METHOD FOR IMPROVING BREAKDOWN FIELD STRENGTH OF POLYETHYLENE BASED ON NANO-PARTICLES GRAFTED WITH VOLTAGE STABILIZER

Abstract

The invention relates to a method for improving a breakdown field strength of polyethylene based on nano-particles grafted with a voltage stabilizer, comprising: 1) dehydration and condensation of nano-particles; 2) carboxyl activation of SDA; 3) grafting with SDA; and 4) preparation of modified nano-composite material. According to the invention, a surface of the nano-particles is modified by an organic group while improving a migration resistance capacity of the voltage stabilizer, and the obtained nano-particles grafted with the voltage stabilizer are doped into a polymer matrix material, so that an electrical property of the matrix material can be improved by both the nano-particles and the voltage stabilizer, and the improvement is stable; and a polyethylene nano-composite material with a significantly improved breakdown field strength can be obtained, thus improving an electrical property of an insulating material, and being beneficial for ensuring the stability of long-term operation of the insulating material.

Claims

1. A method for improving a breakdown field strength of polyethylene based on nano-particles grafted with a voltage stabilizer, wherein the method comprises the following steps: S1: selecting nano-particles with a purity greater than 99%, and dehydrating and condensing hydroxyl on a surface of the nano-particles by using a silane coupling agent -aminopropyl triethoxysilane KH550 to complete chemical bond connection, so as to form an intermediate carrier; S2: selecting SDA as a voltage stabilizer, adding the SDA into a dimethyl sulfoxide DMSO solvent for uniform dispersion, and adding a catalyst tetramethylurea hexafluorophosphate HATU into the mixed solution to activate a carboxyl group of the SDA, so as to form an activation solution; S3: adding the intermediate carrier in the S1 into the activation solution and carrying out ultrasonic treatment to uniformly disperse the intermediate carrier, magnetically stirring the mixture for full reaction at the same time, so that carboxyl on one side of the voltage stabilizer SDA is subjected to an amidation reaction with amino, and grafting the voltage stabilizer SDA on the surface of the nano-particles, so as to form nano-particle-SDA; S4: washing, drying and grinding the reaction product nano-particle-SDA in the S3 for later use; S5: adding the ground product of the SDA-grafted nano-particles in the S4 into the DMSO solution, adding the HATU to activate carboxyl on the other side of the SDA at the same time, selecting alkylamine for end capping of the SDA-grafted nano-particles through the amidation reaction, and washing and drying the reaction product after the reaction is completed; and S6: adding the product in the S5 into low-density polyethylene and carrying out melt blending in a torque rheometer to obtain a modified nano-composite material.

2. The method for improving the breakdown field strength of polyethylene based on the nano-particles grafted with the voltage stabilizer according to claim 1, wherein the intermediate carrier obtained in the S1 needs to be dried before adding into the activating solution, which specifically comprises pouring the intermediate carrier into a watch glass and drying in a vacuum drying oven for 3 hours at a drying temperature of 80 C.

3. The method for improving the breakdown field strength of polyethylene based on the nano-particles grafted with the voltage stabilizer according to claim 1, wherein the reaction product nano-particle-SDA in the S3 is collected by centrifugal separation through a centrifuge and then washed with deionized water and anhydrous ethanol respectively, and then dried in a vacuum drying oven and ground.

4. The method for improving the breakdown field strength of polyethylene based on the nano-particles grafted with the voltage stabilizer according to claim 1, wherein the low-density polyethylene in the S6 is washed with distilled water to remove impurities, then dried in a vacuum drying oven at 60 C. for 24 hours, and then subjected to melt blending with the product in the S5.

Description

DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a flow chart of the present invention;

[0024] FIG. 2 is a schematic diagram of a nano-particle grafted with a voltage stabilizer in the present invention; and

[0025] FIG. 3 is a curve graph of Weibull distribution of direct current breakdown strengths of different samples.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] The present invention is further described in detail hereinafter by the specific embodiments, the following embodiments are only descriptive, not restrictive, and cannot limit the scope of protection of the present invention.

[0027] As shown in FIG. 1, a method for improving a breakdown field strength of polyethylene based on nano-particles grafted with a voltage stabilizer was innovative in that the method comprised the following steps.

[0028] 1. SiO.sub.2 nano-particles with a purity of 99% and a particle size of about 20 nm were selected, a silane coupling agent Y-aminopropyl triethoxysilane (KH550) was used to dehydrate and condense hydroxyl on a surface of the SiO.sub.2 nano-particles to realize chemical bond connection, and amino at the other end could not only generate a hydrogen-bond interaction with a polymer to enhance an interface interaction, but also provide an intermediate carrier for further modification and grafting of the SiO.sub.2 nano-particles.

[0029] 2. SDA was selected as the voltage stabilizer for surface grafting, a molecular structure with a high conjugation effect of the SDA was beneficial for improving the property of cable insulation, and carboxyl at one end of the SDA could react with an amino group of the KH550 through an amidation reaction, so that the SDA was grafted on the SiO.sub.2 nano-particles.

[0030] 3. The SiO.sub.2KH550 was poured into a watch glass and dried in a vacuum drying oven at 80 C. for 3 hours to remove water.

[0031] 4. 0. 75 of SDA the and 2.13 g of 2-(7-azabenzotriazole)-N,N,N,N-tetramethylurea hexafluorophosphate (HATU) were weighed, add into 100 ml of dimethyl sulfoxide (DMSO) solution, and ultrasonically treated for 15 minutes to activate the carboxyl.

[0032] 5. 0.4 g of the dried SiO.sub.2KH550 was weighed, added into the solution, ultrasonically treated for 30 minutes for uniform dispersion, and magnetically stirred continuously at room temperature for 12 hours for full reaction.

[0033] 6. The product was collected by centrifugal separation through a high-speed centrifuge (at 8000 rpm for 10 minutes), the product was dispersed in deionized water to be washed twice and then washed once in absolute ethanol, and the obtained reaction product (SiO.sub.2-SDA) was dried in a vacuum drying oven at 80 C. for 12 hours and then ground for later use.

[0034] 7. 0.6 g of the SiO.sub.2-SDA was weighed, added into 100 ml of DMSO solution, and ultrasonically treated for 30 minutes, and after uniform dispersion of the particles, the mixture was added with 2 g of HATU, and ultrasonically treated for 15 minutes to activate the carboxyl.

[0035] 8. After ultrasonic treatment, 1.2 mL of n-octyl amine was slowly dropwise added into the solution under constant stirring, and magnetically stirred continuously at room temperature for 12 hours. After full reaction, the product was collected by centrifugal separation through a high-speed centrifuge (at 8000 rpm for 10 minutes), washed and then dried to obtain alkyl-end capped SiO.sub.2 nano-particles (SiO.sub.2-SDAC8) grafted with the voltage stabilizer.

[0036] 9. The LDPE particles were fully washed with distilled water to remove impurities, and then dried into a vacuum drying oven at 60 C. for 24 hours.

[0037] 10. The prepared SiO.sub.2-SDAC8 particles were doped into LDPE in a ratio of 3 wt %, jointly added into an internal mixer, and subjected to melt blending at a melting temperature set as 130 C. and a rotating speed set as 60 r/min for 6 minutes to obtain a modified nano-composite material.

[0038] According to the present invention, based on the nano-particles grafted with the voltage stabilizer, taking SiO.sub.2 and SDA as an example, a schematic diagram of reaction was shown in FIG. 2, a large number of hydroxyls dangling on the surface of SiO.sub.2 were mainly used in the reaction to react with a silane coupling agent, then amino was introduced, and the SDA was grafted on the surface of SiO.sub.2 through an amidation reaction.

[0039] After SiO.sub.2 before and after grafting modification was introduced into the LDPE matrix, numbers of samples were shown in Table 1, and an influence on a breakdown property of the LDPE matrix was shown in Table 2 and FIG. 3.

[0040] In FIG. 3, a to f were Weibull distribution curves of direct current breakdown strengths of a PE group, a PENV group, a PEN group, a PENV group, a PES group and a PESC group respectively. Test results showed that, compared with simple physical blending, SDA-grafted SiO.sub.2 could improve the breakdown field strength of the LDPE more obviously, and achieve a stable effect. This improvement effect was further enhanced after end capping with alkylamine.

TABLE-US-00001 TABLE 1 Names and ingredients of samples Ingredients Content of Type of nano- Content of nano- voltage Name Matrix particles particles/wt % stabilizer/wt % PE PEV2 0.05 PEV3 0.15 PEN1 SiO.sub.2-KH550 0.5 PEN2 SiO.sub.2-KH550 1 PEN3 SiO.sub.2-KH550 3 PENV1 SiO.sub.2-KH550 0.5 0.025 PENV2 LDPE SiO.sub.2-KH550 1 0.05 PENV3 SiO.sub.2-KH550 3 0.15 PES1 SiO.sub.2-SDA 0.5 PES2 SiO.sub.2-SDA 1 PES3 SiO.sub.2-SDA 3 PESC1 SiO.sub.2-SDAC8 0.5 PESC2 SiO.sub.2-SDAC8 1 PESC3 SiO.sub.2-SDAC8 3

TABLE-US-00002 TABLE 2 Weibull distribution parameters of direct current breakdown strengths of samples Name Scale parameter (kV/mm) Shape parameter PE 273.47 13.22 PEV2 315.06 8.76 PEV3 298.95 6.13 PEN1 301.36 9.79 PEN2 321.03 14.29 PEN3 309.70 13.19 PENV1 307.81 9.88 PENV2 316.36 12.50 PENV3 287.05 10.20 PES1 319.08 9.67 PES2 332.94 11.93 PES3 322.82 12.83 PESC1 331.84 10.65 PESC2 356.87 19.51 PESC3 339.08 13.69

[0041] According to the present invention, in combination with the improvement of a dielectric property of polyethylene by the nano-particles and the voltage stabilizer, the breakdown field strength of the matrix material is greatly improved. Meanwhile, the grafting reaction can improve the migration resistance of the voltage stabilizer, so as to avoid the voltage stabilizer from migrating from the polymer matrix in long-term use to lead to the property decline of the composite material in long-term use. Moreover, the compatibility between the nano-particles and the polymer matrix can be improved through secondary grafting. Theoretical analysis and experiments prove that the studied modification method of grafting the voltage stabilizer on the surface of the nano-particles by grafting reaction can be realized, and there is obvious improvement effect on the breakdown field strength of the polyethylene matrix. This method provides a new scheme for the selection and design of the insulating materials for the polyethylene high-voltage direct current cable in the future.

[0042] Although the embodiments and the drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art may understand that various alternatives, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and the drawings.