Preparation And Performance Study Of Novel Hydrophobic Cellulose Insulation Paper

As a major agricultural country,agriculture plays a significant role in China’s economic development.With the progress of modernization,agricultural modernization has also advanced in step with the times,and the requirements for various infrastructure construction are gradually increasing.At present,the increasing agricultural power load puts forward higher requirements for the safe and stable operation of power equipment in distribution networks(rural power grid).For transformers,which are the core equipment of the power grid,the improvement of its operating life is particularly important for improving the performance of insulating paper in the insulation systems.Research has shown that water can accelerate the degradation of cellulose insulating paper,which contains hydroxyl groups that can bind with water molecules through hydrogen bonds.As cellulose absorbs more water,its hydrolysis rate increases,causing faster decline in insulating paper performance.Eventually,when the insulation performance of the insulating paper drops to a threshold,breakdown occurs,leading to complete loss of insulation performance.Therefore,to extend the service life of insulating paper,reducing its water content and improving its hydrophobicity in oil-immersed transformers is necessary.Therefore,this paper fabricates a novel cellulose insulating paper with both hydrophobic and lipophilic properties,as well as certain self-repairing capability on the basis of traditional pure cellulose insulation paper.The self-repairing properties of the novel cellulose insulating paper were tested under physical and chemical damages.Then,an accelerated aging test was carried out at 130°C for 45 days on the prepared novel cellulose insulating paper and normal pure cellulose insulating paper to investigate the effect of adding hydrophobic coatings on the thermal aging characteristics of oil-paper insulation systems.Additionally,molecular dynamics simulation was used to explore the micro-mechanism of the improvement of the thermal aging properties of oil-paper insulation systems by hydrophobic coatings.The main conclusions of this study are as follows:(1)A stable coating solution was formed using a ternary system composed of PTFE hydrophobic nanoparticles,the fluorocarbon surfactant ST-110,and fluorinated alkyl silane(FAS),which were applied onto the traditional pure cellulose insulating paper substrate via a wet chemistry method.The interaction between ST-110/FAS/PTFE resulted in the formation of a hydrophobic film containing fluorine groups on the surface of the insulating paper.The repulsion between fluorine atoms also enhanced the repulsion of water molecules,thus exhibiting strong hydrophobic characteristics.Additionally,the presence of the hydrophobic film reduced the surface free energy of the insulating paper to a level similar to that of insulating oil,while the surface free energy of water was much higher than that of insulating oil and the novel cellulose insulating paper,resulting in the spontaneous absorption of oil into the fiber voids of the novel cellulose insulating paper and the exclusion of water.As a result,the coating exhibited hydrophobic and lipophilic properties and improved the conductivity and insulation performance of the insulating paper.(2)The novel cellulose insulating paper prepared exhibits good hydrophobic stability,with a water droplet contact angle of 141° and a mineral insulating oil contact angle of less than 20°.It can withstand strong acid and alkali corrosion.And the novel cellulose insulating paper can self-repair its hydrophobic properties.The novel cellulose insulating paper maintaining its hydrophobic properties after being exposed to water,mineral oil,and high temperature conditions for ten days.Moreover,the novel cellulose insulating paper is resistant to strong acid and alkali attacks,without altering its water repellency.Furthermore,when the surface of the coating is damaged,the novel cellulose insulating paper can regain its hydrophobic properties at 80℃ for 12 hours.Notably,this selfrepairing property is repeatable,even after ten cycles of chemical/physical surface damage and heating treatment,the novel cellulose insulating paper maintains its hydrophobicity,with a contact angle of water droplet still above 90°.The self-repairing ability demonstrated after the heat treatment is due to the migration of FAS from the inner fiber layer to the surface at high temperatures.During the heating process,the driving force for the fluorinated alkyl chain migrating towards the coating surface is to minimize its surface free energy.(3)A novel cellulose insulating paper prepared by applying a hydrophobic coating on the surface of cellulose insulating paper can enhance its resistance to aging and has better compatibility with mineral oil.During the process of thermal aging,insulating oil impregnated with novel cellulose insulating paper produces less acid and moisture content.The existence of the hydrophobic coating reduces the impact of acid and moisture on the insulating paper,thereby slowing down the aging of the oil-paper insulation system and improving its thermal aging properties.Results from accelerated thermal aging tests show that the tensile strength and elongation at break of the novel cellulose insulating paper are higher than those of the pure cellulose insulating paper throughout the aging process,with a more gradual decrease.Furthermore,after 45 days of aging,the relative permittivity and dielectric loss factor of the novel cellulose insulating paper decreased by10.4% and 9.9%,respectively,compared to the pure cellulose insulating paper.Based on molecular dynamics calculations,it is found that in the model without the coating,water mainly accumulates in the cellulose layer,whereas in the model with the coating,water primarily accumulates in the insulating oil layer.In addition,the novel cellulose insulating paper has fewer hydrogen bonds with water molecules,which weakens the absorption of water molecules and reduces their diffusion into the cellulose,thereby mitigating the promotion of water to the degradation of cellulose paper.In summary,applying a hydrophobic coating on cellulose insulating paper can slow down the promotion of water and thermal aging degradation on cellulose paper and mineral oil,reducing the number of polar molecules generated from the aging of oil-paper insulation,thus resulting in better mechanical and dielectric properties of the novel cellulose insulating paper and better basic electrical properties of the mineral oil that it immerged in.