Study on the Effect of Cleaning and Swelling Action of Cleaning and Repairing Agents on the Properties of Silicone Rubber

Silicone rubber composite materials are prone to fouling under outdoor conditions for a long time, leading to a decrease in hydrophobicity and even the occurrence of pollution flashover. Generally, the silicone rubber surface is cleaned and repaired with cleaning and repair agents, which can quickly restore its hydrophobicity to the factory state and even reach HC1. Under the action of cleaning and repairing agents, silicone rubber will undergo a certain swelling effect. This article conducts in-depth research on the impact of the cleaning and swelling effect of cleaning and repairing agents on the performance of silicone rubber. Research has found that this cleaning and repairing agent can significantly improve the surface hydrophobicity of silicone rubber. When silicone rubber is immersed in the cleaning and repairing agent for up to 10 hours, its surface undergoes swelling equilibrium, where the evaporation volume and swelling index remain unchanged. Through testing its mechanical properties, it was found that its tear resistance and fracture performance have been improved to a certain extent, with growth rates of 23.36% and 2.55%, respectively; Through electrical performance testing, it was found that its volume resistivity and dielectric strength were both improved to a certain extent, with volume resistivity and dielectric strength increased by 16.5% and 14.3%, respectively. Moreover, after reaching swelling equilibrium in the cleaning and repairing agent, the hydrophobicity of silicone rubber did not decrease, and it can still maintain HC1 for a long time, exhibiting good hydrophobicity.


Introduction
With the rapid development of China's power industry, a large amount of emissions continue to exacerbate environmental pollution, and pollution flashover accidents of power transmission and transformation equipment occur frequently.Silicone rubber has become the focus of attention in the external insulation industry of power system equipment due to its excellent hydrophobicity and hydrophobicity migration [1][2].Room temperature vulcanized silicone rubber, as an organic material, is inevitably subject to aging due to the combined effects of surface discharge, ultraviolet radiation, and surface pollution.Once the surface of the insulator is polluted and forms a uniform solid pollution layer, its surface hydrophobicity and migration will also be lost, and it will even seriously threaten the safe and stable operation of the power system [3][4][5].However, as the operating time increases, the accumulation of pollution on the surface of the insulator continues to increase.When the pollution accumulates to a certain extent, it may affect the hydrophobicity of the insulator.Therefore, it is necessary to regularly clean the surface of composite insulators during operation to improve their safety and service life [6].
At present, insulator cleaning is mainly divided into two categories: physical cleaning and chemical cleaning [7][8].Physical cleaning often involves water cleaning and mechanical cleaning, which can to some extent reduce the degree of contamination on the surface of insulators.However, water cleaning requires high conditions and cannot be operated with electricity, and the cleaning effect of water on inorganic salts and oil stains is not very obvious.Although mechanical cleaning is a technology used in industry, due to the large space occupied by the robotic arm, for insulators of different shapes, it is easy to create blind corners that cannot be cleaned during cleaning, which affects the cleaning effect.In addition, chemical cleaning involves spraying a chemical cleaning agent onto the surface of insulators through a spray gun.Under various effects such as surface tension and dissolution, dirt is soaked, decomposed, and peeled off.Although the effect of chemical cleaning is relatively ideal, the use of chemical cleaning agents can easily cause environmental pollution.It is of great significance to propose a new method for cleaning insulators.
This cleaning and repairing agent can quickly remove dust, oil, carbon powder, and other dirt from composite insulators.After cleaning, the composite insulators achieve a refreshing effect and can extend the service life of the composite insulators.It is the best product for equipment insulation cleaning.At present, most literature reports on the cleaning of composite insulators using cleaning agents are difficult to apply due to the adverse effects of silicone rubber swelling.Different formulations of silicone rubber materials exhibit varying degrees of swelling under the infiltration of different formulations of small molecule cleaning agents, and the strength of the swelling effect is related to the duration of cleaning agent residue and the type of surfactant [9][10].The volatility of cleaning agents is directly related to their residual time on the surface of insulators, and fast volatile insulation cleaning agents can reduce the negative impact of cleaning agent swelling effect.This study uses hydroxysilicone oil as the main formulation of the cleaning and repairing agent, and conducts volatilization rate tests, swelling tests, hydrophobicity tests, mechanical tests, electrical tests, etc. to provide experimental data and theoretical basis for the impact of the swelling effect of the cleaning and repairing agent on the surface performance of insulators.

Preparation Process of Cleaning and Repairing Agents
Weigh hydroxy silicone oil and RJ-1419 according to the ratio, mix them at a high speed at a stirring rate of 800~1000r/min, adjust the stirring rate after 20~30min, add KH550 and KH560 at a low stirring rate, increase the stirring rate to 1200~1500r/min, and mix for 20~30min.Prepare cleaning and repairing agent after standing for 4-6 hours.Finally, wipe the silicone rubber insulation material with cleaning and repairing agent, let it dry, and wait for testing.

Performance Testing
The main performance indicators can be tested according to the following standards: GB/T 30693-2014 "Measurement of the Contact Angle between Plastic Films and Water" for hydrophobicity testing; GB/T 528-2009 "Determination of tensile stress-strain properties of vulcanized or thermoplastic rubber" for testing tensile strength and elongation at break; GB/T 529-2008 "Determination of Tear Strength of Vulcanized or Thermoplastic Rubber (Trouser shaped, Square shaped, and Crescent shaped Specimens)" for testing tear strength.

Hydrophobicity of Cleaning and Repairing Agents on Silicone Rubber
The static contact Angle was tested for 5 times respectively on the uncleaned silicone rubber and the silicone rubber insulation sample after 20 minutes of cleaning and repairing agent.The data and average values are shown in table 1, and the variation of static contact angle is shown in figure 1.
Table 1.Comparative data on hydrophobicity of silicone rubber before and after cleaning with cleaning and repairing agents.

Contact Angle
No. From the above data, it can be seen that the hydrophobicity of silicone rubber samples significantly improves after being cleaned with cleaning and repair agents.Before cleaning, the static contact angle of the silicone rubber surface was between 96.2 ° and 98.6 °, with an average value of 97.24 °.After being cleaned with cleaning and repairing agents, the static contact angle of silicone rubber increased to 103.4 °~104,9 °, with an average value of 104.06 °.The static contact angle increased by 7.01%.Therefore, cleaning and repairing agents have a promoting effect on the hydrophobicity of silicone rubber surfaces.This is because the cleaning and repairing agent has the same silicon molecular structure as silicone rubber, which is easy to wet on the surface of silicone rubber, enter the interior of silicone rubber, and cause the broken structure to reorganize, thereby improving the surface hydrophobicity of silicone rubber.

Swelling Effect of Cleaning and Repairing Agents on Silicone Rubber
Due to the use of cleaning and repairing agents in outdoor conditions, their volatility is also a key factor affecting their performance.Table 2 and figure 2 show the volume of volatilization of cleaning and repairing agents.From table 2 and figure 2, it can be seen that under outdoor conditions, the average volume of volatilization per hour of the cleaning and repairing agent is 0.2mL, which is almost non volatile.
During the infiltration process of cleaning and repairing agents, silicone rubber may experience different swelling phenomena due to differences in its formula, cleaning agent, and other components.Silicone rubber molecules combine with each other through chemical bonds to form a three-dimensional network structure, providing space for solvent molecules to penetrate.The penetration of small solvent molecules in silicone rubber leads to volume expansion.The swelling characteristics of silicone rubber are reflected by its swelling index.The swelling index of silicone rubber completely immersed in the cleaning and repairing agent changes over time as shown in figure 1.From figure 1, it can be seen that under outdoor conditions, the swelling curve of silicone rubber in cleaning and repairing agents increases with the increase of swelling time and gradually approaches saturation.After soaking for about 10 hours, the swelling index remains constant, and the silicone rubber reaches swelling equilibrium.There are two reasons for the above trend phenomenon: firstly, this cleaning and repairing agent does not change the internal structure of silicone rubber.Due to the silicon molecular structure of the cleaning and repairing agent, which has its own characteristics of non-polar groups and low surface tension, it is easy to wet and spread on the surface of silicone rubber, and thus more easily enter the interior of silicone rubber with non-polar groups; Secondly, the cleaning and repairing agent provides chemical binding sites for silicone rubber, increasing the crosslinking density.Therefore, in the later stage, as the soaking time increases, the penetration of solvent molecules becomes more easily hindered.

Changes in Mechanical Properties of Silicone Rubber after Reaching Swelling Equilibrium
This study mainly investigates the changes in mechanical properties of silicone rubber after soaking in cleaning and repairing agents for 10 hours to reach swelling equilibrium, including its tensile strength, elongation at break, and tear strength.Table 3 shows the changes in the mechanical properties of silicone rubber after reaching swelling equilibrium during the soaking process of cleaning and repairing agents.
Figure 3 shows the changes in the mechanical properties of silicone rubber after reaching swelling equilibrium during the soaking process of cleaning and repairing agents.From table 3 and figure 3, it can be seen that before being cleaned, the tensile strength of silicone rubber was 2.43MPa, the elongation at break was 66.6%, and the tear strength was 6.25MPa;After soaking the silicone rubber in the cleaning and repairing agent for 10 hours to reach swelling equilibrium, its tensile strength is 2.25 MPa, elongation at break is 68.3%, and tear strength is 7.71 MPa.Research has found that its tearing performance and elongation at break have been improved to a certain extent, with growth rates of 23.36% and 2.55%, respectively.And the tensile strength has decreased to a certain extent, with a decrease of 7.4%, and the performance decrease is not significant.
Overall, after soaking and swelling with cleaning and repair agents, the mechanical properties of silicone rubber did not show a significant decrease, and on the contrary, there was a certain improvement in its tear resistance.This is because after aging, the cross-linking points inside the silicone rubber break.By adding cleaning and repairing agents, the aging silicone rubber can restore some cross-linking points, increase its cross-linking density, and thus improve the tear strength of the silicone rubber.In summary, the swelling effect of cleaning and repairing agents has little impact on silicone rubber.

Changes in Electrical Properties of Silicone Rubber after Reaching Swelling Equilibrium
This study mainly investigates the changes in electrical properties of silicone rubber after soaking in cleaning and repairing agents for 10 hours to reach swelling equilibrium, including its volume resistivity and dielectric strength.Table 4 shows the changes in the electrical properties of silicone rubber after reaching swelling equilibrium during the soaking process of cleaning and repairing agents.Figure 4 shows the changes in the electrical properties of silicone rubber after reaching swelling equilibrium during the soaking process of cleaning and repairing agents.From table 4 and figure 4, it can be seen that the volume resistivity and dielectric strength of silicone rubber before cleaning are 1.15 * 011 Ω * cm and 22.4 KV/mm, respectively.After cleaning and swelling with cleaning and repairing agents, the volume resistivity and dielectric strength of silicone rubber reach a swelling equilibrium of 1.34 * 011 Ω * cm and 25.6 KV/mm, respectively.It is obvious that after soaking in the cleaning and repairing agent for 10 hours to reach swelling equilibrium, the electrical properties of silicone rubber have been improved to a certain extent, with volume resistivity and dielectric strength increased by 16.5% and 14.3%, respectively.This indicates that cleaning and repairing agents have a certain promoting effect on the electrical properties of insulation materials.This is because when the surface of silicone rubber ages, microcracks will appear on its surface.The raw material for cleaning and repairing agents is organic silicon.When it infiltrates the surface of silicone rubber, due to the insulation properties of organic silicon, the electrical properties of the cleaned silicone rubber are improved to a certain extent.

Changes in Hydrophobicity of Silicone Rubber after Swelling Equilibrium
This study mainly investigates the changes in hydrophobicity of silicone rubber before and after reaching swelling equilibrium during immersion in cleaning and repairing agents.Table 5 shows the hydrophobicity changes of silicone rubber before and after reaching swelling equilibrium during immersion in cleaning and repair agents.
Table 5. Hydrophobicity changes of silicone rubber before and after reaching swelling equilibrium during immersion in cleaning and repairing agents.

Hydrophobicity level
Uncleaned Unswelling Swelling Equilibrium hydrophobicity HC4 HC1 HC1 From table 5, it can be seen that the uncleaned silicone rubber surface has poor hydrophobicity, with a hydrophobicity level of HC4.After using cleaning and repairing agents to clean the surface of silicone rubber, its hydrophobicity has significantly improved, with the hydrophobicity level raised from HC4 to HC1.And after soaking the silicone rubber in the cleaning and repairing agent for 10 hours to reach swelling equilibrium, its hydrophobicity did not decrease, and its hydrophobicity level remained at HC1, and it could maintain good hydrophobicity for a long time.
This indicates that after being treated with cleaning and repairing agents, the surface of silicone rubber can maintain its good hydrophobicity and stability for a long time, thereby reducing the maintenance frequency and later maintenance costs of silicone rubber, and providing practical guidance and theoretical basis for the environmental adaptability of cleaning and repairing agents.

Conclusion
(1) Research has found that this cleaning and repairing agent can significantly improve the surface hydrophobicity of silicone rubber.The static contact angle increased from 97.24 ° to 104.06 °, and the static contact angle increased by 7.01%.When silicone rubber is immersed in the cleaning and repairing agent for up to 10 hours, its surface undergoes swelling equilibrium, where the evaporation volume and swelling index remain unchanged.This is because the cleaning and repairing agent has a silicon molecular structure, which has characteristics such as non polar groups and low surface tension.It is easy to wet and spread on the surface of silicone rubber, and thus more easily enter the interior of silicone rubber with non polar groups; Secondly, the cleaning and repairing agent provides chemical binding sites for silicone rubber, increasing the crosslinking density.Therefore, in the later stage, as the soaking time increases, the penetration of solvent molecules becomes more easily hindered.
(2) Through testing its mechanical properties, it was found that its tear resistance and fracture performance have been improved to a certain extent.Its tearing performance and elongation at break have been improved to a certain extent, with growth rates of 23.36% and 2.55%, respectively.Through electrical performance testing, it was found that its volume resistivity and dielectric strength have been improved to a certain extent.After cleaning and swelling with cleaning and repairing agents, the volume resistivity and dielectric strength of silicone rubber increased by 16.5% and 14.3% respectively after reaching swelling equilibrium.
(3) After soaking the silicone rubber in the cleaning and repairing agent for 10 hours to reach swelling equilibrium, its hydrophobicity did not decrease, and its hydrophobicity level remained at HC1, and it maintained good hydrophobicity for a long time.

Figure 1 .
Figure 1.Comparison of hydrophobicity of silicone rubber before and after cleaning with cleaning and repair agents.

Figure 3 .
Figure 3. Changes in the mechanical properties of silicone rubber after reaching swelling equilibrium.

Figure 4 .
Figure 4. Changes in electrical properties of silicone rubber after reaching swelling equilibrium.

Table 2 .
Volatile volume and swelling characteristics data of cleaning and repairing agents under outdoor conditions.

Table 3 .
Data on the changes in mechanical properties of silicone rubber after reaching swelling equilibrium.

Table 4 .
Data on the changes in electrical properties of silicone rubber after reaching swelling equilibrium.