Abstract: This study employs molecular dynamics (MD) simulations to address the performance limitations of traditional cellulose insulating paper. Hydroxylated Al2O3 nanoparticle models are constructed to systematically investigate the effects of Al2O3 nanoparticles (0.5 nm, 0.9 nm; 0wt%~7wt% doping content) on the mechanical properties, hydrogen bond interactions, and free volume of cellulose insulating paper. The results demonstrate that the Young's modulus, shear modulus, and bulk modulus of the nanocomposite system all exhibit a distinct trend of initial increase followed by a decrease as the doping content rises. The internal hydrogen bond density of the system varies synchronously with the mechanical properties, while the potential energy of the cellulose single chains shows an opposite trend, first decreasing and then increasing. Furthermore, the fraction free volume (FFV) initially decreases and subsequently increases with increasing doping content, displaying a significant negative correlation with the mechanical performance of the modified system. 3wt% is identified as the optimal doping content, and the 0.9 nm particle size achieves a superior modification effect. Mechanistic analysis reveals that the intermolecular interactions within the cellulose matrix serve as the dominant factor regulating the mechanical properties of the composite. At low doping contents, the thermodynamic and structural stability of the cellulose is effectively enhanced through the synergistic effects of physical filling, hydrogen bond formation, and van der Waals forces between the Al2O3 nanoparticles and the cellulose molecular chains. Conversely, excessive doping leads to nanoparticle agglomeration within the cellulose matrix, which causes the failure of the nanomodification. This agglomeration induces an abnormal increase in the system's free volume and ultimately leads to significant degradation in the performance of the modified insulating paper. With the calculation and discussion of mechanical properties, molecular structures, and the underlying mechanisms, this study provides a theoretical foundation for the optimization of insulating paper for ultra-high-voltage transformers.

Key words: Al2O3 nanoparticles, molecular dynamics simulation, particle size effect, doping content optimization, mechanical properties, hydrogen bond interaction, free volume

摘要： 变压器绝缘纸的主要成分为纤维素，针对传统纤维素绝缘纸性能缺陷，本研究采用分子动力学(MD)模拟方法，构建经羟基化修饰的Al2O3纳米粒子模型，系统探究了不同粒径及掺杂量的Al2O3纳米粒子(半径0.5和0.9 nm；0wt%~7wt%掺杂量)对纤维素力学性能、氢键作用及自由体积的影响。结果表明，改性体系的杨氏模量、剪切模量与体积模量均随掺杂量呈先升后降趋势，内部氢键密度与力学性能同步先增后减，纤维素单链势能呈先降后升的变化；自由体积分数则呈先减后增的变化，且与力学性能呈负相关。其中3wt%为最优掺杂量，0.9 nm粒径改性效果更优。纤维素分子内部作用是力学性能调控的主导机制，低掺杂量通过物理填充、氢键作用与范德华力的协同作用提升稳定性，过量掺杂则因粒子团聚引发失效，进而导致自由体积异常增大，引发性能衰减。本研究可为特高压变压器绝缘纸优化提供理论参考。

关键词: 纳米Al2O3, 分子动力学模拟, 粒径效应, 掺杂量优化, 力学性能, 氢键作用, 自由体积