Toughened polypropylene composite material for high-voltage direct-current cable and preparation method of toughened polypropylene composite material

Abstract

The invention provides a toughened polypropylene composite material for a high-voltage direct-current cable and a preparation method of the toughened polypropylene composite material. Belongs to the field of modification of toughened polypropylene composite materials for high-voltage direct-current cables. According to the invention, the dispersibility of the polypropylene and elastomer composite material can be effectively improved, and the interface is weakened. The method comprises the following steps: putting maleic anhydride grafted polypropylene, SBS, 4-mercapto-1-butanol and an antioxidant into a torque rheometer, and uniformly mixing at a certain temperature; and 2, shaping in a press vulcanizer at a certain temperature, and carrying out vacuum drying to obtain the toughened polypropylene composite material for the high-voltage direct-current cable. According to the invention, through the polarity effect of 4-mercapto-1-butanol and a styrene unit in SBS, a local state trap is introduced into polypropylene, the carrier concentration and migration speed in the material are reduced under the effect of an electric field, the conductivity of the material is reduced, and the electric strength is obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of modification of toughened polypropylene composite materials for high-voltage DC cables, specifically relating to a toughened polypropylene composite material for high-voltage DC cables based on click chemistry and its preparation method. Technical Background Highly crystalline polypropylene exhibits high hardness and high modulus, often requiring toughening modification to reduce its hardness in practical applications. Thermoplastic elastomers are typically melt-blended with polypropylene to obtain polypropylene composites with suitable flexibility. However, differences in the chain structure and melt chain relaxation of polypropylene and elastomers make it difficult to achieve ideal dispersion during blending, resulting in significant interfacial defects at the mesoscale. This leads to poor mechanical and physical properties in the composites, and these interfacial defects also cause a sharp deterioration in the material's DC electrical properties. Therefore, interfacial control of polypropylene / elastomer composites is a major problem limiting the development of their mechanical and dielectric properties. Summary of the Invention

[0002] The purpose of this invention is to propose a toughened polypropylene composite material based on click chemistry and its preparation method. This invention can effectively improve the dispersibility of polypropylene and elastomer composite materials and weaken the interface.

[0003] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a toughened polypropylene composite material for high-voltage DC cables, which is prepared by melt blending the following raw materials in parts by weight: 50-100 parts of maleic anhydride-grafted polypropylene SBS 0~50 copies 1.0 to 3.0 parts of 4-mercapto-1-butanol Antioxidant 0.05~2.0 parts.

[0004] Furthermore, the maleic anhydride-grafted polypropylene is maleic anhydride-grafted modified homopolymer polypropylene, impact copolymer polypropylene, or random copolymer polypropylene, with a grafting rate of 1-5%, including but not limited to one or more of homopolymer polypropylene, impact copolymer polypropylene, or random copolymer polypropylene grafted with maleic anhydride in any proportion.

[0005] Furthermore, the SBS is a styrene-butadiene-styrene front copolymer with a melt index of 5-20 g / 10 min (230 °C, 2.16 kg).

[0006] Furthermore, the purity of the 4-mercapto-1-butanol is greater than or equal to 95%.

[0007] Furthermore, the antioxidant is one or more of antioxidant 1010, antioxidant 1035, and antioxidant 300.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned toughened polypropylene composite material for high-voltage DC cables.

[0009] A method for preparing toughened polypropylene composite material for high-voltage DC cables includes the following steps: Step 1: Place maleic anhydride-grafted polypropylene, SBS, 4-mercapto-1-butanol and antioxidant in a torque rheometer and mix them evenly at a certain temperature. Step 2: Then, the material is shaped in a flat vulcanizing machine at a certain temperature and then vacuum dried to obtain toughened polypropylene composite material for high-voltage DC cables.

[0010] Furthermore, in step 1, the mixture is thoroughly mixed at 180℃~220℃.

[0011] Furthermore, in step 2, the material is set at 180℃~210℃.

[0012] The beneficial effects of this invention are as follows: The introduction of SBS elastomer in this invention effectively toughens polypropylene, significantly reduces hardness, and achieves covalent bonding between polypropylene and SBS chains through transesterification and mercapto-Michael addition reaction, thereby improving the elastomer phase dispersion, weakening the interphase interface, and enhancing the consistency of the material.

[0013] This invention introduces localized state traps within polypropylene through the polar interaction between 4-mercapto-1-butanol and the styrene units in SBS. Under the influence of an electric field, this reduces the carrier concentration and migration velocity within the material, thereby decreasing the material's conductivity and significantly improving its electrical strength. Detailed Implementation

[0014] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0015] The grafting rate of the maleic anhydride-grafted polypropylene used below is 2.5%.

[0016] The SBS used below is a styrene-butadiene-styrene front copolymer with a melt index of 0.5 g / 10 min (230℃, 2.16 kg).

[0017] The purity of the 4-mercapto-1-butanol used below is 95%.

[0018] Example 1: The toughened polypropylene composite material for high-voltage DC cables described in this embodiment is prepared by melt blending the following raw materials in parts by weight: 70 parts of maleic anhydride-grafted polypropylene SBS 30 copies 1.5 parts of 4-mercapto-1-butanol Antioxidant 10100.3 parts.

[0019] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this embodiment is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, 4-mercapto-1-butanol, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a 200µm thick, 10cm square sample, and then vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBSg1) for high voltage DC cables.

[0020] Example 2: The toughened polypropylene composite material for high-voltage DC cables described in this embodiment is prepared by melt blending the following raw materials in parts by weight: 60 parts of maleic anhydride-grafted polypropylene SBS 40 1.5 parts of 4-mercapto-1-butanol Antioxidant 10100.3 parts.

[0021] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this embodiment is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, 4-mercapto-1-butanol, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a 200µm thick, 10cm square sample, and then vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBSg2) for high voltage DC cables.

[0022] Example 3: The toughened polypropylene composite material for high-voltage DC cables described in this embodiment is prepared by melt blending the following raw materials in parts by weight: 50 parts of maleic anhydride-grafted polypropylene SBS 50 copies 1.5 parts of 4-mercapto-1-butanol Antioxidant 10100.3 parts.

[0023] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this embodiment is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, 4-mercapto-1-butanol, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a 200µm thick, 10cm square sample, and then vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBSg3) for high voltage DC cables.

[0024] Comparative Example 1: The toughened polypropylene composite material for high-voltage DC cables described in this comparative example is prepared by melt blending the following raw materials in parts by weight: 100 parts of maleic anhydride-grafted polypropylene Antioxidant 10100.3 parts.

[0025] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this comparative example is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene and antioxidant 1010 in a torque rheometer at 200°C for 10 minutes at the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a square sample with a thickness of 200 μm and a diameter of 10 cm. Then, it is vacuum dried at 80℃ for 24 hours to obtain toughened polypropylene composite material (PP) for high voltage DC cables.

[0026] Comparative Example 2: The toughened polypropylene composite material for high-voltage DC cables described in this comparative example is prepared by melt blending the following raw materials in parts by weight: 70 parts of maleic anhydride-grafted polypropylene SBS 30 copies Antioxidant 10100.3 parts.

[0027] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this comparative example is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a 200µm thick, 10cm square sample, and then vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBS1) for high voltage DC cables.

[0028] Comparative Example 3: The toughened polypropylene composite material for high-voltage DC cables described in this comparative example is prepared by melt blending the following raw materials in parts by weight: 60 parts of maleic anhydride-grafted polypropylene SBS 40 Antioxidant 10100.3 parts.

[0029] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this comparative example is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a square sample with a thickness of 200 μm and a diameter of 10 cm. Then, it is vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBS2) for high voltage DC cables.

[0030] Comparative Example 4: The toughened polypropylene composite material for high-voltage DC cables described in this comparative example is prepared by melt blending the following raw materials in parts by weight: 50 parts of maleic anhydride-grafted polypropylene SBS 50 copies Antioxidant 10100.3 parts.

[0031] The method for preparing toughened polypropylene composite material for high-voltage DC cables described in this comparative example is carried out according to the following steps: Step 1: Mix maleic anhydride-grafted polypropylene, SBS, and antioxidant in a torque rheometer at 200°C for 10 minutes according to the following weight fractions: Step 2: The prepared material is shaped in a flat vulcanizing machine at 190℃ to obtain a 200µm thick, 10cm square sample, and then vacuum dried at 80℃ for 24 hours to obtain a toughened polypropylene composite material (PP / SBS3) for high voltage DC cables.

[0032] By comparing pure maleic anhydride-grafted polypropylene (PP), PP / SBS blends without 4-mercapto-1-butanol (PP / SBS1~3), and PP / SBS grafted blends with 4-mercapto-1-butanol (PP / SBSg1~3), the optimization effect of the mercapto-Michael addition-based interface modification strategy on the mechanical and electrical properties of toughened polypropylene composites for high-voltage DC cables was systematically verified. From a mechanical property perspective, without the addition of 4-mercapto-1-butanol, as the SBS content increased from 30% to 50%, the yield strength of PP / SBS1~3 decreased from 15.6 MPa to 9.4 MPa, the tensile strength from 24.3 MPa to 13.1 MPa, and the elongation at break from 537% to 382%. This continuous deterioration trend stems from the lack of effective interfacial bonding between PP and SBS. Mesoscale interfacial defects easily lead to stress concentration under load, thereby compromising the mechanical consistency of the material. However, after adding 4-mercapto-1-butanol, the mechanical properties of PP / SBS1~3 were significantly improved, with S... PP / SBSg2 with 40% BS content performed particularly well, with a tensile strength of 28.6 MPa, which is 50% higher than PP / SBS2 with the same SBS content (19.1 MPa) and close to pure PP (29.2 MPa). Its elongation at break of 619% is 32% higher than PP / SBS2 (468%). This is because 4-mercapto-1-butanol forms a covalent bond between PP and SBS through transesterification and mercapto-Michael addition reaction, which optimizes the elastomer phase dispersion and weakens the interphase interface, so that the two phases form a synergistic effect when under stress, thus avoiding excessive strength loss while retaining the toughening effect. From an electrical performance perspective, unmodified PP / SBS1~3 exhibited a sharp increase in conductivity and a continuous decrease in DC breakdown strength with increasing SBS content. Specifically, the conductivity of PP / SBS3 (6.73E-13 A / m²) was over 160 times higher than that of pure PP (4.00E-15 A / m²), while its breakdown strength (238 kV / mm) was 29% lower than that of pure PP (337 kV / mm). This is because interfacial defects became channels for carrier migration, leading to increased carrier concentration and migration velocity, thus compromising the material's insulation performance. However, the introduction of 4-mercapto-1-butanol completely reversed this situation. The conductivity of PP / SBSg1~3 was all lower than that of pure PP, with PP / SBSg2 reaching as low as 7.86E-16 A / m², significantly lower than that of PP / SBS2 (5.80E-13 A / m²). The breakdown strength (A / m²) decreased by nearly 740 times, while the breakdown strength surpassed that of pure PP across the board. The breakdown strength of PP / SBSg2 reached 403kV / mm, which is 19.6% higher than that of pure PP and 67% higher than that of PP / SBS2. This is due to the polar interaction between 4-mercapto-1-butanol and the styrene unit in SBS to form a localized state trap, which can capture free carriers and reduce carrier concentration and migration speed, thus achieving both low conductivity and high breakdown strength.Overall, the data in the table clearly demonstrates that 4-mercapto-1-butanol-mediated interfacial modification successfully resolved the core contradiction of "toughening at the expense of performance" in traditional PP / SBS blends. In particular, PP / SBSg2 with 40% SBS content possesses tensile strength comparable to pure PP, superior toughness, and electrical properties far exceeding those of pure PP. It perfectly meets the comprehensive requirements of high-voltage DC cables for materials with "high toughness, high strength, and excellent insulation," fully verifying the effectiveness and practicality of the invention.

[0033] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A toughened polypropylene composite material for high-voltage DC cables, characterized in that, It is made by melt blending the following raw materials in parts by weight: 50-100 parts of maleic anhydride-grafted polypropylene SBS 0~50 copies 1.0 to 3.0 parts of 4-mercapto-1-butanol Antioxidant 0.05~2.0 parts.

2. The toughened polypropylene composite material according to claim 1, characterized in that, Maleic anhydride-grafted polypropylene is maleic anhydride-grafted modified homopolymer polypropylene, impact copolymer polypropylene, or random copolymer polypropylene, with a grafting rate of 1-5%, including but not limited to one or a combination of homopolymer polypropylene, impact copolymer polypropylene, or random copolymer polypropylene grafted with maleic anhydride.

3. The toughened polypropylene composite material according to claim 1, characterized in that, SBS is a styrene-butadiene-styrene front copolymer with a melt index of 5-20 g / 10 min (230℃, 2.16 kg).

4. The toughened polypropylene composite material according to claim 1, characterized in that, The purity of 4-mercapto-1-butanol is greater than or equal to 95%.

5. The toughened polypropylene composite material according to claim 1, characterized in that, The antioxidant is one or a combination of antioxidant 1010, antioxidant 1035, and antioxidant 300.

6. The method for preparing the toughened polypropylene composite material according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Place maleic anhydride-grafted polypropylene, SBS, 4-mercapto-1-butanol and antioxidant in a torque rheometer and mix them evenly at a certain temperature. Step 2: Then, the material is shaped in a flat vulcanizing machine at a certain temperature and then vacuum dried to obtain toughened polypropylene composite material for high-voltage DC cables.

7. The method according to claim 6, characterized in that, In step 1, the mixture is thoroughly mixed at 180℃~220℃.

8. The method according to claim 6, characterized in that, In step 2, the material is set at 180℃~210℃.

9. The method according to claim 6, characterized in that, In step 2, vacuum drying is performed at 80°C.

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