparation example A1 were dispersed in a combination of DOS and DOP, ultrasonically dispersed for 30 min, mechanically stirred for 2 h, and then placed in a sealed container and aged at room temperature for 8 h to obtain the first premixed system.

[0076] S2. Add the remaining components to a high-speed mixer and heat to 130°C at 800 rpm to gel the system. Mix for 10 minutes to obtain the second premixed system for later use.

[0077] S3. Transfer the second premixed system to an internal mixer and add the first premixed system. Mix at 165°C for 10 minutes, then extrude through a single-screw extruder (temperature settings 160°C / 170°C / 175°C / 175°C / 170°C, extruder head temperature 180°C) and cool to set.

[0078] Examples 2-20 and Comparative Examples 1-2 differ from Example 1 in that different preparation examples A and B were selected and different amounts were added, as shown in Table 1.

[0079]

[0080] The difference between Example 3 and Example 3 is that the carbon nanotubes are not modified.

[0081] Furthermore, based on Example 3, the processing procedure was adjusted to obtain the following example:

[0082] Example 21 differs from Example 3 in that aging is not performed in step S1.

[0083] Example 22 differs from Example 3 in that the aging time in step S1 is 6 hours.

[0084] Example 23 differs from Example 3 in that the aging time in step S1 is 12 hours.

[0085] Example 24 differs from Example 3 in that step S1 is omitted, and in step S2, all materials are directly mixed together.

[0086] The samples obtained in Examples 1-24 and Control Examples 1-3 were verified through the following experimental steps.

[0087] 1. The electromagnetic shielding effect of the system is evaluated by volume resistivity. Specifically, refer to GB / T 15662-1995 "Test Method for Volume Resistivity of Conductive and Antistatic Plastics" to determine the volume resistivity of the sample in an environment of 23±2℃ and 50±5% relative humidity.

[0088] 2. Referring to GB / T 5470-2008 "Determination of Embrittlement Temperature of Plastics by Impact Test", the samples were prepared into type A specimens and placed in a low-temperature air environment for 10 minutes. The impact test was then conducted using a type A testing machine at an impact speed of 200 cm / s, starting at -20℃ and decreasing the temperature by 2.5℃ at each level until at least 70% of the specimens broke. The temperature was then recorded and used to measure the antifreeze properties of the rubber.

[0089] 3. Determine the tensile strength of the rubber in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets".

[0090] 4. Prepare a 25mm×50mm×2mm sample, then immerse it in olive oil at 70℃ for 24h. After that, take it out, wipe off the surface olive oil, and then determine the antifreeze performance of the system again according to the method in Experiment 2.

[0091] The experimental results of the above embodiments and comparative examples are shown in Table 2.

[0092]

[0093] First, comparing Comparative Examples 1-3 with Example 3, it can be seen that in this application, if polylactic acid grafting is not performed on the carbon nanotubes, significant plasticizer diffusion occurs, leading to a significant decrease in the system's freeze-thaw resistance after oil immersion. Regarding the conductive filler, comparing Examples 3, Examples 23-24, and Comparative Examples 1-2, it can be seen that excessive addition of PLA-g-CNT not only leads to a sharp increase in cost but also a slight decrease in the system's conductivity. This may be because carbon fibers and expanded graphite can provide a larger overlap pattern; the two-dimensional and three-dimensional overlap system can achieve better conductivity, thus providing better electromagnetic shielding performance. In Comparative Example 1, without the addition of PLA-g-CNT, in addition to a certain weakening of conductivity, a significant decrease in low-temperature resistance after oil immersion, similar to Comparative Example 3, is observed.

[0094] By comparing preparation examples B1-B6, it can be seen that in the example using preparation example B6, the absence of mixed acid treatment on the filler significantly affects the oil immersion resistance, leading to a noticeable decrease in cold resistance after oil immersion. This phenomenon is observed to some extent in different modified carbon nanotube systems. Furthermore, comparing examples A1-A5, it can be seen that the grafting rate of polylactic acid has a certain impact on product performance. An excessively high grafting rate leads to a decrease in the system's electrical conductivity and overall strength, while an excessively low grafting rate results in a significant reduction in both cold resistance and cold resistance after oil immersion.

[0095] By comparing Examples 21-24, it can be seen that in the above preparation process, the lack of aging leads to a significant decrease in the adhesion performance of the plasticizer on the surface of carbon nanotubes. In addition to affecting the overall strength, it also reduces the migration inhibition effect of PLA-g-CNT, resulting in a significant decrease in its low-temperature resistance after oil immersion. A similar phenomenon was observed in Example 24, where all materials were directly mixed, indicating that the premixing and aging steps of PLA-g-CNT significantly improve the migration inhibition performance of small molecule plasticizers.

[0096] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable, characterized in that, It contains the following components according to parts by weight: 100 parts of polyvinyl chloride 10-20 parts of inorganic composite conductive agent 40-60 parts of small molecule plasticizer 5-10 parts compatibilizer 0-10 parts of excipients The inorganic composite conductive agent comprises the following components: 1-5 parts of polylactic acid-grafted carbon nanotubes The balance is a combination of carbon fiber and expanded graphite, wherein the carbon fiber and / or expanded graphite are treated with a mixed acid containing nitric acid and / or sulfuric acid to introduce oxygen-containing functional groups, and the mass ratio of the carbon fiber to expanded graphite is 1:0.2 to 0.

5. The excipients include any number of stabilizers, antioxidants, impact modifiers, lubricants, release agents, and coupling agents. The small molecule plasticizer comprises DOS and DOP, wherein the mass percentage of DOS in the small molecule plasticizer is 75-90%. The preparation method of this composite shielding material includes the following steps: S1. Polylactic acid grafted carbon nanotubes and small molecule plasticizers are premixed and then aged for 6-12 hours to obtain the first premixed system. S2. The remaining components are initially mixed at the gelation temperature of PVC to obtain a second mixed system; S3. Mix the first and second mixing systems, and then discharge the material.

2. The polyvinyl chloride composite shielding material for the middle layer of an extremely cold-resistant cable according to claim 1, characterized in that, The steps for treating the expanded graphite and carbon fiber with mixed acid are as follows: Expanded graphite and carbon fiber were added to a mixed acid at a solid-liquid ratio of 1:10 to 30 and reacted at 40 to 80°C for 1 to 5 hours. The mixture was then washed with water until neutral and dried. The carbon fiber is pretreated with acetone for desizing.

3. The extremely cold-resistant cable middle layer polyvinyl chloride composite shielding material according to claim 1, characterized in that, The specific steps for grafting polylactic acid onto carbon nanotubes are as follows: The carbon nanotube surface is hydroxylated, then an initiator is fixed to the surface of the carbon nanotube, and then grafted onto the surface of the carbon nanotube by in-situ polymerization of lactide.

4. The extremely cold-resistant cable middle layer polyvinyl chloride composite shielding material according to claim 3, characterized in that, The grafting rate of polylactic acid onto carbon nanotubes is 30-60%, and / or, The initiator is 0.2 to 0.5% of the mass of lactide.

5. The extremely cold-resistant cable middle layer polyvinyl chloride composite shielding material according to claim 4, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes, and / or the initiator is stannous octoate.

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