Estimating the Thermal Stability of Cellulose Insulation using MSD and Tg parameters by Molecular Dynamics Simulation

Abstract

Oil-impregnated cellulose paper is the main insulation material used in power transformers. The thermal stability of cellulose insulation is important for the steady and safe operation of a transformer. The reinforcement of the thermal stability of cellulose via physical and chemical modification has attracted much research attention. Considering that traditional experiments are costly and time-consuming, molecular dynamics simulation is introduced to predict or estimate the performance of modified cellulose by calculating several key parameters. However, linking the model performance parameters with macroscopic properties of materials at the molecular simulation scale is difficult. In this study, two parameters, namely, mean square displacement (MSD) and glass transition temperature (Tg), are proposed to evaluate the thermal stability of cellulose. The validity of these two parameters to characterize the thermal stability of cellulose is verified by the simulation results from natural cellulose and acetylation-grafted cellulose models. In engineering application, acetylation-grafted cellulose performs better than natural cellulose in terms of thermal stability. According to the simulation results, the Tg of acetylation-grafted cellulose is approximately 111 K higher than that of natural cellulose. Compared with the natural cellulose, the MSD of acetylation-grafted cellulose considerably decreased, indicating that the intensity of movement for the acetylation-grafted cellulose chain is prominently smaller than the natural cellulose chain at every time step. These results also show that acetylation-grafted cellulose can improve the thermal stability of cellulose, which is consistent with previous studies.