Properties of cellulose insulating paper modified by anti-agglomerated double-layer coated nano-SiO2@PDA-KH560

Incorporating nanoparticles into cellulose insulation paper is regarded as an effective strategy for improving the insulation performance of oil-immersed power transformers; however, the tendency of nanoparticles to agglomerate significantly constrains the achievable performance improvement. To address this issue, this study develops a composite modification method based on a core–shell–branched SiO2@PDA-KH560 structure. By leveraging steric hindrance and strengthened interfacial bonding, an anti-agglomeration nanomodifier with high dispersibility and excellent interfacial compatibility was prepared. Furthermore, a nearest-neighbor index (NNI) model based on SEM images is proposed for the first time to quantitatively evaluate the dispersion of nanoparticles in the paper. The analysis of nano-SiO2-modified paper samples with concentrations ranging from 1 to 5 wt. % revealed that the sample doped with 3 wt. % SiO2@PDA-KH560 exhibits the lowest particle aggregation degree and the distribution closest to a random state according to the NNI quantitative evaluation, which is consistent with the results of macroscopic performance evaluations. At this concentration, the modified paper exhibited the best overall performance: tensile strength and elongation at break increased by 16.4% and 16.3%, respectively; relative permittivity decreased by 9.65%, dielectric loss decreased by 0.182%, and breakdown strength increased by up to 10.2%. The anti-agglomeration design and quantitative dispersion evaluation method proposed in this study offer a novel approach for the development of high-performance nanocomposite dielectric materials.