Enhancing comprehensive performance of cellulose insulating paper modified by atmospheric pressure low-temperature plasma with Octamethylcyclotetrasiloxane/O2 addition

In oil-immersed transformers, cellulose insulating paper deteriorates when exposed to electric field, moisture, and high temperature for a long time, leading to decrease in mechanical strength and insulating performance, which affects the service life and operational reliability. In this paper, dielectric barrier discharge (DBD) is adopted to generate atmospheric pressure low-temperature plasma for the treatment of cellulose insulating paper with Octamethylcyclotetrasiloxane (OMCTS)/O2 as the reaction medium. The influences of medium flow rate and treatment time on the comprehensive performance of insulating paper are investigated to obtain optimal treatment effect. The results show that the water resistance, breakdown strength, and mechanical strength of the modified insulating paper are significantly improved. Under optimal conditions, the surface wettability of the insulating paper changes from hydrophilic to hydrophobic (with a water contact angle exceeding 150°), and the water absorption rate is reduced by 57.1%. Meanwhile, the breakdown strength is increased by 41.9%, and the maximum stress is increased by 31.5%. After plasma modification, a 44.8% improvement in the breakdown strength of the oil-impregnated paper is achieved. Combined with the characterization of physicochemical properties such as SEM, EDS, and FTIR, it is found that the low-polarity Si–O–Si and Si–CHx fragments, generated by the plasma, not only form a dense film on the paper surface, but also are deposited inside the bulk. This process reduces surface polarity, fills air gaps, and introduces deep traps, thereby realizing the improvement of the comprehensive performance of the insulating paper.