High-strength and aging-resistant overhead insulated wire

Abstract

The application relates to the technical field of insulated conductors, and discloses a high-strength and anti-aging overhead insulated conductor. The high-strength and anti-aging overhead insulated conductor comprises a conductor and an insulation layer from inside to outside. The raw material of the insulation layer comprises the following components in parts by weight: 80 parts of polyethylene, 15-20 parts of butadiene styrene rubber, 10-18 parts of ethylene propylene diene rubber, 3-5 parts of zinc oxide, 1-2 parts of vulcanizing agent, 0.5-1 part of accelerator, 5-7 parts of compatibilizer, 2-3 parts of zinc stearate and 8-12 parts of reinforcing auxiliary agent. The raw material of the reinforcing auxiliary agent comprises the following components in parts by weight: 20 parts of carbon black, 4-8 parts of silicone powder and 5-10 parts of zinc diacrylate. Through the technical scheme, the problem of relatively poor mechanical performance of the insulation layer of the overhead insulated conductor in the related art is solved.

Description

Technical Field

[0001] This invention relates to the field of insulated conductor technology, specifically to a high-strength, aging-resistant overhead insulated conductor. Background Technology

[0002] Overhead insulated conductors are an important component of power transmission and distribution networks. By covering the conductor with an insulation layer, they effectively avoid the safety hazards such as short circuits and leakage that exist in traditional bare conductors directly exposed to the environment. They also reduce the space occupied by the line corridors, improving the reliability and safety of power supply. Therefore, overhead insulated conductors are widely used in power transmission in urban power grids, industrial and mining enterprises, and rural power grid upgrades.

[0003] With the continuous growth of electricity demand, power systems are placing higher demands on the performance of overhead insulated conductors. Especially during long-term outdoor operation, insulated conductors need to withstand a variety of complex factors, including mechanical stress, changes in ambient temperature, and ultraviolet radiation. This requires insulation materials to not only possess excellent initial electrical insulation properties but also good mechanical strength and resistance to environmental aging.

[0004] Currently, commonly used insulation materials for overhead insulated conductors mainly include polyethylene (PE), polyvinyl chloride (PVC), and rubber-based materials. Among them, ethylene propylene diene monomer (EPDM) rubber exhibits good weather resistance due to its high main chain saturation (all carbon-carbon single bonds, with only a small number of unsaturated carbon-carbon double bonds in the side chains) and relatively stable molecular structure. However, EPDM rubber itself lacks self-reinforcing properties, and the mechanical properties of pure rubber are relatively low. Although it helps with electrical insulation and aging resistance in the insulation layer, it limits the effective improvement of its mechanical properties.

[0005] To improve the mechanical properties of rubber insulation materials in the insulation layer, reinforcing fillers such as carbon black and silica are usually added. Carbon black is the most commonly used reinforcing agent, but its dispersion uniformity in the rubber matrix and its interfacial bonding strength with rubber molecules are relatively poor, easily forming stress concentration points within the material. This not only hinders the improvement of mechanical strength but may also accelerate the aging and failure process of the material under thermo-oxidative conditions. Therefore, this paper proposes an overhead insulated conductor with excellent mechanical properties in its insulation layer, which is of great significance for meeting the power system's requirements for high-reliability, long-life overhead insulated conductors. Summary of the Invention

[0006] This invention proposes a high-strength, aging-resistant overhead insulated conductor, which solves the problem of relatively poor mechanical properties of the insulation layer in related technologies.

[0007] The technical solution of the present invention is as follows:

[0008] This invention proposes a high-strength, aging-resistant overhead insulated conductor, comprising, from the inside out, a conductor and an insulation layer. The insulation layer is made of the following components in parts by weight:

[0009] 80 parts polyethylene, 15-20 parts styrene-butadiene rubber, 10-18 parts ethylene propylene diene monomer (EPDM) rubber, 3-5 parts zinc oxide, 1-2 parts vulcanizing agent, 0.5-1 part accelerator, 5-7 parts compatibilizer, 2-3 parts zinc stearate, and 8-12 parts reinforcing agent;

[0010] The raw materials of the reinforcing agent include the following components in parts by weight:

[0011] 20 parts carbon black, 4-8 parts silicone powder, and 5-10 parts zinc diacrylate.

[0012] As a further technical solution, the conductor is either an aluminum alloy conductor or a copper alloy conductor, preferably an aluminum alloy conductor.

[0013] As a further technical solution, the raw materials of the reinforcing agent also include a silane coupling agent, wherein the amount of the silane coupling agent added is 8% to 15% of the weight of the carbon black, for example, it can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, preferably 8%, 12%, 15%.

[0014] In this invention, the reinforcing agent also includes a silane coupling agent in its raw materials. The addition of the silane coupling agent can better bind zinc diacrylate with carbon black and silicone powder, improve the stability of the reinforcing agent, and better exert its reinforcing effect. The silane coupling agent can be any conventional silane coupling agent in the art, such as an aminosilane coupling agent or a mercaptosilane coupling agent; the aminosilane coupling agent can be, for example, γ-aminopropyltriethoxysilane or γ-aminopropyltrimethoxysilane; the mercaptosilane coupling agent can be, for example, γ-mercaptopropyltriethoxysilane, preferably γ-aminopropyltriethoxysilane.

[0015] As a further technical solution, the preparation method of the reinforcing agent includes the following steps:

[0016] A1. Add the silane coupling agent to an ethanol aqueous solution, add the carbon black and the silicone powder, mix evenly, concentrate, and dry to obtain a pretreated mixture;

[0017] A2. The zinc diacrylate and the pretreated mixture are blended and ball-milled to obtain the reinforcing agent.

[0018] As a further technical solution, the mass fraction of ethanol in the ethanol aqueous solution is 75%~85%, for example, it can be 75%, 80%, 85%, preferably 80%.

[0019] As a further technical solution, the vulcanizing agent includes one or two of sulfur and dicumyl peroxide, preferably dicumyl peroxide;

[0020] The accelerator includes one or both of accelerator H and accelerator TMTD, preferably accelerator TMTD.

[0021] As a further technical solution, the compatibilizer includes one or two of maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber, preferably maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber.

[0022] In the overhead insulated conductor insulation layer of this invention, the addition of a compatibilizer can improve the compatibility of polyethylene, styrene-butadiene rubber, and ethylene propylene diene monomer (EPDM) rubber, reduce interfacial tension, and thus prevent phase separation during processing and subsequent long-term use of the blended system. The compatibilizer includes one or two of maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber, preferably maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber. When maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber are used together, by optimizing the ratio of their dosages, the weight ratio of maleic anhydride-grafted polyethylene to maleic anhydride-grafted EPDM rubber is 3:1, which has a better effect on improving the compatibility of the three.

[0023] As a further technical solution, the raw materials of the insulating layer also include 1-3 parts of antioxidant and 2-5 parts of plasticizer.

[0024] As a further technical solution, the antioxidant includes one or more of antioxidant 1010, antioxidant 1024, and antioxidant 264, preferably antioxidant 1024;

[0025] The plasticizer includes one or more of dinonyl phthalate, tricresyl phosphate, and dioctyl phthalate, preferably dioctyl phthalate.

[0026] As a further technical solution, the raw materials of the reinforcing agent also include 2 to 6 parts of zinc acetylacetonate, for example, 2, 3, 4, 5, or 6 parts, preferably 4 to 5 parts.

[0027] In the overhead insulated conductor insulation layer of this invention, the reinforcing additive also includes zinc acetylacetonate. Through the combined action of zinc acetylacetonate, zinc diacrylate, and silicone powder on carbon black, the agglomeration of carbon black in the rubber component can be further reduced. Simultaneously, the presence of zinc acetylacetonate can, to a certain extent, inhibit the oxidation reaction of the rubber component, improving its stability. While ensuring the mechanical properties of the insulation layer, it can also improve its aging resistance. Furthermore, by adjusting the amount of zinc acetylacetonate, when its addition to the reinforcing additive is 4-5 parts, its synergistic effect with the other raw materials in the reinforcing additive is better, resulting in a better improvement in the aging resistance of the insulation layer.

[0028] As a further technical solution, the preparation method of the reinforcing agent includes the following steps:

[0029] B1. Add the silane coupling agent to an ethanol aqueous solution, add the carbon black and the silicone powder, mix evenly, concentrate, and dry to obtain the first pretreated mixture;

[0030] B2. Disperse the acetylacetic copper zinc in anhydrous ethanol, add the first pretreatment mixture, mix evenly, concentrate, and dry to obtain the second pretreatment mixture;

[0031] B3. The zinc diacrylate and the second pretreatment mixture are blended and ball-milled to obtain the reinforcing agent.

[0032] As a further technical solution, in steps B1 and B2, the stirring speed for uniform mixing is independently 400~600 rpm, and the time is independently 30~40 min.

[0033] As a further technical solution, in step B3, the ball milling speed is 200~300 rpm and the time is 15~25 min.

[0034] This invention also proposes a method for preparing a high-strength, aging-resistant overhead insulated conductor, comprising the following steps:

[0035] After the styrene-butadiene rubber, the ethylene propylene diene monomer (EPDM) rubber, and the reinforcing agent are mixed evenly, the remaining components of the insulation layer are added, the mixture is compounded, extruded and coated onto the outer layer of the conductor, and vulcanized to obtain the high-strength, aging-resistant overhead insulated conductor.

[0036] The working principle and beneficial effects of this invention are as follows:

[0037] This invention incorporates a reinforcing agent composed of carbon black, silicone powder, and zinc diacrylate into the insulation layer of overhead insulated conductors, effectively improving the mechanical properties of the insulation layer. The EPDM rubber main chain in the insulation layer has a high degree of saturation, with only a small number of unsaturated carbon-carbon double bonds in the side chains. While the structure is relatively stable, it lacks self-reinforcing properties. To address the issue of relatively poor mechanical properties of EPDM rubber in the insulation layer, which limits the overall improvement of the insulation layer's mechanical properties, a reinforcing agent composed of carbon black, silicone powder, and zinc diacrylate is introduced into the insulation layer. The presence of zinc diacrylate and silicone powder improves the dispersion of carbon black in the EPDM rubber system, enhancing the rubber's processing performance. Simultaneously, the high activity of the diacrylate groups in zinc diacrylate improves the interfacial bonding between the reinforcing agent and EPDM rubber, improving the internal cross-linking degree of EPDM rubber and making the entire reinforcing system more stable. When the insulation layer is subjected to external tension, the enhanced cross-linked network structure of the EPDM rubber in the system can better transmit stress, thereby improving the overall mechanical properties of the insulation layer. Therefore, combining carbon black, silicone powder, and zinc bisacrylate to form a reinforcing agent, and adding it to the insulation layer of overhead insulated conductors can effectively improve their mechanical properties. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] In the following examples and comparative examples, the polyethylene is low-density polyethylene, model LD163;

[0040] Styrene-butadiene rubber, model SBR1502;

[0041] Ethylene propylene diene monomer (EPDM) rubber, model EPDM 3640;

[0042] Zinc oxide with an average particle size of 50 nm;

[0043] Maleic anhydride-grafted polyethylene, model number ADMER NF408E;

[0044] Maleic anhydride-grafted EPDM rubber, grade K-7M;

[0045] Carbon black, model N330, average particle size 200nm;

[0046] Silicone powder, model K6105;

[0047] Zinc acetylacetonate, CAS No. 14024-63-6, has an active ingredient content of 98%.

[0048] Copper acetylacetonate, CAS No. 13395-16-9, with an active ingredient content of 99%;

[0049] Zinc diacrylate, CAS No. 14643-87-9, with an active ingredient content of 99%;

[0050] Zinc methacrylate, CAS No. 13189-00-9, has an active ingredient content of 99%.

[0051] Example 1

[0052] The preparation method of the reinforcing agent includes the following steps:

[0053] A1. Add 1.6 parts of γ-aminopropyltriethoxysilane to 50 parts of ethanol aqueous solution (ethanol mass fraction is 80%), add 20 parts of carbon black and 4 parts of silicone powder, stir at 500 rpm for 40 min, concentrate, dry, and obtain the pretreated mixture.

[0054] A2. Mix 5 parts of zinc diacrylate with the above pretreated mixture and ball mill at 200 rpm for 25 min to obtain the reinforcing agent;

[0055] A method for preparing a high-strength, aging-resistant overhead insulated conductor includes the following steps:

[0056] After mixing 15 parts of styrene-butadiene rubber, 10 parts of ethylene propylene diene monomer (EPDM) rubber, and 8 parts of reinforcing additives evenly, 80 parts of polyethylene, 3 parts of zinc oxide, 1 part of dicumyl peroxide, 0.5 parts of accelerator TMTD, 3.75 parts of maleic anhydride-grafted polyethylene, 1.25 parts of maleic anhydride-grafted EPDM rubber, 2 parts of zinc stearate, 1 part of antioxidant 1024, and 2 parts of dioctyl phthalate were added. The mixture was then compounded, extruded, and coated onto the outer layer of an aluminum alloy conductor. After vulcanization, a high-strength, aging-resistant overhead insulated conductor was obtained.

[0057] Example 2

[0058] The preparation method of the reinforcing agent includes the following steps:

[0059] A1. Add 2.4 parts of γ-aminopropyltriethoxysilane to 50 parts of ethanol aqueous solution (ethanol mass fraction is 80%), add 20 parts of carbon black and 5 parts of silicone powder, stir at 500 rpm for 40 min, concentrate, dry, and obtain pretreated mixture.

[0060] A2. Mix 5 parts of zinc diacrylate with the above pretreated mixture and ball mill at 250 rpm for 20 min to obtain the reinforcing agent;

[0061] A method for preparing a high-strength, aging-resistant overhead insulated conductor includes the following steps:

[0062] After mixing 18 parts of styrene-butadiene rubber, 15 parts of ethylene propylene diene monomer (EPDM) rubber, and 10 parts of reinforcing additives evenly, 80 parts of polyethylene, 4 parts of zinc oxide, 1.5 parts of dicumyl peroxide, 0.8 parts of accelerator TMTD, 4.5 parts of maleic anhydride-grafted polyethylene, 1.5 parts of maleic anhydride-grafted EPDM rubber, 2.5 parts of zinc stearate, 2 parts of antioxidant 1024, and 4 parts of dioctyl phthalate were added. The mixture was then compounded, extruded, and coated onto the outer layer of an aluminum alloy conductor. After vulcanization, a high-strength, aging-resistant overhead insulated conductor was obtained.

[0063] Example 3

[0064] The preparation method of the reinforcing agent includes the following steps:

[0065] A1. Add 3 parts of γ-aminopropyltriethoxysilane to 50 parts of ethanol aqueous solution (ethanol mass fraction is 80%), add 20 parts of carbon black and 8 parts of silicone powder, stir at 500 rpm for 40 min, concentrate, dry, and obtain pretreated mixture.

[0066] A2. Mix 5 parts of zinc diacrylate with the above pretreated mixture and ball mill at 300 rpm for 15 min to obtain the reinforcing agent;

[0067] A method for preparing a high-strength, aging-resistant overhead insulated conductor includes the following steps:

[0068] After mixing 20 parts of styrene-butadiene rubber, 18 parts of ethylene propylene diene monomer (EPDM) rubber, and 12 parts of reinforcing additives evenly, 80 parts of polyethylene, 5 parts of zinc oxide, 2 parts of dicumyl peroxide, 1 part of accelerator TMTD, 5.25 parts of maleic anhydride-grafted polyethylene, 1.75 parts of maleic anhydride-grafted EPDM rubber, 3 parts of zinc stearate, 3 parts of antioxidant 1024, and 5 parts of dioctyl phthalate were added. The mixture was then compounded, extruded, and coated onto the outer layer of an aluminum alloy conductor. After vulcanization, a high-strength, aging-resistant overhead insulated conductor was obtained.

[0069] Example 4

[0070] The only difference between this embodiment and Embodiment 2 is that in the preparation method of the reinforcing agent in this embodiment, 8 parts of zinc diacrylate are added.

[0071] Example 5

[0072] The only difference between this embodiment and Embodiment 2 is that in the preparation method of the reinforcing agent in this embodiment, 10 parts of zinc diacrylate are added.

[0073] Example 6

[0074] The only difference between this embodiment and Example 4 is that the preparation method of the reinforcing agent in this embodiment is different, specifically:

[0075] B1. Add 2.4 parts of γ-aminopropyltriethoxysilane to 50 parts of an aqueous ethanol solution (ethanol mass fraction of 80%), add 20 parts of carbon black and 5 parts of silicone powder, stir at 500 rpm for 40 min, concentrate, and dry to obtain the first pretreated mixture.

[0076] B2. Disperse 2 parts of acetylacetonine zinc in 50 parts of anhydrous ethanol, add the above first pretreatment mixture, stir at 500 rpm for 40 min, concentrate, dry, and obtain the second pretreatment mixture.

[0077] B3. Mix 8 parts of zinc diacrylate with the above second pretreatment mixture and ball mill at 250 rpm for 20 min to obtain the reinforcing agent.

[0078] Example 7

[0079] The only difference between this embodiment and Embodiment 6 is that in the preparation method of the reinforcing agent in this embodiment, 4 parts of acetylacetonine zinc are added.

[0080] Example 8

[0081] The only difference between this embodiment and Embodiment 6 is that, in the preparation method of the reinforcing agent in this embodiment, 5 parts of acetylacetonine zinc are added.

[0082] Example 9

[0083] The only difference between this embodiment and Example 6 is that in the preparation method of the reinforcing agent in this embodiment, the amount of acetylacetonine zinc added is 6 parts.

[0084] Example 10

[0085] The only difference between this embodiment and Example 6 is that in the preparation method of the reinforcing agent in this embodiment, acetylacetonine zinc is replaced with an equal amount of acetylacetone copper.

[0086] Comparative Example 1

[0087] The only difference between this comparative example and Example 2 is that, in the preparation method of the reinforcing agent in this comparative example, zinc bisacrylate is replaced with an equal amount of zinc methacrylate.

[0088] Comparative Example 2

[0089] The only difference between this comparative example and Example 2 is that the preparation method of the reinforcing agent in this comparative example is different, specifically:

[0090] 24 parts carbon black and 6 parts silicone powder were mixed and ball-milled at 250 rpm for 20 min to obtain a reinforcing agent.

[0091] Comparative Example 3

[0092] The only difference between this comparative example and Example 2 is that the preparation method of the reinforcing agent in this comparative example is different, specifically:

[0093] A1. Add 2.4 parts of γ-aminopropyltriethoxysilane to 50 parts of ethanol aqueous solution (ethanol mass fraction is 80%), add 25 parts of carbon black, stir at 500 rpm for 40 min, concentrate, dry, and obtain pretreated mixture.

[0094] A2. Mix 5 parts of zinc diacrylate with the above pretreated mixture and ball mill at 250 rpm for 20 min to obtain the reinforcing agent.

[0095] Experimental Example 1

[0096] Sufficiently long samples were cut from the insulation layers of the overhead insulated conductors prepared in Examples 1-5 and Comparative Examples 1-3, according to GB / T 2951.11. After preparing a dumbbell-shaped specimen with a thickness of 1.5 mm using the method in 2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods for Thickness and Dimensional Measurement and Mechanical Properties Test", tensile strength was tested at a test speed of 250 mm / min.

[0097] The test results are shown in Table 1.

[0098] Table 1 Performance test results of Examples 1-5 and Comparative Examples 1-3

[0099]

[0100] Compared with Comparative Examples 1-3, the tensile strength of the insulation layer of the overhead insulated conductors in Examples 1-5 is improved, indicating that the addition of carbon black, silicone powder and zinc diacrylate to the insulation layer of the overhead insulated conductor can effectively improve the mechanical properties of the insulation layer, so that its tensile strength can reach more than 24.9 MPa.

[0101] Experiment Example 2

[0102] Sufficiently long sample segments were cut from the insulation layer of the overhead insulated conductors prepared in Examples 4, 6-10. After tensile strength testing according to the above test method, aging resistance testing was carried out according to the method in GB / T 2951.12-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Cables - Part 12: General Test Methods - Thermal Aging Test Method". After aging, tensile strength testing was carried out according to the above method. The aging resistance test method was the air oven aging method, with a temperature of 135℃ and a time of 240h. The test results are shown in Table 2.

[0103] Table 2 Performance test results of Examples 4, 6-10

[0104]

[0105] Compared with Examples 4 and 10, the tensile strength of the overhead insulated conductors in Examples 6-9 decreased less after the aging resistance test. Calculated using the formula: tensile strength retention rate = tensile strength after aging / tensile strength before aging × 100%, the tensile strength retention rate of the insulation layers in Examples 6-9 reached over 96.4%, indicating that the addition of zinc acetylacetonate to the reinforcing agent improved the aging resistance while maintaining the mechanical strength of the insulation layer. Furthermore, compared with Examples 6 and 9, the tensile strength retention rate of the overhead insulated conductors in Examples 7-8 further increased after the aging resistance test, reaching over 96.8%. This indicates that adjusting the amount of zinc acetylacetonate, when added to the reinforcing agent at 4-5 parts, resulted in better synergy with the other raw materials in the reinforcing agent, further improving the aging resistance of the insulation layer.

[0106] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, aging-resistant overhead insulated conductor, comprising, from the inside out, a conductor and an insulation layer, characterized in that, The raw material of the insulating layer comprises the following components in parts by weight: 80 parts polyethylene, 15-20 parts styrene-butadiene rubber, 10-18 parts ethylene propylene diene monomer (EPDM) rubber, 3-5 parts zinc oxide, 1-2 parts vulcanizing agent, 0.5-1 part accelerator, 5-7 parts compatibilizer, 2-3 parts zinc stearate, and 8-12 parts reinforcing agent; The raw materials of the reinforcing agent include the following components in parts by weight: 20 parts carbon black, 4-8 parts silicone powder, 5-10 parts zinc diacrylate; The reinforcing agent also includes 2-6 parts of zinc acetylacetonate as a raw material.

2. The high-strength, aging-resistant overhead insulated conductor according to claim 1, characterized in that, The conductor is either an aluminum alloy conductor or a copper alloy conductor.

3. The high-strength, aging-resistant overhead insulated conductor according to claim 1, characterized in that, The reinforcing agent also includes a silane coupling agent, wherein the amount of the silane coupling agent added is 8% to 15% of the weight of the carbon black.

4. The high-strength, aging-resistant overhead insulated conductor according to claim 1, characterized in that, The vulcanizing agent includes one or two of sulfur and dicumyl peroxide; The accelerator includes one or both of accelerator H and accelerator TMTD.

5. A high-strength, aging-resistant overhead insulated conductor according to claim 1, characterized in that, The compatibilizer includes one or both of maleic anhydride-grafted polyethylene and maleic anhydride-grafted EPDM rubber.

6. The high-strength, aging-resistant overhead insulated conductor according to claim 1, characterized in that, The raw materials for the insulating layer also include 1-3 parts of antioxidant and 2-5 parts of plasticizer.

7. A high-strength, aging-resistant overhead insulated conductor according to claim 6, characterized in that, The antioxidant includes one or more of antioxidant 1010, antioxidant 1024, and antioxidant 264; The plasticizer includes one or more of dinonyl phthalate, tricresyl phosphate, and dioctyl phthalate.

8. A high-strength, aging-resistant overhead insulated conductor according to claim 3, characterized in that, The preparation method of the reinforcing agent includes the following steps: B1. Add the silane coupling agent to an ethanol aqueous solution, add the carbon black and the silicone powder, mix evenly, concentrate, and dry to obtain the first pretreated mixture; B2. Disperse the acetylacetic copper zinc in anhydrous ethanol, add the first pretreatment mixture, mix evenly, concentrate, and dry to obtain the second pretreatment mixture; B3. The zinc diacrylate and the second pretreatment mixture are blended and ball-milled to obtain the reinforcing agent.

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