On The Influence Of SiO₂ Nano-doping And Surface Modification On The Properties Of PMIA

Oil-paper composite insulation is the most important insulation method in power transformers.In all accidents of transformers,it is more caused by the aging of its insulation system.Compared with insulating oil,the aging of insulating paper is irreversible.Its performance directly determines the service life of the transformer and even affects the safe and stable operation of the entire power network.Meta-aramid fiber(PMIA)is a new type of high-tech material with superior insulation performance,which has been applied in the field of transformer insulation.In terms of improving the service life of the transformer and the safe operation of the power grid,the research on PMIA and its insulation performance has certain practical significance.In this paper,based on the method of molecular simulation,the thermal stability and mechanical properties of PMIA are studied,and the microscopic mechanism behind the performance improvement is deeply analyzed.After comprehensive analysis of the simulation results,the following main research results were obtained:1)By comparing the simulation results of PMIA modified with nano-SiO₂and unmodified,it is found that the glass transition temperature of PMIA after modification is improved.During the glass transition process,the movement and mechanics of the meta-aramid molecular chain Abrupt changes in performance,obviously the temperature range of the unmodified model is higher than the modified model.The microscopic mechanism analysis found that the change in free volume is also related to the change in glass transition temperature.After PMIA is doped with nano-SiO₂,the free volume in the whole system is reduced,making its internal connection more tight,which is beneficial to enhance the thermal stability and mechanical properties of the body.2)By studying the simulation results of the surface modification of nano-SiO₂by the silane coupling agent KH550 and the degree of modification to PMIA performance,it can be known that proper grafting of KH550 on the surface of SiO₂can further improve the thermal stability and mechanical properties of PMIA.In terms of improving the performance,the improvement effect when the grafting rate of SiO₂surface is 12%is not more significant than that when the grafting rate is 6%,and the shearing resistance is even weaker than that when it is not grafted.Microscopic mechanism analysis found that proper grafting on the surface of SiO₂can further reduce the free volume inside the system,but when the grafting rate is higher,the grafted KH550 molecular chains are closer to each other,and it is easy to form a semi-closed space structure,which not only hinders The interaction between SiO₂and the matrix is increased,and the free volume of the system is increased,and there is more space for the movement of the molecular chain.This is an important reason why the thermal stability and mechanical properties are not as good as the former.3)To suppress the harm of moisture to PMIA performance,the effect of two different modification methods on the surface of SiO₂on the performance of PMIA in water was compared and studied.The simulation results show that under the water environment,the thermal stability and mechanical properties of PMIA can be further improved after KH550 is grafted on the surface of nano-SiO₂,but compared with the SiO₂after melamine grafting,the latter improves PMIA thermal stability and mechanical properties In terms of performance is better.The microscopic mechanism analysis shows that after melamine is grafted onto the surface of SiO₂nanoparticles,the diffusion ability of H₂O molecules is more effectively suppressed,thereby reducing the destructive effect of H₂O molecules on the internal stability of the body.Compared with the method using KH550 to modify SiO₂modified with melamine,the former forms more hydrogen bonding sites on the surface of SiO₂,which restricts the diffusion movement of H₂O molecules and strengthens the tighter connection between molecular chains.In the aspect of improving the thermal stability and mechanical properties of PMIA under water environment,the reason why melamine is better than KH550 to modify SiO₂ is better.